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The AC induction motor drive is the fastest growing segment of the motor control market in the world. There are various reasons for this fast growth of AC induction motor drive. These reasons are presented blow for your reference:

1. Ease of programming
2. Low investment cost for the development
3. Flexibility to add additional features with minimal increase in hardware cost
4. Faster time to market

Savings from variable speed drives (VSDs, variable frequency drives, VFDs, frequency converters, ac drives) come from reduced load of the fan, pump, or driven device. With fans and pumps, energy consumed is proportional to the cube root of shaft speed. If shaft speed is reduced by 10%, flow is reduced by 10%, while power consumption is reduced by 27%. And if shaft speed is reduced by 20%, power is reduced by 49%.

Compared to throttling as a means of flow control, speed reduction provides dramatic energy savings. Throttling to reduce flow in a fan or pump backs the device up on its operating curve, increasing pressure and often increasing power consumption.

2. Find the full power required to run this ac motor by calculating the full load wattage.

A basic electrical formula for wattage is voltage times amperage (w = v X a). Multiply the 480 volts times 20 amperes and the operation wattage is equal to 9600 w. All frequency inverters (variable speed drives, VSDs, variable frequency drives, VFDs) are rated in kilowatt (kW). One kilo is equal to 1,000. The ac motor will use 9.6 kW of electrical power.

3. Find the maximum power that variable frequency drive (VFD) can provide according to the specifications.

In the example above, a 10 kW (10,000 watt) frequency inverter will be needed to power the electric ac motor. The important point here is that it is always better to use a slightly larger drive unit than one that is too small to provide full power. Find the full load amperage of frequency inverters (variable speed drives, VSDs, variable frequency drives, VFDs) when it is providing full power to the motor at 480 volts. Divide the 10 kW by 480 volts to find that 20.83 amperes will be required.

These AC drives control the speed of AC motors in a very accurate fashion. In most all applications the adjustable frequency drives provide overcurrent protection for the motors. The main feed of electrical power to the frequency drive must still have some form of overcurrent protection to safely power the drive unit. Sizing the overcurrent protection, regardless of the specifications provided with the drive unit, may still require calculation.

How to size overcurrent protection for frequency inverter? Let's follow these 4 steps:

1. Obtain the electrical specifications from the electrical alternating current (AC) motor's nameplate tag. The nameplate data tag is generally placed on the motor, near the topside of the exterior frame. The operational voltage, the full load amperage, the horsepower and the power factor rating are recorded on the motor nameplate.

Variabl frequency drives (VFDs, variable speed drives, VSDs) are an excellent choice for adjustable-speed drive users. They allow drive users to fine-tune processes while reducing costs for energy and equipment maintenance.

At water and waste-water facilities, the applications of variable frequency drives (VFDs) are so popular.

Figure below illustrates the reduced energy consumption of Variabl frequency drives (VFDs, variable speed drives, VSDs) over valve control systems at water and waste-water facilities.

For applications where flow requirements vary, mechanical devices such as flow-restricting valves or moveable air vanes are often used to control flow, which is akin to riving a car at full throttle while using the brake to control speed.

Further, the rapid rise time of the pulses may cause trouble with the motor bearings. The stray capacitance of the windings provide paths for high frequency currents that close through the bearings. If the voltage between the shaft and the shield of the motor exceeds few volts the stored charge is discharged as a small spark. Repeated sparking causes erosion in the bearing surface that can be seen as fluting pattern. In order to prevent sparking the motor cable should provide a low impedance return path from the motor frame back to the inverter. Thus it is essential to use a cable designed to be used with variable frequency drives (VFDs, variable speed drives, VSDs).

In big motors, a slip ring with brush can be used to provide a bypass path for the bearing currents. Alternatively isolated bearings can be used.

The output voltage of a Pulse Width Modulation (PWM) variable frequency drive (VFD) consists of a train of pulses switched at the carrier frequency. Because of the rapid rise time of these pulses, transmission line effects of the cable between frequency inverter (vfd) and the motor must be considered. Since the transmission-line impedance of the cable and motor are different, pulses tend to reflect back from the motor terminals into the cable. The resulting voltages can produce up to twice the rated line voltage for lone cable runs, putting high stress on the cable and motor winding and eventual insulation failure.

Increasing the cable or motor size/type for long runs and 480v or 600v motors will help offset the stresses imposed upon the equipment due to the VFD (modern 230v single phase motors not effected). At 460 V, the maximum recommended cable distances between VFDs and motors can vary by a factor of 2.5:1. The longer cables distances are allowed at the lower Carrier Switching FrequencY (CSF) of 2.5 kHz. The lower Carrier Switching FrequencY (CSF) can produce audible noise at the motors.

A thorough understanding on how to match frequency inverter to the driven load is the key to a successful application. When applied properly, frequency inverter (variable speed drive) is the most effective motor controller in the industry. Variable frequency drives (VFDs, variable speed drives, VSDs) are affordable and reliable, and having flexibility of control, plus offering significant electrical savings through reducing electric bills.

Today Frequency Inverters are widely used in a variety of applications for various reasons.

In pump and fan application, variable frequency drives (VFDs, variable speed drives, VSDs) are the most effective energy savers. In most facilities, centrifugal pumps and fans run at one constant speed. Traditionally an automatic value, or some mechanical means varies fluid flow rates. With a frequency inverter (variable speed drive), you can change motor speeds electronically. By being able to adjust a pump or fan speed to get the desired rate, you can significant reduce energy cost. Thus money is saved through reducing electric bills.

Cost-effective variable frequency drives (frequency inverters) from GreenDriv Tech Limited:

Variable frequency drive (VFD, adjustable frequency drive) has been successfully applied to large boiler feedwater pumps in power plants, hot water circulation pumps in commercial buildings, and for waste water treatment plants in our city. Variable frequency drives (VFDs, adjustable frequency drives) provide soft-start capabilities, which will decrease electrical stresses and line voltage sags associated with full voltage motor start-ups, especially when driving high-inertia loads.

Frequency inverter, in different countries, exists different names, including frequency changer, frequency converter, variable speed drive, variable frequency drive, adjustable speed drive, adjustable frequency drive, ac drive, variable voltage variable frequency drive, vvvf drive, even microdrive.

A frequency inverter is an electronic device, that converts alternating current (AC) of one frequency to alternating current (AC) of another frequency. Frequency inverter may also change the voltage, but if it does, that is incidental to the principal purpose.
The image of frequency inverter from GreenDriv Tech Limited

But where's the market for frequency inverter?

I think different demands exists in different areas. The requirements for frequency inverter in Japan may be different from that in India. The requirements for frequency inverters in USA are different from Mexico. So different qualities meet the demands of different countries because of the cost.