Everything about variable frequency drives (VFDs) – quick answers to your questions

The Sustainable Development Goals (SDGs) of the United Nations provide a global framework for sustainable development.
Variable frequency drives and electric motors directly contribute to several of these goals.
For example: SDG 7 (Affordable and Clean Energy), as VFDs significantly reduce electricity consumption of motors;
SDG 9 (Industry, Innovation and Infrastructure) by improving productivity and efficiency in industrial processes;
and SDG 13 (Climate Action), as lower energy consumption leads to reduced CO₂ emissions.

In addition, VFDs support SDG 12 (Responsible Consumption and Production) by extending the lifespan of electric motors
and reducing waste streams through soft start and controlled stopping.
Through process optimization, they also contribute to SDG 6 (Clean Water and Sanitation), as they enable water pumps
and treatment installations to operate more efficiently. In this way, both energy and resources are conserved.

Read more about the role of SDGs (Wikipedia)
and explore our Fluxcon wiki on energy.
Practical guidelines for integrating VFDs into sustainable strategies can be found in the
FLC500 manual p.76–80,
which covers energy measurement and logging.

A modern variable frequency drive consists of several core components that together convert
fixed mains frequency into a variable output frequency and voltage.
Key components include: the rectifier (AC to DC), the DC bus (energy storage and filtering),
and the inverter (DC back to AC with variable frequency via PWM).
In addition, there are supporting components such as IGBTs or MOSFETs (semiconductors), capacitors and chokes
for energy and harmonic filtering, heat sinks and fans for thermal management, and EMC filters
to reduce interference.

A VFD also includes control and measurement circuits, such as microprocessors, drivers, sensors and I/O modules
that enable communication and control. Together, these components form the foundation for controlling electric motors
efficiently and reliably.

See the Wikipedia page on VFDs
for an overview and the Fluxcon wiki.
A block diagram of the internal structure can be found in the
Fluxcon Applications Manual p.14.

The rectifier is the first stage in the internal structure of variable frequency drives and electric motors.
It converts the incoming alternating current (AC) into direct current (DC).
This is typically done using a 6-pulse or 12-pulse diode bridge, sometimes supplemented with active components
such as IGBTs in an Active Front End (AFE) to enable regeneration back to the grid.

The purpose of the rectifier is to create a stable DC link on which the inverter can operate.
The quality of this conversion affects harmonic distortion (THDi) and the power factor of the system.
Modern drives often include DC chokes or line reactors to limit harmonic currents and improve power quality.

Further information can be found in the Wikipedia page on rectifiers
and the Fluxcon EMC wiki.
For practical specifications see the
FLC500 manual p.139–140.

The DC bus forms the core of variable frequency drives and electric motors.
After the rectifier converts mains voltage into DC, the DC bus acts as a buffer and stabilizer.
Key components include electrolytic capacitors (for energy storage and smoothing)
and inductors (for damping ripple and harmonics).

The DC bus provides a stable voltage for the inverter stage.
During regenerative braking, the DC bus absorbs energy which is temporarily stored.
Without countermeasures, voltage can rise, which is why many drives include a braking chopper and resistor
or an Active Front End to feed energy back to the grid.

See Wikipedia: direct current
and the Fluxcon wiki.
Practical diagrams and explanations of the DC bus can be found in the
Fluxcon Applications Manual p.15
and protection options in the FLC500 manual p.96–98.

The inverter in variable frequency drives and electric motors converts the DC voltage from the DC bus back into
an AC voltage with variable frequency and amplitude. This is done using semiconductor switches such as
IGBTs or MOSFETs controlled via PWM (Pulse Width Modulation).

By switching these components at high frequency, a “simulated sine wave” is created that allows the motor
to run smoothly. By varying pulse width and frequency, motor speed and torque can be precisely controlled.
Depending on the application, this can be done in open-loop (sensorless) or closed-loop (with encoder feedback).

More information can be found on
Wikipedia: inverter
and in the Fluxcon wiki.
Practical diagrams are available in the
Fluxcon Applications Manual p.16.

PWM (Pulse Width Modulation) is a technique used in variable frequency drives and electric motors
to generate variable voltage and frequency from a DC source. Instead of producing a smooth sine wave directly,
the inverter rapidly switches semiconductors (IGBTs or MOSFETs) on and off. By varying the pulse width,
an average voltage is created that the motor experiences as a sinusoidal signal.

The PWM frequency determines how smooth the resulting waveform is: higher switching frequencies produce smoother voltage and current.
PWM enables precise control of motor speed and torque with minimal semiconductor losses.

See Wikipedia: PWM
and the Fluxcon wiki.
For detailed settings, see
FLC500 manual p.60–62.