Output impedance of PWM UPS inverter-feedback vs. filters

The output impedance of an uninterruptible power supply (UPS), which determines the voltage distortion caused by switchmode power supplies, rectifiers, and other nonlinear loads, is reviewed. Step-wave inverters that use shunt filter traps to attenuate the voltage harmonics and thereby present a low impedance to the harmonic load currents of the same order are discussed. Another approach to reducing the output impedance of pulse-width modulation (PWM) inverters, using the negative-feedback technique of the amplifier, is also discussed. Conclusions concerning the use of filters and feedback in the design of PWMs for UPSs are summarized.<
>