Inverter Drives

Over 25% of the world’s electrical energy is consumed by electric motors in industrial applications. The under of inverter drives reduces a motor’s electricity consumption and improves their electrical efficiency.

An inverter drive is a type of adjustable speed drive or motor controller used in electro-mechanical drive systems to control motor speed and torque by varying the input frequency and voltage to a motor. Inverter drives are also referred to as variable speed drives (VFDs), adjustable frequency drives, variable frequency drives (VFDs), AC drives and micro drives. They can be in AC-AC or DC-AC configurations.

Variable Speed Starters

Variable Speed Starters also help to improve energy efficiency and are a product category that sits between conventional motor starters and variable speed or frequency drives. Variable speed starters have the same ease of use as a motor starter with the added advantages of:

Motor starting current is reduced to the rated operational current at full torque on start-up
Motor speeds can be varied
Provide integrated motor protection

For more information on our inverter drives call the Eco Power Projects team for advice or to arrange an energy efficiency site survey or quotation on 0800 612 7388, email us or complete our enquiry form.

How Variable Speed Drives Improve Energy Efficiency

Inverter or variable speed drives are connected to a mains power supply and from this they connection the drive generates a DC power source using a built-in AC-DC rectifier. The DC supply is smoothed using DC capacitors and a choke before the supply is inverted back into AC using an output stage DC-AC inverter via a network of IGBTs (integrated gate bipolar transistors). The IGBT network is a smaller inverter drive or ‘Intelligent Power Module (IPM)’ with its own protection and basic control circuits.

The inverter section generates an AC output sine wave supply using Pulse Width Modulated (PWM) control. PWM refers to the chopping or switching on/off of the DC supply via the IGBT network. The sine wave is made by a series of DC pulses with the IGBTs controlled to switch at any time base. The pulse frequency is known as the switching frequency and is typically 3-4kHz.

The output voltage is supplied to the motor and the voltage and frequency of the supply are used to control the motor speed. The Voltage is controlled by the width of the fixed voltage pulses and the Frequency by spreading the pulse widths over the switching frequency base.

The IPM module actually controls the voltage and frequency supplied to the motor and will operate to a range of set-up parameters. The parameters are normally set at installation allowing an inverter drive to run a 230Vac Delta configured motor from a 240Vac single-phase mains power supply (50Hz frequency) or a 400Vac Star configured motor from a 400Vac three-phase configured mains power supply or any other combination required to flux the motor.

Some inverter drives can also apply electrical braking when a braking resistor (DBR) is available. This is because the output of an inverter drive is bi-directional allowing power to flow both ways. In such an instance the motor load will return stored mechanical energy to the inverter drive when it is actively slowed to a slower speed rather than allowed to decelerate or coast. When braking, the bus voltage rises and the smoothing DC capacitors are charged and apply braking in return to the motor shaft with the amount dependent on the size of the DC capacitor bank. For this type of application a brake switch or chopper is required to diver the braking energy into the braking resistor.