![]() The bridge uses capacitors to maintain consistent DC voltage, as well as storing energy for the drive system. The difference is that the VSI uses a diode bridge rectifier to achieve the conversion. Voltage Source Inverter (VSI) conversion functions similarly to that of the CSI – converting incoming AC to DC voltage. Symmetrical Gate-Commutated Thyristors (SGCT). ![]() The CSI converts incoming AC to a variable DC voltage using: Current Source Inverter (CSI)Ī Current Source Inverter (CSI) converts the incoming AC voltage as well as controlling the frequency and voltage that supplies the AC Induction Motor. The sections of a VFD include a Converter, DC Link, and Inverter. Variable Frequency Drives (VFDs) come in three basic types: The inverter converts the DC voltage back AC as output at the desired frequency. There are three main components of an AC Speed Controller:ĪC input is converted to DC by a rectifier. This adjustable output allows precise control of motor speed. The AC Motor receives power with a varying frequency generated by the AC Controller. AC Motor Speed ControllerĪn AC Controller controls the speed of the AC Motor is also be referred to as a Variable Frequency Drive (VFD), Adjustable Speed Drive (ASD), and Frequency Converter (FC). An AC induction motor will be damaged if the incoming supply voltage varies significantly. The VFD performs two functions: First, it converts the incoming AC signal to a DC signal by rectification secondly it inverts the rectified DC signal back to a variable frequency AC signal.Ī DC motor could have its speed changed by increasing or decreasing the applied voltage. Because the number of poles in a machine is fixed, the only variable that’s left to change is the incoming line frequency - this is the basis for the operation of a motor speed controller known as the Variable Frequency Drive (VFD). This difference in speed is called the slip and is usually expressed as a percentage. In the field, however, as the load is applied to the motor it will run at less than 1,800 rpm. Since in the United States, the AC line frequency is 60 Hertz at 120 Volts, therefore an AC induction motor with four poles would have a synchronous speed of 1,800 rpm. The synchronous speed (S) of a motor is defined as S = 120(F) ÷ P, where (F) is the incoming line frequency, and (P) is the number of poles in the motor. The speed of the rotating magnetic field is referred to as synchronous speed. The AC induction motor is essentially a constant speed device. Wherever any machines use electric motors some type of motor speed control is invariably part of that machine. There is a wide range of appliances that are part of our lives, from household electrical appliances used in the home like vacuum cleaners and hair dryers to pumps, conveyor belts, and machine tools in large industrial plants.
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