Design and Evaluation of Controllers for Wave Energy Based Electricity Generation System

Abstract

The research work presented in this thesis is an effort to recognize the potential issues associated with harnessing wave energy based on oscillating water column principle. A model of oscillating water column based on energy balance concept is proposed. Dynamic model of a wave energy conversion system based on OWC principle consisting of a variable speed Wells turbine driven permanent magnet synchronous generator connected to the grid by means of back to back converters is developed. Results exhibit the randomness in the various quantities like speed of the turbine, torque and powers developed of the turbine and the generators when the input to the system is varying randomly. This demonstrates uncertainty in the wave power due to arbitrariness in the waves and reveals the difficulties in developing an efficient wave harnessing system. Controllers for the generator side and the grid side converters for a grid connected wave energy conversion system are developed. The overall scheme is evaluated under steady state, dynamic and transient operating conditions. Under different operating conditions it is observed that the control scheme provides a good response in terms of power quality and power control. An important constituent for developing the wave energy conversion systems is the Wave Turbine Emulator. It offers a controllable test environment that allows the evaluation and improvement of control schemes for electric generators without construction of costly turbine and help in determining the strength and weakness of energy conversion scheme and the related control technologies. In view of this a wave turbine emulator is designed. For the realization of the wave turbine emulator a three phase permanent magnet synchronous motor is used with VSC controller as a drive. Results presented for different wave pattern as input indicates that the speed dynamics of the wave turbine model is exactly followed by wave turbine emulator developed in laboratory. An attempt is also made to study the behavior of the three phase permanent magnet synchronous generator coupled to the emulator developed.