Virtual impedance construction method and high-bandwidth working condition simulation test method and system

Abstract

The invention provides a high-bandwidth working condition simulation test method and system based on virtual impedance control, and the method comprises the steps: building virtual impedance through an electrical impedance model and a digital low-pass filter or a target working condition model; the control bandwidth of the working condition simulation system can be obviously improved under the conditions that a differential operator is not directly used, control parameters are not improved and the stability margin is not sacrificed; meanwhile, the high-bandwidth working condition simulation test system still comprises a closed-loop control structure, so that the voltage stress and the current stress of the converter to be tested can be simulated more accurately. In addition, the simulation converter is adopted to reproduce the voltage and current stress of the converter to be tested; a current-mode / voltage-mode impedance network is adopted to suppress differential-mode current / voltage ripples and differential-mode current / current harmonics; a ripple passive suppression module and a ripple active suppression module are adopted to suppress common-mode current ripples, and the size and the cost of the ripple passive suppression module are reduced.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a method for constructing a virtual impedance, and a high-bandwidth working condition simulation test method and system based on virtual impedance control. Background Art

[0002] With the development of power electronics technology, it is particularly important to conduct comprehensive functional and reliability testing of power electronic converters. Currently, operating condition simulation testing is becoming the mainstream method for testing power electronic converters due to its flexible operating condition programmability and high test efficiency. Generally, operating condition simulation testing simulates the port voltage and current characteristics of the converter under test through a power electronic converter. In order to accurately reproduce the port voltage and current characteristics of the converter under test across the entire frequency band, the control bandwidth of the simulated converter needs to be sufficiently high. Currently, there are various methods to improve the control bandwidth of the simulated converter, but these methods often have the following limitations:

[0003] The control bandwidth is improved by increasing the control parameters; this bandwidth improvement method is simple and effective, but it will also reduce the stability margin of the simulated converter and cause the working condition simulation test system to become unstable.

[0004] Alternatively, the control bandwidth can be increased through the use of higher-order controllers, such as model predictive controllers. This approach can significantly increase the control bandwidth, but such high-order controllers often require significant computational resources and multiple iterations, placing high demands on the controller and hindering universal applicability.

[0005] Furthermore, open-loop control can be used to increase control bandwidth. Open-loop control generally achieves the ultimate control bandwidth, but due to the lack of closed-loop feedback, the accuracy of open-loop control is extremely low, and the control results are greatly affected by model errors, voltage, and current disturbances, which in turn affects test precision and accuracy.

[0006] A search revealed Chinese patent application number CN104716886A, which discloses a virtual synchronous motor control method based on a virtual impedance voltage-source converter. This method simulates virtual impedance by calculating the voltage errors on the d-axis and q-axis. However, this method cannot avoid introducing differential operations when constructing the virtual impedance, nor can it improve the bandwidth based on the established virtual impedance. Summary of the Invention

[0007] In response to one of the defects in the prior art, the purpose of this application is to provide a method for constructing virtual impedance, a high-bandwidth working condition simulation test method and system.

[0008] In a first aspect of the present application, a method for constructing a virtual impedance is provided, comprising any one of the following three methods:

[0009] The first method: simulate the working condition target model Gm Input value, input impedance network model G f and the working condition simulation target model G m The transfer function G of the constructed virtual impedance m / G f , get the virtual impedance;

[0010] The second method: simulate the working condition target model G m The reference value of the output, input impedance network model G f With digital low-pass filter G d The transfer function G of the constructed virtual impedance d / G f , get the virtual impedance; wherein, the low-pass filter G d , whose cut-off frequency is greater than the highest frequency required by the actual control bandwidth, and whose transfer function order is greater than or equal to the electrical impedance network G f The order of

[0011] The third method: simulate the working condition target model G m The reference value of the output, input impedance network model G f Constructed transfer function 1 / G f , get the virtual impedance; in this process, use the electrical impedance network model G f , the working condition simulation target model G m The differential value of the reference value solved algebraically replaces the differential operation on the reference value.

[0012] A second aspect of the present application provides a high-bandwidth working condition simulation test method based on virtual impedance control, comprising:

[0013] Obtaining a virtual impedance, wherein the virtual impedance is a virtual impedance constructed using the method of claim 1;

[0014] Obtain the error between the output value of the target model of the working condition simulation and the reference value;

[0015] Through closed-loop control, the error between the output value of the working condition simulation target model and the reference value is first corrected to obtain a control closed-loop output; based on the control closed-loop output, the error introduced into the virtual impedance is corrected to obtain an output reference given by the simulated converter.

[0016] Optionally, the closed-loop control first corrects an error between an output value of a working condition simulation target model and a reference value to obtain a control closed-loop output; and based on the control closed-loop output, corrects an error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including:

[0017] The reference value is calculated based on the input value of the working condition simulation target model;

[0018] Calculate the difference between the reference value and the corresponding sampled output value;

[0019] Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output;

[0020] According to the input value of the target model of the working condition simulation, the virtual impedance is calculated using the first method;

[0021] Adding the virtual impedance to the closed-loop control output to obtain a control instruction;

[0022] The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

[0023] Optionally, the closed-loop control first corrects an error between an output value of a working condition simulation target model and a reference value to obtain a control closed-loop output; and based on the control closed-loop output, corrects an error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including:

[0024] The reference value is calculated based on the input value of the working condition simulation target model;

[0025] Calculate the difference between the reference value and the corresponding sampled output value;

[0026] Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output;

[0027] According to the reference value, a second method is used to calculate the virtual impedance;

[0028] Adding the control closed-loop output to the virtual impedance to obtain a control instruction;

[0029] The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

[0030] Optionally, the closed-loop control first corrects an error between an output value of a working condition simulation target model and a reference value to obtain a control closed-loop output; and based on the control closed-loop output, corrects an error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including:

[0031] The reference value is calculated based on the input value of the working condition simulation target model;

[0032] Calculate the difference between the reference value and the corresponding sampled output value;

[0033] Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output;

[0034] Calculating a differential value of the reference value based on an input value of the working condition simulation target model and the reference value;

[0035] The virtual impedance is calculated using a third method according to the reference value and the differential value of the reference value;

[0036] Adding the virtual impedance to the closed-loop control output of the closed-loop control to obtain a control instruction;

[0037] The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

[0038] A third aspect of the present application provides a high-bandwidth working condition simulation test system based on virtual impedance control, comprising:

[0039] A simulation converter, used to reproduce the voltage and current stress of the converter to be tested, wherein the AC port of the simulation converter is connected to the electrical impedance network and the DC port of the simulation converter is connected to the DC voltage source;

[0040] An electrical impedance network, for filtering out differential mode harmonics generated by the analog converter and, at the same time, participating in constructing a virtual impedance;

[0041] Sampling module, collects various voltages and currents according to different working conditions;

[0042] A model calculation module, which generates a voltage reference value or a current reference value of the simulated converter according to a working condition simulation target model and data from the sampling module;

[0043] a virtual impedance control module, generating a control instruction for controlling the output of the analog converter with reference to a given value;

[0044] a pulse width modulation module, converting the control instruction generated by the virtual impedance control module into a pulse width control signal of the analog converter;

[0045] Wherein, the virtual impedance control module includes:

[0046] A virtual impedance submodule, which constructs a virtual impedance using the method of claim 1;

[0047] The closed-loop control submodule corrects the error between the output value of the analog converter and the reference value and the error introduced by the virtual impedance submodule, and generates a control instruction.

[0048] Optionally, in the model calculation module, the operating condition simulation target model includes a motor model and a power grid model;

[0049] The current reference value of the motor model is calculated as follows:

[0050]

[0051] i ref is the current reference value; u sample is the voltage sampling value of the AC port of the converter to be tested; L s is the equivalent inductance of the motor rotor; R s is the equivalent resistance of the motor rotor, s is the complex frequency in the Laplace domain;

[0052] The corresponding working condition simulation target model is

[0053] The voltage reference value of the power grid model is calculated as follows:

[0054] u ref =u actual -i sample ·(sL line +R line )

[0055] u ref is the voltage reference value; u actual is the actual voltage of the power grid to be simulated; i sample is the AC bus current sampling value; L line is the line inductance of the power grid to be simulated; R line is the line resistance of the power grid to be simulated, s is the complex frequency in the Laplace domain;

[0056] The corresponding working condition simulation target model is G m =sL line +R line .

[0057] Optionally, the electrical impedance network adopts one of a current-type electrical impedance network and a voltage-type electrical impedance network;

[0058] The current-type electrical impedance network is used to suppress differential-mode current ripple and differential-mode current harmonics, and adopts any of the following electrical impedance network models:

[0059] Electrical impedance network model corresponding to L-type filter

[0060] L f is the inductance value, R f is the equivalent series resistance of the inductor, s is the complex frequency in the Laplace domain;

[0061] or:

[0062] The corresponding electrical impedance network model of the LCL filter

[0063] L g is the inductance value of the grid side, R gis the equivalent series resistance of the grid-side inductor, L c is the inductance value of the converter side, R c is the equivalent series resistance of the converter side inductor, s is the complex frequency in the Laplace domain;

[0064] The voltage-type electrical impedance network is used to suppress differential-mode voltage ripple and differential-mode voltage harmonics, and adopts any of the following electrical impedance models:

[0065] Electrical impedance model corresponding to C-type filter

[0066] or:

[0067] Electrical impedance model corresponding to LC filter

[0068] s is the complex frequency in the Laplace domain, C is the capacitance, and L is the inductance.

[0069] Optionally, the pulse width modulation module adopts SPWM or SVPWM modulation mode;

[0070] The simulated converter is composed of fully controlled or partially controlled power semiconductor devices, and the corresponding topology and circuit structure are selected according to the topology of the converter to be tested; wherein:

[0071] The topology adopts any one of a three-phase two-level topology, a three-phase three-level topology, and a single-phase two-level topology;

[0072] The circuit structure includes a single analog converter, multiple analog converters connected in parallel, and multiple analog converters connected in series.

[0073] Optionally, one or more of the following features are also included:

[0074] - a ripple passive suppression module, which is connected in series between the analog converter and the AC port of the converter to be tested, and is used to passively suppress common-mode current ripple;

[0075] - an active ripple suppression module, which is connected in series between the converter controller to be tested and the pulse width modulation module, and is used to actively suppress common-mode current ripple, thereby reducing the size and cost of the passive ripple suppression module;

[0076] - a temperature control module, connected to the converter to be tested, and used to simulate the environmental thermal stress of the converter to be tested under actual working conditions.

[0077] The method for constructing a virtual impedance provided in this application adopts the technical means of constructing a virtual impedance through an electrical impedance model and a digital low-pass filter or a target operating condition model, which brings the technical effect of significantly improving the control bandwidth of the operating condition simulation system without directly using a differential operator, increasing control parameters, or sacrificing stability margin.

[0078] Other technical effects brought about by the additional features will be further explained in the corresponding embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Other features, objects and advantages of the present application will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0080] Figure 1 is a flow chart of a method for constructing a virtual impedance according to an exemplary embodiment;

[0081] Figure 2 According to an exemplary embodiment, a virtual impedance G is shown. m / G f Flowchart of the high-bandwidth operating condition simulation test method for control;

[0082] Figure 3 According to an exemplary embodiment, a virtual impedance G is shown. d / G f Flowchart of the high-bandwidth operating condition simulation test method for control;

[0083] Figure 4 According to an exemplary embodiment, a virtual impedance 1 / G is shown. ff Flowchart of the high-bandwidth operating condition simulation test method for control;

[0084] Figure 5 Schematic diagram of the structure of a high-bandwidth working condition simulation test system based on virtual impedance control according to an exemplary embodiment.

[0085] In the figure, 1 is the simulation test system, 2 is the simulation converter, 3 is the electrical impedance network, 4 is the passive ripple suppression module, 5 is the temperature control module, 6 is the sampling module, 7 is the model calculation module, 8 is the virtual impedance control module, 9 is the pulse width modulation module, 10 is the active ripple suppression module, 11 is the converter controller to be tested, and 12 is the converter to be tested and its electrical impedance network. DETAILED DESCRIPTION

[0086] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0087] In the current technical field, when increasing and expanding the control bandwidth of analog converters, the stability margin is reduced. Based on the above problems, the embodiments of the present application provide a method for constructing a virtual impedance, a high-bandwidth working condition simulation test method and system to solve the above problems.

[0088] like Figure 1 As shown, in some specific implementations of the present application, a method for constructing a virtual impedance includes any one of the following three methods:

[0089] 1. A method for constructing a virtual impedance, characterized by comprising any one of the following three methods:

[0090] The first method: simulate the working condition target model G m Input value, input impedance network model G f and the working condition simulation target model G m The transfer function G of the constructed virtual impedance m / G f , get the virtual impedance;

[0091] The second method: simulate the working condition target model G m The reference value of the output, input impedance network model G f With digital low-pass filter G d The transfer function G of the constructed virtual impedance d / G f , get the virtual impedance; wherein, the low-pass filter G d , whose cut-off frequency is greater than the highest frequency required by the actual control bandwidth, and whose transfer function order is greater than or equal to the electrical impedance network G f The order of

[0092] The third method is to simulate the target model G m The reference value of the output, input impedance network model G f Constructed transfer function 1 / G f , get the virtual impedance; in this process, use the electrical impedance network model G f , the working condition simulation target model G m The differential value of the reference value solved algebraically replaces the differential operation on the reference value.

[0093] Specifically, such as Figure 5 As shown, the working condition simulation target model G m This is the model of the object to which the converter under test is connected. It represents the voltage and current characteristics of the AC port connected to the converter under test and its electrical impedance network 12, as well as the operating condition simulation test system 1. If the converter under test is an electric drive converter, the target operating condition model is the motor model. If the converter under test is a grid-connected converter, the target operating condition model is the grid model. The electrical impedance network model refers to the impedance model of the portion shown in module 3.

[0094] For example, the target working condition is the power grid, and the digital low-pass filter G is designed. d If the 7th harmonic (350Hz) needs to be simulated at this time, the control bandwidth needs to be greater than 3.5kHz, so the cutoff frequency of the digital low-pass filter needs to be greater than 3.5kHz.

[0095] It's important to note that increasing the control bandwidth by introducing virtual impedance does not require increasing the bandwidth of the closed-loop controller itself. Furthermore, the introduction of virtual impedance does not affect system stability and therefore does not reduce the stability margin. Furthermore, after implementing virtual impedance, there's no need to iterate the controller, so there's no need to increase the controller's control parameters.

[0096] In the above embodiments of the present application, the electrical impedance model and the digital low-pass filter or the target operating condition model are used to construct the virtual impedance, which can avoid the introduction of differential operation when constructing the virtual impedance, thereby avoiding the problems of noise amplification and system instability caused by the differential operation. Unlike the prior art that uses virtual impedance to limit current or improve stability, the present application adds the virtual impedance to the simulation or real device, which can significantly improve the control bandwidth of the operating condition simulation without directly using the differential operator, increasing the control parameters, or sacrificing the stability margin. The various virtual impedance construction methods proposed in the above embodiments are applicable to a variety of different situations and can be selected according to actual needs.

[0097] The purpose of this application is to expand the control bandwidth. When only the virtual impedance part is included, the control bandwidth is the highest. However, the control accuracy at this time is relatively low due to the constraints of the virtual impedance. Therefore, a closed-loop control part is introduced to correct the error introduced by the virtual impedance. In some specific embodiments of this application, a high-bandwidth working condition simulation test method based on virtual impedance control is provided, and the steps are as follows:

[0098] First, a virtual impedance is obtained, where the virtual impedance is the virtual impedance constructed by the method for constructing the virtual impedance in the above embodiment;

[0099] Next, the error between the output value of the target model of the working condition simulation and the reference value is obtained;

[0100] Finally, through closed-loop control, the error between the output value of the working condition simulation target model and the reference value is first corrected to obtain the control closed-loop output; based on the control closed-loop output, the error of the introduced virtual impedance is corrected to obtain the output reference given by the simulated converter.

[0101] The above-mentioned embodiments of the present application can significantly improve the control bandwidth of the working condition simulation test system, expand the range of working conditions that can be actually simulated, and improve the steady-state and transient accuracy of the simulation.

[0102] For three different virtual impedance construction methods, some specific implementations of this application correspond to three impedance-based high-bandwidth working condition simulation test methods. Specifically:

[0103] like Figure 2 As shown, the first high-bandwidth working condition simulation test method can adopt the following steps:

[0104] S101, calculating a reference value based on a model input value, where the model here refers to a target model for a working condition simulation;

[0105] S102, calculating the difference between the reference value and the corresponding sampled output value;

[0106] Specifically, the corresponding sampled value here depends on the specific target model. When the target model is a motor, the sampled value is the output current of the converter under test; when the target model is a power grid, the sampled value is the voltage at the grid connection point. In other words, the sampled value refers to the voltage / current at the common coupling point.

[0107] S103, performing closed-loop control on the result of the difference calculation in S102 to obtain a control closed-loop output;

[0108] S104, according to the working condition simulation target model, using the first virtual impedance construction method described above, to calculate and obtain the virtual impedance;

[0109] S105, adding the virtual impedance of S104 to the closed-loop control output to obtain a control instruction;

[0110] S106: The control instruction is pulse-width modulated and then outputted by the analog converter.

[0111] Specifically, the model input value in S101 simulates the target model G according to the specific working conditions. m The model input of the motor model is the terminal voltage sampling value; the input value of the power grid model is the AC current sampling value.

[0112] The reference value is the control target for the operating condition simulation and depends on the specific target model. For motors, the reference value is current; for grids, the reference value is voltage. Accordingly, the sampled value corresponds to the reference value. If the reference value is current, the sampled value is current; if the reference value is voltage, the sampled value is voltage.

[0113] Specifically, the closed-loop control in S103 may adopt a closed-loop control method such as proportional-integral control and hysteresis control.

[0114] Specifically, in S104, the virtual impedance is in the form of G m / G f , which is the transfer function of the virtual impedance. The output value of the model input value or output value after the transfer function is the obtained virtual impedance value.

[0115] For example, here, taking the target model as the motor model, the impedance network as the inductor model, and the closed-loop control as the PI control, the expressions of S101-S106 under the dq axis are given as follows:

[0116] S101:

[0117]

[0118] S102:

[0119]

[0120] S103:

[0121]

[0122] S104:

[0123]

[0124] S105:

[0125]

[0126] In the above formulas S101-S105, i sd / q_ref are the d / q axis current reference values, L sd / q are the target motor d / q axis equivalent inductance, R sd / q are the target motor d / q axis equivalent resistance, u sd / q are the target motor d / q axis port voltage, w e is the electrical angular velocity, ψ f is the permanent magnet flux, i sd / q_err are the d / q axis current error values, i sd / q_sample are the d / q axis current sampling values, Kp / i are the proportional coefficient and integral coefficient of the PI controller, Lf is the filter inductance value, R f is the equivalent series resistance of the filter inductor, u od / q_VIC / PI They are the d / q axis values ​​output by the virtual impedance / PI controller respectively.

[0127] The above embodiments of the present application make full use of the elements of the analog test system and can construct virtual impedance and avoid differential operations without additional operations / new elements.

[0128] like Figure 3 As shown, the second high-bandwidth working condition simulation test method can adopt the following steps:

[0129] S201, calculating a reference value based on an input value of a working condition simulation target model;

[0130] S202, performing a difference calculation between the reference value and the corresponding sampled output value;

[0131] S203, performing closed-loop control on the result of the difference calculation to obtain a closed-loop control output result;

[0132] S204, calculating and obtaining a virtual impedance using the second method for constructing a virtual impedance in the above embodiment according to the reference value obtained in S201;

[0133] S205, adding the virtual impedance and the closed-loop control output result to obtain a control instruction;

[0134] S206, the control instruction is pulse-width modulated and then outputted by the analog converter.

[0135] Specifically, in S204, the virtual impedance is in the form of G d / G f , which is the transfer function of the virtual impedance. The output value of the model input value after the transfer function is the obtained virtual impedance value.

[0136] For example, here we still take the target model as the motor model, the impedance network as the inductance model, and the closed-loop control as PI control as an example, and give the expressions of S201-S206 under the dq axis as follows:

[0137] S201:

[0138]

[0139] S202:

[0140]

[0141] S203:

[0142]

[0143] S204:

[0144]

[0145] S205:

[0146]

[0147] In the formulas S201-S205, i sd / q_ref are the d / q axis current reference values, L sd / q are the target motor d / q axis equivalent inductance, R sd / q are the target motor d / q axis equivalent resistance, u sd / q are the target motor d / q axis port voltage, w e is the electrical angular velocity; ψ f is the permanent magnet flux, i sd / q_err are the d / q axis current error values, i sd / q_sample are the d / q axis current sampling values, K p / i are the proportional coefficient and integral coefficient of the PI controller, L f is the filter inductance value, R f is the equivalent series resistance of the filter inductor; u od / q_VIC / PI are the d / q axis values ​​output by the virtual impedance / PI controller respectively; a1 / a2 / a3 are the designed digital low-pass filter coefficients, which are purely numerical and have no physical meaning.

[0148] In the above embodiments of the present application, the analog test system does not have elements for directly constructing virtual impedance and cannot directly avoid the differential operation. Therefore, a digital low-pass filter is added according to the actual control bandwidth requirements to avoid the differential operation.

[0149] like Figure 4 As shown, the third high-bandwidth working condition simulation test method can adopt the following steps:

[0150] S301, calculating a reference value based on an input value of a working condition simulation target model;

[0151] S302, performing a difference calculation between the reference value and the corresponding sampled output value;

[0152] S303, performing closed-loop control on the result of the difference calculation to obtain a closed-loop control output result;

[0153] S304, calculating a differential value of the reference value based on the input value of the working condition simulation target model and the reference value;

[0154] Specifically, the differential operation may cause noise in the system and lead to system instability. Therefore, in this embodiment, the differential value of the reference value is solved algebraically to avoid the differential operation.

[0155] S305, using a third method to calculate a virtual impedance based on the reference value and the differential value of the reference value;

[0156] Specifically, the virtual impedance is in the form of 1 / G f , which is the transfer function of the virtual impedance. The output value of the model input value after the transfer function is the obtained virtual impedance value.

[0157] S306, adding the virtual impedance to the closed-loop control output result to obtain a control instruction;

[0158] S307, the control instruction is outputted by the analog converter after being subjected to pulse width modulation.

[0159] For example, here we still take the target model as the motor model, the impedance network as the inductance model, and the closed-loop control as the PI control as an example, and give the expressions of S301-S307 under the dq axis as follows:

[0160] S301:

[0161]

[0162] S302:

[0163]

[0164] S303:

[0165]

[0166] S304:

[0167]

[0168] S305:

[0169]

[0170] S306:

[0171]

[0172] In the above formulas S301-S306, i sd / q_ref are the d / q axis current reference values, L sd / q are the target motor d / q axis equivalent inductance, R sd / q are the target motor d / q axis equivalent resistance, u sd / q are the target motor d / q axis port voltage, w e is the electrical angular velocity, ψ f is the permanent magnet flux, i sd / q_err are the d / q axis current error values, i sd / q_sampleare the d / q axis current sampling values, Kp / i are the proportional coefficient and integral coefficient of the PI controller, L f is the filter inductance value, R f is the equivalent series resistance of the filter inductor, u od / q_VIC / PI They are the d / q axis values ​​output by the virtual impedance / PI controller respectively.

[0173] The above embodiments of the present application make full use of the elements of the analog test system and can construct virtual impedance and avoid differential operations without additional operations / new elements.

[0174] Based on the same technical concept, in some specific implementations of the present application, such as Figure 5 As shown, a high-bandwidth working condition simulation test system 1 based on virtual impedance control includes a simulation converter 2, an electrical impedance network 3, a sampling module 6, a model calculation module 7, a virtual impedance control module 8 and a pulse width modulation module 9.

[0175] The analog converter 2 is used to reproduce the voltage and current stress of the converter to be tested, and its AC port is connected to the electrical impedance network 3, and its DC port is connected to the DC voltage source;

[0176] The electrical impedance network 3 is used to filter out the differential mode harmonics generated by the analog converter 2; at the same time, it participates in constructing the virtual impedance;

[0177] Sampling module 6 collects various voltages and currents according to different working conditions, including: AC voltage and AC current at the common coupling point; port voltage and port current of the converter to be tested; port voltage and port current of the simulated converter; current of the reactor capacitor branch that may be included in the impedance network; DC bus voltage, etc.

[0178] Model calculation module 7, generates a voltage reference value or a current reference value of the simulated converter according to the working condition simulation target model and the data of the sampling module;

[0179] The virtual impedance control module 8 generates a control instruction for controlling the output of the analog converter 2 with reference to a given value;

[0180] The pulse width modulation module 9 converts the control instruction generated by the virtual impedance control module 8 into a pulse width control signal of the analog converter 2;

[0181] The virtual impedance control module 8 includes:

[0182] A virtual impedance submodule, which constructs a virtual impedance using the method of the above embodiment;

[0183] The closed-loop control submodule corrects the error between the analog converter output value and the reference value and the error introduced by the virtual impedance submodule, and generates control instructions.

[0184] The system of the above-mentioned embodiment of the present application uses an electrical impedance model and a digital low-pass filter or a target operating condition model to construct a virtual impedance, which can significantly improve the control bandwidth of the operating condition simulation without directly using a differential operator, increasing the control parameters, or sacrificing the stability margin.

[0185] In order to make the model calculation module feasible, in some specific embodiments of the present application, the operating condition simulation target model that can be calculated by the model calculation module 7 adopts a motor model or a power grid model.

[0186] Among them, the current reference value of the motor model is calculated as follows:

[0187]

[0188] i ref is the current reference value; u sample is the voltage sampling value of the AC port of the converter to be tested; L s is the equivalent inductance of the motor rotor; R s is the equivalent resistance of the motor rotor, s is the complex frequency in the Laplace domain;

[0189] At this time, the target model of the working condition simulation is

[0190] Among them, the voltage reference value of the power grid model is calculated as follows:

[0191] u ref =u actual -i sample ·(sL line +R line )

[0192] u ref is the voltage reference value; u actual is the actual voltage of the power grid to be simulated; i sample is the AC bus current sampling value; L line is the line inductance of the power grid to be simulated; R line is the line resistance of the power grid to be simulated;

[0193] At this time, the target model of the working condition simulation is G m =sL line +R line .

[0194] The operating condition simulation target model of the above-mentioned embodiment of the present application can reproduce the characteristics of the port voltage and current of the converter to be tested.

[0195] The electrical impedance network can be used in various forms to meet different needs. In some specific embodiments of the present application, the electrical impedance network can be used to meet two needs: suppressing differential mode current ripple and differential mode current harmonics and suppressing differential mode voltage ripple and differential mode voltage harmonics.

[0196] Specifically, if differential mode current ripple and differential mode current harmonics need to be suppressed, a current source impedance network should be used.

[0197] Exemplarily, the structure of the current-mode electrical impedance network is:

[0198] L-type filter, at this time, the model of the impedance network

[0199] L f is the inductance value, R f is the equivalent series resistance of the inductor, s is the complex frequency in the Laplace domain;

[0200] or:

[0201] LCL filter, at this time, the model of the impedance network

[0202] L g is the inductance value of the grid side, R g is the equivalent series resistance of the grid-side inductor, L c is the inductance value of the converter side, R c is the equivalent series resistance of the converter side inductor, s is the complex frequency in the Laplace domain;

[0203] Specifically, if differential mode voltage ripple and differential mode voltage harmonics need to be suppressed, a voltage type impedance network should be used.

[0204] Exemplarily, the structure of the voltage-type electrical impedance network is:

[0205] C-type filter, at this time, the model of the impedance network

[0206] or:

[0207] LC type filter, at this time, the model of the impedance network

[0208] s is the complex frequency in the Laplace domain, C is the capacitance value, and L is the inductance value.

[0209] The above-mentioned embodiments of the present application use the above-mentioned voltage-type / current-type electrical impedance network to suppress the high-frequency voltage / current ripple generated by the converter; at the same time, the corresponding electrical impedance network model can be used to construct a virtual impedance.

[0210] Similarly, there are many different ways to control pulse width. In some specific embodiments of the present application, the pulse width modulation module adopts SPWM or SVPWM modulation. Among them, SPWM is simple to implement, and SVPWM has a high DC voltage utilization rate.

[0211] In order to perform closed-loop control and ensure the control effect, in some specific embodiments of the present application, for the closed-loop control module, closed-loop control methods such as proportional-integral control and hysteresis control can be adopted.

[0212] Specifically, proportional-integral control can completely eliminate the steady-state error of the system by accumulating historical errors;

[0213] Hysteresis control can limit the error within the hysteresis band through on-off control.

[0214] The closed-loop control module in the above-mentioned embodiment of the present application can correct the error introduced by the virtual impedance and control the error within an acceptable range.

[0215] In order to ensure the simulation effect, in some specific embodiments of the present application, the simulated converter is composed of fully controlled or half-controlled power semiconductor devices, and the corresponding topology and circuit structure are selected according to the topology of the converter to be tested.

[0216] Exemplarily, the selectable topology is any one of a three-phase two-level topology, a three-phase three-level topology, and a single-phase two-level topology;

[0217] Exemplarily, the selectable circuit structures include a single analog converter, multiple analog converters in parallel, multiple analog converters in series, and the like.

[0218] In order to suppress common-mode current ripple, in some specific embodiments of the present application, a ripple passive suppression module 4 and a ripple active suppression module 10 may be used for the entire test system.

[0219] Specifically, the ripple passive suppression module 4 is connected in series between the analog converter 2 and the AC port of the converter to be tested 12 , and is used for passively suppressing common-mode current ripple.

[0220] Specifically, the ripple active suppression module 10 has as its input the synchronization signal (carrier signal) of the converter controller 11 to be tested or the port voltage of the converter to be tested, and automatically synchronizes the pulse width modulation module 9 (carrier frequency and carrier phase) of the simulated converter according to the input signal to reduce the ripple, thereby actively reducing the fluctuation of the common-mode current ripple, so as to reduce the volume and cost of the ripple passive suppression module.

[0221] In the above embodiments of the present application, the active ripple suppression module reduces the ripple amplitude by adjusting the carrier phase, thereby reducing the need for the passive ripple suppression module; the passive ripple suppression module suppresses the ripple that the active ripple suppression module cannot completely eliminate. The two work together to minimize the cost and volume of the passive suppression module.

[0222] In order to obtain the environmental thermal stress under actual working conditions, in some specific embodiments of the present application, a temperature control module 5 may be used for the entire test system.

[0223] Specifically, the temperature control module is connected to the converter to be tested and the electrical impedance network.

[0224] Exemplarily, an incubator is used to perform environmental thermal stress simulation on the converter under test, or a heating rod and a fan are used to perform environmental thermal stress simulation on the converter under test.

[0225] The temperature control module of the above-mentioned embodiment of the present application can simulate the environmental working conditions by controlling the temperature of the converter to be tested, thereby enriching the working condition simulation dimension of the working condition simulation test.

[0226] In some specific embodiments of the present application, the inverter under test may be used in a motor-driven inverter, a grid-following inverter, or a grid-forming inverter. Accordingly, the system also includes a inverter under test controller 11 for controlling the inverter under test. A test impedance network is provided for filtering out voltage and current harmonics and ripple generated during the operation of the inverter under test.

[0227] The preferred features of the above embodiments can be used alone in any embodiment, or in any combination without conflict. In addition, parts not described in detail in the embodiments can be implemented using existing technologies.

Claims

1. A method for constructing a virtual impedance, characterized in that: This includes any of the following three methods: The first method: simulate the working condition target model G m Input value, input impedance network model G f and the working condition simulation target model G m The transfer function G of the constructed virtual impedance m / G f , get the virtual impedance; The second method: simulate the working condition target model G m The reference value of the output, input impedance network model G f With digital low-pass filter G d The transfer function G of the constructed virtual impedance d / G f , get the virtual impedance; wherein, the low-pass filter G d , whose cut-off frequency is greater than the highest frequency required by the actual control bandwidth, and whose transfer function order is greater than or equal to the electrical impedance network G f The order of The third method: simulate the working condition target model G m The reference value of the output, input impedance network model G f Constructed transfer function 1 / G f , get the virtual impedance; in this process, use the electrical impedance network model G f , the working condition simulation target model G m The differential value of the reference value solved algebraically replaces the differential operation on the reference value.

2. A high-bandwidth working condition simulation test method based on virtual impedance control, characterized in that: include: Obtaining a virtual impedance, wherein the virtual impedance is a virtual impedance constructed using the method of claim 1; Obtain the error between the output value of the target model of the working condition simulation and the reference value; Through closed-loop control, the error between the output value of the working condition simulation target model and the reference value is first corrected to obtain the control closed-loop output. Based on the control closed-loop output, the error introduced into the virtual impedance is corrected to obtain the output reference given by the simulated converter.

3. The high-bandwidth working condition simulation test method based on virtual impedance control according to claim 2, characterized in that: The closed-loop control method first corrects the error between the output value of the working condition simulation target model and the reference value to obtain a control closed-loop output, and based on the control closed-loop output, corrects the error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including: The reference value is calculated based on the input value of the working condition simulation target model; Calculate the difference between the reference value and the corresponding sampled output value; Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output; According to the input value of the target model of the working condition simulation, the virtual impedance is calculated using the first method; Adding the virtual impedance to the closed-loop control output to obtain a control instruction; The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

4. The high-bandwidth working condition simulation test method based on virtual impedance control according to claim 2, characterized in that: The closed-loop control method first corrects the error between the output value of the working condition simulation target model and the reference value to obtain a control closed-loop output, and based on the control closed-loop output, corrects the error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including: The reference value is calculated based on the input value of the working condition simulation target model; Calculate the difference between the reference value and the corresponding sampled output value; Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output; According to the reference value, a second method is used to calculate the virtual impedance; Adding the control closed-loop output to the virtual impedance to obtain a control instruction; The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

5. The high-bandwidth working condition simulation test method based on virtual impedance control according to claim 2, characterized in that: The closed-loop control method first corrects the error between the output value of the working condition simulation target model and the reference value to obtain a control closed-loop output, and based on the control closed-loop output, corrects the error introduced into the virtual impedance to obtain an output reference setting of the simulated converter, including: The reference value is calculated based on the input value of the working condition simulation target model; Calculate the difference between the reference value and the corresponding sampled output value; Performing closed-loop control on the result of the difference calculation to obtain a control closed-loop output; Calculating a differential value of the reference value based on an input value of the working condition simulation target model and the reference value; According to the reference value and the differential value of the reference value, a third method is used to calculate the virtual impedance; Adding the virtual impedance to the closed-loop control output of the closed-loop control to obtain a control instruction; The control instruction is pulse-width modulated and then outputted by the analog converter, ie, the output reference given.

6. A high-bandwidth working condition simulation test system based on virtual impedance control, characterized in that: include: A simulated current transformer is used to reproduce the voltage and current stress of the current transformer to be tested. Its AC port is connected to the impedance network, and its DC port is connected to the DC voltage source. An electrical impedance network, for filtering out differential mode harmonics generated by the analog converter and, at the same time, participating in constructing a virtual impedance; Sampling module, collects various voltages and currents according to different working conditions; A model calculation module, which generates a voltage reference value or a current reference value of the simulated converter according to a working condition simulation target model and data from the sampling module; a virtual impedance control module, generating a control instruction for controlling the output of the analog converter with reference to a given value; a pulse width modulation module, converting the control instruction generated by the virtual impedance control module into a pulse width control signal of the analog converter; Wherein, the virtual impedance control module includes: A virtual impedance submodule, which constructs a virtual impedance using the method of claim 1; The closed-loop control submodule corrects the error between the output value of the analog converter and the reference value and the error introduced by the virtual impedance submodule, and generates a control instruction.

7. The high-bandwidth working condition simulation test system based on virtual impedance control according to claim 6, characterized in that: The model calculation module, wherein the operating condition simulation target model includes a motor model and a power grid model; The current reference value of the motor model is calculated as follows: i ref is the current reference value; u sample is the voltage sampling value of the AC port of the converter to be tested; L s is the equivalent inductance of the motor rotor; R s is the equivalent resistance of the motor rotor, s is the complex frequency in the Laplace domain; The corresponding working condition simulation target model is The voltage reference value of the power grid model is calculated as follows: in ref =in actual -and sample ·(sL line +R line ) u ref is the voltage reference value; u actual is the actual voltage of the power grid to be simulated; i sample is the AC bus current sampling value; L line is the line inductance of the power grid to be simulated; R line is the line resistance of the power grid to be simulated, s is the complex frequency in the Laplace domain; The corresponding working condition simulation target model is G m =sL line +R line .

8. The high-bandwidth working condition simulation test system based on virtual impedance control according to claim 6, characterized in that: The electrical impedance network is a current-type electrical impedance network or a voltage-type electrical impedance network; The current-type electrical impedance network is used to suppress differential-mode current ripple and differential-mode current harmonics, and adopts any of the following electrical impedance network models: Electrical impedance network model corresponding to L-type filter L f is the inductance value, R f is the equivalent series resistance of the inductor, s is the complex frequency in the Laplace domain; or: The corresponding electrical impedance network model of the LCL filter L g is the inductance value of the grid side, R g is the equivalent series resistance of the grid-side inductor, L c is the inductance value of the converter side, R c is the equivalent series resistance of the converter side inductor, s is the complex frequency in the Laplace domain; The voltage-type electrical impedance network is used to suppress differential-mode voltage ripple and differential-mode voltage harmonics, and adopts any of the following electrical impedance models: Electrical impedance model corresponding to C-type filter or: Electrical impedance model corresponding to LC filter s is the complex frequency in the Laplace domain, C is the capacitance, and L is the inductance.

9. The high-bandwidth working condition simulation test system based on virtual impedance control according to claim 6, characterized in that: The pulse width modulation module adopts SPWM or SVPWM modulation mode; The simulated converter is composed of fully controlled or partially controlled power semiconductor devices, and the corresponding topology and circuit structure are selected according to the topology of the converter to be tested; wherein: The topology adopts any one of a three-phase two-level topology, a three-phase three-level topology, and a single-phase two-level topology; The circuit structure includes a single analog converter, multiple analog converters connected in parallel, and multiple analog converters connected in series.

10. The high-bandwidth working condition simulation test system based on virtual impedance control according to claim 6, characterized in that: Also includes one or more of the following characteristics: - a ripple passive suppression module, which is connected in series between the analog converter and the AC port of the converter to be tested, and is used to passively suppress common-mode current ripple; - an active ripple suppression module, which is connected in series between the converter controller to be tested and the pulse width modulation module, and is used to actively suppress common-mode current ripple, thereby reducing the size and cost of the passive ripple suppression module; - a temperature control module, connected to the converter to be tested, and used to simulate the environmental thermal stress of the converter to be tested under actual working conditions.

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