JP2015192556A - Power control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power control unit capable of suppressing loss of generated power in a generating set by highly precisely detecting a DC component of an output from an inverter with a simple configuration.SOLUTION: The power control unit includes: a plurality of inverters connected with respective generating sets, and a control section 13 that acquires a first DC component of an aggregated output obtained by aggregating outputs from the plurality of inverters and controls the plurality of inverters so that the first DC component is not more than a predetermined value.

Description

  The present invention relates to a power control apparatus.

  In recent years, with the widespread use of power generation devices such as solar cells and fuel cells, the demand for inverters has also increased. The inverter converts DC power generated by the power generator into AC power. Some inverters are provided in each power generator and have a configuration in which a plurality of inverters are used as a set. Such an inverter has a structure that is connected in parallel before a pole transformer of a commercial system. For example, in a photovoltaic power generation system using such an inverter, it is not necessary to install a large-capacity inverter even if a large number of solar cell modules are used. Since mistakes are less likely to occur, there is an advantage that construction is easy even if the engineer is not an expert engineer.

Since the inverter is installed in each solar cell (or solar cell string) and its AC output side is connected in parallel, each inverter has a current sensor (hereinafter referred to as CT) for detecting the DC component of the AC output. Called a sensor). This is because the ratio of direct current components included in the rated alternating current is within 1% according to the grid connection regulation JEAC9701-2010, and a high-accuracy CT sensor is required to detect direct current components. That's why. However, since CT sensors are relatively expensive, increasing the number of CT sensors increases the cost. Thus, a method for detecting a DC component without using a CT sensor has been proposed (see, for example, Patent Document 1).

JP 2002-272140 A

  However, when a DC component is detected without using a CT sensor, the PWM control unit that generates AC power in the inverter is complicated, such as the difference between the switching pulse execution value components and the AC positive / negative half-wave deviation. Arithmetic must be performed. For this reason, the load on the CPU or the like that performs the calculation increases, and as a result, an expensive CPU may be inevitably adopted.

  In addition, when a CT sensor is provided according to each inverter as in the past, there is an allowable error in each CT sensor itself, so that it is set to be within the specified value of the DC component including the error. There must be. In this setting, the smaller the current to be measured, the more complicated the correction calculation may be.

  One object of the present invention is to provide a power control device that reduces the loss of generated power in a power generation device by accurately detecting a direct current component output from an inverter with a simple configuration.

  A power control apparatus according to an embodiment of the present invention acquires a first DC component of a combined calculation force obtained by adding together a plurality of inverters connected to each power generator and outputs from the plurality of inverters. And a control unit that controls the plurality of inverters so that the first DC component is a predetermined value or less.

  According to one embodiment of the present invention, even if there is an inverter that exceeds a specified value determined by the grid connection rule alone, the DC component of the combined calculation force of a plurality of inverters connected to the grid can be controlled to be equal to or less than the specified value. Therefore, it is possible to normally realize grid connection without stopping the driving of the inverter exceeding the specified value. As a result, it is possible to reduce a decrease in output due to the stop of driving of the inverter.

It is a figure which shows schematic structure of the solar energy power generation system which comprises the electric power control apparatus which concerns on embodiment of this invention. It is a figure which shows schematic structure of the power control apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating control of the power control apparatus in embodiment of this invention. It is a flowchart for demonstrating an example of the control method of the electric power control apparatus in this invention embodiment. It is a figure which shows schematic structure of the electric power control apparatus which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the broken lines in FIGS. 1 and 2 represent the flow of signals used for exchanging information between the inverter and the control unit.

≪Power control device configuration≫
FIG. 1 shows a configuration of a photovoltaic power generation system which is one of power supply systems having a power control apparatus according to an embodiment of the present invention. The power control apparatus 1 according to the present embodiment is connected to the first solar cell 2a, the second solar cell 2b, the commercial system 3, and the current collecting cable 4.

  The power control apparatus 1 includes a first inverter 11, a second inverter 12, a control unit 13, and a first CT sensor 14. In the power control apparatus 1, the control unit 13 and the first CT sensor 14 are housed in a control box 15. The control unit 13 and the first CT sensor 14 may be disposed inside a device such as a switchboard without using the control box 15.

  In a photovoltaic power generation system installed in a general house, DC power collected by connecting a plurality of solar cells adjusted to have the same voltage in parallel is converted into AC power by a power conditioner. .

  On the other hand, the power control device 1 is provided with a plurality of inverters connected to the respective power generation devices. Therefore, the 1st inverter 11 converts the direct-current power output from the 1st solar cell 2a as a power generator into alternating current power. In addition, the second inverter 12 converts the DC power output from the second solar cell 2b as the power generation device into AC power. Thus, in the power control device 1, an inverter is provided for each solar cell. Therefore, the AC waveform of each AC power converted by the inverter can be made equivalent to the AC waveform of the commercial system 3. Thereby, the output voltage from the solar cell connected to each inverter may differ. Therefore, the degree of freedom in design is high and the construction is easy.

The first inverter 11 and the second inverter 12 are voltage-type control inverters, and as shown in FIG. 2, the DC power input to the positive input part (a) and the negative input part (b) It converts into electric power and outputs from the output part (c) on the positive electrode side and the output part (d) on the negative electrode side. The first inverter 11 includes a PWM control unit 111 (Pulse Width Modulation) that generates a switching signal that generates an AC waveform by controlling a switching duty and the like, and a positive-side electric circuit based on the switching signal from the PWM control unit 111. It has the 1st switching element 112 which performs switching by ON-OFF between the electric circuit of a negative electrode side, and the 1st coil 113 which arranges the electric power waveform switched by the switching element 112 into an alternating current waveform.

  The second inverter 12 includes a second PWM control unit 121, a second switching element 122, and a second coil 123 that play the same role as the configuration of the first inverter 11.

  The PWM control unit 111 of the first inverter 11 and the PWM control unit 121 of the second inverter 12 have an external input terminal that receives a change in switching timing, and an AC waveform is generated by a command from the control unit 13. The switching timing for generating can be changed.

  The control unit 13 has a function of controlling the inverter based on the DC component value measured by the first CT sensor 14. Control of the inverter is performed by transmitting a control signal to each inverter. Such communication may be wired communication using a signal cable, or wireless communication using infrared rays or low-power radio waves. Note that the signal form may be dedicated, or may conform to some standard (for example, Centronics or ECHONET Lite).

  The first CT sensor 14 is a sensor that measures the current value of the combined calculation force obtained by adding the outputs from the first inverter 11 and the second inverter 12. Therefore, the first CT sensor 14 can measure the current value of the power generation output that is input to the commercial system 3 (reverse power flow) or used for the load. For example, the first CT sensor 14 is configured as a non-contact type using a Hall element. Then, the current value information obtained by the first CT sensor 14 is transmitted to the control unit 13 using a signal or the like.

  The control unit 13 acquires a direct current component (first direct current component) of the combined calculation force obtained based on information of the first CT sensor 14. As a method for calculating the DC component, there is a method in which a current waveform is generated based on the current value obtained by the first CT sensor 14 and the DC waveform is extracted by comparing the current waveform with the voltage waveform of the commercial system 3. It is done.

  In the present embodiment, the control unit 13 controls the plurality of inverters so that the ratio of the DC component of the combined calculation force is equal to or less than a predetermined value. As described above, in the grid connection regulations, the ratio of the direct current component included in the rated alternating current is defined as 1% or less. Therefore, the control unit 13 controls the inverter so that at least the ratio of the DC component does not exceed 1%. Specifically, when the ratio of the direct current component exceeds 1%, the control unit 13 sends a command for reducing the direct current component to the PWM control unit of each inverter. By this command, the switching timing of the PWM control unit of each inverter is changed so that the DC component is reduced.

  The control box 15 includes a terminal block for connecting the AC output from each inverter and the commercial system 3 in parallel. In the control box 15, when the AC output of the first inverter 11 and the AC output of the second inverter 12 are connected in parallel at the terminal block, the current collecting cable 4 connected to the AC output of the first inverter 11 and the second inverter 12. A separate cable is used as the current collecting cable 4 connected to the AC output. As the current collecting cable 4, for example, a cab tire cable having excellent weather resistance is used. The current collecting cable 4 from each inverter is connected to a terminal block (not shown). The terminal block is provided with wiring so as to be connected in parallel for each phase of AC. Therefore, the AC outputs (AC currents) of the first inverter 11 and the second inverter 12 are electrically added together at this connection portion. On the terminal block, a power line connected to the commercial system 3 is connected in parallel with each inverter. Thus, the combined calculation force is input (reverse flow) to the commercial system 3 or supplied to the load.

  Next, an embodiment of control performed when a DC component is detected by the control unit 13 will be described with reference to the drawings. FIG. 3 is a main flowchart used in each embodiment. Note that the control of the main flowchart and the control of subflows to be described later are all performed by the control unit 13.

  First, the first CT sensor 14 measures (detects) the current value from the total calculated force obtained by adding the outputs of all inverters.

  Next, the control unit 13 acquires a direct current component of the total calculation force based on the current value (STEP 1). Specifically, first, the control unit 13 generates a current waveform of an alternating current based on the information on the current value. Next, the generated current waveform and the voltage waveform of the commercial system 3 are compared to calculate (acquire) a DC component (first DC component).

  In STEP2, it is determined whether or not the value of the DC component is equal to or less than a predetermined value. Here, as the predetermined value, the grid connection regulation value (the ratio of the DC component is 1%) may be used, but a value smaller than 1% may be set. If it is determined that the DC component is zero or less than the predetermined value, it is determined that the DC component is in a normal state, and the flow ends.

  On the other hand, when it is determined that the direct current component exceeds the predetermined value, each inverter is controlled by the control unit 13 so that the direct current component becomes equal to or less than the predetermined value (STEP 3). In STEP 3, control is performed to reduce the direct current component of the alternating current output of each inverter by controlling each inverter so that the direct current component becomes a predetermined value or less.

  As described above, the power control apparatus 1 controls the plurality of inverters such that the direct current component (first direct current component) of the combined calculation force obtained by adding the outputs from the plurality of inverters is equal to or less than a predetermined value. Thereby, in the power control apparatus 1, even if there is an inverter that exceeds the specified value determined by the grid connection rule alone, the DC component of the combined calculation force of a plurality of inverters connected to the grid can be controlled below the specified value. The grid interconnection can be normally realized without stopping the drive of the inverter exceeding the above specified value. As a result, it is possible to reduce a decrease in output due to the stop of driving of the inverter. For example, in the case of a photovoltaic power generation system as shown in FIG. 1, the power control device 1 can be controlled so that the generated power of each solar cell can be output.

  Next, an embodiment of the power control device 1 will be described in detail.

<First Embodiment>
In this embodiment, a value calculated by equally dividing the value of the direct current component (first direct current component) exceeding the predetermined value by the number of inverters of the power control device 1 is used as a correction value, and a plurality of inverters are used with the correction value. The DC component at each output is reduced. In order to reduce the DC component, a command for reducing the DC component by an amount corresponding to the correction value is sent from the control unit 3 to each inverter. The number of inverters in the power control device 1 may be stored in the control unit 13 in advance, but the number of connected units may be detected by the control unit 13 through the external input terminal of each inverter.

  In the present embodiment, a command is transmitted to the external input terminals of the first inverter 11 and the second inverter 12 so as to perform control for reducing the direct current component using the calculated correction value. The first inverter 11 changes the switching timing of the PWM control unit 111 based on the correction value, and changes the value of the DC component. The second inverter 12 also changes the value of the direct current component by performing the same operation as the first inverter 11.

The direct current component may take a positive value or a negative value. Specifically, the DC component is detected as a positive value when the current waveform is shifted to the plus side from the normal time. On the other hand, the DC component is detected as a negative value when the current waveform is shifted to the negative side compared with the normal state. Therefore, the specified value in the grid connection regulations (the ratio of the DC component included in the rated AC current is within 1%) means that the DC component is between zero and + 1%, or between zero and -1%. Show. Therefore, when the DC component is reduced, if the DC component is calculated as a positive value, the correction value becomes a negative value. On the other hand, when the DC component is calculated as a negative value, the correction value is a positive value.

  In this embodiment, since all inverters are controlled using the same correction value, for example, the DC component of the total calculation force is a positive value, the actual DC component of the first inverter 11 is a positive value, and the second inverter Even if the DC component of 12 has a negative value, the second inverter 12 is controlled so that the DC component increases, that is, the negative value increases. However, in this embodiment, since the direct current component of the combined calculation force can be made equal to or less than a predetermined value, the second inverter 12 need not be stopped.

  Thus, in this embodiment, since control is performed using the same correction value for all inverters, the direct current component of the alternating current output (total calculated force) of the power control device 1 is specified without specifying an inverter that exceeds the specified value. Can be reduced. Therefore, in this embodiment, the complicated operation | movement of the control part 13 becomes unnecessary and the burden to the calculating part of the control part 13 which performs control operation can be reduced.

Second Embodiment
This embodiment is different from the first embodiment in that an inverter to be controlled is selected. In the present embodiment, the control unit 13 obtains a direct current component (second direct current component) from a combined calculation force obtained by adding outputs from other inverters after stopping driving of one inverter among a plurality of inverters. Have acquired. Next, the control unit 13 sequentially executes a step of obtaining the DC component of the stopped inverter from the second DC component and the DC component (first DC component) of the total calculation force of all the inverters, thereby executing each inverter. The DC component of is calculated. The inverter to be controlled is selected based on the value of the DC component of each inverter.

  Control of the inverter in this embodiment will be described with reference to FIG.

  In STEP 31, a command to fix the suppression control of the DC component, that is, a command to maintain the value of the DC component from the current state is transmitted from the control unit 13 to the PWM control unit 121 of the second inverter 12. Next, a command is transmitted to the PWM control unit 111 of the first inverter 11 to stop the AC output. Specifically, the transmission of the switching signal to the first switching element 112 of the PWM control unit 111 is stopped. As a result, the combined calculation force measured by the first CT sensor 14 is reduced by the amount of the first inverter 11.

  In STEP 32, the control unit 13 acquires the value of the direct current component (second direct current component) of the combined current value based on the current value of the combined power measured by the first CT sensor 14 (hereinafter referred to as the combined current value).

  In STEP 33, the control unit 13 calculates the DC component of the first inverter 11 from the difference between the DC component (first DC component) and the second DC component of the combined calculation force of all the inverters detected in STEP 1.

  In STEP 34, after releasing the restraint control of the second inverter 12 stopped in STEP 31, a command to cancel the switching stop of the first inverter 11 is transmitted to the first inverter 11, thereby temporarily operating each inverter. Return to the normal state. That is, in STEP 34, the control executed for each inverter in STEP 31 is released. When there are three or more inverters, the above-described fixed DC component suppression control of the second inverter in STEP 31 is executed for all the inverters except the first inverter 11.

  Next, the DC component of the second inverter 12 is acquired by executing the same method as that of the first inverter 11 (STEP 35 to STEP 38). In addition, when there are three or more inverters, the fixing of the suppression control of the DC component of the first inverter in STEP 35 described above is performed for all the inverters except the second inverter.

  Thus, in this embodiment, the value of each DC component of the first inverter 11 and the second inverter 12 can be acquired by STEP31 to STEP38. In STEP 39, the inverter to be controlled is selected based on the DC component of each inverter, and control is executed. Below, the concrete control method of STEP39 is demonstrated.

(First control method)
In this control method, an inverter having a large DC component is selected from the plurality of inverters, and control is performed to reduce the DC component in order from the inverter. This control is performed by the control unit 13. Thereby, in this control method, since the number of inverters to be controlled can be reduced, the calculation burden of the control unit 13 can be reduced. As a result, with this control method, control speed can be improved and power consumption can be reduced.

  Further, in the present control method, for example, even when the DC component of the inverter having the largest DC component is controlled to be zero, the DC component (first DC component) of the power control device 1 does not become a predetermined value or less. Selects the inverter having the next largest DC component and controls to reduce the DC component of the inverter. For this reason, in the present control method, there is an inverter in which control for reducing the direct current component is not executed.

(Second control method)
In this control method, the DC component of each inverter is controlled to be uniform by changing the amount of reduction of the DC component of each inverter in accordance with the magnitude of each DC component of the plurality of inverters. This control is performed by the control unit 13. That is, in this control method, the amount of reduction of the DC component is increased for an inverter having a large DC component, and the amount of reduction of the DC component is decreased for an inverter having a small DC component. In addition, control is performed so that the current waveform shifts in the negative direction for the inverter in which the DC component shows a positive value. On the other hand, for the inverter whose DC component shows a negative value, control is performed so that the current waveform is shifted in the positive direction. Thereby, the DC component of each inverter is controlled to be uniform.

  In this control method, since the control is performed so that the DC component of each inverter has a uniform magnitude, even if the generated power of the power generation device (in this embodiment, a solar cell) connected to any inverter decreases. The fluctuations in which the direct current component greatly exceeds a predetermined value can be reduced. As a result, the solar power generation system including the power conversion device 1 that executes this control method is not easily affected by the solar radiation intensity.

(Third control method)
In this control method, control is performed to reduce the DC component of the inverter by performing PWM control on the inverter whose DC component exceeds the upper limit value among the plurality of inverters. Specifically, first, the DC component of each inverter is acquired by the method described above. Next, an inverter that exceeds the upper limit value of the DC component is selected. The upper limit value is not particularly limited. For example, a value (uniform value) obtained by equally dividing the value of the direct current component (first direct current component) exceeding a predetermined value by the number of inverters connected to the power control device 1. May be used.

For example, when both the first inverter 11 and the second inverter 12 exceed the upper limit value, first, after acquiring the DC component of the first inverter 11, the PWM control unit for the value of the DC component to approach zero A correction value for correcting the switching timing of 111 is calculated. Next, a command is transmitted from the control unit 13 to the first inverter 11 so as to execute correction for the correction value. Similarly, a correction value is calculated for the second inverter 12 and a command is transmitted from the control unit 13 to the second inverter 12 so as to execute correction for the correction value. Thus, by transmitting the command to the inverter, the DC component of the inverter that has received the command can be reduced.

  In this control method, when the upper limit value is set at the above uniform value in a plurality of inverters, the DC component as a whole is kept within a predetermined value only by reducing the DC component only for the inverter exceeding the upper limit value. Can fit. Thereby, since the number of inverters to be controlled can be minimized, the calculation burden of the control unit 13 can be reduced. As a result, the calculation speed of the control unit 13 can be improved and the power consumption can be reduced.

  In addition, this invention is not limited to the above-mentioned embodiment. For example, the power control device 1 shown in FIG. 5 is different in that a CT sensor is provided in each of the first inverter 11 and the second inverter 12 of the power control device 1 shown in FIG.

  In the power control apparatus 1 according to the present embodiment, as shown in FIG. 5, a second CT sensor 16 a and a second CT sensor 16 b are arranged inside the first inverter 11 and the second inverter 12, respectively.

  The first inverter 11 can transmit information on the current value measured by the second CT sensor 16 a to the control unit 13 through the signal line 17. Moreover, the control part 13 can acquire the approximate direct current component of the electric current output from the 1st inverter 11 using the 2nd CT sensor 16a. At this time, it can also be determined whether the DC component is generated on the plus side or the minus side of the waveform of the AC current.

  The second inverter 12 can transmit information on the current value measured by the second CT sensor 16 b to the control unit 13 through the signal line 17. Moreover, the control part 13 can acquire the approximate direct current component of the electric current output from the 1st inverter 11 using the 2nd CT sensor 16a.

  Thus, by providing a CT sensor in each inverter, the control unit 13 can reduce the DC component using the third control method described above for an inverter having a significantly large DC component. Thus, the inverter that greatly contributes to the increase of the DC component (first DC component) of the combined calculation force can be controlled before executing the control based on the DC component of the combined calculation force of each inverter. Control of the inverter becomes easy.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. In the above-described embodiment, a solar cell is taken as an example of a power generation device, but a power generation device that converts DC power into AC power, such as a fuel cell, may be used. Moreover, about the method of detecting a direct current component, the method of calculating from the current waveform of the alternating current power mentioned above may be used.

DESCRIPTION OF SYMBOLS 1 Power control system 2a 1st solar cell 2b 2nd solar cell 3 Commercial system 4 Current collection cable 11 1st power conversion part 12 2nd power conversion part 13 Control part 14 1st CT sensor 15 Control box 16 2nd CT sensor 17 Signal line 111 1st PWM control part 112 1st switching element 113 1st coil 121 2nd PWM control part 122 2nd switching element 123 2nd coil ab input part cd output part ef system connection output part

Claims (6)

A plurality of inverters connected to each power generator;
A control unit that acquires a first DC component of a combined calculation force obtained by adding outputs from the plurality of inverters, and controls the plurality of inverters so that the first DC component is a predetermined value or less; A power control device.   The control unit performs control to reduce the DC component at each output of the plurality of inverters by a correction value calculated by equally dividing the value of the first DC component exceeding the predetermined value by the number of the plurality of inverters. The power control apparatus according to claim 1.   The control unit obtains a second DC component from a combined calculation force obtained by adding outputs from other inverters after stopping driving of one inverter among the plurality of inverters, And calculating the DC component of each inverter by sequentially executing the step of acquiring the DC component of the stopped inverter from the first DC component, and then selecting the inverter to be controlled based on the DC component of each inverter. The power control apparatus according to claim 1.   The power control apparatus according to claim 3, wherein the control unit performs control to reduce a DC component in order from an inverter having a larger DC component among the plurality of inverters.   The said control part controls so that the direct current | flow component of each inverter may become uniform by changing the reduction amount of the direct current | flow component of each inverter according to the magnitude | size of each direct current | flow component of these inverters. The power control device described in 1. 4. The power control according to claim 3, wherein, in the plurality of inverters, power control according to claim 3, wherein PWM control is performed on an inverter having a DC component exceeding an upper limit value to reduce a DC component of the inverter. apparatus.

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