FPGA based multiplex PWM generator for diode-clamped cascaded inverter in the direct-driven wind power system

Power inverter is widely used in direct-driven variable speed constant frequency (VSVF) wind power system. A topology of diode-clamped cascaded inverter is presented to be applied in direct-driven VSVF wind power system. First, the principle of wind power system is discussed. Then, a series of detailed analysis are made on the topology and modulation strategy of diode-clamped H-bridge inverter cell and diode-clamped cascaded inverter. Meanwhile, phase disposition SPWM (PD-SPWM) and carrier phase-shifted SPWM (CPS-SPWM) modulation strategies are illustrated clearly. Next, field programmable gate array (FPGA) is applied to implement the driving signals. An FPGA chip can achieve all the function of modules, such as triangular carrier generation module, sine wave generation module, comparing module, dead time module and so on. Finally simulation is carried with MATLAB/simulink. Results of simulation prove that the design of diode-clamped cascaded inverter is feasible, which can output a higher voltage with lower total harmonic distortion (THD), lower du/dt and higher equal switching frequency. The proposed inverter will have a better prospect in direct-driven VSVF wind power system.