JP2024139962A - Hydroelectric Power System - Google Patents

Abstract

[Problem] To expand the flow rate adjustment range in a hydroelectric power generation system. [Solution] A controller (30) performs a first operation in which a first control and a second control are executed. In the first control, when the flow rate is within a first range greater than zero and equal to or less than a first flow rate, the controller (30) controls a generator (12) and a motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate approaches a target flow rate. In the second control, when the flow rate is within a second range greater than the first flow rate and equal to or less than a second flow rate, the controller (30) controls a generator (12) and a motor-operated valve (15) so that the output of the generator (12) approaches a limit value and the flow rate approaches a target flow rate. [Selected Figure] Figure 5

Description

This disclosure relates to hydroelectric power generation systems.

Patent Document 1 discloses a hydroelectric power generation system. In this hydroelectric power generation system, a memory unit stores the relationship between the effective head of the water turbine and the rotation speed of the generator to obtain maximum efficiency from the generator. The control unit controls the rotation speed of the generator according to the effective head, thereby obtaining maximum efficiency from the generator.

Patent No. 5268871

In the flow paths in which hydroelectric power generation systems are used, there is a demand to meet a predetermined target flow rate. However, as in Patent Document 1, there is a limit to the range of flow rates at which maximum efficiency can be achieved. Specifically, if the adjustment range of the target flow rate is large compared to the range of flow rates at which maximum efficiency can be achieved, there is a problem in that these target flow rates cannot be fully met.

The present disclosure aims to expand the range of flow rate adjustment in hydroelectric power generation systems.

In the first aspect, a hydroelectric power generation system includes a water turbine (11) arranged in a flow path (4) through which a fluid flows, a generator (12) connected to the water turbine (11), a motor-operated valve (15) provided in series with the water turbine (11) in the flow path (4), and a controller (30) that controls the torque or rotation speed of the generator (12) and the opening of the motor-operated valve (15). The controller (30) performs a first operation that executes a first control and a second control. In the first control, when the flow rate is within a first range from greater than zero to a first flow rate or less, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate approaches a target flow rate. In the second control, when the flow rate is within a second range that is greater than the first flow rate and is equal to or less than a second flow rate, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the output of the generator (12) approaches a limit value and so that the flow rate approaches a target flow rate.

In the first aspect, when the flow rate is in a first range greater than zero and equal to or less than a first flow rate, the controller (30) executes a first control. In the first control, the controller (30) adjusts the rotation speed or torque of the water turbine (11) and the opening of the motor-operated valve (15) so that the efficiency of the water turbine (11) or the hydroelectric power generation system (10) approaches the maximum efficiency and the flow rate of the flow path (4) approaches the target flow rate. This makes it possible to obtain maximum efficiency in the water turbine (11) or the hydroelectric power generation system (10) while bringing the flow rate of the flow path (4) closer to the target flow rate.

On the other hand, when the flow rate is in a second range greater than the first flow rate and equal to or less than the second flow rate, the controller (30) executes the second control. In the second control, the controller (30) adjusts the rotation speed or torque of the water turbine (11) and the opening of the motor-operated valve (15) so that the output of the generator (12) approaches the limit value and the flow rate of the flow path (4) approaches the target flow rate. In the second control, the output of the generator (12) approaches its maximum, so that the generated power of the generator (12) can be secured. Since the output of the generator (12) does not exceed the limit value, it is possible to avoid malfunctions in the control of the inverter, converter, etc. for controlling the generator (12) or in the hardware. Furthermore, the flow rate adjustment range can be expanded.

In the second aspect, the first aspect is provided with a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11), and the controller (30) is configured to control the generator (12), the motor-operated valve (15), and the bypass valve (17) when the target flow rate is greater than the second flow rate in the first operation so that the output of the generator (12) approaches a limit value and the flow rate approaches the target flow rate, or so that the opening of the motor-operated valve (15) is maximized and the flow rate approaches the target flow rate.

In the second aspect, when the target flow rate is greater than the second flow rate, the flow rate adjustment range can be expanded by controlling the bypass valve (17). In this case, the power generated by the generator (12) can be increased by bringing the output of the generator (12) closer to the limit value or maximizing the opening of the motor-operated valve (15).

In the third aspect, in the first or second aspect, the controller (30) maximizes the opening of the motor-operated valve (15) when the flow rate approaches the second flow rate in the second control.

In the third aspect, in the second control, the opening of the motor-operated valve (15) is maximized, thereby increasing the flow rate through the water turbine (11) and the generated power of the generator (12).

In a fourth aspect, in any one of the first to third aspects, the controller (30) executes a second operation in which a third control, a fourth control, and a fifth control are performed. In the third control, when the flow rate is within a third range from greater than zero to a third flow rate or less, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate approaches a target flow rate. In the fourth control, when the flow rate is within a fourth range from greater than the third flow rate to a fourth flow rate or less, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the output of the generator (12) approaches a limit value and the flow rate approaches the target flow rate. In the fifth control, when the flow rate is within a fifth range greater than the fourth flow rate and equal to or less than a fifth flow rate, the controller (30) controls the generator (12) so that the flow rate approaches a target flow rate while maintaining the opening of the motor-operated valve (15).

In the fourth aspect, in the third control, the target flow rate can be met while obtaining the highest efficiency. In the fourth control, the target flow rate can be met while the output of the generator (12) is at its maximum and does not exceed the limit value. In addition, in the fifth control, the controller (30) controls the rotation speed or torque of the water turbine (11) so that the flow rate approaches the target flow rate while maintaining the opening of the motor-operated valve (15). This allows the flow rate adjustment range to be further expanded.

In the fifth aspect, the fourth aspect is provided with a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11), and the controller (30) is configured to control the generator (12), the motor-operated valve (15), and the bypass valve (17) when the target flow rate is greater than the fifth flow rate in the second operation so that the output of the generator (12) approaches a limit value and the flow rate approaches the target flow rate, or so that the opening of the motor-operated valve (15) is maximized and the flow rate approaches the target flow rate.

In the fifth aspect, when the target flow rate is greater than the fifth flow rate, the flow rate adjustment range can be expanded by controlling the bypass valve (17). In this case, the power generated by the generator (12) can be increased by bringing the output of the generator (12) closer to the limit value or maximizing the opening of the motor-operated valve (15).

In the sixth aspect, in the fourth or fifth aspect, the controller (30) maximizes the opening of the motor-operated valve (15) in the fifth control.In the sixth aspect, by maximizing the opening of the motor-operated valve (15) in the fifth control, the generated power of the generator (12) can be increased.

In the seventh aspect, the controller (30) executes a third operation in which a sixth control and a seventh control are performed. In the sixth control, when the flow rate is within a sixth range greater than zero and equal to or less than a sixth flow rate, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate approaches a target flow rate. In the seventh control, when the flow rate is within a seventh range greater than the sixth flow rate and equal to or less than a seventh flow rate, the controller (30) controls the generator (12) so that the flow rate approaches a target flow rate while maintaining the opening of the motor-operated valve (15).

In the seventh aspect, in the seventh control, the flow rate can be quickly brought close to the target flow rate. This is because the response speed of the control based on the rotation speed and torque of the generator (12) is faster than the response speed of the control of the opening of the motor-operated valve (15).

In the eighth aspect, in the seventh aspect, the controller (30) sets the opening of the motor-operated valve (15) to a first opening that is smaller than the maximum when the flow rate approaches the sixth flow rate in the sixth control. In the seventh control, the controller (30) controls the generator (12) so that the flow rate approaches the target flow rate while maintaining the opening of the motor-operated valve (15) at the first opening.

In the eighth aspect, in the seventh control, the controller (30) does not maximize the opening of the motor-operated valve (15), but maintains it at a smaller first opening. Therefore, in the seventh control, the flow rate can be quickly brought close to the target flow rate.

In the ninth aspect, when the flow rate reaches a target flow rate in the seventh control, the controller (30) performs an eighth control to control the generator (12) and the motor-operated valve (15) so that the flow rate is maintained at the target flow rate and the opening of the motor-operated valve (15) is maximized.

In the ninth aspect, when the flow rate reaches the target flow rate through the seventh control, the controller (30) maximizes the opening of the motor-operated valve (15) through the eighth control, thereby increasing the power generated by the generator (12).

The tenth aspect includes a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11), and the controller (30) controls the generator (12), the motor-operated valve (15), and the bypass valve (17) in the seventh control such that, when the flow rate reaches a target flow rate, the flow rate is maintained at the target flow rate and the opening of the motor-operated valve (15) is maximized, or the flow rate is maintained at the target flow rate and the output of the generator (12) approaches a limit value.

In the tenth aspect, in the seventh control, when the flow rate reaches the target flow rate, the output of the generator (12) can be brought close to the limit value or the opening of the motor-operated valve (15) can be maximized while maintaining the target flow rate by controlling the bypass valve (17). As a result, the power generated by the generator (12) can be increased.

The eleventh aspect is any one of the first to tenth aspects, in which, for a given effective head, the flow rate of the water turbine (11) at which the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) is at its maximum efficiency is smaller than the flow rate of the water turbine (11) at which the generator (12) is in an unconstrained state.

The twelfth aspect is the eleventh aspect, in which the water turbine (11) is an axial flow type or a mixed flow type.

In the hydroelectric power generation systems of the eleventh and twelfth inventions, the range of the target flow rate tends to be larger than the flow rate range where maximum efficiency is obtained. By performing the second control, however, such a target flow rate can be covered.

FIG. 1 is a schematic configuration diagram of a hydroelectric power generation system according to an embodiment. FIG. 2 is a configuration diagram of a hydroelectric power generation system including each element of the controller. FIG. 3 is a characteristic map showing the relationship between the flow rate and the effective head of a water turbine. FIG. 4 is a flow chart of the basic operation. FIG. 5 is a characteristic map for explaining the first operation. FIG. 6 is a flowchart of the first operation. FIG. 7 is a characteristic map for explaining the first mode of the second operation. FIG. 8 is a characteristic map for explaining the second mode of the second operation. FIG. 9 is a flowchart of the second operation. FIG. 10 is a characteristic map for explaining the transient operation of the hydroelectric power generation system according to the first modification. FIG. 11 is a schematic configuration diagram of a hydroelectric power generation system according to the second modification. FIG. 12 is a characteristic map for explaining the first bypass control. FIG. 13 is a characteristic map for explaining the second bypass control. FIG. 14 is a characteristic map for explaining the third bypass control.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical spirit of the present disclosure. Since the drawings are intended to conceptually explain the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding.

(1) Overall Configuration The hydroelectric power generation system (10) shown in Fig. 1 is applied to a water supply system (1). The hydroelectric power generation system (10) in this example is applied to the terminal side of the water supply system (1). Water (fluid) that flows through the hydroelectric power generation system (10) is supplied to houses, buildings, etc.

The water supply system (1) includes a water tank (2), a flow path (4), and a water tank (8). The flow path (4) constitutes a pipeline between the water tank (2) and the water tank (8). The flow path (4) is a waterway through which water flows with a drop in height. Downstream of the water tank (8) are the targets of water supply, such as houses.

The flow path (4) includes a first flow path (5) and a second flow path (6). The first flow path (5) is formed upstream of the water turbine (11). The first flow path (5) is formed between the water tank (2) and the water turbine (11). The second flow path (6) is formed downstream of the water turbine (11). The second flow path (6) is formed between the water turbine (11) and the water tank (8).

As shown in Figures 1 and 2, the hydroelectric power generation system (10) includes a water turbine (11), a generator (12), a motor-operated valve (15), and a first flow rate sensor (16). As shown in Figure 2, the hydroelectric power generation system (10) includes a controller (30) and a grid-connected inverter (50).

(1-1) Water Turbine The water turbine (11) is disposed midway through the flow path (4). The water turbine (11) includes a casing and an impeller housed in the casing (not shown). A rotating shaft (13) is fixed to the center of the impeller. When the water turbine (11) is rotated by water flowing through the flow path (4), the rotating shaft (13) is driven to rotate.

The water turbine (11) is either an axial flow type or a mixed flow type. An axial flow type water turbine (11) is, for example, a propeller water turbine. In an axial flow type water turbine (11), the water passing through the impeller flows in the axial direction of the impeller. An mixed flow type water turbine (11) is, for example, a Delia water turbine. In a mixed flow type water turbine (11), the water passing through the impeller flows in a direction inclined to the axial direction of the impeller. Axial flow and mixed flow water turbines (11) are more suitable for large flow rates than Francis turbines.

(1-2) Generator The generator (12) is connected to the water turbine (11) via a rotating shaft (13). The generator (12) has a rotor and a stator (not shown). The rotor is of an embedded permanent magnet type. The stator has a coil.

When the water wheel (11) rotates, the water wheel (11) drives the generator (12). This causes the generator (12) to perform regenerative operation. During regenerative operation, the generator (12) generates electric power. The electric power generated by the generator (12) is supplied to the electric power system (60) via the electric power circuit (C). The electric power system (60) is, for example, a commercial power source. The electric power circuit (C) is configured to be able to supply electric power from the electric power system (60) to the generator (12), as will be described in detail later.

(1-3) Motor-operated valve The motor-operated valve (15) is disposed in series with the water turbine (11) in the flow path (4). The motor-operated valve (15) is disposed upstream of the water turbine (11) in the first flow path (5). The motor-operated valve (15) is a motor-driven pressure control valve. The opening of the motor-operated valve (15) is adjusted by a motor. The motor-operated valve (15) adjusts the effective head (H) of the water turbine (11).

(1-4) Flow Rate Sensor The first flow rate sensor (16) is disposed in the first flow path (5). The first flow rate sensor (16) detects the flow rate of water passing through the water turbine (11). The flow rate detected by the first flow rate sensor (16) is input to the controller (30).

2 includes an AC/DC converter (31) and a grid-connected inverter (50). The power circuit (C) is configured to be capable of supplying electric power in both directions between the generator (12) and the power grid.

The AC/DC converter (31) is provided in the controller (30). The AC/DC converter (31) has a plurality of switching elements. The AC/DC converter (31) converts the AC power generated by the generator (12) into DC power and outputs the converted DC power to the grid-connected inverter (50). The AC/DC converter (31) converts the DC power output from the grid-connected inverter (50) into AC power and outputs the converted AC power to the generator (12). In this way, the AC/DC converter (31) is a bidirectional converter.

The grid-connected inverter (50) has a plurality of switching elements that constitute an inverter section. The grid-connected inverter (50) converts the DC power output from the AC/DC converter (31) into AC power and supplies the converted AC power to the power system (60). The grid-connected inverter (50) converts the AC power supplied from the power system into DC power and outputs the converted DC power to the AC/DC converter (31). In this way, the grid-connected inverter (50) has a bidirectional inverter.

(1-6) Controller The controller (30) shown in Fig. 2 controls the generator (12) and the motor-operated valve (15). The controller (30) includes a microcomputer and a memory device in which a program for operating the microcomputer is stored.

The controller (30) controls the rotation speed and torque of the generator (12) and the opening of the motor-operated valve (15). The controller (30) has the above-mentioned AC/DC converter (31), a rotation speed detection unit (32), a turbine operating point estimation unit (33), a flow rate detection unit (34), a flow rate control unit (35), a generator control unit (36), and a valve control unit (37).

The rotation speed detection unit (32) detects the rotation speed of the generator (12). The rotation speed detected by the rotation speed detection unit (32) is output to the turbine operating point estimation unit (33) and the generator control unit (36). The turbine operating point estimation unit (33) determines the turbine operating point based on the rotation speed of the generator (12) and the torque command value of the generator (12). The flow rate detection unit (34) receives the flow rate (Q) detected by the first flow rate sensor (16).

The flow control unit (35) generates a torque command value for the generator (12) based on a preset target flow rate (Qo) and the flow rate (Q). The torque command value corresponds to the torque of the generator (12) for converging the flow rate (Q) to the target flow rate (Qo). The flow control unit (35) outputs the generated torque command value to the generator control unit (36).

In addition, the flow control unit (35) generates an opening command value for the motor-operated valve (15). The opening command value corresponds to the opening of the motor-operated valve (15) for converging the turbine operating point to the normal operating region. The flow control unit (35) outputs the generated opening command value to the valve control unit (37).

The generator control unit (36) controls the torque of the generator (12) so that the flow rate (Q) converges to the target flow rate (Qo). The generator control unit (36) receives the torque command value output from the flow rate control unit (35) and the rotation speed output from the rotation speed detection unit (32). The generator control unit (36) calculates a voltage command value according to the input torque command value and rotation speed. The generator control unit (36) controls the switching element of the AC/DC converter (31) based on the voltage command value. This causes the torque of the generator (12) to converge to the torque command value.

The valve control unit (37) controls the opening of the motor-operated valve (15) so that the flow rate (Q) converges to the target flow rate (Qo). The opening command value output from the flow rate control unit (35) is input to the valve control unit (37). The valve control unit (37) outputs a predetermined control signal to the motor-operated valve (15) in accordance with the input opening command value. This causes the opening of the motor-operated valve (15) to converge to the opening command value.

(1-7) Operation Unit As shown in FIG. 2, the hydroelectric power generation system (10) has an operation unit (40). The operation unit (40) is operated by an operator of the hydroelectric power generation system (10). The operator can use the operation unit (40) to set the operation mode of the hydroelectric power generation system (10) and a target flow rate (Qo) corresponding to the flow path (4). Information input to the operation unit (40) is output to the controller (30).

(1-8) Characteristics of the Hydroelectric Power Generation System and the Flow Channel The characteristics of the hydroelectric power generation system (10) and the flow channel (4) will be described with reference to FIGS. 1 and 3. FIG.

Figure 3 is a graph showing the characteristics of the water turbine, a so-called characteristics map. The vertical axis of Figure 3 is the effective head (H) of the water turbine (11), and the horizontal axis is the flow rate (Q) through the water turbine (11). The effective head (H) is the total head (Ho) shown in Figure 1 minus the head corresponding to the flow path resistance, the pressure loss of the motor valve (15), and the secondary pressure downstream of the water turbine (11). The total head (Ho) is the head between the liquid level in the water tank (2) and the liquid level in the water receiving tank (8). The flow path resistance corresponds to the resistance of the pipeline of the flow path (4).

The relationship between the effective head (H) and flow rate (Q) of the turbine (11) can be expressed by the system loss curve (flow resistance characteristic line) shown in Figure 3. The system loss curve has the characteristic that the effective head (H) decreases as the flow rate (Q) increases. The point (turbine operating point) corresponding to the flow rate (Q) and effective head (H) of the turbine (11) always moves on the system loss curve.

When the opening of the motor-operated valve (15) increases, the system loss curve shifts upward in the characteristic map. When the opening of the motor-operated valve (15) increases, the flow rate (Q) and the available head (H) of the flow path (4) increase. When the opening of the motor-operated valve (15) decreases, the system loss curve shifts downward in the characteristic map. When the opening of the motor-operated valve (15) decreases, the flow rate (Q) and the available head (H) decrease.

The maximum efficiency curve in Figure 3 is a curve that indicates the characteristics at which the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) is at its maximum efficiency. The maximum efficiency curve is obtained by plotting the flow rate (Q) at which maximum efficiency is obtained for each effective head (H). In the hydroelectric power generation system (10), if the turbine operating point is located on the maximum efficiency curve, it can be operated at maximum efficiency.

The unconstrained curve in Figure 3 is a constant torque curve that represents the torque of the generator (12) where the torque is zero. Therefore, when the turbine operating point reaches the unconstrained curve, the generator (12) cannot generate electricity.

The limit curve in FIG. 3 is a curve showing the limit value of the control range of the output of the generator (12). The limit value is, for example, the maximum torque or maximum output of the generator (12), or the maximum output of the hydroelectric power generation system (10). If the turbine operating point is above the limit curve, it means that the output of the generator (12) exceeds the limit value. If the output of the generator (12) exceeds the limit value, a malfunction such as a control malfunction or overheating occurs in the generator (12), the AC/DC converter (31), or the grid-connected inverter (50). If the turbine operating point is on the limit curve, the output of the generator (12) is maximum within the control range of the generator (12).

The characteristics and curves shown in FIG. 3 are stored in the memory device of the controller (30) as data such as tables and functions. Therefore, the controller (30) can use this data to determine various indices.

(2) Basic Operation The basic operation of the hydroelectric power generation system (10) will be described with reference to Figs.

Water in the water tank (2) flows through the flow path (4). After passing through the motor-operated valve (15), the water in the flow path (4) flows through the water wheel (11). When the water wheel (11) rotates due to the water flow, electricity is generated from the generator (12). The AC power generated by the generator (12) is converted to DC power by the AC/DC converter (31). The DC power converted by the AC/DC converter (31) is converted to AC power by the grid-connected inverter (50) and supplied to the power grid (60). The water that passes through the water wheel (11) is sent to the water tank (8).

(3) Problems In the hydraulic power generation system (10) of this embodiment, the unconstrained curve is located to the right of the maximum efficiency curve in the characteristic map shown in Fig. 3. In other words, for a given available head, the flow rate of the hydraulic turbine (11) at which the efficiency of the hydraulic turbine (11) or the efficiency of the hydraulic power generation system (10) is at its maximum efficiency is smaller than the flow rate of the hydraulic turbine (11) at which the generator (12) is in an unconstrained state. When the hydraulic turbine (11) is of an axial flow type or a diagonal flow type, the unconstrained curve tends to be located to the right of the maximum efficiency curve.

As described above, in the hydroelectric power generation system (10), maximum efficiency can be achieved by controlling the turbine operating point on the maximum efficiency curve. However, as shown in FIG. 3, if the characteristics of the hydroelectric power generation system (10) are such that the unconstrained curve is far to the right of the maximum efficiency curve, there is a problem that a relatively large target flow rate (Qo) cannot be met.

(4) Basic Control In order to solve the above problems, in the hydroelectric power generation system (10) of this embodiment, the control range of the target flow rate (Qo) is expanded by the following first and second operations. The first operation is an operation mode that prioritizes power generation output, and the second operation is an operation mode that prioritizes the target flow rate (Qo). The operator can select the first or second operation using the operation unit (40).

As shown in FIG. 4, when a command to start operation is input from the operation unit (40) to the controller (30) in step ST1, the process proceeds to step ST2. When the first operation is selected in the operation unit (40), the controller (30) executes the first operation in step ST3. When the second operation is selected in the operation unit (40), the controller (30) executes the second operation in step ST4. When a command to stop operation is input from the operation unit (40) to the controller (30) in step ST5, the controller (30) stops the first operation or the second operation in step ST6.

(5) First Operation In the first operation, the controller (30) switches between the first control and the second control shown in FIG.

As shown in FIG. 5, the controller (30) executes the first control when the flow rate (Q) is within a first range. The first range is a range greater than zero and equal to or less than a first flow rate (Q1). The first flow rate (Q1) is a flow rate corresponding to point a, which is an intersection point between the restriction curve and the maximum efficiency curve. In the example of FIG. 5, point a is lower than point b in the characteristic map. Point b is an intersection point between the system loss curve (hereinafter also referred to as the maximum system loss curve) when the opening degree of the motor-operated valve (15) is maximum, and the maximum efficiency curve. The meaning of "the opening degree of the motor-operated valve is maximum" includes not only that the motor-operated valve (15) is mechanically fully open, but also that the opening degree of the motor-operated valve (15) is at the upper limit value of its control range.

In the first control, the flow rate (Q) is adjusted so that the turbine operating point is along the maximum efficiency curve. Therefore, in the first control, the efficiency of the turbine (11) or the hydroelectric power generation system (10) can be brought closer to maximum efficiency.

When point a is above point b due to the operating conditions of the hydroelectric power generation system (10), the turbine operating point does not reach the limit curve even if the opening of the motor-operated valve (15) is maximized. Therefore, under such conditions, the controller (30) controls the motor-operated valve (15) and the generator (12) so that the turbine operating point is along the maximum efficiency curve in the range of the flow rate (Q) from zero to the flow rate at which the opening of the motor-operated valve (15) is maximized.

As shown in FIG. 5, the controller (30) executes the second control when the flow rate (Q) is within the second range. The second range is a range greater than the first flow rate (Q1) and equal to or less than the second flow rate (Q2). As shown in FIG. 5, the second flow rate (Q2) is a flow rate corresponding to point c, which is the intersection point between the maximum system loss curve and the limit curve. Therefore, when the turbine operating point reaches point c, the opening of the motor-operated valve (15) becomes maximum. In the second control, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the output of the generator (12) approaches the limit value and the flow rate (Q) approaches the target flow rate (Qo). "So that the output of the generator (12) approaches the limit value" strictly speaking means that the output of the generator (12) approaches the maximum and does not exceed the limit value. In the second control, the adjustment range of the flow rate (Q) can be expanded while preventing the turbine operating point from exceeding the limit curve.

In the second control, the controller (30) maximizes the opening of the motor-operated valve (15) when the flow rate (Q) approaches the second flow rate (Q2). Therefore, by maximizing the opening of the motor-operated valve (15), the power generated by the generator (12) can be increased.

When the target flow rate (Qo) is greater than the second range, the controller (30) controls the motor-operated valve (15) and the generator (12) so that the flow rate (Q) approaches the second flow rate (Q2). In this case, the target flow rate (Qo) cannot be satisfied, but the power generated by the generator (12) can be ensured.

(5-1) Control Example of the First Operation A specific control example of the first operation will be described with reference to FIG. 6. In the first operation, the process shown in FIG. 6 is repeatedly executed. In the first operation, the controller (30) controls the opening of the motor-operated valve (15) in the direction of the target flow rate (Qo) in step ST11. Specifically, in step ST11, the controller (30) changes the opening of the motor-operated valve (15) by a predetermined amount Δα so that the flow rate (Q) approaches the target flow rate (Qo). If the turbine operating point has not reached the limit curve in step ST12, the controller (30) controls the generator (12) in step ST13 so that the turbine operating point is maintained on the maximum efficiency curve. In this way, if the turbine operating point has not reached the limit curve, the adjustment of the opening of the motor-operated valve (15) in step ST11 and the control of the generator (12) in step ST13 are alternately repeated. This control corresponds to the first control.

If the turbine operating point has reached the limit curve in step ST12, then in step ST14 the controller (30) controls the generator (12) so that the turbine operating point is maintained on the limit curve. In this way, if the turbine operating point has reached the limit curve, adjustment of the opening of the motor-operated valve (15) in step ST11 and control of the generator (12) in step ST14 are alternately repeated. This control corresponds to the second control.

(6) Second Operation In the second operation, control is performed in the first mode or the second mode depending on the environment in which the hydroelectric power generation system (10) is installed and the operating conditions.

(6-1) First Mode of Second Operation The first mode of the second operation is performed under the condition that point a, which is the intersection point between the limit curve and the maximum efficiency curve, is below point b, which is the intersection point between the maximum system loss curve and the maximum efficiency curve, as shown in Fig. 7. In the first mode of the second operation, the controller (30) switches between and performs the third control, the fourth control, and the fifth control. Here, the third control is substantially the same as the first control of the first operation, and the fourth control is substantially the same as the second control of the first operation.

The controller (30) executes a third control when the flow rate (Q) is within a third range. The third range is a range greater than zero and equal to or less than a third flow rate (Q3). The third flow rate (Q3) corresponds to the first flow rate (Q1) in the first operation. In the third control, the controller (30) controls the motor-operated valve (15) and the generator (12) so that the turbine operating point is along the maximum efficiency curve and the flow rate (Q) approaches the target flow rate (Qo).

The controller (30) executes the fourth control when the flow rate (Q) is within the fourth range. The fourth range is a range greater than the third flow rate (Q3) and equal to or less than the fourth flow rate (Q4). The fourth flow rate (Q4) corresponds to the second flow rate (Q2) in the first operation. In the fourth control, the controller (30) controls the motor-operated valve (15) and the generator (12) so that the turbine operating point is along the limit curve and the flow rate (Q) approaches the target flow rate (Qo).

The controller (30) executes the fifth control when the flow rate (Q) is within the fifth range. The fifth range is a range greater than the fourth flow rate (Q4) and equal to or less than the fifth flow rate (Q5). The fifth flow rate (Q5) is a flow rate corresponding to point d shown in FIG. 7. Point d corresponds to a predetermined turbine operating point on the maximum system loss curve between the restricted curve and the unconstrained curve.

In the fifth control, the controller (30) controls the generator (12) so that the flow rate (Q) approaches the target flow rate (Qo) while maintaining the opening of the motor-operated valve (15). In other words, in the fifth control, the controller (30) controls the generator (12) so that the turbine operating point converges to the target flow rate (Qo) while following the maximum system loss curve. This makes it possible to further expand the adjustment range of the flow rate (Q) while continuing power generation by the generator (12).

In the fifth control, the opening of the motor-operated valve (15) is maintained at its maximum. This ensures that the generator (12) can generate sufficient power.

When the target flow rate (Qo) is greater than the fifth range, the controller (30) controls the generator (12) so that the flow rate (Q) approaches the fifth flow rate (Q5). In this case, the target flow rate (Qo) cannot be satisfied, but the power generated by the generator (12) can be ensured.

(6-2) Second Mode of Second Operation The second mode of the second operation is performed under the condition that point a, which is the intersection point between the limit curve and the maximum efficiency curve, is above point b, which is the intersection point between the maximum system loss curve and the maximum efficiency curve, as shown in Fig. 8. In the second mode of the second operation, the controller (30) switches between and performs the sixth control and the seventh control.

The controller (30) executes the sixth control when the flow rate (Q) is within the sixth range. The sixth range is a range greater than zero and equal to or less than a sixth flow rate (Q6). The sixth flow rate (Q6) corresponds to the flow rate at point b. In the sixth control, the controller (30) controls the motor-operated valve (15) and the generator (12) so that the turbine operating point is along the maximum efficiency curve and the flow rate (Q) approaches the target flow rate (Qo).

The controller (30) executes the seventh control when the flow rate (Q) is within the seventh range. The seventh range is greater than the sixth flow rate (Q6) and is equal to or less than the seventh flow rate (Q7). The seventh flow rate (Q7) is the flow rate corresponding to point e shown in FIG. 8. Point e corresponds to a predetermined turbine operating point on the maximum system loss curve between the maximum efficiency curve and the unconstrained curve.

In the seventh control, the controller (30) controls the generator (12) so that the flow rate (Q) approaches the target flow rate (Qo) while maintaining the opening of the motor-operated valve (15). In other words, in the seventh control, the controller (30) controls the generator (12) so that the turbine operating point converges to the target flow rate (Qo) while following the maximum system loss curve. This makes it possible to further expand the adjustment range of the flow rate (Q) while continuing power generation by the generator (12).

In the seventh control, the opening of the motor-operated valve (15) is maintained at its maximum. This ensures that the generator (12) can generate sufficient power.

When the target flow rate (Qo) is greater than the seventh range, the controller (30) controls the generator (12) so that the flow rate (Q) approaches the seventh flow rate (Q7). In this case, the target flow rate (Qo) cannot be satisfied, but the power generated by the generator (12) can be secured.

(6-3) Control Example of the Second Operation A specific control example of the second operation will be described with reference to FIG. 9. In the second operation, in step ST21, the controller (30) determines whether the opening of the motor-operated valve (15) is maximum. If the opening of the motor-operated valve (15) is not maximum in step ST21, the controller (30) controls the opening of the motor-operated valve (15) in the direction of the target flow rate in step ST22. Specifically, in step ST22, the controller (30) changes the opening of the motor-operated valve (15) by a predetermined amount Δα so that the flow rate (Q) approaches the target flow rate (Qo). If the turbine operating point has not reached the limit curve in step ST23, the controller (30) controls the generator (12) in step ST24 so that the turbine operating point is maintained on the maximum efficiency curve. In this manner, when the turbine operating point has not reached the limit curve, adjustment of the aperture of the motor-operated valve (15) in step ST22 and control of the generator (12) in step ST24 are alternately repeated. This control corresponds to the third control or the sixth control.

If the turbine operating point has reached the limit curve in step ST23, then in step ST25, the controller (30) controls the generator (12) so that the turbine operating point is maintained on the limit curve. In this way, if the turbine operating point has reached the limit curve, adjustment of the opening of the motor-operated valve (15) in step ST22 and control of the generator (12) in step ST25 are alternately repeated. This control corresponds to the fourth control.

In step ST21, if the opening of the motor-operated valve (15) is maximum and the flow rate (Q) is smaller than the target flow rate (Qo) in step ST26, the flow rate (Q) cannot be increased by the opening of the motor-operated valve (15). Therefore, in this case, in step ST28, the controller (30) controls the generator (12) so that the turbine operating point converges to the target flow rate (Qo). Specifically, the controller (30) increases the flow rate (Q) by controlling the torque of the generator (12). Also, in step ST26, if the flow rate (Q) is greater than the target flow rate (Qo) and the turbine operating point has not reached the limit curve or the maximum efficiency curve in step ST27, the process proceeds to step ST28. In this case, the flow rate (Q) is reduced by controlling the generator (12). These controls in step ST28 correspond to the fifth control and the seventh control.

(7) Effects of the embodiment In the first operation, when the flow rate (Q) is within a first range greater than zero and equal to or less than a first flow rate (Q1), the controller (30) performs a first control to control the generator (12) and the motor-operated valve (15) so that the efficiency of the hydraulic turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate (Q) approaches a target flow rate (Qo). Therefore, when the target flow rate (Qo) is within the first range, the flow rate (Q) can be brought close to the target flow rate (Qo) while obtaining maximum efficiency by the first control.

In the first operation, when the flow rate (Q) is within a second range that is greater than the first flow rate (Q1) and is equal to or less than the second flow rate (Q2), the controller (30) performs a second control that controls the generator (12) and the motor-operated valve (15) so that the output of the generator (12) approaches the limit value and the flow rate (Q) approaches the target flow rate (Qo). Therefore, even when the target flow rate (Qo) is greater than the first range, the flow rate (Q) can be brought closer to the target flow rate (Qo) by the second control. At this time, the output of the generator (12) approaches the maximum output, so that the power generated by the generator (12) can be sufficiently secured. In addition, since the output of the generator (12) does not exceed the limit value, it is possible to avoid the occurrence of problems such as control or overheating abnormality in the generator (12), the AC/DC converter (31), and the grid-connected inverter (50). Therefore, even in the second range, the turbine operating point can be reliably controlled and the flow rate (Q) can be converged to the target flow rate (Qo).

In the second control, the opening of the motor-operated valve (15) is maximized when the flow rate (Q) approaches the second flow rate (Q2). By maximizing the opening of the motor-operated valve (15), the power generated by the generator (12) can be increased in the second range.

In the first mode of the second operation, the controller (30) executes a fifth control in addition to the third control (corresponding to the first control) and the fourth control (corresponding to the second control). In the fifth control, when the flow rate (Q) is within the fifth range, the controller (30) controls the generator (12) so that the flow rate (Q) approaches the target flow rate (Qo) while maintaining the opening of the motor-operated valve (15). This allows the flow rate adjustment range to be further expanded compared to the first operation. In the fifth control, the opening of the motor-operated valve (15) is not adjusted, so that the flow rate (Q) can be quickly brought close to the target flow rate (Qo). This is because the response speed of the generator (12) to adjust the flow rate is faster than the response speed of the control of the opening of the motor-operated valve (15).

In the fifth control, the controller (30) maintains the opening of the motor-operated valve (15) at the maximum. This results in a larger power generation by the generator (12) compared to when the opening of the motor-operated valve (15) is smaller than the maximum.

In the second mode of the second operation, when the flow rate (Q) is within a sixth range from greater than zero to a sixth flow rate or less, the controller (30) performs a sixth control that controls the generator (12) and the motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches maximum efficiency and the flow rate (Q) approaches a target flow rate (Qo). Therefore, when the target flow rate (Qo) is within the sixth range, the sixth control can bring the flow rate (Q) closer to the target flow rate (Qo) while obtaining maximum efficiency.

In the second mode of the second operation, when the flow rate (Q) is within a seventh range greater than the sixth flow rate (Q6) and equal to or less than the seventh flow rate (Q7), the controller (30) performs a seventh control that controls the generator (12) so that the flow rate (Q) approaches the target flow rate (Qo) while maintaining the opening of the motor-operated valve (15). Therefore, when the target flow rate (Qo) is within the seventh range, the seventh control can quickly bring the flow rate (Q) closer to the target flow rate (Qo).

In the seventh control, the controller (30) maintains the opening of the motor-operated valve (15) at the maximum. This results in a larger power generation by the generator (12) compared to when the opening of the motor-operated valve (15) is smaller than the maximum.

The hydroelectric power generation system (10) has an operation unit (40) (setting unit) that can set the first operation and the second operation. Therefore, the operator can freely switch between the first operation, i.e., an operation that emphasizes power generation efficiency, and the second operation, i.e., an operation that emphasizes the target flow rate (Qo).

(6) Modifications The above embodiment may have the following modified configurations. The following describes the differences from the above embodiment.

(6-1) Modification 1
The hydroelectric power generation system (10) of the first modification performs a transient operation. The transient operation is executed, for example, when a first condition is satisfied, which indicates that the flow rate (Q) deviates from the target flow rate (Qo). The first condition is, for example, that the absolute value of the difference between the flow rate (Q) and the target flow rate (Qo) is greater than a predetermined value. In the transient operation, the generator (12) is controlled to adjust the opening of the motor-operated valve (15) after the flow rate (Q) quickly approaches the target flow rate (Qo).

As shown in FIG. 10, similar to the above-described embodiment, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches the maximum efficiency and the flow rate (Q) approaches the target flow rate (Qo). This control corresponds to the sixth control.

In the sixth control, it is assumed that the first condition is satisfied when the turbine operating point is at point f1 on the maximum efficiency curve. In this case, the controller (30) controls the generator (12) while maintaining the current opening of the motor-operated valve (15) at the first opening, thereby bringing the flow rate (Q) closer to the target flow rate (Qo). In the first modification, this control corresponds to the seventh control. The first opening is a predetermined opening smaller than the maximum opening of the motor-operated valve (15). Therefore, the turbine operating point approaches the target flow rate (Qo) so as to follow the system loss curve (dashed line in FIG. 10) corresponding to this first opening. When the turbine operating point reaches point f2, the flow rate (Q) becomes the target flow rate (Qo). This makes it possible to quickly meet the target flow rate (Qo).

After that, when the flow rate (Q) reaches the target flow rate (Qo) in the seventh control, the controller (30) controls the generator (12) and the motor-operated valve (15) so that the flow rate (Q) is maintained at the target flow rate (Qo) and the opening of the motor-operated valve (15) is maximized. This control corresponds to the eighth control. When the turbine operating point reaches point f3, the opening of the motor-operated valve (15) is maximized. As a result, the power generated by the generator (12) can be increased.

In addition, in the first modification, the controller (30) may execute the eighth control before the flow rate (Q) reaches the target flow rate (Qo) in the seventh control, and control the motor-operated valve (15) and the generator (12) so that the opening of the motor-operated valve (15) is maximized and the flow rate (Q) approaches the target flow rate (Qo).

(6-2) Modification 2
As shown in FIG. 11 , the hydroelectric power generation system (10) according to the second modification includes a bypass flow path (7) and a bypass valve (17). The bypass flow path (7) is connected to the flow path (4) so as to bypass the water turbine (11). An inlet end of the bypass flow path (7) is connected to the first flow path (5), and an outlet end of the bypass flow path (7) is connected to the second flow path (6). The bypass flow path (7) is provided with a bypass valve (17) and a second flow rate sensor (18). The bypass valve (17) is, for example, an electric valve. The second flow rate sensor (18) detects the flow rate of water in the bypass flow path (7). The flow rate detected by the second flow rate sensor (18) is input to a controller (30). The controller (30) controls the opening degree of the bypass valve (17).

In the second modification, the adjustment range of the flow rate (Q) can be expanded by opening the bypass valve (17). Here, the flow rate (Q) is the sum of the flow rate passing through the water turbine (11) (water turbine side flow rate (Qa)) and the flow rate passing through the bypass flow path (bypass side flow rate (Qb)). The first flow rate sensor (16) detects the water turbine side flow rate (Qa). The second flow rate sensor (18) detects the bypass side flow rate (Qb). Therefore, the controller (30) can adjust the water turbine side flow rate (Qa) and the bypass side flow rate (Qb), as well as the flow rate (Qo), by controlling the generator (12), the motor-operated valve (15), and the bypass valve (17).
(6-2-1) First Bypass Control The controller (30) of the second modification performs the first bypass control as shown in FIG. 12 in the first operation described above. In the first bypass control, when the target flow rate (Qo) is greater than the second flow rate (Q2), the controller (30) controls the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the output of the generator (12) approaches the limit value, the aperture of the motor-operated valve (15) becomes maximum, and the flow rate (Q) approaches the target flow rate (Qo). Specifically, in the example of FIG. 12, the controller (30) controls the torque of the generator (12), the aperture of the motor-operated valve (15), and the aperture of the bypass valve (17) by the first bypass control so that the turbine operating point reaches point b, which is the intersection point of the limit curve and the maximum system loss curve. As a result, it is possible to secure a sufficient amount of power generated by the generator (12) while securing a target flow rate (Qo) greater than the second flow rate (Q2).

In the first bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the opening of the motor-operated valve (15) is maximized and the flow rate (Q) approaches the target flow rate (Qo). In other words, in this case, the turbine operating point is on the maximum system loss curve but does not reach the limit curve.

In the first bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the output of the generator (12) approaches the limit value and the flow rate (Q) approaches the target flow rate (Qo). That is, in this case, the turbine operating point is on the limit curve but does not reach the maximum system loss curve.

(6-2-2) Second Bypass Control The controller (30) of the second modification performs the second bypass control in the second operation described above, as shown in FIG. 13. In the second bypass control, the controller (30) controls the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the aperture of the motor-operated valve (15) is maximized and the flow rate (Q) approaches the target flow rate (Qo) when the target flow rate (Qo) is greater than the fifth flow rate (Q5). Specifically, in the example of FIG. 13, the controller (30) controls the torque of the generator (12), the aperture of the motor-operated valve (15), and the aperture of the bypass valve (17) by the second bypass control so that the turbine operating point reaches point f on the maximum system loss curve. As a result, it is possible to ensure a sufficient amount of power generated by the generator (12) while ensuring a target flow rate (Qo) greater than the fifth flow rate (Q5).

In the second bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the output of the generator (12) approaches the limit value, the opening of the motor-operated valve (15) is maximized, and the flow rate (Q) approaches the target flow rate (Qo). In other words, in this case, the turbine operating point reaches the maximum system loss curve and the limit curve.

In the second bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the output of the generator (12) approaches the limit value and the flow rate (Q) approaches the target flow rate (Qo). That is, in this case, the turbine operating point is on the limit curve but not on the maximum system loss curve.

(6-2-3) Third Bypass Control The controller (30) of the second modification performs the third bypass control in the transient operation of the first modification as shown in Fig. 14. In the third bypass control, when the flow rate (Q) reaches the target flow rate (Qo) in the seventh control, the controller (30) controls the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the flow rate (Q) is maintained at the target flow rate (Qo), the aperture of the motor-operated valve (15) becomes maximum, and the output of the generator (12) approaches a limit value. Specifically, as shown in Fig. 14, when the turbine operating point reaches point f2 by the seventh control of the transient operation, the controller (30) controls the torque of the generator (12), the aperture of the motor-operated valve (15), and the aperture of the bypass valve (17) so that the turbine operating point reaches point b. As a result, even when the target flow rate (Qo) is relatively large, the target flow rate (Qo) can be quickly achieved while ensuring a sufficient amount of power generated by the generator (12).

In the third bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the opening of the motor-operated valve (15) is maximized and the flow rate (Q) approaches the target flow rate (Qo). In other words, in this case, the turbine operating point is on the maximum system loss curve but does not reach the limit curve.

In the third bypass control, the controller (30) may control the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the output of the generator (12) approaches the limit value and the flow rate (Q) approaches the target flow rate (Qo). That is, in this case, the turbine operating point is on the limit curve but does not reach the maximum system loss curve.

The controller (30) may execute the third bypass control before the flow rate (Q) reaches the target flow rate (Qo) in the seventh control.

(7) Other Embodiments In the above-described embodiment and modified examples, the following configurations may be adopted.

The controller (30) may adjust the flow rate (Q) by controlling the rotation speed of the generator (12) instead of the torque.

The hydroelectric power generation system (10) can also be installed in industrial water supplies, recycled water supplies, and sewerage systems, and is not limited to mains water supplies (1).

The fluid supplied to the fluid machine (e.g., the water turbine (11)) is not limited to water.

The controller (30) may estimate the above-mentioned flow rate (Q) based on a pre-stored system loss curve or characteristic map data.

The controller (30) may be configured separately from the hydroelectric power generation system (10). The controller (30) may be provided in a server device connected to the hydroelectric power generation system (10) via a network.

The present disclosure also covers a control method for performing the above-mentioned control executed by the controller (30), and a program for executing this control method.

Although the embodiments and modifications have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments, modifications, and other embodiments may be combined or substituted as appropriate as long as the functionality of the subject matter of this disclosure is not impaired.

The descriptions "first," "second," "third," etc. mentioned above are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words.

As described above, the present disclosure is useful for hydroelectric power generation systems.

4 Flow Path
7 Bypass flow path
10 Hydroelectric Power System
11 Waterwheel
12. Generator
15 Motor-operated valve
17 Bypass valve
30 Controller
Q1 First flow rate
Q2 Second flow rate
Q3 Third flow rate
Q4 4th flow rate
Q5 5th flow rate
Q6 6th flow rate
Q7 7th flow rate
Qo target flow rate

Claims (12)

A water turbine (11) disposed in a flow path (4) through which a fluid flows;
a generator (12) coupled to the water turbine (11);
a motor-operated valve (15) provided in series with the water turbine (11) in the flow path (4);
a controller (30) that controls the torque or rotation speed of the generator (12) and the opening of the motor-operated valve (15);
The controller (30)
a first control for controlling the generator (12) and the motor-operated valve (15) when the flow rate is within a first range greater than zero and equal to or less than a first flow rate, so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches a maximum efficiency and the flow rate approaches a target flow rate;
and, when the flow rate is within a second range that is greater than the first flow rate and equal to or less than a second flow rate, a second control is performed to control the generator (12) and the motor-operated valve (15) so that the output of the generator (12) approaches a limit value and so that the flow rate approaches a target flow rate. a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11),
2. The hydroelectric power generation system according to claim 1, wherein the controller (30) is configured to control the generator (12), the motor-operated valve (15), and the bypass valve (17) when, in the first operation, the target flow rate is greater than the second flow rate, so that the output of the generator (12) approaches a limit value and the flow rate approaches the target flow rate, or so that the opening degree of the motor-operated valve (15) is maximized and the flow rate approaches the target flow rate. The hydroelectric power generation system according to claim 1, wherein, in the second control, the controller (30) maximizes the opening degree of the motor-operated valve (15) when the flow rate is brought closer to the second flow rate. The controller (30)
a third control for controlling the generator (12) and the motor-operated valve (15) when the flow rate is within a third range greater than zero and equal to or less than a third flow rate, so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches a maximum efficiency and the flow rate approaches a target flow rate;
a fourth control for controlling the generator (12) and the motor-operated valve (15) so that an output of the generator (12) approaches a limit value and so that the flow rate approaches the target flow rate when the flow rate is within a fourth range that is greater than the third flow rate and is equal to or less than a fourth flow rate;
and a fifth control, when the flow rate is within a fifth range that is greater than the fourth flow rate and not greater than a fifth flow rate, to control the generator (12) so that the flow rate approaches a target flow rate while maintaining an opening degree of the electric valve (15). a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11),
5. The hydroelectric power generation system according to claim 4, wherein the controller (30) is configured to control the generator (12), the motor-operated valve (15), and the bypass valve (17) when, in the second operation, the target flow rate is greater than the fifth flow rate, so that the output of the generator (12) approaches a limit value and the flow rate approaches the target flow rate, or so that the opening degree of the motor-operated valve (15) is maximized and the flow rate approaches the target flow rate. The hydroelectric power generation system according to claim 4, wherein the controller (30) maximizes the opening degree of the motor-operated valve (15) in the fifth control. The controller (30)
a sixth control for controlling the generator (12) and the motor-operated valve (15) when the flow rate is within a sixth range greater than zero and equal to or less than a sixth flow rate, so that the efficiency of the water turbine (11) or the efficiency of the hydroelectric power generation system (10) approaches a maximum efficiency and the flow rate approaches a target flow rate;
and a seventh control for controlling the generator (12) so that the flow rate approaches a target flow rate while maintaining an opening degree of the motor-operated valve (15) when the flow rate is within a seventh range greater than the sixth flow rate and equal to or less than a seventh flow rate. The controller (30)
in the sixth control, when the flow rate is brought closer to the sixth flow rate, the opening degree of the motor-operated valve (15) is set to a first opening degree that is smaller than a maximum opening degree;
The hydroelectric power generation system according to claim 7, wherein in the seventh control, the generator (12) is controlled so that the flow rate approaches the target flow rate while maintaining the opening degree of the motor-operated valve (15) at the first opening degree. 8. The hydroelectric power generation system according to claim 7, wherein, when the flow rate reaches a target flow rate in the seventh control, the controller (30) performs an eighth control to control the generator (12) and the motor-operated valve (15) so that the flow rate is maintained at the target flow rate and an opening degree of the motor-operated valve (15) is maximized. a bypass valve (17) provided in a bypass flow path (7) that bypasses the water turbine (11),
8. The hydroelectric power generation system according to claim 7, wherein, in the seventh control, when the flow rate reaches a target flow rate, the controller (30) controls the generator (12), the motor-operated valve (15), and the bypass valve (17) so that the flow rate is maintained at the target flow rate and the opening degree of the motor-operated valve (15) is maximized, or so that the flow rate is maintained at the target flow rate and the output of the generator (12) approaches a limit value. The hydroelectric power generation system according to any one of claims 1 to 10, wherein, for a given effective head, the flow rate of the hydroelectric power generation system (10) at which the efficiency of the hydroelectric power generation system (10) is maximized is smaller than the flow rate of the hydroelectric power generation system (10) at which the generator (12) is in an unconstrained state. The hydroelectric power generation system according to claim 11, wherein the water turbine (11) is of an axial or mixed flow type.