An analog harmonic analyzing meter using PLLs

In general, the harmonics in a power system are measured with a heterodyne receiver if one is using analog methods or by a FFT (Fast Fourier Transform) when digital methods are being used. The harmonics can be analysed over a wide range of frequencies by means of these methods. However, since the circuit configurations that are needed can become very complicated, the equipment tends to be too expensive for practical use. This paper presents a novel harmonic meter using a PLL (phase locked loop) circuit. By means of the phase feedback loop, a reference sinusoidal wave is locked on to the input signal along with the harmonics that one wishes to measure, and hence the corresponding harmonic component in the input signal is easily detected. The effectiveness of the proposed harmonic meter is confirmed by experiment