A universal compensation control scheme based on cascade active power filter and static var compensator

How to keep system stability and optimize var compensation capability is the key issue in the combined system based on cascade multilevel active power filter (CS-APF) and static var compensator (SVC). A universal control strategy is proposed for the combined system. For the SVC, a feed forward control for the compensation of positive sequence reactive component and negative sequence component of the load is adopted. The network susceptance (with no components of CS-APF) feedback control is applied to decrease the compensation error. For the CS-APF control, a feed forward control of harmonic compensation for thyristor control reactor (TCR) and the load is applied. The network harmonic current feedback control is applied to decrease the compensation error. The fixed capacitor (in SVC) current component is removed from the network current feedback control loop of CS-APF to improve the stability of the combined system. The var compensation capability of CS-APF is enabled to optimize the performance of SVC. Moreover, a novel pre-calculation method for the TCR harmonic current detection is proposed. According to the triggering angle of the thyristor in TCR and the network voltage phase, the harmonic current is constructed with no time delay. Finally, the simulation and experimental results show that: 1) the system stability is high without closed loop between the control of CS-APF and SVC; 2) the real-time harmonic compensation of TCR is realized; 3) the system responsibility is quick; and 4) the capability of var compensation of SVC is improved.