Application of magnetic energy storage unit as continuous VAR controller

Abstract

It is shown that magnetic energy storage units can simultaneously operate as continuous VAr (volt-ampere reactive) controllers while performing the role of load-frequency stabilizers in electrical power systems. This is achieved by operating the converter in the buck-boost mode with a switched capacitor bank placed across its terminals. The P versus Q modulation ranges of the 12-pulse converter depend on the source inductance, secondary voltage of the input transformers, and output current. Once the input transformer is chosen, the Q modulation range depends on the active power transfer and the current through the inductor at any instant of time. The actual reactive power consumption of the converter is varied continuously, depending on the requirements of the power system, while keeping within the Q-modulation range. Switching of the capacitor bank keeps the required Q consumption of the converter within the available range. It is shown that this mode of control improves the overall performance of the power system in P-f and Q-V loops and obviates the use of any additional VAr compensator in the power area where the SMES (superconducting magnetic energy storage) unit is located.