JP2011164964A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow operation while a plurality of power converters are connected in parallel to a solar battery. <P>SOLUTION: A plurality of DC/DC converters 5<SB>1</SB>to 5<SB>3</SB>are connected in parallel to a plurality of solar battery panels 1<SB>1</SB>to 1<SB>3</SB>, a PFM control part 17 generates a current increase/decrease command so as to perform the maximum power conversion control as the entire DC/DC converters 5<SB>1</SB>to 5<SB>3</SB>, a distributing part 18 corrects the current increase/decrease command to distribute the corrected current increase/decrease command to the respective DC/DC converters 5<SB>1</SB>to 5<SB>3</SB>so as to cause current of a predetermined distribution rate to flow, and the respective DC/DC converters 5<SB>1</SB>to 5<SB>3</SB>perform current control on the basis of the distributed current increase/decrease command. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power converter that converts a DC power of a solar cell panel by connecting a plurality of power converters in parallel to the solar cell panel.

  In recent years, development of distributed power systems using solar cells, fuel cells, and the like that have little environmental impact has been actively promoted from the viewpoint of global environmental protection. In such a distributed power supply system, DC power generated by a solar cell or the like is converted into AC power of a commercial frequency by a power conditioner including a DC / DC converter and an inverter as a power converter. In addition to being connected and supplied to a load, surplus power is reversely flowed to a commercial power system (see, for example, Patent Document 1).

JP 2001-161032 A

  As the DC / DC converter, there is a high-frequency transformer insulation type DC / DC converter (hereinafter referred to as a “high-frequency insulation DC / DC converter”). In such a high-frequency insulation DC / DC converter, an efficient and large-capacity high-frequency transformer is used. It is difficult to manufacture, and if the capacity is increased, the efficiency does not increase. At present, the capacity is about 2 kW.

  For this reason, for example, when obtaining large generated power of 10 kW or more, for example, five DC / DC converters of the above capacity are individually connected to each of the five solar cell panels, and the DC power of each solar cell panel is individually supplied. It is conceivable that the generated power of 10 kW or more is obtained by conversion, but in such a connection form, when the generated power is increased, the number of solar cell panels and DC / DC converters increases and the number of wirings increases. Wiring work becomes more complicated.

  Therefore, a plurality of solar cell panels are collectively connected in parallel, and a plurality of DC / DC converters are collectively connected in parallel, and each solar cell panel and each DC / DC converter are connected in parallel. It is conceivable to simplify the wiring work by reducing the total number of wires by connecting the sides to each other.

  However, conventionally, each of the above DC / DC converters is changed so that the operating point of the solar cell follows the maximum output point, and maximum power tracking control (MPPT: Maximum Power Point Tracking) for extracting the maximum output from the solar cell. However, there is a problem in that each DC / DC converter performs power conversion by controlling the input currents separately.

  Therefore, the present invention has been made in view of the above-described problems, and in order to obtain a larger power generation output, a plurality of power converters are connected in parallel to simplify the wiring of the solar cell. An object of the present invention is to provide a power conversion device that enables current control when performing maximum power tracking control.

  In order to achieve the above object, the present invention is configured as follows.

  The power conversion device of the present invention is a power conversion device including a plurality of power converters connected in parallel to a solar cell, and a current command so as to perform maximum power tracking control of the solar cell as the whole of the plurality of units. Alternatively, a generation unit that generates a current increase / decrease command and a distribution unit that distributes the current command generated by the generation unit or the current increase / decrease command to each of the plurality of power converters.

  The power converter may be a DC / DC converter or an inverter.

  In the distribution means, it may be simply distributed, or may be distributed with some processing such as correction.

  According to the power conversion device of the present invention, a current command or a current increase / decrease command is generated so as to perform maximum power follow-up control as a whole of a plurality of power converters, and the generated current command or current increase / decrease command is converted to each power conversion. Therefore, each power converter can perform control based on the distributed current command or current increase / decrease command, and each power converter cannot perform current control as in the conventional example in which maximum power tracking control is performed. There is no such thing.

  In one embodiment of the power conversion device of the present invention, the solar cell is a single solar cell panel or a plurality of solar cell panels whose outputs are connected in parallel, and the distribution unit is generated by the generation unit. A current command is distributed as an input current command for each power converter, and each power converter performs current control based on the input current command.

  The input current command is a current command within the allowable current of the power converter.

  According to this embodiment, the current command generated by the generating unit is distributed as an input current command for each power converter, and each power converter can perform current control based on the input current command. Furthermore, since power conversion is performed by connecting a plurality of solar cell panels and a plurality of power converters in parallel, the generated power can be increased, and a plurality of solar cell panels and a plurality of power converters are individually connected. The number of wirings can be reduced as compared with the configuration in which each is connected.

  In another embodiment of the power conversion device of the present invention, the solar cell is a single solar cell panel or a plurality of solar cell panels whose outputs are connected in parallel, and the distributing means is a current generated by the generating means. The increase / decrease command is corrected and distributed based on each input current of each power converter and a predetermined current distribution ratio, and each of the power converters is controlled by the corrected current increase / decrease command. Is.

  The current distribution ratio defines the ratio of the current flowing through each power converter, and this ratio may be changed according to a change in the generated power of the solar cell.

  Further, the current distribution ratio may be an equal ratio or an unequal ratio, and a ratio that provides the maximum efficiency as a whole of the plurality of power converters, for example, a plurality of power converters. The ratio may be such that at least one of them is stopped.

  In the distribution means, when the input current is substantially equal to the current defined by the predetermined current distribution ratio, the current increase / decrease signal is distributed without correction, while the input current is defined by the predetermined current distribution ratio. When the current is different from the current, the current increase / decrease signal is preferably corrected and distributed so that the current is defined by a predetermined current distribution ratio.

  According to this embodiment, the current increase / decrease command generated by the generating means is corrected so that each input current of each power converter becomes a current based on a predetermined current distribution ratio, The power converter can be controlled. Furthermore, since power conversion is performed by connecting a plurality of solar cell panels and a plurality of power converters in parallel, the generated power can be increased, and a plurality of solar cell panels and a plurality of power converters are individually connected. The number of wirings can be reduced as compared with the configuration in which each is connected.

  In another embodiment of the present invention, each of the power converters may be a DC / DC converter including a step-up chopper or a current resonance type DC / DC converter.

  According to the present invention, the current command or the current increase / decrease command is generated so as to perform the maximum power follow-up control as a whole of the plurality of power converters, and the generated current command or the current increase / decrease command is distributed to each power converter. In each power converter, control based on the distributed current command or current increase / decrease command is possible, and current control cannot be performed unlike the conventional example in which each power converter performs maximum power tracking control.

It is a schematic structure figure of a photovoltaic power generation system concerning one embodiment of the present invention. It is a schematic block diagram of the solar energy power generation system of other embodiment of this invention. It is a schematic block diagram of the solar energy power generation system which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system including a power conversion device according to one embodiment of the present invention.

The photovoltaic power generation system includes a plurality of the DC power source, and three of the solar cell panel 1 ₁ to 1 ₃ in this embodiment, the DC power from the solar cell panel 1 ₁ to 1 _3, and converted into AC power And a power conditioner 3 as a power conversion device linked to the single-phase power supply 2, for example, which is a commercial power supply system. Outputs of the _three solar cell panels 1 ₁ to ₁₃ are connected in parallel to each other through backflow prevention diodes 4 ₁ to 4 ₃ .

The power conditioner 3 includes a plurality of DC / DC converters 5 _{1 to} 53 ₃ having high frequency transformer insulation as the power converters, and a DC / DC converter having three or more power converters in which the input side and the output side are connected in parallel. DC power from 5 ₁ to 5 _3, and an inverter 25 for interconnection to the single-phase power supply 2 of the commercial is converted into AC power of single-phase.

Each DC / DC converter ₅ 1 to 5 _3, the converter is of a current resonance type by the half-bridge coupling system. Each DC / DC converter ₅ 1 to 5 _3, for example, a switching element 6a and the switching element 6b as the main switch and auxiliary switch comprising a MOS-FET, the diode 7a, and 7b, the partial voltage resonant capacitor 8, the current resonance A capacitor 9 and a high-frequency transformer 10 are provided, and a voltage doubler rectifier circuit including diodes 11 and 12 and capacitors 13 and 14 is provided on the secondary side. The high-frequency transformer 10 includes a leakage inductance 15 on the primary side and is used for current resonance.

Each DC / DC converter ₅ 1 to 5 ₃ includes switching elements 6a, drive circuit 16a for switching driving 6b, the 16b. Each drive circuit 16a, 16b applies a drive signal having a frequency corresponding to a required pulse width of a PFM control signal described later to the gates of the switching elements 6a, 6b.

Each of the current resonance type DC / DC converters 5 _{1 to} 5 ₃ operates by PFM (pulse frequency modulation) control, and the switching elements 6a and 6b are switched in a complementary manner to perform zero voltage switching. it can.

In this embodiment, in order to enable the current control of the solar cell panel 1 ₁ to 1 ₃ in parallel connected three DC / DC converter 5 ₁ to 5 _3, is constructed as follows.

That is, the power conditioner 3 of this embodiment outputs a PFM control signal as a current increase / decrease command so as to perform maximum power follow-up control (MPPT) of the solar cell as a whole of the _three DC / DC converters 5 _{1 to} 53. A PFM control unit 17 serving as a generation unit to generate, and a PFM control signal from the PFM control unit 17 is divided into input currents and predetermined current distribution ratios k1 to k3 of the DC / DC converters 5 _{1 to} 5 _3. based on, it has been modified each DC / DC converter ₅ 1 to 5 ₃ of the drive circuit 16a, and a distributor 18 that distributes the 16b.

The PFM controller 17, the detection output of the voltage detector 19 for detecting the output voltage of the solar cell panel ₁ 1 to 1 _3, and, each detecting a respective input currents of the DC / DC converter ₅ 1 to 5 _3, respectively The output of the adder 21 that gives the total current by adding the detection outputs of the current detectors 20 _{1 to} 20 ₃ is given. That is, the PFM controller 17, the detection output in accordance with the output voltage and output current of the solar cell panel 1 ₁ to 1 ₃ are respectively given, based on these, PFM control unit 17, so-called, by hill climbing method performed to extract the maximum power from the solar battery panel 1 ₁ to 1 _3, the maximum power follow-up control with the pulse width is computed outputs PFM control signal is a pulse width decrease signals controlled (MPPT).

That is, the PFM controller 17 to extract the maximum power from the solar battery panel ₁ 1 to 1 _3, and outputs a PFM control signal is a current increase or decrease instruction to increase or decrease the output current of the solar cell panel ₁ 1 to 1 ₃ .

Distributor 18 for distributing to modify the PFM control signal to each DC / DC converter ₅ 1 to 5 _3, the output of the adder 21 is the sum of the input current of the DC / DC converter ₅ 1 to 5 _3, Multipliers 22 _{1 to} 22 ₃ that respectively multiply the distribution ratios k1 to k3, and subtractors that calculate the deviation between the outputs of the multipliers 22 _{1 to} 22 _{3 and} the outputs of the current detectors 20 _{1 to} 20 ₃ described above. 23 _{1-23 3,} based on the output of the subtracters ₂₃ 1 to 23 _3, the correction unit 24 gives to the PFM control signal to modify the respective DC / DC converter ₅ 1 to 5 ₃ of the PFM controller 17 and a _{1-24 3.}

The current distribution ratios k1 to k3 in the multipliers 22 _{1 to} 22 ₃ are k1 + k2 + k3 = 1. In this embodiment, for example, k1 = k2 = k3 = 1/3, and each DC / DC converter 5 ₁ It is the ratio of flow equal currents to 5 _3.

In the subtracters ₂₃ 1 ~ 23 _3, the DC / DC converter ₅ 1 to 5 and current the total current was aliquoted into 1/3 by the multiplier ₂₂ 1 to 22 ₃ of _3, the DC / DC converter ₅₁ to 5 ₃ deviation of the actual current is calculated.

In each of the correction units 24 _{1 to} 24 ₃ , the PFM control signal that is a pulse width increase / decrease signal from the PFM control unit 17 is corrected, for example, as follows according to the deviation from each of the subtractors 23 ₁ to 23 _3. and it applies the same to the DC / DC converter ₅ 1 to 5 _5.

  That is, when the deviation is zero or small, it is determined that the desired distribution is performed, and the pulse width increase / decrease signal is output to the corresponding DC / DC converter without correcting the pulse width increase / decrease signal. .

  Also, for example, when the deviation is negative and large, that is, when a larger amount of current is flowing compared to the desired distribution, when the pulse width increase / decrease signal is in the direction of increasing the pulse width, increasing the pulse width, Since more current flows, a pulse width increase / decrease signal corrected so as not to increase the pulse width is output to the corresponding DC / DC converter. Further, when a larger amount of current flows than the desired distribution, when the pulse width increase / decrease signal is in the direction of decreasing the pulse width, the corresponding DC / DC converter is directly used without correcting the pulse width increase / decrease signal. Output. As a result, in the DC / DC converter in which a larger amount of current flows than in the desired distribution, the current is suppressed.

  Further, when the deviation is positive and large, that is, when the current flowing is small compared to the desired distribution, if the pulse width increase / decrease signal is in a direction to increase the pulse width, the pulse width increase / decrease signal is not corrected and remains unchanged. Output to the corresponding DC / DC converter. In addition, when the current flowing is smaller than the desired distribution, if the pulse width increase / decrease signal is in a direction to reduce the pulse width, the current will decrease further if the pulse width is reduced, so the pulse width is not reduced. The pulse width increase / decrease signal is output to the corresponding DC / DC converter. As a result, in a DC / DC converter in which the current that flows is smaller than the desired distribution, the current is controlled to increase.

Note that the correction in each of the correction units 24 _{1 to} 24 ₃ is not limited to the above, and may be further finely corrected according to the conditions.

Each of the drive circuits 16a and 16b of the DC / DC converters 5 _{1 to} 5 ₃ to which the PFM control signal which is a pulse width increase / decrease signal from each of the correction units 24 _{1 to} 24 ₃ is given according to the pulse width of the PFM control signal. The switching elements 6a and 6b are switched and driven.

As a result, the DC / DC converters 5 _{1 to} 5 ₃ are configured to receive current evenly in accordance with the distribution ratios k ₁ to k ₃ so as to extract the maximum power from the solar cell panels 1 ₁ to 13 as a whole. Become.

As described above, the PFM control unit 17 generates a PFM control signal as a current increase / decrease command so that the three DC / DC converters 51 to 53 perform the maximum power tracking control as a whole, and the distribution unit 18 generates the generated PFM control. since signal, current corresponding to the distribution ratio k1~k3 modifies to distribute to flow for each DC / DC converter ₅ 1 to 5 _3, three DC / DC converter ₅ 1 to 5 ₃ cooperation may convert the DC power from the solar cell panel 1 ₁ to 1 _3.

DC power from these DC / DC converter 5 ₁ to 5 ₃ is converted by inverter 25 into AC power of the communication system with single-phase commercial power source.

(Embodiment 2)
FIG. 2 is a schematic configuration diagram of a photovoltaic power generation system including a power conversion device according to another embodiment of the present invention, and parts corresponding to those in FIG.

Photovoltaic system of this embodiment, the three solar panels 1 ₁ to 1 _3, a commercial power system DC power from the solar cell panel 1 ₁ to 1 _3, and converted into AC power, for example, And a power conditioner 3a as a power converter connected to the single-phase power source 2. Outputs of the _three solar cell panels 1 ₁ to ₁₃ are connected in parallel to each other through backflow prevention diodes 4 ₁ to 4 ₃ .

The power conditioner 3a includes a plurality of DC / DC converters 5 ₁ a to 5 ₃ a serving as power converters, and a DC / DC converter 5 ₁ a as a plurality of power converters in which the input side and the output side are connected in parallel. The inverter 25 connected to the commercial single-phase power source 2 by converting the DC power from ˜5 ₃ a into single-phase AC power.

Each of the DC / DC converters 5 ₁ a to 5 ₃ a includes a switching element 26 formed of a transistor, and a non-insulated boost chopper including an inductance 27, a diode 28, and a capacitor 29. Each is driven by PWM (pulse width modulation) as described later.

In this embodiment, in order to enable the current control of three DC / DC converter ₅ 1 _{a~5 3} a which is connected in parallel to the solar cell panel ₁ 1 to 1 _3, is configured as follows .

That is, the power conditioner 3a of this embodiment generates a current command so as to perform the maximum power follow-up control (MPPT) of the solar cell as a whole of the _three DC / DC converters 5 ₁ a to 5 ₃ a. And a distribution unit 32 that distributes a current command from the maximum power tracking control unit 31 to each of the DC / DC converters 5 ₁ a to 5 ₃ a as an input current command. And.

Each DC / DC converter 5 ₁ to 5 _3, based on the input current command from the distribution unit 32, and a current control so as to perform, respectively.

The maximum power follow-up control unit 31, the detection output of the voltage detector 19 for detecting the output voltage of the solar cell panel ₁ 1 to 1 _3, and, each input current of each DC / DC converter ₅ 1 _{a~5 5} a The outputs of the adders 21 that calculate the total current by adding the detection outputs of the respective current detectors 20 _{1 to} 20 ₃ to be detected are given. That is, the maximum power follow-up control unit 31, the detection output in accordance with the output voltage and output current of the solar cell panel 1 ₁ to 1 ₃ are respectively given, on the basis of these, the maximum power follow-up control unit 31 is a so-called , the hill climbing method, performed to extract the maximum power from the solar battery panel 1 ₁ to 1 _3, the maximum power follow-up control for calculating an output current command a (MPPT).

The distribution unit 32 that distributes the current command to the DC / DC converters 5 ₁ a to 5 ₃ a includes multipliers 22 _{1 to} 22 ₃ that multiply the current command by the distribution ratios k _{1 to} k ₃ , respectively. The current distribution ratios k1 to k3 in the multipliers 22 _{1 to} 22 ₃ are k1 + k2 + k3 = 1. In this embodiment, for example, k1 = k2 = k3 = 1/3. These current commands are equally divided into input current commands for the DC / DC converters 5 ₁ a to 5 ₃ a.

That is, in this embodiment, the maximum power follow-up control unit 31, generates a current command to extract the maximum power from the solar battery panel ₁ 1 to 1 ₃ as a whole three DC / DC converter ₅ 1 _{a~5 3} a The distribution unit 32 equally divides the current command and distributes it as input current commands to the DC / DC converters 5 ₁ a to 5 ₃ a.

The DC / DC converters 5 ₁ a to 5 ₃ a respectively calculate first deviations 33 ₁ to 33 that calculate deviations between the input current commands and the actual input currents detected by the current detectors 20 _{1 to} 20 ₃ , respectively. 33 ₃ , compensators 34 _{1 to} 34 ₃ that compensate so as to eliminate deviations, and comparators 36 _{1 to} 36 ₃ that compare the outputs of the compensators 34 _{1 to} 34 ₃ with the carrier waves from the carrier wave generator 35. includes a drive of the comparators ₃₆ 1 ~ 36 PWM signal from the ₃ are respectively given to the driving circuits 30 each switching element 26 is controlled.

Thus, each DC / DC converter ₅ 1 to 5 _3, so that uniform current corresponding to an input current command from the distribution unit 32 flows.

Thus, the maximum power follow-up control unit 31 generates a current command so as to perform the maximum power follow-up control as a whole of the DC / DC converters 5 _{1 to} 5 ₃ , and the distribution unit 32 receives the current from the maximum power follow-up control unit 31. command, distribute as input current command for each DC / DC converter ₅ 1 to 5 _3, each DC / DC converter ₅ 1 to 5 _3, since the current control according to the input current command, the three DC / DC converter ₅ 1 to 5 ₃ in cooperation can convert the DC power from the solar cell panel ₁ 1 to 1 _3.

DC power from these DC / DC converter 5 ₁ to 5 ₃ is converted by inverter 25 into AC power of the communication system with single-phase commercial power source.

In the above-described embodiment, the current command is evenly distributed to the _three DC / DC converters 5 _{1 to} 5 _3. However, as another embodiment of the present invention, the three DC / DC converters 5 _{1 to} 5 _{3 are used.} For example, when the input voltage is low, an input current command that reduces the number of operating DC / DC converters 5 _{1 to} 5 ₃ is given so that the most efficient operation as a whole can be performed. You may do it.

Each DC / DC converter 5 ₁ to 5 _3, if not connected in parallel, as in the prior art, each may perform the maximum power follow-up control.

In each of the above-described embodiments, description has been made by applying the present invention to a DC / DC converter as a power converter. However, the present invention can also be applied to an inverter without the DC / DC converter. As shown in the power conditioner 3b, the same maximum power follow-up control unit 31 and distribution unit 32 as those in the above-described embodiment are provided, and an input current command generated by the maximum power follow-up control unit 31 and distributed by the distribution unit 32 is received. , while providing a respective current control inverter _{25 to} 253 of three, the detection output of the current detector ₂₀ 1 to 20 _3, respectively provided in each of the current control inverter _{25 to} 253 of three, each of the current control Current control according to the input current command may be performed by the inverters 25 _{1 to} 25 ₃ . In each inverter _{25 to} 253, is also performed similar to the conventional power factor controller.

  In each of the above-described embodiments, the commercial power supply system is connected to the single-phase power supply 2, but it is needless to say that the commercial power supply system may be connected to a three-phase power supply.

  The present invention is useful for power conversion of a photovoltaic power generation system that converts power from a solar cell.

1 ₁ to 1 ₃ Solar panel 2 Single phase power supply 3, 3 a, 3 b Power conditioner 5 _{1 to} 5 ₃ , 5 ₁ a to 5 ₃ a DC / DC converter 17 PFM control unit 18, 32 Distribution unit 25, 25 ₁ -25 ₃ Inverter 31 Maximum power tracking controller

Claims (5)

A power conversion device comprising a plurality of power converters connected in parallel to a solar cell,
Generating means for generating a current command or a current increase / decrease command so as to perform maximum power follow-up control of the solar cells as a whole of the plurality of units;
Distributing means for distributing the current command or current increase / decrease command generated by the generating means to each of the plurality of power converters;
A power conversion device comprising: The solar cell is a single solar cell panel or a plurality of solar cell panels whose outputs are connected in parallel,
The distribution unit distributes the current command generated by the generation unit as an input current command to each power converter,
Each of the power converters performs current control based on the input current command,
The power conversion device according to claim 1. The solar cell is a single solar cell panel or a plurality of solar cell panels whose outputs are connected in parallel,
The distribution unit corrects and distributes the current increase / decrease command generated by the generation unit based on each input current of each power converter and a predetermined current distribution ratio,
Each of the power converters is controlled by a corrected current increase / decrease command.
The power conversion device according to claim 1.   The power converter according to claim 2, wherein each of the power converters is a DC / DC converter including a step-up chopper.   The power converter according to claim 3, wherein each of the power converters is a current resonance type DC / DC converter.

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