A method and system for adaptively adjusting control parameters of AC / DC rectifier

Abstract

The present invention discloses an adaptive adjustment method and system for control parameters of an AC / DC rectifier. The adaptive adjustment method for control parameters of an AC / DC rectifier adopted by the present invention is: based on the proportional-integral-differential control system of the frequency domain theory offline design mode, firstly, a small disturbance voltage of the same phase is injected into the AC side of the rectifier to obtain the change of the voltage and current on the AC side, and an online parameter identification calculation of the recursive least squares algorithm with a forgetting factor is performed under the dq axis, and then the resistance and inductance identification values ​​of the transmission line are used for calculation in real time, and finally, the control parameters are set by outputting to the current inner loop through hysteresis comparison. Based on the classic PID control, the present invention considers the transmission line impedance to adaptively update the control parameter value, improves the stability of the current inner loop to a certain extent, and solves the problems of complex calculation and difficulty in engineering application.

Description

Technical Field

[0001] The invention belongs to the field of AC / DC rectifier control, in particular to an AC / DC rectifier control parameter adaptive adjustment method and system. Background Art

[0002] Parameter identification techniques include active perturbation techniques and passive techniques. Active grid impedance estimation techniques intentionally perturb the grid and then perform data acquisition and signal processing; compared with passive techniques, it provides more accurate results. Grid impedance estimation based on rectifier output power changes has attracted more attention due to its simple implementation and significant reduction in computational burden. This technology was originally proposed for single-phase grid-connected systems controlled in a stationary reference coordinate system. It relies on two operating points sampled in a specific instance when active and reactive power change. There are many measurements and it cannot guarantee that the response voltage and current are within the stability margin. However, directly perturbing the voltage and current can directly control the size of the disturbance in the grid and avoid the instability caused by unreasonable selection of disturbance in active grid impedance estimation.

[0003] Common online parameter identification algorithms include genetic algorithm (GA), recursive least squares algorithm (RLS), particle swarm optimization (PSO), extended Kalman filter (EKF), etc. These algorithms have their own advantages and disadvantages, and the appropriate algorithm needs to be selected according to the specific situation. Among them, the identification accuracy and convergence speed of GA are closely related to the algorithm parameters, but it is easy to fall into the local optimal solution. RLS has a simple structure, but the identification error is large. PSO is used for parameter identification, but its accuracy is lower than that of RLS and EKF. EKF needs to calculate the Jacobian matrix, which has a large amount of calculation. In order to improve the identification accuracy of RLS, many studies have optimized it, such as forgetting factor least squares (FFRLS), which balances new and old data by adjusting the forgetting factor and speeds up the convergence of the algorithm. At present, some scholars have proposed adaptive expressions, which adaptively process the forgetting factor by correcting the error to improve the accuracy and response speed of parameter identification. However, in the adaptive forgetting factor least squares method, the selection of the undetermined coefficient has an important influence on the error tracking ability of the algorithm. The range of values ​​of the undetermined coefficient is large, which brings certain difficulties to the algorithm in practical applications.

[0004] The impedance of the AC side transmission line is closely related to the short-circuit ratio of the AC / DC rectifier system. When transmission line blocking, voltage imbalance, frequency fluctuation and other operating conditions occur, the transmission line impedance will change, and the short-circuit ratio of the AC / DC rectifier system will also change accordingly. The proportional-integral-differential (PID) control system based on the offline design mode of the classic frequency domain theory has the disadvantage of being highly conservative. The low short-circuit ratio and weak grid characteristics lead to insufficient system voltage support capacity, which is easy to further cause broadband oscillation stability problems.

[0005] The proportional-integral-derivative (PID) control system of the classic frequency domain theory offline design mode has the disadvantage of being highly conservative. The low short-circuit ratio and weak grid characteristics lead to insufficient system voltage support capacity, which can further cause wide-band oscillation stability problems. Methods based on model predictive control and deep reinforcement learning can improve control performance to a certain extent, but the computational complexity is high and requires a large amount of training data and computing resources; while methods based on fuzzy control and genetic algorithms have good real-time and robustness, but require more manual parameter adjustment and computing time. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide an AC / DC rectifier control parameter adaptive adjustment method and system, which is based on classic PID control, considers the transmission line impedance to adaptively update the controller parameter value, improves the stability of the current inner loop to a certain extent, and solves the problems of complex calculation and difficulty in engineering application.

[0007] To this end, the present invention adopts the following technical solution.

[0008] In the first aspect, the present invention provides an adaptive adjustment method for control parameters of an AC / DC rectifier, which is based on a proportional-integral-differential control system of a frequency domain theory offline design mode. First, a small disturbance voltage of the same phase is injected into the AC side of the rectifier to obtain the change of the voltage and current on the AC side, and an online parameter identification calculation is performed under the dq axis using a recursive least squares algorithm with a forgetting factor, and then the resistance and inductance identification values ​​of the transmission line are used for calculation in real time, and finally the control parameters are set by outputting them to the current inner loop through hysteresis comparison.

[0009] Furthermore, the expression of online parameter identification calculation is:

[0010] ,

[0011] in, and are the resistance and inductance of the transmission line respectively; and are the values ​​of the voltage change on the AC side under the d-axis and q-axis respectively; and are the values ​​of the AC side current change under the d-axis and q-axis respectively; is the angular frequency on the AC side; is the response current of the AC side voltage disturbance;

[0012] The steps to establish the recursive least squares algorithm model are as follows:

[0013] The first step is to , , and The disturbance change matrix of transmission line identification is calculated and the calculation formula is:

[0014] ,

[0015] In the formula, is the sampling point, is the disturbance variation matrix for transmission line resistance identification, is the disturbance variation matrix for transmission line inductance identification;

[0016] The second step is to generate the response current of the AC side voltage disturbance Compute the squared disturbance response matrix , the calculation formula is:

[0017] ;

[0018] The third step is to establish coupling equations of the recursive coefficient matrix and the recursive coefficient calculation factor matrix of resistance and inductance respectively based on the results of the first and second steps;

[0019] The coupling equations of the resistance recursion coefficient matrix and the recursion coefficient calculation factor matrix are:

[0020] ,

[0021] The coupling equations of the inductance recursion coefficient matrix and the recursion coefficient calculation factor matrix are:

[0022] ,

[0023] in, is the transmission line resistance recursion coefficient matrix; is the transmission line inductance recursion coefficient matrix; Calculate the factor matrix for the resistance recursion coefficient; Calculate the factor matrix for the inductance recursion coefficient; and They are the forgetting factors for resistance and inductance parameter identification respectively; Indicates the AC side current; is the square term of the response current for transmission line resistance identification; is the square term of the response current for the inductance identification of the transmission line;

[0024] Thus, the recursive least squares algorithm model of the transmission line resistance and inductance is obtained:

[0025] ,

[0026] in, is the resistance identification value calculated by using the recursive least squares algorithm with forgetting factor; is the inductance identification value calculated using the recursive least squares algorithm with a forgetting factor.

[0027] Furthermore, the , , and Measured by sensors.

[0028] Furthermore, the impedance of the transmission line is taken into account and the control parameters of the current inner loop are calculated.

[0029] Furthermore, in order to enable the inner current loop to obtain faster current following performance, the regulator of the inner current loop is designed according to the typical type I system.

[0030] Furthermore, the proportional coefficient of the current inner loop regulator is and the integral coefficient It is expressed as:

[0031] ,

[0032] in, is the filter inductance of the rectifier, is the sampling period, is the rectifier gain.

[0033] Furthermore, the small disturbance voltage is 1.5-2.5% of the rated voltage of the AC measurement.

[0034] Furthermore, after the current inner loop control parameter is calculated, a hysteresis comparison is performed to compare the current inner loop control parameter value with the parameter value when the control parameter was last updated. If the deviation is not within a preset range, the current inner loop control parameter value is updated.

[0035] Furthermore, the preset range is [-0.5, 0.5].

[0036] In a second aspect, the present invention provides an AC / DC rectifier control parameter adaptive adjustment system, which is used to implement the above-mentioned AC / DC rectifier control parameter adaptive adjustment method.

[0037] The beneficial effects of the present invention are as follows: the present invention adopts a recursive least squares algorithm with a forgetting factor, which greatly overcomes the uncertainty of the parameter model and reduces the amount of information of old data, so that the real-time characteristics of the system can be captured more accurately; based on classical PID control, the control parameter value is adaptively updated considering the transmission line impedance, which improves the stability of the current inner loop to a certain extent and solves the problems of complex calculation and difficulty in engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 The schematic diagram of the method for adaptively adjusting control parameters of an AC / DC rectifier according to the present invention;

[0040] Figure 2 is a flow chart of the online parameter identification method of the present invention;

[0041] Figure 3 This is a diagram of inductance identification results of the online parameter identification method of the present invention;

[0042] Figure 4 It is a resistance identification result diagram of the online parameter identification method of the present invention;

[0043] Figure 5 is a graph of inductance identification error rate of the online parameter identification method of the present invention;

[0044] Figure 6 is a resistance identification error rate curve diagram of the online parameter identification method of the present invention;

[0045] Figure 7 It is a root locus diagram of the current inner loop open loop transfer function before and after the control parameter adaptive update of the present invention;

[0046] Figure 8 Schematic diagram of controller parameter hysteresis comparison of the present invention;

[0047] Fig. 9 A comparison diagram of the simulation results of the AC side current before and after the adaptive update of the control parameters under the weak power grid of the present invention;

[0048] Fig.10 This is a comparison diagram of the DC side current simulation results before and after the adaptive update of the control parameters under the weak power grid of the present invention. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] This embodiment provides an adaptive adjustment method for control parameters of an AC / DC rectifier. Based on the proportional-integral-differential control system of the frequency domain theory offline design mode, an online parameter identification link is added to identify the resistance and inductance of the transmission line in real time, and the control parameters of the current inner loop are adaptively adjusted, such as Figure 1 shown. Figure 1 middle, is the DC side capacitance, is the filter capacitor of the LC filter on the AC side, is the DC side voltage, is the DC side voltage reference value, is the reference value of the d-axis component of the AC side current, is the reference value of the q-axis component of the AC side current, is the current of the transmission line, is the current of each phase on the AC side, AC side phase voltage, is the phase-locked loop output phase angle, is the d-axis component of the AC side current, is the q-axis component of the AC side current, is the d-axis component of the AC side voltage, is the q-axis component of the AC side voltage, is the d-axis component of the double closed-loop output voltage, is the q-axis component of the dual closed-loop output voltage, LPF is the filter, PLL is the phase-locked loop, PWM is the pulse width modulation, express and , express and , represents the disturbance voltage injected into the AC side grid voltage, abc represents the abc three-phase stationary coordinate system, and dq represents the dq two-phase rotating coordinate system.

[0051] The specific steps of the AC / DC rectifier control parameter adaptive adjustment method are as follows:

[0052] First, a small disturbance voltage of the same phase is injected into the AC side of the rectifier to obtain the changes in the voltage and current on the AC side, and an online parameter identification calculation is performed under the dq axis using a recursive least squares algorithm with a forgetting factor, and then the resistance and inductance identification values ​​of the transmission line are used for real-time calculation, and finally, the output is output to the current inner loop through hysteresis comparison to set the adjustment parameters. The small disturbance voltage is 2% of the rated voltage of the AC.

[0053] Specifically, the process of online parameter identification is as follows: Figure 2 shown.

[0054] The expression of online parameter identification calculation is:

[0055] ,

[0056] in, and are the resistance and inductance of the transmission line respectively; and are the values ​​of the voltage change on the AC side under the d-axis and q-axis respectively; and are the values ​​of the AC side current change under the d-axis and q-axis respectively; is the angular frequency on the AC side; is the response current of the AC side voltage disturbance; , , and Measured by sensors.

[0057] The steps to establish the recursive least squares algorithm model are as follows:

[0058] The first step is to , , and The disturbance change matrix of transmission line identification is calculated and the calculation formula is:

[0059] ,

[0060] In the formula, is the sampling point, is the disturbance variation matrix for transmission line resistance identification, is the disturbance variation matrix for transmission line inductance identification;

[0061] The second step is to generate the response current of the AC side voltage disturbance Compute the squared disturbance response matrix , the calculation formula is:

[0062] ;

[0063] The third step is to establish coupling equations of the recursive coefficient matrix and the recursive coefficient calculation factor matrix of resistance and inductance respectively based on the results of the first and second steps;

[0064] The coupling equations of the resistance recursion coefficient matrix and the recursion coefficient calculation factor matrix are:

[0065] ,

[0066] The coupling equations of the inductance recursion coefficient matrix and the recursion coefficient calculation factor matrix are:

[0067] ,

[0068] in, is the transmission line resistance recursion coefficient matrix; is the transmission line inductance recursion coefficient matrix; Calculate the factor matrix for the resistance recursion coefficient; Calculate the factor matrix for the inductance recursion coefficient; and They are the forgetting factors for resistance and inductance parameter identification respectively; Indicates the AC side current; is the square term of the response current for transmission line resistance identification; is the square term of the response current for the inductance identification of the transmission line;

[0069] Thus, the recursive least squares algorithm model of the transmission line resistance and inductance is obtained:

[0070] ,

[0071] in, is the resistance identification value calculated by using the recursive least squares algorithm with forgetting factor; is the inductance identification value calculated using the recursive least squares algorithm with a forgetting factor.

[0072] The online parameter identification method is simulated, and the identification results of the online parameter identification method are shown in the figure Figure 3 and Figure 4 As shown in the figure, the identification error rate curve of the online parameter identification method is as follows Figure 5 and Figure 6 As shown in the figure, the parameter identification of the transmission line with an impedance value of 0.23+j1.57Ω verified in the simulation, the multiple sets of identification results obtained by simulation are about 0.231+j1.582Ω, and the identification errors of inductance and resistance are respectively + 0.87% and + The error is within 0.31%, which is within a reasonable range and can accurately perform adaptive optimization of the current inner loop control parameters.

[0073] In order to make the current inner loop obtain faster current following performance, the regulator of the current inner loop is designed according to the typical type I system. The proportional coefficient of the current inner loop regulator is and the integral coefficient It is expressed as:

[0074] ,

[0075] in, is the filter inductance of the rectifier, is the sampling period, is the rectifier gain.

[0076] The transmission line resistance and inductance are obtained by using the recursive least squares algorithm with a forgetting factor, and the control parameters of the current inner loop are calculated by considering the impedance of the transmission line. After the current inner loop control parameters are calculated, a hysteresis comparison is performed to compare the current inner loop control parameter value with the parameter value when the control parameter was last updated. If the deviation is not within the preset range, the current inner loop control parameter value is updated. The preset range is preferably [-0.5, 0.5].

[0077] The root locus of the current inner loop open-loop transfer function before and after the adaptive update of the control parameters considering the transmission line impedance is as follows: Figure 7 shown.

[0078] Considering the transmission line design of the current inner loop PI parameters under each short-circuit ratio, the cut-off frequency under each grid strength increases, the response speed of the current inner loop becomes faster, and the impact on the power frequency of 50Hz is small. At low frequencies, even if the grid strength decreases (the impedance modulus of the transmission line increases), the amplitude-frequency response of the current inner loop remains almost unchanged, with a large positive gain, the amplitude margin of the system is large, and the stability of the system is superior to that when only the filter inductor is considered to design the PI parameters.

[0079] After the current inner loop parameters are calculated, hysteresis comparison is performed. The controller parameter hysteresis comparison is as follows: Figure 8 As shown in the figure, when the current inner loop control parameter value is compared with the parameter value at the last control parameter update, the deviation exceeds + That is, the current inner loop control parameter value is updated only when the deviation between the controller adaptively calculated parameter and the parameter at the last update is not within the shaded range [-0.5, 0.5].

[0080] Comparison of grid current simulation results before and after adaptive update of control parameters in weak grid Fig. 9 and Fig.10 As shown, it can be clearly seen that the quality of the current on both the AC and DC sides improves after adaptive compensation of the current inner loop control parameters considering the transmission line impedance.

[0081] This embodiment also provides an AC / DC rectifier control parameter adaptive adjustment system, which is used to implement the above-mentioned AC / DC rectifier control parameter adaptive adjustment method.

[0082] It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for adaptively adjusting control parameters of an AC / DC rectifier, characterized in that: Based on the proportional-integral-differential control system of the frequency domain theory offline design mode, a small disturbance voltage of the same phase is first injected into the AC side of the rectifier to obtain the changes in the voltage and current on the AC side. The online parameter identification calculation of the recursive least squares algorithm with a forgetting factor is performed under the dq axis, and then the resistance and inductance identification values ​​of the transmission line are used for real-time calculation. Finally, the output is output to the current inner loop through hysteresis comparison to set the control parameters. The expression of online parameter identification calculation is: ， in, and are the resistance and inductance of the transmission line respectively; and are the values ​​of the voltage change on the AC side under the d-axis and q-axis respectively; and are the values ​​of the AC side current change under the d-axis and q-axis respectively; is the angular frequency on the AC side; is the response current of the AC side voltage disturbance; The steps to establish the recursive least squares algorithm model are as follows: The first step is to , , and The disturbance change matrix of transmission line identification is calculated and the calculation formula is: ， In the formula, is the sampling point, is the disturbance variation matrix for transmission line resistance identification, is the disturbance variation matrix for transmission line inductance identification; The second step is to generate the response current of the AC side voltage disturbance Compute the squared disturbance response matrix , the calculation formula is: ； The third step is to establish coupling equations of the recursive coefficient matrix and the recursive coefficient calculation factor matrix of resistance and inductance respectively based on the results of the first and second steps; The coupling equations of the resistance recursion coefficient matrix and the recursion coefficient calculation factor matrix are: ， The coupling equations of the inductance recursion coefficient matrix and the recursion coefficient calculation factor matrix are: ， in, is the transmission line resistance recursion coefficient matrix; is the transmission line inductance recursion coefficient matrix; Calculate the factor matrix for the resistance recursion coefficient; Calculate the factor matrix for the inductance recursion coefficient; and They are the forgetting factors for resistance and inductance parameter identification respectively; Indicates the AC side current; is the square term of the response current for transmission line resistance identification; is the square term of the response current for the inductance identification of the transmission line; Thus, the recursive least squares algorithm model of the transmission line resistance and inductance is obtained: ， in, is the resistance identification value calculated by using the recursive least squares algorithm with forgetting factor; is the inductance identification value calculated using the recursive least squares algorithm with a forgetting factor.

2. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 1, characterized in that: The , , and Measured by sensors.

3. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 1, characterized in that: Considering the impedance of the transmission line, the control parameters of the inner current loop are calculated.

4. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 1, characterized in that: In order to make the inner current loop obtain faster current following performance, the regulator of the inner current loop is designed according to the typical type I system.

5. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 4, characterized in that: The proportional coefficient of the current inner loop regulator and the integral coefficient It is expressed as: ， in, is the filter inductance of the rectifier, is the sampling period, is the rectifier gain.

6. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 1, characterized in that: The small disturbance voltage is 1.5-2.5% of the rated voltage on the AC side.

7. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 1, characterized in that: After the current inner loop control parameter is calculated, a hysteresis comparison is performed to compare the current inner loop control parameter value with the parameter value when the control parameter was last updated. If the deviation is not within the preset range, the current inner loop control parameter value is updated.

8. The method for adaptively adjusting control parameters of an AC / DC rectifier according to claim 7, characterized in that: The default range is [-0.5, 0.5].

9. An AC / DC rectifier control parameter adaptive adjustment system, characterized in that: Used to implement the AC / DC rectifier control parameter adaptive adjustment method described in any one of claims 1-8.

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