| Driven by environmental protection,clean energy vehicles represented by electric vehicles are developing rapidly.In the next 15 years,it will be the trend of the times to replace fuel vehicles with electric vehicles.However,there are still technical bottlenecks in charging technology aiming at being safe and fast and energy storage technology going after long duration time for electric vehicles.The complete banning of oil from vehicles will not happen in an action.Hybrid Electric Vehicles,as a transitional product,have been highly favored in terms of fuel saving and long duration time.However,the complicated structure of the HEV dual-drive system not only contradicts the demand of miniaturization and light-weight of automobiles,but also has relatively high failure rates of the power drive devices of the electric drive system.Therefore,it is of significance to study the influence of HEV converter control strategies on power switching devices and DC-link capacitors under driving conditions.Based on the voltage source inverter in HEV as the background,a series of reliability problems about DC-link capacitor such as current ripple and hotspot temperature are explored under the different PWM strategies at the same time to ensure the loss of VSI as little as possible.The main work of the paper is as follows:Firstly,a simplified model of HEV electric drive system is established.The key role of DC-link capacitors in power conversion and the electrothermal stress of DC-link capacitors are analyzed.The influence of the control strategies optimization aimed at reducing VSI power switch module losses on the reliability of capacitors is also pointed out.Secondly,the basic principles of SVPWM and six DPWM strategies are described in details.The Matlab/Simulink simulation model is constructed based on space vector synthesis and zero-sequence component injection,respectively.Taking the loads as resistance-inductance loads,the VSI simulation is implemented.Both the switching loss calculation model and the switching loss function model are established under seven kinds of PWM strategies in order to compare the loss difference of VSI from different PWM strategies and to determine the optimal control strategy with the goal of minimizing the loss of VSI power switching modules.Thirdly,bilateral Fourier transform of the switching function under different PWM strategies is introduced.Based on the current constraint equation of DC input side of VSI,the analytic expression and effective value formula of DC-link capacitor instantaneous current are derived.DC-link capacitor current spectral characteristics is analyzed.Both Matlab/Simulink simulation and DSpace hardware experiment are employed to verify the results of theoretical analysis.Finally,based on the analysis of DC-link capacitor current spectrum under different PWM strategies,the qualitative analysis of capacitance hotspot temperature is carried out.Under the typical urban and high-speed conditions,the transient current and its frequency spectrum are simulated to find out the control strategy that has the least impact on the safety and life of DC-link capacitors. |
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