HARMONICS REDUCTION AND RIDETHROUGH ADJUSTABLE SPEED DRIVES DURING SYMMETRICAL VOLTAGE SAG
Dr. S. S. Deswal1, Dr. Rajveer Mittal2, L. P. Singh3, Jitender Lather3
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An increasing demand for high quality, reliable electrical power and increasing number of distorting loads may leads to an increased awareness of power quality both by customers and utilities. The most common power quality problems today are voltage sags, harmonic distortion and low power factor. Trading-off between the importance, the efficiency, the size, and the cost of any Voltage Sag Ride-Through system is the core of choosing the best topology. In addition, choosing the best topology for any give system depends on the interruption nature. For example, if the dominant interruption event is voltage sag; not a full outage, a ride-through system from the advanced hardware modification ASD’s category is preferred. And vice versa, if the dominant event is a full outage, an ASD with ride through mechanism from the energy storage devices category is the best in order to maintain ride-through for long durations. In this paper, a voltage sag ride-through for an ASD from the advanced hardware modification category will be investigated. The proposed system utilizes a boost converter along with supercapacitor as an energy storage device to compensate the DC-link voltage during the symmetrical voltage sag condition. The boost convert is activated to compensate the difference between the reference voltage of the DC-link and the actual voltage once it receives a signal from the voltage sag detection system. An additional advantage of using boost converter is its ability to improve the shape of the supply currents waveforms during the steady state normal operation. Thus lower total harmonic distortion (THD) can be obtained. Based on the designed topology, simulation model in MATLAB 7.5 (Sim Power Block set) has been developed for voltage unbalance conditions with supercapacitor as an energy storage device. The designed control technique is modeled, simulated and successfully implemented in the laboratory. The extensive simulation results are provided to validate the proposed system.