Improved control for high power static var compensator using novel vector product phase locked loop (VP-PLL)

This paper presents a new dual loop control using novel vector product phase locked loop (VP-PLL) for a high power static var compensator (SVC) with three-level GTO voltage source inverter (VSI). From a simple dq-axis equivalent circuit obtained by circuit DQ-transformation method, steady-state analysis is achieved for maximum controllable phase angle αmax per unit current between AC source and switching function of inverter. In addition, the system parameters L and C are designed and thus transient analysis is made for open-loop transfer function. This paper proposes software VP-PLL for more accurate α control than conventional hardware PLL because αmax becomes very small in high power SVC. Therefore, the overall controller has dual loop structure of inner VP-PLL for synchronizing the phase angle with AC source and outer Q-loop for compensating reactive power of load. Finally, the usability of the proposed control method is verified through the experiment of 100kvar power capacity with both stand alone a...