Harmonic Mitigation in Variable Frequency Drives: 6-Pulse Drive with MTE Matrix AP Harmonic Filter vs. 18-Pulse Drive

The proliferation of variable frequency drives (VFDs) has brought increased attention to harmonic effects created by drives. A standard 6-pulse drive without any harmonic mitigation technology may interfere with neighboring equipment, reduce equipment life, and negatively impact the utility power quality. Under some circumstances the total harmonic current distortion (THID) may approach the level of the fundamental current. Drive manufacturers offer a low harmonic, 18-pulse drive to combat these effects. An alternative solution is the use of a traditional 6-pulse drive equipped with a passive harmonic filter; however, typical passive harmonic filters experience reduced effectiveness at loads less than 100%. With the introduction of adaptive passive technology, the Matrix AP harmonic filter maintains strong harmonic filtering performance across a wide range of loads. This paper compares the performance of a 100 HP 18-pulse drive with the performance of a standard 100 HP 6-pulse drive equipped with a 128 amp Matrix AP harmonic filter. The 6-Pulse drive with Matrix AP harmonic filter outperformed the 18-pulse drive in the following important areas:  Power loss: Approximately 665 less watts consumed.  Overall efficiency: 0.5% more efficient (99.0% vs. 98.5%).  Harmonic performance under balanced line conditions: 1-2% better THID performance for loads 25-75% and equal performance for loads greater than 75%.  Harmonic performance under line imbalance conditions: Significantly better performance. For example under 3% line imbalance, performance was 32.5% better (17.5% vs 50% THID) at 25% load and 13% better (12% vs 25% THID) at 50% load.  Power Factor: Better to equal performance for loads 50-100%.* A 6-pulse drive with a Matrix AP harmonic filter has a number of additional benefits over the 18-pulse drive: smaller equipment size and weight, lower price, and shortened lead time/increased availability of drives and corresponding replacement parts. *The Matrix AP harmonic filter exhibited a reduced leading power factor under light loads. While advantageous in some circumstances, a capacitor contactor option may be used to remove the filter capacitors from the circuit and eliminate this condition.