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Home>DRIVES & MOTORS>Controls>Drive control - centralised or decentralised?

Drive control - centralised or decentralised?

29 April 2014

Should the drive technology in a machine or system be designed as centralised or decentralised? Michael Burghardt, Product Manager HVAC/R, Danfoss VLT Drives, suggests that the best approach might be to let the application decide

Both concepts have advantages, depending on the structure of the production system and the products being manufactured. What should rather be considered is the total amount of energy used in relation to process reliability, production output, maintenance, the cost of switch rooms and wiring. One thing remains crucial: how to apply speed control and improve process quality with a frequency converter.

Central control

Many systems are based on central control with frequency converters placed in cabinets or switch rooms. This means that control electronics and motors are placed far apart, which reduces the risk of environmental influences, all of which have a negative effect on the drive, such as corrosive gasses, dust or moisture.

Drive components are relatively inexpensive, but often require shielded motor cables. While separating the electronic controls and the motor enables use at higher ambient temperatures inside the plant, the spaces where the electronics are installed need to be cooled.

It is simple to use air conditioning for the control cabinet/switch room. However this also uses energy. But it can be an advantage in complex systems to place all control components in a single location for easy overview and management.

Decentralised control

In decentralised systems, motor control is built directly into the application, where the drive is fitted close to the motor. This approach is an advantage when the goal is to have a modular setup, for example to save installation costs or when there is no space for cabinets. It also reduces the complexity of the system, making it easier to expand. Integrating the drives directly with the application means that the cooling costs for the panels and switch rooms are reduced or even eliminated.

Often the installation of fieldbus and the cost of perimeter and control lines drive the decision to build a decentralised installation. As a result, the modular design provides plant owners and manufacturers with new possibilities. When used consistently modular design reduces project costs because entire machines or lines can be built on-site and put into operation immediately.

Switching from a centralised to a decentralised system requires owners to rethink their entire planning and production setup.

Mixed environments tend to offer a good balance of flexibility, availability and cost

The materials used in decentralised designs must also be robust enough to work in harsh environments and be efficient. A particularly suitable drive for decentralised environments is Danfoss’ new VLT DriveMotor FCM 106. The DriveMotor is a motor-mounted drive where the same drive component is delivered from the factory with either an asynchronous or permanent magnet (PM) motor. When combined with a PM motor, the DriveMotor satisfies IE4 Super Premium. ensures high efficiency with low heat dissipation. The VLT DriveMotor FCP 106 can be used with motors from most manufacturers.

Ultimately the application determines the optimal control concept. An accurate and detailed analysis of systems costs together with the drive supplier will provide help the analysis.

In many cases, a mixed approach will be chosen, depending on the requirements of the system and which concept delivers most benefits at the specific location. Mixed environments tend to offer a good balance of flexibility, availability and cost. As a rule of thumb, the higher the required functionality of the drive, the more economical it usually is to move the intelligence closer to the motor.

Key Points

  • In centrally controlled systems frequency converters are placed in cabinets or switch rooms
  • In decentralised systems, motor control is built directly into the application, where the drive is fitted close to the motor
  • Whether control is central or decentralised, applying speed control and improving process quality with a frequency converter is crucial