| The high-power power electronic switching devices in the electric vehicle motor drive system will produce significant electromagnetic interference when working.These interference noises will not only propagate inside the motor drive system,affecting the normal operation of various low voltage control systems,but also spread outward affecting other systems(such as anti-lock braking systems,electronic stability program,etc.)which directly involves active safety.Internet of vehicles,driverless cars and other advanced technologies integrate a large number of electronic products,making the electromagnetic environment in the car more complex.Electromagnetic interference brings new challenges.Therefore,analyzing and solving the electromagnetic interference problem of the motor drive system are important for improving the design of the electric system of the electric vehicle and enhancing the electronic safety of the electric vehicle.For the advanced and widely used "three-in-one" motor drive system assembly of a pure electric vehicle,the conducted interference characteristics of the system were studied,with the focus on the system-level modeling of conducted interference.The main tasks were as follows:1)According to the structural and functional principles of the "three-in-one" motor drive system,main electromagnetic interference sources and propagation paths of it were analyzed.Based on the relevant requirements of the automotive component electromagnetic interference test standard “GB/T 18655-2018”(corresponding to the European standard “CISPR 25: 2016”),the components of the conducted interference model under the standard test state were combed,and a system-level modeling method of conducted interference was proposed with limited modeling input parameters;2)Built the driving signal model: Based on the theoretical formula and implementation method analysis of the seven-segment space vector pulse width modulation(SVPWM)method,the mathematical model was built in Simulink software,and the six-channel SVPWM driving signals were output.The accuracy of the model was verified according to duty cycle;3)Built the Inverter bridge model: According to the static and dynamic characteristic test circuits of the insulated gate bipolar transistor(IGBT),an IGBT behavioral model including parasitic resistances,parasitic inductances,and parasitic capacitances was established through the IGBT parametric modeling tool provided by circuit simulation software Saber.And the accuracy of the model was evaluated by IGBT double pulse test.The parasitic capacitance between the IGBT and the heat sink was calculated based on the analytical method and verified by the port impedance.Based on the three-phase full-bridge inverter topology,an equivalent circuit model of the inverter bridge was established;4)Built the drive motor model: According to the test results of the port impedance amplitude-frequency characteristic curve,the common-mode and differential-mode impedances of the drive motor were decoupled based on the analytical method,and the common-mode and differential-mode impedance characteristics of the drive motor were fitted through the "RLC" resonance unit to establish the drive motor "?" type equivalent circuit model.Finally,the port impedance amplitude-frequency characteristic curves of the model were solved by a two-port impedance analysis tool to evaluate the accuracy of the model;5)Built the DC bus,DC connector,AC busbar models: According to the structure,size and material parameters,three-dimensional electromagnetic field models of the DC bus,DC connector,and AC busbar were established in the finite element electromagnetic simulation software ANSYS Q3 D.Based on the electrically small size idea,the equivalent circuit structure of each component was analyzed.The parasitic resistance,parasitic inductance,and parasitic capacitance of each port were extracted,and the equivalent circuit models of the DC bus,DC connector,and AC busbar were built and verified by the impedance test method;6)Built line impedance stabilization network,bus capacitors,and DC busbar model: According to the electrical structure diagram and parameter table provided by the standard,the equivalent circuit model of the high-voltage line impedance stability network(LISN)is established;According to the electrical structure diagram,and based on the system-level modeling method of conducted interference with limited modeling input parameters,equivalent circuit models of the bus capacitor(a film capacitor across the positive and negative poles of the DC bus,integrated with two film capacitors which connect positive pole or negative pole to ground)and DC busbar were established and passed the overall system verification;7)Through the Saber-Simulink co-simulation method,a system-level simulation platform for conducted interference was established.Based on the parameter setting of GB / T 18655-2018 standard,the conducted emissions(voltage method)of the 150 kHz-30 MHz frequency band in high-voltage loops that are easily exceeded in the high-frequency loop were simulated and predicted,and the test results verify the accuracy of the entire system model interference loop.The accuracy of the interference source was verified by comparing the time domains and frequency domains of the IGBT output voltage;8)Based on the simulation platform,the conducted emission characteristics of the highvoltage circuit at the instant of system startup and after stabilization were analyzed.And the influence of the key parasitic parameters,return path of the motor drive system on the conducted emissions of the high-voltage circuit was also studied.Based on this,a port filter was designed to optimize the system's conducted interference performance,and the conducted emission optimization effect of the filter was evaluated by simulation. |
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