JP7298260B2 - POWER CONVERSION DEVICE AND CONTROL METHOD OF POWER CONVERSION DEVICE - Google Patents

Description

The present invention relates to a power conversion device and a control method for the power conversion device, and more particularly to a power conversion device having a control section including an adjustment section that equalizes voltages of capacitors of a plurality of converter cells, and a control method for the power conversion device.

2. Description of the Related Art Conventionally, a power conversion device including a control unit including an adjustment unit that equalizes voltages of capacitors of a plurality of converter cells, and a control method for the power conversion device are known (see, for example, Patent Document 1).

The power converter of Patent Document 1 is provided between an AC power supply and a load to which power is supplied from the AC power supply. The power converter is configured to suppress voltage fluctuations between an AC power supply and a load using power (reactive power) of a DC capacitor provided in the power converter. The power converter includes a bridge cell in which a DC capacitor and a semiconductor switch group including two semiconductor switches connected in series are connected in parallel. Also, in the power converter, three bridge cells are connected in series in each of the U phase, V phase, and W phase.

The power converter is also provided with integrated control means for generating switching signals used for controlling the switching operations of the semiconductor switches of the three bridge cells of each phase. Also, the integrated control means has a balance control section that equalizes the voltages of the three DC capacitors of each phase. The balance control section is configured to output a voltage command value based on the current flowing into the bridge cell of each phase. Then, the voltage command value generation unit generates voltage command values for the three bridge cells of each phase based on the voltage command values output by the balance control unit.

WO2012/099176

However, in the power converter of Patent Document 1, at least when there is no load, the current flowing into the bridge cells of each phase becomes zero (no current flows), so control is performed based on the current flowing into the bridge cells. There is a problem that the balance control unit that performs this does not operate normally. In this case, due to the unbalanced voltages of the DC capacitors in each phase, an overvoltage is applied to the DC capacitors, resulting in destruction of the DC capacitors.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and one object of the present invention is to prevent a capacitor from being destroyed due to voltage imbalance of the capacitor. It is an object of the present invention to provide a power conversion device and a control method for the power conversion device.

To achieve the above object, a power converter according to a first aspect of the present invention is provided with a capacitor and a semiconductor switch group having a plurality of semiconductor switches connected in series, wherein the capacitor and the semiconductor switch group a power conversion unit in which a plurality of parallel-connected converter cells are connected in series; and a control unit including an adjustment unit that equalizes voltages of capacitors of the plurality of converter cells based on reactive current flowing into the power conversion unit. , and the control unit controls the reactive current by a correction value that varies according to the absolute value of the reactive current command so that the absolute value of the reactive current command for controlling the reactive current is greater than zero at least when there is no load. is configured as

In the power converter according to the first aspect of the present invention, as described above, the reactive current command is set so that the absolute value of the reactive current command for controlling the reactive current is greater than zero (0) at least during no load. is controlled by a correction value that varies according to the absolute value of In this case, at least when there is no load, the current (reactive current) flowing into the power conversion unit has a constant magnitude greater than 0. Therefore, the adjustment unit that performs control based on the current flowing into the power conversion unit can be normally operated. can be operated. As a result, the voltages of the plurality of capacitors of the power conversion unit are equalized by the adjustment unit, so that application of overvoltage to the capacitors can be suppressed. This can prevent the capacitor from being destroyed.

In the power conversion device according to the first aspect, preferably, the control unit, at least during no load, reduces the reactive current by a second reactive current command obtained by adding a correction value to the first reactive current command based on the power command. is configured to control the absolute value of is greater than zero. With this configuration, the reactive current command can be corrected by relatively simple control (calculation) of adding the correction value, so the control load on the control section can be reduced.

In this case, preferably, when the absolute value of the first reactive current command under no load is equal to or less than the first value, the control unit adds the correction value to the first reactive current command and sets the correction value to the first 1 is configured to be adjusted according to the magnitude of the absolute value of the reactive current command. According to this configuration, the absolute value of the corrected second reactive current command can be appropriately adjusted by adjusting the correction value according to the magnitude of the absolute value of the first reactive current command.

In the power converter that adjusts the correction value according to the magnitude of the absolute value of the first reactive current command, preferably, the control unit, when the absolute value of the first reactive current command is equal to or less than a first value, The value of the correction value is adjusted so that the absolute value of the second reactive current command after correction becomes a constant value. Here, when the correction value is always constant, depending on the magnitude of the first reactive current command before correction, the value of the second reactive current command after correction becomes inappropriate (excessively large or small). There is On the other hand, since the absolute value of the second reactive current command after correction becomes a constant value, if the constant value is set to an appropriate value, the value of the second reactive current command after correction becomes inappropriate. never As a result, the control by the adjustment section can be performed more stably.

In this case, preferably, when the absolute value of the first reactive current command is equal to or less than the first value and when the first reactive current command is a positive value, the corrected second reactive current command The correction value is adjusted so that the current command is a constant positive value, the absolute value of the first reactive current command is equal to or less than the first value, and the first reactive current command is a negative value. In this case, the correction value is adjusted so that the corrected second reactive current command is a constant negative value. With this configuration, when the first reactive current command is a positive value, the value of the second reactive current command can be controlled to an appropriate positive value, and the first reactive current command is negative. , the value of the second reactive current command can be controlled to an appropriate negative value.

In the power conversion device in which the absolute value of the second reactive current command is controlled to a constant value, preferably, the control unit controls the first reactive current command within a range in which the absolute value of the first reactive current command is equal to or less than the first value. When the positive and negative of the first reactive current command is reversed due to a change in the value of the current command, control is performed to suppress the reversal of the positive and negative of the second reactive current command. With this configuration, even if the first reactive current command is slightly changed in the vicinity of 0 and the sign of the first reactive current command is reversed, the reversal of the sign of the second reactive current command is suppressed. can do. As a result, when the value of the first reactive current command slightly fluctuates in the vicinity of 0 and the polarity of the first reactive current command is reversed, the value of the second reactive current command is suppressed from changing rapidly. can be done. Thereby, the control by the adjusting section can be performed more stably.

In this case, preferably, the control unit adjusts the correction value so that the correction value changes in a hysteresis manner based on changes in the value of the first reactive current command, thereby decreasing the value of the first reactive current command. Thus, when the absolute value of the value of the first reactive current command becomes equal to or less than a second value smaller than the first value, the value of the second reactive current command is kept constant at a positive value, and the first reactive current command is set to a constant positive value. When the absolute value of the value of the first reactive current command becomes equal to or less than the second value due to an increase in the value of the current command, control is performed to keep the value of the second reactive current command constant at a negative value. It is configured. With this configuration, when the absolute value of the first reactive current command is within the range of the second value (within the hysteresis), the positive/negative of the value of the second reactive current command is reversed within the range (within the hysteresis). can be suppressed. As a result, even when the positive and negative of the first reactive current command is reversed due to the value of the first reactive current command slightly fluctuating near 0, the reversal of the positive and negative of the second reactive current command can be easily suppressed. can be done.

In the power conversion device that suppresses the positive/negative inversion of the second reactive current command, preferably, the control unit receives the value of the first reactive current command and receives the value of the input first reactive current command. and a filter unit configured to adjust the correction value according to the magnitude of the filter signal value output by the filter unit, the filter unit including the first invalidity When the value of the first reactive current command changes within the range where the absolute value of the current command is equal to or less than the first value, the rate of change of the value of the first reactive current command input this time with respect to the filter signal value output last time. If the absolute value is less than or equal to the predetermined threshold, the filter signal value equal to the value of the first reactive current command input this time is output this time, and if the absolute value of the change rate is greater than the predetermined threshold, the current input It is configured to output a filter signal value at which the absolute value of the rate of change with respect to the value of the first reactive current command is equal to or less than a predetermined threshold. With this configuration, the rate of change can always be limited to a predetermined threshold value or less. As a result, even if the value of the first reactive current command changes in polarity due to a relatively large change in the value of the first reactive current command, the positive and negative of the filter signal value to be output this time is suppressed from being inverted from the previous time. be able to.

In the power converter in which the absolute value of the second reactive current command is controlled to a constant value, preferably the constant value is a minimum value required for normal operation of the adjusting section. With this configuration, it is possible to prevent the absolute value of the second reactive current command from becoming excessively large due to the correction. As a result, application of an excessively large voltage to the capacitor can be suppressed.

In the power converter that adjusts the correction value according to the magnitude of the absolute value of the first reactive current command, preferably, the control unit corrects when the absolute value of the first reactive current command is a predetermined value or more. Adjust the value to zero. With this configuration, when the absolute value of the first reactive current command is greater than a predetermined value (a value greater than 0), the absolute value of the second reactive current command can be adjusted so as not to change. .

A control method for a power converter according to a second aspect of the present invention is provided with a capacitor and a semiconductor switch group having a plurality of semiconductor switches connected in series with each other, and the capacitor and the semiconductor switch group are connected in parallel. equalizing the voltages of the capacitors of the plurality of converter cells by the adjustment unit based on the reactive current flowing into the power conversion unit in which the plurality of converter cells are connected in series; and controlling the reactive current at least during no load. and a step of controlling with a correction value that varies according to the absolute value of the reactive current command so that the absolute value of the reactive current command is greater than zero.

In the method for controlling a power converter according to the second aspect of the present invention, as described above, at least when there is no load, the absolute value of the reactive current command varies according to the absolute value of the reactive current command so that the absolute value of the reactive current command is greater than zero. is controlled by a correction value that As a result, the current flowing into the power conversion unit does not become zero, so the adjustment unit that performs control based on the current flowing into the power conversion unit can be operated normally. As a result, the voltages of the plurality of capacitors of the power conversion unit are equalized by the adjustment unit, so that application of overvoltage to the capacitors can be suppressed. As a result, destruction of the capacitor can be suppressed.

According to the present invention, as described above, it is possible to suppress the destruction of the capacitor due to the unbalanced voltage of the capacitor.

It is a figure showing the arrangement configuration of the load by a 1st embodiment, an exchange power supply, and a power converter. BRIEF DESCRIPTION OF THE DRAWINGS It is the figure which showed the structure of the power converter device by 1st Embodiment. It is the figure which showed the structure of the control part of the power converter device by 1st Embodiment. It is a diagram showing the configuration of the power control means of the control unit of the power converter according to the first embodiment. 4 is a diagram showing the configuration of inter-stage balance control means of the control unit of the power converter according to the first to third embodiments; FIG. FIG. 2 is a diagram showing the configuration of a voltage command value generating means of a control section of the power converter according to the first to third embodiments; It is a figure for demonstrating the control by the correction|amendment means of the power control means of the power converter device by 1st Embodiment. FIG. 5 is a flow chart for explaining control for correcting a reactive current command by power control means of the power converter according to the first to third embodiments; It is the figure which showed the structure of the power control means by 2nd Embodiment. FIG. 10 is a diagram for explaining control by a correction means according to the second embodiment (a diagram of correction values and filter values); FIG. 11 is a diagram for explaining control by a correction means according to the second embodiment (a diagram of a reactive current command value after correction); FIG. 11 is a diagram showing a reactive current command value after correction when the reactive current command value increased from a value smaller than −MIN slightly fluctuates within the hysteresis according to the second embodiment; FIG. 10 is a diagram showing a reactive current command value after correction when the reactive current command value decreased from a value larger than MIN slightly fluctuates within the hysteresis according to the second embodiment; It is the figure which showed the structure of the power control means by 3rd Embodiment. FIG. 12 is a diagram showing a reactive current command value after correction when the reactive current command value, which has decreased to near 0, slightly fluctuates near 0 according to the third embodiment; FIG. 11 is a diagram showing a reactive current command value after correction when the reactive current command value that has increased to near 0 slightly fluctuates near 0 according to the third embodiment;

Embodiments embodying the present invention will be described below with reference to the drawings.

[First embodiment]
A configuration of a power converter 100 according to the first embodiment will be described with reference to FIGS. 1 to 8. FIG.

First, with reference to FIG. 1, a general configuration of a circuit provided with a power conversion device 100 will be described. As shown in FIG. 1 , the power converter 100 is connected between an AC power supply 101 and a load 102 . A reactor component 103 of system impedance exists between the three-phase AC power supply 101 and the power converter 100 . A transformer 104 is provided between the power converter 100 and the load 102 . Note that the load 102 may be, for example, an arc furnace.

Power converter 100 performs high-speed positive-phase and negative-phase reactive power control and low-frequency active power control in order to suppress voltage drop and voltage fluctuation caused by load 102 . The load current (current i _L in FIG. 1) flowing into the load 102 includes, in addition to the positive-phase active current, a positive-phase reactive current, a negative-phase reactive current, and low frequency active currents. Here, if the power conversion device 100 is not provided, these currents appear in the power supply current (the current i _s in FIG. 1), so voltage flicker occurs. Power converter 100 generates a compensation current (current i _c in FIG. 1) to suppress voltage flicker. The current i _c corresponds to compensation currents (I _u , I _v , I _w ), which will be described later.

(Configuration of power converter)
Next, the configuration of the power converter 100 will be described with reference to FIG.

The power converter 100 is a reactive power compensator of MMC (Modular Multilevel Converter). Specifically, the power conversion device 100 is internally provided with the delta connection section 10 . The power converter 100 also includes a U-phase power converter 11 , a V-phase power converter 12 , and a W-phase power converter 13 . The power converter 11 is connected to a U-phase wiring 101 a that connects the AC power supply 101 and the load 102 . The power conversion unit 12 is also connected to a V-phase wiring 101 b that connects the AC power supply 101 and the load 102 . The power conversion unit 13 is also connected to a W-phase wiring 101 c that connects the AC power supply 101 and the load 102 .

Power conversion unit 11, power conversion unit 12, and power conversion unit 13 are delta-connected to each other. A reactor 100 a is provided between the delta connection unit 10 and each of the power conversion units 11 , 12 , and 13 .

Note that the power supply voltage applied to the wiring 101a, the power supply voltage applied to the wiring 101b, and the power supply voltage applied to the wiring 101c are denoted by V _Su , V _Sv , and V _Sw , respectively. Further, the line voltage (voltage difference) between the wiring 101a and the wiring 101b, the line voltage between the wiring 101b and the wiring 101c, and the line voltage between the wiring 101c and the wiring 101a are respectively Denote V _Suv , V _Svw and V _Swu .

In this case, the following formulas (1), (2) and (3) hold.

Further, the compensating current flowing from the wiring 101a to the power converter 100, the compensating current flowing from the wiring 101b to the power converter 100, and the compensating current flowing from the wiring 101c to the power converter 100 are represented by I _u , I _v , and , _Iw . Also, currents flowing into the power conversion unit 11, the power conversion unit 12, and the power conversion unit 13 are denoted as _Iuv , _Ivw , and _Iwu , respectively.

In this case, the following formulas (4), (5) and (6) hold.

Power conversion unit 11 also includes converter cells 11a, 11b, and 11c connected in series with each other. Power conversion unit 12 also includes converter cells 12a, 12b, and 12c that are connected in series with each other. Power conversion unit 13 also includes converter cells 13a, 13b, and 13c that are connected in series with each other. Each of converter cells 11a to 11c, converter cells 12a to 12c, and converter cells 13a to 13c is provided with a DC capacitor 1 and two semiconductor switch groups 2 connected in parallel to DC capacitor 1. there is The semiconductor switch group 2 has two semiconductor switches 2a connected in series with each other. The semiconductor switch 2a is composed of a bipolar element and a diode element connected in anti-parallel to each other. Note that the DC capacitor 1 is an example of a "capacitor" in the scope of claims.

Note that the output voltages of the power converter 11, the power converter 12, and the power converter 13 are denoted as V _uv , V _vw , and V _wu , respectively. The output voltages of converter cells 11a-11c are denoted as V _ua , V _ub and V _uc respectively. Also, the output voltages of the converter cells 12a to 12c are denoted as V _va , V _vb and V _vc respectively. Also, the output voltages of the converter cells 13a to 13c are denoted as V _wa , V _wb and V _wc respectively.

In this case, the following formulas (7), (8) and (9) hold.

By PWM (Pulse-Width Modulation) controlling each of the converter cells 11a to 11c, the converter cells 12a to 12c, and the converter cells 13a to 13c, the output voltage of each phase of the delta connection section 10 of the power converter 100 It is possible to control (output voltage of the power conversion section of each phase) V _uv , V _vw , and V _wu .

The voltages (DC voltages) of the DC capacitors 1 of the converter cells 11a to 11c are denoted by V _Cua , V _Cub and V _Cuc respectively. Voltages (DC voltages) of DC capacitors 1 of converter cells 12a to 12c are denoted by V _Cva , V _Cvb , and V _Cvc , respectively. Voltages (DC voltages) of DC capacitors 1 of converter cells 13a to 13c are denoted by V _Cwa , V _Cwb and V _Cwc , respectively.

The power conversion device 100 also includes a control section 20 that controls operations of the power conversion sections 11 to 13 .

As shown in FIG. 3 , the control unit 20 includes power control means 21 , interphase balance control means 22 , interstage balance control means 23 , and voltage command value generation means 24 . The functions of the power control means 21, interphase balance control means 22, interstage balance control means 23, and voltage command value generation means 24 can be realized by software such as a program. Note that the inter-stage balance control means 23 is an example of the "adjustment section" in the scope of claims.

Power control means 21 (control unit 20) sets command values (V _uv ^* , V _vw ^* , V _wu ^* ) that are line voltage command values for executing positive phase reactive power control and negative phase reactive power control. Generate. Specifically, the power control means 21 controls the instantaneous active power command value p ^* , the instantaneous reactive power command value q ^* , the voltage command value _Vc ^* of the DC capacitor 1, the line voltage ( _Vsuv , _Vsvw , _Vswu) . , see FIG. 2), the currents (I _uv , I _vw , I _wu ) flowing into the power converters 11 to 13, and the zero-phase current I _zf ^* , which will be described later, as input values, the command values (V _uv ^* , V _vw ^* , _Vwu ^* ). The power control means 21 has a feedback loop that causes the average voltage value V _Cave (see FIG. 4) of the DC capacitor 1 for three phases to follow the voltage command value V _c ^* of the DC capacitor 1 .

Specifically, as shown in FIG. 4, _the power ^control means 21 (control unit 20) generates _a ^value _{By subtracting} ^{the zero} _- ^phase _{current I zf} ^* _from Generate.

The command value I _d ^** is obtained by PI-controlling the difference between the voltage command value V _c ^* of the DC capacitor 1 and the average voltage value V _Cave of the three phases of the DC capacitor 1, and the instantaneous active power command value p ^* . is generated by adding the command value I _d ^* generated from Also, the command value I _q ^** is generated by correcting the command value I _q ^* generated from the instantaneous reactive power command value q ^* by the correction means 21b. A detailed description of the correction means 21b will be given later. Note that the instantaneous reactive power command value q ^* is an example of the "power command" in the claims. Also, the command value I _q ^* and the command value I _q ^** are examples of the "first reactive current command" and the "second reactive current command" in the scope of claims, respectively.

Further, the power control means 21 (control unit 20) subtracts the currents ( _Iuv , _Ivw , _Iwu ) from the three-phase AC current command values ( _Iuv ^* , _Ivw ^* , _Iwu ^* ), respectively. Along with P control, command values (V _uv *, V _vw ^* , V _wu ^* ) are generated by adding line voltages (V _Suv , V _Svw ^, V _Swu ) to values generated by P control. do.

Further, the phase balance control means 22 (control unit 20) (see FIG. 3) controls the average voltage value V _Cuave of the three U-phase DC capacitors 1, the average voltage value V _Cvave of the three V-phase DC capacitors 1, and , and W-phase DC capacitors 1 to equalize the average voltage values V _Cwave . Specifically, the interphase balance control means 22 uses the average voltage value V _Cave , the average voltage value V _Cuave , the average voltage value V _Cvave , and the average voltage value V _Cwave of the DC capacitor 1 for three phases as input values, A zero-phase current I _zf ^* of the fundamental frequency to be supplied to the delta connection portion 10 is calculated.

In addition, the inter-stage balance control means 23 (control unit 20) (see FIG. 3) controls the currents (I _uv , I _vw , I _wu ) flowing into the respective power conversion units (11 to 13) for the same phase. It is configured to equalize voltages of DC capacitors 1 of a plurality of converter cells (for example, converter cells 11a, 11b, and 11c).

Specifically, as shown in FIG. 5, the inter-stage balance control means 23 (control unit 20) controls the average voltage value V _Cuave and the voltages (V _Cua , V _Cub , V _Cuc ) as input values (indicated as V _Cu in FIG. 3) to generate command values (V _Bua ^* , V _Bub ^* , V _Buc ^* ) (indicated as V _Bu ^* in FIG. 3) .

In addition, the inter-stage balance control means 23 inputs _the average voltage value V _Cvave and the voltages (V _Cva , V _Cvb , V _Cv ), command values (V _Bva ^* , V _Bvb ^* , V _Bvc ^* ) (in FIG. 3, V _Bv ^* ) are generated.

In addition, the inter-stage balance control means 23 inputs the average voltage value V _Cwave and the voltages (V _Cwa , V _Cwb , V _Cwc ) of the DC capacitors 1 of the converter cells 13a to 13c as input values (in FIG. 3, V _Cw ), command values (V _Bwa ^* , V _Bwb ^* , V _Bwc ^* ) (in FIG. 3, V _Bw ^* ) are generated.

As an example, a method of calculating command value V _Bua ^* for converter cell 11a by inter-stage balance control means 23 will be described. The inter-stage balance control means 23 multiplies the difference between the average voltage value V _Cvave and the voltage V _Cua of the DC capacitor 1 by a gain of K times and the current I _uv to obtain the command value V _Bua ^* Calculate Command values for other converter cells are also calculated by the same method, and detailed description thereof will be omitted.

As described above, the command values (V _Bu ^* , V _Bv ^* , V _Bw ^* ) are calculated by multiplication using the currents (I _uv , I _vw , I _wu ), whereby the command values (V _Bu ^* , V _Bv ^* , V _Bw ^* ) will be in phase or out of phase with the current (I _uv , I _vw , I _wu ). As a result, the output voltages (V _{ua to} V uc , V _va to V _vc , V _wa to V _{wc )} of each converter cell generated based on the command values (V _Bu ^* , V _Bv ^* , V _Bw ^* ) are also includes components in phase with or opposite to the currents (I _uv , I _vw , I _wu ), so the output voltages of each converter cell (V _ua to V _uc , V _va to V _vc , V _wa to V _wc ) and currents (I _uv , I _vw , I _wu ). As a result, in each phase, the voltages of the DC capacitors 1 follow the average voltage values (V _Cuave , V _Cvave , V _Cwave ) of the DC capacitors 1 and are equalized with each other.

Also, the voltage command value generation means 24 (control unit 20) (see FIG. 3) generates the command values (V _uv ^* , V _vw ^* , V _wu ^* ) generated by the power control means 21 and the inter-stage balance control means voltage command values ( _Vu ^* , _Vv ^* , _Vw ^* ) for each converter cell based on the command values (VBu ^* , _VBv ^* , _{VBw *} ) generated by 23 (see FIG. 3 ⁾ . to generate Each converter cell (11a to 11c, 12a to 12c, 13a to 13c) is controlled by the voltage command values (V _u ^* , V _v ^* , V _w ^* ) generated by the voltage command value generation means 24 (control unit 20). The voltages (V _Cua to V _Cuc , V _Cva to V _Cvc , V _Cwa to V _Cwc ) of the respective DC capacitors 1 are made uniform. That is, the voltages of the nine DC capacitors 1 of the power conversion device 100 are controlled to be substantially equal to each other.

Specifically, as shown in FIG. 6, the voltage command value generation unit 24 (control unit 20) sets the value obtained by multiplying the command value V _uv ^* from the power control unit 21 by 1/3. By adding the command values (V _Bua ^* , V _Bub ^* , V _Buc ^* ) from 23, the voltage command values (V _ua ^* , V _ub ^* , V _uc ^* ) of the converter cells 11a to 11c of the power conversion unit 11 are obtained. ) (denoted as V _u ^* in FIG. 3). Further, the voltage command value generating means 24 adds the command values (V _Bva ^* , V _Bvb ^* , V _Bvc ^* ) to the value obtained by multiplying the command value V _vw ^* by 1/3, thereby It generates voltage command values (V _va ^* , V _vb ^* , V _vc ^* ) (denoted as V _v ^* in FIG. 3) for converter cells 12a to 12c. Further, the voltage command value generating means 24 adds the command values (V _Bwa ^* , V _Bwb ^* , V _Bwc ^* ) to the value obtained by multiplying the command value V _wu ^* by 1/3, thereby Voltage command values (V _wa ^* , V _wb ^* , V _wc ^* ) (denoted as V _w ^* in FIG. 3) for converter cells 13a to 13c are generated.

Voltage command values ( _Vua ^* , _Vub ^* , _Vuc ^* ), ( _Vva ^* , _Vvb ^* , _Vvc ^* ), and ( _Vwa ^* , _Vwb ^* , _Vwc ^* ) are each DC It is used as a switching command value for the capacitor 1 . A switching control means (not shown) generates a PWM switching signal by comparing the switching command value with a triangular wave carrier signal having a carrier frequency. The PWM switching signal generated by the switching control means is used for switching control of the semiconductor switch 2a in the corresponding converter cell.

Now, with reference to FIG. 7, the control of the correction means 21b of the power control means 21 (control section 20) will be described.

In the first embodiment, as shown in FIG. 7, the power control means 21 (control unit 20) (see FIG. 3) controls the reactive currents ( _Iuv , _Ivw , _Iwu ) during no load. It is configured to control the absolute value of the reactive current command (command value I _q ^** ) to be greater than zero. Specifically, when there is no load, the correction value _Ih (see FIG. 4) generated by the correction means 21b in the power control means 21 (control unit 20) is changed to the command value _Iq ^* (reactive current command before correction) is added to generate a command value I _q ^** (corrected reactive current command). This command value _Iq ^** (reactive current command after correction) controls the absolute values of the reactive currents ( _Iuv , _Ivw , _Iwu ) to be greater than zero. At no load, the absolute value of the correction value _Ih is a value greater than zero. Note that the no-load state means that the absolute value of the reactive current command (command value _Iq ^* ) is MIN or less. That is, the no-load state means that the absolute value of the reactive current command (command value I _q ^* ) is in the range from -MIN to MIN. In FIG. 7, the horizontal axis represents the magnitude of the command value _Iq ^* , and the vertical axis represents the magnitudes of the command value _Iq ^** and the correction value _Ih . MIN is an example of the "first value" in the scope of claims.

That is, when the absolute value of the reactive current command (command value _Iq ^* ) is equal to or less than MIN, the power control means 21 (control unit 20) adjusts the reactive current command (command value _Iq ^* ) to the correction value _Ih configured to add. In this case, the correction value _Ih is adjusted according to the magnitude of the absolute value of the reactive current command (command value _Iq ^* ) before correction. Specifically, when the absolute value of the reactive current command (command value _Iq ^* ) is MIN or less, the correction value _Ih is set according to the magnitude of the absolute value of the reactive current command (command value _Iq ^* ). It changes linearly (linearly). More specifically, in the range of the reactive current command (command value I _q ^* ) from zero to MIN or less, the correction value I _h increases as the reactive current command (command value I _q ^* ) decreases (approaches zero). change as In addition, when the reactive current command (command value I _q ^* ) is in the range of −MIN or more and zero or less, the correction value I _h becomes smaller as the reactive current command (command value I _q ^* ) increases (approaches zero). change to

Further, when the absolute value of the reactive current command (command value I _q ^* ) is equal to or less than MIN, the power control means 21 (control unit 20) controls the absolute value of the reactive current command (command value I _q ^** ) after correction. The value of the correction value _Ih is adjusted so that is a constant value.

Specifically, when the absolute value of the reactive current command (command value I _q ^* ) is MIN or less and the reactive current command (command value I _q ^* ) is correct , the correction value _Ih is adjusted so that the corrected reactive current command (command value _Iq ^** ) is a constant positive value. Further, the power control means 21 (control unit 20) controls the reactive current command (command value _Iq *) when the absolute value of the reactive current command (command value Iq ^* ) is MIN or less and when the reactive current command (command value _Iq ^* ) is a negative value. In some cases, the correction value _Ih is adjusted so that the corrected reactive current command (command value _Iq ^** ) is a constant negative value.

Specifically, when the reactive current command (command value I _q ^* ) is in the range of 0 to MIN, the corrected reactive current command (command value I _q ^** ) becomes MIN. Further, in the range of the reactive current command (command value I _q ^* ) from −MIN to zero, the reactive current command (command value I _q ^** ) after correction becomes −MIN.

When the correction value I _h is represented by a formula, the correction value I _h = MIN−I _q ^* when the reactive current command (command value I _q ^* ) is equal to or greater than zero and equal to or less than MIN. Further, when the reactive current command (command value I _q ^* ) is greater than or equal to −MIN and less than or equal to zero, the correction value I _h =−MIN−I _q ^* .

Also, the magnitude of MIN is the minimum value required for the inter-stage balance control means 23 to operate normally. In other words, when the reactive current command (command value _Iq ^** in this case) is smaller than MIN, the inter-stage balance control means 23 does not operate normally, and the voltages of the three DC capacitors 1 in each phase drop. balance.

Specifically, when the absolute value of the corrected reactive current command (command value _Iq ^** ) is smaller than MIN, the three-phase AC current command values ( _Iuv ^* , _Ivw ^* , _Iwu ^* ) (Fig. 4) is not large enough. Along with this, the magnitude of the currents (I _uv , I _vw , I _wu ) does not become sufficiently large (substantially zero), and the currents (I _uv , I _vw , I _wu ) are input between stages. A normal (appropriate) command value is no longer output from the balance control means 23 . On the other hand, when the absolute value of the corrected reactive current command (command value I _q ^** ) is MIN or more, the reactive current (I _uv , I _vw , I _wu ) of a certain magnitude flows. A normal (appropriate) command value is output from the balance control means 23 .

Further, in the first embodiment, the power control means 21 (control unit 20) controls the correction value _Ih to be zero when the absolute value of the reactive current command (command value _Iq ^* ) is greater than MIN. adjust. That is, when the absolute value of the reactive current command (command value I _q ^* ) is greater than MIN, the power control means 21 (control unit 20) does not change the value of the reactive current command (command value I _q ^* and command is equal to the value I _q ^** ).

Next, with reference to FIG. 8, the control flow for correcting the reactive current command by the control unit 20 will be described.

First, in step S1, the control unit 20 (inter-stage balance control means 23) performs control to equalize the voltages of the DC capacitors 1 between the same phases. Next, in step S2, if there is no load (if the absolute value of the command value I _q ^* is greater than MIN), control is performed to repeat the control in step S1. If there is no load (if the absolute value of the command value I _q ^* is equal to or less than MIN), the process proceeds to step S3. Then, in step S3, the reactive current command (command value Iq _** ) is generated by adding the correction value _Ih to the reactive ^current command (command value _Iq ^* ).

(Effect of the first embodiment)
The following effects can be obtained in the first embodiment.

In the first embodiment, as described above _, the plurality of converter cells (11a- _11c , 12a- _12c , 13a- The power conversion device 100 is provided with a control section 20 including an inter-stage balance control means 23 for equalizing the voltage of the DC capacitor 1 (between the same phases) in 13c). As a result, the currents (I _uv , I _vw , I _wu ) flowing into the power conversion units 11 to 13 (reactive current) have a constant magnitude greater than 0 when there is no load, so the power conversion units 11 to 13 The controller 20 (inter-stage balance control means 23) that performs control based on the currents ( _Iuv , _Ivw , _Iwu ) flowing into the circuit can be operated normally. As a result, the voltages of the plurality of DC capacitors 1 of the power converters 11 to 13 are equalized (between the same phases) by the inter-stage balance control means 23, thereby suppressing the application of overvoltage to the DC capacitors 1. be able to. Thereby, it is possible to suppress the destruction of the DC capacitor 1 .

Further, in the first embodiment, as described above, the control unit 20 (power control unit 21) adds the reactive current command (command value Iq*) to the reactive current command (command value _Iq ^* ) by adding the correction value _Ih . The power converter 100 is configured to control the absolute values of the reactive currents (I _uv , I _vw , I _wu ) to be greater than zero based on the current command (command value I _q ^** ). As a result, the reactive current command (command value I _q ^* ) can be corrected by relatively simple control (calculation) of adding the correction value I _h , so that the control unit 20 (power control means 21) can be controlled load can be reduced.

Further, in the first embodiment, as described above, when the absolute value of the reactive current command (command value I _q ^* ) under no load is MIN or less, The power conversion is performed so that the correction value I _h is added to the current command (command value I _q ^* ) and the correction value I _h is adjusted according to the magnitude of the absolute value of the reactive current command (command value I _q ^* ). Configure the device 100 . Accordingly, by adjusting the correction value _Ih according to the magnitude of the absolute value of the reactive current command (command value _Iq ^* ), the absolute value of the reactive current command (command value _Iq ^** ) after correction is can be properly adjusted.

Further, in the first embodiment, as described above, when the absolute value of the reactive current command (command value _Iq ^* ) is MIN or less, the control unit 20 (power control means 21) controls the reactive current command after correction. The power converter 100 is configured to adjust the value of the correction value _Ih so that the absolute value of (the command value _Iq ^** ) becomes a constant value (MIN). Here, if the correction value _Ih is always constant, depending on the magnitude of the reactive current command (command value _Iq ^* ) before correction, the value of the reactive current command (command value _Iq ^** ) after correction may be inappropriate (too large or small). On the other hand, since the absolute value of the reactive current command (command value I _q ^** ) after correction becomes a constant value (MIN), when the constant value (MIN) is set to an appropriate value, after correction The value of the reactive current command (command value _Iq ^** ) never becomes inappropriate. As a result, the control by the inter-stage balance control means 23 (control section 20) can be performed more stably.

Further, in the first embodiment, as described above, the control unit 20 (power control means 21) controls the reactive current command (command value Iq*) when the absolute value of the reactive current command (command value _Iq ^* ) is MIN or less and the reactive current command ( When the command value I _q ^* ) is a positive value, the _power is adjusted so that the corrected reactive current command (command value I _q ^** ) is a constant positive value. A conversion device 100 is configured. Further, when the absolute value of the reactive current command (command value I _q ^* ) is MIN or less and the reactive current command (command value I _q ^* ) is a negative value, the control unit 20 (power control means 21) In some cases, the power converter 100 is configured to adjust the correction value _Ih so that the corrected reactive current command (command value _Iq ^** ) is a constant negative value. Thereby, when the value of the reactive current command (command value _Iq ^* ) is a positive value, the value of the reactive current command (command value _Iq ^** ) can be controlled to an appropriate positive value. In addition, when the reactive current command (command value I _q ^* ) is a negative value, the value of the reactive current command (command value I _q ^** ) can be controlled to an appropriate negative value.

Further, in the first embodiment, as described above, the constant value (MIN) is the minimum value required for the inter-stage balance control means 23 (control unit 20) to operate normally. A power conversion device 100 is configured. As a result, it is possible to prevent the absolute value of the reactive current command (command value I _q ^** ) from becoming excessively large due to the correction. As a result, application of an excessively large voltage to DC capacitor 1 can be suppressed.

Further, in the first embodiment, as described above, the control unit 20 (power control means 21) sets the correction value _Ih to zero when the absolute value of the reactive current command (command value _Iq ^* ) is MIN or more. The power conversion device 100 is configured to adjust so that Thereby, when the absolute value of the reactive current command (command value I _q ^* ) is larger than MIN (a value larger than 0), the absolute value of the reactive current command (command value I _q ^** ) is not changed. can be adjusted.

Further, in the first embodiment, as described above, the voltage of the DC capacitors 1 of the plurality of converter cells (11a to 11c, 12a to 12c, 13a to 13c) is uniformed by the interstage balance control means 23 (control unit 20). and a step of controlling so that the absolute value of the reactive current command (command value I _q ^** ) becomes greater than zero when there is no load. do. Accordingly, since the currents (I _uv , I _vw , I _wu ) flowing into the power converters 11 to 13 have a constant magnitude when there is no load, the currents (I _uv , I _vw , I _wu ), the control unit 20 (inter-stage balance control means 23) can be operated normally. As a result, the voltages of the plurality of DC capacitors 1 of the power converters 11 to 13 are equalized (between the same phases) by the inter-stage balance control means 23, thereby suppressing the application of overvoltage to the DC capacitors 1. be able to. As a result, destruction of DC capacitor 1 can be suppressed.

[Second embodiment]
Next, the configuration of the power converter 200 according to the second embodiment will be described with reference to FIGS. 9 to 13. FIG. In the power conversion device 200 of the second embodiment, unlike the first embodiment in which the command value I _q ^* is directly input to the correction means 21b, the filter value I _f obtained by converting the command value I _q ^* is It is input to the correction means 121b. In addition, the structure similar to the said 1st Embodiment attaches|subjects the same code|symbol as 1st Embodiment, and abbreviate|omits description while it is illustrated.

As shown in FIG. 9 , the power electronics device 200 includes a control section 120 . Further, the control unit 120 includes power control means 121 . Note that the function of the power control means 121 can be realized by software such as a program.

Power control means 121 (control unit 120) converts a reactive current command (command value I _q ^* ) generated from instantaneous reactive power command value q ^* into a filter value If by filter means _121a (for example, a digital filter). configured to control. The power control means 121 (control section 120) is configured to generate the correction value _Ih by the correction means 121b based on the filter _value If converted by the filter means 121a.

Here, in the second embodiment, as shown in FIG. 10, the control unit 120 (power control means 121) controls the reactive current command (command value Iq ^* ) within a range where the absolute value of the reactive current command (command value _Iq *) is MIN or less. When the sign of the reactive current command (command value _Iq ^* ) is reversed due to a change in the value of (command value _Iq ^* ), the sign of the reactive current command (command value _Iq ^** ) after correction is reversed. It is configured to perform control to suppress In FIG. 10, the horizontal axis represents the magnitude of the command value _Iq ^* , and the vertical axis represents the magnitudes of the filter value _If and the correction value _Ih .

Specifically, the control unit 120 (power control unit 121 ₎ sets the correction value Ih so that the correction value _Ih changes in a hysteresis manner based on changes in the value of the reactive current command (command value _Iq ^* ). configured to adjust. That is, the controller 120 (power control means 121) reduces the value of the reactive current command (command value _Iq ^* ) so that the absolute value of the reactive current command (command value _Iq ^* ) becomes smaller than MIN. When it becomes equal to or less than LIMIT, the value of the reactive current command (command value _Iq ^** ) after correction is configured to be constant at a positive value (MIN). In addition, the control unit 120 (power control means 121) increases the value of the reactive current command (command value _Iq ^* ) so that the absolute value of the reactive current command (command value _Iq ^* ) becomes LIMIT or less. In this case, the value of the reactive current command (command value I _q ^** ) after correction is controlled to be constant at a negative value (-MIN). Further details are given below. LIMT is an example of the "second value" in the claims.

When the value of the reactive current command (command value I _q ^* ) is greater than LIMIT (I _q ^* >LIMIT), and when the value of the reactive current command (command value I _q ^* ) is less than -LIMIT (I _q ^* <-LIMIT), the filter value I _f is controlled by the filter means 121a to be equal to the value of the reactive current command (command value I _q ^* ) (I _f =I _q ^* ).

In addition, as the value of the reactive current command (command value I _q ^* ) decreases from a value greater than LIMIT, the absolute value of the reactive current command (command value I _q ^* ) becomes LIMIT or less (−LIMIT≦I _q ^* ≤LIMIT), the filter value I _f is controlled by the filter means 121a so as to be constant at LIMIT (I _f =LIMIT).

In addition, by increasing the value of the reactive current command (command value I _q ^* ) from a value smaller than -LIMIT, the absolute value of the reactive current command (command value I _q ^* ) becomes LIMIT or less (-LIMIT ≤ I _q ^* ≤ LIMIT), the filter value I _f is controlled by the filter means 121a so as to be constant at -LIMIT (I _f = -LIMIT).

Further, when the filter value I _f is greater than MIN (I _f >MIN), the correction value I _h is controlled by the correction means 121b to be 0 (I _h =0).

If the filter _value If is greater than LIMIT and less than or equal to MIN (LIMT< _{If ≤} MIN), the correction value _Ih is the value obtained by subtracting the filter value _{If from MIN (Ih =} MIN- _If ). is controlled by the correction means 121b as follows.

Also, when the filter _value If is LIMIT (I _h =LIMIT), the correction value I _h is controlled by the correction means 121b to be MIN (I _h =MIN).

Further, when the filter value I _f is -LIMIT (I _h =-LIMIT), the correction value I _h is controlled by the correcting means 121b to be -MIN (I _h =-MIN).

If the filter _value If is less than -LIMIT and equal to or greater than -MIN ( _-MIN≤If <-LIMIT), the correction value _Ih is _-MIN minus the filter value If ( _Ih = -MIN −I _f ) is controlled by the correction means 121b.

Further, when the filter value I _f is smaller than -MIN (I _f <-MIN), the correction value I _h is controlled by the correction means 121b to be 0 (I _h =0).

As a result, as shown in FIG. 11, the value of the reactive current command (command value _Iq ^** ) is such that the value of the reactive current command (command value _Iq ^* ) is greater than MIN (Iq _* ^> MIN). is equal to the value of the reactive current command (command value _Iq ^* ) ( _Iq ^** = _Iq ^* ). In FIG. 11, the value of the reactive current command (command value I _q ^** ) ignores minute fluctuations in the value of the reactive current command (command value I _q ^* ) that occur due to noise or the like when there is no load. is described.

In addition, when the value of the reactive current command (command value I _q ^* ) is greater than LIMIT and equal to or less than MIN (LIMIT < I _q ^* ≤ MIN), the value of the reactive current command (command value I _q ^** ) is constant at MIN. (I _q ^** = MIN).

In addition, when the value of the reactive current command (command value I _q ^* ) decreases from a value greater than LIMIT to -LIMIT or more and LIMIT or less (-LIMIT ≤ I _q ^* ≤ LIMIT), the reactive current command (command The value of the value I _q ^** ) becomes constant at MIN.

In addition, when the value of the reactive current command (command value I _q ^* ) is smaller than -LIMIT and equal to or greater than -MIN (-MIN≤I _q ^* <-LIMIT), the value of the reactive current command (command value I _q ^** ) becomes constant at -MIN (I _q ^** = -MIN).

Further, the value of the reactive current command (command value I _q ^** ) is set to the value of the reactive current command (command value I _q ^* ) when the value of the reactive current command (command value I _q ^* ) is smaller than -MIN. (I _q ^** = I _q ^* ).

In addition, when the value of the reactive current command (command value I _q ^* ) increases from a value smaller than -LIMIT to become greater than or equal to -LIMIT and less than or equal to LIMIT (-LIMIT ≤ I _q ^* ≤ LIMIT), the reactive current command ( The command value I _q ^** ) becomes constant at -MIN.

That is, the control unit 120 (power control means 121) adjusts the value of the reactive current command (command value _Iq ^** ) to the change in the value of the reactive current command (command value _Iq ^* ) in the same way as the correction value _Ih . It is configured to perform control to change in hysteresis based on.

FIG. 12 shows each case when the value of the reactive current command (command value I _q ^* ) increases from a value smaller than -LIMIT to become greater than or equal to -LIMIT and less than or equal to LIMIT (-LIMIT ≤ I _q ^* ≤ LIMIT). Illustrate the values.

In this case, as shown in FIG. 12, even if the value of the reactive current command (command value I _q ^* ) slightly fluctuates across 0 (minor fluctuation within the range of hysteresis), the filter value _If is −LIMIT (I _f =−LIMIT). As a result, each of the correction value _Ih and the value of the reactive current command (command value _Iq ^** ) is fixed at -MIN ( _Iq ^** = _Ih = -MIN) without minute fluctuations.

Next, FIG. 13 shows the case where the value of the reactive current command (command value I _q ^* ) decreases from a value greater than LIMIT to be greater than or equal to -LIMIT and less than or equal to LIMIT (-LIMIT ≤ I _q ^* ≤ LIMIT). , to illustrate each value.

In this case, as shown in FIG. 13, even if the value of the reactive current command (command value I _q ^* ) varies slightly across 0 (minor variation within the range of hysteresis), the filter value _If does not reach LIMIT. It is fixed (I _f =LIMIT). As a result, each of the correction value _Ih and the value of the reactive current command (command value _Iq ^** ) is fixed at MIN ( _Iq ^** = _Ih =MIN) without minute fluctuations.

Other configurations of the second embodiment are the same as those of the first embodiment.

(Effect of Second Embodiment)
The following effects can be obtained in the second embodiment.

In the second embodiment, as described above, the control unit 120 (power control means 121) controls the reactive current command (command value I q *) within the range where the absolute value of the reactive current command (command value I _q ^* ) is MIN or less _. ^* ), when the sign of the reactive current command (command value Iq _* ) is reversed due to a change in the value of the reactive current command (command value Iq ^** ), control is performed to suppress the reversal of the sign of the reactive current command (command value _Iq ^** ). The power conversion device 200 is configured as follows. As a result, even if the reactive current command (command value _Iq ^* ) is reversed in polarity due to minute fluctuations in the value of the reactive current command (command value _Iq ^* ) in the vicinity of 0, the reactive current command (command value Iq*) _q ^** ) can be suppressed from being inverted. As a result, when the value of the reactive current command (command value I _q ^* ) slightly fluctuates in the vicinity of 0 and the sign of the reactive current command (command value I _q ^* ) is reversed, the reactive current command (command value I _q ^** ) can be suppressed from changing abruptly. Thereby, the control by the inter-stage balance control means 23 can be performed more stably.

Further, in the second embodiment, as described above, the control unit 120 (power control means 121) causes the correction value I _h to change in a hysteresis manner based on changes in the value of the reactive current command (command value I _q ^* ). By adjusting the correction value I _h so that the value of the reactive current command (command value I _q ^* ) decreases, the absolute value of the reactive current command (command value I _q ^* ) becomes smaller than MIN The power conversion device 200 is configured to keep the value of the reactive current command (command value I _q ^** ) constant at a positive value when it becomes equal to or less than LIMIT. Further, the control unit 120 (power control means 121) adjusts the correction value _Ih so that the correction value _Ih changes in a hysteresis manner based on changes in the value of the reactive current command (command value _Iq ^* ). When the absolute value of the reactive current command (command value I _q ^* ) becomes LIMIT or less due to an increase in the value of the reactive current command (command value I _q ^* ), the reactive current command (command value I _q ^** ) is configured to be controlled to be a constant negative value. As a result, when the absolute value of the reactive current command (command value I _q ^* ) is within the range of LIMIT (within the hysteresis), the positive or negative of the value of the reactive current command (command value I _q ^** ) is within the above range (within the hysteresis). You can suppress the inversion with . As a result, even if the sign of the reactive current command (command value _Iq ^* ) is reversed due to minute fluctuations in the value of the reactive current command (command value _Iq ^* ) in the vicinity of 0, the reactive current command (command value Iq*) It is possible to easily suppress the inversion of the sign of _q ^** ).

Other effects of the second embodiment are the same as those of the first embodiment.

[Third embodiment]
Next, the configuration of the power converter 300 according to the third embodiment will be described with reference to FIGS. 7 and 14 to 16. FIG. In the power conversion device 300 of the third embodiment, unlike the first embodiment in which the command value I _q ^* is directly input to the correction means 21b, control is performed to limit the rate of change of the command value I _q ^* . will be In addition, the structure similar to the said 1st Embodiment attaches|subjects the same code|symbol as 1st Embodiment, and abbreviate|omits description while it is illustrated.

As shown in FIG. 14 , the power conversion device 300 has a control section 220 . Further, the control unit 220 includes power control means 221 . Note that the function of the power control means 221 can be realized by software such as a program.

Power control means 221 (control unit 220) includes filter means 221a (for example, a digital filter) to which a reactive current command (command value I _q ^* ) generated from instantaneous reactive power command value q ^* is input. The filter means 221a is configured to output a _filter value If determined according to the magnitude of the input reactive current command (command value _Iq ^* ). The control unit 220 (correction means 21b) is configured to adjust the correction value _Ih according to the magnitude of _the filter value If output from the filter means 221a. Note that the filter means 221a and the filter _value If are examples of the "filter section" and the "filter signal value" in the claims, respectively.

Here, in ^the third embodiment, the control unit 220 (power control means ₂₂₁ ) controls the reactive current command (command When the sign of the reactive current command (command value I _q ^* ) is reversed due to a change in the value of the value I _q ^* ), the reversal of the sign of the reactive current command (command value I _q ^** ) is suppressed. configured to control.

Specifically, the filter unit 221a (control unit 220) changes the value of the reactive current command (command value _Iq ^* ) within a range in which the absolute value of the reactive current command (command value _Iq ^* ) is MIN or less. , the absolute value of the rate of change of ^the value of the reactive current command (command value I _{q *} ) input this time with respect to the previously output filter value If is less than or equal to the threshold value X, the reactive current command (command It is configured to output a filter value I _f equal to the value of the value I _q ^* ) this time. On the other hand, when the absolute value of the rate of change is larger than the threshold value X, the filtering means 221a (control unit 220) determines that the absolute value of the rate of change with respect to the value of the reactive current command (command value _Iq ^* ) input this time is It is configured to output a filter value If that is equal to or less than the threshold value _X this time. Note that the threshold X is an example of a "predetermined threshold" in the scope of claims.

Here, it is assumed that the filter means 221a outputs the filter value If based on the reactive current command (command value _Iq ^* ), which is _the input value, every second. The description will be made assuming that the absolute value of the reactive current command (command value I _q ^* ) is within the range of MIN or less.

In this case, the change amount of the reactive current command (command value I _q ^* (n)) input to the filter means 221a this time with respect to the filter value I _f (n−1) output last time by the filter means 221a is If the absolute value (absolute value of rate of change) is less than or equal to X (|I _f (n-1) - I _q ^* (n) | ≤ X), it is equal to the value of the reactive current command (command value I _q ^* ) The filtered value I _f of the value is output by the filter means 221a as the current filtered value I _f (n) (I _f (n)=I _q ^* (n)).

_On the other ^hand , _the amount of change (change is greater than X (|I _f (n−1)−I _q ^* (n)|>X).

Specifically, the value obtained by subtracting the current reactive current command (command value I _q ^* (n)) from the previous filter value I _f (n−1) is greater than X ( _If (n−1)− If _Iq ^* (n)>X) _, the filter value If obtained by adding _X to the previous filter value If(n-1) is output by the filter means 221a as the current filter value _If (n). (I _f (n)=I _f (n−1)+X).

Also, the value obtained by subtracting the current reactive current command (command value I _q ^* (n)) from the previous filter value I _f (n−1) is smaller than −X (I _f (n−1)−I _q ^* If (n)<-X), the filter value I _f obtained by subtracting X from the previous filter value I _f (n-1) is output by the filter means 221a as the current filter value I _f (n). (I _f (n)=I _f (n−1)−X).

Therefore, when the amount of change (rate of change) is X or less, the filter _value If follows the reactive current command (command value _Iq ^* ). Further, when the amount of change (rate of change) is larger than X, the filter _value If follows the reactive current command (command value _Iq ^* ) with a lag behind the reactive current command (command value _Iq ^* ). .

As a result, even if the value of the reactive current command (command value I _q ^* ) varies slightly across 0, _the filter value If is positive in the vicinity of 0 (see FIG. 15) or in the vicinity of 0 It is maintained in a negative state (see FIG. 16). As a result, the reactive current command (command value I _q ^** ) (and correction value I _h ) is maintained (fixed) at MIN (see FIG. 15) or −MIN (see FIG. 16). FIG. 15 shows a case where the value of the reactive current command (command value I _q ^* ) decreases to near 0 and then slightly fluctuates near 0. FIG. FIG. 10 is a diagram in which the value of _q ^* ) slightly fluctuates near 0 after increasing near 0;

Other configurations of the third embodiment are the same as those of the first embodiment.

(Effect of the third embodiment)
The following effects can be obtained in the third embodiment.

In the third embodiment, as described above, the control unit 220 (power control means 221) controls the reactive current command (command value I q *) within the range where the absolute value of the reactive current command (command value I _q ^* ) is MIN or less _. ^* ), when the sign of the reactive current command (command value _Iq ^* ) is reversed due to a change in the value of the reactive current command (command value Iq**), control is performed to suppress the reversal of the sign of the reactive current command (command value _Iq ^** ). The power conversion device 300 is configured as follows. As a result, even if the reactive current command (command value _Iq ^* ) is reversed in polarity due to minute fluctuations in the value of the reactive current command (command value _Iq ^* ) in the vicinity of 0, the reactive current command (command value Iq*) _q ^** ) can be suppressed from being inverted. As a result, when the value of the reactive current command (command value I _q ^* ) slightly fluctuates in the vicinity of 0 and the sign of the reactive current command (command value I _q ^* ) is reversed, the reactive current command (command value I _q ^** ) can be suppressed from changing abruptly. Thereby, the control by the inter-stage balance control means 23 can be performed more stably.

Further, in the third embodiment, as described above, the control unit 220 causes the filter means 221a to set the absolute value of the reactive current command (command value I _q ^* ) within the range of MIN or less. _q ^* ) changes, if the absolute value of the rate of change of the currently input reactive current command (command value _{Iq *} ⁾ with respect to the previously output filter value If is less than or equal to the threshold value X, this time A _filter value If equal to the input reactive current command (command value I _q ^* ) is output. In addition, when the absolute value of the rate of change is larger than the threshold value X, the control unit 220 sets the absolute value of the rate of change with respect to the currently input reactive current command (command value I _q ^* ) to the threshold value X or less. It is configured to output _If . With this configuration, the rate of change can always be limited to the threshold value X or less. As a result, even if the sign of the reactive current command (command value _Iq ^* ) is reversed due to a relatively large change in the value of the reactive current command (command value _Iq ^* ), the positive/negative of the filter value to be output this time can be suppressed from reversing from the previous time.

Other effects of the third embodiment are the same as those of the first embodiment.

[Modification]
It should be noted that the embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present invention is indicated by the scope of claims rather than the description of the above-described embodiments, and includes all modifications (modifications) within the scope and meaning equivalent to the scope of claims.

For example, in the above-described first to third embodiments, an example in which the reactive current command is corrected under no load has been shown, but the present invention is not limited to this. The reactive current command may be corrected even when there is no load.

Further, in the above-described first to third embodiments, an example in which the correction value _Ih is added to the reactive current command (command value _Iq ^* ) under no load is shown, but the present invention is not limited to this. For example, when there is no load, a command value separate from the reactive current command (command value I _q ^* ) is used as the reactive current command without correcting the reactive current command (command value I _q ^* ). may be configured.

Further, in the above-described first to third embodiments, an example was shown in which the correction value I _h is adjusted according to the magnitude of the reactive current command (command value I _q ^* ) when there is no load. It is not limited to this. For example, the correction value _Ih may be a constant value regardless of the magnitude of the reactive current command (command value _Iq ^* ).

Further, in the above-described first to third embodiments, an example in which the corrected reactive current command (command value I _q ^** ) is constant under no load has been shown, but the present invention is not limited to this. For example, the corrected reactive current command (command value I _q ^** ) may be configured to change according to the magnitude of the reactive current command (command value I _q ^* ) at no load.

Further, in the first to third embodiments, an example in which the power conversion unit 11, the power conversion unit 12, and the power conversion unit 13 are delta-connected to each other has been shown, but the present invention is not limited to this. . For example, power conversion unit 11, power conversion unit 12, and power conversion unit 13 may be star-connected to each other.

In addition, in the above-described first to third embodiments, the power conversion device 100 (200, 300) is a three-phase AC power device, but the present invention is not limited to this. The power conversion device 100 may be a device for single-phase AC power.

In addition, in the first to third embodiments, each of the power conversion unit 11, the power conversion unit 12, and the power conversion unit 13 is provided with three converter cells. is not limited to this. Each of power conversion unit 11 , power conversion unit 12 , and power conversion unit 13 may be provided with a plurality of (for example, four) converter cells other than three.

In addition, in ^{the third embodiment, the filter means 220a (filter section) sets the currently input reactive current command (command value Iq*} _{) (} first reactive current command) is larger than the threshold value X (predetermined threshold value), the currently input reactive current command (command value I _q ^* ) (first reactive current command) value is the filter value to be output this time. Although an example of performing control to set the absolute value of the rate of change of I _f (filter signal value) to the threshold value X (predetermined threshold value) has been shown, the present invention is not limited to this. In the above case, control may be performed such that the change rate is smaller than the threshold value X (predetermined threshold value).

1 DC capacitor (capacitor)
2 semiconductor switch group 2a semiconductor switch 11, 12, 13 power conversion unit 11a, 11b, 11c, 12a, 12b, 12c, 13a, 13b, 13c converter cell 20, 120, 220 control unit 23 interstage balance control means (adjustment unit )
100, 200, 300 power converter 220a filter section (filter means)
I _f filter value (filter signal value)
I _h correction value I _q ^* command value (first reactive current command)
I _q ^** command value (second reactive current command)
I _uv , I _vw , I _wv currents (reactive currents) (currents flowing into the power converter)
q ^* Instantaneous reactive power command value (power command)
X threshold (predetermined threshold)

Claims (11)

a power conversion unit provided with a capacitor and a semiconductor switch group including a plurality of semiconductor switches connected in series with each other, and in which a plurality of converter cells in which the capacitor and the semiconductor switch group are connected in parallel are connected in series;
a control unit including an adjustment unit that equalizes the voltages of the capacitors of the plurality of converter cells based on the reactive current flowing into the power conversion unit;
The control unit performs control using a correction value that varies according to the absolute value of the reactive current command so that the absolute value of the reactive current command for controlling the reactive current is greater than zero at least during no load. A power conversion device configured to: The control unit controls the absolute value of the reactive current to be greater than zero by a second reactive current command obtained by adding the correction value to the first reactive current command based on the power command at least during no load. 2. The power converter of claim 1, configured to control. The control unit adds the correction value to the first reactive current command when the absolute value of the first reactive current command under no load is equal to or less than a first value, and adds the correction value to the first reactive current command. 3. The power converter according to claim 2, configured to adjust according to the magnitude of the value of one reactive current command. The control unit adjusts the correction value so that the absolute value of the corrected second reactive current command becomes a constant value when the absolute value of the first reactive current command is equal to or less than the first value. 4. The power converter of claim 3, configured to regulate. When the absolute value of the first reactive current command is equal to or less than the first value and when the first reactive current command is a positive value, the controller controls the second reactive current after correction. The correction value is adjusted so that the command is a constant positive value, and the absolute value of the first reactive current command is equal to or less than the first value, and the first reactive current command is negative. 5 . The power conversion apparatus according to claim 4 , wherein the correction value is adjusted so that the second reactive current command after correction is a constant negative value when the second reactive current command is a negative value. When the absolute value of the first reactive current command changes within the range of the first value or less, the control unit controls the operation when the positive or negative of the first reactive current command is reversed. 5. The power converter according to claim 4, further configured to perform control for suppressing inversion of the polarity of said second reactive current command after correction. The control unit reduces the value of the first reactive current command by adjusting the correction value so that the correction value changes in a hysteresis manner based on changes in the value of the first reactive current command. When the absolute value of the value of the first reactive current command becomes equal to or less than a second value smaller than the first value, the value of the second reactive current command after correction is made constant at a positive value In addition, when the absolute value of the value of the first reactive current command becomes equal to or less than the second value due to the increase in the value of the first reactive current command, the value of the second reactive current command after correction is 7. The power conversion device according to claim 6, configured to perform control to make it constant at a negative value. The control unit includes a filter unit to which the value of the first reactive current command is input, and which outputs a filter signal value determined according to the magnitude of the input value of the first reactive current command. configured to adjust the correction value according to the magnitude of the filter signal value output by a unit;
The filter unit is configured to change the value of the first reactive current command within the range of the absolute value of the first reactive current command to the current input relative to the previously output filter signal value. When the absolute value of the rate of change of the value of the first reactive current command is equal to or less than a predetermined threshold value, the filter signal value equal to the value of the first reactive current command input this time is output this time, and the change If the absolute value of the rate is greater than the predetermined threshold, the filter signal value that makes the absolute value of the rate of change with respect to the value of the first reactive current command input this time less than or equal to the predetermined threshold is output this time. 7. The power converter according to claim 6, configured to: The power converter according to any one of claims 4 to 8, wherein said constant value is a minimum value required for said adjustment unit to operate normally. The control unit according to any one of claims 3 to 9, wherein when the absolute value of the first reactive current command is equal to or greater than the first value, the correction value is adjusted to zero. Power converter. A capacitor and a semiconductor switch group including a plurality of semiconductor switches connected in series with each other are provided, and the power flows into a power conversion unit in which a plurality of converter cells in which the capacitor and the semiconductor switch group are connected in parallel are connected in series. equalizing the voltages of the capacitors of the plurality of converter cells by an adjustment unit based on the reactive current generated;
At least when there is no load, controlling with a correction value that varies according to the absolute value of the reactive current command so that the absolute value of the reactive current command for controlling the reactive current is greater than zero; A control method for a power converter.

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