Frequency inverter: installation in the control cabinet or decentralised in the field?

The classic: control cabinet inverter

Traditionally, all electrical and electronic components of a system – and thus also the frequency inverters – are housed in a control cabinet. It protects both the sensitive electronics inside and the external production environment. Dirt, dust, heat, humidity and electromagnetic influences cannot enter and electromagnetic emissions, dangerous voltages or possibly occurring fires cannot get outside.

In general, the drive electronics are located in the control cabinet in 80 percent of all applications. This control architecture is particularly dominant in mechanical engineering. In most cases, the spatial separation of motor and control technology has historical reasons, but in certain applications it is also advantageous – particularly when it comes to high powers and extreme environmental conditions. Although decentralised drive systems are common for the explosion hazard areas of zone 22 (explosive dusts), explosive gases, mists and vapours require such high protective measures that decentralisation is technically possible but would not make sense in terms of economic efficiency. Sensitive areas such as the process industry, the chemical industry and painting tasks therefore use an installation point in the control cabinet in most cases. In some applications, it may also be necessary to have central access to the frequency inverters.

With these requirements, installation in the control cabinet makes sense:

• High powers
• Extreme ambient conditions such as explosive gases, mists and vapours
• High hygienic requirements
• Central frequency inverter access required

The future belongs to decentralised frequency inverters

In many places, the control cabinet is still considered the ultimate solution for housing frequency inverters – it is uncertain whether this remains the case in the future. For in general, an increasing system concept can be observed; decentralised automation concepts are gaining ground. Wherever possible, users are resorting to solutions that are distributed in the system – driven by the shift towards modular production plants and the increasing demand for compact, service-friendly and economic drives. Europe is leading the way, but the USA and Asia are following suit. In particular, sectors such as intralogistics, conveyor technology, the food industry, airport technology and the packaging industry are increasingly relying on decentralised concepts with frequency inverters installed on or close to the motor. This is not surprising, because the specific advantages of decentralised drive technology come into effect particularly with extensive plants as well as in modular and mobiles systems.

Decentralisation means that the drive tasks are distributed to individual, intelligent components in the field. They are installed where they are needed – i.e. on or close to the motor. Decentralisation of drive technology is primarily used in the lower and middle power range and enables a system design that consists of autonomous production islands that largely regulate their processes themselves. This reduces the load on the higher level control system and decreases system complexity. For the user, this means faster commissioning and simplified maintenance and repair processes. With a modular concept there is also maximum flexibility, as changes to the system architecture can be made at any time without large structural modifications. As a result, this means: reduced costs and more efficiency.

Advantages of decentralisation

The decentralised automation concept leads to a more cost-effective and uncomplicated control cabinet construction. If the frequency inverters are installed directly in the field, less space is required in the control cabinet. Consequently, the control cabinet can be smaller or may even be eliminated entirely. As there is no frequency inverter as an extra source of heat in the control cabinet, costs for air conditioning are also reduced. This in turn has a positive effect on the energy balance.

Thanks to spatial proximity of motor and frequency inverter, both the wiring effort and the cabling between cabinet and drive in the system field are also reduced to a minimum. The advantage here is that decentralised solutions are often available as plug-in versions. This further simplifies the installation. No or only short cables are required, which – thanks to the optimal EMC properties of motor-mounted frequency inverters – do not necessarily have to be shielded. Although shielded cables cannot be dispensed with an installation close to the motor, they can be very short and are therefore cost-effective. Since the frequency inverters are mounted directly on the motor or in its immediate vicinity, commissioning close to the motor is also possible. As the connections for the power supply and the bus system are usually pluggable and looped through, this can be carried out quickly and easily – quite in contrast to star-shaped point-to-point wiring in the control cabinet. This reduces the costs.

Advantages of decentralised frequency inverters:

• Control cabinet may be smaller
• Minimal wiring and cabling work
• Simple maintenance
• Rapid commissioning thanks to pre-configuration at the factory
• Modifications and extensions to the system design easily possible at any time
• Reduced costs for the plant design
• Reduces the complexity of the system
• Increases the efficiency of the entire drive system
• Can be integrated into all automation architectures

Frequency inverters from NORD have condition monitoring solutions for predictive maintenance systems and are well equipped for use in IIoT and Industry 4.0. The integrated PLC can process data from connected sensors and actuators, initiate control sequences and communicate with other system components. The periodic or continuous recording of drive and status data allows for an early detection and avoidance of impermissible operating states. Unscheduled downtimes can be significantly reduced and status-oriented maintenance (predictive maintenance) replaces time-based maintenance. Machinery and plant downtimes can be scheduled.

Frequency inverters for any drive application:

• Integrated PLC
• POSICON positioning module
• Lifting gear function
• On-board brake chopper and braking resistor
• Closed-loop operation with incremental encoder and/or absolute encoder
• Functional safety
• Energy-saving function for partial load range
• Support of all common field bus and Ethernet dialects
• Operation of synchronous and asynchronous motors
• Protection class IP55 / IP66
• All relevant international certifications for global use

Decentralised frequency inverters in combination with control cabinet inverters

Control cabinet inverter or decentralised frequency inverter? The question suggests that these are two opposing strategies that categorically exclude each other. But this not the case at all. Quite the opposite. In many cases, a combination of both drive concepts is a sensible solution. Bottling systems in the beverage industry are a good example for such mixed concepts, i.e. the coexistence and interaction of control cabinet and decentralised technology. Where work is carried out directly with the product and corresponding hygiene standards have to be met, a control cabinet solution may be recommended. However, decentralised solutions are usually the better choice for the conveyor belts between the individual stations. Thanks to the platform concept, NORD DRIVESYSTEMS is also able to provide suitable drive solutions for these requirements with a combination of control cabinet and decentralised frequency inverters. There are no differences between the control cabinets and decentralised inverters in the field in terms of performance, communication, control and parameterisation.