Field measurements and modeling of harmonic distortion caused by distributed single-phase ASD heat pumps

Power electronic loads such as adjustable-speed drives (ASDs), AC/DC power supplies, light dimmers, and electronic ballasts offer the advantages of increased efficiency and controllability. As a result, many conventional loads such as motors and incandescent lamps, which draw nearly sinusoidal currents, are being converted to power electronic loads. This paper focuses on the harmonic distortion that could result from the proliferation of one type of large power electronic load-the residential single-phase ASD heat pump. This device offers much higher efficiencies than conventional heat pumps and air conditioners because the compressor operates over a wide speed range to match load requirements while avoiding thermal cycling. As do other power electronics loads, however, most ASD heat pumps (but not all) have high current distortion levels. This paper is divided into two parts. First, the results of harmonic field measurements taken at two electric utility companies are summarized. Second, a distribution substation and its connected feeders are simulated with an electrical circuit analysis computer program to predict voltage distortion levels as the percentage of ASD load increases. The simulation results confirm that unfiltered ASD heat pumps have the potential to cause high distortion levels in power systems.