Filter circuit and multiphase power system

Abstract

The present disclosure relates to a filter circuit and a multiphase power system. The filter circuit provided therein comprises: a direct-current power supply; a resonant unit and a first capacitor connected to the direct-current power supply in series; and a converter connected to the first capacitor in parallel. The resonant unit comprises an inductor and a second capacitor connected to each other in parallel. The multiphase power system provided therein comprises the filter circuit. The filter circuit and the multiphase power system of the present disclosure are capable of reducing harmonic currents in a filter circuit.

Description

Filtering circuits and multiphase power systems Technical Field

[0001] This application relates to a filter circuit and a multiphase power system, and more particularly, to a filter circuit and a multiphase power system capable of reducing current fluctuations. Background Technology

[0002] When converting direct current (DC) to alternating current (AC), a filter circuit is needed between the DC and AC to reduce inrush current from DC power sources such as batteries, thus protecting the DC power supply. This filter circuit is also called an AC-DC coupling circuit. In such a filter circuit, harmonic currents, such as second-harmonic currents, may be superimposed on the DC current. Harmonic currents not only increase DC voltage ripple and affect control stability but also shorten the lifespan of DC power sources such as batteries. Summary of the Invention

[0003] This disclosure is proposed to reduce harmonic currents in filter circuits.

[0004] According to one aspect of this disclosure, a filter circuit is provided, comprising: a DC power supply; a resonant unit and a first capacitor connected in series with the DC power supply; and a converter connected in parallel with the first capacitor, wherein the resonant unit includes an inductor and a second capacitor connected in parallel with each other.

[0005] According to another aspect of this disclosure, a multiphase power system is provided, comprising at least two phase power systems, each phase of the at least two phase power system comprising at least one filter circuit as described above.

[0006] The filter circuit and multiphase power system disclosed herein can reduce harmonic currents in the filter circuit. Attached Figure Description

[0007] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0008] Figure 1 shows a schematic diagram of a prior art filter circuit in the case where the DC power supply is a battery or battery pack (i.e., a battery cluster).

[0009] Figure 2 shows a prior art filter circuit with a harmonic series resonant branch connected in parallel on the side of the filter inductor closest to the DC power supply.

[0010] Figure 3 shows a prior art filter circuit with a harmonic series resonant branch connected in parallel on the side of the filter inductor near the converter.

[0011] Figure 4 shows a schematic diagram of a filter circuit according to an embodiment of the present disclosure.

[0012] Figure 5 shows an exemplary schematic diagram of filter circuits connected in series with each other in one phase of a multiphase power system according to an embodiment of the present disclosure.

[0013] Figure 6 shows a curve of the current flowing through the DC power supply obtained by simulation in a power system using the prior art filter circuit shown in Figure 1.

[0014] Figure 7 shows the current variation curves flowing through the DC power supply obtained through simulation in a power system employing the filter circuit of this disclosure shown in Figure 4.

[0015] The accompanying drawings are not drawn to scale. Detailed Implementation

[0016] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0017] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the allowable tolerance range. "Parallel" is not parallel in the strict sense, but within the allowable tolerance range.

[0018] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this application. It should also be noted in the description of this application that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0019] For example, in energy storage unit applications, when converting DC power to AC power, a filter circuit is needed between the DC and AC to reduce inrush current from DC power sources such as batteries and protect the DC power supply. This filter circuit is also called an AC / DC coupling circuit.

[0020] Figure 1 shows a schematic diagram of an exemplary filter circuit (basic AC / DC coupling circuit) in the prior art when the DC power source is a battery or battery pack (i.e., a battery cluster). As shown in Figure 1, the basic AC / DC coupling circuit includes a filter inductor L1 and a filter capacitor C1. The DC power source, such as a battery or battery pack, is connected in series with the filter inductor L1 and the filter capacitor C1, and the converter (PCS) for outputting AC power is connected in parallel with the filter capacitor C1.

[0021] In the AC / DC coupling circuit shown in Figure 1, while the DC power supply provides DC current to the converter, harmonic currents, such as second-harmonic currents, may be superimposed on the DC current flowing through it. More specifically, when the converter outputs AC current, the voltage across the filter capacitor C1 fluctuates at a frequency twice that of the AC current output by the converter, known as a second-harmonic current. This fluctuation in the voltage across the filter capacitor C1 inevitably causes fluctuations in the current flowing through the DC power supply, forming the so-called second-harmonic current. Besides the second-harmonic current, other non-DC currents may also exist in the current flowing through the DC power supply. These second-harmonic currents and other non-DC currents can be collectively referred to as harmonics or harmonic currents.

[0022] Harmonic currents, such as second-harmonic currents, not only increase the ripple of the DC voltage supplied to the converter and affect the stability of control, but also affect the lifespan of DC power sources such as batteries (e.g., battery cycle life).

[0023] Therefore, it is necessary to reduce harmonic currents such as second harmonic currents in the filter circuit (AC-DC coupling circuit).

[0024] In the prior art, to reduce harmonic current, a harmonic series resonant branch (also called a second harmonic series resonant branch) is connected in parallel on one side (left or right) of the filter inductor L1, as shown in the dashed boxes in Figures 2 and 3, to reduce harmonic current in DC power supplies such as batteries. Figure 2 shows a prior art filter circuit with a harmonic series resonant branch connected in parallel on the side of the filter inductor L1 closest to the DC power supply. Figure 3 shows a prior art filter circuit with a harmonic series resonant branch connected in parallel on the side of the filter inductor L1 closest to the converter. The harmonic series resonant branch shown in Figures 2 and 3 includes a capacitor and an inductor connected in series.

[0025] The filter circuits shown in Figures 2 and 3 can reduce harmonic currents (including second-harmonic currents) in the DC power supply, but they require an additional harmonic series resonant branch connected in parallel between the main positive and main negative terminals of the DC power supply. This necessitates at least two high-voltage components, increasing losses and insulation safety risks. Furthermore, this harmonic series resonant branch may oscillate along with other parts of the filter circuit, affecting the unit's operational stability.

[0026] In one embodiment of the present disclosure, the inventors of the present disclosure propose a filter circuit comprising: a DC power supply; a resonant unit and a first capacitor connected in series with the DC power supply; and a converter connected in parallel with the first capacitor, wherein the resonant unit includes an inductor and a second capacitor connected in parallel with each other.

[0027] Figure 4 shows a schematic diagram of a filter circuit according to an embodiment of the present disclosure. In the filter circuit shown in Figure 4, based on the conventional filter circuit shown in Figure 1, a second capacitor C0 is connected in parallel with a portion or the entire inductor L1. For example, as shown in Figure 4, the second capacitor C0 can be connected in parallel with a portion of the inductor L1 (i.e., L... 12 The inductor L1 (which is the portion of the inductor closest to the first capacitor C1) is connected in parallel. The inductor L1 and the parallel-connected second capacitor C0 form a resonant unit, as shown by the dashed box in Figure 4.

[0028] Alternatively, for example, the second capacitor C0 can be connected to the portion of inductor L1 closest to the DC power supply (i.e., L...). 11 The two capacitors are connected in parallel. However, the following only considers the portion of the second capacitor C0 and the inductor L1 closest to the first capacitor C1 (i.e., L1). 12 The parallel connection case will be used as an example for explanation.

[0029] In the above embodiments, for example, the first capacitor C1 can function as a filter. Furthermore, in the above embodiments, the inductor L1 can function as a filter. Additionally, in one embodiment, the inductor L1 can function as a resonant element, for example. Furthermore, in one embodiment, the inductor L1 can function as both a filter and a resonant element.

[0030] In one embodiment, the ratio between the inductance of the portion of inductor L1 connected in parallel with the second capacitor C0 and the total inductance of inductor L1 is adjustable.

[0031] In one embodiment, the parameters of the above-described filter circuit are determined through simulation, and the parameters include one or more of the following: the inductance value of inductor L1, the capacitance value of the second capacitor C0, the capacitance value of the first capacitor C1, and the portion of inductor L1 connected in parallel with the second capacitor C0. 12The ratio between the inductance value of L1 and the total inductance value of L1. In one embodiment, the above simulation is performed with the voltage of the DC power supply (e.g., the battery cluster shown in Figure 4) set to the desired voltage.

[0032] In one embodiment, the parameters of the filter circuit are determined by performing simulation with the goal of reducing the total harmonic distortion (THD) or second harmonic current ratio of the current flowing through the DC power supply in the filter circuit to below a predetermined threshold. The THD is the ratio of all non-DC currents flowing through the DC power supply to the DC current flowing through the DC power supply. The second harmonic current ratio is the ratio of the second harmonic (AC) current flowing through the DC power supply to the DC current flowing through the DC power supply. The predetermined threshold can be appropriately set according to actual needs.

[0033] In one embodiment, inductor L1 is a single inductor. In this case, with the second capacitor C0 connected in parallel with a portion of inductor L1, for example, one end of the second capacitor C0 can be connected to a tap or lead of inductor L1 located at an appropriate position in inductor L1 to achieve a parallel connection with a portion of inductor L1.

[0034] In one embodiment, inductor L1 consists of two or more inductors that are separate from each other. In this case, the second capacitor C0 may be connected in parallel with one or more of the two or more inductors.

[0035] In one embodiment, the DC power source can be a battery or battery pack (or battery cluster), or any other type of DC power source (e.g., a linear DC power source, a switching DC power source, etc.).

[0036] In one embodiment, for example, the converter can be a single-phase converter containing four insulated-gate bipolar transistors (IGBTs). The four IGBTs can form an H-bridge, which is also called a single-phase converter.

[0037] In one embodiment, this disclosure provides a multiphase power system including at least two phases of power system, each phase of the at least two phases of power system including a filter circuit according to any of the embodiments described above.

[0038] In one embodiment, each phase of the power system in the at least two-phase power system includes a plurality of filter circuits connected in series with each other. In one embodiment, the plurality of filter circuits connected in series with each other may be identical filter circuits or filter circuits with different parameters.

[0039] Figure 5 shows an exemplary schematic diagram of filter circuits connected in series in one phase of a multiphase power system according to an embodiment of the present disclosure. For the sake of simplicity, the one-phase power system shown in Figure 5 includes three filter circuits connected in series as shown in Figure 1. Each phase of the power system according to the present disclosure actually includes two or more filter circuits connected in series as shown in Figure 4, that is, each of the three filter circuits connected in series in Figure 5 also includes a second capacitor (i.e., the second capacitor C0 shown in Figure 4), not shown, connected in parallel with a portion or the entire inductor. The black rectangular blocks shown in Figure 5 represent the load of the power system.

[0040] In one embodiment, the number of filter circuits to be connected in series can be determined based on the output voltage and base voltage of each phase in the multiphase power system. For example, in the case of a three-phase power system, if each phase contains 32 filter circuits connected in series, then the three-phase power system contains a total of 96 filter circuits. A power system with multiple filter circuits connected in series can increase the system's output voltage, improve system reliability, facilitate system transportation and operation and maintenance, or achieve a more suitable current waveform.

[0041] In one embodiment, when a multiphase power system is connected to the rated load of the multiphase power system, the parameters of the filter circuit are determined by simulation. The parameters include one or more of the following: the inductance value of the inductor, the capacitance value of the second capacitor, the capacitance value of the first capacitor, and the ratio between the inductance value of the portion of the inductor connected in parallel with the second capacitor and the total inductance value of the inductor.

[0042] In one embodiment, when a multiphase power system is connected to a rated load, the parameters of the filter circuit are determined by performing simulation with the aim of reducing the total harmonic distortion rate or the second harmonic current ratio of the current flowing through the DC power supply in the filter circuit to below a predetermined threshold.

[0043] In this disclosure, each filter circuit (as described above, or AC / DC coupling circuit) in each phase of a multiphase power system can be a filter circuit described in any of the above embodiments of this disclosure.

[0044] According to this disclosure, by adding an inductor L1 or a portion thereof to the basic filter circuit, 12The second capacitor C0, connected in parallel, forms a parallel resonant unit to increase the reactance in the current loop of the DC power supply for second-harmonic currents or other non-DC currents. Since the voltage across the inductor L1 is very low, adding the second capacitor C0 does not lead to the addition of high-voltage components, does not increase the insulation risk of the filter circuit, and also has the advantages of low loss, fewer components, and no voltage or current oscillations.

[0045] In the prior art solutions shown in Figures 2 and 3, a "supplementary" approach is adopted, that is, by adding a series resonant branch, the voltage fluctuation across the filter capacitor C1 is reduced. Completely different from the prior art, this disclosure adopts a "blocking" approach, by adding a series resonant branch to the inductor L... 12 A second capacitor C0 is connected in parallel across the two ends to form a parallel resonant unit. Theoretically, the impedance of this parallel resonant unit to non-DC currents such as second harmonic currents is infinite. Since this parallel resonant unit is located in the current loop of the DC power supply, it achieves the purpose of significantly reducing the second harmonic current and other harmonic currents of the DC power supply.

[0046] Figure 6 shows a simulation curve of the current flowing through a DC power supply in a power system employing the prior art filter circuit shown in Figure 1. The horizontal axis represents time, and the vertical axis represents the magnitude of the current, showing harmonic currents such as second harmonic currents superimposed on the DC current flowing through the DC power supply. As shown in Figure 6, in this case, the total harmonic distortion (THD) is 20.42%, with the second harmonic current accounting for 20.42% of the DC current. Furthermore, in this case, the current flowing through the DC power supply oscillates continuously with a large amplitude.

[0047] Figure 7 shows a simulation curve of the current flowing through the DC power supply in a power system using the filter circuit of this disclosure shown in Figure 4, where the horizontal axis represents time and the vertical axis represents the magnitude of the current. As shown in Figure 7, after connecting the second capacitor C0 in parallel, the total harmonic distortion (THD) is reduced to THD = 1.64%, with the second harmonic current accounting for 0.56% of the DC current flowing through the DC power supply (the current also includes other harmonic currents besides the second harmonic current). Compared to Figure 6, both the THD and the second harmonic current ratio are significantly reduced. Furthermore, the oscillation amplitude of the harmonic current in this case is very small.

[0048] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A filter circuit, comprising: DC power supply; A resonant unit and a first capacitor connected in series with a DC power supply; as well as The converter connected in parallel with the first capacitor, The resonant unit comprises an inductor and a second capacitor connected in parallel with each other.

2. The filter circuit according to claim 1, wherein, The second capacitor is connected in parallel with a portion of the inductor.

3. The filter circuit according to claim 2, wherein, The second capacitor is connected in parallel with the portion of the inductor closest to the DC power source.

4. The filter circuit according to claim 2, wherein, The second capacitor is connected in parallel with the portion of the inductor closest to the first capacitor.

5. The filter circuit according to claim 2, wherein, The ratio between the inductance value of the portion of the inductor connected in parallel with the second capacitor and the total inductance value of the inductor is adjustable.

6. The filter circuit according to claim 2, wherein, The parameters of the filter circuit are determined through simulation, and the parameters include one or more of the following: the inductance value of the inductor, the capacitance value of the second capacitor, the capacitance value of the first capacitor, and the ratio between the inductance value of the portion of the inductor connected in parallel with the second capacitor and the total inductance value of the inductor.

7. The filter circuit according to claim 4, wherein, The parameters of the filter circuit are determined by performing simulation with the goal of reducing the total harmonic distortion rate or the second harmonic current ratio of the current flowing through the DC power supply in the filter circuit to below a predetermined threshold.

8. The filter circuit according to claim 2, wherein, The inductor is a single inductor.

9. The filter circuit according to claim 2, wherein, The inductance comprises two inductors that are separate from each other.

10. The filter circuit according to claim 1, wherein, The DC power source is a battery or battery pack.

11. The filter circuit according to claim 1, wherein, The converter is a single-phase converter containing four insulated-gate bipolar transistors.

12. A multiphase power system comprising at least two phases of power system, wherein each phase of the at least two phases of power system comprises at least one filter circuit according to any one of claims 1 to 11.

13. The multiphase power system according to claim 12, wherein, Each phase of the power system in the at least two-phase power system includes a plurality of the filter circuits connected in series with each other.

14. The multiphase power system according to claim 12, wherein, The parameters of the filter circuit are determined by simulation when the multiphase power system is connected to a rated load.

15. The multiphase power system according to claim 12, wherein, When the multiphase power system is connected to a rated load, the parameters of the filter circuit are determined by performing simulation with the goal of reducing the total harmonic distortion rate or second harmonic current ratio of the current flowing through the DC power supply in the filter circuit to below a predetermined threshold.

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