Double-loop control method and system for LCL type grid-connected inverter

Abstract

The invention discloses a double-loop control method and system for an LCL type grid-connected inverter. The control method comprises the following steps that S10, a negative sequence compensator control unit is introduced into an outer loop of the LCL type grid-connected inverter system, and a cascade active damping control unit is introduced into an inner loop of the LCL type grid-connected inverter system; s20, establishing a state feedback link and an integral control link considering compensation non-oscillation reactive power in the negative sequence compensator control unit to eliminate interference of the reactive power on voltage regulation and power factor correction; and S30, cascading a resonance component separation module and a second-order leading filtering module in the active damping control unit to eliminate inductive current disturbance, load disturbance and digital control delay.

Description

Technical Field

[0001] The present invention relates to the technical field related to stable control and energy saving and consumption reduction of grid-connected inverters, and in particular to a dual-loop control method and system for an LCL type grid-connected inverter. Background Art

[0002] In order to cope with the increasingly urgent energy crisis, the development of renewable energy power generation systems represented by clean energy such as solar energy and wind energy has become a practical solution. Grid-connected inverter equipment, as the interface connecting the renewable energy power generation system with the public power grid, plays an important role. However, with the development of economy and technology, the penetration rate of new energy power generation has continued to increase, and more nonlinear loads have been connected to the power grid, resulting in serious power quality problems such as unbalanced grid voltage sag, which often causes unbalanced current and power oscillations at the interface between the inverter and the grid, interfering with national production and life. In addition, with the increase in the number of inverters connected to the grid, the resonant peaks of the LCL filter on the AC side of the inverter have seriously restricted the development of distributed power generation. Existing resonance suppression methods mostly use capacitor current and capacitor voltage to design feedback loops, but this method requires additional high-precision current and voltage sensors, and does not consider power control under unbalanced grid voltage sag conditions. Summary of the invention

[0003] In response to the problems and needs raised above, this solution proposes a dual-loop control method and system for an LCL-type grid-connected inverter. By adopting the following technical features, the above technical objectives can be achieved and many other technical effects can be brought about.

[0004] An object of the present invention is to provide a dual-loop control method for an LCL type grid-connected inverter, comprising the following steps:

[0005] S10: introducing a negative sequence compensator control unit into the outer loop of the LCL type grid-connected inverter system, and introducing a cascade active damping control unit into the inner loop of the LCL type grid-connected inverter system;

[0006] S20: establishing a state feedback link and an integral control link in the negative sequence compensator control unit that take into account compensation of non-oscillating reactive power to eliminate interference of reactive power on voltage regulation and power factor correction in power control;

[0007] S30: cascading a resonance component separation module and a second-order pilot filter module in an active damping control unit to eliminate inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

[0008] In addition, the LCL type grid-connected inverter dual-loop control method according to the present invention may also have the following technical features:

[0009] In one example of the present invention, in step S20, establishing a state feedback link and an integral control link taking into account compensation of non-oscillating reactive power includes the following steps:

[0010] S21: Collect the voltage and current signals of the unbalanced AC power grid at the front end, extract the positive and negative sequences, and define the compensation non-oscillating reactive power Q according to the relationship between voltage, current and power. ref ;

[0011] S22: Combined with the power control principle, according to the inequality Construct state feedback link and integral control link, and calculate the optimal control gain;

[0012] Among them, w 0 represents a positive definite matrix with uncertain parameters

[0013] S23: Compensation of non-oscillating reactive power Q obtained according to the above steps ref , state feedback robust gain F k and integral control robust gain F L , combining Clark transform, Park transform and Kirchhoff's voltage law, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is obtained.

[0014] In one example of the present invention, in step S21, the compensation non-oscillating reactive power Q is defined according to the relationship between voltage, current and power. ref , where the relationship between voltage, current and power is:

[0015]

[0016] In the formula, Represent the components of the positive and negative sequence grid current on the d and q axes, respectively. Represents the components of the positive and negative sequence grid voltage on the d and q axes, respectively, Q ref To compensate for non-oscillating reactive power.

[0017] In one example of the present invention, in step S22, the expression for calculating the optimal control gain is:

[0018]

[0019] In the formula, F k represents the state feedback robust gain, F L represents the integral control robust gain, R g Represents the filter resistance, L g Represents the total inductance of the filter, w 0 represents a positive definite matrix with uncertain parameters

[0020] In one example of the present invention, in step S23, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is expressed as:

[0021]

[0022] In the formula, m(k) represents the integral link, c represents the second-order unit matrix, Q ref Indicates non-oscillating reactive power, F k represents the state feedback robust gain, F L represents the integral control robust gain, Indicates negative sequence grid voltage; Respectively represent the components of the negative sequence grid current on the d and q axes, They represent the components of the positive and negative sequence grid voltage on the d and q axes respectively.

[0023] In one example of the present invention, in step S30, cascading the resonance component separation module and the second-order pilot filter module in the active damping control unit includes the following steps:

[0024] S31: Cascade the resonance component separation module and the second-order pilot filter module to obtain the transfer function G of the cascade active damping control unit CA (z);

[0025] S32: According to the differential equation of the frequency response characteristics, the resonant frequency component in the inverter current feedback is extracted to obtain the transfer function G of the resonant component separation module in the complex frequency domain. RS (z):

[0026] S33: Considering the interference of system delay on the damping range, a phase advance is provided at the extracted resonance frequency to obtain the transfer function G of the second-order pilot filter module in the complex frequency domain. SOLF (z).

[0027] In one example of the present invention, in step S31, the transfer function G of the cascade active damping control unit is CA (z):

[0028] G CA (z) = G RS (z)·G SOLF (z)(4)

[0029] In the formula, G RS (z) represents the transfer function of the resonance component separation module in the complex frequency domain, G SOLF (z) represents the transfer function of the second-order pilot filter module in the complex frequency domain.

[0030] In one example of the present invention, in step S32, the transfer function G of the resonance component separation module in the complex frequency domain is RS The expression of (z) is:

[0031]

[0032] In the formula, K AD represents a gain used to suppress load disturbance and inductor current disturbance, ω res represents the resonant frequency, ω RS represents the center frequency, Q RS Denotes the quality factor, T S represents the sampling time, and z represents a complex variable.

[0033] In one example of the present invention, in step S33, the transfer function G of the second-order pilot filter module in the complex frequency domain is SOLF The expression of (z) is:

[0034]

[0035] In the formula, K p =ζω 1 , K q =ζω 2 , ζ represents the damping ratio of the SOLF zero and pole, and z represents a complex variable.

[0036] Another object of the present invention is to provide a dual-loop control system for an LCL-type grid-connected inverter, comprising: an LCL-type grid-connected inverter system, further comprising:

[0037] A negative sequence compensator control unit coupled to an outer loop of the LCL type grid-connected inverter system;

[0038] An active damping control unit coupled to an inner loop of the LCL type grid-connected inverter system;

[0039] Among them, the negative sequence compensator control unit includes a state feedback link and an integral control link that take into account the compensation of non-oscillating reactive power, and is configured to eliminate the interference of power control reactive power on voltage regulation and power factor correction; the active damping control unit includes a cascaded resonance component separation module and a second-order pilot filter module, which is configured to eliminate the inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The invention introduces a negative sequence compensator control unit (NSCU) in the outer loop of the LCL type grid-connected inverter system, thereby compensating for the non-oscillating reactive power in the case of unbalanced grid voltage sag and eliminating the unbalanced oscillation of grid current and power; and introduces a cascade active damping control unit (CADCU) in the inner loop of the LCL type grid-connected inverter system, thereby widening the damping range under the resonant frequency and improving the system low-frequency gain. The LCL type grid-connected inverter dual-loop control scheme is applied to the new energy grid-connected system. Without the need for additional current sensors, the dynamic response of the LCL type filter can be improved, and it has good robustness to grid impedance changes and high-frequency noise. It can be applied to LCL type grid-connected inverter systems with small filter capacitors.

[0042] The best embodiment for carrying out the present invention will be described in more detail below with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0044] Figure 1 A dual-loop control block diagram of an LCL-type grid-connected inverter according to an embodiment of the present invention;

[0045] Figure 2 1 is an overall architecture diagram of a dual-loop control system of an LCL-type grid-connected inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not necessarily indicate a quantity limitation. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] According to a first aspect of the present invention, a dual-loop control method for an LCL type grid-connected inverter is Figure 1 and Figure 2 As shown, the following steps are included:

[0049] S10: In view of the harmonic resonance and unbalanced oscillation of grid current and power in the LCL type grid-connected inverter system under the condition of unbalanced grid voltage sag, a negative sequence compensator control unit (NSCU) is introduced in the outer loop of the LCL type grid-connected inverter system, and a cascade active damping control unit (CADCU) is introduced in the inner loop of the LCL type grid-connected inverter system;

[0050] S20: establishing a state feedback link and an integral control link that take into account compensation of non-oscillating reactive power in a negative sequence compensator control unit (NSCU) to eliminate interference of reactive power on voltage regulation and power factor correction in power control;

[0051] S30: A cascade resonance component separation module (RCSM) and a second-order lead filter module (SOLFM) are connected in an active damping control unit to eliminate inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

[0052] In short, a negative-sequence compensator control unit is introduced into the outer loop to compensate for non-oscillating reactive power, and a cascaded active damping control unit is introduced into the inner loop to broaden the damping range of the resonant frequency. Thus, a dual-loop control strategy for an LCL-type grid-connected inverter is obtained, which takes into account voltage, current, power control and harmonic suppression when the voltage of an unbalanced power grid is temporarily sagged.

[0053] The dual-loop control method introduces a negative sequence compensator control unit (NSCU) in the outer loop of the LCL type grid-connected inverter system to compensate for the non-oscillating reactive power in the case of unbalanced grid voltage sag and eliminate the unbalanced oscillation of grid current and power; the cascade active damping control unit (CADCU) is introduced in the inner loop of the LCL type grid-connected inverter system to broaden the damping range under the resonant frequency and improve the low-frequency gain of the system. The dual-loop control strategy of the LCL type grid-connected inverter is applied to the new energy grid-connected system. Without the need for additional current sensors, the dynamic response of the LCL type filter can be improved, and it has good robustness to grid impedance changes and high-frequency noise. It can be applied to the LCL type grid-connected inverter system with a small filter capacitor.

[0054] It should be noted that Figure 1 The control block diagram after the negative sequence compensator and cascade active damping controller are introduced into the outer loop and inner loop respectively; Figure 2 This is the overall architecture diagram of the improved system. In the figure, L 1 represents the inverter side inductance in the filter, L 2 represents the grid-side inductance in the filter, C represents the filter capacitance, K PWM Represents the inverter gain, G NS (z) represents the transfer function of the negative sequence compensator control unit, i 1 Indicates the inverter current, i 2 Represents the grid current, v inv Indicates the inverter voltage, v c Represents capacitor voltage, v g Indicates the grid voltage.

[0055] In one example of the present invention, in step S20, establishing a state feedback link and an integral control link taking into account compensation of non-oscillating reactive power includes the following steps:

[0056] S21: Collect the voltage and current signals of the unbalanced AC power grid at the front end, extract the positive and negative sequences, and define the compensation non-oscillating reactive power Q according to the relationship between voltage, current and power. ref ;

[0057] S22: Combined with the power control principle, according to the inequality Construct state feedback link and integral control link, and calculate the optimal control gain;

[0058] Among them, w 0 represents a positive definite matrix with uncertain parameters

[0059] S23: Compensation of non-oscillating reactive power Q obtained according to the above steps ref , state feedback robust gain F kand integral control robust gain F L , combining Clark transform, Park transform and Kirchhoff's voltage law, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is obtained.

[0060] In one example of the present invention, in step S21, the compensation non-oscillating reactive power Q is defined according to the relationship between voltage, current and power. ref , where the relationship between voltage, current and power is:

[0061]

[0062] In the formula, Represent the components of the positive and negative sequence grid current on the d and q axes, respectively. Represents the components of the positive and negative sequence grid voltage on the d and q axes, respectively, Q ref To compensate for non-oscillating reactive power.

[0063] In one example of the present invention, in step S22, the expression for calculating the optimal control gain is:

[0064]

[0065] In the formula, F k represents the state feedback robust gain, F L represents the integral control robust gain, R g Represents the filter resistance, L g Represents the total inductance of the filter, w 0 represents a positive definite matrix with uncertain parameters

[0066] inequality The solution process is as follows: multiply both sides of the above formula by We get the inequality:

[0067]

[0068] Thus, the optimal control gain F is obtained. Among them, I represents the second-order identity matrix.

[0069] In one example of the present invention, in step S23, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is expressed as:

[0070]

[0071] In the formula, m(k) represents the integral link, c represents the second-order unit matrix, Qref Indicates non-oscillating reactive power, F k represents the state feedback robust gain, F L represents the integral control robust gain, Indicates negative sequence grid voltage; Respectively represent the components of the negative sequence grid current on the d and q axes, They represent the components of the positive and negative sequence grid voltage on the d and q axes respectively.

[0072] In one example of the present invention, in step S30, cascading the resonance component separation module and the second-order pilot filter module in the active damping control unit includes the following steps:

[0073] S31: Cascade the resonance component separation module and the second-order pilot filter module to obtain the transfer function G of the cascade active damping control unit CA (z);

[0074] S32: According to the differential equation of the frequency response characteristics, the resonant frequency component in the inverter current feedback is extracted to obtain the transfer function G of the resonant component separation module in the complex frequency domain. RS (z):

[0075] S33: Considering the interference of system delay on the damping range, a phase advance is provided at the extracted resonance frequency to obtain the transfer function G of the second-order pilot filter module in the complex frequency domain. SOLF (z).

[0076] The significance of cascading the two is that although the resonance component separation module can effectively separate the resonance frequency for feedback, it exhibits a narrow resonance frequency damping range. Using the second-order pilot filter module to provide phase advance at the resonance frequency can expand the resonance frequency damping range, improve the low-frequency gain, and have better robustness to high-frequency noise.

[0077] In one example of the present invention, in step S31, the transfer function G of the cascade active damping control unit is CA (z):

[0078] G CA (z) = G RS (z)·G SOLF (z)(4)

[0079] In the formula, G RS (z) represents the transfer function of the resonance component separation module in the complex frequency domain, G SOLF (z) represents the transfer function of the second-order pilot filter module in the complex frequency domain.

[0080] In one example of the present invention, in step S32, the transfer function G of the resonance component separation module in the complex frequency domain isRS The expression of (z) is:

[0081]

[0082] In the formula, K AD represents a gain used to suppress load disturbance and inductor current disturbance, ω res represents the resonant frequency, ω RS represents the center frequency, Q RS Denotes the quality factor, T S represents the sampling time, and z represents a complex variable.

[0083] In one example of the present invention, in step S33, the transfer function G of the second-order pilot filter module in the complex frequency domain is SOLF The expression of (z) is:

[0084]

[0085] In the formula, K p =ζω 1 , K q =ζω 2 , ζ represents the damping ratio of the SOLF zero and pole, and z represents a complex variable.

[0086] According to the second aspect of the present invention, a dual-loop control system of an LCL type grid-connected inverter is Figure 1 and Figure 2 As shown, it includes: LCL type grid-connected inverter system, and also includes:

[0087] A negative sequence compensator control unit coupled to an outer loop of the LCL type grid-connected inverter system;

[0088] An active damping control unit coupled to an inner loop of the LCL type grid-connected inverter system;

[0089] Among them, the negative sequence compensator control unit includes a state feedback link and an integral control link that take into account the compensation of non-oscillating reactive power, and is configured to eliminate the interference of power control reactive power on voltage regulation and power factor correction; the active damping control unit includes a cascaded resonance component separation module and a second-order pilot filter module, which is configured to eliminate the inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

[0090] In order to solve the harmonic resonance and unbalanced oscillation of grid current and power in the LCL type grid-connected inverter system under the condition of unbalanced grid voltage sag, a negative sequence compensator control unit is introduced into the outer loop to provide non-oscillating reactive power compensation, and a cascade active damping control unit is introduced into the inner loop to broaden the damping range of the resonance frequency. Thus, a dual-loop control strategy for the LCL type grid-connected inverter is obtained, which takes into account voltage, current, power control and harmonic suppression when the unbalanced grid voltage sag is applied.

[0091] The dual-loop control system introduces a negative sequence compensator control unit (NSCU) in the outer loop of the LCL type grid-connected inverter system to compensate for the non-oscillating reactive power in the case of unbalanced grid voltage sag and eliminate the unbalanced oscillation of grid current and power; the cascade active damping control unit (CADCU) is introduced in the inner loop of the LCL type grid-connected inverter system to broaden the damping range under the resonant frequency and improve the low-frequency gain of the system. The dual-loop control strategy of the LCL type grid-connected inverter is applied to the new energy grid-connected system. Without the need for additional current sensors, the dynamic response of the LCL type filter can be improved, and it has good robustness to grid impedance changes and high-frequency noise. It can be applied to the LCL type grid-connected inverter system with a small filter capacitor.

[0092] In one example of the present invention, the negative sequence compensator control unit includes:

[0093] Definition module, configured to collect voltage and current signals of the power grid at the front end of the unbalanced AC power grid, extract positive and negative sequences, and define the compensation non-oscillating reactive power Q according to the relationship between voltage, current and power ref ;

[0094] The gain block is configured to be used in conjunction with the power control principle, according to the inequality Construct state feedback link and integral control link, and calculate the optimal control gain;

[0095] Among them, w 0 represents a positive definite matrix with uncertain parameters

[0096] A transfer function module configured to compensate for the non-oscillating reactive power Q obtained according to the definition module ref , the state feedback robust gain F obtained by the gain module k and integral control robust gain F L , combining Clark transform, Park transform and Kirchhoff's voltage law, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is obtained.

[0097] In one example of the present invention, in the definition module, the compensation non-oscillating reactive power Q is defined according to the relationship between voltage, current and power. ref, where the relationship between voltage, current and power is:

[0098]

[0099] In the formula, Represent the components of the positive and negative sequence grid current on the d and q axes, respectively. Represents the components of the positive and negative sequence grid voltage on the d and q axes, respectively, Q ref To compensate for non-oscillating reactive power.

[0100] In one example of the present invention, in the gain module, the expression for calculating the optimal control gain is:

[0101]

[0102] In the formula, F k represents the state feedback robust gain, F L represents the integral control robust gain, R g Represents the filter resistance, L g Represents the total inductance of the filter, w 0 represents a positive definite matrix, with uncertain parameters

[0103] In one example of the present invention, in the transfer function module, the expression of the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is:

[0104]

[0105] In the formula, m(k) represents the integral link, c represents the second-order unit matrix, Q ref Indicates non-oscillating reactive power, F k represents the state feedback robust gain, F L represents the integral control robust gain, Indicates negative sequence grid voltage; Respectively represent the components of the negative sequence grid current on the d and q axes, They represent the components of the positive and negative sequence grid voltage on the d and q axes respectively.

[0106] In one example of the present invention, the active damping control unit comprises:

[0107] The first calculation module is configured to cascade the resonance component separation module and the second-order pilot filter module to obtain a transfer function G of the cascade active damping control unit. CA (z);

[0108] The second calculation module is configured to extract the resonant frequency component in the inverter current feedback according to the differential equation of the frequency response characteristic, and obtain the transfer function G of the resonant component separation module in the complex frequency domain. RS (z):

[0109] The third calculation module is configured to consider the interference of system delay on the damping range, provide phase advance at the resonant frequency extracted by the second calculation module, and obtain the transfer function G of the second-order pilot filter module in the complex frequency domain SOLF (z).

[0110] In one example of the present invention, in the first calculation module, the transfer function G of the cascade active damping control unit is CA (z):

[0111] G CA (z) = G RS (z)·G SOLF (z)(4)

[0112] In the formula, G RS (z) represents the transfer function of the resonance component separation module in the complex frequency domain, G SOLF (z) represents the transfer function of the second-order pilot filter module in the complex frequency domain.

[0113] In one example of the present invention, in the second calculation module, G RS The expression of (z) is:

[0114]

[0115] In the formula, K AD represents a gain for suppressing load disturbance and inductor current disturbance, ω res represents the resonant frequency, ω RS represents the center frequency, Q RS Denotes the quality factor, T S represents the sampling time, and z represents a complex variable.

[0116] In one example of the present invention, in the third calculation module, G SOLF The expression of (z) is:

[0117]

[0118] In the formula, K p =ζω 1 , K q =ζω 2 , ζ is the damping ratio of the SOLF zero and pole.

[0119] The exemplary implementation scheme of the dual-loop control method and system for the LCL-type grid-connected inverter proposed in the present invention is described in detail above with reference to the preferred embodiments. However, those skilled in the art will appreciate that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A dual-loop control method for an LCL type grid-connected inverter, characterized in that: The steps include: S10: introducing a negative sequence compensator control unit into the outer loop of the LCL type grid-connected inverter system, and introducing a cascade active damping control unit into the inner loop of the LCL type grid-connected inverter system; S20: establishing a state feedback link and an integral control link in the negative sequence compensator control unit that take into account compensation of non-oscillating reactive power to eliminate interference of reactive power on voltage regulation and power factor correction in power control; S30: cascading a resonance component separation module and a second-order pilot filter module in an active damping control unit to eliminate inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

2. The dual-loop control method for LCL type grid-connected inverter according to claim 1, characterized in that: In step S20, establishing a state feedback link and an integral control link that take into account compensation of non-oscillating reactive power includes the following steps: S21: Collect the voltage and current signals of the unbalanced AC power grid at the front end, extract the positive and negative sequences, and define the compensation non-oscillating reactive power Q according to the relationship between voltage, current and power. ref ; S22: Combined with the power control principle, according to the inequality Construct the state feedback link and integral control link, and calculate the optimal control gain F; Among them, w0 represents a positive definite matrix, and the uncertain parameters S23: Compensation of non-oscillating reactive power Q obtained according to the above steps ref , state feedback robust gain F k and integral control robust gain F L , combining Clark transform, Park transform and Kirchhoff's voltage law, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is obtained.

3. The dual-loop control method for LCL type grid-connected inverter according to claim 2, characterized in that: In step S21, the compensation non-oscillating reactive power Q is defined according to the relationship between voltage, current and power. ref , where the relationship between voltage, current and power is: In the formula, Represent the components of the positive and negative sequence grid current on the d and q axes, respectively. Represents the components of the positive and negative sequence grid voltage on the d and q axes, respectively, Q ref To compensate for non-oscillating reactive power.

4. The dual-loop control method for LCL type grid-connected inverter according to claim 2, characterized in that: In step S22, the expression for calculating the optimal control gain is: In the formula, F k represents the state feedback robust gain, F L represents the integral control robust gain, R g Represents the filter resistance, L g represents the total inductance of the filter, w0 represents a positive definite matrix, and the uncertain parameters 5. The dual-loop control method for LCL type grid-connected inverter according to claim 2, characterized in that: In step S23, the transfer function of the negative sequence compensator for compensating non-oscillating reactive power in the discrete domain is expressed as: In the formula, m(k) represents the integral link, c represents the second-order unit matrix, Q ref Indicates non-oscillating reactive power, F k represents the state feedback robust gain, F L represents the integral control robust gain, Indicates negative sequence grid voltage; Respectively represent the components of the negative sequence grid current on the d and q axes, They represent the components of the positive and negative sequence grid voltage on the d and q axes respectively.

6. The dual-loop control method for LCL type grid-connected inverter according to claim 1, characterized in that: In step S30, cascading the resonance component separation module and the second-order pilot filter module in the active damping control unit includes the following steps: S31: Cascade the resonance component separation module and the second-order pilot filter module to obtain the transfer function G of the cascade active damping control unit CA (z); S32: According to the differential equation of the frequency response characteristics, the resonant frequency component in the inverter current feedback is extracted to obtain the transfer function G of the resonant component separation module in the complex frequency domain. RS (z): S33: Considering the interference of system delay on the damping range, a phase advance is provided at the extracted resonance frequency to obtain the transfer function G of the second-order pilot filter module in the complex frequency domain. SOLF (z).

7. The dual-loop control method for LCL type grid-connected inverter according to claim 6, characterized in that: In step S31, the transfer function G of the cascade active damping control unit is CA (z): G CA (z)=G RS (z)·G SOLF (z)(4) In the formula, G RS (z) represents the transfer function of the resonance component separation module in the complex frequency domain, G SOLF (z) represents the transfer function of the second-order pilot filter module in the complex frequency domain.

8. The dual-loop control method for LCL type grid-connected inverter according to claim 6, characterized in that: In step S32, the transfer function G of the resonance component separation module in the complex frequency domain is RS The expression of (z) is: In the formula, K AD represents a gain used to suppress load disturbance and inductor current disturbance, ω res represents the resonant frequency, ω RS represents the center frequency, Q RS Denotes the quality factor, T S represents the sampling time, and z represents a complex variable.

9. The dual-loop control method for LCL grid-connected inverter according to claim 6, characterized in that: In step S33, the transfer function G of the second-order pilot filter module in the complex frequency domain is SOLF The expression of (z) is: In the formula, K p =ζω1,K q =ζω2, ζ represents the damping ratio of the SOLF zero and pole, and z represents a complex variable.

10. A dual-loop control system for an LCL-type grid-connected inverter, comprising: The LCL type grid-connected inverter system is characterized by further comprising: A negative sequence compensator control unit coupled to an outer loop of the LCL type grid-connected inverter system; An active damping control unit coupled to an inner loop of the LCL type grid-connected inverter system; Among them, the negative sequence compensator control unit includes a state feedback link and an integral control link that take into account the compensation of non-oscillating reactive power, and is configured to eliminate the interference of power control reactive power on voltage regulation and power factor correction; the active damping control unit includes a cascaded resonance component separation module and a second-order pilot filter module, which is configured to eliminate the inductor current disturbance, load disturbance and digital control delay in the outer loop inverter current control.

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