Power Quality Improvement by Using Multipulse AC-DC Converters for Varying Loads

Power electronic devices are non-linear loads that create harmonic distortion and can be susceptible to voltage dips if not adequately protected. The most common economically damaging power quality problem encountered involves the use of variable-speed drives. Variable-speed motor drives or inverters are highly susceptible to voltage dip disturbances and cause particular problems in industrial processes where loss of mechanical synchronism is an issue. Three-Phase Ac?Dc conversion of electric power is widely employed in adjustable-speeds drive (ASDs), uninterruptible power supplies (UPSs), HVDC systems, and utility interfaces with non conventional energy sources such as solar photovoltaic systems (PVs), etc., battery energy storage systems (BESSs), in process technology such as electroplating, welding units, etc., battery charging for electric vehicles, and power supplies for telecommunication systems. Traditionally, ac?dc converters, which are also known as rectifiers, are developed using diodes and thyristors to provide uncontrolled and controlled unidirectional and bidirectional dc power. They have the problems of poor power quality in terms of injected current harmonics, resultant voltage distortion and poor power factor at input ac mains and slowly varying rippled dc output at load end, low efficiency, and large size of ac and dc filters It is well known that undesirable harmonic line currents may be generated during a transformer-rectifier combination. The rectification of AC power to DC power itself may in general produce undesirable current harmonics. These non-linear loads cause severe current harmonics that may not be tolerated by either a shutdown of the device or unacceptable powering of the devices. The great majority of power electronic equipment operates from an ac source but with an intermediate dc link. Thus, a significant opportunity exists to facilitate power electronics applications by using ac to dc rectifiers that produce low harmonic current in the ac source. Multi-pulse converters in general and non-isolated multi-pulse converters in particular can be applied to achieve clean power which is of major interest in higher power ratings. In general, by increasing the number of pulses in multi-pulse converters THD (total harmonic distortion) can be reduced and other associated performance parameters can be enhanced.This project work is an endeavor towards analyzing the different multi-pulse converters in solving the harmonic problem in a three-phase converter system. The effect of increasing the number of pulses on the performance of AC to DC converters is analyzed.