Energy management for automation 
Energy management and responsible handling of resources is currently the number one topic in industry. In light of this, the Automation Initiative of German Automobile Manufacturers (AIDA) asked the PROFIBUS organization and PROFINET International (PI) to provide functions and mechanisms for PROFINET that support energy-efficient production.
In response, PI is working on a vendor-neutral energy savings profile called PROFIenergy. The objective is to develop a uniform (standardized) interface for data exchange between a controller and a wide range of devices with energy savings options. The profile will be used for exchanging data and commands, but will not contain any logic functions in terms of process control. The first release of PROFIenergy should be available by the end of this year (2009).
The PROFIenergy roadmap.
Energy-efficient production means more than just the use of variable-speed drives and efficient motors. The question going forward is how to selectively place complete production lines or portions thereof into stand-by mode during unproductive times. Ethernet networks such as PROFINET play a key role in this.
Main switch OFF: all production activities cease and the factory lights go out. This is possible during idle times, such as weekends or factory holidays, in almost every facility around the world. But what happens during shorter breaks? Here, the equipment continues running and consumes energy, even in the absence of value-adding activities or productive results.
For example, a bodyshop factory in the automotive industry continues to demand 20 kW of power during idle times. For this reason, shutting down the entire facility on the weekend is not sufficient.
Rather, it is worthwhile to selectively switch off individual components or portions of the plant during production, if they are not required at the moment. When considered over an extended time period, switching off a device for just 30 seconds can be profitable in certain cases, such as for lasers.
This could significantly improve the energy balance of a production unit. In today's automotive industry, several models already run over the same production lines. Accordingly, it would be possible to respond to fluctuations in sales of individual models by selectively shutting down model-specific portions of the plant.
However, the current approach of disconnecting production components from the supply system using one or more 'main' switches, that is, deactivating different production units with a high degree of selectivity, is not sufficient for this purpose. Permanently wired switching paths for permanently defined production areas are simply too inflexible to fulfill the new requirements for energy efficiency.
German automobile manufacturers, in particular, have recognized this fact and are currently searching intensively for concepts and solutions that will improve the energy balance at both existing and future factories.
The launch of PROFINET IO for plant communication in November 2004 represented a decisive step in the commitment to modern Ethernet technology: According to the conceptions of the Automation Initiative of German Automobile Manufacturers (AIDA), each plant component " whether an industrial robot, a converter, a process control system, or an I/O module " should be accessible in the future via a uniform and comprehensive communication infrastructure, ideally through Ethernet-based protocols such as PROFINET.
Each component of the higher-level control system or the line PLC can then be selectively activated and controlled via the IP address and the device name. In short: The decision to introduce PROFINET laid the foundation for a new and forward-looking energy management.
Future-looking energy management means: switching off equipment is no longer accomplished by means of the conventional and very 'coarse' main switch method but rather by means of the network. The general supply network of components remains activated, and the components, when initiated by a 'network command', pass into a defined energy-saving mode.
One possible solution involves the definition of different energy-saving modes (see figure) for devices. This profile allows a controller to easily and uniformly activate energy-saving modes of devices and to evaluate their responses. As a result, energy can be managed without adversely affecting the production process.
Definition of efficiency modes.
When developing the energy efficiency modes, an attempt was made to allow for the diversity and technical options of as many component groups and suppliers as possible. If PC-based systems are used, as is the case for some process controllers or for the robot controller of Kuka, the standard 'Wake on LAN' service can be used in many cases. This protocol, also referred to as 'Magic Packet', was defined and standardized in 1995 by Hewlett Packard.
With this technology, which is currently used in PCs throughout the world, the controller passes into an extreme energy savings mode. Only the connection to the network is kept alive in order to react to the wake-up command in the form of the 'Magic Packet'. Besides this mode, three other modes are conceivable:
Mode 0: All energy-consuming systems of components are shut down, switches integrated into the component and the PROFINET IO stack are deactivated, and safety-relevant functions of components are no longer supported; a changeover to operating mode can only be initiated by the 'Magic Packet'.
Mode 1: This mode was defined specially for highly integrated components. It differs from Mode 0 only in that the PROFINET IO stack and, thus, the integrated switches remain activated " meaning that the network infrastructure continues to function. I/O statuses of the component are still not available, and the transition to a higher mode is initiated by a standardized PROFINET protocol.
Mode 2: This is targeted specifically at modular I/O modules. In this mode, the PROFINET IO stack and the integrated switches are active, and I/O statuses and safety-relevant functions are available in some cases, depending on the preceding configuration. The transition to operating mode is initiated by a standardized PROFINET protocol.
Mode 3: Operating mode " all subsystems of the component are activated, and the component signals that it is 'ready to operate'.
For simpler configuration of the overall system, information is needed regarding the energy efficiency modes supported by the component along with its time behavior. Since PROFINET IO is the communication layer of the future power management level, it would be useful to describe the individual capabilities of a component in the GSDML file.
Among other things, the standardized description would indicate which energy efficiency modes the component supports and the length of the individual power-up times until the "ready-to-operate" status is reached. The higher-level management software can use this information to calculate the time- and energy-optimized power-up of the (sub)system from the individual parameters, that is, to achieve the optimal sequence.
As described previously, all changeovers from one energy efficiency mode to another, except for 'wake up' from Mode 0, are managed via the PROFINET IO communication layer. For this purpose, PI is offering a standardized data record that allows the required mode transitions to be initiated via defined action bits.
Saving of energy by PI.
In addition, the data record provides standardized diagnostic information regarding the current status of the component. With this approach, a deliberate decision was made to eliminate the mapping of functions and status information onto a pure I/O interface. By defining a uniform data record, the interface is kept the same for all components, which greatly simplifies the programming of the power management. The current content of the data record can be read and written via acyclic read/write services.
Conclusion
The PROFINET IO-based energy efficiency functions and the Wake on LAN command will provide plant operators in the future a means of optimizing the overall energy balance within a plant. The success of this approach is contingent on a speedy standardization by PI and quick-turnaround implementation of functions within components. In addition, new energy management tools are needed to close the gaps between production planning and production equipment control.
Dr. Peter Wenzel is managing director of the PROFIBUS User Organization in Germany