A system and method for inverter phase control and regulating current imbalance

Abstract

The application discloses a system and method for inverter split-phase control and distribution transformer current imbalance regulation, wherein the system comprises a distributed power supply and a three-phase full-bridge inverter; the three-phase full-bridge inverter is connected with the distributed power supply; the three-phase full-bridge inverter is connected with three-phase lines through a three-phase reactor; when the imbalance degree corresponding to the three-phase lines is greater than a preset starting value, a three-phase compensation current reference value is obtained according to the current three-phase front-end load current, the rear-end three-phase load current and the capacitor voltage control component, so that the three-phase full-bridge inverter outputs the three-phase compensation current based on the three-phase compensation current reference value; therefore, the three-phase full-bridge inverter can output the required compensation current of each phase of the three-phase lines by using the output power of the distributed power supply, so as to realize the three-phase current imbalance regulation of the distribution transformer, and balance the three-phase current of the distribution transformer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and in particular to a system and method for inverter phase control and distribution transformer current imbalance adjustment. BACKGROUND

[0002] With the advancement of new power system construction, a large number of single-phase distributed power sources are connected to the distribution area. Due to the randomness and intermittence of the distributed power sources and household single-phase loads and the different power consumption habits of users, the distributed power sources and single-phase loads are not always put into operation and cut off, which makes it difficult to achieve balanced distribution of A, B and C three-phase load currents of the distribution transformer, causes overloading of a certain phase, seriously affects the service life of the distribution transformer, and even burns the distribution transformer. In related technologies, a single-phase APF active filter is used to output a current value equal in size and opposite in direction to the phase current to compensate for the zero sequence current, so as to realize three-phase balance of the distribution network system. However, this method cannot utilize the control resources of the inverter under the condition of a large number of distributed power sources being connected, requires additional equipment and investment, and cannot realize decentralized control, so the power of the distribution area cannot be balanced locally, resulting in large loss.

[0003] Therefore, how to completely realize three-phase balance of the distribution transformer has become a technical problem to be solved by those skilled in the art. SUMMARY

[0004] Therefore, the present application provides an inverter phase control and distribution transformer current imbalance adjustment system and method, which is used to solve the three-phase imbalance problem of the distribution network system in the prior art.

[0005] To achieve one or part or all of the above purposes or other purposes, the first aspect of the present application provides an inverter phase control and distribution transformer current imbalance adjustment system and method, which is applied to a power system. The power system includes a distribution transformer and a-phase line, b-phase line, c-phase line and neutral line n connected to the low-voltage side of the distribution transformer. The inverter phase control and distribution transformer current imbalance adjustment system includes:

[0006] a distributed power source, provided with a positive power output end and a negative power output end;

[0007] The three-phase full-bridge inverter is provided with a positive inverter input end, a negative inverter input end, an inverter a-phase output end, an inverter b-phase output end and an inverter c-phase output end, the positive inverter input end is connected with the positive power output end, the negative inverter input end is connected with the negative power output end, the inverter a-phase output end, the inverter b-phase output end and the inverter c-phase output end are connected with the a-phase line, the b-phase line and the c-phase line through a three-phase reactor respectively; the three-phase full-bridge inverter is used for outputting corresponding compensation currents to the a-phase line, the b-phase line and the c-phase line through the three-phase reactor respectively to perform three-phase imbalance regulation.

[0008] A first filter capacitor is connected with the positive inverter input end and the positive power output end.

[0009] A second filter capacitor is connected in series with the first filter capacitor, and the second filter capacitor is connected with the negative inverter input end and the negative power output end, and the neutral line n is connected between the first filter capacitor and the second filter capacitor.

[0010] Preferably, the distributed power supply adopts a distributed photovoltaic power supply, and the total output power of the distributed photovoltaic power supply meets the required power for realizing three-phase current imbalance treatment.

[0011] Preferably, in the case of load current imbalance of the a-phase line, the b-phase line and the c-phase line, the distributed power supply operates in a maximum power mode, and the three-phase full-bridge inverter outputs compensation currents for each phase based on the load currents of the a-phase line, the b-phase line and the c-phase line respectively to adjust the currents of each phase of the distribution transformer to a balanced state.

[0012] In the case of load current balance of the a-phase line, the b-phase line and the c-phase line, the power output to the a-phase line, the b-phase line and the c-phase line by the three-phase full-bridge inverter is equal, and the total output power of the three-phase full-bridge inverter is equal to the total output power of the distributed photovoltaic power supply.

[0013] In a second aspect, the embodiment of the present application also provides an inverter phase control and distribution transformer current imbalance regulation method, which is applied to the inverter phase control and distribution transformer current imbalance regulation system in the first aspect.

[0014] An initial imbalance degree is obtained according to the a-phase load current of the a-phase line on the low-voltage side of the distribution transformer, the b-phase load current of the b-phase line and the c-phase load current of the c-phase line.

[0015] In the case that the initial unbalance degree reaches a preset starting value, an a-phase front-end load current, a b-phase front-end load current and a c-phase front-end load current of a front-end load side of the three-phase full-bridge inverter are obtained, and an a-phase rear-end load current, a b-phase rear-end load current and a c-phase rear-end load current of a rear-end load side of the three-phase full-bridge inverter are obtained.

[0016] According to the a-phase front-end load current, the b-phase front-end load current, the c-phase front-end load current, the a-phase rear-end load current, the b-phase rear-end load current and the c-phase rear-end load current, sequence component decomposition processing is performed to obtain corresponding a-phase negative sequence currents, b-phase negative sequence currents and c-phase negative sequence currents, and a-phase zero sequence currents, b-phase zero sequence currents and c-phase zero sequence currents.

[0017] According to a voltage between both ends of the first filter capacitor and the second filter capacitor in series connection and a preset reference voltage, a-phase capacitor voltage control components, b-phase capacitor voltage control components and c-phase capacitor voltage control components are calculated.

[0018] According to the a-phase negative sequence current, the a-phase zero sequence current and the a-phase capacitor voltage control component, an a-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, a b-phase compensation current reference value is obtained, and according to the c-phase negative sequence current, the c-phase zero sequence current and the c-phase capacitor voltage control component, a c-phase compensation current reference value is obtained.

[0019] The a-phase compensation current, the b-phase compensation current and the c-phase compensation current are respectively output to the a-phase line, the b-phase line and the c-phase line, and the output a-phase compensation current, the b-phase compensation current and the c-phase compensation current are respectively tracked to the a-phase compensation current reference value, the b-phase compensation current reference value and the c-phase compensation current reference value through hysteresis control, so as to regulate unbalanced currents in a phase.

[0020] Preferably, the inverter phase control and distribution current imbalance regulation method of the embodiment of the present application further comprises:

[0021] A current unbalance degree is obtained, and the current unbalance degree is obtained from the current a-phase load current, the current b-phase load current and the current c-phase load current.

[0022] When the current unbalance degree reaches a preset setting value, the output a-phase compensation current, the output b-phase compensation current and the output c-phase compensation current are updated according to the current a-phase load current, the current b-phase load current, the current c-phase load current, the a-phase capacitor voltage control component, the b-phase capacitor voltage control component and the c-phase capacitor voltage control component.

[0023] The sequence component decomposition processing according to the a-phase front-end load current, the b-phase front-end load current, the c-phase front-end load current, the a-phase rear-end load current, the b-phase rear-end load current and the c-phase rear-end load current obtains corresponding a-phase negative sequence current, b-phase negative sequence current and c-phase negative sequence current, and a-phase zero sequence current, b-phase zero sequence current and c-phase zero sequence current, and includes:

[0024] The difference between the a-phase front-end load current and the a-phase rear-end current is obtained as an a-phase current difference value, the difference between the b-phase front-end load current and the b-phase rear-end current is obtained as a b-phase current difference value, and the difference between the c-phase front-end load current and the c-phase rear-end current is obtained as a c-phase current difference value.

[0025] The sequence component decomposition processing on the a-phase current difference value, the b-phase current difference value and the c-phase current difference value obtains corresponding a-phase negative sequence current, b-phase negative sequence current and c-phase negative sequence current, and a-phase zero sequence current, b-phase zero sequence current and c-phase zero sequence current.

[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, which follow the formulas as follows:

[0027]

[0028]

[0029]

[0030] Wherein, I a_ref represents the a-phase compensation current reference value, I b_ref represents the b-phase compensation current reference value, I c_ref represents the c-phase compensation current reference value; represents the a-phase negative sequence current, represents the b-phase negative sequence current, represents the c-phase negative sequence current; I 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 system of inverter split-phase control and distribution current imbalance regulation further comprises a PI controller, and 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 terminals of the series connection of the first filter capacitor and the second filter capacitor and a preset reference voltage, comprising:

[0032] obtaining a filter voltage, the filter voltage being used to represent the voltage between the positive and negative terminals of the series connection of the first filter capacitor and the second filter capacitor;

[0033] obtaining a capacitor voltage difference by subtracting the filter voltage from a preset voltage reference value;

[0034] inputting the capacitor voltage difference into the PI controller to obtain a D-axis active component required for phase coordinate transformation processing;

[0035] performing phase coordinate transformation processing according to the D-axis active component and a 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 be zero.

[0036] Preferably, the system of inverter split-phase control and distribution current imbalance regulation further comprises a hysteresis controller;

[0037] The method further comprises:

[0038] obtaining an a-phase compensation current difference by subtracting the a-phase compensation current reference value from the a-phase compensation current, obtaining a b-phase compensation current difference by subtracting the b-phase compensation current reference value from the b-phase compensation current, and obtaining a c-phase compensation current difference by subtracting the c-phase compensation current reference value from the c-phase compensation current;

[0039] inputting the a-phase compensation current difference, the b-phase compensation current difference and the c-phase compensation current difference into the hysteresis controller to obtain the switching signal of the three-phase full-bridge inverter;

[0040] 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 through the inverter a-phase output end, the inverter b-phase output end and the inverter c-phase output end respectively according to the switching signal;

[0041] the three-phase reactor outputs the 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 output current, the b-phase output current and the c-phase output current to perform three-phase imbalance regulation.

[0042] Preferably, the method for inverter phase control and distribution transformer current imbalance adjustment of the embodiment of the present application further comprises: when the three-phase load of the distribution transformer is balanced, controlling the a-phase output power output by the three-phase full-bridge inverter to the a-phase line, the b-phase output power output by the three-phase full-bridge inverter to the b-phase line, and the c-phase output power output by the three-phase full-bridge inverter to the c-phase line to be equal, and the sum of the a-phase output power, the b-phase output power and the c-phase output power being equal to the total output power of the distributed photovoltaic power supply.

[0043] The embodiment of the present application has the following beneficial effects:

[0044] The system for inverter phase control and distribution transformer current imbalance adjustment of the embodiment of the present application comprises a distributed power supply and a three-phase full-bridge inverter, the three-phase full-bridge inverter is connected with the distributed power supply, and the three-phase full-bridge inverter is connected with three-phase lines through a three-phase reactor. In the case that the unbalance degree corresponding to the three-phase lines is greater than a preset starting value, a three-phase compensation current reference value is obtained according to the current of the front-end three-phase load, the current of the rear-end three-phase load and the capacitor voltage control component, so that the three-phase full-bridge inverter outputs a three-phase compensation current based on the three-phase compensation current reference value. Therefore, in the embodiment of the present application, the three-phase full-bridge inverter can output the compensation current required by each phase of the three-phase lines by using the output power of the distributed power supply, so as to realize the three-phase current imbalance regulation of the distribution transformer, and balance the three-phase current of the distribution transformer.

[0045] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the structure particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0047] In the formula, I is the current of the three-phase load, U is the voltage of the three-phase load, and C is the capacitance of the capacitor.

[0048] Figure 1 is a structural schematic diagram of the system for inverter phase control and distribution transformer current imbalance adjustment provided by the embodiment of the present application;

[0049] Figure 2 is a flowchart of the method for inverter phase control and distribution transformer current imbalance adjustment provided by the embodiment of the present application;

[0050] Figure 3is a specific flowchart of the method for inverter split-phase control and distribution transformer current imbalance regulation provided by the embodiment of the present application;

[0051] Figure 4 is a specific flowchart of the method for inverter split-phase control and distribution transformer current imbalance regulation provided by another embodiment of the present application;

[0052] Figure 5 is a specific flowchart of the method for inverter split-phase control and distribution transformer current imbalance regulation provided by another embodiment of the present application;

[0053] Figure 6 is a flowchart of phase coordinate transformation provided by the embodiment of the present application;

[0054] Figure 7 is a specific flowchart of the method for inverter split-phase control and distribution transformer current imbalance regulation provided by another embodiment of the present application;

[0055] Figure 8 is a three-phase unbalanced current waveform diagram of a back-end load provided by a specific example of the present application;

[0056] Figure 9 is a three-phase unbalanced current waveform diagram of a front-end load provided by a specific example of the present application;

[0057] Figure 10 is an output current waveform diagram of a three-phase full-bridge inverter provided by a specific example of the present application;

[0058] Figure 11 is a current waveform diagram of three-phase lines before current compensation provided by a specific example of the present application;

[0059] Figure 12 is a current waveform diagram of three-phase lines after current compensation provided by a specific example of the present application;

[0060] Figure 13 is a structural schematic diagram of the device for regulating unbalanced current of a distribution transformer provided by the embodiment of the present application. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0062] The embodiment of the present application provides a system and method for inverter phase control and distribution transformer current imbalance regulation.

[0063] For the convenience of understanding, the embodiment of the present application is described in detail below with reference to the drawings.

[0064] Refer to Figure 1 , Figure 1 is a structural schematic diagram of the system for inverter phase control and distribution transformer current imbalance regulation provided by the embodiment of the present application. The system for inverter phase control and distribution transformer current imbalance regulation is applied to a power system, and the power system comprises a distribution transformer and a-phase line, b-phase line, c-phase line and neutral line n connected to the low-voltage side of the distribution transformer, that is, the load side of the power system.

[0065] Specifically, the low-voltage side of the distribution transformer is connected with a front-end load and a rear-end load, and the connection position of the front-end load on the three-phase line is located between the connection position of the distribution transformer on the three-phase line and the connection position of the three-phase reactor 104 on the three-phase line. The connection position of the rear-end load on the three-phase line is located after the connection position of the three-phase reactor 104 on the three-phase line, so that the connection position of the three-phase reactor 104 on the three-phase line is located between the connection positions of the front-end load and the rear-end load on the three-phase line.

[0066] Specifically, the system for inverter phase control and distribution transformer current imbalance regulation provided by the embodiment of the present application comprises a distributed power supply 100, and the distributed power supply 100 is provided with a positive power supply output end and a negative power supply output end. The distributed power supply 100 is used for supplying power to a three-phase full-bridge inverter 103.

[0067] Specifically, the distributed power supply 100 adopts a distributed photovoltaic power supply.

[0068] The three-phase full-bridge inverter 103 is equipped with a positive inverter input terminal, a negative inverter input terminal, an inverter a-phase output terminal, an inverter b-phase output terminal, and an inverter c-phase output terminal. The positive inverter input terminal is connected to the positive power output terminal, and the negative inverter input terminal is connected to the negative power output terminal. The inverter a-phase output terminal, inverter b-phase output terminal, and inverter c-phase output terminal are connected to the a-phase line, b-phase line, and c-phase line respectively through a three-phase reactor 104. The three-phase full-bridge inverter 103 is used to output corresponding compensation currents to the a-phase line, b-phase line, and c-phase line respectively through the three-phase reactor 104 to perform three-phase imbalance adjustment. The three-phase full-bridge inverter 103 is used to calculate and output the compensation current of each phase of the three-phase line to realize three-phase current imbalance control, so that the three-phase currents on the three-phase line reach balance.

[0069] Specifically, the inverter phase control and distribution transformer current imbalance adjustment system provided in this embodiment of the invention further includes a filtering module. The filtering module includes a first filtering capacitor 101 and a second filtering capacitor 102. The first filtering capacitor 101 is connected to the positive inverter input terminal and the positive power supply output terminal. The second filtering capacitor 102 is connected in series with the first filtering capacitor 101 and is connected to the negative inverter input terminal and the negative power supply output terminal. The neutral line n is connected between the first filtering capacitor 101 and the second filtering capacitor 102.

[0070] It should be noted that the three-phase full-bridge inverter 103 can utilize the output power of the distributed power source 100 to output the compensation current required by each phase of the three-phase line, so as to realize the three-phase current imbalance regulation and make the three-phase current on the three-phase line reach balance.

[0071] In one embodiment, when the load current of each phase of the three-phase line is unbalanced, the distributed photovoltaic power supply operates in maximum power mode, and the three-phase full-bridge inverter 103 outputs compensation current for each phase based on the load current of each phase of the three-phase line on the low-voltage side of the distribution transformer, so as to adjust the current of each phase of the three-phase line to a balanced state.

[0072] Specifically, when the three-phase load currents Ia, Ib, and Ic of the distribution transformer are unbalanced, that is, when the load currents of phase a, phase b, and phase c on phase a, phase b, and phase c are unbalanced, the three-phase full-bridge inverter 150 is controlled to output three-phase compensation currents Ioa, Iob, and Ioc to provide power to the unbalanced load, while ensuring that the distributed photovoltaic power source operates in the maximum power generation mode, that is, when the total output power P is at its maximum.

[0073] In one embodiment, when the load current of each phase of the three-phase line is balanced, the power output of the three-phase full-bridge inverter 103 to each phase of the three-phase line is equal, and the total output power of the three-phase full-bridge inverter 103 is equal to the total output power of the distributed photovoltaic power source.

[0074] Specifically, when the three-phase load currents Ia, Ib, and Ic of the distribution transformer are balanced, the three-phase balanced power output of the three-phase full-bridge inverter 103 is controlled to satisfy Pa = Pb = Pc = P / 3.

[0075] This invention achieves the reuse of optimal power generation by the three-phase full-bridge inverter 103 and three-phase imbalance compensation of the distribution transformer. When the three-phase load of the distribution transformer is balanced, the distributed power source 100 can act as a normal power source to supply power to the load, improving the system's economy. When the three-phase of the distribution transformer is unbalanced, and the three-phase imbalance compensation capacity is sufficient, the output of the three-phase inverter can be controlled to balance the three-phase imbalance compensation power and the power generation power, taking into account both the three-phase imbalance regulation of the distribution transformer and the grid connection of photovoltaic power generation; it realizes the phase-by-phase grid connection of distributed photovoltaic and energy storage power generation, governance, distribution, and three-phase balance of the distribution transformer.

[0076] It should be noted that, in the embodiments of the present invention, the capacitance values ​​of the first filter capacitor 101 and the second filter capacitor 102 are selected according to the actual situation, and the inductance value of the three-phase reactor 104 is selected according to the actual situation. This application does not impose specific restrictions on these aspects.

[0077] The inverter phase control and distribution transformer current imbalance regulation system and application scenarios described in the embodiments of the present invention are for the purpose of more clearly illustrating the technical solutions of the embodiments of the present invention, and do not constitute a limitation on the technical solutions provided by the embodiments of the present invention. Those skilled in the art will know that with the evolution of power distribution systems and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present invention are also applicable to similar technical problems.

[0078] It will be understood by those skilled in the art that Figure 1 The inverter phase control and distribution transformer current imbalance regulation system shown in the figure does not constitute a limitation on the embodiments of the present invention. It may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0079] Based on the above-described inverter phase control and distribution transformer current imbalance regulation system, various embodiments of the inverter phase control and distribution transformer current imbalance regulation method of the present invention are proposed.

[0080] Figure 2 This is a flowchart of the method for inverter phase-by-phase control and distribution transformer current imbalance adjustment provided in the embodiments of the present invention. Figure 2 In the example, the method for inverter phase control and distribution transformer current imbalance adjustment includes, but is not limited to, steps S100 to S600:

[0081] Step S100: Obtain the initial unbalance based on the load current of phase a of phase a line, the load current of phase b of phase b line, and the load current of phase c of phase c line on the low-voltage side of the distribution transformer.

[0082] Step S200: When the initial imbalance reaches the preset start-up value, obtain the front-end load current of phase a, phase b and phase c on the front-end load side of the three-phase full-bridge inverter, and the rear-end load current of phase a, phase b and phase c on the rear-end load side of the three-phase full-bridge inverter.

[0083] Step S300: Perform sequence component decomposition processing on the front-end load current of phase a, the front-end load current of phase b, the front-end load current of phase c, the rear-end load current of phase a, the rear-end load current of phase b, and the rear-end load current of phase c to obtain the corresponding negative sequence current of phase a, negative sequence current of phase b, and negative sequence current of phase c, as well as the zero sequence current of phase a, zero sequence current of phase b, and zero sequence current of phase c.

[0084] Step S400: Calculate the phase a capacitor voltage control component, phase b capacitor voltage control component, and phase c capacitor voltage control component based on the voltage between the positive and negative terminals of the first and second filter capacitors connected in series and the preset reference voltage.

[0085] Step S500: Obtain the reference value of the phase a compensation current based on the phase a negative sequence current, phase a zero sequence current and phase a capacitor voltage control component; obtain the reference value of the phase b compensation current based on the phase b negative sequence current, phase b zero sequence current and phase b capacitor voltage control component; obtain the reference value of the phase c compensation current based on the phase c negative sequence current, phase c zero sequence current and phase c capacitor voltage control component.

[0086] In step S600, the corresponding phase a compensation current, phase b compensation current, and phase c compensation current are output to phase a line, phase b line, and phase c line respectively. Hysteresis control is used to make the output phase a compensation current, phase b compensation current, and phase c compensation current track the phase a compensation current reference value, phase b compensation current reference value, and phase c compensation current reference value respectively, so as to regulate the unbalanced current by phase.

[0087] The inverter phase-by-phase control and distribution transformer current imbalance regulation system of this invention, when the imbalance degree corresponding to the three-phase line is greater than the preset start value, can obtain the three-phase compensation current reference value based on the current front-end three-phase load current, the back-end three-phase load current, and the capacitor voltage control component. This reference value is then used by the three-phase full-bridge inverter to output the three-phase compensation current. Therefore, the three-phase full-bridge inverter can utilize the output power of the photovoltaic power supply to output the compensation current required by each phase of the three-phase line, thereby achieving three-phase current imbalance regulation and balancing the three-phase currents on the three-phase line. Thus, this invention can achieve full compensation of the three-phase imbalance current on the load side, reduce the loss of the three-phase line, and improve the power quality of the power distribution system.

[0088] Specifically, in this embodiment, when the initial imbalance reaches the preset starting value, it indicates that the power system has a three-phase imbalance. The initial imbalance degree is obtained based on the load current of phase a of phase a line, the load current of phase b of phase b line, and the load current of phase c of phase c line.

[0089] Specifically, when a three-phase imbalance is detected, a power control signal is output to make the photovoltaic power module operate in the maximum power generation mode, thereby enabling the photovoltaic power module to output maximum power.

[0090] Reference Figure 3 The inverter phase-by-phase control and distribution transformer current imbalance adjustment method of this embodiment of the invention further includes steps S700 to S800:

[0091] Step S700: Obtain the current unbalance, which is obtained from the current a-phase load current, b-phase load current and c-phase load current;

[0092] Step S800: When the current imbalance reaches the preset set value, update the output phase a compensation current, phase b compensation current and phase c compensation current according to the current phase a load current, phase b load current, phase c load current, phase a capacitor voltage control component, phase b capacitor voltage control component and phase c capacitor voltage control component.

[0093] By repeatedly detecting the current imbalance during the adjustment process, the compensation current reference value can be iterated to adapt to the current imbalance, thereby making the adjustment process more precise.

[0094] Specifically, the preset value is 5%.

[0095] Reference Figure 4 Step S300 also includes, but is not limited to, steps S310 and S320:

[0096] Step S310: Calculate the difference between the front-end load current of phase a and the rear-end current of phase a to obtain the phase a current difference value; calculate the difference between the front-end load current of phase b and the rear-end current of phase b to obtain the phase b current difference value; calculate the difference between the front-end load current of phase c and the rear-end current of phase c to obtain the phase c current difference value.

[0097] Step S320: Perform sequence component decomposition on the current difference between phase a, phase b, and phase c to obtain the corresponding negative sequence currents of phase a, phase b, and phase c, as well as the zero sequence currents of phase a, phase b, and phase c.

[0098] Specifically, when the three-phase load of the distribution transformer is unbalanced, the three-phase currents Ia1, Ib1, and Ic1 on the front-end load side and the three-phase currents Ia2, Ib2, and Ic2 on the rear-end load side are detected via remote communication. The differences between Ia1 and Ia2, Ib1 and Ib2, and Ic1 and Ic2 are calculated, and the negative sequence current to be compensated is obtained by decomposing the difference values ​​according to the current sequence components. and zero-sequence current

[0099] In one embodiment, the negative-sequence and zero-sequence currents are superimposed with the capacitor voltage control components Ia*, Ib*, and Ic* to obtain the compensation current reference values ​​Ia_ref, Ib_ref, and Ic_ref; the actual output compensation currents Ioa, Iob, and Ioc are obtained by making the actual compensation current output by the three-phase full-bridge inverter track the compensation current reference values ​​Ia_ref, Ib_ref, and Ic_ref.

[0100] Specifically, the reference value of the phase a compensation current is obtained based on the phase a negative sequence current, phase a zero sequence current, and phase a capacitor voltage control component; the reference value of the phase b compensation current is obtained based on the phase b negative sequence current, phase b zero sequence current, and phase b capacitor voltage control component; and the reference value of the phase c compensation current is obtained based on the phase c negative sequence current, phase c zero sequence current, and phase c capacitor voltage control component, following the formula below:

[0101]

[0102]

[0103]

[0104] Among them, I a_ref I represents the reference value of the phase a compensation current. b_ref I represents the reference value of the phase b compensation current. c_ref This indicates the reference value for the c-phase compensation current; This represents the negative sequence current of phase a. This represents the negative sequence current of phase b. Indicates the negative sequence current of phase c; I a * I represents the phase a capacitor voltage control component. b * I represents the control component of the phase b capacitor voltage. c * This represents the voltage control component of phase c capacitor.

[0105] In one embodiment, the inverter phase control and distribution transformer current imbalance regulation system of the present invention is further provided with a linear controller.

[0106] Specifically, the linear controller uses a proportional-integral (PI) controller to adjust the capacitor voltage difference to obtain the D-axis active component required for phase coordinate transformation.

[0107] Reference Figure 5 Step S400 also includes, but is not limited to, steps S410 to S430:

[0108] Step S410: Obtain the filter voltage. The filter voltage is used to characterize the voltage between the positive and negative terminals of the first and second filter capacitors connected in series.

[0109] Step S420: Calculate the difference between the filtered voltage and the preset voltage reference value to obtain the capacitor voltage difference.

[0110] Step S430: Input the capacitor voltage difference into the PI controller to obtain the D-axis active component required for phase coordinate transformation.

[0111] Step S440: Perform phase coordinate transformation based on the active component of the D-axis and the preset reactive component of the Q-axis 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 reactive component of the Q-axis is preset to zero.

[0112] Reference Figure 6 , Figure 6 This is a schematic flowchart of the phase coordinate transformation provided in an embodiment of the present invention. Specifically, the filter voltage is the voltage difference between the positive and negative terminals of the first and second filter capacitors connected in series, denoted by U. dc The preset voltage reference value is the voltage reference value across the positive and negative terminals of the first and second filter capacitors connected in series, denoted by U. dc_ref The process involves calculating the difference between the filtered voltage and a preset voltage reference value to obtain the reference voltage difference. This reference voltage difference is then input to the PI controller to obtain the active power component parameter. This active power component parameter characterizes the d-axis active power component required for phase coordinate transformation. Next, a dq / abc coordinate transformation is performed based on the active power component parameter and the preset reactive power component parameter to obtain the capacitor voltage control component. The reactive power component parameter characterizes the q-axis reactive power component required for phase coordinate transformation and is set to 0. The capacitor voltage control component is obtained after the dq / abc transformation.

[0113] Specifically, Park's Transformation is used for dq / abc transformation.

[0114] In one embodiment, the inverter phase control and distribution transformer current imbalance regulation system of the present invention is further provided with a hysteresis controller for sending switching signals to the three-phase full-bridge inverter, and the three-phase full-bridge inverter tracks the compensation current reference value according to the switching signals.

[0115] Reference Figure 7 The embodiments of the present invention further include steps S900 to S1200:

[0116] Step S900: Calculate the difference between the reference value of the compensation current of phase a and the compensation current of phase a to obtain the difference value of the compensation current of phase a; calculate the difference between the reference value of the compensation current of phase b and the compensation current of phase b to obtain the difference value of the compensation current of phase b; calculate the difference between the reference value of the compensation current of phase c and the compensation current of phase c to obtain the difference value of the compensation current of phase c.

[0117] Step S1000: Input the compensation current difference values ​​of phase a, phase b, and phase c into the hysteresis controller to obtain the switching signals of the three-phase full-bridge inverter.

[0118] Step S1100: Control the three-phase full-bridge inverter to output phase a current, phase b current and phase c current to the three-phase reactor through the inverter phase a output terminal, inverter phase b output terminal and inverter phase c output terminal respectively according to the switching signal;

[0119] In step S1200, the three-phase 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, so as to perform three-phase imbalance adjustment.

[0120] Specifically, the switching signals of the three-phase full-bridge inverter are obtained by subtracting Ia_ref from Ioa, Ib_ref ​​from Iob, and Ic_ref from Ioc. The difference values ​​are then sent to the hysteresis controller, which outputs the switching signals of the three-phase full-bridge inverter. This allows the actual compensation currents Ioa, Iob, and Ioc to be obtained by tracking the current reference values ​​Ia_ref, Ib_ref, and Ic_ref through hysteresis control.

[0121] In one embodiment, the method for inverter phase control and distribution transformer current imbalance adjustment according to an embodiment of the present invention further includes controlling the a-phase output power, the b-phase output power, and the c-phase output power of the three-phase full-bridge inverter to the a-phase line, the b-phase output power, and the c-phase output power to the c-phase line to be equal when the three-phase load of the distribution transformer is balanced, and the sum of the a-phase output power, the b-phase output power, and the c-phase output power is equal to the total output power of the distributed photovoltaic power source.

[0122] Please refer to Figure 8 to Figure 12 , Figure 8This is a waveform diagram of the three-phase unbalanced current of the back-end load provided in a specific example of the present invention. Figure 9 This is a waveform diagram of the three-phase unbalanced current of the front-end load provided in a specific example of the present invention. Figure 10 This is an output current waveform diagram of a three-phase full-bridge inverter provided in a specific example of the present invention. Figure 11 This is a specific example of the present invention, showing the current waveforms of the three-phase lines before current compensation. Figure 12 This is a current waveform diagram of a three-phase line after current compensation, provided in a specific example of the present invention.

[0123] Depend on Figure 8 to Figure 12 As can be seen, in a specific example of the present invention, when the load current on the three-phase lines is in an unbalanced state, the current imbalance is 37.2%. After adjustment by the above-mentioned inverter phase control and distribution transformer current imbalance adjustment methods, the load current on the three-phase lines is in a balanced state, and the imbalance is 1.8%. Therefore, the technical solution of the embodiment of the present invention can completely achieve the three-phase balance of the distribution transformer.

[0124] This invention also proposes a device for phase-by-phase regulation of unbalanced current in a distribution transformer, comprising:

[0125] At least one memory;

[0126] At least one processor;

[0127] At least one program;

[0128] The program is stored in memory, and the processor executes at least one program to implement the inverter phase control and distribution transformer current imbalance regulation methods described above. The computer device can be any smart terminal, including mobile phones, tablets, personal digital assistants (PDAs), and in-vehicle computers.

[0129] Specifically, refer to Figure 13 The device for phase-by-phase regulation of unbalanced current in a distribution transformer according to an embodiment of the present invention includes:

[0130] The processor 210 can be implemented using a general-purpose central processing unit (CPU), microprocessor, application specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this disclosure.

[0131] The memory 220 can be implemented as a read-only memory (ROM), static storage device, dynamic storage device, or random access memory (RAM). The memory 220 can store the operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 220 and called by the processor 210 to execute the inverter phase control and distribution transformer current imbalance adjustment methods of the embodiments of this disclosure.

[0132] Input / output interface 230 is used to implement information input and output;

[0133] The communication interface 240 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0134] Bus 250 transmits information between various components of the device (e.g., processor 210, memory 220, input / output interface 230, and communication interface 240);

[0135] The processor 210, memory 220, input / output interface 230 and communication interface 240 are connected to each other within the device via bus 250.

[0136] This invention also provides a computer-readable storage medium storing computer-executable instructions for causing a computer to perform the above-described methods for inverter phase control and distribution transformer current imbalance adjustment.

[0137] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0138] The embodiments described in this disclosure are for the purpose of more clearly illustrating the technical solutions of this disclosure and do not constitute a limitation on the technical solutions provided by this disclosure. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by this disclosure are also applicable to similar technical problems.

[0139] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this disclosure, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0140] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0141] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0142] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0143] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0144] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0145] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0146] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0147] If the integrated unit is implemented as 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 this application, in essence, 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. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0148] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for inverter phase-by-phase control and distribution transformer current imbalance adjustment, characterized in that, A system for inverter phase-by-phase control and distribution transformer current imbalance regulation is applied to a power system, which includes a distribution transformer and phase a, phase b, phase c, and neutral n connected to the low-voltage side of the distribution transformer. The inverter phase control and distribution transformer current imbalance regulation system includes: Distributed power supply, equipped with a positive power output terminal and a negative power output terminal; A three-phase full-bridge inverter is provided with a positive inverter input terminal, a negative inverter input terminal, an inverter a-phase output terminal, an inverter b-phase output terminal, and an inverter c-phase output terminal. The positive inverter input terminal is connected to the positive power output terminal, and the negative inverter input terminal is connected to the negative power output terminal. The inverter a-phase output terminal, the inverter b-phase output terminal, and the inverter c-phase output terminal are connected to the a-phase line, the b-phase line, and the c-phase line respectively through a three-phase 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 three-phase reactor to perform three-phase imbalance adjustment. The first filter capacitor is connected to the positive inverter input terminal and the positive power output terminal; The 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 power supply output terminal. The neutral line n is connected between the first filter capacitor and the second filter capacitor. The method includes: The initial unbalance is obtained based on the load current of phase a on the low-voltage side of the distribution transformer, the load current of phase b on the low-voltage side, and the load current of phase c on the low-voltage side. When the initial imbalance reaches the preset start-up value, the front load current of phase a, phase b and phase c on the front load side of the three-phase full-bridge inverter, and the rear load current of phase a, phase b and phase c on the rear load side of the three-phase full-bridge inverter are obtained. Based on the front-end load current of phase a, the front-end load current of phase b, the front-end load current of phase c, the rear-end load current of phase a, the rear-end load current of phase b, and the rear-end load current of phase c, the sequence component decomposition process is performed to obtain the corresponding negative sequence current of phase a, negative sequence current of phase b, and negative sequence current of phase c, as well as the zero sequence current of phase a, zero sequence current of phase b, and zero sequence current of phase c. The phase a capacitor voltage control component, phase b capacitor voltage control component, and phase c capacitor voltage control component are calculated based on the voltage between the positive and negative terminals of the first and second filter capacitors connected in series and the preset reference voltage. The reference value of the phase a compensation current is obtained based on the phase a negative sequence current, the phase a zero sequence current, and the phase a capacitor voltage control component; the reference value of the phase b compensation current is obtained based on the phase b negative sequence current, the phase b zero sequence current, and the phase b capacitor voltage control component; and the reference value of the phase c compensation current is obtained based on the phase c negative sequence current, the phase c zero sequence current, and the phase c capacitor voltage control component. The corresponding a-phase compensation current, b-phase compensation current, and c-phase compensation current are output to the a-phase line, the b-phase line, and the c-phase line, respectively. Hysteresis control is used to make the output a-phase compensation current, b-phase compensation current, and c-phase compensation current track the a-phase compensation current reference value, b-phase compensation current reference value, and c-phase compensation current reference value, respectively, so as to regulate the unbalanced current by phase.

2. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 1, characterized in that, Also includes: The current imbalance is obtained from the current load current of phase a, the load current of phase b, and the load current of phase c. When the current imbalance reaches a preset value, the output of the phase a compensation current, phase b compensation current, and phase c compensation current is updated based on the current phase a load current, phase b load current, phase c load current, phase a capacitor voltage control component, phase b capacitor voltage control component, and phase c capacitor voltage control component.

3. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 1, characterized in that, The step of performing sequence component decomposition processing on the front-end load current of phase a, the front-end load current of phase b, the front-end load current of phase c, the rear-end load current of phase a, the rear-end load current of phase b, and the rear-end load current of phase c to obtain the corresponding negative sequence current of phase a, negative sequence current of phase b, and negative sequence current of phase c, as well as the zero sequence current of phase a, zero sequence current of phase b, and zero sequence current of phase c, includes: The difference between the front-end load current of phase a and the rear-end current of phase a is obtained to get the phase a current difference value. The difference between the front-end load current of phase b and the rear-end current of phase b is obtained to get the phase b current difference value. The difference between the front-end load current of phase c and the rear-end current of phase c is obtained to get the phase c current difference value. The current difference between phase a, phase b, and phase c is decomposed into sequence components to obtain the corresponding negative sequence currents of phase a, phase b, and phase c, as well as the zero sequence currents of phase a, phase b, and phase c.

4. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 1, characterized in that, The reference value of the phase a compensation current is obtained based on the phase a negative sequence current, the phase a zero sequence current, and the phase a capacitor voltage control component; the reference value of the phase b compensation current is obtained based on the phase b negative sequence current, the phase b zero sequence current, and the phase b capacitor voltage control component; and the reference value of the phase c compensation current is obtained based on the phase c negative sequence current, the phase c zero sequence current, and the phase c capacitor voltage control component, following the formula below: I a_ref = + + I a * I b_ref = + + I b * I c_ref = + + I c * in, I a_ref This represents the reference value of the phase a compensation current. I b_ref This represents the reference value for the phase b compensation current. I c_ref This indicates the reference value of the c-phase compensation current; This represents the negative sequence current of phase a. This represents the negative sequence current of phase b. This represents the negative sequence current of phase c; I a * This represents the phase a capacitor voltage control component. I b * This represents the voltage control component of the b-phase capacitor. I c * This represents the voltage control component of the c-phase capacitor. , , Phase a zero-sequence current, phase b zero-sequence current, and phase c zero-sequence current.

5. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 2, characterized in that, The inverter phase-by-phase control and distribution transformer current imbalance regulation system further includes a PI controller. The calculation of the phase a capacitor voltage control component, phase b capacitor voltage control component, and phase c capacitor voltage control component based on the voltage between the positive and negative terminals of the first and second filter capacitors connected in series and a preset reference voltage includes: Obtain the filter voltage, which is used to characterize the voltage between the positive and negative terminals of the first filter capacitor and the second filter capacitor connected in series; The difference between the filtered voltage and the preset voltage reference value is used to obtain the capacitor voltage difference. The capacitor voltage difference is input into the PI controller to obtain the D-axis active component required for phase coordinate transformation. The phase coordinate transformation is performed based on the active component of the D-axis and the preset reactive component of the Q-axis 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 reactive component of the Q-axis is preset to zero.

6. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 1, characterized in that, The inverter phase control and distribution transformer current imbalance regulation system also includes a hysteresis controller; The method further includes: The difference between the reference value of the phase a compensation current and the phase a compensation current is obtained. The difference between the reference value of the phase b compensation current and the phase b compensation current is obtained. The difference between the reference value of the phase c compensation current and the phase c compensation current is obtained. The phase a compensation current difference, the phase b compensation current difference, and the phase c compensation current difference are input into the hysteresis controller to obtain the switching signal of the three-phase full-bridge inverter; The three-phase full-bridge inverter is controlled to output phase a current, phase b current, and phase c current to the three-phase reactor through the inverter phase a output terminal, the inverter phase b output terminal, and the inverter phase c output terminal, respectively, according to the switching signal. The three-phase 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 based on the a-phase output current, the b-phase output current, and the c-phase output current, so as to perform three-phase imbalance adjustment.

7. The method for inverter phase-by-phase control and distribution transformer current imbalance adjustment according to claim 1, characterized in that, Also includes: When the three-phase load of the distribution transformer is balanced, the output power of phase a to phase a, phase b to phase b, and phase c to phase c of the three-phase full-bridge inverter are equal, and the sum of the output power of phase a, phase b, and phase c is equal to the total output power of the distributed photovoltaic power source.

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