A method and system for treating three-phase imbalance in a distribution network

Abstract

The present invention discloses a method and system for controlling three-phase imbalance in a distribution network, wherein the method for controlling three-phase imbalance in a distribution network can perform sequence decomposition calculation based on the load current on the three-phase line on the load side of an electric power system to obtain the corresponding negative-sequence current and zero-sequence current in the three-phase line on the load side of the electric power system, and then obtain the corresponding compensation current reference values ​​in the three-phase line on the load side of the electric power system by superimposing the negative-sequence current, the zero-sequence current and the capacitor voltage control component, so that the modulation voltage of each phase can be obtained according to the compensation current reference value of each phase and the current compensation current of each phase, and the compensation current corresponding to each phase line can be obtained through the modulation voltage of each phase, and the negative-sequence current generated by the system and the zero-sequence current on the neutral line of the system can be accurately suppressed by outputting the corresponding compensation current to each phase line, thereby effectively solving the problem of three-phase current imbalance of a distribution transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method and system for controlling three-phase imbalance in a distribution network. Background Art

[0002] High-quality power quality is the premise of ensuring high-quality and economical power supply to users. With the development of social economy and the improvement of people's living standards, various production enterprises and residents have higher and higher requirements for power quality. The low-voltage area of ​​the domestic distribution network is powered by three-phase four-wire. Due to the disorderly access of single-phase loads and inconsistent power usage time sequence, the three-phase of the distribution network system is generally unbalanced.

[0003] In recent years, with the access of a large number of distributed power sources, non-linear loads, and impact loads, the three-phase imbalance in the substation has been further aggravated, and problems such as low voltage and increased line loss have become increasingly prominent. In severe cases, the single-phase distribution transformer is overloaded and burned, affecting the normal production and living electricity use of residents.

[0004] However, the power distribution systems in the related technologies cannot completely suppress the negative-sequence and zero-sequence currents on the lines and achieve full compensation of unbalanced currents. They can only reduce the system imbalance to a certain extent and cannot fully achieve the three-phase balance of the distribution transformer. Therefore, how to reduce the three-phase imbalance of the distribution network is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of this, the present invention provides a method and system for managing three-phase imbalance in a distribution network, which are used to solve the problem of three-phase imbalance of three-phase current in the distribution network.

[0006] To achieve one or part or all of the above purposes or other purposes, in a first aspect, the present invention provides a method for managing three-phase imbalance in a distribution network, which is applied to a three-phase imbalance management system for a distribution transformer. The three-phase imbalance management system for a distribution transformer is applied to a power system, which includes a distribution transformer and a phase a line, a phase b line, a phase c line, and a neutral line n connected to a low-voltage side of the distribution transformer;

[0007] The three-phase unbalance management system of the distribution transformer comprises:

[0008] A single-phase bridge rectifier is provided with a rectifier input terminal, a positive rectifier output terminal and a negative rectifier output terminal, wherein the rectifier input terminal is connected to any two of the a-phase line, the b-phase line and the c-phase line;

[0009] A three-phase full-bridge inverter is provided with a positive inverter input terminal, a negative inverter input terminal and an inverter output terminal, wherein the positive inverter input terminal is connected to the positive rectifier output terminal, the negative inverter input terminal is connected to the negative rectifier output terminal, and the inverter output terminal is respectively connected to the a-phase line, the b-phase line and the c-phase line through a reactor; the three-phase full-bridge inverter is used to output corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line respectively through the reactor to perform three-phase unbalance treatment;

[0010] A first filter capacitor connected to the positive inverter input terminal and the positive rectifier output terminal;

[0011] A second filter capacitor is connected in series with the first filter capacitor, and the second filter capacitor is connected to the negative inverter input terminal and the negative rectifier output terminal, and the neutral line n is connected between the first filter capacitor and the second filter capacitor;

[0012] The method for treating three-phase imbalance in a distribution network comprises:

[0013] Obtaining an initial unbalance degree according to the a-phase load current of the a-phase line, the b-phase load current of the b-phase line, and the c-phase load current of the c-phase line;

[0014] When the initial unbalance degree is greater than a preset starting value, the a-phase load current, the b-phase load current and the c-phase load current are subjected to sequence component decomposition processing to obtain corresponding a-phase negative-sequence current, b-phase negative-sequence current and c-phase negative-sequence current, as well as a-phase zero-sequence current, b-phase zero-sequence current and c-phase zero-sequence current;

[0015] The a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component are calculated according to the voltage between the positive and negative ends of the first filter capacitor and the second filter capacitor after being connected in series and a preset reference voltage;

[0016] According to the a-phase negative-sequence current, the a-phase zero-sequence current and the a-phase capacitor voltage control component, a reference value of the a-phase compensation current is obtained; according to the b-phase negative-sequence current, the b-phase zero-sequence current and the b-phase capacitor voltage control component, a reference value of the b-phase compensation current is obtained; according to the c-phase negative-sequence current, the c-phase zero-sequence current and the c-phase capacitor voltage control component, a reference value of the c-phase compensation current is obtained;

[0017] Obtaining an a-phase modulation voltage according to the a-phase compensation current reference value and the currently output a-phase compensation current, obtaining a b-phase modulation voltage according to the b-phase compensation current reference value and the currently output b-phase compensation current, and obtaining a c-phase modulation voltage according to the c-phase compensation current reference value and the currently output c-phase compensation current;

[0018] According to the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage, the corresponding a-phase compensation current, the b-phase compensation current and the c-phase compensation current are output to the a-phase line, the b-phase line and the c-phase line respectively to perform three-phase imbalance control.

[0019] Preferably, the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component are calculated based on the voltage between the positive and negative ends of the first filter capacitor and the second filter capacitor after being connected in series and a preset reference voltage, including:

[0020] Acquire a filter voltage, where the filter voltage is used to represent a voltage between a positive terminal and a negative terminal of the first filter capacitor and the second filter capacitor connected in series;

[0021] Calculating the difference between the filtered voltage and a preset voltage reference value to obtain a capacitor voltage difference;

[0022] Obtaining a D-axis active component required for phase coordinate transformation processing according to the capacitor voltage difference;

[0023] Phase coordinate transformation processing is performed according to the D-axis active component and the preset Q-axis reactive component to obtain the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component, wherein the Q-axis reactive component is preset to zero.

[0024] Preferably, the three-phase unbalanced management system of the distribution transformer further includes a PI controller, and the D-axis active component required for phase coordinate transformation processing is obtained according to the capacitor voltage difference, including:

[0025] The capacitor voltage difference is input into the PI controller to obtain the D-axis active component required for phase coordinate transformation processing.

[0026] Preferably, the a-phase compensation current reference value is obtained according to the a-phase negative-sequence current, the a-phase zero-sequence current and the a-phase capacitor voltage control component, the b-phase compensation current reference value is obtained according to the b-phase negative-sequence current, the b-phase zero-sequence current and the b-phase capacitor voltage control component, and the c-phase compensation current reference value is obtained according to the c-phase negative-sequence current, the c-phase zero-sequence current and the c-phase capacitor voltage control component, following the following formula:

[0027]

[0028]

[0029]

[0030] Among them, I a_refIndicates the a-phase compensation current reference value, I b_ref Indicates the b-phase compensation current reference value, I c_ref Indicates the c-phase compensation current reference value; represents the negative sequence current of phase a, represents the b-phase negative sequence current, I represents the negative sequence current of phase c; a * represents the a-phase capacitor voltage control component, I b * represents the b-phase capacitor voltage control component, I c * Represents the c-phase capacitor voltage control component.

[0031] Preferably, the distribution transformer three-phase unbalance management system further includes a quasi-PR controller;

[0032] The method of obtaining the a-phase modulation voltage according to the a-phase compensation current reference value and the currently output a-phase compensation current, obtaining the b-phase modulation voltage according to the b-phase compensation current reference value and the currently output b-phase compensation current, and obtaining the c-phase modulation voltage according to the c-phase compensation current reference value and the currently output c-phase compensation current comprises:

[0033] Subtract the a-phase compensation current reference value from the current a-phase compensation current to obtain an a-phase current difference value, subtract the b-phase compensation current reference value from the current b-phase compensation current to obtain a b-phase current difference value, and subtract the c-phase compensation current reference value from the current c-phase compensation current to obtain a c-phase current difference value;

[0034] The a-phase current difference, the b-phase current difference and the c-phase current difference are input into the quasi-PR controller to obtain the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage.

[0035] Preferably, the method for managing three-phase imbalance in a distribution network of an embodiment of the present invention further includes: obtaining a current imbalance degree, wherein the current imbalance degree is obtained by the current a-phase load current, the b-phase load current and the c-phase load current;

[0036] Obtaining a three-phase imbalance variation amplitude according to the initial imbalance and the current imbalance;

[0037] When the change amplitude of the three-phase imbalance exceeds the preset offset value, the output a-phase compensation current, b-phase compensation current and c-phase compensation current are updated according to the current a-phase load current, b-phase load current, c-phase load current, a-phase capacitor voltage control component, b-phase capacitor voltage control component and c-phase capacitor voltage control component to perform three-phase imbalance control.

[0038] Preferably, the method for controlling three-phase imbalance in a distribution network of an embodiment of the present invention further includes: controlling the three-phase full-bridge inverter to obtain the a-phase load current, the b-phase load current and the c-phase load current.

[0039] Preferably, the inverter output end of the three-phase full-bridge inverter includes an inverter a-phase output end, an inverter b-phase output end and an inverter c-phase output end, the inverter a-phase output end is connected to the a-phase line through the inductor, the inverter b-phase output end is connected to the b-phase line through the inductor, and the inverter c-phase output end is connected to the c-phase line through the inductor.

[0040] Preferably, the outputting the corresponding a-phase compensation current, the b-phase compensation current and the c-phase compensation current to the a-phase line, the b-phase line and the c-phase line respectively according to the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage to perform three-phase unbalance management further includes:

[0041] Performing SPWM modulation on the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage to obtain a switching signal of the three-phase full-bridge inverter;

[0042] Controlling the three-phase full-bridge inverter to output an a-phase output current, a b-phase output current and a c-phase output current to the reactor through the inverter a-phase output terminal, the inverter b-phase output terminal and the inverter c-phase output terminal according to the switching signal;

[0043] The reactor outputs the corresponding a-phase compensation current, b-phase compensation current and c-phase compensation current to the a-phase line, the b-phase line and the c-phase line respectively according to the a-phase output current, the b-phase output current and the c-phase output current to perform three-phase imbalance control.

[0044] In a second aspect, an embodiment of the present invention further provides a three-phase unbalance management system for a distribution transformer, which is applied to a power system, wherein the power system includes a distribution transformer and a phase line a, a phase line b, a phase line c and a neutral line n connected to a low-voltage side of the distribution transformer;

[0045] The distribution transformer three-phase imbalance control system is used to execute a distribution network three-phase imbalance control method as described in any one of the first aspect embodiments above;

[0046] The three-phase unbalance management system of the distribution transformer comprises:

[0047] A single-phase bridge rectifier is provided with a rectifier input terminal, a positive rectifier output terminal and a negative rectifier output terminal, wherein the rectifier input terminal is connected to any two of the a-phase line, the b-phase line and the c-phase line;

[0048] A three-phase full-bridge inverter is provided with a positive inverter input terminal, a negative inverter input terminal and an inverter output terminal, wherein the positive inverter input terminal is connected to the positive rectifier output terminal, the negative inverter input terminal is connected to the negative rectifier output terminal, and the inverter output terminal is respectively connected to the a-phase line, the b-phase line and the c-phase line through a reactor; the three-phase full-bridge inverter is used to output corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line respectively through the reactor to perform three-phase unbalance treatment;

[0049] A first filter capacitor connected to the positive inverter input terminal and the positive rectifier output terminal;

[0050] A second filter capacitor is connected in series with the first filter capacitor, and the second filter capacitor is connected to the negative inverter input terminal and the negative rectifier output terminal, and the neutral line n is connected between the first filter capacitor and the second filter capacitor.

[0051] Implementing the embodiments of the present invention will have the following beneficial effects:

[0052] The method for treating the three-phase imbalance of the distribution network of the embodiment of the present invention can perform sequence decomposition calculation based on the load current on the three-phase line on the load side of the power system to obtain the corresponding negative-sequence current and zero-sequence current in the three-phase line on the load side of the power system, and then by superimposing the negative-sequence current, zero-sequence current and capacitor voltage control components, the corresponding compensation current reference values ​​in the three-phase line on the load side of the power system can be obtained, so that the modulation voltage of each phase can be obtained according to the compensation current reference value of each phase and the current compensation current of each phase, and the compensation current corresponding to each phase line can be obtained through the modulation voltage of each phase. By outputting the corresponding compensation current to each phase line, the negative-sequence current generated by the system and the zero-sequence current on the neutral line of the system can be accurately suppressed, and the problem of three-phase current imbalance of the distribution transformer can be effectively solved. Thereby, the power loss of the transformer can be greatly reduced, the transformer can be prevented from burning due to single-phase overload, the service life of the transformer can be extended, and the safe operation of electrical equipment can be ensured.

[0053] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0055] in:

[0056] Figure 1 A schematic diagram of the system structure of a three-phase unbalance management system for a distribution transformer in one embodiment;

[0057] Figure 2 It is a flow chart of a method for treating three-phase imbalance in a power distribution network in one embodiment;

[0058] Figure 3 It is a specific flow chart of a method for treating three-phase imbalance in a distribution network in another embodiment;

[0059] Figure 4 A specific flow chart of a method for treating three-phase imbalance in a power distribution network in another embodiment;

[0060] Figure 5 A specific flow chart of a method for treating three-phase imbalance in a power distribution network in another embodiment;

[0061] Figure 6 It is a schematic diagram of the process of performing quasi-proportional resonance processing and sinusoidal pulse width modulation processing in one embodiment;

[0062] Figure 7 A specific flow chart of a method for treating three-phase imbalance in a power distribution network in another embodiment;

[0063] Figure 8 A waveform diagram of three-phase unbalanced current on the load side in one embodiment;

[0064] Fig. 9 is a current waveform diagram output by a three-phase full-bridge inverter in one embodiment;

[0065] Fig.10 A current waveform diagram of a target current adjusted by the method for treating three-phase imbalance in a power distribution network of the present invention in one embodiment;

[0066] Fig.11 FIG. 4 is a schematic diagram of the structure of an operation control device in an embodiment. DETAILED DESCRIPTION

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] The embodiment of the present invention provides a method and system for managing the three-phase imbalance of a distribution network. The method for managing the three-phase imbalance of a distribution network of the embodiment of the present invention can perform sequence decomposition calculation based on the load current on the three-phase line on the load side of the power system to obtain the corresponding negative-sequence current and zero-sequence current in the three-phase line on the load side of the power system, and then by superimposing the negative-sequence current, zero-sequence current and capacitor voltage control components, the corresponding compensation current reference values ​​in the three-phase line on the load side of the power system can be obtained, so that the modulation voltage of each phase can be obtained according to the compensation current reference value of each phase and the current compensation current of each phase, and the compensation current corresponding to each phase line can be obtained through the modulation voltage of each phase. By outputting the corresponding compensation current to each phase line, the negative-sequence current generated by the system and the zero-sequence current on the neutral line of the system can be accurately suppressed, and the problem of three-phase current imbalance of the distribution transformer can be effectively solved. Thereby, the power loss of the transformer can be greatly reduced, the transformer can be prevented from burning due to single-phase overload, the service life of the transformer can be extended, and the safe operation of electrical equipment can be ensured.

[0069] For ease of understanding, embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0070] Please refer to Figure 1 , Figure 1 1 is a schematic diagram of the system structure of the three-phase unbalanced distribution transformer management system 100 provided in an embodiment of the present invention. The three-phase unbalanced distribution transformer management system 100 is applied to a power system, which includes a distribution transformer and a phase line a, a phase line b, a phase line c and a neutral line n connected to the low-voltage side of the distribution transformer, that is, the load side of the power system;

[0071] The distribution transformer three-phase unbalance management system 100 includes a single-phase bridge rectifier 120, a three-phase full-bridge inverter 110, a filter component 130 and a reactor 140.

[0072] Specifically, the single-phase bridge rectifier 120 is provided with a rectifier input terminal, a positive rectifier output terminal and a negative rectifier output terminal. The rectifier input terminal is connected to any two of the a-phase line, the b-phase line and the c-phase line. The single-phase bridge rectifier 120 can convert the two-phase output AC power on the low-voltage side of the distribution transformer into DC power to supply the three-phase full-bridge inverter 110.

[0073] Specifically, the three-phase full-bridge inverter 110 is provided with a positive inverter input terminal, a negative inverter input terminal and an inverter output terminal, the positive inverter input terminal is connected to the positive rectifier output terminal, the negative inverter input terminal is connected to the negative rectifier output terminal, and the inverter output terminal is respectively connected to the a-phase line, the b-phase line and the c-phase line through the reactor 140; the three-phase full-bridge inverter 110 is used to output corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line respectively through the reactor 140 to perform three-phase unbalance treatment;

[0074] Specifically, the filter component 130 includes a first filter capacitor 131 and a second filter capacitor 132, the first filter capacitor 131 is connected to the positive inverter input terminal and the positive rectifier output terminal; the second filter capacitor 132 is connected in series with the first filter capacitor 131, and the second filter capacitor 132 is connected to the negative inverter input terminal and the negative rectifier output terminal, and the neutral line n is connected between the first filter capacitor 131 and the second filter capacitor 132.

[0075] Specifically, the inverter output end of the three-phase full-bridge inverter 110 includes an inverter a-phase output end, an inverter b-phase output end and an inverter c-phase output end. The inverter a-phase output end is connected to the a-phase line through the inductor 140, the inverter b-phase output end is connected to the b-phase line through the inductor 140, and the inverter c-phase output end is connected to the c-phase line through the inductor 140. The inductor 140 can output corresponding compensation currents to corresponding phase lines according to the voltages output by the output ends of each phase of the three-phase full-bridge inverter 110.

[0076] It should be noted that, in the embodiment of the present invention, the capacitance values ​​of the first filter capacitor 131 and the second filter capacitor 132 and the inductance value of the reactor 140 are selected according to actual conditions, and the present invention does not impose any specific limitation on this.

[0077] The distribution transformer three-phase unbalance control system 100 and the application scenario described in the embodiment of the present invention are intended to more clearly illustrate the technical solution of the embodiment of the present invention, and do not constitute a limitation on the technical solution provided by the embodiment of the present invention. Those skilled in the art can know that with the evolution of the distribution system and the emergence of new application scenarios, the technical solution provided by the embodiment of the present invention is also applicable to similar technical problems.

[0078] It can be understood by those skilled in the art that Figure 1 The distribution transformer three-phase unbalance management system 100 shown in the figure does not constitute a limitation on the embodiments of the present invention, and may include more or less components than those shown in the figure, or combine certain components, or arrange the components differently.

[0079] Based on the above-mentioned distribution transformer three-phase imbalance control system, various embodiments of the distribution network three-phase imbalance control method of the present invention are proposed.

[0080] Reference Figure 2 The embodiment of the present invention provides a method for managing three-phase imbalance in a distribution network. The method for managing three-phase imbalance in a distribution network includes but is not limited to steps S100 to S600:

[0081] Step S100, obtaining an initial unbalance degree according to the a-phase load current of the a-phase line, the b-phase load current of the b-phase line and the c-phase load current of the c-phase line;

[0082] Step S200, when the initial unbalance degree is greater than a preset starting value, the a-phase load current, the b-phase load current and the c-phase load current are subjected to sequence component decomposition processing to obtain the corresponding a-phase negative-sequence current, the b-phase negative-sequence current and the c-phase negative-sequence current, and the a-phase zero-sequence current, the b-phase zero-sequence current and the c-phase zero-sequence current;

[0083] Step S300, calculating the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component according to the voltage between the positive and negative ends of the first filter capacitor and the second filter capacitor after being connected in series and a preset reference voltage;

[0084] Step S400, obtaining a phase a compensation current reference value according to the phase a negative sequence current, the phase a zero sequence current and the phase a capacitor voltage control component, obtaining a phase b compensation current reference value according to the phase b negative sequence current, the phase b zero sequence current and the phase b capacitor voltage control component, and obtaining a phase c compensation current reference value according to the phase c negative sequence current, the phase c zero sequence current and the phase c capacitor voltage control component;

[0085] Step S500, obtaining an a-phase modulation voltage according to an a-phase compensation current reference value and a currently output a-phase compensation current, obtaining a b-phase modulation voltage according to a b-phase compensation current reference value and a currently output b-phase compensation current, and obtaining a c-phase modulation voltage according to a c-phase compensation current reference value and a currently output c-phase compensation current;

[0086] Step S600, output corresponding a-phase compensation current, b-phase compensation current and c-phase compensation current to a-phase line, b-phase line and c-phase line respectively according to a-phase modulation voltage, b-phase modulation voltage and c-phase modulation voltage to perform three-phase unbalance control.

[0087] The method for treating the three-phase imbalance of the distribution network of the embodiment of the present invention can perform sequence decomposition calculation based on the load current on the three-phase line on the load side of the power system to obtain the corresponding negative-sequence current and zero-sequence current in the three-phase line on the load side of the power system, and then by superimposing the negative-sequence current, zero-sequence current and capacitor voltage control components, the corresponding compensation current reference values ​​in the three-phase line on the load side of the power system can be obtained, so that the modulation voltage of each phase can be obtained according to the compensation current reference value of each phase and the current compensation current of each phase, and the compensation current corresponding to each phase line can be obtained through the modulation voltage of each phase. By outputting the corresponding compensation current to each phase line, the negative-sequence current generated by the system and the zero-sequence current on the neutral line of the system can be accurately suppressed, and the problem of three-phase current imbalance of the distribution transformer can be effectively solved. Thereby, the power loss of the transformer can be greatly reduced, the transformer can be prevented from burning due to single-phase overload, the service life of the transformer can be extended, and the safe operation of electrical equipment can be ensured.

[0088] Specifically, the a-phase load current, the b-phase load current and the c-phase load current are obtained through a three-phase full-bridge inverter.

[0089] Specifically, when the initial imbalance is greater than the preset starting value, it indicates that there is a three-phase imbalance in the power system, and three-phase imbalance compensation is required to ensure the quality and stability of electricity consumption for various production enterprises and residents. Three-phase imbalance compensation can balance the three-phase current in the three-phase transmission line, reduce power loss in the substation, improve power quality, prevent distribution transformers from being damaged due to excessive single-phase load, improve the durability of three-phase transmission lines and substation transformers, and ensure the safe operation of electrical equipment.

[0090] Reference Figure 3 In some embodiments, step S300 includes but is not limited to steps S310 to S340:

[0091] Step S310, obtaining a filter voltage, where the filter voltage is used to represent the voltage between the positive terminal and the negative terminal of the first filter capacitor and the second filter capacitor connected in series;

[0092] Step S320, calculating the difference between the filtered voltage and a preset voltage reference value to obtain a capacitor voltage difference;

[0093] Step S330, obtaining the D-axis active component required for phase coordinate transformation processing according to the capacitor voltage difference;

[0094] Step S340, performing phase coordinate transformation processing according to the D-axis active component and the preset Q-axis reactive component to obtain the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component, wherein the Q-axis reactive component is preset to zero.

[0095] Specifically, in this embodiment, the capacitor voltage difference is represented by the voltage difference between the positive terminal and the negative terminal of the first filter capacitor and the second filter capacitor connected in series, denoted by U dc The preset reference voltage is the voltage reference value between the positive and negative ends of the filter component, expressed as U dc_ref By calculating the difference between the filtered voltage and the preset reference voltage, the capacitor voltage difference can be obtained. The difference is input into a proportional integral (PI) controller, i.e., a linear controller, for calculation processing, so that the capacitor voltage difference is adjusted by the PI controller to obtain the D-axis active component required for phase coordinate transformation processing.

[0096] Specifically, phase coordinate transformation processing is performed according to the D-axis active component and the preset Q-axis reactive component to obtain the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component, wherein the Q-axis reactive component is preset to zero.

[0097] Specifically, the phase coordinate transformation process adopts dq / abc coordinate transformation, and the D-axis active component and the preset Q-axis reactive component are transformed by dq / abc to obtain the corresponding voltage control components in the three-phase line of the power system.

[0098] Specifically, in this embodiment, the three-phase negative sequence current, the three-phase zero sequence current and the capacitor voltage control component are processed, so that the reference current of each phase can be obtained. For example, the three-phase negative sequence current includes the a-phase negative sequence current, the b-phase negative sequence current and the c-phase negative sequence current; the three-phase zero sequence current includes the a-phase zero sequence current, the b-phase zero sequence current and the c-phase zero sequence current, and the voltage control component includes the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component; the three-phase reference current includes the a-phase reference current, the b-phase reference current and the c-phase reference current. The a-phase negative sequence current, the a-phase zero sequence current and the a-phase control component are superimposed and calculated to obtain the a-phase reference current. The b-phase reference current can be obtained by adding the b-phase negative sequence current, the b-phase zero sequence current and the b-phase control component. The c-phase reference current is the sum of the c-phase negative sequence current, the c-phase zero sequence current and the c-phase control component.

[0099] For example, Indicates the negative sequence current of phase a, Indicates the negative sequence current of phase b, represents the negative sequence current of phase c, represents the zero-sequence current of phase a, Indicates the zero-sequence current of phase b, Indicates the zero-sequence current of phase c, I a_ref Indicates the reference value of phase a compensation current, I b_ref Indicates the b-phase compensation current reference value, Ic_ref Indicates the reference value of phase C compensation current, represents the a-phase control component, represents the b-phase control component, represents the c-phase control component. Then the following formula holds:

[0100]

[0101]

[0102]

[0103] The a-phase compensation current reference value, the b-phase compensation current reference value and the c-phase compensation current reference value are calculated by formulas (1) and (3).

[0104] In some embodiments, the distribution transformer three-phase unbalance management system further includes a quasi-proportional resonance (PR) controller.

[0105] Reference Figure 4 In some embodiments, step S500 includes but is not limited to steps S510 to S520:

[0106] Step S510, subtracting the a-phase compensation current reference value from the current a-phase compensation current to obtain an a-phase current difference value, subtracting the b-phase compensation current reference value from the current b-phase compensation current to obtain a b-phase current difference value, and subtracting the c-phase compensation current reference value from the current c-phase compensation current to obtain a c-phase current difference value;

[0107] Step S520, inputting the a-phase current difference, the b-phase current difference and the c-phase current difference into the quasi-PR controller to obtain the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage.

[0108] Specifically, in this embodiment, the compensation current reference value of each phase is calculated one by one with the compensation current of each phase to obtain the current difference of each phase. The current difference of each phase is input into the PR controller for quasi-PR control processing to obtain the corresponding modulation voltage. The quasi-PR controller consists of a proportional link and a resonant link, which can realize zero-static error control of the sinusoidal quantity, suppress the harmonics generated by the distribution network, and help improve the stability and reliability of the compensation current provided subsequently. The modulation voltage is used to control the conduction state of each transistor in the three-phase full-bridge inverter, thereby outputting the corresponding current. Therefore, the current value output by the three-phase full-bridge inverter can be controlled by the difference between the three-phase reference current and the three-phase compensation current, and the compensation current of the three-phase line can be adjusted to achieve high accuracy of the three-phase current compensation.

[0109] Reference Figure 5In some embodiments, step S600 includes but is not limited to steps S610 to S630:

[0110] Step S610, performing SPWM modulation on the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage to obtain a switching signal of a three-phase full-bridge inverter;

[0111] Step S620, controlling the three-phase full-bridge inverter to output the a-phase output current, the b-phase output current and the c-phase output current to the reactor through the inverter a-phase output terminal, the inverter b-phase output terminal and the inverter c-phase output terminal according to the switching signal;

[0112] In step S630, the reactor outputs corresponding a-phase compensation current, b-phase compensation current and c-phase compensation current to the a-phase line, b-phase line and c-phase line respectively according to the a-phase output current, b-phase output current and c-phase output current to perform three-phase unbalance control.

[0113] Reference Figure 6 In this embodiment, the modulation voltage of each phase is processed by sinusoidal pulse width modulation (SPWM), and a switching signal of the three-phase full-bridge inverter can be obtained. The switching signal can control the output current of the three-phase full-bridge inverter. For example, the switching signal can control the conduction state of each transistor in the three-phase full-bridge inverter, and then control the output current of the three-phase full-bridge inverter. Therefore, the three-phase full-bridge inverter is controlled according to the switching signal obtained based on SPWM modulation.

[0114] Reference Figure 7 In some embodiments, the method for treating three-phase imbalance in a distribution network according to an embodiment of the present invention further includes steps S700 to S900:

[0115] Step S700, obtaining the current unbalance degree, where the current unbalance degree is obtained by the current a-phase load current, b-phase load current and c-phase load current;

[0116] Step S800, obtaining a three-phase imbalance variation range according to the initial imbalance and the current imbalance;

[0117] Step S900, when the change amplitude of the three-phase imbalance exceeds the preset offset value, the output a-phase compensation current, b-phase compensation current and c-phase compensation current are updated according to the current a-phase load current, b-phase load current, c-phase load current, a-phase capacitor voltage control component, b-phase capacitor voltage control component and c-phase capacitor voltage control component to perform three-phase imbalance control.

[0118] Specifically, the preset offset value is between 1% and 5%. When the change in the three-phase imbalance exceeds the preset offset value, it indicates that the output compensation current needs to be updated according to the current three-phase imbalance situation to achieve more accurate three-phase imbalance control.

[0119] Please refer to Figures 8 to 10 ,in, Figure 8 is a waveform diagram of three-phase unbalanced current on the load side in one embodiment, Fig. 9 is a current waveform diagram output by a three-phase full-bridge inverter in one embodiment, Fig.10 The current waveform diagram is a current waveform diagram of a target current adjusted by the method for treating three-phase imbalance in a power distribution network of the present invention in one embodiment.

[0120] Depend on Figure 8 It can be calculated that the current imbalance of the three-phase initial current is 66.6%, which is obtained from Fig.10 The current imbalance of the target current can be calculated to be 1.24%. Therefore, the method for treating the three-phase imbalance of the distribution network proposed in the embodiment of the present invention can completely achieve the three-phase balance of the current, and solve the problem of three-phase imbalance of the three-phase current in the prior art.

[0121] The embodiment of the present invention further provides an operation control device, comprising:

[0122] at least one memory;

[0123] at least one processor;

[0124] at least one program;

[0125] The program is stored in the memory, and the processor executes at least one program to implement the above-mentioned method for controlling the three-phase imbalance of the distribution network in the present disclosure. The operation control device can be any intelligent terminal including a mobile phone, a tablet computer, a personal digital assistant (PDA), a car computer, etc.

[0126] Combine the following Fig.11 The operation control device of an embodiment of the present application is introduced in detail.

[0127] like Fig.11 , Fig.11 The hardware structure of the operation control device of another embodiment is illustrated, and the operation control device includes:

[0128] The processor 1210 may be implemented by a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated systems, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of the present disclosure;

[0129] The memory 1220 can be implemented in the form of a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 1220 can store an operating system and other application programs. When the technical solution provided in the embodiment of this specification is implemented by software or firmware, the relevant program code is stored in the memory 1220, and the processor 1210 calls and executes the method for controlling the three-phase imbalance of the distribution network in the embodiment of the present disclosure;

[0130] Input / output interface 1230, used to implement information input and output;

[0131] The communication interface 1240 is used to realize the communication interaction between the device and other devices. The communication can be realized through a wired manner (such as USB, network cable, etc.) or a wireless manner (such as mobile network, WIFI, Bluetooth, etc.);

[0132] The bus 1250 transmits information between the various components of the device (e.g., the processor 1210, the memory 1220, the input / output interface 1230, and the communication interface 1240);

[0133] The processor 1210 , the memory 1220 , the input / output interface 1230 , and the communication interface 1240 are connected to each other in communication within the device via a bus 1250 .

[0134] The embodiment of the present disclosure also provides a computer-readable storage medium, which stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the above-mentioned method for controlling three-phase imbalance in the distribution network.

[0135] The memory, as a non-transient computer-readable storage medium, can be used to store non-transient software programs and non-transient computer executable programs. In addition, the memory may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory may optionally include a memory remotely disposed relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0136] The embodiments described in the embodiments of the present disclosure are intended to more clearly illustrate the technical solutions of the embodiments of the present disclosure and do not constitute a limitation on the technical solutions provided by the embodiments of the present disclosure. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present disclosure are also applicable to similar technical problems.

[0137] Those skilled in the art will appreciate that the technical solutions shown in the figures do not limit the embodiments of the present disclosure and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

[0138] The device embodiments described above are merely illustrative, and the units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0139] Those skilled in the art will appreciate that all or some of the steps in the methods disclosed above, and the functional modules / units in the systems and devices may be implemented as software, firmware, hardware, or a suitable combination thereof.

[0140] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0141] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0142] In the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0143] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0144] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0145] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including multiple instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of each embodiment method of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store programs.

[0146] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for treating three-phase imbalance in a distribution network, applied to a three-phase imbalance treatment system for a distribution transformer, wherein the three-phase imbalance treatment system for a distribution transformer is applied to a power system, wherein the power system comprises a distribution transformer and a phase a line, a phase b line, a phase c line and a neutral line n connected to a low-voltage side of the distribution transformer; It is characterized in that The three-phase unbalance management system of the distribution transformer comprises: A single-phase bridge rectifier, comprising a rectifier input terminal, a positive rectifier output terminal and a negative rectifier output terminal, wherein the rectifier input terminal is connected to any two of the a-phase line, the b-phase line and the c-phase line; A three-phase full-bridge inverter, comprising a positive inverter input terminal, a negative inverter input terminal and an inverter output terminal, wherein the positive inverter input terminal is connected to the positive rectifier output terminal, the negative inverter input terminal is connected to the negative rectifier output terminal, and the inverter output terminal is respectively connected to the a-phase line, the b-phase line and the c-phase line through a reactor; the three-phase full-bridge inverter is used to output corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line through the reactor, so as to perform three-phase unbalance treatment; A first filter capacitor connected to the positive inverter input terminal and the positive rectifier output terminal; A second filter capacitor is connected in series with the first filter capacitor, and the second filter capacitor is connected to the negative inverter input terminal and the negative rectifier output terminal, and the neutral line n is connected between the first filter capacitor and the second filter capacitor; The method for treating three-phase imbalance in a distribution network comprises: Obtaining an initial unbalance degree according to the a-phase load current of the a-phase line, the b-phase load current of the b-phase line, and the c-phase load current of the c-phase line; When the initial unbalance degree is greater than a preset starting value, the a-phase load current, the b-phase load current and the c-phase load current are subjected to sequence component decomposition processing to obtain corresponding a-phase negative-sequence current, b-phase negative-sequence current and c-phase negative-sequence current, as well as a-phase zero-sequence current, b-phase zero-sequence current and c-phase zero-sequence current; The a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component are calculated according to the voltage between the positive and negative ends of the first filter capacitor and the second filter capacitor after being connected in series and a preset reference voltage; According to the a-phase negative-sequence current, the a-phase zero-sequence current and the a-phase capacitor voltage control component, a reference value of the a-phase compensation current is obtained; according to the b-phase negative-sequence current, the b-phase zero-sequence current and the b-phase capacitor voltage control component, a reference value of the b-phase compensation current is obtained; according to the c-phase negative-sequence current, the c-phase zero-sequence current and the c-phase capacitor voltage control component, a reference value of the c-phase compensation current is obtained; Obtaining an a-phase modulation voltage according to the a-phase compensation current reference value and the currently output a-phase compensation current, obtaining a b-phase modulation voltage according to the b-phase compensation current reference value and the currently output b-phase compensation current, and obtaining a c-phase modulation voltage according to the c-phase compensation current reference value and the currently output c-phase compensation current; According to the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage, the corresponding a-phase compensation current, the b-phase compensation current and the c-phase compensation current are output to the a-phase line, the b-phase line and the c-phase line respectively to perform three-phase imbalance control.

2. A method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: The method of calculating the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component according to the voltage between the positive and negative ends of the first filter capacitor and the second filter capacitor connected in series and a preset reference voltage includes: Acquire a filter voltage, where the filter voltage is used to represent a voltage between a positive terminal and a negative terminal of the first filter capacitor and the second filter capacitor connected in series; Calculating the difference between the filtered voltage and a preset voltage reference value to obtain a capacitor voltage difference; Obtaining a D-axis active component required for phase coordinate transformation processing according to the capacitor voltage difference; Phase coordinate transformation processing is performed according to the D-axis active component and the preset Q-axis reactive component to obtain the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component, wherein the Q-axis reactive component is preset to zero.

3. A method for treating three-phase imbalance in a distribution network according to claim 2, characterized in that: The three-phase unbalanced distribution transformer treatment system further includes a PI controller, and the D-axis active component required for phase coordinate transformation processing is obtained according to the capacitor voltage difference, including: The capacitor voltage difference is input into the PI controller to obtain the D-axis active component required for phase coordinate transformation processing.

4. A method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: The a-phase compensation current reference value is obtained according to the a-phase negative-sequence current, the a-phase zero-sequence current and the a-phase capacitor voltage control component, the b-phase compensation current reference value is obtained according to the b-phase negative-sequence current, the b-phase zero-sequence current and the b-phase capacitor voltage control component, and the c-phase compensation current reference value is obtained according to the c-phase negative-sequence current, the c-phase zero-sequence current and the c-phase capacitor voltage control component, following the following formula: Among them, I a_ref Indicates the a-phase compensation current reference value, I b_ref Indicates the b-phase compensation current reference value, I c_ref represents the c-phase compensation current reference value; represents the negative sequence current of phase a, represents the b-phase negative sequence current, I represents the negative sequence current of phase c; a * represents the a-phase capacitor voltage control component, I b * represents the b-phase capacitor voltage control component, I c * represents the c-phase capacitor voltage control component, represents the a-phase zero-sequence current, The b-phase zero-sequence current, The c-phase zero-sequence current.

5. The method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: The distribution transformer three-phase unbalance management system also includes a quasi-PR controller; The method of obtaining the a-phase modulation voltage according to the a-phase compensation current reference value and the currently output a-phase compensation current, obtaining the b-phase modulation voltage according to the b-phase compensation current reference value and the currently output b-phase compensation current, and obtaining the c-phase modulation voltage according to the c-phase compensation current reference value and the currently output c-phase compensation current comprises: Subtract the a-phase compensation current reference value from the current a-phase compensation current to obtain an a-phase current difference value, subtract the b-phase compensation current reference value from the current b-phase compensation current to obtain a b-phase current difference value, and subtract the c-phase compensation current reference value from the current c-phase compensation current to obtain a c-phase current difference value; The a-phase current difference, the b-phase current difference and the c-phase current difference are input into the quasi-PR controller to obtain the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage.

6. A method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: Also includes: Obtaining a current unbalance degree, wherein the current unbalance degree is obtained by the current a-phase load current, the b-phase load current, and the c-phase load current; Obtaining a three-phase imbalance variation amplitude according to the initial imbalance and the current imbalance; When the change amplitude of the three-phase imbalance exceeds the preset offset value, the output a-phase compensation current, b-phase compensation current and c-phase compensation current are updated according to the current a-phase load current, b-phase load current, c-phase load current, a-phase capacitor voltage control component, b-phase capacitor voltage control component and c-phase capacitor voltage control component to perform three-phase imbalance control.

7. A method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: Also includes: The three-phase full-bridge inverter is controlled to obtain the a-phase load current, the b-phase load current and the c-phase load current.

8. The method for treating three-phase imbalance in a distribution network according to claim 1, characterized in that: The inverter output end of the three-phase full-bridge inverter includes an inverter a-phase output end, an inverter b-phase output end and an inverter c-phase output end. The inverter a-phase output end is connected to the a-phase line through the inductor, the inverter b-phase output end is connected to the b-phase line through the inductor, and the inverter c-phase output end is connected to the c-phase line through the inductor.

9. A method for treating three-phase imbalance in a distribution network according to claim 8, characterized in that: The method outputs the corresponding a-phase compensation current, the b-phase compensation current and the c-phase compensation current to the a-phase line, the b-phase line and the c-phase line respectively according to the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage to perform three-phase unbalance treatment, and further includes: Performing SPWM modulation on the a-phase modulation voltage, the b-phase modulation voltage and the c-phase modulation voltage to obtain a switching signal of the three-phase full-bridge inverter; The three-phase full-bridge inverter is controlled to output a-phase output current, b-phase output current and c-phase output current to the reactor through the inverter a-phase output terminal, the inverter b-phase output terminal and the inverter c-phase output terminal according to the switching signal; the reactor outputs the corresponding a-phase compensation current, b-phase compensation current and c-phase compensation current to the a-phase line, the b-phase line and the c-phase line according to the a-phase output current, the b-phase output current and the c-phase output current, so as to perform three-phase imbalance control.

10. A three-phase unbalanced management system for a distribution transformer, applied to a power system, the power system comprising a distribution transformer and a phase line a, a phase line b, a phase line c and a neutral line n connected to the low-voltage side of the distribution transformer; It is characterized in that The distribution transformer three-phase unbalance control system is used to execute a distribution network three-phase unbalance control method as claimed in any one of claims 1 to 9; The three-phase unbalance management system of the distribution transformer comprises: A single-phase bridge rectifier is provided with a rectifier input terminal, a positive rectifier output terminal and a negative rectifier output terminal, wherein the rectifier input terminal is connected to any two of the a-phase line, the b-phase line and the c-phase line; A three-phase full-bridge inverter is provided with a positive inverter input terminal, a negative inverter input terminal and an inverter output terminal, wherein the positive inverter input terminal is connected to the positive rectifier output terminal, the negative inverter input terminal is connected to the negative rectifier output terminal, and the inverter output terminal is respectively connected to the a-phase line, the b-phase line and the c-phase line through a reactor; the three-phase full-bridge inverter is used to output corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line respectively through the reactor to perform three-phase unbalance treatment; A first filter capacitor connected to the positive inverter input terminal and the positive rectifier output terminal; A second filter capacitor is connected in series with the first filter capacitor, and the second filter capacitor is connected to the negative inverter input terminal and the negative rectifier output terminal, and the neutral line n is connected between the first filter capacitor and the second filter capacitor.

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