JP2009165265A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter in which a first single-phase inverter 2 for inputting a DC voltage generated by a solar cell 1 is connected in series with a second single-phase inverter 4 for DC-inputting a second capacitor 5 so as to output AC power as the total sum of the respective generated voltages, capable of suppressing a voltage rise in the second capacitor 5 when a load 7 changes suddenly. <P>SOLUTION: When a voltage command 13a generated according to the voltage of the load 7 exceeds specified voltage threshold values 14, 15, by outputting voltage from the first single-phase inverter 2, the first single-phase inverter 2 outputs one pulse voltage in a half period and the second single-phase inverter 4 outputs the difference by PWM control. When the voltage of the second capacitor 5 becomes a predetermined voltage value 26 or higher, the specified voltage threshold values 14, 15 are changed to voltage threshold values 17, 18 of which absolute values are increased. Therefore, the amount of power output from the first single-phase inverter 2 is reduced to increase the discharged capacity of the second capacitor 5 through the second single-phase inverter 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

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, a first single-phase inverter that receives a first DC power source generated by boosting from a distributed power source that is a solar cell, and a second DC power source having a lower voltage than the first DC power source. Is connected in series with the second single-phase inverter having the input as the input, and the output voltage is obtained by the sum of the voltages generated by the single-phase inverters. In addition, control is performed so that the total fluctuating power amount due to discharging and charging of the second DC power supply via the second single-phase inverter becomes substantially zero (see, for example, Patent Document 1).

JP 2006-238628 A

  In the power converter as described above, the second single-phase inverter that receives the second DC power supply is output so as to compensate for the difference between the overall output target voltage and the output of the first single-phase inverter, At this time, the power balance of the second single-phase inverter is controlled so as to be substantially zero in one cycle. However, when the voltage of the load (system) suddenly decreases due to a momentary drop or the like, the output target voltage of the power converter also decreases accordingly, and the power balance of the second single-phase inverter is controlled to be substantially zero in one cycle. However, the state where the second DC power supply is charged is increased. When a capacitor is used for the second DC power supply, the voltage applied to the capacitor increases due to overcharging.

  The present invention has been made to solve the above problems, and even if the load (system) voltage suddenly changes, the capacitor constituting the DC power supply of the second single-phase inverter is excessive. The object is to obtain a stable capacitor voltage by avoiding a charged state.

  A power conversion device according to the present invention includes a first DC power source, an AC side of a first single-phase inverter that converts DC power of a first capacitor supplied with power from the first DC power source into AC power, and The AC side of the second single-phase inverter that converts the DC power of the second capacitor having a lower voltage than the first capacitor into AC power is connected in series, and the generated voltages of the first and second single-phase inverters are connected. The inverter unit that outputs a voltage based on the sum of the two and the inverter unit is controlled so that the second single-phase inverter is output in multiple pulses from the first inverter based on a voltage command generated according to the load. And a control unit. The control unit controls the inverter unit so that the output power balance in the half cycle or one cycle of the second single-phase inverter is substantially zero, and the voltage of the second capacitor is preset. When the voltage exceeds a predetermined voltage value, the amount of output power from the first single-phase inverter is reduced.

  In the power conversion device according to the present invention, when the voltage of the second capacitor becomes equal to or higher than a predetermined voltage value, the output electric power from the first single-phase inverter is decreased, so that the voltage command is suddenly lowered due to a sudden change in the voltage of the load. Even so, an increase in the charge amount of the second capacitor can be quickly suppressed, and an overcharge state can be avoided. For this reason, the voltage of the second capacitor can be stabilized.

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 inverter part is configured by connecting the alternating current sides of a plurality (two in this case) of first and second single-phase inverters 2 and 4 in series. Each single-phase inverter 2, 4 is composed of a plurality of self-extinguishing semiconductor switching elements (not shown) such as IGBTs having diodes connected in antiparallel, and one AC terminal of the first single-phase inverter 2 40 a is connected to one AC terminal 41 a of the second single-phase inverter 4, and the other AC terminals 40 b and 41 b are connected to the output filter 6.

The first capacitor 3 serving as the input of the first single-phase inverter 2 is charged from a solar panel 1 (hereinafter referred to as a solar cell 1) as a first DC power source. The second capacitor 5 serving as the input of the second single-phase inverter 4 is provided as an independent DC power supply, so that the voltage V1 of the first capacitor 3 is higher than the voltage V2 of the second capacitor 5. Is set. The voltages V1 and V2 of the first and second capacitors 3 and 5 are detected by voltage detectors 8 and 9, respectively, and detection signals are input to the control unit 10. The control unit 10 generates and outputs control signals 11 and 12 for controlling the first and second single-phase inverters 2 and 4, respectively. Each of the single-phase inverters 2 and 4 can generate a positive or negative voltage or zero as an output, and the inverter unit outputs a voltage as a total sum of these generated voltages. This output voltage is smoothed by the output filter 6 and the alternating voltage _Vout is supplied to the system (load) 7.

Next, the operation of this power conditioner will be described. The waveforms of the output voltage and output current of the power conditioner and each single-phase inverter 2, 4 are shown in FIG. Reference numeral 13 denotes an output voltage of the power conditioner, 16 denotes an output voltage of the first single-phase inverter 2, 20 denotes an output voltage of the second single-phase inverter 4, and 21 denotes a waveform indicating an output current of the power conditioner. Reference numerals 14 and 15 denote positive and negative voltage thresholds having the same absolute value, which are used for the timing output by the first single-phase inverter 2.
The output voltage 13 of the power conditioner connected to the system 7 is substantially equal to the waveform of the system voltage. The output voltage 13 is the output voltage 16 of the first single-phase inverter 2 and the output voltage of the second single-phase inverter 4. The sum of 20 is generated. In actual control, the voltage command 13a of the power conditioner is generated with a voltage substantially equal to the system voltage, and the first and second single-phase inverters 2 and 4 are controlled based on the voltage command 13a.

  As shown in FIG. 2A, the first single-phase inverter 2 outputs when the voltage command 13 a exceeds the voltage thresholds 14 and 15. That is, the first single-phase inverter 2 outputs a positive voltage pulse when the voltage command 13a is higher than the voltage threshold value 14, and outputs a negative voltage pulse when the voltage command 13a is lower than the voltage threshold value 15. The output voltage 16 is 1 pulse. Then, as shown in FIG. 2B, the output voltage 20 is output from the second single-phase inverter 4 so as to compensate for the difference between the voltage command 13a and the output voltage 16 of the first single-phase inverter 2. The output voltage 20 has a complicated waveform shape and is output by PWM control in this case.

Next, the energy balance of the second capacitor 5 serving as the DC input of the second single-phase inverter 4 will be described.
FIG. 3 is a diagram showing the energy balance of the second capacitor 5. The second capacitor 5 is charged / discharged via the second single-phase inverter 4, and the energy balance is indicated by the output power amount of the second single-phase inverter 4. That is, the instantaneous power of the second single-phase inverter 4 is obtained from the output current 21 of the power conditioner and the output voltage 20 of the second single-phase inverter 4, and the instantaneous power integrated value (output power) obtained by time-integrating the instantaneous power. (Quantity) indicates the energy balance of the second capacitor 5.
The second capacitor 5 is an independent DC power source, and is controlled so that the energy balance becomes almost zero in a half cycle or one cycle as shown by the normal energy balance 22 in the normal operation of the power conditioner. . That is, the second single-phase inverter 4 is controlled so that the output power amount becomes substantially zero in a half cycle or one cycle.

Controlling the output power amount of the second single-phase inverter 4 to be substantially zero is achieved by appropriately setting the voltage thresholds 14 and 15 for determining the output of the first single-phase inverter 2. it can. The voltage thresholds 14 and 15 may be set and used in advance. For example, the output power amount of the second single-phase inverter 4 in the immediately preceding half cycle or one cycle, the output voltage 13 of the power conditioner, or the system voltage If it is calculated from the above and revised as needed, it can be controlled with high accuracy so that the normal output power amount of the second single-phase inverter 4 becomes substantially zero.
FIG. 4 is a diagram illustrating a voltage change of the second capacitor 5. In the normal operation of the power conditioner, the energy balance of the second capacitor 5 is substantially 0. Therefore, the voltage of the second capacitor 5 is set every half cycle or every cycle as indicated by the normal capacitor voltage 24. If you look at it, it will not change. For example, when 4 kW of power is output from the power conditioner to the system voltage of 210 Vrms and the power conditioner is operated from 0 to 2π, the voltage of the second capacitor 5 starts at 140 V and ends at 140 V.

  By the way, when the voltage of the system 7 is suddenly lowered due to a momentary drop or the like, the voltage command 13a of the power conditioner is also lowered accordingly. Does not change. Even when the voltage thresholds 14 and 15 are revised by calculation, the voltage thresholds 14 and 15 do not change immediately because they are revised later. When the voltage is output from the second single-phase inverter 4 so as to compensate for the difference between the voltage command 13a and the output voltage 16 of the first single-phase inverter 2, the energy balance of the second capacitor 5 changes to excessive charge. The voltage of the second capacitor 5 increases.

  In this embodiment, when the predetermined voltage value 26 that is equal to or higher than the normal voltage range of the second capacitor 5 is set in advance, and the voltage of the second capacitor 5 increases to become the predetermined voltage value 26 or higher, Control for suppressing the second capacitor 5 from being overcharged and suppressing the voltage rise of the second capacitor 5 is performed. Details of this control will be described later. Here, an example in which the voltage thresholds 14 and 15 do not change and the output of the first single-phase inverter 2 continues similarly in the case of a sudden voltage change in the grid 7 is shown as a comparative example. For example, when the system voltage is instantaneously changed to 180 Vrms while outputting 4 kW of power to the system voltage of 210 Vrms from the power conditioner, the energy balance of the second capacitor 5 is shown by the comparative example energy balance 23 in FIG. Thus, it will be in an overcharged state. In this case, when the power conditioner is operated from 0 to 2π, the voltage of the second capacitor 5 starts at 140V and increases to about 160V as indicated by the comparative capacitor voltage 25 in FIG.

Next, the control for suppressing the voltage rise of the second capacitor 5 will be described in detail below.
The voltages of the first and second capacitors 5 are detected by voltage detectors 8 and 9, and the detection signals are input to the control unit 10. The control unit 10 generates and outputs control signals 11 and 12 for controlling the first and second single-phase inverters 2 and 4, respectively. Further, the control unit 10 holds a predetermined voltage value 26 that is preset in the normal voltage range of the second capacitor 5, and immediately when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26. The output load of the second single-phase inverter 4 is increased by the following control, the amount of discharge of the second capacitor 5 is increased, and the energy balance is changed from excessive charge to excessive discharge.

Control for increasing the output load of the second single-phase inverter 4 and increasing the discharge amount of the second capacitor 5 will be described based on the voltage waveform diagram shown in FIG. 5A shows the output voltage waveform of the first single-phase inverter 2, and FIG. 5B shows the output voltage waveform of the second single-phase inverter 4.
As shown in FIG. 5A, the first single-phase inverter 2 outputs when the voltage command 13a exceeds a set voltage threshold. As soon as the voltage of the second capacitor 5 reaches a predetermined voltage value 26 or more, the normal voltage thresholds 14 and 15 are forcibly changed to voltage thresholds 17 and 18 having large absolute values. The first single-phase inverter 2 outputs a voltage of one pulse in a half cycle, but the pulse based on the voltage thresholds 17 and 18 is changed from the output voltage 16 based on the normal voltage thresholds 14 and 15 by changing the voltage threshold. The output voltage 19 shifts to a short output voltage 19 and the output power amount of the first single-phase inverter 2 decreases. Note that the output voltage and the output current have the same phase.

  As shown in FIG. 5B, the second single-phase inverter 4 outputs the PWM command so as to compensate for the difference between the voltage command 13a and the output voltage of the first single-phase inverter 2. Since the first single-phase inverter 2 shifts to the output voltage 19 having a short pulse width and the output power amount decreases, the second single-phase inverter 4 shifts from the output voltage 20 to the output voltage 27 and outputs power. The amount increases. Here, from 0 to π, when the output voltage of the second single-phase inverter 4 is positive, the second capacitor 5 is in a discharged state. From π to 2π, the output voltage of the second single-phase inverter 4 is When the anode is negative, the second capacitor 5 is in a discharged state.

  For this reason, as shown in FIG. 6, the energy balance 28 of the second capacitor 5 becomes excessively discharged, and the voltage increase of the second capacitor 5 can be suppressed. 6 and 23 in FIG. 6 are the same as those in FIG. FIG. 7 shows how the voltage increase of the second capacitor 5 is suppressed. As shown in the figure, when the voltage of the second capacitor 5 rises to reach a predetermined voltage value 26, it is detected and the pulse width of the output voltage of the first single-phase inverter 2 is detected as described above. Therefore, the voltage rise of the second capacitor 5 is suppressed as indicated by the suppression capacitor voltage 29.

As described above, when the voltage of the second capacitor 5 increases, the inverter unit is controlled so as to suppress the voltage increase of the second capacitor 5. However, such control and normal control are included. The output control flow of the inverter part by the control part 10 is shown below based on FIG.
First, initial values of positive and negative voltage thresholds 14 and 15 for output from the first single-phase inverter 2 are set (S1). The voltages of the first and second capacitors 3 and 5 are taken from the voltage detectors 8 and 9 (S2), and it is determined whether or not the voltage of the second capacitor 5 is equal to or higher than a predetermined voltage value 26 set in advance ( S3). When the voltage of the second capacitor 5 is equal to or higher than the predetermined voltage value 26, the voltage thresholds 14 and 15 are changed to voltage thresholds 17 and 18 having large absolute values. At this time, the change amount of the voltage threshold value may be constant or may be changed in consideration of an error between the voltage of the second capacitor 5 and the predetermined voltage value 26 (S4).
Next, the voltage command 13a that changes substantially the same as the system voltage is compared with the voltage threshold values 14 (17) and 15 (18) (S5), and the voltage command 13a exceeds the voltage threshold values 14 (17) and 15 (18). At this time, the first single-phase inverter 2 is set to output the voltage of the first capacitor 3 positively or negatively (S6), otherwise the first single-phase inverter 2 is set to output 0. (S7).

Next, the voltage target value of the second single-phase inverter 4 is calculated by subtracting the output voltage of the first single-phase inverter 2 from the voltage command 13a (S8). Next, the power balance is calculated by integrating the output power amount of the second single-phase inverter 4 (S9). When an abnormality is detected, interrupt stop processing is performed at this point (S10). Next, control signals 11 and 12 for driving the switching elements in the single-phase inverters 2 and 4 are generated and output to the first and second single-phase inverters 2 and 4 (S11).
The processes of S2 to S11 are repeated for a predetermined cycle (for example, half cycle or one cycle) of a preset output voltage, and when the predetermined cycle ends (S12), the second single-phase inverter 4 integrated in s9 The voltage thresholds 14 and 15 are updated by calculating and setting the voltage thresholds 14 and 15 from the power balance (S13), and the integrated power balance value of the second single-phase inverter 4 is initialized (S14). , Return to s2.

  Although the output power amount of the second single-phase inverter 4 is set by calculating the voltage thresholds 14 and 15 from the integrated power balance in a specified period, the power in a half cycle or one cycle is described above. It may be calculated from the output voltage 13 of the conditioner or the system voltage.

  In this embodiment, the voltage of the second capacitor 5 is compared with a predetermined voltage value 26, and when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26, the normal voltage thresholds 14, 15 Are forcibly changed to voltage thresholds 17 and 18 having large absolute values. This process can be performed at any timing in one period, and can be performed quickly without waiting for a process of updating the voltage thresholds 14 and 15 based on the energy balance in a predetermined period. Thereby, even if the voltage of the load (system) 7 changes suddenly, it is possible to prevent the second capacitor 5 from being overcharged and suppress the voltage increase of the second capacitor 5.

  In addition, when using a preset fixed value for the voltage thresholds 14 and 15, after the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26 and the absolute value is changed to the voltage thresholds 17 and 18 Return to the original voltage thresholds 14 and 15 after a predetermined period, or set the lower limit value of the voltage of the second capacitor 5, and when the voltage of the second capacitor 5 falls below the lower limit value, the original voltage threshold values 14 and 15 You may make it return to. Also in this case, the voltage rise of the second capacitor 5 can be quickly suppressed, and the same effect can be obtained.

  Further, in the above embodiment, the first single-phase inverter 2 is output when the voltage command 13a exceeds the set voltage threshold value. Therefore, by increasing the absolute value of the voltage threshold value, the first single-phase inverter 2 can be easily set to 1 in a half cycle. Although the output voltage of the first single-phase inverter 2 can be reduced by shortening the width of the voltage pulse of the pulse, the pulse width of the output voltage of the first single-phase inverter 2 may be adjusted by other methods. . Even in this case, when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26, the first output voltage of the first single-phase inverter 2 is adjusted so as to shorten the pulse width of the output voltage of the first single-phase inverter 2 at a normal time. The voltage increase of the second capacitor 5 can be suppressed.

Embodiment 2. FIG.
Next, a power conversion device (hereinafter referred to as a power conditioner) according to Embodiment 2 of the present invention will be described with reference to FIG.
As shown in FIG. 9, a voltage adjustment circuit 30 is provided at the subsequent stage of the solar cell 1 to adjust the voltage of the solar cell 1 to a desired voltage and output it to the first capacitor 3. The voltage adjusting circuit 30 is composed of a booster circuit 31a for increasing the voltage and a step-down circuit 31b for decreasing the voltage, and boosts or steps down the voltage of the solar cell 1 as necessary. The control unit 10 generates and outputs control signals 11 and 12 for controlling the first and second single-phase inverters 2 and 4, respectively, and outputs a voltage adjustment signal 32 to the voltage adjustment circuit 30. Other configurations are the same as those of the first embodiment shown in FIG.

Next, the operation of this power conditioner will be described.
The voltages of the first and second capacitors 5 are detected by voltage detectors 8 and 9, and the detection signals are input to the control unit 10. The control unit 10 generates and outputs control signals 11 and 12 for controlling the first and second single-phase inverters 2 and 4, respectively. Further, the control unit 10 holds a predetermined voltage value 26 that is preset in the normal voltage range of the second capacitor 5, and immediately when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26. A voltage adjustment signal 32 is output to the voltage adjustment circuit 30.
In the power conditioner connected to the system 7, the voltage command 13a is generated at a voltage substantially equal to the system voltage, and the first and second single-phase inverters 2 and 4 are controlled based on the voltage command 13a. At normal times, as in the first embodiment, the first single-phase inverter 2 outputs when the voltage command 13a exceeds the voltage thresholds 14 and 15. That is, the first single-phase inverter 2 outputs a positive voltage pulse when the voltage command 13a is higher than the voltage threshold value 14, and outputs a negative voltage pulse when the voltage command 13a is lower than the voltage threshold value 15. The output voltage 16 is 1 pulse. Then, the output voltage 20 is output from the second single-phase inverter 4 by PWM control so as to compensate for the difference between the voltage command 13a and the output voltage 16 of the first single-phase inverter 2 (see FIG. 2).

Similarly to the first embodiment, the voltage thresholds 14 and 15 for determining the output of the first single-phase inverter 2 are appropriately set, and the output power amount of the second single-phase inverter 4 is substantially reduced. Control to be zero. The voltage thresholds 14 and 15 may be set and used in advance. For example, the output power amount of the second single-phase inverter 4 in the immediately preceding half cycle or one cycle, the output voltage 13 of the power conditioner, or the system voltage If it is calculated from the above and revised as needed, it can be controlled with high accuracy so that the normal output power amount of the second single-phase inverter 4 becomes substantially zero.
Also in this embodiment, when the voltage of the grid 7 suddenly decreases due to a momentary drop or the like, the voltage command 13a of the power conditioner also decreases accordingly, and the energy of the second capacitor 5 is reduced as in the first embodiment. The balance changes to overcharging and the voltage on the second capacitor 5 increases. For this reason, when the predetermined voltage value 26 that is equal to or higher than the normal voltage range of the second capacitor 5 is set in advance and the voltage of the second capacitor 5 increases to become the predetermined voltage value 26 or higher, the second voltage value 26 is increased. Control is performed to suppress the capacitor 5 from being overcharged and suppress the voltage rise of the second capacitor 5.

Next, the control for suppressing the voltage rise of the second capacitor 5 will be described in detail below.
When the voltage of the second capacitor 5 reaches a predetermined voltage value 26 or more, the control unit 10 immediately outputs a voltage adjustment signal 32 for reducing the output voltage to the voltage adjustment circuit 30. In the voltage adjustment circuit 30, when the voltage of the solar cell 1 is being boosted by the booster circuit 31a, the voltage target value of the booster circuit 31a is reduced to lower the output voltage, or the operation is switched to the operation by the step-down circuit 31b. When the voltage adjustment circuit 30 is stopped or the voltage of the solar cell 1 is being stepped down by the step-down circuit 31b, the voltage target value of the step-down circuit 31b is reduced to lower the output voltage.

FIG. 10 shows an output voltage waveform of the first single-phase inverter 2.
As shown in FIG. 10, the first single-phase inverter 2 outputs when the voltage command 13a exceeds the set voltage thresholds 14 and 15. When the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26, the output of the voltage adjustment circuit 30 is immediately reduced from the normal output voltage, and the first power source of the first single-phase inverter 2 is the first power source. The voltage of the capacitor 3 decreases. The first single-phase inverter 2 outputs the voltage of the first capacitor 3 in one pulse in a half cycle, but the voltage magnitude of the first capacitor 3 is reduced from the normal output voltage 16 due to the voltage drop of the first capacitor 3. It shifts to the reduced output voltage 31, and the output electric energy of the 1st single phase inverter 2 reduces. Note that the output voltage and the output current have the same phase.

The second single-phase inverter 4 outputs by PWM control so as to compensate for the difference between the voltage command 13a and the output voltage of the first single-phase inverter 2. Since the first single-phase inverter 2 shifts to the output voltage 31 in which the magnitude of the voltage is reduced and the output power amount decreases, the second single-phase inverter 4 increases the output power amount. As described above, the second single-phase inverter 4 increases the output load, increases the discharge amount of the second capacitor 5, and changes the energy balance from excessive charge to excessive discharge.
For this reason, as shown in FIG. 11, the energy balance 33 of the second capacitor 5 is in an excessive discharge state, and the voltage increase of the second capacitor 5 can be suppressed. FIG. 11 shows an example of control when the system voltage is instantaneously changed to 180 Vrms while outputting 4 kW of power to the system voltage of 210 Vrms from the power conditioner. 3 is a comparative example energy balance when normal control is continued at the time of a sudden voltage change in the system 7, as in FIG.

  FIG. 12 shows how the voltage increase of the second capacitor 5 is suppressed. Moreover, the change of the output voltage of the 1st single phase inverter 2 at this time is shown in FIG. When the voltage of the second capacitor 5 rises and reaches a predetermined voltage value 26, it is detected and adjustment is performed to reduce the voltage of the first capacitor 3, and the output of the first single-phase inverter 2 Is shifted from the normal output voltage 16 to the output voltage 31 having a reduced voltage magnitude. Thereby, the voltage rise of the 2nd capacitor | condenser 5 is suppressed as the capacitor voltage 34 at the time of suppression shows.

As described above, when the voltage of the second capacitor 5 increases, the inverter unit and the voltage adjustment circuit 30 are controlled so as to suppress the voltage increase of the second capacitor 5. The output control flow by the control unit 10 including the control is shown below based on FIG.
First, initial values of positive and negative voltage thresholds 14 and 15 for output from the first single-phase inverter 2 are set (t1). The voltages of the first and second capacitors 3 and 5 are taken in from the voltage detectors 8 and 9 (t2), and it is determined whether or not the voltage of the second capacitor 5 is equal to or higher than a predetermined voltage value 26 set in advance ( t3). When the voltage of the second capacitor 5 is equal to or higher than the predetermined voltage value 26, the target voltage of the output of the voltage adjustment circuit 30 is lowered. At this time, the amount of change in the target voltage may be constant, or may be changed in consideration of an error between the voltage of the second capacitor 5 and the predetermined voltage value 26 (t4).
Next, the voltage command 13a that changes substantially the same as the system voltage is compared with the voltage thresholds 14 and 15 (t5). When the voltage command 13a exceeds the voltage thresholds 14 and 15, the first single-phase inverter 2 The voltage of the capacitor 3 is set so as to be output positively or negatively (t6), and otherwise, the output is set to be 0 from the first single-phase inverter 2 (t7).

Next, the voltage target value of the second single-phase inverter 4 is calculated by subtracting the output voltage of the first single-phase inverter 2 from the voltage command 13a (t8). Next, the power balance is calculated by integrating the output power amount of the second single-phase inverter 4 (t9). When an abnormality is detected, interrupt stop processing is performed at this time (t10). Next, control signals 11 and 12 for driving the switching elements in the single-phase inverters 2 and 4 are generated and output to the first and second single-phase inverters 2 and 4 (t11), and the voltage is adjusted. A voltage adjustment signal 32 based on the target voltage is output to the circuit 30 (t12).
The processing from t2 to t12 is repeated for a predetermined cycle (for example, half cycle or one cycle) of a preset output voltage, and when the predetermined cycle ends (t13), the second single-phase inverter 4 integrated at t9 The voltage thresholds 14 and 15 are updated by calculating and setting the voltage thresholds 14 and 15 from the power balance (t14), and the integrated power balance value of the second single-phase inverter 4 is initialized (t15). , Return to t2.

  Although the output power amount of the second single-phase inverter 4 is set by calculating the voltage thresholds 14 and 15 from the integrated power balance in a specified period, the power in a half cycle or one cycle is described above. It may be calculated from the output voltage 13 of the conditioner or the system voltage.

  In this embodiment, the voltage of the second capacitor 5 is compared with a predetermined voltage value 26, and the voltage of the solar cell 1 is adjusted when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26. The voltage of the first capacitor 3 is forcibly lowered by reducing the output voltage of the voltage adjustment circuit 30. This process can be performed at any timing in one period, and can be performed quickly without waiting for a process of updating the voltage thresholds 14 and 15 based on the energy balance in a predetermined period. Thereby, even if the voltage of the load (system) 7 changes suddenly, it is possible to prevent the second capacitor 5 from being overcharged and suppress the voltage increase of the second capacitor 5.

  In addition, after the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26 and the output voltage of the voltage adjustment circuit 30 is adjusted, the output of the voltage adjustment circuit 30 is returned to the original output voltage after a predetermined period. A lower limit value of the voltage of the second capacitor 5 may be set so that when the voltage of the second capacitor 5 becomes equal to or lower than the lower limit value, the original output voltage is restored.

  In addition, a fixed value preset in the voltage thresholds 14 and 15 is used, and the output voltage of the voltage regulator 30, that is, the voltage of the first capacitor 3 is used as the second single-phase inverter in the immediately preceding half cycle or one cycle. It may be controlled so that it is calculated from the output power amount of 4, the output voltage 13 of the power conditioner or the system voltage and revised as needed. Also in this case, when the voltage of the second capacitor 5 becomes equal to or higher than the predetermined voltage value 26, the process of forcibly reducing the voltage of the first capacitor 3 by reducing the output voltage of the voltage adjustment circuit 30 is 1 It can be implemented at any timing in the cycle, and can be implemented quickly without waiting for update processing in a predetermined cycle, and the same effect can be obtained.

  In the above embodiment, the output voltage of the voltage adjustment circuit 30 is reduced by a predetermined change amount when the voltage of the second capacitor 5 is equal to or higher than the predetermined voltage value 26. FIG. As shown, it may be changed so as to be gradually reduced. Alternatively, a target voltage may be provided for the voltage of the second capacitor 5 and the output voltage of the voltage adjustment circuit 30 may be controlled so that the detected voltage of the second capacitor 5 becomes the target voltage.

  The above embodiment can also be applied to the voltage adjustment circuit 30 having no step-down function. In this case, the voltage adjustment circuit 30 is configured by a step-up circuit 30a.

  In the first and second embodiments, two single-phase inverters 2 and 4 are connected in series. However, a plurality of second single-phase inverters 4 having independent capacitors 3 as DC power supplies are provided. A power conditioner may be configured by connecting AC sides of three or more single-phase inverters in series. In this case, the plurality of second single-phase inverters 4 are controlled in the same manner, and the voltage rise of the plurality of second capacitors 5 can be suppressed as in the above embodiments.

  In the first and second embodiments, the solar cell 1 is used as the first DC power source, but the present invention can also be applied to other distributed power sources.

It is a schematic block diagram which shows the power conditioner by Embodiment 1 of this invention. It is a figure which shows the operation waveform of each part in the normal time of the power conditioner by Embodiment 1 of this invention. It is a figure which shows the energy balance in the normal time of the 2nd capacitor | condenser by Embodiment 1 of this invention. It is a figure which shows the voltage change in the normal time of the 2nd capacitor | condenser by Embodiment 1 of this invention. It is a figure explaining control of the power conditioner by Embodiment 1 of this invention based on the operation waveform of each part. It is a figure which shows the energy balance of the 2nd capacitor | condenser by Embodiment 1 of this invention. It is a figure which shows the voltage change of the 2nd capacitor | condenser by Embodiment 1 of this invention. It is a figure which shows the output control flow 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 which shows the output voltage waveform of the 1st single phase inverter by Embodiment 2 of this invention. It is a figure which shows the energy balance of the 2nd capacitor | condenser by Embodiment 2 of this invention. It is a figure which shows the voltage change of the 2nd capacitor | condenser by Embodiment 2 of this invention. It is a figure explaining control of the power conditioner by Embodiment 1 of this invention based on the operation | movement waveform of a 1st single phase inverter. It is a figure which shows the output control flow of the power conditioner by Embodiment 2 of this invention. It is a figure explaining control of the power conditioner by another example of Embodiment 2 of this invention based on the operation | movement waveform of a 1st single phase inverter.

Explanation of symbols

1 solar cell as first DC power supply, 2 first single-phase inverter,
3 first capacitor, 4 second single phase inverter, 5 second capacitor,
7 systems (load), 8, 9 voltage detector, 10 control unit, 13 output voltage,
13a voltage command, 14, 15, 17, 18 voltage threshold,
16, 19, 31, 32 First single-phase inverter output voltage,
20, 27 Second single-phase inverter output voltage, 26 predetermined voltage value,
30 voltage adjustment circuit, 31a step-up circuit, 31b step-down circuit.

Claims (6)

A first DC power supply;
The AC side of the first single-phase inverter that converts the DC power of the first capacitor supplied from the first DC power source into AC power, and the DC of the second capacitor having a lower voltage than the first capacitor An inverter unit for connecting the AC side of a second single-phase inverter that converts power to AC power in series, and outputting a voltage by the sum of the generated voltages of the first and second single-phase inverters;
A control unit that controls the inverter unit so as to output the second single-phase inverter in multiple pulses from the first inverter based on a voltage command generated according to a load;
The control unit controls the inverter unit so that the output power balance in the half cycle or one cycle of the second single-phase inverter becomes substantially zero, and the voltage of the second capacitor is set in advance. A power conversion device that reduces the amount of output power from the first single-phase inverter when a voltage value exceeds a predetermined voltage value. The first single-phase inverter outputs a voltage of one pulse in a half cycle, and the second single-phase inverter outputs a voltage so as to compensate for the difference between the voltage command and the output of the first single-phase inverter. And
When the voltage of the second capacitor becomes equal to or higher than the predetermined voltage value, the control unit shortens the pulse width of the output voltage of the first single-phase inverter to reduce the output power amount. The power conversion device according to claim 1. The first single-phase inverter outputs a voltage of the first capacitor when the voltage command exceeds a predetermined threshold value, thereby outputting a voltage of one pulse in a half cycle, and the magnitude of the predetermined threshold value. The power converter according to claim 2, wherein the pulse width of the output voltage of the single-phase inverter is shortened by increasing. A voltage adjustment circuit for adjusting the voltage of the first DC power supply and outputting the voltage to the first capacitor;
When the voltage of the second capacitor becomes equal to or higher than the predetermined voltage value, the control unit reduces the output power amount from the first single-phase inverter by reducing the output voltage of the voltage adjustment circuit. The power converter according to claim 1, wherein The power converter according to claim 4, wherein the voltage adjustment circuit has a boosting function. The power converter according to claim 4, wherein the voltage adjustment circuit has both a step-up function and a step-down function.

Images