JP6035845B2 - AC power supply system - Google Patents

Description

  The present invention provides a circuit for equalizing the voltages of capacitors in a capacitor series circuit connected to a DC circuit of an AC power supply system in which a plurality of power converters using DC power supplies having three voltage levels are connected in parallel. And control technology.

  FIG. 6 shows a first conventional example of the three-level power conversion circuit described in Patent Document 1. A series circuit of capacitors C1 and C2 is connected between the positive electrode P and the negative electrode N of the DC power supply, and the series connection point becomes the zero pole M. A series circuit of semiconductor switches S1 and S2 in parallel with the DC power supply is connected to a bidirectional switch in which semiconductor switches S3 and S4 are connected in reverse parallel between the series connection point of the series circuit and the zero pole of the DC power supply. Then, the series connection point of the semiconductor switches S1 and S2 is connected to the AC terminal U to form a circuit for one phase (U phase). The V phase and the W phase have the same configuration. The U phase will be described as an example. When the semiconductor switch S1 is turned on, the potential of the positive electrode P is applied to the AC terminal U. When the bidirectional switch composed of the semiconductor switches S3 and S4 is turned on, the potential of the zero pole M is applied to the AC terminal U and the semiconductor switch S2 is turned on. The AC terminal U outputs a potential of the negative electrode N, and can output a three-level potential. At this time, the AC terminal U has a mode for supplying power from the capacitor C1, a mode for supplying power from the capacitor C2, and a mode for supplying power from the series circuit of the capacitors C1 and C2.

FIG. 7 shows a second conventional example of the three-level power conversion circuit described in Patent Document 2. The P terminal of the DC circuit is connected to the positive pole P of the DC power supply, the M terminal of the DC circuit is connected to the zero pole M of the DC power supply, and the N terminal of the DC circuit is connected to the negative electrode N of the DC power supply. The power supply is omitted. A series circuit of capacitors C1 and C2 is connected between the positive electrode P and the negative electrode N of the DC power supply, and the series connection point becomes the zero pole M.
In the three-level power conversion circuit, as in the first conventional example, the AC terminals U, V, and W are supplied with voltages of three levels of the positive electrode P potential, the zero pole M potential, and the negative electrode N potential in the DC circuit. Output is possible, but details are omitted. Similar to the circuit shown in FIG. 6, the AC terminal has a mode in which power is supplied from the capacitor C1, a mode in which power is supplied from the capacitor C2, and a mode in which power is supplied from a series circuit of the capacitors C1 and C2. Since the amount of discharge differs between the voltage of the capacitor C1 and the voltage of the capacitor C2 depending on the state of the load connected to the AC terminal, there is a problem that the voltage becomes unbalanced and a desired voltage cannot be output to the AC terminal. As means for solving this, there are known a method of providing a balancer circuit as shown in FIG. 7 in the main circuit and a method of using a control circuit as described in Patent Document 3 shown in FIG.

  The balancer circuit shown in FIG. 7 is a circuit for balancing the voltage of the capacitor C1 and the voltage of C2. In a configuration in which a series circuit of IGBTDB1 and DB2 is connected in parallel with a series circuit of capacitors C1 and C2, and a reactor L1 is connected between a series connection point of capacitors C1 and C2 and a series connection point of IGBTDB1 and DB2. is there. The operation in such a configuration will be described. When the voltage of the capacitor C1 is higher than the voltage of the capacitor C2, the IGBT DB1 is turned on, energy is accumulated in the reactor L1, and the capacitor C2 is charged when the IGBTDB1 is turned off. When the voltage of the capacitor C2 is higher than the voltage of the capacitor C1, the IGBT DB2 is turned on, energy is accumulated in the reactor L1, and the capacitor C1 is charged when the IGBTDB2 is turned off. By repeating such an operation, the voltages of the capacitors C1 and C2 are balanced.

  FIG. 8 shows a conventional example in which the capacitor voltage described in Patent Document 3 is balanced by a control circuit. A balance control circuit 10 is a control system that corrects the AC output voltage command (VR *, VS *, VT *) so that the voltage difference between the capacitors C1 and C2 becomes zero. The voltage EDC1 of the capacitor C1 and the voltage EDC2 of the capacitor C2 are input to the adder 11, the difference a1 is obtained, and the correction amount a2 is obtained through the regulator 12 for making this a1 zero. The correction amount and the sine wave signal obtained from the sine wave table are multiplied by a multiplier (14R, 14S, 14T) to obtain a corrected sine wave, and the corrected sine wave and voltage command (VR *, VS *, VT *). ) Are added by adders (21R, 21S, 21T) to form new voltage command signals (VR **, VS **, VT **).

JP 2011-109789 A JP 2002-199738 A Japanese Patent Laid-Open No. 7-79574

As described above, in the three-level power conversion circuit, as a method of balancing the voltage of each capacitor connected in series, a method of providing a balancer circuit in the main circuit and a method of correcting the voltage command in the control circuit (in the case of a converter) However, in a parallel system in which power supply devices are connected in parallel, the method of correcting the voltage command by the control circuit has the following problems.
In the parallel system, as shown in FIG. 9, the converter 1 and the converter 2 output the same voltage in order to share the load current equally. That is, I1 = I2 = I / 2.
Here, when the output voltages of the converter 1 and the converter 2 are different, a current (cross current) circulating between the two converters flows. As a result, the converter bears more current than the supply current to the load, and the capacity of the apparatus increases, so that it is necessary to suppress cross current as much as possible. However, in the method of correcting the voltage command by the control circuit, the correction value to the voltage command is determined from the balance state of each capacitor voltage, so the output voltage of each converter connected in parallel becomes a different value, There is a problem that occurs.
On the other hand, the method of providing a balancer circuit in the main circuit does not interfere with the parallel operation control of the converter and is a useful method in a parallel system. However, it is necessary to add a semiconductor switch and a reactor to the converter main circuit. There is a problem that the apparatus is large and expensive.

  Accordingly, an object of the present invention is to provide a compact and low-cost capacitor voltage balancing means applicable to an AC power supply system in which three-level power converters are connected in parallel.

In order to solve the above-described problems, in the first invention, an AC-DC conversion circuit that converts an AC input voltage into a DC power source having three levels of a positive electrode, a zero electrode, and a negative electrode, and a positive electrode of the DC power source The first capacitor connected between the first and second poles, the second capacitor connected between the first and second negative poles of the DC power supply, and the voltages of the first and second capacitors are equalized. AC-AC converter composed of a balancer circuit to be converted and a DC-AC converter circuit that generates an AC voltage having three levels from the DC power supply, and an alternating current in which a plurality of AC inputs and AC outputs are connected in parallel in the power supply system, and the output current of the balancer circuit when less than the predetermined value, by controlling only the balancer circuit, the output current of the balancer circuit detects that equal to or greater than a predetermined value , The AC - Enable DC voltage balance control for equalizing the first and second capacitors each voltage either of the control circuit of the AC conversion circuit - control circuit or the DC-DC converter circuit.

In the second invention, the balancer circuit in the first invention includes a semiconductor switch series circuit in which respective diodes connected between a positive electrode and a negative electrode of a DC power supply are connected in reverse parallel, and the semiconductor switch series circuit. It is comprised from the series circuit of the reactor and current detector which were connected between the series connection point and the zero pole of the said DC power supply.

In a third invention, a bidirectional three-level buck-boost chopper circuit is connected to the positive electrode, the zero electrode, and the negative electrode of each DC power supply of each of the AC-AC converters connected in parallel in any one of the first to second inventions. Connect the storage battery via

In the fourth invention, the positive electrode, the zero electrode and the negative electrode of each of the plurality of AC-AC converters connected in parallel in the first to second inventions are connected to each other, and the connection line A storage battery is connected via a bidirectional three-level buck-boost chopper circuit.

  In the present invention, the output current of the balancer circuit connected to the main circuit is detected. When this current is less than a predetermined value, the balance control of the capacitor voltage is performed only by the balancer circuit, and when the current reaches the predetermined value (upper limit value), the conversion is performed. The balance control in the control circuit of the vessel was made effective.

  As a result, the current of the balancer circuit is limited to a predetermined value or less, and the balancer circuit becomes small and inexpensive. In addition, when there is no positive / negative imbalance in the load, only the balancer circuit operates, so that the combined use period with the balance control of the control circuit can be minimized, and the occurrence of cross current during parallel operation can be minimized.

It is a first AC power supply parallel system diagram for explaining the present invention. It is a 2nd alternating current power supply parallel system figure for demonstrating this invention. It is a detailed circuit diagram of the balancer circuit of the present invention. It is a control circuit block diagram of the balancer circuit of the present invention. It is an example of the balance control circuit of this invention. It is Example 1 of a 3 level power converter circuit. They are Example 2 of a 3 level power converter circuit, and the prior art example of a balancer circuit. It is an example of the balance control circuit in a converter control circuit. It is a figure for demonstrating a parallel system.

  The main point of the present invention is to balance each capacitor voltage of a capacitor series circuit connected to a DC circuit of an AC power supply system in which AC-AC converters using a three-level conversion circuit are connected in parallel. The control circuit of the converter is provided with a balance control circuit, respectively, and the balance control circuit of the control circuit is made effective when the output current of the balancer circuit exceeds a predetermined value.

FIG. 1 shows a first AC power supply system diagram targeted by the present invention, and FIG. 2 shows a second AC power supply system diagram.
Fig. 1 is an AC power supply system diagram in which No.1 UPS (uninterruptible power supply) and No.2 UPS are connected in parallel, and a storage battery is connected to each DC circuit of the AC-AC converter circuit via a bidirectional three-level chopper. It is the structure which aimed at uninterruptible power supply. Since both have the same circuit configuration, No. 1 UPS will be described. An AC input (Ui, Vi, Wi) of the AC-AC conversion circuit is connected to a converter circuit CV having a three-level circuit configuration via an input filter Fi and a reactor Li. The DC output of the converter circuit CV includes a series circuit of capacitors C1 and C2, a balancer circuit BL for balancing the capacitor voltage, an output of a bidirectional three-level chopper CH, and a three-level circuit for converting DC to AC. The inverter circuits IN having the configuration are connected to each other. A storage battery BT is connected to the input of the bi-directional three-level chopper CH when the AC power supply fails, and an output filter Fo for waveform improvement is connected to the AC output of the inverter circuit IN. The output of the output filter Fo becomes the AC output (Uo, Vo, Wo) of the AC power supply system.

  FIG. 2 shows a configuration in which the DC circuits of the AC-AC conversion circuits (No. 1 power source and No. 2 power source in FIG. 2) described in FIG. 1 are connected in parallel. It is the structure which aimed at uninterruptible power by connecting a storage battery via a chopper. In both systems shown in FIGS. 1 and 2, the principle of the present invention for balancing capacitor voltages is the same.

  FIG. 3 shows details of the balancer circuit BL. In the balancer circuit BL, an IGBT series circuit in which IGBTs 5 and S6 in which diodes are connected in reverse parallel are connected in series between the positive electrode P and the negative electrode N of the DC circuit, and the series connection point of the IGBT series circuit and the DC circuit are connected. A series circuit of a reactor L1 and a current detector CT is connected between the zero pole M and the zero pole M. Further, the voltage detector VD1 is connected to the capacitor C1, and the voltage detector VD2 is connected to the capacitor C2. The detection value iBAL at the current detector CT, the detection value EDC1 at the voltage detector VD1, and the detection value EDC2 at the voltage detector VD2 are respectively input to the control circuit of the balancer circuit BL shown in FIG.

FIG. 4 is a control circuit block diagram of the balancer circuit BL. The difference between the detection voltage EDC1 of the capacitor C1 and the detection voltage EDC2 of the capacitor C2 is obtained by the adder AD1, averaged by the moving average circuit AV, and then input to the voltage regulator AVR. The output of the voltage regulator AVR is the balancer. It becomes the output current command value of the circuit BL. This command value and the output current detection value iBAL of the balancer circuit BL are input to the adder AD2, and controlled by the current adjuster ACR so that the difference between them becomes zero, and the modulation factor λ is controlled by the PWM (pulse width modulation) control circuit. It is sent to a PWM (pulse width modulation) control circuit through a λ conversion circuit that converts it into an input quantity. The PWM control circuit generates on / off signals for the IGBTs 5 and S6 of the balancer circuit BL.
The output current command value of the balancer circuit BL, which is the output of the voltage regulator AVR, is limited by the limiter circuit LM so that a current exceeding a predetermined value does not flow through components such as the IGBT and the reactor. Here, it is detected that the current command value to the balancer circuit BL has reached the limiter value, and a balance control start command is output to the control circuit of the conversion circuit.

  FIG. 5 shows an example of a balance control circuit in the conversion circuit of the present invention. This is an embodiment in the voltage control circuit of the inverter circuit IN. In this control method, the AC output voltage command (VR *, VS *, VT *) is corrected so that the voltage difference between the capacitors C1 and C2 becomes zero. The voltage EDC1 of the capacitor C1 and the voltage EDC2 of the capacitor C2 are input to the adder 11, the difference a1 is obtained, and the correction amount a2 is obtained through the regulator 12 for making a1 zero. A changeover switch SW is connected to the output of the regulator 12, and when a balance control start command is input from the balancer control circuit, the correction amount S2 and a sine wave signal obtained from the sine wave table are multiplied by a multiplier ( 14R, 14S, 14T) to obtain a corrected sine wave, and this corrected sine wave and the voltage command (VR *, VS *, VT *) are added by an adder (21R, 21S, 21T) Voltage command signals (VR **, VS **, VT **).

  When the balance control start command from the balancer control circuit is not input, the changeover switch SW is on the 0V side, one input of the multiplier (14R, 14S, 14T) is set to 0, and the voltage command (VR *, VS *, The correction amount for (VT *) is set to zero. Accordingly, balance control is performed only when a balance control start command is input from the balancer control circuit.

  In this embodiment, the balance control is performed by the inverter control circuit. However, the converter control circuit can perform the same control. The converter circuit can be realized by correcting either the voltage command or the command value of the AC input current.

  The present invention relates to a capacitor voltage balance control in a power supply system using three-level power converters connected in parallel, and can be applied to an uninterruptible power supply (UPS), a grid interconnection device, and the like. .

S1 to S6, DB1, DB2 ... IGBT C1, C2 ... Capacitor L1, Li ... Reactor CT ... Current detector VD1, VD2 ... Voltage detector Fi, Fo ... Filter BL .. Balancer circuit IN ... Inverter circuit CV ... Converter circuit CH ... Chopper BT ... Storage battery 10 ... Balance control circuit ACR ... Current regulator 11, 21R, 21S, 21T, AD1, AD2 ... adder 12, AVR ... voltage regulator 13 ... Sin table 14R, 14S, 14T ... multiplier LM ... limiter circuit SW ... changeover switch

Claims (4)

An AC-DC conversion circuit for converting an AC input voltage into a DC power supply having three levels of a positive electrode, a zero electrode, and a negative electrode; a first capacitor connected between the positive electrode and the zero electrode of the DC power supply; A second capacitor connected between the zero pole and the negative electrode of the DC power supply, a balancer circuit for equalizing the voltages of the first and second capacitors, and three levels from the DC power supply. In an AC power supply system in which a plurality of AC inputs and AC outputs of an AC-AC converter configured with a DC-AC converter circuit that generates an AC voltage are connected in parallel,
When the output current of the balancer circuit is less than a predetermined value, it is controlled only by the balancer circuit, and when it is detected that the output current of the balancer circuit has exceeded a predetermined value, the AC-DC conversion circuit An AC power supply system, wherein a DC voltage balance control for equalizing the voltages of the first and second capacitors is made effective by either a control circuit or a control circuit of the DC-AC conversion circuit. The balancer circuit includes a semiconductor switch series circuit in which respective diodes connected between a positive electrode and a negative electrode of a DC power supply are connected in reverse parallel, a series connection point of the semiconductor switch series circuit, and a zero pole of the DC power supply. The AC power supply system according to claim 1, comprising a series circuit of a reactor and a current detector connected between each other . The storage battery is connected to a positive electrode, a zero electrode, and a negative electrode of each DC power source of each of the AC-AC converters connected in parallel via a bidirectional three-level buck-boost chopper circuit . The AC power supply system according to any one of the above. The positive, zero, and negative electrodes of each of the plurality of AC-AC converters connected in parallel are connected to each other, and a storage battery is connected to the connection line via a bidirectional three-level buck-boost chopper circuit. The AC power supply system according to claim 1 , wherein the AC power supply system is a power supply system.

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