Design Of Offshore Wind Power Converter Based On DC/DC Direct Access

For its better continuity and stronger power, offshore wind power energy is becoming more and more ability to capture the attention of scholars and experts who are at home or on abroad. There are two electric energy collection ways of offshore wind power field which are ac and dc collection. When offshore wind farms using dc power grid interconnection, there are four advantages, first it does not need to the synchronization of each generator set completely. Second each generator can independent achieve MPPT.Third with the use of high frequency transformer in DC/DC converter the volume and weight of the variable flow system is significantly reduced. Fourth when the dc collection way was used a third of transmission line would been saved. So it is very good when the dc collection way was used in offshore wind power collection system.A method which is a PMSG independent, direct access to VSC- HVDC transformation line has been proposed. The method consists of a three-phase three-level PWM rectifier and diode clamping type high frequency inverter DC/AC,high-frequency transformer, single-phase diode rectifier bridge.The insulating type DC/DC module is made up of the Diode clamping type high frequency inverter DC/AC, high frequency transformer, single-phase diode Rectifier Bridge. Each module is parallel connected at input and series connected at output to raise the output voltage. There are many advantages when use this method which are highly modular,extensible, high power, small volume; output voltage can be directly connected to the VSC-HVDC.etc.An insulating DC/DC converter has been designed and a method to calculate the input and output capacitor of the DC/DC converter the basic parameters of the high frequency transformer and the maximum permissible leakage inductance has been supplied, In-depth analysis has been carried through the design of the parallel DC/DC controller, the parallel DC/DC module topology structure, work mode. Mathematical model for DC/DC modules has also been established. Corresponding control strategy which is the three-phase PWM rectifier DC bus voltage output ring and the inner ring of module's output voltage strategy has been designed. Through the in-depth analysis of the leakage inductance when the child module's output capacitance, the leakage inductance of the transformer, the ratio parameters of transformer are changed. Thereason of the child module's output capacitor voltage imbalance has been achieved. A2 MW PMSG system has been built for validity and correctness the theoretical analysis is verified.The corresponding solutions to solve the child module's voltage unbalanced have been put forward. Influence of each generator into the HVDC has been evaluated also.