Integrated Motor Drives and Battery Chargers for Electric or Plug-in Hybrid Electric Vehicles

University dissertation from Chalmers University of Technology

Abstract: Plug-in vehicles, electric vehicles or plug-in hybrid electric vehicles, use grid power to charge the battery. The components in the traction circuit, like the electric motor and the inverter, are not used during the battery charging, so there is a possibility to use them in the charger circuit to reduce the size, weight and price of the on-board charger; that is called an integrated motor drive and battery charger or simply an integrated charger which can be galvanically isolated or non-isolated from the utility grid. Different examples of integrated chargers reported by academia or industry, isolated or non-isolated, are reviewed and compared in terms of circuit configuration, control strategy, degree of integration, and efficiency. Moreover some new isolated and non-isolated solutions are presented and explained. A patented integrated motor drive and isolated battery charger based on a split-phase permanent magnet (PM) motor is described where the motor windings are reconfigured for the traction and charging mode by using a relay-based switching device. To reduce the magnetization current due to the motor airgap, the motor rotates at synchronous speed during the battery charging. So, an extra clutch is used in the system to disconnect the motor from the vehicle transmission during the charge operation. The mathematical model of the split-phase PM motor based on a double $dq$ approach, the developed controllers, and the system functionality are explained. Moreover, simulation and experimental results show that the system has a good performance in terms of system efficiency and dynamic response with two PM motor alternatives in two separate practical systems. Two new categories of integrated motor drives and non-isolated battery chargers are presented and explained. The first scheme is based on the winding's reconfiguration of a split-phase PM motor which simulation and practical results are provided. The second scheme is a single-phase solution that a split-phase PM motor and two inverters enable battery charging. Based on the double $dq$ model of the split-phase PM motor that provides the theoretical framework, a modal filed-oriented controller is proposed for a drive system that utilizes two identical inverters and a split-phase PM motor. A decoupling strategy is proposed based on the eigenvalue decomposition to impart a systematic methodology for the current controllers design. Moreover, a maximum torque per ampere strategy is derived to reach an optimal torque development in the drive system. Simulation results are provided to show the system performance in the steady-state and dynamic for a speed control system. For a reference speed profile, the drive system has a fast speed response while the torque and currents are tracking the optimal trajectories.

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