JPH10234185A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device which is free from unbalanced input voltage, capable of maintaining high power conversion efficiency using relatively simple circuitry. SOLUTION: A power conversion device contains two parallel-connected half bridge inverters 3A, 3B, and turns on/off switching elements, using the voltage of a series capacitor as an input voltage. A direct-current power supply 1, such as a solar cell, is connected with both the ends of a capacitor 6. Two switch arms are connected vertically with each other in series to form a series switching circuit 38. The circuit 38 is parallel-connected with the series circuit of the capacitor 6 and a capacitor 15, and a reactor 10 is connected between the point of interconnection between the upper and lower arms of the circuit 38, and the point of interconnection between the capacitors 6, 15 to form a direct-current voltage-dividing circuit 2. Switching elements 4, 13 in the series switching circuit 38 are on/off-controlled, so that the voltage of the capacitor 15 not connected with the direct-current power supply 1 be equal to the voltage of the capacitor 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-phase three-wire output type power converter for converting DC power generated by a DC power supply such as a solar cell or a fuel cell into AC power.

[0002]

2. Description of the Related Art FIGS. 16 and 17 show a prior art of a single-phase three-wire output type power converter that uses a solar cell as a power source, converts its DC power into AC power, and connects it to a system power source. In FIG. 16, the voltage across the series circuit of solar cells 1a and 1b is applied to the series circuit of capacitors 6 and 15 via diodes 37a and 37b, and a semiconductor switch element 31 such as an IGBT and a diode 32 connected in anti-parallel are connected.
The PWM control is performed by the half-bridge inverters 3A and 3B composed of This AC voltage is filtered by a filter including reactors 7a and 7b and capacitors 8a and 8b to remove high-frequency components by PWM control, and is connected to a single-phase three-wire system power supply 9.

On the other hand, in FIG. 17, a DC voltage of the solar cell 1 is boosted by a boosting circuit including a reactor 33, a semiconductor switch element 34 and a diode 35 via a diode 37, and applied to a series circuit of capacitors 6 and 15. After being PWM-controlled by the half-bridge inverters 3A and 3B and converted into an AC voltage as in FIG. 16, the reactors 7a and 7b and the capacitor 8
The high-frequency components are removed by the filters composed of a and 8b, and are connected to the single-phase three-wire system power supply 9. These figures 1
6, the prior art shown in FIG. 17 is a voltage-type power converter, so that the AC output side can be separated from the system power supply 9 to operate independently as an AC voltage source.

Next, another conventional technique will be described. FIG.
1 shows an overall configuration of a photovoltaic power generation inverter that uses a solar cell as a power source, converts its DC power into AC power, and connects it to a system power supply. In general, photovoltaic inverter for system interconnection solar in order to effectively use the solar cell 1, by varying and adjust the output power P of the inverter INV at a constant period, the DC voltage E _d as shown in FIG. 19 cell 1 controls the voltage E _t for generating the maximum power P _max, it is performed a so-called maximum power follow-up control. FIG. 20 shows a conventional technique in which a storage battery 101 is connected to the DC side of the inverter INV for performing a peak cut operation or the like. Is this case, since the predetermined range of charge and discharge voltage of the storage battery 101, the inverter INV is controlled to a voltage value determined by the battery 101 to the DC voltage E _d by the DC voltage constant control,
Or to take the matching of the charging voltage of the DC voltage E _t and the storage battery 101 which is determined by the maximum power follow-up control shown in FIG. 19, a DC - it is separately installed DC converter 102.

Next, another conventional technique will be described. FIG.
Reference numeral 1 denotes an example which has substantially the same configuration as that of the conventional technique shown in FIG. 17 and does not include the DC voltage balance circuit 36. Since the neutral point of the single-phase three-wire power system is grounded, the configuration shown in FIG.
Is also grounded. However, a DC circuit side because it is connected across the series capacitor 6 and 15, to ground potential at the point V _n of the connection point between the semiconductor switch element 34 and the diode 35, the positive and negative by the switching frequency of the semiconductor switching element 34 fluctuate.

[0006]

In the prior art shown in FIG. 16, the connection is complicated because the solar cells 1a and 1b are connected in series. Also, due to errors in the power generated by each of the solar cells 1a and 1b, power supply to an asymmetric load during self-sustained operation, and the like, imbalance in the input voltage (the voltage of the capacitors 6 and 15) occurs, causing distortion in the output voltage and DC components May cause spills into the system. Furthermore, since the two solar cells 1a and 1b are connected in series, the semiconductor switch element 31 used in the power converter is considered in consideration of the operating range of the solar cells.
Requires a high breakdown voltage, which leads to a decrease in power conversion efficiency due to an increase in switching loss.

In the prior art shown in FIG. 17, since the number of power conversion stages is increased by one by the booster circuit including the semiconductor switch element 34 and the diode 35, a reduction in conversion efficiency is inevitable. Furthermore, a DC voltage balance circuit 36 for balancing the voltages of the capacitors 6 and 15 connected in series is newly required, and there is a problem that the circuit configuration becomes complicated.

[0008] Therefore, the invention according to claims 1 to 3 is
An object of the present invention is to provide a power conversion device that has a relatively simple circuit configuration, has no imbalance in input voltage, and can maintain high power conversion efficiency. In addition, the invention according to claim 4 aims to provide a power conversion device that prevents a decrease in power conversion efficiency due to an increase in switching loss.

On the other hand, since the photovoltaic inverter of Figure 20 described above, when controlling the DC voltage E _d of the inverter INV into a voltage value determined by the battery 101, which can not be taken out the maximum power of the solar cell 1, System efficiency is reduced. Further, if the DC-DC converter 102 is separately installed, the number of conversion stages increases, which causes a problem that the system becomes complicated, large, and expensive.

Therefore, the invention according to claim 5 prevents a decrease in system efficiency by simultaneously performing the maximum power tracking control and the charge / discharge control of the storage battery with one inverter.
An object of the present invention is to provide a power conversion device that prevents the system from becoming complicated and large.

Further, in the prior art of FIG. 21, to ground potential at the point V _n of the connection point between the semiconductor switch element 34 and the diode 35 as described above, is swung between positive and negative by the switching frequency of the semiconductor switching element 34. For this reason, a potential change occurs in the DC input terminal due to a ratio of a reactor component of the connection line between the reactor of the booster circuit (boost chopper) and the solar cell 1, and the change (dV / dt) is caused by noise generation / noise. This causes an increase in terminal voltage. To cope with this, it is necessary to add a noise filter on the DC side or to enhance the filter function, which has led to an increase in the complexity, size, and price of the device.

[0012] Thus the invention described in claim 6, prevent and suppress variations in the the isolation point potential V _n, system complexity of the system due to such as adding noise filter DC side, the size, etc. It is an object of the present invention to provide a power conversion device capable of performing the above.

Further, according to the present invention, when a load is connected to the AC output terminal of the half-bridge inverter, as described later, the control delay of the DC voltage dividing circuit and the residual energy of the reactor during a sudden load change are reduced. As a result, the voltage of the capacitor to which the DC power supply is not connected becomes excessively large, which necessitates an increase in the capacity of the capacitor and the use of a semiconductor switch element having a high withstand voltage. And to avoid the inconvenience of forcibly stopping the operation of the power converter when an overvoltage of the capacitor is detected.

[0014]

According to a first aspect of the present invention, there is provided a half-bridge inverter in which two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode are vertically connected in series. A single-phase three-wire circuit that outputs two single-phase AC voltages by turning on and off the semiconductor switch element using the voltages of two capacitors connected in parallel and connected in series as the input voltage of the half-bridge inverter. In an output-type power converter, a DC power supply is connected to both ends of one of the capacitors, and two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically to form a series switch circuit. And connecting this series switch circuit in parallel with the series circuit of the two capacitors, and A reactor is connected between an interconnection point of the upper and lower switch arms of the column switch circuit and an interconnection point of the two capacitors to form a DC voltage dividing circuit, and a DC power supply of the two capacitors is connected. A control means is provided for controlling the on / off of the semiconductor switch element of the series switch circuit so that the voltage of the capacitor that has not been made becomes equal to the voltage of the other capacitor.

According to a second aspect of the present invention, a DC voltage dividing circuit is formed in the same manner as described above, and the voltage of a capacitor to which a DC power supply is not connected among two capacitors connected in series is a constant value. A control means for controlling on / off of the semiconductor switch element of the series switch circuit is provided.

According to a third aspect of the present invention, when the voltages of the two capacitors become unequal by operating the control means of the second aspect, the voltage detection values V1 and V2 of these capacitors and the half bridge The firing time T _on of the upper arm of the inverter and the firing time T _off of the lower arm (=
T−T _on ) and carrier cycle T, λ = 1− (V 1−V _out ) / E ₀ (where V _out (: output voltage reference command value) = (V 1 × T _on / T)
− (V2 × T _off / T) A control means for controlling ON / OFF of the semiconductor switch element of the half-bridge inverter based on the output voltage command value λ obtained by the equation:

According to a fourth aspect of the present invention, two half-bridge inverters in which two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode are connected in series up and down are connected in parallel. A power supply device of a single-phase three-wire output type that outputs two single-phase AC voltages by turning on and off the semiconductor switch element using the voltage of the capacitor as an input voltage of the half-bridge inverter. A DC power supply is connected to both ends of the capacitor, and two switch arms, each composed of an anti-parallel circuit of a semiconductor switch element and a diode, are vertically connected in series to form a series switch circuit. Connected in parallel with the series circuit of capacitors, and the upper and lower switch arms of the series switch circuit. A reactor is connected between the interconnection point and the interconnection point of the two capacitors to form a DC voltage dividing circuit, and based on a voltage detection value of one of the two capacitors, the other capacitor is connected. A voltage command value is generated, and the on / off of the semiconductor switch element of the series switch circuit is controlled so that the voltage of the other capacitor matches the voltage command value, so that the total value of the voltages of the two capacitors is obtained. And a control means for suppressing the pressure of the semiconductor switch element of the half-bridge inverter to be equal to or less than the withstand voltage of the semiconductor switch element.

According to a fifth aspect of the present invention, two half-bridge inverters in which two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically are connected in parallel, and two half-bridge inverters are connected in series. A power supply device of a single-phase three-wire output type that outputs two single-phase AC voltages by turning on and off the semiconductor switch element using the voltage of the capacitor as an input voltage of the half-bridge inverter. A DC power supply is connected to both ends of the capacitor, and two switch arms, each composed of an anti-parallel circuit of a semiconductor switch element and a diode, are vertically connected in series to form a series switch circuit. Connected in parallel with the series circuit of capacitors, and the upper and lower switch arms of the series switch circuit. A reactor is connected between an interconnection point and an interconnection point of the two capacitors to form a DC voltage dividing circuit, and a DC cutoff is applied to both ends of the two capacitors to which a DC power supply is not connected. By connecting a series circuit of a battery and a storage battery, and controlling ON / OFF of the semiconductor switch element of the half-bridge inverter so that the voltage of the capacitor connected to the DC power supply matches the voltage command value. It controls the maximum power follow-up of the power supply, and controls the on / off of the semiconductor switch element of the series switch circuit so that the voltage of the capacitor to which the DC power supply is not connected matches the voltage command value. And control means for controlling charging and discharging of the storage battery by controlling opening and closing of the container.

According to a sixth aspect of the present invention, two half-bridge inverters in which two switch arms each comprising an antiparallel circuit of a semiconductor switch element and a diode are vertically connected in series are connected in parallel. A power supply device of a single-phase three-wire output type that outputs two single-phase AC voltages by turning on and off the semiconductor switch element using the voltage of the capacitor as an input voltage of the half-bridge inverter. A DC power supply is connected to both ends of the capacitor, a semiconductor switch element and a diode are connected in series to form a series switch circuit, and an interconnection point between the semiconductor switch element and the diode constituting the series switch circuit and the two Connect a reactor between the capacitor's interconnection point to form a DC voltage divider circuit. The interconnection point of the two capacitors is connected to the neutral line of the system power supply, and the series connection is performed such that the voltage of the capacitor to which the DC power supply is not connected is equal to the voltage of the other capacitor. The switch circuit includes a control unit for controlling on / off of the semiconductor switch element.

According to a seventh aspect of the present invention, two half-bridge inverters in which two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically are connected in parallel. A power supply device of a single-phase three-wire output type that outputs two single-phase AC voltages by turning on and off the semiconductor switch element using the voltage of the capacitor as an input voltage of the half-bridge inverter. A DC power supply is connected to both ends of the capacitor, a semiconductor switch element and a diode are connected in series to form a series switch circuit, and an interconnection point between the semiconductor switch element and the diode constituting the series switch circuit and the two Connect a reactor between the capacitor's interconnection point to form a DC voltage divider circuit. The interconnection point of the two capacitors is connected to the neutral point of the AC load, and the suppression voltage level and the recovery voltage level are set with respect to the total voltage value of the two capacitors, so that the total voltage value increases. And a control means for stopping the operation of the DC voltage dividing circuit when the suppression voltage level is reached, and restarting the DC voltage dividing circuit when the voltage level decreases and reaches the restoration voltage level.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a circuit diagram showing a first embodiment of the invention described in claim 1, and the same components as those in FIGS. 16 and 17 are denoted by the same reference numerals. In FIG. 1A, reference numeral 2 denotes a DC voltage dividing circuit. In this embodiment, the DC voltage dividing circuit 2, a DC power supply such as a solar cell 1 or a fuel cell, half-bridge inverters 3A and 3B, and two And an output filter. Here, the DC voltage dividing circuit 2
Operates so that the DC voltage of the solar cell 1 is converted into electric power and the voltages of the two capacitors 6 and 15 connected in series become equal.

Hereinafter, the configuration of the DC voltage dividing circuit 2 will be described. In FIG. 1A, the solar cell 1 is connected to both ends of one capacitor 6 via a diode 37. A switch arm including a semiconductor switch element 4 such as an IGBT and a diode 5 connected in anti-parallel;
Similarly, two switch arms each including a switch element 13 and a diode 14 connected in anti-parallel are connected in series to form a series switch circuit 38, and both ends thereof are connected to the positive electrode of the capacitor 6 and the negative electrode of the capacitor 15. Furthermore,
The DC voltage dividing circuit 2 is configured by connecting the reactor 10 between the interconnection point of the two switch arms and the interconnection point of the capacitors 6 and 15.

The operation of this embodiment will be described. Since the voltage of the capacitor 6 to which the solar cell 1 is connected (V1) is clamped to the voltage of the solar cell 1, the capacitor 15 to which the solar cell 1 is not connected is connected. Voltage (V2)
Control the DC voltage dividing circuit 2 so that the voltage becomes equal to the voltage V1. As a specific method of this control, the voltage of each of the capacitors 6 and 15 is detected, and the ignition period for the switch elements 4 and 13 of each arm of the series switch circuit 38 is controlled so that the deviation between V1 and V2 becomes zero. I do.

FIG. 2 shows the operation of the DC voltage dividing circuit 2. FIG.
5 when energy is supplied to the switching element 4
Is stored in the reactor 10 through the route of the switch element 4 → reactor 10 → condenser 6 indicated by a solid line, and this energy is dissipated by the extinction of the switch element 4 along the route of the broken line.
To supply.

On the other hand, FIG. 2B shows a case in which energy is supplied from the capacitor 15 to the capacitor 6. By igniting the switch element 13, the reactor is switched along the route of the switch element 13 → capacitor 15 → reactor 10 shown by a solid line. The energy is stored in the capacitor 10 and is supplied to the other capacitor 6 by the dashed route by the extinction of the switch element 13. Therefore, the voltages V1 and V2 can be controlled by controlling the firing period of each of the switch elements 4 and 13 according to the capacitor voltage.

FIG. 3 is a control block diagram for performing the above control. In the figure, reference numerals 16 and 17 denote switches for inputting voltages V1 (detected values) and V2 (command values) of capacitors 6 and 15, respectively, and reference numeral 20 denotes these switches 1
An adder to which the output signals 6, 17 and the voltage V2 (detected value) of the capacitor 15 are input with the reference numerals shown in the figure, and 22 is an adder 2
An adjuster 24 performs an adjustment operation so that the output of 0 becomes zero. A comparator (PWM signal generation circuit) 24 compares a voltage command value output from the adjuster 22 with an output signal (carrier) of the carrier generation circuit 23. Yes, this comparator 24
Is an ignition signal for the switch elements 4 and 13.

FIG. 4 shows a firing pattern of the DC voltage dividing circuit 2. When the changeover switch 16 in FIG. 3 is turned on, if V1> V2, the on duty of the switch element 4 becomes 50% or more, and if V1 <V2, 50%.
It is as follows.

The capacitor voltages V1 and V2 controlled by the above method serve as power supplies for the half-bridge inverters 3A and 3B at the subsequent stage in FIG. Note that the half-bridge inverters 3A and 3B are connected to the IGB
A capacitor 32 is composed of a semiconductor switch element 31 such as T and a diode 32 connected in anti-parallel. After the capacitor voltages V1 and V2 are converted into an AC voltage by the PWM control, the capacitors 7a and 7b and the capacitors 8a and 8b The high frequency component by the PWM control is removed by the filter, and is connected to the single-phase three-wire system power supply 9. Here, a self-sustaining operation in which the output of the filter is directly connected to the AC load without being connected to the system power supply 9 may be performed.

FIG. 1B shows a second embodiment of the invention according to claim 1, except that the solar cell 1 is connected to the other capacitor 15 via a diode 37.
The configuration is the same as the first embodiment. In this embodiment, control is performed so that the voltage V1 of the capacitor 6 to which the solar cell 1 is not connected is equal to the voltage V2 of 15 of the other capacitor. Since a specific control method in the DC voltage dividing circuit 2 is the same as that in the first embodiment, the description is omitted here.

Next, an embodiment of the present invention will be described. In the embodiment of the present invention, the voltage of the capacitor to which the solar cell 1 is not connected (V2 in FIG. 1A and V1 in FIG. 1B) is equal to the voltage of the other capacitor (FIG. The control is performed so as to be equal to V1 in a) and V2) in FIG. That is, FIG.
In FIG. 3, the DC voltage command value is V1 as shown in FIG.
In (b), the voltage command value is V2.

In the embodiment of the present invention, the DC voltage command value is set to a constant value, and in FIG.
In (b), V1 is controlled to be kept constant at all times. Here, for example, when _VS is required as the output voltage of the power converter, a DC voltage of at least √2 times is required. For example, if the output is 100 V (effective value), 1
A voltage of 41 V is required as a DC voltage. Therefore, in the case of FIG. 1A, the voltage command value of V2 is 141V.
Actually, it is generally set to about 170 V in consideration of output fluctuation, control margin of the converter, and the like.

As described above, when the voltage of the capacitor to which the solar cell 1 is not connected is controlled to the minimum value determined by the output AC voltage required for the power converter, the power converter (half-bridge inverters 3A and 3B) As long as the maximum voltage _Emax + V2 (or V1) of the solar cell 1 can be tolerated as the breakdown voltage of the semiconductor switch element used for the above, compared with the case where two solar cells are connected in series as shown in FIG.
It is possible to use a switch element having a low withstand voltage. In order to perform such control, turns on the switch 17 shown in FIG. 3, may be controlled direct current voltage divider circuit a voltage command value V2 ^* as E _max. It may be controlled so that the deviation between V1 (detected value) of the voltage command value V1 ^* as E _max becomes zero in the example of FIG. 1 (b).

Next, an embodiment of the present invention will be described. For example, when the capacitor voltage V2 is controlled to be constant by the invention of claim 2, the capacitor voltage V
1 and V2 are not equal. The invention of claim 3 proposes an output voltage correction control method for making the output voltage waveform of the half-bridge inverter positive and negative symmetric when the respective input voltages of the half-bridge inverter are not equal.

First, the relationship between the output voltage reference command value _Vout and the capacitor voltages V1 and V2 is expressed by the following equation (1). In Equation 1, T _{on is the} firing time of the upper arm of the half-bridge inverter, T _{off is the} firing time of the lower arm, and T is the carrier cycle.

[0035]

V _out = (V1 × T _on / T) − (V2 × T _off / T)

Now, assuming that T _on / T = k 1 and T _off = k 2, Equations 2 to 4 are obtained. Note that λ in Equation 3 is an output voltage command value.

[0037]

## EQU2 ## k1 × V1−k2 × V2 = V _out

[0038]

Λ = k1-k2

[0039]

## EQU4 ## k1 + k2 = 1

When these equations 2 to 4 are expanded, equation 5 is obtained.

[0041]

Λ = 1− (V1−V _out ) / E ₀ where E ₀
= (V1 + V2) / 2

The output voltage correction control when the input voltages (V1, V2) are unbalanced is calculated according to the above equation (5).
2. It can be realized by calculating λ from _Vout , comparing this λ with the carrier, and generating a firing signal for the upper and lower arms of the half-bridge inverter. FIG. 5 is a control block diagram for realizing this. In order to realize Equation 5, adders 20a, 20b, and 20c, a multiplier 25, a divider 26, a carrier generation circuit 27, and a comparator 28
It consists of.

Next, an embodiment of the invention described in claim 4 will be described. In the embodiment of FIG. 1, as described above, control is performed such that the voltage of the capacitor to which the solar cell 1 is not connected is equal to the voltage of the other capacitor. When performing such control, the half-bridge inverter 3A, the semiconductor switching element used to 3B, it is necessary to have a breakdown voltage of more than 2 times the maximum voltage V _max of V1 or V2. In general, the loss of a semiconductor switch element is larger as the withstand voltage of the element is higher. Therefore, when a DC power supply such as a solar cell 1 or a fuel cell is used as a DC power supply, the loss of the semiconductor switch element is smaller than that of another converter having the same capacity. It becomes bigger.

For this reason, in the present embodiment, for example, the solar cell 1 is connected to the capacitor 6 and the solar cell 1 is connected to the capacitor 15 in order to reduce the applied voltage of the semiconductor switch element and reduce the generation loss. If not, the voltage command value V2 ^* of the capacitor 15 which is not connected is set as in Expression 6.

[0045]

[6] V2 ^* = E _max -V1

It should be noted that in Equation 6, E_maxIs a semiconductor
The withstand voltage of the switch element, V1 is the voltage of the capacitor 6.
Here, the minimum value of V2 is determined by the output required for the power converter.
Assuming that the voltage is determined by the AC voltage value,
Switches used in the bridge inverters 3A and 3B).
The withstand voltage of the switch element is the maximum voltage of the solar cell 1 (semiconductor switch
Element breakdown voltage) E _maxIt is good if the minimum voltage of + V2 is allowed
In the case where the control of V1 = V2 is performed as in the embodiment of FIG.
Switch elements with lower breakdown voltage can be used
become.

FIG. 6 shows the configuration of this embodiment. Now, the operation will be described by taking a case where the solar cell 1 is connected to the capacitor 6 and the solar cell 1 is not connected to the capacitor 15 as an example. First, to detect the voltage (the voltage of the solar cell 1) V1 of the capacitor 6, is compared with a set value E ₀ by the comparator 41 in FIG. 6. Here, the set value E ₀ is determined as follows. Maximum value V _max of V1, the minimum value of V2 when the V _min, the withstand voltage E _max of the switching element becomes as Equation 7.

[0048]

[Equation 7] E _max = V _max + V _min

[0049] V1 = because the voltage range of the control is possible V2 of V2 is up to 1/2 of the E _max, set value E ₀ as the its criteria, the equation 8.

[0050]

E ₀ = E _max / 2

According to the magnitude relationship between the set value E ₀ thus determined and the detected value of V ₁ , the voltage command value V 2 ^* is expressed by the following equation (9).

[0052]

[Equation 9] ^{_{E 0> V1 → V2 * =}} V1 E 0 ≦ V1 → V2 * = E max -V1

That is, in the configuration of FIG. 6, E ₀ > V1
In this case, the output signal of the comparator 41 becomes “H” level, and V1 is output through the analog switch 42 in the ON state.
Is directly input to the adder 45 as the command value V2 ^* . When E ₀ ≦ V1, the comparator 41
Becomes "L" level and the analog switch 4
The output side of the switch 4 becomes "H" level and the switch 44 is turned on. Thereby, E output from the adder 43 is output.
The value of _max- V1 is input to the next-stage adder 45 as the command value V2 ^* . In the adder 45, the command value V2 ^* and the detection value V2
Is obtained, and this difference is input to the controller 46. Then, the output signal and the carrier from the carrier generation circuit 47 are compared with a comparator (PWM signal generation circuit) 4.
8, and a firing signal for the switching elements 4 and 13 of the series switching circuit 38 is output.

[0054] In this embodiment, it is set in accordance with the magnitude relationship between the detected value of the voltage command value V2 ^* set value E ₀ of the capacitor 15 towards the solar cell 1 is not connected to V1. For this reason, the withstand voltage of the semiconductor switch elements constituting the half-bridge inverters 3A and 3B is
It is only necessary to allow the maximum voltage E _max + V2, and it is possible to use an element having a low withstand voltage and a small switching loss. In the above embodiment, the case where the voltage command value V2 ^* of the capacitor 15 to which the solar cell 1 is not connected has been described, but the solar cell 1 is not connected to the other capacitor 6, and The present invention is also applicable when setting the voltage command value V1 ^* .

Next, an embodiment of the invention described in claim 5 will be described. FIG. 7 shows a main circuit of this embodiment, and the same components as those in FIG. 1A are denoted by the same reference numerals. 7, 49 is the output current i _d of the solar cell 1
, 50 is a DC circuit breaker, and 51 is a storage battery. The series circuit of the DC breaker 50 and the storage battery 51 is connected in parallel to the capacitor 15 to which the solar cell 1 is not connected. The DC circuit breaker 50 is cut off by a circuit breaker control signal S1 as described later in order to disconnect the main circuit of the power converter from the storage battery 51 when the storage battery 51 is fully charged and overdischarged. is there.

FIG. 8 is a control block diagram for performing maximum power tracking control in this embodiment. First, in this embodiment the solar cell 1 because it is connected to the capacitor 6, to detect an output current i _d of the voltage V1 and the solar cell 1 of the capacitor 6. Then, the voltage command generation circuit 52
Detects the current output power of the solar cell 1, compares this power with the previous output power, and generates the next voltage command value V1 ^* of the capacitor 6. The voltage command value is determined from the characteristics of the solar cell 1. For example, if the output power increases as a result of increasing the current power command value from the previous power command value, it is apparent from the characteristics of the solar cell shown in FIG. Since it is in the operation region a, the next voltage command value is made larger than the current voltage command value. If the output power decreases, the next voltage command value is set smaller than the current voltage command value because the output power is in the region b in FIG.

The voltage command value V1 thus generated
^{The difference} between ^* and the detected value V1 is determined by the adder 53, and this difference is input to the controller 54 to be the output current command value i ^{* of the} half-bridge inverters 3A and 3B. A deviation between the output current command value i ^* and the detection value i is obtained by an adder 55, and this deviation is input to a controller 56, and the output and the carrier from the carrier generation circuit 57 are compared by a comparator (PW
M signal generating circuit) 58 to obtain a firing signal for the switch element 31 of the half-bridge inverters 3A and 3B. Thus, the maximum power follow-up control is performed by controlling the voltage V1 of the capacitor 6 to which the solar cell 1 is connected.

FIG. 9 is a control block diagram for controlling the charging and discharging of the storage battery 51. First, the charge / discharge command generation circuit 59 calculates an applied voltage command value of the storage battery 51 from the state of the storage battery 51 and the power generation operation state of the solar cell 1. This applied voltage command value is set as the voltage command value V2 ^* of the capacitor 15 to which the solar cell 1 is not connected, a deviation from the detected value V2 is obtained by the adder 60, and the deviation is determined by the controller 54.
To enter. Then, the output of the adjuster 54 and the carrier are input to the comparator 58, and a firing signal for the switch elements 4 and 13 is obtained. By controlling the voltage V2 of the capacitor 15 to which the solar cell 1 is not connected in this way, the charge / discharge control of the storage battery 51 is performed. The storage battery 51
Is in a fully charged state or an overcharged state, or in accordance with the operating state of the system, the charge / discharge command generation circuit 59 outputs a breaker control signal S1 to open the DC breaker 50 connected in series to the storage battery 51. Thus, voltage control and protection of the storage battery 51 and the capacitor 15 are performed.

According to this embodiment, the charge / discharge control of the storage battery 51 can be performed while performing the maximum power tracking control of the solar cell 1 without using the DC-DC converter 102 as shown in FIG. . Although not shown, the present invention is also applicable to a case where the solar cell 1 is connected to the capacitor 15 and a series circuit of the DC breaker 50 and the storage battery 51 is connected to both ends of the capacitor 6. In that case, a voltage command value V2 ^* of the capacitor 15 is generated, and each switch element 3 is set so that V2 matches this command value V2 ^*.
1 to control the maximum power follow-up control, generate a voltage command value V1 ^* of the capacitor 6, and set each switch element 4 so that V1 matches the command value V1 ^* .
The charge / discharge control of the storage battery 51 is performed by controlling the ON / OFF of the power supply 13 and the opening / closing of the DC breaker 50.

Next, an embodiment of the invention described in claim 6 will be described. FIG. 10A is a circuit diagram showing a first embodiment of the present invention, and FIG. 10B is a circuit diagram showing a second embodiment, in which the same components as those in FIGS. 1A and 1B are used. Are denoted by the same reference numerals. FIG. 10A shows a case where the solar cell 1 is connected to the capacitor 6. The circuit configuration differs from FIG. 1A in the configuration and the diagram of the series switch circuit 381 in the DC voltage dividing circuit 201. 1 (a) is that the diode 37 does not exist. That is, the series switch circuit 381 is configured by connecting the semiconductor switch element 4 and the diode 14 in series. Similarly, FIG.
FIG. 1B shows a case where the solar cell 1 is connected to the capacitor 15. The circuit configuration differs from FIG. 1B in the configuration of the series switch circuit 382 in the DC voltage dividing circuit 202 and FIG. The point is that the diode 37 in b) does not exist. That is, the series switch circuit 382 is configured by connecting the semiconductor switch element 13 and the diode 5 in series.

Next, since the operations of FIGS. 10A and 10B are similar to each other, the operation of the first embodiment of FIG. 10A will be described. In the DC voltage dividing circuit 201, the voltage V1 of the capacitor 6 to which the solar cell 1 is connected is clamped to the voltage of the solar cell 1, so that the voltage V2 of the capacitor 15 to which the solar cell 1 is not connected becomes equal to V1. Control. The control is performed for each capacitor 6,
The ignition period of the switch element 4 of the series switch circuit 381 is controlled so that the voltage of No. 15 is detected and the deviation between V1 and V2 becomes zero.

FIG. 11A shows a DC voltage dividing circuit 20 for supplying energy from the solar cell 1 to the capacitor 15.
1 shows the operation of FIG. By igniting the switch element 4, energy is accumulated in the reactor 10 along the route of the solar cell 1 → the switch element 4 → the reactor 10 shown by the solid line, and this energy is transferred to the capacitor by the arc of the switch element 4 along the broken line. 15

FIG. 11 (b) shows the operation of the DC voltage dividing circuit 202 in the second embodiment of FIG. 10 (b), and shows the operation when energy is supplied from the solar cell 1 to the capacitor 6. Yes, by igniting the switch element 13, energy is accumulated in the reactor 10 along the route of the solar cell 1 → reactor 10 → switch element 13 shown by the solid line, and this energy is dissipated by the extinction of the switch element 13 by the dashed line. To supply to the capacitor 6.

Therefore, by controlling the firing period of the switch element 4 or 13 in accordance with the capacitor voltage, the voltages V1 and V2 can be controlled.
1 and V2 serve as DC power supplies for the half-bridge inverters 3A and 3B. Here, the control block diagram for performing the above control is the same as that of FIG. 3 described above, and the ignition signal output from the comparator 24 in FIG. 3 is applied to the switch element 4 or 13.

By the above-described operation, the voltages of the two capacitors 6 and 15 are controlled.
The voltage at the connection point between the switch element 4 and the diode 14 or the connection point between the switch element 13 and the diode 5 at 202 is positively and negatively changed as in FIG. However, the voltage between the DC input terminals in FIGS. 10A and 10B is clamped to the voltage of the solar cell 1 by the capacitors 6 and 15, and the positive or negative electrode of the solar cell 1 is connected to the neutral line (ground) of the system power supply 9. Line), the ground potential is stable without fluctuation. For this reason, generation of noise and an increase in noise terminal voltage can be suppressed.

Next, an embodiment of the invention described in claim 7 will be described. FIG. 12 is a main circuit diagram showing another embodiment of the invention described in claim 6, wherein the same components as those in FIG. 10 (a) are denoted by the same reference numerals. In the figure, 61 is a gate firing signal, 62 is a current transformer, 63
Is a circuit breaker, and 91 is an AC load. In the power converter of FIG. 12, the voltage V2 of the capacitor 15 to which the DC power supply 1 is not connected is similar to the embodiment of FIG.
Is controlled by the DC voltage dividing circuit 201 to control the voltage between the DC terminals of the half-bridge inverters 3A and 3B.
In FIG. 12, unlike FIG. 10A, two single-phase AC voltages are supplied to the AC load 91. FIG.
In the above, the current of the reactor 10 is detected by the current transformer 62, and the control of this current is used as a minor loop to control the voltage V2 of the capacitor 15.

As shown in FIG. 14, when the AC load 91 fluctuates from a heavy load to a light load at time T1, the circuit of FIG. due to the residual energy current i ₁₀ of the reactor 10 is reduced. For this reason, the energy of the hatched portion unnecessary for the load supply is accumulated in the capacitor 15, and as a result, the voltage V2 of the capacitor 15 increases. In addition, the half-bridge inverters 3A, 3B
(That is, the total voltage value V _T = V1 + V
2) also increases. The larger the load fluctuation, the more the capacitor 15
The energy (the area of the hatched portion in FIG. 14) stored in the semiconductor device increases, which may destroy the semiconductor switching element.

To prevent this, methods such as increasing the capacitance of a capacitor or using a high-voltage switch element can be considered. However, these methods directly lead to an increase in the size and cost of the power converter. As another method, it is effective to set the overvoltage level of the capacitor and forcibly stop the operation of the power converter when an overvoltage is detected, but in this case, stop the operation within the rated load range. Because of this, the reliability of the device is reduced. The invention according to claim 7 has been made in view of the above problems.

FIG. 13 (a) is a control block diagram showing an embodiment of the invention described in claim 7, and FIG. 13 (b) is an operation explanatory diagram thereof. The main circuit of the power converter is shown in FIG.
Is the same as In FIG. 13A, the voltage command value V2 ^* of the capacitor 15 to which the solar cell 1 is not connected is shown.
The difference between the detected value V2 and the detected value V2 is obtained by the adder 64, and this difference is input to the controller 54 to be the command value i ₁₀ ^{* of the} current flowing through the reactor 10. The above current command value i ₁₀ ^* and detection value i
The deviation from ₁₀ is obtained by an adder 65, and this deviation is input to a controller 56, and its output and the carrier from a carrier generation circuit 57 are compared with a comparator (PWM signal generation circuit) 58.
To obtain an ignition signal 61 for the semiconductor switch element 4 of the series switch circuit 381.

The present embodiment is characterized by a block 70 surrounded by a dashed line in FIG. That is, calculated by the adder 71 the sum V _T and the voltage V2 of the voltage V1 and the capacitor 15 of the capacitor 6, compared to the inhibit voltage level V _LIM by the level setter 72 by a comparator 74. This suppression voltage level V _LIM is the maximum applied voltage value determined from the breakdown voltage of the semiconductor switch element.
Set based on overvoltage protection level. The comparator 74 detects that V _T has reached V _LIM , and sends this detection signal to the reset terminal R of the flip-flop 76 to turn off the operation signal ZH (Low level). Turn off 61. This allows
The regulators 54 and 56 to which the operation signal ZH is applied are held at zero, the switch element 4 of the series switch circuit 381 enters a pulse-off state, and the operation of the DC voltage dividing circuit 201 stops.

[0071] On the other hand, V _T that falls below the recovery voltage level by another level setter 73 V (recovery) is detected by comparator 75, the operation signal ZH send this detection signal to the set terminal S of the flip-flop 76 On (Hi
gh level), and the ignition signal is turned on via the AND circuit 77. That is, the controller 54 and 56 are operated to restart the DC voltage dividing circuit 201. Here, the recovery voltage level V (recovery) is set to a level at which the DC voltage dividing circuit 201 can operate normally. FIG. 13 (b)
Are V _T , V _LIM , V (recovery) and operation signal Z obtained by comparators 74, 75 and flip-flop 76.
The relationship with H is shown.

FIG. 15 shows a reactor 1 according to the present embodiment.
0 current i ₁₀ of, shows the relationship between the voltage sum V _T and the operating signal ZH. In the figure, gradually reduces the current i ₁₀ by load fluctuation at time T1, rises as the voltage V2 of the capacitor 15 is shown due to this. Then, at time T2, the voltage total value V _T (= V1 + V
When 2) reaches the suppression voltage level V _LIM , FIG.
The circuit after the comparator 74 shown in (1) operates to turn off the operation signal ZH and stop the DC voltage dividing circuit 201. As a result, the energy supply from the solar cell 1 is cut off, and the voltage rise after the DC voltage dividing circuit is stopped is only the rise due to the residual energy of the reactor 10. This value is sufficiently smaller than the voltage rise due to the control delay of the DC voltage dividing circuit 201. After the DC voltage dividing circuit 201 is stopped, the capacitor 15
Is supplied to the AC load 91, the voltage V2 of the capacitor 15 decreases. At time T3, when the voltage total value _VT reaches the recovery voltage level V (recovery), the circuits subsequent to the comparator 75 shown in FIG. 13A operate and turn on the operation signal ZH to turn on the DC voltage dividing circuit 201. restart.

The above is the operation of the present embodiment, but the above operation is limited to only the DC voltage dividing circuit 201, and the half-bridge inverters 3A and 3B continue the normal operation. Therefore, the capacitor 15 which accompanies the load fluctuation, which is the subject of the present invention,
This prevents the occurrence of overvoltage, increases the capacity of the capacitor, uses a high-voltage switch element, and avoids forced shutdown of the power converter due to overvoltage detection.
In this embodiment, the case where the overvoltage of the capacitor 15 to which the solar cell 1 is not connected has been described, but the case where the solar cell 1 is not connected to the other capacitor 6 and the overvoltage is prevented. In addition, the present invention is applicable.

In the above embodiments, the case where the solar cell 1 is used as the DC power supply has been described. However, the type of the DC power supply is not limited to this, and a fuel cell or a storage battery may be used.

[0075]

As described above, according to the first aspect of the present invention, two equal capacitor voltages, which are input voltages of a half-bridge inverter, are obtained from one DC power supply by the operation of the DC voltage dividing circuit. Can be. Therefore, as in the prior art shown in FIG. 6, the error in the power generated by the two solar cells and the imbalance in the capacitor voltage due to the power supply to the asymmetric load during the self-sustained operation are eliminated, and the distortion of the output voltage and the generation of power to the system are eliminated. Outflow of the DC component can be prevented. Further, since only one DC power supply is required, the wiring connection does not become complicated. Further, although the number of power conversion stages is two, the converted power of the DC voltage dividing circuit is の of the converted power of the boost chopper shown in FIG. 7, so that the power converter can be downsized.

According to the second aspect of the present invention, by controlling the voltage of the capacitor to which the DC power supply is not connected to the minimum voltage determined by the output AC voltage value required for the power converter, the withstand voltage of the semiconductor switch element is controlled. Suffices to allow (the maximum voltage of the DC power supply + the fixed voltage of the capacitor). Therefore, a switch element having a lower withstand voltage can be used as compared with a case in which two DC power supplies are connected in series, reducing switching loss during power conversion, improving conversion efficiency,
Manufacturing costs can be reduced.

According to the third aspect of the present invention, the output waveform can be corrected when the input voltage of the half-bridge inverter becomes uneven according to the second aspect of the present invention. Thus, stable power supply can be performed.

According to the fourth aspect of the present invention, there is provided control means for suppressing the total value of the voltages of the two capacitors of the DC voltage dividing circuit to be equal to or less than the withstand voltage of the semiconductor switching element used in the half-bridge inverter. Accordingly, a switch element having a lower breakdown voltage can be used as compared with a case where two solar cells are connected in series and used. For this reason, it is possible to reduce switching loss during power conversion and improve conversion efficiency.

According to the fifth aspect of the present invention, it is possible to execute the charge / discharge control of the storage battery in parallel while performing the maximum power follow-up control of the solar cell without using the DC-DC converter as in the related art. The size and the price can be reduced, and the efficiency can be increased by the minimum number of conversion stages.

According to the invention, the voltage between the DC input terminals is clamped to the DC power supply voltage by the capacitor of the DC voltage dividing circuit, and the positive or negative electrode of the DC power supply is connected to the neutral line (ground line) of the system power supply. ), The potential with respect to the ground point is stabilized without fluctuation. Therefore, there is an effect of suppressing generation of noise and generation of a noise terminal voltage, and it is possible to prevent the system from becoming complicated, large-sized, and expensive due to addition and reinforcement of a noise filter on the DC side.

According to the seventh aspect of the present invention, the total voltage of the capacitor is compared with the suppression voltage level and the recovery voltage level, and the operation of the DC voltage dividing circuit is stopped or restarted according to the result. Further, it is possible to prevent an overvoltage from being applied to the half-bridge inverter due to a load change. This avoids an increase in the capacitance of the capacitor and the use of a high-withstand-voltage switch element, and increases the size of the device.
High cost can be prevented. Further, since the half-bridge inverter continuously generates a voltage even when the operation of the DC voltage dividing circuit is stopped, the reliability of the power converter can be improved.

[Brief description of the drawings]

FIG. 1 is a main circuit configuration diagram showing an embodiment of the invention described in claim 1;

FIG. 2 is an operation explanatory diagram of the DC voltage dividing circuit in the embodiment of FIG. 1;

FIG. 3 is a control block diagram of a DC voltage dividing circuit according to an embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the DC voltage dividing circuit in the embodiment of FIG. 1;

FIG. 5 is a control block diagram according to an embodiment of the present invention.

FIG. 6 is a control block diagram according to an embodiment of the present invention.

FIG. 7 is a main circuit configuration diagram showing an embodiment of the invention described in claim 5;

FIG. 8 is a control block diagram for performing maximum power tracking control in the embodiment of FIG. 7;

9 is a control block diagram for performing charge / discharge control of a storage battery in the embodiment of FIG. 7;

FIG. 10 is a main circuit configuration diagram showing an embodiment of the invention described in claim 6;

11 is an operation explanatory diagram of the DC voltage dividing circuit in the embodiment of FIG.

FIG. 12 is a main circuit configuration diagram showing another embodiment of the invention described in claim 6 and an embodiment of the invention described in claim 7.

FIG. 13 is a control block diagram and an operation explanatory diagram showing an embodiment of the invention described in claim 7;

FIG. 14 is an operation explanatory diagram of the embodiment in FIG. 12;

FIG. 15 is an operation explanatory view of the embodiment in FIG. 13;

FIG. 16 is a circuit diagram showing a conventional technique.

FIG. 17 is a circuit diagram showing a conventional technique.

FIG. 18 is a schematic circuit diagram showing a conventional technique.

19 is a characteristic diagram of the solar cell in FIG.

FIG. 20 is a schematic circuit diagram showing a conventional technique.

FIG. 21 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solar cell 2,201,202 DC voltage dividing circuit 3A, 3B Half bridge inverter 4,13,31 Semiconductor switch element 5,14,32,37 Diode 6,8a, 8b, 15 Capacitor 7a, 7b, 10 Reactor 9 system Power supply 16, 17 Voltage command changeover switch 20, 20a, 20b, 20c, 43, 45, 53, 5
5, 60, 64, 65, 71 Adder 22, 46, 54, 56 Controller 23, 27, 47, 57 Carrier generation circuit 24, 28, 41, 48, 58, 74, 75 Comparator 25 Amplifier 26 Divider 38 , 381, 382 Series switch circuit 42, 44 Analog switch 50 DC circuit breaker 51 Battery 52 Voltage command generation circuit 59 Charge / discharge command generation circuit 61 Firing signal 62 Current transformer 63 Circuit breaker 70 Block 72, 73 Level setter 76 Flip Step 77 AND circuit 91 AC load

Claims (7)

[Claims] 1. A half-bridge inverter comprising two switch arms, each comprising an anti-parallel circuit of a semiconductor switch element and a diode, connected in series vertically, and two half-bridge inverters are connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, and two switch arms each composed of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically to form a series switch circuit. This series switch circuit is connected to the series circuit of the two capacitors. The connection points of the upper and lower switch arms of the series switch circuit connected in parallel and the two A DC voltage dividing circuit is formed by connecting a reactor between the capacitor and an interconnection point thereof, so that a voltage of a capacitor to which a DC power supply is not connected among the two capacitors is equal to a voltage of the other capacitor. A power converter, comprising: control means for controlling on / off of a semiconductor switch element of the series switch circuit. 2. A half-bridge inverter comprising two switch arms each comprising an anti-parallel circuit of a semiconductor switch element and a diode connected in series vertically, and two half-bridge inverters connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switching element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, and two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically to form a series switch circuit. This series switch circuit is connected to the series circuit of the two capacitors. The connection points of the upper and lower switch arms of the series switch circuit connected in parallel and the two A DC voltage dividing circuit is formed by connecting a reactor between the capacitor and an interconnection point of the capacitor, and the series switch circuit is configured such that a voltage of a capacitor to which a DC power supply is not connected among the two capacitors has a constant value. A power conversion device comprising control means for controlling on / off of the semiconductor switch element of (1). 3. A half-bridge inverter in which two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically, and two half-bridge inverters are connected in parallel, and the voltage of two series-connected capacitors is adjusted. A single-phase three-wire output-type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, and both ends of one of the capacitors. And a switch arm composed of an anti-parallel circuit of a semiconductor switch element and a diode connected in series vertically to form a series switch circuit, and this series switch circuit is connected in series with the two capacitors. A connection point of the upper and lower switch arms of the series switch circuit connected in parallel with the circuit and the two A DC voltage dividing circuit formed by connecting a reactor between the interconnection points of the capacitors; and the series switch circuit such that a voltage of a capacitor to which a DC power supply is not connected among the two capacitors has a constant value. Control means for controlling on / off of the semiconductor switch element of the above. When the voltage of the two capacitors becomes unequal by operating the control means, the voltage of these capacitors is Detection values V1, V2, firing time T _on of upper arm of half-bridge inverter, firing time T of lower arm
control means for controlling on / off of the semiconductor switch element of the half-bridge inverter based on the output voltage command value λ obtained by the following equation using _off (= T−T _on ) and the carrier cycle T: Characteristic power converter. λ = 1− (V1− _Vout ) / E ₀ (where _Vout (: output voltage reference command value) = (V1 × _Ton / T) −
(V2 × T _off / T), E ₀ = (V1 + V2) / 2)) 4. A half-bridge inverter in which two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically, and two half-bridge inverters are connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, and two switch arms each composed of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically to form a series switch circuit. This series switch circuit is connected to the series circuit of the two capacitors. The connection points of the upper and lower switch arms of the series switch circuit connected in parallel and the two Connect the reactor between an interconnection point of the capacitor to form a DC voltage divider circuit, it generates a voltage command value of the other capacitor based on the voltage detection value of one capacitor of the two capacitors,
By controlling the on / off of the semiconductor switch element of the series switch circuit so that the voltage of the other capacitor matches the voltage command value, the total value of the voltages of the two capacitors is changed to the semiconductor value of the half-bridge inverter. A power conversion device comprising control means for suppressing the breakdown voltage of the switch element to a value equal to or lower than the breakdown voltage of the switch element. 5. A half-bridge inverter in which two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically, and two half-bridge inverters are connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, and two switch arms each composed of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically to form a series switch circuit. This series switch circuit is connected to the series circuit of the two capacitors. The connection points of the upper and lower switch arms of the series switch circuit connected in parallel and the two A DC voltage dividing circuit is formed by connecting a reactor between the capacitors and an interconnection point thereof, and a series circuit of a DC breaker and a storage battery is provided at both ends of a capacitor to which a DC power supply is not connected among the two capacitors. The maximum power follow-up control of the DC power supply is performed by controlling ON / OFF of the semiconductor switch element of the half-bridge inverter so that the voltage of the capacitor to which the DC power supply is connected matches the voltage command value. And controlling the on / off of the semiconductor switch element of the series switch circuit and controlling the opening / closing of the DC breaker so that the voltage of the capacitor not connected to the DC power supply matches the voltage command value. A power converter, comprising: a control unit that controls charging and discharging of the storage battery. 6. A half-bridge inverter in which two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically, and two half-bridge inverters are connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, a semiconductor switch element and a diode are connected in series to form a series switch circuit, and an interconnection point between the semiconductor switch element and the diode constituting the series switch circuit and an interconnection point between the two capacitors. To form a DC voltage dividing circuit and connect the two capacitors A semiconductor switch element of the series switch circuit, wherein an interconnection point is connected to a neutral line of a system power supply, and a voltage of a capacitor to which a DC power supply is not connected among the two capacitors is equal to a voltage of the other capacitor. A power conversion device comprising control means for controlling ON and OFF of the power converter. 7. A half-bridge inverter in which two switch arms each consisting of an anti-parallel circuit of a semiconductor switch element and a diode are connected in series vertically, and two half-bridge inverters are connected in parallel. In a single-phase three-wire output type power converter that outputs two single-phase AC voltages by turning on and off the semiconductor switch element as an input voltage of a half-bridge inverter, a DC voltage is applied across one of the capacitors. A power supply is connected, a semiconductor switch element and a diode are connected in series to form a series switch circuit, and an interconnection point between the semiconductor switch element and the diode constituting the series switch circuit and an interconnection point between the two capacitors. To form a DC voltage dividing circuit and connect the two capacitors Connect the interconnection point to the neutral point of the AC load, set the suppression voltage level and the recovery voltage level for the total voltage of the two capacitors, and increase the total voltage to the suppression voltage level. A power converter comprising: control means for stopping the operation of the DC voltage dividing circuit when the voltage reaches the voltage level, and restarting the DC voltage dividing circuit when the voltage level decreases and reaches the restoration voltage level.