A Decentralized Control Scheme for Multimodular Shunt Active Harmonic Filters

In high-power industrial installations, instead of a single shunt active harmonic filter (SAHF), parallel-connected multiple modular units of SAHF having lower current rating are generally preferred. In order to ensure that these modules share the compensating current in proportion to their individual current ratings, an intermodular communication network is generally being employed. This intermodular communication network reduces the overall reliability of the system, and it can be avoided if every individual module can autonomously estimate the compensating current to be shared by it. In case of voltage-source inverters operating in parallel, a droop-based current control scheme is generally employed to achieve the aforesaid requirement. However, in the SAHF, the inverters are operated in the current control mode, and hence, the existing droop-based control scheme needs appropriate modification. In this article, a modified droop-based scheme is proposed for a multimodular SAHF operating in the current control mode. The principle of operation of the proposed control scheme and its detailed mathematical analysis are presented. The feasibility of the scheme is verified by performing detailed simulation studies. A laboratory prototype having two SAHF modules, each having a VA rating of 30 kVA, is fabricated. Detailed experimental studies are carried out utilizing the laboratory prototype to confirm the viability of the proposed scheme.