FPGA Based Active Power Filter for Harmonics Mitigation

The application of power electronics devices such as arc furnaces, adjustable speed drives, computer power supplies etc. are some typical non-linear characteristic loads used in most of the industrial applications and are increasing rapidly due to technical improvements of semiconductor devices, digital controller and flexibility in controlling the power usage. The use of the above power electronic devices in power distribution system gives rise to harmonics and reactive power disturbances. The harmonics and reactive power cause a number of undesirable effects like heating, equipment damage and Electromagnetic Interference effects in the power system. The conventional method to mitigate the harmonics and reactive power compensation is by using passive LC filters but this method has drawbacks like large size, resonance problem and fixed compensation behaviour etc., so this solution becomes ineffective [7]. Subsequently, the active power filter (APF) comes in to the picture, which gives promising solution to compensate for the above adverse effects of harmonics and reactive power simultaneously by using suitable control algorithms. Different APF topology has proposed by many authors, such as series, shunt and hybrid type and these may be based on current source or voltage source. Series APF is used to compensate the voltage harmonics and shunt type for current harmonics. As non-linear loads are injecting current harmonics to the power system, the suitable choice to eliminate current harmonics and reactive power is voltage source shunt APF. To extract the fundamental component of source current synchronous reference frame (SRF) theory [12] is suitable because of its easy mathematical calculation compared to p-q (Instantaneous theory) control algorithm. Further, switching signals to drive the VSI of the APF two popular control strategies namely hysteresis current controller (HCC) and adaptive hysteresis current controller (Adaptive- HCC) are used. Also fuzzy logic controller is used generate the reference current and maintain the DC side capacitor voltage almost constant. A comparative study of the performances of two current control strategies HCC and Adaptive-HCC is carried out in this thesis and it has been observed from simulation results that AHCC exhibits superior performance compared to the HCC. These current controllers have some disadvantages such as high cost, slow response, and large size etc., during real-time implementation. But by using digital controller one can avail the advantages like reconfigurable hardware designs, low cost developments, selection of bit width according to applications etc. In this thesis, a PI current control algorithm together with a hysteresis current controller is written in VHDL code and then is implemented using FPGA platform