Analysis and design of some new active power filters for power quality enhancement

To most electrical power engineers, power quality refers to a certain sufficiently high grade of electric service. To power electronic engineers power quality refers to any measure of quality that can be improved through power electronic means. Cost of poor power quality has become an important issue. The typical cost of a power interruption to an automotive assembly is {dollar}250,000 a month until it is corrected. Power interruption to a semiconductor batch processing is {dollar}30,000 to {dollar}1 million per incident. In recent years there has been a steady growth in the use of power electronic equipment, such as, ac/dc motor drives. Their ease of control introduced a large number of nonlinear loads into the power system resulting in increased voltage and current distortions. The failure of sensitive electronic equipment connected to the power system, such as, data processing and process control equipment due to poor power quality caused much concern for power quality. In response to these concerns this dissertation presents the analysis, design and development of some new active power filters. The focus is on three power quality issues and three active power filters to mitigate them. They are, (1)~An active power filter for balancing unbalanced three-phase three-wire loads. (2)~An active power filter for balancing unbalanced three-phase voltages. (3) An active power filter for correcting voltage sags.; The active filter to balance unbalanced loads is based on canceling the negative sequence component of the load currents. The design and selection of various components of the active power filter are discussed. Laboratory level test results are provided to prove the feasibility of the proposed scheme.; The proposed Active Line Conditioner for balancing unbalanced voltages incorporates two novel features, (1) The voltage is balanced by injecting a voltage in only one phase. (2) The volt-amperes required for correcting the unbalance is small and hence is cost effective.; The proposed system is targeted at induction motor loads connected to a weak ac system with frequent supply unbalance. Experimental results on a laboratory prototype active line conditioner are provided to verify the principle of operation.; A third active power filter is proposed to guard sensitive data processing, telecommunication and process control equipment against line voltage sags. Line voltage sags are described in detail and specifications for an active filter are also proposed. The proposed active filter employs a series transformer and a power electronic active filter to respond to voltage sags in the input supply. Experimental results demonstrating the practical feasibility of the proposed approach are provided.