Fourier Based Three Phase Power Metering System

Scott C. Smith, Missouri University of Science and Technology
M. J. Devaney

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The increased application of higher frequency nonlinear loads, such as electronic fluorescent ballasts and higher speed adjustable drives, has resulted in the need to monitor the higher power system harmonics which were largely ignored in earlier power monitors. Addressing this need requires a meter with substantially higher sample rate and greater computational power. This paper describes a zero-blind, three-phase, three-element power meter that samples three voltages and four currents at 256 points per cycle. The instrument relies on the FFT to compute real and reactive power at each harmonic and reports total real, reactive, and distortion power on each phase. The innovative design is based on a multiprocessor chip which incorporates a DSP for acquisition and point metering, a CISC processor for floating point summary data, and a RISC processor for interface to support communications with the host PC. The paper concludes with a system evaluation on highly distorted industrial power system waveforms.