A micro-grid harmonic isolation device control system

Abstract

The application discloses a kind of micro-grid harmonic isolation device control systems, belong to harmonic control technical field.It includes: primary side voltage / current fundamental and harmonic separation module, secondary side reference voltage calculation module, secondary side fundamental leakage reactance identification module and PWM generator module.Primary side voltage / current fundamental and harmonic separation module is used to separate the fundamental, harmonic component of transformer primary side voltage and current.Secondary side reference voltage calculation module is used to calculate transformer secondary side voltage.Secondary side fundamental leakage reactance identification module is used to identify transformer secondary side fundamental leakage reactance.PWM generator module generates PWM signal according to secondary side reference voltage to drive single-phase inverter module.The application makes harmonic isolation device present the small impedance characteristic of transformer secondary side leakage reactance to fundamental, and present the large impedance characteristic of 2n times fundamental excitation impedance to harmonic, so as to force harmonic current to flow into passive filter branch, finally realize the isolation of micro-grid to the harmonic generated by harmonic load.

Description

Technical Field

[0001] This invention belongs to the field of harmonic control technology, and more specifically, relates to a control system for a harmonic isolation device applied to a microgrid. Background Technology

[0002] With the widespread integration of new energy power generation, distributed power sources, and power electronic devices into microgrids, power quality issues are becoming increasingly prominent. In particular, the large amount of harmonic current introduced by nonlinear loads and high-power converters can lead to voltage distortion, equipment overheating, relay protection malfunctions, and reduced grid stability, threatening the safe and stable operation of microgrids. Existing control methods for harmonic isolation devices are mainly divided into fundamental current control and harmonic voltage control. For the fundamental current control method, the fundamental equivalent impedance of the harmonic isolation device is the primary leakage reactance of the transformer, and the harmonic equivalent impedance is one times the transformer's excitation impedance. Furthermore, because the secondary side of the transformer needs to follow the fundamental current, the single-phase inverter capacity required for the fundamental current control method is relatively large. For the harmonic voltage control method, the fundamental equivalent impedance of the harmonic isolation device is the sum of the primary and secondary leakage reactances of the transformer, and the harmonic equivalent impedance is 2n times the fundamental excitation impedance of the transformer. Because the secondary side of the transformer needs to follow the fundamental current, the single-phase inverter capacity required for the harmonic voltage control method is relatively small. Summary of the Invention

[0003] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a microgrid harmonic isolation device control system, which aims to solve the power quality problems caused by the large-scale connection of new energy power generation, distributed power sources and power electronic devices to the microgrid, especially the phenomenon of voltage distortion, equipment overheating, relay protection malfunction and reduced grid connection stability caused by harmonic currents generated by nonlinear loads and high-power converters.

[0004] To address the above problems, this invention provides a microgrid harmonic isolation device control system, comprising: a primary side voltage / current fundamental and harmonic separation module, a secondary side reference voltage calculation module, a secondary side fundamental leakage reactance identification module, and a PWM generator module;

[0005] The primary voltage / current fundamental and harmonic separation module is connected to the primary side of the transformer in the harmonic isolation device. It is used to decompose the collected primary voltage and current of the transformer into fundamental and harmonic components.

[0006] The secondary reference voltage calculation module is connected to the output of the primary voltage / current fundamental and harmonic separation module and the secondary fundamental leakage reactance identification module, and is used to calculate the secondary reference voltage.

[0007] The output end of the secondary side fundamental leakage reactance identification module is connected with the secondary side reference voltage calculation module, for identifying the secondary side fundamental leakage reactance of the harmonic isolation transformer, and taking the identified secondary side fundamental leakage reactance as the input of the secondary side reference voltage calculation module;

[0008] The PWM generator module is connected with the output end of the secondary side reference voltage calculation module, and generates a PWM signal to drive the single-phase inverter module in the harmonic isolation device according to the calculated secondary side reference voltage;

[0009] The harmonic isolation device includes a transformer, a bidirectional thyristor module, a PWM filter module, a single-phase inverter module and a passive filter module. The transformer is connected between the power grid and the harmonic load, for isolating harmonics. The bidirectional thyristor module is connected between the transformer and the PWM filter module, for bypassing / putting in the harmonic isolation device. The PWM filter module is connected between the bidirectional thyristor and the single-phase inverter module, for filtering the PWM wave generated by the single-phase inverter module. The single-phase inverter module is connected with the PWM filter module, for controlling the voltage on the secondary side of the transformer. The passive filter is connected between the transformer and the harmonic load, for providing a flow channel for harmonics.

[0010] Preferably, the primary side voltage / current fundamental and harmonic separation module includes a primary side voltage fundamental and harmonic separation module and a primary side current fundamental and harmonic separation module.

[0011] Preferably, the primary side voltage fundamental and harmonic separation module for separating the fundamental and harmonic components of the primary side voltage of the transformer of the harmonic isolation device includes a first delay module, a first multiplexer, a voltage decoupling module, a first second-order generalized integrator module, a fundamental voltage calculator, a harmonic voltage calculation module, a second multiplexer and a harmonic voltage adder.

[0012] The first delay module is used for delaying the collected primary side β axis voltage signal by one quarter of a period, and the calculation formula is

[0013] ;

[0014] The first multiplexer is used for gathering the primary side α axis voltage signal and the primary side β axis voltage signal.

[0015] The voltage decoupling module is used for removing the interference between different harmonic voltages, and realizing the decoupling of each voltage component, and the calculation formula is

[0016] ;

[0017] The first second-order generalized integrator module is used for extracting the primary side α axis and βFundamental and harmonic signals of shaft voltage;

[0018] Fundamental voltage calculator is used for calculating α Fundamental voltage of shaft, the calculation formula is

[0019] ;

[0020] Harmonic voltage calculation module is used for calculating α Harmonic voltage of shaft, the calculation formula is

[0021] ;

[0022] Second multiplexer is used for gathering each output signal of harmonic voltage calculation module;

[0023] Harmonic voltage adder is used for adding the signal (i.e. harmonic voltage signal) gathered in the second multiplexer, the calculation formula is

[0024] .

[0025] Preferably, the fundamental and harmonic separation module of primary side current is used for separating the fundamental and harmonic components of transformer primary side current of harmonic isolation device, comprising: a second delay module, a third multiplexer, a current decoupling module, a second second-order generalized integrator module, a fundamental current calculator, a harmonic current calculation module, a fourth multiplexer and a harmonic current adder;

[0026] The second delay module is used for delaying the collected primary side β Fundamental and harmonic signals of shaft current for a quarter of a period, the calculation formula is

[0027] ;

[0028] The third multiplexer is used for gathering the primary side α Fundamental and harmonic signals of shaft current and the primary side β Fundamental and harmonic signals of shaft current;

[0029] The current decoupling module is used for removing the interference between different harmonic currents, realizing the decoupling of each current component, the calculation formula is

[0030] ;

[0031] The second second-order generalized integrator module is used for extracting the primary side α Fundamental and harmonic signals of shaft and β Fundamental and harmonic signals of shaft current;

[0032] The fundamental current calculator is used for calculating the primary side

[0033] ;

[0034] The harmonic current calculator is used to calculate the harmonic current, and the calculation formula is

[0035] ;

[0036] The fourth multiplexer is used to aggregate the output signals of the harmonic current calculation modules;

[0037] The harmonic current adder is used to add the signals (i.e. harmonic current signals) aggregated in the second multiplexer, and the calculation formula is

[0038] .

[0039] Preferably, the secondary side reference voltage calculation module is used to calculate the reference voltage on the secondary side of the transformer in the harmonic isolation device according to the separated harmonic voltage, fundamental current and set harmonic control coefficient, and includes a first multiplier, a second multiplier, a first adder and a first divider.

[0040] The first multiplier multiplies the harmonic control coefficient α n -j β n with the separated harmonic voltage on the primary side;

[0041] The second multiplier multiplies the negative number of the secondary side fundamental leakage reactance with the separated fundamental current on the primary side;

[0042] The first adder adds the outputs of the first multiplier and the second multiplier;

[0043] The first divider divides the output of the first adder by the DC bus voltage value to finally obtain the voltage on the secondary side of the harmonic isolation device;

[0044] Preferably, the calculation formula of the reference voltage on the secondary side is

[0045]

[0046] wherein, , .

[0047] Preferably, the fundamental impedance of the harmonic isolation device is

[0048]

[0049] The harmonic impedance of the harmonic isolation device is

[0050]

[0051] Preferably, the secondary side fundamental leakage reactance identification module identifies the secondary side fundamental leakage reactance of the harmonic isolation device transformer before the harmonic isolation device is put into operation. Before the harmonic isolation device is put into operation, the transformer secondary side is short-circuited by the bidirectional thyristor module, and the transformer mathematical model is

[0052]

[0053] According to the transformer mathematical model, a linear model is established as

[0054]

[0055] The linear model is solved by the least square method, and the secondary side fundamental leakage reactance of the harmonic isolation device transformer is

[0056]

[0057] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects:

[0058] 1. The harmonic isolation device control system proposed by the present application combines the advantages of fundamental current control method and harmonic voltage control method, and innovatively realizes the characteristics that the fundamental equivalent impedance is only the leakage reactance of the transformer primary side, and the harmonic equivalent impedance reaches 2n times the fundamental excitation impedance of the transformer. It can effectively improve the harmonic isolation capability of the harmonic isolation device, and the harmonic isolation effect is better than that of a single control method. Since the secondary side does not need to completely follow the fundamental current, the control coefficient is only of the same order of magnitude as the leakage reactance of the transformer secondary side, which greatly reduces the capacity demand of the single-phase inverter, thereby significantly reducing the system cost and loss while ensuring good harmonic suppression capability. Therefore, the system described in the present application has obvious advantages in improving harmonic isolation performance, reducing inverter capacity demand, improving system operation stability and economy, and can better meet the application requirements in complex power environment in microgrid.

[0059] 2. The single-phase inverter required by the present application has small capacity, which can improve the harmonic isolation capability of the harmonic isolation device in the microgrid without significantly increasing the hardware complexity, reduce the cost of the device, and has high practical value. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 A microgrid harmonic isolation device control system overall framework schematic diagram is provided for the embodiments of the present application.

[0061] Figure 2 A primary side voltage / current fundamental and harmonic separation module schematic diagram is provided for the embodiments of the present application.

[0062] Figure 3 A primary side voltage fundamental and harmonic separation module schematic diagram is provided for the embodiments of the present application.

[0063] Figure 4 The schematic diagram of the primary side current fundamental wave and harmonic wave separation module provided for the embodiment of the present application.

[0064] Figure 5 The schematic diagram of the secondary side reference voltage calculation module provided for the embodiment of the present application. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0066] The following explains the concepts related to the present application:

[0067] Two-phase stationary coordinate system: corresponding to the virtual two-phase orthogonal stationary winding, having two coordinate axes intersecting at the origin α axis and β axis, the two coordinate axes are stationary in space and differ by 90 degrees, in the counterclockwise direction, in turn α axis and β axis;

[0068] PWM generator: the PWM generator module in the present application belongs to this category; based on the triangular carrier modulation method, a PWM signal for driving the switching device of the two-level converter is generated. In the present application, the PWM signal is provided for the single-phase inverter module;

[0069] Multiplexer: the first multiplexer, the second multiplexer, the third multiplexer and the fourth multiplexer in the present application all belong to this category; the multiplexer combines inputs with the same data type and complex / real into one signal output;

[0070] Second-order generalized integrator: the first second-order generalized integrator module and the second second-order generalized integrator module in the present application both belong to this category; the second-order generalized integrator module performs a 90-degree phase shift on the input, and its transfer function is:

[0071]

[0072] wherein, is the value of the input signal after filtering; is the input signal; is the damping coefficient; is the resonance frequency; is the Laplace transform symbol, whose value is ; For The value of 90 degrees of hysteresis;

[0073] Multiplier: the first multiplier and the second multiplier in the application belong to this category; the multiplier multiplies the input signal, and the output signal is the product of the input signal;

[0074] Divisor: the first divisor in the application belongs to this category; the divisor divides the input signal, and the output signal is the quotient of the input signal;

[0075] Adder: the first adder in the application belongs to this category; the adder adds the input signal, and the output signal is the sum of the input signal;

[0076] Least square method: a mathematical optimization technique that finds the best function match for a set of data by minimizing the sum of squares of errors; in the application, it is used to solve the linear model constructed by the secondary side fundamental leakage reactance identification module to obtain the transformer secondary side fundamental leakage reactance parameters of the harmonic isolation device;

[0077] The 1 in the lower right corner of the electrical quantity represents the primary side of the harmonic isolation device transformer, and the 2 represents the secondary side of the harmonic isolation device transformer, αβ Indicates two-phase stationary coordinate system; the number in the bracket in the upper right corner represents the harmonic number, "*" represents the reference value, and ' " represents the reduced value.

[0078] The physical meanings involved in the application are as follows:

[0079]

[0080] Embodiment

[0081] As Figure 1 shown, the application provides a micro-grid harmonic isolation device control system, which comprises a primary side voltage / current fundamental and harmonic separation module, a secondary side reference voltage calculation module, a secondary side fundamental leakage reactance identification module and a PWM generator module, and the whole control method comprises the following steps:

[0082] Before the harmonic isolation device is put into operation, the bidirectional thyristor module is short-circuited, the secondary side fundamental leakage reactance identification module identifies the fundamental leakage reactance of the harmonic isolation device transformer secondary side, and the primary side voltage / current fundamental and harmonic separation module separates the fundamental and harmonic components of the collected primary side voltage / current of the harmonic isolation device transformer. After the secondary side reference voltage calculation module receives the identified harmonic isolation device transformer secondary side fundamental leakage reactance, the sum of the primary side fundamental current and the primary side harmonic voltage, the secondary side reference voltage of the harmonic isolation device transformer is output to the PWM generator module. The PWM generator module outputs the PWM wave according to the harmonic isolation device transformer secondary side reference voltage, and drives the single-phase inverter module. The bidirectional thyristor module is open-circuited, and the harmonic isolation device is put into operation.

[0083] The secondary side fundamental leakage reactance identification module identifies the fundamental leakage reactance of the harmonic isolation device transformer secondary side before the harmonic isolation device is put into operation. Before the harmonic isolation device is put into operation, the transformer secondary side is short-circuited by the bidirectional thyristor module, and the transformer mathematical model is

[0084]

[0085] According to the transformer mathematical model, a linear model is established as

[0086]

[0087] The linear model is solved by the least square method, and the harmonic isolation device transformer secondary side fundamental leakage reactance is obtained as

[0088]

[0089] Specifically, as shown in Figure 2 the primary side voltage / current fundamental and harmonic separation module is connected to the harmonic isolation device transformer primary side, and is used to separate the collected transformer primary side voltage and current into fundamental and harmonic components; it includes: a primary side voltage fundamental and harmonic separation module and a primary current fundamental and harmonic separation module;

[0090] Specifically, as shown in Figure 3 the primary side voltage fundamental and harmonic separation module is used to separate the harmonic isolation device transformer primary side voltage fundamental and harmonic components, and includes: a first delay module, a first multiplexer, a voltage decoupling module, a first second-order generalized integrator module, a fundamental voltage calculator, a harmonic voltage calculation module, a second multiplexer and a harmonic voltage adder;

[0091] The first delay module is used to delay the collected primary side voltage signal by one quarter of a period, and obtain the harmonic isolation device transformer primary side β axis voltage, and the calculation formula includes

[0092]

[0093] The first multiplexer is used to aggregate the primary side α axis voltage and the primary side β axis voltage two-way signal.

[0094] The voltage decoupling module is used to remove the interference between different harmonic voltages, realize the decoupling of each voltage component, and its calculation formula includes

[0095]

[0096] The first second-order generalized integrator module is used to extract the primary side α axis and β axis voltage fundamental and harmonic signal.

[0097] The fundamental voltage calculator is used to calculate the primary side voltage fundamental, and its calculation formula includes

[0098]

[0099] The harmonic voltage calculation module is used to calculate the voltage harmonic, and its calculation formula includes

[0100]

[0101] The second multiplexer is used to aggregate the output signals of the harmonic voltage calculation module.

[0102] The harmonic voltage adder is used to add the signals (i.e. harmonic voltage signals) aggregated in the second multiplexer, and its calculation formula includes

[0103]

[0104] Specifically, as shown in Figure 4 The primary side current fundamental and harmonic separation module is used to separate the harmonic isolation device transformer primary side current fundamental and harmonic components, including: a second delay module, a third multiplexer, a current decoupling module, a second second-order generalized integrator module, a fundamental current calculator, a harmonic current calculator, a fourth multiplexer and a harmonic current adder.

[0105] The second delay module is used to delay the collected primary side current signal by one quarter of a period, and obtain the harmonic isolation device transformer primary side β axis current, and its calculation formula includes

[0106]

[0107] The third multiplexer is used to aggregate the primary side α axis current and the primary side β axis current two-way signal.​​​

[0108] The current decoupling module is used to remove interference between different harmonic currents, achieving decoupling of each current component. Its calculation formula includes...

[0109] ;

[0110] The first and second order generalized integrator modules are used to extract the primary side. α shaft and β Axial current fundamental and harmonic signals;

[0111] The fundamental current calculator is used to calculate the fundamental primary current. Its calculation formula includes...

[0112] ;

[0113] The harmonic current calculator is used to calculate current harmonics. Its calculation formula includes...

[0114] ;

[0115] The fourth multiplexer is used to aggregate the output signals of the harmonic current calculation module;

[0116] The harmonic current adder is used to perform addition operations on the signals (i.e., harmonic current signals) concentrated in the second multiplexer. Its calculation formula includes...

[0117] .

[0118] Specifically, such as Figure 5 As shown, the secondary reference voltage calculation module is used to calculate the secondary reference voltage of the transformer in the harmonic isolation device based on the separated harmonic voltage, fundamental current and set control coefficients, and includes a first multiplier, a second multiplier and a first divider.

[0119] The first multiplier will use the harmonic control coefficient α n -j β n Multiply by the first harmonic voltage obtained from the separation;

[0120] The second multiplier multiplies the negative of the secondary side fundamental leakage reactance with the separated primary side fundamental current.

[0121] The first adder adds the outputs of the first multiplier and the second multiplier;

[0122] The first divider divides the output of the first adder by the DC bus voltage value to obtain the secondary voltage of the harmonic isolation device.

[0123] The formula for calculating the secondary reference voltage is as follows:

[0124]

[0125] wherein, , .

[0126] The bidirectional thyristor module is driven open circuit, so that the harmonic isolation device is put into operation. The harmonic isolation device has a fundamental impedance of

[0127]

[0128] The harmonic isolation device has a harmonic impedance of

[0129]

[0130] It is to be understood that the above-described embodiments are merely illustrative of the principles of the application and that numerous modifications, equivalents and improvements can be resorted to by those skilled in the art without departing from the spirit and scope of the application.

Claims

1. A micro-grid harmonic isolation device control system, the harmonic isolation device comprising a transformer, a bidirectional thyristor module, a PWM filter module, a single-phase inverter module and a passive filter module, the transformer being connected between a power grid and a harmonic load for isolating harmonics, the bidirectional thyristor module being connected between the transformer and the PWM filter module for bypassing / throwing in the harmonic isolation device, the PWM filter module being connected between the bidirectional thyristor and the single-phase inverter module for filtering PWM waves generated by the single-phase inverter module, the single-phase inverter module being connected with the PWM filter module for controlling a voltage on a secondary side of the transformer, and the passive filter being connected between the transformer and the harmonic load for providing a flow-through channel for the harmonics; characterized in that, The application relates to a harmonic isolation device and a control method thereof. The harmonic isolation device comprises a primary side voltage / current fundamental wave and harmonic wave separation module, a secondary side reference voltage calculation module, a secondary side fundamental wave leakage resistance identification module and a PWM generator module. The primary side voltage / current fundamental wave and harmonic wave separation module is connected to the primary side of a harmonic isolation device transformer; the secondary side reference voltage calculation module is connected to the output ends of the primary side voltage / current fundamental wave and harmonic wave separation module and the secondary side fundamental wave leakage resistance identification module; and the PWM generator module is connected to the output end of the secondary side reference voltage calculation module. The primary side voltage / current fundamental wave and harmonic wave separation module is used for separating the fundamental wave and harmonic wave components of voltage and current through collected primary side voltage and current signals of the harmonic isolation device transformer; the primary side voltage / current fundamental wave and harmonic wave separation module comprises a primary side voltage fundamental wave and harmonic wave separation module and a primary side current fundamental wave and harmonic wave separation module. The secondary side reference voltage calculation module is used for calculating the transformer secondary side reference voltage in the harmonic isolation device according to the separated fundamental wave and harmonic wave components of the voltage and the current, the secondary side fundamental wave leakage resistance and the set harmonic control coefficient ; , wherein is a direct current parent voltage; and is a harmonic voltage control coefficient of the harmonic isolation device secondary side reference voltage calculation module, and ; is a transformer secondary side voltage reference value of the harmonic isolation device; is a transformer primary side fundamental wave current of the harmonic isolation device; is a transformer primary side harmonic voltage of the harmonic isolation device; is a transformer secondary side leakage resistance reduction value of the harmonic isolation device, ; j represents an imaginary unit; n represents a harmonic number; The secondary side fundamental wave leakage resistance identification module is used for identifying the secondary side fundamental wave leakage resistance of the harmonic isolation device transformer and taking the identified secondary side fundamental wave leakage resistance as the input of the secondary side reference voltage calculation module; and the bidirectional thyristor module is short-circuited before the harmonic isolation device is put into operation. The PWM generator module generates a PWM signal to drive a single-phase inverter module in the harmonic isolation device according to the calculated secondary side reference voltage.

2. The control system of a microgrid harmonic isolation device according to claim 1, wherein, The primary side voltage / current fundamental wave and harmonic wave separation module comprises a primary side voltage fundamental wave and harmonic wave separation module and a primary side current fundamental wave and harmonic wave separation module. The primary side voltage fundamental wave and harmonic wave separation module comprises a first delay module, a first multiplexer, a voltage decoupling module, a first second-order generalized integrator module, a fundamental wave voltage calculator, a harmonic wave voltage calculation module, a second multiplexer and a harmonic wave voltage adder. The first delay module is used for delaying the collected primary side voltage signal by one quarter of a period. The first multiplexer is configured to aggregate primary side α The shaft voltage signal and the primary side β The shaft voltage signal; The voltage decoupling module is used for removing the interference between different harmonic voltages and realizing the decoupling of each voltage component. The first second-order generalized integrator module is configured to extract a primary side α shaft and β shaft voltage fundamental and harmonic signals; The fundamental voltage calculator and the harmonic voltage calculation module calculate the voltage fundamental and the voltage harmonic according to the extracted primary side α axis and β axis voltage fundamental and harmonic signal The second multiplexer is used for gathering the output signals of the harmonic wave voltage calculation module. The harmonic wave voltage adder is used for performing addition operation on the separated voltage harmonics. The primary side current fundamental wave and harmonic wave separation module comprises a second delay module, a third multiplexer, a current decoupling module, a second second-order generalized integrator module, a fundamental wave current calculator, a harmonic wave current calculation module, a fourth multiplexer and a harmonic wave current adder. The second delay module is used for delaying the collected primary side current signal by one quarter of a period. The third multiplexer is used to aggregate primary side α axis current signal and primary side β axis current signal; The current decoupling module is used for removing the interference between different harmonic voltages and realizing the decoupling of each current component. The second second-order generalized integrator module is configured to extract a primary side α axis and β axis current fundamental and harmonic signals; The fundamental current calculator and the harmonic current calculation module calculate the fundamental current and the harmonic current according to the extracted primary side α axis and β The axis current fundamental and harmonic signal calculates the fundamental current and the harmonic current; The fourth multiplexer is used for gathering the output signals of the harmonic wave current calculation module. The harmonic wave current adder is used for performing addition operation on the separated current harmonics.

3. The control system of a microgrid harmonic isolation device according to claim 2, wherein, The secondary side reference voltage calculation module is used for calculating the secondary side reference voltage of the transformer in the harmonic isolation device according to the separated harmonic voltage, the fundamental wave current and the set harmonic control coefficient, and comprises a first multiplier, a second multiplier, a first adder and a first divider. The first multiplier multiplies the harmonic control coefficient α n -j β n with the primary side harmonic voltage obtained by the separation; The second multiplier multiplies the negative of the secondary side fundamental wave leakage resistance with the separated primary side fundamental wave current. The first adder adds the outputs of the first multiplier and the second multiplier; The first divider divides the output of the first adder by the DC bus voltage value, and finally obtains the secondary side voltage of the harmonic isolation device.

4. The control system of a microgrid harmonic isolation device according to claim 1, wherein, The harmonic isolation device has a fundamental impedance of wherein, is the fundamental equivalent impedance of the harmonic isolation device; is the leakage impedance of the primary side of the transformer of the harmonic isolation device; is the leakage impedance of the secondary side of the transformer of the harmonic isolation device; represents the excitation impedance of the transformer of the harmonic isolation device; and is the fundamental current control coefficient of the secondary side reference voltage calculation module of the harmonic isolation device, and j represents an imaginary unit. The harmonic isolation device has a harmonic impedance of wherein, is the harmonic equivalent impedance of the harmonic isolation device; is the leakage impedance of the primary side of the transformer of the harmonic isolation device; is the leakage impedance of the secondary side of the transformer of the harmonic isolation device; represents the excitation impedance of the transformer of the harmonic isolation device; represents the fundamental excitation impedance of the transformer of the harmonic isolation device; and is the harmonic voltage control coefficient of the secondary side reference voltage calculation module of the harmonic isolation device, and ; j represents an imaginary unit; n represents the harmonic order.

5. The control system of a microgrid harmonic isolation device according to claim 1, wherein, The secondary side fundamental leakage impedance identification module identifies the secondary side fundamental leakage impedance of the transformer of the harmonic isolation device before the harmonic isolation device is put into operation. Before the harmonic isolation device is put into operation, the secondary side of the transformer is short-circuited by the bidirectional thyristor module, and the linear model established is wherein, Vthrepresents the harmonic isolation device transformer primary side voltage; Ithrepresents the harmonic isolation device transformer primary side current; Ithrepresents the harmonic isolation device transformer secondary side current; Rthrepresents the harmonic isolation device transformer primary side resistance; Rthrepresents the harmonic isolation device transformer secondary side resistance; Lthrepresents the harmonic isolation device transformer primary side leakage inductance; Lthrepresents the harmonic isolation device transformer secondary side leakage inductance; t t represents time; k Nthrepresents the harmonic isolation device transformer primary to secondary turns ratio; d D represents the differential operator; The least square method is used to solve the linear model established, and the secondary side fundamental leakage impedance of the transformer of the harmonic isolation device is obtained as wherein, represents the fundamental leakage reactance of the transformer secondary side of the harmonic isolation device; represents the resistance of the transformer secondary side of the harmonic isolation device; represents the leakage inductance of the transformer secondary side of the harmonic isolation device; represents the fundamental electrical frequency; k represents the ratio of the number of turns of the primary side to the number of turns of the secondary side of the transformer of the harmonic isolation device; j represents the imaginary unit.

Images