WO2013080469A1 - Power conversion device - Google Patents

Abstract

The purpose of the present invention is to provide a power conversion device capable of individually power-controlling a plurality of solar cells, improving the utilization rate of the solar cells, and increasing power conversion efficiency. First to third DC/AC converters (11-13) are connected to first to third solar cell panels (SP1-SP3), respectively. The first to third DC/AC converters (11-13) are connected in series. A control circuit (20) individually controls the first to third DC/AC converters (11-13). The first to third DC/AC converters (11-13) convert first to third output voltages (V1-V3) to first converted output voltages (Va-Vc). The first converted output voltages (Va-Vc) are superimposed and become a combined output voltage (Vt), which is output to a filter circuit (2).

Description

Power converter

The present invention relates to a power converter.

Conventionally, to produce 4.8 kW (= 200 W x 24), when 24 solar panels are used and a solar power system is manufactured with each solar panel having a rated output of 200 W, 25 V, Eight solar panels are connected in series. A series solar panel produces an output voltage of 200 V (= 25 V × 8). At this time, a series-parallel solar cell panel was manufactured by preparing three series solar cell panels and connecting them in parallel to secure a current.

The output of the series-parallel solar cell panel thus configured is supplied to the DC / AC converter via a DC / DC converter (booster). The DC output is converted to AC and AC200 V system interconnection is performed while performing maximum power point tracking control such that the output of the series solar cell panel is maximized by the DC / AC converter.

However, in this photovoltaic power generation system, the outputs of a plurality of series-parallel solar panels are grouped into one and maximum power point tracking control is performed, so that there is a problem that each series solar panel does not generate the maximum output.

Therefore, in another system, each series solar cell panel is configured by connecting eight solar cell panels in series to generate an output voltage of 200 V (= 25 V × 8), and three series solar cells are formed. Three DC / DC converters are respectively connected to the battery panel (for example, Patent Document 1). Three series solar panels are connected in parallel, and each DC / DC converter supplies an output voltage to the DC / AC converter. Thus, the output voltages of the three series solar cell panels are supplied to one DC / AC converter via the corresponding three DC / DC converters. The output of the DC / AC converter is grid-connected to the 200 V AC system.

This system configuration has higher efficiency than the former system configuration because each series solar cell panel is individually subjected to maximum power point tracking control by the DC / DC converter.

JP 2003-124429 A

In the former solar power generation system described above, the DC / DC converter used may not have to have a sufficiently high output voltage of the series-parallel solar cell panel. However, without the DC / DC converter, it is more difficult to ensure the safety of the photovoltaic system when the output of the series-parallel solar panel gets too high, than with the DC / DC converter. There is. In addition, without the DC / DC converter, it is necessary to increase the withstand voltage of the DC / AC converter components, leading to high cost. Therefore, as a real problem, a configuration using a DC / DC converter has been used.

Therefore, the output voltage of the series-parallel solar cell panel passes through two converters of DC / DC converter and DC / AC converter, so the loss in the converter increases and the efficiency of the photovoltaic system decreases. There was a problem that.

Moreover, in the latter solar power generation system mentioned above, a DC / DC converter is essential to each series solar cell panel. Therefore, the output voltage of each series solar cell panel passes through two converters, a DC / DC converter and a DC / AC converter. As a result, since the output voltage of each series solar cell panel passes through two converters, the loss in the converter increases, and similarly, there is a problem that the efficiency of the solar power generation system decreases.

An object of the present invention is to provide a power conversion device capable of individually controlling the power of a plurality of solar cells and increasing the utilization efficiency of the solar cells and improving the power conversion efficiency.

In order to solve the above-mentioned subject, a power converter of the present invention is a plurality of DC / AC converters connected to a plurality of solar cells, and a plurality of DC / AC converters are connected in series. And a control circuit that controls the plurality of DC / AC converters.

According to the present invention, power control of a plurality of solar cells can be performed individually, and utilization efficiency of the solar cells can be increased to improve power conversion efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of the solar energy power generation system of 1st Embodiment. The electric circuit diagram of a power converter device. It is a wave form diagram for explaining the operation of a power converter, and (a) is a wave form diagram of the 1st conversion output voltage, (b) is a wave form diagram of the 2nd conversion output voltage, (c) is the 3rd conversion output The waveform diagram of a voltage, (d) is a waveform diagram of a combined output voltage and an output voltage. The block diagram of the solar energy power generation system of 2nd Embodiment.

First Embodiment
A power converter according to a first embodiment of the present invention will now be described with reference to the drawings.

The photovoltaic power generation system shown in FIG. 1 has a first solar cell panel SP1, a second solar cell panel SP2, and a third solar cell panel SP3, and is configured of three power grids. The power system connected to the solar power generation system is a commercial power system, and the power source G is AC 200V. Therefore, the total value of the rated output voltages of the first to third solar cell panels SP1 to SP3 is set to be larger than the maximum value (283 V) of the grid voltage.

In the power conversion device of the first embodiment, the output voltage (first output voltage V1) of the first solar cell panel SP1 is set to 100 V, and the output voltage (second output voltage V2) of the second solar cell panel SP2 is 200 V The output voltage (third output voltage V3) of the third solar cell panel SP3 is set to 120V.

The first solar cell panel SP1 includes a plurality of series unit solar cell panels connected in parallel. Each series unit solar panel includes a plurality of unit solar panels connected in series. Each unit solar cell panel includes a plurality of series circuits connected in parallel. Each series circuit has a plurality of solar cell elements connected in series. The first solar cell panel SP1 generates a direct current first output voltage V1 (= 100 V) at the first positive electrode output terminal T1a and the first negative electrode output terminal T1b.

The second solar panel SP2 includes a plurality of series unit solar panels connected in parallel. Each series unit solar panel includes a plurality of unit solar panels connected in series. Each unit solar cell panel includes a plurality of series circuits connected in parallel. Each series circuit has a plurality of solar cell elements connected in series. The second solar cell panel SP2 generates a direct current second output voltage V2 (= 200 V) at the second positive electrode output terminal T2a and the second negative electrode output terminal T2b.

The third solar cell panel SP3 includes a plurality of series unit solar cell panels connected in parallel. Each series unit solar panel includes a plurality of unit solar panels connected in series. Each unit solar cell panel includes a plurality of series circuits connected in parallel. Each series circuit has a plurality of solar cell elements connected in series. The third solar cell panel SP3 generates a direct current third output voltage V3 (= 120 V) at the third positive electrode output terminal T3a and the third negative electrode output terminal T3b.

The first to third solar cell panels SP1 to SP3 are connected to a power conditioner PC for grid connection to the AC 200 V system. The power conditioner PC includes the power conversion device 1 connected to the first to third solar cell panels SP1 to SP3, the filter circuit 2, and the grid connection circuit unit 3.

(Power converter 1)
The power converter 1 includes first to third DC / AC converters 11 to 13 and a control circuit 20.

The first DC / AC converter 11 includes a positive input terminal and a negative input terminal (not shown). The positive electrode input terminal and the negative electrode input terminal are respectively connected to the first positive electrode output terminal T1a and the first negative electrode output terminal T1b of the first solar cell panel SP1. A first output voltage V1 (= 100 V) is supplied to the first DC / AC converter 11 from the first solar cell panel SP1. In addition, a smoothing first capacitor C1 is connected between the positive and negative electrode input terminals of the first DC / AC converter 11. Furthermore, between the positive electrode and the negative electrode input terminal of the first DC / AC converter 11, a first voltage detector DV1 that detects the first output voltage V1 of the first solar cell panel SP1 is connected.

The second DC / AC converter 12 includes a positive input terminal and a negative input terminal which are not shown. The positive electrode input terminal and the negative electrode input terminal are respectively connected to the second positive electrode output terminal T2a and the second negative electrode output terminal T2b of the second solar cell panel SP2. The second DC / AC converter 12 is supplied with a second output voltage V2 (= 200 V) from the second solar cell panel SP2. In addition, a smoothing second capacitor C2 is connected between the positive electrode and the negative electrode input terminal of the second DC / AC converter 12. Between the positive electrode and the negative electrode input terminal of the second DC / AC converter 12, a second voltage detector DV2 that detects the occasional second output voltage V2 of the second solar cell panel SP2 is connected.

The third DC / AC converter 13 includes a positive input terminal and a negative input terminal not shown. The positive electrode input terminal and the negative electrode input terminal are respectively connected to the third positive electrode output terminal T3a and the third negative electrode output terminal T3b of the third solar cell panel SP3. The third output voltage V3 (= 120 V) is supplied to the third DC / AC converter 13 from the third solar cell panel SP3. A smoothing third capacitor C3 is connected between the positive and negative electrode input terminals of the third DC / AC converter 13. Between the positive electrode and the negative electrode input terminal of the third DC / AC converter 13, a third voltage detector DV3 for detecting the occasional third output voltage V3 of the third solar cell panel SP3 is connected.

The first to third DC / AC converters 11 to 13 are connected in series. The first to third DC / AC converters 11 to 13 are serially connected in this order from the positive electrode side to the first DC / AC converter 11, the second DC / AC converter 12, and the third DC / AC converter 13.

Specifically, the first DC / AC converter 11 has a positive output terminal P1a and a negative output terminal P1b. The second DC / AC converter 12 has a positive electrode output terminal P2a and a negative electrode output terminal P2b. The third DC / AC converter 13 has a positive electrode output terminal P3a and a negative electrode output terminal P3b.

The positive electrode output terminal P1a of the first DC / AC converter 11 is connected to the positive electrode input terminal P4a of the filter circuit 2, and the negative electrode output terminal P1b of the first DC / AC converter 11 is a positive electrode output terminal P2a of the second DC / AC converter 12. It is connected to the. The negative output terminal P2b of the second DC / AC converter 12 is connected to the positive output terminal P3a of the third DC / AC converter 13, and the negative output terminal P3b of the third DC / AC converter 13 is the negative input terminal P4b of the filter circuit 2. It is connected to the.

A current detector DI is connected between the negative electrode output terminal P3b of the third DC / AC converter 13 and the negative electrode input terminal P4b of the filter circuit 2. The current detector DI is configured to detect the current It flowing from the power conversion device 1 to the filter circuit 2 at each time.

(1st DC / AC converter 11)
As shown in FIG. 2, the first DC / AC converter 11 includes a bridge circuit having four first to fourth switching elements Q11 to Q14 connected in a bridge shape. The first to fourth switching elements Q11 to Q14 are formed of N-channel MOS transistors, and a body diode D is connected between the sources and drains of the switching elements Q11 to Q14. In the present embodiment, the first to fourth switching elements Q11 to Q14 are embodied as MOS transistors to which a body diode D is connected. This may be implemented by another switching element such as an IGBT (Insulated Gate Bipolar Transistor) in which diodes are connected in parallel.

The first and second switching elements Q11 and Q12 are connected in series, the third and fourth switching elements Q13 and Q14 are connected in series, and the series circuit is connected in parallel.

The first and second switching elements Q11 and Q12 connected in series are connected in series in the order of the first switching element Q11 and the second switching element Q12 from the positive electrode output terminal T1a side. Further, the third and fourth switching elements Q13 and Q14 connected in series are connected in series in the order of the third switching element Q13 and the fourth switching element Q14 from the positive electrode output terminal T1a side. The drain terminals of the first and third switching elements Q11 and Q13 are connected to the positive electrode output terminal T1a. The source terminals of the second and third switching elements Q12 and Q13 are connected to the negative output terminal T1b.

Incidentally, among the first to fourth switching elements Q11 to Q14, the two first and third switching elements Q11 and Q13 on the positive electrode side are referred to as the switching elements of the upper arm. Further, the two second and fourth switching elements Q12 and Q14 on the negative electrode side are referred to as switching elements of the lower arm.

The connection point (node N1) of the first switching element Q11 and the second switching element Q12 is connected to the positive electrode output terminal P1a of the first DC / AC converter 11, and the positive electrode output terminal P1a is the positive electrode input terminal P4a of the filter circuit 2. It is connected to the. The connection point (node N2) of the third switching element Q13 and the fourth switching element Q14 is connected to the negative electrode output terminal P1b of the first DC / AC converter 11, and the negative electrode output terminal P1b is the second DC / AC converter 12 It is connected to the positive electrode output terminal P2a.

The first drive signal CT11 is supplied from the control circuit 20 to the gate terminal of the first switching element Q11. The first switching element Q11 is turned on by the high level first drive signal CT11 and turned off by the low level first drive signal CT11.

The second drive signal CT12 is supplied from the control circuit 20 to the gate terminal of the second switching element Q12. The second switching element Q12 is turned on by the high level second drive signal CT12 and turned off by the low level second drive signal CT12.

The third drive signal CT13 is supplied from the control circuit 20 to the gate terminal of the third switching element Q13. The third switching element Q13 is turned on by the high level third drive signal CT13 and turned off by the low level third drive signal CT13.

The fourth drive signal CT14 is supplied from the control circuit 20 to the gate terminal of the fourth switching element Q14. The fourth switching element Q14 is turned on by the high level fourth drive signal CT14 and turned off by the low level fourth drive signal CT14.

In the first DC / AC converter 11, the first to fourth switching elements Q11 to Q14 are on / off controlled by the control circuit 20. The first DC / AC converter 11 converts the first output voltage V1 (= 100 V) from the first solar cell panel SP1 into a three-stage first converted output voltage Va of “100 V, 0 V, −100 V” It can be supplied between the positive and negative electrode output terminals P1a and P1b.

That is, when the first and fourth switching elements Q11 and Q14 are turned on and the second and third switching elements Q12 and Q13 are turned off, the first converted output voltage Va of 100 V is generated at the positive and negative output terminals P1a and P1b. Be done.

Further, when the first and fourth switching elements Q11 and Q14 are turned off and the second and third switching elements Q12 and Q13 are turned on, the first converted output voltage Va of -100 V is obtained at the positive and negative output terminals P1a and P1b. It is generated.

Furthermore, when the first and third switching elements Q11 and Q13 are turned on and the second and fourth switching elements Q12 and Q14 are turned off, the first converted output voltage Va of 0 V is generated at the positive and negative output terminals P1a and P1b. Be done. Even when the second and fourth switching elements Q12 and Q14 are turned on and the first and third switching elements Q11 and Q13 are turned off, the first converted output voltage Va of 0 V is obtained at the positive and negative output terminals P1a and P1b. It is generated.

(2nd DC / AC converter 12)
As shown in FIG. 2, the second DC / AC converter 12 includes a bridge circuit having four fifth to eighth switching elements Q21 to Q24 connected in a bridge shape. The fifth to eighth switching elements Q21 to Q24 are formed of N-channel MOS transistors, and a body diode D is connected between the sources and drains of the switching elements Q21 to Q24. In the present embodiment, the fifth to eighth switching elements Q21 to Q24 are embodied as MOS transistors to which the body diode D is connected. However, even if other switching elements such as IGBTs having diodes connected in parallel are used. Good.

The fifth and sixth switching elements Q21 and Q22 are connected in series, the seventh and eighth switching elements Q23 and Q24 are connected in series, and the series circuit is connected in parallel.

The fifth and sixth switching elements Q21 and Q22 connected in series are connected in series in the order of the fifth switching element Q21 and the sixth switching element Q22 from the positive electrode output terminal T2a side. The seventh and eighth switching elements Q23 and Q24 connected in series are connected in series in the order of the seventh switching element Q23 and the eighth switching element Q24 from the positive electrode output terminal T2a side. The drain terminals of the fifth and seventh switching elements Q21 and Q23 are connected to the positive electrode output terminal T2a. The source terminals of the sixth and eighth switching elements Q22 and Q24 are connected to the negative output terminal T2b.

Incidentally, among the fifth to eighth switching elements Q21 to Q24, the two fifth and seventh switching elements Q21 and Q23 on the positive electrode side are referred to as switching elements of the upper arm. Also, the two sixth and eighth switching elements Q22 and Q24 on the negative electrode side are referred to as the switching elements of the lower arm.

The connection point (node N3) of the fifth switching element Q21 and the sixth switching element Q22 is connected to the positive electrode output terminal P2a of the second DC / AC converter 12, and the positive electrode output terminal P2a is the negative electrode of the first DC / AC converter 11. It is connected to the output terminal P1b. The connection point (node N4) of the seventh switching element Q23 and the eighth switching element Q24 is connected to the negative electrode output terminal P2b of the second DC / AC converter 12, and the negative electrode output terminal P2b is the third DC / AC converter 13 It is connected to the positive electrode output terminal P3a.

The gate terminal of the fifth switching element Q21 is supplied with a fifth drive signal CT21 from the control circuit 20. The fifth switching element Q21 is turned on by the high level fifth drive signal CT21 and turned off by the low level fifth drive signal CT21.

The control circuit 20 supplies a sixth drive signal CT22 to the gate terminal of the sixth switching element Q22. The sixth switching element Q22 is turned on by the high level sixth drive signal CT22 and turned off by the low level sixth drive signal CT22.

The seventh drive signal CT23 is supplied from the control circuit 20 to the gate terminal of the seventh switching element Q23. The seventh switching element Q23 is turned on by the high level seventh drive signal CT23 and turned off by the low level seventh drive signal CT23.

The eighth drive signal CT24 is supplied from the control circuit 20 to the gate terminal of the eighth switching element Q24. The eighth switching element Q24 is turned on by the high level eighth drive signal CT24 and turned off by the low level eighth drive signal CT24.

In the second DC / AC converter 12, the fifth to eighth switching elements Q21 to Q24 are on / off controlled by the control circuit 20. The second DC / AC converter 12 converts the second output voltage V2 (= 200 V) from the second solar cell panel SP2 into a three-stage second converted output voltage Vb of “200 V, 0 V, −200 V”. The positive and negative electrode output terminals P2a and P2b can be generated.

That is, when the fifth and eighth switching elements Q21 and Q24 turn on and the sixth and seventh switching elements Q22 and Q23 turn off, the second converted output voltage Vb of 200 V is generated at the positive and negative output terminals P2a and P2b. Be done.

When the fifth and eighth switching elements Q21 and Q24 are turned off and the sixth and seventh switching elements Q22 and Q23 are turned on, the second converted output voltage Vb of -200 V is obtained at the positive and negative output terminals P2a and P2b. It is generated.

Furthermore, when the fifth and seventh switching elements Q21 and Q23 turn on and the sixth and eighth switching elements Q22 and Q24 turn off, a second converted output voltage Vb of 0 V is generated at the positive and negative output terminals P2a and P2b. Be done. Even when the sixth and eighth switching elements Q22 and Q24 are turned on and the fifth and seventh switching elements Q21 and Q23 are turned off, the second converted output voltage Vb of 0 V is obtained at the positive and negative output terminals P2a and P2b. It is generated.

(3rd DC / AC converter 13)
As shown in FIG. 2, the third DC / AC converter 13 has a bridge circuit-like circuit configuration and includes four ninth to twelfth switching elements Q31 to Q34. The ninth to twelfth switching elements Q31 to Q34 are formed of N-channel MOS transistors, and a body diode D is connected between the sources and drains of the switching elements Q31 to Q34. In the present embodiment, the ninth to twelfth switching elements Q31 to Q34 are embodied as the MOS transistors to which the body diode D is connected, but even if they are implemented by other switching elements such as IGBTs in which the diodes are connected in parallel Good.

The ninth and tenth switching elements Q31 and Q32 are connected in series, the eleventh and twelfth switching elements Q33 and Q34 are connected in series, and the series circuit is connected in parallel.

The ninth and tenth switching elements Q31 and Q32 connected in series are connected in series in the order of a ninth switching element Q31 and a tenth switching element Q32 from the positive electrode output terminal T3a side. The eleventh and twelfth switching elements Q33 and Q34 connected in series are connected in series in the order of an eleventh switching element Q33 and a twelfth switching element Q34 from the positive electrode output terminal T3a side. The drain terminals of the ninth and eleventh switching elements Q31 and Q33 are connected to the positive output terminal T3a. The source terminals of the ninth and eleventh switching elements Q31 and Q33 are connected to the negative output terminal T3b.

Incidentally, among the ninth to twelfth switching elements Q31 to Q34, the two ninth and eleventh switching elements Q31 and Q33 on the positive electrode side are referred to as the switching elements of the upper arm. The two tenth and twelfth switching elements Q32 and Q34 on the negative electrode side are referred to as switching elements of the lower arm.

The connection point (node N5) of the ninth switching element Q31 and the tenth switching element Q32 is connected to the positive electrode output terminal P3a of the third DC / AC converter 13, and the positive electrode output terminal P3a is the negative electrode of the second DC / AC converter 12. It is connected to the output terminal P2b. Further, the connection point (node N6) of the eleventh switching element Q33 and the twelfth switching element Q34 is connected to the negative output terminal P3b of the third DC / AC converter 13, and the negative output terminal P3b is connected via the current detector DI. The negative input terminal P4 b of the filter circuit 2 is connected.

The control circuit 20 supplies a ninth drive signal CT31 to the gate terminal of the ninth switching element Q31. The ninth switching element Q31 is turned on by a high level ninth drive signal CT31 and turned off by a low level ninth drive signal CT31.

The tenth drive signal CT32 is supplied from the control circuit 20 to the gate terminal of the tenth switching element Q32. The tenth switching element Q32 is turned on by the high level tenth drive signal CT32 and turned off by the low level tenth drive signal CT32.

An eleventh drive signal CT33 is supplied from the control circuit 20 to the gate terminal of the eleventh switching element Q33. The eleventh switching element Q33 is turned on by a high level eleventh drive signal CT33 and turned off by a low level eleventh drive signal CT33.

The control circuit 20 supplies a twelfth drive signal CT34 to the gate terminal of the twelfth switching element Q34. The twelfth switching element Q34 is turned on by a high level twelfth drive signal CT34 and turned off by a low level twelfth drive signal CT34.

In the third DC / AC converter 13, the ninth to twelfth switching elements Q 31 to Q 34 are on / off controlled by the control circuit 20. The third DC / AC converter 13 converts the third output voltage V3 (= 120 V) from the third solar cell panel SP3 into a third conversion output voltage Vc of three stages of “120 V, 0 V, −120 V” The positive and negative electrode output terminals P3a and P3b can be generated.

That is, when the ninth and twelfth switching elements Q31, Q34 are turned on and the tenth and eleventh switching elements Q32, Q33 are turned off, the third converted output voltage Vc of 120 V is generated at the positive and negative output terminals P3a, P3b. Be done.

When the ninth and twelfth switching elements Q31 and Q34 are turned off and the tenth and eleventh switching elements Q32 and Q33 are turned on, the third converted output voltage Vc of -120 V is obtained at the positive and negative output terminals P3a and P3b. It is generated.

Furthermore, when the ninth and eleventh switching elements Q31 and Q33 turn on and the tenth and twelfth switching elements Q32 and Q34 turn off, a third converted output voltage Vc of 0 V is generated at the positive and negative output terminals P3a and P3b. Be done. Even when the tenth and twelfth switching elements Q32 and Q34 are turned on and the ninth and eleventh switching elements Q31 and Q33 are turned off, the third converted output voltage Vc of 0 V is obtained at the positive and negative output terminals P3a and P3b. It is generated.

As shown in FIG. 2, the first to third DC / AC converters 11 to 13 configured in this manner are connected in series. Therefore, the first to third converted output voltages Va, Vb and Vc of the first to third DC / AC converters 11 to 13 are superimposed. The superimposed combined output voltage Vt indicated by the alternate long and short dash line in FIG. 3D is filtered from the positive electrode output terminal P1a of the first DC / AC converter 11 and the negative electrode output terminal P3b of the third DC / AC converter 13. Supplied to

The power converter 1 includes a control circuit 20.

The control circuit 20 controls the first to third DC / AC converters to generate an output voltage Vo having a sine waveform W1 shown by a solid line in FIG. 3D at the positive and negative output terminals P5a and P5b of the filter circuit 2. Control 11 to 13. That is, the control circuit 20 drives the first to twelfth switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 of the first to third DC / AC converters 11 to 13. CT11 to CT14, CT21 to CT24, and CT31 to CT34 are generated.

More specifically, for the first DC / AC converter 11, the control circuit 20 generates, from the first output voltage V1, a first conversion output voltage Va having two levels shown in FIG. 3A. First to fourth drive signals CT11 to CT14 are generated.

Further, for the second DC / AC converter 12, the control circuit 20 generates a fifth conversion output voltage Vb of three levels shown in FIG. 3B from the second output voltage V2. To generate eighth to eighth drive signals CT21 to CT24.

Furthermore, for the third DC / AC converter 13, the control circuit 20 generates a ninth converted output voltage Vc of two levels shown in FIG. 3C from the third output voltage V3. And 12th drive signals CT31 to CT34 are generated.

In the present embodiment, the output voltage Vo having the sine waveform W1 supplied from the filter circuit 2 shown by the solid line in FIG. 3D has the same frequency and output voltage as that of the AC 200 V system for grid connection. Therefore, the frequency of the output voltage Vo of the sine waveform W1 is determined by the AC 200 V system that is grid-connected. Then, time t0 to time t6 which is one cycle T of the output voltage Vo of the sine waveform W1 are determined in advance by the frequency of the AC 200 V system which is grid-connected.

Then, the control circuit 20 controls the first to third DC / AC converters 11 to 13 individually in time series, and the first to third DC / AC converters 11 to 13 obtained in time series are controlled. A combined output voltage Vt is generated by superimposing the first to third converted output voltages Va to Vc. Therefore, the control circuit 20 needs to generate a combined output voltage Vt for generating an output voltage Vo having a sine waveform W1 supplied from the filter circuit 2 shown by a solid line in FIG. 3D.

Further, when generating the combined output voltage Vt, the control circuit 20 divides the first to third DC / AC converters 11 to 13 into low frequency groups and high frequency groups. In this embodiment, the second DC / AC converter 12 is divided into low frequency groups, and the first and third DC / AC converters 11 and 13 are divided into high frequency groups.

The control circuit 20 operates the fifth to eighth switching elements Q21 to Q24 of the second DC / AC converter 12 of the low frequency group at a low frequency (100%). On the other hand, the control circuit 20 includes first to fourth switching elements Q11 to Q14 of the first DC / AC converter 11 in the high frequency group and ninth to twelfth switching elements Q31 to Q34 of the third DC / AC converter To operate at high frequency.

Here, the condition that belongs to the low frequency group and the high frequency group is that the low frequency group includes one DC / AC converter, the high frequency group includes two DC / AC converters, and the total output voltage of the low frequency group Is smaller than the total output voltage of the high frequency group.

Further, the control circuit 20 is supplied with first to third voltage detection signals SV1 to SV3 from the first to third voltage detectors DV1 to DV3. The control circuit 20 detects the first output voltage V1 of the first solar cell panel SP1 at that time based on the first voltage detection signal SV1 from the first voltage detector DV1. The control circuit 20 detects the second output voltage V2 of the second solar cell panel SP2 at that time based on the second voltage detection signal SV2 from the second voltage detector DV2. The control circuit 20 detects the third output voltage V3 of the third solar cell panel SP3 at that time based on the third voltage detection signal SV3 from the third voltage detector DV3.

The control circuit 20 receives the current detection signal SI from the current detector DI. The control circuit 20 detects the current It flowing through the filter circuit 2 based on the current detection signal SI from the current detector DI.

The control circuit 20 generates first to third output powers PW1 (= V1 × It) of the first to third solar cell panels SP1 to SP3 from the first to third output voltages V1 to V3 and the current It calculated at each time. , PW2 (= V2 × It), and PW3 (= V3 × It) are respectively calculated.

The control circuit 20 controls the first to third solar cell panels SP1 to SP3 based on the first to third output powers PW1, PW2, and PW3 of the first to third solar cell panels SP1 to SP3 obtained each time. An operation for maximum power point tracking (MPPT) control is performed each time. In the calculation for the maximum power point tracking (MPPT: Maixmum Power Point Track Inng) control, in the present embodiment, the maximum power point is determined for each of the first to third solar cell panels SP1 to SP3 by the hill climbing method. The control circuit 20 controls on / off of the first to twelfth switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 of the first to third DC / AC converters 11 to 13 so as to obtain the determined maximum power point. (Duty control) is configured.

The control performed by the control circuit 20 on the first to third DC / AC converters 11 to 13 will be described below.

(1st DC / AC converter 11)
The first DC / AC converter 11 belongs to a high frequency group and is duty controlled at high frequency as shown in FIG. 3 (a). More specifically, the control circuit 20 controls the first DC / AC converter 11 such that the first half cycle (time t0 to t3) of one cycle T is between 0 V and 100 V, and the first converted output voltage Va is a high frequency. The first to fourth drive signals CT11 to CT14 whose duty is controlled are generated. Further, the control circuit 20 performs duty control of the first converted output voltage Va at a high frequency with respect to the first DC / AC converter 11 with the remaining second half cycle (time t3 to t6) between 0 volt and -100 V. First to fourth drive signals CT11 to CT14 are generated.

In the present embodiment, the occasional high frequency duty control for the first DC / AC converter 11 is performed by using the maximum of the first solar cell panel SP1 calculated by the control circuit 20 using the first output power PW1 of the first solar cell panel SP1. The duty ratio is determined based on the power point.

(2nd DC / AC converter 12)
The second DC / AC converter 12 belongs to the low frequency group and is duty controlled at low frequency as shown in FIG. 3 (b). More specifically, the control circuit 20 controls the second DC / AC converter 12 to switch the level of the second converted output voltage Vb in three steps at a predetermined timing in one cycle T. Here, the timing of switching the level of the second converted output voltage Vb is determined by the AC 200 V system commercial frequency that is grid-connected, and is the timing at which the output voltage Vo of the sine waveform W1 passes 200 V and -200 V .

As shown in FIGS. 3B and 3D, the half cycle of the sine waveform W1 of the output voltage Vo is set to time t3 at times t0 to t6. When one cycle T is equally divided into eight and time t0 is used as a reference, time of T / 8 cycle is time t1, time of 3T / 8 cycle is time t2, and time of 5T / 8 cycle is time t4. And the time of the 7T / 8 cycle is time t5.

Time t1 is timing when the output voltage Vo of the sine waveform W1 passes the level of 200 V toward the maximum value.

Further, time t2 is timing when the output voltage Vo of the sine waveform W1 passes a level of 200 V toward 0 volt.

Further, time t4 is the timing when the output voltage Vo of the sine waveform W1 passes the level of -200 V toward the minimum value.

Furthermore, time t5 is the timing when the output voltage Vo of the sine waveform W1 passes the level of -200 V toward 0 volt.

The control circuit 20 generates fifth to eighth drive signals CT21 to CT24 maintaining the second converted output voltage Vb at 0 V from time t0 to t1. Subsequently, the control circuit 20 generates fifth to eighth drive signals CT21 to CT24 maintaining the second converted output voltage Vb at 200 V from time t1 to t2. Next, the control circuit 20 generates fifth to eighth drive signals CT21 to CT24 which maintain the second converted output voltage Vb at 0 V from time t2 to t4. Subsequently, the control circuit 20 generates fifth to eighth drive signals CT21 to CT24 maintaining the second converted output voltage Vb at -200 V from time t4 to t5. Finally, the control circuit 20 generates fifth to eighth drive signals CT21 to CT24 maintaining the second converted output voltage Vb at 0 V from time t5 to t6 (= t0).

(3rd DC / AC converter 13)
The third DC / AC converter 13 belongs to a high frequency group and is duty controlled at high frequency as shown in FIG. 3 (c). More specifically, the control circuit 20 controls the third DC / AC converter 13 so that the first conversion period V (time t0 to t3) is between 0 V and 100 V, and the third converted output voltage Vc is high frequency First to fourth drive signals CT11 to CT14 to be controlled are generated. Further, the control circuit 20 performs duty control of the third converted output voltage Vc at a high frequency with respect to the third DC / AC converter 13 with the remaining second half cycle (time t3 to t6) between 0 volt and -100 V. First to fourth drive signals CT11 to CT14 are generated.

In the present embodiment, the occasional high frequency duty control for the third DC / AC converter 13 is the maximum of the third solar cell panel SP3 calculated by the control circuit 20 using the third output power PW3 of the third solar cell panel SP3. The duty ratio is determined based on the power point.

The control circuit 20 drives and controls the first to third DC / AC converters 11 to 13 in time series between time t0 to t6 to make time series of the first to third converted output voltages Va to Vc. Generated on The first to third converted output voltages Va to Vc generated in time series are superimposed to form a combined output voltage Vt having a waveform shown by an alternate long and short dash line in FIG. Ru.

(Filter circuit 2)
As shown in FIG. 1, the filter circuit 2 has a first alternating current reactor L1, a second alternating current reactor L2, and a smoothing capacitor Cx. One end of the first AC reactor L1 is connected to the positive electrode output terminal P1a of the first DC / AC converter 11 via the positive electrode input terminal P4a. One end of the second AC reactor L2 is connected to the negative electrode output terminal P3b of the third DC / AC converter 13 via the negative electrode input terminal P4b and the current detector DI. The smoothing capacitor Cx is connected between the positive electrode output terminal P5a and the negative electrode output terminal P5b of the filter circuit 2.

The filter circuit 2 is generated between the positive and negative electrode input terminals P4a and P4b and between the positive electrode output terminal P1a of the first DC / AC converter 11 and the negative electrode output terminal P3b of the third DC / AC converter 13 (FIG. 3D) A combined output voltage Vt indicated by a one-dot chain line is input. The filter circuit 2 averages the input combined output voltage Vt and outputs an output voltage Vo having a sine waveform W1 shown by a solid line in FIG. 3D from the positive and negative output terminals P5a, P5b. It supplies to the grid connection circuit unit 3 via P5a and P5b.

(Network connection circuit unit 3)
The grid connection circuit unit 3 receives an output voltage Vo having a sine waveform W1 from the filter circuit 2 and supplies a current with a power factor of approximately 1 to the wiring of the AC 200 V system. Power is supplied to the load Z of the AC 200 V system.

Next, the operation of the power conversion device 1 configured as described above will be described.

Now, the control circuit 20 generates from the filter circuit 2 a combined output voltage Vt shown by an alternate long and short dash line in FIG. 3 (d) for generating an output voltage Vo having a sine waveform W1 shown by a solid line in FIG. 3 (d). Control of the first to third DC / AC converters 11 to 13 is started.

(Time t0 to t1)
The control circuit 20 performs duty control of the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at high frequency, and performs duty control of the first conversion output at a level between 0 V and 100 V. Generate voltage Va.

That is, between time t0 and t1, the third switching element Q13 is turned off and the fourth switching element Q14 is turned on. The first switching element Q11 and the second switching element Q12 are complementarily turned on and off.

Incidentally, when the first switching element Q11 is turned on and the second switching element Q12 is turned off, the first converted output voltage Va is 100V. Conversely, when the first switching element Q11 is turned off and the second switching element Q12 is turned on, the first converted output voltage Va becomes 0V.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 to generate a second converted output voltage Vb maintained at 0V. That is, between the time t0 and t1, the fifth and seventh switching elements Q21 and Q23 are turned off, and the sixth and eighth switching elements Q22 and Q24 are turned on.

Furthermore, the control circuit 20 performs duty control of the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at a high frequency to perform duty control at a level between 0 V and 120 V. A conversion output voltage Vc is generated.

That is, between time t0 and t1, the eleventh switching element Q33 is turned off and the twelfth switching element Q34 is turned on. The ninth switching element Q31 and the tenth switching element Q32 are complementarily turned on and off.

Incidentally, when the ninth switching element Q31 is turned on and the tenth switching element Q32 is turned off, the third converted output voltage Vc becomes 120V. On the other hand, when the ninth switching element Q31 is turned off and the tenth switching element Q32 is turned on, the third converted output voltage Vc becomes 0V.

Therefore, the power conversion device 1 generates a combined output voltage Vt of a waveform obtained by adding the first to third converted output voltages Va to Vc at times t0 to t1, as shown by the one-dot chain line in FIG. Output.

(Time t1 to t2)
The control circuit 20 performs duty control on the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at a high frequency, similarly to time t0 to t1, to a level between 0 V and 100 V. A duty-controlled first converted output voltage Va is generated.

That is, during the period from time t1 to t2, the third switching element Q13 is turned off and the fourth switching element Q14 is turned on. Similar to time t0 to t1, the first switching element Q11 and the second switching element Q12 are complementarily turned on and off.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 to generate a second converted output voltage Vb maintained at 200V. That is, between time t1 and t2, the fifth and eighth switching elements Q21 and Q24 are turned on, and the sixth and seventh switching elements Q22 and Q23 are turned off.

Furthermore, the control circuit 20 performs duty control of the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at a high frequency as in the time t0 to t1 to set between 0V and 120V. A third conversion output voltage Vc duty-controlled at the level is generated.

That is, between time t1 and t2, the eleventh switching element Q33 is turned off and the twelfth switching element Q34 is turned on. Similar to time t0 to t1, the ninth switching element Q31 and the tenth switching element Q32 are complementarily turned on and off.

Therefore, the power conversion device 1 generates the combined output voltage Vt of the waveform obtained by adding the first to third converted output voltages Va to Vc at times t1 to t2, as shown by the one-dot chain line in FIG. Output.

(Time t2 to t3)
The control circuit 20 performs duty control on the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at a high frequency, as at times t0 to t2, to a level between 0 V and 100 V. A duty-controlled first converted output voltage Va is generated.

That is, between time t2 and t3, the third switching element Q13 is turned off and the fourth switching element Q14 is turned on. Then, as in the times t0 to t2, the first switching element Q11 and the second switching element Q12 are complementarily turned on and off.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 to generate a second converted output voltage Vb maintained at 0V. That is, between time t2 and t3, the fifth and seventh switching elements Q21 and Q23 are turned off and the sixth and eighth switching elements Q22 and Q24 are turned on as in the time t0 to t1.

Furthermore, the control circuit 20 performs duty control of the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at high frequency similarly to the time t0 to t2, and the voltage is between 0V and 120V. A third conversion output voltage Vc duty-controlled at the level is generated.

That is, between time t2 and t3, the eleventh switching element Q33 is turned off and the twelfth switching element Q34 is turned on. Similar to times t0 to t2, the ninth switching element Q31 and the tenth switching element Q32 are complementarily turned on and off.

Therefore, the power conversion device 1 generates a combined output voltage Vt of a waveform obtained by adding the first to third converted output voltages Va to Vc at times t2 to t3, as shown by the alternate long and short dash line in FIG. Output.

(Time t3 to t4)
The control circuit 20 performs duty control of the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at a high frequency to perform duty control at a level between 0 V and -100 V. An output voltage Va is generated.

That is, between time t3 and t4, the first switching element Q11 is turned off and the second switching element Q12 is turned on. The third switching element Q13 and the fourth switching element Q14 are complementarily turned on and off.

Incidentally, when the third switching element Q13 is turned on and the fourth switching element Q14 is turned off, the first converted output voltage Va becomes -100V. Conversely, when the third switching element Q13 is turned off and the fourth switching element Q14 is turned on, the first converted output voltage Va becomes 0V.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 like the time t2 to t3 to maintain the second converted output voltage maintained at 0 V. Generate Vb. That is, between times t3 and t4, the fifth and seventh switching elements Q21 and Q23 are turned off and the sixth and eighth switching elements Q22 and Q24 are turned on, as in the times t2 to t3.

Furthermore, the control circuit 20 performs duty control of the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at a high frequency to perform duty control at a level between 0 V and -120 V. 3 Generate a converted output voltage Vc.

That is, during the time t3 to t4, the ninth switching element Q31 is turned off and the tenth switching element Q32 is turned on. The eleventh switching element Q33 and the twelfth switching element Q34 are complementarily turned on and off.

Incidentally, when the eleventh switching element Q33 is turned on and the twelfth switching element Q34 is turned off, the third converted output voltage Vc becomes -120V. On the other hand, when the eleventh switching element Q33 is turned off and the twelfth switching element Q34 is turned on, the third converted output voltage Vc becomes 0V.

Therefore, the power conversion device 1 generates the combined output voltage Vt of the waveform obtained by adding the first to third converted output voltages Va to Vc at times t3 to t4, as shown by the alternate long and short dash line in FIG. Output.

(Time t4 to t5)
The control circuit 20 performs duty control on the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at high frequency similarly to the time t3 to t4, and the level between 0 V and -100 V To generate the first conversion output voltage Va that is duty controlled.

That is, between time t4 and t5, the first switching element Q11 is turned off and the second switching element Q12 is turned on. Then, the third switching element Q13 and the fourth switching element Q14 are complementarily turned on / off as in the time t3 to the time t4.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 to generate a second converted output voltage Vb maintained at -120V. That is, between time t4 and t5, the sixth and seventh switching elements Q22 and Q23 are turned on, and the fifth and eighth switching elements Q21 and Q24 are turned on.

Furthermore, the control circuit 20 performs duty control on the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at a high frequency as in the time t3 to t4, and between 0V and -120V. To generate a third conversion output voltage Vc that is duty controlled at the level of

That is, during the period from time t4 to t5, the ninth switching element Q31 is turned off and the tenth switching element Q32 is turned on. Then, the eleventh switching element Q33 and the twelfth switching element Q34 are complementarily turned on / off as in the time t3 to t4.

Therefore, the power conversion device 1 generates the combined output voltage V of the waveform obtained by adding the first to third converted output voltages Va to Vc at times t4 to t5, as indicated by the one-dot chain line in FIG. Output.

(Time t5 to t6)
The control circuit 20 performs duty control on the first to fourth switching elements Q11 to Q14 with respect to the first DC / AC converter 11 at high frequency similarly to the time t3 to t5, and sets the level between 0V and -100V. To generate the first conversion output voltage Va that is duty controlled.

That is, between time t5 and t6, the first switching element Q11 is turned off and the second switching element Q12 is turned on. Then, as in the times t3 to t5, the third switching element Q13 and the fourth switching element Q14 are complementarily turned on and off.

Further, the control circuit 20 controls the fifth to eighth switching elements Q21 to Q28 with respect to the second DC / AC converter 12 to generate a second converted output voltage Vb maintained at 0V. That is, between time t5 and t6, the fifth and seventh switching elements Q21 and Q23 are turned off, and the sixth and eighth switching elements Q22 and Q24 are turned on.

Furthermore, the control circuit 20 performs duty control of the ninth to twelfth switching elements Q31 to Q34 with respect to the third DC / AC converter 13 at high frequency similarly to the time t3 to t5 to between 0V and -120V. To generate a third conversion output voltage Vc that is duty controlled at the level of

That is, during the period from time t5 to time t6, the ninth switching element Q31 is turned off and the tenth switching element Q32 is turned on. Then, as in the case of time t3 to time t5, the eleventh switching element Q33 and the twelfth switching element Q34 are complementarily turned on and off.

Therefore, the power conversion device 1 generates a combined output voltage Vt of a waveform obtained by adding the first to third converted output voltages Va to Vc at times t5 to t6, as indicated by the one-dot chain line in FIG. Output.

As described above, the control circuit 20 sets the time t0 to t6 as one cycle T, and the first to twelfth switching elements Q11 to Q14, Q21 to Q24, Q31 to Q34 of the first to third DC / AC converters 11 to 13. Drive control repeatedly in time series. Then, the power conversion device 1 repeatedly generates a combined output voltage Vt having a waveform indicated by a dashed dotted line in FIG. 3D and supplies the combined output voltage Vt to the filter circuit 2.

The filter circuit 2 inputs and averages the combined output voltage Vt, and supplies an output voltage Vo of a sine waveform W1 shown by a solid line in FIG.

Next, the effects of the embodiment configured as described above will be described below.

(1) According to the first embodiment, the power conversion device 1 transmits the first to third DC / DC converters individually without using DC / DC converters for the first to third solar cell panels SP1 to SP3. AC converters 11 to 13 were connected respectively. The first to third DC / AC converters 11 to 13 are connected in series, and the first to third conversion output voltages Va to Vc supplied from the first to third DC / AC converters 11 to 13 are superimposed and synthesized. An output voltage Vt was generated.

Therefore, in the power conversion device 1, the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 are directly supplied to the first to third DC / AC converters 11 to 13. As a result, it is not necessary to consider the loss in the DC / DC converter, and the efficiency of the solar power generation system can be improved.

In addition, the first to third DC / AC converters 11 to 13 provided in the first to third solar cell panels SP1 to SP3 respectively have maximum power points individually for the corresponding solar cell panels in the control circuit 20. Followed control is performed. Therefore, it is possible to realize a solar power generation system with higher utilization efficiency and high power conversion efficiency.

(2) According to the first embodiment, the first DC / AC converter 11 for the first solar cell panel SP1 and the third DC / AC converter 13 for the third solar cell panel SP3 are duty controlled at high frequency, First and third converted output voltages Va and Vc are generated. On the other hand, the second DC / AC converter 12 for the second solar cell panel SP2 is duty-controlled (100%) at a low frequency to generate a second converted output voltage Vb.

Therefore, by reducing the number of operations of the second DC / AC converter 12, the conversion efficiency of power can be increased.

(3) According to the first embodiment, the first conversion output voltage Va of two steps is generated by the first DC / AC converter 11, and the second conversion output voltage Vb of three steps is generated by the second DC / AC converter 12, The second DC / AC converter 13 generates a two-stage third converted output voltage Vc. Then, the first to third converted output voltages Va to Vc are combined in time series to generate a combined output voltage Vt indicated by a one-dot chain line in FIG. 3D at seven levels.

Therefore, the voltage change amount of the combined output voltage Vt can be reduced. As a result, it is possible to reduce the loss in the first and second AC reactors L1, L2 of the filter circuit 2 to which the combined output voltage Vt is supplied.

(4) According to the first embodiment, the first to third DC / AC converters 11 to 13 are divided into the low frequency group and the high frequency group. The second DC / AC converter 12 of the second solar panel SP2 generates a second output voltage V2 higher than the first and third output voltages V1 and V3 of the first and third solar panels SP1 and SP3. , Divided into low frequency groups.

Therefore, since the second output voltage V2 having a high voltage is duty-controlled (100%) at a low frequency by the second DC / AC converter 12, the switching loss due to the high voltage can be reduced, and the power conversion device 1 is very It has high efficiency.

Second Embodiment
Hereinafter, a power conversion device according to a second embodiment of the present invention will be described with reference to FIG.

The power conversion device of the second embodiment has a feature in which a new configuration is partially added to the configuration of the power conversion device 1 of the first embodiment. Therefore, the added configuration will be described in detail, and the description of the common components will be omitted for the sake of convenience.

In FIG. 4, a step-up converter is provided between a connection point (node N7) between the positive electrode input terminal of the first DC / AC converter 11 and the first capacitor C1 and the first positive electrode output terminal T1a of the first solar cell panel SP1. A first DC / DC converter 21 configured is provided. The first changeover switch SW1 is connected in parallel to the first DC / DC converter 21.

The first changeover switch SW1 includes an N channel MOS transistor. In the first changeover switch SW1, the gate circuit is supplied with the first changeover signal SG1 from the control circuit 20. The first changeover switch SW1 is turned on when the high level first switching signal SG1 is supplied, and is turned off when the low level first switching signal SG1 is supplied. When the first changeover switch SW1 is turned on, the first output voltage V1 of the first solar cell panel SP1 is directly supplied to the first DC / AC converter 11 via the first changeover switch SW1. Conversely, when the first changeover switch SW1 is turned off, the first output voltage V1 of the first solar cell panel SP1 is supplied to the first DC / AC converter 11 via the first DC / DC converter 21.

Further, a boost converter is formed between a connection point (node N8) between the positive electrode input terminal of the second DC / AC converter 12 and the second capacitor C2 and the second positive electrode output terminal T2a of the second solar cell panel SP2. A second DC / DC converter 22 is provided. A second changeover switch SW2 is connected in parallel to the second DC / DC converter 22.

The second switch SW2 includes an N channel MOS transistor. In the second changeover switch SW2, a second changeover signal SG2 is supplied from the control circuit 20 to the gate terminal. The second changeover switch SW2 turns on when the high level second switching signal SG2 is supplied, and turns off when the low level second switching signal SG2 is supplied. When the second changeover switch SW2 is turned on, the second output voltage V2 of the second solar cell panel SP2 is directly supplied to the second DC / AC converter 12 via the second changeover switch SW2. Conversely, when the second changeover switch SW2 is turned off, the second output voltage V2 of the second solar cell panel SP2 is supplied to the second DC / AC converter 12 via the second DC / DC converter 22.

A third boost converter is connected between a connection point (node N9) between the positive input terminal of the third DC / AC converter 13 and the third capacitor C3 (node N9) and the third positive output terminal T3a of the third solar cell panel SP3. A 3DC / DC converter 23 is provided. A third changeover switch SW3 is connected in parallel to the third DC / DC converter 23.

The third switch SW3 includes an N-channel MOS transistor. In the third changeover switch SW3, the third changeover signal SG3 is supplied from the control circuit 20 to the gate terminal. The third switch SW3 is turned on when the high level third switch signal SG3 is supplied, and is turned off when the low level third switch signal SG3 is shared. When the third switch SW3 is turned on, the third output voltage V3 of the third solar cell panel SP3 is directly supplied to the third DC / AC converter 13 through the third switch SW3. Conversely, when the third switch SW3 is turned off, the third output voltage V3 of the third solar cell panel SP3 is supplied to the third DC / AC converter 13 via the third DC / DC converter 23.

In the present embodiment, the first to third changeover switches SW1 to SW3 are embodied by N channel MOS transistors. However, the first to third changeover switches SW1 to SW3 may be implemented by switching devices such as IGBTs or relays having a slow switching speed.

The control circuit 20 calculates the total of the first to third output voltages V1 to V3 calculated from the detection signals SV1 to SV3 of the first to third voltage detectors DV1 to DV3 corresponding to the AC 200 V system. It is determined whether it is 283 V (maximum value). That is, the control circuit 20 determines whether or not the total voltage is less than or equal to the maximum value because the total voltage deviates from a predetermined voltage band exceeding the maximum value of the AC 200 V system predetermined.

When the total voltage of the first to third output voltages V1 to V3 becomes 283 V or less, the control circuit 20 sets the first to third switching signals SG1 to SG1 to the low level to the first to third changeover switches SW1 to SW3. By supplying SG3 respectively, the first to third changeover switches SW1 to SW3 are turned off.

That is, for example, there is a possibility that the total voltage of the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 may be 283 V or less because the sun is behind. In this case, the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 are supplied to the first to third DC / DC converters 21 to 23, respectively. The control circuit 20 drives and controls the first to third DC / DC converters 21 to 23 to boost the first to third output voltages V1 to V3 so that the total voltage exceeds 283 V. The third DC / AC converters 11 to 13 are respectively supplied. Similar to the first embodiment, the control circuit 20 drives and controls the first to third DC / AC converters 11 to 13 to generate a combined output voltage Vt based on the first to third output voltages V1 to V3. Generate

On the other hand, when the total voltage of the first to third output voltages V1 to V3 exceeds 283 V, the control circuit 20 performs the first to third high levels with respect to the first to third changeover switches SW1 to SW3. The switching signals SG1 to SG3 are supplied to turn on the first to third switching switches SW1 to SW3. The control circuit 20 directly supplies the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 to the first to third DC / AC converters 11 to 13, respectively. The control circuit 20 drives and controls the first to third DC / AC converters 11 to 13 to generate a combined output voltage Vt, as in the first embodiment.

In addition, the control circuit 20 controls the second output voltage V2 of the second solar cell panel SP2 of the low frequency group to the first and third output voltages V1 and V3 of the first and third solar panels SP1 and SP3 of the high frequency group. Determine if it has become greater than the total voltage of That is, the second output voltage V2 has the first and third output voltages V1 and V3 out of a predetermined voltage range in which the second output voltage V2 exceeds the total voltage of the first and third output voltages V1 and V3 determined in advance. Determine if it has become greater than the total voltage.

When the second output voltage V2 becomes larger than the total voltage of the first and third output voltages V1 and V3, the control circuit 20 sets the second output voltage V2 to the first and third output voltages V1 and V3. Control to be smaller than the total voltage. That is, the control circuit 20 supplies the first output voltage V1 of the first solar cell panel SP1 to the first DC / DC converter 21 to boost it. Specifically, the control circuit 20 turns off the first changeover switch SW1 and boosts the first output voltage V1 of the first DC / DC converter 21.

In addition, even if the first output voltage V1 of the first DC / DC converter 21 is boosted, the second output voltage V2 may be larger than the total voltage of the first and third output voltages V1 and V3. In this case, the control circuit 20 turns off the third changeover switch SW3 to boost the third output voltage of the third DC / DC converter 23.

In the present embodiment, although the first output voltage V1 is boosted first, the third output voltage V3 may be boosted first. Further, the first output voltage V1 and the third output voltage V3 may be simultaneously boosted.

Next, the operation of the second embodiment configured as described above will be described.

If the total voltage of the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 exceeds 283 V, the control circuit 20 operates the first to third changeover switches SW1 to SW3. Turn on. That is, when the total voltage of the first to third output voltages V1 to V3 exceeds 283 V which is the maximum value of the AC 200 V system, the first to third output voltages V1 to V3 are switched to the first to third changeover switches SW1 to The respective first to third DC / AC converters 11 to 13 are supplied via SW3. Then, the same control as in the first embodiment is performed to generate a combined output voltage Vt.

When the total voltage of the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 is 283 V or less, the control circuit 20 turns off the first to third changeover switches SW1 to SW3. Let That is, when the total voltage of the first to third output voltages V1 to V3 becomes 283 V or less, which is the maximum value of 200 V AC, the first to third DC / DC converters can output the first to third output voltages V1 to V3. Feed to 21-23.

The control circuit 20 drives and controls the first to third DC / DC converters 21 to 23 such that the total voltage of the first to third output voltages V1 to V3 exceeds 283 V, and the first to third output voltages are controlled. Boost V1 to V3. The first to third output voltages V1 to V3 boosted by the first to third DC / DC converters 21 to 23 are supplied to the corresponding first to third DC / AC converters 11 to 13.

The first to third DC / AC converters 11 to 13 perform the same control as in the first embodiment based on the boosted first to third output voltages V1 to V3 to generate a combined output voltage Vt. Therefore, the output voltage Vo output via the filter circuit 2 is adjusted to a sine waveform W1 exceeding 283 V which is the maximum value of the AC 200 V system.

Also, for example, depending on the direction of the sun, the second output voltage V2 of the second solar cell panel SP2 is greater than the total voltage of the first and third output voltages V1 and V3 of the first and third solar cell panels SP1 and SP3. It can be large. In this case, the control circuit 20 controls the second DC / DC converter 22 such that the second output voltage V2 is smaller than the sum of the first and third output voltages V1 and V3.

That is, the control circuit 20 supplies the first output voltage V1 of the first solar cell panel SP1 to the first DC / DC converter 21 to boost it. Specifically, the control circuit 20 turns off the first changeover switch SW1 to boost the first output voltage V1 of the first DC / DC converter 21.

Then, even if the first output voltage V1 of the first DC / DC converter 21 is boosted, the second output voltage V2 of the low frequency group is higher than the total voltage of the first and third output voltages V1 and V3 of the high frequency group. It may be big. In this case, the control circuit 20 collectively boosts the third output voltage of the third DC / DC converter 23 by turning off the third changeover switch SW3, and the high frequency higher than the second output voltage V2 of the low frequency group A sum of the first and third output voltages V1, V3 of the group is generated.

The second embodiment configured as described above has the following effects in addition to the effects of the first embodiment.

(1) According to the present embodiment, even if the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 largely change, the first to third DC / DC converters 21 to 21 23 can generate an output voltage Vt that can be boosted and interconnected with an AC 200 V system.

(2) According to the present embodiment, the total voltage of the first and third output voltages V1 and V3 of the first and third solar cell panels SP1 and SP3 is smaller than the second output voltage V2 of the second solar cell panel SP2 May be Even in such a case, the control circuit 20 can generate a total voltage of the first and third output voltages V1 and V3 larger than the second output voltage V2. Therefore, the first to third output voltages V1 to V3 of the first to third solar cell panels SP1 to SP3 can be controlled with high efficiency in a wide range.

The above embodiment may be modified as follows.

In each of the above embodiments, the low frequency group is embodied as the second DC / AC converter 12, and the high frequency group is embodied as the first and third DC / AC converters 11 and 13.

However, the low frequency group may be embodied as the first DC / AC converter 11 and the high frequency group may be embodied as the second and third DC / AC converters 12 and 13. The low frequency group may be embodied as the third DC / AC converter 13 and the high frequency group may be embodied as the first and second DC / AC converters 11 and 12.

In the first and second embodiments, when performing duty control of the first and third DC / AC converters 11 and 13 of the high frequency group with the high frequency, the first power point is the hill climbing method for maximum power point tracking (MPPT). The maximum power point was determined for each of the third solar cell panels SP1 to SP3. The first and third DC / AC converters 11 and 13 were duty controlled to obtain the determined maximum power point. A method other than hill climbing may be used as a method of determining the maximum power point.

Further, as a method of controlling the first to third DC / AC converters 11 to 13, a method other than maximum power point tracking (MPPT) may be used.

In the first and second embodiments, the first to third DC / ACs 11 to 13 are divided into the low frequency group and the high frequency group, but they may not be divided into groups.

For example, all of the first to third DCs / ACs 11 to 13 may be implemented with the first to third DCs / ACs 11 to 13 as high frequency groups. In this case, the second DC / AC 12 is duty controlled at a high frequency when generating the second converted output voltage Vb including 200 V, 0 V, and -200 V.

In the first and second embodiments, the power conversion device 1 of the solar power generation system is configured by connecting the three first to third solar cell panels SP1, SP2, and SP3. However, the power conversion device 1 may be applied to a power conversion device in which four, five or more solar cell panels are connected.

In the first and second embodiments, the first to third solar cell panels SP1 to SP3 are solar cells for connecting to the AC 200 V system.

That is, a plurality of series circuits including a plurality of solar cell elements connected in series are connected in parallel to form a unit solar cell panel, and a plurality of unit solar cell panels are connected in series to form a series unit solar cell panel A plurality of series unit solar cell panels were connected in parallel to form a solar cell. The first to third solar cell panels SP1 to SP3 generate a first output voltage V1 (= 100 V), a second output voltage V2 (= 200 V), and a third output voltage V3 (= 120 V).

However, the power conversion device 1 of such a solar cell may be applied to a power conversion device of a solar cell other than a solar cell for connecting to an AC 200 V system.

Claims (6)

1. A power converter used for a plurality of solar cells, comprising:
   A plurality of DC / AC converters each connected to a plurality of solar cells, wherein the plurality of DC / AC converters are connected in series with each other;
   And a control circuit for controlling the plurality of DC / AC converters.
2. In the power converter according to claim 1,
   The plurality of DC / AC converters are divided into a first group of DC / AC converters and a second group of DC / AC converters,
   The power conversion apparatus, wherein the control circuit duty-controls the DC / AC converter of the first group at low frequency and duty-controls the DC / AC converter of the second group at high frequency.
3. In the power converter according to claim 2,
   The first group of DC / AC converters is connected to a solar cell producing a relatively high output voltage,
   The power converter according to claim 2, wherein the second group of DC / AC converters is connected to a solar cell that generates a relatively low output voltage.
4. The power converter according to any one of claims 1 to 3.
   The control circuit performs maximum power point tracking control on each of the plurality of DC / AC converters based on the output voltage of the corresponding solar cell and the output current flowing to the DC / AC converter. , Power converter.
5. In the power converter according to any one of claims 1 to 4,
   A plurality of DC / DC converters respectively provided between the plurality of DC / AC converters and a plurality of solar cells;
   And a plurality of shorting switches connected in parallel to the plurality of DC / DC converters,
   The control circuit turns off the plurality of short circuit switches when the output voltage of the plurality of solar cells deviates from a predetermined voltage range, so that the output voltage of the solar cells falls within the predetermined voltage range. A power converter controlling the plurality of DC / DC converters.
6. In the power converter according to any one of claims 1 to 5,
   Each of the plurality of DC / AC converters is
   A bridge circuit having first and second series circuits connected in parallel, each of the first and second series circuits including two switching elements connected in series; And the second series circuit is the bridge circuit to which the output voltage of the solar cell is applied;
   A positive output terminal connected to a connection point between two switching elements in the first series circuit;
   And a negative electrode output terminal connected to a connection point between two switching elements in the second series circuit.

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