JP5507919B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter that converts DC power into AC power, and more particularly to a power converter that is suitable for connection to a three-phase commercial power system.

  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 as a power conversion device including a DC / DC converter and an inverter, and a commercial power system 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).

  In order to connect to a three-phase commercial power system, it is only necessary to convert it to three-phase AC power using a power converter equipped with a three-phase inverter, but a three-phase inverter is constructed using multiple inexpensive single-phase inverters. In this case, there is a problem that a problem of three-phase imbalance may occur.

JP 2001-161032 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a power converter suitable for linking with a three-phase commercial power system using a plurality of inexpensive single-phase inverters. And

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

  The power conversion device of the present invention is a V-connection connection type power conversion device in which a first single-phase inverter is connected between UV terminals of a three-phase power source, and a second single-phase inverter is connected between VW terminals. By controlling the current that one single-phase inverter flows into the three-phase power source in phase with the U-phase voltage, and by controlling the current that the second single-phase inverter flows into the three-phase power source in phase with the W-phase voltage, Is a three-phase balanced current having a power factor of 1.

  When two conventional single-phase inverters connected to the system are V-connected to a three-phase power supply, the line voltage and current are controlled in the same phase. As a result, the U-phase current is 30 degrees higher than the U-phase voltage. The phase advances and the W-phase current is delayed by 30 degrees from the W-phase voltage. As a result, an unbalanced current flows through the three-phase power source. According to the present invention, the first phase connected between the UV terminals is used. The single-phase inverter controls the current flowing into the three-phase power source in phase with the U-phase voltage, and the second single-phase inverter connected between the VW terminals controls the current flowing into the three-phase power source into phase with the W-phase voltage. Thus, it becomes possible to flow a three-phase balanced current having a power factor of 1 to the three-phase power supply, and thereby it is possible to configure a power conversion device linked to the three-phase power supply without using an expensive three-phase inverter. it can.

  In one embodiment of the present invention, a DC / DC converter that converts a voltage of a DC power from a DC power source and distributes the voltage to the first and second single-phase inverters is connected to the commercial three-phase power source. It is something to be related.

  As the DC power source, a solar cell or a fuel cell is preferable.

  The DC / DC converter preferably distributes and outputs the DC power via a transformer to two single-phase inverters V-connected to a three-phase power source.

  According to this embodiment, it is possible to distribute DC power to two single-phase inverters V-connected to a three-phase power source and link them to the three-phase power source.

  In another embodiment of the present invention, the amplitudes of the current flowing into the three-phase power source by the first single-phase inverter and the current flowing into the three-phase power source from the second single-phase inverter are controlled to be the same.

  According to this embodiment, a three-phase balanced current having the same amplitude can be supplied to the three-phase power source.

  In a preferred embodiment of the present invention, the first single-phase inverter controls the current flowing into the three-phase power source so as to be in phase with the U-phase voltage with a phase delay of 30 degrees with respect to the U-V line voltage, The second single-phase inverter controls the current flowing into the three-phase power source so as to be in phase with the W-phase voltage with a phase advance of 30 degrees with respect to the V-W line voltage.

  According to this embodiment, the first single-phase inverter connected between the UV terminals is controlled to be in phase with the U-phase voltage by controlling so that the phase is delayed by 30 degrees with respect to the U-V line voltage. The second single-phase inverter connected between the terminals is controlled to be in phase with the W phase by controlling so that the phase advances by 30 degrees with respect to the V-W line voltage.

  According to the present invention, the first single-phase inverter connected between the UV terminals controls the current flowing into the three-phase power source in phase with the U-phase voltage, and the second single-phase inverter connected between the VW terminals is By controlling the current flowing into the three-phase power supply in the same phase as the W-phase voltage, it becomes possible to flow a three-phase balanced current with a power factor of 1 to the three-phase power supply, and without using an expensive three-phase inverter, A power conversion device linked to a three-phase power source can be configured.

It is a schematic block diagram of a photovoltaic power generation system provided with the power conditioner which concerns on one embodiment of this invention. It is a circuit block diagram of the DC / DC converter of FIG. FIG. 3 is another circuit configuration diagram of the DC / DC converter of FIG. 1. FIG. 4 is still another circuit configuration diagram of the DC / DC converter of FIG. 1. It is a circuit block diagram of the single phase inverter of FIG. It is a figure which shows the three-phase power supply and power converter device of a star connection. It is a figure which shows the V connection connection state of a three-phase power supply and single phase inverter 27a, 27b. It is a figure for demonstrating the three-phase unbalanced current by the conventional single phase inverter. It is a figure for demonstrating the three-phase balanced current by the single phase inverter of embodiment. It is a schematic block diagram of a solar energy power generation system provided with the power conditioner 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 solar power generation system according to this embodiment includes a solar cell 1 serving as a DC power source, and power connected to a three-phase power source 2 that is a commercial power system by converting DC power from the solar cell 1 into AC power. A power conditioner 3 as a conversion device is provided.

  The power conditioner 3 of this embodiment is an insulating type that transforms and distributes DC power from the solar cell 1 so that it can be connected to a commercial three-phase power source 2 without using a three-phase inverter. DC / DC converter 4 and two first and second single-phase inverters that convert DC power from DC / DC converter 4 into single-phase AC power and link to commercial three-phase power source 2 5-1 and 5-2.

  The first single-phase inverter 5-1 is connected between the U-phase and V-phase of the commercial three-phase power supply 2, and the second single-phase inverter 5-2 is connected between the V-phase and W-phase of the commercial three-phase power supply 2. Connected. That is, these single-phase inverters 5-1 and 5-2 are V-connected to a commercial three-phase power source 2.

  FIG. 2 shows a circuit configuration of the DC / DC converter 4 of FIG.

  The DC / DC converter 4 includes a smoothing capacitor 6 connected in parallel to the solar cell 1, a high-frequency inverter circuit 7 that converts direct-current power into alternating-current power, and transforms alternating-current power from the high-frequency inverter circuit 7. High-frequency transformer 8 that distributes equally so as to correspond to the single-phase inverters 5-1 and 5-2, and rectifier circuits 9-1 and 9-2 that rectify the full-wave rectification of the AC output from the high-frequency transformer 8, respectively. The smoothing circuits 10-1 and 10-2 that respectively smooth the outputs of the rectifying circuits 9-1 and 9-2 and apply them to the single-phase inverters 5-1 and 5-2, and the outputs of the smoothing circuit 10-2. A conversion control circuit 11 that performs switching control of the high-frequency inverter circuit 7 is provided.

  The high-frequency inverter circuit 7 includes four switching elements 12a to 12d such as IGBTs configured in a full bridge, and diodes 13a to 13d connected in antiparallel to the switching elements 12a to 12d. The high-frequency inverter circuit 7 is switching-controlled by the conversion control circuit 11 to convert DC power into high-frequency AC power.

  The high-frequency transformer 8 includes a single primary winding N1 and two secondary windings N2-1 and N2-2. The high-frequency transformer 8 transforms AC power from the high-frequency inverter circuit 7 to each rectifier circuit 9. -1, 9-2.

  Thus, in the high frequency transformer 8, in order to evenly distribute the insulated output to the two first and second single-phase inverters 5-1 and 5-2 that are V-connected to the commercial three-phase power source 2. Are provided with two secondary windings N2-1 and N2-2.

  For example, as shown in FIG. 3, the subsequent stage of the secondary windings N2-1 and N2-2 so that an equal current flows through the two secondary windings N2-1 and N2-2 of the high-frequency transformer 8. In addition, the primary windings of the current transformers (current transformers) CT1, CT2 may be connected in series, and the secondary windings of the current transformers CT1, CT2 may be connected in series, or as shown in FIG. As described above, the current transformer CT1 ′ may be configured, and the number of turns of the secondary windings N2-1 and N2-2 may be varied so that an equal current flows.

  As shown in FIG. 2, the rectifier circuits 9-1 and 9-2 at the subsequent stage of the high-frequency transformer 8 are configured by diode bridges, and are connected to the secondary windings N2-1 and N2-2 of the high-frequency transformer 8. The high-frequency current is rectified by the rectifier circuits 9-1 and 9-2, and further smoothed by the smoothing circuits 10-1 and 10-2 including the reactor 14 and the capacitor 15, so that each single-phase inverter 5- 1 and 5-2, respectively.

  The conversion control circuit 11 performs MPPT (maximum power point tracking) control in the same manner as in the prior art, and based on the output voltage of the smoothing circuit 10-2 that is the output voltage to the single-phase inverter 5-2, the high-frequency inverter circuit 7 The switching elements 12a to 12d are subjected to switching control, and the output voltage is controlled to a constant voltage, whereby the output voltages of the other smoothing circuits 10-1 and 10-2 become substantially the same voltage.

  In this way, by the insulated DC / DC converter 4, the DC power from the solar cell 1 can be evenly distributed to the two insulated outputs and supplied to the single-phase inverters 5-1 and 5-2. It becomes possible.

  FIG. 5 shows a circuit configuration of the single-phase inverters 5-1 and 5-2 in FIG. Since the configurations of the single-phase inverters 5-1 and 5-2 are the same except for control by an inverter control circuit 18 which will be described later, FIG.

  The single-phase inverter 5 includes an inverter circuit 16 connected to any one of the smoothing circuits 10-1 and 10-2 of the DC / DC converter 4, and a filter that removes harmonics of AC power converted by the inverter circuit 16. A circuit 17 and an inverter control circuit 18 that controls switching of the inverter circuit 16 based on the output of the inverter circuit 16 are provided.

  The inverter circuit 16 is a full bridge circuit composed of switching elements 19a to 19d such as IGBTs and diodes 20a to 20d. The inverter circuit 16 is controlled by an inverter control circuit 18 as will be described later, and direct current power from the DC / DC converter 4 is supplied. , Convert to AC power. The filter circuit 17 includes a reactor 21 and a capacitor 22.

  In the conventional single-phase inverter connected to the system, the current is controlled to be in phase with respect to the voltage, that is, the power factor is set to 1. When the base is connected to a three-phase power source by V-connection, there is a problem that an unbalanced current flows to the system.

  This will be described below.

  In FIG. 6, reference numeral 25 denotes a three-phase power source having terminals R, S, and T on the commercial power system side. Reference numeral 26 denotes a load-side power converter connected to the three-phase power source 25 and interconnected with the three-phase power source 25.

The three-phase power supply 25 is star-connected, and E _R , E _S , and E _T are phase voltages, and I _R , I _S , and I _T are phase currents. In the specification, the phase voltage, phase current, line voltage, and line current do not have a dot (•) indicating a vector above the symbol, but in the figure, the dot is added to indicate that the vector is a vector. Show.

  The power converter 26 includes a first single-phase inverter 27a connected between the terminals RS of the three-phase power supply 25, a second single-phase inverter 27b connected between the terminals ST, and both the single-phase inverters 27a and 27b. And a DC / DC converter 29 for supplying a direct current from the solar cell 28. As described above, the first and second single-phase inverters 27 a and 27 b are V-connected to the three-phase power source 1.

FIG. 7 shows a V-connection connection between the three-phase power supply 25 and the single-phase inverters 27a and 27b. In the three-phase power supply 25, the line voltage V _La and the line current I _La indicate the voltage and current of the single-phase inverter 27a, and the line voltage V _Lb and line current I _Lb indicate the voltage and current of the single-phase inverter 27b. In this case, the line voltage V _La and the line current I _La are controlled to be in phase, and the line voltage V _Lb and the line current I _Lb are controlled to be in phase according to the single-phase inverter regulations linked to the commercial power system.

In this state, as shown in FIGS. 8A and 8B, the phase currents I _R and I _T of the three-phase power source 25 are equal to the line current I _La . Since equal to I _Lb, the phase interval of the phase current I _S, I _R, I _T in order not to phase interval of 120 °, it becomes a three-phase unbalanced currents and phase voltages E _R, I _R is not in phase. Also, E _T and I _R are not in phase and the power factor is not 1.

That is, when two conventional single-phase inverters 27a and 27b linked to the system are V-connected to the three-phase power supply 25, the current I _R is 30 degrees ahead of the phase voltage E _R , and the phase current I _T is As a result of the phase being delayed by 30 degrees from the phase voltage E _T , a three-phase balanced current cannot be supplied to the three-phase power source 25. The phase current I _S is in phase with the phase voltage E _{S as} a result of the vector synthesis of the phase current I _R and the phase current I _T.

Therefore, in this embodiment, as shown in FIG. 9A, the line current I _L2 that the single-phase inverter 27a flows into the terminal R of the three-phase power source 1, that is, the phase current I _R is in phase with the phase voltage E _R. In addition, the line current I _L2 that the single-phase inverter 27b flows into the terminal T, that is, the phase current I _T is controlled in phase with the phase voltage E _T , so that the phase currents I _R , I _S , I _T is a three-phase balanced current with a power factor of 1. In this case, the amplitude of the current I _La that the single-phase inverter 27a flows into the terminal R and the amplitude of the current I _Lb that the single-phase inverter 27b flows into the terminal T are controlled to be the same.

Specifically, the single-phase inverter 27a controls the line current I _L2 flowing into the terminal R so as to be in phase with the phase voltage E _R with a phase delay of 30 degrees with respect to the line voltage V _La . Similarly, the single-phase inverter 27b controls the line current I _{Lb so} as to be in phase with the phase voltage E _T with a phase advance of 30 degrees with respect to the line voltage E _Lb.

As a result, as shown in the vector diagram of FIG. 9A, in the three-phase power source, the phase voltage E _R and the phase current I _R have the same phase, and the phase voltage E _T and the phase current I _T have the same phase power factor of 1. in addition, it is possible to flow the phase currents I _R, as shown in FIG. 9 (b), I _S, the three-phase power supply 25 to the three-phase balanced currents I _T.

  Next, description will be made in more detail by applying to the specific embodiment of FIG.

  In the embodiment shown in FIG. 1, in the first single-phase inverter 5-1 connected between the UV terminals of the three-phase power source 2, the inverter control circuit 18 shown in FIG. The second single-phase inverter 5-2 connected between the VW terminals is controlled so as to be in phase with the U-phase voltage with a phase delay of 30 degrees with respect to the U-V line voltage, and the inverter control shown in FIG. The circuit 18 controls the current flowing into the three-phase power supply 2 so as to be in phase with the W-phase voltage by a phase advance of 30 degrees with respect to the V-W line voltage.

  That is, the inverter control circuit 18 of the first single-phase inverter 5-1 generates a current command that is delayed by 30 degrees from the detected voltage phase of the system, and the current flowing into the three-phase power supply 2 is in phase with the U-phase voltage. The inverter control circuit 18 of the second single-phase inverter 5-2 generates a current command that is 30 degrees ahead of the detected voltage phase of the system, and supplies the current to the three-phase power source 2. Control is performed so that the current flowing in is in phase with the W-phase voltage.

  As a result, as shown in FIG. 9 described above, a three-phase balanced current having a power factor of 1 can be supplied to the three-phase power source 2, and two single-phase inverters 5-5 can be used without using an expensive three-phase inverter. The power conditioner 3 linked to the three-phase power source 2 can be configured using 1,5-2, and the cost can be reduced.

  In the power conditioner 3 of the above-described embodiment, as shown in FIG. 1, the DC power from one DC / DC converter 4 is distributed to the two single-phase inverters 5-1 and 5-2. As another embodiment, a plurality of DC / DC converters, for example, direct current from three solar cells 1-1 to 1-3 in which solar cell modules are grouped (stringed) as shown in FIG. Three DC / DC converters 4-1 to 4-3 to which power is applied are connected in parallel to two single-phase inverters 5-1 and 5-2, and each DC / DC converter 4-1 to 4-4 is connected. 3 outputs may be supplied to the two single-phase inverters 5-1 and 5-2, respectively. The three DC / DC converters 4-1 to 4-3 have the same configuration as the DC / DC converter 4 described above.

  In FIG. 10, even if the power generation output of each of the solar cells 1-1 to 1-3 varies depending on the sunshine state or the like, the output is evenly distributed to the single-phase inverters 5-1 and 5-2. As described above, each single-phase inverter 5-1, 5-2 controls the current flowing into the three-phase power source 2 to be in phase with the U-phase voltage or the W-phase voltage. It is possible to flow a phase equilibrium current.

  In the above-described embodiment, the rectifier circuit of the DC / DC converter is a full-wave rectifier circuit. However, as another embodiment of the present invention, a voltage doubler rectifier circuit is used, and the secondary winding voltage of the high-frequency transformer is The voltage may be boosted to twice the voltage.

  The present invention is useful as a power converter.

DESCRIPTION OF SYMBOLS 1,1-1-1-3 Solar cell 2 Three-phase power supply 3,3-1 Power conditioner 4,4-1-4-3 DC / DC converter 5-1,5-2 Single phase inverter 8 High frequency transformer

Claims (1)

A V-connection connection type power converter in which a first single-phase inverter is connected between UV terminals of a three-phase power source and a second single-phase inverter is connected between VW terminals,
By controlling the current that the first single-phase inverter flows into the three-phase power supply in phase with the U-phase voltage, and by controlling the current that the second single-phase inverter flows into the three-phase power supply in phase with the W-phase voltage, The phase current of the power source is a three-phase balanced current with a power factor of 1,
A high-frequency inverter circuit that converts DC power from a DC power source into AC power, a single primary winding and two secondary windings, transform the converted AC power, and A high-frequency transformer equally distributed to two outputs so as to correspond to the phase inverter, and at least one current transformer connected to the subsequent stage so that an equal current is output from the two secondary windings of the high-frequency transformer And a DC / DC converter having two rectifier circuits for full-wave rectifying each of the distributed AC power,
DC power from the DC power source is evenly distributed to two outputs insulated by a high frequency transformer in the DC / DC converter , and an equal current is output from each secondary winding by the current transformer. A power converter that feeds power to the first and second single-phase inverters and is linked to the commercial three-phase power source.

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