Choosing the optimal industrial automation equipment such as motors, drivers, and communication modules requires special attention to details. For example, there are many differences in motor and driver ratings between the National Electrical Manufacturers Association (NEMA) in North America and the International Electrotechnical Commission (IEC) in Europe.

When selecting motors, drivers, and controllers, factors to consider include input and output voltage and tolerances, required speed range and regulation requirements, torque requirements, acceleration, brake duty cycle, fast or torque response, and environmental factors including thermal management.

The communication requirements vary depending on the device's position in the industrial control hierarchy. At the level closest to the edge of the factory workshop, protocols such as IO Link can be used for smart sensors and actuators, while EtherCAT, PROFINET, Modbus, and other protocols can connect motion, safety, I/O, and vision systems.

The highest level of factory automation networks typically uses Ethernet/IP to connect with various automation controllers, programming interfaces, and cloud connections, and uses protocols such as DisplayPort to connect with human-machine interfaces (HMI). Between these two, the combination of Ethernet/IP, EtherCAT, and other protocols can connect the on-site level of the factory workshop with the operational and control levels.

The details are too numerous to elaborate on one by one. However, this article will introduce several guiding principles to consider when specifying motors, drivers, and communication modules, as well as application, hardware, and protocol examples from Siemens, Phoenix Contact, Omron Automation, Panasonic Industrial, and Schneider Electric.

Focus shift
Motors and drivers are common concerns in many industrial automation systems. As a starting point for the discussion, understanding the position of motor energy efficiency in broader industrial automation system performance considerations and how the focus shifts will be helpful for the discussion.

Using more energy-efficient motors can save up to 6% of energy. This is very good. However, adding an efficient driver and supporting components can increase energy efficiency by up to 30%.

When the focus shifts to overall system optimization, the game rules begin to overturn. Considering all mechanical components and adding communication capabilities to connect the Industrial Internet of Things (IIoT) including operations and factory levels, ultimately connecting to the enterprise level and cloud can save up to 60% of energy and increase productivity (Figure 1).

Images of energy conservation and productivity improvement
Figure 1: Improving integration and communication levels can save more energy and increase productivity. (Image source: Siemens)

Ecological Design of Motor Systems
IEC 61800-9 Part 2 "Ecological design of motor systems - Determination and classification of energy efficiency" is an important resource. This standard does not only focus on motor energy efficiency, but details a series of higher-level performance factors of the "motor drive system". VFD can be regarded as a part of the complete driver module (CDM), which includes the AC input "feeding part", the VFD like "basic driver module" (BDM), and "auxiliary equipment" including input and output filters, line chokes, and other supporting components.

The standard also defines a power drive system (PDS) as a CDM plus motor. Next is the hierarchy, which describes the motor system as PDS plus motor control equipment such as contactors.

The highest level is to expand the product or the overall system in Figure 1, which adds mechanical drive equipment such as transmissions and loaders. For more details on the IEC 61800-9-2 PDS energy efficiency standard, please refer to the article "What are the different types of variable speed industrial motor drives

The starting point for specifying the 'motor drive system' is the motor.

The motor is very important
If specified and used properly, motors can be very efficient machines. Therefore, specifying the motor is an important task for machine designers.

IEC quantifies motor power in kW, while NEMA uses hp, and the two can be easily converted. However, IEC and NEMA use different energy efficiency calculation methods, and for the same motor design, the IEC nameplate energy efficiency may be slightly higher than the NEMA rated value.

The actual energy efficiency of a motor is closely related to specific use cases. Therefore, motor energy efficiency standards are usually discussed from the perspective of reducing energy loss rather than absolute energy efficiency.

IEC 60034-30-1 specifies five motor energy efficiency levels, ranging from IE1 to IE5. The energy loss between different levels has decreased by 20%. This means that the losses of the IE5 "ultra high efficiency" motor are 20% lower than those of the IE4 "ultra high efficiency" motor. There are more factors to consider. In some cases, the power factor (PF) of motors with higher energy efficiency may decrease.

In North America, NEMA has fewer energy efficiency ratings, but they are equally important. NEMA recognizes motor service factors (SF) that are not included in IEC standards. A NEMA motor with an SF of 1.15 can operate continuously at 115% of its rated power, but the high operating temperature of the motor can lead to a shortened lifespan of the bearings and insulation materials.

IEC does not use SF, but determines ten working systems or service factors (S1 to S10) based on factors such as continuous and intermittent operation, speed changes, and braking usage.

The operating voltage and frequency range of NEMA and IEC are different, but both are expressed in terms of "per unit" (p.u.). In the p.u. system, values are expressed as scores of benchmark values. NEMA recognizes a range of motor voltage and frequency. IEC recognizes two "zones" (Figure 2).