What is the difference between AC variable frequency speed control and DC variable frequency speed regulation?
AC variable frequency speed regulation, change the number of poles of the motor, characterized by fixed gear, that is, high and lowDC speed regulation is the first to AC shaping into DC, and then through the controllable inverter back to AC, characterized by speed range, but because of plastic, inverter will have a conversion efficiency problem.For example, AC speed range is 100%, 70%, 40% speed, 3 gear,DC speed regulation range of 30%~100% can be stepless speed regulationThen in 100%, 70%, 40% the third near operation, energy efficiency than AC DC, but when the compressor only needs 55% when operation meet the requirements, at this time also with the speed of 70% AC, DC inverter operation, energy consumption will not pay the small flow
Reason of brush and volume of DC motor, limits its scope of application, can be said to be a variable speed fan and pump development, is due to the need of fan and pump energy saving, variable frequency speed regulation is the best choice, but I personally think that compared to the current price and the price of this inverter, energy saving is meaningless, because the inverter investment back, at least 5-6 years, in the 5-6 years, conditions also do not know what happens.
AC variable speed DC speed is widely used because the ratio of AC motor, not the principle of frequency conversion has the advantage of frequency control can only be applied to control, and the torque is unable to achieve precise control, the reason is very simple, the DC motor armature and field is coupled, are separated, such of armature current and exciting current to achieve accurate control. The AC speed control, armature current and exciting current is coupled, is unable to achieve precise control, although the frequency current vector control, which is based on the modern control theory, through the vector transformation, the armature current and exciting current coupling in AC motor solutions, in order to control, which is the principle of simulation DC speed regulation. But it is difficult to control the DC speed. Therefore, in the rolling mills, paper and other requirements of the high torque industry, DC speed control is still widespread. And only for speed control, at present, variable frequency speed regulation can be realistic DC speed control characteristics, because the advantages of AC motor is DC motor can not do.
