Harmonic Mitigation Using Unified Power Quality Conditioners and Hybrid Active Power Filters

The power quality issues are of great concern now a days. The increasing use of power electronic devices based nonlinear loads deteriorate the quality of power. Power electronic appliances are widely used in industrial, commercial and utility system thus leading to various power quality problems. This leads to harmonics being injected into the distribution system and also reactive power burden. Power electronic devices based custom power devices can be used to mitigate these power quality problems. Some of these custom power devices are DSTATCOM, Dynamic voltage restorer(DVR), unified power quality conditioners(UPQC), and filters. In this paper the power quality improvement is done by mitigating harmonics using the custom power devices like UPQC and Hybrid active power filters(HAPF). UPQC consists of combination of series and shunt active filters. Series filter inject voltage which gets added at the point of common coupling and hence the voltage at the load end gets unchanged with the voltage disturbances. Shunt active filter compensates the load reactive power demand and hence mitigates the harmonics from supply current and also maintains the DC link voltage. The other custom power device discussed in this paper is hybrid active power filter. Hybrid active power filter is the combination of passive and active filters. Passive filters are LC tuned filters used for the harmonic mitigation but are bulky and has compensation problem. Active filters are effective in harmonic mitigation but its cost increases with higher ratings. Hence M. Sharanya et al 122 hybrid active filter provides cost effective harmonic mitigation solution. The active filters are designed using IGBT based switches and are controlled by using PI controllers. Simulation is done using MATLAB/SIMULINK environment and the results show that both these custom power devices, UPQC and HAPF reduces the harmonics. The total harmonic distortion (THD) values by this control method is reduced to less than 5% as per IEEE standards. The proposed controls scheme provides better steady state and dynamic responses.