Method and device for designing double-loop control parameters of power electronic converter

Abstract

The invention relates to a power electronic converter (VSC) double-loop control parameter design method and device, and belongs to the technical field of power electronics. The method comprises the following steps: establishing a small-signal state-space equation model according to a power system operation mode and a VSC control strategy, and obtaining a state matrix of the small-signal state-space equation model; then according to a singular perturbation correlation theory and participation factor analysis, obtaining a reduced order form of an original state matrix; designing control parameters of a current inner loop and a reactive power outer loop by using an I-type system setting method; establishing an optimization model to design active power outer loop parameters; according to the double-loop control parameter design method, the parameter optimization adjustment scheme of the power electronic converter is obtained, so that the overshoot is smaller and the response time is shorter in the transient process, and the stability of the system is further improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a double-loop control parameter design method and device for a power electronic converter (voltage source converter, VSC). BACKGROUND

[0002] With the increasing demand for electric energy and the progress of power electronics technology, renewable energy and power electronic devices have made great development in the application of power systems. The control strategy of power electronic converters and the design method of their controllers have always been the focus of attention in the field of power electronics technology and "double high" power system analysis. Among them, the double-loop control has been widely used in many fields such as distributed generation inverters, wind / solar + energy storage converters, virtual synchronous generator control, ultra / extra high voltage direct current transmission and wind farm flexible direct current transmission due to its simple structure and strong adaptability.

[0003] Although the double-loop controller has a simple structure and mature principle, the tuning of the parameters of the four PI controllers has always been a problem in double-loop control. At present, according to whether the interaction between devices is considered, the double-loop controller parameter design method can be divided into transfer function method and parameter collaborative optimization method. The transfer function method is the mainstream method, and the general practice is to regard the direct current side and the alternating current side of the converter as ideal voltage sources, and at the same time ignore the dynamic process of the phase-locked loop and the power electronic devices to establish a small signal model of the system. On this basis, the inner and outer loop parameter design is realized according to the design principle of "first inner loop and then outer loop". The typical system tuning method designs the controller parameters of the inner and outer loops according to the mature I-type and II-type system parameter tuning methods in control theory, and finally verifies the rationality of the parameter design through simulation and hardware experiment. Although this method has been widely used, the design parameters in the single-converter infinite system ignore the interaction between the power electronic converter and the devices in the AC / DC network, which may make the design results too optimistic. The parameter collaborative optimization method establishes a state space model of the whole system including the inner and outer loop parameters, calculates the damping ratio of the oscillation mode and takes it as the objective function, and then establishes an optimization model with the parameters to be optimized as the constraint conditions, and uses an intelligent algorithm to design the inner and outer loop parameters of the controller. However, these methods treat the inner and outer loop parameters equally, ignore their different contributions to the system oscillation mode, and are prone to "dimension disaster" problem when the dimension of the system state matrix is high, which may be difficult to obtain the optimization solution.

[0004] Model reduction is an important tool for power system analysis. In recent years, the related research has been used for modeling, stability mechanism analysis and controller parameter design of power system with power electronic converters. Therefore, it is planned to realize the design of power electronic converter double-loop control parameters by combining the typical system setting method and parameter collaborative optimization method under the reduced model. Compared with the transfer function method, the interaction between the system and the converter is considered, and the "dimension disaster" problem faced by the parameter collaborative optimization method is avoided.

[0005] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the general background of the application and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art with regard to the natural person skilled in the art. SUMMARY

[0006] The purpose of the present application is to solve the problems of the prior art and provide a power electronic converter double-loop control parameter design method and device. The method is based on small signal model and singular perturbation principle, and the double-loop control parameters of the power electronic converter VSC are optimized to make the overshoot smaller and the response time shorter in the transient process, thereby improving the stability of the system.

[0007] According to the small signal model related theory, the steady-state working point linearization equation is established for the AC side, the DC side and the controller respectively, and the corresponding state space equation model is obtained. Where Δx is the state variable, Δu is the input variable, Δy is the output variable, A is the state matrix, B is the input matrix, C is the output matrix, and D is the transfer matrix.

[0008] According to the singular perturbation related theory, the state variable Δx needs to be divided before model reduction. First, the complete oscillation mode of the state matrix A is obtained, and according to the size sorting, the dominant mode is close to the virtual axis, and the appropriate participation factor threshold can achieve the above purpose, and the calculation method is as follows: Where φ ij is the right eigenvector matrix element of the state matrix A; ψ ij is the left eigenvector matrix element of the state matrix A, and p ij is the participation factor matrix element.

[0009] Through the above method, the state variable is divided into fast variable Δx f and slow variable Δx s , and the original state space equation can be expressed as: In the formula, J(ε) is the Jacobian matrix. and f and g are functions with respect to x, respectively. s and x f The partial derivatives of . When When the model is nonsingular and ε is sufficiently small, a reduced-order model can be obtained:

[0010] Equation (9) shows that the state matrix under the reduced-order model According to relevant theories of power system analysis, the oscillation mode of the reduced-order system state matrix should be a part of the oscillation mode of the original system, meaning that reducing the model order does not affect the system accuracy. Therefore, a reduced-order model can be used to replace the original model for dual-loop control parameter design, thus considering the interaction of equipment and avoiding the "curse of dimensionality" problem.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] In a first aspect, the present invention provides a method for designing dual-loop control parameters for a power electronic converter, comprising:

[0013] Based on the control strategy and parameters of VSC, the operating conditions of the power system, etc., a state-space equation model is established to obtain its state matrix A.

[0014] Calculate the oscillation modes of the state matrix A, sort them by size, and identify the dominant mode as the one closest to the imaginary axis. Calculate the corresponding participation factor p, select an appropriate threshold to partition the state variables, and thus obtain the reduced-order model state matrix A. r The oscillation mode expression was obtained, and it was found that there was a decoupling phenomenon between the dual-loop control parameters and the oscillation mode.

[0015] The parameter optimization adjustment schemes for the inner current loop, the outer active power loop, and the outer reactive power loop are obtained according to the Type I system tuning method. An optimization model is established based on the decision variables of the outer active power loop, the upper and lower limit constraints of the parameters to be designed, and the objective function to obtain the parameter optimization adjustment scheme for the outer active power loop.

[0016] Based on the parameter optimization and adjustment scheme, the dual-loop control parameters of the power electronic converter of the power system to be optimized are adjusted to improve the system stability within the parameter range of interest.

[0017] Furthermore, the Type I system tuning method includes tuning the current inner loop control parameters and tuning the power outer loop control parameters, and their mathematical models are as follows: In the formula, T s K is the sampling period of the inner loop. PWM For PWM equivalent gain, k p The inner loop proportional gain is T, where L is the bridge arm inductance and T is the inner loop proportional gain.p is the sampling period of the outer power loop, k pp is the proportional gain of the outer power loop. When the system damping ratio is 0.707, the following equation needs to be satisfied: where K is the open-loop gain and T is the time constant. Substitute K and T in equation (10) and equation (11) into equation (12) respectively, and the corresponding control parameter expression can be obtained:

[0018] Further, the decision variable is the active power outer loop control parameter, including the proportional gain and the integral gain; the constraint condition is the upper and lower limits of the to-be-designed parameter; and the objective function is the distance from the real part of the reduced-order model oscillation mode to the expected real part of the oscillation mode, so the optimization model is: where N is the number of oscillation modes to be considered, M is the total number of operating conditions to be considered, σ i is the real part of the i-th oscillation mode of the system reduced-order model, σ d is the expected real part of the oscillation mode, and α i is the corresponding weight, k pp and k ip are the proportional gain and the integral gain of the active power outer loop, and k droop is the droop coefficient, k pp,min , k pp,max , k ip,min , k ip,max , k droop,min and k droop,max are the upper and lower limits of the to-be-designed parameter.

[0019] Further, the optimization adjustment scheme of the double-loop control parameters of the power electronic converter can be obtained by solving the type I system setting model and the optimization model.

[0020] In the second aspect, the application provides a double-loop control device of a power electronic converter designed according to the above parameter design method, which comprises:

[0021] The first part: the main circuit part, including an AC side, a power electronic converter, a DC side and a phase-locked loop, which undertakes tasks such as obtaining grid phase information, dq decomposition and PWM modulation wave generation;

[0022] The second part: the active power outer loop part, which is used for realizing control of the DC voltage and the active power, needs to satisfy the droop characteristic, and outputs the current d-axis component reference value;

[0023] The third part is a reactive power outer loop part, used for realizing control of reactive power, and realizing decoupling control of active power and reactive power together with the second part, and outputting a current q-axis component reference value;

[0024] The fourth part is a current inner loop part, used for realizing control of current, and constituting a double-loop control together with the second and third parts, and outputting for PWM modulation.

[0025] Compared with the prior art, the power electronic converter double-loop control parameter optimization method provided by the present application has the following beneficial effects:

[0026] The present application provides a power electronic converter double-loop control parameter design method and device, which optimizes the power electronic converter double-loop control parameters, so that the system has smaller overshoot and shorter response time, thereby improving the system stability. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description.

[0028] Figure 1 The flowchart of the power electronic converter double-loop control parameter optimization method for improving system stability provided by the present application is shown in

[0029] Figure 2 The double-loop control single-converter infinite device diagram designed according to the above parameter design method provided by the present application is shown in

[0030] Figure 3 The DC voltage curve of the power system after disturbance under different optimization parameters provided by the present application is shown in DETAILED DESCRIPTION

[0031] The present application will be further described in detail below with reference to the embodiments.

[0032] Those skilled in the art will understand that the following embodiments are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. If the specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the manufacturer of the material or equipment is not specified, it is a conventional product that can be obtained by purchase.

[0033] Figure 1 The flowchart of the power electronic converter double-loop control parameter optimization method for improving system stability provided by the present application is shown in Figure 1 The present application provides a power electronic converter double-loop control parameter optimization method for improving system stability, which comprises:

[0034] Step 101, according to the control strategy and parameters of VSC, the operation condition of power system, etc., a state space equation model is established, and a state matrix A is obtained.

[0035] Figure 2 A double-loop control single converter infinite device schematic diagram provided by the application is shown in the embodiment. n = 100pi, C = 500muF, R dc = 1.39ohm, L dc = 0.0159H, V acN = 220kV, P N = 1000MW, V dcN = 500kV. Four working conditions are provided for subsequent parameter design, which are all in the unit of per unit: i d1 = -0.2870, i d2 = -0.2988, i d3 = 0.2004, i d4 = 0.4019, i q1 = 0.0156, i q2 = -0.0162, i q3 = i q4 = 0, V cd1 = V cd2 = V cd3 = V cd4 = 1, V cq1 = 0.2013, V cq2 = 0.2096, V cq3 = -0.1402, V cq4 = -0.2808, V dc1 = V dc2 = 1, V dc3 = 1.012, V dc4 = 1.0141, V sd1 = V sd2 = V sd3 = V sd4 = 1, V sq1 = V sq2 = V sq3 = V sq4 = 0, L c = 0.15, R c = 0.005,

[0036] In the embodiment of the application, reference Figure 2 is made to the final established state matrix structure, wherein the state variables are: Delta x = [Delta i d , Delta i q , Delta v dc, Δz1, Δz2, Δz3, Δz4] T

[0037] Step 102, calculate the state matrix A oscillation mode, sort according to the distance to the imaginary axis, the near is the dominant mode, calculate the corresponding participation factor p, select the threshold value as 0.1 to divide the state variable, and finally obtain the reduced order model state matrix A r , and the oscillation mode expression is obtained, and it is found that there is a double-loop control parameter and oscillation mode decoupling phenomenon; Here, taking the working condition one as an example, the full oscillation mode of the state matrix A is shown in Table 1. Table 1 Select the oscillation modes 1 to 4 as the dominant modes, and the participation factors p are shown in Table 2. Table 2 Serial number Dominant modal value p>0.1 0.001<p<0.1 1 -25.246 [CAT] Δz3, Δz4 Δi d , Δi q , Δz1, Δz2]] 2 -25.246 [CAT] Δz3, Δz4 Δi d , Δi q , Δz1, Δz2]] 3 -10.001 [CAT] Δz1, Δz2 Δi d , Δi q ]]> 4 -10.001 [CAT] Δz1, Δz2 Δi d , Δi q ]]> Based on the above results, the eight state variables can be divided into fast variables and slow variables, wherein the fast variables are: Δx f =[Δi d , Δi q , ΔV dc , Δl dc ], and the slow variables are: Δx s =[Δz1, Δz2, Δz3, Δz4], and then the eight-order full-order model can be reduced to a four-order reduced-order model, that is, the reduced-order model state matrix A r .

[0038] Further, the reduced-order model state matrix A r The oscillation mode expression is as follows: Among them, the oscillation mode 3 expression is as follows, which shows the oscillation mode and inner and outer loop parameter decoupling phenomenon.

[0039] Step 103, according to the parameter optimization adjustment scheme of the current inner loop, the active power outer loop and the reactive power outer loop obtained by the I-type system tuning method; according to the decision variable of the active power outer loop, the upper and lower limit constraint conditions of the to-be-designed parameters and the objective function, an optimization model is established to obtain the parameter optimization adjustment scheme of the active power outer loop.

[0040] In this embodiment, K PWM is 1.633, T p is 0.02s, and T sis 1 / 1350 s, the current inner loop parameters (k p ,k i ) are (0.39, 5.79) by using the type I system setting method; the reactive power outer loop parameters (k pq ,k iq ) are (3, 150).

[0041] The parameter optimization adjustment scheme of the active power outer loop is obtained by the following optimization model: In the embodiment, M = 4; k pv,min = 0, k pv,max = 10, k iv,min = 0, k iv,max = 100, k droop,min = 0, k droop,max = 20.

[0042] In the embodiment of the application, the particle swarm (PSO: particle swarm optimization) method is used to calculate the above optimization model, and the specific steps are as follows:

[0043] Step S1, first, population initialization processing is performed. Here, the number of particle swarm iterative calculations is set to 200 times, the number of particles is 100, and the particles are randomly generated with 3-dimensional initial positions and speeds, which correspond to [k pp ,k ip ,k droop ] 3 components respectively. The initial position of each component of each particle is required to be within the corresponding upper and lower limit range, and the initial speed is 1% of the difference between the upper and lower limits multiplied by a random number less than or equal to 1. For example, the initial value of a certain particle i is the initial speed is set to 0, and the superscript 1 indicates the first iteration.

[0044] Step S2, each particle in the particle swarm is evaluated, and the objective function value of each particle is calculated. The position of each particle is brought into the oscillation modal expression for calculation. The objective function value of particle i at the kth iteration is represented as The particle position corresponding to the optimal individual value (here, the minimum value of the calculated objective function) of the particle at the end of the k-1th iteration is represented as p i The minimum value of the individual optimal of each particle of the whole group of particles is the group optimal, and the position thereof is g. In step S1, the particle initialization, the individual optimal position of each particle is the initial position thereof, and the group optimal position is the position of particle No. 1.

[0045] Step S3, comparing the objective function value of each particle with the individual optimal value, if better than the individual optimal value, the historical best position is updated to the current position, thereby updating the position p of the individual optimal value i ;

[0046] Step S4, comparing the objective function value of each particle with the group optimal value, if better than the group optimal value, the optimal position searched in the whole particle group is updated to the current position, thereby updating the position g of the group optimal value

[0047] Step S5, updating the particle speed according to the particle speed updating formula:

[0048] and the particle position updating formula: updating the speed and position of the i-th particle at the next time k+1, wherein rand() represents a random function with a value of [0, 1], the flight speed of each component of each particle is limited within 1% of the upper and lower limits of each component. If it exceeds this range, the boundary value is taken as the actual speed. The position of each component of each particle is limited within the upper and lower limits of each component, and if it exceeds this range, it is limited on the boundary value. pso = 0.9, c1 = 2, c2 = 2. According to this method, all 100 particles are processed.

[0049] Step S6, if the iteration number reaches 200 times, stop iteration, and obtain the adjustment scheme of the active power outer loop control parameter, otherwise return to step S2.

[0050] Table 1 shows the double-loop parameter design scheme of the method of the application for the single converter infinite device shown in Figure 2 Table 1 shows the double-loop parameter design scheme of the method of the application for the single converter infinite device shown in Table 3

[0051] In order to illustrate the specific implementation effect of the application, in the embodiment of the application, different double-loop control parameters are selected for simulation and comparison for the device shown in Figure 2 In order to more intuitively compare the effect of the embodiment of the application, as a comparison, the double-loop control parameter adjustment scheme selected by the general method is also listed in Table 1. The method calculates the active power outer loop parameter through the type II system setting, and the rest of the parameter calculation method is consistent with the method of the application. Figure 3 The dynamic response of the DC voltage under three conditions of the double-loop control parameters designed by the method of the application, the double-loop control parameters designed by the general method and the double-loop control parameters without design is given. It can be seen that the method of the application has stronger system stability.

[0052] Figure 2 The double-loop control single converter infinite device schematic diagram provided by the embodiment of the present application. The double-loop control single converter infinite device schematic diagram provided by the embodiment of the present application comprises a first part, a second part, a third part and a fourth part. The first part comprises four parts of an alternating current side, a power electronic converter, a direct current side and a phase-locked loop, undertakes tasks such as obtaining power grid phase information, dq decomposition and PWM modulation wave generation; the second part is used for realizing control of direct current voltage and active power, needs to satisfy droop characteristics, and outputs a current d-axis component reference value; the third part is used for realizing control of reactive power, and realizes decoupling control of active power and reactive power together with the second part, and outputs a current q-axis component reference value; the fourth part is used for realizing control of current, and constitutes double-loop control together with the second part and the third part, and the output thereof is used for PWM modulation.

[0053] The device embodiments described above are only schematic. Those skilled in the art can understand and implement without creative labor.

[0054] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for designing parameters of double-loop control of a power electronic converter, characterized in that, The application relates to a double-loop control parameter optimization adjustment scheme for a power electronic converter. The application comprises the following steps: An optimization model is established according to the decision variables of the active power outer loop, the upper and lower limit constraint conditions of the to-be-designed parameters and the objective function; The optimization model is solved by using a modern intelligent optimization algorithm to obtain the active power outer loop control parameter closest to the expected real part of the oscillation mode real part; According to the control parameter, the double-loop control parameter optimization adjustment scheme of the power electronic converter is obtained.

2. The power electronic converter double-loop control parameter design method according to claim 1, characterized in that, The control parameter expression under the I-type system setting method is as follows: Wherein, L is the bridge arm inductance unit value, R is the bridge arm resistance unit value, K PWM is the PWM equivalent gain, T p is the power ring measurement time, T s is the system sampling time; since the reactive power outer ring and the active power outer ring structure is symmetrical, the control parameter expression remains the same.

3. The design method of double-loop control parameters for power electronic converters according to claim 1, characterized in that, The optimization model is as follows: The decision variable is the active power outer loop parameter k pp , k ip and droop coefficient k droop ; The objective function is as follows: where N is the number of oscillation modes to be considered, M is the total number of operating conditions to be considered, σ i is the real part of the i-th oscillation mode of the reduced order model of the system, σ d is the real part of the desired oscillation mode, α i is the corresponding weight; The constraint condition is as follows: wherein k pp and k ip are the proportional and integral gains of the active power outer loop, k droop is the lower cooking coefficient, k pp,min , k pp,max , k ip,min , k ip,max , k droop,min and k droop,max are the upper and lower limits of the parameters to be designed.

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