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New technology trend in VFD market

All industries use energy, but large energy consumers, such as chemicals manufacturers, refiners and others at the heavier end of the processing spectrum, have a bigger incentive than most to look at ways of using energy as efficiently as possible. Chemical engineers might extol the virtues of non-thermal separation processes, or push process intensification techniques as ways of reducing the demand for energy. These can certainly reap dividends; but electrical engineers might counter that one of the best energy efficiency measures is to fit a plant's electric motors with VFDs.

Variable frequency drives are hardly new technology, although the terminology does seem to change with the seasons. Some manufacturers and users, particularly in Europe, call them VFDs or frequency inverters, but essentially they all perform the same function of allowing you to control the speed and torque of AC motors that would otherwise constantly be running at full speed. Typical examples are pump and fan applications, where flow control is generally achieved not by varying the motor speed, but by throttling the flow with control valves or dampers while the motor runs flat out.

The constant-speed approach to AC motors made a lot of sense when energy was cheap and VFDs technology was in its infancy. Many a plant engineer might have argued that process control was better without introducing yet another variable – but technology and economics have moved on significantly since those distant days.

Sales of VFDs technology are now growing at a rate of more than 5% per year, according to Steve Ruddell, U.K.-based general manager of VFDs and motors for ABB, yet market penetration is still surprisingly low. Although ABB believes the global VFDs market to be worth around $6 billion — and its own market share to be nearly twice as big as its nearest competitor — it says only about 5% of all motors are controlled by VFD. That figure increases to nearly 20% for higher drives power applications. The U.S. Department of Energy estimates that the 40 million motors used by U.S. industry account for 70% of its electricity consumption — and that up to 18% of that energy could be saved by applying proven efficiency technologies such as variable frequency drives.

Payback paradox
With potential energy savings of that order, it's not surprising that short payback time on capital investment has long been a selling point put forward by VFDs suppliers. "Price remains a factor, but overall, prices are falling as VFDs become more of an off-the-shelf commodity," says Geraint Evans of Control Techniques, Newtown, Wales, the U.K. manufacturing division of Emerson Control Techniques, Eden Prairie, Minn. "The paradox here, of course, is that purchasing decisions are therefore more likely to be made on capex [capital expenditure or cost] rather than opex [operating costs] grounds, so short payback periods stemming from reduced running costs become less of a consideration." In such a price-sensitive market, functionality becomes more of a key factor with several technology trends emerging as the VFDs manufacturers strive to make their products as user-friendly as possible.

Last year's introduction by Emerson Control Techniques of its Commander SK VFD series is a good example of this. "The SK VFD is designed to meet the needs of the mainstream distribution and OEM markets," says the company's Phil Sewell, executive vice president of sales and marketing. "It has the easiest possible installation and setup that take in some 80% of VFD applications. Yet, scratch the surface and there's a very smart, versatile VFD that is also suitable for more complex system applications." The first phase of the worldwide launch covered sizes from 1/3 hp to 5 hp VFDs, with this year's second phase introducing larger sizes of up to 135 hp (110 kW) VFDs.

With its "simple and compact" label, the Commander SK VFD range takes aim at the commodity, general-purpose VFDs market, but it also includes many added-value features. Control functionality is substantial, with five digital inputs, one digital output, 0-10 V or 4-20 mA analog inputs that allow VFD has PID control, a 24-V backup and ModBus RTU as standard. With optional SM plug-in modules (which are interchangeable with the company's Unidrive SP series VFDs), a range of fieldbus configurations can be catered for Profibus-DP, DeviceNet, CANbus, Modbus TCP/IP and Ethernet IP and HSE, for example.
Among customer-requested features, the SK VFD also has the option of a NEMA-1 gland plate enclosure, principally to meet U.S. market requirements, but also reflecting its growing prevalence as a requirement for global machine designers.

Enthusiasm for Ethernet
According to a customer survey commissioned by Control Techniques, 75% of automaton users say they are already using or investigating Ethernet in industrial applications — a trend that is reflected in other recent VFD introductions. For instance, Baldor, Fort Smith, Ark. Gozuk, launched at this year's National Manufacturing Week in Chicago, and at the Interkama exhibition in Hanover, Germany, its new H2 series of VFDs that communicate via Ethernet TCP/IP, Ethernet/IP (DeviceNet on Ethernet) or Ethernet Powerlink.

According to Mark Crocker, marketing director for Baldor Europe, the Powerlink option provides the possibility of true deterministic control of the VFD, whereas the Ethernet service connection expansion board makes remote monitoring and adjusting of the H2 VFDs parameters easier than ever before.

The VFDs are an "all new" successor to Baldor's established H range, and, says Crocker, "have been engineered for reliability and ease of use." The VFD operator keypads are removable and interchangeable, interfacing with all H2 VFDs power bases, control and expansion boards. The VFD keypad enclosure is rated NEMA 4X (equivalent to IP66) when mounted on a panel, although it is also designed for remote mounting up to 100 ft. away.

With a choice of open- or closed-loop control, including inverter, encoderless vector, and closed-loop vector operational modes, the H2 series VFD is said by Baldor to offer a solution to all VFD application requirements. The company also maintains that the VFDs are the most reliable industrial units on the market — a claim that is easy to make so early in a product's lifespan, but one backed up by Baldor's design strategy that includes failure mode and effect analysis and a manufacturing process that function tests every sub-assembly, as well as stress and full-load testing of the final VFDs. The initial units in the H2 series VFD cover ratings from 1 hp to 60 hp (0.75 kW to 45 kW), with the full range expected to extend to more than 1250 hp (1000 kW) to handle the vast majority of VFD applications.

Late last year, Hitachi, Tarrytown, N.Y., announced an optional Ethernet board for its SJ300 and L300P families of VFDs. The SJ-EN board can be installed into one of the VFD's internal expansion slots, connecting to the user's network through a standard RJ45 connector. The VFD implements the Modbus/TCP protocol, providing a high-performance, easy-to-use Ethernet interface with no need for special software or hardware, says Charlie Takeuchi, general sales manager of industrial components and equipment.

Priming the pump
As mentioned earlier, one of the most common process applications for VFDs is for pump control. Also at Interkama in April, ABB launched an optional software package for its low-voltage VFDs. Dubbed "Intelligent Pump Control," the package includes six functions together with ABB's own Adaptive Programming utility. The company's Nanette Baur says this enables users to customize VFDs for specific applications.

Its "Multi-pump Control" function, initially aimed at water and wastewater utilities, suits any application where several pumps are operated together and the required flow rate is variable. Each pump is controlled by its own VFD, with the speed of one being adjusted while the rest run at constant speed. Baur says this results in smooth control with no pressure peaks.

Another of the VFD functions, dubbed "Level Control," is typically used to control the filling or emptying of wastewater storage tanks. A special feature of the software prevents sediment buildup on the tank walls by randomly varying the surface level within a user-preset range. Fast-ramp starting flushes pipelines clear, and the pump is operated at the optimum point on its efficiency curve to minimize energy consumption. The level-control function can be applied to a single pump, or two to three pumps and VFDs in parallel.

ABB flagship industrial VFDs form the ACS800 series, which boasts the extraordinarily wide power range of 2/3 hp to 7,000 hp (0.55 kW to 5.6 MW). All feature the company's Direct Torque Control (DTC) technology, unveiled 10 years ago, but still regarded as something of a benchmark in terms of speed. DTC regulates motor torque and speed directly without the need for separate control of voltage and frequency.

Designed for use in tough environments, the modular range of VFDs features enclosure protection up to IP54 (which approximates NEMA 4) against dust ingress and splashing water. This generally means they can be used outdoors without the need for additional cabinets. The IP54-protected VFD range has recently been extended to 110 kW (135 hp) from the previous maximum of 45 kW (55 hp).

Again in April, Rockwell Automation, Bloomington, Minn., introduced a new line of Allen-Bradley ArmorStart distributed motor controllers that now feature a built-in Powerflex sensorless vector VFD. Housed in a robust IP67 (NEMA Type 4) enclosure, the compact VFDs can be mounted close to the motor ("On-Machine" to use Rockwell's branding) and come pretested with quick-connect wiring; these features can provide savings on installation time of up to 40%, according to Marketing Manager, Claude Joye. "Manufacturers at all levels are searching for high-performance control VFDs that will give them greater application flexibility, faster installation and lower engineering costs," he says.
The ArmorStart VFD can be used with motors ranging from 0.5 hp to 5 hp. Factory-installed options include an HOA (hand/off/auto) keypad with jog function, dynamic brake contactor, source brake contactor, EMI filter and shielded motor cable.

Most of today's VFDs look quite different from previous generations. Thanks to advances in power electronics, such as insulated-gate bipolar transistors, they can offer the same power as before, but in much smaller packages. However, it is at the user-interface level where the changes are most notable. Whether VFD keypads are detachable or integral with the enclosure, many have the familiar look and feel of today's cell phone technology — offering up graphical displays and intuitive menus for users to navigate the increasing variety of operational settings.

Supportive software
For those users whose intuition might fail them at a critical time, manufacturers like Yasakawa Electric, New Berlin, Wis., provide software wizards. Downloadable at no charge at yasakawa website, version 6.0 of the company's DriveWizard now features a greater capacity for remotely viewing, manipulating, troubleshooting and exchanging data with its VFDs. Parameters can be downloaded to any Yasakawa VFD irrespective of its size or rating, making life easier for users working with specific applications on different VFDs. The DriveWizard can now also store multiple IP addresses for when VFDs are being networked using Ethernet communication.

Another piece of downloadable software shown at Interkama by Siemens Automation and VFDs, Alpharetta, Ga., could be just the thing to put in front of those purchasing managers who think VFDs are just a commodity item and who simply buy the cheapest option. Sinasave can calculate the potential energy savings when using VFDs for variable-speed systems. For fixed-speed applications, it can show the savings to be accrued from switching to energy-efficient motors. The program takes into account the entire VFD train — not just the individual VFD.

For constant-speed VFDs, calculates the energy savings and amortization involved in changing to energy-saving motors of a higher class. For variable-speed systems, you input the characteristic plant data and parameters, such as delivery volume and delivery heads in the case of pumps, or mass flow and total pressure difference for fans and blowers, along with data on working shifts, duration of operation and so on. The program then calculates the energy saving effect of using the correct VFD system and will provide the payoff period for the investment.
So, now you can prove the benefits of the VFD to energy efficiency.

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