1, the use of inverter operation, the motor starting current, starting torque how?
Adopting frequency converter to operate, the starting current is limited to 150% of rated current (125% ~ 200% according to different models) as the motor accelerates correspondingly to increase the frequency and voltage. With the power frequency direct start, the starting current of 6 to 7 times, therefore, will have a mechanical and electrical impact. Driven by the inverter can be smoothly started (start-up time longer). The starting current is 1.2 ~ 1.5 times of the rated current, and the starting torque is 70% ~ 120% of the rated torque. For the inverter with automatic torque increasing function, the starting torque is more than 100% and can be started with full load.
2, V / f mode is what does this mean?
The voltage V decreases proportionally as the frequency drops, as explained in answer 1. Maintaining V / f ratio constant control is the most basic control method of induction motor speed control. It controls the voltage output by the inverter while controlling the power frequency of the motor, and makes the ratio V / f constant so that Keep the flux of the motor constant. Under rated motor operation, the voltage drop of the stator resistance and leakage reactance of the motor is relatively small, and the terminal voltage of the motor and the induced potential of the motor are approximately equal.
The main problem with V / f ratio control is poor low speed performance. The reason is that the proportion of stator resistance voltage drop in asynchronous motor becomes larger at low speed and can not be neglected. It can not be considered that the stator voltage and motor induced potential are approximately equal, and the motor flux can not be kept constant by V / f ratio control. The decrease of the flux of the motor will inevitably lead to the reduction of the electromagnetic torque of the motor. In addition, the dead time of the power device of the frequency converter is also an important factor that affects the low speed performance of the motor. The voltage drop caused by the dead time also causes the torque ripple. Conditions will also cause speed, current oscillation.
V / f ratio constant control commonly used in general-purpose inverter. This type of inverter is mainly used for fan, pump speed control functions, and less demanding on the speed range of the occasion. The outstanding advantage of V / f ratio control is that it is possible to control the motor’s open-loop speed.
3, in proportion to change V and f, how the motor torque changes?
If the frequency decreases completely and the voltage is reduced proportionally, then the resistance will not change due to the smaller AC impedance, which will cause the torque generated at low speed to decrease.
Therefore, given low frequency V / f, to make the output voltage increase in order to obtain a certain starting torque, this compensation said enhanced start. Various methods can be used, there are automatic methods, select V / f mode or adjust the potentiometer and other methods.
4, What is the meaning of open loop?
To the motor used to install speed sensor, the actual speed feedback to the control device for control, called “closed loop” without speed sensor operation is called “open-loop”, general-purpose inverter is mostly open-loop.