The series resonant voltage withstand device is mainly composed of a frequency converter controller, an excitation transformer, a high-voltage reactor, a high-voltage divider, etc. Its principle is to use the series resonant principle, and the excitation transformer of the frequency series resonant output circuit is used to excite the frequency. The controller adjusts the series resonant frequency of the test circuit inductance L and C, and the resonant voltage is the voltage applied to the test strip. The technology of variable frequency system controllers can be divided into two categories: desktop control environment for 20KW and above, and portable box type for 20KW and below; It can be composed of a controller and a filter.

Variable frequency speed regulation and energy-saving of fan and pump: There are various methods for adjusting the flow rate of fan and pump, each with its own characteristics, but they can be summarized into three types:

(1) Conventional  mechanical  methods  for  adjusting  the  valve  opening  of  the  fan  baffle,  deflector,  and  pump;

(2) Using traditional electromagnetic differential clutch or hydraulic mechanical coupling to regulate and control the speed of the fan system water pump (while the electric motor runs at a constant speed);

(3) Control scheme for AC motor frequency.

Variable frequency speed regulation and soft start and soft stop: that is, the power grid and production process require motor soft start and soft stop:

1) The starting current of an AC motor is generally 5-7 times the rated working current. If it can be started directly, it will cause an impact on the national power grid and affect the normal and economic operation of other electrical engineering equipment on the same power grid for enterprises. In addition, the huge starting current can cause serious electromagnetic and mechanical stress on motors and mechanical equipment, shortening the service life of the equipment. Therefore, power systems hope to have soft starting (especially for high-voltage and high-capacity motors).

2) Some processing machines, such as automatic production lines (bottles, cans, conveyors, etc.), are designed to start and stop smoothly in order to avoid collisions and mutual reverse tilting; Pump to prevent water hammer, vibration, soft start and soft stop.