JP2009151832A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion device for inputting the power of a plurality of DC power supply sources each of which is connected between function units and which have different output characteristics, while independently controlling the output of a voltage regulator and the output of an inverter connected to the rear stage thereof. <P>SOLUTION: The power conversion device includes a maximum power follow-up control circuit 5 for regulating the power of the DC power supply source using a voltage regulating means 2a; inputting the output of the voltage regulating means to an inverter means 7 to convert it into AC power; and regulating the input/output voltage ratio of the voltage regulating means 2a, to follow the maximum power of the DC power supply source, and an output voltage control circuit 6 for controlling the output voltage in priority to the maximum power follow-up control circuit 5 so that the output voltage does not exceed predetermined maximum link voltage. The inverter means 7 uses an output power control circuit 14 for controlling input power to be a predetermined input operating voltage which is set to be a value lower than the maximum link voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power conversion device, for example, a power conversion device that receives power from a DC power supply source such as a solar cell or a fuel cell and converts it into AC power.

  In a solar cell power generation system, DC power generated from a solar cell is converted into AC power of 50 Hz or 60 Hz, and this AC power is supplied to an electric device operated with commercial AC power.

  For example, in a private house, a plurality of solar cells are arranged on the roof of the building, and the DC power generated by these solar cells receiving sunlight is converted into AC power having the same frequency as the commercial frequency. The AC power is supplied to the electrical equipment via the commercial distribution line system. Further, when the generated power from the solar battery is small, the shortage of commercial power is supplemented from the commercial distribution line system so that the electric device can be operated stably.

  By the way, when installing a solar cell on the roof of a house, a plurality of solar cell modules are connected in series to form a string, and a plurality of strings are connected in parallel to form the whole as a solar cell array. However, the shape of the roof surface on which the solar cells are placed is not necessarily a shape obtained by a combination of the rectangular standard dimensions of the solar cell modules, and the number of string solar cell modules in a string may not be uniform.

  FIG. 6 is a diagram showing power-voltage characteristics of strings A and strings B having different numbers of series solar cell modules. As is apparent from FIG. 6, the maximum output voltage value V (Pmax−str) of the string A and the string B has different voltage values.

  Normally, the grid-linking inverter is controlled so as to have a maximum output voltage value V (Pmax-arr) at which the solar cell array outputs the maximum power according to the amount of solar radiation at that time. When the maximum output voltage value V (Pmax−str) of each string is the same, ΣPmax−str = Pmax−arr (Pmax−str: maximum power of the string, Pmax−arr: maximum power of the solar cell array) However, as shown in FIG. 6, when the maximum output voltage values V (Pmax−str) of the strings are different, ΣPmax−str> Pmax−arr, and the conventional grid-linked inverter has the original power generation capacity of each string. Cannot be fully extracted.

  Therefore, conventionally, in Japanese Patent Application Laid-Open No. 59-144327, Japanese Patent Application Laid-Open No. 8-46231 and Japanese Patent Application Laid-Open No. 8-70533, as shown in FIG. The voltages output to the inverter 7 are made equal. The voltage regulator 8 includes a voltage variable circuit that varies the output voltage of the solar cell module, and an output that can operate the solar cell module with maximum power based on the voltage and current signals input from the solar cell module side. A circuit for obtaining a voltage, and a control circuit for controlling the voltage variable circuit based on an operation voltage obtained from the circuit and a preset input voltage of the inverter 7 are provided.

  FIG. 8 is a circuit diagram showing the configuration of such a voltage regulator. In FIG. 8, the direct current output of the solar cell module is input to the switching circuit 17 via the reactor 16. The switching circuit 17 temporarily stores the energy of the solar cell module in the reactor 16 when turned on, stores the energy stored when turned off in the capacitor 19 via the diode 18, and outputs it as a DC voltage to the inverter side. Voltage adjustment is performed by controlling the duty of the on-time of the switching circuit.

  The DC voltage and DC current of the solar cell module detected by the voltage detector 9 and the current detector 10 provided on the input side of the switching circuit 17 are input to the maximum power tracking circuit 11. The maximum power follow-up circuit 11 obtains an output voltage Vc that can operate the solar cell module with the maximum power, and gives the output voltage to the control circuit 12.

  The voltage between the terminals of the capacitor 19 detected by the voltage detector 20 is input to the control circuit 12, and the output voltage Vc obtained by the maximum power tracking circuit 11 and a constant voltage value VI set in advance as an inverter input voltage value. The switching circuit 17 is controlled so that the ratio (VI / Vc) becomes the boost ratio of the voltage regulator 8 of FIG.

  In this way, the voltage regulator 8 controls the output of the solar cell to the DC voltage V (Pmax-str) that outputs the maximum power of the solar cell string 1, and the voltage on the input side of the inverter 7 is set to a predetermined constant. The voltage is controlled to be VI. Furthermore, on the inverter 7 side, if the inverter output is increased too much, the power supplied from the voltage regulator 8 becomes insufficient and the above-mentioned constant voltage value VI cannot be maintained, but decreases. In order to prevent the decrease of the inverter 7, the inverter output is adjusted in a timely manner so that the inverter 7 does not fall below the constant voltage value VI.

JP 59-144327 A JP-A-8-46231 JP-A-8-70533

  As described above, conventionally, in a solar cell power generation system in which solar cell strings 1 in which solar cell modules are connected in series are connected in parallel to form a solar cell array, and the DC output power is converted into AC power by an inverter 7. In order to obtain the maximum power of all the solar cell strings 1 when the output voltage of each solar cell string 1 is not uniform, such as when the number of modules of the solar cell strings 1 is different, all the solar cell strings 1 It is necessary to provide a voltage regulator 8 in In the voltage regulator 8, the ratio (VI / Vc) between the output voltage Vc obtained by the maximum power tracking circuit 11 and the constant voltage value VI set in advance as the inverter input voltage value becomes the boost ratio of the voltage regulator 8. The switching circuit 17 is controlled.

  However, in such a system, it is necessary to set the constant voltage value VI in advance in the voltage regulator 8 as the input voltage value on the inverter 7 side, and the input on the inverter 7 side set in the voltage regulator 8. It is necessary to match the voltage value VI with the target value of the input operating voltage to be maintained by the inverter-side output control. For this reason, the combination of the voltage regulator 8 and the inverter 7 is limited by matching. Further, the inverter 7 must always be operated at the preset input voltage value VI.

  Therefore, the main object of the present invention is that the output control of the voltage regulator connected to the previous stage of the inverter and the output control on the inverter side can operate independently without setting a constant voltage value VI. An object of the present invention is to provide a power conversion device having a control configuration capable of varying the input operating voltage of an inverter.

  The present invention relates to a power converter for converting the power of a DC power supply source into AC power, a voltage adjusting means for adjusting the voltage of the DC power supply source, and an inverter for inputting the output of the voltage adjusting means and converting it into AC power A voltage adjusting means for adjusting the input / output voltage ratio so as to follow the maximum power of the DC power supply source, and the output voltage is set to a predetermined value in preference to the maximum power conversion control section. An output voltage control unit for controlling the output voltage so as not to exceed the maximum link voltage is provided, and the inverter means includes an output control unit for controlling the input voltage to a predetermined input operating voltage set to a value lower than the maximum link voltage. It is characterized by.

  Thus, the voltage adjustment means for adjusting the voltage of the DC power supply source is controlled by the maximum power tracking control unit that adjusts the input / output voltage ratio so as to track the maximum power of the DC power supply source. The voltage adjusting means is controlled so that the power input to the voltage adjusting means is maximized.

  Also, a plurality of voltage adjusting means are provided, and the outputs of the voltage adjusting means are coupled in parallel and input to the inverter means.

  The voltage adjusting means coupled in parallel at these output ends perform the control operation independently, and follow the maximum power of the DC power supply source input to each voltage adjusting means.

  Another invention relates to a power converter for converting the power of a DC power supply source into AC power, voltage adjusting means for adjusting the voltage of the DC power supply source, and converting the AC power by inputting the output of the voltage adjusting means A voltage control means for adjusting the input / output voltage ratio so as to extract predetermined power from a direct current power supply source, and a maximum link for which the output voltage has a predetermined maximum priority over the power control section. Including an output voltage control unit that controls the output voltage so as not to exceed the voltage, and the inverter means includes an output control unit that controls the input voltage to a predetermined input operating voltage set to a value lower than the maximum link voltage. It is characterized by.

  Furthermore, at least one of the plurality of voltage adjusting means includes a power control unit and an output voltage control unit.

  Thereby, it can comprise as a system | strain connection inverter apparatus which can input the electric power of the some direct-current power supply source from which an output characteristic differs.

  According to the present invention, a power converter is constituted by voltage adjusting means for adjusting the voltage of the DC power supply source and inverter means for inputting the output of the voltage adjusting means and converting it to AC power, and the voltage adjusting means is A maximum power tracking control unit that adjusts the input / output voltage ratio so as to track the maximum power of the power supply source, and the output voltage does not exceed a predetermined maximum link voltage VL in preference to the maximum power tracking control unit. An output voltage control unit that controls the output voltage is included, and the inverter means controls the input voltage to an input operating voltage that is set to a value lower than the maximum link voltage VL. Therefore, matching the upper limit voltage that can be input to the inverter means If only this is taken, the output control of the voltage adjusting means connected to the preceding stage of the inverter means and the output control of the inverter means can be performed independently. As a result, the voltage adjusting means and the inverter means can be handled as independent general-purpose function units. In addition, since the inverter means is not subject to much restrictions on the voltage adjusting means side, the input operating voltage can be varied, and controllability is improved.

  Furthermore, a power conversion device that can input power from a plurality of DC power supply sources having different output characteristics can be easily configured by combining each unit. Thereby, for example, it is possible to cope with a system in which a plurality of solar cell strings having different output voltages exist.

  The voltage adjustment means includes voltage adjustment means for adjusting the voltage of the DC power supply source, and inverter means for inputting the output of the voltage adjustment means and converting it into AC power. A power control unit that adjusts the input / output voltage ratio so as to take out the output, and an output voltage control unit that controls the output voltage so that the output voltage does not exceed a predetermined maximum link voltage VL in preference to the power control unit, The means includes an output control unit that controls the input voltage to a predetermined input operating voltage set to a value lower than the maximum link voltage VL, so that the output voltage of the voltage adjusting means exceeds the maximum link voltage set value VL. Then, the control of the output voltage control unit starts to be effective, and the output voltage can be maintained so as not to exceed the maximum link voltage VL.

  Furthermore, at least one of the plurality of voltage adjusting means includes a power control unit and an output voltage control unit. As a result, the power of a DC power supply source that requires maximum power tracking, such as a solar cell, and the power of a constant output DC power supply source, such as a fuel cell, are connected in parallel via voltage control means of control specifications that correspond to each other. Can be connected. At this time, since each control is independent, the extension by additional connection is possible.

It is a block diagram of the grid connection inverter apparatus of one Embodiment of this invention. It is a circuit diagram which shows an example of the voltage adjustment means shown in FIG. It is a circuit diagram which shows the other example of the voltage adjustment means shown in FIG. FIG. 6 is a circuit diagram showing still another example of the voltage adjusting means shown in FIG. 1. It is a block diagram of the system | strain cooperation inverter apparatus of 2nd Embodiment of this invention. It is a power-voltage characteristic view of a solar cell array. It is a block diagram which shows the structure of the conventional solar cell power generation system. It is a figure which shows the circuit structure of the voltage adjustment means in the solar cell power generation system shown in FIG.

  FIG. 1 is a block diagram showing a configuration of a solar cell power generation system using a power conversion device according to an embodiment of the present invention. In FIG. 1, a system linkage inverter device 13 which is one form of a power conversion device is composed of two voltage adjustment means 2 a and 2 b and an inverter means 7. The DC power of the solar cell strings 1a and 1b is input to the corresponding voltage adjusting means 2a and 2b, respectively. The voltage adjusting means 2a, 2b adjust the DC voltage from the solar cell strings 1a, 1b, and the output DC output is connected in parallel and input to the inverter means 7. Inverter means 7 converts DC power into AC power having a commercial frequency and performs linked operation with the commercial system.

  The main circuit of the voltage adjusting means 2a, 2b is composed of a voltage adjusting circuit 21 and a capacitor 19, and serves as a DC power source for the inverter means 7. The input current Ib input to the voltage adjustment circuit 21 is detected by the current detector 10 and input to the maximum power tracking control circuit 5. Further, the input voltage Vb of the voltage adjustment circuit 21 is also detected by the voltage detector 9 and input to the maximum power tracking control circuit 5. The maximum power tracking control circuit 5 calculates the input power to the voltage adjustment circuit 21 from the input current Ib and the input voltage Vb, and changes the target input voltage setting value Vb_ref so that this input power becomes maximum. Then, the input voltage set value Vb_ref is output to the gate pulse generation circuit 4.

  Next, the link voltage Va, which is the output of the voltage adjustment circuit 21, is input to the output voltage control unit 6. The output voltage control unit 6 compares the predetermined maximum link voltage VL and the actual link voltage Va, and outputs a signal E = 0 to the gate pulse generation unit 4 if the difference Va−VL is positive. . When the difference Va−VL is negative, the signal E = 1 is output to the gate pulse generator 4.

  The gate pulse generation circuit 4 inputs the input voltage Vb and the input voltage set value Vb_ref, and drives the switching element in the voltage adjustment circuit 21 so that the input voltage Vb matches the input voltage set value Vb_ref. A gate drive signal S is created. Further, the gate pulse generation circuit 4 receives the signal E from the output voltage control circuit 6, takes the product of the signal E and the gate drive signal S, and generates a gate pulse G by PWM modulating the product, thereby adjusting the voltage. The switching element in the circuit 21 is driven.

  Therefore, when the difference Va−VL is negative, the link voltage Va does not exceed the maximum link voltage VL, and the gate drive signal S is PWM-modulated. When the link voltage Va becomes larger than the maximum link voltage VL and the difference Va−VL becomes positive, the signal to be PWM is 0, and the gate pulse G is turned off. In this way, the link voltage Va is prevented from exceeding a predetermined maximum link voltage VL.

  On the other hand, the outputs of the voltage adjusting means 2a and 2b are connected in parallel and input to the inverter means 7. The inverter means 7 receives DC power from the voltage adjusting means 2a, 2b and converts it into AC power of commercial frequency, and an inverter circuit 15 linked to the commercial system, and an output power control circuit 14 for adjusting the output of the inverter circuit 15; Consists of. Although not shown, the inverter circuit 15 also includes an output current waveform control unit for controlling the output current to a sine wave having a commercial frequency. The DC voltage Va input to the inverter circuit 15 is detected by the voltage detector 16 and input to the output power control circuit 14. The output power control circuit 14 adjusts the output power of the inverter circuit 15 so that the DC voltage Va becomes a predetermined input operation reference voltage Va_ref.

  That is, the output power control circuit 14 adjusts to increase the output of the inverter circuit 15 when the DC voltage Va is larger than the input operation reference voltage Va_ref, and when the DC voltage Va is smaller than the input operation reference voltage Va_ref, It adjusts so that the output of the inverter circuit 15 may be reduced. Here, the input operation reference voltage Va_ref is smaller than the maximum link voltage VL. For example, the maximum link voltage VL = 350V and the input operation reference voltage Va_ref = 330V are set.

  Further, the value of the input operation reference voltage Va_ref set in the output power control circuit 14 does not always need to be a constant value, and may be set so as to change according to the output power of the inverter circuit 15. This can be used in the case where the loss can be reduced by changing the input operating voltage in consideration of the conduction loss and switching loss of the switching element used in the inverter circuit 15.

  FIG. 2 is a circuit diagram showing a specific example of the voltage adjustment circuit shown in FIG. In FIG. 2, the DC power input to the voltage adjustment circuit 21 a is input to the switching element 17 via the reactor 16. The switching element 17 temporarily stores DC input energy in the reactor 16 when the switch is turned on, and stores the energy stored in the reactor 16 in the capacitor 19 via the diode 18 when the switch is turned off.

  When the voltage adjustment circuit 21a of FIG. 2 is used, the duty α of the ON time of the switching element 17 can be calculated as follows. That is, the step-up ratio of the voltage adjustment circuit 21a is determined as Va / Vb_ref from the link voltage Va and the input voltage setting value Vb_ref that are sequentially detected. At this time, the duty α is calculated as 1−Vb_ref / Va. In this case, the link voltage Va is input to the gate pulse generation circuit 4 of FIG. 1, and there is no need to input the input voltage Vb.

  FIG. 3 is a circuit diagram showing another example of the voltage adjustment circuit. In FIG. 3, the voltage adjustment circuit 21 b includes a high-frequency PWM inverter 22, a high-frequency insulation transformer 23, a diode bridge 24, and two reactors 16 and 16. The DC voltage input to the voltage adjustment circuit 21 b is once converted into a high-frequency AC voltage by the high-frequency PWM inverter 22, boosted by the high-frequency insulation transformer 23, and DC by the secondary diode bridge 24 of the high-frequency insulation transformer 23. Full-wave rectified to voltage. This is smoothed by the reactor 16 and stored in the capacitor 19. In this case, the gate pulse generating circuit 4 of FIG. 1 generates a gate pulse for driving each switching element constituting the high frequency PWM inverter 22. The circuit of FIG. 3 is used when the input / output of the inverter 7 needs to be insulated.

  FIG. 4 is a circuit diagram showing still another example of the voltage adjustment circuit. In FIG. 4, the voltage adjustment circuit 21 c includes a switching element 17, a leakage transformer 25, a resonance capacitor 26, voltage doubler rectifying diodes 27 and 28, and a capacitor 29. The input DC voltage is input to a monolithic resonance circuit including a switching element 17, a resonance capacitor 26, and a leakage transformer 25. On the secondary side of the leakage transformer 25, a half wave is doubled by diodes 27 and 28 and a capacitor 29. Voltage rectification is performed and a DC voltage is stored in the capacitor 19. When this circuit configuration is used, the gate pulse generation circuit 4 shown in FIG. 1 uses the PFM modulation (pulse frequency modulation) instead of the PWM modulation to achieve soft switching of the switching element 17.

  FIG. 5 is a block diagram of a system linkage inverter device showing a second embodiment of the present invention. In the embodiment shown in FIG. 5, a power control circuit 30 is provided instead of the maximum power follow-up control circuit 5 in FIG. 1, and the other configurations are the same as those in FIG. This embodiment corresponds to the case where a power source that operates at a constant power, such as the fuel cells 1c and 1d, is input as the DC power supply source. The power control circuit 30 adjusts the input / output voltage ratio so as to extract predetermined power from the fuel cell 1c. The power control circuit 30 receives the input current Ib and the input voltage Vb input to the voltage adjustment circuit 21 and calculates the input power Pb to the voltage adjustment circuit 21.

  A gate drive signal S for adjusting the input / output voltage ratio of the voltage adjustment circuit 21 so as to match this input power with a predetermined reference input voltage Pref is created and applied to the gate pulse generation circuit 4. The gate pulse generation circuit 4 receives the signal E from the output voltage control circuit 6, takes the product of the signal E and the gate drive signal S, and modulates this to generate a gate pulse G to create a voltage adjustment circuit. The switching element in 21 is driven.

  Here, the gate drive signal S is created so that the predetermined reference input power matches the actually detected input power. However, the operating voltage and the power are proportional to each other due to the characteristics of the DC power supply source. In this case, the input voltage set value Vb_ref may be determined so that the actual input voltage Vb matches this.

  Furthermore, if the voltage adjusting means 2a shown in FIG. 1 and the voltage adjusting means 2c shown in FIG. 5 are mixed and each output is connected in parallel, and this is input to the inverter means 7, a plurality of output characteristics differing. It can be simply configured as a grid-linked inverter device capable of inputting the power of the DC power supply source.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1a, 1b Solar cell string, 1c, 1d Fuel cell, 2a-2d Voltage adjustment means, 4 Gate signal generation circuit, 5 Maximum power tracking control circuit, 6 Output voltage control circuit, 7 Inverter means, 9, 16, 20 Voltage detection 10 Current detector 11 Maximum power tracking control circuit 14 Output power control circuit 15 Inverter circuit 30 Power control circuit 16 Reactor 17 Switching element 18, 27, 28 Diode, 19, 29 Capacitor, 22 High frequency PWM inverter, 23 high frequency isolation transformer, 24 diode bridge, 25 leakage transformer.

Claims (4)

In the power conversion device that converts the power of the DC power supply source into AC power,
Voltage adjusting means for adjusting the voltage of the DC power supply source, and inverter means for inputting the output of the voltage adjusting means and converting it into AC power,
Voltage adjustment means
A maximum power tracking control unit that adjusts the input / output voltage ratio so as to track the maximum power of the DC power supply source;
An output voltage control unit that controls the output voltage so that the output voltage does not exceed a predetermined maximum link voltage in preference to the maximum power tracking control unit,
The inverter means includes an output control unit that controls the input voltage to a predetermined input operating voltage set to a value lower than the maximum link voltage. 2. The power conversion apparatus according to claim 1, wherein a plurality of voltage adjusting means are provided, and outputs of the respective voltage adjusting means are respectively coupled in parallel and input to the inverter means. In the power conversion device that converts the power of the DC power supply source into AC power,
Voltage adjusting means for adjusting the voltage of the DC power supply source, and inverter means for inputting the output of the voltage adjusting means and converting it into AC power,
Voltage adjustment means
A power control unit that adjusts the input / output voltage ratio so as to extract predetermined power from a DC power supply source;
Including an output voltage control unit that controls the output voltage so that the output voltage does not exceed a predetermined maximum link voltage in preference to the power control unit;
The inverter means includes an output control unit that controls the input voltage to a predetermined input operating voltage set to a value lower than the maximum link voltage. The power converter according to claim 3, wherein a plurality of voltage adjusting means are provided, and at least one of them includes a power control unit and an output control unit.

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