Design and Control of On-board Bidirectional Battery Chargers with Islanding Detection for Electric Vehicle Applications

Electric vehicles have gained popularity over the last decade due to concerns regarding climate change as well as depleting fossil fuel reserves. One of the important components of electric vehicles is the battery charging system that has been the focus of recent research interest in terms of vehicle to grid (V2G) power transfer with the aim of providing peak load levelling for the grid as well as a buffer for excess renewable energy. The research addressed in this thesis is focused on single-phase on- board bidirectional chargers for electric vehicle applications where emphasis is given to the design, control and islanding detection aspects.
A comparative study between a low frequency transformer based and high frequency DAB based bidirectional charging system is carried out and the weight, cost and efficiency between the two topologies compared. An optimised LCL filter design method for the two converters is presented which characterises the high frequency current ripple as well as the losses in the damping resistor. Controller design, simulation and experimental validation of the two converters are also presented.
The impact of 3rd harmonics on the performance of second order generalised integrator (SOGI) phase locked loops (PLLs) is investigated through an analytical method to predict the resulting output harmonic magnitudes. Two modified SOGI PLLs are presented where the harmonic rejection performance has been improved.
A new PLL structure based on the novel IIR filter proposed by Ed Daw et al. is investigated for application in grid converters. The new PLL is evaluated with hardware-in-the-loop (HIL) simulations for transient and abnormal grid conditions and compared with the SOGI PLL for performance evaluation as well as computational requirements. The new PLL is validated in bidirectional charger hardware.
A new islanding detection algorithm based on the detection of high frequency switching harmonic signature with frequency hopping is presented which has the advantage of multi-inverter compatibility. The difficulty in detection for PWM harmonic based methods when capacitive loads are present is analysed. Furthermore, the algorithm is validated in hardware.