Three-port high-frequency transformer based current-source electric drive system for hybrid electric vehicles

With the increasing problems of emission from oil/gas powered vehicles and the decreasing of fossil fuel around the world, the electric vehicles (EV) and hybrid electric vehicles (HEV) have gained wide attention. Among them, the internal combustion (IC) engine and the electric machine based HEV become the most promising alternatives for the next generation vehicles [1]. The HEV provides the advantages of better fuel economy, long operating range and easy refueling systems [2]. Currently, most of EV and HEV adopt the voltage source inverters (VSI) for electric propulsion. Fig. 1 shows the configuration of conventional series HEV based on VSI, where an IC engine/ generator, a traction motor, and the batteries are paralleled with a common DC voltage link by power converters [3-4]. But this configuration suffers from some drawbacks: First, the reliability of electrolytic capacitor in DC link is limited. But the cost of film capacitor is high. Second, the dv/dt of two-level VSI fed motor drive is relatively high, which might produce problems of electromagnetic interference (EMI), insulation and leakage current in bearing. Third, the VSI fed motor drive only has the buck ability for voltage, and the flux weakening is required for the extended-speed operation of electric machine. Different from the conventional VSI fed HEV drive, a current-source-inverter (CSI) fed electric drive system has been proposed in [5]. The CSI fed drive enables longer life for energy storage in DC link and higher fault-current tolerant capability. It offers the voltage boosting ability, which extends the constant-torque and constant-power speed range for HEV [5]. Furthermore, the filter capacitors of CSI drive not only facilitate current commutation among different phases, but also provide good output voltage waveforms and lower dv/dt values [6]. In this paper, a three-port high-frequency transformer (THT) based CSI drive is proposed for HEV. The proposed THT based CSI drive inherits the merits - f CSI fed drive, provides isolation and protection for the traction motor, and enables light weight and small size for the system.