Research On Under Actuated Control Method Of Active Power Filter

Three phase six-switch active power filter is considered the most effective devices toimprove power quality. However, reliability of power devices of the six-switch active powerfilter in practical applications is inevitable in the long-running. When short circuit fault ofsome IGBT occurs, the compensation effect of the filter can’t be guaranteed. Even seriousconsequences may be caused. Three phase four-switch active power filter is a fault-toleranttopology circuit of six-switch active power filter after fault reconstruction, and the cost isreduced due to reduced switching device. So four-switch active power filter is of importanttheoretical and practical application value. Since active power filter have similarcharacteristics with mechanical systems, the controller of three phase four-switch filter isdesigned based on the full consideration of the under actuated characteristic. The maincontents include:1) Complex plane is introduced into Lyapunov stability theorem. Based on this andanalyzed in complex plane, a switching control strategy applied to fault tolerant three phasefour-switch APF is proposed. And reasonable DC side voltage is designed which guaranteescontrollability of error current. The whole control system is divided into two separate loops,namely current inner loop and DC voltage outer loop considering DC side voltage changingslower than compensation current. In complex plane, four basic voltage vectors correspondingwith four switch modes determine four vectors of error current changing rate. In current innerloop, first, the angle relationships which is between error current vector and each error currentchanging rate vector are determined, and then DC voltage and switch rules are obtainedaccording to angle relationships.2) For shortcoming of high DC side voltage of three phase four-switch APF, this paperputs forward a new kind of active power filter topology, three phase four-switch hybrid filter.As a result of topology changing, original design of controller which is based on lyapunovand space vector become difficult. Based on Lyapunov method, a controller is designed. Thistopology is composed of the passive filter tuning in seven harmonic and a small capacity ofthree phase four-switch active filter. The passive filter series with four-switch active powerfilter. The hybrid filter not only overcome the shortcomings of passive filter, but alsocombines the advantages of the two kinds of filters. Dc side voltage is steadily maintained in100v, and compensation current can effectively track instruction current.3) First, these methods above are validated by simulation; and then experiment platformis built. Steady state and dynamic state experiment results have also verified the compensation effectiveness in different loads situation. While the compensation effect is a little poorcompared with six-switch APF, the result still meets IEEE Std519-1992standards. Whensome IGBT of six-switch APF breaks down, the system can also compensate harmonicinstead of exiting operation and realize fault-tolerant.