Under frequency/under voltage detection in a demand response unit

摘要

A demand response unit (DRU) interposed between a utility's electrical power line (PL) and at least one load (L1-Ln) to which power is supplied by the utility over the line. A detector (Fdet or Vdet) measures a characteristic (frequency F, voltage V) of an electrical waveform (W) by which power is transmitted by the utility to the load. The detector determines both when the measured frequency or voltage exceeds a predetermined threshold for a first predetermined period of time; and, if the threshold is exceeded, when the frequency or voltage exceeds the second predetermined threshold for a second predetermined period of time. For this purpose, the detector processes a predetermined number of intervals of the waveform and produces an average value of the characteristic which is compared to the threshold. This is done to reduce the effect of extraneous events which may temporarily change the value of the frequency or voltage. A power control (PC) is responsive to an output from the detector to, at least, partially interrupt flow of power to the load during the period of time when the measured frequency or voltage exceeds the threshold, thereby to reduce the load on the utility.

主权项

1. A demand response unit (DRU) interposed between a utility's electrical power line and at least one load to which power is supplied by the utility over the line, comprising:
at least one detector measuring a characteristic of an electrical waveform by which power is transmitted by the utility to the load, the detector determining when a value of the measured characteristic exceeds a predetermined threshold for a first predetermined period of time, and if the threshold is exceeded, when the measured value exceeds a second predetermined threshold for a second predetermined period of time, and the detector processing a predetermined number of samples acquired during each cycle of the waveform to produce an average value of the characteristic which is compared to the threshold thereby to reduce the effect of extraneous events which may temporarily change the value of the measured characteristic, successive samples acquired for processing not being acquired at the same phase location on the cycle of the waveform during which they are acquired; and, power control means responsive to an output from the detector to at least partially interrupt flow of power to the load during the period of time when the measured value exceeds the predetermined threshold thereby to reduce the load on the utility.