Normalization evaluation method and system for grid-connected inverter

Abstract

The present invention discloses a normalized evaluation method and system for a grid-connected inverter, belonging to the technical field of power quality control of power grids. The evaluation method not only evaluates the stability of the grid-connected inverter, but also evaluates the rapid control performance of the grid-connected inverter. The specific steps are: normalizing the filter parameters, calculating and simplifying the transfer function of the controlled object of the grid-connected inverter, calculating the control closed-loop transfer function of the grid-connected inverter, solving the normalized control parameters, controlling the grid-connected inverter, and calculating the normalized instability evaluation index S of the grid-connected inverter. inv and the normalized evaluation index N of the grid-connected inverter control rapidity inv The normalized evaluation index of the control rapidity of the grid-connected inverter obtained by the present invention provides a direction for the subsequent parameter design and performance optimization of the grid-connected inverter.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid power quality control, and in particular to the field of parameter design and performance evaluation of new energy inverters, and specifically to a normalized evaluation method and system for grid-connected inverters. Background Art

[0002] Grid-connected inverters, as the key interface between distributed energy resources and the power grid, play a vital role in improving system efficiency, power quality, and reliability. Due to their rapid output power regulation capabilities, grid-connected inverters have gained widespread acceptance in renewable energy generation. However, a variety of renewable energy sources, such as wind and photovoltaic power generation, are currently being integrated on a large scale. Wind power generation is generally a large-capacity, low-switching-frequency power station, while photovoltaic power generation is generally a small-capacity, high-switching-frequency power station. The large-scale integration of different types of renewable energy power stations makes the power system overly sensitive to disturbances, increasing the risk of grid voltage and frequency fluctuations. Therefore, evaluating the stability and rapidity of grid-connected inverters with different switching frequencies is crucial.

[0003] There have been extensive studies at home and abroad on the stability of grid-connected inverters under conditions of large grid impedance fluctuations and extremely weak grid conditions. It has been found that phase-locked loop parameters, grid voltage feedforward control, active damping strategies, positive and negative sequence frequency coupling, etc. will affect the stability of grid-connected inverters. However, there are grid-connected inverters with different switching frequencies in power stations. The switching frequency affects the capacity, filtering parameters and control bandwidth of the grid-connected inverter. These three factors are coupled together and are affected by the switching frequency. Moreover, when evaluating the rapidity of grid-connected inverters with different switching frequencies, if only the actual adjustment time is used for comparison, it is too one-sided because the switching cycle of grid-connected inverters with different switching frequencies is not taken into account. At present, there are many academic papers and patents on the performance evaluation of grid-connected inverters, such as:

[0004] 1. Chinese patent document CN 201910572524.0, published on September 20, 2019, entitled "A Method for Evaluating the Stability of a Multi-Inverter Grid-Connected System in Two Dimensions," derives and establishes the global admittance of a multi-inverter grid-connected system. This global admittance is divided into two dimensions: real and imaginary. These two dimensions reflect the stability of the multi-inverter system and provide accurate resonance point information. However, the switching frequency affects the capacity, filtering parameters, and control bandwidth of the grid-connected inverter. These three factors, coupled together, are all affected by the switching frequency. The stability evaluation method does not compare grid-connected inverters based on a unified design standard. This evaluation system is no longer applicable to grid-connected inverters with different capacities and control bandwidths.

[0005] 2. Chinese patent document CN 202110604445.0, published on April 13, 2021, entitled "A Method for Evaluating the Transient Stability Margin of a New Energy Grid-Connected Inverter," uses the output angular frequency, equivalent limit cut-off angle, and transient stability margin of the new energy grid-connected inverter's phase-locked loop to determine the stability of the grid-connected inverter before a fault, during the fault duration, and during the fault recovery phase, and quantitatively calculates the stability margin value. However, the performance evaluation does not include calculation of the adjustment time during the fault duration phase, nor does it consider the performance of controlling the adjustment speed.

[0006] Based on the above documents, the prior art has the following deficiencies:

[0007] 1. New energy power stations contain grid-connected inverters with different capacities and control bandwidths. Existing stability assessment methods do not compare these grid-connected inverters under a unified design standard. They only reflect the stability information of the grid-connected inverter system and do not consider the relationship between software and hardware parameters and stability. Therefore, they cannot provide guidance for subsequent parameter design.

[0008] 2. In the performance evaluation of grid-connected inverters, existing studies have focused on grid stability evaluation, ignoring the inverter's control speed performance. In addition, the switching frequency of the grid-connected inverter has a direct impact on the control speed. The existing evaluation system generally uses the adjustment time to evaluate the control speed, and does not exclude the delay effect caused by the switching cycle. Summary of the Invention

[0009] To overcome the limitations of the above-mentioned scheme, the present invention proposes a normalized evaluation method for grid-connected inverters. The method takes into account the influence and limitation of switching frequency on filtering performance and control bandwidth, designs normalized filtering parameters and normalized control parameters of the grid-connected inverter under rated parameters, and uses the normalized parameters to perform a normalized evaluation of the grid-connected stability and control rapidity of the grid-connected inverter, providing a direction for performance comparison and parameter design of different types of grid-connected inverters.

[0010] The object of the present invention is achieved in this way. The present invention provides a normalized evaluation method for a grid-connected inverter, comprising the following steps:

[0011] S1, calculate the filtering parameters and normalize the filtering parameters;

[0012] S2, calculating the transfer function of the grid-connected inverter controlled object according to the reference value of the filtering parameters and simplifying it;

[0013] S3, calculating the control closed-loop transfer function of the grid-connected inverter;

[0014] S4, solve the normalized control parameters through the unified standard control bandwidth to complete the parameter normalization design of the current controller;

[0015] S5, controlling the grid-connected inverter to operate using the normalized designed parameters, and calculating a normalized instability evaluation index of the grid-connected inverter;

[0016] S6, setting the current setpoint of the grid-connected inverter to step to full load, and calculating the normalized evaluation index of the control rapidity of the grid-connected inverter.

[0017] Preferably, S1 further includes the following steps:

[0018] S11, according to the rated DC voltage U of the grid-connected inverter dc , the rated AC voltage U of the grid-connected inverter rated , the rated current of the grid-connected inverter I rated , the fundamental frequency f0 of the grid-connected inverter and the switching frequency f s , calculate the filtering parameters of the three-phase LCL filter of the grid-connected inverter, including the resonant frequency f res , the machine side filter inductance value L1, the network test filter inductance value L2 and the filter capacitor value C f ;

[0019] S12, normalize the filtering parameters of the three-phase LCL filter obtained in S1, and equalize them to the reference voltage capacity level to obtain the voltage transformation ratio k of the three-phase LCL filter. Based on the voltage transformation ratio k of the three-phase LCL filter, calculate the filtering parameter reference value of the three-phase LCL filter, including the machine-side filter inductance reference value. Filter resistance reference value Filter capacitor reference value And the machine side filter inductor reference value

[0020] Preferably, the resonant frequency f of the three-phase LCL filter is res , the machine side filter inductance value L1, the network test filter inductance value L2 and the filter capacitor value C f The calculation formulas are as follows:

[0021]

[0022] Where k sw is the current ripple coefficient during PWM modulation, Δi L1_max is the maximum value of the AC current ripple.

[0023] Preferably, the voltage transformation ratio k of the three-phase LCL filter and the machine-side filter inductance reference value are Filter resistance reference value Filter capacitor reference value And the machine side filter inductor reference value The calculation formulas are:

[0024]

[0025] Where U B is the AC voltage reference value of the grid-connected inverter, I B is the AC current reference value of the grid-connected inverter, R d is the filter resistance value.

[0026] Preferably, S2 is specifically: establishing a function G of the grid-connected inverter controlled object according to the filter parameter reference value of the three-phase LCL filter p (s), and then according to the function G of the grid-connected inverter controlled object p (s) Establish the function G of the equivalent controlled object of the grid-connected inverter peq (s), s is the Laplace operator.

[0027] Preferably, the function G of the controlled object of the grid-connected inverter is p (s) is:

[0028]

[0029] The function G of the equivalent controlled object of the grid-connected inverter is peq (s) is:

[0030]

[0031] Where K pl is the equivalent proportional coefficient, T pl is the equivalent integration time constant.

[0032] Preferably, S3 specifically includes: establishing the transfer function of each link in the current control of the grid-connected inverter, including the transfer function G of the current controller c (s), transfer function G of the control delay link d (s) and the transfer function G of the ideal power amplifier link PWM .

[0033] Preferably, the transfer function G of the current controller is c (s), transfer function G of the control delay link d (s) and the transfer function G of the ideal power amplifier link PWM for:

[0034]

[0035] Where K p is the proportional coefficient of the current controller, T i is the integral time constant of the current controller, T s is the switching period, T s =1 / fs , K PWM is the modulation gain.

[0036] Preferably, S4 is specifically: the function G of the equivalent controlled object of the grid-connected inverter peq (s) and the transfer functions of each link in the current control to establish the control closed-loop transfer function G of the grid-connected inverter cl (s), and then through the closed-loop transfer function G cl (s) Solve for the proportional coefficient K of the current controller p and the integral time constant T i , complete the parameter normalization design of the current controller.

[0037] Preferably, the control closed-loop transfer function G of the grid-connected inverter is cl (s) are as follows:

[0038]

[0039] Where K p is the proportional coefficient of the current controller, T i is the integral time constant of the current controller, T s is the switching period, T s =1 / f s , K PWM is the modulation gain;

[0040] The proportional coefficient K of the current controller p and the integral time constant T i The calculation formulas are:

[0041]

[0042]

[0043] Where, ω c is the current loop control bandwidth, θ is the current loop phase margin, K pl is the equivalent proportional coefficient, T pl is the equivalent integration time constant.

[0044] Preferably, the normalized instability evaluation index S of the grid-connected inverter in S5 is inv The calculation formula is:

[0045]

[0046] Where, L g_crit Grid reactance corresponding to different phase margins when the grid-connected inverter is operated using normalized designed parameters.

[0047] Preferably, S6 specifically comprises: setting the current of the grid-connected inverter to a given value I ref Set it to step to full load and get the adjustment time t of step response s , the normalized evaluation index N of the grid-connected inverter control rapidity inv The calculation formula is:

[0048]

[0049] Where, T s is the switching period, T s =1 / f s .

[0050] Preferably, a normalized evaluation system for a grid-connected inverter is characterized by comprising:

[0051] A DC side power supply 10, a three-phase full-bridge inverter circuit 20, a three-phase LCL filter 30, a three-phase grid impedance 40 and a three-phase grid 50 are sequentially connected in series;

[0052] A first processing module for calculating filtering parameters and performing normalization processing on the filtering parameters;

[0053] a first calculation module for calculating and simplifying a transfer function of a controlled object of a grid-connected inverter according to a reference value of a filtering parameter;

[0054] a second calculation module for calculating a control closed-loop transfer function of a grid-connected inverter;

[0055] A second processing module for solving normalized control parameters through a unified standard control bandwidth to complete parameter normalization design of the current controller;

[0056] It is used to control the grid-connected inverter to operate using the above normalized design parameters and calculate the normalized instability evaluation index S of the grid-connected inverter. inv The third computing module;

[0057] Used to set the current setting value of the grid-connected inverter to step to full load and calculate the normalized evaluation index N of the grid-connected inverter control rapidity inv The fourth computing module.

[0058] The present invention also provides a computer-readable storage medium storing a computer program programmed or configured to execute a normalized evaluation method for a grid-connected inverter.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] 1. In the performance evaluation of grid-connected inverters, the method of the present invention not only evaluates the stability of the grid-connected inverter, but also evaluates the control speed performance of the grid-connected inverter. It also takes into account the influence of the switching frequency of the grid-connected inverter on the control speed, eliminates the delay effect caused by the switching cycle, and obtains a normalized evaluation index of the control speed of the grid-connected inverter;

[0061] 2. In new energy power stations, there are grid-connected inverters with different capacities and control bandwidths. The method of the present invention takes into account the relationship between software and hardware parameters and stability, normalizes the filtering parameters and control parameters, and places the grid-connected inverters under a unified design standard for stability evaluation, providing direction for subsequent parameter design. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a main circuit topology diagram of a high-proportion new energy power generation system using the present invention.

[0063] Figure 2 This is the equivalent circuit diagram of the controlled object of the grid-connected inverter.

[0064] Figure 3 Block diagram of single-phase current control for a grid-connected inverter.

[0065] Figure 4 Flowchart of the normalized evaluation method for grid-connected inverters.

[0066] Figure 5 T s =0.2ms when the step signal response curve of the grid-connected inverter.

[0067] Figure 6 T s =0.45ms when the step signal response curve of the grid-connected inverter.

[0068] Figure 7 The graph shows the change curve of normalized instability evaluation index for different types of grid-connected inverters. DETAILED DESCRIPTION

[0069] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0070] In the embodiment of the present invention, the main circuit topology diagram of the new energy grid-connected inverter using the present invention is shown in FIG. Figure 1 .exist Figure 1 In the figure, 10 is the DC side power supply, 20 is the three-phase full-bridge inverter circuit, 30 is the three-phase LCL filter, 40 is the three-phase grid impedance, and 50 is the three-phase grid. Figure 1It can be seen that the grid-connected inverter is composed of a DC side power supply 10, a three-phase full-bridge inverter circuit 20, a three-phase LCL filter 30, a three-phase grid impedance 40 and a three-phase grid 50 connected in series in sequence, wherein the connection point between the three-phase LCL filter 30 and the three-phase grid impedance 40 is recorded as the common coupling point PCC.

[0071] exist Figure 1 Middle,U dc is the rated DC side voltage of the DC side power supply, C f is the filter capacitance value of the three-phase LCL filter, L1 is the machine-side filter inductance value of the three-phase LCL filter, R d is the filter resistance value of the three-phase LC filter, L2 is the grid-side filter inductance value, U g is the three-phase grid voltage.

[0072] In the present invention, the grid-connected inverter adopts a grid-following control method.

[0073] The present invention provides a normalized evaluation method for a grid-connected inverter. Figure 4 The figure is a flow chart of the normalized evaluation method for grid-connected inverters. Figure 4 It can be seen that the following steps are included:

[0074] Step 1: Based on the rated DC voltage U dc , the rated AC voltage U of the grid-connected inverter rated , the rated current of the grid-connected inverter I rated , the fundamental frequency f0 of the grid-connected inverter and the switching frequency f s , calculate the filtering parameters of the three-phase LCL filter of the grid-connected inverter, including the resonant frequency f res , the machine side filter inductance value L1, the network test filter inductance value L2 and the filter capacitor value C f .

[0075] In the embodiment of the present invention, the resonant frequency f of the three-phase LCL filter is res , the machine side filter inductance value L1, the network test filter inductance value L2 and the filter capacitor value C f The calculation formulas are as follows:

[0076]

[0077] Where k sw is the current ripple coefficient during PWM modulation, Δi L1_max is the maximum value of the AC current ripple.

[0078] Step 2: Normalize the filter parameters of the three-phase LCL filter obtained in S1 and convert them to the reference voltage capacity level to obtain the voltage transformation ratio k of the three-phase LCL filter. Based on the voltage transformation ratio k of the three-phase LCL filter, calculate the filter parameter reference value of the three-phase LCL filter, including the machine-side filter inductance reference value. Filter resistor reference value Filter capacitor reference value And the machine side filter inductor reference value

[0079] In the embodiment of the present invention, the voltage transformation ratio k of the three-phase LCL filter and the machine-side filter inductance reference value are Filter resistance reference value Filter capacitor reference value And the machine side filter inductor reference value The calculation formulas are:

[0080]

[0081] Where U B is the AC voltage reference value of the grid-connected inverter, I B is the AC current reference value of the grid-connected inverter, R d is the filter resistance value.

[0082] Step 3: Establish the function G of the grid-connected inverter controlled object according to the filter parameter reference value of the three-phase LCL filter. p (s), and then according to the function G of the grid-connected inverter controlled object p (s) Establish the function G of the equivalent controlled object of the grid-connected inverter peq (s), s is the Laplace operator.

[0083] In the embodiment of the present invention, the function G of the grid-connected inverter controlled object is p (s) is:

[0084]

[0085] The function G of the equivalent controlled object of the grid-connected inverter is peq (s) is:

[0086]

[0087] Where K pl is the equivalent proportional coefficient, T pl is the equivalent integration time constant.

[0088] Figure 2 is the equivalent circuit diagram of the controlled object of the three-phase grid-connected inverter, where U i is the equivalent DC voltage, Ig is the grid-connected inverter output current, U g is the three-phase grid voltage.

[0089] Step 4: Establish the transfer function of each link in the current control of the grid-connected inverter, including the transfer function G of the current controller. c (s), transfer function G of the control delay link d (s) and the transfer function G of the ideal power amplifier link PWM .

[0090] In the embodiment of the present invention, the transfer function G of the current controller is c (s), transfer function G of the control delay link d (s) and the transfer function G of the ideal power amplifier link PWM for;

[0091]

[0092] Where K p is the proportional coefficient of the current controller, T i is the integral time constant of the current controller, T s is the switching period, T s =1 / f s , K PWM is the modulation gain.

[0093] Figure 3 The single-phase current control block diagram of the three-phase grid-connected inverter, where I ref is the given current command value.

[0094] Step 5: Equivalent function G of the controlled object of the grid-connected inverter peq (s) and the transfer functions of each link in the current control to establish the control closed-loop transfer function G of the grid-connected inverter cl (s), and then through the closed-loop transfer function G cl (s) Solve for the proportional coefficient K of the current controller p and the integral time constant T i , complete the parameter normalization design of the current controller.

[0095] In the embodiment of the present invention, the control closed-loop transfer function G of the grid-connected inverter is cl (s) are as follows:

[0096]

[0097] Where K p is the proportional coefficient of the current controller, T i is the integral time constant of the current controller, T sis the switching period, T s =1 / f s , K PWM is the modulation gain.

[0098] The proportional coefficient K of the current controller p and the integral time constant T i The calculation formulas are:

[0099]

[0100]

[0101] Where, ω c is the current loop control bandwidth, θ is the current loop phase margin, K pl is the equivalent proportional coefficient, T pl is the equivalent integration time constant.

[0102] Step 6: The grid-connected inverter is operated using the above normalized design parameters to calculate the normalized instability evaluation index S of the grid-connected inverter. inv .

[0103] In the embodiment of the present invention, the normalized instability evaluation index S of the grid-connected inverter is inv The calculation formula is:

[0104]

[0105] Where, L g_crit Grid reactance corresponding to different phase margins when the grid-connected inverter is operated using normalized designed parameters.

[0106] Normalized instability evaluation index S inv It can not only evaluate the stability of grid-connected inverters, but also conduct stability evaluation on different types of grid-connected inverters under a unified standard, providing direction for subsequent parameter design.

[0107] Step 7: Set the current of the grid-connected inverter to the given value I ref Set it to step to full load and get the adjustment time t of step response s , calculate the normalized evaluation index N of the grid-connected inverter control rapidity inv .

[0108] In the embodiment of the present invention, the normalized evaluation index N of the grid-connected inverter control rapidity inv The calculation formula is:

[0109]

[0110] Where, T s is the switching period, T s=1 / f s .

[0111] Adjustment time t s It is a rapidity evaluation index in the conventional evaluation system. The evaluation method of the present invention combines the adjustment time t s , excluding the delay effect caused by the switching cycle, the normalized evaluation index N of the grid-connected inverter control rapidity is calculated inv .

[0112] In order to demonstrate the beneficial effects of the evaluation method provided by the present invention, a simulation of the evaluation method provided by the present invention was performed.

[0113] Figure 5 Given T s =0.2ms when the grid-connected inverter responds to the step signal. Figure 6 Given T s =0.45ms, the step signal response of the grid-connected inverter can be seen. Figure 5 Middle adjustment time t s =1s, Figure 6 Middle adjustment time t s =1.2s, Figure 5 Normalized evaluation index N of control rapidity of grid-connected inverter inv =5000, Figure 6 Normalized evaluation index N of control rapidity of grid-connected inverter inv =2666, that is Figure 6 The actual regulation time is slower, but the number of switching cycles required is less. Figure 7 is the normalized instability evaluation index of different types of grid-connected inverters, and the normalized instability evaluation index S of inverters with different switching frequencies under different grid-connected phase margins PM is inv , it can be seen that when PM = 30°, the normalized instability index of the grid-connected inverter with different switching frequencies using normalized parameters is the same. When PM = 0°, that is, when the grid-connected inverter system is in critical stability, it can be seen that the lower the switching frequency, the higher the normalized instability evaluation index S of the grid-connected inverter. inv The larger it is, the worse the stability when connected to a weak power grid.

[0114] The present invention also provides a grid-connected inverter normalization evaluation system, comprising:

[0115] A DC side power supply 10, a three-phase full-bridge inverter circuit 20, a three-phase LCL filter 30, a three-phase grid impedance 40 and a three-phase grid 50 are sequentially connected in series;

[0116] A first processing module for calculating filtering parameters and performing normalization processing on the filtering parameters;

[0117] a first calculation module for calculating and simplifying a transfer function of a controlled object of a grid-connected inverter according to a reference value of a filtering parameter;

[0118] a second calculation module for calculating a control closed-loop transfer function of a grid-connected inverter;

[0119] A second processing module for solving normalized control parameters through a unified standard control bandwidth to complete parameter normalization design of the current controller;

[0120] It is used to control the grid-connected inverter to operate using the above normalized design parameters and calculate the normalized instability evaluation index S of the grid-connected inverter. inv The third computing module;

[0121] Used to set the current setting value of the grid-connected inverter to step to full load and calculate the normalized evaluation index N of the grid-connected inverter control rapidity inv The fourth computing module.

[0122] The present invention also provides a computer-readable storage medium storing a computer program programmed or configured to execute a normalized evaluation method for a grid-connected inverter.

[0123] The circuit topology structure and evaluation method of the present invention described above can be viewed as hardware embodiments of the circuit topology structure alone, as software embodiments of the evaluation method alone, or as a combination of hardware and software embodiments based on the circuit topology structure and module evaluation method. Furthermore, the evaluation method portion of the present invention can be implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code, in the form of a computer program product. The method can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0124] Furthermore, the embodiments of the present invention are described in conjunction with flowcharts and / or block diagrams. It should be understood that each process and / or block in the flowcharts and / or block diagrams of the present invention, as well as the combination of the processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the present invention. Figure 1 a process or multiple processes and / or boxes Figure 1These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the function specified in the process of the present invention. Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process of the present invention. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0125] Therefore, the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Changes and modifications made by those skilled in the art based on the specific implementation methods of the present invention and the above circumstances should be regarded as equivalent solutions of this application and should fall within the scope of protection of the present invention.

Claims

1. A normalized evaluation method for a grid-connected inverter, characterized in that: The following steps are involved: S1, calculate the filtering parameters and normalize the filtering parameters; S2, calculating the transfer function of the grid-connected inverter controlled object according to the reference value of the filtering parameters and simplifying it; S3, calculating the control closed-loop transfer function of the grid-connected inverter; S4, solve the normalized control parameters through the unified standard control bandwidth to complete the parameter normalization design of the current controller; S5, control the grid-connected inverter to operate using the above normalized design parameters, and calculate the normalized instability evaluation index of the grid-connected inverter ; S6, set the current setting value of the grid-connected inverter to step to full load, and calculate the normalized evaluation index of the grid-connected inverter control rapidity ; S4 is specifically: the function of the equivalent controlled object of the grid-connected inverter The control closed-loop transfer function of the grid-connected inverter is established by combining the transfer functions of each link in the current control , and then through the closed-loop transfer function of the grid-connected inverter Solve for the proportional coefficient of the current controller and the integration time constant , complete the parameter normalization design of the current controller; Normalized instability evaluation index of grid-connected inverter described in S5 The calculation formula is: Where, The grid reactance corresponding to different phase margins when the grid-connected inverter is operated using normalized designed parameters; is the rated AC voltage of the grid-connected inverter, is the rated current of the grid-connected inverter, is the fundamental frequency of the grid-connected inverter; S6 is specifically: set the current of the grid-connected inverter to a given value Set to step to full load and get the adjustment time of step response , the normalized evaluation index of the grid-connected inverter control rapidity The calculation formula is: Where, is the switching period, .

2. A normalized evaluation method for a grid-connected inverter according to claim 1, characterized in that: S1 also includes the following steps: S11, according to the rated DC voltage of the grid-connected inverter , rated AC voltage of grid-connected inverter , rated current of grid-connected inverter , the fundamental frequency of the grid-connected inverter and the switching frequency of the grid-connected inverter , calculate the three-phase of the grid-connected inverter Filter parameters of the filter, including resonant frequency , the machine side filter inductance value , network measurement filter inductance value and filter capacitor value ; S12, the three-phase The filter parameters of the filter are normalized and equalized to the reference voltage capacity level to obtain the three-phase Voltage transformation ratio of the filter , and according to the three-phase Voltage transformation ratio of the filter , calculate the three-phase The filter parameter reference value of the filter, including the machine-side filter inductance reference value , filter resistor reference value , filter capacitor reference value And the machine side filter inductor reference value .

3. A normalized evaluation method for grid-connected inverters according to claim 2, characterized in that: The three-phase Resonant frequency of the filter , the machine side filter inductance value , network measurement filter inductance value and filter capacitor value The calculation formulas are as follows: Where, is the current ripple coefficient during PWM modulation, is the maximum value of the AC current ripple.

4. A normalized evaluation method for grid-connected inverters according to claim 3, characterized in that: The three-phase Filter voltage transformation ratio k, machine-side filter inductance reference value , filter resistor reference value , filter capacitor reference value And the machine side filter inductor reference value The calculation formulas are: Where, is the AC voltage reference value of the grid-connected inverter, is the AC current reference value of the grid-connected inverter, is the filter resistance value.

5. A normalized evaluation method for a grid-connected inverter according to claim 2, characterized in that S2 Specifically: According to the three-phase The filter parameter reference value of the filter establishes the function of the grid-connected inverter controlled object , and then according to the function of the controlled object of the grid-connected inverter Function to establish equivalent controlled object of grid-connected inverter , is the Laplace operator.

6. A normalized evaluation method for a grid-connected inverter according to claim 5, characterized in that: The function of the grid-connected inverter controlled object for: The function of the grid-connected inverter equivalent controlled object for: Where, is the equivalent proportional coefficient, is the equivalent integration time constant.

7. A normalized evaluation method for grid-connected inverters according to claim 5, characterized in that: S3 Specifically: Establish the transfer function of each link in the current control of the grid-connected inverter, including the transfer function of the current controller , transfer function of control delay link and the transfer function of the ideal power amplifier link .

8. A normalized evaluation method for a grid-connected inverter according to claim 7, characterized in that: The transfer function of the current controller is , transfer function of control delay link and the transfer function of the ideal power amplifier link for: Where, is the proportional coefficient of the current controller, is the integral time constant of the current controller, is the switching period, , is the modulation gain.

9. The normalized evaluation method for a grid-connected inverter according to claim 5, wherein: The control closed-loop transfer function of the grid-connected inverter is as follows: Where, is the proportional coefficient of the current controller, is the integral time constant of the current controller, is the switching period, , is the modulation gain; The proportional coefficient of the current controller and the integration time constant The calculation formulas are: Where, is the current loop control bandwidth, is the current loop phase margin, is the equivalent proportional coefficient, is the equivalent integration time constant.

10. A grid-connected inverter normalization evaluation system according to the grid-connected inverter normalization evaluation method according to any one of claims 1 to 9, characterized in that: include: A DC side power supply 10, a three-phase full-bridge inverter circuit 20, a three-phase LCL filter 30, a three-phase grid impedance 40 and a three-phase grid 50 are sequentially connected in series; A first processing module for calculating filtering parameters and performing normalization processing on the filtering parameters; a first calculation module for calculating and simplifying a transfer function of a controlled object of a grid-connected inverter according to a reference value of a filtering parameter; a second calculation module for calculating a control closed-loop transfer function of a grid-connected inverter; A second processing module for solving normalized control parameters through a unified standard control bandwidth to complete parameter normalization design of the current controller; Used to control the grid-connected inverter to operate using the above normalized design parameters and calculate the normalized instability evaluation index of the grid-connected inverter The third computing module; Used to set the current reference value of the grid-connected inverter to step to full load and calculate the normalized evaluation index of the grid-connected inverter control rapidity The fourth computing module.

11. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program programmed or configured to execute the normalized evaluation method for a grid-connected inverter according to any one of claims 1 to 9.

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