AC Power

 Supplies Some applications of ac power supplies are ac motor drives, uninterruptible power supply (UPS) used as a standby ac source for critical loads (e.g., in hospitals, computers), and dc source to-utility interface (either to meet peak power demands or to augment energy by connecting unconventional energy sources like photovoltaic arrays to the utility line). In ac induction motor drives, the ac power main is rectified and filtered to obtain a smooth dc source, and then an inverter single-phase version is used to obtain a variable-frequency, variable-voltage ac source. The sinusoidal pulse width modulation technique can be used to obtain a sinusoidal output voltage. Some other methods used to get sinusoidal voltage output are a number of phase-shifted inverter outputs summed in an output transformer to get a stepped waveform that approximates a sine wave and the use of a bang-bang controller. All these methods use line-frequency (60 Hz) transformers for voltage translation and isolation purposes. To reduce the size, weight, and cost of such systems, one can use dc-to-dc converters as an intermediate stage. such a system in block schematic form. One can use an HF inverter circuit (discussed earlier) followed by a cycloconverter stage. The major problem with these schemes is the reduction in efficiency due to the extra power stage. a typical UPS scheme. The battery shown has to be charged by a separate rectifier circuit. AC-to-ac conversion can also be achieved using cyclo converters