Research On A Novel Modulation Strategy For Fuel Cell Vehicle Drive System

Environmental and energy issues promote the rapid development of global electric vehicles.As one of the most promising development directions of next-generation transportation system,fuel cell vehicles(FCVs)are expected to solve the problems of petroleum dependence,air pollution and global climate change.At present,the modulation strategy of automotive drive systems is usually based on a constant bus voltage.Therefore,electrolytic capacitors are usually required to stabilize the bus voltage.However,electrolytic capacitor is bulky,costly and susceptible to temperature,which has become one of the key hurdles to limit the development of electric drive systems.This paper introduces a Pulse-Width-Amplitude-Modulation(PWAM)strategy for FCVs motor drive system.The PWAM system,in which the dc-link voltage is controlled to have a 6? fluctuation following the output peak voltage envelop,provides several advantages over the traditional SPWM system,such as less switching loss,less dc-link capacitor,higher power density and lighter weight.The low voltage energy storage system(ESS)is employed to regulate the 6? fluctuation dc bus while the fuel cell stack serving as the main power source of the propulsion system.A small-signal model of the front-stage converter is built and a multiloop control strategy is adopted to achieve the requirement of fast control.A 6? fluctuation dc bus voltage of certain frequency range has been generated in the simulation.PWAM technique can only be applied in high speed areas due to the step-up nature of front-stage converter.A hybrid modulation strategy is adopted to achieve V/f control and the simulation verification has been carried out.Finally,an experimental prototype is built and the PWAM scheme is verified experimentally.An induction motor vector control syst em based on PWAM is proposed and a simulation model is established for verification.The simulation confirmes that the vector control system based on PWAM can achieve good dynamic control,but also reduce the bus capacitance and improve drive system power density and reliability.