JP5132797B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that converts DC power into AC power, and more particularly to a power conversion device that is used in a power conditioner or the like that connects a distributed power source to a system.

In a conventional power conditioner, for example, as shown in a solar power conditioner, the voltage is boosted using a chopper from a distributed power source that is a solar cell, and a PWM controlled inverter is inserted in the subsequent stage to generate an output AC voltage. doing.
The basic operation of such a conventional power conditioner will be described below. The DC power output from the solar cell drives the internal control power supply of the power conditioner, and the internal circuit can operate. Using a chopper circuit, the voltage of the solar cell is boosted to a voltage required to connect to the grid. The inverter unit is composed of four switches, and performs PWM switching so that the output current has a phase synchronized with the system voltage. In this way, a strip-like waveform is output to the output, the output voltage is controlled by changing the output time ratio, the output voltage is averaged by the smoothing filter provided on the output side, and the system is AC Electric power is output (for example, refer nonpatent literature 1).

“Development of Solar Power Conditioner Type KP40F” OMRON TECHNICS Vol. 42 no. 2 (Vol. 142) 2002,

  In the conventional power conditioner that links the solar voltage to the system, the maximum value of the output voltage of the inverter is determined by the magnitude of the boosted voltage by the chopper. For this reason, for example, when outputting an AC voltage of 200 V, the boosted DC voltage needs to be 282 V or higher, and is usually set higher with a margin. The output voltage of the solar voltage is usually about 200 V or less, and needs to be boosted to 282 V or more as described above. When the step-up ratio increases, the loss of switching elements and diodes in the chopper section increases. Further, if the input / output voltage of the inverter is large, it is necessary to increase the withstand voltage of the elements constituting the inverter, and the loss of each element increases. As described above, there is a problem that the efficiency of the entire power conditioner is lowered.

  The present invention was made to solve the above-described problems, and in a power conversion device that converts electric power from a direct-current power source such as sunlight into alternating current and outputs the alternating current to a system or a load, each unit The purpose is to improve the conversion efficiency by reducing the loss.

  In the power converter according to the present invention, a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power are connected in series, and the output voltage is controlled by the sum of the generated voltages of the plurality of single-phase inverters. And a second DC power supply and a step-down circuit for stepping down the voltage of the second DC power supply, and the DC power supply voltage of the first inverter having the maximum voltage among the plurality of single-phase inverters is When the DC power supply voltage generated from the second DC power supply through the step-down circuit and detected by a single-phase inverter other than the first inverter exceeds the predetermined voltage, the second power supply voltage is detected. Control is performed to reduce the DC power supply voltage of the first inverter generated from the DC power supply, and the amount of discharge from the DC power supply through the other single-phase inverter is increased.

Since the power converter according to the present invention outputs the sum of the generated voltages of a plurality of single-phase inverters, each single-phase inverter only needs to output a voltage lower than the overall output voltage, and constitutes each single-phase inverter. The breakdown voltage of each element can be reduced. In addition, since the DC power supply voltage of the first inverter having the maximum voltage is generated from the second DC power supply via the step-down circuit, the second inverter can be operated even when there is a voltage rise of the second DC power supply. The destruction of each element in one inverter can be prevented, and the power converter can be operated stably. For this reason, the withstand voltage of each element which comprises each single-phase inverter can be reduced reliably, and the power converter device with high conversion efficiency with which the loss was reduced is obtained.
Further, when the DC power supply voltage of the single-phase inverter other than the first inverter exceeds a predetermined voltage, control is performed to reduce the DC power supply voltage of the first inverter generated from the second DC power supply, Since the amount of discharge from the DC power supply through the other single-phase inverter is increased, the increase in the DC power supply can be suppressed, and an increase in loss can be suppressed, and the reliability of the power converter can be improved.

It is a schematic block diagram which shows the power conditioner by Embodiment 1 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 1 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 1 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 1 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 1 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 2 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 2 of this invention. It is a figure which shows the structure and operation | movement of a power conditioner by Embodiment 3 of this invention. It is a figure explaining operation | movement of the power conditioner by Embodiment 3 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 4 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 5 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 6 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 7 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 8 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 9 of this invention. It is a voltage waveform diagram explaining operation | movement of the power conditioner by Embodiment 10 of this invention. It is a voltage waveform diagram explaining operation | movement of the power conditioner by Embodiment 11 of this invention.

Embodiment 1 FIG.
Hereinafter, a power conversion apparatus (hereinafter referred to as a power conditioner) according to Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a power conditioner according to Embodiment 1 of the present invention. As shown in FIG. 1, the AC side of a plurality (three in this case) of single-phase inverters 6 to 8 is connected in series to constitute an inverter unit. Each of the single-phase inverters 6 to 8 includes a plurality of self-extinguishing semiconductor switching elements such as IGBTs having diodes connected in anti-parallel, and a first inverter having a first capacitor 3 serving as a DC power supply as an input. The second inverter 7 is connected to one of the six AC side terminals, and the third inverter 8 is connected to the other. Moreover, two self-extinguishing semiconductor switching elements such as IGBTs connected in reverse parallel as a short-circuit switch 9 for short-circuiting both terminals on the AC side of the first inverter 6 are connected in series with opposite polarities, This shorting switch 9 is connected in parallel to the first inverter 6.

  Further, a step-down converter 17 as a step-down circuit and a step-up chopper 11 as a step-up circuit are connected in series via the input capacitor 2 after the direct-current power source 1 using sunlight as the second DC power source. The first capacitor 3 serving as the input of the first inverter 6 is charged from the DC power source 1 through the step-down converter 17 and the step-up chopper 11. The step-down converter 17 includes a step-down switching element 23, a reactor 27, and a step-down diode 24 having a cathode connected to a connection point between the elements 23 and 27. The step-up chopper 11 includes a reactor 27 that is also used as a step-down converter 17, a step-up diode 25 as a rectifying element, and a step-up switch element 26 connected to a connection point between the elements 27 and 25. .

In addition, a bypass circuit 12 (third bypass circuit) that bypasses a circuit in which the step-down converter 17 and the step-up chopper 11 are connected in series is connected. The bypass circuit 12 includes a bypass relay 21 and first and second bypass switch elements 19 and 20 that are connected in parallel to the bypass relay 21 and constitute a blocking circuit for blocking the bypass relay 21. The first bypass switch element 19 and the second bypass switch element 20 are connected in series with opposite polarities by two semiconductor switches having diodes connected in antiparallel.
Further, a first bypass circuit 18 that bypasses the step-down converter 17 is connected. The first bypass circuit 18 includes a first bypass relay 22 connected so as to bypass the step-down switch element 23.

The voltage V1 of the first capacitor 3 serving as an input of the first inverter 6 is applied to the second and third capacitors 4 and 5 serving as DC power sources serving as inputs of the other second and third inverters 7 and 8. The voltages V2 and V3 are higher than the voltages V2 and V3, and are controlled by the DC / DC converter 10 so as to be, for example, predetermined voltages. Here, it is assumed that the voltages of the second and third capacitors 4 and 5 are equal.
These inverters 6 to 8 can generate positive and negative voltages and zero as outputs, and the inverter units 6 to 8 output a voltage as a sum total of these generated voltages. The output voltage is smoothed by a smoothing filter including reactors 13 and 14 and a capacitor 15, and an AC voltage _Vout is supplied to a system (load) 16. It is assumed that the system 16 is grounded at the midpoint with a columnar transformer.

The output of the second inverter 7 and the output of the third inverter 8 are equal, and each inverter 7, 8 is output by PWM control so as to compensate for the difference between the target output voltage and the output voltage of the first inverter 6. Is done.
Further, during a period in which the output voltage of the first inverter 6 is 0, the shorting switch 9 for short-circuiting both terminals on the alternating current side of the first inverter 6 is turned on to make it conductive, and the first inverter 6 All the semiconductor switches in are turned off. As a result, the first capacitor 3 and the system 16 (AC output power line) are cut off, and the intermediate point potential of the first capacitor 3 can maintain the ground potential. Each side can maintain a constant DC potential from earth potential. A solar panel (DC power supply 1) that generates sunlight has a large stray capacitance with respect to the ground, but since the midpoint potential of the first capacitor 3 generated from the DC power supply 1 can be fixed to the ground potential, the DC power supply 1 can be suppressed, and the current flowing through the stray capacitance can also be suppressed.

By the way, the maximum output voltage necessary for the AC output of 200 V is about 282 V, and the output voltages of the inverter units 6 to 8 can output up to V1 + V2 + V3. For this reason, if V1 + V2 + V3 is about 282V or more, the power conditioner can output an alternating current of 200V.
When the rated voltage of the DC power supply 1 is 240 V, it is not necessary to boost the voltage at the rated voltage as in the conventional case, and the voltage V1 of the first capacitor 3 can be generated. The first inverter 6 can be formed of a semiconductor element suitable for the rated voltage 240V, that is, with a reduced withstand voltage. Since the voltages V2 and V3 of the second and third capacitors 4 and 5 are lower than V1, each of the inverters 6 to 8 can also be composed of an element having a low withstand voltage, and an efficient inverter unit 6 with reduced loss. ~ 8.

The charging operation to the first capacitor 3 will be described below.
In the case of the DC power supply 1 using sunlight, the voltage of the DC power supply 1 may be higher than the rated voltage during no-load operation. For example, when the DC power supply voltage with a rated voltage of 240 V is no load at the time of starting the system, the output voltage may be about 350 V. As described above, when the voltage of the DC power supply 1 exceeds the rated voltage during operation, the voltage is stepped down by the step-down converter 17 to generate the voltage V1 of the first capacitor 3. Further, when the DC power source 1 falls below the rated voltage and further becomes a predetermined voltage, for example, 200 V or less, the voltage is boosted by the boost chopper 11 to generate the voltage V1 of the first capacitor 3.

First, when the voltage generated by the DC power supply 1 is within a predetermined range including the rated voltage (for example, 200 V to rated voltage), the current is obtained by conducting the bypass relay 21 of the bypass circuit 12 as shown in FIG. It flows through the rated current path 30.
Next, when the voltage of the DC power source 1 is out of the predetermined range and the step-down converter 17 or the step-up chopper 11 needs to be operated, the bypass circuit 12 is shut off. At this time, first, as shown in FIG. 3, the first bypass switch element 19 and the second bypass switch element 20 are brought into conduction to generate a commutation current path 31. Next, when the bypass relay 21 is turned off, the current flowing through the bypass relay 21 flows through the first and second bypass switch elements 19 and 20, and the bypass relay 21 can be shut off at high speed. By turning off the first and second bypass switch elements 19 and 20, the bypass circuit 12 can be reliably and reliably cut off, and current flows to the step-down converter 17 and the step-up chopper 11.

When the voltage of the DC power supply 1 becomes equal to or lower than a predetermined voltage (for example, 200 V) and boosting is necessary, the bypass circuit 12 is shut off and the step-down converter 17 is bypassed as described above. That is, as shown in FIG. 4, the first bypass relay 22 is turned on, and the current flows through the step-down bypass path 32. Then, the boosting switch element 26 is turned on / off to boost the voltage to a predetermined voltage. In this way, loss generation in the step-down switch element 23 can be prevented, and a step-up operation by the step-up chopper 11 can be realized.
When the voltage of the DC power source 1 exceeds the rated voltage and the voltage needs to be stepped down, the bypass circuit 12 is shut off as described above, and the voltage is lowered by the step-down converter 17. As shown in FIG. 5, the step-down switch element 23 is turned on and off, and the first bypass relay 22 is opened. By doing so, the first bypass relay 22 can be cut off without generating an arc, and the current can be passed through the current path 33 to start the step-down operation of the step-down converter 17.
Further, when the voltage of the DC power source 1 returns to a predetermined range (200 V to rated voltage) during the operation of the step-down converter 17 or the step-up chopper 11, the step-down operation and the step-up operation are stopped and the bypass relay in the bypass circuit 12 is stopped. The operation by the rated current path 30 can be returned to by conducting 21.

As described above, in this embodiment, the first inverter 6 using the DC voltage V1 of the first capacitor 3 generated from the DC power supply 1 as the DC source and the other second and third inverters 6 and 7 are used. The inverter was connected in series, and the power conditioner was configured to obtain the output voltage as the sum of the voltages generated by each inverter. In the power conditioner configured as described above, each of the inverters 6 to 8 can be configured with an element having a low withstand voltage. Semiconductor switch elements tend to have higher conduction loss as the breakdown voltage increases, and an efficient device configuration with reduced loss can be achieved. Further, a voltage higher than the DC voltage V1 of the first capacitor 3 can be output, the boosting rate of the boosting chopper 11 can be reduced, and the loss can be reduced.
Further, since the step-down converter 17 is provided so that the voltage is stepped down when the voltage of the DC power supply 1 exceeds the rated voltage, the voltage input to each of the inverters 6 to 8 is prevented from increasing and exceeding the withstand voltage of the element. And element destruction can be prevented. For this reason, the withstand voltage of each element which comprises each inverter 6-8 can be reduced reliably, and the power conditioner with high conversion efficiency with which the loss was reduced is obtained.

  Furthermore, since the first bypass circuit 18 is provided so that the step-down switch element 23 in the step-down converter 17 can be bypassed, loss generation in the step-down switch element 23 can be prevented when the step-down operation is unnecessary, and the loss Reduction can be achieved. Furthermore, when neither the step-down operation nor the step-up operation is required, the step-down converter 17 and the step-up chopper 11 are bypassed by the bypass circuit 12, so that the conduction loss can be further reduced and the conversion efficiency can be improved. Further, since the bypass circuit 12 includes the bypass relay 21 and the cutoff circuit (first and second bypass switch elements 19 and 20) connected in parallel to the bypass relay 21, the bypass circuit 12 is bypassed when the bypass circuit 12 is shut off. The relay 21 can be reliably interrupted without generating an arc.

  Further, the power conditioner selectively operates either the step-up operation by the step-up chopper 11 or the step-down operation by the step-down converter 17 in accordance with the voltage of the DC power source 1 or does not operate both of them. Therefore, the DC voltage V1 can be stably generated, and a stable AC output can be obtained with high reliability.

In this case, the power conditioner supplies the output power to the grid 16, but the same effect can be obtained when the power conditioner is supplied to the load.
In this embodiment, the two inverters 7 and 8 connected to both sides of the first inverter 6 are shown in which the outputs are made equal and the voltage waveform is accurately controlled by PWM control. You don't have to. Further, a plurality of inverters may be connected to both sides of the first inverter 6 as long as the sum of output voltages on both sides is equal.
Furthermore, although the effect of fixing the midpoint potential of the first capacitor 3 to the ground potential is lost, the shorting switch 9 for short-circuiting both terminals on the AC side of the first inverter 6 may be omitted. A plurality of inverters 6, 7 other than the first inverter 6 may be connected in series only on one side of the first inverter 6, and each inverter output may be different.

Embodiment 2. FIG.
Next, what provided the bypass circuit in the step-up chopper 11 of the power conditioner by the said Embodiment 1 is demonstrated below.
As shown in FIG. 6, a second bypass circuit 28 that bypasses the boosting diode 25 in the boosting chopper 11 is connected to the boosting diode 25 in parallel. The second bypass circuit 28 is composed of a second bypass relay 29 that has less conduction loss than the boosting diode 25.
When the voltage of the DC power supply 1 exceeds the rated voltage, the step-down converter 17 performs a step-down operation, and the step-up chopper 11 does not perform a step-up operation. In this case, as shown in FIG. 7, the current flows through the boost diode bypass current path 34, and the current flowing through the boost diode 25 is bypassed by the second bypass circuit 28. Thereby, conduction loss can be reduced and a more efficient power conditioner can be obtained.

Embodiment 3 FIG.
In the second embodiment, the boosting diode 25 is bypassed by the second bypass circuit 28 when the boosting chopper 11 does not perform the boosting operation. However, in this embodiment, when the boosting chopper 11 performs the boosting operation, the boosting diode 25 is bypassed. 25 is bypassed. As shown in FIG. 8, a bypass semiconductor switch 35 made of an FET or the like having a conduction loss less than that of the boosting diode 25 is connected in parallel to the boosting diode 25.
In this case, the bypass semiconductor switch 35 is turned on at a timing when the current is about to flow through the boosting diode 25, and the current flows through the second boosting diode bypass current path 37. Then, immediately before the direction of the current is reversed, the bypass semiconductor switch 35 is turned off, and the forward current is commutated so as to flow to the boosting diode 25. As a result, as shown in FIG. 9, when a current flows through the boost current path 36, a reverse current flows through the boost diode recovery current path 39 from the first capacitor 3 side to the boost diode 25, and the boost current path 36 A recovery loss occurs in the diode 25.

By the way, a diode is connected to the bypass semiconductor switch 35 in antiparallel, but the recovery loss of this diode is larger than the recovery loss of the boosting diode 25 which is a single diode.
In this embodiment, the conduction loss can be reduced by bypassing the boosting diode 25 by the bypass semiconductor switch 35. Further, since the recovery loss is generated in the boosting diode 25, the loss can be further reduced, and an efficient power conditioner can be obtained.

Embodiment 4 FIG.
In the first to third embodiments, the circuits 12, 18, 28 and 35 for bypassing the step-down converter 17 and the step-up chopper 11 are shown. However, as shown in FIG. 10, these bypass circuits are not provided. Also good.
In this case, if the step-down switching element 23 of the step-down converter 17 is held in the ON state, the step-up chopper 11 can perform a step-up operation, and the voltage from the DC power source 1 can be stepped up. When stepping down, the step-down converter 17 is stepped down, and the output current is passed through the step-up diode 25 in the step-up chopper 11.
In the power conditioner configured as described above, each of the inverters 6 to 8 can be configured by an element having a low withstand voltage, and an efficient device configuration with reduced loss can be achieved. Further, a voltage higher than the DC voltage V1 of the first capacitor 3 can be output, the boosting rate of the boosting chopper 11 can be reduced, and the loss can be reduced. Further, since the step-down converter 17 is provided, the voltage of the first capacitor 3 can be controlled to a voltage that does not exceed the withstand voltage of the elements constituting the first inverter 6. Destruction can be prevented. For this reason, the withstand voltage of each element which comprises each inverter 6-8 can be reduced reliably, and the power conditioner with high conversion efficiency with which the loss was reduced is obtained.

Embodiment 5 FIG.
In the fourth embodiment, the circuit without the step-down converter 17 and the step-up chopper 11 is shown. However, as shown in FIG. 11, only the first bypass circuit 18 that bypasses the step-down converter 17 is connected. Also good. As described above, the first bypass circuit 18 includes the first bypass relay 22 connected to bypass the step-down switching element 23.
As described above, when it is not necessary to step down the voltage from the DC power supply 1, the step-down switch element 23 in the step-down converter 17 can be bypassed, so that loss generation in the step-down switch element 23 can be prevented, A boosting operation by the boosting chopper 11 can be realized, and loss can be reduced.

Embodiment 6 FIG.
In each of the above-described embodiments, the power conditioner including the boost chopper 11 is shown, but a booster circuit such as the boost chopper 11 may not be provided. In this case, as shown in FIG. 12, the step-down converter 17 is disposed between the DC power supply 1 and the first capacitor 3.
Even in such a power conditioner, the voltage of the first capacitor 3 can be controlled to a voltage that does not exceed the withstand voltage of the elements constituting the first inverter 6. Destruction can be prevented. For this reason, the withstand voltage of each element which comprises each inverter 6-8 can be reduced reliably, and the power conditioner with high conversion efficiency in which the loss was reduced is obtained.
Also in this case, the first bypass circuit 18 that bypasses the step-down converter 17 may be connected, and loss reduction can be achieved.

Embodiment 7 FIG.
13 is a schematic configuration diagram showing a power conditioner according to Embodiment 7 of the present invention. This is because, in the power conditioner according to the first embodiment shown in FIG. 1, a backflow prevention diode 47 as a backflow prevention element is provided in the current path from the DC power supply 1 to the first capacitor via the bypass circuit 12. It is provided.
As described above, when the voltage generated by the DC power source 1 is within a predetermined range including the rated voltage (200 V to rated voltage), the current flows through the rated current path 30 by making the bypass relay 21 of the bypass circuit 12 conductive. Flows (see FIG. 2). At this time, the voltages of the DC power supply 1 and the first capacitor 3 are substantially equal. In this state, for example, even if the voltage of the DC power supply 1 suddenly drops, no current flows from the first capacitor 3 to the DC power supply 1 via the bypass circuit 12 because the backflow prevention diode 47 is provided.
As described above, since no current flows from the first capacitor 3 to the DC power supply 1, even if the voltage of the DC power supply 1 suddenly decreases, the voltage of the first capacitor 3 does not fluctuate and distortion occurs in the output voltage waveform. Can be avoided, and a stable output can be obtained.

Embodiment 8 FIG.
FIG. 14 is a schematic configuration diagram showing a power conditioner according to Embodiment 8 of the present invention. Similar to the seventh embodiment, a backflow prevention element is provided in the current path from the DC power supply 1 to the first capacitor via the bypass circuit 12.
In this embodiment, as shown in the figure, the bypass circuit 12 is connected in parallel to the step-down switch element 23 and the reactor 27, and the connection point on the reactor 27 side is between the reactor 27 and the step-up diode 25. . In this way, by arranging the boosting diode 25 in the boosting chopper 11 outside the bypassed path and connecting it, the boosting diode 25 is also used as the backflow preventing element.

As described above, when the voltage generated by the DC power source 1 is within a predetermined range including the rated voltage (200 V to rated voltage), the current flows through the rated current path 30 by making the bypass relay 21 of the bypass circuit 12 conductive. Flows (see FIG. 2). At this time, the voltages of the DC power supply 1 and the first capacitor 3 are substantially equal. In this state, for example, even if the voltage of the DC power supply 1 suddenly drops, the boosting diode 25 functions as a backflow preventing diode, so that a current is supplied from the first capacitor 3 to the DC power supply 1 via the bypass circuit 12. There is no flow.
As described above, since no current flows from the first capacitor 3 to the DC power supply 1, even if the voltage of the DC power supply 1 suddenly decreases, the voltage of the first capacitor 3 does not fluctuate and distortion occurs in the output voltage waveform. Can be avoided, and a stable output can be obtained. Further, since the boosting diode 25 is also used as the backflow preventing element, the number of parts can be reduced, and the device configuration is small and inexpensive.

Embodiment 9 FIG.
FIG. 15 is a schematic configuration diagram showing a power conditioner according to Embodiment 9 of the present invention. The power conditioner according to the first embodiment shown in FIG. 1 includes the step-down converter 17 and the step-up chopper 11, but in this embodiment, between the DC power source 1 and the first capacitor 3, A step-up / down converter 48 capable of boosting or lowering the voltage of the DC power supply 1 is provided.
Next, the operation will be described.
When the voltage from the DC power source 1 is lower than the specified voltage for charging the first capacitor 3, the buck-boost converter 48 increases the voltage to the specified voltage and charges the voltage of the first capacitor 3 to the specified voltage. keep. Further, when the voltage of the DC power supply 1 is higher than the specified voltage of the first capacitor 3, the voltage from the DC power supply 1 is lowered by the step-up / down converter 48 so that the voltage of the first capacitor 3 is charged to the specified voltage. keep.

Here, the upper limit of the range of the prescribed voltage of the first capacitor 3 is designed so as not to exceed the withstand voltage of the switch element constituting the first inverter 6. As for the lower limit, the maximum voltage output from the power conditioner is set to a value that can be sufficiently output by the sum of the output voltages of the inverters 6 to 8.
As described above, since the step-up / down converter 48 is provided, the switching elements in the inverters 6 to 8 are not destroyed with respect to the voltage fluctuation of the DC power supply 1. For this reason, the withstand voltage of each element which comprises each inverter 6-8 can be reduced reliably, and the power conditioner with high conversion efficiency with which the loss was reduced is obtained.

  In this embodiment as well, a circuit that bypasses the step-up / down converter 48 may be configured by the bypass circuit 12 similar to that of the first embodiment, so that conduction loss can be reduced and conversion efficiency can be improved.

Embodiment 10 FIG.
Each of the above embodiments includes the step-down converter 17 or the step-up / step-down converter 48 and steps down the voltage when the voltage of the DC power supply 1 is higher than the specified range. Is described below.
For example, in a power conditioner using photovoltaic power generation, the rated voltage of the output is 200 Vrms when connected to the system, whereas the rated voltage of the output is operated at 100 Vrms during the independent operation such as a power failure of the system. . As described above, when the target voltage serving as the output voltage command value is changed, the level of the output voltage from the first inverter 6 is adjusted by adjusting the voltage charged in the first capacitor 3 from the DC power supply 1. Change.

FIG. 16 shows the output voltage waveform of the power conditioner when the rated voltage is 200 Vrms and when the rated voltage is 100 Vrms. As shown in the figure, in the output target voltage waveform 40 under the output condition of the rated voltage of 200 Vrms, the first inverter 6 generates the first output voltage 42, but the output target voltage waveform under the output condition of the rated voltage of 100 Vrms. In 41, the first inverter 6 generates a second output voltage 43.
Thus, when the voltage command value changes, such as when the rated voltage changes from 200 Vrms to 100 Vrms, the voltage charged in the first capacitor 3 is adjusted (stepped down) by the step-down converter 17 or the step-up / down converter 48. Thus, the output voltage of the first inverter 6 is changed, and the control according to the target voltage waveform of the output voltage of the power conditioner, which is the sum of the output voltages of the inverters 6 to 8, can be easily realized with good controllability.

By the way, if it is going to cope with the change of voltage command values, such as changing a rated voltage, without changing the charging voltage of each capacitor | condenser 3-5, the output pulse width of the 1st inverter 6 is narrowed. Since the difference voltage between the target voltage and the first inverter output voltage is output by the second inverter 7 and the third inverter 8, the burden on the second and third inverters 7 and 8 is increased, and in particular the PWM. When a waveform is generated by control, a lot of loss occurs.
In this embodiment, since the control for adjusting the voltage charged in the first capacitor 3 according to the change of the voltage command value is performed, the load on the second and third inverters 7 and 8 is increased as described above. Loss can be prevented.

  In the above embodiment, the voltage charged in the first capacitor 3 is adjusted (stepped down) by the step-down converter 17 or the step-up / down converter 48. However, the voltage is stepped up by the step-up chopper 11 or the step-up / down converter 48 as necessary. And adjust.

Embodiment 11 FIG.
Next, in the power conditioner shown in the first to ninth embodiments, the control for adjusting the voltage charged in the first capacitor 3 in relation to the charging voltage of the second and third capacitors 4 and 5 is performed. This will be described below.
In the power conditioner, since the difference voltage between the target voltage and the first inverter output voltage is output by the second inverter 7 and the third inverter 8, the second and third inverters 7, 8 output Accordingly, the second and third capacitors 4 and 5 are discharged, or the second and third capacitors 4 and 5 are charged. When the output voltage and the output current are out of phase, the charge amount of the second and third capacitors 4 and 5 may be larger than the discharge amount.
The second and third capacitors 4 and 5 are supplied with energy from the first capacitor 3 via the DC / DC converter 10, and the voltages V 2 and V 3 are controlled by the DC / DC converter 10. As described above, when the charge amount of the second and third capacitors 4 and 5 is larger than the discharge amount, and when the DC / DC converter 10 has a step-down function, the second and third capacitors 4 and 5 The voltages V2 and V3 can be controlled to desired voltages by the DC / DC converter 10. Control in the case where the DC / DC converter 10 does not have a step-down function will be described below.

In this embodiment, the voltages V2 and V3 of the second and third capacitors 4 and 5 are detected, and when these voltages respectively exceed a predetermined voltage, the voltage that charges the first capacitor 3 from the DC power source 1 Control for reducing V1 by the step-down converter 17 and the step-up / down converter 48 is performed.
FIG. 17 shows the output voltage waveform of the power conditioner when the voltages V2 and V3 of the second and third capacitors 4 and 5 are steady and when the voltages V2 and V3 rise above a predetermined voltage. As shown in FIG. 17A, when the voltages V2 and V3 are steady, the first inverter 6 generates the output voltage 45 of the magnitude V1 with respect to the output target voltage waveform 46, and the second inverter 7 and The burden voltage 44 by the output sum with the third inverter 8 is not so large. When the voltages V2 and V3 rise above a predetermined voltage, the voltage V1 charged in the first capacitor 3 is reduced, and the first inverter 6 with respect to the output target voltage waveform 46 as shown in FIG. The output voltage 45 of the magnitude V1 at which the voltage is generated is also reduced, and the burden voltage 44 due to the output sum of the second inverter 7 and the third inverter 8 is increased. The burden voltage 44 is a voltage obtained by subtracting the first output voltage 45 from the voltage of the output target voltage waveform 46.

  As described above, when the voltages V2 and V3 of the second and third capacitors 4 and 5 rise above a predetermined voltage, the voltage V1 charged in the first capacitor 3 is reduced to thereby reduce the second and third inverters. The output burden voltage 44 of 7 and 8 is increased. In the second and third inverters 7 and 8, the output burden voltage 44 is output by, for example, PWM control. However, since the output voltage increases, the second and third capacitors 4 and 5 are more charged than the charge amount. The amount of discharge increases and the voltages V2 and V3 decrease.

As described above, in this embodiment, even when the DC / DC converter 10 does not have a step-down function, the voltage V1 charged from the DC power supply 1 to the first capacitor 3 is reduced by the step-down converter 17 and the step-up / step-down converter 48. By performing the control, it is possible to suppress the voltages V2 and V3 of the second and third capacitors 4 and 5 from rising beyond a predetermined voltage.
For this reason, it is possible to suppress an increase in loss, and it is possible to prevent destruction of the switch elements constituting the second and third inverters 7 and 8 due to an overvoltage caused by the increase of the voltages V2 and V3, and a highly reliable power conditioner Is obtained.

  In the above embodiment, the voltage charged in the first capacitor 3 is reduced by the step-down converter 17 or the step-up / step-down converter 48. However, the step-up rate of the step-up chopper 11 or the step-up / down converter 48 is changed as necessary. Reduce and adjust.

1 DC power supply (second DC power supply), 3 First capacitor as DC power supply,
4 Second capacitor as DC power supply, 5 Third capacitor as DC power supply,
6 first inverter (single phase inverter),
7 Second inverter as a single-phase inverter,
8 Third inverter as a single-phase inverter, 10 DC / DC converter,
11 boost chopper as a boost circuit, 12 bypass circuit (third bypass circuit),
17 step-down converter as step-down circuit, 18 first bypass circuit,
19, 20 First and second bypass switch elements as cutoff circuits,
21 bypass relay, 22 first bypass relay, 23 step-down switch element,
24 step-down diode, 25 step-up diode as a rectifying element,
26 switch element for boosting, 27 reactor, 30 rated current path,
32 step-down bypass path, 28 second bypass circuit, 29 second bypass relay,
34 boost diode bypass current path, 35 bypass semiconductor switch,
37 second boost diode bypass current path;
47 Backflow prevention diode as a backflow prevention element, 48 Buck-boost converter.

Claims (15)

In a power converter that connects a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power, and controls the output voltage by the sum of the generated voltages of the plurality of single-phase inverters,
A second DC power supply, and a step-down circuit for stepping down the voltage of the second DC power supply,
The DC power supply voltage of the first inverter having the maximum voltage among the plurality of single-phase inverters is generated from the second DC power supply through the step-down circuit,
When the DC power supply voltage of another single-phase inverter other than the first inverter is detected and the DC power supply voltage exceeds a predetermined voltage, the DC power supply voltage of the first inverter generated from the second DC power supply is A power conversion device characterized in that the amount of discharge from the DC power source through the other single-phase inverter is increased by performing control to be reduced. The DC power source of the first inverter having the maximum voltage among the plurality of single-phase inverters and each DC power source of other single-phase inverters are connected via a DC / DC converter. Item 4. The power conversion device according to Item 1. A bypass circuit that bypasses the step-down circuit is configured by a relay, and when the voltage of the second DC power source is equal to or lower than a predetermined voltage, the step-down operation of the step-down circuit is stopped, the bypass circuit is turned on, and the bypass circuit is turned on. The power converter according to claim 1 or 2, wherein the step-down circuit is bypassed. A step-up / down converter comprising one step-down circuit and one step-up circuit is provided between the second DC power source and the DC power source of the first inverter, and according to the voltage of the second DC power source. 3. The power conversion device according to claim 1, wherein either the step-up operation or the step-down operation is selectively operated or both are not operated. A booster circuit is connected between the second DC power source and the DC power source of the first inverter so as to be connected in series with the step-down circuit, and the booster circuit is increased according to the voltage of the second DC power source. 4. The power conversion device according to claim 1, wherein either the step-up operation by the circuit, the step-down operation by the step-down circuit is selectively operated, or both are not operated. 5. The booster circuit includes a reactor, a rectifying element, and a switch, and a second bypass circuit that bypasses the rectifying element is configured as a relay, and the voltage of the second DC power source has a predetermined voltage. 6. The power conversion device according to claim 5, wherein when it exceeds, the boosting operation of the boosting circuit is stopped, the second bypass circuit is turned on, and the rectifying element is bypassed. The booster circuit includes a reactor, a rectifying element, and a switch, and includes a semiconductor switch that bypasses the rectifying element, and conducts the semiconductor switch to bypass the current from the DC power source. The power converter according to claim 5, wherein the semiconductor switch is cut off immediately before the direction of current is reversed. A third bypass circuit that bypasses the step-up / step-down converter, the third bypass circuit including a bypass relay and a cutoff circuit that is connected in parallel to the bypass relay and cuts off the bypass relay; 5. The power conversion device according to claim 4, wherein the circuit is configured by connecting two semiconductor switches, each having a diode connected in reverse parallel, in series with opposite polarities. A third bypass circuit that bypasses a series circuit in which the step-down circuit and the step-up circuit are connected in series; and the third bypass circuit is connected in parallel to the bypass relay and the bypass relay to cut off the bypass relay. The cutoff circuit comprises: two semiconductor switches having diodes connected in reverse parallel and connected in series with opposite polarities. The power converter device described in 1. 10. The backflow prevention element is provided in a current path from the second DC power source to the DC power source of the first inverter through the third bypass circuit. Power conversion device. The third bypass circuit arranges and connects the rectifying element in the booster circuit outside the bypassed path, and connects the rectifying element from the second DC power source to the third bypass circuit. 10. The power converter according to claim 9, wherein the power converter is also used for backflow prevention in a current path to the DC power source of the first inverter. In a power converter that connects a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power, and controls the output voltage by the sum of the generated voltages of the plurality of single-phase inverters,
A step-up / step-down converter configured to include a second DC power supply, a step-down circuit, and a step-up circuit to increase / decrease the voltage of the second DC power supply, and a third bypass circuit that bypasses the step-up / down converter. Prepared,
The DC power supply voltage of the first inverter having the maximum voltage among the plurality of single-phase inverters is selectively selected from the step-up / step-down operation of the step-up / down converter according to the voltage of the second DC power source. Is generated from the second DC power source through the step-up / down converter so that the two or both of them are not operated.
The third bypass circuit includes a bypass relay and a cutoff circuit connected in parallel to the bypass relay and configured to cut off the bypass relay. The cutoff circuit includes two semiconductor switches having diodes connected in reverse parallel. A power conversion device, which is configured by being connected in series with opposite polarities. In a power converter that connects a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power, and controls the output voltage by the sum of the generated voltages of the plurality of single-phase inverters,
A series circuit in which a second DC power supply, a step-down circuit that steps down the voltage of the second DC power supply, and a step-up circuit that steps up the voltage are connected in series; and a third bypass circuit that bypasses the series circuit;
The DC power supply voltage of the first inverter having the maximum voltage among the plurality of single-phase inverters is
Depending on the voltage of the second DC power source, either the step-up operation by the step-up circuit or the step-down operation by the step-down circuit is selectively operated, or both are not operated, and the second DC power source is operated. Is generated from the above series circuit,
The third bypass circuit includes a bypass relay and a cutoff circuit connected in parallel to the bypass relay and configured to cut off the bypass relay. The cutoff circuit includes two semiconductor switches having diodes connected in reverse parallel. A power conversion device, which is configured by being connected in series with opposite polarities. 14. A backflow prevention element is provided in a current path from the second DC power source to the DC power source of the first inverter through the third bypass circuit. 14. Power conversion device. The third bypass circuit arranges and connects the rectifying element in the booster circuit outside the bypassed path, and connects the rectifying element from the second DC power source to the third bypass circuit. The power converter according to claim 13, wherein the power converter is also used for backflow prevention in a current path to the DC power source of the first inverter.

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