Kinco Automation carries a broad line of rugged AC Variable Frequency Drives for OEM and Industrial applications, combining high performance and cost efficiency into one powerful package. Available in input voltages of 120V and 240V and capable of powering AC motors from 0.25 to 30Hp, these VFDs are great for normal duty and soft-start operation. These drives provide energy savings and increased efficiency, making them ideal for fan, pump, and HVAC applications. They are equipped with a number of different features such as momentary power loss restarts, flying starts, auto-acceleration/deceleration, and sensorless vector control. These features make the VFDs compatible with most AC motors and allow for flexibility within an application. If you require assistance in selecting the appropriate VFD for your application, please contact an Anaheim Automation Applications Engineer, we are happy to help.

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Frequently Asked Questions

What are the components of a Variable Frequency Drive?

In Variable Frequency Drives (VFDs), each component is responsible for carrying out a particular task in order to operate a Three Phase AC Induction Motor. The components that make up a VFD are a Rectifier (Diode Bridge), DC Link and an Inverter.

Rectifier - This part of the drive uses a full wave rectifier (diode bridge) to convert both the positive and negative signal of an AC Voltage into a pulsating DC Voltage.

DC Link - This part of the drive filters the pulsating DC Voltage into a fixed DC Voltage value. A DC Links main component is a capacitor. The capacitor smooths out the rippling voltage and converts it into a fixed DC Voltage Line.

Inverter - This part of the drive changes the fixed DC Voltage to an adjustable AC Voltage and frequency of the PWM waveform. Various methods can be implemented in this section of a VFD such as IBGTs, SCRs and Control Logic (microprocessor) to name a few.

Which motor is typically applied to a Variable Frequency Drive (VFD)?

The typical AC electric motor used with Variable Frequency Drives (VFDs). The AC electric motor used with VFDs is a three phase motor. Only some types of single phase electric motors may be used, but three phase electric motors are preferred for optimum performance.

What is the difference between a Variable Frequency Drive and a Variable Speed Drive?

Variable Frequency Drives (VFD) typically refers only to an AC drive, while Variable Speed Drives (VSD) can pertain to either an AC or DC drive. VFD's can change the speed of an AC three phase induction motor by varying the frequency. On the other hand, VSD's change the speed of DC electric motors by varying the voltage.

What is a Variable Frequency Drive (VFD)?

When an Induction Motor is operated by a constant frequency power source of 50 or 60 Hz, the motor speed is fixed. However, by using a variable frequency drive (VFD) the speed of the AC motor can be changed. Variable Frequency Drives (VFDs) able to vary the frequency and voltage applied to the motor therefore controlling the motor speed. Furthermore, not only does the VFD vary the frequency but also regulates the output voltage in proportion to the frequency to allow for a constant voltage to frequency (V/Hz) ratio. This ratio allows the AC Induction motor to provide adequate torque and prevent excess energy waste.

What types of Variable Frequency Drives (VFDs) are there?

There are three common Variable Frequency Drives (VFDs) that offer both advantages and disadvantages depending on the application they are used for. The three common VFD designs used include: Current Source Inverter (CSI), Voltage Source Inverter (VSI), and Pulse Width Modulation (PWM). However, there is a fourth type of VFD called Flux Vector Drive, which is emerging in popularity among end-users for its closed-loop control feature. Each VFD consists of a Converter, DC Link and Inverter section but how each one is constructed varies from drive to drive. Although the sections of each VFD are similar, they require a variation in circuitry in how they supply the frequency and voltage to the motor.

What is a Current Source Inverter (CSI)?

A Current Source Inverter (CSI) is a type of variable frequency drive (VFD) which converts incoming AC voltage and varies the frequency and voltage supplied to the AC Induction Motor. The general configuration of this type of VFD is like that of other VFDs in that it consists of a Converter, DC Link, and Inverter. The converter part of the CSI uses silicon-controlled rectifiers (SCRs), gate-commutated thyristors (GCTs) or symmetrical gate-commutated thyristors (SGCTs) to convert the incoming AC voltage to a variable DC voltage. In order to maintain the correct voltage to frequency (Volt/Hertz), the voltage must be regulated by the correct sequencing of the SCRs. The DC Link for this type of variable frequency drive uses an inductor to regulate the current ripple and to store the energy used by the motor. The inverter, which is responsible for converting the DC Voltage back to an AC sine-like waveform, comprises of SCRS, gate turn-off thyristors (GTOs) or symmetrical gate-commutated thyristors (SGCTs). These thyristors behave like switches which are turned on and off to create pulse width modulation (PWM) output that regulates the frequency and voltage to the motor. CSI variable frequency drives regulate current, require a large internal inductor and a motor load to operate. An important note about CSI VFD designs is the requirement of input and output filters which are necessary due to high harmonics in the power input and poor power factor. To work around this issue, many manufacturers implement either input transformers or reactors and harmonic filters at the point of common coupling (users electrical system connected to the drive) to help reduce the effects harmonics have on the drive system. Of the common VFD drive systems, CSI VFDs are the only type of drives that have regenerative power capability. Regenerative power capability means that power is driven back from the motor to the power supply can be absorbed.

What are some of the advantages and disadvantages of a Current Source Inverter (CSI)?

Some of the advantages of CSI Variable Frequency Drives (VFDs) are:

  • Regenerative power capability
  • Simple circuitry
  • Reliability (Current Limiting Operation)
  • Clean current waveform

  • Some of the disadvantages of CSI Variable Frequency Drives (VFDs) are:

  • Motor cogging when PWM output is below 6 Hz
  • Inductor used are large and costly
  • Large power harmonic generation sent back into power source
  • Dependent on motor load
  • Low input power factor

  • What is a Voltage Source Inverter (VSI)?

    Another type of Variable Frequency Drive (VFD) is the Voltage Source Inverter. As in most Variable Frequency Drives (VFDs) the converter section of the VSI is similar to the converter section of the CSI in that the incoming AC Voltage is converted into a DC Voltage. The difference from the CSI and VSI converter section is that the VSI uses a diode bridge rectifier to convert the AC Voltage to DC Voltage. The DC Link of the VSI uses capacitors to smooth out the ripple in the DC voltage and to also store energy for the drive system. The inverter section is comprised of insulated gate bipolar transistors (IGBTs), insulated gate-commutated thyristors (IGCTs) or injection-enhanced gate transistors (IEGTs). These transistors or thyristors behave like switches which are turned on and off to create a pulse width modulation (PWM) output that regulates the frequency and voltage to the motor.

    What are some of the advantages and disadvantages of a Voltage Source Inverter (VSI)? Some of the advantages of the Voltage Source Inverter Variable Frequency Drives (VFDs) are:

  • Simple Circuitry
  • Can be used in multi-motor applications
  • Independent of load

  • Some of the disadvantages of the Voltage Source Inverter Variable Frequency Drives (VFDs) are:

  • Large power harmonic generation into power source
  • Motor cogging when PWM output is below 6 Hz
  • Non-Regenerative operation
  • Low power factor

  • What is a Pulse Width Modulation (PWM) Variable Frequency Drive (VFD)?

    Pulse Width Modulation (PWM) Variable Frequency Drives (VFDs) is among the most commonly used controllers and has proven to work well with motors that range in size from 1/2HP to 500HP. Most PWM VFDs are rated for 230V or 460V, 3-Phase operation, and provide output frequencies in the range of 2-400Hz. Like the VSI VFD, the PWM VFD uses a diode bridge rectifier to convert the incoming AC voltage to a DC voltage. The DC Link uses large capacitors to remove the ripple evident after the rectifier and creates a stable DC bus voltage. The six-step inverter stage of this driver uses high power rated IGBTs which turn on and off to regulate the frequency and voltage to the motor. These transistors are controlled by a microprocessor or motor IC which monitors various aspects of the drive to provide the correct sequencing. This produces a sine-like waveform output to the motor. So how does turning a transistor on and off help create the sine-like wave output? By varying the voltage pulse width you are obtaining an average power which is the voltage supplied to the motor. The frequency supplied to the motor is determined by the number of positive to negative transitions per second.

    What are Harmonics?

    One major problem with Variable Frequency Drives (VFDs) and other AC Drivers and Controllers is system harmonics. Harmonics are found in non-linear electrical loads such as home or office equipment, lighting, speed drivers, etc. These non-linear electrical loads interrupt current flow into the system due to their switching action which creates the distorted sinusoidal waveform. Harmonics are multiples of the power frequency of a wave which cause irregularities in the sinusoidal voltage and current waveform. For example, if the power frequency is 60Hz, then multiples of it would be 120Hz for the second harmonic, 180Hz for the third harmonic, etc.

    Helpful Information


    - Process temperature can be controlled without a separate controller - Low maintenance - Longer lifespan for your AC motor and other machinery - Lower operating costs - Equipment in your system that cannot handle excessive torque is protected


    Variable Frequency Drives can be used in many different industrial and commercial applications. Most often used to control fans in air conditioning and heating systems, Variable Frequency Drives allow for more control of the airflow. Variable Frequency Drives also aid in adjusting the speed of pumps and blowers. More recent applications include conveyors, cranes and hoists, machine tools, extruders, film lines, and textile-fiber spinning machines.


    Variable Frequency Drives are a particular kind of adjustable-speed drive that is used to control the speed of an AC motor. In order to control the motor's rotational speed, Variable Frequency Drives control the frequency of the electrical power supplied to it. Adding Variable Frequency Drives to an application allows the motor speed to be adjusted in accordance with the motor's load, ultimately saving energy. Commonly used in a myriad of applications, Variable Frequency Drives can be found operating ventilation systems, pumps, conveyors and machine tool drives.

    Components of Variable Frequency Drives

    Typically, Variable Frequency Drives consist of three basic parts: the rectifier, and inverter, and a DC link to connect the two. The rectifier converts AC input into DC (direct current), while the inverter switches the DC voltage to an adjustable frequency AC output voltage. The inverter can also be used to control output current flow if needed. Both the rectifier and inverter are directed by a set of controls to generate a specific amount of AC voltage and frequency to match the AC motor system at a given point in time.


    Nikola Tesla invented the first AC Induction Motor in 1888, introducing a more reliable and efficient motor than the DC motor; however, AC speed control was a challenging task. When precise speed control was required, the DC motor became a replacement for the AC motor, because of its efficient and economical means of controlling speed accurately. It wasn't until the 1980's that Variable Frequency Drives became a competitor. Over time, Variable Frequency Drives technology eventually transformed into an inexpensive and reliable competitor to the traditional DC control. Now, Variable Frequency Drives are capable of speed control with full torque attained from 0 RPM through the maximum rated speed.

    How Variable Frequency Drives Works

    When complete voltage is applied to an AC motor, it accelerates the load and drops torque initially, keeping current especially high until the motor reaches full speed. Variable Frequency Drives operate differently; they eliminate excessive current, increasing voltage and frequency in a controlled manner as the motor starts. This allows the AC motor to generate up to 150% of its rated torque, which could potentially be generated from the beginning, all the way up to full speed, without wasting energy. Variable Frequency Drives convert power through three different stages. Firstly, AC power is converted to DC power, followed by the switching on and off of the power transistors, causing a voltage waveform at the desired frequency. This waveform then adjusts output voltage according to the preferred designated value.

    Physical Properties

    Typically, Variable Frequency Drives involve an AC motor, controller, and operator interface. The three-phase induction motor is most commonly applied to Variable Frequency Drives because it offers versatility and cost-effectiveness in comparison to a single-phase or synchronous motor. Though they can be advantageous in some circumstances, Variable Frequency Drives often utilize motors that are designed for fixed-speed operation. Variable Frequency Drives operator interfaces allow for the user to adjust operating speed, and start and stop the motor. The operator interface might also allow the user to switch and reverse between automatic control, or manual speed adjustment.