AC DC LLC Resonant Converter Topologies and Simplified DTC Drive Schemes for E mobility Applications

Abstract

AC/DC resonant converters and electric motor drives with advanced modulation schemes operating at high switching frequency find a wide range of applications in Electric Vehicles (EV) and industries. The desirable features of an EV charger (AC/DC newlinePWM rectifier) in E-mobility applications include soft switching, high power density, newlinelow harmonics, high efficiency, and high power factor whereas the desirable features of electric drives include low torque ripple, quick dynamics, low computation effort and newlinehigh efficiency. This research work deals with the topological enhancements in single- newlinephase, single-stage LLC soft-switched resonant converter for AC/DC power conversion newlineand also proposes simplified direct torque control (DTC) schemes for space vector newlinemodulated induction motor drives. newlineOut of the different resonant converter topologies available in the literature, LLC- newlinebased resonant converters have several advantages such as less circulating current, load regulation even at light loads, and Zero Voltage Switching (ZVS) of the power devices. newlineThey can regulate the output DC voltage using frequency control with relatively small newlinevariations in the switching frequency. To improve the power factor, it usually requires newlinea boost power factor correction stage at the front end. In order to reduce the size newlineand cost of the system, it is possible to control both the boost stage and LLC stages newlineby the same switches while operating the boost converter in discontinuous conduction newlinemode. However, line voltage variations and load changes can cause wide variations in newlinethe DC-bus capacitor voltage, which can lead to unstable operation of the converter newlineand sometimes lead to failure of the DC-bus capacitor.In the first work, a simplified bridgeless two-level LLC AC/DC converter topology newlineis proposed to avoid this issue by returning the additional energy stored in the bus newlinecapacitor back to supply thus maintaining the bus voltage. The bridgeless topology newlinereduces the number of power diodes and thereby reduces the losses.