Principle of frequency conversion control of high pressure fan

Due to the high power of high voltage equipment. Its power may account for a significant portion of the grid's capacity, so its shutdown and operation may affect the supply voltage. In addition, if the inverter output high harmonic components are too high, it will cause overheating of the motor, causing common mode voltage and drV mountain. In order to realize the speed regulation and energy-saving operation of the fan, and considering the technical requirements of the high-voltage and large-capacity equipment, the unit series multi-level high-pressure fan variable frequency speed control system is designed.

Each power unit is powered by a set of secondary windings of the input transformer, and the power units are insulated from each other between the secondary windings of the transformer. If six phases are connected in series per phase, each power unit is subjected to the full output current, but only withstands 1/6 of the output phase voltage and 1/18 of the output power; for a 6 kV motor system, the output voltage per cell is 590V. Adjustable, the frequency is adjustable at 050Hz, which enables constant voltage-to-frequency ratio control.

Each level step has only a unit DC bus voltage and is therefore small. The motor insulation is not affected. The power unit uses a lower switching frequency. In order to reduce the switching loss, and without the surge absorbing circuit, the efficiency of the inverter can be improved. Due to the multi-transmission phase-phase PWM technology, the equivalent output switching frequency is high, and the number of output levels is increased, which can greatly improve the output waveform, reduce the output harmonics, and cause motor heating caused by harmonics.

Both noise and torque ripple are greatly reduced. Therefore, this type of frequency converter has no special requirements for the motor and can be used for ordinary high-voltage motors without derating. Since the output is low, there is no problem that the insulation voltage of the inverter is increased due to the surge voltage caused by the reflection of the traveling wave when the output cable is long, so there is no particular limitation on the cable length between the inverter output and the motor.

The frequency converter has low harmonic pollution to the power grid, high input power factor, and does not need to adopt the input harmonic filter and power factor compensation device; the output waveform is good. There are no advantages of additional heating and torque ripple, noise, output dxvd, common mode voltage, etc. caused by harmonics.