Abstract:
Bidirectional inductive power transfer (IPT) systems for regulating wireless power flow between power supply and batteries have been developed and tested at the University of Auckland. It is a crucial technology for vehicle to grid (V2G) system, which integrates huge amount of EV batteries to a large scaled storage facility for the power grid, and makes renewable energy more reliable. Bidirectional IPT systems are higher order resonant circuits and their modelling and control is a challenging task. The objective of this research has been to develop dynamic models and better controllers to control the power flow in this system. Due to the extraordinary developments of very large scale integration (VLSI) technologies, one technique called Sigma-Delta Modulation is attracting more attentions in research. This technique converts multi-bit signal to one-bit signal, which is also known as bit-stream signal, simplifies the wire routings and signal processing in the integrated circuits (ICs) and reduces significantly the hardware resources. The bit-stream based controller has been successfully being applied to various control applications in recent past including the control of DC motor, magnetic levitation systems, and etc. In this study a new Sigma-Delta (-) based proportional and integral (PI) controller, which is also known as bit-stream PI controller, has been proposed for power control of bidirectional IPT system. A dynamic state variable model of the bidirectional IPT system was developed and the behaviour of the system was investigated. During the first phase of the research, a bit-stream based PI controller was designed for this system and its performance was compared with the conventional multi-bit PI controller via simulations through Simulink. The results of the simulation indicate that with proper design, the performance of bit-stream based PI controller is similar to that of the conventional multi-bit PI controller. After successfully simulating the controller, in the next phase of the research the performance of the bit-stream based PI controller is studied using an experimental prototype of bidirectional IPT system. A new approach for driving H-bridge without using sinusoidal function was developed. The open loop experiment indicated that the H-bridge driver was functioning properly. The closed-loop tests compared performances between bit-stream based PI controller and conventional multi-bit PI controller. The experimental results indicate that the bit-stream based PI controller has a better performance compared to conventional multi-bit PI controller, as there were much less noise in the power waveforms, which means that the power transfer is more stable.