Cheaper fast charging by integrating motor windings into charger circuit

Using motor windings as part of the charging circuit is an old idea. But with the need to develop a fast charging system, many are looking at the idea again. The ideal is for electric cars to recharge in a few minutes, but that’s not practically affordable. The observation is that the electric motor and inverter are not used while the vehicle is charging. Therefore, if they could be used in the charger circuit designers could make dual use of those components, reduce the vehicle cost, while offering fast charging.

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Model of the integrated motor drive and battery charger. The image shows a plug-in hybrid electric vehicle, which also has a fuel tank and a combustion engine, but the technology system works equally well with a purely electric vehicle.

“Instead of having a separate isolated battery charger, we introduced a new concept for the power transfer, the rotating transformer, which was developed to transfer electric power while rotating,” says Saeid Haghbin, a recent PHD grad from Chalmers in Sweden. “The battery is charged through the transformer and a split-phase electric motor that was especially designed for this purpose.”

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

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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.

About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.

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