What controls the speed on an electric motor is an AC drive, which changes the frequency of the electrical supply to the motor. A rotating magnetic field is then produced through the three-phase voltage coming from the electrical grid. As the rotor follows such a magnetic field, an energy is created which powers the motor. The motor speed is controlled in proportion to the frequency of the network, which can be anything between 300Hz or more. So, what comprises an AC drive that makes it able to control motor speed? Here are the three major technologies behind it all.
DC Circuit
The key function of the DC circuit of an AC drive is to store the electrical energy in a high-power capacitor in the rectifier unit. This stored energy will then be reserved for the inverter to utilize.
The Rectifier Unit
This part of the drive is what receives the electrical energy coming from the network and comes either as unidirectional or bidirectional. If working in a unidirectional system, the drive can increase its speed and operate the motor by supplying it with the electrical energy coming from the electrical network. Conversely, an AC drive that operates in a bidirectional system takes the mechanical energy produced by the motor itself and feeds it back to the electrical supply.
The Inverter Unit
As the name suggests, the inverter unit works by taking the electrical energy stored in the capacitor and feeds it to the motor to run. The unit employs a modulation technique in order to produce the required three-phase AC voltage needed by the motor. It is through this process that the AC drive can adjust the frequency to match the requirement of the entire process. This is why it is also called the frequency variable drive. The rule of thumb is the higher the frequency of the voltage is, the greater the motor speed, and so is the process output.
Kommentare