A New Hybrid Cascaded Inverter

For high-power applications, multilevel inverter structures have the particular advantage, such as high level output voltage without series strings of switching devices, lower du/dt and reduction in output voltage harmonics, so great emphasis has been putting on it in the application of power system and high-capacity AC drive applications. Nowadays, there are three prominent multilevel topologies, diode-clamped multilevel inverter, capacitor-clamped multilevel inverter and cascaded multilevel inverter. The cascaded inerter uses series strings of single-phase full-bridge inverters to construct multilevel phase legs. This topology that the modulation, control, and protection requirements of each bridge are modular leads to advantages in terms of manufacturing and flexibility of application. However each single-phase inverter requires its own isolated dc supply. This complexity has generally restricted cascaded inverters to the higher power range. In this paper, a new hybrid cascaded multilevel inverter is proposed to solve cascaded inverter's primary disadvantage, a number of separate dc sources required. At first, the concept of the new hybrid cascaded multilevel inverter is derived by analysis single phase inverter's theory, and then a series of diagram and waveform based on MATLAB/simulink are given for reference. This new hybrid cascaded multilevel inverter has much advantage, such as simple topology, five or seven level output voltage, only one or two isolated dc source required and high dc source's utilization ratio. The improved new hybrid cascade multilevel inverter needs one isolated dc source for each phase, but the output voltage is of seven or eleven steps. This new hybrid cascaded multilevel inverter requires half of isolated dc source at most, so the inverter system is simple, and the reliability is enhanced.