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FAQ

What is an Inverter Drive, VSD or VFD?

An inverter drive, also known as a Variable Frequency Drive (VFD) or Variable Speed Drive (VSD), is an electronic device used to control the speed and torque of an AC electric motor. It does this by varying the frequency and voltage supplied to the motor.

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  • An inverter drive converts fixed-frequency, fixed-voltage AC power from the mains supply into a variable-frequency, variable-voltage output, allowing accurate control of three-phase electric motors.
  • Internally, a rectifier converts AC power into DC, which is smoothed by capacitors. An inverter then uses IGBTs to convert this back into adjustable AC.
  • The inverter typically uses Pulse Width Modulation (PWM) to control the output voltage and frequency supplied to the motor.
  • By allowing motor speed to be matched to the required load, inverter drives can significantly reduce energy consumption, particularly in fan and pump applications.
  • Inverter drives allow accurate speed regulation, torque control and controlled acceleration and deceleration, helping to reduce mechanical stress on motors.
  • By eliminating harsh starts and allowing motors to run at lower speeds where appropriate, inverter drives can reduce wear and tear on machinery.
  • Inverter drives are used in HVAC (heating, ventilation and air conditioning) systems, conveyors, water pumps, fans, mixers, compressors and many other types of industrial machinery.
  • Also known as: Variable Frequency Drive (VFD), Variable Speed Drive (VSD), Frequency Inverter and AC Drive.
What are the key differences between an Inverter Drive and a Soft Starter?

A soft starter is primarily used to control the starting and stopping of a motor, reducing high starting currents and mechanical stress. An inverter drive can also provide controlled starting and stopping, but additionally allows the motor's running speed and torque to be controlled.

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  • A soft starter gradually increases the voltage supplied to the motor while maintaining the supply frequency, providing a controlled start and reducing starting current.
  • A soft starter is generally used where the motor normally needs to operate at full speed but a controlled start and stop is required.
  • An inverter drive varies the frequency and voltage supplied to the motor, allowing variable-speed operation as well as controlled acceleration and deceleration.
  • An inverter drive can provide precise speed and torque control, in addition to soft-start functionality.
  • A soft starter can reduce starting current and mechanical stress during starting and stopping.
  • An inverter drive can provide additional motor protection and control functions, although the exact features depend on the model.
  • Inverter drives can offer significant energy savings in applications where reducing motor speed reduces the load, particularly with fans and pumps.
  • Inverter drives are generally more expensive than equivalent soft starters, although the price difference varies according to manufacturer, rating and specification.
  • Inverter drives are typically larger and generate more heat than an equivalent soft starter due to the switching electronics used to generate the variable-frequency output.
What are the different types of Inverter Drive?

There are several types of inverter drive, each designed for different applications, environments and levels of motor control. These include standard open-loop drives, open-loop vector drives, closed-loop vector drives, servo drives and regenerative drives.

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  • Standard open-loop inverter drives are designed for general-purpose speed control of three-phase AC induction motors. They are widely used for applications including fans, pumps, compressors, conveyors, agriculture, cranes and hoists.
  • Open-loop vector inverter drives use more advanced motor-control algorithms to provide improved speed and torque control, particularly at low speeds. They are commonly used in applications requiring good low-speed torque performance, such as cranes, hoists, augers and specialist machinery. Additional motor cooling may be required for prolonged low-speed operation.
  • Closed-loop vector inverter drives use a feedback device, normally an incremental encoder, mounted on the motor. This provides the inverter with accurate information about motor operation, allowing highly precise speed and torque control. They are commonly used in applications such as CNC machines, precision lathes, winders and unwinders.
  • Servo drives/inverters use feedback, normally from a resolver or encoder, to provide highly precise control of torque, rotor position, speed and acceleration. They are used with specialist servo motors in applications requiring precise motion and positioning, including CNC machines, robotics and automated machinery.
  • Regenerative inverters, or regen drives, can return energy generated during motor deceleration to the electrical supply rather than dissipating it as heat. They are useful in applications involving frequent braking or deceleration, such as passenger lifts, equipment lifts, cranes, hoists, winders and unwinders.
  • Regenerative drives can improve energy efficiency and reduce heat generation in applications with frequent braking, although they are generally more expensive than equivalent non-regenerative drives.
  • Inverter drives are available with different IP ratings and enclosure designs to suit different installation environments.
Can Inverter Drives be mounted outside in the weather?

Some inverter drives are specifically designed for outdoor installation. The drive must have an appropriate enclosure, environmental rating and construction for the conditions in which it will be installed, and the manufacturer's installation requirements should always be followed.

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  • An outdoor inverter drive should have an appropriate IP (Ingress Protection) rating for the environment in which it is installed. IP66 is commonly used for outdoor-rated inverter drives.
  • The inverter should have UV-resistant materials suitable for prolonged exposure to sunlight.
  • Where possible, units should be mounted in the shade, preferably north-facing, out of direct sunlight and under cover.
  • A rain cover should generally be fitted above the inverter to protect it from driving rain.
  • Care should be taken to prevent snow and ice from accumulating in the heatsink cooling fins.
  • Maintaining a permanent power supply to the inverter can help maintain its internal temperature and reduce the risk of condensation and frost forming inside the unit.
  • A ventilation plug can be fitted to the terminal cover where recommended by the manufacturer. This allows the unit to breathe with changes in temperature and pressure while helping prevent moisture ingress.
  • A bag of desiccant gel can be placed inside the terminal cover as an additional precaution against moisture.
  • Ambient temperature limits must always be observed. Outdoor-rated inverter drives will typically have specified operating temperature limits, which vary according to the model.
What is an Enclosed Inverter Drive and what's different about it?

Enclosed inverter drives are inverter systems designed to provide additional protection and/or integrated controls. They are generally available as either a purpose-built IP-rated inverter or an inverter mounted inside a protective control panel.

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  • The first type is an IP55/IP66 high water and dust protection variant of a standard IP20 panel-mounted inverter drive.
  • These drives are designed to provide significantly greater protection against dust, water and physical contact than a standard IP20 inverter.
  • Their enclosed construction makes them suitable for a wider range of industrial and environmental conditions.
  • The second type is an IP20 inverter mounted inside a control panel by a third-party manufacturer like us.
  • These panels can incorporate additional control features such as start/stop push buttons, mains isolators, speed potentiometers, indicator lamps and other application-specific controls.
  • Enclosed control panels are generally manufactured from powder-coated steel and may incorporate ventilation fans where required.
  • They can be supplied as standard off-the-shelf products or tailored to suit a specific application.
  • Applications range from fans and pumps to conveyors, agricultural machinery and other industrial equipment.
What are the differences between Invertek Optidrive E3 and Imoticon ID700 inverter drives?

The Invertek Optidrive E3 is a general-purpose inverter drive designed to provide simple and straightforward setup, while the Imoticon ID700 offers a more comprehensive range of parameters and programmable functions for more complex applications.

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  • The Optidrive E3 has a relatively simple parameter set designed to make the inverter easy to configure and operate.
  • The E3 is designed to cater for the majority of standard applications.
  • The E3 is available in IP66 and single-phase output variants.
  • The Imoticon ID700 has a more comprehensive parameter set, allowing it to be configured for more complex applications.
  • The ID700's control terminals are fully programmable, providing greater flexibility when configuring external control signals.
  • The ID700 has additional control terminals and a more extensive programmable PID control loop.
  • The additional programming features make the ID700 more flexible for complex applications, although they can also make it more involved to configure.
What are the differences between Swift Start Lite, Swift Start Classic and Swift Start Pro Safe enclosed inverter drives?

The Swift Start range offers different levels of enclosed inverter control. The Swift Start Lite provides simple motor control, the Classic adds additional operator controls, and the Pro Safe adds an integrated SIL2 emergency-stop system and enhanced inverter functionality.

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  • Swift Start Lite is designed for simple and reliable motor control in a powder-coated steel IP54 enclosure. It includes start and stop buttons and a mains isolator.
  • When the start button is pressed, the inverter starts and ramps up to the speed set in parameter P00.16. When the stop button is pressed, the inverter ramps to a stop.
  • Swift Start Classic includes all the features and controls of the Lite, with additional functionality including an externally mounted speed potentiometer, forward/reverse switch, inverter disable button and indicator lamps.
  • When the start button is pressed, provided the inverter disable button is not pressed, the inverter starts and ramps up to the speed set by the speed potentiometer.
  • The forward/reverse switch controls the direction of the motor.
  • The inverter disable button disables the output of the drive, allowing the motor to coast to a stop. This is not an emergency-stop button and must not be used as a substitute for safety isolation.
  • The healthy lamp indicates that the inverter is in a healthy state and has not tripped. The running lamp indicates that the inverter is running and its output is enabled.
  • Swift Start Pro Safe includes all the control features of the Classic, together with an industrially recognised SIL2 emergency-stop system.
  • The Pro Safe can be used for applications requiring an integrated emergency-stop circuit, such as conveyors.
  • The inverter drive within the Pro Safe also offers additional features and higher performance where required.
  • When the start button is pressed, provided the emergency-stop button is not pressed and the blue reset button has been pressed, the inverter starts and ramps up to the speed set by the speed potentiometer.
  • The emergency-stop button removes power from the drive via the safety contactor and disables the drive's STO, monitored by the safety relay.
  • The healthy lamp indicates that the inverter is in a healthy state and has not tripped. The running lamp indicates that the inverter is running and its output is enabled.
  • The Pro Safe is compatible with Invertek's range of option modules. With an encoder module, it can provide closed-loop speed control.