Three-phase four-leg neutral point balance control device and power supply equipment

Abstract

The present invention provides a neutral point balance control device and a power supply device for a three-phase four-leg inverter, which relates to the technical field of power supplies. The device includes a three-leg inverter, a target leg circuit, an auxiliary circuit, and a processor. The three-leg inverter is electrically connected to a load, and the auxiliary circuit is electrically connected between the three-leg inverter and the load. The auxiliary circuit, the target leg circuit, and the three-leg inverter are all electrically connected to a DC power supply. The processor is electrically connected to the target leg circuit and is also electrically connected between the three-leg inverter and the load. The three-leg inverter converts the direct current provided by the DC power supply into three-phase alternating current. The auxiliary circuit acquires the harmonic current output by the three-leg inverter and processes the harmonic current to obtain a harmonic voltage. The processor obtains a control signal based on the three-phase alternating current and controls the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage. It has the advantages of simple control, few detection quantities, and good waveform quality.

Description

Technical Field

[0001] The present invention relates to the technical field of power supplies, and more particularly, to a three-phase four-leg neutral point balance control device and a power supply device. Background Art

[0002] In order to improve the ability of a three-phase inverter to drive unbalanced loads, common techniques include three-phase combined inverters and three-phase four-leg inverters. The three-phase combined inverter requires too many power devices (12 pieces), and is generally composed of the secondaries of three single-phase transformers. Its topological structure is complex and the cost is high. The three-phase four-leg inverter is most widely used in non-isolated three-phase inverters. The basic structure of the three-phase four-leg inverter is to add a fourth leg on the basis of a three-phase three-leg inverter.

[0003] Since the three-phase four-leg inverter adds a leg, its control vectors increase from 2 3 to 2 4 , which increases the control difficulty. Its control strategy has become a research hotspot. Currently, there are two main control ideas. One is to consider the 16-vector rhombus space vector control technology; the other is to maintain the three-leg control strategy for the first three legs and the independent control technology for the fourth leg. The independent control strategy for the fourth leg includes a control method aimed at providing a 3nth harmonic current path; and a control method aimed at maintaining the neutral point potential balance.

[0004] Conventional similar technical solutions for maintaining neutral point balance include "direct capacitor splitting type". Since the "direct capacitor splitting type" uses relatively large splitting capacitors, it has the disadvantages of high cost and large volume. Slight drift of the neutral point of the splitting capacitors will affect the output waveform quality. There is also a method of directly connecting the detected zero-sequence current to the fourth leg through an inductive element, which has the disadvantages of being unable to ensure that the neutral point voltage is 0 and the output waveform is affected. Then there is the split-capacitor three-phase four-leg inverter that improves the DC voltage utilization rate. In order to improve the DC voltage utilization rate, this scheme adopts the method of injecting the third harmonic into the neutral point of the split capacitor and adopts a vertical orthogonal control strategy, which is complex to control. Summary of the Invention

[0005] The objectives of the present invention include, for example, providing a three-phase four-leg neutral point balance control device and a power supply device, which can reduce the volume of the target leg circuit elements, reduce the cost, and also have the advantages of simple control, few detection quantities, and good waveform quality.

[0006] Embodiments of the present invention may be implemented as follows:

[0007] In a first aspect, the present invention provides a neutral point balance control device for a three-phase four-leg inverter, which includes a three-leg inverter, a target leg circuit, an auxiliary circuit, and a processor. The three-leg inverter is electrically connected to a load. The auxiliary circuit is electrically connected between the three-leg inverter and the load. The auxiliary circuit, the target leg circuit, and the three-leg inverter are all electrically connected to a DC power supply. The processor is electrically connected to the target leg circuit, and the processor is also electrically connected between the three-leg inverter and the load;

[0008] The three-leg inverter is configured to invert the direct current provided by the DC power supply into three-phase alternating current, and supply the three-phase alternating current to the load and the processor;

[0009] The auxiliary circuit is configured to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit;

[0010] The processor is configured to obtain a control signal based on the three-phase alternating current, and control the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage.

[0011] In an optional embodiment, the auxiliary circuit includes a zero-sequence current path unit. The zero-sequence current path unit is electrically connected to both the target leg circuit and the DC power supply. The zero-sequence current path unit is also electrically connected between the three-leg inverter and the load;

[0012] The zero-sequence current path unit is configured to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit.

[0013] In an optional embodiment, the zero-sequence current path unit includes a first capacitor, a second capacitor, and a first inductor. The first capacitor and the second capacitor connected in series are electrically connected between the positive and negative poles of the DC power supply. One end of the first inductor is electrically connected between the first capacitor and the second capacitor, and the other end of the first inductor is electrically connected to the target leg circuit. The connection point of the first capacitor and the second capacitor is also electrically connected between the three-leg inverter and the load.

[0014] In an optional embodiment, the parameters of the first capacitor, the second capacitor, and the first inductor are calculated according to the following formula:

[0015]

[0016] Wherein, f1 is the fundamental frequency of the three-phase alternating current, fc is the cut-off frequency of the zero-sequence current path unit, LN is the inductance value of the first inductor, CN is the capacitance value of the first capacitor or the second capacitor, I1 is the rated phase current amplitude of the three-phase alternating current, and V1 is the fundamental amplitude of the three-phase alternating current.

[0017] In an alternative embodiment, the auxiliary circuit further includes a midpoint balancing unit, and the midpoint balancing unit is electrically connected to the DC power supply;

[0018] The midpoint balancing unit is used to provide a potential reference point.

[0019] In an alternative embodiment, the midpoint balancing unit includes a third capacitor, a fourth capacitor, a first midpoint balancing controller, and a second midpoint balancing controller. The third capacitor and the fourth capacitor connected in series are electrically connected between the positive and negative poles of the DC power supply. The first midpoint balancing controller is connected in parallel across the third capacitor, and the second midpoint balancing controller is connected in parallel across the fourth capacitor.

[0020] In an alternative embodiment, the processor is further configured to calculate the harmonic voltage and the three-phase summation voltage based on the three-phase alternating current;

[0021] The processor is further configured to perform a subtraction calculation on the harmonic voltage and a control preset value to obtain an error voltage;

[0022] The processor is further configured to obtain a first processed voltage after processing the error voltage through a preset first PI controller;

[0023] The processor is further configured to perform a subtraction calculation on the first processed voltage and the three-phase summation voltage to obtain a second processed voltage;

[0024] The processor is further configured to obtain a third processed voltage after processing the second processed voltage through a preset second PI controller;

[0025] The processor is further configured to obtain the control signal based on the third processed voltage.

[0026] In an alternative embodiment, the processor is further configured to obtain the control signal after processing the third processed voltage through a preset comparator.

[0027] In an alternative embodiment, the processor is further configured to obtain the control signal after processing the third processed voltage through a preset hysteresis generator.

[0028] In a second aspect, the present invention provides a power supply device, including the three-phase four-leg midpoint balancing control device described in the first aspect.

[0029] The beneficial effects of the three-phase four-leg midpoint balance control device and the power supply device provided by the embodiments of the present invention include: The three-phase four-leg midpoint balance control device includes a three-leg inverter, a target leg circuit, an auxiliary circuit, and a processor. The three-leg inverter is electrically connected to a load. The auxiliary circuit is electrically connected between the three-leg inverter and the load. The auxiliary circuit, the target leg circuit, and the three-leg inverter are all electrically connected to a DC power supply. The processor is electrically connected to the target leg circuit, and the processor is also electrically connected between the three-leg inverter and the load. The three-leg inverter is used to invert the direct current provided by the DC power supply into three-phase alternating current, and provide the three-phase alternating current to the load and the processor. The auxiliary circuit is used to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit. The processor is used to obtain a control signal based on the three-phase alternating current, and control the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage. It can be seen that the processor obtains a control signal based on the three-phase alternating current provided by the three-leg inverter, and the processor controls the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage. At the same time, the auxiliary circuit also processes the harmonic current output by the three-leg inverter to obtain a harmonic voltage, which can ensure the balance of the three-phase alternating current when the three-phase load is unbalanced, without the need to detect the phase and inject the third harmonic through an orthogonal vertical controller or a P-R controller, simplifies the control link, and facilitates the development of products. Moreover, the auxiliary circuit and the target leg circuit have a simple structure, and have the advantages of small volume and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0031] Figure 1 It is a schematic structural diagram of a power supply device provided by an embodiment of the present invention;

[0032] Figure 2 It is a schematic structural diagram of a three-phase four-leg midpoint balance control device provided by an embodiment of the present invention;

[0033] Figure 3 It is a schematic circuit diagram of a three-phase four-leg midpoint balance control device provided by an embodiment of the present invention;

[0034] Figure 4 It is a schematic diagram of the control strategy principle of a three-phase four-leg midpoint balance control device provided by an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of the control strategy principle of another three-phase four-leg neutral point balance control device provided by an embodiment of the present invention;

[0036] Figure 6 Schematic diagram of the simulation result of a three-phase four-leg neutral point balance control device provided by an embodiment of the present invention.

[0037] Icon: 10 - power supply device; 100 - three-phase four-leg neutral point balance control device; 110 - three-leg inverter; 120 - target leg circuit; 130 - auxiliary circuit; 131 - zero-sequence current path unit; 132 - neutral point balance unit; 140 - processor; 141 - comparator; 142 - hysteresis generator; 200 - DC power supply; 20 - load; C1 - first capacitor; C2 - second capacitor; C3 - third capacitor; C4 - fourth capacitor; C5 - fifth capacitor; C6 - sixth capacitor; C7 - seventh capacitor; L1 - first inductor; L2 - second inductor; L3 - third inductor; L4 - fourth inductor; RS1 - first neutral point balance controller; RS2 - second neutral point balance controller; T1 - first switching tube; T2 - second switching tube; T3 - third switching tube; T4 - fourth switching tube; T5 - fifth switching tube; T6 - sixth switching tube; T7 - seventh switching tube; T8 - eighth switching tube. Detailed implementation manners

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0040] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0041] In the description of the present invention, it should be noted that if terms such as "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0042] In addition, if terms such as "first", "second", etc. are only used for distinguishing descriptions, they cannot be understood as indicating or implying relative importance.

[0043] It should be noted that, without conflict, the features in the embodiments of the present invention can be combined with each other.

[0044] Please refer to Figure 1 , this embodiment provides a power supply device 10, which includes a three-phase four-leg midpoint balance control device 100 and a DC power supply 200. The DC power supply 200 is electrically connected to a load 20 through the three-phase four-leg midpoint balance control device 100. The three-phase four-leg midpoint balance control device 100 is used to invert the direct current provided by the DC power supply 200 into three-phase alternating current, obtain a control signal based on the three-phase alternating current to adjust the harmonic voltage. Wherein, the harmonic voltage is obtained by converting the harmonic current output by the three-phase four-leg midpoint balance control device 100. By adjusting the harmonic voltage, when the three-phase of the load 20 is unbalanced, the output of the three-phase alternating current can be made balanced.

[0045] Please refer to Figure 2 , for Figure 1 a schematic structural diagram of an implementable three-phase four-leg midpoint balance control device 100 as shown. The three-phase four-leg midpoint balance control device 100 includes a three-leg inverter 110, a target leg circuit 120, an auxiliary circuit 130, and a processor 140. The three-leg inverter 110 is electrically connected to the load 20. The auxiliary circuit 130 is electrically connected between the three-leg inverter 110 and the load 20. The auxiliary circuit 130, the target leg circuit 120, and the three-leg inverter 110 are all electrically connected to the DC power supply 200. The processor 140 is electrically connected to the target leg circuit 120, and the processor 140 is also electrically connected between the three-leg inverter 110 and the load 20.

[0046] In this embodiment, the three-leg inverter 110 is used to invert the direct current provided by the direct current power supply 200 into three-phase alternating current and supply the three-phase alternating current to the load 20 and the processor 140; the auxiliary circuit 130 is used to obtain the harmonic current output by the three-leg inverter 110, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit 120; the processor 140 is used to obtain a control signal based on the three-phase alternating current and control the on and off of the target leg circuit 120 according to the control signal to adjust the harmonic voltage.

[0047] As Figure 3 shown, the auxiliary circuit 130 includes a zero-sequence current path unit 131. The zero-sequence current path unit 131 is electrically connected to both the target leg circuit 120 and the direct current power supply 200, and the zero-sequence current path unit 131 is also electrically connected between the three-leg inverter 110 and the load 20.

[0048] It can be understood that the midpoint n of the zero-sequence current path unit 131 is connected to the midpoint N of the three-leg inverter 110 and is led out as the neutral line of the three-phase four-wire system output. This neutral line is connected to the midpoint N of the load 20 ’ connected.

[0049] In this embodiment, the zero-sequence current path unit 131 is used to obtain the harmonic current output by the three-leg inverter 110, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit 120.

[0050] It can be understood that the zero-sequence current path unit 131 includes a first capacitor C1, a second capacitor C2, and a first inductor L1. The first capacitor C1 and the second capacitor C2 connected in series are electrically connected between the positive and negative poles of the direct current power supply 200. One end of the first inductor L1 is electrically connected between the first capacitor C1 and the second capacitor C2, and the other end of the first inductor L1 is electrically connected to the target leg circuit 120. The connection point of the first capacitor C1 and the second capacitor C2 is also electrically connected between the three-leg inverter 110 and the load 20.

[0051] Among them, the harmonic current output by the three-leg inverter 110 first flows into the connection point of the first capacitor C1 and the second capacitor C2, and then flows into the target leg circuit 120 through the first inductor L1. The zero-sequence current path unit 131 composed of the first capacitor C1, the second capacitor C2, and the first capacitor C1 not only provides a path for the harmonic current, but also can filter the harmonic current.

[0052] In this embodiment, the auxiliary circuit 130 further includes a midpoint balance unit 132. The midpoint balance unit 132 is electrically connected to the direct current power supply 200; the midpoint balance unit 132 is used to provide a potential reference point.

[0053] It can be understood that the midpoint balance unit 132 includes a third capacitor C3, a fourth capacitor C4, a first midpoint balance controller RS1, and a second midpoint balance controller RS2. The third capacitor C3 and the fourth capacitor C4 connected in series are electrically connected between the positive and negative poles of the DC power supply 200. The first midpoint balance controller RS1 is connected in parallel across the third capacitor C3, and the second midpoint balance controller RS2 is connected in parallel across the fourth capacitor C4.

[0054] Among them, the first midpoint balance controller RS1 and the second midpoint balance controller RS2 can adopt an electrical balancer circuit formed by including precision resistors or active devices. In the schematic diagram of FIG. 3 provided in this embodiment, the first midpoint balance controller RS1 and the second midpoint balance controller RS2 adopt precision resistors, and other electrical balancer circuits can also be used, which is not limited here.

[0055] In this embodiment, by adjusting the resistances of the first midpoint balance controller RS1 and the second midpoint balance controller RS2, a potential reference point with a voltage of 0V can be provided at the connection point of the third capacitor C3 and the fourth capacitor C4. When the three-phase AC power output is balanced, the voltage drop between the connection point of the first capacitor C1 and the second capacitor C2 and the connection point of the third capacitor C3 and the fourth capacitor C4 is zero, and the voltage drop between the connection point of the first capacitor C1 and the second capacitor C2 and the connection point of the third capacitor C3 and the fourth capacitor C4 is the harmonic voltage. When the three-phase AC power output is unbalanced, the voltage drop between the connection point of the first capacitor C1 and the second capacitor C2 and the connection point of the third capacitor C3 and the fourth capacitor C4 is not zero, that is, the harmonic voltage is not zero. If the harmonic voltage is not zero, the processor 140 can adjust the on-off time of the target bridge arm circuit 120 through a control signal, adjust the harmonic voltage to zero, and thus make the three-phase AC power output balanced.

[0056] In this embodiment, the target bridge arm circuit 120 includes a first switching tube T1 and a second switching tube T2. The first pin of the first switching tube T1 and the first pin of the second switching tube T2 are both electrically connected to the processor 140. The second pin of the first switching tube T1 is electrically connected to the positive pole of the DC power supply 200. The third pin of the first switching tube T1 is electrically connected to the second pin of the second switching tube T2. The third pin of the second switching tube T2 is electrically connected to the negative pole of the DC power supply 200. The auxiliary circuit 130 is electrically connected between the third pin of the first switching tube T1 and the second pin of the second switching tube T2.

[0057] It can be understood that the other end of the first inductor L1 is electrically connected between the third pin of the first switching tube T1 and the second pin of the second switching tube T2. The processor 140 can obtain a control signal based on the three-phase alternating current and control the on-off of the target bridge arm circuit 120 according to the control signal. When the harmonic voltage is not zero, the harmonic voltage can be adjusted to zero, and thus the three-phase AC output can be balanced.

[0058] In this embodiment, the three - leg inverter 110 includes a third switch tube T3, a fourth switch tube T4, a fifth switch tube T5, a sixth switch tube T6, a seventh switch tube T7, an eighth switch tube T8, a second inductor L2, a third inductor L3, a fourth inductor L4, a fifth capacitor C5, a sixth capacitor C6, and a seventh capacitor C7.

[0059] The first pins of the third switch tube T3, the fourth switch tube T4, the fifth switch tube T5, the sixth switch tube T6, the seventh switch tube T7, and the eighth switch tube T8 are all electrically connected to the processor 140. The second pins of the third switch tube T3, the fifth switch tube T5, and the seventh switch tube T7 are all electrically connected to the positive pole of the DC power supply 200. The third pins of the fourth switch tube T4, the sixth switch tube T6, and the eighth switch tube T8 are all electrically connected to the negative pole of the DC power supply 200. The third pin of the third switch tube T3 is electrically connected to the second pin of the fourth switch tube T4. The third pin of the fifth switch tube T5 is electrically connected to the second pin of the sixth switch tube T6. The third pin of the seventh switch tube T7 is electrically connected to the second pin of the eighth switch tube T8. One end of the second inductor L2 is electrically connected between the third pin of the third switch tube T3 and the second pin of the fourth switch tube T4. One end of the third inductor L3 is electrically connected between the third pin of the fifth switch tube T5 and the second pin of the sixth switch tube T6. One end of the fourth inductor L4 is electrically connected between the third pin of the seventh switch tube T7 and the second pin of the eighth switch tube T8. The other ends of the second inductor L2, the third inductor L3, and the fourth inductor L4 are respectively electrically connected to the load 20. One end of the fifth capacitor C5 is electrically connected between the other end of the second inductor L2 and the load 20. One end of the sixth capacitor C6 is electrically connected between the other end of the third inductor L3 and the load 20. One end of the seventh capacitor C7 is electrically connected between the other end of the fourth inductor L4 and the load 20. The other ends of the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 are all electrically connected between the first capacitor C1 and the second capacitor C2.

[0060] It can be understood that the mid - point n of the zero - sequence current path unit 131 is the connection point of the first capacitor C1 and the second capacitor C2, and the mid - point N of the three - leg inverter 110 is the connection point of the other ends of the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7. Since the load 20 can be a three - phase four - wire load, the mid - point N of the load 20 ’ is the neutral - wire connection point of the three - phase four - wire load.

[0061] In this embodiment, the processor 140 controls the on / off states of the third switch tube T3, the fourth switch tube T4, the fifth switch tube T5, the sixth switch tube T6, the seventh switch tube T7, and the eighth switch tube T8, so as to invert the direct current provided by the direct current power supply 200 into three-phase alternating current. The second inductor L2, the third inductor L3, the fourth inductor L4, the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 are used to filter the three-phase alternating current.

[0062] In this embodiment, the harmonic current output by the three-bridge-arm inverter 110 flows through the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 into the connection point of the first capacitor C1 and the second capacitor C2, and then flows through the first inductor L1 into the target bridge arm circuit 120.

[0063] In this embodiment, in order to better regulate the harmonic voltage, it is necessary to limit the parameter selection of the first capacitor C1, the second capacitor C2, and the first inductor L1. The parameters of the first capacitor C1, the second capacitor C2, and the first inductor L1 are calculated according to the following formula:

[0064]

[0065] where f1 is the fundamental frequency of the three-phase alternating current, f c is the cut-off frequency of the zero-sequence current path unit 131, the L N is the inductance value of the first inductor L1, C N is the capacitance value of the first capacitor C1 or the second capacitor C2, I1 is the rated phase current amplitude of the three-phase alternating current, and V1 is the fundamental amplitude of the three-phase alternating current.

[0066] It can be understood that the parameters of the first capacitor C1, the second capacitor C2, and the first inductor L1 are designed according to the above formula, and the harmonic voltage can be adjusted to zero without affecting the output waveform of the three-phase alternating current.

[0067] In this embodiment, without considering 100% imbalance, the following formula can be obtained by combining the above formulas:

[0068]

[0069] where R aN is the output single-phase rated load 20.

[0070] In this embodiment, after the hardware circuit parameters are designed, the processor 140 is also required to cooperate with software to regulate the harmonic voltage. Such as Figure 4As shown, it is a schematic diagram of a feasible control strategy principle of the three-phase four-leg neutral point balance control device 100. The processor 140 is also used to calculate the harmonic voltage and the three-phase sum voltage based on the three-phase alternating current; the processor 140 is also used to perform a subtraction calculation on the harmonic voltage and the control preset value to obtain the error voltage; the processor 140 is also used to process the error voltage through a preset first PI controller to obtain the first processed voltage; the processor 140 is also used to perform a subtraction calculation on the first processed voltage and the three-phase sum voltage to obtain the second processed voltage; the processor 140 is also used to process the second processed voltage through a preset second PI controller to obtain the third processed voltage; the processor 140 is also used to obtain the control signal based on the third processed voltage.

[0071] It can be understood that the three-phase alternating current is Figure 4 V shown in a , V b and V c (or I a , I b and I c ), the three-phase sum voltage is Figure 4 ΔV or ΔV shown in I , the harmonic voltage is Figure 4 V shown in no , the control preset value is Figure 4 shown in The error voltage is Figure 4 e(t) shown in Figure 4 , the first processed voltage is C1 u Figure 4 shown in C2 (t), the second processed voltage is Figure 4 u C3 (t), the third processed voltage is Figure 4 G shown in C1 is the first PI controller, Figure 4 G shown in C2 is the second PI controller.

[0072] Among them, the control preset value is set to zero. When the unbalanced current flows into the network composed of the first inductor L1, the first capacitor C1, the second capacitor C2, the first switching tube T1 and the second switching tube T2, the three-phase alternating current output by the three-leg inverter 110 can be output to the processor 140, and the processor 140 can calculate the harmonic voltage according to the three-phase alternating current. The processor 140 can use the formula to calculate the harmonic voltage. Among them, V no is the harmonic voltage, V3 is the third harmonic amplitude, ω3 is the third harmonic angular frequency of the three-phase alternating current, is the phase shift angle of three-phase alternating current. ω3 = 3ω1, which is the angular frequency of the three-phase alternating current of ω1.

[0073] In this embodiment, the processor 140 performs a subtraction calculation on the harmonic voltage and the control preset value to obtain an error voltage. The error voltage can be calculated using the formula e(t) = -V3sinω3t.

[0074] In this embodiment, after the processor 140 processes the error voltage through a preset first PI controller, a first processed voltage is obtained. The first processed voltage can be calculated using the formula where k v is the transfer function of the first PI controller and can be calculated using the formula to calculate.

[0075] Substituting the formula into the formula can calculate the formula where k p1 is the amplification coefficient of the first PI controller, and τ = R1C2 is the integral constant of the first PI controller.

[0076] The first processed voltage serves as the preset value for clamping the algebraic sum of the three-phase alternating current and directly represents the magnitude of the harmonic voltage. The difference between the first processed voltage and the three-phase summation voltage, the second processed voltage, is amplified by a second PI controller to obtain a third processed voltage. The processor 140 can obtain a control signal based on the third processed voltage and then control the target bridge arm circuit 120 to operate.

[0077] In this embodiment, as Figure 5 shown, the processor 140 is further configured to process the third processed voltage through a preset comparator 141 to obtain a control signal. Alternatively, the processor 140 is further configured to process the third processed voltage through a preset hysteresis generator 142 to obtain a control signal.

[0078] It can be understood that if the harmonic voltage is greater than zero, the processor 140 controls the first switch tube T1 to conduct through the control signal, so that the harmonic voltage decreases towards the zero value; if the harmonic voltage is less than zero, the processor 140 controls the second switch tube T2 to conduct through the control signal, so that the harmonic voltage increases towards the zero value.

[0079] For ease of understanding, as Figure 6 shown, it is a schematic diagram of the simulation result of the three-phase four-bridge arm midpoint balance control device 100 provided by the embodiment of the present application. Set the direct current V provided by the direct current power supply 200 dc= 650V; The A-phase of the load 20 is a pure resistive load of 8Ω, the B-phase is a pure resistive load of 8Ω, and the C-phase is a pure resistive load of ∞Ω; The second inductor L2, the third inductor L3, and the fourth inductor L4 are all L f = 500uH; The fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 are all C f = 60uF; The third capacitor C3 and the fourth capacitor C4 are both 500uF; The first midpoint balance controller RS1 and the second midpoint balance controller RS2 are both 50KΩ, the first capacitor C1 and the second capacitor C2 are 20uF; The first inductor L1 is 3000uH.

[0080] It can be seen from the simulation diagram that Ia = Ib ≈ (38 / 1.412) A ≈ 27.5A, Ic = 0, Va = Vb =Vc ≈ (310 / 1.412) V ≈ 220V, and the output is a sine wave, indicating that the three-phase alternating current can be kept balanced under the condition of unbalanced load 20; where, Ia is the A-phase alternating current, Ib is the B-phase alternating current, Ic is the C-phase alternating current, Va is the A-phase alternating voltage, Vb is the B-phase alternating voltage, and Vc is the C-phase alternating voltage. And Vno is the harmonic voltage, that is, the voltage waveform between the connection point of the first capacitor C1 and the second capacitor C2 and the connection point of the third capacitor C3 and the fourth capacitor C4. The harmonic voltage is formed by the harmonic current flowing into the first capacitor C1; the second capacitor C2 and the first inductor L1, indicating that the target bridge arm circuit 120 and the zero-sequence current path unit 131 provide a path for the harmonic current and support the balanced three-phase alternating current output under the condition of unbalanced load 20. In is the harmonic current, further verifying that the target bridge arm circuit 120 and the zero-sequence current path unit 131 can effectively provide a path for the harmonic current.

[0081] In summary, the embodiment of the present invention provides a three-phase four-leg neutral point balance control device and a power supply device. The three-phase four-leg neutral point balance control device includes a three-leg inverter, a target leg circuit, an auxiliary circuit, and a processor. The three-leg inverter is electrically connected to a load. The auxiliary circuit is electrically connected between the three-leg inverter and the load. The auxiliary circuit, the target leg circuit, and the three-leg inverter are all electrically connected to a DC power supply. The processor is electrically connected to the target leg circuit, and the processor is also electrically connected between the three-leg inverter and the load. The three-leg inverter is configured to invert the direct current provided by the DC power supply into three-phase alternating current, and provide the three-phase alternating current to the load and the processor. The auxiliary circuit is configured to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit. The processor is configured to obtain a control signal based on the three-phase alternating current, and control the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage. It can be seen that the processor obtains the control signal based on the three-phase alternating current provided by the three-leg inverter, and the processor controls the on / off of the target leg circuit according to the control signal to adjust the harmonic voltage. At the same time, the auxiliary circuit also processes the harmonic current output by the three-leg inverter to obtain a harmonic voltage, which can ensure the balance of the three-phase alternating current when the three-phase load is unbalanced, without detecting the phase and injecting the third harmonic through an orthogonal vertical controller or a P-R controller, simplifying the control link and facilitating the development of the product. Moreover, the auxiliary circuit and the target leg circuit have simple structures and have the advantages of small volume and low cost.

[0082] As described above, the above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A three-phase four-leg neutral point balance control device, characterized in that, It includes a three-leg inverter, a target leg circuit, an auxiliary circuit and a processor. The three-leg inverter is electrically connected to a load. The auxiliary circuit is electrically connected between the three-leg inverter and the load. The auxiliary circuit, the target leg circuit and the three-leg inverter are all electrically connected to a DC power supply. The processor is electrically connected to the target leg circuit, and the processor is also electrically connected between the three-leg inverter and the load; The three-leg inverter is used to invert the direct current provided by the DC power supply into three-phase alternating current, and supply the three-phase alternating current to the load and the processor; The auxiliary circuit is used to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit; The processor is used to obtain a control signal based on the three-phase alternating current, and control the on-off of the target leg circuit according to the control signal to adjust the harmonic voltage; The processor is also used to calculate the harmonic voltage and the three-phase summation voltage based on the three-phase alternating current; perform a subtraction calculation on the harmonic voltage and a control preset value to obtain an error voltage; After processing the error voltage through a preset first PI controller, a first processed voltage is obtained; Perform a subtraction calculation on the first processed voltage and the three-phase summation voltage to obtain a second processed voltage; After processing the second processed voltage through a preset second PI controller, a third processed voltage is obtained; obtain the control signal based on the third processed voltage.

2. The three-phase four-leg neutral point balance control device according to claim 1, wherein The auxiliary circuit includes a zero-sequence current path unit. The zero-sequence current path unit is electrically connected to both the target leg circuit and the DC power supply, and the zero-sequence current path unit is also electrically connected between the three-leg inverter and the load; The zero-sequence current path unit is used to obtain the harmonic current output by the three-leg inverter, process the harmonic current to obtain a harmonic voltage, and transmit the harmonic voltage to the target leg circuit.

3. The three-phase four-leg neutral point balance control device according to claim 2, wherein The zero-sequence current path unit includes a first capacitor, a second capacitor and a first inductor. The first capacitor and the second capacitor connected in series are electrically connected between the positive and negative poles of the DC power supply. One end of the first inductor is electrically connected between the first capacitor and the second capacitor, and the other end of the first inductor is electrically connected to the target leg circuit. The connection point of the first capacitor and the second capacitor is also electrically connected between the three-leg inverter and the load.

4. The three-phase four-leg neutral point balance control device according to claim 3, wherein The parameters of the first capacitor, the second capacitor and the first inductor are calculated according to the following formula: where f1 is the fundamental frequency of the three-phase alternating current, and f c is the cut-off frequency of the zero-sequence current path unit, L N is the inductance value of the first inductor, C N is the capacitance value of the first capacitor or the second capacitor, I1 is the rated phase current amplitude of the three-phase alternating current, and V1 is the fundamental amplitude of the three-phase alternating current.

5. The three-phase four-leg neutral point balance control device according to claim 2, characterized in that The auxiliary circuit further includes a midpoint balance unit. The midpoint balance unit is electrically connected to the DC power supply; The midpoint balance unit is used to provide a potential reference point.

6. The three-phase four-leg neutral point balance control device according to claim 5, characterized in that, The midpoint balancing unit includes a third capacitor, a fourth capacitor, a first midpoint balancing controller, and a second midpoint balancing controller. The third capacitor and the fourth capacitor connected in series are electrically connected between the positive and negative electrodes of the DC power supply. The first midpoint balancing controller is connected in parallel across the third capacitor, and the second midpoint balancing controller is connected in parallel across the fourth capacitor.

7. The three-phase four-leg neutral point balance control device according to claim 1, wherein The processor is further configured to obtain the control signal after processing the third processed voltage through a preset comparator.

8. The three-phase four-leg neutral point balance control device according to claim 1, characterized in that The processor is further configured to obtain the control signal after processing the third processed voltage through a preset hysteresis generator.

9. A power supply device, characterized in that, It includes the three-phase four-leg midpoint balancing control device according to any one of claims 1-8.

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