A cascade control method for inverter grid voltage based on robust prediction

Abstract

A method for cascading control of inverter network voltage based on robust prediction relates to the technical field of inverter network voltage control. The method cascades to observe the concentrated disturbance of inverter network voltage and output current, and establishes the inverter output current reference and basic voltage vector reference, thereby eliminating the influence of disturbances such as parameters in the network inverter system on the network voltage control, and ensuring the robustness and reliability of the inverter network voltage control. The present invention effectively solves the problem caused by the inconsistency between the model parameters and the actual parameters of the network inverter, avoids the risk of inaccurate voltage prediction and voltage waveform distortion, and reduces the influence of external interference on parameter identification. In addition, the method does not need to adjust the system gain or store a large amount of data according to changes in working conditions, thereby reducing the complexity of voltage control and improving control performance.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter grid-forming voltage control, and specifically relates to a cascaded control method for inverter grid-forming voltage based on robust prediction. Background Art

[0002] As a flexible distributed power system, the AC-DC hybrid microgrid has the ability to flexibly connect to or disconnect from the main grid. This system integrates multiple components such as local renewable energy generation, inverter systems, energy storage units, and load management systems. In this system, the inverter uses an LC filter to convert the direct current generated by renewable energy into stable alternating current to form a grid, ensuring that the energy storage and load systems can obtain a stable AC power supply, thereby maintaining the stability of the grid voltage.

[0003] In recent years, model predictive control (MPC) has been widely used in the field of grid-forming inverter control due to its excellent dynamic response performance and multi-functional control characteristics. MPC predicts the future state of the system based on the discrete model of the grid-forming inverter and optimally selects the best output state according to the cost function. However, the MPC method is very sensitive to the accuracy of the filter model parameters in the grid-forming inverter. When the model parameters are inconsistent with the actual parameters, it may lead to prediction errors of the grid-forming voltage, affect the output performance of the inverter, and even cause damage to the AC-DC hybrid microgrid.

[0004] In terms of improving the robustness of MPC parameters, scholars have developed many optimization strategies, which can be roughly classified into two main categories: one is the MPC technology based on parameter identification, and the other is the data-driven MPC technology. For the MPC technology based on parameter identification, researchers collect the input and output data of the grid-forming inverter and use specific algorithms to process these data to estimate and determine the parameters of the grid-forming inverter, and then build an accurate model to perform prediction and control tasks. However, the accuracy of parameter identification is often easily affected by external disturbances, which may have an adverse impact on the performance of the grid-forming inverter in terms of grid-forming voltage. As for the data-driven MPC technology, it predicts the future state based on the current state and historical behavior of the system by collecting data in real time and building a model. This method does not require the establishment of an accurate mathematical model, but determines the optimal output through a value function to achieve effective control of the grid current. However, the existing data-driven MPC technology not only needs to adjust the system gain according to the changes in the operating conditions of the grid-forming inverter to ensure the accuracy of prediction, but also needs to store a large amount of current and voltage data, which may have a negative impact on the dynamic performance of the system.

[0005] Therefore, this application aims to propose a cascaded control method for inverter grid-forming voltage based on robust prediction to eliminate the influence of disturbances such as grid-forming inverter parameters on grid-forming voltage control. Summary of the Invention

[0006] In view of the deficiencies in the above-mentioned background technology, the present invention proposes a cascaded control method for the grid-connected voltage of an inverter based on robust prediction. This method cascades the observation of the concentrated disturbance of the grid-connected voltage of the inverter and the concentrated disturbance of the output current, cascades the establishment of the reference of the inverter output current and the reference of the basic voltage vector, eliminates the influence of disturbances such as parameters in the grid-connected inverter system on the grid-connected voltage control, and ensures the robustness and reliability of the grid-connected voltage control of the inverter.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A cascaded control method for the grid-connected voltage of an inverter based on robust prediction, the specific steps are as follows:

[0009] Step 1: According to the three-phase grid-connected inverter topology, establish its mathematical model in the stationary coordinate system, and then establish a grid-connected voltage prediction equation in the presence of concentrated grid-connected voltage disturbances;

[0010] Step 2: According to the grid-connected voltage prediction equation in the presence of concentrated grid-connected voltage disturbances obtained in Step 1, establish a grid-connected voltage error function, and derive the reference value of the inverter output current;

[0011] Step 3: According to the reference value of the inverter output current obtained in Step 2, establish a concentrated grid-connected voltage disturbance observation equation, estimate the concentrated grid-connected voltage disturbance in real time, and then eliminate the influence of the concentrated disturbance on the reference value of the inverter output current;

[0012] Step 4: According to the three-phase grid-connected inverter topology, establish an inverter output current prediction equation in the presence of concentrated inverter output current disturbances;

[0013] Step 5: According to the inverter output current prediction equation in the presence of concentrated inverter output current disturbances obtained in Step 4, establish an inverter output current error function, and derive the reference value of the basic voltage vector of the inverter;

[0014] Step 6: According to the reference value of the basic voltage vector of the inverter obtained in Step 5, establish a concentrated inverter output current disturbance observation equation, estimate the concentrated inverter output current disturbance in real time, and then eliminate the influence of the concentrated disturbance on the reference value of the basic voltage vector of the inverter;

[0015] Step 7: According to the reference value of the basic voltage vector of the inverter obtained in Step 5, establish a cost function, select the optimal basic voltage vector, and set the three-phase modulation wave for the next control cycle.

[0016] The present invention proposes an innovative data-driven weak-connected microgrid inverter grid-forming voltage support control strategy. This strategy uses cascaded observation technology to monitor the concentrated disturbances of the inverter grid-forming voltage and output current, and then constructs a reference model for the inverter output current and the basic voltage vector. This method effectively neutralizes the effect of parameter disturbances in the system on the grid-forming voltage control, thus ensuring the robustness and stability of the inverter during the grid-forming voltage control process.

[0017] Compared with the traditional model predictive control strategy, the inverter grid-forming voltage cascaded control method based on robust prediction proposed by the present invention significantly improves the robustness and reliability of voltage control. It effectively solves the problems caused by the inconsistency between the model parameters and the actual parameters of the grid-forming inverter, avoids the risks of inaccurate voltage prediction and voltage waveform distortion, and at the same time reduces the influence of external disturbances on parameter identification. In addition, this method does not need to adjust the system gain according to the change of working conditions or store a large amount of data, thus reducing the complexity of voltage control and improving the control performance.

[0018] The control strategy implemented by the present invention successfully overcomes the limitations of the traditional model predictive control in terms of the influence of parameter fluctuations, and is especially suitable for system environments where the line impedance often changes. This technological innovation provides a more flexible and stable effective solution for the grid-forming inverter in the field of grid-forming voltage control in AC-DC hybrid microgrids. Brief Description of the Drawings

[0019] Figure 1 It is the topological structure diagram of the grid-forming inverter of the present invention.

[0020] Figure 2 It is the control block diagram implemented by the present invention. Detailed Embodiment

[0021] The following further details the present invention in conjunction with the embodiments and the drawings.

[0022] Based on the three-phase grid-forming inverter topological structure as Figure 1 shown, the present invention proposes a cascaded control method for the grid-forming voltage of the inverter based on robust prediction. Please refer to Figure 2 , which mainly includes five parts: concentrated disturbance observation of grid-forming voltage, reference calculation of inverter output current, concentrated disturbance observation of inverter output current, reference calculation of inverter basic voltage vector, and cost function evaluation. First, measure the voltage and current data of the grid-forming inverter to observe the concentrated disturbance of the grid-forming voltage; then, calculate the reference of the inverter output current based on the concentrated disturbance of the grid-forming voltage; next, observe the concentrated disturbance of the inverter output current; furthermore, calculate the reference of the inverter basic voltage vector based on the concentrated disturbance of the inverter output current; finally, evaluate the optimal basic voltage vector applied in the next control cycle according to the cost function. The specific detailed steps are as follows:

[0023] Step 1: According to Figure 1 the three-phase grid-forming inverter topology shown, establish its mathematical model in the stationary coordinate system, and then establish the grid-forming voltage prediction equation in the presence of a concentrated grid-forming voltage disturbance. Specifically as follows:

[0024] According to Figure 1 the weak-connected microgrid inverter topology shown, its mathematical model in the stationary coordinate system can be obtained and expressed as:

[0025]

[0026] In the formula: L m is the model parameter of the filter inductor, and C m is the model parameter of the filter capacitor. i i , i l , v i , v c are the inverter output current, AC load current, basic voltage vector of the inverter, and grid-forming voltage in the stationary coordinate system, respectively.

[0027] Among them, the inverter has 8 basic voltage vectors, that is, i ∈ 0 to 7, which are v 0 (0, 0, 0), v 1 (1, 0, 0), v 2 (1, 1, 0), v 3 (0, 1, 0), v 4 (0, 1, 1), v 5 (0, 0, 1), v 6 (1, 0, 1), v 7 (1, 1, 1).

[0028] Considering the load disturbance and system parameter uncertainty, the grid-forming voltage v c in formula (1) is further expressed as:

[0029]

[0030] In the formula: d vc is the concentrated grid-forming voltage disturbance, which is expressed as:

[0031]

[0032] In the formula: ΔC is the parameter error between the capacitor model parameter and the actual parameter, and d s is the system disturbance.

[0033] According to the forward Euler method and the grid-forming voltage mathematical model shown in formula (2), the grid-forming voltage v c is discretized and expressed as:

[0034]

[0035] Where: v c [k + 1] is the predicted value of the grid-forming voltage at the (k + 1)-th moment in the stationary coordinate system, v c [k] is the sampled value of the grid-forming voltage at the k-th moment in the stationary coordinate system, i i [k] is the sampled value of the inverter output current at the k-th moment in the stationary coordinate system, i l [k] is the sampled value of the AC load current at the k-th moment in the stationary coordinate system. d vc [k] is the concentrated disturbance of the grid-forming voltage at the k-th moment in the stationary coordinate system. T s is the control period.

[0036] Step 2: According to the grid-forming voltage prediction equation obtained in Step 1 when there is a concentrated disturbance of the grid-forming voltage, establish a grid-forming voltage error function and derive the reference value of the inverter output current. Specifically as follows:

[0037] To improve the robustness of the grid-forming voltage control, based on the grid-forming voltage reference v cref and the grid-forming voltage v c design a discrete error function between them, which is expressed as:

[0038] e vc [k] = ρ v [v cref [k] - v c [k]] + λ v σ v [k] (5)

[0039] Where: e vc [k] is the grid-forming voltage error function at the k-th moment in the stationary coordinate system, ρ v is the grid-forming voltage error gain, λ v is the grid-forming voltage error integral gain. v cref [k] is the grid-forming voltage reference value at the k-th moment in the stationary coordinate system. σ v [k] is the grid-forming voltage error integral at the k-th moment in the stationary coordinate system, which is expressed as:

[0040] σ v [k] = σ v [k - 1] + [v cref [k] - v c [k]] (6)

[0041] Where: σ v [k - 1] is the grid-forming voltage error integral at the (k - 1)-th moment in the stationary coordinate system.

[0042] When the inverter is in steady-state operation, it can be considered that the grid-forming voltage error function at time k + 1 is equal to the grid-forming voltage error function at time k, and we get:

[0043] e vc [k + 1] = e vc [k] (7)

[0044] In the formula: e vc [k + 1] is the grid-forming voltage error function at time k + 1 in the stationary coordinate system, which is obtained through the one-step forward formula (5):

[0045] e vc [k + 1] = ρ v [v cref [k + 1] - v c [k + 1]] + λ v [σ v [k] + v cref [k + 1] - v c [k + 1]] (8)

[0046] In the formula: v cref [k + 1] is the grid-forming voltage reference value at time k + 1 in the stationary coordinate system. Since the inverter generally operates at a relatively high power frequency, it can be considered that v cref [k + 1] = v cref [k]. Therefore, formula (8) is further deduced as:

[0047]

[0048] Substitute formula (9) and formula (5) into formula (7) to get:

[0049]

[0050] In the formula: i iref [k] is the inverter output current reference value at time k in the stationary coordinate system.

[0051] According to formula (10), it can be seen that an accurate grid-forming voltage concentrated disturbance d vc [k] is required to ensure the accuracy of the inverter output current reference value i iref [k].

[0052] Step 3: Based on the inverter output current reference value obtained in Step 2, establish a grid-forming voltage concentrated disturbance observation equation to estimate the grid-forming voltage concentrated disturbance in real time, and then eliminate the influence of the concentrated disturbance on the inverter output current reference value. Specifically as follows:

[0053] In order to estimate the grid-forming voltage concentrated disturbance d vc[k], establish the concentrated disturbance observation equation according to formula (2) and express it as:

[0054]

[0055] Where: is the estimated value of the grid-forming voltage in the stationary coordinate system, is the estimated value of the concentrated disturbance of the grid-forming voltage in the stationary coordinate system.

[0056] Discretize formula (11) and express it as:

[0057]

[0058] Where: α v is the grid-forming voltage estimation gain, β v is the concentrated disturbance estimation gain of the grid-forming voltage. is the estimated value of the grid-forming voltage at the (k + 1)-th moment in the stationary coordinate system, is the estimated value of the grid-forming voltage at the k-th moment in the stationary coordinate system. is the estimated value of the concentrated disturbance of the grid-forming voltage at the (k + 1)-th moment in the stationary coordinate system, is the estimated value of the concentrated disturbance of the grid-forming voltage at the k-th moment in the stationary coordinate system.

[0059] According to formula (12), the concentrated disturbance of the grid-forming voltage can be estimated in real time so as to obtain the reference value i iref [k] of the inverter output current at the k-th moment in the stationary coordinate system according to formula (10). Since the grid-forming inverter generally operates at a relatively high control frequency, it can be considered that i iref [k + 1] = i iref [k], and obtaining the reference value of the inverter output current effectively avoids the influence of system disturbances in the grid-forming inverter on the reference value of the inverter output current.

[0060] Step Four: According to Figure 1 the three-phase grid-forming inverter topology shown, establish the inverter output current prediction equation when there is a concentrated disturbance in the inverter output current. Specifically as follows:

[0061] After obtaining the reference value of the inverter output current, the predicted value of the inverter output current is required. According to formula (1), it is expressed as:

[0062]

[0063] Where: i i [k + 1] is the predicted value of the inverter output current at the (k + 1)-th moment in the stationary coordinate system, i i [k] is the sampled value of the inverter output current at the k-th moment in the stationary coordinate system, v i[k] is the basic voltage vector of the inverter at time k in the stationary coordinate system, v c [k] is the sampled value of the grid-forming voltage at time k in the stationary coordinate system.

[0064] According to Equation (13), it can be known that the predicted value of the inverter output current at time k+1 in the stationary coordinate system will be affected by the filter inductor model parameter L m . When the filter inductor model parameter is not equal to the actual parameter, it will affect the accuracy of the predicted value of the inverter output current. At this time, the predicted value of the inverter output current at time k+1 in the stationary coordinate system is expressed as:

[0065]

[0066] In the formula: d ii [k] is the concentrated disturbance of the inverter output current at time k in the stationary coordinate system.

[0067] Step Five: Based on the inverter output current prediction equation when there is a concentrated disturbance of the inverter output current obtained in Step Four, establish an inverter output current error function and derive the reference value of the basic voltage vector of the inverter. Specifically as follows:

[0068] Based on the reference value of the inverter output current i iref and the error between the inverter output current v c , design a discrete error function, which is expressed as:

[0069] e ii [k] = ρ i [i iref [k] - i i [k]] + λ i σ i [k] (15)

[0070] In the formula: e ii [k] is the inverter output current error function at time k in the stationary coordinate system, ρ i is the inverter output current error gain, λ v is the inverter output current error integral gain. i iref [k] is the reference value of the inverter output current at time k in the stationary coordinate system. σ i [k] is the integral of the inverter output current error at time k in the stationary coordinate system, which is expressed as:

[0071] σ i [k] = σ i [k - 1] + [i iref [k] - i i [k]] (16)

[0072] In the formula: σi [k - 1] is the integral of the inverter output current error at the (k - 1)-th moment in the stationary coordinate system.

[0073] When the inverter is operating in a steady state, it can be considered that the inverter output current error function at the (k + 1)-th moment is equal to that at the k-th moment, and we get:

[0074] e ii [k + 1] = e ii [k] (17)

[0075] In the formula: e ii [k + 1] is the inverter output current error function at the (k + 1)-th moment in the stationary coordinate system, which is obtained through the one-step forward formula (15):

[0076] e ii [k + 1] = ρ i [i iref [k + 1] - i i [k + 1]] + λ i [σ i [k] + i iref [k + 1] - i i [k + 1]] (18)

[0077] In the formula: i iref [k + 1] is the reference value of the inverter output current at the (k + 1)-th moment in the stationary coordinate system. Since the inverter generally operates at a relatively high power frequency, it can be considered that i iref [k + 1] = i iref [k]. Therefore, formula (18) is further deduced as:

[0078]

[0079] Substituting formula (19) and formula (15) into formula (17), we get:

[0080]

[0081] In the formula: v iref [k] is the reference value of the basic voltage vector of the inverter at the k-th moment in the stationary coordinate system.

[0082] According to formula (20), it can be seen that an accurate concentrated disturbance d ii [k] of the inverter output current is required to ensure the accuracy of the reference value v iref [k] of the basic voltage vector of the inverter.

[0083] Step 6: Based on the reference value of the basic voltage vector of the inverter obtained in Step 5, establish an observation equation for the concentrated disturbance of the inverter output current, estimate the concentrated disturbance of the inverter output current in real time, and then eliminate the influence of the concentrated disturbance on the reference value of the basic voltage vector of the inverter. Specifically as follows:

[0084] To estimate the concentrated disturbance d ii [k] of the inverter output current in real time, establish a concentrated disturbance observation equation according to formula (2) and express it as:

[0085]

[0086] In the formula: is the estimated value of the inverter output current in the stationary coordinate system, is the estimated value of the concentrated disturbance of the inverter output current in the stationary coordinate system.

[0087] Discretize formula (21) and express it as:

[0088]

[0089] In the formula: α i is the estimated gain of the inverter output current, β i is the estimated gain of the concentrated disturbance of the inverter output current. is the estimated value of the inverter output current at the (k + 1)-th moment in the stationary coordinate system, is the estimated value of the inverter output current at the k-th moment in the stationary coordinate system. is the estimated value of the concentrated disturbance of the inverter output current at the (k + 1)-th moment in the stationary coordinate system, is the estimated value of the concentrated disturbance of the inverter output current at the k-th moment in the stationary coordinate system.

[0090] According to formula (22), the concentrated disturbance of the inverter output current can be estimated in real time So as to obtain the reference value v iref [k] of the basic voltage vector of the inverter at the k-th moment in the stationary coordinate system according to formula (20). Since the grid-forming inverter generally operates at a relatively high control frequency, it can be considered that v iref [k + 1] = v iref [k], and obtaining the reference value of the basic voltage vector of the inverter effectively avoids the influence of system disturbances in the grid-forming inverter on the reference value of the basic voltage vector of the inverter.

[0091] Step 7: Based on the reference value of the basic voltage vector of the inverter obtained in Step 5, establish a cost function, select the optimal basic voltage vector, and set the three-phase modulation wave for the next control period. Specifically as follows:

[0092] To ensure that the predicted value v i[k + 1] can track the reference value v of the basic voltage vector of the inverter iref [k + 1], and design the cost function J i and express it as:

[0093] J i = |v iref [k + 1] - v i [k + 1]| (23)

[0094] At this time, the 8 basic voltage vectors of the inverter correspond to 8 cost functions. Select the basic voltage vector with the lowest cost function as the optimal vector, and set the three-phase modulation wave of the next control period according to its switching state. The three-phase modulation wave can also be set in combination with space vector modulation.

[0095] The above content is only an example and explanation of the concept of the present invention. Those skilled in the art of the present technology make various modifications or supplements to the described specific embodiments or use similar methods to replace them. As long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A method for controlling inverter grid voltage cascade based on robust prediction, characterized in that: The specific steps are as follows: Step 1: According to the three-phase grid inverter topology, establish its mathematical model in the stationary coordinate system, and then establish the grid voltage prediction equation when the grid voltage concentrated disturbance exists; the detailed steps are as follows: According to the topological structure of the weakly connected microgrid inverter, its mathematical model in the stationary coordinate system can be obtained and expressed as: Where: L m is the filter inductor model parameter, C m is the filter capacitor model parameter; i i 、i l 、v i 、v c They are the inverter output current, AC load current, inverter basic voltage vector, and grid voltage in the stationary coordinate system respectively; Among them, the inverter has 8 basic voltage vectors, i∈0~7, which are v0(0,0,0), v1(1,0,0), v2(1,1,0), v3(0,1,0), v4(0,1,1), v5(0,0,1), v6(1,0,1), v7(1,1,1); Taking into account the load disturbance and system parameter uncertainty, the grid voltage v in formula (1) is c Further expressed as: Where: d vc To construct the concentrated disturbance of the grid voltage, it is expressed as: Where: ΔC is the parameter error between the capacitance model parameters and the actual parameters, d s is the system disturbance; According to the front-line Euler method and the grid voltage mathematical model shown in formula (2), the grid voltage v c Discretized and expressed as: Where: v c [k+1] is the predicted value of the grid voltage at time k+1 in the stationary coordinate system, v c [k] is the grid voltage sampling value at time k in the stationary coordinate system, i i [k] is the inverter output current sampling value at time k in the stationary coordinate system, i l [k] is the AC load current sampling value at time k in the stationary coordinate system; d vc [k] is the concentrated disturbance of the grid voltage at time k in the stationary coordinate system; T s To control the cycle; Step 2: According to the grid voltage prediction equation obtained in step 1 when the grid voltage concentrated disturbance exists, a grid voltage error function is established, and the inverter output current reference value is derived; the detailed steps are as follows: In order to improve the robustness of grid voltage control, based on the grid voltage reference v cref and network voltage v c The error between the two designs a discrete error function, which is expressed as: e vc [k]=ρ v [v] cref [k]-v c [k]]+λ v s v [k] (5) Where: e vc [k] is the grid voltage error function at time k in the stationary coordinate system, ρ v is the network voltage error gain, λ v is the network voltage error integral gain; v cref [k] is the reference value of the grid voltage at time k in the stationary coordinate system; σ v [k] is the integral of the grid voltage error at time k in the stationary coordinate system, which is expressed as: σ v [k]=σ v [k-1]+[v cref [k]-v c [k]] (6) Where: v [k-1] is the integral of the grid voltage error at time k-1 in the stationary coordinate system; When the inverter is in steady-state operation, the grid voltage error function at time k+1 can be considered to be equal to the grid voltage error function at time k, and we get: yes vc [k+1]=e vc [k] (7) Where: e vc [k+1] is the grid voltage error function at time k+1 in the stationary coordinate system, which is obtained by one-step forward formula (5): e vc [k+1]=ρ v [v cref [k+1]-v c [k+1]]+λ v [σ v [k]+v cref [k+1]-v c [k+1]] (8) Where: v cref [k+1] is the grid voltage reference value at time k+1 in the stationary coordinate system; since the inverter generally operates at a higher power frequency, it can be considered that v cref [k+1]=v cref [k], therefore, formula (8) is further derived as: Substituting formula (9) and formula (5) into formula (7), we obtain: Where: i iref [k] is the reference value of the inverter output current at time k in the stationary coordinate system; According to formula (10), we need to obtain the accurate network voltage concentrated disturbance d vc [k] can ensure the inverter output current reference value i iref The accuracy of [k]; Step 3: According to the inverter output current reference value obtained in step 2, a grid voltage concentrated disturbance observation equation is established to estimate the grid voltage concentrated disturbance in real time, thereby eliminating the influence of the concentrated disturbance on the inverter output current reference value; Step 4: According to the three-phase grid inverter topology, establish the inverter output current prediction equation when the inverter output current concentrated disturbance exists; Step 5: According to the inverter output current prediction equation obtained in step 4 when the inverter output current concentrated disturbance exists, establish the inverter output current error function, and derive the inverter basic voltage vector reference value; Step 6: According to the basic voltage vector reference value of the inverter obtained in step 5, establish the concentrated disturbance observation equation of the inverter output current, estimate the concentrated disturbance of the inverter output current in real time, and then eliminate the influence of the concentrated disturbance on the basic voltage vector reference value of the inverter; Step 7: According to the basic voltage vector reference value of the inverter obtained in step 5, a cost function is established, the optimal basic voltage vector is selected, and the three-phase modulation wave of the next control cycle is set.

2. The inverter grid voltage cascade control method based on robust prediction according to claim 1, characterized in that: Step 3: Detailed steps are as follows: In order to estimate the concentrated disturbance of grid voltage in real time vc [k], the concentrated disturbance observation equation is established according to formula (2) and expressed as: Where: is the estimated value of the grid voltage in the stationary coordinate system, is the estimated value of the concentrated disturbance of the grid voltage in the stationary coordinate system; Formula (11) is discretized and expressed as: Where: α v is the grid voltage estimation gain, β v To estimate the gain of concentrated disturbance of grid voltage; is the estimated value of the grid voltage at time k+1 in the stationary coordinate system, is the estimated value of the grid voltage at time k in the stationary coordinate system; is the estimated value of the concentrated disturbance of the grid voltage at time k+1 in the stationary coordinate system, is the estimated value of the concentrated disturbance of the grid voltage at time k in the stationary coordinate system; According to formula (12), the concentrated disturbance of grid voltage can be estimated in real time: Thus, according to formula (10), the inverter output current reference value i at time k in the stationary coordinate system is obtained: iref [k]; Since the grid inverter generally works at a higher control frequency, it can be considered that i iref [k+1]=i iref [k], obtaining the inverter output current reference value effectively avoids the influence of system disturbance in the grid-connected inverter on the inverter output current reference value.

3. The inverter grid voltage cascade control method based on robust prediction according to claim 2, characterized in that: Step 4: The detailed steps are as follows: After obtaining the reference value of the inverter output current, it is necessary to know the predicted value of the inverter output current, which is expressed as follows according to formula (1): Where: i i [k+1] is the predicted value of the inverter output current at time k+1 in the stationary coordinate system, i i [k] is the inverter output current sampling value at time k in the stationary coordinate system, v i [k] is the basic voltage vector of the inverter at time k in the stationary coordinate system, v c [k] is the grid voltage sampling value at time k in the stationary coordinate system; According to formula (13), the predicted value of the inverter output current at time k+1 in the stationary coordinate system is affected by the filter inductance model parameter L m When the filter inductance model parameters are not equal to the actual parameters, the accuracy of the inverter output current prediction value will be affected; at this time, the inverter output current prediction value at time k+1 in the stationary coordinate system is expressed as: Where: d ii [k] is the concentrated disturbance of the inverter output current at time k in the stationary coordinate system.

4. The inverter grid voltage cascade control method based on robust prediction according to claim 3, characterized in that: Step 5 The detailed steps are as follows: Based on the inverter output current reference i iref and the inverter output current v c The error between the two designs a discrete error function, which is expressed as: e ii [k]=ρ i [i iref [k]-i i [k]]+λ i s i [k] (15) Where: e ii [k] is the inverter output current error function at time k in the stationary coordinate system, ρ i is the inverter output current error gain, λ v is the inverter output current error integral gain; i iref [k] is the reference value of the inverter output current at time k in the stationary coordinate system; σ i [k] is the integral of the inverter output current error at time k in the stationary coordinate system, which is expressed as: s i [k]=σ i [k-1]+[i iref [k]-i i [k]] (16) Where: i [k-1] is the integral of the inverter output current error at time k-1 in the stationary coordinate system; When the inverter is in steady-state operation, it can be considered that the inverter output current error function at time k+1 is equal to the inverter output current error function at time k, and we get: yes ii [k+1]=e ii [k] (17) Where: e ii [k+1] is the inverter output current error function at time k+1 in the stationary coordinate system, which is obtained by one-step forward formula (15): e ii [k+1]=ρ i [i iref [k+1]-i i [k+1]]+λ i [s i [k]+i iref [k+1]-i i [k+1]] (18) Where: i iref [k+1] is the reference value of the inverter output current at time k+1 in the stationary coordinate system; since the inverter generally operates at a higher power frequency, it can be considered that i iref [k+1]=i iref [k], therefore, formula (18) is further derived as: Substituting formula (19) and formula (15) into formula (17), we obtain: Where: v iref [k] is the basic voltage vector reference value of the inverter at time k in the stationary coordinate system; According to formula (20), we need to obtain the accurate inverter output current concentrated disturbance d ii [k] can ensure the basic voltage vector reference value v of the inverter iref The accuracy of [k].

5. The inverter grid voltage cascade control method based on robust prediction according to claim 4, characterized in that: Step 6 The detailed steps are as follows: In order to estimate the concentrated disturbance d of the inverter output current in real time ii [k], the concentrated disturbance observation equation is established according to formula (2) and expressed as: Where: is the estimated value of the inverter output current in the stationary coordinate system, is the estimated value of the concentrated disturbance of the inverter output current in the stationary coordinate system; Formula (21) is discretized and expressed as: Where: α i is the inverter output current estimation gain, β i estimating gain for concentrated disturbance of inverter output current; is the estimated value of the inverter output current at time k+1 in the stationary coordinate system, is the estimated value of the inverter output current at time k in the stationary coordinate system; is the estimated value of the concentrated disturbance of the inverter output current at time k+1 in the stationary coordinate system, is the estimated value of the concentrated disturbance of the inverter output current at time k in the stationary coordinate system; According to formula (22), the concentrated disturbance of the inverter output current can be estimated in real time Thus, according to formula (20), the basic voltage vector reference value v of the inverter at time k in the stationary coordinate system is obtained: iref [k]; Since the grid inverter generally works at a higher control frequency, it can be considered that v iref [k+1]=v iref [k], obtaining the basic voltage vector reference value of the inverter effectively avoids the influence of system disturbance in the grid-connected inverter on the basic voltage vector reference value of the inverter.

6. The inverter grid voltage cascade control method based on robust prediction according to claim 5, characterized in that: Step 7 The detailed steps are as follows: To ensure the inverter basic voltage vector prediction value v i [k+1] can track the inverter basic voltage vector reference value v iref [k+1], design cost function J i And expressed as: J i =|v iref [k+1]-v i [k+1]| (23) At this time, the eight basic voltage vectors of the inverter correspond to eight cost functions. The basic voltage vector with the lowest cost function is selected as the optimal vector, and the three-phase modulation wave of the next control cycle is set according to its switching state. The three-phase modulation wave can also be set in combination with space vector modulation.

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