Motor drive upgrades boost industrial plant performance

Today’s motor drive technologies offer virtually limitless design possibilities. Motion control offers a means to an end for OEM plant managers, integrators, and design engineers engaged in demanding automation and production lines.

By Tom Robbins, Lenze April 7, 2011

Leading OEM plants are seeing firsthand the value of upgraded motor controls and variable frequency drives (VFD) over conventional fixed-speed motor drives. Advanced motor controls and VFD can process or convey equivalent volumes with substantially improved efficiency, while expending less energy and reducing mechanical wear and maintenance.

Today’s motor drive technologies offer virtually limitless design possibilities. Motion control offers a means to an end for OEM plant managers, integrators, and design engineers engaged in demanding automation and production lines. The objectives might be to make a process more cost-effective, a product more robust, or a production line faster, but the overarching goal is bringing products to market faster and more competitively.

Selecting the right motor drive technology and peripherals can advance that goal, while improving energy efficiency, motor performance, and functionality in plant operations.

Industrial motor control overview

Available in a range of basic voltage models, with single or three phase power, operating a 230V or 480V or 600V motor, drive selection is contingent on motor type, voltage, current rating, input source and I/O requirements. Sizing depends on a number of application-specific factors, including the full load rating and maximum voltage under full load conditions for the motor.

Speed variability is the primary advantage of a frequency inverter. Rather than running a motor directly across the available power supply, the inverter converts the voltage during start up and at varying stages during operation, depending on the application requirements. An HVAC fan, for example, may not need to run at full speed 24/7 across the line. An inverter reduces the voltage and energy usage of the fan.

Although still a relatively new technology itself, pulse-width modulation (PWM) has more than a decade of proven reliability relative to cost. The carrier frequency controls the pulses of the PWM output waveform, and therefore controls voltage to the motor. This in turn reduces power usage as opposed to running the motor across the line. PWM technology supports motors found in a wide range of industrial plant operations, especially when there is a need for immediacy and accuracy of controllable constant and variable speeds during start-up, operation, and motor braking.

Conveying and other automation applications sometimes call for high load, slow motor speeds. A standard AC 3-phase induction motor shouldn’t run below 50% of its base speed, but can only run at speeds based on applied voltage. Reduced voltage slows fan speed, preventing motor cooling, eventually leading to burn-out often seen in traditional AC 3-phase motors. Advances in variable frequency drives, coupled with sensorless vector technology, make it a strong value proposition for challenging industrial plant applications.

VFD-vector technology delivers torque

While a VFD delivers close to 100% starting torque, vector technology can offer 200% starting torque to overcome the initial load. As a result, an engineer can significantly decrease motor size, thus reducing application cost. At the core of sensorless vector technology are sophisticated, patented algorithms that achieve optimal torque production, speed and process control.

Vector-controlled drives provide more information to the motor, with greater flexibility in dynamic positioning and speed. While a standard drive typically has a 10:1 motor speed range, flux vector mode operates at a 60:1 factor to speed, with superior motor and torque control even at very low speeds.

A higher starting torque places less demand for current drawn by the motor at lower speeds, thereby reducing the risk of burning up the motor. Another advantage of sensorless vector control is that it doesn’t require closed-loop feedback. Open-loop speed regulation eliminates the additional cost of a feedback device associated with closed-loop systems.

Sensorless vector drive options are numerous in today’s marketplace. The most advanced vector drives on the market today can be used with 3-phase AC induction motors and are available in NEMA 1 (IP31) and NEMA 4X (IP65). Programmable digital and analog I/Os allow the drive to be configured for many application-specific tasks, such as multiple preset speeds, electronic braking, and motor jogging.

Operation modes include V/Hz, Enhanced V/Hz, Vector Speed, and Torque. Benefits include high starting torque, auto-tuning, advanced low-speed control, and dynamic speed regulation. With a power range up to 20 HP (40 HP for 480v and 600v NEMA-1), the sensorless vector drives excel in environments where inverter technology was once considered too costly, including packaging machinery, food processing equipment, material handling/conveyors, and HVAC systems.

NEMA-Rated asset protection

At any NEMA rating, sensorless vector drives are suitable and competitively priced compared to other drives with less functionality. NEMA rating is typically matched to the mounting environment and conditions, whether the enclosure is indoor or outdoor use, and available shielding from direct sunlight. Plant temperature, humidity, and other environmental conditions determine the NEMA rating of a drive enclosure.

For indoor installation in a relatively clean environment, a NEMA 1 enclosure can provide limited protection against normal ambient temperature, humidity and other conditions. NEMA 4X for indoor applications protects against windblown dust and rain, splashing water, hose-directed water, corrosive or caustic agents, and damage from external ice formation.

NEMA 4X for outdoor installations extends the same benefits in a more robust encasement. Remote keypads make it possible to mount a drive in a protected location, while operating the drive at a distance. This would be advantageous in certain circumstances, such as a wet environment that might require a remote watertight keypad.

Integrated communication protocol

Optional integrated serial communication motor control capabilities are available for applications where multiple communication software systems intersect. Drive communication options include Ethernet/IP, Profibus-DP, DeviceNet, CANopen and Modbus/RS485, among others. Users can maintain their own preferences, with plug-in communication modules factory-installed or inserted into an existing drive, enabling compatibility in virtually any control environment.

Dynamic braking circuits can allow a drive to decelerate the motor in conjunction with load to prevent motor voltage spikes and trips when used under a heavy load. PID controls can save energy by maintaining a set pressure, temperature or water level in a unit holding tank or any application involving motor control of a plant process.

Industrial Application #1

A recent automotive production line, designed to convey objects up to 3306 lbs along a production line process, required a carrier system capable of moving very precisely and with variable speed. The project comprised both a driving-the-chain conveyor and assembling carriers moving around the track. The high loads required high power, which had caused a space issue. Fitting a normal standard sized motor was not an option. The space available allowed for a series of small motors. Another constant on the carrier system was component cost, which had to be kept under control in order to meet target pricing of the entire conveyor system.

Lenze PositionServo drives provided a simple solution. The four motors had to be driven at the same speed to ensure smooth conveyor movement. The Position Servo drives are used in electronic gearing position mode using a master to encoder system ratio to remain completely synchronous. A frequency inverter would not have allowed the required precision control.

The economical PositionServo drives offered the perfect cost-performance solution. Controlling speed of the line between .13-5.25 in/second was also simplified by controlling the drives via a PLC. The solution addressed engineering demands, in terms of space and layout, and cost constraints, while delivering value-added performance benefits: precise synchronized control, speed, positioning and flexibility of material flow.

Industrial Application #2

A packaging operation designed for handling cosmetic samples had developed a robust and reliable foil pouch filling machine process using mechanical web tensioning and mechanical liquid filling process. They selected an electronically controlled alternative using PositionServo drives as master and slave to provide web tension.

Using servo gearboxes and MCS motors for pump control, the PositionServo control the rollers that draw the material into the area where the bottom is heat sealed. Then liquid is pumped into it and the material indexes down to the next area where the sides and top are heat-sealed. SMV Vector controls the main shaft, which also functions as the timing for the sealing process. Both processes used mechanical or stepper motors to achieve the moves.

Changing products or moves was a costly and time consuming for each set-up. Replacing the mechanical control with the integrated PositionServo, SMV Vector control, and an HMI controller, improved both speed control and accuracy. In addition to gaining machine speed, they realized a commensurate reduction in set-up time, because they gained the flexibility of being able to adjust the move distance easily, in order to run many different products sequentially.

The environment in which a motor drive is designed to operate is arguably one of the most important critical determinants of inverter selection. A high level of familiarity and knowledge about an application, production process, and user environment is recommended as a critical first step to specifying the right drive.

A number of important advances in drive technology make the plant engineer’s job easier, and helping OEMs deliver products to market more competitively.

A summary of the EISA standard

  • General purpose motors (subtype I) manufactured after December 19, 2010, with a power rating of at least one horsepower but not greater than 200 horsepower, shall have a nominal full-load efficiency that is not less than as defined in NEMA MG-1 (2006) Table 12-12 (aka "NEMA Premium" efficiency levels).
  • General purpose motors (subtype II), with a power rating of at least one horsepower but no more than 200 horsepower, manufactured after December 19, 2010, shall have a nominal full-load efficiency that is not less than as defined in NEMA MG-1 (2006) Table 12-11. Subtype II motors now include:
    • U-Frame motor
    • Design C motor
    • Close-coupled pump motor
    • Footless motor
    • Vertical solid-shaft normal thrust motor (tested in a horizontal configuration)
    • 8-pole motor (900 rpm)
    • Poly-phase motor with voltage of no more than 600 volts (other than 230 or 460 volts)
  • Fire pump motors manufactured after December 19, 2010 shall have nominal full-load efficiency no less than as defined in NEMA MG-1 (2006) Table 12-11.
  • NEMA Design B, general purpose electric motors, with a power rating at least 200 horsepower but no more than 500 horsepower, manufactured after December 19, 2010, shall have a nominal full-load efficiency that is not less than as defined in NEMA HG-1 (2006) Table 12-11.

The NEMA MG-1 (2006) Table 12-11 referenced above can be found in the NEMA Premium Efficiency standard.

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