Author: veikong

A variable frequency drive (VFD) is an electronic mechanism used to control the speed of an AC induction motor. Variable speed requirements for AC induction motors are fulfilled by a 3-phase motor, an inverter, or VFD.  Depending on VFD and how it is installed, the variable frequency drive operates on a single or 3-phase input and the output matches the required voltage. Because the motors are generally designed with a single operating speed, VFD is required to alter and control the speed of the motor. Understanding Variable Frequency Drive (VFD) There is a significant layer of control between the input and output processes of variable frequency drive (VFD). The control panel works as an interface that turns AC input to DC and then puts it on AC output using a conversion called power width modulation (PWM). Since the output is well-controlled by VFD on a motor, the input doesn’t require to match the desired output. VFDs and Single-Phase Input It is necessary to have 3-phase input to operate a 3-phase motor with a variable frequency drive. VFD will facilitate single-phase current during the conversion stage. For doing this, input power is initially turned to DC using diodes and then turned to the desired output using diodes and capacitors that result in AC. 3 phase motor is attached to the output connectors on the VFD, wherein the input voltage isn’t a considerable factor. VFDs and 3-Phase Input When you are using a 3-phase input, the wiring needs to be processed through an inverter to produce DC. The mechanical function of VFD remains the same and output is controlled by VFD. In order to reduce complications and chances of errors, it is good to work with a 3-phase variable frequency drive manufacturer or AC motor speed control manufacturer to get the best assistance. Speed Control Method for AC Induction Motors Many industrial AC induction motors are 4 pole type, so the motor speed works in sync with input power supply frequency (Hz). A VFD controls the motor speed by using pulse width modulation to modify the power supply frequency. To use VFDs, you may require a 3-phase AC induction motor with an inverter having at least a continuous duty rating. The phase control motor exhibits less electrical noise as compared to VFD-driven motors, where VFDs run at a much faster rate. For applications like polishing machines, dual conveyors, or stirring machines, frequent speed fluctuations can affect the final product due to load. If constant torque and speed control are necessary, connecting VFDs to a 3-phase motor is worth considering.

Any engineer using a variable frequency drive needs a bypass contractor and soft starter to efficient and reliable function of three-phase motors. Using a drive with an in-built soft starter and bypass offers significant benefits in itself, such as minimizing shock to mechanical parts, extending system lifespan, increasing reliability, reducing downtime, and lowering costs. A bypass contractor connected with a VKS-8000 Bypass Soft Starter reduces the need for integrating additional components, which reduces enclosure size and installation time. Bypass contractor drastically minimizes heat produced by the starter, which eventually decreases voltage drop and cuts heat build-up in the starter. Keep reading to learn more about configurations of bypass, soft starters, and adjustable frequency drive. Why Connect Bypass Contractor with a Soft Starter? Comprehensive drive packages are usually comprised of robust and steady solutions. Using a soft starter device can help minimize slippage, stretching and squealing, and extend the belt life as compared to traditional across-the-line starters. It ensures shock resistance on conveyors and material handling equipment, which reduces the costs of damage to products.  For instance, in pump applications, soft starters can be able to gently stop the motor, thus easing the general water hammer effect, Bypass Contractor, Soft Starter, and Frequency Drive Configurations As a whole, all these three components are typically used to control the motor and its related operations. Let’s look at their specific configuration: Bypass Contractors Connect the motor across the AC line, which will further accelerate to full speed and emit a remarkable amount of current during the process. Soft Starters It is used to slow draw the motor to the full speed or even ramp down to stop. To minimize current draw as well as mechanical pressure on the mechanism, soft starters are used often in place of contractors. With smooth acceleration and deceleration of the system, it reduces wear on gears, belts, clutches, chains, bearings, and shafts. In general, large pumps and fans need at least 30-second of ramp time to avoid mechanical damage. They are mainly used for applications where an abrupt stop of the load and mechanical strain is required to prevent. Frequency Drive Alongside a great ramp ability of a soft starter, variable frequency drive let speed be varied in critical applications, which offer greater flexibility and numerous additional features. Enclosed adjustable frequency drive generally includes a bypass for applications that cannot afford downtime. Connecting a soft starter allows the motor to be ramped to full speed, thereby reducing mechanical and electrical pressure on the system. Conclusively, adding a bypass with a soft starter works as an efficient backup to operate the motor. Especially, large drive systems should include soft starters in the bypass contractor, else it adversely affects the power system and can damage bearings.

There have been many discussions about new technology and AC motors. Varying AC motor speed control has always been hard, so for many years, DC motors are the only option when accurate speed control and motor power are needed. But advances in the last few years have changed this. And these advances have resulted in variable frequency drives competing with traditional DC motor control in an application where they were earlier too expensive or also lacked the power to perform properly. Here are some most common types of VFD that are used in different applications. Current Source Inversion Current source inversion derives are generally favored over-voltage source inverter drives in high power applications where the self-motivated response is not required. Conventional CSI drives come with their limitations, such as resonance, instability at low speeds, and high torque ripple that can restrict the applications where they are used. They have been used in signal processing and also industrial power applications. This VFD also offers a very clean current waveform but needs large and expensive inductors in its construction and causes cogging below 6 Hz. Voltage Source Inversion They are widely used with a pulse width modular. The DC output of the diode bridge converter usually stores energy in the capacitor bus for supplying stiff voltage input to the inverter. The factor the voltage source inversion drives with diode rectifies is constant or also better over the normal operating range. The power converting rate that is based on the capacities of the power semiconductors devices and also the cooling system is the only limitation in this VFD’s designs. The normal rating of this VFD is based on 40° C maximum ambient temperature and altitudes less than 1OOOm. Applications outside these circumstances need de-rating. Pulse Width Modulation They are used in industry because of their excellent input power factor because of fixed DC bus voltage, no motor cogging, high efficiencies, and lower cost. A PWM VFD uses a series of voltage pulses of dissimilar lengths for simulating a sinusoidal wave. The pulses are timed so that the time average integral of this drive yields an ideal sinusoid. Load Commutated Inverter They are basically synchronous motor drives that have been usually used in very high-power applications. They are also used in variable speed applications including pumps, compressors, and fan drives. They also tend to be larger than the comparative power VSI. The advantage of this inverter is that it employs converter-grade thyristors that are able to control a large amount of power and voltage. And it can also utilize the natural communication of the semiconductor device. While this drive is simple and durable; it requires careful attention to AC power system problems related to harmonic currents and reactive power. They also need specially designed motors with low reactance and should work with harmonic heating and also air gap torque harmonics. These are some different types of VFD that are used in different types of industries. You can use VFD for matching the speed of motor-driven equipment to the load requirement. You can also find a reliable variable frequency drive manufacturer for buying high-quality products for your applications.