JP2006280106A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion device capable of bringing electric power into a reverse power flow and a utility interactive system using this power conversion device. <P>SOLUTION: The power conversion device includes: a power conversion unit that converts the direct-current power of a direct-current power source into alternating-current power and supplies it to a single-phase, three-wire commercial system and an alternating-current load to interconnect them; a commercial system voltage monitoring unit that monitors the commercial system voltage between phases U and O and that between phase O and W of the single-phase, three-wire commercial system; and an output changing unit that connects the power conversion unit to any of between phases U and O, between phases O and W, and between phases U and W. The output changing unit is changed to any of between phases U and O, between phases O and W, and phases U and W according the respective voltages between phase U and O, between phase O and W, and between phases U and W, and brings the power conversion unit and the single-phase, three-wire commercial system into utility interconnected operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power conversion device for connecting a DC power source such as a solar cell, wind power generation, and a fuel cell and a commercial power system.

  Conventionally, as shown in FIG. 5, the grid connection system J is a single-phase commercial power system in which a DC power source 1 such as a solar cell is connected to a power conditioner 5 that is a power conversion device that converts DC to AC. It is connected to a three-wire distribution line 3. In general, a single-phase three-wire distribution line 3 is connected to a U-phase electric wire U3, an O-phase (neutral wire) O3, and a W-phase electric wire W3. , 100V can be obtained between the O-W phases, and is supplied to a load 4 (4a, 4b) of AC 100V used in a general home. In addition, since a voltage of 200 V can be obtained between U and W, a device with less current loss than the 100 V system such as an AC 200 V load (for example, an air conditioner) can be used.

  By the way, the power conditioner 5 converts the DC power generated by the DC power source 1 into an AC voltage of 200 V, supplies power to the load 4 via the single-phase three-wire distribution line 3, and sells the power to the power company. However, at this time, power is transmitted only at 200 V between the two phases of the terminal portion U31 and the terminal portion W31, and no power is output from the O-phase terminal portion O31. Therefore, the AC power of 200 V output from the power conditioner 5 can only be supplied to the single-phase three-wire distribution line 3 as 200 V once, but by connecting to the single-phase three-wire distribution line 3, Since the electric wire O31 which is the O phase of the single-phase three-wire distribution line 3 can be used as a neutral wire, it can be supplied to the loads 4a and 4b as 100V electric power. Normally, the power conditioner 5 is connected to the O-phase terminal portion O31 from the single-phase three-wire distribution line 3, but this is not for power transmission but to suppress the system voltage rise described later. It is necessary to detect the voltage between the U-O phase and the OW phase, which are single-phase three-wire distribution lines, and for this purpose, a neutral wire is connected.

  In general, there are a load 4a between the U-O phase and a load 4b between the OW phases in the home load, and the U-O phase voltage 3a and the OW phase voltage 3b are balanced by the capacity balance of these loads. The balance is determined. That is, if the consumption of the load 4a is large and the consumption of the load 4b is small, the voltage of the U-O interphase voltage 3a is lowered, and a phenomenon occurs in which the balance with the almost unchanged O-W interphase voltage 3b is lost. This is shown in FIG. As shown in FIG. 6, for example, even if the U-O voltage 3a is reduced to 95V due to an increase in consumption of the load 4a, the relatively low consumption O-W voltage 3b is about 105V. At this time, the power conditioner 5 outputs 200V power to the U phase and W phase (31 and 33 points) of the single-phase three-wire distribution line 3, so the voltage between the U phase and the W phase is 200V (95V + 105V = 200V). Therefore, power can be supplied without problems and reverse power flow is possible.

  In addition to the above, the system voltage in ordinary houses has a change such as a voltage increase, which is caused by the following two points.

  (A) When there is an environment that uses a large amount of power, such as a factory, in the area surrounding the house, and when the factory is on a holiday, the power is not used, so the load on the system is reduced and the factory operates on weekdays. The voltage may rise several days from the day. For example, the system is usually in the state where the system around 100V becomes 103 to 105V, but this is defined as a range of 101 ± 6V by definition, and is not abnormal.

  (B) In the case of a change in household load or a reverse power flow due to a private power generator, if the power consumption in the area greatly increases or decreases depending on the usage status of home appliances, the power will not decrease during use. The company responds by increasing the supply amount, but if the usage amount decreases, the voltage increases, so the supply amount is limited.

  In addition to these, the electric power used in the home also increases in voltage when it changes in each room depending on the time of day. This can be understood from the load balance described above. When the load 4a between the U-O phases and the load 4b between the OW phases in the single-phase three-wire distribution line 3 change, the system voltage also increases or decreases depending on the magnitude of the load. When considering the case where the load decreases, it can be seen that the system voltage changes in an increasing direction.

  Here, for example, if the situation (a) and the situation (a) overlap, first, as shown in FIG. 7A, the U-O phase voltage and the OW phase voltage of the system are both 105V. As shown in FIG. 7 (b), the U-O phase voltage rises due to sudden load reduction, and becomes higher than an arbitrary voltage (generally 107 V or less, which is a voltage to be suppressed). .

  In addition, when there are many things that supply power to the AC load in the house or reverse power flow to the commercial power system, such as solar power generators installed on the roofs of ordinary houses, the commercial power in the district is generated by the reverse power flow. There are also cases where power is excessively supplied to the system and the voltage rises.

  In such a case, the power company recovers by adjusting the amount of power, but the voltage does not drop to the optimum value until the power remaining in the power line such as the transmission line is consumed, so it takes time to recover. Cost. In Japan, if it exceeds 107V, it will deviate from the standard value of the commercial power system, so it is necessary for the grid-connected system to suppress the system voltage rise for system protection. It operates so that the system voltage becomes 107V or less by stopping the reverse power flow from the power generator.

  As a result, the U-O phase voltage becomes lower than 107 V, as shown at least in FIG. However, there is a problem in that the reverse power flow from a private power generation device such as a solar power generation device must be stopped, and the generated power during that time cannot be used effectively.

As a countermeasure against this, a method has been proposed in which the pull-in column voltage at an arbitrary time can be estimated so that the pull-in column voltage during reverse flow does not always exceed 107V regardless of load fluctuations. (For example, refer to Patent Document 1).
JP 2000-31438 A

  However, the above-described method for suppressing the system voltage increase in the system interconnection system described above suppresses the increase in the system voltage by intentionally decreasing the output power at that time and decreasing the reverse power flow to the system. This means that even if there is no problem with the DC power supply, the output power may be reduced, which will reduce the total efficiency for the user. Is also connected.

  The present invention has been made in view of the above-described conventional problems, and makes it possible to perform a control that does not cause or hardly causes a voltage increase due to a collapse of the load balance of the system voltage phase, and suppresses a voltage increase in the unlikely event. When this occurs, it is an object of the present invention to provide a power converter that can perform control to maintain the voltage balance of each phase and can reversely flow without leaving power and a grid interconnection system using the power converter.

  In order to solve the above-described problems, a power conversion device according to the present invention converts DC power of a DC power source into AC power, and supplies the AC power to a single-phase three-wire commercial system and an AC load for system interconnection. A converter, a commercial system voltage monitoring unit that monitors respective commercial system voltages between the U-O phase and the OW phase of the single-phase three-wire commercial system, and the power conversion unit between the U-O phase or A power conversion device including an output switching unit linked to either the O-W phase or the U-W phase, wherein each voltage between the U-O phase, the O-W phase, and the U-W phase Accordingly, the output switching unit is switched between the U-O phase, the O-W phase, or the U-W phase, and the power conversion unit and the AC power are connected to a single-phase three-wire commercial system. It was made to let it be made to do.

  According to the power conversion device of the present invention, the DC power of the DC power supply is converted into AC power, the AC power is supplied to a single-phase three-wire commercial system and an AC load, and the power conversion unit is connected to the grid, and A commercial system voltage monitoring unit that monitors the commercial system voltage between the U-O phase of the single-phase three-wire commercial system and the OW phase, and the power conversion unit between the U-O phase or the OW phase, A power conversion device including an output switching unit linked to any of the U-W phases, wherein the output switching is performed according to respective voltages between the U-O phase, between the OW phase, and between the U-W phases. The unit is switched between the U-O phase, the OW phase, or the U-W phase so that the power conversion unit and the AC power are connected to the single-phase three-wire commercial system. The voltage rise due to the imbalance of the load balance of the system voltage phase Not staggered, or allow control of difficult to occur and then, it is possible to construct a system interconnection system using a power converter and its possible reverse flow without leaving power.

  In the unlikely event that a voltage increase occurs, depending on the status of the system voltage during which the voltage increase is being suppressed, the phase to be linked (any of U-O phase, OW phase, or U-W phase) and output voltage ( After switching between 100V system and 200V system), it is possible to reconnect to a lower voltage phase depending on the status of the system voltage during the voltage increase suppression because the return from the voltage increase suppression control and the system interconnection are performed. In addition, it is possible to provide a power conversion device that enables control to maintain the voltage balance of each phase and can reversely flow without leaving power.

Can be built.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a power conversion device and a grid interconnection system using the same according to the present invention will be described in detail based on the drawings.

  As shown in FIG. 1, the grid interconnection system S includes a DC power source 1 such as a solar cell, a wind power generation unit, or a fuel cell via a power conditioner 2 that is a power conversion device that converts direct current to alternating current. It is connected to a single-phase three-wire distribution line 3 which is a single-phase three-wire commercial power system. A U-O interphase load 4a and an O-W interphase load 4b are connected to the single-phase three-wire distribution line 3.

  The power conditioner 2 includes a system voltage monitoring unit 25 that monitors system voltages between the U-O phase and the OW phase, and between the U-O phase, the OW phase, and the U-W phase. The output switching unit 24 to be connected, the voltage conversion unit 22 capable of switching the voltage to be reversely flowed to either the 100V system or the 200V system, and the single-phase three-wire system by tuning the voltage and phase. The power conversion unit 23 is configured to perform reverse power flow, and the control unit 21 is configured to control the output switching unit, the voltage conversion unit, and the power conversion unit based on voltage information from each system voltage monitoring unit.

  The output switching unit 24 includes a phase changeover switch 24a for connecting the output of the first output line INV1 from the power conversion unit 23 to the U phase or the O phase, and the output of the second output line INV2 from the power conversion unit 23. Is constituted by a phase changeover switch 24b for connecting the O to the O phase or the W phase.

  Here, the power conditioner 2 monitors the voltage between the U-O phase and the OW phase, and depending on the state of the system voltage immediately before the linkage, the linked phases (between the U-O phase, the OW phase, the U-W, Any one of the -W phases) and the output voltage (either 100V system or 200V system) are switched before grid interconnection.

  Then, the power conversion device configured as described above is provided between the DC power source 1 and the single-phase three-wire system, and the grid interconnection is used to reversely flow the power from the DC power source 1 to the single-phase three-wire system. A system is being built.

  The operation of the grid interconnection system of the present invention will be described below.

  As for the voltages between the U phase U3, O phase O3, and W phase W3, which are commercial power systems, the U-O phase voltage 3a is typically 101V ± 6V, and the OW phase voltage 3b is also 101V ± 6V. The power conditioner 2 performs orthogonal transformation (DC / AC conversion) to match the electric power obtained from the DC power source 1 such as a solar cell with the AC voltage described above, and outputs it to the single-phase three-wire distribution line 3.

  The system voltage monitoring unit 25 sends system voltage and phase information to the control unit 21. The control unit 21 determines the output mode based on the voltage information immediately before the interconnection, and issues a command to the output switching unit 24, the voltage conversion unit 22, and the power conversion unit 23.

  The output switching unit 24 switches the phase changeover switches 24 a and 24 b according to a command from the control unit 21. Here, the switching pattern of the output switching unit 24 is shown in FIG. There are three output modes: (1) U-W output mode, (2) U-O output mode, and (3) O-W output mode.

  The voltage conversion unit 22 switches the output voltage (either 100V system or 200V system) according to a command from the control unit 21.

  The power conversion unit 23 performs orthogonal transform (DC / AC conversion), adjusts the phase of the output power based on the phase information from the control unit 21, and is linked to the system.

  If the load balance of the grid at the time of interconnection is not constant in time and the load balance changes while the grid interconnection system S is in operation, the voltage of the grid rises even in the above system, and the power condition In this case, the control unit 21 obtains the status of the system voltage during the suppression of the voltage increase from the system voltage monitoring unit 25, determines the output mode again, and outputs the signal. Commands are issued to the switching unit 24, the voltage conversion unit 22, and the power conversion unit 23. When returning from the voltage rise suppression control, it is possible to operate in the most efficient output mode in the time zone in which the voltage rise suppression works.

  FIG. 3 is a flowchart showing a method for determining the output voltage mode immediately before the start of interconnection according to the present embodiment. The output voltage mode determination method according to this embodiment will be described below with reference to FIG.

  If it is determined by the activation determination of the power conditioner 2 that the interconnection is possible, the flow shown in FIG. 3 is executed immediately before the start of the interconnection.

  First, the system voltages (U-O phase voltage 3a and OW phase voltage 3b) are measured, and both are compared in magnitude. In step A, it is verified whether or not the difference between the two is substantially equal (whether the difference between the two is within a preset error range). If the difference between the two is substantially equal, the output voltage mode is set to the U-W output mode. Set this to end this flow. If a difference between the two is recognized in step A, the process proceeds to step B. In Step B, it is verified whether the U-O interphase voltage 3a is larger by comparing the U-O interphase voltage 3a and the O-W interphase voltage 3b. When the U-O interphase voltage 3a is larger, the output voltage mode is set to the O-W output mode, and this flow ends. In step B, if the U-O interphase voltage 3a is smaller, the output voltage mode is set to the U-O output mode, and this flow ends.

  FIG. 4 is a flowchart showing a method for re-determination of the output voltage mode during voltage rise suppression according to the present embodiment. Hereinafter, the re-determination method of the output voltage mode according to the present embodiment will be described with reference to FIG.

  When the power conditioner 2 performs the voltage rise suppression control and reaches the output suppression limit (normal output is limited to 0 kW), the flow shown in FIG. 4 is executed.

  First, in Step C, it is verified whether the U-O interphase voltage 3a is larger than the voltage rise suppression determination value. If it is determined that the voltage is large, the process proceeds to step D, and this time, it is verified whether the O-W interphase voltage 3b is larger than the voltage rise suppression determination value. When it is determined that the voltage is large, both the U-O phase voltage 3a and the OW phase voltage 3b exceed the voltage rise suppression determination value, so that the U-O phase voltage 3a and the OW phase voltage again. The size is determined to be 3b. The size determination is the same as the flow shown in FIG. After the determination is completed, this flow ends. When it is determined in step D that the OW phase voltage 3b is smaller than the voltage rise suppression determination value, only the U-O phase voltage 3a is larger than the voltage rise suppression determination value. Is changed to the O-W output mode, and this flow ends.

  When it is determined in step C that the U-O interphase voltage 3a is smaller than the voltage increase suppression determination value, the process proceeds to step E. In Step E, it is verified whether the O-W phase voltage 3b is larger than the voltage rise suppression determination value. If it is determined that the voltage is larger, only the O-W interphase voltage 3b is larger than the voltage increase suppression determination value, so the output voltage mode is changed to the U-O output mode, and this flow ends. When it is determined in step E that the O-W interphase voltage 3b is smaller than the voltage increase suppression determination value, the present flow is terminated without changing the output mode.

  By doing so, it is possible to perform control that does not cause or hardly causes a voltage increase due to the load balance of the system voltage phase being lost, and a power converter that can reversely flow without leaving power, and a grid connection using the power converter. It is possible to provide a system.

  In addition, a power conversion device that can be reconnected to a low voltage phase depending on the system voltage condition during which voltage rise is being suppressed, and that can maintain the voltage balance of each phase, and that can perform reverse power flow without excess power, and its use It is possible to provide a grid interconnection system.

  In this embodiment, in the description of the flowchart, the description is based on the determination based on the U-O phase voltage, but the present invention can also be applied by performing the determination based on the O-W phase voltage. is there.

1 is a schematic configuration diagram schematically illustrating an embodiment of a grid interconnection system according to the present invention. It is explanatory drawing explaining the switching pattern of an output mode in the grid connection system which concerns on this invention. It is a flowchart which shows the determination method of the output voltage mode immediately before the grid connection start concerning this embodiment. It is a flowchart which shows the re-determination method of the output voltage mode in the voltage rise suppression concerning this embodiment. It is a schematic block diagram which illustrates typically the embodiment of the conventional grid connection system. It is a schematic explanatory drawing explaining the mode of the voltage rise of the conventional single phase 3 wire commercial electric power system. It is a schematic explanatory drawing explaining the mode of the voltage change of the commercial electric power system of a single phase 3 line | wire in the grid connection system which concerns on this invention.

Explanation of symbols

1: DC power supply 2: Power conditioner 21: Control unit 22: Voltage conversion unit 23: Power conversion unit 24: Output switching unit 24a: U-O phase switching switch 24b: OW phase switching switch 25: System voltage monitoring unit 3: Single-phase three-wire distribution line 3a: U-O phase voltage 3b: O-W phase voltage 4, 4a, 4b: Load U3, U31: U-phase O3, O31: O-phase W3, W31: W-phase J: Grid interconnection system S: Grid interconnection system

Claims (1)

A power conversion unit that converts DC power of a DC power source into AC power, supplies the AC power to a single-phase three-wire commercial system and an AC load, and interconnects the power; and U- of the single-phase three-wire commercial system A commercial system voltage monitoring unit that monitors the commercial system voltage between the O phases and between the O-W phases, and the power conversion unit is connected to either the U-O phase, the O-W phase, or the U-W phase. An output switching unit, wherein the output switching unit is connected between the U-O phase or the O--phase according to the respective voltages between the U-O phase, the OW phase, and the U-W phase. A power conversion device, wherein the power conversion unit and the AC power are switched to a single-phase three-wire commercial system by switching between W phase or U-W phase.

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