The quality of power quality directly affects the quality of industrial products. There are three standards for evaluating power quality. The first is voltage, which includes voltage fluctuation, voltage offset, voltage flicker, etc; The second is frequency fluctuation; Finally, the quality of voltage waveform, that is, the symmetry of three-phase voltage waveform and the distortion rate of sine wave, that is, the proportion of harmonics. China has clear standards and specifications for the three aspects of power quality.

With the development of science and technology and the improvement of industrial production level and people's living standards, a large number of nonlinear electrical equipment are put into operation in the power grid, resulting in an increasing proportion of harmonic components in the power grid. It not only increases the power supply loss of the power grid, but also interferes with the normal operation of the protection devices and automation devices of the power grid, resulting in the misoperation and refusal of these devices, which directly threatens the safe operation of the power grid.