Multilevel Modular High Power Converters for 10MW Wind Turbines

Medium voltage power conversion is generally favored for future large wind turbines, e.g. 10MW, in terms of higher power density, reduced current level and associated losses and cost of power cables, switchgears, etc. This paper has presented and compared three potential high-power, medium-voltage (e.g. 10kV) multilevel modular wind power converter topologies based on a generalized converter structure with different types of isolation. The topology with a 10kV generator, a modular power converter and a multi-winding step-up transformer has been specifically investigated and the control strategy has been developed. Further, a solution to reduce the large dc-link capacitance has been proposed in order to minimize the system cost, size and improve the system reliability. A proportional-integral-resonant (PIR) controller is therefore adopted to regulate the three-phase inverter power to compensate the low-frequency power ripple from the H-bridge side, without negatively affecting the sinusoidal current fed into the grid. Simulation results with a 10MW, 10kV system have validated the proposed converter topology and control strategy, which can achieve maximum power point tracking (MPPT) as well as reduced dc-link voltage ripple.