Power electronic hybrid distribution transformer and control method thereof

Abstract

The invention discloses a power electronic hybrid distribution transformer and a control method thereof. According to the method, the power electronic hybrid distribution transformer comprises a traditional distribution transformer, a parallel converter, a direct-current bus and a series converter, the alternating-current side of the parallel converter is connected to the low-voltage side of the traditional distribution transformer in parallel, and the direct-current side of the parallel converter is connected with the direct-current bus; the AC side of the series converter is connected in series with the low-voltage side of the traditional distribution transformer, and the DC side is connected with the DC bus.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution transformers, and more particularly, to a power electronic hybrid distribution transformer and a control method thereof. Background Art

[0002] With the construction of new power systems, the connection of a large number of new energy sources to the grid and the access of power electronic equipment, the operating conditions of transformers have changed significantly. For distribution transformers, the access of a high proportion of distributed photovoltaics has caused a series of problems such as bidirectional over-limit of low-voltage side voltage and three-phase imbalance. Based on traditional distribution transformers, hybrid power electronic converters, with the help of control technology, have limited cost increase, taking into account both transient flexible control and steady-state efficient operation. Before pure power electronic transformers are fully mature, hybrid distribution transformers are more suitable for national conditions, and at the same time, they can tap the potential of a large number of existing distribution transformers and help build a new power system. However, the current existing technology has a series of problems such as bidirectional over-limit of low-voltage side voltage and three-phase imbalance. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a power electronic hybrid distribution transformer and a control method thereof.

[0004] According to one aspect of the present invention, a power electronic hybrid distribution transformer is provided, comprising: a conventional distribution transformer, a parallel converter, a DC bus and a series converter, wherein:

[0005] The AC side of the parallel converter is connected in parallel to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus; the AC side of the series converter is connected in series to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus.

[0006] According to another aspect of the present invention, there is provided a series converter control method, comprising:

[0007] Calculate the voltage compensation value in the αβ coordinate system based on the target voltage phase angle and the target voltage value in the dq coordinate system;

[0008] After the voltage compensation value in the αβ coordinate system is calculated by the voltage and current double closed-loop control in the αβ coordinate system, a space vector operation is performed to obtain and process the converter modulation signal;

[0009] The series converter that sends the series converter modulation signal to the power electronic hybrid distribution transformer compensates and regulates the low voltage side voltage of the conventional distribution transformer.

[0010] Optionally, based on the target voltage phase angle and the target voltage value in the dq coordinate system, the voltage compensation value in the αβ coordinate system is calculated, including:

[0011] Performing Park transformation on the target voltage phase angle and the target voltage value in the dq coordinate system to obtain the target voltage value in the αβ coordinate system;

[0012] Perform Clark transformation on the three-phase voltage on the low-voltage side to obtain the measured voltage value in the αβ coordinate system;

[0013] The voltage compensation value in the αβ coordinate system is obtained by subtracting the measured voltage value from the target voltage value.

[0014] According to another aspect of the present invention, a parallel converter control method is provided, comprising:

[0015] The three-phase voltage and three-phase current of the conventional distribution transformer in the power electronic hybrid distribution transformer are detected to obtain the positive sequence fundamental voltage, the positive sequence fundamental current, the negative sequence fundamental voltage and the negative sequence fundamental current;

[0016] Calculate parallel converter control command parameters of parallel converters in a power electronic hybrid distribution transformer based on positive sequence fundamental voltage, positive sequence fundamental current, negative sequence fundamental voltage, and negative sequence fundamental current;

[0017] generating a parallel converter modulation signal according to a parallel converter control command parameter;

[0018] The power electronic hybrid distribution transformer is controlled according to the modulation signal of the parallel converter.

[0019] Optionally, the three-phase voltage and three-phase current of the conventional distribution transformer in the power electronic hybrid distribution transformer are detected to obtain the positive-sequence fundamental voltage, the positive-sequence fundamental current, the negative-sequence fundamental voltage and the negative-sequence fundamental current, including:

[0020] The voltage and current values ​​in the αβ coordinate system are obtained by performing Clark transformation on the three-phase current and three-phase voltage on the low-voltage side of the traditional distribution transformer;

[0021] The voltage and current values ​​in the αβ coordinate system are transformed by positive-sequence and negative-sequence Park transformation to obtain the positive-sequence voltage value, positive-sequence current value, negative-sequence voltage value and negative-sequence current value in the dq coordinate system;

[0022] The positive sequence voltage value, positive sequence current value, negative sequence voltage value and negative sequence current value are filtered through a low pass filter to remove the interference of harmonics, and the positive sequence fundamental voltage, positive sequence fundamental current, negative sequence fundamental voltage and negative sequence fundamental current are obtained. At the same time, the phase angle of the positive sequence and negative sequence voltage is obtained by phase locking the three-phase voltage on the low voltage side, and the phase angle provides the phase reference for Park transformation.

[0023] Optionally, the parallel converter control command parameters include: a DC bus voltage adjustment value, a harmonic current compensation value in an αβ coordinate system, a negative sequence power compensation value in a dq coordinate system, and a positive sequence power adjustment value in a dq coordinate system.

[0024] Optionally, calculating a parallel converter control command parameter of a parallel converter in a power electronic hybrid distribution transformer based on the positive-sequence fundamental voltage, the positive-sequence fundamental current, the negative-sequence fundamental voltage, and the negative-sequence fundamental current includes:

[0025] The measured DC bus voltage of the power electronic hybrid distribution transformer is subtracted from the DC bus voltage target value to obtain a DC bus voltage adjustment value;

[0026] Based on the positive sequence fundamental current and the negative sequence fundamental current in the dq coordinate system, the harmonic current compensation value in the αβ coordinate system is obtained;

[0027] The negative sequence power compensation value in the dq coordinate system is obtained by multiplying the negative sequence fundamental current and the negative sequence fundamental voltage in the dq coordinate system on the d axis and the q axis respectively;

[0028] The positive-sequence fundamental current and the positive-sequence fundamental voltage in the dq coordinate system are multiplied on the d-axis and q-axis respectively to obtain the current positive-sequence power in the dq coordinate system, and the positive-sequence power is subtracted from the target value to obtain the positive-sequence power adjustment value in the dq coordinate system.

[0029] Optionally, obtaining a harmonic current compensation value in an αβ coordinate system based on the positive-sequence fundamental current and the negative-sequence fundamental current in a dq coordinate system includes:

[0030] Perform positive-sequence Park inverse transformation and negative-sequence Clark inverse transformation on the positive-sequence fundamental current and negative-sequence fundamental current in the dq coordinate system, respectively, and then perform Clark inverse transformation to obtain the three-phase positive-sequence fundamental current and the three-phase negative-sequence fundamental current;

[0031] The harmonic current after removing the fundamental current is obtained by subtracting the three-phase positive sequence fundamental current and the three-phase negative sequence fundamental current from the three-phase current on the low voltage side;

[0032] The harmonic current is transformed by Clark transformation to obtain the harmonic current compensation value in the αβ coordinate system.

[0033] Optionally, generating a parallel converter modulation signal according to a parallel converter control command parameter includes:

[0034] The DC bus voltage adjustment value is passed through the PI regulator and then through the Park inverse transformation, and then superimposed with the harmonic current compensation value in the αβ coordinate system, and the current feedforward decoupling control calculation in the αβ coordinate system is performed to obtain the current calculation result;

[0035] After superimposing the positive sequence power adjustment value and the negative sequence power compensation value in the dq coordinate system, the power feedforward decoupling control calculation in the dq coordinate system is performed, the power calculation result is obtained and then the Park inverse transformation is performed to obtain the control algorithm calculation result in the αβ coordinate system;

[0036] The control algorithm calculation result and the current calculation result are superimposed and then space vector operation is performed to obtain the parallel converter modulation signal.

[0037] Optionally, the calculation equation of the power feedforward decoupling control is:

[0038]

[0039] In the formula, e q and e d is the measured value of the positive sequence voltage of the q-axis and d-axis in the dq coordinate system, u sq and u sd is the positive sequence voltage control value of the q-axis and d-axis in the dq coordinate system, k P and k I are the proportional gain and integral gain of the PI controller, s is the complex frequency in the complex frequency domain, ω is the angular frequency of the three-phase power supply, P * and Q * are the positive sequence power target values ​​in the dq coordinate system, P and Q are the positive sequence power measured values ​​in the dq coordinate system, L e =L / e d , Re=R / e d , R is the load equivalent resistance, L is the load equivalent inductance.

[0040] Optionally, the regulation includes: stabilizing the DC bus voltage, compensating for harmonic current on the low-voltage side of a traditional distribution transformer, compensating for three-phase imbalance on the low-voltage side of a traditional distribution transformer, and regulating active and reactive power flows on the low-voltage side of a traditional distribution transformer.

[0041] Therefore, the present invention provides a power electronic hybrid distribution transformer, including: a traditional distribution transformer, a parallel converter, a DC bus and a series converter, wherein the AC side of the parallel converter is connected in parallel to the low-voltage side of the traditional distribution transformer, the AC side of the series converter is connected in series to the low-voltage side of the traditional distribution transformer, and the DC sides of the parallel and series converters are both connected to the DC bus. By connecting the parallel and series converters to the low-voltage side of the traditional distribution transformer, the low-voltage side active / reactive power flow regulation, three-phase unbalance compensation, harmonic current compensation and voltage regulation functions can be realized, and the DC bus between the parallel and series converters can be used to realize the flexible interconnection of different distribution stations, and can also be directly connected to a DC source, a DC load or connected to an AC source and an AC load through a DC / AC interface unit, which greatly improves the flexible operation performance of the distribution transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0043] Figure 1 is a schematic diagram of a power electronic hybrid distribution transformer provided by an exemplary embodiment of the present invention;

[0044] Figure 2 is a flow chart of a series converter control method provided by an exemplary embodiment of the present invention;

[0045] Figure 3 is a flow chart of a method for calculating a control command of a series converter provided by an exemplary embodiment of the present invention;

[0046] Figure 4 is a flow chart of a series converter control strategy provided by an exemplary embodiment of the present invention;

[0047] Figure 5 is a flow chart of a parallel converter control method provided by an exemplary embodiment of the present invention;

[0048] Figure 6 is a flow chart of a detection algorithm for a power electronic hybrid distribution transformer provided by an exemplary embodiment of the present invention;

[0049] Figure 7 is a flow chart of a method for calculating a control command for a parallel converter provided by an exemplary embodiment of the present invention;

[0050] Figure 8 is a flow chart of a parallel converter control strategy provided by an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0051] Below, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described here.

[0052] It should be noted that the relative arrangement of components and steps, the numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

[0053] Those skilled in the art can understand that the terms "first" and "second" in the embodiments of the present invention are only used to distinguish different steps, devices or modules, etc., and neither represent any specific technical meaning nor indicate the necessary logical order between them.

[0054] It should also be understood that, in the embodiments of the present invention, “plurality” may refer to two or more than two, and “at least one” may refer to one, two or more than two.

[0055] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more, unless explicitly limited or otherwise indicated in the context.

[0056] In addition, the term "and / or" in the present invention is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0057] It should also be understood that the description of the various embodiments of the present invention focuses on the differences between the various embodiments, and the same or similar aspects thereof can be referenced to each other, and for the sake of brevity, they will not be described one by one.

[0058] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0059] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0060] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0061] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0062] Figure 1 is a schematic diagram of a power electronic hybrid distribution transformer provided by an exemplary embodiment of the present invention, such as Figure 1 As shown, the power electronic hybrid distribution transformer includes: a traditional distribution transformer, a parallel converter, a DC bus and a series converter, wherein:

[0063] The AC side of the parallel converter is connected in parallel to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus; the AC side of the series converter is connected in series to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus.

[0064] Specifically, Figure 1As shown, the power electronic hybrid distribution transformer includes a traditional distribution transformer, a parallel converter, a DC bus and a series converter; wherein the AC side of the parallel converter is connected in parallel to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus; the AC side of the series converter is connected in series to the low-voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus.

[0065] Traditional distribution transformers are double-winding transformers with a rated voltage of 35kV or 10kV on the high-voltage side and a rated voltage of 0.4kV on the low-voltage side.

[0066] The capacity of the parallel converter and the series converter is not less than 20% of the capacity of the traditional distribution transformer. The converter topology can be selected as a two-level, three-level or matrix converter topology according to the capacity.

[0067] The functions that can be achieved by the parallel converter include stabilizing the DC bus voltage, compensating for the harmonic current on the low-voltage side of the traditional distribution transformer, compensating for the three-phase imbalance on the low-voltage side of the traditional distribution transformer, and regulating the active and reactive power flows on the low-voltage side of the traditional distribution transformer.

[0068] The function that the series converter can achieve is mainly to compensate and adjust the voltage on the low-voltage side of the traditional distribution transformer.

[0069] The rated voltage of the DC bus is 800V. It can be directly connected to the DC source of the photovoltaic power supply and DC loads such as electric vehicle charging piles. It can also be connected to the AC source and AC load through the DC / AC interface unit. In addition, it can also be used to connect the distribution transformer of another substation to achieve flexible interconnection between substations.

[0070] Figure 2 A flow chart of a series converter control method provided by another aspect of the present invention is shown in FIG. Figure 2 As shown, the series converter control method 200 comprises the following steps:

[0071] Step 201: Calculate a voltage compensation value in the αβ coordinate system based on a target voltage phase angle and a target voltage value in the dq coordinate system;

[0072] Step 202: after performing voltage and current dual closed-loop control calculation on the voltage compensation value in the αβ coordinate system, perform space vector operation to obtain and process the converter modulation signal;

[0073] Step 203: Send the series converter modulation signal to the series converter of the power electronic hybrid distribution transformer to compensate and adjust the low voltage side voltage of the traditional distribution transformer.

[0074] Specifically, Figure 3It is a flow chart of a method for calculating a control command of a series converter according to a specific implementation of the present invention. The function of the series converter is to compensate and adjust the voltage on the low-voltage side of a traditional distribution transformer. Therefore, the control command to be calculated is the voltage compensation value in the αβ coordinate system.

[0075] The specific process is as follows: Park transform the target voltage phase angle and the target voltage value in the dq coordinate system to obtain the target voltage value in the αβ coordinate system, and Clark transform the three-phase voltage on the low-voltage side to obtain the measured voltage value in the αβ coordinate system, and then subtract the measured voltage value from the target voltage value to obtain the voltage compensation value in the αβ coordinate system.

[0076] Figure 4 It is a flow chart of the control strategy of the series converter according to a specific implementation mode of the present invention. The specific process is as follows:

[0077] After the voltage compensation value in the αβ coordinate system is calculated by the voltage and current double closed-loop control in the αβ coordinate system, the SVPWM (space vector) operation is performed to send a modulation signal to the series inverter.

[0078] Figure 5 A flow chart of a parallel converter control method provided by another aspect of the present invention is shown in FIG. Figure 5 As shown, the parallel converter control method 500 includes the following steps:

[0079] Step 501: Detect the three-phase voltage and three-phase current of a conventional distribution transformer in a power electronic hybrid distribution transformer to obtain a positive-sequence fundamental voltage, a positive-sequence fundamental current, a negative-sequence fundamental voltage, and a negative-sequence fundamental current;

[0080] Step 502: Calculate parallel converter control command parameters of parallel converters in a power electronic hybrid distribution transformer based on the positive-sequence fundamental voltage, the positive-sequence fundamental current, the negative-sequence fundamental voltage, and the negative-sequence fundamental current;

[0081] Step 503: Generate a parallel converter modulation signal according to the parallel converter control command parameter;

[0082] Step 504: regulating the power electronic hybrid distribution transformer according to the parallel converter modulation signal.

[0083] Specifically, Figure 6 It is a flow chart of the detection algorithm of the power electronic hybrid distribution transformer of the specific implementation mode of the present invention. Since the three-phase on the low-voltage side of the distribution transformer is unbalanced and contains harmonics, it is necessary to detect the three-phase voltage and current to obtain the fundamental wave (and the voltage and current at the industrial frequency of 50Hz) of the positive and negative sequence to support the calculation of the control command.

[0084] The detection algorithm process is as follows: the voltage and current values ​​in the αβ coordinate system are obtained by performing Clark transformation on the three-phase current and three-phase voltage on the low-voltage side of the traditional distribution transformer, and the positive-sequence and negative-sequence voltage and current values ​​in the dq coordinate system are obtained by performing positive-sequence and negative-sequence Park transformations. The interference of harmonics is then filtered out through a low-pass filter to obtain the positive-sequence and negative-sequence fundamental voltage and current values. At the same time, the phase angles of the positive-sequence and negative-sequence voltages are obtained by phase-locking the three-phase voltage on the low-voltage side. The phase angles provide a phase reference for the Park transformation.

[0085] Figure 7 It is a flow chart of a method for calculating control commands for a parallel converter according to a specific implementation of the present invention. The functions of the parallel converter include stabilizing the DC bus voltage, compensating for harmonic currents on the low-voltage side of a traditional distribution transformer, compensating for three-phase imbalance on the low-voltage side of a traditional distribution transformer, and regulating active and reactive currents on the low-voltage side of a traditional distribution transformer. Therefore, the control commands to be calculated include a DC bus voltage adjustment value, a harmonic current compensation value in an αβ coordinate system, a negative-sequence power compensation value in a dq coordinate system, and a positive-sequence power adjustment value in a dq coordinate system.

[0086] The DC bus voltage regulation value is obtained by making a difference between the measured DC bus voltage and the target value.

[0087] The calculation process of the harmonic current compensation value in the αβ coordinate system is as follows: perform positive-sequence and negative-sequence Park inverse transformation on the positive-sequence fundamental current and negative-sequence fundamental current in the dq coordinate system respectively, and then perform Clark inverse transformation to obtain the three-phase positive-sequence and negative-sequence fundamental currents, and then subtract them from the three-phase current on the low-voltage side to obtain the harmonic current after removing the fundamental current, and then perform Clark transformation to obtain the harmonic current compensation value in the αβ coordinate system.

[0088] The negative-sequence power compensation value in the dq coordinate system is obtained by multiplying the negative-sequence fundamental current and the negative-sequence fundamental voltage in the dq coordinate system on the d-axis and the q-axis respectively.

[0089] The calculation process of the positive-sequence power regulation value in the dq coordinate system is as follows: multiply the positive-sequence fundamental current and the positive-sequence fundamental voltage in the dq coordinate system on the d-axis and q-axis respectively to obtain the current positive-sequence power in the dq coordinate system, and then obtain it by subtracting it from the target value.

[0090] Figure 8 It is a flow chart of the parallel converter control strategy of a specific implementation mode of the present invention, and the specific process is as follows:

[0091] (1) The DC bus voltage regulation value passes through the PI regulator and then undergoes Park inverse transformation, and is superimposed with the harmonic current compensation value in the αβ coordinate system to perform current feedforward decoupling control calculation in the αβ coordinate system;

[0092] (2) After the positive sequence power adjustment value and the negative sequence power compensation value in the dq coordinate system are superimposed, the power feedforward decoupling control calculation in the dq coordinate system is performed, and the calculation result is then subjected to Park inverse transformation;

[0093] (3) The calculation results of step (2) and step (1) are superimposed and SVPWM (space vector PWM) operation is performed to send a modulation signal to the parallel inverter.

[0094] In the power feedforward decoupling control algorithm, active power and reactive power are controlled by PI controllers. The calculation equation of the control algorithm is as follows:

[0095]

[0096] In the above formula, e q and e d is the measured value of the positive sequence voltage of the q-axis and d-axis in the dq coordinate system, u sq and u sd is the positive sequence voltage control value of the q-axis and d-axis in the dq coordinate system, k P and k I are the proportional gain and integral gain of the PI controller, s is the complex frequency in the complex frequency domain, ω is the angular frequency of the three-phase power supply, P * and Q * are the positive sequence power target values ​​in the dq coordinate system, P and Q are the positive sequence power measured values ​​in the dq coordinate system, L e =L / e d , Re=R / e d , R is the load equivalent resistance, L is the load equivalent inductance.

[0097]

[0098] Through the power feedforward decoupling PI control algorithm in the above formula, the decoupling control of active power and reactive power can be achieved.

[0099] Therefore, the present invention provides a power electronic hybrid distribution transformer, including: a traditional distribution transformer, a parallel converter, a DC bus and a series converter, wherein the AC side of the parallel converter is connected in parallel to the low-voltage side of the traditional distribution transformer, the AC side of the series converter is connected in series to the low-voltage side of the traditional distribution transformer, and the DC sides of the parallel and series converters are both connected to the DC bus. By connecting the parallel and series converters to the low-voltage side of the traditional distribution transformer, the low-voltage side active / reactive power flow regulation, three-phase unbalance compensation, harmonic current compensation and voltage regulation functions can be realized, and the DC bus between the parallel and series converters can be used to realize the flexible interconnection of different distribution stations, and can also be directly connected to a DC source, a DC load or connected to an AC source and an AC load through a DC / AC interface unit, which greatly improves the flexible operation performance of the distribution transformer.

[0100] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. A power electronic hybrid distribution transformer, characterized in that: include: Traditional distribution transformers, shunt converters, DC bus and series converters, among which, The AC side of the parallel converter is connected in parallel to the low voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus; the AC side of the series converter is connected in series to the low voltage side of the traditional distribution transformer, and the DC side is connected to the DC bus.

2. A control method for a series converter of a power electronic hybrid distribution transformer according to claim 1, characterized in that: include: Calculate the voltage compensation value in the αβ coordinate system based on the target voltage phase angle and the target voltage value in the dq coordinate system; After the voltage compensation value in the αβ coordinate system is calculated by the voltage and current double closed-loop control in the αβ coordinate system, a space vector operation is performed to obtain and process the converter modulation signal; The series converter modulation signal is sent to the series converter of the power electronic hybrid distribution transformer to compensate and adjust the low voltage side voltage of the traditional distribution transformer.

3. The method according to claim 2, characterized in that Based on the target voltage phase angle and the target voltage value in the dq coordinate system, the voltage compensation value in the αβ coordinate system is calculated, including: Performing Park transformation on the target voltage phase angle and the target voltage value in the dq coordinate system to obtain the target voltage value in the αβ coordinate system; Perform Clark transformation on the three-phase voltage on the low-voltage side to obtain the measured voltage value in the αβ coordinate system; The measured voltage value is subtracted from the target voltage value to obtain a voltage compensation value in the αβ coordinate system.

4. A parallel converter control method for a power electronic hybrid distribution transformer according to claim 1, characterized in that: include: The three-phase voltage and three-phase current of the conventional distribution transformer in the power electronic hybrid distribution transformer are detected to obtain the positive sequence fundamental voltage, the positive sequence fundamental current, the negative sequence fundamental voltage and the negative sequence fundamental current; Calculate the parallel converter control command parameters of the parallel converters in the power electronic hybrid distribution transformer based on the positive-sequence fundamental voltage, the positive-sequence fundamental current, the negative-sequence fundamental voltage, and the negative-sequence fundamental current; generating a parallel converter modulation signal according to the parallel converter control command parameter; The power electronic hybrid distribution transformer is regulated according to the parallel converter modulation signal.

5. The method according to claim 4, characterized in that The three-phase voltage and three-phase current of the traditional distribution transformer in the power electronic hybrid distribution transformer are detected to obtain the positive sequence fundamental voltage, positive sequence fundamental current, negative sequence fundamental voltage and negative sequence fundamental current, including: The voltage value and current value in the αβ coordinate system are obtained by performing Clark transformation on the three-phase current and three-phase voltage on the low-voltage side of the conventional distribution transformer; The voltage and current values ​​in the αβ coordinate system are transformed by positive-sequence and negative-sequence Park transformation to obtain the positive-sequence voltage value, positive-sequence current value, negative-sequence voltage value and negative-sequence current value in the dq coordinate system; The positive sequence voltage value, positive sequence current value, negative sequence voltage value and negative sequence current value are filtered through a low pass filter to remove the interference of harmonics, and the positive sequence fundamental voltage, positive sequence fundamental current, negative sequence fundamental voltage and negative sequence fundamental current are obtained. At the same time, the phase angle of the positive sequence and negative sequence voltage is obtained by phase locking the three-phase voltage on the low voltage side, and the phase angle provides the phase reference for Park transformation.

6. The method according to claim 4, characterized in that The parallel converter control command parameters include: a DC bus voltage adjustment value, a harmonic current compensation value in an αβ coordinate system, a negative sequence power compensation value in a dq coordinate system, and a positive sequence power adjustment value in a dq coordinate system.

7. The method according to claim 6, characterized in that Calculating the parallel converter control command parameters of the parallel converters in the power electronic hybrid distribution transformer based on the positive-sequence fundamental voltage, the positive-sequence fundamental current, the negative-sequence fundamental voltage, and the negative-sequence fundamental current includes: Subtracting the measured DC bus voltage of the power electronic hybrid distribution transformer from the DC bus voltage target value to obtain the DC bus voltage adjustment value; Based on the positive sequence fundamental current and the negative sequence fundamental current in the dq coordinate system, the harmonic current compensation value in the αβ coordinate system is obtained; The negative sequence power compensation value in the dq coordinate system is obtained by multiplying the negative sequence fundamental current and the negative sequence fundamental voltage in the dq coordinate system on the d axis and the q axis respectively; The positive-sequence fundamental current and the positive-sequence fundamental voltage in the dq coordinate system are multiplied on the d-axis and the q-axis respectively to obtain the current positive-sequence power in the dq coordinate system, and the positive-sequence power is subtracted from the target value to obtain the positive-sequence power adjustment value in the dq coordinate system.

8. The method according to claim 7, characterized in that The harmonic current compensation value in the αβ coordinate system is obtained based on the positive sequence fundamental current and the negative sequence fundamental current in the dq coordinate system, including: Perform positive-sequence Park inverse transformation and negative-sequence Clark inverse transformation on the positive-sequence fundamental current and negative-sequence fundamental current in the dq coordinate system, respectively, and then perform Clark inverse transformation to obtain the three-phase positive-sequence fundamental current and the three-phase negative-sequence fundamental current; Subtracting the three-phase positive-sequence fundamental current and the three-phase negative-sequence fundamental current from the three-phase current on the low-voltage side to obtain a harmonic current after removing the fundamental current; The harmonic current is subjected to Clark transformation to obtain a harmonic current compensation value in an αβ coordinate system.

9. The method according to claim 6, characterized in that Generating a parallel converter modulation signal according to the parallel converter control command parameter includes: The DC bus voltage adjustment value is passed through a PI regulator and then through a Park inverse transformation, and then superimposed with the harmonic current compensation value in the αβ coordinate system, and a current feedforward decoupling control calculation is performed in the αβ coordinate system to obtain a current calculation result; After superimposing the positive sequence power adjustment value and the negative sequence power compensation value in the dq coordinate system, the power feedforward decoupling control calculation in the dq coordinate system is performed, the power calculation result is obtained and then the Park inverse transformation is performed to obtain the control algorithm calculation result in the αβ coordinate system; The control algorithm calculation result and the current calculation result are superimposed and then space vector operation is performed to obtain the parallel converter modulation signal.

10. The method according to claim 9, characterized in that The calculation equation of the power feedforward decoupling control is: In the formula, e q and e d is the measured value of the positive sequence voltage of the q-axis and d-axis in the dq coordinate system, u sq and u sd is the positive sequence voltage control value of the q-axis and d-axis in the dq coordinate system, k P and k I are the proportional gain and integral gain of the PI controller, s is the complex frequency in the complex frequency domain, ω is the angular frequency of the three-phase power supply, P* and Q* are the positive sequence power target values ​​in the dq coordinate system, P and Q are the positive sequence power measured values ​​in the dq coordinate system, L e =L / e d , Re=R / e d , R is the load equivalent resistance, L is the load equivalent inductance.

11. The method according to claim 4, characterized in that The control includes: stabilizing the DC bus voltage, compensating for the harmonic current on the low-voltage side of the traditional distribution transformer, compensating for the three-phase imbalance on the low-voltage side of the traditional distribution transformer, and regulating the active and reactive power flows on the low-voltage side of the traditional distribution transformer.

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