Generation of Compensating Currents for Shunt Active Power Filter Using DSP TMS320LF2407: A Step Towards Power Quality Improvement

Abstract

Current harmonics, which are injected in the utility by nonlinear loads, cause major problems that tend to deteriorate the power quality at the mains. Nonlinear loads such as adjustable speed drives, switched mode power converters etc. create such har- monics. Conventional measure to eliminate these harmonics is use of passive lters. However, passive lters have the disadvantage of series and parallel resonance within the network impedance, overcompensation of reactive power at fundamental frequency and poor exibility. To reduce such harmonics, Shunt Active Power Filters (SAPF) are commonly employed. The active power lters inject compensating currents into the source to cancel the harmonics contained in the load current. The compensation currents are derived by sensing three-phase voltages at the point of common cou- pling and load currents. Using the Instantaneous Reactive Power Theory (which is also known as P-Q theory) and Fryze Current Computation Technique, the reference compensating currents are derived using appropriate mathematical derivations and calculations. These compensating currents act as reference currents for the current controller block which generate control signals for the Shunt Active Power Filter. Us- ing DSP TMS320LF2407 the proposed algorithms are implemented and compensating currents for the Shunt Active Power Filter are obtained. This DSP is a 16-bit xed point processor which has the capability of executing 40 million instructions per sec- ond which is well suited for performing complex calculations very quickly. Simulation based on the Instantaneous Reactive Power Theory and Fryze Current Computa- tion Technique are carried using Matlab/Simulink. Also a prototype is developed for voltage and current sensing wherein these signals are given to the ADC of the DSP TMS320LF2407. According to the Instantaneous Reactive Power Theory and Fryze Current Computation Technique Theory calculations are performed and results of compensating currents are obtained. The results obtained by experimental work are having very close resemblance with the simulation results. Also the correctness of the proposed technique is proved by subtracting the load current from generated reference currents and it shows the sinusoidal nature of the current. Similar studies are also done in simulation to prove the experimental work.