Design of a Nearly Harmonic-Free Adjustable AC Power Source With Large Range of Output Voltage

The need for sinusoidal voltage waveforms with adjustable amplitude and frequency is essential in many applications. Power electronics converter-based supplies with pulse-width modulation (PWM) introduce high-order harmonics at their output and the use of filters is mandatory to remove the harmonic distortion. However, output filters are undesired in some specific applications such as B-H meter of magnetic devices because they act as the inverter output load together with the actual load affecting the measurement results. This paper explains the principles of operation and design considerations of a controlled AC power supply with nearly sinusoidal output. The proposed AC power supply consists of switching-mode DC-DC converters connected at the DC links of asymmetric cascaded H-bridges (ACHB). The proposed AC power supply offers a nearly sinusoidal output even at high-current low-voltage outputs. A modular compact 63-level supply is designed for the special case of the B-H meter and the simulation results are presented.