There are two types of drive configurations on the market today: centralized and decentralized. A centralized drive is characterized by a customer using an electrical enclosure and mounting the drives and power distribution hardware within that enclosure. Then, the customer runs cable lead lengths from the enclosure to the line or field devices being controlled.
In the decentralized approach, the drive is placed on the machine or assembly line; this is applicable to a variety of products currently available. The main benefit of having a decentralized drive is that heat is removed from the electrical enclosure and there can be a considerable cost savings in machine or line build time as a result.
The basic modular drive consists of a power module (PM), control unit, and an operator panel (OP). The power module supplies voltage to the motor, the control unit monitors the power module and is the brains of the drive, and the operator panel is the user interface for the drive and motor control. OEMs can prewire the drives before panel builders mount the equipment. As a result, time-to-market is greatly reduced. The PM saves space as a result of having the same frame size with or without an integrated filter. Integrated energy recovery enables excess energy to be regenerated to the line supply, which eliminates the need for braking resistors. Side-by-side mounting saves space in the control cabinet and reduces costs without de-rating.
Regenerative power modules on the drive can help take the excess energy and apply it back to the grid or even redirect it into the plant to power other equipment. While regen power has been a viable concept for decades, it can today be applied to a much lower power range of motors, plus the use of the concept with variable-speed drives means the applications broaden considerably, from the simple on/off pump or motor to a high-performance hydraulic injection molding machine, lift table, stamping press, mining conveyor line, and many types of process equipment that fluctuate greatly in their running power demands.
The OP features simple setup and configuration using wizards with integrated plain text help functions. In addition, the OP includes quick access to all parameters and displays fault codes without scrolling. Simple, individualized, local drive operations and visualizations are often provided. If a user receives a fault, the fault number appears on the user interface. The fault will provide a user with a description and reason for the fault as well as a remedy appearing in the Smart Access Module (SAM) as a Wi-Fi hotspot and a Web interface built into the module. This SAM is ideal for configuring drives within a mobile device or laptop.
In reviewing drive options, machine builders and end users need to seek out a drives supplier with a commonality of configurable parameters and compatible hardware offerings. This achieves a reduction in commissioning and training time as well, thereby achieving an overall lower total cost of ownership (TCO).
Within the OP on such a flexible drive, standard dual-port Ethernet/IP supports Ethernet/IP and Profinet and integrates into an engineering portal or third-party controllers, making them ideal for a greenfield project or brownfield application, with different brands onboard the component elements. The 24-VDC terminals allow the communications of the drive to continue functioning even if 480-V power is removed. Thus, customers can safely program the drive from the front without risking an arc flash. An integrated encoder offers incremental/high resolution feedback, while the memory card quickly backs up parameters or recovers a program. Several selectable application-specific modes include pumps and fans, mixers, agitators, conveyors, and extruders for such a drive. Seeking out such components, even if the initial cost is somewhat higher, will accrue benefits to the machine builder and their customers in the long run, owing to the overall cost savings in commissioning, training and maintenance.
If a customer still wants a centralized drive design, they can benefit from the use of today’s push-through design feature. This means hanging the heat sync of the drive out into the environment. Heat sync and power unit fans are now easily located outside the enclosure. The AC unit can now be sized for the control unit heat watt loss. Circulating fans can replace AC units. The advantages include a lower energy bill up to 50%, a smaller shop floor footprint, and a lower cost for AC unit maintenance. As a rule, for every 10 °C increase in temperature, a reduction by half in the life of the product occurs. Therefore, keeping drives cool is always important, especially in warmer climates.
All popular drives from major manufacturers use common parameters, although some are more beneficial, owing to their integration of this feature with other design and electrical characteristics. This makes it easier to program and remember settings and locations for the operators and maintenance personnel. Once applied to one drive, the same procedure applies to most others in the system. The most advanced drives have safety features built-in such as safe brake control, safe torque off, and safe stop 1. These features are available in hardwire versions and on a network basis.
Drive investment can be a gateway to digitalization. Drives and motors are integrated throughout the machine building cycle, using several engineering tools. From setup to commissioning to the actual run conditions, maintenance procedures, and issue resolution, the construction, installation, and running of today’s machines can be simulated in this virtual world, meaning the startup time is greatly reduced and productivity levels reach their optimum mark much faster and remain there more consistently.
In popular use today, there are three different types of motor controls. Across-the-line is the least expensive initial investment. Essentially, the full voltage and current are applied to the motor at the time of engagement (up to 600%). The motor will then run at nameplate speed. Soft start is in the middle price range and provides the ability to control current, acceleration, and deceleration. As with across-the-line, the motor will run at nameplate speed. Variable frequency drives (VFDs) are the most expensive in their initial investment. Still, there are many advantages of using VFDs such as the ability to control speed at any set point, to control current and torque throughout the entire speed range, and to realize energy savings through regenerative braking.
VFDs are an attractive option for users due to the fact they reduce mechanical and electrical stress on systems, control process variables, reduce in-rush current, enable energy reduction, and provide connectivity, with full data analytics. Conventional full voltage starting can cause mechanical shock to the equipment and the work in process when frequent stopping and starting of a conveyor system places stress on all mechanical linkage.
Conventional full voltage starting can’t control the acceleration and deceleration rates of a machine, nor the speed of the machine. Furthermore, conventional full voltage starting can’t control the in-rush current that the motor draws when it starts and typically allows 600% of the rated motor current during startup. As a result, the in-rush can cause voltage dips and other power disturbances.
Utilities establish their pricing based on average power consumption. “Peak demand” charges may occur when starting large motors across the line (typically a 15-minute penalty at higher than agreed rate). Reduced energy consumption is achieved when applying drives on variable torque loads. Variable Frequency Drives connect easily to offsite programming portals and can offer Ethernet and Profinet connectivity for running additions to a brownfield installation.
Drives are also being integrated into virtual systems and cloud databases more often today. These are perhaps hidden but very real cost-saving potentials for a machine builder or end user. Careful consideration should be given to such factors when developing a new machine or retrofit plan.
Depending on the application, a variable torque or a constant torque inverter is used. The torque needed to perform a function increases as the speed increases in variable torque. Constant torque means that torque remains the same as power increases. Variable torque is applied to pumps and fans, while constant torque applies to everything else. In centrifugal applications, like pumps and fans, a reduction in speed results in a proportional reduction in flow.
Energy savings can be monitored and reduced through VFDs. In air systems, a VFD replaces the contactor to control flow or pressure and the outlet damper is opened fully. The same procedure applies to water systems, replacing the contactor with a VFD and opening the throttling valve fully.
An OEM must think about how to build a machine that will work on any kind of power system. When building a piece of equipment, how would a low harmonic solution be provided? Other issues that should be considered include: How hot is the plant? What kinds of contaminants are in the atmosphere?
Both OEMs and end users need to design for two types of systems — grounded and ungrounded — and they must consider the locally required electrical standards. Drives can play a significant role in this process. Being cognizant of the options and available features on the market today will benefit you and your customers in trackable ways.
This article was written by Chad White, Motion Control Business, Siemens Industrial, Atlanta, GA. For more information, visit here .