A novel hysteresis current controller for multilevel single phase voltage source inverters

The application and benefits of hysteresis current control for two level voltage source inverters are well understood, but the extension of the strategy to multilevel inverters is much less established. Previous approaches have used either multiple hysteresis bands or a time based lockout strategy to decide when to switch to successive voltage levels, but these approaches are either complex, and/or have restricted applicability. This paper presents a simple hysteresis strategy which uses the slope of the current error to confine this error to within a single hysteresis band, by recursively stepping the inverter output between successive voltage levels when the hysteresis band is exceeded. The algorithm can be used with any level of multilevel inverter, and achieves a robust steady state operation that fully utilises the multiple DC levels available. Theory, simulation and experimental results are presented.