Frequency inverter: key to flexibility and efficiency in electric motors

In many industrial sectors, electric motors are the backbone of a wide range of processes—whether it's pumping systems, conveyor belts, ventilation, or automated production lines. However, these applications often require precise speed and torque control, highlighting the importance of variable frequency drives. Also known as VFDs (Variable Frequency Drives), or simply "drives," these devices allow for precise motor speed regulation while optimising energy efficiency and reducing the mechanical stress caused by abrupt starts and stops.
 
In what follows, we’ll explore how a frequency inverter works, the benefits it brings to industrial applications, and how electric motors can be customised to work more efficiently with these systems—including the option to apply specific finishes for optimal compatibility with frequency inverters.
 
 
 
1. What is a frequency inverter and how does it work?
 
A variable frequency drive is an electronic device that adjusts the frequency and voltage of the power supplied to a motor. This is achieved through a two-step process:
 
  1. AC to DC conversion: the alternating current from the power grid is first rectified into direct current.
  2. DC to AC inversion: then, an inverter module converts this DC back into alternating current at the desired frequency and voltage, based on the control settings programmed into the drive.
This setup allows the motor speed to vary within a defined range, enabling dynamic speed control and significant energy savings—especially in applications that don’t always require full power. This form of current conversion operation means that they are often also referred to as "inverters".
 
 
 
2. Main advantages of variable frequency drives
 
  • Energy efficiency: when a process doesn't require the motor to run at full speed, a VFD can reduce both speed and power consumption. This is particularly beneficial in applications such as pumps or fans, where—according to the affinity laws—energy consumption drops significantly as speed is reduced.
  • Soft starts and stops: starting motors directly from the mains often causes high inrush currents and mechanical stress. VFDs allow for smooth acceleration and deceleration, reducing wear on shafts, bearings, and belts and extending the lifespan of the equipment.
  • Precise process control: by adjusting frequency (and thus speed), you can precisely regulate flow rates, conveyor speeds, or fan intensities based on real-time needs—optimising the process and potentially improving product quality.
  • Built-in monitoring and protection: most VFDs come equipped with alarms and protection features (e.g. overcurrent, overheating), as well as real-time monitoring of power consumption and other parameters. This enables better control of the production environment and supports predictive maintenance strategies.
  • Lower maintenance costs: a motor operating under a VFD experiences less wear due to reduced operating speeds, particularly in its moving parts like bearings.
  • Reduced noise emissions: lower speeds also mean less mechanical noise, mainly from air movement, vibration, and component friction.
 
 
3. Customising motors for use with frequency inverters
 
While many standard motors can be used with VFDs, there are cases where specific customisations are needed to ensure optimal performance. These include:
 
  • Winding configuration: the motor winding design can impact its ability to run at extremely low or high speeds without overheating.
  • Vibration isolation and damping systems: variable speeds can introduce unwanted vibrations that need to be controlled.
  • Housing and protection: in environments with high humidity or temperature, motors may require special coatings or finishes to prevent corrosion and overheating.
  • Special bearings: the modified waveforms generated by VFDs can damage standard bearings over time. Depending on the application and manufacturer recommendations, insulated, ceramic, or shielded bearings may be advisable.
Proper customisation ensures that the motor works in harmony with the drive, preventing issues such as mechanical resonance, overcurrent, or premature wear.
 
 
 
4. How to choose the right VFD and motor
 
Several key factors should be considered when selecting a motor-drive combination:
 
  1. Power requirements: accurately determine the minimum and maximum power needs to correctly size both the motor and the drive.
  2. Speed range: define the desired speed range and required torque for each operating condition.
  3. Environmental conditions: variables such as humidity, dust, temperature, or potentially explosive atmospheres must be accounted for.
  4. Load type: a constant load (like a conveyor) differs significantly from a variable load (like a pump or fan), each requiring different motor and drive characteristics.
 
 
5. Conclusion
 
Variable frequency drives have become essential tools in today’s industrial landscape. They not only provide precise motor control but also significantly improve energy efficiency and equipment lifespan. When motors are specifically tailored to operate in conjunction with VFDs, the result is smoother performance, lower maintenance requirements, and reduced operating costs.
 
At EMPE, we believe that this synergy between technology, customisation, and process expertise is what truly makes the difference in demanding industrial environments.