Frequency inverter in electric motors: efficiency and control

In many industrial sectors, electric motors are the basis of processes such as pumping, ventilation, conveyor belts and automated production systems. However, not all applications require the motor to always operate at the same speed or with the same torque.

In these cases, the frequency inverter, also known as a variable frequency drive or VFD, is a key element for controlling motor speed, adapting operation to the real needs of the process and improving the energy efficiency of the installation.

Table of contents

1. What is a frequency inverter?
2. How does a VFD or inverter work?
3. Energy efficiency and savings in electric motors
4. Soft starts and stops
5. Process control, torque and speed
6. Electric motors prepared to work with frequency inverters
7. How to select the motor and VFD combination
8. Do you need a motor prepared for frequency inverter use?

What is a frequency inverter?

A frequency inverter is an electronic device that regulates the rotational speed of an electric motor by modifying the frequency and voltage of the power supplied to the motor.

It is also known as a VFD, from Variable Frequency Drive, or simply as an inverter. Its main function is to adapt motor behaviour to the needs of the process, preventing the motor from always running at full speed when this is not necessary.

This regulation is especially useful in applications such as pumps, fans, conveyor belts, industrial machinery and automated systems where speed, flow rate, torque or production rhythm need to be adjusted.

How does a VFD or inverter work?

The operation of a frequency inverter is based on the conversion and regulation of the electrical energy that powers the motor. In a simplified way, the process can be divided into two stages:

1. Conversion from alternating current to direct current: the alternating current from the grid is rectified and converted into direct current.
2. Conversion from direct current to regulated alternating current: the inverter module generates alternating current again, but with the frequency and voltage required according to the control commands programmed in the drive.

In this way, the inverter can modify the motor speed within a defined range, allowing more precise and dynamic adjustment of the installation’s operation.

Energy efficiency and savings in electric motors

One of the main advantages of frequency inverters is the improvement of energy efficiency. When the process does not require the motor to operate at its rated speed, the inverter makes it possible to reduce speed and, in many cases, also reduce electrical consumption.

This is especially relevant in pumping or ventilation applications, where reducing speed can have a significant impact on consumed power and operating costs.

A motor controlled by a frequency inverter can better adapt its operation to the real demand of the process, avoiding unnecessary consumption and contributing to a more efficient installation.

To learn more about this topic, you can read the article on efficient electric motors and sustainable industry.

Soft starts and stops

With direct-on-line starting, the motor can experience high current peaks and significant mechanical stress. These stresses can affect shafts, bearings, transmission belts and other components linked to the system.

With a frequency inverter, starting and stopping can be performed progressively. This helps reduce mechanical and electrical stress, improve system stability and extend the service life of the components.

This function is especially useful in applications with frequent starts, variable loads or systems where mechanical shocks and sudden vibrations must be avoided.

Process control, torque and speed

The frequency inverter makes it possible to adjust motor speed according to the real needs of each moment. This helps regulate the flow rate of a pump, the intensity of a fan, the speed of a conveyor belt or the rhythm of an automated process.

This control can also help improve process quality, reduce variations, optimize consumption and adapt production to different working conditions.

In addition, many drives include protection and monitoring functions, such as alarms for overcurrent, overheating or other operating parameters. This information can help detect deviations and support preventive or predictive maintenance strategies.

Electric motors prepared to work with frequency inverters

Although many motors can operate with a frequency inverter, not all applications have the same requirements. In some cases, the motor needs specific characteristics to work optimally with variable speed operation.

Some aspects to consider include winding type, insulation system, ventilation, thermal behaviour, bearings, housing and protection against humidity, temperature or demanding environmental conditions.

It may also be necessary to consider special bearings, such as insulated, ceramic or shielded bearings, always according to the manufacturer’s recommendations and the working conditions of the application.

At EMPE, we can study the motor design and assess specific adaptations to improve compatibility with frequency inverters, reduce the risk of premature wear and support more stable operation.

You can also read the article on design and customization of electric motors.

How to select the motor and VFD combination

Selecting the motor-VFD combination requires considering different technical factors. It is not only about choosing a drive suitable for the motor power, but also about analysing how the system will operate within the process.

• Required power: it is necessary to determine the minimum and maximum power required to correctly size both the motor and the drive.
• Speed range: it is important to define the working speeds and the torque required at each operating point.
• Load type: a constant load, such as a conveyor belt, does not require the same behaviour as a variable load, such as a pump or a fan.
• Environmental conditions: humidity, dust, temperature or special atmospheres can influence motor design and drive protection.
• Duty cycle: service hours, start-stop cycles and load conditions influence the final selection.

Correct selection helps avoid problems such as overheating, vibration, mechanical resonance, overcurrent or premature component wear.

To explore the technical analysis of the motor in more detail, you can read the article on motor diagnosis, redesign and improvement.

Do you need a motor prepared for frequency inverter use?

If your application requires speed control, reduced energy consumption, soft starts or a motor adapted to work with a frequency inverter, EMPE can study the needs of the project and assess the most suitable solution.

Contact our technical team