CN110323749B - Interference suppression method for LCL filter grid-connected inverter - Google Patents
Interference suppression method for LCL filter grid-connected inverter Download PDFInfo
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Abstract
The invention discloses an interference suppression method for a grid-connected inverter of an LCL filter. The LCL filter is converted into a first-order system, and a first-order self-interference rejection system model of the LCL filter is designed; simplifying a first-order self-interference rejection system model of the LCL filter, enabling an input signal to pass through a tracking differentiator, listing transient states by the tracking differentiator, and calculating each order derivative of the input signal; the extended state observer is used for calculating an equation of the linear extended state observer, estimating state variables and total disturbance through the second-order linear extended state observer and integrating the disturbance and self resonance; performing feedback control on the state error, and combining a reference signal of a tracking differentiator and an output differential signal of an extended state observer to generate an intermediate control voltage signal; and selecting the observer gain to enable the observer characteristic value to be in a stable state, designing an independent first-order linear controller for each current component, and inhibiting external interference and internal interference.
Description
Technical Field
The invention relates to the technical field of LCL filters, in particular to an interference suppression method for a grid-connected inverter of an LCL filter.
Background
In recent years, global energy shortage and environmental pollution are becoming more serious, and in order to solve the energy crisis and protect the environment in which human beings live, the search for new energy becomes the current first problem. Such as solar energy, wind energy, tidal energy, etc., are renewable clean energy sources. Distributed power generation is being widely used, and as an important form of renewable energy utilization, these can be divided into off-grid power generation and grid-connected power generation systems according to different application occasions, and the off-grid system stores electric energy converted from solar energy in a storage battery and then supplies the electric energy to user equipment through a controller. The grid-connected power generation system is connected with a power grid of the power system, the converted electric energy is merged into the power grid, and then the power grid uniformly distributes the electric energy to users. The grid-connected system has the advantages of maintenance free, low cost and the like, so that domestic and foreign scholars put main attention to the grid-connected power generation technology taking the grid-connected inverter as a core, and the grid-connected power generation system becomes the mainstream of the current development.
The inverter plays an important role in connecting a power grid and energy, the control strategy of the grid-connected inverter causes that a voltage waveform output by the inverter contains a large amount of switching frequency subharmonics, and in order to reduce high-frequency switching harmonics existing in the current of the power grid and obtain grid-connected current with high sine degree, a proper filter needs to be selected on the output side of the inverter. The common filters are mainly of the L type and the LCL type. Compared with the L-shaped filter topology, the LCL-shaped filter has the advantages that the capacitance branch is added, so that the LCL-shaped filter has high resistance to higher harmonics, the suppression effect on the higher harmonics is better, and when the filtering effect is the same, the LCL-shaped filter has better high-frequency harmonic attenuation, smaller device size and lower cost, so that the LCL-shaped filter is widely concerned. The conventional LCL filter exhibits a large impedance for high frequency harmonic currents, but exhibits a small impedance for certain specific frequency harmonics, which are not only not suppressed but amplified by the LCL filter. Traditional passive damping methods, such as connecting damping resistors in series with the capacitor branches of the LCL filter, increase the damping of the filter at the resonant frequency. But the introduced passive damping resistor brings extra loss, causing the converter to heat up. However, such a filter has a problem of resonance, and it is necessary to secure stability of a system by suppressing resonance. Meanwhile, small disturbance of the grid voltage can greatly increase the current distortion rate of the inverter injected into the grid, which may cause the system to be unstable. Measures are taken to suppress unknown disturbances of the grid and the resonance induced by the LCL itself.
In order to solve this problem, active damping control and interference suppression control need to be added to the control, and at least two control loops are required. The invention integrates external interference and self resonance, and reduces control loop.
Disclosure of Invention
The invention provides an interference suppression method for a grid-connected inverter of an LCL filter, aiming at solving the problems that the small disturbance of the grid voltage can greatly increase the current distortion rate of the inverter injected into a grid and cause the instability of a system in the uncertainty of grid parameters, and the invention provides the following technical scheme:
an interference suppression method for an LCL filter grid-connected inverter comprises the following steps:
the method comprises the following steps: converting the LCL filter into a first-order system, and designing a first-order self-interference rejection system model of the LCL filter;
step two: simplifying a first-order auto-disturbance rejection system model of the LCL filter, enabling an input signal to pass through a tracking differentiator, listing transient states by the tracking differentiator, and calculating each order derivative of the input signal;
step three: the extended state observer is used for calculating an equation of the linear extended state observer, estimating state variables and total disturbance through the second-order linear extended state observer and integrating the disturbance and self resonance;
step four: performing feedback control on the state error, and combining a reference signal of a tracking differentiator and an output differential signal of an extended state observer to generate an intermediate control voltage signal;
step five: and selecting the observer gain to enable the observer characteristic value to be in a stable state, designing an independent first-order linear controller for each current component, and inhibiting external interference and internal interference.
Preferably, the first step is specifically: the LCL filter is converted into a first-order L-type filter system, a first-order self-interference rejection system model of the LCL filter is designed, and the self-interference rejection system model of the LCL filter is expressed by the following formula:
wherein the content of the first and second substances,
for the output signal of the first-order self-interference rejection system of the LCL filter, f (t, y, w) is the total interference to be estimated to be mitigated, w is the external interference signal, t is time, y represents the input signal, u is the reference input of the inverter, and b is the system parameter.
Preferably, the second step is specifically:
the first step, simplifying a first-order self-interference rejection system model of the LCL filter, expanding f (t, y, w) into a vector state, and expressing a differential equation of the vector state by the following formula:
wherein the content of the first and second substances,
is the differential of the vector state, x (t) is the vector state, u (t) is the second vector state,
assuming differentiation, y (t) is an expansion state, A, B, C and E respectively represent a system matrix, a control matrix, an output matrix and a disturbance matrix;
the third step: the input signal passes through a tracking differentiator to calculate each order derivative of the input signal, and each order derivative of the input signal is expressed by the following formula:
wherein v is n Is the input signal of the digital signal processing circuit,
is the derivative of the input signal, ψ is a closed function, n is the system order, and r is the velocity factor.
Preferably, the third step is specifically:
the first step is as follows: simplifying an LCL filter first-order auto-disturbance rejection system model, constructing a corresponding second-order linear extended state observer on the simplified LCL filter model, and representing the second-order linear extended state observer by the following formula:
wherein the content of the first and second substances,
is the differential of a second-order linear extended state observer, z (T) is the output of the second-order linear extended state observer, L is the gain vector of the second-order linear extended state observer, T d Is a time delay module, and is used for delaying the time,
is ideal power grid current;
the second step: second order linear extended state observer state z 1 And z 2 Will track y and f (t, y, w), respectively;
the third step: and estimating the state variable and the total disturbance, and integrating the total disturbance and self resonance.
Preferably, the gain vector of the second order linear extended state observer is calculated by:
L＝[β 1 β 2 ] T (6)
wherein, beta 1 、β 2 Are all adjustment parameters, T is the desired stabilityAnd (5) timing.
Preferably, laplace transform is carried out on the expression of the second-order linear extended state observer to obtain the observer state z 1 And z 2 Z is represented by the formula 1 And z 2 ：
Where s is the laplacian, r is the reference input, and kp is the controller gain.
Preferably, the fourth step is specifically:
the first step is as follows: feedback control is performed on the state error, the SEF combines a reference signal from the TD and an observer output differential signal from the ESO, and a nonlinear function is adopted to generate a voltage signal u of intermediate control 0 ；
The second step: compensating the total disturbance in the suppression loop, the compensated total disturbance being represented by:
wherein u is the total disturbance after compensation, u 0 The voltage signal is controlled by adopting the end point of the nonlinear function birthday;
the third step: after the rejection loop compensates for the total disturbance, the output signal and the input signal are represented by:
where kp is the controller gain.
Regarding the power grid as a pure integral link, using a linear proportional controller for control, wherein the linear proportional controller is represented by the following formula:
u(t)＝k p (t(t)-z 1 (t)) (11)
where u (t) is a linear proportional controller, t (t) is a reference input, z 1 (t) is the actual input.
Preferably, the step five specifically includes:
the first step is as follows: determining a closed-loop pole according to the desired stabilization time T, obtaining a controller gain, selecting the observer gains such that all observer characteristic values are located at- ω o Then, at this time:
wherein, ω is o Is the observer bandwidth;
the second step is that: when the observer characteristic value is in a stable state, obtaining a control strategy for control, wherein the control strategy is represented by the following formula:
u(s)＝G c (s)(r(s)-H(s)y(s)) (13)
wherein u(s) is a control strategy, G c (s) is a control link transfer function, H(s) is a feedback link transfer function, r(s) is an input signal function, and y(s) is an output signal function;
the third step: finding a control output in the frequency domain, the control output in the frequency domain being represented by:
y(s)＝G fy (s)f(s)+G ry (s)r(s) (16)
wherein f(s) is a perturbation, G fy (s) is a disturbance transfer function, G ry (s) a reference input transfer function.
Preferably, when the disturbance is ignored, the control output expression is simplified, and the simplified control output expression is expressed by:
the invention has the following beneficial effects:
according to the invention, the LCL filter grid-connected inverter current control has good robustness to external interference and internal disturbance, and the control method can actively estimate and compensate unknown dynamics and interference in real time, so that the feedback control is more stable and less depends on a detailed mathematical model in practice. And establishing a control model, determining parameters according to the stability and the trackability of the control model, and inhibiting external interference and LCL self resonance. The proposed current controller is thus fast to respond and has good stability even in the case of uncertain parameters and grid disturbances.
Drawings
FIG. 1 is a control block diagram of a first order linear controller;
fig. 2 is a bode plot of Gfy when changing the bandwidth ω c;
fig. 3 is a bode plot of Gfy when observer bandwidth ω o is changed;
FIG. 4 is a grid voltage and a grid current at rated power;
FIG. 5 grid current with varying grid inductance;
fig. 6 grid voltage and grid current under grid voltage disturbance.
Detailed Description
The present invention will be described in detail with reference to specific examples.
The first embodiment is as follows:
according to the block diagram shown in fig. 1, the invention provides an interference suppression method for an LCL filter grid-connected inverter, which comprises the following steps:
the method comprises the following steps: converting the LCL filter into a first-order system, and designing a first-order self-interference rejection system model of the LCL filter;
step two: simplifying a first-order self-interference rejection system model of the LCL filter, enabling an input signal to pass through a tracking differentiator, listing transient states by the tracking differentiator, and calculating each order derivative of the input signal;
step three: the extended state observer is used for calculating an equation of the linear extended state observer, estimating state variables and total disturbance through the second-order linear extended state observer and integrating the disturbance and self resonance;
step four: performing feedback control on the state error, and combining a reference signal of a tracking differentiator and an output differential signal of an extended state observer to generate an intermediate control voltage signal;
step five: and selecting the observer gain to enable the observer characteristic value to be in a stable state, designing an independent first-order linear controller for each current component, and inhibiting external interference and internal interference.
Further, the first step specifically comprises: the LCL filter is converted into a first-order L-type filter system, a first-order auto-disturbance rejection system model of the LCL filter is designed, and the model of the LCL filter auto-disturbance rejection system is expressed by the following formula:
wherein the content of the first and second substances,
for the output signal of the LCL filter first-order auto-interference rejection system, f (t, y, w) is the total interference to be estimated to be mitigated, w is the external interference signal, t is time, y represents the input signal, u is the reference input of the inverter, and b is the system parameter.
Further, the second step specifically comprises:
the first step, simplifying a first-order self-interference rejection system model of the LCL filter, expanding f (t, y, w) into a vector state, and expressing a differential equation of the vector state by the following formula:
wherein the content of the first and second substances,
is the differential of the vector state, x (t) is the vector state, u (t) is the second vector state,
assuming differentiation, y (t) is an expansion state, A, B, C and E respectively represent a system matrix, a control matrix, an output matrix and a disturbance matrix;
the third step: the input signal passes through a tracking differentiator to calculate each order derivative of the input signal, and each order derivative of the input signal is represented by the following formula:
wherein v is n Is the input signal of the digital signal processing system,
is the derivative of the input signal, psi is a closed function, n is the system order, and r is the velocity factor.
Further, the third step is specifically:
the first step is as follows: simplifying an LCL filter first-order auto-interference rejection system model, constructing a corresponding second-order linear extended state observer on the simplified LCL filter model, and representing the second-order linear extended state observer by the following formula:
wherein the content of the first and second substances,
is a second order lineThe derivative of the extended state observer, z (T) is the output of the second order linear extended state observer, L is the gain vector of the second order linear extended state observer, T d In order to be a time delay module, the time delay module,
is an ideal grid current;
the second step is that: second order linear extended state observer state z 1 And z 2 Will track y and f (t, y, w), respectively;
the third step: and estimating the state variable and the total disturbance, and integrating the total disturbance and self resonance.
Further, the gain vector of the second order linear extended state observer is calculated by:
L＝[β 1 β 2 ] T (6)
wherein beta is 1 、β 2 Are all adjustment parameters, and T is the expected stabilization time.
Further, performing Laplace transform on a second-order linear extended state observer expression to obtain the observer state z 1 And z 2 Z is represented by the formula 1 And z 2 ：
Where s is the laplacian, r is the reference input, and kp is the controller gain.
Further, the fourth step is specifically:
the first step is as follows: feedback control is performed on the state error, the SEF combines a reference signal from the TD and an observer output differential signal from the ESO, and a nonlinear function is adopted to generate a voltage signal u of intermediate control 0 ；
The second step is that: compensating the total disturbance in the suppression loop, the compensated total disturbance being represented by:
wherein u is the total disturbance after compensation, u 0 The voltage signal is controlled by adopting the terminal point of a nonlinear function birthday;
the third step: after the rejection loop compensates for the total disturbance, the output signal and the input signal are represented by:
where kp is the controller gain.
Regarding the power grid as a pure integral link, using a linear proportional controller to control, wherein the linear proportional controller is represented by the following formula:
u(t)＝k p (t(t)-z 1 (t)) (11)
where u (t) is a linear proportional controller, t (t) is a reference input, z 1 (t) is the actual input.
Further, the fifth step is specifically:
the first step is as follows: determining a closed-loop pole according to the desired stabilization time T, obtaining a controller gain, selecting the observer gains such that all observer characteristic values are located at- ω o Then, at this time:
wherein, ω is o Is the observer bandwidth;
the second step is that: when the observer characteristic value is in a stable state, obtaining a control strategy for control, wherein the control strategy is represented by the following formula:
u(s)＝G c (s)(r(s)-H(s)y(s)) (13)
wherein u(s) is a control strategy, G c (s) is a control link transfer function, H(s) is a feedback link transfer function, r(s) is an input signal function, and y(s) is an output signal function;
the third step: finding a control output in the frequency domain, the control output in the frequency domain being represented by:
y(s)＝G fy (s)f(s)+G ry (s)r(s) (16)
wherein f(s) is a perturbation, G fy (s) is the disturbance transfer function, G ry (s) a reference input transfer function.
Further, when the disturbance is ignored, the control output expression is simplified, and the simplified control output expression is expressed by:
the second concrete embodiment:
firstly, an LCL filter is approximated to a first-order system, and a system model of a controller and the approximated LCL filter is designed on the basis of the first-order system as follows:
in the formula: f (t, y, w) represents the total disturbance estimated to be mitigated, including external disturbance w and internal dynamics, t represents time, y represents grid current, u is the reference input of the inverter, and b is a system parameter.
The input signal passes through a tracking differentiator link to calculate each order derivative of the input signal. For a first order system, the output y is defined as a first state x1; the total perturbation f is defined as the extended state x2. Assuming that f is differentiable, the addition point represents the differentiation, and the system model is expressed in the state space of the vector state x as follows:
in the formula:
wherein, A, B, C and E respectively represent a system matrix, a control matrix, an output matrix and a disturbance matrix. Then, a corresponding extended state observer is constructed on the simplified LCL filter model:
in the formula: l = [ β 1 β 2] t is the observer gain vector, z represents the observer output, β 1, β 2 are the tuning parameters.
Further, the SEF combines the reference signal from the TD and the observer output differential signal from the ESO, using a non-linear function to generate the intermediate controlled voltage signal u0.
Finally, the total disturbance is compensated in a disturbance rejection loop, and the expression of u is as follows:
the relationship between the output signal and the input signal can be expressed as follows:
regarding the power grid as a pure integral element, a linear proportional controller of the following form is used for control:
u(t)＝k p (t(t)-z 1 (t))
in the formula: kp is the controller gain.
When the parameters are determined, firstly, performing Laplace transform on the extended state observer to obtain the following expression:
in the formula, r is a reference input, and s represents a laplacian operator.
According to total disturbance u, linear proportional controller control u (t) and extended state observer expression z after Laplace transformation 1 And in z 2 The control law of the controller can be further obtained as follows:
u(s)＝G c (s)(r(s)-H(s)y(s))
where r(s) and y(s) are the input signal and the output signal, respectively, and Gc(s) and H(s) are represented as follows:
finally, the expression of the control output in the s domain is obtained as follows:
in the formula, G fy (s) is the disturbance transfer function, G ry (s) is a reference input transfer function.
If the perturbation f(s) is ignored, the simplified output expression is:
therefore, by increasing the control bandwidth, the stability margin is increased, and the tracking speed is higher; increasing the observer bandwidth or controller bandwidth has better immunity to interference.
For the design of the controller, the closed-loop pole is determined according to the desired settling time T, and the controller gain kp is obtained. Therefore, the following are provided:
k p ＝-ω c and is and
the observer gains are chosen such that all observer eigenvalues are at- ω o, when:
finally, the b value is gradually increased until the dynamic performance is satisfied.
The third concrete example:
and the output signal is subjected to difference with the input signal through a tracking differentiator through a linear extended state observer to obtain a differential signal, and the differential signal is controlled. The embodiment is a method suitable for realizing robust current control of an inverter adopting an LCL filter under a power grid with various disturbances so as to realize active suppression of external interference and internal interference. Due to the reasons of power grid load or power grid faults and the like, disturbance can occur in the power grid, resonance of the LCL filter is caused, and the system is unstable. This requires that the current control still allows a high quality grid current in the presence of disturbances. As can be seen in particular from fig. 1, the control essentially comprises two control loops. The inner loop, called the interference suppression loop, is responsible for compensating the total disturbance; the outer loop, referred to as the feedback control loop, implements the desired signal through the feedback controller. Where w is external interference, b is a given constant, k p Is the controller gain.
And step one, replacing a third-order system of the LCL filter with a first-order system, and establishing a first-order control system mathematical model based on an approximate LCL filter model. The output signal is y, the input signal is u, and the interference signal is w, as shown in fig. 1.
Step two, tracking differentiation, listing transient states and calculating each order derivative of input signals by a tracking differentiator based on a simplified system model, wherein v is the input signals, v is the order derivative of the input signals i (i =1, 2.. N.) is the output signal, n representing the system order.
And step three, the linear extended state observer estimates the state variable and the total disturbance of the object, considers the disturbance and the self resonance as a whole, and calculates the equation of the linear extended state observer based on the simplified model.
Step four, performing feedback control on the state error, combining a reference signal from a tracking differentiator and an observer output differential signal from an extended state observer, and generating an intermediate control voltage signal u by using a nonlinear function 0 。
Step five: combining fig. 2 and fig. 3, wherein fig. 2 is a diagram for changing the control bandwidth ω c A bode plot of a time-low pass filter; FIG. 3 is a diagram of changing observer bandwidth ω o The baud plot of Gfy, based on which the traceability and stability of the system is studied according to the frequency response. According to the desired stabilization time T settle And determining a closed loop pole to obtain the gain of the controller. The observer gain is selected such that the observer characteristic value is in a steady state. Finally, the b value is gradually increased until the dynamic performance is satisfied.
Step six: an independent first-order linear controller is designed for each current component to suppress external interference and internal interference, and a current waveform diagram and a current harmonic analysis diagram are obtained and are shown in fig. 4 to 6. Wherein, the simulation result of the robust current control based on the active damping is shown in fig. 4. The grid current is regulated to the nominal value and is in phase with the grid voltage, as shown in fig. 4. The simulation result of the power grid current waveform based on the robust current control of the active damping control under the condition of parameter change is shown in fig. 5, and it can be seen that the robust current control can also realize stable and efficient control under the condition of parameter change. As can be seen from fig. 6, under the condition of grid voltage disturbance, the robust current control can still track the reference grid current well, and the active interference suppression strategy is adopted to control and suppress the grid disturbance, so as to obtain good stability.
The above description is only a preferred embodiment of the interference suppression method for the LCL filter grid-connected inverter, and the protection scope of the interference suppression method for the LCL filter grid-connected inverter is not limited to the above embodiments, and all technical solutions belonging to the idea belong to the protection scope of the present invention. It should be noted that modifications and variations that do not depart from the gist of the invention are intended to be within the scope of the invention.
Claims (7)
1. An interference suppression method for a grid-connected inverter of an LCL filter is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: converting the LCL filter into a first-order system, and designing a first-order self-interference rejection system model of the LCL filter;
step two: simplifying a first-order auto-disturbance rejection system model of the LCL filter, enabling an input signal to pass through a tracking differentiator, listing transient states by the tracking differentiator, and calculating each order derivative of the input signal;
step three: the extended state observer is used for calculating an equation of the linear extended state observer, estimating state variables and total disturbance through the second-order linear extended state observer and integrating the disturbance and self resonance;
the third step is specifically as follows:
the first step is as follows: simplifying an LCL filter first-order auto-interference rejection system model, constructing a corresponding second-order linear extended state observer on the simplified LCL filter model, and representing the second-order linear extended state observer by the following formula:
wherein, the first and the second end of the pipe are connected with each other,
is the differential of the second order linear extended state observer, z (T) is the output of the second order linear extended state observer, L is the gain vector of the second order linear extended state observer, T d In order to be a time delay module, the time delay module,
is ideal power grid current;
the second step is that: second order linear extended state observer state z 1 And z 2 Will track y and f (t, y, w), respectively;
the third step: estimating state variables and total disturbance, and integrating the total disturbance and self resonance;
step four: performing feedback control on the state error, and combining a reference signal of a tracking differentiator and an output differential signal of an extended state observer to generate an intermediate control voltage signal;
step five: selecting the gain of the observer to enable the characteristic value of the observer to be in a stable state, designing an independent first-order linear controller for each current component, and inhibiting external interference and internal interference;
the fifth step is specifically as follows:
the first step is as follows: determining a closed-loop pole according to the expected stabilization time T, obtaining a controller gain, and selecting the observer gain so that all observer characteristic values are positioned at-omega o Then, then there are:
β 1 ＝2ω o ,
wherein, ω is o Is the observer bandwidth;
the second step is that: when the observer characteristic value is in a stable state, obtaining a control strategy for control, wherein the control strategy is represented by the following formula:
u(s)＝G c (s)(r(s)-H(s)y(s)) (13)
wherein u(s) is a control strategy, G c (s) is a control link transfer function, H(s) is a feedback link transfer function, r(s) is an input signal function, and y(s) is an output signal function
The third step: finding a control output in the frequency domain, the control output in the frequency domain being represented by:
y(s)＝G fy (s)f(s)+G ry (s)r(s) (16)
wherein f(s) is a perturbation, G fy (s) is a disturbance transfer function, G ry (s) reference input transfer function.
2. The method for suppressing the interference of the LCL filter grid-connected inverter according to claim 1, wherein the method comprises the following steps:
the first step is specifically as follows: the LCL filter is converted into a first-order L-type filter system, a first-order auto-disturbance rejection system model of the LCL filter is designed, and the model of the LCL filter auto-disturbance rejection system is expressed by the following formula:
wherein the content of the first and second substances,
for the output signal of the LCL filter first-order auto-interference rejection system, f (t, y, w) is the total interference to be estimated to be mitigated, w is the external interference signal, t is time, y represents the input signal, u is the reference input of the inverter, and b is the system parameter.
3. The method for suppressing the interference of the LCL filter grid-connected inverter according to claim 1, wherein the method comprises the following steps: the second step is specifically as follows:
the first step, simplifying a first-order self-interference rejection system model of the LCL filter, expanding f (t, y, w) into a vector state, and expressing a differential equation of the vector state by the following formula:
wherein, the first and the second end of the pipe are connected with each other,
is the differential of the vector state, x (t) is the vector state, u (t) is the second vector state,
assuming differentiation, y (t) is an expansion state, A, B, C and E respectively represent a system matrix, a control matrix, an output matrix and a disturbance matrix;
the third step: the input signal passes through a tracking differentiator to calculate each order derivative of the input signal, and each order derivative of the input signal is represented by the following formula:
wherein v is n Is an input signal, v n Is the derivative of the input signal, ψ is a closed function, n is the system order, and r is the velocity factor.
4. The interference suppression method for the LCL filter grid-connected inverter according to claim 1, wherein the interference suppression method comprises the following steps: the gain vector of the second order linear extended state observer is calculated by:
L＝[β 1 β 2 ] T (6)
wherein, beta 1 、β 2 Are all adjustment parameters, and T is the expected stabilization time.
5. The method for suppressing the interference of the LCL filter grid-connected inverter according to claim 1, wherein the method comprises the following steps: performing Laplace transform on the expression of the second-order linear extended state observer to obtain the state z of the observer 1 And z 2 Z is represented by the formula 1 And z 2 ：
Where s is the laplacian, r is the reference input, and kp is the controller gain.
6. The interference suppression method for the LCL filter grid-connected inverter according to claim 1, wherein the interference suppression method comprises the following steps: the fourth step is specifically as follows:
the first step is as follows: feedback control is performed on the state error, the SEF combines a reference signal from the TD and an observer output differential signal from the ESO, and a nonlinear function is adopted to generate a voltage signal u of intermediate control 0 ；
The second step is that: compensating the total disturbance in the suppression loop, the compensated total disturbance being represented by:
wherein u is the total disturbance after compensation, u 0 The voltage signal is controlled by adopting the terminal point of a nonlinear function birthday;
the third step: after the rejection loop compensates for the total disturbance, the output signal and the input signal are represented by:
where kp is the controller gain.
Regarding the power grid as a pure integral link, using a linear proportional controller for control, wherein the linear proportional controller is represented by the following formula:
u(t)＝k p (t(t)-z 1 (t)) (11)
where u (t) is a linear proportional controller, t (t) is a reference input, z 1 (t) is the actual input.
7. The interference suppression method for the LCL filter grid-connected inverter according to claim 6, wherein the interference suppression method comprises the following steps: when the disturbance is ignored, the control output expression is simplified, and the simplified control output expression is expressed by the following formula:
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