A PR controller-based inverter nonlinear compound control method and system

Abstract

The application discloses an inverter nonlinear composite control method and system based on a PR controller and belongs to the field of power electronics. In view of the problems that the existing control scheme is weak in control performance or even fails when facing actual inverter parameter uncertainty, external disturbance during grid connection or load access operation and the like, Taylor series is adopted to solve the problem that a nonlinear model predictive control structure is complex and difficult to implement, and a nonlinear disturbance observer is introduced to improve control accuracy, so that the finally constructed grid-connected inverter nonlinear composite control inverter has the advantages of simple control structure implementation and convenient actual application while being capable of realizing good tracking capability on a reference signal and rapid inhibition capability on external interference.

Description

TECHNICAL FIELD

[0001] The application relates to an inverter nonlinear composite control method and system based on a PR controller and belongs to the field of power electronics. BACKGROUND

[0002] As a key of power output of photovoltaic, wind power and other new energy power generation inverters which are widely deployed, the inverter is directly related to the reliable and efficient operation of the inverter.

[0003] The grid-connected current control of the existing inverter often adopts a proportional resonant (PR) or proportional-integral (PI) controller. Compared with the PI controller, the PR controller can improve the loop gain at the fundamental or a certain specific harmonic, eliminate the steady-state error of the grid-connected current and effectively suppress the influence of the grid voltage background harmonic on the grid-connected current. However, for photovoltaic, wind turbine and other new energy power generation inverters, the disturbance such as the fluctuation of the direct-current voltage on the power generation side and the disturbance on the grid or load side will cause the performance of the PR controller to decline, thereby affecting the operation stability and output power quality of the inverter.

[0004] In order to realize the high-quality stable output of the inverter with significant nonlinear characteristics under the fluctuation of the operating parameters on the basis of maintaining the advantages such as practicability and maturity of the traditional controller, the current mainstream scheme is to combine the typical controller with the predictive control for hybrid control. The commonly used predictive control methods mainly include two categories of nonlinear model predictive control (NMPC) and nonlinear disturbance observer (NDO). The NMPC mainly approximates the nonlinear inverter by using a Taylor expansion of a specific order, which simplifies the difficulty of continuous domain modeling of the nonlinear inverter but also brings the closed solution problem. The NDO integrates the observer into the original control loop to compensate for the unknown disturbance which is not considered in the nominal model of the inverter, so that the inverter can have good tracking performance and fast disturbance suppression capability. However, the existing hybrid control scheme is mainly based on the PI controller and is limited to dealing with the linear disturbance of the inverter, and the final controller design effect is highly dependent on the accuracy of the inverter model, so not only will the overall control structure design and actual application of the inverter be relatively complex, but the control performance improvement will also be insufficient. SUMMARY

[0005] In view of the above problems, the application provides an inverter nonlinear composite control method based on a PR controller.

[0006] The technical scheme for achieving the object of the application is as follows: an inverter nonlinear composite control method based on a PR controller, comprising the following steps.

[0007] Step 1: obtaining the alpha-axis and beta-axis component values of the grid-connected voltage and current of the inverter;

[0008] Step 2: based on the alpha axis and beta axis component values of the grid-side current of the inverter, the disturbance observer is used to estimate the grid-side alpha axis and beta axis disturbance prediction values during the operation of the inverter;

[0009] Step 3: according to the grid-side alpha axis and beta axis disturbance prediction values, the alpha axis and beta axis component values of the grid-side voltage and current of the inverter, the NMPC controller is used to obtain the inverter output voltage reference value;

[0010] Step 4: the three-phase stationary coordinate axis reference value of the inverter output voltage is obtained by performing inverse Clarke transformation on the inverter output voltage reference value, and the SPWM modulation is used to realize the inverter control pulse output.

[0011] The application also provides an inverter nonlinear composite control system based on a PR controller, which comprises an inverter grid-side voltage and current acquisition module, a disturbance observer, a PR type NMPC controller, an inverse Clarke transformation module and an SPWM modulation module, the inverter grid-side voltage and current acquisition module is used to acquire the alpha axis and beta axis component values of the inverter grid-side voltage and current, the disturbance observer is used to estimate the grid-side alpha axis and beta axis disturbance prediction values during the operation of the inverter based on the alpha axis and beta axis component values of the inverter grid-side current; the PR type NMPC controller is used to obtain the inverter output voltage reference value according to the grid-side alpha axis and beta axis disturbance prediction values, the alpha axis and beta axis component values of the inverter grid-side voltage and current; the inverse Clarke transformation module is used to perform inverse Clarke transformation on the inverter output voltage reference value to obtain the three-phase stationary coordinate axis reference value of the inverter output voltage; and the SPWM modulation module is used to realize the inverter control pulse output.

[0012] Compared with the prior art, the inverter nonlinear composite control based on the PR controller adopted by the application can simplify the inverter control structure, make the inverter have excellent tracking performance and fast disturbance dynamic suppression ability, and greatly improve the stable operation ability of the inverter under complex operation conditions. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a principle block diagram of an inverter control method based on a nonlinear PR predictive controller.

[0014] Figure 2 It is a flowchart of an inverter control method based on a nonlinear PR predictive controller. DETAILED DESCRIPTION

[0015] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0016] As shown in Figure 1 , 2 , a kind of inverter control method based on nonlinear PR predictive controller, while keeping PR controller fast and accurate tracking performance, combined with NMPC and NDO technology improves control inverter dynamic response speed, eventually build PR composite control inverter of inverter, which can effectively deal with nonlinear disturbance of inverter, relatively simple control structure is also relatively convenient in practical application, specific steps are as follows:

[0017] Step 1: obtain the α-axis and β-axis component values of the grid-connected side voltage and current of the inverter. Measure and obtain the three-phase voltage , , and three-phase current , , at the grid-connected point of the inverter, and obtain the α-axis component value of the grid-connected side voltage of the inverter , the β-axis component value of the grid-connected side voltage of the inverter , the α-axis component value of the grid-connected side current of the inverter and the β-axis component value of the grid-connected side current of the inverter by Clarke transformation.

[0018] Step 2: according to the α-axis component value of the grid-connected side current of the inverter and the β-axis component value of the grid-connected side current of the inverter , estimate the α-axis and β-axis disturbance prediction values of the grid side during operation of the inverter using the disturbance observer.

[0019] Under the premise that the disturbance b(t) needs to satisfy the following conditions

[0020]

[0021] The selected inverter disturbance estimation formula is as follows:

[0022]

[0023] Wherein, is the disturbance estimation value; , respectively represent the α-axis and β-axis disturbance prediction values of the grid side; is the differential of the disturbance estimate, d is the observer gain; and R2 are the grid-side filter inductance and its parasitic resistance of the inverter, respectively; is the differential of the variable ; ; ; ; , and are the α and β axis components of the grid-side current, respectively, and are the α and β axis components of the reference value of the inverter output voltage, respectively;

[0024] the estimation error of the disturbance is limited by

[0025]

[0026] when the disturbance gain is a constant matrix, d is selected by

[0027]

[0028] where μ = diag{μ α , μ β} is a 2x2 diagonal matrix, and μ α and μ β are the α and β components of μ, respectively.

[0029]

[0030] where ξ, ω0, T s are the damping ratio, the fundamental angular frequency and the sampling period, respectively.

[0031] By setting , global asymptotic stability is achieved, and the simplified observer expression is

[0032]

[0033] where and represent the grid current tracking error of the controlled inverter; T r is the prediction period value.

[0034] Considering that the initial disturbance is zero, the final disturbance observer function can be obtained according to the above formula as follows:

[0035]

[0036] where and These are the predicted disturbance values ​​for the α-axis and β-axis on the grid side, respectively.

[0037] The inverter grid-connected current α-axis component value obtained in step 1 and the β-axis component of the inverter grid-connected current The predicted values ​​of the α-axis and β-axis disturbances on the grid side can be obtained using the above formula. , .

[0038] Step 3: Based on the predicted values ​​of α-axis and β-axis disturbances on the grid side , α-axis component of inverter grid-connected voltage β-axis component of inverter grid-connected voltage α-axis component of inverter grid-connected current and the β-axis component of the inverter grid-connected current The inverter output voltage reference value is obtained using the NMPC controller. The specific method is as follows:

[0039] First, an equation for the inverter output current in nonlinear affine form is established based on NMPC theory.

[0040]

[0041] in, ; ; , and These are the α-axis and β-axis components of the grid-side current, respectively. and These are the reference values ​​for the α-axis and β-axis components of the inverter output voltage, respectively. and These are the predicted perturbation values ​​for the α-axis and β-axis, respectively.

[0042] ; ; ; ; R1 and R2 are the filter inductor and parasitic resistance on the grid-connected side of the inverter, respectively; For variables The derivative of .

[0043] To better obtain the analytical solution of the function, a first-order Taylor expansion is used to simplify the NMPC current controller output equation:

[0044]

[0045] In the formula, This represents the predicted value of y(t). is the time step.

[0046] The relative degree parameter p between the input and output of the inverter in actual operation needs to be equal to 1, so the output function reference value is reconstructed by using the Lie derivative Specifically,

[0047]

[0048] wherein, ; , and are the derivatives of f, and with respect to x. The output function reference value is determined according to the required output power size, P = UI, and the grid voltage U is generally constant, so the inverter needs to output how much power, and the current output reference value in the control system is adjusted to a specific value.

[0049] The mathematical equation of the PR optimal NMPC controller according to the simplified and reconstructed output function is as follows

[0050]

[0051] wherein, ; ; ; ; , is a second-order unit matrix; is the reconstructed output function reference value.

[0052] Based on the inverter grid-side voltage alpha-axis component value obtained in step 1 , the inverter grid-side voltage beta-axis component value , the inverter grid-side current alpha-axis component value , and the inverter grid-side current beta-axis component value , and the alpha-axis and beta-axis prediction values of the grid-side disturbance obtained in step 2 , , the PR optimal NMPC controller in the above formula can be used to obtain the reference values of the inverter output voltage alpha-axis and beta-axis and .

[0053] Step 4: Based on the inverter output voltage alpha-axis and beta-axis reference values and output by the PR nonlinear predictive controller, the three-phase stationary coordinate axis reference values of the inverter output voltage are obtained by performing inverse Clarke transformation: , and Finally, the SPWM modulation is used to realize the inverter control pulse output.

[0054] The inverter nonlinear composite control system based on the PR controller comprises an inverter grid-side voltage and current acquisition module, a disturbance observer, a PR type NMPC controller, an inverse Clarke transformation module and an SPWM modulation module, the inverter grid-side voltage and current acquisition module is used to acquire the alpha-axis and beta-axis component values of the inverter grid-side voltage and current, the disturbance observer is used to estimate the grid-side alpha-axis and beta-axis disturbance prediction values during the operation of the inverter based on the alpha-axis and beta-axis component values of the inverter grid-side current, the PR type NMPC controller is used to acquire the inverter output voltage reference value according to the grid-side alpha-axis and beta-axis disturbance prediction values, the alpha-axis and beta-axis component values of the inverter grid-side voltage and current, the inverse Clarke transformation module is used to perform inverse Clarke transformation on the inverter output voltage reference value to obtain the three-phase stationary coordinate axis reference value of the inverter output voltage, and the SPWM modulation module is used to realize the inverter control pulse output.

[0055] The above embodiments only show the technical idea of the present application, and cannot limit the protection scope of the present application, and any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.

Claims

1. A nonlinear composite control method for inverters based on a PR controller, characterized in that, include: Step 1: Obtain the α-axis and β-axis component values ​​of the inverter's grid-connected voltage and current; Step 2: Based on the α-axis and β-axis component values ​​of the inverter's grid-connected current, a disturbance observer is used to estimate the predicted α-axis and β-axis disturbance values ​​on the grid side during inverter operation. The specific formula is as follows: ； In the formula, and These represent the α-axis and β-axis components of the inverter's grid-connected current tracking error, respectively. To predict the periodic value, , These are the α-axis and β-axis components of the perturbation observer gain matrix, respectively. and These are the predicted disturbance values ​​for the α-axis and β-axis on the grid side, respectively. For integration variables, For time; Step 3: Based on the predicted α-axis and β-axis disturbance values ​​on the grid side, and the α-axis and β-axis component values ​​of the inverter's grid-connected voltage and current, obtain the inverter output voltage reference value using the NMPC controller. The specific formula is as follows: ； In the formula, , , These are the predicted disturbance values ​​for the α-axis and β-axis on the grid side, respectively. For input quantity, , These are the α-axis and β-axis components of the inverter's grid-connected current, respectively. For output quantity, , , These are the reference values ​​for the α-axis and β-axis components of the inverter's grid-connected current, respectively. It is a second-order identity matrix. To predict the periodic value, , and f, respectively and for The derivative, For the input gain matrix, Let f be the perturbation gain matrix, and f be the vector field matrix. , To reconstruct the reference value of the output function, This is the reference value for the inverter output voltage. , , These are the α-axis and β-axis components of the inverter output voltage reference value, respectively. Step 4: Perform inverse Clarke transformation on the inverter output voltage reference value to obtain the three-phase stationary coordinate axis reference value of the inverter output voltage, and use SPWM modulation to realize the inverter control pulse output.

2. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The α-axis and β-axis components of the inverter's grid-connected current tracking error are as follows: ； ； In the formula, , Let α and β be the α-axis and β-axis components of the inverter's grid-connected current at time t, respectively. , These are the reference values ​​for the α-axis and β-axis components of the inverter's grid-connected current at time t.

3. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The α-axis and β-axis components of the perturbation observer gain matrix are as follows: ,ξ、 , These are the damping ratio, fundamental angular frequency, and sampling period, respectively.

4. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The input gain matrix is ​​as follows: ； In the formula, This is the filter inductor on the grid-connected side of the inverter.

5. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The perturbation gain matrix is ​​as follows: ， In the formula, This is the filter inductor on the grid-connected side of the inverter.

6. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The vector field matrix is ​​specifically: ， In the formula, R1 and R2 are the filter inductor and parasitic resistance on the grid-connected side of the inverter, respectively. , These are the α-axis and β-axis components of the inverter's grid-connected voltage, respectively.

7. The inverter nonlinear composite control method based on a PR controller according to claim 1, characterized in that, The specific method for obtaining the α-axis and β-axis component values ​​of the inverter's grid-connected voltage and current is as follows: Measure and acquire the three-phase voltages a, b, and c at the inverter grid connection point. , , and three-phase current , , The α-axis component of the inverter grid-connected voltage is obtained through Clarke transformation. β-axis component of the inverter grid-connected voltage The α-axis component of the inverter grid-connected current β-axis component of the inverter grid-connected current .

8. A nonlinear composite control system for an inverter based on a PR controller, according to any one of claims 1 to 7, characterized in that, include: The system includes an inverter grid-connected voltage and current acquisition module, a disturbance observer, a PR-type NMPC controller, an inverse Clarke transform module, and an SPWM modulation module. The grid-connected voltage and current acquisition module acquires the α-axis and β-axis components of the inverter's grid-connected voltage and current. The disturbance observer estimates the predicted α-axis and β-axis disturbances on the grid side during inverter operation based on the α-axis and β-axis components of the inverter's grid-connected current. The PR-type NMPC controller acquires the inverter output voltage reference value based on the predicted α-axis and β-axis disturbances on the grid side and the α-axis and β-axis components of the inverter's grid-connected voltage and current. The inverse Clarke transform module performs an inverse Clarke transform on the inverter output voltage reference value to obtain the three-phase stationary coordinate axis reference value of the inverter output voltage. The SPWM modulation module implements inverter control pulse output.

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