Suppressing harmonics of differential-mode voltage with a variable capacitance filter in single-phase inverters

In a single-phase inverter, the problem of the differential-mode harmonics suppression at switching frequency is very prominent while the switching frequency is low. This paper presents a variable capacitance filter, which is composed of a conventional LCL filter and a single tuned filter with a variable capacitor. It can not only suppress the harmonics of the inverter´s output voltage as a whole, but also filter its harmonics near the switching frequency specifically. The design of the variable capacitance filter breaks the original restriction that one end of the variable capacitor must be grounded. Thus the application of the filter becomes more widely. The feasibility and validity of the variable capacitance filter are verified through the simulations and experiments.