本文讲的是伏特每赫兹控制和vfd与通量矢量控制，每赫兹伏特法是最简单的驱动控制方法。VFD的输出电压与输出频率之比为常数。利用这种方法，可以通过改变电机磁链的频率来调节电机转速。因此，扭矩对速度的特性类似于单独励磁直流电机(理想的标准)可以实现。大多数vfd的V/f比是恒定的。V/f控制在电源频率低于3hz时性能较差。即在频率低于3Hz时，电机的启动力矩不够。本篇代写论文价格文章由英国论文时Essay Times教育网整理，供大家参考阅读。
Volts-per-Hertz method is the simplest drive control. The ratio of the output voltage and output frequency of VFD is constant. Using this method, motor speed can be regulated by varying the supply frequency with a constant motor flux. Therefore a torque vs speed characteristic similar with that of a separately excited DC motor (ideal standard) can be achieved. Most VFDs operates with a constant V/f ratio. V/f control has poor performance at the supply frequency lower than 3 Hz. That is that the motor starting torque is not enough at frequency lower than 3Hz.
But for most cases, the starting torque is acceptable. Thus, this type of drive control is suitable for many simple applications.There are two types of flux vector control: closed loop vector control and open loop vector control.Closed loop vector control is also called flux vector control with speed sensor.In a flux vector drive, a sensor is used. It is installed on the motor shaft. The microprocessor in the VFD gets feedback from the sensor. The exact vector algorithm of voltage and frequency can be processed in the microprocessor. Therefore, the VFD can produce any required speed or torque which solves the deficiency of basic V/f drive.
Open loop vector control is called open loop vector control as well.In this control method, feedback information is obtained from the current transducers in the VFD instead of an external speed sensors. The performance is better than basic V/f control, but not good as closed loop vector control.For an open loop vector drive, the reduced performance will occurs when the frequency is lower than 1Hz.
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