There is always a contradiction between the power supply system and the power-using equipment: the power-using equipment requires uninterrupted, transient-free, pure sine-wave AC power supply and pulsation-free, transient-free DC power supply; while the power supply system expects the power-using equipment to be a constant load, which should not result in voltage waveform distortion due to the fluctuation of the load. For ordinary small appliances, even if they stop working under the influence of fluctuations in the power supply system, it will not cause too much damage. However, for public transportation such as airplanes and ships, the stability of the electrical system should not be taken lightly.