Research on Improvement of Transmission Capability of Power Supply/Distribution line via Combined Control of an Active Filter-Inverter System

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Injection of reactive power into industrial and power systems has been used for many years in order to ; increase power transmission capability of transmission and distribution systems, regulate and stabilize transmission lines, improve power factor as seen from the terminals of the load (generally to unity), avoid undesirable effects of unbalance operation, flicker, voltage sags, etc. In this research project, there are some interesting contributions to this field as follows :(1) Different control system designs are applied for both shunt and series types of VSI based compensators. Two different control systems designed in a-b-c stationary axis frame and d-q synchronously rotating frame were obtained for both of the connection types in this work.(2) It is demonstrated that reference signal tracking control principle has many application areas from reactive power compensators, to UPFC and motor controllers.(3) With the designed controller of the shunt type, the system is effective also on balancing the supply side current. The Series type controller balances well for the unbalanced load voltage.(4) For designing controllers that can handle unbalanced sags or unbalanced loads, it is necessary to decompose the electrical signals to their positive and negative sequences. This method is the decomposition of the signals in α-β frame.(5) NPC inverters are promising for large capacity power converters. This research contributes for improvement of control algorithm for NPC inverters.In the two years' work, the topics have concerned about different types of reactive power compensation systems, and specifically focused on their control principles and operation performances. In the results, compensators are categorized according to their compensation principles of shunt current or series voltage injection. Research results contribute for stabilizing of power supply system and decrease of high harmonics on the system