Control Techniques for a Single-Phase Bi-Directional Full-Bridge Active Rectifier for Vehicle-to-Grid and Grid-to-Vehicle Applications

Abstract

As electric vehicles (EV) continue to gain market traction, more research is being conducted in the control of the power conditioning system. This thesis focuses on control strategies for the front-end AC/DC converter. Current EV chargers in the market are unidirectional which limits the opportunity for EV owners to participate in vehicle –to-grid services. The core work on this thesis is two bi-directionally capable controllers for EV chargers that have improved performance or added functionality over the traditional chargers on the market. The controllers were simulated and implemented on a single-phase full bridge converter.

The first controller focuses on improving the dynamic performance of EV chargers compared to the conventional linearly regulated chargers. This nonlinear controller is designed based on Lyapunov control theory which guarantees that the energy of the system is always decreasing thereby guaranteeing stability. A better version of this controller is designed by adding integral terms into the system. These terms compensate for parameter variations and converter model inaccuracies. Finally, a practical version of the controller is implemented by using the Tikhonov theorem to decouple the fast current loop and the slow voltage loop of the system.

The second part of the thesis focuses on the design of a controller which allows for four quadrant operation of the AC/DC converter by directly controlling the active and reactive power. This will allow EV owners to participate in ancillary services such as voltage control of the grid. This has potential to generate additional revenue for the owners and can also benefit the utility operators. This controller was designed in the synchronous frame using the Alpha-Beta to DQ transformation. In order to design this controller, an orthogonal version of the system had to be created. Several methods of orthogonal signal generation were compared and the one most suitable for this application was used.

The result of this work is two controllers for EV chargers that tackle current challenges that exist in EV chargers. These controllers were simulated in PSIM and experimentally verified on a 1kW single phase full-bridge active rectifier.