Improve ment of Direct Power Control in Three-Level Inverter

The control strategy and topology of multilevel inverters, as well as the work principle of three-level inverter, are firstly analyzed. And then, a three-level direct power-based control algorithm is proposed, which can coordinately control the active power, reactive power and midpoint voltage. The proposed algorithm is implemented by three hysteretic controllers. By analyzing the change of active power, reactive power and midpoint voltage after applying every inverter voltage vector, the appropriate inverter voltage vector can be chosen to control the on-off of every IGBT. It is shown from the simulation results that both the output voltage and waveform of three-level inverter based on direct power control are in good shape, D C voltage is stable, and the midpoint voltage hysteresis control can inhibit the fluctuation of midpoint voltage.