Research On The Power Conversion System For Wave Energy MHD Generator

Our country is a great oceanic country with abundant ocean wave energy.Wave energy magnetohydrodynamic generator is a single-phase AC motor which can convert ocean wave energy into electrical energy.The energy it generates has the characteristics of low voltage and high current,hence a power converter is needed to convert it into electricity which can be used directly in human life.In order to improve the efficiency,the power converter needs to have the function of power factor correction.This paper is of great significance to solve the energy and environmental problems.The power conversion system of wave energy magnetohydrodynamic generator consists of an AC/DC converter,a battery and a DC/DC converter.The full-bridge PFC converter is used as the AC/DC converter and the push-pull forward converter is used as the DC/DC converter.Several single-phase PFC converters are compared in this paper,in which the full-bridge PFC converter has only two semiconductor devices in every conduction loop and uses a MOSFET instead of a diode to reduce its turn-on loss,so the full-bridge PFC converter has significant advantages in low-voltage and high-current situations.The working principle of full-bridge PFC converter is introduced and its transfer function of control loop with one-cycle control is also given in this paper.The scheme of synchronous rectification of the full bridge PFC converter is also determined.This paper also analyses and the loss of the inductor and the loss of switches by taking the commutation between the power MOSFET and the body diode of synchronous rectifier into account.The DC/DC converter used in this paper is a push-pull forward converter,which is suitable for low-voltage and high-current situations.This paper elaborates its working principle,analyzes the current circulation phenomenon and gives the function of the clamp capacitor as well as the calculation formula.The using of a clamp capacitor provides a release circuit for the energy of the leakage inductance of transformer and reduces the voltage spike.In addition,the clamp capacitor can suppress transformer core bias and decrease input current ripple to reduce the volume and weight of the input filter.Aiming at reducing the voltage spike of the switches,this paper compares two different winding methods of the transformer and optimizes the design of transformer.In order to suppress the voltage spike of the rectifier diode,the lossless CDD snubber circuit is introduced in the secondary winding of PPFC.The operating principles and features of the converter are analyzed in detail and the design principle of the snubber capacitor is also given.Finally,a 3kW prototype of the power conversion system of wave nergy magnetohydrodynamic generator is built to verify the correctness of theoretical analysis.