Application of dominant harmonic active filter system with 12 pulse nonlinear loads

Twelve pulse rectifier loads are widely used for high power applications such as large rated dc drives and ac drives, and for large rated dc power supplies. Harmonic filtering is required for 12 pulse rectifier-utility interface to meet IEEE 519 harmonic current limits. Passive filter techniques employ tuned L-C filters at dominant llth and 13th harmonic frequencies. However, they also require 5th and 7th tuned filters to avoid series and parallel resonance conditions. State of the art active filtering solutions require high bandwidth and relatively large rating PWM inverters for harmonic filtering of 12 pulse rectifier loads. Thus existing passive and active harmonic filtering solutions are not cost-effective for high power 12 pulse rectifier loads. Dominant Harmonic Active Filter (DHAF) based on square-wave inverters is proposed to cost-effectively meet IEEE 519 harmonic current limits for 12 pulse rectifier loads. The proposed DHAF system employs square-wave inverters switching at 5th and rth harmonic frequencies, which are transformer coupled in series with llth and 13th passive filters respectively. The square-wave inverters are controlled to provide ‘harmonic isolation’ between the supply and load at 5th and 7th harmonic frequencies. The square-wave inverters are rated 1% - 2% of the load kVA rating. The proposed DHAF system eliminates the need for large kVAR rated and bulky gth and 7th passive filters, delivers superior harmonic filtering performance, and provides cost-effective harmonic filtering solution. Simulation results are given to validate the ‘harmonic isolation’ feature at 5 t h and 7 t h harmonic frequencies, and also demonstrate harmonic filtering required to meet IEEE 519 harmonic current limits.