How Inverter Drives Work

Electrical motors are everywhere in daily life, moving and running things behind the scenes, but most of the time we don’t give them a second thought. All these motors run on electricity and need to have an output that corresponds to the amount of energy coming in.SD1-10A-23 - SD1 Series Inverter 2.2Kw, 3Phase, 220v, 10Amp IP20

The speed of a motor should match the energy required for the task it is performing, if it doesn’t it will mean inefficiency and wasted energy. The way to control these motors and conserve energy is to use an inverter drive.


The Principle Behind Inverter Drives

The simplest way of looking at an inverter drive is to see it as an energy transformer. The drive is a frequency converter that lies between the electrical supply and the motor. When the power enters the drive it is first converted from AC to DC, next passing through capacitors to smooth out the electrical wave before transistors pass the power through an inverter.

This changes the power from DC input to AC output ready to power the motor. All this then allows the motor to be controlled efficiently and produce exceptional speed and torque performance when needed.

Method of Control

The control method for inverter drives is pulse width modulation. This PWM uses the transistors to rapidly switch the DC on and off, producing pulses that create a sine wave current. As the pulses increase in length they will appear in the middle of the positive sine wave, the pulses are then shortened until the DC is flipped and the pulses produce the negative share of the sine wave.

Pulse Width Modulation

The frequency of the pulses produced by the transistors rapidly turning on and off is known as the switching frequency. This process will allow the inverter drive to control frequency and voltage, ensuring the motor connected to it receives the correct amount of power it needs and only when it needs it.


If the device you are running has the capacity for braking, then the inverter drive can also control this as the inverter output lets power flow both in and out. As the motor is slowed it will begin to act as a generator and return its energy to the inverter. This will charge the capacitors in the drive and will mean a gentle braking force of around 10% is applied to the shaft of the motor.

If the braking energy becomes too much for the capacitors, it needs to be diverted into a braking resistor. This will dissipate the energy released by the slowing motor, preventing the voltage from rising above the limit and damaging the drive. On most inverter drives it is possible to set it to coast to a stop, allowing the motor to run down without any braking.

Total Control and Distribution are able to supply a variety of IMO drives to suit your needs. Recognised for their reliability and quality, TCAD is proud to be able to help their customers find what they require to get the job done properly.

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