KR102142074B1 - Controller of Hybrid Uninterruptible Power Supply including Energy Storage System - Google Patents

Abstract

In the hybrid UPS control device having the ESS (Energy Storage System) function of the present invention, by controlling the active and reactive power in both directions to the connected system, peak shaving and load leveling of the customer at peak times (Load) AC/DC converter performing leveling or adjusting the power factor of the customer, a switch for connecting or disconnecting a wire in a distribution line between the system and the AC/DC converter, connected to the output terminal of the AC/DC converter The battery is charged in the DC/AC converter and charging mode to supply a stable AC voltage to the load by performing constant voltage constant frequency control to supply an AC voltage having a certain size and frequency by receiving a DC-link voltage. And a DC/DC converter that controls the battery to be discharged in the discharge mode and controls the charging mode and the discharge mode so that the DC-link voltage is a constant voltage, and the switch is closed during normal operation. In the state, the system and the AC/DC converter are connected, and in an emergency operation, the switch is opened to cut off between the system and the AC/DC converter, wherein the AC/DC converter is stopped and the DC/DC The converter maintains control so that the DC-link voltage becomes constant. According to the present invention, in a hybrid UPS having an ESS function, it is possible to supply stable, high-quality power to a critical load by preventing a transient phenomenon caused by switching of a control mode.

Description

Controller of hybrid UPS with ESS function {Controller of Hybrid Uninterruptible Power Supply including Energy Storage System}

The present invention relates to an uninterruptible power supply (UPS), and more particularly, to a control device of a hybrid UPS including an energy storage system (ESS) function.

In general, an uninterruptible power supply (UPS) is a device that stores a portion of commercial power in a battery and supplies power from a battery when an abnormality occurs in the commercial power to supply AC power to the load side of the inverter. . That is, the AC power is normally converted to DC (DC) and stored in a battery. When an emergency such as a power outage, instantaneous power outage or voltage change occurs, the DC power stored in the battery is an inverter. It is a device that converts back to AC power. Such an uninterruptible power supply is used in various fields that require high power supply stability, such as power plants, telecommunication companies, broadcasting stations, and hospitals.

The UPS is composed of a power conversion system (PCS) and a battery, similar to an energy storage system (ESS). The main difference between UPS and ESS is that UPS operates only in emergency situations, such as a power outage, while ESS is always available. Therefore, the energy stored in the expensive UPS battery can be used only in an emergency, so the utilization rate is very low compared to the investment cost of the battery. If UPS and ESS are integrated, the cost of PCS can be reduced and battery utilization can be increased. Therefore, recently, UPS and ESS functions are integrated to perform peak shaving and load leveling during peak hours of electricity use, and in the event of an emergency, a hybrid UPS that supplies emergency power to critical loads. Research and development is in progress.

Unlike conventional UPSs, hybrid UPSs act as peak load reduction and load leveling by charging and discharging energy stored in the battery at normal times, so it is necessary to switch to a mode to supply stable power to critical loads in an emergency. do. Mode switching of such a hybrid UPS can cause transients instantaneously, and this transient decreases the safety and reliability of critical loads, so a rapid mode switching is required.

In the conventional proposed hybrid UPS control method, the AC/DC converter constantly controls the DC-link voltage regardless of the normal charging and discharging mode, and the bidirectional DC/DC converter takes charge of charging and discharging power of the battery. This control method may be advantageous in terms of battery management since the bidirectional DC/DC converter directly connected to the battery becomes the main charge and discharge control subject of the battery. However, when an accident occurs in the system, the AC/DC converter stops operating and the DC/DC converter must perform DC-link voltage constant control instead of the AC/DC converter that previously controlled the DC-link voltage constantly. do. Therefore, the DC/DC converter must switch the control method from charging/discharging power control to DC-link voltage constant control. However, there is a problem in that the switching of the control method may cause a serious transient of the DC-link voltage and degrade the quality of the voltage delivered to the critical load.

Republic of Korea Patent Publication 10-2016-0128706

The present invention has been devised to solve the above problems, and in a hybrid UPS having an ESS function, a control device for a hybrid UPS capable of supplying high-quality power to a critical load by preventing transients due to switching of a control mode The purpose is to provide.

The object of the present invention is not limited to the above-mentioned object, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

In the control device of a hybrid UPS having an ESS (Energy Storage System) function of the present invention for achieving the above object, by controlling the active power and reactive power for the power system to be connected, the peak load of the customer is reduced at the peak time ( AC/DC converter for performing peak shaving and load leveling or adjusting the power factor of the customer, a switch for connecting or disconnecting a wire in a distribution line between a grid and the AC/DC converter, the AC/DC converter DC/AC inverter for supplying a stable AC voltage to the load by being connected to the output terminal of the DC-link voltage and performing constant voltage constant frequency control to supply an AC voltage having a certain size and frequency. -Contains a DC/DC converter that operates in charge and discharge modes so that the link voltage is a constant voltage. In normal operation, the system and the AC/DC converter are connected while the switch is closed, and in emergency operation When the switch is opened, the system is disconnected from the AC/DC converter, where the AC/DC converter is stopped, and the DC/DC converter maintains control so that the DC-link voltage is constant.

The DC/DC converter stores the power in the battery by switching to a charging mode when the power received by the AC/DC converter is greater than the power supplied to the load in order to control the DC-link voltage to be constant. The AC/DC converter may transfer power stored in the battery to the connected system side and the load by switching to a discharge mode in which the commanded electric power is less than the power supplied to the load or the power supplied to the connected system side is required.

The AC/DC converter is capable of bidirectional power current control to supply and receive active and reactive power to the connected system side.

According to the present invention, in a hybrid UPS having an ESS function, it is possible to supply stable, high-quality power to a critical load by preventing a transient phenomenon caused by switching of a control mode.

That is, the hybrid UPS to which the control method proposed in the present invention is applied has an advantage of preventing transients from occurring in the emergency mode and supplying more stable power to critical loads.

1 is a view showing a control device of a hybrid UPS according to an embodiment of the present invention.
2 is a view showing that the α-β coordinates are converted to dq rotation coordinates.
3 is a diagram illustrating a current controller for controlling active power and reactive power according to an embodiment of the present invention.
4 is a diagram illustrating a constant voltage constant frequency control model according to an embodiment of the present invention.
5 is a diagram illustrating a constant voltage constant frequency controller model according to an embodiment of the present invention.
6 is a diagram illustrating a bidirectional DC/DC converter according to an embodiment of the present invention.
7 shows the DC-link voltage waveform of the first experimental example to which the control scheme proposed in the present invention is applied.
8 and 9 show the instantaneous voltage waveform of the critical load in the first experimental example.
10 shows a DC-link voltage waveform of the second experimental example to which the control scheme proposed in the present invention is applied.
11 and 12 show the instantaneous voltage waveform of the critical load in the second experimental example.
13 shows the DC-link voltage waveform of the third experimental example to which the control scheme proposed in the present invention is applied.
14 and 15 show the instantaneous voltage waveform of the critical load in the third experimental example.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

In addition, in the description with reference to the accompanying drawings, the same reference numerals are assigned to the same components regardless of reference numerals, and redundant descriptions thereof will be omitted. In the description of the present invention, when it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

The present invention relates to a control device of a hybrid UPS (Uninterruptible Power Supply) having an Energy Storage System (ESS) function.

1 is a view showing a control device of a hybrid UPS according to an embodiment of the present invention. In Figure 1 (a) is a normal operating state of the system, (b) shows an emergency operating state.

1, the control device of the hybrid UPS of the present invention includes a switch 10, AC/DC converter 100, DC/DC converter 200, battery 300, DC/AC converter 400 do.

As shown in Figure 1 (a), in the normal operation of the system, the control method of the hybrid UPS proposed in the present invention, the DC/DC converter 200 constantly controls the DC-link (DC-link) voltage. At this time, the inverter performs a constant voltage constant frequency (CVCF) constant voltage (CVCF) control that supplies an AC voltage having a constant size and frequency as a DC-link voltage to supply a stable voltage to a critical load. In addition, the bi-directional AC/DC converter 100 receives charge/discharge power and controls active power and reactive power to perform peak shaving and load leveling of customers at peak times or load leveling. It serves to adjust the power factor.

On the other hand, as shown in Figure 1 (b), in case of emergency, the switch 10 quickly cuts off between the grid and the UPS. Therefore, at this time, the AC/DC converter 100 stops the operation, and the DC/DC converter 200 that controls the DC-link voltage maintains control of the DC-link voltage as it is. In addition, since the DC/AC converter 400 needs to continuously supply a stable voltage to a critical load, it maintains constant voltage constant frequency (CVCF) control.

In the control method proposed in the present invention, the bi-directional DC/DC converter 200 always controls the DC-link voltage constantly in all cases such as charging mode, discharging mode, and emergency mode. Since there is no, it is possible to supply high-quality power to the critical load.

The switch 10 serves to connect or block electric wires in the distribution line between the system and the AC/DC converter 100.

The bi-directional AC/DC converter 100 serves to convert AC power to DC power by receiving charge/discharge power from a system that supplies power, and controls active and reactive power to reduce the peak load of customers during peak hours. (Peak shaving) and load leveling are performed or the role of adjusting the power factor of the consumer is performed.

The DC/DC converter 200 controls the battery 300 to be charged in the charging mode, controls the battery 300 to be discharged in the discharge mode, and sets the charging mode and the discharging mode so that the DC-link voltage becomes a constant voltage. Control.

The DC/AC converter 400 is connected to the output terminal of the AC/DC converter 100, receives a DC-link voltage, performs constant voltage constant frequency control to supply an AC voltage having a constant size and frequency, and loads the DC/AC converter. It serves to supply a stable AC voltage.

In the normal operation in the present invention, the system and the AC/DC converter 100 are connected while the switch 10 is closed.

And, in an emergency operation, the switch 10 is opened and the system and the AC/DC converter 100 are cut off, wherein the AC/DC converter 100 is stopped and the DC/DC converter 200 is DC- Maintain control so that the link voltage becomes constant.

In the present invention, the DC/DC converter 200 switches to the charging mode when the power received by the AC/DC converter 100 is greater than the power supplied to the load in order to control the DC-link voltage to be constant. 300). In addition, when the AC/DC converter 100 receives the commanded power is less than the power supplied to the load, it switches to a discharge mode and transmits the power stored in the battery 300 to the load.

The AC/DC converter 100 controls active power and reactive power. This control can be performed by simplifying the calculation of the three-phase circuit using the abc-αβ-dq transformation. Changing the three-phase voltage ( v _a,b,c ) and three-phase current ( i _a,b,c ) to the stop coordinates α-β is as follows.

At this time, assuming that the three-phase equilibrium is a three-phase four-wire line, since there is no image component, v ₀ and i ₀ are removed and can be expressed as follows.

When α-β is converted to d-q rotation coordinate, it is as follows.

2 is a view showing that α-β coordinates are converted to d-q rotation coordinates.

는 순시 상 전압과 선 전류에 의해 다음과 같이 계산된다. 3-phase instantaneous active power

Is calculated as follows by instantaneous phase voltage and line current.

Therefore, the relationship between the instantaneous active power (p) and the instantaneous reactive power (q) and the d-q axis current is calculated as in the following equation.

을 곱해주는 이유는 좌표변환 시 동일한 순시 전압과 전류 및 일정한 순시전력 관계인 변환행렬을 사용하기 때문이다.Here, v _d is the d-axis voltage obtained by converting the LC filter output voltage to dq coordinates, v _q is the q-axis voltage obtained by converting the LC filter output voltage to dq coordinates, and i _d is the current flowing through the interconnection line to dq coordinate conversion. Is the d-axis current, and i _q is the q-axis current resulting from the dq coordinate transformation of the current flowing in the interconnection line. Then, in equations 10 and 11

The reason for multiplying is because the same instantaneous voltage and current and constant instantaneous power relations are used in the transformation process.

When the output voltage is coordinate-converted, the value of V _d becomes 0 when V is based on (-)sine, and the value of V _q is the magnitude of the voltage. For this reason, the d-axis current can independently control reactive power and the q-axis current can control active power independently. Using this relationship, the reference current for outputting desired active power and reactive power can be summarized as follows.

Here, P ^* is an active power output command value, and Q ^* is a reactive power output command value, and a desired output value can be set. And, v _d is the d-axis voltage obtained by converting the output voltage into dq coordinates, v _q is the q-axis voltage obtained by converting the output voltage into dq coordinates, and i _{d_ref} is the d-axis current command value for controlling active power and reactive power. And i _{q_ref} is a q-axis current command value for controlling active power and reactive power.

3 is a diagram illustrating a current controller for controlling active power and reactive power according to an embodiment of the present invention.

In the current controller of FIG. 3(a), reactive power is controlled by the d-axis current, and active power is controlled by the q-axis current.

In the hybrid UPS control device proposed in the present invention, the DC/AC inverter 400 always operates with constant voltage constant frequency control because a stable voltage must be supplied to an important load. Constant Voltage Constant Frequency (CVCF) control method is used to maintain a constant voltage and frequency.

4 is a diagram illustrating a constant voltage constant frequency control model according to an embodiment of the present invention.

As shown in FIG. 4, the constant voltage constant frequency (CVCF) control method operates as an ideal voltage source having a low output impedance, which controls the magnitude and frequency of a constant voltage using a control loop.

5 is a diagram illustrating a constant voltage constant frequency controller model according to an embodiment of the present invention.

및 주파수

에 추종하도록 제어한다.As shown in FIG. 5, in the constant voltage constant frequency controller model, the voltage controller determines the voltage magnitude and frequency of the point to be controlled by the voltage magnitude created by the reference waveform oscillator.

And frequency

Control to follow.

는 기준파형의 상전압이고,

는 기준파형의 3상 전압을 d-q변환한 전압이다.here,

Is the phase voltage of the reference waveform,

Is a voltage obtained by dq converting the three-phase voltage of the reference waveform.

These parameters are summarized as follows.

6 is a diagram illustrating a bidirectional DC/DC converter according to an embodiment of the present invention.

Referring to FIG. 6, in the control method of the hybrid UPS proposed in the present invention, the bidirectional DC/DC converter 200 controls the DC-link voltage to be constant at all times.

In addition, the bidirectional DC/DC converter 200 stores the power in the battery 300 by operating in a step-down mode when the power received by the AC/DC converter 100 is greater than the load while the DC-link voltage is constantly controlled. Is done. Conversely, the DC/DC converter 200 operates in a boost mode when the power received by the AC/DC converter 100 is smaller than the load, and transmits the power stored in the battery 300 to the load.

Now, the results of the simulation of the hybrid UPS of the present invention in various modes will be described.

First, simulation results for the first experimental example, which is a case of switching from the charging mode to the emergency mode, will be described.

7 shows the DC-link voltage waveform of the first experimental example to which the control scheme proposed by the present invention is applied, and FIGS. 8 and 9 show the instantaneous voltage waveform of the critical load in the first experimental example.

Referring to FIGS. 7 to 9, in the first experimental example, a failure occurs at a point of 1.5 seconds during the charging mode, and a circuit breaker operates after 10 cycles (0.16 seconds) to separate a system from a critical load. However, the control method proposed in the present invention does not require a mode change because the DC/DC converter 200 continuously controls the DC-link voltage to be constant even if a failure occurs. Therefore, in the present invention, there is almost no transient phenomenon due to switching of the control mode, and the UPS of a general on-line structure satisfies within 4 ms, which is a time to ensure stable power.

The second experimental example is an experimental example of switching from a discharge mode to an emergency mode.

10 shows the DC-link voltage waveform of the second experimental example to which the control scheme proposed in the present invention is applied, and FIGS. 11 and 12 show the instantaneous voltage waveform of the critical load in the second experimental example.

Referring to FIGS. 10 to 12, in the second experimental example, a breakdown occurs at a point of 1.5 seconds while the system and the battery share power required by each important load, and the circuit breaker occurs after 10 cycles (0.16 seconds). This is a situation where the system is separated from the main load by operating. In this case, since the DC/DC converter 200 proposed in the present invention continuously controls the DC-link voltage to be constant, there is almost no transient, and the general on-line structure UPS guarantees stable power. It satisfies the time within 4ms.

The third experimental example is an experimental example of switching from the power trading mode to the emergency mode.

13 shows the DC-link voltage waveform of the third experimental example to which the control scheme proposed in the present invention is applied, and FIGS. 14 and 15 show the instantaneous voltage waveform of the critical load in the third experimental example.

13 to 15, in the third experimental example, the battery 300 shares the power required by the critical load and sends the remaining surplus power to the system, a failure occurs at the point of 1.5 seconds and causes 10 cycles (0.16 seconds). ) After that, the circuit breaker operates to separate the system from the critical load. In this case as well, since the DC/DC converter 200 proposed by the present invention continuously controls the DC-link voltage to be constant, there is almost no transient, and a UPS with a general on-line structure guarantees stable power. You can see that it satisfies within 4ms, the time to do.

As can be seen from the above, it can be confirmed that the hybrid UPS using the control method proposed in the present invention has almost no transient in an emergency and satisfies within 4 ms, which is a time for ensuring a stable power supply in a typical on-line structure.

Although the present invention has been described above using some preferred embodiments, these embodiments are illustrative and not limiting. Those skilled in the art to which the present invention pertains will understand that various changes and modifications can be made without departing from the spirit of the present invention and the scope of the rights set forth in the appended claims.

10 switch 100 AC/DC converter
200 DC/DC converter 300 battery
400 DC/AC converter

Claims (3)

In the control unit of the hybrid UPS having an Energy Storage System (ESS) function,
An AC/DC converter that performs peak shaving and load leveling of the customer or adjusts the power factor of the customer in a peak time period in which active and reactive power can be controlled in both directions with respect to a connected system;
A switch for connecting or disconnecting a wire in a distribution line between the system and the AC/DC converter;
DC/AC for supplying a stable AC voltage to a load by performing constant voltage constant frequency control that is connected to the output terminal of the AC/DC converter and receives a DC-link voltage to supply an AC voltage having a certain size and frequency. Converter; And
And a DC/DC converter that controls the DC-link voltage to be a constant voltage to charge the battery in the charge mode and discharge the battery in the discharge mode,
In normal operation, the system and the AC/DC converter are connected while the switch is closed.
During an emergency operation, the switch is opened to cut off between the system and the AC/DC converter, where the AC/DC converter is stopped and the DC/DC converter maintains control so that the DC-link voltage is constant. ,
In order to control the DC/DC converter to have a constant DC-link voltage,
When the AC/DC converter receives the commanded power is greater than the power supplied to the load, it switches to a charging mode to store power in the battery,
When the AC/DC converter receives the commanded power is less than the power supplied to the load or when power to be supplied to the connection system side is required, the system switches to the discharge mode and transmits the power stored in the battery to the connection system side and the load. ,
The AC/DC converter serves to control active and reactive power in both directions with respect to the connected system, and by controlling the active power and reactive power, the peak shaving and load leveling of the customer during peak times are performed. leveling) or to adjust the power factor of the consumer.
The DC/DC converter controls the DC-link voltage to be kept constant in all cases including charging mode, discharging mode, normal operation and emergency operation,
The AC/DC converter is a control device for a hybrid UPS, characterized in that it performs output control of active power and reactive power in a manner that simplifies calculation of a three-phase circuit using abc-αβ-dq conversion.
delete delete

Images