Current error space phasor based hysteresis controller for two-level and three-level converters used in Shunt Active Power Filters

Shunt Active Power Filters (SAPF) are commonly employed to reduce current harmonics, which are injected in the utility by nonlinear loads. This paper presents performance of current error space phasor based hysteresis controller for three-level Neutral Point Clamped (NPC) and Flying Capacitor (FC) converters used in SAPF. Operation of two-level converter based SAPF is also demonstrated in this paper with the proposed controller. The proposed controller is self-adaptive in nature and does not require any particular calculation of Point of Common Coupling (PCC) voltage vector (E) because of proper sector change detection logic used. The proposed current controller overcomes inherent problem of random voltage vector switching encountered in conventional hysteresis current controller based SAPFs. It allows switching of only adjacent voltage vectors for position of PCC voltage vector in a given sector of voltage space phasor of SAPF. Region detection logic causes switching of SAPF voltage vector which keeps the current error well within the prescribed hexagonal boundary. The SAPF based on the proposed controller provides adequate compensation for removal of harmonics produced by nonlinear loads. Detailed theoretical analysis and simulation studies are presented in the paper and the claimed performance of the proposed controller is evident from the simulation results provided in the paper. This paper addresses issues like dc-link capacitor voltage unbalance for NPC and clamping capacitor voltage unbalance for Flying Capacitor based SAPF and also provides solution. The proposed controller can be easily extended for any multi-level converter topology used for SAPFs.