Mains-connected drives have been increasingly giving way to more efficient and flexible alternatives such as combinations of geared motors with frequency inverters.
Earlier situated at a distance from the machine in a control cabinet, power electronics such as inverters are now mounted near the motor with integrated units combining drive mechanics and electronics opening up new possibilities. Distributed control installations, however have their limits that users should be familiar with when designing drive concepts.
New approach for large-scale facilities
Drive electronics moving from the control cabinet to the machine have economical as well as technological reasons. The systems save costs over their total lifecycle, take up less space, and allow for increased flexibility in facility design.
Facilities with many drives used to require centrally installed frequency inverters in control cabinets with the drives installed near the machine or application. Since the control cabinet with the drive electronics was the starting point for cabling all motors or geared motors in the field, star wiring was the automatic result.
Materials handling facilities in particular, such as loading zones in high-bay warehouses and belt or roller conveyors benefit from the fact that integrated drive solutions do not require the usual long motor cables and large numbers of control cabinets. Instead, highly flexible setups become possible in many cases, with minimal wiring and installation effort.
Easier handling decreases costs
Integrated drive units can be completely wired and tested before installation. In addition, designing the drive concept and commissioning takes up much less time. The remaining control cabinets are much smaller and cooler and easier to standardise. The solutions also support current communication buses and allow line wiring. Shielded motor cables are either not required at all or are very short.
Integrated drive units in the field are easily accessible for service personnel with diagnostics performed directly at the site. Due to pluggable connections, many units can even be exchanged without an electrician if required. Data can comfortably be transmitted to higher-level controllers using sensor and actuator interfaces while integrated status LEDs facilitate on-site diagnosis.
Applications with distributed drive technology can reap considerable economic advantages over centrally installed power electronics. The 20-30% higher purchase price of the components is offset by up to 40% lower engineering costs, up to 60% savings during installation and commissioning, and up to 50% reduction in maintenance costs with the savings amounting to about 30% over the product lifecycle depending on the size and type of application.
Have cabinet-installed inverters done their duty?
Advantages of distributed electronics units suggest that conventional installations with control cabinet inverters are outdated, particularly when compared with the latter’s constraints. When connecting remote geared motors with a centrally situated control cabinet, the maximum motor cable lengths must not be exceeded. Furthermore, depending on possible interferences, shielded cables might be obligatory.
Alongside the power lines, a number of other wiring lines including signal cables for motor brakes, temperature sensors, incremental encoders, and other components must be laid; the drive solution is complicated by the fact that all these diverse components need to be made compatible. Furthermore, different floor plans with drives in different positions require different control cabinet configurations. Consequently, it remains difficult to standardise control cabinets.
Central option for difficult cases
Despite the obvious drawbacks over the new integrated drive electronics, there is often no way around centrally installed control cabinet inverters even today. The requirements of widespread, distributed facilities are quite different from those for shredders, chippers and similar machines. In applications such as these, the extreme environmental conditions alone are reason enough to put the electronic drive technology somewhere safe and enclose it in a robust housing.
Additionally, in some applications, drives installed in too close proximity of each other or for high power outputs make distributed inverter solutions difficult since the temperature can quickly rise above their limit. These applications should therefore follow the centralised route. In such cases, even large drive components such as motor chokes or mains filters can be integrated in control cabinets without problems.
In distributed systems, on the other hand, space for all kinds of optional equipment is considerably limited. Also, certain applications appreciate the fact that cabinet inverters can be accessed and operated along with the controller. Another typical application, series machines that are shipped in one piece will keep on profiting from centralised drive technology as the most cost-efficient solution.
Distributed drive solutions have opened up new avenues for mechanical engineering and plant construction in recent years, resulting in decreased handling effort and costs. The optimal concept for electric drive control however, depends on the specific application requirements and needs to be determined individually.
It is therefore recommended that companies consult with leading drive manufacturers such as NORD Drivesystems
who can supply compatible inverter lines for both options, and who continues to invest in the development of both technologies.