The arrival of advanced microprocessors has allowed the VFD works as an extremely versatile device that not only controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide methods of braking, power boost during ramp-up, and a variety of controls during ramp-down.
The biggest savings that the VFD provides is that it can ensure that the motor doesn't pull excessive current when it starts, so the overall demand factor for the entire factory can be controlled to keep the utility bill as low as possible. This feature alone can provide payback in excess of the price of the VFD in less than one year after purchase. It is important to remember that with a traditional motor starter, they will draw locked-rotor amperage LRA when they are starting.
When the locked-rotor amperage occurs across many motors in a manufacturing plant, it pushes the electrical demand too high which often results in the plant paying a penalty for all of the electricity consumed during the billing period.
Today the VFD is perhaps the most common type of output or load for a control system. As applications become more complex the VFD has the ability to control the speed of the motor, the direction the motor shaft is turning, the torque the motor provides to a load and any other motor parameter that can be sensed.
Newer VFDs have a variety of parameters that can be controlled by numbers programmed into it or downloaded from another microprocessor-controlled system such as a programmable controller PLC. These VFDs are also available in smaller sizes that are cost-efficient and take up less space.
The block diagram of a typical VFD can be divided into three major sections: the power-conversion section the microprocessor control section CPU and the control section that includes the external switches an signals to control the VFD operations the power section where AC voltage is converted to DC and then DC is inverted back to 3-phase AC voltage The block diagram below contains three separate sections to indicate the basic working principle of a VFD: the rectifier the filter the switching section that uses regular transistors, darlington pair transistors, or insulated gate bipolar transistors IGBT to invert the DC voltage back to AC voltage with the proper frequency.
VFD connect to standard AC induction motors, and have capabilities of adjustable speed, torque, and horsepower control similar to the principles of DC drives. AC induction motor speed depends on the number of motor poles and the frequency of the applied power.
The number of poles on the stator of the motor could be increased or decreased, but this has limited usefulness. Although the AC frequency of the power source in the China is fixed at 50 Hz, advances in power electronics make it practical to vary the frequency and make the induction motor working at different speed.
Three phase motors are usually preferred, but some types of single phase motors can be used with single phase variable frequency drives. So what exactly is a VFD? Well, it stands for Variable Frequency Drive. Some people simply call them drives. VFDs work by adjusting the frequency of the motor to adjust the rpms. This is accomplished with diodes.
A check valve, like a diode with electricity, only allows water to flow in one direction. The capacitor acts as a water filter to keep everything clean and useable. The operator can monitor water flow and manually adjust the VFD accordingly. As always, be sure to check back soon for more RealPars videos and blog posts! Thanks for reading and sharing our blog posts with your friends and colleagues. The RealPars Team. Search for:. By Kevin Cope. As for the setup, VFDs are wired in a series between the motor and the main power source.
Lower energy consumption and therefore lower energy costs is one of the reasons VFDs attract commercial property owners and HVAC professionals. To date, there are no other methods you can use for AC electric motor control that can do the same. In other words, more money in your pocket. When airflow needs decrease, the VFD consumes less energy.
The efficiency of HVAC systems will make it easier to operate machinery, such as conveyors and belts. No more jerking during startup or other costly mistakes that can slow down production. VFDs help to optimize motor application speed, which, in turn, helps equipment last longer and reduces maintenance requirements.
The VFD offers protection to the motor because it controls the frequency and voltage, which can provide phase protection and prevent :. Screenshot via ControlDesign. How ferries in Amsterdam use VFDs to run on battery power.
All these names refer to the same kind of devices, also known AC variable speed drives, AC variable frequency drives, VFD inverters or variable voltage variable frequency drives. There are many diverse types of drives available since they are widely used in industry. The differences in drive types include the methods used for frequency and voltage control; and harmonic mitigation technology. Learn more about harmonic mitigation solutions from Danfoss Drives.
The three major variable frequency designs used in drives are pulse-width modulation PWM , current source inverter and voltage source inverter. The PWM technique is the most common. Controlling and varying the width of the pulses is how PWM varies the output frequency and voltage to achieve VFD control. Tap into the knowledge center to learn more about optimizing system efficiency with VFDs.
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