1) Pulse width modulation speed regulation. The input DC adopts diode bridge rectifier with high power factor and high modulation frequency. Generally, the working frequency is set at about 20 kHz. Due to the high frequency, it can not only reduce the noise, but also reduce the volume of filter inductor. At present, there are many kinds of integrated circuits for PWM waveform generator, and the control circuit is simple. But the power devices are controllable electronic devices, such as GTR, MOSFET and IGBT. The overload capacity of these devices is relatively low, and the requirements for trigger drive circuit (DC) are high. The front and back edge of trigger pulse should be steep. At the same time, there should be a fast over-current protection circuit. At present, a variety of intelligent special drive integrated circuits have come out, which have a variety of automatic protection functions, which create favorable conditions for the wide application of DC pulse width speed regulation system.

2) Thyristor rectifier speed regulation. The thyristor has strong overload capacity and works reliably. This is one of the reasons why thyristor DC speed regulation still has vitality. The waveform distortion caused by the change of thyristor conduction angle reduces the power factor of rectifier, especially when the conduction angle is small, the higher harmonic component is large, the current ripple component is large, and a large smoothing reactor is needed. When using three-phase controlled rectifier, it needs three-phase transformer to shift phase synchronously and three trigger pulse forming circuit, so the control circuit is complex. At present, a variety of integrated phase-shift flip flops are available at home and abroad, which improves the reliability of the circuit. Using full control bridge rectifier can improve commutator spark.

Frequency conversion ) adjust speed

The inverter is developing in the direction of large capacity and high performance. Its price and performance can be compared with that of DC drive. At present, it has formed the form of step by step ) The trend of replacing DC drive system.

Its price and performance can be compared with that of DC drive. At present, it has formed the form of step by step ) The trend of replacing DC drive system. At present, the quality of frequency converter is stable, the parameter setting is convenient and flexible, the function is increasing, the performance is improving, and the price is declining ( descend

The trend of replacing DC drive system. At present, the quality of frequency converter is stable, the parameter setting is convenient and flexible, the function is increasing, the performance is improving, and the price is declining ( descend