Phase-orthogonal FIR filter based reactive power measurement for power meters

In filter based reactive power measurements, the voltage is phase shifted by 90∘ relative to the current. This paper presents a technique of measuring reactive power based on differential 90∘ shifter. According to this method, the sampled voltage and the current signal passes through a pair of FIR filters that shifts +45∘ and −45∘. Then, the two outputs are multiplied to measure the reactive power. A pair of FIR filters that are having identical flat magnitude responses and orthogonal phase responses are designed. Multiplier-less FIR structure is adopted for hardware implementation to reduce the chip area cost making the technique implementable in digital power meter. A detailed hardware architecture and its implementation in FPGA is presented. Furthermore, the measurement of reactive power for various frequencies between 50 and 250 Hz is also presented.