JP5673118B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that controls a motor.

  Conventionally, power converters that control motors such as compressors are widely known.

  For example, Patent Document 1 discloses a power conversion device that varies the output torque of a motor in accordance with the pulsation of load torque during one rotation of the compressor. That is, for example, as shown in FIG. 16, in the rotary compressor, when the piston makes one revolution, the compression torque varies according to the rotation angle, and the load torque of the motor also pulsates accordingly. Therefore, in the power conversion device of Patent Document 1, the output torque of the motor is varied so as to be synchronized with the pulsation of the load torque. Thereby, the load torque of the motor is reduced to suppress vibration during operation of the compressor.

  On the other hand, Patent Document 2 discloses a power conversion device having a very small capacitor for smoothing the output voltage. Specifically, this power conversion device includes a converter circuit, a DC link unit connected in parallel to the converter circuit, and an inverter circuit having a plurality of switching elements. In the converter circuit, the power supply voltage of the AC power supply is full-wave rectified and output to the DC link unit. A capacitor having a very small capacitance is connected to the DC link portion. Specifically, this capacitor has a capacitance of about 1/100 that of a normal smoothing capacitor. For this reason, the rectified voltage is output from the DC link unit as a pulsating DC voltage without being smoothed. The inverter circuit converts this DC voltage into AC power and supplies this power to the motor to drive the motor. In the power conversion device of Patent Document 2, the size of the power conversion device is reduced and the cost is reduced by reducing the capacity of the capacitor in this way.

  Furthermore, Patent Literature 3 discloses a device that performs torque control as described above for a power converter having a small capacitor capacity as disclosed in Patent Literature 2. That is, when the capacitance of the capacitor of the DC link portion is small, the output voltage to the inverter circuit also has a pulsating component. Therefore, in Patent Document 3, the pulsation component of the load torque of the motor and the pulsation component of the output voltage of the power supply voltage are superimposed on the output torque, and the output torque is varied according to the load torque of the motor. Vibration is reduced.

Japanese Patent Laid-Open No. 2005-046000 JP 2002-51589 A Japanese Patent No. 4192979

  By the way, in the power converter as disclosed in Patent Document 3, when the fluctuation range of the output torque becomes relatively large, the output torque may reach a minus side (that is, minus torque). In this way, when the output torque of the motor reaches the negative side, the motor performs a regenerative operation.

  Under such circumstances, for example, as disclosed in Patent Document 1, if the capacity of the capacitor of the DC link unit is relatively large, even if the motor performs a regenerative operation, the regenerative energy can be sufficiently absorbed by the capacitor. . However, as disclosed in Patent Documents 2 and 3, for example, in a power converter having a very small capacity of the capacitor, the regenerative energy of the motor cannot be sufficiently absorbed by the capacitor. Therefore, an overvoltage is generated in the DC link portion, and there is a possibility that a problem such as destruction of the switching element of the inverter circuit may be caused.

  In particular, in a power converter that performs torque control as described above, when the primary component (fundamental frequency component) that is the main factor of vibration in the load torque is to be sufficiently reduced, the fluctuation range of the output torque increases. easy. As a result, the output torque of the motor is likely to reach the minus side, and it is likely to cause a problem due to the regeneration of the motor as described above.

  This invention is made | formed in view of this point, The objective is to prevent the overvoltage resulting from the regeneration operation | movement of a motor in the power converter device which has a small capacity | capacitance capacitor | condenser.

A first invention is directed to a power converter, and includes a converter circuit (11) for rectifying a power supply voltage of an AC power supply (6), and a capacitor (16) connected in parallel to the output of the converter circuit (11). A DC link part (15) for outputting a pulsating DC voltage, and an inverter circuit (20) for switching the output of the DC link part (15) to convert it to AC and supplying it to the connected motor (5) ) And a command value obtained by superimposing a pulsation component of the output voltage of the AC power source (6) on a torque command value having a fluctuation range larger than the average value of the load torque of the motor (5). And a control unit (40) for controlling the output torque of the motor (5), and the control unit (40) prevents the motor (5) from having a negative output torque during the torque control. (5) Limiting part that limits output torque Characterized in that it comprises 60).

  In the first invention, the output torque of the motor (5) pulsates so that the pulsation component of the output voltage of the AC power supply (6) is superimposed on the output torque of the motor (5). When the output torque of the motor (5) reaches the negative side, the motor (5) may perform a regenerative operation. Therefore, the limiting unit (60) of the present invention limits the output torque so that the output torque of the motor (5) does not become negative. Thereby, the regenerative operation of the motor (5) can be prohibited.

In the first invention, the output torque of the motor (5) varies according to the load torque of the motor (5). Thereby, the vibration of the motor (5) is suppressed. On the other hand, when torque control is performed in this way, the fluctuation range of the output torque of the motor (5) increases, and this output torque tends to reach the minus side. Therefore, the limiting unit (60) of the present invention limits the output torque so that the output torque of the motor (5) does not fluctuate to the negative side during the torque control operation. Thereby, the regenerative operation of the motor (5) can be prohibited during torque control.

In the second aspect of the invention, the fundamental frequency component of the load torque of the motors (5) can be effectively suppressed, thereby improving the effect of suppressing the vibration of the motor (5).

  On the other hand, when the fluctuation range of the output torque of the motor (5) increases in this way, the output torque tends to reach the minus side. However, the limiter (60) restricts the output torque of the motor (5) from fluctuating to the negative side during torque control, so that the output torque reaches the negative side and the motor (5) performs regenerative operation. It is not going to go.

In a second aspect based on the first aspect, the control unit (40) is configured to multiply the torque obtained by multiplying an average value of the load torque of the motor (5) by an index indicating a fundamental frequency component of the load torque. It is obtained as a command value.

According to a third invention, in the first or second invention, the control unit (40) is based on a power supply voltage of the AC power supply (6) or an output voltage of the DC link unit (15) during a torque control operation. Then, the fluctuation range of the output torque of the motor (5) is corrected.

In the torque control operation of the third invention, the fluctuation range of the output torque of the motor (5) is corrected based on the power supply voltage of the AC power supply (6) and the output voltage (DC link voltage) of the DC link section (15). Is done. Thus, for example, the fluctuation range of the output torque of the motor (5) can be limited under a condition where the power supply voltage is relatively high or a condition where the power supply voltage is relatively low. As a result, for example, the resonance between the reactor and the capacitor (16) due to the excessive fluctuation range of the output torque during torque control operation under the condition where the power supply voltage is relatively high is avoided. As a result, the output voltage of the DC link section (15) can be prevented from becoming excessive. Further, for example, it is possible to avoid deterioration in controllability of the torque control operation due to an excessive fluctuation range of the output torque under a condition where the power supply voltage is relatively low.

The fourth invention is the first to third any one invention, the control unit (40), the peak current of the motor (5) when the torque control operation exceeds a predetermined upper limit value, the The variation range of the output torque of the motor (5) is reduced.

In the fourth invention, the output torque of the motor (5) is limited according to the peak current of the motor (5). When the torque control operation is performed by the power converter of the present invention (that is, the power converter having a very small capacity of the capacitor), the pulsation component of the output voltage of the DC link unit (15) and the pulsation of the load torque of the motor (5) Since the components are superposed, if the peaks of the two pulsating components overlap, the peak current of the motor (5) will rise extremely. As a result, this peak current may exceed the rated maximum allowable current value of the switching element, for example, and the switching element may be destroyed. Therefore, in the present invention, when the peak current of the motor (5) exceeds a predetermined upper limit value, the fluctuation range of the output torque of the motor (5) is reduced. As a result, an increase in the peak current of the motor (5) is suppressed, and the switching elements and the like are protected.

According to a fifth invention , in the fourth invention, the control unit (40) has a peak hold unit (55) for holding the maximum value of the current of the motor (5) as a peak current for a predetermined determination time. The output torque of the motor (5) is reduced when the peak current held by the peak hold unit (55) exceeds a predetermined upper limit value.

In the fifth aspect , the peak hold unit (55) holds the maximum value of the current of the motor (5) as the peak current, so that the peak current of the motor (5) can be reliably derived. This point will be described in detail.

  As described above, the current of the motor (5) becomes the largest when the peak of the load torque of the motor (5) coincides with the peak of the output voltage of the DC link section (15). However, the pulsation cycle of the load torque of the motor (5) and the pulsation cycle of the output voltage of the DC link section (15) are not necessarily the same, so the current of the motor (5) is not synchronized with the peak of both. Even if this is detected, this current value becomes a relatively small value. That is, if the current of the motor (5) is not detected at the timing when the peaks of both are superimposed, the peak current of the motor (5) that can occur during the torque control operation cannot be reliably derived.

  Therefore, in the present invention, the peak hold unit (55) holds the maximum value of the current of the motor (5) every predetermined determination period. Thereby, in this determination period, it becomes easy to derive the peak current at the timing when the peak of the load torque of the motor (5) and the peak of the output voltage of the DC link voltage overlap. The torque control amount adjusting unit (54) performs control to reduce the fluctuation range of the output torque of the motor (5) when the peak current derived in this way exceeds a predetermined upper limit value.

In a sixth aspect based on the fifth aspect , the control unit (40) is configured such that the peak of the pulsation component of the load torque of the motor (5) and the DC link during the determination period of the peak hold unit (55). A speed command adjusting unit (72) for correcting the operating frequency of the motor (5) is provided so that the peak of the pulsating component of the output voltage of the unit (15) is superimposed.

In the sixth invention, during the peak hold determination period, the speed command adjustment unit (72) superimposes the load torque peak of the motor (5) and the output voltage peak of the DC link unit (15). The operating frequency of the motor (5) is corrected. As a result, in this determination period, the peak current of the motor (5) at the time when both peaks are superimposed can be reliably derived.

In a seventh aspect based on the sixth aspect , the control unit (40) is configured such that the frequency of the output voltage of the AC power source (6) or the DC link unit (15), the operating frequency of the motor (5), A period deriving unit (71) for deriving a period in which the peak of the load torque of the motor (5) and the peak of the output voltage of the DC link unit (15) are superimposed, and the speed command adjusting unit ( 72) corrects the operating frequency of the motor (5) so that the period derived by the period deriving unit (71) is equal to or shorter than the determination period of the peak hold unit (55). .

In the seventh invention, the cycle deriving unit (71) uses the DC link unit (15) based on the frequency of the output voltage of the AC power source (6) and the DC link unit (15) and the operating frequency of the motor (5). ) And the peak of the load torque of the motor (5) are derived. The speed command adjustment unit (72) corrects the operating frequency of the motor (5) so that the cycle derived in this way is equal to or less than the determination period of the peak hold unit (55). As a result, during this determination period, the peak of the output voltage of the DC link section (15) can always be matched once, and the peak current can be reliably derived.

  According to the present invention, the limiter (60) limits the output torque of the motor (5) so that the output torque of the motor (5) does not become negative. Thereby, the regenerative operation of the motor (5) can be surely avoided to prevent overvoltage. As a result, even if the capacity of the capacitor (16) of the DC link portion (15) is small, it is possible to reliably prevent the switching elements and the like from being damaged due to the regenerative operation of the motor (5).

In particular, in the first invention, vibration of the motor (5) can be prevented by performing the torque control operation. Further, in the second aspect of the present invention can be reliably prevent vibration of the motor (5) to effectively suppress the primary component of the load torque. On the other hand, in the first invention, even if the fluctuation range of the output torque increases in this way, it is possible to reliably prevent the output torque from becoming negative, and the regenerative operation of the motor (5) can be avoided.

In the third aspect of the present invention, a problem caused by the increase or decrease of the power supply voltage during the torque control operation can be avoided by controlling the fluctuation range of the output torque.

In the fourth invention, when the peak current of the motor (5) exceeds a predetermined value, the fluctuation range of the output torque of the motor (5) is reduced. For this reason, it can avoid beforehand that the electric current value of a motor (5) becomes excessive and a switching element etc. are damaged.

In particular, in the fifth aspect of the invention, since the peak hold is performed to hold the current value of the motor (5) in a predetermined determination period, the peak of the load torque and the peak of the DC link voltage are overlapped. The peak current can be derived.

Furthermore, in the sixth and seventh inventions, the operating frequency of the motor (5) is adjusted so that the peak of the load torque and the peak of the DC link voltage coincide within the determination period. Since this operation frequency is generally determined based on the power supply frequency, for example, even when the power supply frequency of the AC power supply (6) varies with respect to a desired frequency (for example, 50 Hz or 60 Hz), Beats can be generated with a period of For example, even when the microcomputer clock varies, beats can be generated at a desired cycle. As a result, it is possible to reliably derive the peak current at the timing when the peak of the load torque and the peak of the DC link voltage coincide within this determination period.

FIG. 1 is a schematic circuit diagram of a power converter according to an embodiment. FIG. 2 is a block diagram illustrating details of the control unit of the power conversion apparatus. FIG. 3 is a block diagram showing details of the torque control unit of the power converter. FIG. 4 is a chart showing waveforms of the motor load torque, the DC link voltage, and the motor output torque in the torque control operation (torque control amount = 100%). FIG. 5 is a chart showing waveforms of motor load torque, DC link voltage, and motor output torque in torque control operation (torque control amount = 150%), and the negative torque is not limited by the limiter. Is in state. FIG. 6 is a chart showing waveforms of the motor load torque, the DC link voltage, and the motor output torque in the torque control operation (torque control amount = 150%), in a state where the negative torque is limited by the limiter. Is. FIG. 7 is a chart showing waveforms of the motor load torque, DC link voltage, and motor output torque in the torque control operation, in which the peak of the load torque and the peak of the DC link voltage are superimposed. is there. FIG. 8 is a chart for explaining the peak hold operation in the torque control operation. FIG. 9 is a chart for explaining a state in which the peak of the load torque of the motor and the peak of the DC link voltage are gradually shifted. FIG. 10 is a block diagram of the speed command correction unit. FIG. 11 is a chart showing the beat generation period and the peak hold determination period, and shows a state in which no beat occurs in each determination period. FIG. 12 is a flowchart showing the control operation of the speed command correction unit. FIG. 13 is a chart showing a beat generation cycle and a peak hold determination cycle, and shows a state in which a beat occurs for each determination period. FIG. 14 is a chart showing an example of an increase in the DC link voltage accompanying the resonance between the reactor and the capacitor. FIG. 15 is a schematic circuit diagram of a power conversion device according to another embodiment. FIG. 16 is a chart showing an example of fluctuations in compression torque.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are essentially preferable examples, and are not intended to limit the scope of the present invention, its application, or its use.

<< Embodiment of Invention >>
The power converter (10) according to the present invention is connected to a three-phase AC motor (5) of a compressor connected to a refrigerant circuit of an air conditioner, for example. The compressor is composed of a rotary compressor having one cylinder, for example. That is, in this compressor, when the drive shaft makes one rotation, the compression torque (that is, the load torque of the motor (5)) pulsates. The motor (5) is, for example, a 4-pole 6-slot concentrated winding DC brushless motor. As will be described later, the power conversion device (10) is configured to be able to execute a torque control operation that reduces the load torque of the motor (5) and suppresses the vibration of the motor (5).

<Overall configuration of power converter>
As shown in FIG. 1, the power conversion device (10) includes a converter circuit (11), a DC link unit (15), an inverter circuit (20), and a control unit (40). The power conversion device (10) converts AC power supplied from the single-phase AC power supply (6) into power of a predetermined frequency and supplies it to the motor (5).

  The converter circuit (11) is connected to the AC power source (6). The converter circuit (11) is a so-called diode bridge circuit in which a plurality (four in this embodiment) of diodes (D1 to D4) are connected in a bridge shape. The converter circuit (11) is a full-wave rectification circuit that full-wave rectifies the alternating current output from the alternating-current power supply (6) into direct current.

  The DC link unit (15) is connected in parallel to the output side of the converter circuit (11). A reactor (12) is connected between the converter circuit (11) and the DC link unit (15). The DC link part (15) has a capacitor (16). The DC voltage (DC link voltage Vdc) generated at both ends of the capacitor (16) is connected to the input node of the inverter circuit (20).

  The capacitor (16) is constituted by, for example, a film capacitor. The capacitor (16) is set to have a relatively small capacitance (for example, several tens of μF). Specifically, the capacitor (16) has a ripple voltage (voltage) generated corresponding to the frequency of the switching operation when the switching element (Su, Sv, Sw, Sx, Sy, Sz) of the inverter circuit (20) operates. (Capacitance) can be smoothed. On the other hand, the capacitor (16) has a capacitance that cannot smooth the voltage rectified by the converter circuit (11) (voltage fluctuation caused by the power supply voltage). Therefore, the DC link unit (15) receives the output of the converter circuit (11), and the DC link voltage Vdc having a pulsation having a frequency twice the power supply voltage Vin of the AC power supply (6) from both ends of the capacitor (16). Is output. The DC link voltage Vdc output from the DC link unit (15) has a large pulsation such that the maximum value is twice or more the minimum value.

  The inverter circuit (20) constitutes a conversion unit, the input node is connected in parallel to the capacitor (16) of the DC link unit (15), and the output of the DC link unit (15) is switched to provide a three-phase AC And supply to the connected motor (5). The inverter circuit (20) of the present embodiment is configured by a plurality of switching elements being bridge-connected. Since this inverter circuit (20) outputs three-phase alternating current to the motor (5), it has six switching elements (Su, Sv, Sw, Sx, Sy, Sz). Specifically, the inverter circuit (20) includes three switching legs in which two switching elements are connected in series with each other. In each switching leg, the switching elements of the upper arm (Su, Sv, Sw) and the lower arm are switched. The midpoints of the elements (Sx, Sy, Sz) are respectively connected to coils (not shown) of each phase of the motor (5). In addition, free-wheeling diodes (Du, Dv, Dw, Dx, Dy, Dz) are connected in antiparallel to each switching element (Su, Sv, Sw, Sx, Sy, Sz). The inverter circuit (20) switches the DC link voltage (vdc) input from the DC link unit (15) by turning on and off these switching elements (Su, Sv, Sw, Sx, Sy, Sz). Convert to phase AC voltage and supply to motor (5).

  The power conversion device (10) includes various detection units. Specifically, the power converter (10) includes a power supply voltage detector (25) that detects a power supply voltage (Vin) of the AC power supply (6) and a power supply phase (θin) of the power supply voltage of the AC power supply (6). The power supply phase detection unit (26) for detecting and the power supply frequency detection unit (27) for detecting the frequency (fin) of the power supply voltage of the AC power supply (6) are included. The power converter (10) includes an input current detector (28) that detects the input current (Iin) of the converter circuit (11) and a DC that detects the DC link voltage (Vdc) of the DC link unit (15). And a link voltage detector (29). Further, the power conversion device (10) includes a motor current detection unit (30) that detects a current (Idq) flowing through the motor (5) (specifically, a current flowing through each phase of the motor (5)), a motor ( The motor phase detector (31) that detects the phase (θm) of 5) and the motor rotation speed detector (32) that detects the actual rotational speed (ωm) of the motor (5) are provided.

  The control unit (40) outputs a gate signal (G) for controlling switching (on / off operation) of the inverter circuit (20) to the inverter circuit (20). The control unit (40) of the present embodiment superimposes the pulsating component of the power supply voltage, and performs a torque control operation that varies the output torque of the motor (5) in accordance with the load torque variation of the motor (5). It is configured.

<Detailed configuration of control unit>
As shown in FIG. 2, the control unit (40) includes a speed control unit (41), a torque control unit (50), a torque control superposition unit (42), a torque command modulation unit (43), and a secondary harmonic application unit. (44), an input current command generation unit (45), an amplifier (46), a limiter (60), a current control unit (47), and a PWM calculation unit (48).

  The deviation after the actual rotational speed (ωm) of the motor (5) is subtracted from the speed command (ω *) of the motor rotational speed in the subtractor (34) is input to the speed controller (41). . The speed controller (41) calculates the average (average torque) of the load torque of the motor (5) by performing proportional / integral calculation (PI calculation) on the deviation between the actual rotation speed (ωm) and the speed command (ω *). Is calculated. This average torque is an average value of load torque pulsating at a predetermined cycle. The speed control unit (41) outputs the average torque as a command value (average torque command value (Tave *)) to the torque control superimposing unit (42).

  In the torque control superimposing unit (42), the average torque command value (Tave *) is multiplied by the command value output from the torque control unit (50) described in detail later. As a result, the torque control superimposing unit (42) generates a torque command value (T *) in which the pulsation component of the load torque of the motor (5) is superimposed. The command value generated by the torque control superimposing unit (42) is input to the torque command modulating unit (43).

The torque command modulation unit (43) generates a sine value sinθin by using the phase angle (power supply phase (θin)) of the AC power supply (6) as an input, and sets the modulation coefficient r corresponding to this to the torque command value (T *). Multiply and output to the secondary harmonic application unit (44). The secondary harmonic application unit (44) applies a frequency component twice the power supply frequency to the output value of the torque command modulation unit (43) so that the output power from the motor (5) is sinusoidal. The modulation coefficient r is, for example, | sin (θin) | or sin ² (θin). Note that the modulation coefficient r may be changed according to the power supply frequency (50 Hz or 60 Hz) in order to make the output power of the motor (5) close to a sine wave. Alternatively, the modulation coefficient r may be determined according to a sine value sin (θin + Δ) obtained by shifting the phase (θin) by a predetermined amount Δ so that the output power of the motor (5) becomes a sine wave. As a result, it is possible to obtain substantially the same effect as when a frequency component twice the power supply frequency is applied.

  On the other hand, the input current command generation unit (45) extracts the fundamental frequency component by Fourier transforming the input current (Iin), and multiplies it by sin (θin) to obtain the input current command value (Iin *). Generate. This command value (Iin *) is output to the amplifier (46) after the absolute value (| Iin |) of the input current is subtracted in the subtractor (35). In the amplifier (46), the output value after the subtraction is multiplied by a predetermined gain.

  The output value from the secondary harmonic application unit (44) and the output value from the amplifier (46) are added in the adder (36). The command value after the addition is processed by a limiter (60) described later in detail, and then input to the subtracter (37). In the subtractor (37), the actual motor current (Idq) is subtracted from the command value output from the limiter (60) side, and this value is output to the current control unit (47). The current control unit (47) generates a voltage command value (Vdq *) based on the current command value, and outputs the voltage command value (Vdq *) to the PWM calculation unit (48).

  The PWM calculation unit (48) generates a gate signal (G) for controlling the on / off operation of each switching element (Su, Sv, Sw, Sx, Sy, Sz) based on the voltage command value (Vdq *). Thereby, each switching element (Su, Sv, Sw, Sx, Sy, Sz) performs an on / off operation at a predetermined duty.

<Basic configuration of torque control unit>
The torque control unit (50) is for determining / outputting the control amount of the torque command described above based on the load torque of the motor (5) and the like. As shown in FIG. 3, the torque control unit (50) includes a primary component extractor (52), an amplifier (53), a torque control amount adjustment unit (54), and a peak hold unit (55).

  The primary component extractor (52) extracts a primary component (fundamental frequency component) that most affects the vibration of the motor (5) from the pulsating component of the load torque of the motor (5) by Fourier transform. The amplifier (53) multiplies the primary component extracted by the primary component extractor (52) by a predetermined gain, and outputs the result to the torque control amount adjustment unit (54).

  The torque control amount adjusting unit (54) outputs the command value multiplied by the above-described average torque command value (Tave *) to the torque control superimposing unit (42) as a final torque control amount. For this reason, a torque command value (T *) having a larger fluctuation range than the average torque command value (Tave *) is output from the torque control superimposing unit (42). When the fluctuation range of the torque command value (T *) after multiplication is the same as the average torque command value (Tave *), the fluctuation range of the output torque of the motor (5) is the average value of the load torque (average Torque), and the ratio of the fluctuation range of the output torque to the average torque at this time is defined as torque control amount = 100%. In the present embodiment, since the primary component that is the main component of the vibration of the motor (5) is larger than the average torque, normally, when torque control is performed to sufficiently suppress vibration, the torque control amount is 100% or more. Become. That is, in the present embodiment, during the torque control operation, the output torque of the motor (5) is adjusted so as to have a waveform including a fluctuation range larger than the average value of the load torque of the motor (5).

  The peak hold unit (55) shown in FIG. 3 constitutes a peak current deriving unit for deriving the peak current while holding the maximum value of the current (Idq) flowing through the motor (5) in a predetermined determination period. When the peak current exceeds a predetermined upper limit value, the torque control amount adjustment unit (54) adjusts the output command value so as to reduce the torque control amount. The torque control amount adjusting unit (54) limits the output command value of the torque control amount based on the DC link voltage (Vdc) detected by the DC link voltage detecting unit (29).

<Basic torque control operation>
The torque control operation will be described more specifically. A torque command value for generating an output torque for suppressing the load torque of the motor (5) is superimposed on the input command value of the current control unit (47). Thus, during the torque control operation, the output torque of the motor (5) is controlled, for example, as shown in FIG. 4 shows the load torque of the motor (5) and the DC link section under the conditions of the power supply frequency fin = 50 Hz of the AC power supply (6), the rotational speed of the motor (5) = 30 rps, and the torque control amount = 100%. It shows the changes over time in the DC link voltage (Vdc) output from (15) and the output torque of the motor (5).

  In the power converter (10) of the present embodiment, the DC link voltage (Vdc) pulsates with a period (Tdc), and the load torque of the motor (5) also pulsates with a period (Tc). For this reason, the output torque is controlled so that the pulsation of the power supply voltage of the AC power supply (6) and the pulsation of the load torque are superimposed. Therefore, for example, at the timing when the peak of the DC link voltage (Vdc) and the peak of the load torque are relatively close, the output torque is also relatively large. Thereby, since the output torque of the motor (5) is controlled so as to be synchronized with the load torque, the speed fluctuation of the motor (5) is suppressed and the vibration of the motor (5) is reduced. In particular, in the present embodiment, the output torque of the motor (5) is controlled so as to suppress the fundamental frequency component of the load torque, which is the main cause of vibration, and thus the vibration of the motor (5) is effectively suppressed. be able to.

<About the limiter>
In the torque control operation as described above, the torque control amount becomes 100% or more in order to suppress the primary component of the vibration of the motor (5). For this reason, in this torque control, the fluctuation range (amplitude) of the output torque of the motor (5) tends to be large. Therefore, when the amplitude of the output torque increases in this way and the output torque reaches the minus side, the motor (5) may perform a regenerative operation.

  Specifically, for example, the example shown in FIG. 5 shows that the motor (5) has a power supply frequency fin = 50 Hz, a rotational speed of the motor (5) = 30 rps, and a torque control amount = 150%. It shows changes over time in load torque, DC link voltage (Vdc) output from the DC link unit (15), and output torque of the motor (5). In this example, the fluctuation range of the output torque is increased due to the increase of the torque control amount, and accordingly, the output torque is less than 0 and fluctuates to the minus side. As a result, in the region surrounded by the broken line in FIG. 5, the motor (5) performs a regenerative operation.

  On the other hand, in the power converter (10) of the present embodiment, the capacitance of the capacitor (16) of the DC link unit (15) is set to be extremely low. For this reason, when the motor (5) performs the regenerative operation in this way, the regenerative energy cannot be sufficiently absorbed by the capacitor (16), the DC link portion (15) becomes overvoltage, and the switching element (Su, (Sv, Sw, Sx, Sy, Sz) etc. may be destroyed. Therefore, in the present embodiment, as shown in FIG. 2, a limiter (60) is provided in the control unit (40) to limit the output torque from reaching minus torque. That is, the limiter (60) generates a command value that limits the output torque on the negative side so that the output torque of the motor (5) does not reach a negative value with respect to the input command value. As a result, as shown in FIG. 6, for example, the output torque (output torque indicated by the two-dot chain line in FIG. 6) that has fluctuated negatively in the prior art is higher than the negative value (eg, output torque = 0). Is maintained. As a result, the regenerative operation of the motor (5) is surely prevented, and the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and the like are protected. On the other hand, in the control of the limiter (60), no limitation is imposed on the output torque on the plus side. For this reason, in the torque control operation, the output torque of the motor (5) can be sufficiently obtained, and the vibration of the motor (5) can be effectively suppressed.

  In the present embodiment, the limiter (60) is provided immediately before the input side of the current control unit (47), thereby reliably preventing the output torque from reaching the negative side. However, the limiter (60) may be provided at another location on the input side of the current control unit (47). Specifically, the limiter (60) may be provided on the output side of the torque control amount adjusting unit (54) of the torque control unit (50).

<Suppression of motor current during torque control operation>
During the torque control operation described above, the current (Idq) of the motor (5) increases due to the increase in the output torque of the motor (5). Specifically, as shown in FIG. 7, for example, the peak of the load torque of the motor (5) (the peak (Pl) indicated by the two-dot chain line in FIG. 7) and the peak of the DC link voltage (Vdc) (in FIG. 7). When the peak (Pdc) indicated by a white dot is superimposed, the output torque of the motor (5) becomes extremely large. Therefore, when these two peaks (Pl, Pdc) coincide, the current of the motor (5) rises rapidly. In this way, when the current of the motor (5) rises sharply, the current value of the switching element (Su, Sv, Sw, Sx, Sy, Sz) exceeds the rated maximum allowable current value and the switching element (Su, Sv, Sw, Sx, Sy, Sz) may be destroyed, or the magnet of the motor (5) may be demagnetized. Further, if the current capacity of the device is increased as such a measure, the cost of the power conversion device (10) is increased.

  As a countermeasure against such a problem, the current value of the motor (5) is appropriately detected, and the torque control amount of the torque control amount adjustment unit (54) is limited so that the current does not exceed a predetermined upper limit value. Can be considered. However, in this embodiment, since the DC link voltage (Vdc) pulsates at a predetermined frequency as described above, the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque are not necessarily They do not match (see, for example, FIG. 4). For this reason, even if the current of the motor (5) is detected at the timing when the peaks (Pdc, Pl) of both are shifted, the current value becomes a relatively low value, and the desired peak current cannot be detected.

  Therefore, the above-described peak hold unit (55) is provided in the control unit (40) of the present embodiment so that the peak current of the motor (5) can be reliably detected.

  The peak hold unit (55) controls the motor current detected by the motor current detection unit (30) (strictly speaking, the control period of the phase current of the motor (5)) for each predetermined determination period (Td). The maximum value of each peak value) is held. This point will be described more specifically with reference to FIG.

  A motor current is appropriately input to the peak hold unit (55). The peak hold unit (55) derives the maximum value of the motor current (that is, the peak current (Ip)) for each predetermined determination period (Td). In the present embodiment, the peak current (Ip) derived in the previous determination period is also retained in the next determination period (Td). In this way, by maintaining the peak current (Ip) in the predetermined determination period (Td), the load torque peak (Pl) and the DC link voltage (Vdc) peak (Pdc) are superimposed at the timing. It becomes easy to detect the current of the motor (5). The determination period (Td) is set to a time (for example, 1 second) that can sufficiently detect the timing at which both peaks (Pl, Pdc) overlap.

  Further, as shown in FIG. 8, within one determination period (Td), when the detected motor current becomes larger than the peak current (Ip) so far, the peak current (Ip) is updated. That is, in one determination period (Td), the peak current (Ip) is updated so as to trace the maximum value of the motor current as appropriate. Thereby, even when the average torque suddenly increases within the determination period (Td), the current peak can be detected quickly.

  The peak current (Ip) detected by the peak hold unit (55) is output to the torque control amount adjusting unit (54). When the peak current (Ip) exceeds a predetermined upper limit value, the torque control amount adjustment unit (54) limits the torque control amount and reduces the output torque of the motor (5). As a result, in the torque control operation, it is possible to prevent the motor current from becoming excessive, so that the above-described problems can be avoided in advance. The upper limit value of the peak current (Ip) is set to a predetermined value lower than the rated maximum allowable current value of the switching element (Su, Sv, Sw, Sx, Sy, Sz), for example.

<Speed command correction during torque control operation>
As described above, even if the peak current (Ip) of the motor current is held for each determination period (Td) by the peak hold unit (55), if this determination period (Td) is too long, the torque control amount is controlled. Sexuality may deteriorate. Specifically, for example, when the peak torque (Ip) is maintained within the determination period (Td) and then the average torque decreases during this determination period (Td), the torque control amount is actually increased slightly. However, the torque control amount is limited as described above, and the torque control performance is deteriorated.

  This point will be described in detail with reference to FIG. FIG. 9 shows an example of the waveform of the DC link voltage (Vdc) and the waveform of the load torque of the motor (5). In this example, the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque of the motor (5) are superimposed at time t1. On the other hand, in this example, the frequency (fdc) of the DC link voltage and the integer n times the frequency of the load torque (that is, the operating frequency fc of the motor (5)) are slightly shifted. For this reason, in FIG. 9, after both peaks (Pl, Pdc) coincide, the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque are gradually shifted. The peak deviation interval (ΔT shown in FIG. 9) gradually increases. Under such conditions, the peaks (Pl, Pdc) of the two do not readily coincide with each other, and the peak current (Ip) cannot be accurately detected over a long period of time. On the other hand, if the determination period (Td) is set to be long so that the peak current (Ip) can be reliably detected under such conditions, the torque control performance deteriorates as described above.

  Therefore, the control unit (40) of the present embodiment is provided with a speed command correction unit (70) for reliably detecting the peak current (Ip) even under such conditions (see FIG. 10). ). The speed command correction unit (70) includes a beat cycle calculation unit (71) and a speed command adjustment unit (72). In the torque control operation, the beat cycle calculation unit (71) is a cycle of timing at which the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque overlap (hereinafter, this is referred to as the beat cycle ( A period deriving section for deriving Tb)) is formed. The speed command adjustment unit (72) corrects the speed command (ω *) of the motor (5) based on the beat cycle (Tb) derived by the beat cycle calculation unit (71), and the operating frequency of the motor (5) (Fc) is adjusted.

  Specifically, for example, in the torque control operation, as schematically shown in FIG. 11, the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque are matched during the determination period (Td). It is assumed that the beat cycle (Tb) is considerably longer than the determination period (Td) of the peak hold unit (55). Under such conditions, the peak current (Ip) cannot be reliably detected even if the above-described peak hold is performed.

  Therefore, the speed command correction unit (70) performs control as shown in FIG. In step S1, the beat period calculation unit (71) derives the pulsation frequency (fdc) of the DC link voltage (Vdc). The pulsation frequency (fdc) of the DC link voltage (Vdc) is, for example, doubling the pulsation frequency (fin) of the power supply voltage of the AC power supply (6) detected by the power supply frequency detector (27) (fdc = fin × 2).

  Next, in step S2, the beat cycle calculation unit (71) has the highest frequency (fdc) of the pulsation of the DC link voltage (Vdc) and the integer multiple (n times) of the operating frequency (fc) of the motor (5). Calculate a near integer n. For example, assuming that the frequency (fin) of the power supply voltage of the AC power supply (6) is 50.1 Hz, the pulsation frequency (fdc) of the DC link voltage (Vdc) is 100.2 Hz, and the operating frequency (fc) is 25 Hz. This integer n is 4.

  Next, in step S3, the beat cycle calculation unit (71) calculates the frequency (beat frequency (fb)) at which the beat occurs according to the following equation (1).

fb = fdc− (fc × n) (1) Next, in step S4, the beat cycle calculation unit (71) obtains the reciprocal of the calculated beat frequency (fb) and calculates the beat cycle (Tb). calculate. Assuming that the calculated DC link voltage frequency (fdc) is 100.2 Hz, the motor (5) operating frequency (fc) is 25 Hz, and the integer n is 4, the beat frequency (fb) is 1) According to the equation, 100.2Hz-25Hz × 4 = 0.2Hz and the beat cycle (Tb) is 5sec.

  In step S5, the speed command adjustment unit (72) compares the calculated beat cycle (Tb) with the determination period (Td) set in the peak hold unit (55). For example, when the beat cycle (Tb) = 5 sec and the determination period (Td) = 1 sec and the beat period (Tb) is larger than the determination period (Td), the DC link voltage (Vdc) for each determination period (Td) The motor current at the time when the peak current (Ip) of the peak (Pdc) and the peak (Pl) of the load torque coincide with each other cannot be reliably detected as the peak current (Ip). Therefore, in step S5, when Tb> Td, the speed command (ω *) is corrected so as to shift to step S6 and adjust the operating frequency (fc) of the motor (5).

  Specifically, in step S6, the speed command adjustment unit (72) calculates an operation frequency (fc *) for making the beat cycle (Tb) the same as the determination period (Td) by the following equation (2). .

fc * = (fdc- (1 / Td)) / n (2) Formula For example, the pulsation frequency (fdc) of the DC link voltage (Vdc) is 100.2 Hz, and the judgment period (Td) is 1 sec. If the integer n is 4, the operating frequency (fc *) for making the beat period (Tb) and the determination period (Td) the same is calculated by the above equation (2) (100.2Hz-1.0Hz) /4=24.8Hz. Therefore, the speed command adjustment unit (72) inputs the speed command (ω *) so as to correct the current operation frequency (fc, for example, 25 Hz) to the calculated operation frequency (fc *, for example, 24.8 Hz). Correct. As a result, in the subsequent operation, the beat cycle (Tb) and the determination period (Td) are the same period. For example, as shown in FIG. 13, the DC link voltage (Vdc) is determined for each determination period (Td). The peak current (Ip) can be derived by always superimposing the peak (Pdc) and the load torque peak (Pl) once.

  Note that the speed command adjustment unit (72) of the present embodiment ensures that the beat period (Tb) and the determination period (Td) are the same when the beat period (Tb) is greater than the determination period (Td). The operating frequency (fc) of the motor (5) is corrected. However, when the beat cycle (Tb) is larger than the determination period (Td), the speed command adjustment unit (72) operates the operating frequency (fc) so that the beat cycle (Tb) is smaller than the determination period (Td). May be corrected. That is, in the determination period (Td), the peak (Pdc) of the DC link voltage (Vdc) and the peak (Pl) of the load torque may be overlapped at least once.

<Correction of torque control amount based on DC link voltage>
During the torque control operation, if the output torque becomes excessive under a condition where the power supply voltage (Vin) of the AC power supply (6) is relatively high or low, there is a risk of inconvenience. Specifically, if the power supply voltage (Vin) is relatively high and the DC link voltage (Vdc) is relatively high, and the torque control amount is relatively large, the reactor (12) and the capacitor (16) And the DC link voltage (Vdc) may become excessively high (see, for example, FIG. 14). Also, in order to obtain the desired output torque even when the torque control amount is relatively large under the condition that the power supply voltage (Vin) is relatively low and the DC link voltage (Vdc) is also relatively low. In addition, the duty of the pulse signal of the PWM calculation unit (48) becomes high as a whole. As a result, there is a possibility that the followability of the current control is delayed and the controllability of the torque control operation is deteriorated.

  Therefore, in the present embodiment, the torque control amount adjustment unit (54) corrects the torque control amount based on the peak of the DC link voltage (Vdc) during the half cycle of the power source. Specifically, for example, when the peak of the DC link voltage (Vdc) in the half cycle of the power source exceeds a predetermined upper limit value, the torque control amount adjusting unit (54) is set so that the DC ink unit (15) does not become an overvoltage. Reduce torque control amount. Thereby, in the torque control amount adjusting unit (54), the command value of the torque control amount is limited to a predetermined value (a command value that prevents the DC link voltage Vdc from becoming an overvoltage). As a result, resonance between the reactor (12) and the capacitor (16) as described above is suppressed, and an increase in the DC link voltage (Vdc) as shown in FIG. 14 is suppressed.

  Further, for example, even when the peak of the DC link voltage (Vdc) in the half cycle of the power source falls below a predetermined lower limit value, the torque control amount adjustment unit (54) reduces the torque control amount. Thereby, in the torque control amount adjusting unit (54), the command value of the torque control amount is limited to a predetermined value. As a result, it is possible to suppress the pulse signal duty of the PWM calculation unit (48) from becoming too high, thereby avoiding deterioration in controllability of the torque control operation.

  Note that the torque control amount adjustment unit (54) of the present embodiment limits the torque control amount based on the DC link voltage (Vdc) detected by the DC link voltage detection unit (29). However, for example, based on the power supply voltage (Vin) of the AC power supply (6), the torque control amount may be limited in the same manner as described above.

-Effect of the embodiment-
According to the above embodiment, the limiter (60) limits the output torque so that the output torque of the motor (5) does not reach the negative side during the torque control operation (see FIG. 6). For this reason, the regenerative operation of the motor (5) can be reliably prevented, and the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and the like can be reliably protected.

  Further, in the present embodiment, during the torque control operation, the maximum value of the current of the motor (5) is held by the peak hold unit (55), and the peak current (Ip) is derived (FIG. 8). reference. For this reason, it becomes easy to derive the motor current value when the peak of the output torque and the peak of the DC link voltage (Vdc) overlap as the peak current (Ip). When the peak current (Ip) exceeds a predetermined value, the switching element (Su, Sv, Sw, Sx, Sy, Sz) and the like can be reliably protected by reducing the fluctuation range of the output torque.

  Furthermore, in the determination period (Td) of the peak hold unit (55), the beat cycle (Pdc) and the peak of the load torque (Pl) do not easily coincide with the beat cycle (Pd) The operating frequency of the motor (5) is adjusted so that the Tb) and the determination period (Td) are the same. For this reason, for example, as shown in FIG. 13, the peak current (Ip) can be derived by reliably superimposing the peaks (Pdc, Pl) of the two for each determination period (Td).

In the above embodiment, when the peak of the DC link voltage (Vdc) in the half cycle of the power source exceeds a predetermined upper limit value, the control amount of the output torque is limited to the predetermined value. Thereby, it is possible to prevent the DC link voltage (Vdc) from increasing due to resonance between the reactor (12) and the capacitor (16). Further, even when the peak of the DC link voltage (Vdc) during the half cycle of the power source falls below a predetermined lower limit value, the control amount of the output torque is limited to a predetermined value. Thereby, it is possible to prevent the controllability of the torque control operation from deteriorating due to the increase in the duty in the PWM calculation unit (48) .

<Other embodiments>
In the above embodiment, the single-phase AC power source (6) is used as the power source. The converter circuit (11) shown in FIG. 15 is a diode bridge circuit in which six diodes (D1 to D6) are connected in a bridge shape. Also in this configuration, the control unit (40) according to the present invention can be employed.

  As described above, the present invention is useful for a power conversion device that controls a motor.

5 Motor
6 AC power supply
10 Power converter
11 Converter circuit
15 DC link section
16 capacitors
20 Inverter circuit
21 capacitor
40 Control unit
54 Torque control amount adjustment section
55 Peak hold section
60 Limiter (Limiting part)
71 Beat cycle calculator (cycle derivation unit)
72 Speed command adjuster

Claims (7)

A converter circuit (11) for rectifying the power supply voltage of the AC power supply (6);
A DC link unit (15) having a capacitor (16) connected in parallel to the output of the converter circuit (11) and outputting a pulsating DC voltage;
An inverter circuit (20) for switching the output of the DC link section (15) to convert to AC and supplying the connected motor (5);
The output of the motor (5) according to the command value obtained by superimposing the pulsation component of the output voltage of the AC power supply (6) on the torque command value having a fluctuation range larger than the average value of the load torque of the motor (5) A control unit (40) for performing torque control for controlling torque,
The control unit (40) includes a limiting unit (60) that limits the output torque of the motor (5) so that the output torque of the motor (5) does not become negative during the torque control. A power conversion device. In claim 1,
The control unit (40) obtains, as the torque command value, a value obtained by multiplying an average value of load torque of the motor (5) by an index indicating a fundamental frequency component of the load torque. . In claim 1 or 2 ,
The control unit (40) corrects the fluctuation range of the output torque of the motor (5) based on the power supply voltage of the AC power supply (6) or the output voltage of the DC link unit (15) during the torque control operation. The power converter characterized by the above-mentioned. In any one of Claims 1 thru | or 3 ,
The control unit (40) reduces the fluctuation range of the output torque of the motor (5) when the peak current of the motor (5) exceeds a predetermined upper limit during the torque control operation. Conversion device. In claim 4 ,
The control unit (40) has a peak hold unit (55) that holds the maximum value of the current of the motor (5) as a peak current at a predetermined determination time, and is held by the peak hold unit (55). A power converter characterized by reducing the fluctuation range of the output torque of the motor (5) when the peak current exceeds a predetermined upper limit value. In claim 5 ,
During the determination period of the peak hold unit (55), the control unit (40) generates a peak of the pulsating component of the load torque of the motor (5) and a peak of the pulsating component of the output voltage of the DC link unit (15). And a speed command adjustment unit (72) that corrects the operating frequency of the motor (5) so as to overlap with each other. In claim 6 ,
The control unit (40) is configured to load torque of the motor (5) based on the frequency of the output voltage of the AC power source (6) or the DC link unit (15) and the operating frequency of the motor (5). A period deriving unit (71) for deriving a period in which the peak of the DC link unit (15) and the peak of the output voltage of the DC link unit (15) are superimposed,
The speed command adjustment unit (72) corrects the operating frequency of the motor (5) so that the cycle derived by the cycle deriving unit (71) is equal to or less than the determination period of the peak hold unit (55). The power converter characterized by doing.

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