MODELING AND ANALYSIS OF DISTRIBUTION LOAD CURRENTS PRODUCED BY AN AD JUSTABLE SPEED DRIVE HEAT PUMP
Abstract
A number of demand side management techniques have been proposed for the efficient use of electric power in the commercial and residential sector. The adjustable speed drive heat pump is a technology which has the prospect of decreasing power demands for space heating. This design has the advantage over conventional designs of higher efficiency and, potentially, reduction of peak power demand. Its main disadvantage is higher cost. Further, it has the disadvantage that it produces a load current with a substantial harmonic content. This load current waveform is injected into the distribution system and causes extra losses in the distribution transformer. These high efficiency heat pumps are being promoted by some utility rebate programs to encourage residential customers to install the high efficiency devices. This thesis presents an introduction to adjustable speed drives as they are applied to the refrigeration cycle. The impact of these devices on distribution transformers and the significant transformer derating is discussed. In addition, an Advanced Continuous Simulation Language, (ACSL), simulation is presented that models the induction motor, six step adjustable speed drive, and distribution transformer. The results of this simulation are presented1 to show typical system waveforms, such as the load current and its frequency spectrum. These waveforms are compared to results obtained from an actual installation. In addition, the ANSI Standard C57.110 is used to assess the transformer derating. The main contribution of the thesis is the presentation of a detailed method for the analysis of adjustable speed drive heat pump loads. General conclusions are drawn concerning the appliciability of the high efficiency, adjustable speed drive heat pump including the added losses in the distribution system.
Date of this Version
December 1993