A Circuit Impedance Modeling Method, System and Equipment for CRH5 EMU

Abstract

The present invention discloses a method, system and device for circuit impedance modeling of CRH5 EMUs, which relates to the field of impedance modeling of EMUs. In this application, the three-phase stator current is obtained through the state equation of the inverter on the DC side of the CRH5 EMU, and then the DC current on the DC side is obtained by multiplying the three-phase stator current by the duty cycle of the upper bridge arm switch of the three-phase half bridge. The resistance value of the load resistor is obtained based on the power balance relationship of the equivalent parallel circuit. Then, the current value of the current source of the equivalent parallel circuit is determined in sequence. Then, the steady-state value of the state variable is obtained by combining the calculated resistance value and current value with the electrical parameters of the rectifier of the CRH5 EMU. Finally, the final circuit impedance model is determined based on the steady-state value of the state variable, thus solving the problem of inaccurate impedance models of existing EMUs and providing a more accurate theoretical basis for the analysis of low-frequency oscillation, harmonic resonance and harmonic instability of the vehicle-grid system of CRH5 EMUs.

Description

Technical Field

[0001] The present invention relates to the field of impedance modeling of EMUs, and more specifically, to a method, system and device for circuit impedance modeling of CRH5 EMUs. Background Art

[0002] The traction AC drive system mainly includes main components such as a traction rectifier, an intermediate DC link, a traction inverter, and a traction motor. The interaction between the multi-car converters of CRH5 EMUs and the traction network causes problems such as low-frequency oscillation, harmonic resonance, and harmonic instability, which will not only endanger the traction network and locomotive high-voltage equipment, but also lead to traction block. Establishing accurate simulation and mathematical models to reveal the mechanisms of low-frequency oscillation, harmonic resonance, and harmonic instability is of great significance. The impedance analysis method is the mainstream analysis method for the stability of the vehicle-network system at present.

[0003] The prior art mainly analyzes the stability of the vehicle-network system from two aspects: dq-axis impedance modeling and harmonic linearized impedance modeling. Among them, the dq-axis impedance modeling method is based on the state-space model of the rectifier main circuit, thereby establishing a small-signal impedance model of the rectifier, and considering current loops, voltage loops, phase-locked loops, and generalized second-order integrators in the control circuit. However, since the locomotive is in the pantograph-raising preparation state and does not move forward when analyzing low-frequency oscillation, this type of method equivalentizes the traction inverter and the motor to a DC resistor, and assigns a specific resistance value to the DC resistor according to experience, without giving a clear resistance calculation formula. Based on the harmonic linearization method, this type of method uses harmonic linearization to establish positive and negative mirror frequency impedance models, or uses the method of multiple harmonic linearizations to establish high-order impedance models to realize the analysis of the vehicle-network stability. Similarly, this method still equivalentizes the traction inverter and the motor to a DC resistor, and assigns a specific resistance value to the DC resistor according to experience, without giving a clear resistance calculation formula.

[0004] In summary, looking at the existing impedance modeling methods, the dq-axis based modeling and harmonic linearized modeling methods are relatively mature in themselves, but their modeling processes equivalentize the traction inverter and the motor to a DC resistor, without giving a clear resistance calculation formula, and only take values according to human experience, which will affect the accuracy of stability analysis. Therefore, it is necessary to establish an accurate equivalent circuit model of the traction inverter and the motor, thereby establishing a complete resistance impedance model of CRH5 EMUs and improving the accuracy of stability analysis. Summary of the Invention

[0005] This application aims to solve the problem that in the prior art, the equivalent resistance is only determined empirically without a clear method for determining the resistance, which will affect the accuracy of stability analysis. The purpose of the present invention is to provide a method, system, and device for modeling the circuit impedance of CRH5 EMUs. In this application, the state equation of the inverter on the DC side of the CRH5 EMU is used to obtain the three-phase stator currents. Then, the DC current on the DC side is obtained by multiplying the three-phase stator currents by the duty cycle of the upper-arm switches of the three-phase half-bridge. The resistance value of the load resistor is calculated through the power balance relationship of the equivalent parallel circuit. Based on the DC current and the resistance value, the current value of the current source of the equivalent parallel circuit is determined. The state equation of the rectifier is established by combining the resistance value, the current value, and the electrical parameters of the rectifier. Through the inverse Park transformation, the main circuit state equation in the dq axis is obtained, and the steady-state values of the state variables are determined when the vehicle-grid system is in a steady state. Finally, the perturbation is set to zero and the transfer matrix corresponding to the perturbation is derived to obtain the final main circuit impedance model of the CRH5 EMU. In this application, the resistance value of the load resistor is obtained based on the power balance relationship of the equivalent parallel circuit. Then, the current value of the current source of the equivalent parallel circuit is determined in sequence. Then, the steady-state values of the state variables are obtained by combining the calculated resistance value and current value with the electrical parameters of the rectifier in the traction AC drive system of the CRH5 EMU. Based on the steady-state values of the state variables, the final impedance model is determined. Therefore, this application solves the problem of inaccurate impedance models of existing EMUs and provides a more accurate theoretical basis for the analysis of low-frequency oscillations, harmonic resonances, and harmonic instabilities in the vehicle-grid system of CRH5 EMUs.

[0006] The above technical objectives of this application are achieved through the following technical solutions:

[0007] In the first aspect, this application provides a method for modeling the circuit impedance of CRH5 EMUs, including:

[0008] Construct the state equation of the three-phase inverter circuit of the inverter on the DC side of the CRH5 EMU, and solve the state equation of the inverter to obtain the three-phase stator currents of the three-phase inverter circuit;

[0009] Obtain the DC current on the DC side of the CRH5 EMU by multiplying the three-phase stator currents by the duty cycle of the upper-arm switches of the three-phase half-bridge;

[0010] Equivalent the three-phase inverter circuit of the inverter and the traction motor into a parallel circuit of a load resistor and a current source. Calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value;

[0011] Based on the resistance value, current value and electrical parameters of the rectifier, establish the state equation of the rectifier, and transform the state equation of the rectifier to the dq axis based on the inverse Park transformation to obtain the main circuit state equation of the rectifier on the dq axis;

[0012] Determine the steady-state values of the state variables of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq axis;

[0013] Set the perturbations of the input voltage vector and the input duty ratio vector of the steady-state values of the state variables to zero and derive the corresponding transfer function matrix to obtain the circuit impedance model of the main circuit topology of the CRH5 EMU.

[0014] In one embodiment, the calculation formula of the three-phase stator current is: i k =A k e -t / τ +Isin(α k -γ), where τ is the time constant, and τ = L e / R e , R e represents the per-phase equivalent resistance of the traction motor, L e represents the per-phase equivalent inductance of the traction motor, k represents the ABC three phases of the power grid, γ represents the three-phase current phase shift, I is the three-phase current amplitude, α k represents the reference phase, A k represents the initial value of the transient component, and t represents time.

[0015] In one embodiment, the calculation formula of the DC current on the DC side of the CRH5 EMU is I is the three-phase current amplitude, t represents time, γ represents the three-phase current phase shift, τ is the time constant, and τ = L e / R e , R e represents the per-phase equivalent resistance of the traction motor, L e represents the per-phase equivalent inductance of the traction motor.

[0016] In one implementation, the three-phase inverter circuit of the inverter and the traction motor are equivalent to a parallel circuit of a load resistor and a current source. Calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value. The specific process is as follows:

[0017] Based on the equivalent principle of the parallel circuit, use the power balance relationship to obtain the resistance value of the load resistor of the parallel circuit R e represents the per-phase equivalent resistance of the traction motor, L eIt represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter;

[0018] Based on Kirchhoff's current law, the relational expression for the current value of the current source in the parallel circuit is U dc It represents the steady-state value of the DC-side voltage, and i dc represents the DC current on the DC side;

[0019] Based on the equivalent resistance, DC current, and steady-state value of the DC-side voltage, the current value of the current source in the parallel circuit is as follows:

[0020] ω e is the stator three-phase current frequency of the motor.

[0021] In one implementation, the calculation formula for the steady-state value of the state variable is: where E d , I d , D d and D q respectively represent the steady-state values of e d , i d , d d and d q , e d , i d respectively represent the voltage and current on the d-axis, d d , d q respectively represent the d-axis duty ratio and q-axis duty ratio, ω1 represents the AC current frequency, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC-side voltage, R d represents the resistance value of the load resistor, and I1 represents the current value of the current source in the parallel circuit.

[0022] In one implementation, the mathematical model of the circuit impedance model is:

[0023] where Z in_ol is the open-loop impedance, G id is the to transfer matrix, G ue is the to transfer matrix, G ud is the to transfer matrix, I d , I q , D d and D qrespectively represent i d ,i q ,d d and d q of the steady-state values, i d represents the current of the d-axis, i q represents the current of the q-axis, d d 、d q respectively represent the duty ratio of the d-axis, the duty ratio of the q-axis, ω1 represents the frequency of the alternating current, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC-side voltage, R d represents the resistance value of the load resistor, C d is the DC-side support capacitor, Z RC represents the DC-side RC impedance, s represents the Laplace domain variable.

[0024] In a second aspect, the present application provides a CRH5 EMU circuit impedance modeling system, including:

[0025] A three-phase stator current calculation module, configured to construct a state equation of the three-phase inverter circuit of the inverter on the DC side of the CRH5 EMU and solve the state equation of the inverter to obtain the three-phase stator current of the three-phase inverter circuit;

[0026] A DC current calculation module, configured to obtain the DC current on the DC side of the CRH5 EMU according to the product of the three-phase stator current and the duty ratio of the upper bridge arm switch of the three-phase half-bridge;

[0027] An equivalent circuit parameter calculation module, configured to equivalent the three-phase inverter circuit of the inverter and the traction motor into a parallel circuit of a load resistor and a current source, calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value;

[0028] A rectifier state equation calculation module, configured to establish a state equation of the rectifier based on the resistance value, the current value, and the electrical parameters of the rectifier, and transform the state equation of the rectifier to the dq axis based on the inverse park transformation to obtain the main circuit state equation of the rectifier on the dq axis;

[0029] A state variable steady-state value calculation module, configured to determine the steady-state value of the state variable of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq axis;

[0030] The circuit impedance model module is configured to zero the perturbations of the input voltage vector and the input duty cycle vector of the steady-state values of the state variables and derive the corresponding transfer function matrix, thereby obtaining the circuit impedance model of the main circuit topology of the CRH5 EMU.

[0031] In one embodiment, the equivalent circuit parameter calculation module includes:

[0032] The load resistance value calculation module is configured to obtain the resistance value of the load resistance of the parallel circuit based on the equivalent principle of the parallel circuit and using the power balance relationship R e represents the per-phase equivalent resistance of the traction motor, L e represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter;

[0033] The current source current calculation module is configured to obtain the relational expression of the current value of the current source of the parallel circuit based on Kirchhoff's current law as U dc represents the steady-state value of the DC side voltage, i dc represents the DC current on the DC side;

[0034] Based on the equivalent resistance, DC current, and steady-state value of the DC side voltage, the current value of the current source of the parallel circuit is as follows:

[0035] ω e is the stator three-phase current frequency of the motor.

[0036] In one embodiment, the steady-state value calculation module of the state variable is specifically calculated as: wherein, E d , I d , D d and D q respectively represent the steady-state values of e d , i d , d d and d q , e d , i d respectively represent the voltage and current on the d-axis, d d , d q respectively represent the duty cycle on the d-axis and the duty cycle on the q-axis, ω1 represents the AC current frequency, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC side voltage, R d represents the resistance value of the load resistance.

[0037] In a third aspect, the present application provides an electronic device, including:

[0038] One or more processors;

[0039] A memory coupled to the processor for storing one or more programs;

[0040] When the one or more programs are executed by the one or more processors, the one or more processors implement the steps of a method for modeling the circuit impedance of a CRH5 EMU according to any one of the first aspect.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] In this application, the three-phase stator current is obtained through the state equation of the inverter on the DC side of the CRH5 EMU, and then the DC current on the DC side is obtained by multiplying the three-phase stator current by the duty cycle of the upper bridge arm switch of the three-phase half-bridge. The resistance value of the load resistor is obtained based on the power balance relationship of the equivalent parallel circuit. Then, the current value of the current source of the equivalent parallel circuit is determined in sequence. Then, the steady-state value of the state variable is obtained by combining the calculated resistance value and current value with the electrical parameters of the rectifier of the traction AC drive system of the CRH5 EMU. Finally, the final impedance model is determined based on the steady-state value of the state variable. Therefore, this application solves the problem of inaccurate impedance models of existing EMUs and provides a more accurate theoretical basis for the analysis of low-frequency oscillations, harmonic resonances, and harmonic instabilities in the vehicle-network system of CRH5 EMUs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0044] Figure 1 is a schematic flow chart of a method for modeling the circuit impedance of a CRH5 EMU provided by an embodiment of this application;

[0045] Figure 2 is an equivalent circuit model of a two-level traction inverter provided by an embodiment of this application;

[0046] Figure 3 is a schematic diagram of the DC equivalence of a traction inverter provided by an embodiment of this application;

[0047] Figure 4 is a block diagram of a small-signal model of the main circuit dq system of a single-phase rectifier provided by an embodiment of this application;

[0048] Figure 5 is a comparison diagram of the dq impedance theoretical curve and measurement points provided by an embodiment of this application;

[0049] Figure 6It is a block diagram of the principle of a CRH5 EMU circuit impedance modeling system provided by an embodiment of this application. Detailed implementation manners

[0050] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and do not limit the present invention.

[0051] The impedance modeling methods of the existing traction AC drive systems of EMUs include the modeling based on the dq system and the modeling of harmonic linearization. These two analysis methods are relatively mature, but in their modeling processes, the traction inverter and the motor are equivalent to DC resistors, and no clear resistor calculation formula is given. The load resistor values are all taken according to human experience, which affects the accuracy of the stability analysis. Therefore, it is necessary to establish an accurate equivalent circuit model of the traction inverter and the motor, so as to establish a complete CRH5 EMU resistance impedance model and improve the accuracy of the stability analysis. Therefore, the embodiments of this application provide a CRH5 EMU circuit impedance modeling method, which determines the resistance value of the load resistor and the current value of the corresponding current source by calculation. The calculated resistance value and current value are combined with the electrical parameters of the rectifier of the traction AC drive system of the CRH5 EMU to obtain the steady-state values of the state variables, and then the final impedance model is determined based on the steady-state values of the state variables, thereby solving the problem of inaccurate impedance models of existing EMUs and providing a more accurate theoretical basis for the analysis of low-frequency oscillations, harmonic resonances and harmonic instabilities of the vehicle-grid system of CRH5.

[0052] As Figure 1 shown, the impedance modeling method includes the following steps:

[0053] S110, construct the state equation of the three-phase inverter circuit of the inverter on the DC side of the CRH5 EMU, and solve the state equation of the inverter to obtain the three-phase stator currents of the three-phase inverter circuit;

[0054] S120, obtain the DC current on the DC side of the CRH5 EMU according to the product of the three-phase stator currents and the duty cycle of the three-phase half-bridge upper-arm switch;

[0055] S130, equivalent the three-phase inverter circuit of the inverter and the traction motor to a parallel circuit of a load resistor and a current source, calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value;

[0056] S140. Establish the state equation of the rectifier based on the resistance value, current value, and electrical parameters of the rectifier, and transform the state equation of the rectifier to the dq-axis based on the inverse Park transformation to obtain the main circuit state equation of the rectifier on the dq-axis;

[0057] S150. Determine the steady-state values of the state variables of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq-axis;

[0058] S160. Set the perturbations of the input voltage vector and the input duty ratio vector of the steady-state values of the state variables to zero and derive the corresponding transfer function matrix to obtain the circuit impedance model of the main circuit topology of the CRH5 EMU.

[0059] Specifically, it should be noted that the existing EMU series includes HXD series electric locomotives, CRH series Harmony EMUs, and CR series Fuxing EMUs. The circuit composition structures of the components of the traction AC drive system of each type of EMU are different, and the circuit impedance model established in the embodiments of the present application is for the CRH5 EMU of the CRH series Harmony EMUs.

[0060] In step S110, in the AC-DC-AC traction drive system (i.e., the traction AC drive system) in the electrified railway, the train mainly consists of an on-vehicle transformer, a four-quadrant rectifier, an intermediate DC link, an inverter, and a traction motor. Since low-frequency oscillations usually occur in the low-power condition where multiple trains raise the pantographs and prepare at the same location, at this time the traction motor does not work, and the motor can be equivalently in the form of a series circuit of resistance and inductance. The equivalent circuit model of the two-level traction inverter is as Figure 2 shown. Among them, u dc represents the DC-side voltage, and i dc represents the DC-side current. u k (k = 1, 2, 3) represents the instantaneous value of the three-phase voltage of the inverter. R e represents the equivalent resistance per phase of the traction motor, and L e represents the equivalent inductance per phase of the traction motor.

[0061] According to Figure 2 the state-space average model of the three-phase inverter circuit is obtained as shown in the following formula (1):

[0062] In the formula, i k (k = 1, 2, 3) represents the three-phase stator current. Among them, f1, f2, f3 are the duty ratios of the upper-bridge-arm switches of the three-phase half-bridge, and f M is the average value of the three-phase duty ratios. Expand and recombine the matrix to obtain the following formula (2), specifically:

[0063] Among them, In Equation (3), m is the modulation coefficient of the PWM inverter, and ω e is the frequency of the three-phase current of the motor stator.

[0064] By solving differential equations (2) and (3), the calculation formula for the three-phase stator current can be obtained as shown in the following Equation (4):

[0065] i k = A k e -t / τ + Isin(α k - γ)(4), where τ is the time constant, and τ = L e / R e , R e represents the equivalent resistance per phase of the traction motor, L e represents the equivalent inductance per phase of the traction motor, k represents the ABC three phases of the power grid, γ represents the three-phase current phase shift, I is the three-phase current amplitude, α k represents the reference phase, A k represents the initial value of the transient component, t represents time; the calculation formulas for each parameter in Equation (4) are as shown in the following (5): In Equation (5), I is the three-phase current amplitude, U k represents the three-phase voltage amplitude of the inverter, U dc represents the steady-state value of the DC-side voltage u dc .

[0066] In step S120, according to Kirchhoff's current law, the DC current and the three-phase stator current satisfy the relationship shown in Equation (6): where the meaning of f k has been explained in detail in the above Equation (3). Then, substituting the parameters of Equation (3) and Equation (4) into Equation (6), the calculation formula for the DC current on the DC side of the CRH5 EMU is obtained as where I is the three-phase current amplitude, t represents time, γ represents the three-phase current phase shift, τ is the time constant, and τ = L e / R e , R e represents the equivalent resistance per phase of the traction motor, L e represents the equivalent inductance per phase of the traction motor. In step S130, considering that the value of the time constant τ is generally small, after ignoring the transient process, the inverter circuit and the motor can be equivalent to a parallel connection of a load resistance R d and a current source I1, as shown in Figure 3 . Considering that Figure 2 the active power consumed by the three resistors in is equal to Figure 3 the active power consumed by the resistor R d in, the power balance relationship shown in the following equation can be obtained, as shown in the following Equation (8): Based on the equivalent principle of the parallel circuit, the resistance value of the load resistor of the parallel circuit is obtained by using the formula (8) of the power balance relationship. R e represents the per-phase equivalent resistance of the traction motor, and L e represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter.

[0067] As Figure 3 shown, based on Kirchhoff's current law, the relational expression for the current value of the current source of the parallel circuit is U dc represents the steady-state value of the DC-side voltage, and i dc represents the DC current on the DC side;

[0068] Further, substituting formula (7) in step S120 and formula (9) in step 130 into formula (10), and ignoring the transient process in the DC current i dc in, the final expression for the current value of the equivalent current source I1 can be obtained as:

[0069]

[0070] In step S140, as Figure 2 shown, e n represents a single-phase AC power source, i n represents the AC-side current, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, and C d is the DC-side support capacitor. According to Figure 3 the main circuit of the grid-side converter, the state equation is written as the following formula (12): Among them, when VD1 and VD4 are conducting and VD2 and VD3 are cut off, the duty cycle d n is 1; when VD2 and VD3 are conducting and VD1 and VD4 are cut off, d n is 0. Since the target model established in the present invention is a dq-axis impedance model, it is necessary to decompose the state variables into the dq-axis through the inverse Park transformation, and the relational expression is: xα = x d cosωt - x q sinωt (13). Based on the conversion relationship of formula (13), and ignoring the DC-side second-order power-frequency ripple at the same time, equation (12) can be transformed into the dq-axis to obtain the main circuit state equation in the dq-axis as: In the formula, e d , i d respectively represent the voltage and current on the d-axis, e q , i q respectively represent the voltage and current on the q-axis, and dd , d q respectively represent the d-axis duty ratio and the q-axis duty ratio, ω1 represents the AC current frequency, and L n represents the equivalent inductance of the on-vehicle transformer, and R n represents the equivalent resistance of the on-vehicle transformer, and U dc represents the steady-state value of the DC-side voltage, and R d represents the resistance value of the load resistor.

[0071] In step S150, by solving and analyzing the static operating point of the average model in the dq frame, the values of the duty ratio, state variables, and output variables of the circuit under steady-state conditions can be obtained. Since in the steady state of the circuit, the phase locked by the phase-locked loop is the grid voltage phase, and the power factor of the vehicle-grid is 1 at this time, so E q , I q are 0. In the steady state, the steady-state values of the state variables of the rectifier are shown in the following formula (15): where E d , I d , D d and D q respectively represent the steady-state values of e d , i d , d d and d q . e d , i d respectively represent the voltage and current on the d-axis, d d , d q respectively represent the d-axis duty ratio and the q-axis duty ratio, ω1 represents the AC current frequency, L n represents the equivalent inductance of the on-vehicle transformer, and R n represents the equivalent resistance of the on-vehicle transformer, and U dc represents the steady-state value of the DC-side voltage, and R d represents the resistance value of the load resistor.

[0072] In step S160, by performing small-signal linearization expansion and Laplace transform on formula (14), the main circuit model of the single converter can be obtained, as specifically shown in Figure 4 . In Figure 4 , the input current vector and the DC-side voltage can be determined by the input voltage vector and the duty ratio vector . T represents the transpose of the matrix, respectively represent the input current vector on the d-axis and the input current vector on the q-axis, respectively represent the input voltage vector on the d-axis and the input voltage vector on the q-axis, They respectively represent the duty ratio vector of the d-axis and the duty ratio vector of the q-axis. By combining the steady-state values of the state variables in Equation (15) in Step A150, setting the perturbations of the input voltage vector and the duty ratio vector to zero respectively to derive the corresponding transfer function matrix, the circuit impedance model in the dq system of the main circuit topology of the CRH5 EMU can be obtained, as shown in Equation (16). The mathematical model of the circuit impedance model is shown in the following Equation (16):

[0073] Among them, Z in_ol is the open-loop impedance, G id is the to transfer matrix, G ue is the to transfer matrix, G ud is the to transfer matrix, I d , I q , D d and D q respectively represent the steady-state values of i d , i q , d d and d q , i d represents the current of the d-axis, i q represents the current of the q-axis, d d , d q respectively represent the duty ratio of the d-axis and the duty ratio of the q-axis, ω1 represents the alternating current frequency, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC-side voltage, R d represents the resistance value of the load resistor, C d is the DC-side support capacitor, Z RC represents the DC-side RC impedance, and s represents the Laplace domain variable.

[0074] To verify the accuracy of the circuit impedance model obtained in the embodiments of the present application, a train time-domain simulation model is built based on the Matlab / Simulink platform, and the impedance measurement is carried out using the dq sweep method based on the Hilbert transform. The Bode curves of the impedance model considering the inverter are compared, and the results are as Figure 5 shown. The impedance curve of the circuit impedance model established in this embodiment coincides well with the impedance measurement points obtained by the time-domain simulation scan, and the accuracy is good.

[0075] Therefore, the circuit impedance model obtained by the impedance modeling method provided in the embodiments of the present application solves the problem of inaccurate impedance models of existing EMUs, and provides a more accurate theoretical basis for the analysis of low-frequency oscillation, harmonic resonance, and harmonic instability of the vehicle-grid system of CRH5 EMUs.

[0076] Based on the same inventive concept, this embodiment provides a circuit impedance modeling system for CRH5 EMUs. Since the principles of these systems for solving problems are similar to Figure 1 a circuit impedance modeling method shown, the implementation of these systems can refer to Figure 1 the embodiments of the method shown. Repeated parts will not be elaborated. As Figure 6 shown, the circuit impedance modeling system for CRH5 EMUs includes:

[0077] A three-phase stator current calculation module, configured to construct a state equation of a three-phase inverter circuit of an inverter on the DC side of a CRH5 EMU and solve the state equation of the inverter to obtain three-phase stator currents of the three-phase inverter circuit;

[0078] A DC current calculation module, configured to obtain a DC current on the DC side of a CRH5 EMU according to the product of the three-phase stator currents and the duty cycle of the upper bridge arm switches of a three-phase half-bridge;

[0079] An equivalent circuit parameter calculation module, configured to equivalent the three-phase inverter circuit of the inverter and the traction motor to a parallel circuit of a load resistor and a current source, calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value;

[0080] A rectifier state equation calculation module, configured to establish a state equation of the rectifier based on the resistance value, the current value, and the electrical parameters of the rectifier, and transform the state equation of the rectifier to the dq axis based on the inverse park transformation to obtain the main circuit state equation of the rectifier on the dq axis;

[0081] A state variable steady-state value calculation module, configured to determine the steady-state value of the state variable of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq axis;

[0082] A circuit impedance model module, configured to set the perturbations of the input voltage vector and the input duty cycle vector of the steady-state value of the state variable to zero and derive the corresponding transfer function matrix to obtain the circuit impedance model of the main circuit topology of the CRH5 EMU.

[0083] In an implementation, the equivalent circuit parameter calculation module includes:

[0084] The load resistance value calculation module is configured to obtain the resistance value of the load resistance of the parallel circuit based on the equivalent principle of the parallel circuit and using the power balance relationship. R e represents the per-phase equivalent resistance of the traction motor, L e represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter;

[0085] The current source current calculation module is configured to obtain the relational expression of the current value of the current source of the parallel circuit based on Kirchhoff's current law as U dc represents the steady-state value of the DC side voltage, i dc represents the DC current on the DC side;

[0086] Based on the equivalent resistance, DC current, and steady-state value of the DC side voltage, the current value of the current source of the parallel circuit is as follows:

[0087] ω e is the stator three-phase current frequency of the motor.

[0088] In an implementation, the state variable steady-state value calculation module is specifically calculated as: where E d , I d , D d and D q respectively represent the steady-state values of e d , i d , d d and d q , e d , i d respectively represent the voltage and current on the d-axis, d d , d q respectively represent the d-axis duty ratio and q-axis duty ratio, ω1 represents the AC current frequency, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC side voltage, R d represents the resistance value of the load resistance.

[0089] The beneficial effects of the CRH5 EMU circuit impedance modeling system provided in this embodiment are as follows: In this application, the three-phase stator current is obtained through the state equation of the inverter on the DC side of the CRH5 EMU, and then the DC current on the DC side is obtained by multiplying the three-phase stator current by the duty cycle of the upper-bridge-arm switch of the three-phase half-bridge. The resistance value of the load resistor is calculated through the power balance relationship of the equivalent parallel circuit. The current value of the current source of the equivalent parallel circuit is determined based on the DC current and the resistance value. The state equation of the rectifier is established by combining the resistance value, the current value, and the electrical parameters of the rectifier. The main circuit state equation in the dq axis is obtained through the inverse Park transformation, and the steady-state values of the state variables are determined when the vehicle-grid system is in a steady state. Finally, the perturbation is set to zero and the transfer matrix corresponding to the perturbation is derived to obtain the final main circuit impedance model of the CRH5 EMU. In this application, the resistance value of the load resistor is obtained based on the power balance relationship of the equivalent parallel circuit, and then the current value of the current source of the equivalent parallel circuit is determined in sequence. Then, the steady-state values of the state variables are obtained by combining the calculated resistance value and current value with the electrical parameters of the rectifier of the traction AC drive system of the CRH5 EMU. Based on the steady-state values of the state variables, the final impedance model is determined. Therefore, this application solves the problem of inaccurate impedance models of existing EMUs and provides a more accurate theoretical basis for the analysis of low-frequency oscillations, harmonic resonances, and harmonic instabilities in the vehicle-grid system of CRH5 EMUs.

[0090] In another embodiment of the present invention, an electronic device is provided. The electronic device includes one or more processors; a memory coupled to the processor for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the method for modeling the circuit impedance of a CRH5 EMU according to any one of the first aspects. The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the method for modeling the circuit impedance of a CRH5 EMU.

[0091] In another embodiment of the present invention, the present invention further provides a readable storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a computer device and is used to store programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and, of course, the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, and the operating system of the terminal is stored in this storage space. Moreover, one or more instructions suitable for being loaded and executed by the processor are stored in this storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. One or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the method for modeling the circuit impedance of the CRH5 EMU in the above embodiment.

[0092] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0093] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for modeling the circuit impedance of CRH5 multiple units, characterized in that, Including: Construct the state equation of the three-phase inverter circuit on the DC side of the CRH5 EMU inverter, solve the state equation of the inverter, and obtain the three-phase stator currents of the three-phase inverter circuit; Obtain the DC current on the DC side of the CRH5 EMU by multiplying the three-phase stator currents by the duty cycles of the three-phase upper-arm switches of the half-bridge; Equivalent the three-phase inverter circuit of the inverter and the traction motor to a parallel circuit of a load resistor and a current source. Calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value; Establish the state equation of the rectifier based on the resistance value, current value and electrical parameters of the rectifier, and transform the state equation of the rectifier to the dq axis based on the inverse Park transformation to obtain the main circuit state equation of the rectifier on the dq axis; Determine the steady-state values of the state variables of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq axis; Set the perturbations of the input voltage vector and the input duty cycle vector of the steady-state values of the state variables to zero and derive the corresponding transfer function matrix to obtain the circuit impedance model of the main circuit topology of the CRH5 EMU; 2. The method for modeling the circuit impedance of a CRH5 type multiple unit according to claim 1, characterized in that, The calculation formula for the three-phase stator current is: i k = A k e -t / τ + Isin(α k - γ), where τ is the time constant, and τ = L e / R e , R e represents the equivalent resistance per phase of the traction motor, L e represents the equivalent inductance per phase of the traction motor, k represents the ABC three phases of the power grid, γ represents the three-phase current phase shift, I is the three-phase current amplitude, α k represents the reference phase, A k represents the initial value of the transient component, and t represents time.

3. A method for modeling the circuit impedance of a CRH5 type multiple unit, as claimed in claim 1, wherein The calculation formula for the DC current on the DC side of the CRH5 EMU is I is the amplitude of the three-phase current, t represents time, γ represents the phase shift of the three-phase current, τ is the time constant, and τ = L e / R e , R e represents the equivalent resistance per phase of the traction motor, and L e represents the equivalent inductance per phase of the traction motor.

4. A method for modeling the circuit impedance of a CRH5 type multiple unit, as claimed in claim 1, wherein Equivalent the three-phase inverter circuit of the inverter and the traction motor to a parallel circuit of a load resistor and a current source. Calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value. The specific process is as follows: Based on the equivalent principle of the parallel circuit, the resistance value of the load resistance of the parallel circuit is obtained by using the power balance relationship R e represents the per-phase equivalent resistance of the traction motor, L e represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter; The relational expression for the current value of the current source in a parallel circuit obtained based on Kirchhoff's current law is U dc represents the steady-state value of the DC-side voltage, and i dc represents the DC current on the DC side; Based on the steady-state values of the equivalent resistance, DC current and DC side voltage, the current value of the current source of the parallel circuit is obtained as follows: ω e is the frequency of the three-phase current of the stator of the motor.

5. A method for modeling the circuit impedance of a CRH5 type multiple unit, as claimed in claim 1, wherein The calculation formula for the steady-state value of the state variable is as follows: Among them, E d , I d , D d and D q respectively represent the steady-state values of e d , i d , d d and d q . e d , i d respectively represent the voltage and current on the d-axis. d d , d q respectively represent the duty cycle on the d-axis and the duty cycle on the q-axis. ω1 represents the alternating current frequency. L n represents the equivalent inductance of the on-vehicle transformer. R n represents the equivalent resistance of the on-vehicle transformer. U dc represents the steady-state value of the DC-side voltage. R d represents the resistance value of the load resistor. I1 represents the current value of the current source in the parallel circuit.

6. A method for modeling the circuit impedance of a CRH5 type multiple unit, as claimed in claim 1, wherein The mathematical model of the circuit impedance model is: Among them, Z in_ol is the open-loop impedance, G id is the to transfer matrix, G ue is the to transfer matrix, G ud is the to transfer matrix, I d , I q , D d and D q respectively represent the steady-state values of i d , i q , d d and d q . i d represents the current of the d-axis, i q represents the current of the q-axis, d d , d q respectively represent the duty ratio of the d-axis and the duty ratio of the q-axis. ω1 represents the frequency of the alternating current, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC-side voltage, R d represents the resistance value of the load resistor, C d is the DC-side support capacitor, Z RC represents the DC-side RC impedance, and s represents the Laplace domain variable.

7. A circuit impedance modeling system for the CRH5 type multiple unit train, characterized in that, Including: A three-phase stator current calculation module configured to construct the state equation of the three-phase inverter circuit of the inverter on the DC side of the CRH5 EMU, solve the state equation of the inverter, and obtain the three-phase stator currents of the three-phase inverter circuit; A DC current calculation module configured to obtain the DC current on the DC side of the CRH5 EMU by multiplying the three-phase stator currents by the duty cycles of the three-phase upper-arm switches of the half-bridge; An equivalent circuit parameter calculation module configured to equivalent the three-phase inverter circuit of the inverter and the traction motor to a parallel circuit of a load resistor and a current source, calculate the resistance value of the load resistor of the parallel circuit according to the power balance relationship of the parallel circuit, and determine the current value of the current source of the parallel circuit according to the DC current and the resistance value; A rectifier state equation calculation module configured to establish the state equation of the rectifier based on the resistance value, current value and electrical parameters of the rectifier, and transform the state equation of the rectifier to the dq axis based on the inverse Park transformation to obtain the main circuit state equation of the rectifier on the dq axis; A state variable steady-state value calculation module configured to determine the steady-state values of the state variables of the rectifier when the vehicle-grid system is in a steady state from the main circuit state equation of the rectifier on the dq axis; The circuit impedance model module is configured to zero the perturbations of the input voltage vector and the input duty ratio vector of the steady-state values of the state variables and derive the corresponding transfer function matrix, thereby obtaining the circuit impedance model of the main circuit topology of the CRH5 EMU.

8. A CRH5 EMU circuit impedance modeling system according to claim 7, characterized in that The equivalent circuit parameter calculation module includes: A load resistance value calculation module, configured to obtain the resistance value of the load resistance of the parallel circuit based on the equivalent principle of the parallel circuit and using the power balance relationship R e represents the per-phase equivalent resistance of the traction motor, and L e represents the per-phase equivalent inductance of the traction motor, and m is the modulation coefficient of the inverter; The current source current calculation module is configured to obtain a relational expression for the current value of the current source in the parallel circuit based on Kirchhoff's current law as U dc represents the steady-state value of the DC side voltage, and i dc represents the DC current on the DC side; Based on the steady-state values of the equivalent resistance, direct current, and DC-side voltage, the current value of the current source of the parallel circuit is obtained as follows: ω e is the frequency of the three-phase current of the stator of the motor.

9. The CRH5 EMU circuit impedance modeling system according to claim 6, wherein The steady-state value calculation module of the state variable calculates specifically as follows: Among them, E d , I d , D d and D q represent the steady-state values of e d , i d , d d and d q respectively, e d , i d represent the voltage and current of the d-axis respectively, d d , d q represent the duty ratio of the d-axis and the duty ratio of the q-axis respectively, ω1 represents the alternating current frequency, L n represents the equivalent inductance of the on-vehicle transformer, R n represents the equivalent resistance of the on-vehicle transformer, U dc represents the steady-state value of the DC-side voltage, R d represents the resistance value of the load resistor, and I1 represents the current value of the current source in the parallel circuit.

10. An electronic device, characterized in that, Including: One or more processors; A memory coupled to the processor for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the steps of a method for modeling the circuit impedance of a CRH5 EMU according to any one of claims 1 to 6.

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