A method for optimizing control of a converter accessing a traction power supply system

Abstract

The application discloses a converter access traction power supply system optimization control strategy and relates to the technical field of electrified railway traction power supply, which initializes the control strategy of the converter access traction power supply system; determines the range of the converter control parameters and filter parameters according to the limiting conditions; calculates the influence degree of each parameter of the converter on resonance, thereby determining the control strategy and optimization parameters; establishes the optimization target of preventing resonance, filtering out harmonics, meeting the performance standard of the controller, and minimizing the investment cost of the converter; designs the converter control parameters and filter parameters based on the particle swarm optimization algorithm, and finally outputs the complete control strategy; under the premise of preventing the over-standard reactive power and over-standard ripple current caused by the inductance and capacitance, guaranteeing the stability, accuracy and rapidity of the control system, the target of preventing resonance first, considering the harmonic filtering and reducing the investment cost of the converter at the same time is achieved, and the efficient, safe and economic operation of the converter access traction power supply system is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of traction power supply technology for electrified railways, and in particular to an optimized control method for a converter connected to a traction power supply system. Background Technology

[0002] To meet the requirements of safe, convenient, efficient, green, intelligent, and economical railway operation, future railways will gradually become more "electrically electronic." However, the addition of a large number of converters may introduce wider-band harmonics into the traction power supply system, altering the impedance characteristics of the traditional traction power supply system and leading to the risk of broadband oscillations. Currently, research on the impact of converter grid connection has been conducted in the power system field. To ensure the safe operation of the system after converter connection, the main focus is on designing converter control strategies and LCL filter parameters. Research on control strategies considers the stability of the control system and the resonance problem caused by the LCL filter. However, the design of LCL filter parameters only considers the harmonic problems introduced by the converter, without considering the potential broadband oscillation problem. Furthermore, LCL filter parameters can affect the stability of the control system, and control parameters may also lead to an increase in harmonic content. Therefore, existing converter design strategies cannot meet the future operational requirements of railways. To ensure the safe and reliable operation of converters connected to the traction power supply system, converter design needs to comprehensively consider the resonance suppression of the traction power supply system, the stability, speed, and accuracy of control, harmonic suppression, and the economy of the filter. Summary of the Invention

[0003] The purpose of this invention is to provide an optimized control method for converters connected to traction power supply systems. This method can effectively solve the technical problems of excessive reactive power and ripple current caused by inductors and capacitors. Under the premise of ensuring the stability, accuracy and speed of the control system, it aims to prevent resonance, while also considering harmonic filtering and reducing the investment cost of converters, thus ensuring the efficient, safe and economical operation of converters connected to traction power supply systems.

[0004] The objective of this invention is achieved by employing the following technical solution: An optimized control method for a converter connected to a traction power supply system specifically includes the following steps: (1) Initialize the control strategy for connecting the converter to the traction power supply system; (2) Calculate the influence of each parameter of the converter on the resonance, so as to determine the control strategy and optimization parameters; (3) Determine the range of converter control parameters and filter parameters based on the constraints; (4) Establish an optimization objective that prioritizes the prevention of resonance while also considering harmonic filtering and reducing converter investment costs; (5) Based on the optimization objective, the converter control parameters and filter parameters are obtained using the particle swarm optimization algorithm, and finally the complete control strategy is output.

[0005] The converter control strategy in step (1) is as follows: [The inductor...] Command current With inductance Measurement current The difference is fed into the proportional resonant PR controller, and the inductor Harmonic current feedback quantity ,inductance Harmonic voltage feedback quantity ,capacitance C Harmonic current feedback quantity ,capacitance C Harmonic voltage feedback quantity ,inductance Harmonic current feedback quantity The difference is then fed into the pulse width modulation (PWM) module; where the feedback quantity... , , , , The magnitudes are determined by the feedback coefficients. , , , , The equivalent impedance of the converter can be obtained by determining this. The following is an explanation of the equivalent impedance of the converter. Substitute into the traction power supply system model: ; in, , The imaginary unit, For harmonic order, This is the filter transfer function, designed to filter out power frequency components. For the controller delay element, For PWM equivalent elements, The transfer function of the proportional resonant (PR) controller is expressed as follows: ;in, For proportional gain, For resonant gain, For bandwidth, It is the resonant angular frequency.

[0006] The calculation of the influence of each parameter of the converter on the resonance in step (2) specifically includes the following steps: (2-1) According to the formula Forming the nodal admittance matrix of the traction power supply system ,in For voltage matrix, It is a current matrix; (2-2) Find the nodal admittance matrix eigenvalue matrix The specific expression is as follows: , in, Eigenvalue matrix The diagonal eigenvalues ​​in the model are used to obtain the resonance distribution by solving the reciprocals of the eigenvalues ​​at different frequencies; (2-3) Calculate the equivalent impedance of the converter. The influence of control parameters and filter parameters on resonant impedance as follows: ; in, For the first k There are eigenvalues, where real represents the value of finding eigenvalues. The real part of the expression is given by imag, which indicates the solution for the imaginary part. For converter parameters, including , , , , , , , , , ; (2-4) Calculate the equivalent impedance of the converter. The influence of control parameters and filter parameters on the resonant frequency as follows: , in, For frequency; (2-5) Comprehensive comparison of the influence of resonant impedance Influence of resonant frequency Determine the control strategy and optimize the parameters.

[0007] The limiting conditions for the filter parameters in step (3) are to prevent excessive reactive power and ripple current caused by inductance and capacitance. The inductance is determined accordingly. The range of values ,capacitance The range of values ,inductance The range of values The constraints on the control parameters are to ensure the stability, accuracy, and speed of the control system, that is, the real parts of all poles of the control system are less than 0, and the inductance... Command current With inductance Measurement current The difference is less than the reference error transition time Less than standard time The range of the control parameters selected in steps (2-1) to (2-4) is determined based on the influence of resonant impedance and the influence of resonant frequency.

[0008] The optimization objective in step (4) specifically includes the following steps: (4-1) Objective 1: Obtain the harmonic currents existing in the traction power supply system based on on-site testing or analytical calculations, and identify the harmonic current frequency bands HB1-HB n and eigenvalue matrix Then change the equivalent impedance of the converter To achieve resonance prevention, and to set the fitness value of objective 1 as... If satisfied ,but ,otherwise ,in Set the impedance value; (4-2) Objective 2: Based on the requirements for grid-connected harmonics of power electronic equipment, limit high-frequency harmonics to within... Within this range, and taking into account both filtering characteristics and inductor size, it makes... Let the fitness value of objective 2 be... If objective 2 is satisfied, then ,otherwise ,in It needs to be set according to the engineering design requirements; (4-3) Objective 3: To ensure the dynamic performance of the control system, the real parts of the dominant poles of the control system are all less than -100. Let the fitness value of objective 3 be... If satisfied, then ,otherwise ; (4-4) Objective 4: Establish a filter and price function based on the actual prices of inductors and capacitors. This ensures the lowest possible investment in filters; (4-5) Finally, the total fitness value is formed. The fitness values ​​of the four objectives need to satisfy... To determine the priority of each objective.

[0009] Compared with the prior art, the beneficial effects of the present invention are: I. This invention, while preventing excessive reactive power and ripple current caused by inductors and capacitors and ensuring the stability, accuracy, and speed of the control system, aims to prevent resonance while also considering harmonic filtering and reducing converter investment costs, thus ensuring the efficient, safe, and economical operation of the converter connected to the traction power supply system. Second, this invention selects a control strategy through sensitivity calculation. By changing the feedback quantity, the converter can present different harmonic impedances, thereby achieving the purpose of changing the harmonic impedance of the traction power supply system, while having no effect on the fundamental voltage and current. Third, this invention can be applied to any traction power supply system with converter connected to different power supply methods, and can calculate the control strategy most suitable for system operation based on the operating status of the traction power supply system. Attached Figure Description

[0010] Figure 1 This is a flowchart of an optimized control system for a converter connected to a traction power supply system, as described in Embodiment 1 of the present invention.

[0011] Figure 2 This is a block diagram of the converter initial control strategy described in Embodiment 1 of the present invention.

[0012] Figure 3 is a resonance distribution diagram, impedance influence bar chart, and frequency influence bar chart of the converter connected to the traction power supply system in Embodiment 1 of the present invention.

[0013] Figure 4 The diagram shows the traction network voltage waveform and spectrum after the optimized converter is connected to the traction power supply system, as described in Embodiment 1 of this invention.

[0014] Figure 5 This is a diagram of the optimization process described in Embodiment 1 of the present invention.

[0015] Figure 6 The optimized converter output current waveform, spectrum diagram, and traction network voltage waveform and spectrum diagram are described in Embodiment 1 of the present invention. Detailed Implementation

[0016] To better understand the inventive concept of this invention, its working principle is briefly described below: While preventing excessive reactive power and ripple current caused by inductors and capacitors, and ensuring the stability, accuracy, and speed of the control system, the invention aims to achieve the goals of prioritizing resonance prevention while also considering harmonic filtering and reducing converter investment costs, thus ensuring the efficient, safe, and economical operation of the converter connected to the traction power supply system. The invention will be further described below with reference to the accompanying drawings and specific embodiments. Example

[0017] This embodiment is implemented under the following system parameters: traction network length 19.04km, traction transformer capacity 25MVA, converter connected to the traction substation outlet, DC voltage 2000V, capacity 1MVA. This embodiment provides a multi-objective optimization control strategy for converter connection to the traction power supply system, such as... Figure 1 As shown, the specific steps include: (1) Initialization method of converter control is as follows Figure 2 As shown, the inductor Command current With inductance Measurement current The difference is fed into the proportional resonant PR controller, and the inductor Harmonic current feedback quantity ,inductance Harmonic voltage feedback quantity ,capacitance C Harmonic current feedback quantity ,capacitance C Harmonic voltage feedback quantity ,inductance L 2 harmonic current feedback quantity The difference is then fed into the pulse width modulation (PWM) module. The feedback quantity... , , , , The magnitudes are respectively determined by the feedback coefficients , , , , The equivalent impedance of the converter can be obtained by determining this. The following is an explanation of the equivalent impedance of the converter. Substitute into the traction power supply system model.

[0018]

[0019] in, , The imaginary unit, For harmonic order, This is the filter transfer function, designed to filter out power frequency components. For controller delay, For PWM equivalent elements, The transfer function of the proportional resonant (PR) controller is expressed as follows:

[0020] in, For proportional gain, For resonant gain, For bandwidth, It is the resonant angular frequency.

[0021] (2) Calculate the influence of each converter parameter on resonance according to the following steps, so as to determine the control strategy and optimization parameters: (2-1) According to the formula Forming the node admittance matrix of the traction power supply system ,in For voltage matrix, It is a current matrix; (2-2) Find the nodal admittance matrix eigenvalue matrix The specific expression is as follows:

[0022] in, Eigenvalue matrix The diagonal eigenvalues ​​in the equation are used. The resonant distribution is obtained by solving for the reciprocals of the eigenvalues ​​at different frequencies, as shown in Figure 3(a).

[0023] (2-3) Calculate the equivalent impedance of the converter using the following formula. The influence of control parameters and filter parameters on the resonant impedance at the 45.3rd and 76.9th frequencies. As shown in Figure 3(b).

[0024]

[0025] in, For the first k There are eigenvalues, where real represents the expression for finding eigenvalues. The real part of the expression is given by imag, which indicates the solution for the imaginary part. For converter parameters, including , , , , , , , , , .

[0026] (2-4) Calculate the equivalent impedance of the converter using the following formula. The influence of control parameters and filter parameters on the resonant frequencies of the two resonant points at the 45.3rd and 76.9th frequencies. As shown in Figure 3(c).

[0027]

[0028] in, For frequency.

[0029] (2-5) Comprehensive comparison of resonant impedance sensitivity in Figure 3(b) And the resonant frequency sensitivity in Figure 3(c) It can be seen that in the control parameters , and filter parameters , , It exhibits high sensitivity to both resonant impedance and resonant frequency; therefore, the control method is determined to be inductance. Current Closed loop plus inductor Harmonic current feedback and capacitor Harmonic voltage feedback.

[0030] (3) Based on the constraints of the filter parameters, namely, to prevent excessive reactive power and ripple current caused by inductance and capacitance, determine the inductance. The range of values ,capacitance The range of values ,inductance The range of values Based on the constraints of the control parameters, namely ensuring the stability, accuracy, and speed of the control system, i.e., the real parts of all poles of the control system are less than 0, the inductance... Command current With inductance Measurement current The difference is less than 2% of the reference error, and the transition time Less than 0.035s less than the standard time, confirmed. The range of values , The range of values .

[0031] Optimize the traction network voltage, such as Figure 4 As shown, due to resonance, the traction network voltage waveform is severely distorted, with the harmonic voltage distortion rate reaching 15.5%, which is seriously exceeding the limit.

[0032] (4) Establish an optimization objective based on the following steps, prioritizing the prevention of resonance while also considering harmonic filtering and reducing converter investment costs: (4-1) Objective 1: Obtain the harmonic currents existing in the traction power supply system based on on-site testing or analytical calculations, and identify the harmonic current frequency bands HB1-HB1. n and eigenvalue matrix Then change the equivalent impedance of the converter To achieve resonance prevention, since most electric locomotives currently have low switching frequencies, and even some locomotives employing multiplexing technology have an equivalent switching frequency of only around the 50th order, the harmonic current frequency band is selected as 2-50th order, and the fitness value of objective 1 is set to... If the conditions are met ,but ,otherwise ,in Set the impedance value; (4-2) Based on the requirements for grid-connected harmonics of power electronic equipment, high-frequency harmonics are limited to... Within this range, and taking into account both filtering characteristics and inductor size, it makes... Let the fitness value of objective 2 be... If objective 2 is satisfied, then... ,otherwise ,in It can be set according to engineering design requirements; (4-3) Objective 3: To ensure the dynamic performance of the control system, the real parts of the dominant poles of the control system are all less than -100. Let the fitness value of objective 3 be... If satisfied, then ,otherwise ; (4-4) Objective 4: Establish a filter and price function based on the actual prices of inductors and capacitors. This ensures the lowest possible investment in filters; (4-5) Finally, the total fitness value is formed. The fitness values ​​of the four objectives need to satisfy... To determine the priority of each objective.

[0033] (5) Based on the particle swarm optimization algorithm , , , , Optimize to make , , The optimization process is as follows: Figure 5 As shown, it can be seen The fluctuations reached a minimum value, satisfying all objectives, and finally the values ​​of each parameter were output.

[0034] The optimized converter was connected to the traction power supply system to obtain the waveforms and spectrum diagrams of the converter output current under normal operating conditions and the traction grid voltage under resonant conditions, as shown in the figure. Figure 6 As shown in the waveform of the converter output current, the adjustment time... The harmonic distortion rate is 0.009s (less than 0.035s), the high-frequency harmonic distortion rate of the converter output current is 0.0285% (less than 0.3%), and the control error is 0.35%. The traction grid voltage spectrum shows that the harmonic distortion rate is 2.52%, indicating that resonance has been suppressed. All optimization objectives are met.

Claims

1. An optimized control method for a converter connected to a traction power supply system, specifically comprising the following steps: (1) Initialize the control strategy for connecting the converter to the traction power supply system; (2) Calculate the influence of each parameter of the converter on the resonance, so as to determine the control strategy and optimization parameters; (3) Determine the range of converter control parameters and filter parameters based on the constraints; (4) Establish an optimization objective that prioritizes the prevention of resonance while also considering harmonic filtering and reducing converter investment costs; (5) Based on the optimization objective, the converter control parameters and filter parameters are obtained using the particle swarm optimization algorithm, and finally the complete control strategy is output. The converter control strategy in step (1) is as follows: [The inductor...] Command current With inductance Measurement current The difference is fed into the proportional resonant PR controller, and the inductor Harmonic current feedback quantity ,inductance Harmonic voltage feedback quantity ,capacitance C Harmonic current feedback quantity ,capacitance C Harmonic voltage feedback quantity ,inductance Harmonic current feedback quantity The difference is then fed into the pulse width modulation (PWM) module; where, Feedback volume , , , , The magnitudes are determined by the feedback coefficients. , , , , The equivalent impedance of the converter can be obtained by determining this. The following is an explanation of the equivalent impedance of the converter. Substitute into the traction power supply system model: ； in, , The imaginary unit, For harmonic order, This is the filter transfer function, designed to filter out power frequency components. For the controller delay element, For PWM equivalent elements, The transfer function of the proportional resonant (PR) controller is expressed as follows: ;in, For proportional gain, For resonant gain, For bandwidth, It is the resonant angular frequency; The calculation of the influence of each parameter of the converter on the resonance in step (2) specifically includes the following steps: (2-1) According to the formula Forming the nodal admittance matrix of the traction power supply system ,in For voltage matrix, It is a current matrix; (2-2) Find the nodal admittance matrix eigenvalue matrix The specific expression is as follows: ， in, Eigenvalue matrix The diagonal eigenvalues ​​in the model are used to obtain the resonant distribution by solving the reciprocals of the eigenvalues ​​at different frequencies; (2-3) Calculate the equivalent impedance of the converter. The influence of control parameters and filter parameters on resonant impedance as follows: ； in, For the first k There are eigenvalues, where real represents the value of finding eigenvalues. The real part of the expression is given by imag, which indicates the solution for the imaginary part. For converter parameters, including , , , , , , , , , ; (2-4) Calculate the equivalent impedance of the converter. The influence of control parameters and filter parameters on the resonant frequency as follows: ， in, For frequency; (2-5) Comprehensive comparison of the influence of resonant impedance Influence of resonant frequency Determine the control strategy and optimization parameters; The limiting conditions for the filter parameters in step (3) are to prevent excessive reactive power and ripple current caused by inductance and capacitance. The inductance is determined accordingly. The range of values ,capacitance The range of values ,inductance The range of values The constraints on the control parameters are to ensure the stability, accuracy, and speed of the control system, that is, the real parts of all poles of the control system are less than 0, and the inductance... Command current With inductance Measurement current The difference is less than the reference error transition time Less than standard time The range of the control parameters selected in steps (2-1) to (2-4) is determined based on the influence of resonant impedance and the influence of resonant frequency.

2. The optimized control method for a converter connected to a traction power supply system according to claim 1, characterized in that: The optimization objective in step (4) specifically includes the following steps: (4-1) Objective 1: Obtain the harmonic currents existing in the traction power supply system based on on-site testing or analytical calculations, and identify the harmonic current frequency bands HB1-HB n and eigenvalue matrix Then change the equivalent impedance of the converter To achieve resonance prevention, and to set the fitness value of objective 1 as... If satisfied ,but ,otherwise ,in Set the impedance value; (4-2) Objective 2: Based on the requirements for grid-connected harmonics of power electronic equipment, limit high-frequency harmonics to within... Within this range, and taking into account both filtering characteristics and inductor size, it makes... Let the fitness value of objective 2 be... If objective 2 is satisfied, then ,otherwise ,in It needs to be set according to the engineering design requirements; (4-3) Objective 3: To ensure the dynamic performance of the control system, the real parts of the dominant poles of the control system are all less than -100. Let the fitness value of objective 3 be... If satisfied, then ,otherwise ; (4-4) Objective 4: Establish a filter and price function based on the actual prices of inductors and capacitors. This ensures the lowest possible investment in filters; (4-5) Finally, the total fitness value is formed. The fitness values ​​of the four objectives need to satisfy... To determine the priority of each objective.

Images