JP2006246676A - Power conversion equipment, self-excited reactive power compensating system using this power conversion equipment, and power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide power conversion equipment that can realize turning into high of voltage, increase in capacity, reduction in loss, and high performance. <P>SOLUTION: The power conversion equipment includes a three-phase, three-level inverter circuit 11, that converts direct-current voltage into three-phase alternating-current voltage and outputs voltages of three levels that are controlled by pulse width modulation to the respective phases; power supply circuits 12a, 12b, and 12c, that are connected in series with the outputs in the respective phases of the three-phase, three-level inverter circuit 11 in the respective phases on the output side of the three-phase, three-level inverter circuit 11; and a control device 7 that controls the three-phase, three-level inverter circuit 11 and the power supply circuits 12a, 12b, and 12c and causes a desired three-phase alternating-current voltage to be outputted as the total value of their output voltages. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power converter that converts a DC voltage into a three-phase AC voltage and outputs the same, and a self-excited reactive power compensation system and a power supply system that use the power converter.

  Conventionally, studies have been made to realize a low-loss power converter for high-voltage and large-capacity applications. For example, a three-level inverter device as shown in Patent Document 1 can be easily combined with a high-voltage DC power supply and is suitable for increasing the voltage and capacity of a power converter. However, this three-level inverter device needs to increase the number of switching of the semiconductor switch elements constituting the power conversion device when the output voltage is required to have high quality as in the case of grid connection. As a result, there is a problem that power loss due to the semiconductor switching element increases and high efficiency cannot be achieved.

On the other hand, for example, as shown in Patent Document 2, the method of using a circuit in which single-phase inverter devices are connected in series for three phases is such that the output voltage approaches a sine wave as the series number of single-phase inverters increases, and the number of pulses is smaller But high quality output voltage can be obtained. However, in this method, since the DC power supply must be insulated for each inverter, it is necessary to install independent DC power supplies as many as the number of inverters. Further, since each DC power supply needs a function of outputting energy, there is a problem that the DC power supply system becomes large-scale.
JP 2000-166252 A JP 2000-050643 A

  Accordingly, the present invention has been made to solve the above-mentioned problems all at once, and it is a main aim of providing a high-voltage / large-capacity power converter capable of realizing high efficiency and high performance. It is what.

  That is, the power conversion device according to the present invention includes a three-phase three-level inverter circuit that converts a DC voltage into a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse for each positive and negative pulse per cycle of the fundamental frequency, and the 3 A power supply circuit that is connected in series to each phase on the output side of the phase three-level inverter circuit and outputs a single-phase AC voltage, and controls the three-phase three-level inverter circuit and the respective power supply circuits to output them. And a control device that outputs a desired three-phase AC voltage as a sum of voltages.

  In such a case, since a three-phase three-level inverter circuit is used, it is suitable for increasing the voltage and capacity, and the voltage difference between the target voltage and the output voltage from the three-phase three-level inverter circuit. Since the power supply circuit is made to correct, a high-quality voltage can be output without making the three-phase three-level inverter circuit multipulse, which is higher than the system using only the three-phase three-level inverter circuit. High performance and high efficiency can be achieved.

  As a concrete embodiment for making the effect of the present invention more remarkable, the power supply circuit is a circuit in which a single-phase inverter and a DC power supply are combined, and one or more sets are connected in series on the output side of the single-phase inverter. It is desirable that the single-phase inverter be controlled by pulse width modulation by the control device.

  The control device adjusts the peak value of the third harmonic in the zero-phase voltage component of the voltage output from the power converter, and sets the pulse width of the output voltage from the three-phase three-level inverter circuit. By changing, it is desirable to control the ratio between the energy output from the three-phase three-level inverter circuit and the energy output from the power supply circuit.

  It is conceivable that the control device changes the pulse width of the output voltage from the three-phase three-level inverter circuit to make the accumulated value of the output energy of the power supply circuit as zero as possible.

  Further, the self-excited reactive power compensation system according to the present invention is connected to an electric power system, and supplies reactive power to the electric power system, thereby adjusting the voltage of the electric power system and improving the power factor of the load. A three-phase three-level inverter circuit that converts a DC voltage charged in a capacitor into a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse for each positive and negative frequency per cycle; A capacitor connected in series to each phase on the output side of the three-phase three-level inverter circuit, a capacitor different from the capacitor of the three-phase three-level inverter circuit, and a DC voltage charged to the capacitor are subjected to pulse width modulation control. A power supply circuit configured by connecting two sets of single-phase inverters that are converted into phase alternating voltage and output, and the three-phase three-level input circuit And a control device that controls the data circuit and each of the power supply circuits to output a desired three-phase AC voltage as a sum of their output voltages, and the control device includes the three-phase three-level inverter circuit. The sum of the charging energy of the capacitor and the charging energy of the capacitor of the power supply circuit becomes a desired value, and the charging voltage of the capacitor of the three-phase three-level inverter circuit and the two capacitors of the power supply circuit The three-phase three-level inverter circuit and the power supply circuit are controlled so as to maintain a ratio of 4: 4: 2: 1.

  If this is the case, the effect of the power converter according to the present invention can output a high-quality voltage without making the three-phase three-level inverter circuit multi-pulsed. The power compensation system can be provided with high performance and high efficiency.

  In order to increase the output voltage from the self-excited reactive power compensation system in multiple stages, the voltage of the capacitor of the three-phase three-level inverter circuit and the capacitor of the power supply circuit can be increased. The ratio may be 5: 5: 2: 1 or 6: 6: 2: 1.

  Furthermore, the power supply system using the power converter according to the present invention is a power supply system that is connected to the power system and inputs / outputs power to / from the power system, and a DC voltage charged in the capacitor is A three-phase three-level inverter circuit that converts and outputs a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse of positive and negative one pulse per basic frequency, and a DC power source that is connected in parallel to the capacitor and outputs a DC voltage Are connected in series to the respective phases on the output side of the three-phase three-level inverter circuit, and a capacitor different from the capacitor of the three-phase three-level inverter circuit and the DC voltage charged in the capacitor are subjected to pulse width modulation control. A power supply circuit configured by connecting two sets of single-phase inverters that are converted into single-phase AC voltage and output in series, and the three-phase circuit And a control device for controlling the level inverter circuit and each of the power supply circuits to output a desired three-phase AC voltage as a sum of their output voltages, and the voltage output from the DC power supply is the power system The ratio of the rated voltage to the peak value is approximately 12/7, and the control device has a desired sum of the charging energy of the capacitor of the three-phase three-level inverter circuit and the charging energy of the capacitor of the power supply circuit. The pulse width of the output voltage from the three-phase three-level inverter circuit is changed by adjusting the peak value of the third harmonic of the zero-phase voltage component of the desired three-phase AC voltage. Thus, the ratio of the energy output from the three-phase three-level inverter circuit and the energy output from the power supply circuit is controlled and output from the DC power supply. In order to maintain the ratio of the DC voltage, the charging voltage of the capacitor of the three-phase three-level inverter circuit, and the charging voltage of the two capacitors of the power supply circuit in the relationship of 12: 6: 6: 2: 1. A phase three-level inverter circuit and the power supply circuit are controlled.

  If it is such, since the high-quality voltage can be output without making the three-phase three-level inverter circuit multipulse due to the effect of the power conversion device according to the present invention, a high-voltage / large-capacity power supply system Can be provided with high performance and high efficiency.

  In such a case, the output power of the three-phase three-level inverter circuit can be changed to a desired output power by adjusting the pulse width of the voltage output from the three-phase three-level inverter circuit using the present invention. As close as possible. That is, the power output from the power supply circuit can be made as close to zero as possible, and an auxiliary circuit for charging and regenerating energy can be omitted or minimized in the DC power supply of the power supply circuit. Therefore, it is not necessary to arrange a large-scale DC power supply for inverters other than the three-phase three-level inverter circuit. Compared with a method in which only a single-phase inverter is connected in series and a DC power supply of a considerable scale is arranged for each, A small and low-cost power supply system can be provided.

  According to the present invention configured as described above, since the three-phase three-level inverter circuit is used, it is suitable for high voltage and large capacity, and the target voltage and the output voltage from the three-phase three-level inverter circuit are Since the power supply circuit corrects the difference voltage, a high-quality voltage can be output without making the three-phase three-level inverter circuit multipulse, and a system using only the three-phase three-level inverter circuit In comparison, higher performance and higher efficiency can be achieved.

  Furthermore, the power converter according to the present invention is applied to a high-voltage / large-capacity self-excited reactive power compensation system and a high-voltage / large-capacity power supply system for load leveling, power failure countermeasures, DC power transmission, etc. By doing so, a high-performance and highly efficient system can be provided.

  <First Embodiment>

  Next, a first embodiment in which the power conversion device 1 according to the present invention is used in a self-excited reactive power compensation system SS will be described with reference to the drawings.

As shown in FIG. 1, the self-reactive reactive power compensation system SS according to the present embodiment includes a three-phase AC power supply 2 and a three-phase AC load 3, and includes a three-phase circuit including an a-phase 31, a b-phase 32, and a c-phase 33 In the AC power system, the system voltage Vtj (j = a, b, c) of the power system is supplied by being connected to the three-phase AC power source 2 in parallel with the three-phase AC load 3 and supplying reactive power to the power system. Is adjusted to be the target voltage V _ref . Then, as will be described later, single-phase inverter circuits 121j (j = a, b, c) and 122j (j = a, b) of the three-phase three-level inverter circuit 11 and the power supply circuit 12j (j = a, b, c). , C), voltages Vh ₁ , Vh ₂ , Vmj (j = a, b, c) of capacitors C 1, C 2, C 3 j (j = a, b, c), C 4 j (j = a, b, c) connected to ), The ratio of Vlj (j = a, b, c) is controlled to be maintained at 4: 4: 2: 1, and is operated at a predetermined timing, for example, as shown in FIG. 2, to output desired reactive power The system voltage Vtj (j = a, b, c) is adjusted.

  In the following, when the subscript j (j = a, b, c) is omitted, the a-phase, the b-phase, and the c-phase are treated in common or necessary.

The configuration of the self-excited reactive power compensation system SS includes a power converter 1, and the interconnection reactor _{X SVG,} capacitor C1 to be described later, C2, C3, the voltage _Vh 1 of _C4, Vh 2, Vm, for measuring Vl Capacitor voltage measuring means 5, system voltage measuring means 6 for measuring the system voltage Vt, and a control device 7 for adjusting the peak value and phase of the output voltage V _SVG based on the measurement data therefrom, It has. In FIG. 1, the capacitor voltage measuring means 5, the system voltage measuring means 6, and the control device 7 are omitted.

  These are described in detail below.

The power conversion device 1 converts a DC voltage into a three-phase AC voltage and outputs a three-level voltage to each phase, and each of the output sides of the three-phase three-level inverter circuit 11 In each phase, a power supply circuit 12 that is connected in series to the three-phase three-level inverter circuit 11 and outputs a difference voltage between the output voltage V11 from the three-phase three-level inverter circuit ₁₁ and a desired voltage V _SVG And a control device 7 for controlling the three-phase three-level inverter circuit 11 and the power supply circuit 12 to output a desired voltage V _SVG .

  The three-phase three-level inverter circuit 11 converts the DC voltage of the capacitor C1 or C2 into a three-phase AC voltage and outputs it. The four semiconductor switch elements 111 connected in series and the semiconductor switch element 111 A three-level inverter circuit 110 comprising a diode 112 connected in antiparallel to each other, and two diodes D1 and D2 connected in parallel to two semiconductor switch elements inside four semiconductor switch elements 111 connected in series; It is equipped with. An interconnection point N1 between the diode D1 and the diode D2 is connected to an interconnection point (neutral point) N2 between the capacitors C1 and C2. In this embodiment, an IGBT (Insulated Gate Bipolar Transistor) having a self-extinguishing capability is used as the semiconductor switch element 111. The three-phase three-level inverter circuit 11 is controlled to be turned on / off by a control device 7 to be described later by a drive signal to the gate, so that an operation pattern (switch pattern) is controlled.

  The power supply circuit 12 is configured by connecting single-phase inverter circuits 121 and 122 in series. Single-phase inverter circuits 121 and 122 include capacitors C3 and C4 and single-phase inverters I1 and I2.

  The single-phase inverters I1 and I2 are full-bridge inverters composed of semiconductor switch elements and diodes anti-parallel to them, and are connected to capacitors C3 and C4 to convert the DC voltage of the capacitors C3 and C4 into AC voltage. Output to each phase. As the semiconductor switch element, an IGBT (Insulated Gate Bipolar Transistor) is used as in the three-phase three-level inverter circuit 11. The power supply circuit 12 is controlled to be turned on and off by a drive signal to the gate using a circuit control unit 74 of the control device 7 to be described later, so that an operation pattern (switch pattern) is controlled.

The charging voltages Vh ₁ , Vh ₂ , Vm, and Vl of the capacitors C 1, C 2, C 3, and C 4 are set to a voltage ratio of Vh ₁ = Vh ₂ = 2 × Vm = 2 × 2 × Vl by the control device 7 described later. It is controlled so that

  Capacitors C1, C2, C3, and C4 are preliminarily set to 60%, 60%, 30%, and 15% of the peak values of the rated AC voltage in advance by an initial charging circuit (not shown). ] Is charged. For example, in the case of application to a three-phase 6.6 kV AC system, 0.6 × 6.6 × √2 / √3 [kV] and 0.6 × 6.6 × √2 / √3 [kV] in this order. 0.3 × 6.6 × √2 / √3 [kV], 0.15 × 6.6 × √2 / √3 [kV]. When the charging is completed, the initial charging circuit is electrically disconnected from the capacitors C1, C2, C3, and C4 by a switch (not shown), and does not affect the operation of the self-excited reactive power compensation system SS.

Since the capacitors C1, C2, C3, and C4 are maintained at a voltage ratio of 4: 4: 2: 1 by the control device 7 described later, a three-level inverter is provided as shown in FIGS. Depending on how the operation patterns of the circuit 110 and the power supply circuit 12 are selected, it is possible to output a voltage V _{SVG of} 15 levels in total including 7 levels on the positive side, 7 levels on the negative side, and zero output level. Hereinafter, the levels are referred to as level-7, level-6,..., Level0,.

6 and 7, only the voltages Vh ₁ , Vh ₂ , Vm, and Vl are shown, but these are the charging voltages of the capacitors C1, C2, C3, and C4. In the table, 1, 0, and −1 indicate the presence / absence of voltage output from the three-level inverter circuit 110 and the single-phase inverter circuits 121 and 122 to which the capacitors C1, C2, C3, and C4 are connected, and the polarity of the output voltage. Represents.

In FIG. 6, there are cases where a plurality of operation patterns of the three-level inverter circuit 110 and the power supply circuit 12 are described in outputting the voltage V _{SVG of the} same level. It will be described later.

  The system voltage measuring means 6 measures the peak value and phase of the system voltage Vt, and outputs data indicating the measurement result to the control device 7.

The capacitor voltage measuring means 5 is for measuring the voltages Vh ₁ , Vh ₂ , Vm, Vl charged in the capacitors C 1, C 2, C 3, C 4, and outputs the voltage measurement data to the control device 7. Is.

  The system voltage measuring means 6 and the capacitor voltage measuring means 5 are very general, and detailed description of the configuration is omitted.

  As shown in FIG. 3, the control device 7 is a general purpose or dedicated computer having a CPU 701, a memory 702, an input / output interface 703, an AD converter 704, etc., and is stored in a predetermined area of the memory 702. By cooperating the CPU 701, peripheral devices, and the like according to the predetermined program, the functions as the receiving unit 71, the output voltage calculating unit 72, the circuit control unit 74, and the like are exhibited as shown in FIG.

  The accepting unit 71 receives the measurement data from each of the measuring means 5 and 6 described above and outputs it to the output voltage calculating unit 72 and the circuit control unit 74.

The output voltage calculation unit 72 calculates a voltage V _SVG that the self-excited reactive power compensation system SS should output in order to control the system voltage Vt to the target value V _ref based on each measurement data received by the reception unit 71. The calculated data is output to the circuit control unit 74.

Specifically, the output voltage calculation unit 72 calculates the voltage V _SVG to be output by the self-excited reactive power compensation system SS using the following equation and the block diagram of FIG. 5 to calculate the three-level inverter circuit 110 and the power supply circuit. 12 is controlled.

Here, ω is the fundamental frequency of the power system, Vp _SVG is the peak value of the output voltage V _SVG , and φ is the phase difference of the output voltage V _SVG with respect to the system voltage Vt.

In the block diagram of FIG. 5, the transfer function G (s) determines the peak value Vp _SVG so that the difference between the target voltage V _ref and the system voltage Vt becomes zero in the steady state. The target value E _ref of the charging energy of the capacitors C1, C2, C3, and C4 is the sum of charging voltages Vh ₁ + Vm + Vl of the capacitors C1, C3, and C4 and the total charging voltage Vh ₂ + Vm + Vl of the capacitors C2, C3, and C4. It is determined to be equal to the peak value Vp _SVG . The transfer function H (s) is an effective power input / output to / from the capacitors C1, C2, C3, and C4 so that the difference between the charging energy E _C of the capacitors C1, C2, C3, and C4 and the target value E _ref becomes zero in a steady state. P is determined. The phase difference φ between the system voltage Vt and the output voltage V _SVG for exchanging the active power P between the self-excited reactive power compensation system SS and the power system is determined by conversion using the constant K ₇ .

Note that in FIG. 5, _{C 1} is the capacitance of the capacitors C1 and C2, _{C 3} is the capacitance of the capacitor C3, _{C 4} is the capacitance of capacitor C4.

As described above, the output voltage calculation unit 72 generates reactive power for controlling the system voltage Vt to the target value V _ref from the measurement data of the system voltage Vt and the capacitor voltages Vh ₁ , Vh ₂ , Vm, and Vl. The active power is input to and output from the power system according to the difference between the capacitor charging energy and the initial charging energy, and the charging energy E _{C of} the capacitors C1, C2, C3, and C4 is set to the target value E. as a _ref, i.e. the power system and the capacitor C1, C3, total _Vh 1 + Vm + Vl of the charging voltage of the C4, and the capacitors C2, C3, C4 total _Vh 2 + Vm + Vl charging voltage of peak value of the output voltage _{V SVG} An output voltage V _SVG is calculated for control so as to quickly coincide with Vp _SVG .

The circuit control unit 74 selects an output level from the received output voltage calculation data, the table in FIG. 6, the table in FIG. 7, and the capacitor voltage measurement data so as to be a value closest to the output voltage V _SVG .

Further, the circuit control unit 74 allows the ratio of charging voltages between the capacitors C1, C2, C3, and C4 to be a predetermined value (Vh ₁ : Vh ₂ : Vm: Vl = 4: 4: 2: 1). To output the same level of voltage V _SVG , an appropriate operation pattern is selected from among a plurality of operation patterns of the three-level inverter circuit 110 and the power supply circuit 12 to output the voltage V _SVG of the same level, and the three-level inverter circuit 110 and A drive signal is output to the power supply circuit 12.

As a specific example, a method of selecting an operation pattern in the case where the voltages of output level 1 and output level −1 are output as V _SVG is shown. Here, the output current I _SVG is positive.

  [1] As an inverter operation and charge / discharge relationship for outputting the output level 1, as shown in FIG.

  (1-1) The voltage Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C4 is discharged.

  (1-2) The voltage Vm is output from the single-phase inverter circuit 121, and the voltage -Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C3 is discharged and the capacitor C4 is charged.

(1-3) The voltage Vh ₁ is output from the three-level inverter circuit 110, the voltage −Vm is output from the single-phase inverter circuit 121, and the voltage −Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C1 is discharged, and the capacitor C3 and the capacitor C4 are charged.

  There are three ways.

For example, when the output level 1 is output at the timing of ₂ Vm ≧ Vh ₁ > 4 Vl by utilizing these charge / discharge relationships, the operation pattern (1-2) is selected.

  [2] The inverter operation and the charge / discharge relationship for outputting the output level-1 are as shown in FIG.

  (2-1) The voltage −Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C4 is charged.

  (2-2) The voltage −Vm is output from the single-phase inverter circuit 121, and the voltage Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C3 is charged and the capacitor C4 is discharged.

(2-3) The voltage -Vh ₂ is output from the three-level inverter circuit 110, the voltage Vm is output from the single-phase inverter circuit 121, and the voltage Vl is output from the single-phase inverter circuit 122. At this time, the capacitor C1 is charged, and the capacitor C3 and the capacitor C4 are discharged.

  There are three ways.

Utilizing these charge-discharge relationship, for example in the case of outputting the output level -1 at the timing of Vh ₂ ≦ 2Vm and Vh ₂ ≦ 4Vl selects an operation pattern of (2-3).

The same applies to the output levels ± 2, ± 3, etc. Generally, in the tables of FIGS. 6 and 7, when the output current I _SVG and the output voltage V _SVG have the same polarity, the operation pattern is “ In the case of “1”, the corresponding capacitors C1, C2, C3, and C4 are discharged, and in the case of “−1”, the corresponding capacitors C1, C2, C3, and C4 are charged. When the output current I _SVG and the output voltage V _SVG are opposite in polarity, the charge / discharge relationship is reversed. Further, in this case, the direction of the inequality sign of the capacitor voltage condition for selecting the operation pattern at the same output level is also reversed.

Using the above principle, the circuit control unit 74 has the respective charging voltages Vh ₁ , Vh of the capacitors C 1, C 2, C 3, C 4 at the output level where a plurality of operation patterns of the three-level inverter circuit 110 and the power supply circuit 12 exist. _2. The operation patterns of the three-level inverter circuit 110 and the power supply circuit 12 are selected, that is, discharging and charging are determined depending on which of the capacitor voltage conditions the states of V, Vm, and Vl apply. As a result, the ratio of the charging voltages Vh ₁ , Vh ₂ , Vm, and Vl of the capacitors C1, C2, C3, and C4 can be adjusted.

  Next, the operation of the self-excited reactive power compensation system SS according to this embodiment configured as described above will be described below.

First, when the self-excited reactive power compensation system SS is activated, the system voltage measuring unit 6 measures the system voltage Vt, and the capacitor voltage measuring unit 5 measures the capacitor voltages Vh ₁ , Vh ₂ , Vm, and Vl, and measures them. Data is output to the control device 7. The control device 7 receives the measurement data, and the three-phase three-level inverter circuit 11 and the power supply circuit 12 operate according to the drive signal from the circuit control unit 74. The self-excited reactive power compensation system SS The predetermined reactive power is started to be supplied to the power system so that the voltage Vt becomes a preset target value V _ref .

During the operation of the self-excited reactive power compensation system SS, the output voltage calculation unit 72 in the control device 7 uses the control method shown in the control block diagram of FIG. 5 based on the system voltage measurement data and the capacitor voltage measurement data. The circuit voltage Vt is made to coincide with the target value V _ref , and the output voltage V _SVG is calculated so that the sum E _C of the charging energy of the capacitors C 1, C 2, C 3 and C 4 coincides with the target value E _ref, and the circuit control unit 74 Output to.

The circuit control unit 74 selects the output level to be a value closest to the output voltage V _{SVG based} on the received output voltage calculation data, the table of FIG. 6, the table of FIG. 7, and the capacitor voltage measurement data, and the capacitors C1, C2 , C3, _{E C} is the sum of the charging energy of C4 is equal to the target value _{E ref,} capacitors C1, C2, C3, a predetermined value a voltage ratio of _{C4 (Vh 1: Vh 2:} Vm: Vl = 4: The three-level inverter circuit 110 and the power supply circuit 12 are operated so as to maintain 4: 2: 1).

  According to the self-excited reactive power compensation system SS configured as described above, since the high-quality voltage can be output without making the three-phase three-level inverter circuit 11 multipulse, only the three-phase three-level inverter circuit 11 is used. Compared with the system, it is possible to achieve higher performance and higher efficiency.

  Second Embodiment

  Below, 2nd Embodiment at the time of using the power converter device 1 of this invention for the load leveling system HS is described with reference to drawings.

As shown in FIG. 10, the load leveling system HS according to the present embodiment includes a three-phase alternating current power source 2 and a three-phase alternating current load 3, and includes a three-phase alternating current including a phase 31, a b phase 32, and a c phase 33. In the power system, the power supplied from the three-phase AC power source 2 to the three-phase AC load 3 is connected to the three-phase AC power source 2 in parallel with the three-phase AC load 3 and inputs / outputs active power to / from the power system. For example, the difference between the daytime heavy load and the light load at midnight is leveled, and the equipment capacity of the three-phase AC power source 2 and the like is reduced. Then, as will be described later, single-phase inverter circuits 121j (j = a, b, c) and 122j (j = a, b) of the three-phase three-level inverter circuit 11 and the power supply circuit 12j (j = a, b, c). , C) capacitors C1, C2, C3j (j = a, b, c), C4j (j = a, b, c) voltages Vh ₁ , Vh ₂ , Vmj (j = a, b, c), Vlj Control is performed so that the ratio of (j = a, b, c) is maintained at 6: 6: 2: 1. For example, as shown in FIG. 11, operation is performed at a predetermined timing to output desired power, and load leveling is performed. To do.

  In the following, when the subscript j (j = a, b, c) is omitted, the a-phase, the b-phase, and the c-phase are treated in common or necessary.

The configuration of the load leveling system HS includes a main DC power supply 10, a power conversion device 1 connected to the main DC power supply 10, an interconnection reactor _XHS, and voltages of capacitors C1, C2, C3, and C4 described later. Capacitor voltage measuring means 5 for measuring Vh ₁ , Vh ₂ , Vm, Vl, system voltage measuring means 6 for measuring system voltage Vt, and means for measuring power input / output from the load leveling system HS 4 and a control device 7 for adjusting the peak value and phase of the output voltage V _HS based on the measurement data. In FIG. 10, the input / output power measuring means 4, the capacitor voltage measuring means 5, the system voltage measuring means 6, and the control device 7 are omitted.

  These are described in detail below.

  In the present embodiment, the basic configuration of the power conversion device 1 is the same as that of the first embodiment.

  The main DC power supply 10 is a DC voltage source capable of inputting and outputting energy, such as a lead battery, in which the ratio of the output DC voltage to the peak value of the rated voltage of the power system is approximately 12/7.

The charging voltages Vh ₁ , Vh ₂ , Vm, and Vl of the capacitors C 1, C 2, C 3, and C 4 are set to a voltage ratio of Vh ₁ = Vh ₂ = 3 × Vm = 2 × 3 × Vl by the control device 7 described later. It is controlled so that

  Capacitors C1, C2, C3 and C4 are preliminarily set to 6/7 [pu], 6/7 [pu], 2/7 [ pu], 1/7 [pu]. For example, in the case of application to a three-phase 6.6 kV AC system, 6/7 × 6.6 × √2 / √3 [kV] and 6/7 × 6.6 × √2 / √3 [kV] in this order. 2/7 × 6.6 × √2 / √3 [kV] and 1/7 × 6.6 × √2 / √3 [kV]. When charging is completed, the initial charging circuit is electrically disconnected from the capacitors C1, C2, C3, and C4 by a switch (not shown), and does not affect the operation of the load leveling system HS.

  Since the configurations of the three-phase three-level inverter circuit 11 and the power supply circuit 12 are the same as those in the first embodiment, description thereof is omitted.

The input / output power measuring means 4 measures the power _PHS output from the load leveling system HS to the system, and outputs system voltage measurement data indicating the measurement result to the control device 7. Since the input / output power measuring means 4 is very general, detailed description of the configuration is omitted.

  Since the system voltage measuring unit 6 and the capacitor voltage measuring unit 5 are the same as those in the first embodiment, description thereof is omitted.

  The control device 7 is a general-purpose or dedicated computer having the same device configuration as that of the first embodiment, and the CPU 701, peripheral devices, and the like cooperate in accordance with a predetermined program stored in a predetermined area of the memory 702. As shown in FIG. 4, the functions as the receiving unit 71, the phase calculating unit 73, the zero-phase voltage calculating unit 75, the circuit control unit 74, and the like are exhibited.

  The accepting unit 71 receives the measurement data from each of the measuring means 4, 5, 6 described above and outputs it to the phase calculating unit 73 and the zero phase voltage calculating unit 75.

Based on each measurement received by the receiving unit 71, the phase calculating unit 73 outputs the phase of the voltage that the load leveling system HS should output in order for the load leveling system HS to input and output the target power _Pref , that is, _VHS. The phase difference φ of the positive phase voltage component with respect to the system voltage Vt is calculated, and the calculated data is output to the circuit control unit 74.

The zero-phase voltage calculation unit 75 outputs the power P _HS from the three-level inverter circuit 110 based on each measurement received by the reception unit 71, and performs load leveling so that the power input / output from the power supply circuit 12 is zero. The peak value Vp ₀ of the third harmonic component of the voltage to be output by the control system HS, that is, the zero phase voltage component of V _HS is calculated, and the calculated data is output to the circuit control unit 74.

In the three-phase AC system, the zero-phase voltage component of the output voltage V _HS does not affect the line voltage, and therefore it is common that the output power P _HS and the output current I _HS of the load leveling system HS are not affected. This is an important matter and will not be described.

Specifically, the phase calculation unit 73 and the zero-phase voltage calculation unit 75 calculate the output voltage V _HS j (j = a, b, c) of the load leveling system HS according to the following equations and FIGS. 13 and 14. The three-phase three-level inverter circuit 11 and the power supply circuit 12 are controlled by calculation.

Here, ω is the fundamental frequency of the power system, Vn is the peak value of the rated voltage of the power system, φ is the phase difference of the positive phase voltage component of the output voltage V _HS with respect to the system voltage Vt, and Vp ₀ is the output voltage V _HS. Is the peak value of the third harmonic component. Note that φ in the first term on the right side of the above three expressions is the calculation result of the phase calculation unit 73, and Vp _{0 of} the fourth expression is the calculation result of the zero-phase voltage calculation unit 75.

The phase φ is determined as shown in the block diagram of FIG. 13, and the peak value Vp ₀ is determined as shown in the block diagram of FIG. The transfer function X (s) determines the active power P so that the difference between the output power P _HS of the load leveling system HS and the target value P _ref is 0 in the steady state. By conversion by a constant K _11, a phase difference φ between the positive phase voltage component of the system voltage Vt and output voltage V _HS for exchanging active power P between the load leveling system HS and power system It is determined.

The transfer function Y (s) is an average value of three phases of the average value (Vh ₁ + Vh ₂ ) / 2 of the charging voltage of the capacitors C1 and C2 and the voltage of the capacitors C3 and C4 {(Vma + Vla) + (Vmb + Vlb) ) + (Vmc + Vlc)} / 3 is determined so that the peak value Vp ₀ of the third harmonic of the zero-phase voltage component is 2: 1 in the steady state.

Hereinafter, the principle of controlling the ratio between the charging voltage Vh ₁ (or Vh ₂ ) of the capacitor C1 (or C2) and the total charging voltage Vm + Vl of C3 and C4 by adjusting the peak value Vp ₀ will be described. .

  First, the relationship between the output level of the load leveling system HS and the operation of the three-level inverter circuit 110 will be described.

As shown in FIG. 16, when the zero-phase voltage V ₀ (t) is not used, the voltage can be output from the three-level inverter circuit 110 at the output level 3 or higher. In this embodiment, since Vh ₁ = Vh ₂ = 6/7 pu, Vm = 2/7 pu, and Vl = 1/7 pu, the output voltage V _HS is approximately 0.357 pu (= (Vm + Vl) / 2). The voltage output of the three-level inverter circuit 110 can be started with the phase, that is, the phase θ where sin θ = about 0.357. Here, pu (per unit) used as a unit is based on the peak value of the rated voltage of the power system.

  Next, the relationship between the power output from the three-level inverter circuit 110 and the phase θ will be described.

When the voltage output operation of the three-level inverter circuit 110 is performed at the phase θ, the electric power P ₃ output from the three-level inverter circuit 110 is as follows. Here, it is assumed that the phase α is a phase difference between the output current I _HS and the output voltage V _HS of the load leveling system HS.

As described above, the electric power P ₃ output from the three-level inverter circuit 110 changes depending on the phase θ.

  On the other hand, in order to prevent the power supply circuit 12 from outputting energy, it is only necessary to supply all the energy of the load from the three-level inverter circuit 110. That is,

  Therefore, if the voltage output start phase of the three-level inverter circuit 110 can be set to θ ′ of the following equation, energy is not input / output from the power supply circuit 12.

  Here, when Vh = 6 / 7pu, sin θ ′ = about 0.355. In this way, when Vh = 6 / 7pu, the phase θ (sin θ = about 0.357) at which the voltage output of the three-level inverter circuit 110 can be started and the total energy of the load are supplied from the three-level inverter circuit 110. The phase θ ′ at which voltage output must be started takes a very close value.

  Next, the fact that the phase θ can be controlled will be described with reference to FIG.

The middle diagram (a) in FIG. 15 shows the case where the zero-phase voltage component is zero. On the other hand, if the peak value Vp ₀ of the third harmonic of the zero-phase voltage component of the output voltage V _HS is adjusted as shown in the upper diagram (A) and lower diagram (C) of FIG. It can be seen that the phase θ at which the voltage is output can be controlled.

Further, as shown in FIG. 15, if Vp ₀ is changed in a range of −0.15 ≦ Vp ₀ ≦ 0.15, the phase θ can be adjusted by about 0.357 ± 0.1 [rad]. The phase θ ′ (sin θ ′ = about 0.355) in which the voltage output must be started in order to supply all the energy of the load from the three-level inverter circuit 110 and the phase in which the voltage output of the three-level inverter circuit 110 can be started. There is a sufficient adjustment range of Vp ₀ to match θ. Further, since the phase θ increases monotonously with the increase of Vp ₀ , if feedback control is performed so that Vp ₀ monotonically increases to Vh− (Vm + Vl) × 2 as shown in the block diagram of FIG. In this case, the phase θ ′ at which voltage output must be started in order to supply all the energy of the load from the three-level inverter circuit 110 and the phase θ at which the voltage output of the three-level inverter circuit 110 can be started can be matched. it can. That is, in the load leveling system HS, the output energy of the power supply circuit 12 can be controlled to zero.

The circuit control unit 74, the received phase calculation data, calculates the output voltage V _HS of load leveling system HS from the zero-phase voltage calculation data, from more tables and capacitor voltage measurement data of FIG. 16, most of the output voltage V _HS An output level that is a close value is selected, and the voltage ratio among the capacitors C1, C2, C3, and C4 is set to a predetermined value (Vh ₁ : Vh ₂ : Vm: Vl = 6: 6: 2: 1). The operation patterns of the three-level inverter circuit 110 and the power supply circuit 12 are selected so as to be as close as possible, and drive signals are output to the three-level inverter circuit 110 and the power supply circuit 12.

  Note that description and illustration are omitted for negative and zero output levels.

  Next, the operation of the load leveling system HS configured as described above will be described below.

First, when the load leveling system HS is activated, the system voltage measuring unit 6, the input / output power measuring unit 4, and the capacitor voltage measuring unit 5 perform measurement and output the measurement data to the control device 7. Then, the control device 7 receives the measurement data, the three-level inverter circuit 110 and the power supply circuit 12 operate according to the drive signal from the circuit control unit 74, and the load leveling system HS has a preset load. Based on the leveling pattern, the power system starts to supply a predetermined power _Pref .

During the operation of the load leveling system HS, the phase calculation unit 73 of the control device 7 inputs / outputs the target power P _ref by the control method shown in the control block diagram of FIG. 13 based on the input / output power measurement data. load leveling system HS is the voltage to be output phase, namely the phase difference φ between the system voltage Vt of the positive-phase component of the V _HS is calculated for, and outputs the calculated data to the circuit control unit 74.

Based on the capacitor voltage measurement data, the zero-phase voltage calculation unit 75 uses the control method shown in the control block diagram of FIG. 14 to reduce the power input / output from the power supply circuit 12 to zero. Calculates the peak value Vp ₀ of the third harmonic component of the zero phase voltage component of the voltage V _HS to be output, and outputs the calculated data to the circuit control unit 74.

The circuit control unit 74 calculates the output voltage V _HS of the load leveling system HS from the received phase calculation data and zero-phase voltage calculation data, and is closest to the voltage V _HS from the table of FIG. 16 and the capacitor voltage measurement data. The output level to be a value is selected, and the voltage ratio between the respective capacitors C1, C2, C3, and C4 is maintained at a predetermined value (Vh ₁ : Vh ₂ : Vm: Vl = 6: 6: 2: 1). Thus, the three-level inverter circuit 110 and the power supply circuit 12 are operated.

  According to the load leveling system HS configured as described above, a high-quality voltage can be output without making the three-phase three-level inverter circuit 11 multi-pulsed, and therefore, compared with a system using only the three-phase three-level inverter circuit. High performance and high efficiency can be achieved.

  Furthermore, since a small and low-cost capacitor can be used for the DC power supplies C3 and C4 of the power supply circuit 12, as compared with a method in which only a single-phase inverter is connected in series and a DC power supply of a considerable scale is arranged in each. Thus, a small and low-cost load leveling system HS can be provided.

  <Other modified embodiments>

  The present invention is not limited to the above embodiment.

For example, when the power conversion device 1 according to the present invention is used in the self-excited reactive power compensation system SS, the ratio of the charging voltages Vh ₁ , Vh ₂ , Vm, and Vl is expressed as Vh ₁ : Vh ₂ : Vm: Vl = It may be 5: 5: 2: 1.

In this case, as shown in FIG. 17, the voltage V of the total of 17 levels including the positive 8 levels, the negative 8 levels, and the zero output level is selected depending on how the operation patterns of the 3-level inverter circuit 110 and the power supply circuit 12 are selected. _SVG can be output.

Further, when the power conversion device 1 according to the present invention is used in the self-excited reactive power compensation system SS, the ratios of the charging voltages Vh ₁ , Vh ₂ , Vm, and Vl are expressed as Vh ₁ : Vh ₂ : Vm: Vl = It may be 6: 6: 2: 1. At this time, as shown in FIG. 18, the voltage V _{SVG of} 19 levels in total, that is, 9 levels on the positive side, 9 levels on the negative side, and zero output level, is selected depending on how the operation patterns of the 3-level inverter circuit 110 and the power supply circuit 12 are selected. Can be output.

  Moreover, the power converter device which concerns on this invention can also be used for self-excited direct-current power transmission system TS. Specifically, as shown in FIG. 19, a first power conversion device TS1 that is connected to a three-phase AC system 2A and converts an AC voltage into a DC voltage, and is connected in series to the first power conversion device TS1. The second power conversion device TS2 converts the DC voltage into an AC voltage and outputs the AC voltage to the three-phase AC system 2B. The first power conversion device TS1 and the second power conversion device TS2 have an AC voltage and a DC voltage input / output relationship opposite to each other, and both have a three-phase three-level inverter circuit 11 and a power supply circuit 12.

  In addition to the above, in each of the above embodiments, the power supply circuit is configured by connecting two single-phase inverter circuits of each phase in series, but may be configured by connecting one or more than three in series. .

  In the second embodiment, the DC voltage of the main DC power supply 2 is handled as a fixed value.

For example, if an auxiliary circuit such as a DC-DC converter that can variably control the direct current voltage is used, the maximum value of the output voltage _VHS can be changed greatly. Therefore, the reactive power compensation function as in the first embodiment is also provided. A power supply device can be realized.

  In the second embodiment, the voltage value of the DC power supply and the voltage ratio of the capacitor are used to make the DC power supply of the power supply circuit 12 a small and low-cost capacitor. Conversely, energy is input / output from the DC side to the outside. If an auxiliary circuit for this purpose is provided, there will be no restrictions on the DC voltage value or voltage ratio.

  That is, for example, a DC power supply having a voltage of 9/13 pu, 3/13 pu, or 1/13 pu can be used, and the output voltage of the load leveling system HS is the sum of the positive 13 level, the negative 13 level, and the zero output level. The accuracy is dramatically improved to 27 levels.

  Also in this case, according to the present invention, by changing the pulse width of the output voltage from the three-level inverter circuit 110 and making the output from the three-level inverter circuit 110 as close as possible to the output energy of the load leveling system HS, The power supply circuit 12 can be applied to reduce the capacity of the auxiliary circuit, that is, the device scale.

  In addition, it goes without saying that various modifications are possible without departing from the spirit of the present invention.

1 is a schematic configuration diagram of a self-excited reactive power compensation system according to a first embodiment. The figure which shows the operation | movement timing of the 3 level inverter circuit and power supply circuit in the embodiment. The equipment block diagram of the control apparatus in the embodiment. The function block diagram of the control apparatus in the embodiment. The block diagram which shows the calculation method of the output voltage of the self-excited reactive power compensation system in the embodiment. The table | surface which shows the switching pattern according to the output level 0-7 / 7 in the same embodiment, timing, and the capacitor voltage condition at that time. The table | surface which shows the switching pattern according to the output level 0--7 / 7 in the same embodiment, timing, and the capacitor voltage condition at that time. The figure which shows charge and discharge of a 3 level inverter circuit and power supply circuit at the time of outputting the voltage of the output level 1 in the embodiment. The figure which shows charge and discharge of a 3 level inverter circuit and power supply circuit at the time of outputting the voltage of the output level -1 in the embodiment. The schematic block diagram of the load leveling system which concerns on 2nd Embodiment. The figure which shows the operation | movement timing of the 3 level inverter circuit and power supply circuit in the embodiment. The function block diagram of the control apparatus in the embodiment. The block diagram which shows the calculation method of the output voltage of the load leveling system in the embodiment. The block diagram which shows the calculation method of the output voltage of the load leveling system in the embodiment. The figure which shows the change of an output voltage when the peak value of a zero phase voltage component is changed among the output voltages of the load leveling system in the embodiment, and the change of the operation timing of a 3 level inverter circuit. The table | surface which shows the switching pattern according to the output level in the embodiment. The table | surface which shows the combination of the output level in the self-excitation reactive power compensation system which concerns on other embodiment, and the capacitor voltage condition at that time. The table | surface which shows the combination of the output level in the self-excitation reactive power compensation system which concerns on other embodiment, and the capacitor voltage condition at that time. The schematic diagram of the self-excitation type DC power transmission system which concerns on other embodiment.

Explanation of symbols

1 ... electric power converter 11 ... three-phase three-level inverter circuit 12a, 12b, 12c ... power supply circuit Vt · system voltage _{V ref} ... power system of the target voltage _{V SVG} ... self-excited third output voltage _{V HS} ... output voltage 7 ... controller _V 0 ... AC frequency of the output voltage _V 11 ... 3-phase three-level inverter circuit in the load leveling system of the reactive power compensator Harmonic voltage component SS... Self-excited reactive power compensation system C1, C2... Three-phase three-level inverter circuit DC power supply C3a, C4a, C3b, C4b, C3c, C4c. , I2a, I1b, I2b, I1c, I2c ... Single-phase inverter HS ... Load leveling system

Claims (8)

A three-phase three-level inverter circuit that converts a DC voltage into a three-phase AC voltage that is pulse-width-modulated and controlled with one pulse each for positive and negative pulses per cycle of the fundamental frequency;
A power supply circuit connected in series with each phase on the output side of the three-phase three-level inverter circuit and outputting a single-phase AC voltage;
And a control device that controls the three-phase three-level inverter circuit and the respective power supply circuits to output a desired three-phase AC voltage as a sum of their output voltages.   The power supply circuit is configured by connecting a circuit in which a single-phase inverter and a DC power supply are combined to one or more sets in series on the output side of the single-phase inverter, and the single-phase inverter includes the control device. The power converter according to claim 1, wherein the pulse width modulation is controlled by the power converter.   The control device adjusts the peak value of the third harmonic in the zero-phase voltage component of the voltage output from the power converter, and sets the pulse width of the output voltage from the three-phase three-level inverter circuit. The power conversion device according to claim 1 or 2, wherein a ratio between the energy output from the three-phase three-level inverter circuit and the energy output from the power supply circuit is controlled by changing.   The said control apparatus makes the accumulated value of the output energy of the said power supply circuit zero as much as possible by changing the pulse width of the output voltage from the said 3-phase 3 level inverter circuit. Power conversion device. A self-excited reactive power compensation system that is connected to a power system and supplies reactive power to the power system to adjust the voltage of the power system and improve the power factor of the load,
A three-phase three-level inverter circuit that converts a DC voltage charged in a capacitor into a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse each for a positive and negative frequency per cycle;
Pulse width modulation control was performed on a capacitor different from the capacitor of the three-phase three-level inverter circuit and a DC voltage charged in the capacitor, connected in series to each phase on the output side of the three-phase three-level inverter circuit A power supply circuit configured by connecting two sets of circuits composed of single-phase inverters that convert and output single-phase AC voltage;
A control device that controls the three-phase three-level inverter circuit and the respective power supply circuits, and outputs a desired three-phase AC voltage as a sum of their output voltages,
The control device causes a sum of the charging energy of the capacitor of the three-phase three-level inverter circuit and the charging energy of the capacitor of the power supply circuit to be a desired value, and the capacitor of the three-phase three-level inverter circuit; The three-phase three-level inverter circuit and the power supply circuit are controlled so as to maintain a ratio of charging voltage to two capacitors of the power supply circuit in a relationship of 4: 4: 2: 1. Excited reactive power compensation system. A self-excited reactive power compensation system that is connected to a power system and supplies reactive power to the power system to adjust the voltage of the power system and improve the power factor of the load,
A three-phase three-level inverter circuit that converts a DC voltage charged in a capacitor into a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse each for a positive and negative frequency per cycle;
Pulse width modulation control is performed on a capacitor different from the capacitor of the three-phase three-level inverter circuit and a DC voltage charged in the capacitor, which are connected in series to the respective phases on the output side of the three-phase three-level inverter circuit. A power supply circuit configured by connecting two sets of circuits composed of single-phase inverters that convert and output single-phase AC voltage;
A control device that controls the three-phase three-level inverter circuit and the respective power supply circuits, and outputs a desired three-phase AC voltage as a sum of their output voltages,
The control device is configured so that the sum of the charging energy of the capacitor of the three-phase three-level inverter circuit and the charging energy of the capacitor of the power supply circuit becomes a desired value, and the capacitor of the three-phase three-level inverter circuit; The three-phase three-level inverter circuit and the power supply circuit are controlled so as to maintain a charging voltage ratio of the two capacitors of the power supply circuit to a relationship of 5: 5: 2: 1. Excited reactive power compensation system. A self-excited reactive power compensation system that is connected to a power system and supplies reactive power to the power system to adjust the voltage of the power system and improve the power factor of the load,
A three-phase three-level inverter circuit that converts a DC voltage charged in a capacitor into a three-phase AC voltage that is pulse-width-modulated and controlled with one pulse for each positive and negative frequency per cycle;
Pulse width modulation control is performed on a capacitor different from the capacitor of the three-phase three-level inverter circuit and a DC voltage charged in the capacitor, which are connected in series to the respective phases on the output side of the three-phase three-level inverter circuit. A power supply circuit configured by connecting two sets of circuits composed of single-phase inverters that convert and output single-phase AC voltage;
A control device that controls the three-phase three-level inverter circuit and the respective power supply circuits, and outputs a desired three-phase AC voltage as a sum of their output voltages,
The control device is configured so that the sum of the charging energy of the capacitor of the three-phase three-level inverter circuit and the charging energy of the capacitor of the power supply circuit becomes a desired value, and the capacitor of the three-phase three-level inverter circuit; The three-phase three-level inverter circuit and the power supply circuit are controlled so as to maintain a ratio of charging voltage between the two capacitors of the power supply circuit in a 6: 6: 2: 1 relationship. Excited reactive power compensation system. A power supply system that is connected to a power system and inputs / outputs power to / from the power system,
A three-phase three-level inverter circuit that converts a DC voltage charged in a capacitor into a three-phase AC voltage that is pulse-width-modulated and controlled by one pulse each for a positive and negative frequency per cycle;
A DC power source connected in parallel to the capacitor and outputting a DC voltage;
Pulse width modulation control is performed on a capacitor different from the capacitor of the three-phase three-level inverter circuit and a DC voltage charged in the capacitor, which are connected in series to the respective phases on the output side of the three-phase three-level inverter circuit. A power supply circuit configured by connecting two sets of circuits composed of single-phase inverters that convert and output single-phase AC voltage;
A control device that controls the three-phase three-level inverter circuit and the respective power supply circuits, and outputs a desired three-phase AC voltage as a sum of their output voltages,
The ratio of the voltage output from the DC power supply to the peak value of the rated voltage of the power system is approximately 12/7,
The control device is configured so that the sum of the charging energy of the capacitor of the three-phase three-level inverter circuit and the charging energy of the capacitor of the power supply circuit becomes a desired value, and the zero-phase voltage of the desired three-phase AC voltage Among the components, by adjusting the peak value of the third harmonic and changing the pulse width of the output voltage from the three-phase three-level inverter circuit, the energy output from the three-phase three-level inverter circuit and the A ratio of energy output from the power supply circuit is controlled, and the DC voltage output from the DC power supply, the charging voltage of the capacitor of the three-phase three-level inverter circuit, and the charging of the two capacitors of the power supply circuit The three-phase three-level inverter circuit and the power supply circuit are controlled so as to maintain a ratio with voltage of 12: 6: 6: 2: 1. The power supply system.