Power conversion device, solar power generation system, and power conversion method

Abstract

To provide a power conversion device which is effective for achieving both suppression of a zero-phase current and generation of alternating current and continuation of output.SOLUTION: A power conversion device 3 includes: a power conversion circuit 10 for converting direct current on a primary side into alternating current and outputting the alternating current to a secondary side; and a control unit 100 for controlling the power conversion circuit 10 so as to suppress an increase in a zero-phase current produced in accordance with output of the alternating current by adjusting the magnitude of the alternating current.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device, a solar power generation system, and a power conversion method. [Background technology]

[0002] Patent Document 1 discloses a power conversion device in which a number of capacitors are connected in series between DC input sections, and connections between the plurality of capacitors are connected to a grounded phase of a three-phase, three-wire system power supply, and the ungrounded phase and the DC input section are switched on and off. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-102265 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a power conversion device that is effective in suppressing zero-phase current while continuing to generate and output AC. [Means for solving the problem]

[0005] A power conversion device according to one aspect of the present disclosure includes a power conversion circuit that converts direct current on a primary side into alternating current and outputs it to a secondary side, and a control unit that controls the power conversion circuit so as to suppress an increase in zero-phase current that occurs in response to the output of the alternating current by adjusting the magnitude of the alternating current.

[0006] A solar power generation system according to another aspect of the present disclosure includes a solar power generation device that generates direct current in response to incident sunlight, a power conversion circuit that converts the direct current generated by the solar power generation device into alternating current and outputs it, and a control unit that controls the power conversion circuit so as to suppress an increase in zero-phase current that occurs in response to the output of alternating current by adjusting the magnitude of the alternating current.

[0007] A power conversion method according to yet another aspect of the present disclosure includes converting direct current on a primary side to alternating current using a power conversion circuit and outputting the alternating current to a secondary side, and controlling the power conversion circuit so as to suppress an increase in zero-phase current that occurs in response to the output of the alternating current by adjusting the magnitude of the alternating current. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a power conversion device that is effective in suppressing zero-phase current while continuing to generate and output AC. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of a solar power generation system. [Diagram 2] 4 is a block diagram illustrating a configuration of a current command correction unit; FIG. [Diagram 3] FIG. 13 is a block diagram showing a modified example of a current command correction unit. [Figure 4] 4 is a block diagram illustrating a hardware configuration of a control circuit. FIG. [Diagram 5] 1 is a flow chart illustrating a power conversion procedure. [Figure 6] 10 is a flowchart illustrating a procedure for correcting a current command. [Figure 7] 13 is a flowchart showing a modified example of the procedure for correcting a current command. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the drawings. In the description, the same elements or elements having the same functions are denoted by the same reference numerals, and duplicated description will be omitted.

[0011] [Solar power generation system] The photovoltaic power generation system 1 shown in Fig. 1 is a system that converts a direct current (DC current) generated in response to incidence of sunlight into an alternating current (AC current) corresponding to a power grid 4 and outputs the converted current to the power grid 4. The power grid 4 is a system that supplies AC power to consumers such as factories. The power grid 4 may be a commercial power grid operated by a power company or the like. The AC corresponding to the power grid 4 is, for example, a three-phase AC having an R phase 4R, an S phase 4S, and a T phase 4T. The S phase 4S may be grounded.

[0012] As shown in FIG. 1, the solar power generation system 1 includes a solar power generation device 2 and a power conversion device 3. The solar power generation device 2 is an example of a DC power source, and generates DC in response to the incidence of sunlight and outputs it to a positive electrode 2P and a negative electrode 2N. For example, the solar power generation device 2 includes a solar cell and a DC / DC converter. The DC / DC converter performs DC / DC conversion on the output of the solar cell, and outputs the generated DC to the positive electrode 2P and the negative electrode 2N. The power conversion device 3 converts the DC generated by the solar power generation device 2 into AC corresponding to a power grid 4, and outputs it to the power grid 4. The power conversion device 3 includes a power conversion circuit 10 and a control circuit 100.

[0013] The power conversion circuit 10 converts a direct current input to the power conversion device 3 into an alternating current and outputs the converted alternating current. For example, the power conversion circuit 10 has a first point 11, a second point 12, a third point 13, a first capacitor 14, a second capacitor 15, and a switching circuit 16. The first point 11 is connected to a positive electrode 2P of the solar power generation device 2. The second point 12 is connected to a negative electrode 2N of the solar power generation device 2. The third point 13 is connected to the first point 11 via the first capacitor 14, and is connected to the second point 12 via the second capacitor 15.

[0014] The switching circuit 16 is, for example, an inverter circuit, and converts the direct current generated by the photovoltaic power generation device 2 into alternating current by changing the connection state between the photovoltaic power generation device 2 (primary side) and the power grid 4 (secondary side) using a plurality of switching elements 17. Each of the plurality of switching elements 17 is, for example, a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor), and switches on / off in response to a gate drive signal.

[0015] As an example, the switching circuit 16 generates a three-phase AC corresponding to the power system 4 by maintaining the third point 13 connected to one of the phases of the power system 4 (e.g., the S phase 4S) while connecting and disconnecting the first point 11 and the second point 12, respectively, to the remaining two phases of the power system 4 (e.g., the R phase 4R and the T phase 4T).

[0016] The power conversion circuit 10 further includes a current sensor 21, a zero-phase current sensor 22, and an earth leakage breaker 23. The current sensor 21 outputs an electric signal representing the magnitude of a current flowing between the switching circuit 16 and each phase (R phase 4R, S phase 4S, and T phase 4T) of the power system 4. The zero-phase current sensor 22 outputs an electric signal representing the magnitude of a zero-phase current flowing between the switching circuit 16 and the power system 4. For example, the zero-phase current sensor 22 outputs an electric signal generated by a current transformer that detects an excitation current of a total magnetic flux generated by three lines connecting the switching circuit 16 and the R phase 4R, the S phase 4S, and the T phase 4T. The earth leakage breaker 23 cuts off the connection between the switching circuit 16 and the power system 4 when the magnitude of the zero-phase current (for example, the magnitude of a signal representing the zero-phase current detected by the earth leakage breaker 23 itself, or the magnitude of an electric signal output by the zero-phase current sensor 22) exceeds a predetermined parallel-off level.

[0017] The control circuit 100 controls the power conversion circuit 10 to generate an AC current corresponding to the power system 4 and output it to the power system 4. For example, the control circuit 100 performs MPPT (Maximum Power Point Tracking) control. Specifically, it controls the switching circuit 16 to generate an AC current corresponding to the power system 4 while making the voltage between the positive electrode 2P and the negative electrode 2N (hereinafter referred to as "DC voltage") follow the maximum power point (the voltage value that maximizes the output power).

[0018] A zero-phase current may occur even during normal operation in the power conversion circuit 10. A path of the zero-phase current is formed by stray capacitance between the solar panel of the solar power generation device 2 and the ground, etc.

[0019] For example, in the configuration of the power conversion circuit 10 illustrated above, the S phase 4S is grounded, and the third point 13 is maintained in a state of being connected to the S phase 4S. When the power conversion circuit 10 generates AC, the potentials of the first capacitor 14 and the second capacitor 15 fluctuate according to the AC output to the power grid 4. A current caused by this potential fluctuation flows to the S phase 4S due to the grounding of the S phase 4S and the above-mentioned stray capacitance, generating a zero-phase current. For this reason, the correlation between the AC output by the switching circuit 16 to the power grid 4 and the magnitude of the zero-phase current becomes strong.

[0020] Since the stray capacitance varies greatly depending on the weather, etc., the magnitude of the zero-phase current generated for the same AC also varies depending on the weather, etc. For this reason, even if no particular abnormality occurs in the photovoltaic power generation device 2 and the power conversion device 3, the electrical signal output by the zero-phase current sensor 22 may exceed the above-mentioned parallel-off level, and the earth leakage breaker 23 may cut off the connection between the switching circuit 16 and the power system 4. When the connection between the switching circuit 16 and the power system 4 is cut off, the power from the photovoltaic power generation device 2 cannot be effectively used in the power system 4 even in a situation where the photovoltaic power generation device 2 is able to generate power.

[0021] Therefore, the control circuit 100 is configured to suppress an increase in the zero-phase current occurring in response to the output of the AC by adjusting the magnitude of the AC. Examples of adjusting the magnitude of the AC so as to suppress the increase include limiting the magnitude of the AC to a predetermined upper limit value or less so that the zero-phase current does not exceed a predetermined level, and reducing the magnitude of the AC so that the zero-phase current that exceeds the predetermined level becomes equal to or less than the predetermined level.

[0022] According to the control circuit 100, it is possible to continue generating and outputting AC while effectively suppressing an increase in the zero-phase current by adjusting the magnitude of the AC, and therefore it is effective in achieving both suppression of the zero-phase current and the continuation of generating and outputting AC.

[0023] The control circuit 100 may be configured to generate a current command, correct the current command so as to suppress an increase in zero-phase current that occurs when an alternating current corresponding to the current command is output to the secondary side, and control the power conversion circuit 10 so as to output an alternating current corresponding to the current command to the secondary side.

[0024] For example, the control circuit 100 generates a current command for a control other than the control for suppressing an increase in the zero-phase current, such as the above-mentioned MPPT control. When the magnitude of the zero-phase current generated when AC corresponding to the generated current command is output to the secondary side exceeds a predetermined level, the control circuit 100 corrects the current command so that the magnitude of the zero-phase current is equal to or less than the predetermined level. The magnitude of the zero-phase current generated when AC is output to the secondary side may be the magnitude of the zero-phase current detected as a result of actually outputting AC, or may be the magnitude of the zero-phase current estimated based on the magnitude of the AC to be output without actually outputting AC. The predetermined level may be lower than the above-mentioned parallel-off level.

[0025] By generating a current command for a purpose other than suppressing the increase in zero-phase current, and then correcting the current command as necessary to suppress the increase in zero-phase current, it is possible to coexist control for the other purpose and control aimed at suppressing the increase in zero-phase current, allowing the power conversion circuit 10 to continue to perform more beneficial power conversion.

[0026] As an example, the control circuit 100 has, as functional components (hereinafter referred to as "functional blocks"), a current information acquisition unit 114, a zero-phase current information acquisition unit 115, a current command generation unit 111, a current command correction unit 120, a voltage command generation unit 112, and a switching control unit 113. The current information acquisition unit 114 acquires information on the current detection value Iout output by the switching circuit 16 to the power system 4 based on the electrical signal output by the above-mentioned current sensor 21. The zero-phase current information acquisition unit 115 acquires information on the zero-phase current detection value Irip based on the electrical signal output by the above-mentioned zero-phase current sensor 22.

[0027] The current command generating unit 111 generates a current command. For example, the current command generating unit 111 generates a current command Iref so as to monitor the input power Pin from the solar power generation device 2, change the DC voltage, and search for a DC voltage that maximizes the input power Pin. The current command Iref may include two components of a current vector representing the magnitude and phase of the current. For example, the current command Iref may include two components representing a current vector in a rotating coordinate system that rotates according to the phase of the AC current of the power system 4.

[0028] When the current command Iref includes two components, two components corresponding to the two components of the current command Iref may be extracted from the current detection value Iout acquired by the current information acquisition unit 114. The current command correction unit 120 corrects the current command Iref so as to suppress an increase in the zero-phase current generated when an AC corresponding to the current command Iref is output to the power grid 4. For example, when the magnitude of the zero-phase current generated when an AC corresponding to the current command Iref is output to the power grid 4 exceeds a predetermined zero-phase current limit Irip_lim, the current command correction unit 120 corrects the current command Iref based on the zero-phase current detection value Irip and the current detection value Iout so that the zero-phase current detection value Irip is equal to or less than the predetermined zero-phase current limit Irip_lim.

[0029] Hereinafter, the current command Iref corrected by the current command correction unit 120 is referred to as a corrected current command Iref_r to be distinguished from the current command Iref before correction. When the current command Iref includes the above-mentioned two components, the corrected current command Iref_r may include two components corresponding to the two components of the current command Iref. Note that, if the magnitude of the zero-phase current generated when an AC corresponding to the current command Iref before correction is output to the power system 4 does not exceed the zero-phase current limit Irip_lim, the current command correction unit 120 does not correct the current command Iref. Even when the current command correction unit 120 does not correct the current command Iref, the current command Iref that has passed through the current command correction unit 120 in FIG. 1 is included in the corrected current command Iref_r.

[0030] The voltage command generating unit 112 generates a voltage command Vref so that the current detection value Iout follows the corrected current command Iref_r. For example, the voltage command generating unit 112 generates a voltage command Vref so as to reduce the deviation between the corrected current command Iref_r and the current detection value Iout. For example, the voltage command generating unit 112 generates the voltage command Vref based on the result of a proportional operation, a proportional-integral operation, or a proportional-integral-differential operation on the deviation between the corrected current command Iref_r and the current detection value Iout. When the corrected current command Iref_r includes the above-mentioned two components, the voltage command Vref may include two components corresponding to the two components of the current command Iref.

[0031] The switching control unit 113 controls the power conversion circuit 10 so as to output an AC current corresponding to the corrected current command Iref_r to the power grid 4. For example, the switching control unit 113 controls the switching circuit 16 so as to apply a voltage corresponding to the voltage command Vref to the power grid 4, based on a voltage command Vref generated so as to make the current detection value Iout follow the corrected current command Iref_r.

[0032] Although the above configuration illustrates a case in which the power conversion circuit 10 is a so-called voltage-type inverter, the power conversion circuit 10 may be a current-type inverter.

[0033] 2 is a block diagram illustrating a configuration of the current command correction unit 120. The current command correction unit 120 may specify a relationship between the magnitude of the AC current and the magnitude of the zero-phase current based on first information indicating the magnitude of the AC current output to the power system 4 and second information indicating the magnitude of the zero-phase current, and may correct the current command based on the specified relationship and the predetermined level so that the magnitude of the zero-phase current is equal to or less than a predetermined level. Hereinafter, this correction is referred to as "instantaneous correction." The current command correction unit 120 may repeat reducing the current command so as to reduce the zero-phase current until the magnitude of the zero-phase current is equal to or less than a predetermined level. Hereinafter, this correction is referred to as "sequential correction."

[0034] 2 is configured to execute a combination of instantaneous correction and sequential correction. For example, the current command correction unit 120 is configured to execute the following: determining a relationship between the magnitude of the AC current and the magnitude of the zero-phase current based on first information indicating the magnitude of the AC current output to the power system 4 and second information indicating the magnitude of the zero-phase current; generating a current limit based on the determined relationship and a predetermined level so that the magnitude of the zero-phase current is equal to or less than a predetermined level; correcting the current command so that the current command is equal to or less than the current limit; and further reducing the current command set to or less than the current limit, repeating the above steps until the magnitude of the zero-phase current is equal to or less than the predetermined level.

[0035] For example, the current command correction unit 120 has, as functional blocks, an instantaneous control unit 121, a sequential control unit 122, and a current limiting unit 123. The instantaneous control unit 121 specifies a relationship between the magnitude of the AC current and the magnitude of the zero-phase current based on first information indicating the magnitude of the AC current output to the power system 4 and second information indicating the magnitude of the zero-phase current, and generates a current limit based on the specified relationship and the predetermined level so that the magnitude of the zero-phase current is equal to or less than a predetermined level.

[0036] For example, the instantaneous control unit 121 acquires the current detection value Iout from the current information acquisition unit 114 as an example of the first information, acquires the zero-phase current detection value Irip from the zero-phase current information acquisition unit 115 as an example of the second information, and specifies the relationship between the current detection value Iout and the zero-phase current detection value Irip. For example, the instantaneous control unit 121 calculates the ratio of the zero-phase current detection value Irip to the current detection value Iout as an example of the relationship between the current detection value Iout and the zero-phase current detection value Irip, and multiplies the calculated ratio by the zero-phase current limit Irip_lim to calculate the current limit Iout_lim.

[0037] The current limiting unit 123 corrects the current command Iref so that it is equal to or less than the current limit Iout_lim. For example, when the current command Iref exceeds the current limit Iout_lim, the current limiting unit 123 corrects the current command Iref to a value equal to or less than the current limit Iout_lim, and does not correct the current command Iref if the current command Iref is equal to or less than the current limit Iout_lim. The sequential control unit 122 further reduces the current limit Iout_lim so as to reduce the deviation between the zero-phase current limit Irip_lim and the zero-phase current detection value Irip. For example, the sequential control unit 122 subtracts the zero-phase current detection value Irip from the zero-phase current limit Irip_lim to calculate the deviation, and performs a proportional operation, a proportional-integral operation, or a proportional-integral-differential operation on the calculated deviation to calculate the upper limit correction value ΔIrip_cmp. When the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim, there is no need to further correct the current limit Iout_lim. Therefore, the sequential control unit 122 may be configured to limit the upper limit correction value ΔIrip_cmp to zero or less.

[0038] The current limiting unit 123 corrects the current command Iref to be equal to or less than the value obtained by adding the upper limit correction value ΔIrip_cmp to the current limit Iout_lim. When the upper limit correction value ΔIrip_cmp is less than zero, adding the upper limit correction value ΔIrip_cmp to the current limit Iout_lim is equivalent to subtracting the absolute value of the upper limit correction value ΔIrip_cmp from the current limit Iout_lim. Therefore, by correcting the current command Iref to be equal to or less than the value obtained by adding the upper limit correction value ΔIrip_cmp to the current limit Iout_lim, the current command Iref corrected to be equal to or less than the current limit Iout_lim is further reduced.

[0039] The instantaneous control unit 121, the sequential control unit 122, and the current limiting unit 123 repeatedly execute the above-described processes. As a result, the instantaneous control unit 121 repeatedly acquires the current detection value Iout and the zero-phase current detection value Irip, and instantly updates the relationship between the current detection value Iout and the zero-phase current detection value Irip every time the current detection value Iout and the zero-phase current detection value Irip are acquired. The sequential control unit 122 sequentially repeats the following steps: calculating an upper limit correction value ΔIrip_cmp (drop width) based on the deviation between the zero-phase current limit Irip_lim and the zero-phase current detection value Irip; correcting the current limit Iout_lim with the calculated upper limit correction value ΔIrip_cmp to reduce the current command Iref, until the zero-phase current detection value Irip becomes equal to or less than the zero-phase current limit Irip_lim.

[0040] In addition, the instantaneous correction and the sequential correction do not necessarily have to be performed in combination. The current command correction unit 120 may be configured to perform the instantaneous correction without performing the sequential correction, or may be configured to perform the sequential correction without performing the instantaneous correction.

[0041] When the current command correction unit 120 performs sequential correction without performing instantaneous correction, the current limiting unit 123 corrects the current command Iref so that it is less than or equal to a value obtained by adding a predetermined current limit Iout_lim to an upper limit correction value ΔIrip_cmp, instead of using the current limit Iout_lim calculated for the instantaneous correction.

[0042] When the current command correction unit 120 performs sequential correction without performing instantaneous correction, the sequential control unit 122 may calculate the current limit Iout_lim based on the deviation between the zero-phase current limit Irip_lim and the zero-phase current detection value Irip. The current limiting unit 123 corrects the current command Iref so that it is equal to or less than the current limit Iout_lim calculated by the sequential control unit 122. For example, the sequential control unit 122 may calculate the current limit Iout_lim based on the result of performing a proportional-integral operation or a proportional-integral-differential operation on the deviation. In this case, during a period in which the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim, the current limit Iout_lim is increased to the upper limit value by integrating the positive deviation. When the zero-phase current detection value Irip becomes larger than the zero-phase current limit Irip_lim, the current limit Iout_lim is reduced by the negative deviation until the zero-phase current detection value Irip becomes equal to or less than the zero-phase current limit Irip_lim.

[0043] When the current command correction unit 120 performs sequential correction without performing instantaneous correction, the sequential control unit 122 may be configured to calculate the auxiliary current command Iref2 separately from the current limit Iout_lim based on the deviation between the zero-phase current limit Irip_lim and the zero-phase current detection value Irip. The current limiting unit 123 may be configured to select the smaller of the auxiliary current command Iref2 and the current command Iref calculated by the sequential control unit 122 as the corrected current command Iref_r. For example, the sequential control unit 122 may calculate the auxiliary current command Iref2 based on the result of performing a proportional-integral operation or a proportional-integral-differential operation on the deviation. In this case, during a period in which the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim, the auxiliary current command Iref2 is increased to an upper limit value by integrating the positive deviation. When the zero-phase current detection value Irip becomes larger than the zero-phase current limit Irip_lim, the secondary current command Iref2 is reduced due to the negative deviation until the zero-phase current detection value Irip becomes equal to or smaller than the zero-phase current limit Irip_lim. In this case, the current command may be limited separately by the current limit Iout_lim for the purpose of suppressing heat generation, etc.

[0044] The current command corrector 120 may be configured to, when the zero-phase current detection value Irip is greater than the zero-phase current limit Irip_lim, repeat reducing the zero-phase current limit Irip_lim by a predetermined constant reduction amount (predetermined reduction amount) instead of the upper limit correction value ΔIrip_cmp based on the deviation between the zero-phase current limit Irip_lim and the zero-phase current detection value Irip until the magnitude of the zero-phase current detection value Irip becomes equal to or less than the zero-phase current limit Irip_lim. Also, instead of the current limit Iout_lim, the current command Iref may be reduced.

[0045] 3 is a block diagram illustrating a current command correction unit 120 that reduces the current command Iref at a constant drop width. The current command correction unit 120 illustrated in FIG. 3 has a comparison unit 124, a comparison unit 125, and a current command increase / decrease unit 126 as functional blocks. The comparison unit 124 is a comparator that determines whether or not the zero-phase current detection value Irip is greater than the zero-phase current limit Irip_lim. For example, the comparison unit 124 outputs a true value when the zero-phase current detection value Irip is greater than the zero-phase current limit Irip_lim, and outputs a false value when the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim. The comparison unit 125 is a comparator that determines whether or not the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim. For example, the comparison unit 125 outputs a true value when the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim, and outputs a false value when the zero-phase current detection value Irip is larger than the zero-phase current limit Irip_lim.

[0046] The current command increasing / decreasing unit 126 increases / decreases the current command Iref based on the comparison results by the comparing units 124 and 125. For example, when the comparing unit 124 outputs a true value, the current command increasing / decreasing unit 126 repeatedly decreases the current command Iref by a certain drop width, and when the comparing unit 125 outputs a true value, the current command increasing / decreasing unit 126 repeatedly increases the current command Iref by a certain rise width.

[0047] As an example, the current command increasing / decreasing unit 126 stores the current command Iref at the time when the output of the comparing unit 124 switches from a false value to a true value as the corrected current command Iref_r. After that, when the output of the comparing unit 124 is a true value, the current command increasing / decreasing unit 126 repeatedly decreases the corrected current command Iref_r by a certain drop width. When the output of the comparing unit 124 switches from a true value to a false value and the output of the comparing unit 125 switches from a false value to a true value, the current command increasing / decreasing unit 126 increases the corrected current command Iref_r by a certain increase width. After that, the current command increasing / decreasing unit 126 repeatedly increases the corrected current command Iref_r until the output of the comparing unit 125 switches from a true value to a false value. When the output of the comparison unit 125 switches from a true value to a false value and the output of the comparison unit 124 switches from a false value to a true value, the comparison unit 124 again decreases the corrected current command Iref_r by a certain decrease amount. By the above processing, the zero-phase current detection value Irip is maintained in the vicinity of the zero-phase current limit Irip_lim.

[0048] In the process in which the current command increasing / decreasing unit 126 increases the corrected current command Iref_r, if the corrected current command Iref_r becomes equal to or greater than the current command Iref before the output of the comparing unit 125 switches from a true value to a false value, there is no need to further increase the corrected current command Iref_r. At this point, the current command increasing / decreasing unit 126 completes the correction of the current command Iref, and outputs the current command Iref before correction as it is as the corrected current command Iref_r until the output of the comparing unit 124 becomes a true value again.

[0049] The zero-phase current limit Irip_lim that the comparison unit 124 compares with the zero-phase current detection value Irip and the zero-phase current limit Irip_lim that the comparison unit 125 compares with the zero-phase current detection value Irip may be different from each other. For example, the zero-phase current limit Irip_lim that the comparison unit 124 compares with the zero-phase current detection value Irip may be larger than the zero-phase current limit Irip_lim that the comparison unit 125 compares with the zero-phase current detection value Irip. In addition, the drop width and the rise width may be different from each other.

[0050] Fig. 4 is a block diagram illustrating a hardware configuration of the control circuit 100. As shown in Fig. 4, the control circuit 100 includes, for example, one or more processors 191, a memory 192, a storage 193, an input / output port 194, and a switching control circuit 195.

[0051] The storage 193 includes a non-volatile storage medium such as a flash memory or a hard disk. The storage 193 stores a program for causing the control circuit 100 to control the power conversion circuit 10 so as to suppress an increase in a zero-phase current generated in response to an AC output by adjusting the magnitude of the AC. For example, the storage 193 stores a program for causing the control circuit 100 to configure each of the above-mentioned functional blocks.

[0052] The memory 192 temporarily stores a program loaded from the storage 193 and data generated during the execution of the program. The one or more processors 191 execute the program stored in the memory 192 to cause the control circuit 100 to function as each functional block. The input / output port 194 inputs and outputs electrical signals between the current sensor 21 and the zero-phase current sensor 22 in response to a command from the one or more processors 191. The switching control circuit 195 switches on and off a plurality of switching elements 17 in the switching circuit 16 in response to a command from the one or more processors 191. The above hardware configuration is merely an example and can be changed as appropriate. For example, at least one of the functional blocks may be configured by a dedicated circuit element such as an ASIC (Application Specific Integrated Circuit).

[0053] The configuration of the power conversion device 3 illustrated above is merely an example and can be modified as appropriate. For example, the DC power source to which the power conversion device 3 is applied is not limited to the solar power generation device 2, and may be any power source as long as it outputs the generated power as DC.

[0054] [Power conversion method] As an example of a power conversion method, a power conversion procedure executed by the power conversion device 3 is illustrated. This power conversion procedure includes converting a direct current on the primary side to an alternating current by the power conversion circuit 10 and outputting the alternating current to the secondary side, and controlling the power conversion circuit 10 so as to suppress an increase in a zero-phase current occurring in accordance with the output of the alternating current by adjusting the magnitude of the alternating current. Fig. 5 is a flowchart illustrating the power conversion procedure. The procedure illustrated in Fig. 5 is performed in a state in which the power conversion circuit 10 continues to convert a direct current on the primary side to an alternating current and output the alternating current to the secondary side.

[0055] 5, the control circuit 100 first executes steps S01, S02, and S03. In step S01, the current information acquisition unit 114 acquires information on the current detection value Iout that the switching circuit 16 outputs to the power system 4 based on the electrical signal output by the current sensor 21. Based on the electrical signal output by the zero-phase current sensor 22, the zero-phase current information acquisition unit 115 acquires information on the zero-phase current detection value Irip.

[0056] In step S02, the current command generating unit 111 calculates the current command Iref. For example, the current command generating unit 111 generates the current command Iref so as to search for a DC voltage that maximizes the input power Pin.

[0057] In step S03, the current command corrector 120 corrects the current command Iref so as to suppress an increase in the zero-phase current that occurs when an AC corresponding to the current command Iref is output to the power grid 4. The specific contents of step S03 will be exemplified later.

[0058] Next, the control circuit 100 executes steps S04, S05, and S06. In step S04, the voltage command generating unit 112 generates a voltage command Vref so that the current detection value Iout follows the corrected current command Iref_r. In step S05, the switching control unit 113 starts to control the switching circuit 16 so that a voltage corresponding to the voltage command Vref is applied to the power system 4. In step S06, the switching control unit 113 waits for a predetermined control period to elapse. After that, the control circuit 100 returns the process to step S01. The control circuit 100 repeatedly executes the above process in the above control period.

[0059] FIG. 6 is a flow chart illustrating a procedure for correcting the current command Iref in step S03. As described above, step S03 is repeatedly executed in a predetermined control period. The procedure shown in FIG. 6 shows a processing procedure for one control period. As shown in FIG. 6, the control circuit 100 first executes steps S11 and S12. In step S11, the instantaneous control unit 121 calculates the current limit Iout_lim. For example, the instantaneous control unit 121 acquires the current detection value Iout from the current information acquisition unit 114, acquires the zero-phase current detection value Irip from the zero-phase current information acquisition unit 115, and specifies the relationship between the current detection value Iout and the zero-phase current detection value Irip. The instantaneous control unit 121 calculates the current limit Iout_lim based on the relationship between the current detection value Iout and the zero-phase current detection value Irip and the zero-phase current limit Irip_lim.

[0060] In step S12, the sequential control unit 122 calculates the upper limit correction value ΔIrip_cmp. For example, the sequential control unit 122 calculates the deviation by subtracting the zero-phase current detection value Irip from the zero-phase current limit Irip_lim, and calculates the upper limit correction value ΔIrip_cmp by performing a proportional operation, a proportional-integral operation, or a proportional-integral-derivative operation on the calculated deviation.

[0061] Next, the control circuit 100 executes steps S13 and S14. In step S13, the current limiter 123 adds the upper limit correction value ΔIrip_cmp to the current limit Iout_lim. Hereinafter, the value obtained by adding the upper limit correction value ΔIrip_cmp to the current limit Iout_lim will be referred to as the "corrected current limit."

[0062] In step S14, the current limiting unit 123 checks whether the current command Iref is smaller than the corrected current limit. If it is determined in step S14 that the current command Iref is smaller than the corrected current limit, the control circuit 100 executes step S15. In step S15, the current limiting unit 123 sets the corrected current command Iref_r to be the same value as the current command Iref before correction.

[0063] If it is determined in step S14 that the current command Iref is equal to or greater than the corrected current limit, the control circuit 100 executes step S16. In step S16, the current limiting unit 123 sets the same value as the corrected current limit to the corrected current command Iref_r. This completes the procedure for correcting the current command Iref in step S03.

[0064] FIG. 7 is a flowchart showing a modified example of the procedure for correcting the current command Iref in step S03. As described above, step S03 is repeatedly executed in a predetermined control period. The procedure shown in FIG. 7 shows a processing procedure for one cycle. The correction of the current command Iref is not completed in one cycle, but is completed by repeating the procedure in FIG. 7. As shown in FIG. 7, the control circuit 100 first executes step S21. In step S21, the current command increase / decrease unit 126 checks whether the zero-phase current detection value Irip is greater than the zero-phase current limit Irip_lim (the output of the comparison unit 124 is a true value). If it is determined in step S21 that the zero-phase current detection value Irip is equal to or less than the zero-phase current limit Irip_lim, the control circuit 100 executes step S22. In step S22, the current command increase / decrease unit 126 checks whether the status is "corrected". If it is determined in step S22 that the status is "not corrected", the control circuit 100 executes step S23. In step S23, the current command increase / decrease unit 126 sets the current current command Iref as the corrected current command Iref_r, and completes the correction of the current command Iref in step S03.

[0065] If it is determined in step S21 that the zero-phase current detection value Irip is greater than the zero-phase current limit Irip_lim, the control circuit 100 executes step S24. In step S24, the current command increasing / decreasing unit 126 checks whether the status is "no correction". If it is determined in step S24 that the status is "no correction", the control circuit 100 executes step S25. In step S25, the current command increasing / decreasing unit 126 changes the status from "no correction" to "corrected".

[0066] Next, the control circuit 100 executes step S26. If it is determined in step S24 that the status is "corrected", the control circuit 100 executes step S26 without executing step S25. In step S26, the current command increase / decrease unit 126 decreases the corrected current command Iref_r by a predetermined decrease width, and the correction of the current command Iref in step S03 is completed.

[0067] If it is determined in step S21 that the zero-phase current detection value Irip is equal to or less than the zero-phase current limit Irip_lim, and further determined in step S22 that the status is "corrected", the control circuit 100 executes step S31. In step S31, the current command increase / decrease unit 126 checks whether the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim (the output of the comparison unit 125 is a true value). If it is determined in step S31 that the zero-phase current detection value Irip is smaller than the zero-phase current limit Irip_lim, the control circuit 100 executes step S32. In step S32, the current command increase / decrease unit 126 increases the corrected current command Iref_r by a predetermined increase amount.

[0068] Next, the control circuit 100 executes step S33. When it is determined in step S31 that the zero-phase current detection value Irip is equal to or greater than the zero-phase current limit Irip_lim, the control circuit 100 executes step S33 without executing step S32. In step S33, the current command increasing / decreasing unit 126 checks whether the corrected current command Iref_r is equal to or greater than the current current command Iref.

[0069] If it is determined in step S33 that the corrected current command Iref_r is smaller than the current current command Iref, the current command increase / decrease unit 126 completes the processing of one cycle of the current command Iref in step S03. If it is determined in step S33 that the corrected current command Iref_r is equal to or greater than the current current command Iref, the control circuit 100 executes step S34. In step S34, the current command increase / decrease unit 126 changes the status from "with correction" to "without correction," and completes the processing of one cycle of the current command Iref in step S03. The control circuit 100 repeats the above procedure in the above control period.

[0070] 〔summary〕 The above disclosure includes the following configurations.

[0071] (1) A power conversion device 3 comprising: a power conversion circuit 10 that converts direct current on a primary side into alternating current and outputs the converted alternating current to a secondary side; and a control unit 100 that controls the power conversion circuit 10 so as to suppress an increase in zero-phase current that occurs in response to the output of alternating current by adjusting the magnitude of the alternating current. According to this power conversion device 3, it is possible to continue generating and outputting AC while effectively suppressing an increase in zero-phase current by adjusting the magnitude of AC, which is therefore effective in achieving both suppression of zero-phase current and continuation of generation and output of AC.

[0072] (2) The control unit 100 of the power conversion device 3 described in (1) includes a command generating unit 111 that generates a current command, a command correcting unit 120 that corrects the current command so as to suppress an increase in zero-phase current that occurs when an alternating current corresponding to the current command is output to the secondary side, and a switching control unit 113 that controls the power conversion circuit 10 so as to output an alternating current corresponding to the current command to the secondary side. By generating a current command for a purpose other than suppressing the increase in zero-phase current, and then correcting the current command as necessary to suppress the increase in zero-phase current, it is possible to coexist control for the above-mentioned other purpose with control aimed at suppressing the increase in zero-phase current, thereby enabling more beneficial power conversion to be continued.

[0073] (3) The power conversion circuit 10 includes a first point 11 connected to the positive pole 2P of the DC power supply 2 on the primary side, a second point 12 connected to the negative pole 2N of the DC power supply 2 on the primary side, a third point 13 connected to the first point 11 via a first capacitor 14 and connected to the second point 12 via a second capacitor 15, and a switching circuit 16 that outputs three-phase AC to the secondary side by connecting and disconnecting between each of the first point 11 and the second point 12 and the secondary side while connecting the third point 13 to the secondary side. The power conversion device 3 described in (2). According to this configuration, the correlation between the AC output to the secondary side and the magnitude of the zero-phase current is strong. Therefore, the zero-phase current can be more effectively suppressed by correcting the current command. Therefore, it is more effective in suppressing the zero-phase current while continuing the power conversion.

[0074] (4) A power conversion device 3 described in (2) or (3), in which the command correction unit 120 determines the relationship between the magnitude of the AC and the magnitude of the zero-phase current based on first information representing the magnitude of the AC output to the secondary side and second information representing the magnitude of the zero-phase current, and corrects the current command based on the determined relationship and the specified level so that the magnitude of the zero-phase current is below a specified level. By taking into consideration the relationship between the magnitude of the AC current and the magnitude of the zero-phase current, the zero-phase current can be suppressed quickly.

[0075] (5) The power conversion device 3 according to (4), wherein the command corrector 120 repeatedly acquires the first information and the second information and updates the relationship every time the command corrector 120 acquires the first information and the second information. The relationship between the magnitude of the AC output to the secondary side and the magnitude of the zero-phase current may change over time. For example, when the DC current on the primary side is generated by the photovoltaic power generation device 2, the stray capacitance changes depending on the weather, and the above relationship changes over time according to the change in the stray capacitance. By repeatedly acquiring the first information and the second information and updating the profile every time the first information and the second information are acquired, the current command can be corrected more quickly in response to the change in the above relationship.

[0076] (6) The power conversion device 3 according to any one of (2) to (5), wherein the command correction unit 120 repeats correcting the current command to reduce the zero-phase current until the magnitude of the zero-phase current becomes equal to or less than a predetermined level. The zero-phase current can be suppressed more reliably.

[0077] (7) The power conversion device 3 according to (6), wherein the command corrector 120 repeats reducing the current command by a predetermined drop width until the magnitude of the zero-phase current becomes equal to or lower than a predetermined level. The zero-phase current can be suppressed by a simple calculation.

[0078] (8) A power conversion device 3 described in (6), in which the command correction unit 120 calculates a drop amount based on the deviation between a predetermined level and the magnitude of the zero-phase current, and reduces the current command by the calculated drop amount, repeatedly until the zero-phase current becomes equal to or lower than the predetermined level. The zero-phase current can be suppressed more quickly and more reliably.

[0079] (9) The command correction unit 120 is configured to execute the following steps: determine a relationship between the magnitude of the AC and the magnitude of the zero-phase current based on first information representing the magnitude of the AC output to the secondary side and second information representing the magnitude of the zero-phase current; generate a current limit based on the determined relationship and a predetermined level so that the magnitude of the zero-phase current is equal to or less than the predetermined level; correct the current command so that it is equal to or less than the current limit; and further reduce the current command set to or less than the current limit, repeating this process until the magnitude of the zero-phase current is equal to or less than the predetermined level. The zero-phase current can be suppressed more quickly and more reliably.

[0080] (10) A solar power generation system 1 comprising: a solar power generation device 2 that generates direct current in response to incident sunlight; a power conversion circuit 10 that converts the direct current generated by the solar power generation device 2 into alternating current and outputs it; and a control unit 100 that controls the power conversion circuit 10 so as to suppress an increase in zero-phase current that occurs in response to the output of alternating current by adjusting the magnitude of the alternating current.

[0081] (11) A power conversion method including: converting direct current on a primary side to alternating current using a power conversion circuit 10 and outputting the alternating current to a secondary side; and controlling the power conversion circuit 10 so as to suppress an increase in zero-phase current that occurs in response to the output of the alternating current by adjusting the magnitude of the alternating current. [Explanation of symbols]

[0082] 1...solar power generation system, 2...solar power generation device, 2P...positive electrode, 2N...negative electrode, 2...DC power supply, 3...power conversion device, 10...power conversion circuit, 11...first point, 12...second point, 13...third point, 14...first capacitor, 15...second capacitor, 16...switching circuit, 100...control circuit, 100...control unit, 111...command generation unit, 120...command correction unit, 113...switching control unit.

Claims

1. A power conversion circuit that converts direct current on the primary side into alternating current and outputs the converted alternating current to a secondary side; a zero-phase current sensor for detecting a magnitude of a zero-phase current generated on the secondary side in response to the AC output; a control unit that controls the power conversion circuit so as to suppress an increase in the zero-phase current by adjusting the magnitude of the AC current based on a detection result of the zero-phase current; Equipped with The control unit adjusts the magnitude of the AC current by adjusting a magnitude of a current vector in the AC current.

2. The control unit is A command generating unit that generates a current command; a command correction unit that corrects the current command to adjust the magnitude of the current vector so as to suppress an increase in a zero-phase current that occurs when the AC corresponding to the current command is output to the secondary side; a switching control unit that controls the power conversion circuit so as to output the AC corresponding to the current command to the secondary side; having The power converter according to claim 1 .

3. The power conversion circuit includes: a first point connected to a positive electrode of a DC power supply on the primary side; a second point connected to a negative electrode of the DC power supply on the primary side; a third point connected to the first point via a first capacitor and connected to the second point via a second capacitor; a switching circuit that outputs a three-phase AC to the secondary side by connecting and disconnecting each of the first point and the second point to the secondary side while connecting the third point to the secondary side; having The power converter according to claim 2.

4. The command correction unit is determining a relationship between the magnitude of the AC current and the magnitude of the zero-phase current based on first information representing the magnitude of the AC current output to the secondary side and second information representing the magnitude of the zero-phase current; correcting the current command based on the identified relationship and the predetermined level so that the magnitude of the zero-phase current is equal to or less than a predetermined level; 4. The power conversion device according to claim 2 or 3.

5. The command correction unit is repeatedly acquiring the first information and the second information; updating the relationship every time the first information and the second information are acquired; The power converter according to claim 4.

6. the command correction unit repeats correcting the current command so as to reduce the zero-phase current until the magnitude of the zero-phase current becomes equal to or less than a predetermined level.

4. The power conversion device according to claim 2 or 3.

7. the command correction unit repeats reducing the current command by a predetermined drop width until the magnitude of the zero-phase current becomes equal to or less than the predetermined level. The power converter according to claim 6.

8. The command correction unit is calculating a drop width based on a deviation between the predetermined level and the magnitude of the zero-phase current; Reducing the current command by the calculated drop width; repeating this until the zero-phase current is equal to or lower than the predetermined level. The power converter according to claim 6.

9. The command correction unit is determining a relationship between the magnitude of the AC current and the magnitude of the zero-phase current based on first information representing the magnitude of the AC current output to the secondary side and second information representing the magnitude of the zero-phase current; generating a current limit based on the determined relationship and the predetermined level such that the magnitude of the zero-sequence current is equal to or less than a predetermined level; correcting the current command so that the current command is equal to or less than the current limit; Repeating the process of further reducing the current command that has been set to be equal to or less than the current limit until the magnitude of the zero-phase current becomes equal to or less than the predetermined level; is configured to run 4. The power conversion device according to claim 2 or 3.

10. A solar power generation device that generates direct current in response to the incidence of sunlight; a power conversion circuit that converts a direct current generated by the solar power generation device into an alternating current and outputs the alternating current to a secondary side; a zero-phase current sensor for detecting a magnitude of a zero-phase current generated on the secondary side in response to the AC output; a control unit that controls the power conversion circuit based on a detection result of the zero-phase current so as to suppress an increase in the zero-phase current on the secondary side that occurs in response to the AC output by adjusting the magnitude of the AC output; Equipped with The control unit adjusts the magnitude of the alternating current by adjusting the magnitude of a current vector in the alternating current.

11. converting direct current on the primary side into alternating current by a power conversion circuit and outputting the alternating current to a secondary side; Detecting a magnitude of a zero-phase current generated on the secondary side in response to the AC output; controlling the power conversion circuit so as to suppress an increase in the zero-phase current on the secondary side that occurs in response to the output of the AC current by adjusting the magnitude of the AC current based on a detection result of the zero-phase current; Including, adjusting the magnitude of the alternating current includes adjusting a magnitude of a current vector in the alternating current. Power conversion methods.

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