Voltage vector approximation control of multistage - multilevel inverter using simplified logic implementation

Three-stage redundancy-free multilevel inverter and its innovative control method have been presented. Logic comparators have been implemented in order to ease calculations and to ensure simplicity as well as to improve resultant voltage waveforms. The multistage inverter is formed by high, medium and low voltage stages, connected in series. Six-switch conventional inverter represents the main high-voltage stage. Cascaded H-bridge units are used to build the medium and low voltage stages of the inverter. The proposed control strategy is to keep the state of the high voltage stage if it can lead to the target voltage vector or medium and low approximations otherwise, are triggered. Hysteresis Comparators are used in high and medium voltage stages to hold switching states or to decide the next change. The low voltage stage works to reach the reference voltage vector by using integer rounding and comparators to achieve the best approximations. The designed control technique is verified by simulations as well as testing to prove its advantages over previous control methods.