Abstract—Passive harmonic filter topologies that mitigate harmonic problems in three-phase power system due to low DC bus capacitance of 6-pulse rectifier front end adjustable speed drives are proposed. The first filter topology is the modified typical LLCL harmonic filter with a capacitor added across the input and output reactors of each phase. The second filter topology is also LLCL harmonic filter with a capacitor and damping resistor added in series across the input and output reactors of each phase. Both topologies create high order filters. The filter transfer functions are derived. A prototype was constructed and tested with the results presented. Simulation results correlated well with the prototype test data. The prototype filter for both topologies reduced the total harmonic current distortion (THID) below 5% to meet the limits of IEEE 519.