Instantaneous feedback in voltage source inverters: a comparative study between nonlinear and linear approach

Voltage source inverters used in UPS systems feeding nonlinear loads must be capable of providing an output voltage waveform of quality in spite of all line and load disturbances. Switching algorithms applying output filter state feedback in order to control the instantaneous output voltage are discussed and two approaches are compared. In the case of the nonlinear controller, the driving force is switched at maximum amplitude into the output filter, while the linear discrete-time controller encompasses a synchronous pulse-width modulator placed in the feedback loop. The former gives a higher tolerance level to load disturbances, but encourages randomness in commutations. Simulations and experiments performed show that the latter combines both excellent dynamic performance and synchronous switching. Theoretical background and design considerations are included for both solutions.