Power conversion system and control method thereof

Abstract

To suppress a noise current flowing through a ground line connecting a plurality of power converters connected in parallel.SOLUTION: A power conversion system comprising: a plurality of power conversion devices connected in parallel; a ground line connecting the plurality of power conversion devices; and one or more control circuits configured to synchronize switching of the plurality of power conversion devices with each other to reduce a current flowing through the ground line.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion system and a control method thereof. [Background technology]

[0002] A power conversion system is known that suppresses an increase in noise level by using individual noise filters in each of multiple power conversion devices connected in parallel and a collective noise filter provided on the system side of the parallel connection point of the power conversion devices (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-220272 Summary of the Invention [Problem to be solved by the invention]

[0004] The voltage between the ground and the power conversion device (voltage to ground) fluctuates as the power conversion device switches. When the voltage to ground fluctuates, noise current may flow in the ground wire connecting multiple power conversion devices connected in parallel. Such noise current may cause noise interference, such as malfunctioning of other equipment.

[0005] However, with conventional techniques, it is difficult to suppress noise currents flowing through the grounding wires connecting a plurality of power conversion devices connected in parallel.

[0006] The present disclosure provides a power conversion system and a control method thereof that can suppress noise current flowing in a ground line connecting multiple power conversion devices connected in parallel. [Means for solving the problem]

[0007] As a first aspect of the present disclosure, a plurality of power conversion devices connected in parallel; a first grounding wire connecting the plurality of power conversion devices; and one or more control circuits that synchronize switching of the plurality of power conversion devices with each other to reduce the current flowing through the first ground line.

[0008] As a second aspect of the present disclosure, A control method for a power conversion system including a plurality of power conversion devices connected in parallel and a ground line connecting the plurality of power conversion devices, the method comprising: A control method for a power conversion system is provided, which synchronizes the switching of a plurality of the power conversion devices with each other to reduce the current flowing in the ground line. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to suppress noise current flowing through a ground line connecting a plurality of power conversion devices connected in parallel. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a configuration of a power conversion system according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating an example of a configuration of a power conversion device. [Figure 3] FIG. 4 is a diagram illustrating an example of changes in the voltage to ground of each of two power conversion devices connected in parallel. [Figure 4] 1 is a diagram illustrating an example of a configuration of a power conversion system according to a first example of an embodiment. [Figure 5] FIG. 2 is a diagram illustrating an example of an internal configuration of a switching panel. [Figure 6] FIG. 2 is a diagram illustrating an example of the configuration of a control circuit. [Figure 7] FIG. 10 is a diagram for explaining a method for measuring a leakage current that occurs during isolated operation of one power conversion device. [Figure 8] FIG. 10 is a diagram for explaining a method for adjusting the phase of a carrier signal. [Figure 9] FIG. 10 is a diagram illustrating a configuration example of a power conversion system according to a second example of an embodiment. [Figure 10] 10 is a timing chart of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] Fig. 1 is a diagram showing an example of the configuration of a power conversion system according to an embodiment. The power conversion system 100 shown in Fig. 1 is a system that converts power between a power source 10 and a load 20. In the example shown in Fig. 1, the power conversion system 100 converts direct current (DC) supplied from the power source 10 into alternating current (AC) and supplies the converted AC to the load 20. The power conversion system 100 includes the power source 10, a positive electrode wiring 33, a negative electrode wiring 34, and a plurality (N) of power conversion devices A1 to A N , ground lines 31, 32 and a plurality (N pieces) of control circuits B1 to B N N is an integer equal to or greater than 2. Control circuits B1 to B N are N power electronics devices A1 to A N The power converter is provided inside or outside the corresponding power converter.

[0013] The power supply 10 includes N power conversion devices A1 to A N 1. The power supply 10 is a DC power supply that supplies DC power to the power supply 10 via a positive wiring 33 and a negative wiring 34. The power supply 10 has, for example, a power generation device 11 and a power storage device 12. The power generation device 11 outputs generated DC power. Examples of the power generation device 11 include a solar panel and a fuel cell. The power generation device 11 may be replaced with an AC / DC converter that converts AC power supplied from the power supply into DC power and outputs it, or a DC / DC converter that converts DC power supplied from the power supply into DC power and outputs it. The power storage device 12 stores the power output from the power generation device 11. An example of the power storage device 12 is a secondary battery such as a lithium ion battery.

[0014] N power conversion devices A1 to A NThe power conversion devices A1 to A2 convert DC power supplied from the power source 10 via a positive electrode wiring 33 and a negative electrode wiring 34 into AC power (in this example, three-phase AC power of U, V, and W) and output the AC power. N The AC power output from each of these is supplied to a load 20. The load 20 is, for example, an AC power system. The load 20 may also be another AC load.

[0015] The power conversion system 100 can be applied to power generation systems that use renewable energy such as solar or wind power, or chemical energy such as fuel. In the case of large-scale facilities such as mega solar power generation systems, the rated capacity of a single power conversion device may be insufficient, so by connecting multiple power conversion devices in parallel as shown in Figure 1, the lack of rated capacity can be resolved.

[0016] The power conversion system 100 includes N power conversion devices A1 to A2 that supply power generated by a power generation device 11 such as a solar panel or a fuel cell to a load 20 such as an AC power system. N The output of a solar panel, a fuel cell, or the like is a DC voltage. Therefore, when DC power generated by the power generation device 11 is supplied to an AC power system, power conversion devices A1 to A2 convert the DC voltage into AC voltage at a commercial frequency (for example, 50 Hz or 60 Hz). N A PCS (Power Conditioning System) is used as the power converter. The PCS is a type of inverter that converts DC voltage into AC power by the switching operation of multiple switching elements. N Each of these may be treated as one PCS.

[0017] Power conversion devices A1 to A N have a positive terminal P, a negative terminal N, output terminals U, V, W, and ground terminals G1, G2, respectively.

[0018] The positive terminal P is connected to the positive electrode of the power supply 10 via a positive electrode wiring 33. The negative terminal N is connected to the negative electrode of the power supply 10 via a negative electrode wiring 34. The output terminals U, V, and W are connected to the load 20 via three-phase output lines.

[0019] Power conversion devices A1 to A N The ground terminals G1 of the power conversion device A1 are connected to each other via a ground wire 31. The ground terminal G1 of the power conversion device A1 is connected to the ground terminal G2 of the power conversion device A1 via a conductor G. The ground terminal G2 is grounded to the earth 30 via a ground wire 32. The power supply 10 is also grounded to the earth 30.

[0020] Power conversion device A2~A N is grounded to the earth 30 via the ground wire 31 and the ground terminals G1 and G2 of the power conversion device A1. As a result, for example, when the linear distance between the power conversion device A2 and the power conversion device A1 is shorter than the linear distance between the power conversion device A2 and the earth 30 (ground point), the power conversion device A2 can be grounded to the earth 30 by the relatively short ground wire 31. N Similarly, the power converters A3 to A4 are connected to the power converters A4 to A5 by a relatively short ground wire 31. N can be grounded to earth 30.

[0021] In addition, the power conversion devices A2 to A N At least one of the devices may have its ground terminal G2 grounded to earth 30 via a ground wire 32.

[0022] Fig. 2 is a diagram showing an example of the configuration of a power conversion device. The power conversion device A1 shown in Fig. 2 is an inverter that converts DC power supplied via a positive terminal P and a negative terminal N into three-phase AC power and outputs it from output terminals U, V, and W. Other power conversion devices A2 to A N may have the same configuration as the power conversion device A1, and therefore the description thereof will be omitted by referencing the description of the power conversion device A1.

[0023] The power converter A1 includes a positive bus 41p, a negative bus 41n, a capacitor 42, switching elements Q1 to Q6, and output wirings 43u, 43v, and 43w.

[0024] The positive bus bar 41p is connected to a positive terminal P. The negative bus bar 41n is connected to a negative terminal N. The capacitor 42 is connected between the positive bus bar 41p and the negative bus bar 41n, and smoothes the DC voltage (the voltage of the capacitor 42) between the positive bus bar 41p and the negative bus bar 41n.

[0025] The switching elements Q1 to Q6 are semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), etc. Fig. 2 illustrates the case of an IGBT with a diode connected in antiparallel.

[0026] The connection point between switching element Q1 and switching element Q2 is connected to output terminal U via output wiring 43u. The connection point between switching element Q3 and switching element Q4 is connected to output terminal V via output wiring 43v. The connection point between switching element Q5 and switching element Q6 is connected to output terminal W via output wiring 43w.

[0027] Switching elements Q1 to Q6 convert DC power supplied via positive terminal P and negative terminal N into three-phase AC power by switching in accordance with drive signals generated by control circuit B1 (FIG. 1) according to a known control method.

[0028] 2, power conversion device A1 has a conductor G connecting between ground terminal G1 and ground terminal G2. Conductor G is, for example, a heat sink 40 that dissipates heat from switching elements Q1 to Q6. Conductor G is not limited to heat sink 40, and may be a housing that covers power conversion device A1, or the like.

[0029] As the switching elements Q1 to Q6 switch, the potentials of the output wirings 43u, 43v, and 43w change, causing the voltage V PG1 ,V NG1 The voltage to ground V PG1 represents the potential difference between the conductor G connected to the earth 30 and the positive bus 41p connected to the positive wiring 33, and the voltage V NG1 indicates the potential difference between the conductor G connected to the earth 30 and the negative bus 41n connected to the negative wiring 34.

[0030] Voltage to ground V PG1 ,V NG1 The magnitude of each of C depends on the capacitance of the stray capacitance due to the switching elements Q1 to Q8. 11 represents the stray capacitance between the conductor G and the output wiring 43u. 12 represents the stray capacitance between the conductor G and the output wiring 43v. 13 represents the stray capacitance between the conductor G and the output wiring 43w. There may be stray capacitance between the conductor G and the positive electrode bus 41p. There may be stray capacitance between the conductor G and the negative electrode bus 41n. The stray capacitance C1 of the power conversion device A1 corresponds to the combined capacitance of these stray capacitances.

[0031] Voltage to ground V PG1 ,V NG1 A high-frequency leakage current (common mode current) caused by fluctuations in the capacitance C1 flows to the ground terminals G1 and G2 via the stray capacitance C1 and the conductor G. The common mode current may have adverse effects, such as deterioration, on other devices connected to the ground terminal G1 or G2 of the power conversion device A1 (for example, the power storage device 12 (FIG. 1) connected via the ground wire 32).

[0032] Leakage current (common mode current) is a noise current that contains a wide frequency band. Therefore, leakage current can flow into other devices connected to the power conversion device via the grounding wires 31 and 32, or radiate electromagnetic waves into space, causing noise interference such as malfunction of other devices.

[0033] 1 illustrates a leakage current IL flowing through the ground line 31. N are the power electronics devices A1 to A N The control circuits B1 to B operate the corresponding power conversion devices independently. N represents a plurality of power conversion devices A1 to A N When the power conversion devices A1 to A N Each voltage to ground (V PG1 ,V PG2 ,···V PGN In this case, a difference may occur between the power conversion devices A1 to A N The power conversion devices A1 to A N There is a risk that a noise current (leakage current IL) will flow that circulates between the terminals, causing noise interference such as malfunctioning of other equipment.

[0034] Next, a description will be given of factors that cause a noise current (leakage current IL) that circulates between a plurality of power conversion devices.

[0035] The voltage to ground fluctuates with the switching operation of each switching element inside the power conversion device. N The control circuits B1 to B each control the switching operation of each switching element in the corresponding power conversion device by pulse width modulation (PWM). N When controlling the switching operation by the PWM method, the voltage command and the carrier signal are compared to determine the switching timing of each switching element inside the corresponding power conversion device.

[0036] However, the power conversion devices A1 to A2 are configured so that they all have the same voltage output. N Even if the same voltage command is given between the power conversion devices A1 to A2, the phase of the carrier signal may differ N If the timings of the switching elements differ between the power conversion devices A1 to A N Generally, the voltage command is set so that the output voltage matches the amplitude and phase of the grid voltage.

[0037] Since fluctuations in the voltage to ground occur at the timing of switching, multiple power conversion devices A1 to A N The control circuits B1 to B N Even if the power conversion devices A1 to A N If the carrier signals of the two are not synchronized, a difference in voltage to ground will occur.

[0038] 3A and 3B are diagrams illustrating changes in the voltages to ground of two power conversion devices connected in parallel. FIG. 3A shows a case where the phase difference between the carrier signal of the power conversion device A1 and the carrier signal of the power conversion device A2 is 90°. As shown in FIG. 3A, the voltage V to ground of the power conversion device A1 PG1 and the voltage V to ground of power conversion device A2 PG2 On the other hand, FIG. 3(b) shows a case where the phase difference between the carrier signal of the power conversion device A1 and the carrier signal of the power conversion device A2 is 0°. As shown in FIG. 3(b), the voltage V PG1 and the voltage V to ground of power conversion device A2 PG2 It is consistent with.

[0039] Power conversion devices A1 to A N When a difference occurs in the voltages to ground of the power conversion devices A1 to A N A potential difference occurs between the ground terminals G1 of the respective terminals G1, and a current (leakage current IL) flows through the ground line 31 connecting the ground terminals G1.

[0040] A plurality of control circuits B1 to B2 of a power conversion system 100 according to an embodiment of the present disclosure N At least one of the control circuits includes a plurality of power conversion devices A1 to A N The switching of the power conversion devices A1 to A2 is synchronized with each other to reduce the current flowing through the ground line 32. N By synchronizing the switching of the power conversion devices A1 to A NThis reduces or even eliminates the difference in the voltages to ground between these two terminals, thereby suppressing the leakage current IL flowing through the grounding wire 31. By suppressing the leakage current IL, it is possible to reduce the occurrence of noise interference that may cause other devices to malfunction.

[0041] Multiple control circuits B1 to B N At least one of the control circuits includes, for example, a plurality of power conversion devices A1 to A N The phase difference between the switching of the control circuits B1 to B2 approaches zero, thereby reducing the current flowing through the ground line 31. N At least one of the control circuits includes a plurality of power conversion devices A1 to A N By making the phase difference of the switching of the power conversion devices A1 to A N This allows the switching of the two circuits to be synchronized with each other.

[0042] Multiple power conversion devices A1 to A N The phase difference of the switching of the power conversion devices A1 to A N may be defined as the phase difference between the switching timings of each specific switching element (for example, switching element Q1).

[0043] The phase of the switching of the power conversion device (the switching of the switching elements) is determined by the phase of the carrier signal. N At least one of the control circuits includes a plurality of power conversion devices A1 to A N The carrier signals of the power conversion devices A1 to A2 may be synchronized with each other to reduce the current flowing through the ground line 32. N By synchronizing the carrier signals of the power conversion devices A1 to A N This reduces or even eliminates the difference in the voltages to ground between these two terminals, thereby suppressing the leakage current IL flowing through the grounding wire 31. By suppressing the leakage current IL, it is possible to reduce the occurrence of noise interference that may cause other devices to malfunction.

[0044] Multiple control circuits B1 to B NAt least one of the control circuits includes, for example, a plurality of power conversion devices A1 to A N The phase difference between the carrier signals of the plurality of control circuits B1 to B2 approaches zero, thereby reducing the current flowing through the ground line 31. N At least one of the control circuits includes a plurality of power conversion devices A1 to A N By making the phase difference of the carrier signals of the power conversion devices A1 to A N This allows the switching of the two circuits to be synchronized with each other.

[0045] Fig. 4 is a diagram showing an example of a configuration of a power conversion system according to a first example of an embodiment. Fig. 4 shows a case where N=2. The power conversion system 101 shown in Fig. 4 includes two power electronics devices A1 and A2 connected in parallel, a switchboard 70 that switches the connection of DC inputs (inputs from power sources 10) of the two power electronics devices A1 and A2, and a current sensor S2 that detects a current flowing through a ground wire 31. In the power conversion system 101 of Fig. 4, the same configuration, actions, and effects as those of the above-described power conversion system 100 will not be described here, as the above-described descriptions are incorporated herein.

[0046] 5 is a diagram showing an example of the internal configuration of a switching panel. N The switching panel 70 switches the connection of the DC input (input from the power source 10) of the plurality of power conversion devices A1 to A2 in accordance with an opening / closing command from a control device (not shown). N N relays R1 to R2 switch the connection of the DC input (input from power supply 10) N An example of a control device is a programmable controller (PLC).

[0047] When the relay R1 is closed, DC power is supplied from the power source 10 to the power conversion device A1, and when the relay R1 is open, the supply of DC power from the power source 10 to the power conversion device A1 is cut off. N Similarly, relays R2 to R N By the opening and closing operation of the power supply 10, the power conversion devices A2 to A N The supply of power to the device is controlled.

[0048] The switching panel 70 may have a grounding electrode 71 that connects a plurality of grounding wires together to the earth 30. The grounding electrode 71 connects the grounding wire of the power source 10 and the power converters A1 to A N The ground wires of the above two are grounded together to earth 30.

[0049] In FIG. 4, IL is the first to Nth power electronics devices A1 to A N (In this example, two power conversion devices A1 and A2) are connected to control circuits B1 to B N Let IL0 be the current that flows through the ground line 31 when switching is performed by the control circuits B1 and B2 (in this example). Let IL0 be the current that flows through the ground line 32 when the first power conversion device A1 is switched independently by the control circuit B1 in the absence of the ground line 31.

[0050] When the first power conversion device A1 is switched independently by the control circuit B1 in the absence of the ground wire 31, the leakage current IL0 (common mode current) generated flows from the ground wire 32 to the power supply 10 via the stray capacitances 13 and 14 because there is no ground wire 31. N The current newly increased by newly connecting in parallel to the first power conversion device A1 is a leakage current IL flowing through the ground wire 32. N is newly connected in parallel to the first power conversion device A1, the current equivalent to the leakage current IL0 that occurs during isolated operation will try to flow somewhere.

[0051] Therefore, the control circuit B2 controls the phase of switching of the power conversion device A2 so that the current IL when the power conversion devices A1 and A2 are being switched by the control circuits B1 and B2 becomes the same as the current IL0 when the power conversion device A1 is switching independently without the ground wire 31. This suppresses the leakage current (common mode current) that flows from the ground wire 32 to the power supply 10 via the stray capacitances 13 and 14, thereby reducing the occurrence of noise interference to other devices such as the power supply 10.

[0052] The control circuits B1 and B2 are provided inside or outside the corresponding power conversion devices A1 and A2, respectively. The control circuits B1 and B2 each have a drive control unit 51 that controls the switching timing of each switching element inside the corresponding power conversion device A1 and A2 using a PWM method. The drive control unit 51 may include a drive circuit that drives the gate of each switching element inside the corresponding power conversion device A1 and A2.

[0053] The control circuit B2 controls the first to Nth power conversion devices A1 to A2 based on the detected value of the current flowing through the ground wire 31 detected by the current sensor S2. N The switching of the power converters (in this example, two power converters A1 and A2) is synchronized with each other.

[0054] The control circuit B2 has a phase control unit 52 and a drive control unit 51. The phase control unit 52 adjusts the switching phase θ of the second power conversion device A2 so that the current IL flowing in the ground line 31 detected by the current sensor S2 becomes the same as the current IL0 when the first power conversion device A1 is switching alone. The phase control unit 52 adjusts, for example, the phase θ of the carrier signal of the second power conversion device A2. The drive control unit 51 of the control circuit B2 controls the switching timing of each switching element in the power conversion device A2 by the PWM method in accordance with the phase θ adjusted by the phase control unit 52.

[0055] 6 is a diagram showing an example of the configuration of a control circuit. The control circuit B2 has a phase control section 52 and a drive control section 51. The phase control section 52 controls the phases of the plurality of power conversion devices A1 to A2 based on the deviation Ie between the target value ILa of the leakage current IL flowing in the ground line 31 and the detected value ILb of the current IL flowing in the ground line 31. N The switching of the power converters (in this example, two power converters A1 and A2) is synchronized with each other.

[0056] The current detection value detected by the current sensor S2 contains high-frequency components and its amplitude changes significantly over a short period of time, which may result in unstable control output if used for control as is. The calculation processing unit 53 performs predetermined calculation processing on the current detection value detected by the current sensor S2 to stabilize the control output. The calculation processing unit 53, for example, calculates the root mean square (RMS) value of the detected current IL as the detection value ILb. The calculation processing unit 53 may perform a fast Fourier transform (FFT) on the detected current IL to calculate the maximum amplitude value among the frequency components contained in the detected current IL as the detection value ILb.

[0057] The target value ILa is set based on the current value of the leakage current IL0 when the first power conversion device A1 is switching on and off independently without the grounding line 31. The target value ILa is stored in the memory 54. The target value ILa uses a value obtained by performing the same calculation process as that used to calculate the detected value ILb (the effective value (RMS) of the detected current IL, or the maximum amplitude value among the frequency components included in the detected current IL).

[0058] Fig. 7 is a diagram for explaining a method for measuring leakage current generated during isolated operation of one power conversion device. Leakage current IL0 (common mode current) generated when power conversion device A1 is switching on and off independently without a ground wire 31 flows through the ground wire 32, stray capacitances 13 and 14 of power supply 10, wiring 33 and 34, stray capacitance C1, and ground wire 32 in that order. Leakage current IL0 flowing through ground wire 32 is detected by current sensor S1. Target value ILa in Fig. 6 is set based on the current value of leakage current IL0 detected in advance by current sensor S1.

[0059] In Fig. 6, a subtractor 55 calculates the deviation Ie between a target value ILa and a detected value ILb. A PI controller 56 adjusts the phase θ of a carrier signal C by PI control so that the deviation Ie converges to zero. In PI control, P represents proportional control and I represents integral control. The phase θ output from the PI controller 56 is input to a carrier signal generator 57 as a phase command value for correcting the phase of the carrier signal C. The carrier signal generator 57 updates the phase θ of the carrier signal C in accordance with the phase command value.

[0060] The drive control unit 51 has a comparator 58. The comparator 58 controls the switching timing of each switching element inside the power conversion device by comparing a voltage command Vref with a carrier signal C. The voltage command Vref includes a U-phase voltage command Vu, a V-phase voltage command Vv, and a W-phase voltage command Vw.

[0061] FIG. 8 is a diagram for explaining a method for adjusting the phase of a carrier signal. In FIG. 8, the "reference carrier signal" is a carrier signal for determining the switching of the first power electronics device A1. The "carrier signal to be adjusted" is a carrier signal for determining the switching of the second and subsequent power electronics devices A2 to A3. N The phase θ of the carrier signal C of the second power electronics device A2 is a carrier signal for determining switching of one of the first and second power electronics devices A1 and A2. The phase control unit 52 adjusts the phase θ of the carrier signal C of the second power electronics device A2 so that the current IL flowing in the ground wire 31 detected by the current sensor S2 becomes the same as the current IL0 when the first power electronics device A1 is switching alone. This allows the control circuit B2 to bring the phase difference Δ (the difference between the phase of the carrier signal C of the power electronics device A1 and the phase of the carrier signal C of the power electronics device A2) closer to zero, as shown in FIG. 8.

[0062] 9 is a diagram showing an example of the configuration of a power conversion system according to a second example of an embodiment. A power conversion system 102 shown in FIG. 9 includes N power conversion devices A1 to A N and power conversion devices A1 to A N A switchboard 70 for switching the connection of the DC inputs, and (N-1) current sensors S2 to S5 for detecting the current flowing through the ground wire 31.N 9, the same configurations, actions, and effects as those of the power conversion systems 100 and 101 will not be described again since the above descriptions are incorporated herein.

[0063] Control circuit B2~B N are power conversion devices A1 to A N The current IL when the power conversion device A1 is switching is set to the same as the current IL0 when the power conversion device A1 is switching alone in the absence of the ground line 31. N This controls the switching phase of the power supply 10. This suppresses leakage current (common mode current) that flows from the ground line 32 to the power supply 10 via the stray capacitances 13 and 14, thereby reducing the occurrence of noise interference to the power supply 10 and other devices.

[0064] The control circuit B1 may be the same as the control circuit B1 in the first embodiment. N Each of the control circuits B2 to B N are current sensors S2 to S N Based on the detected value of the current flowing through the ground wire 31, the first to Nth power conversion devices A1 to A N The control circuits B2 to B N respectively correspond to the corresponding current sensors S2 to S N Based on the detected values ​​obtained by N and adjust the phase of the carrier frequency of the corresponding power conversion devices A2 to A N Adjust the switching timing.

[0065] If there is even one power conversion unit among three or more power conversion units connected in parallel that has a different voltage to ground than the other units, a leakage current IL will be generated that circulates between the units, and it is expected that the control will not converge and carrier phase synchronization will not be possible using PI control.

[0066] Therefore, in the second embodiment, the timing of powering on the power electronics devices is sequentially controlled, thereby controlling the phase of each power electronics device one by one, thereby preventing the divergence of control as described above.

[0067] The switching panel 70 is connected to the power converters A1 to A N Relays R1 to R2 are used to switch the power on and off for each input. N (FIG. 5). The power conversion system 102 of FIG. 9 includes the relays R1 to R N The power-on sequence control device includes a programmable controller 80 (PLC80).

[0068] 10 is a timing chart of the second embodiment. First, when powering on the power electronics device A1, the PLC 80 powers on only the first power electronics device A1 and the second power electronics device A2. After a sufficient time has passed until the carrier phases of the power electronics devices A1 and A2 are synchronized by the control circuit B2, the PLC 80 powers on the third power electronics device A3. By repeating this process, carrier synchronization of the N power electronics devices is achieved when the Nth power electronics device is powered on.

[0069] In general, N is the number of the power conversion devices, and k is an integer equal to or greater than 3. N At least one of the control circuits among the plurality of control circuits B1 to B2 synchronizes the switching of the first to (k-1)th power conversion devices with each other to reduce the current IL. After reducing the current IL, the PLC 80 repeatedly turns on the power supply of the kth power conversion device until k becomes N. In this case, the plurality of control circuits B1 to B2 N At least one or more control circuits among the power converters synchronize the switching of the first to (k-1)th power converters with each other to reduce the current IL, and then synchronize the switching of the first to kth power converters with each other to reduce the current IL, repeating this process until k becomes N.

[0070] In this disclosure, the control circuit or control device includes an electronic circuit such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC). The control circuit or control device may be a computer having a memory and a processor. The control circuit or control device performs the various control operations described in this specification by executing a program such as instruction code stored in the memory, or by being a circuit designed for a specific application.

[0071] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0072] For example, the power conversion device is not limited to an inverter that converts DC to AC, but may have a different type of circuit configuration, such as a converter that converts DC to DC. [Explanation of symbols]

[0073] 10 Power supply 11 Power generating equipment 12. Energy storage device 13,14 Stray capacitance 20 Load 30 Earth 31,32 Ground wire 33 Positive wiring 34 Negative wiring 40 Heatsink 51 Drive control unit 52 Phase control section 70 Switching board 80 PLC 100,101,102 Power Conversion Systems A1, A2, A N Power Conversion Device B1, B2, B N Control circuit G Conductor S1,S2,S N Current Sensor

Claims

1. a plurality of power conversion devices connected in parallel; a first ground line connecting the plurality of power conversion devices; one or more control circuits that synchronize switching of the plurality of power conversion devices with each other to reduce the current flowing in the first ground line.

2. When N is the number of the plurality of power conversion devices and k is an integer of 3 or more, 2. The power conversion system according to claim 1, wherein the control circuit synchronizes switching of the first to (k-1)th power conversion devices with each other to reduce the current, and then power is turned on for the kth power conversion device.

3. The power conversion system according to claim 2, wherein the control circuit synchronizes the switching of the first to (k-1)th power conversion devices with each other to reduce the current, and then synchronizes the switching of the first to kth power conversion devices with each other to reduce the current, repeating this process until k becomes N.

4. The power conversion system according to claim 1 , wherein the control circuit reduces the current by bringing a phase difference between switching of the plurality of power conversion devices closer to zero.

5. The power conversion system according to claim 1 , wherein the control circuit reduces the current by synchronizing carrier signals of the plurality of power conversion devices with each other.

6. The power conversion system according to claim 5 , wherein the control circuit reduces the current by bringing a phase difference between carrier signals of the plurality of power conversion devices closer to zero.

7. When N is the number of the plurality of power conversion devices, 7. The power conversion system according to claim 1, wherein the control circuit controls the switching phase of the second to Nth power conversion devices so that the current flowing in the first ground wire when the first to Nth power conversion devices are switching is the same as the current flowing in a second ground wire different from the first ground wire when the first power conversion device is switching alone in the absence of the first ground wire.

8. The power conversion system according to claim 1 , wherein the control circuit synchronizes switching of the plurality of power conversion devices with each other based on the detected value of the current.

9. The power conversion system according to claim 8 , wherein the control circuit synchronizes switching of the plurality of power conversion devices with each other based on a deviation between the target value of the current and the detected value of the current.

10. The power conversion system according to claim 8 , wherein the detected value is an effective value of the current.

11. The power conversion system according to claim 8 , wherein the detected value is a maximum amplitude value among frequency components contained in the current.

12. A control method for a power conversion system including a plurality of power conversion devices connected in parallel and a ground line connecting the plurality of power conversion devices, the method comprising: A control method for a power conversion system, comprising: synchronizing the switching of a plurality of the power conversion devices with each other to reduce a current flowing in the ground line.

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