Its compact design is ideal for small- and medium-horsepower applications. 5: Delta VFD-Mĭelta VFD-M is a sensor-less vector micro AC drive. Selection of Delta VFD-M as AC drive Fig. By pulsing the output, we can achieve any average voltage on the output of the VFD. Thus, the average voltage is half of 480V, that is, 240V. Notice that, during the first half-cycle, voltage is on half the time and off the rest. While this would not be practical for plumbing systems, it works very well for VFDs. Imagine, we could control the pressure in a water line by turning the valve on and off at high speed. But if we reduce frequency, we must also reduce voltage in order to maintain V/Hz ratio. If we want to reduce motor frequency, we simply switch the inverter output transistors more slowly. This rectangular waveform would not be a good choice for a general-purpose distribution system, but is perfectly adequate for a motor. Notice that, the output from the VFD is a rectangular waveform. 4: Waveforms at different operating frequencies and average voltages So we can make any phase positive, negative or zero. Thus, we can make any phase on the motor positive or negative at will and can thus generate any frequency that we want. When we close one of the bottom switches in the converter, that phase is connected to the negative DC bus and becomes negative. When we close one of the top switches in the inverter, that phase of the motor is connected to the positive DC bus and voltage on that phase becomes positive. It has become common in the industry to refer to any DC-to-AC converter as an inverter. The converter that converts DC back to AC is also a converter, but to distinguish it from the diode converter, it is usually referred to as an inverter. The diode bridge converter that converts AC to DC is sometimes just referred to as a converter. It absorbs AC ripple and delivers smooth DC voltage. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system.
We can get rid of AC ripple on DC bus by adding a capacitor. This is called a 6-pulse VFD, which is the standard configuration for current VFDs. Thus, we get six current pulses as each diode opens and closes. The same is true for the three diodes on the negative side of the bus. When B phase becomes more positive than A phase, B-phase diode opens and A-phase diode closes. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B- or C-phase voltages, that diode opens and allows current to flow. These allow current to flow in only one direction the direction shown by the arrow in the diode symbol. The first stage of a VFD is the converter, which comprises six diodes, which are similar to check valves used in plumbing systems. We use the 2-wire method for controlling the speed and direction of the motor. A VFD can be used to vary speed, direction and other parameters of a 3-phase motor.
DEVELOP A DOCUMENTED LADDER LOGIC PROGRAM TO IMPLEMENT THE MOTOR CONTROL SERIES
Each drive in its variable frequency drive (VFD) series is designed to meet specific application needs.ĪC drives accurately control torque, smoothly handle increased load and provide numerous custom control and configuration operating modes. Delta’s AC motor drives are able to efficiently control motor speed, improve machine automation and save energy. Often in the industry, need arises for controlling the speed of a 3 Phase Induction Motor. 2: Block diagram of a drive What drives are In the case of 3-phase AC operation, the most-widely-used motor is the 3 Phase Induction Motor as this type of motor does not require any starting device, being a self-starting motor. An extended Intouch wonderware SCADA can be developed also.Īn electrical motor is an electromechanical device that converts electrical energy into mechanical energy.
We use here Delta AC motor drive for its operation.Ī simple control panel is wired using an Allen Bradley PLC for demonstration. Presented here is a robust system for switching on/off, varying the speed and direction of rotation of an industrial 3 Phase Induction Motor using VFD and PLC. Various automation processes in the industry need control of AC induction motors using AC drives.