Power system and circulating current suppression method thereof

Abstract

To provide a circulating current suppression method applied to a power system including a plurality of power supply modules.SOLUTION: A circulating current suppression method in each power supply module that includes a high-voltage bus bar, a low-voltage bus bar and a balance circuit having a neutral voltage includes steps of: in each balance circuit, disposing a first capacitor electrically coupled between the high-voltage bus bar and the neutral voltage, and disposing a second capacitor electrically coupled between the neutral voltage and the low-voltage bus bar; acquiring a current effective value of an input of each power supply module; if detecting that the current effective value of at least one power supply module does not remain at a current reference value, determining that a circulating current occurs in the at least one power supply module; and operating the balance circuit of the power supply module in which the circulating current occurs to charge the first capacitor or the second capacitor, thereby regulating the neutral voltage for suppressing the circulating current.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a power system and a circulating current suppression method thereof, and more particularly to a power system and a circulating current suppression method thereof that suppresses circulating current by controlling the voltage difference between positive and negative DC bus capacitors. [Background technology]

[0002] In the application of multi-module parallel connection, the volume size of the module is very important because of the large number of modules connected in parallel. In order to reduce the volume of the module, a unidirectional multilevel converter is often used in the front-stage AC / DC topology, and the negative pole of the output end of the rear-stage DC / DC is directly connected to the negative terminal of the DC busbar. Due to the above circuit configuration, when the voltages of the DC busbars of each module are different, a DC circulating current will be generated. The circulating current reduces the power conversion efficiency, and because the front-stage AC / DC is a unidirectional topology, the circulating current will generate many harmonics in the input current, affecting the total harmonic distortion of the input current. In addition, the excessive circulating current will cause a neutral point potential shift of the multilevel converter, affecting the normal operation of the entire system.

[0003] Therefore, there is currently an urgent need to develop a power system and a method for suppressing circulating current therein that can improve upon the above-mentioned conventional technology. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a power system and a method for suppressing circulating current in the power system, which includes a plurality of power supply modules, and in the case where a circulating current occurs in any of the power supply modules, the present invention operates a balancing circuit in the power supply module to adjust the neutral voltage of the balancing circuit and suppress the circulating current. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides a circulating current suppression method applied to a power system including a plurality of power supply modules. Each power supply module includes a high-voltage bus bar, a low-voltage bus bar, and a balancing circuit having a neutral voltage. The circulating current suppression method includes the steps of: installing, in each balancing circuit, a first capacitor electrically coupled between the high-voltage bus bar and the neutral voltage, and installing a second capacitor electrically coupled between the neutral voltage and the low-voltage bus bar; acquiring an effective current value of an input of each power supply module; determining that a circulating current has occurred in the at least one power supply module when it is detected that the effective current value of the at least one power supply module is not maintained at a current reference value; and operating the balancing circuit of the power supply module in which the circulating current has occurred to charge the first capacitor or the second capacitor, thereby adjusting the neutral voltage to suppress the circulating current.

[0006] In order to achieve the above object, the present invention further provides a power system including a plurality of power supply modules. The inputs of each power supply module receive the same AC input, and each power supply module includes a DC power busbar, a balancing circuit, and a controller. The DC power busbar includes a high-voltage busbar and a low-voltage busbar. The balancing circuit includes a first capacitor, a second capacitor, a first switch, a second switch, and an energy storage inductor. The negative terminal of the first capacitor is connected to the positive terminal of the second capacitor, the positive terminal of the first capacitor is electrically connected to the high-voltage busbar, and the negative terminal of the second capacitor is electrically connected to the low-voltage busbar. The first terminal of the first switch is electrically connected to the high-voltage busbar, the second terminal of the first switch is connected to the first terminal of the second switch, and the second terminal of the second switch is electrically connected to the low-voltage busbar. A first terminal of the energy storage inductor is connected to the negative terminal of the first capacitor and the positive terminal of the second capacitor, and a second terminal of the energy storage inductor is connected to the second terminal of the first switch and the first terminal of the second switch. The controller obtains an effective current value of an input of each power supply module. When the controller detects that the effective current value of at least one power supply module is greater than or less than a current reference value, it determines that a circulating current occurs in the at least one power supply module. The controller operates a first switch and / or a second switch of a balancing circuit of the power supply module in which the circulating current occurs to generate an inductor current in the energy storage inductor, and the current direction of the inductor current is opposite to that of the circulating current. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic circuit configuration diagram of a power system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic circuit diagram of a specific embodiment of the power system of FIG. 1. [Diagram 3] 1 is a schematic flowchart of a circulating current suppression method for a power system according to an embodiment of the present invention. [Figure 4]4 shows a control strategy for a circulating current suppression method for a power system according to the present invention. [Diagram 5] 11 is a simulation diagram of a current waveform when a circulating current occurs in a power supply module and circulating current suppression is not performed. FIG. [Figure 6] 1 is a simulation diagram of a current waveform when a circulating current suppression method of the present invention is adopted in the case where a circulating current occurs in a power supply module. [Figure 7] 1 is a simulation diagram of a capacitor voltage waveform when a circulating current suppression method of the present invention is adopted in the case where a circulating current occurs in a power supply module. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Some exemplary embodiments illustrating the features and advantages of the present invention are described in detail in the following description. It should be understood that the present invention can be modified in various ways in different aspects, all without departing from the scope of the present invention, and the description and drawings are illustrative in nature, and are not intended to limit the present invention.

[0009] Fig. 1 is a schematic circuit diagram of a power system according to an embodiment of the present invention. As shown in Fig. 1, the power system 1 includes a plurality of power supply modules 10, the number of the power supply modules 10 being an integer equal to or greater than two, the input of each power supply module 10 receiving the same AC input source 2, and the output of each power supply module 10 electrically coupled to the same load. Generally, a circulating current occurs when a plurality of power supply modules 10 are connected in parallel, but the present invention is not limited thereto.

[0010] In the power system 1, each power supply module 10 includes a DC power bus bar, a balancing circuit 11, and a controller 12. In this embodiment, the AC input source 2 supplies three-phase AC power, but is not limited thereto. In other embodiments, the AC input source 2 can also supply single-phase AC power.

[0011] In each power supply module 10, the DC power busbars include a high voltage busbar 13 and a low voltage busbar 14, and the balancing circuit 11 includes a first capacitor C1, a second capacitor C2, a first switch S1, a second switch S2, and an energy storage inductor L. A positive terminal of the first capacitor C1 is electrically connected to the high voltage busbar 13, a negative terminal of the first capacitor C1 is connected to a positive terminal of the second capacitor C2, and a negative terminal of the second capacitor C2 is electrically connected to the low voltage busbar 14. The first capacitor C1 and the second capacitor C2 can be regarded as a positive DC bus capacitor and a negative DC bus capacitor, respectively. A first terminal of the first switch S1 is electrically connected to the high voltage busbar 13, a second terminal of the first switch S1 is connected to a first terminal of the second switch S2, and a second terminal of the second switch S2 is electrically connected to the low voltage busbar 14. A first terminal of the energy storage inductor L is connected to the negative terminal of the first capacitor C1 and the positive terminal of the second capacitor C2, and a second terminal of the energy storage inductor L is connected to the second terminal of the first switch S1 and the first terminal of the second switch S2. The balancing circuit 11 also has a neutral voltage Vn, which is coupled to the negative terminal of the first capacitor C1, the positive terminal of the second capacitor C2, and the first terminal of the energy storage inductor L.

[0012] 1, when the power system 1 operates under ideal conditions, the low-voltage busbars 14 of each power supply module 10 are maintained at the same reference voltage, and no circulating current is generated. If an abnormality occurs in any of the multiple power supply modules 10, the low-voltage busbars 14 are not maintained at the reference voltage, and a circulating current flows in the abnormal power supply module 10 in the power system 1. In general, the voltage of the low-voltage busbars 14 of the abnormal power supply module 10 is lower than the reference voltage.

[0013] The controller 12 obtains the effective current value iz of the input of each power supply module 10, and the effective current value iz can be, for example, but not limited to, the average value or the mean square value of the current i of the input of the power supply module 10. When the controller 12 detects that the effective current value iz of at least one power supply module 10 is greater than or less than the current reference value iref, the controller 12 determines that a circulating current occurs in the at least one power supply module 10. In response to this, the controller 12 operates the first switch S1 and the second switch S2 of the balance circuit 11 of the power supply module 10 in which the circulating current occurs to generate an inductor current in the energy storage inductor L, thereby charging the first capacitor C1 or the second capacitor C2, and adjusts the neutral voltage Vn to cancel the effect of the circulating current, thereby suppressing the circulating current. The current direction of the inductor current is opposite to that of the circulating current.

[0014] In some embodiments, each power supply module 10 further includes a conversion circuit 15, which receives the AC input source 2 and outputs DC power to the high voltage busbar 13 and the low voltage busbar 14 of the balancing circuit 11. The conversion circuit 15 can be, for example, but is not limited to, a Vienna converter (shown in FIG. 2) and is used for power factor correction of the AC input source 2. In some embodiments, each power supply module 10 further includes a DC-DC converter 16, which receives DC power via the high voltage busbar 13 and the low voltage busbar 14. The DC-DC converter 16 can be, for example, but is not limited to, a flying capacitor converter (FCC) as shown in FIG. 2. The balancing circuit 11 is electrically coupled to the output of the conversion circuit 15 and the input of the DC-DC converter 16 via the high voltage busbar 13 and the low voltage busbar 14. The output of each power supply module 10 is also connected to the same load 3.

[0015] Please refer to FIG. 1 and FIG. 3. FIG. 3 is a schematic flowchart of a circulating current suppression method for a power system according to an embodiment of the present invention. This circulating current suppression method is applied to the power system 1 shown in FIG. 1 and is executed by the controller 12 of the power system 1. As shown in FIG. 3, first, in step ST1, a first capacitor C1 and a second capacitor C2 are installed in each balancing circuit 11. Next, in step ST2, an effective current value iz of the input of each power supply module 10 is acquired. Then, in step ST3, it is detected whether or not the effective current value iz of each power supply module 10 is maintained at the current reference value iref. If the determination result of step ST3 is NO, that is, if the effective current value iz of at least one power supply module 10 is not maintained at the current reference value iref, it is determined that a circulating current has occurred in the at least one power supply module 10. At this time, step ST4 is executed to operate the balancing circuit 11 of the power supply module 10 in which the circulating current has occurred, and charge the first capacitor C1 or the second capacitor C2, thereby adjusting the neutral voltage Vn and suppressing the circulating current. Conversely, if the determination result in step ST3 is YES, that is, if the effective current values ​​iz of all the power supply modules 10 are maintained at the current reference value iref, step ST2 is executed again.

[0016] In some embodiments, when no circulating current occurs in each power supply module 10, i.e., when the effective current value iz of each power supply module 10 is maintained at the current reference value iref, the low-voltage busbar 14 of each power supply module 10 is maintained at the same reference voltage. In some embodiments, when a circulating current occurs in the power supply module 10, the neutral voltage Vn is adjusted to increase the voltage of the low-voltage busbar 14 by charging the first capacitor C1 or the second capacitor C2 in the power supply module 10.

[0017] Please refer to Figures 1 and 4. Figure 4 shows a control measure of the circulating current suppression method for the power system of the present invention. Note that all the controls for the power system 1 of the present invention are executed by the controller 12, and will not be repeated below. As shown in Figure 4, when a circulating current occurs in at least one power supply module 10, the power supply module 10 in which the circulating current occurs is marked as an abnormal power supply module, and the difference between the current effective value iz and the current reference value iref of the abnormal power supply module is obtained, and a compensation voltage Vc is obtained according to the difference. At the same time, a capacitor voltage difference Vd between the second capacitor C2 and the first capacitor C1 in the abnormal power supply module is obtained. The capacitor voltage difference Vd is equal to the voltage of the second capacitor C2 minus the voltage of the first capacitor C1.

[0018] By comparing the compensation voltage Vc and the capacitor voltage difference Vd, the direction of the circulating current can be determined, and the direction of the inductor current and the capacitor to be charged are determined. Specifically, when the compensation voltage Vc is greater than the capacitor voltage difference Vd, it is determined that the circulating current flows from the input of the abnormal power supply module to the abnormal power supply module, and the first switch S1 and / or the second switch S2 are operated to charge the second capacitor C2, and at this time, the inductor current of the energy storage inductor L flows from the second terminal of the energy storage inductor L to the first terminal of the energy storage inductor L. Conversely, when the compensation voltage Vc is smaller than the capacitor voltage difference Vd, it is determined that the circulating current flows from the output of the abnormal power supply module to the abnormal power supply module, and the first switch S1 and / or the second switch S2 are operated to charge the first capacitor C1, and at this time, the inductor current of the energy storage inductor L flows from the first terminal of the energy storage inductor L to the second terminal of the energy storage inductor L. In some embodiments, a reference value iLref of the inductor current is obtained based on the difference between the compensation voltage Vc and the capacitor voltage difference Vd, the reference value iLref of the inductor current is compared with the actual value iL, and the control signals of the first switch S1 and the second switch S2 are generated according to the comparison result, so that the charging time of the first capacitor C1 or the second capacitor C2 can be determined based on the difference between the compensation voltage Vc and the capacitor voltage difference Vd, and the first switch S1 and / or the second switch S2 can be operated accordingly.

[0019] After the first capacitor C1 or the second capacitor C2 in the power supply module 10 in which the circulating current is generated is charged, it is again detected whether the effective current value iz of the power supply module 10 is maintained at the current reference value iref. If the effective current value iz is maintained at the current reference value iref, the operation of the balancing circuit 11 of the power supply module 10 is stopped, and if the effective current value iz is still not maintained at the current reference value iref, the balancing circuit 11 is operated again to charge the first capacitor C1 or the second capacitor C2.

[0020] FIG. 5 is a simulation diagram of a current waveform when a circulating current occurs in a power supply module and circulating current suppression is not performed, FIG. 6 is a simulation diagram of a current waveform when a circulating current occurs in a power supply module and the circulating current suppression method of the present invention is adopted, and FIG. 7 is a simulation diagram of a capacitor voltage waveform when a circulating current occurs in a power supply module and the circulating current suppression method of the present invention is adopted. In FIG. 5 and FIG. 6, a current i of any phase of the input of the power supply module 10 is taken as an example. In FIG. 7, the voltage VC1 of the first capacitor C1 and the voltage VC2 of the second capacitor C2 are represented by a solid line and a dashed line, respectively. When a circulating current occurs, as shown in FIG. 5, the waveform of the current i shifts due to the influence of the circulating current. In this example, the circulating current flows from the output of the power supply module 10 to the power supply module 10, so that the waveform of the current i shifts to a negative value. In this case, by adopting the circulating current suppression method of the present invention, as shown in Figures 6 and 7, the first switch S1 and / or the second switch S2 are operated to generate an inductor current flowing from the second terminal to the first terminal of the energy storage inductor L, thereby charging the first capacitor C1 and increasing the voltage VC1 of the first capacitor C1, thereby suppressing the current shift due to the circulating current and returning the waveform of the current i to a state without a circulating current.

[0021] As described above, the present invention provides a power system and a circulating current suppression method thereof. The power system includes a plurality of power supply modules, and when a circulating current occurs in any of the power supply modules, the present invention operates a balancing circuit in the power supply module to adjust the neutral voltage of the balancing circuit and suppress the circulating current.

[0022] It should be noted that the above are only preferred embodiments proposed to explain the present invention, the present invention is not limited to the above embodiments, and the scope of the present invention is determined by the claims. The present invention can be modified in various ways by those skilled in the art, but does not deviate from the scope defined by the claims. [Explanation of symbols]

[0023] 1: Power system 10: Power supply module 2: AC input source 11: Balanced circuit 12: Controller 13: High voltage busbar 14: Low voltage busbar C1: First capacitor C2: Second capacitor S1: First switch S2: Second switch L: energy storage inductor Vn: Neutral voltage iz: Effective current value i: Current iref: current reference value ST1, ST2, ST3, ST4: Step Vc: Compensation voltage Vd: Capacitor voltage difference 15: Conversion circuit 16: DC-DC converter 3: Load iLref: Inductor current reference value iL: actual value of inductor current VC1: Voltage of the first capacitor C1 VC2: Voltage of the second capacitor C2

Claims

1. A circulating current suppression method applied to a power system having a plurality of power supply modules, comprising: Each of the power supply modules includes a high voltage bus bar, a low voltage bus bar, and a balancing circuit having a neutral voltage; The circulating current suppression method includes: providing, in each of the balancing circuits, a first capacitor electrically coupled between the high voltage busbar and the neutral voltage, and providing a second capacitor electrically coupled between the neutral voltage and the low voltage busbar; obtaining an effective current value at an input of each of the power supply modules; determining that a circulating current has occurred in the at least one power module among the plurality of power modules when detecting that the effective current value of the at least one power module among the plurality of power modules is not maintained at a current reference value; operating the balancing circuit of the at least one power supply module among the plurality of power supply modules to charge the first capacitor or the second capacitor, thereby adjusting the neutral voltage and suppressing the circulating current; A method for suppressing circulating current comprising the steps of:

2. selecting the at least one power module of the plurality of power modules and marking it as an abnormal power module; obtaining a difference between the effective current value of the abnormal power supply module and the reference current value, and obtaining a compensation voltage according to the difference; obtaining a capacitor voltage difference between the second capacitor and the first capacitor in the abnormal power supply module; determining that the circulating current flows from the input of the abnormal power supply module to the abnormal power supply module, or that the circulating current flows from the output of the abnormal power supply module to the abnormal power supply module, by comparing the compensation voltage with the capacitor voltage difference; The method for suppressing a circulating current according to claim 1 , further comprising:

3. determining that the circulating current flows from the input of the abnormal power supply module to the abnormal power supply module if the compensation voltage is greater than the capacitor voltage difference; determining that the circulating current flows from the output of the abnormal power supply module to the abnormal power supply module when the compensation voltage is less than the capacitor voltage difference; The method for suppressing a circulating current according to claim 2 , further comprising:

4. installing an energy storage inductor, a first switch, and a second switch in the balancing circuit, wherein a first terminal of the energy storage inductor is electrically coupled to the neutral voltage, the first switch is electrically coupled between the high voltage bus bar and a second terminal of the energy storage inductor, and the second switch is electrically coupled between the second terminal of the energy storage inductor and the low voltage bus bar; Charging the first capacitor or the second capacitor by operating the first switch and / or the second switch in each of the balancing circuits; The method for suppressing a circulating current according to claim 2 , further comprising:

5. If the compensation voltage is greater than the capacitor voltage difference, the method further includes the step of charging the second capacitor by operating the first switch and / or the second switch; when the second capacitor is charged, an inductor current in the energy storage inductor flows from the second terminal of the energy storage inductor to the first terminal of the energy storage inductor. The method for suppressing a circulating current according to claim 4.

6. If the compensation voltage is smaller than the capacitor voltage difference, the method further includes the step of charging the first capacitor by operating the first switch and / or the second switch; when the first capacitor is charged, an inductor current in the energy storage inductor flows from the first terminal of the energy storage inductor to the second terminal of the energy storage inductor; The method for suppressing a circulating current according to claim 4.

7. After the first capacitor or the second capacitor is charged, the method further includes detecting whether the effective current value of the at least one power supply module among the plurality of power supply modules is maintained at the current reference value; stopping operation of the balancing circuit when the effective current value of the at least one power supply module among the plurality of power supply modules is maintained at the current reference value; The method for suppressing a circulating current according to claim 1 .

8. The circulating current suppression method according to any one of claims 1 to 7, wherein when it is determined that no circulating current is occurring in each of the power supply modules, the low voltage bus bars of each of the power supply modules are maintained at the same reference voltage.

9. The circulating current suppression method according to any one of claims 1 to 7, wherein the neutral voltage is adjusted to increase the voltage of the low voltage busbar by charging the first capacitor or the second capacitor.

10. The method of any one of claims 1 to 7, further comprising the steps of: installing the input of each of the power supply modules to be electrically coupled to an AC input source; and installing the output of the power supply modules to be electrically coupled to a load.

11. The circulating current suppression method according to any one of claims 1 to 7, wherein the effective current value is a current average value or a current root mean square value.

12. 1. A power system including a plurality of power supply modules, the input of each of said power supply modules receiving the same AC input source; Each of the power supply modules includes a DC power bus bar, a balancing circuit, and a controller; The DC power busbars include a high voltage busbar and a low voltage busbar; the balancing circuit includes a first capacitor and a second capacitor, a first switch and a second switch, and an energy storage inductor; a negative terminal of the first capacitor connected to a positive terminal of the second capacitor, the positive terminal of the first capacitor electrically connected to the high voltage bus bar, and the negative terminal of the second capacitor electrically connected to the low voltage bus bar; a first terminal of the first switch electrically connected to the high voltage bus bar, a second terminal of the first switch electrically connected to a first terminal of the second switch, and a second terminal of the second switch electrically connected to the low voltage bus bar; a first terminal of the energy storage inductor is connected to the negative terminal of the first capacitor and the positive terminal of the second capacitor, and a second terminal of the energy storage inductor is connected to the second terminal of the first switch and the first terminal of the second switch; The controller obtains an effective current value of the input of each of the power supply modules; When the controller detects that the effective current value of at least one of the plurality of power supply modules is greater than or less than a reference current value, it is determined that a circulating current has occurred in the at least one of the plurality of power supply modules; and operating, by the controller, the first switch and / or the second switch of the balancing circuit of the at least one power supply module of the plurality of power supply modules to generate an inductor current in the energy storage inductor, the current direction of the inductor current being opposite to that of the circulating current. Power system.

13. The controller: Selecting the at least one power module of the plurality of power modules and marking it as an abnormal power module; Obtain a difference between the effective current value of the abnormal power supply module and the reference current value, and obtain a compensation voltage according to the difference; In the abnormal power supply module, a capacitor voltage difference between the second capacitor and the first capacitor is obtained; Comparing the compensation voltage with the capacitor voltage difference is used to determine that the circulating current flows from the input of the abnormal power supply module to the abnormal power supply module, or that the circulating current flows from the output of the abnormal power supply module to the abnormal power supply module.

13. The power system of claim 12.

14. The controller further comprises: If the compensation voltage is greater than the capacitor voltage difference, it is determined that the circulating current flows from the input of the abnormal power supply module to the abnormal power supply module; When the compensation voltage is smaller than the capacitor voltage difference, it is used to determine that the circulating current flows from the output of the abnormal power supply module to the abnormal power supply module.

14. The power system of claim 13.

15. The controller further comprises: operating the first switch and / or the second switch to flow an inductor current of the energy storage inductor from the second terminal of the energy storage inductor to the first terminal of the energy storage inductor when the compensation voltage is greater than the capacitor voltage difference; used to cause an inductor current of the energy storage inductor to flow from the first terminal of the energy storage inductor to the second terminal of the energy storage inductor by operating the first switch and / or the second switch when the compensation voltage is less than the capacitor voltage difference.

14. The power system of claim 13.

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