Power conversion system

Abstract

To provide a power conversion system having a plurality of current rating circuits in which the number of components is reduced and cost is reduced.SOLUTION: A power conversion system comprises: a power converter 1; a first current rating circuit that has a preceding stage-side current measuring device HCT_A11 having a first current rating, a preceding stage-side reactor L_A11, a first switch MC_B11, a first subsequent stage-side current measuring device HCT_B11 having the first current rating, a first subsequent stage-side reactor L_B11, and an output switch MC_C11; a capacitor C11 that is connected between a contact point of the preceding stage-side reactor L_A11 and the first switch MC_B11 and the other terminal of the power converter 1; second to N-th current rating circuits that has second to N-th switches connected in parallel to the first switch MC_B11, second to N-th reactors, and second to N-th subsequent stage-side current measuring devices having second to N-th current ratings; and a control unit that controls the power converter 1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power conversion system having a plurality of current measuring devices with different ratings in order to control current with high precision, and more particularly to a power conversion system having an LCL filter on the output side. [Background technology]

[0002] Power conversion systems that operate by switching between multiple current measurement devices are known. Figure 1 shows the main circuit configuration of a conventional power conversion system. As shown in Figure 1, an LCL filter is provided on the output side, and current measurement devices HCT_A11, HCT_A21, HCT_A31, HCT_B11, HCT_B21, HCT_B31, HCT_A12, HCT_A22, HCT_A32, HCT_B12, HCT_B22, and HCT_B32 dedicated to each current rating and switches MC_A11, MC_A21, MC_A31, MC_B11, MC_B21, MC_B31, MC_C11, MC_A12, MC_A22, MC_A32, MC_B12, MC_B22, MC_B32, and MC_C12 are provided before and after capacitors C11 and C12. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-180533 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, there are current measuring devices, switches, and reactors dedicated to each current rating before and after capacitor C. For this reason, when configuring a circuit with multiple current ratings, the number of parts increases as the number of current rating circuits increases. Table 1 shows the number of parts for a single-unit configuration (one power conversion unit), and Table 2 shows the number of parts for a two-parallel configuration (two power conversion units). As shown in Tables 1 and 2, having multiple current rating circuits increases the number of parts and the cost of the device.

[0005] [Table 1]

[0006] [Table 2]

[0007] In view of the above, it is an object of the present invention to provide a power conversion system having multiple current rated circuits that reduces the number of components and reduces costs. [Means for solving the problem]

[0008] The present invention was devised in consideration of the above-mentioned problems of the conventional art, and one aspect of the present invention is characterized by comprising a power conversion device, a first current rating circuit having an upstream current measuring device having a first current rating connected between one terminal of the power conversion device and a load, an upstream reactor, a first switch, a first downstream current measuring device having a first current rating, a first downstream reactor, and an output switch, a capacitor connected between the connection point of the upstream reactor and the first switch and the other terminal of the power conversion device, second to Nth current rating circuits having second to Nth (N: an integer of 2 or more) switches connected in parallel to the first switch, second to Nth downstream reactors, and second to Nth downstream current measuring devices having second to Nth current ratings, and a control unit that controls the power conversion device.

[0009] In one aspect, the power conversion device is characterized by comprising: a plurality of power conversion devices arranged in parallel; a first current rating circuit having an upstream current measuring device having a first current rating connected between one terminal of each of the power conversion devices and a load, an upstream reactor, a first switch, a first downstream current measuring device having a first current rating, a first downstream reactor, and an output switch; a capacitor connected between a connection point of each of the upstream reactors and each of the first switches and the other terminal of each of the power conversion devices; second to Nth current rating circuits having second to Nth (N: an integer greater than or equal to 2) switches connected in parallel to each of the first switches, second to Nth downstream reactors, and second to Nth downstream current measuring devices having second to Nth current ratings; and a control unit that controls each of the power conversion devices.

[0010] In one embodiment, the control unit has a current control unit that performs proportional-integral control, and the current control unit uses the current detection value detected by the upstream current measuring device as a feedback signal for the proportional term, and the current detection value of the current rated circuit being used among the current detection values ​​detected by the first to Nth downstream current measuring devices as a feedback signal for the integral term.

[0011] In one aspect, the power conversion device has a configuration in which multiple units are connected in parallel or in an interleaved configuration, and the upstream reactor is a cross current suppression reactor connected to the unit. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a power conversion system having a plurality of current rated circuits, which reduces the number of parts and reduces costs. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of a main circuit configuration of a conventional power conversion system. [Figure 2] FIG. 2 is a diagram showing the main circuit configuration of the power conversion system according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing a current control unit in the first embodiment. [Figure 4] Circuit diagram of an LCL filter. [Figure 5] FIG. 10 is a diagram showing a main circuit configuration of a power conversion system according to a second embodiment. [Figure 6] Circuit diagram of an LCL filter. [Figure 7] FIG. 10 is a diagram showing a main circuit configuration of a power conversion system according to a third embodiment. [Figure 8] FIG. 10 is a diagram showing a main circuit configuration of a power conversion system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, first to fourth embodiments of the power conversion system of the present invention will be described in detail with reference to Fig. 2 to Fig. 8. In this specification, the term "rated current" means "a current specified as the peak value or maximum root mean square value of a DC or AC current assumed as an input or output current."

[0015] [Embodiment 1] Figure 2 shows the basic main circuit configuration of the power conversion system in this embodiment 1. In this embodiment 1, only a front-side current measuring device HCT_A11 and a front-side reactor L_A11, which have a first current rating with a large current rating, are provided in the front stage of capacitor C11 of the LCL filter. Reactors and current measuring devices dedicated to each current rating are provided only in the rear stage. In addition, a switch for switching current ratings is provided only in the rear stage of capacitor C11 of the LCL filter so that a circuit dedicated to each current rating can be selected.

[0016] Specifically, a first current rating circuit having a first current-rated upstream current measuring device HCT_A11, a upstream reactor L_A11, a first switch MC_B11, a first downstream current measuring device HCT_B11, a first downstream reactor L_B11, and an output switch MC_C11 is connected between one terminal (positive terminal in the present embodiment 1) of the first power conversion device 1 and the load 10. A capacitor C11 is connected between the connection point of the upstream reactor L_A11 and the first switch MC_B11 and the other terminal (negative terminal in the present embodiment 1) of the first power conversion device 1.

[0017] A second current rating circuit having a second switch MC_B21, a second rear-side reactor L_B21, and a second rear-side current measuring device HCT_B21 with a second current rating is connected in parallel to the first switch MC_B11. Also, a third current rating circuit having a third switch MC_B31, a third rear-side reactor L_B31, and a third rear-side current measuring device HCT_B31 with a third current rating is connected in parallel to the first switch MC_B11. In the first embodiment, the first current rating is large, the second current rating is medium, and the third current rating is small.

[0018] In the first embodiment, the number of current-rated circuits is three, but the number of current-rated circuits may be N (N: an integer equal to or greater than 2). In the first embodiment, the switch MC is, for example, an electromagnetic contactor, but it may also be a switch that can open and close a circuit, such as a disconnector.

[0019] The first power conversion device 1 assumed in this embodiment 1 is a device that outputs direct current such as AC / DC (alternating current-direct current) or DC / DC (direct current-direct current), or a device that outputs alternating current such as AC / AC (alternating current-alternating current) or DC / AC (direct current-alternating current), but is a device that outputs a frequency band that is sufficiently lower than the resonant frequency of the LCL filter.

[0020] The first power conversion device 1 is controlled by a control unit (not shown). The control unit has a current control unit. Fig. 3 shows the configuration of the current control unit in the first embodiment.

[0021] The subtractor 11 subtracts the current detection value of the upstream current measurement device HCT_A11 from the current command and outputs the deviation. The multiplier 14 multiplies the deviation by a proportional gain Kp.

[0022] Switch 12 selects and outputs one of the current detection values ​​from the first, second, and third downstream current measuring devices HCT_B11, HCT_B21, and HCT_B31 based on a current detection selection signal. Subtractor 13 subtracts the output of switch 12 from the current command and outputs the deviation. Multiplier 15 multiplies the deviation by integral gain Ki.

[0023] An adder 16 adds the output of the multiplier 15 and the output of a buffer 18. A limiter 17 limits the output of the adder 16 to a limit value. The buffer 18 outputs the value of the output of the limiter 17 one sample before. An adder 19 adds the outputs of the multiplier 14 and limiter 17 and outputs the result as a voltage command.

[0024] As shown in FIG. 3, the current detection value of a front-stage current measuring device HCT_A11 provided in the front stage of the capacitor C11 of the LCL filter is applied to the feedback signal of the proportional term.

[0025] The feedback signal of the integral term is applied with the current detection value of the downstream current measuring device provided downstream of the capacitor C11 of the LCL filter. Since the downstream current measuring devices attached downstream of the capacitor C11 of the LCL filter are dedicated to each current rating, one of the current detection values ​​of the current rating circuit being used is selected from the current detection values ​​of the first to third downstream current measuring devices HCT_B11, HCT_B21, and HCT_B31 in accordance with the current detection selection signal.

[0026] In this embodiment 1, as shown in Table 3, the magnitude of the current rating, the selection of the first, second, and third current measuring devices HCT_B11, HCT_B21, and HCT_B31, the opening and closing operations of the first to third switches MC_B11, MC_B21, and MC_B31, and the current detection selection signal are defined.

[0027] [Table 3]

[0028] The circuit configuration of an LCL filter is shown in Figure 4. Here, L1 is the reactor in front of the LCL filter, C2 is the capacitor of the LCL filter, L3 is the reactor in back of the LCL filter, V1 is the voltage applied to the LCL filter, I1 is the current flowing in the reactor in front, I2 is the current flowing in the capacitor, and I3 is the current flowing in the reactor in back.

[0029] The transfer function when voltage V1 is input and current I3 is output is shown in equation (1) below, where s is the Laplace operator, L1 is the inductance value of the upstream reactor, L3 is the inductance value of the downstream reactor, and C2 is the capacitance of the capacitor.

[0030]

number

[0031] From equation (1), the upstream reactor L1 and downstream reactor L3 are s 2 Since the terms s and s are expressed in the same way, changing the value of either the upstream reactor L1 or the downstream reactor L3 does not affect the effect on current I3.As a result, even if the reactors dedicated to each current rating circuit, which are located upstream of capacitor C11 in the LCL filter of the prior art, are moved to the downstream side, the frequency characteristics for the output current do not change, and the desired frequency characteristics can be obtained.Furthermore, the upstream current measuring devices HCT_A21 and HCT_A31 and switches MC_A11, MC_A21, and MC_A31 in Figure 1 can be omitted.

[0032] The number of current measuring devices and switches shown in this embodiment 1 is as shown in Table 4. Compared to the prior art, the number of current measuring devices has been reduced by two and the number of switches by three. This allows for cost reduction by reducing the number of parts.

[0033] [Table 4]

[0034] In the first embodiment, the number of current-rated circuits is set to 3, but even if the number of current-rated circuits is increased or decreased to N (N: an integer of 2 or more), the number of parts can be reduced in the same way.

[0035] The current control unit in this embodiment 1 is configured as a PI controller. In the case of a PI controller, the proportional term contributes greatly to the response, and the integral term contributes to the steady-state deviation in the steady state. As a feedback signal for the integral term, which has a large effect on the current control accuracy in the steady state, a downstream current measurement device with a current rating according to the magnitude of the current is selected.

[0036] For this reason, when there is only one current measuring device, the resolution of current detection deteriorates when the current becomes small, resulting in poor control accuracy. In the first embodiment, by selecting and controlling a current measuring device with a small rating when the current is small, the resolution of current detection does not deteriorate even when the current is constant, enabling highly accurate current control.

[0037] As described above, according to the first embodiment, it is possible to reduce the number of current measuring devices and switches, thereby reducing costs. In addition, a current measuring device with a rating according to the current is used as a feedback signal for the integral term that contributes to the accuracy in the steady state, so that highly accurate current control is possible.

[0038] [Embodiment 2] 5 shows the basic main circuit configuration of the power conversion system in the present embodiment 2. In the present embodiment 2, the upstream current measuring device HCT_A11 and the upstream reactor L_A11, which were provided on the positive side in the first embodiment, are installed on the negative side. The configuration of the current control, the magnitude of the current rating, the selection of the current measuring device, the opening and closing operation of the switch, and the current detection selection signal remain unchanged from the first embodiment.

[0039] The circuit configuration of an LCL filter is shown in Figure 6. Here, L1 is the positive front-end reactor of the LCL filter, C2 is the capacitor of the LCL filter, L3 is the rear-end reactor of the LCL filter, L4 is the negative front-end reactor of the LCL filter, V1 is the voltage applied to the LCL filter, I1 is the current flowing in the front-end reactor, I2 is the current flowing in the capacitor, and I3 is the current flowing in the rear-end reactor.

[0040] The transfer function when voltage V1 is input and current I3 is output is shown in equation (2) below, where s is the Laplace operator, L1 is the inductance value of the positive front-end reactor, L3 is the inductance value of the rear-end reactor, L4 is the inductance value of the negative front-end reactor, and C2 is the capacitance of the capacitor.

[0041]

number

[0042] It can be seen from equation (2) that the formula becomes equal to equation (1) when L1 = 0. As a result, even if the upstream current measuring device HCT_A11 and the upstream reactor L_A11 are moved to the negative side in the configuration of embodiment 1, the frequency characteristics for the output current do not change, and the desired frequency characteristics can be obtained.

[0043] Furthermore, since the number of parts is the same as in the first embodiment, it is possible to reduce the number of parts compared to the prior art, thereby achieving cost reduction.

[0044] As described above, according to the second embodiment, the same effects as those of the first embodiment can be achieved.

[0045] [Embodiment 3] Fig. 7 shows the basic main circuit configuration of the power conversion system in the present embodiment 3. In the present embodiment 3, the circuits applied in the embodiment 1 are configured in parallel. The current control configuration, the magnitude of the current rating, the selection of the current measurement device HCT, the opening and closing operation of the switch MC, and the current detection selection signal are unchanged from the embodiment 1, and the system is applied to the first power conversion device 1 and the second power conversion device 2, respectively.

[0046] Specifically, the third embodiment has a first power conversion device 1 and a second power conversion device 2. The current measuring device, reactor, capacitor, and switch connected to the first power conversion device 1 are the same as those in the first embodiment.

[0047] A first current rating circuit having a first current-rated upstream current measuring device HCT_A12, a upstream reactor L_A12, a first switch MC_B12, a first downstream current measuring device HCT_B12, a first downstream reactor L_B12, and an output switch MC_C12 is connected between one terminal (positive terminal in FIG. 7) of the second power conversion device 2 and the load 10. A capacitor C12 is connected between the connection point of the upstream reactor L_A12 and the first switch MC_B12 and the other terminal (negative terminal in FIG. 7) of the second power conversion device 2.

[0048] A second current rated circuit having a second switch MC_B22, a second rear-stage reactor L_B22, and a second rear-stage current measuring device HCT_B22 with a second current rating is connected in parallel to the first switch MC_B12. Also, a third current rated circuit having a third switch MC_B32, a third rear-stage reactor L_B32, and a third rear-stage current measuring device HCT_B32 with a third current rating is connected in parallel to the first switch MC_B12.

[0049] In Figure 7, upstream current measuring devices HCT_A11, HCT_A12 and upstream reactors L_A11, L_A12 are provided on the positive side of the first and second power conversion devices 1, 2, but they may also be provided on the negative side of the first and second power conversion devices 1, 2 as in embodiment 2.

[0050] When operating at a high current rating, that is, when the first switch MC_B11, output switch MC_C11, first switch MC_B12, and output switch MC_C12 are closed, capacitors C11 and C12 and first rear-stage reactors L_B11 and L_B12 will be present in the circuit of load 10.

[0051] The second rear-stage reactor L_B21, the second rear-stage reactor L_B22, the third rear-stage reactor L_B31, and the third rear-stage reactor L_B32 are not present in the circuit and therefore do not affect the control of cross currents or the current of the load 10. The inductance values ​​of the first rear-stage reactor L_B11 and the first rear-stage reactor L_B12 are set so as to suppress the inrush current of the capacitors C11 and C12.

[0052] During operation at a medium current rating, that is, when the second switch MC_B21, output switch MC_C11, second switch MC_B22, and output switch MC_C12 are closed, the first rear-stage reactor L_B11, second rear-stage reactor L_B21, first rear-stage reactor L_B12, and second rear-stage reactor L_B22 are present in the circuit of capacitor C11 and capacitor C12, and load 10. Since the inductance values ​​of the first rear-stage reactors L_B11 and L_B12 are used to suppress the inrush current of capacitors C11 and C12, the inductance values ​​of the second rear-stage reactors L_B21 and L_B22 are set to achieve the desired frequency characteristics in combination with the inductance values ​​of the first rear-stage reactors L_B11 and L_B12.

[0053] When operating at a small current rating, that is, when the third switch MC_B31, output switch MC_C11, third switch MC_B32, and output switch MC_C12 are closed, the first rear-stage reactor L_B11, third rear-stage reactor L_B31, first rear-stage reactor L_B12, and third rear-stage reactor L_B32 are present in the circuit between capacitors C11 and C12 and load 10. Since the inductance values ​​of the first rear-stage reactors L_B11 and L_B12 are used to suppress the inrush current of capacitors C11 and C12, the inductance values ​​of the third rear-stage reactors L_B31 and L_B32 are set to achieve the desired frequency characteristics in combination with the inductance values ​​of the first rear-stage reactors L_B11 and L_B12.

[0054] The number of current measuring devices and switches shown in the third embodiment is as shown in Table 5. Compared to the conventional technology, the number of current measuring devices can be reduced by four and the number of switches by six. This leads to cost reduction by reducing the number of parts.

[0055] In the third embodiment, the number of current-rated circuits is set to 3, but even if the number of current-rated circuits is increased or decreased to N (N: an integer of 2 or more), the number of parts can be reduced in the same way.

[0056] [Table 5]

[0057] As described above, according to the third embodiment, it is possible to reduce the number of current measuring devices and switches compared to when the conventional circuit is configured in parallel, thereby reducing costs. Also, as in the first embodiment, high-precision current control is possible.

[0058] [Embodiment 4] Fig. 8 shows the basic main circuit configuration of the power conversion system according to the fourth embodiment. In the fourth embodiment, the power conversion device and the reactor are shown as a circuit configuration in which single-phase inverters are connected in parallel and the outputs are coupled by a reactor.

[0059] Specifically, switching elements S1 and S2 are connected in series to a direct-current power supply DC. Furthermore, switching elements S3 and S4 are connected in series to the direct-current power supply DC. Furthermore, switching elements S5 and S6 are connected in series to the direct-current power supply DC. Furthermore, switching elements S7 and S8 are connected in series to the direct-current power supply DC. The switching elements S1 to S4 form a single-phase inverter unit, and the switching elements S5 to S8 form another single-phase inverter unit.

[0060] One end of the upstream reactor L_A11 is connected to the connection point of switching elements S1 and S2. One end of the upstream reactor L_A12 is connected to the connection point of switching elements S3 and S4. One end of the upstream reactor L_A13 is connected to the connection point of switching elements S5 and S6. One end of the upstream reactor L_A14 is connected to the connection point of switching elements S7 and S8. The upstream reactors L_A11, L_A12, L_A13, and L_A14 are cross-current suppression reactors. The other ends of the upstream reactors L_A11 and L_A13 are connected to the positive electrode of capacitor C11 via the upstream current measuring device HCT_A11. The other ends of the upstream reactors L_A12 and L_A14 are connected to the negative electrode of capacitor C11.

[0061] The power converter and the reactor may be of any embodiment as long as the circuit configuration includes a cross-current suppressing reactor that performs unit paralleling or interleaving.

[0062] The upstream stage of the LCL filter is equipped only with a upstream current measuring device with a large current rating and a cross current suppression reactor. Only the downstream stage is equipped with a reactor and current measuring device dedicated to each current rating. The configuration of the downstream stage of the LCL filter is the same as in embodiment 1. A switch for switching current ratings is provided only in the downstream stage so that a circuit dedicated to each current rating can be selected.

[0063] The number of cross current suppression reactors connected can be considered to be connected in parallel. In the case of Figure 8, the total inductance value of the cross current suppression reactors for the output is given by the following equation (3). In equation (3), L_A11 is the inductance value of the upstream reactor L_A11, L_A12 is the inductance value of the upstream reactor L_A12, L_A13 is the inductance value of the upstream reactor L_A13, and L_A14 is the inductance value of the upstream reactor L_A14.

[0064]

number

[0065] This inductance value L is used as the inductance component of the front-stage reactor of the LCL filter, which eliminates the need to place a dedicated front-stage reactor.

[0066] In setting the inductance, for example, the difference between the inductance value of the upstream reactor L_A11 in embodiment 1 and the inductance value L in equation (3) can be reflected in the inductance value of the downstream reactor L_B11 in embodiment 1 to obtain similar frequency characteristics.

[0067] As described above, according to the present embodiment 4, the same effects as those of the embodiment 1 can be achieved. Furthermore, in the case of a circuit configuration in which a power conversion device has a cross current suppression reactor for performing unit paralleling or interleaving, by configuring the reactor value in the upstream stage of the LCL filter to be covered by the cross current suppression reactor, it is not necessary to provide a dedicated upstream reactor, thereby enabling cost reduction.

[0068] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0069] 1, 2...First and second power converters 10...Load HCT_A11...Front-end current measurement device L_A11...Front-stage reactor C11...Capacitor MC_B11, MC_B21, MC_B31...1st, 2nd, 3rd switch HCT_B11, HCT_B21, HCT_B31...First, second, and third rear-stage current measurement devices L_B11, L_B21, L_B31...1st, 2nd, 3rd rear reactors MC_C11…Output switch

Claims

1. a power conversion device; a first current rating circuit including a first current rated upstream current measuring device, a upstream reactor, a first switch, a first current rated downstream current measuring device, a first downstream reactor, and an output switch, which are connected between one terminal of the power conversion device and a load; a capacitor connected between a connection point of the upstream reactor and the first switch and the other terminal of the power conversion device; a second to N-th current rated circuit having second to N-th (N: an integer of 2 or more) switches connected in parallel to the first switch, second to N-th rear-stage reactors, and second to N-th rear-stage current measuring devices having second to N-th current ratings; a control unit that controls the power conversion device; A power conversion system comprising:

2. a plurality of power conversion devices provided in parallel; a first current rating circuit including a first current-rated upstream current measuring device, a upstream reactor, a first switch, a first current-rated downstream current measuring device, a first downstream reactor, and an output switch, which are connected between one terminal of each of the power conversion devices and a load; a capacitor connected between a connection point of each of the upstream reactors and each of the first switches and the other terminal of each of the power conversion devices; second to N-th current rated circuits each including second to N-th (N: an integer of 2 or more) switches connected in parallel to each of the first switches, second to N-th subsequent stage reactors, and second to N-th subsequent stage current measuring devices having second to N-th current ratings; a control unit that controls each of the power conversion devices; A power conversion system comprising:

3. the control unit has a current control unit that performs proportional-integral control, The current control unit The feedback signal of the proportional term is the current detection value detected by the upstream current measurement device, The power conversion system according to claim 1 or 2, characterized in that the feedback signal of the integral term is the current detection value of the current rated circuit being used among the current detection values ​​detected by the first to Nth downstream current measuring devices.

4. The power conversion device has a configuration in which a plurality of units are connected in parallel or an interleaved configuration, 3. The power conversion system according to claim 1, wherein the upstream reactor is a cross current suppression reactor connected to the unit.

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