LCL grid-connected current feedback active damping control method and system

Abstract

The application discloses a kind of LCL grid-connected current feedback active damping control method and system, belong to power filter control technical field, including the grid-connected current i2 of the acquisition inverter net side;Grid-connected current i2 flows through negative low-pass-high-pass filter and is handled, obtains feedback current;Feedback current and the output of inverter current controller are superposed, as the control signal of LCL filter.The application will not amplify high-frequency harmonic current, and the control system still has good robustness when LCL filter parameter changes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power filter control, and particularly relates to a LCL grid-connected current feedback active damping control method and system. BACKGROUND

[0002] In order to obtain better grid-connected current, a grid-connected inverter often adopts an LCL type filter. However, the LCL type filter is a third-order system, and has a resonance problem itself. There is a resonance peak at the resonance frequency, which causes the inverter to be unable to operate stably. At present, the main schemes for eliminating the resonance of the LCL filter include passive damping and active damping. The passive damping scheme adds a damping resistor in the filter circuit, which is simple to implement and does not need to improve the control algorithm, but the damping resistor will cause a loss problem and is affected by the change of grid impedance. The active damping scheme mainly increases the damping of the system through the control structure of the state variable feedback to obtain the effect of suppressing the resonance peak.

[0003] The commonly used state variables of the active damping scheme include the inverter output current, the capacitor current, the capacitor voltage and the grid-side current. When the capacitor current or the capacitor voltage is used as the state variable, an additional sensor needs to be added. In order to save the hardware cost, the grid-side current is often used as the state variable for feedback in the current active damping scheme.

[0004] Some documents propose a method of using the second derivative s 2 of the grid-connected current as feedback to realize active damping control. However, the second derivative s 2 is difficult to realize digitally and is easy to amplify the high-frequency harmonic current. On this basis, some documents propose to use a first-order high-pass filter (NHPF) to fit the second derivative variable s 2 of the equivalent grid-connected current. However, the NHPF still has a certain gain on the high-frequency harmonic current and still amplifies the high-frequency noise. Moreover, the existing grid-connected current feedback active damping method does not consider the stability of the control system under a weak grid condition.

[0005] In the related art, the patent application for invention with publication number CN112217237A proposes an active damping control method for a direct-drive wind power grid-connected system under asymmetric fault. The active damping is introduced through a high-pass filter and a virtual resistor to suppress the positive and negative sequence harmonic currents of the grid. On the basis of not changing the parameters and structure of the internal controller, only by introducing the virtual impedance based on the high-pass filter, the dynamic stability of the direct-drive wind power grid-connected system under the asymmetric fault of the grid can be significantly improved.

[0006] The invention patent application with publication number CN 110266017 B proposes a LCL type active power filter hybrid state feedback virtual damping control method, the implementation steps are: a) two groups of current sensors are used to collect the PCC current is and the inverter side current i1 respectively; b) the difference between the PCC current is and the inverter side current i1 is used as a state variable, which is fed back to the inverter side voltage ui after passing through a second-order high-pass filter; c) the control strategy of voltage outer loop plus current inner loop is used in the fundamental wave ring to obtain the fundamental wave ring current control instruction, and the second-order generalized integrator SOGI is used in the harmonic ring to control the harmonic without static error to obtain the harmonic ring current control instruction; d) the sum of the fundamental wave ring current control instruction obtained in step c and the harmonic ring current control instruction is used as the active power filter control signal together with the feedback value obtained in step a) to control the switching action of the power device and generate a compensation current. By using the original sensor of SAPF, the active damping control of LCL type filter is realized to suppress the resonance peak.

[0007] Compared with the above two patents, the differences of the technical problems, scheme principles and technical effects of the present application are as follows:

[0008] In terms of technical problems, the present application mainly solves the resonance problem caused by LCL filter by proposing a new active damping method, which is similar to the problem to be solved by the invention patent with publication number CN 110266017 B; and the invention patent with publication number CN 112217237 A is mainly used to solve the dynamic stability problem of direct-drive wind power grid-connected system under asymmetric grid fault.

[0009] In terms of scheme principles, the present application adopts grid current active damping feedback, and the active damping is realized through a first-order negative low-high pass filter in the feedback loop. The invention patent with publication number CN 110266017 B adopts mixed state active damping feedback of grid current and inverter current, and the active damping is realized through a second-order high-pass filter in the feedback loop. The invention patent with publication number CN 112217237 A feeds back the positive and negative sequence currents of the grid side current through virtual damping and high-pass filter.

[0010] In terms of technical effects, the present application only uses one set of sensors to realize the suppression of LCL resonance, and has good high-frequency signal suppression performance, overcoming the shortcomings of the prior art and improving the grid current quality. The invention patent with publication number CN 110266017 B needs to use two sets of sensors, and only suppresses LCL resonance. The invention patent with publication number CN 112217237 A realizes the stable operation of direct-drive wind power grid-connected system under asymmetric grid fault. SUMMARY

[0011] The technical problem to be solved by the present application is how to effectively suppress LCL resonance spikes and high-frequency harmonic currents, and still have good robustness when the grid impedance and LCL parameters change.

[0012] The present application solves the above technical problems by the following technical means:

[0013] In one aspect, the present application provides an LCL grid-connected current feedback active damping control method, which comprises:

[0014] Collecting the grid-connected current i2 of the inverter grid side;

[0015] Passing the grid-connected current i2 through a negative low-pass-high-pass filter for processing to obtain a feedback current, wherein the closed-loop transfer function between the output voltage u of the inverter and the grid-connected current i2 is: inv

[0016]

[0017] In the formula, A and B are low-pass active damping feedback functions and high-pass active damping feedback functions, respectively, and G is an open-loop transfer function between the grid-connected current i2 and the output voltage u of the inverter. open inv

[0018] Superimposing the feedback current and the output of the inverter current controller as a control signal of the LCL filter.

[0019] The LCL grid-connected current feedback active damping control method provided by the present application processes the grid-connected current of the inverter grid side through a negative low-high pass filter (NL-HPF) and then feeds back, which not only effectively eliminates the amplification of high-order harmonic currents, but also maintains good stability when the LCL parameters change, and the control system only needs to sample the grid current without the need to increase the sensor, which can save hardware cost.

[0020] Further, the low-pass active damping feedback function A is represented by the following formula:

[0021]

[0022] The high-pass active damping feedback function B is represented by the following formula:

[0023]

[0024] The open-loop transfer function is represented by the following formula:

[0025] ​​​

[0026] where ω l is the cut-off angular frequency of the low-pass filter, k ad is the feedback coefficient, ω h is the cut-off angular frequency of the negative high-pass filter, s is the differential operator, L1 is the bridge arm side inductance, C is the AC side filter capacitance and L2 is the grid side inductance.

[0027] Further, the denominator of the closed-loop transfer function comprises one first pole and four second poles, the first pole is located at the origin, and the second poles are configured as conjugate resonant poles, and the formula is:

[0028]

[0029] Further, two of the four second poles are configured at the fundamental, and the other two are a pair of conjugate poles, and the second poles are configured as follows:

[0030] D * = L1L2Cs(s 2 + 2ξ0ω0s + ω0 2 )(s 2 + 2ξ n ω n s + ω n 2 )

[0031] where ξ0 is the damping ratio at ω0, ω0 is the fundamental angular frequency, ξ n is the damping ratio at ω n , ω n is a freely configurable high-frequency angular frequency, and the values of ξ0 and ξ n range from 0.4 to 0.8.

[0032] Further, the ω n satisfies the following formula:

[0033] kω res ≤ ω n ≤ ω sw / 3

[0034] where ω sw is the switching frequency angular frequency, ω res is 9k, and k > 1.

[0035] Further, the values of ξ0 and ξ n are both 0.6.

[0036] Further, the value of k is 1.5.

[0037] Further, the expression of the cut-off angular frequency of the negative low-pass-high-pass filter is:

[0038]

[0039] Furthermore, the application also provides an LCL grid-connected current feedback active damping control system, an AC side of an LCL type three-phase AC voltage type grid-connected inverter is connected with a power grid through an LCL filter, a grid-side current of the inverter is connected with an output of an inverter current controller through a negative low-pass-high-pass filter, and the system comprises:

[0040] a collection module, configured to collect a grid-connected current i2 of the grid-side of the inverter;

[0041] a processing module, configured to process the grid-connected current i2 flowing through the negative low-pass-high-pass filter to obtain a feedback current, wherein a closed-loop transfer function between an output voltage u inv of the inverter and the grid-connected current i2 is:

[0042]

[0043] In the formula, A and B are respectively a low-pass active damping feedback function and a high-pass active damping feedback function, G open is an open-loop transfer function between the grid-connected current i2 and the output voltage u inv of the inverter;

[0044] a control module, configured to superimpose the feedback current and an output of the inverter current controller to serve as a control signal of the LCL filter.

[0045] Further, the low-pass active damping feedback function A is expressed as follows:

[0046]

[0047] The high-pass active damping feedback function B is expressed as follows:

[0048]

[0049] The open-loop transfer function is expressed as follows:

[0050]

[0051] In the formula, ω l is a cut-off angular frequency of a low-pass filter, k ad is a feedback coefficient, ω h is a cut-off angular frequency of a negative high-pass filter, s is a differential operator, L1 is a bridge arm side inductance, C is an AC side filter capacitance, and L2 is a grid-side inductance.

[0052] The denominator of the closed loop transfer function comprises a first pole and four second poles, the first pole is located at the origin, and the second poles are configured as conjugate resonant poles, and the formula is represented as:

[0053]

[0054] The present application has the advantages of:

[0055] (1) The LCL grid-connected current feedback active damping control method provided by the present application processes the grid-connected current of the inverter grid side through a negative low-high pass filter and then feeds back, which not only effectively eliminates the amplification of high-order harmonic currents, but also maintains good stability when the LCL parameters change, and the control system only needs to sample the grid current without increasing the sensor, which can save hardware cost.

[0056] (2) The parameter design can be performed through the pole configuration method, which is simple and easy to implement.

[0057] Additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a flow chart of the LCL grid-connected current feedback active damping control method in an embodiment of the present application;

[0059] Figure 2 is a three-phase LCL grid-connected inverter system structure diagram in an embodiment of the present application;

[0060] Figure 3 is a control block diagram of the active damping feedback using a negative low-high pass filter in an embodiment of the present application;

[0061] Figure 4 is a characteristic comparison diagram of NHPF and NL-HPF in an embodiment of the present application;

[0062] Figure 5 is a system open loop frequency characteristic Bode diagram using NL-HPF active damping in an embodiment of the present application;

[0063] Figure 6 is a system open loop frequency characteristic Bode diagram when the LCL parameters change in an embodiment of the present application;

[0064] Figure 7 is an open loop transfer function Bode diagram of the control system under different grid impedances in an embodiment of the present application;

[0065] Figure 8 is a grid-connected current simulation waveform and FFT analysis diagram using NHPF and NL-HPF respectively in an embodiment of the present application;

[0066] Figure 9 is the grid current waveform change chart before and after NL-HPF used in the specific experiment of the embodiment of the present application;

[0067] Figure 10 is the grid current waveform chart under weak grid in the embodiment of the present application;

[0068] Figure 11 is the structure chart of LCL grid-connected current feedback active damping control system in an embodiment of the present application. DETAILED DESCRIPTION

[0069] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0070] As shown in Figure 1 , the first embodiment of the present application proposes an LCL grid-connected current feedback active damping control method, which comprises the following steps:

[0071] S10, collecting the grid-connected current i2 of the inverter grid side.

[0072] S20, processing the grid-connected current i2 flowing through the negative low-pass-high-pass filter to obtain a feedback current, wherein the closed-loop transfer function between the output voltage u inv of the inverter and the grid-connected current i2 is:

[0073]

[0074] In the formula, A and B are respectively a low-pass active damping feedback function and a high-pass active damping feedback function, and G open is an open-loop transfer function between the grid-connected current i2 and the output voltage u inv of the inverter.

[0075] S30, superimposing the feedback current and the output of the inverter current controller as a control signal of the LCL filter.

[0076] Specifically, the structure chart of the three-phase LCL grid-connected inverter system is as shown in Figure 2As shown, the AC side of the LCL type three-phase AC voltage type grid-connected inverter is connected with the grid through an LCL filter, and the circuit of the LCL filter is as follows: the AC side of the three-phase inverter is connected with the grid through the series connection of inductors L1 and L2, and the middle point of each series branch (i.e. the connection point of inductors L1 and L2) is connected to a common point through a capacitor C. Figure 2 In the formula, U dc is the DC side voltage; C dc is the DC side filter capacitor; the bridge arm side inductor L1, the AC side filter capacitor C and the grid side inductor L2 form an LCL type filter; u inv is the inverter output voltage, i.e. the LCL filter input voltage; u C , i C are respectively the parallel branch capacitor voltage and the capacitor current; i1 and i2 are respectively the LCL filter bridge arm side current and the grid side current; u g is the common coupling point voltage, u s , L g are respectively the grid voltage and the grid impedance.

[0077] The NL-HPF feedback active damping LCL type grid-connected inverter system proposed in the embodiment is modeled and analyzed, and the inverter system control block diagram of Figure 3 can be obtained. Figure 3 In the formula, G i is a current controller, and the expression is as follows:

[0078]

[0079] In the formula, K p is a proportional coefficient, and K i is an integral coefficient.

[0080] In the embodiment, the grid current is fed back after being processed by the negative low-pass filter, and the grid-connected current i2 is processed by the feedback functions A and B and then loaded at the given point, i.e. in front of u inv (inverter output voltage), and is superimposed with the output of the inverter current controller. Compared with the existing grid-connected current feedback active damping method, this method can not only effectively suppress the LCL resonance peak and high-frequency harmonic current, but also has good robustness when the grid impedance and LCL parameters change; and only the grid current needs to be sampled, without the need to increase the sensor, thereby saving the hardware cost.

[0081] In an embodiment, the formula of the low-pass active damping feedback function A is as follows:

[0082]

[0083] The formula of the high-pass active damping feedback function B is as follows:

[0084]

[0085] The open-loop transfer function is expressed as follows:

[0086]

[0087] where ω l is the cut-off angular frequency of the low-pass filter, k ad is the feedback coefficient, ω h is the cut-off angular frequency of the negative high-pass filter, s is the differential operator, L1 is the bridge-arm-side inductance, C is the AC-side filter capacitance, and L2 is the grid-side inductance.

[0088] In an embodiment, the denominator of the closed-loop transfer function includes one first pole and four second poles, the first pole is located at the origin, and the second poles are configured as conjugate resonance poles, and are expressed as:

[0089]

[0090] It should be noted that the expression formula of the denominator contains five poles, one first pole and four second poles, wherein the first pole is the pole at the origin, and the other four second poles can be freely configured. In order to take into account the resonance damping and dynamic performance of the system, the four system dominant poles are configured as conjugate resonance poles. Two of the poles are configured at the fundamental frequency, which ensures that the system has high gain characteristics at the fundamental frequency.

[0091] Further, two of the four second poles are configured at the fundamental frequency, and the other two are a pair of conjugate poles, and the configuration of the second poles is as follows:

[0092] D * = L1L2Cs(s 2 + 2ξ0ω0s + ω0 2 )(s 2 + 2ξ n ω n s + ω n 2 )

[0093] where ξ0 is the damping ratio at ω0, ω0 is the fundamental angular frequency, ξ n is the damping ratio at ω n , ω n is a freely configurable high-frequency angular frequency, and the values of ξ0 and ξ n range from 0.4 to 0.8.

[0094] Further, the pair of conjugate poles ω nThe decision system at higher frequencies, which determines the position of the system at -180°, thus the system stability margin will be affected by it. At this time, ω n The open loop cutoff frequency needs to be greater than the closed loop cutoff frequency and a certain margin is reserved, so that the system has a higher open loop cutoff frequency.

[0095] Further, the value range of ξ0 and ξ n is 0.4-0.8, so as to ensure that the system has good dynamic characteristics and damping effect. In the embodiment, the values of ξ0 and ξ n are both 0.6.

[0096] In an embodiment, the ω n satisfies the following formula:

[0097] kω res ≤ω n ≤ω sw / 3

[0098] In the formula, ω sw is the switching frequency angular frequency, ω res is 9K, and k>1.

[0099] Further, in the embodiment, the value of k is greater than 1 to ensure that the system has a larger bandwidth, but if the value of k is too large, the cutoff angular frequency of the low-pass filter and the high-pass filter does not have a good value range. Through actual experimental results, it is determined that k=1.05.

[0100] The parameter design of the embodiment is simple and easy to implement through the pole configuration method.

[0101] In an embodiment, the expression of the cutoff angular frequency of the negative low-pass-high-pass filter is:

[0102]

[0103] In the formula, ω h is the cutoff frequency of the high-pass filter, ω l is the cutoff frequency of the low-pass filter, and k ad is the gain coefficient of the negative low-pass-high-pass filter.

[0104] The following analyzes the Bode diagram of the closed-loop transfer function of the NHPF and NL-HPF active damping system to illustrate that the NL-HPF active damping method has a lower gain for high-frequency harmonics and can well suppress high-frequency harmonic currents.

[0105] It can be seen from Figure 4 that the NHPF and NL-HPF active damping have similar gains at low frequencies, but the NL-HPF has a lower gain than the NHPF at high frequencies.

[0106] From Figure 5 It can be seen that when NL-HPF is adopted, the amplitude margin of the inverter control system is 8.42dB, and the phase margin is 68°, which indicates that the control system has good robustness at this time.

[0107] From Figure 6 It can be seen that when NL-HPF is adopted, the inverter control system still has good robustness when the LCL parameters change. Among them Figure 6 (a), (b), (c) in the system open-loop Bode diagram when the inverter side inductance L1, filter capacitor C, and grid side inductance L2 change, respectively.

[0108] In addition, it needs to be considered whether the inverter can stably operate under a weak power grid. Generally speaking, when SCR≤3, it is called a weak power grid. When the short-circuit ratio is 3 in this embodiment, the grid impedance L g =3.3mH. Therefore, this embodiment examines whether the inverter control system has good robustness when the grid impedance changes from 0.2 to 3.3mH.

[0109] From Figure 7 It can be seen that when the grid impedance changes from 0.2 to 3.3mH, the control system adopting the NL-HPF active damping strategy still has good robustness.

[0110] The following compares the effects of NL-HPF and NHPF on grid-connected current through simulation and experiment.

[0111] From Figure 8 It can be seen that NL-HPF and NHPF can both make the harmonic distortion rate of grid-connected current within 5%. NL-HPF and NHPF have good suppression effect on harmonic current at low frequency, but NL-HPF has better suppression effect on high-frequency harmonic current than NHPF. Among them, Figure 8 (a) is the NHPF corresponding grid-connected current waveform diagram, Figure 8 (b) is the NHPF corresponding grid-connected current waveform FFT analysis diagram, Figure 8 (c) is the NL-HPF corresponding grid-connected current waveform diagram, Figure 8 (d) is the NL-HPF corresponding grid-connected current waveform FFT analysis diagram.

[0112] From Figure 9 It can be seen that after adding NL-HPF active damping, the grid-connected current resonance is effectively suppressed, and the waveform quality is improved.

[0113] From Figure 10 It can be seen that under a weak power grid, when the grid impedance changes, NL-HPF active damping makes the grid-connected current waveform quality better, among which,Figure 10 (a) is a grid-connected current waveform when the grid impedance is 0.2 mH, Figure 10 (b) is a grid-connected current waveform when the grid impedance is 1.6 mH, Figure 10 (c) is a grid-connected current waveform when the grid impedance is 3.3 mH.

[0114] Therefore, the common problem of the existing grid-connected current-based active damping strategy is to amplify high-frequency harmonic currents, and none of them considers the stability of the system and the resonance suppression effect when the grid impedance changes under a weak grid. The NL-HPF active damping control method proposed in this embodiment can well suppress high-frequency harmonic currents, and still has good harmonic suppression effect when the grid impedance changes under a weak grid.

[0115] In addition, as Figure 11 shown, another embodiment of the present application proposes an LCL grid-connected current feedback active damping control system. The AC side of the LCL type three-phase AC voltage type grid-connected inverter is connected with the grid through an LCL filter, and the grid-side current of the inverter is connected with the output of the inverter current controller through a negative low-pass-high-pass filter. The system comprises:

[0116] The acquisition module 10 is used for acquiring the grid-connected current i2 of the grid-side of the inverter;

[0117] The processing module 20 is used for processing the grid-connected current i2 flowing through the negative low-pass-high-pass filter to obtain a feedback current, wherein the closed-loop transfer function between the output voltage u inv of the inverter and the grid-connected current i2 is:

[0118]

[0119] In the formula, A and B are respectively a low-pass active damping feedback function and a high-pass active damping feedback function, and G open is an open-loop transfer function between the grid-connected current i2 and the output voltage u inv of the inverter;

[0120] The control module 30 is used for superimposing the feedback current and the output of the inverter current controller as a control signal of the LCL filter.

[0121] In this embodiment, the grid current is processed through the negative low-pass-high-pass filter and then fed back, and the grid-connected current i2 is processed through the feedback functions A and B and then loaded at the given point, that is, u inv(Inverter output voltage) is superimposed on the output of the inverter current controller. Compared with the existing grid-connected current feedback active damping method, this method can not only effectively suppress LCL resonance spikes and high-frequency harmonic currents, but also maintain good robustness when the grid impedance and LCL parameters change; and the control system only needs to sample the grid current, without adding sensors, which can save hardware costs.

[0122] The formula for the low-pass active damping feedback function A is as follows:

[0123]

[0124] The formula for the high-pass active damping feedback function B is as follows:

[0125]

[0126] The formula for the open-loop transfer function is as follows:

[0127]

[0128] In the formula, ω l k is the cutoff angular frequency of the low-pass filter. ad ω is the feedback coefficient. h ω is the cutoff angular frequency of the negative high-pass filter, s is the differential operator, L1 is the bridge arm inductance, C is the AC side filter capacitor and L2 is the grid side inductance;

[0129] The denominator of the closed-loop transfer function includes one first pole and four second poles. The first pole is located at the origin, and the second poles are configured as conjugate resonant poles. The formula is expressed as:

[0130]

[0131] It should be noted that the denominator formula contains five poles: one primary pole and four secondary poles. The primary pole is located at the origin, while the other four secondary poles can be freely configured. To balance the system's resonant damping and dynamic performance, the four dominant system poles are configured as conjugate resonant poles. Two of these poles are located at the fundamental frequency, ensuring high gain characteristics at that frequency.

[0132] Furthermore, two of the four second poles are positioned at the fundamental frequency, and the other two serve as a pair of conjugate poles, ω. n This will determine the system's characteristics at higher frequencies, and it will determine the system's position when crossing -180°, thus affecting the system's stability margin. At this point, ω n It needs to be larger than the open-loop cutoff frequency and have a certain margin in order to give the system a high open-loop cutoff frequency.

[0133] In one embodiment, the cut-off angular frequency of the negative low-pass-high-pass filter is expressed as:

[0134]

[0135] where ω h is the cut-off frequency of the high-pass filter, ω l is the cut-off frequency of the low-pass filter, and k ad is the gain coefficient of the negative low-pass-high-pass filter.

[0136] It should be noted that other embodiments of the LCL grid-connected current feedback active damping control system or methods of implementing the same can refer to the above-mentioned method embodiments, which will not be repeated here.

[0137] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a list of executable instructions for implementing logic functions, which can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus or device, such as a computer-based system, a system including a processor or other system that can fetch the instructions from an instruction execution system, apparatus or device and execute the instructions, or in conjunction with these instruction execution systems, apparatus or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate or transport a program for use by or in connection with an instruction execution system, apparatus or device, or in conjunction with these instruction execution systems, apparatus or devices. More specific examples (non-exhaustive list) of computer-readable media include the following: electrical connections having one or more wires (electronic devices), portable computer disks (magnetic devices), random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memories), fiber optic devices, and portable compact disc read-only memories (CDROMs). In addition, a computer-readable medium can even be paper or other suitable medium on which the program can be printed, as the program can be electronically obtained, for example, by optical scanning of the paper or other medium, followed by electronic conversion of the scanned program into a computer-readable medium, and then storing the program in a computer memory if necessary. The program can be processed before storage or after retrieval, for example, by an electronic conversion of the scanned program into a computer-readable medium, and then storing the program in a computer memory if necessary.

[0138] It should be understood that various parts of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above embodiments, various steps or methods can be implemented in software or firmware that is stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any of the following technologies, known in the art, or their combinations can be used: discrete logic circuitry having logic gates for implementing logic functions upon data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), and the like.

[0139] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0140] In addition, the terms "first", "second", are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0141] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for LCL grid-connected current feedback active damping control, characterized in that, The method comprises: Collecting grid-connected current of inverter grid side i 2; the grid current i 2 is processed by passing through a negative low-pass-high-pass filter to obtain a feedback current, wherein the output voltage of the inverter u inv and the grid current i 2 is: wherein: A , B Gp(s) and Gp(s) are a low-pass and a high-pass active damping feedback function, respectively, G open is the grid-connected current i 2is an open-loop transfer function between the grid-connected current u inv and the output voltage of the inverter; superimposing the feedback current and the output of the inverter current controller as a control signal of the LCL filter; wherein the expression of the cutoff angular frequency of the negative low-pass-high-pass filter is: where L1 is the bridge arm side inductor, C is the AC side filter capacitor and L2 is the grid side inductor, is the cut-off corner frequency of the low-pass filter, is the cut-off corner frequency of the negative high-pass filter, is the is the damping ratio at ω = ω0, is the fundamental corner frequency, is the is the damping ratio at ω = ω0, is the freely configurable high-frequency corner frequency, is the feedback coefficient; The low-pass active damping feedback function A The formula is expressed as follows: The high-pass active damping feedback function B The formula is expressed as follows: The open-loop transfer function is expressed as follows: wherein is a cut-off corner frequency of a low-pass filter, is a feedback coefficient, is a cut-off corner frequency of a negative high-pass filter, s is a differential operator, L1 is a bridge arm side inductance, C is an AC side filter capacitance and L2 is a grid side inductance.

2. The LCL grid-connected current feedback active damping control method of claim 1, wherein, The denominator of the closed-loop transfer function includes one first pole and four second poles, the first pole is located at the origin, and the second poles are configured as conjugate resonance poles, and the formula is expressed as: 。 3. The LCL grid-connected current feedback active damping control method of claim 2, wherein, Four of the second poles are configured at the fundamental wave, and the other two are configured as a pair of conjugate poles, and the configuration of the second poles is as follows: In the formula, is the damping ratio at the point, is the fundamental angular frequency, is the damping ratio at the point, is a freely configurable high-frequency angular frequency, and the value range of is 0.4-0.

8.

4. The LCL grid-connected current feedback active damping control method of claim 3, wherein, The satisfies the following equation: In the formula, is the switching frequency and k >1.

5. The LCL grid-connected current feedback active damping control method of claim 3, wherein, The With The values are all 0.

6.

6. The LCL grid-connected current feedback active damping control method of claim 4, wherein, the values k is 1.

5.

7. A LCL grid-connected current feedback active damping control system, characterized in that, The AC side of the LCL type three-phase AC voltage type grid-connected inverter is connected with the grid through an LCL filter, and the grid-side current of the inverter is connected with the output of the inverter current controller through a negative low-pass-high-pass filter, and the system comprises: The collecting module is configured to collect a grid-connected current at a grid side of the inverter i 2; a processing module for processing the grid-connected current i 2 through a negative low-pass-high-pass filter to obtain a feedback current, wherein the output voltage of the inverter u inv and the grid-connected current i 2 is wherein: A , B Gp(s) and Gp(s) are a low-pass and a high-pass active damping feedback function, respectively, G open is the grid-connected current i 2is an open-loop transfer function between the grid-connected current u inv and the output voltage of the inverter. A control module is configured to superimpose the feedback current and the output of the inverter current controller as a control signal of the LCL filter; wherein the expression of the cutoff angular frequency of the negative low-pass-high-pass filter is: where L1 is the bridge leg side inductor, C is the AC side filter capacitor and L2 is the grid side inductor, is the cut-off corner frequency of the low-pass filter, is the cut-off corner frequency of the negative high-pass filter, is the corner frequency of the high-pass filter, is the damping ratio at the corner frequency, is the fundamental corner frequency, is the corner frequency of the low-pass filter, is the damping ratio at the corner frequency, is the freely configurable high-frequency corner frequency, is the feedback coefficient; The low-pass active damping feedback function A The formula is expressed as follows: The high-pass active damping feedback function B The formula is expressed as follows: The open-loop transfer function is expressed as follows: wherein is a cut-off corner frequency of a low-pass filter, is a feedback coefficient, is a cut-off corner frequency of a negative high-pass filter, s is a differential operator, L1 is a bridge arm side inductance, C is an AC side filter capacitance and L2 is a grid side inductance.

8. The LCL grid-tied current feedback active damping control system of claim 7, wherein, The denominator of the closed-loop transfer function includes one first pole and four second poles, the first pole is located at the origin, and the second poles are configured as conjugate resonance poles, and the formula is expressed as: 。

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