Paving the way
Check the Monday-morning newspaper in the fall for pro football, and you'll see plenty of praise for the running back that gains over 100 yards and scores two or three touchdowns. You may even read how a quarterback "had all day to throw the football," amassing gaudy statistics that make fantasy football leaguers delirious.
Check the Monday-morning newspaper in the fall for pro football, and you'll see plenty of praise for the running back that gains over 100 yards and scores two or three touchdowns. You may even read how a quarterback 'had all day to throw the football,' amassing gaudy statistics that make fantasy football leaguers delirious.
What you won't hear is how well the offensive linemen did their jobs so players in more glorified positions could do theirs. You won't often read about the offensive linemen who paved the way for the running back to get his 100+ yards, or blocked long enough to allow the quarterback with Hollywood looks and the multimillion-dollar contract to throw all day without fear of getting sacked.
AC drives might be the industrial equivalent of NFL linemen. They provide the necessary power so other equipment can perform as required, whether it's operating a pump, fan, or assembly line. Working anonymously in the trenches, they too are rarely glorified.
Control Engineering 's 1999 AC Drive Study examines the types of ac drives respondents use; determines which functional and performance features respondents want most; and looks at how often respondents buy customized versus off-the-shelf ac drives. Of the 1,500 readers that received the questionnaire, 373 responded for a 25% response rate.
Seventy-two percent say they recommend, specify, and/or buy ac adjustable-speed drives for in-plant requirements. Twenty percent do it for OEM requirements, and 2% do it for both.
Just about everywhere
In all applications using ac drives, there isn't one that is particularly dominant. Twenty-eight percent of the respondents use them in pump and fan applications, 25% in material handling equipment, and 16% in assembly lines. Other applications that employ ac drives are packaging machines (13%), pulp and paper (10%), and machine tools (10%). Results exceed 100% due to multiple responses.
Volts/Hertz control-type (open-loop) ac drives are the favorite of respondents; 84% of them use this type in their applications. Field-oriented vector control (closed-loop) type follows with 34%. Sensorless vector control-type ac drives received 30% of the votes.
Jeff Duncan, marketing manager with Danfoss Electronic Drives (Rockford, Ill.), says he isn't surprised that open-loop ac drives are the most favored. Mr. Duncan says, 'The majority of ac drive applications are straightforward. They don't need something too technical, especially when the drive is operating a pump or a fan. If a light switch works, why would I need something new fangled and sophisticated?'
Users want simplicity
Make it simple. It's a statement not unheard of in the industry, and perhaps to nobody's shock, simple controls/setup is the functional feature users want most in ac drives (see graph on previous page). Not only did that feature rank highest, but 92.3% of respondents also rated the feature as a 4 or 5 on the scale.
Related to simple controls/setup, programmability was users' second most-wanted feature. Aside from wanting easy setup, users want simple programming when they must configure and integrate ac drives into their systems. Eighty-six percent of respondents rated programmability as very important or somewhat important.
Other highly-rated functional features are convenient operator interface, price, and EMI/RFI protection.
If we equate performance features with a deck of cards, it has been shuffled significantly. According to last year's survey (see Product Focus, CE , Oct. 1998, p. 138), the top four performance features in descending order were torque control, dynamic braking, tripless operation, and zero speed control. This year, tripless operation narrowly beat out torque control as the most preferred feature. Distance between motor and drive, which didn't make the top four last year, came in third. Dynamic braking, which came in second last year, slipped to fourth. Zero speed control, fourth in last year's survey, came in sixth this year (see graph on previous page).
Doing it by themselves
By a margin of almost three to one, respondents prefer to just let their drives do their job without networking them in any way. Eighty-eight percent say their drives are operating as stand-alone units, while 30.4% have their ac drives connected to a network (results exceed 100% due to multiple responses).
Dave Kokalj, industrial applications manager for Magnetek (New Berlin, Wis.) sees two primary reasons why most ac drives aren't networked: they aren't in areas where networking is needed, and there isn't a standardized communication protocol.
He says in such applications as operating pumps or fans, 'All they need is a couple of contact closures and that's it. They don't justify the cost of networking.' Mr. Kokalj also says in building maintenance and automation, networked ac drives are more common.
The second reason users don't often see networked ac drives, says Mr. Kokalj, is no standardized protocol exists. However, his company, Magnetek, sees Ethernet as a networking force to be reckoned with. The company's next generation of drives all will have Ethernet networking capability.
Of the respondents' ac drives connected to a network, DeviceNet claimed 41% of votes. Profibus followed in second with 24%, while Interbus (15%), SERCOS (5%), and AS-Interface (5%) rounded out the top five.
Thirty-five percent say they use a protocol other than the five above. Among the top 'other' choices were Allen-Bradley's RIO, Modbus, ControlNet, and Ethernet.
The small are the plentiful
Survey respondents employ more small drives than large. Drives that operate in the 1-5 hp range are used by 71%. As power increases, the number of respondents decreases. Fifty-three percent use drives in the 6-10 hp range, 46% use 11-20 hp drives, 42% use 21-50 hp drives, and 36% use drives over 50 hp. Forty percent of respondents use drives with a power output of up to 1 hp.
The 12-month outlook for ac drive purchases is still unclear. What's encouraging is 47% expect ac drive purchases to remain about the same, and 22% expect an increase. Only 5% expect ac drive purchases to decrease. But what could tip the balance is that 21% are unsure.
When it comes time to buy, respondents consistently prefer off-the-shelf drives compared to their custom-made counterparts. Five years ago, respondents bought off-the-shelf drives 63% of the time, compared to 37% for custom-made drives. Since then the margin has widened a little. Today, respondents buy off-the-shelf 67% of the time, compared to 33% for custom made. They predict that two-to-one ratio to remain five years from now.
While other do-everything products in the industry continue to receive more publicity, the ac drive workhorse continues to toil in relative obscurity. Perhaps another football analogy gives credence to their value: a team is only as good as its linemen.
AC drive Products
For more information on ac drive products, circle the following numbers, or go to www.controleng.com/freeinfo .
Three-level control and 32-bit processing
New Berlin, Wis.- GPD 515 Adjustable Speed Drives use 32-bit processing to deliver Volts/Hertz, open-loop, or closed-loop flux vector performance. Speed regulation of 0.01% of rated motor speed is available in closed-loop vector applications, with a controlled range of 1000:1 down to zero speed. Precise controlled speed ranges of 50:1 in open- loop vector mode and 40:1 in V/Hz modes are also available. GPD 515 uses third-generation IGBTs for high torque and improved motor speed characteristics to give smooth, quiet motor operation, even at low speeds. Magnetek
New series offers versatility
Vernon Hills, Ill.- A500 Series Variable Frequency Drives offer compact units with ratings of 1/2 through 100 hp at 240, 480, and 575 V. All units carry UL and CUL listings and the CE mark. The available LCD parameter unit supports users in eight languages. A500 Series units offer a standard LED display user interface that provides access to all configuration and monitoring parameters, as well as extensive diagnostic information. An optional 4 x 13 character, back-lit LED unit is available for easier viewing, as well as advanced diagnostic capability. Special heat sink fan controls and diagnostics maximize VFD run time and reduce troubleshooting time. A500 Series offers an energy-saving mode that can provide significant money savings for light-loaded motors in fan and pump applications as it reduces audible motor noise and increases motor life. Mitsubishi Electric Automation
Save panel space
Mequon, Wis.- Bulletin 160 Smart Speed Controller (SSC) Series C offers expanded ratings through 5 hp (three-phase 230 and 460 V ac) and increased functionality. Added functions include four preset speeds for applications where only digital inputs are available; proportional/integral (PI) control for simple process control applications; and the ability to switch from an analog speed reference to one preset speed via a digital input, providing a predetermined speed change in the event the analog signal is lost. Optional RS-232 and DeviceNet communication modules are available. All units in the Bulletin 160 SSC Series C are DIN-rail mountable. Featured is a feed-through wiring design with power input through the top and motor wiring through the bottom for conversion from electromechanical starters to variable-speed control. Rockwell Automation/Allen-Bradley
Fort Smith, Ark.- Baldor's Series15J and 15P mini inverters are reportedly well-suited for applications requiring variable torque, constant torque, or constant horsepower. Series 15J uses a smaller version of the 12-key, 32-character text display keypad found in other Baldor products, which facilitates easy setup. The keypad includes digital speed control, forward/reverse command, stop command, jog command, and parameter setting and display. Series 15P provides simple rotary speed selection on the operator control panel. A turn of the knob and speed is set. Both come in 1 to 5 hp, are housed in a NEMA 1 enclosure, and have built-in braking. Other features include ground fault, short-circuit, and power loss ride-through protection; overload ratings of 150% for 60 sec or 200% for 2 sec; eight preset speeds; and over 70 adjustable parameters. Baldor Motors and Drives
Simple functionality, small footprint
Rockford, Ill.- VLT Micro adjustable frequency drives are designed for users who require small ac motor control in the 0.5-2 hp range (230 V applications). Programmable dc braking makes it easier to adapt these IP20 enclosed units to various applications. A digital keypad/display module with 'display' and 'control' functionality comes mounted on the front panel of the drive. 'Display' shows the drive's current status while 'control' provides the programming interface. Built-in software reportedly eliminates the need for added hardware. Additional features are: dc performance from a low-cost, low-maintenance ac motor; programmable digital inputs and outputs; low noise operation; overload current (to 150% of rated current for 1 min); automatic voltage regulation; and S-curve or linear ramp profiles. Danfoss
New and improved
Ann Arbor, Mich.- Improvements to the SV Flux Vector Drive Series of adjustable speed drives include new application software, additional models, and high-speed communication options. The improvements were designed to provide solutions to difficult applications, such as ac line regeneration, electronic line shaft, PID loop control, constant tension centerwind control, digital motor-operated pot control, and high-speed serial communications. The product range has been expanded to include 575 V ac input units and is available as standard products up to 250 hp at 460 V ac, or engineered products up to 800 hp. New application software has been designed to serve more applications. Other features include microprocessor control using a digital signal processor; constant torque over a 70:1 speed range without encoder; and full torque at zero speed available with encoder feedback. Warner Electric
High-torque vector drive
Chambersburg, Pa.- E-trAC WF2 sensorless vector drives are general-purpose ac drives that supply a minimum of 150% torque at 0.5 Hz. They're said to provide smooth operation in low-speed, high-torque conveying, mixing, moving, filling, and rotating applications. In addition to constant torque applications, WF2 also can be configured as a Volts/Hertz control for use with fans and pumps. Currently available in a power range of 1-5 hp at 230 V ac, and 2-5 hp at 460 V ac, WF2 comes with user-friendly, 8-button keypads and 2 line x 16 character display. WF2 is equipped with user-configurable digital and analog I/O points to meet demanding applications. TB Wood's
Drive with two configuration types
Waukegan, Ill.- V7 ac vector drive is available in 0.5-10 hp at 230 and 460 V ac. It offers conventional inverter (V/Hz) and open-loop vector configurations, and provides a level of built-in software flexibility the company claims is unique in the industry. Users can enhance the drive to create a simple custom display, or create complex control algorithms for complex applications. This flexibility can be used to optimize drive/machine interface, which is reported to eliminate certain peripheral hardware. Yaskawa Electric America
AC sensorless vector
Charlotte, N.C.- 605 Series inverters offer a combination of a high torque sensorless vector drive with a simple and flexible control interface. These drives feature easy-to-read alphanumeric displays for fast setup. A software configurable block diagram and optional 6053 Technology Box provide flexibility. Chassis and NEMA 1 versions are available, as are operator controls, making what the company says is a complete, stand-alone package. Other features are programmable linear, parabolic, or 'S' ramp useful in lift and hoist applications; fly catching for restarting a rotating motor; and a 16-bit processor that controls all functions including PWM pattern generation, voltage frequency and current loops, drive protection, and input/output functions. Eurotherm Drives
Small drive, big performance
Chanhassen, Minn.- Control Techniques Drives' new Commander SE is an ac open-loop vector drive with models rating 0.33-5 hp at 230 V and 1-5 hp at 460V. The company is confident Commander SE's 10 initial parameters will meet the needs of 80% of typical drive applications. These Level 1 parameters can save a set of motor parameters to allow sequence switching between motors with different operating characteristics. Level 2 and 3 parameters add flexibility and can save a second set of motor parameters. This NEMA 1 package has a small footprint without compromising heat dissipation or dependability. Control Techniques Drives
Versatile ac drive
New Berlin, Wis.- ABB's ACS 400 adjustable speed ac drive is available in two models: one that operates motors from 3 to 30 hp at 200 to 240 V ac; another that operates motors from 3 to 50 hp at 380 to 480 V ac. The drives come in a NEMA 1 enclosure with a NEMA 12 option. According to the company, the ACS400 is ideal for a host of OEM, industrial, and commercial applications, including fans, pumps, and conveyors. ABB Automation
Motion control added
Alpharetta, Ga.- Siemens Simovert Masterdrives have now been supplemented with a Motion Control (MC) version, along with added functionality. The new MC unit features consistent modularity with freely connectable function blocks and integrated technology functions. The units are available for 3-phase supply voltage of 380 V to 480 V ac, 50/60 Hz, depending on the output. The series comes in Compact Plus (0.55 to 18.5 kW, or Compact and Chassis units (2.2 to 200 kW). MC series is uniform throughout with regard to communication, technology, operator control, and visualization. Siemens Energy & Automation
Drive line for most any application
Milwaukee, Wis.- SV9000 Series of drives range from 0.75 to 1,100 hp and 200 to
690 V, and can handle applications from simple variable torque to such complex applications as conveyors, mixers and machine controls. The entire line contains preconfigured, multiple preset applications, enabling the frequency converter to fit almost any application. Each unit has a keyboard or optional enhanced graphic display. The drives also offer connectivity to networks such as DeviceNet, Profibus DP, Interbus-S, Modbus-RTU, and Lonworks. The SV9000 line provides Microsoft Windows-based PC software programming; is UL, CE, and CUL approved; and offers customers the choice of Volts/Hertz or sensorless vector standard, or closed-loop vector settings. Cutler-Hammer
Trends in AC Ddrives