Enhancement of Voltage Quality in Isolated Power Systems

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Author(s) JBV Subrahmanyam | TC Subramanyam
Pages 110-123
Volume 1
Issue 2
Date November, 2011
Keywords Voltage quality, power quality, series compensator, voltage sags/swells

A traditional method to achieve improved power quality (PQ) is to use passive filters connected at the sensitive load terminals. However, this practice has some shortcomings: the effectiveness of the scheme could deteriorate as the source impedance or load condition changes; it can lead to resonance between the filter and the source impedance. In this paper the use of series compensators (SCs) in improving voltage quality of isolated power systems is considered. The roles of the compensators are to mitigate the effects of momentary voltage sags/swells and to control the level of harmonic distortions in the networks. SC injects harmonic currents of the same magnitude but of opposite polarity to cancel the harmonics present there. A control strategy for the SC is developed to regulate power flow. This is achieved through phase adjustment of load terminal voltage. It leads to an increase in the ride through capability of loads to the voltage sags/swells. The isolated power systems are often considered weak in that they possess relatively lower short-circuit ratio, in comparison to a grid. Network voltage control becomes a challenging task as a result. The power quality problem is compounded with the drive-converter load. The sensitive loads would be connected in parallel with the nonlinear drive. Often such sensitive loads also contain input rectifiers that are capacitive in nature. The total capacity of the sensitive loads could be much smaller than that of the main drives; the distorted supply voltage is harmful to the sensitive loads. Excessive voltage distortions could cause the sensitive loads to maloperate. The loads are also sensitive to short-duration disturbances, in the form of voltage sags or swells. Validity of the proposed technique is illustrated through simulation. Simulation has confirmed the effectiveness of the proposed method, as it is applied on the SC to achieve improved quality of supply in the power system.

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