Matrix drives reduce energy consumption for transporter system
A material handling application will be regenerating about $1,500 per year in electrical savings rather than dissipating braking energy as heat. Other savings are expected with a simpler design expected to require less maintenance. In spring 2016, Maxam Inc. and Yaskawa America Inc. developed an asphalt transporter system for Gallagher Asphalt in Thornton, Ill.
The transporter system is a fully integrated asphalt distribution product that is designed to load and evenly distribute asphalt into individual load out silos. The Gallagher Asphalt system’s motor-driven transporter featured an eight-ton high-speed material transfer vessel and recharging storage vessel.
The existing 200-ton asphalt storage silos were retrofitted with the asphalt transported system, replacing a complex system of asphalt material conveyors. Five 40 hp conveyor systems and their inefficient motors were removed and eliminated for the transporter system. The old drag slat-the steel floor in the conveyor-used chains, which required more power in conveyor plate heating than the retrofitted system.
The transporter system used two matrix drives. One drive operates the 60 hp, multi-motor powered carriage and another 30 hp drive operates the transfer vessel power train. The main carriage has four drive motors and the moving vessel (batcher) has two additional motors. The main carriage and the vessel need to be driven at exactly the same speed. The system is designed to be more energy efficient and provide a more maintenance-free, mechanically integral distribution system.
This transporter has been operating since February 2016. The duty cycle requires the motors ramp to full speed in about 1.5 seconds. They will run at speed for about 4 seconds, then ramp down in about 3.5 seconds to stop mode. In about 10 seconds, the system repeats the process. During the fast stop time, the transporter motor’s regenerative load energy normally would be channeled into the ac drives’ system braking resistors and dissipated as heat energy. Since the regenerative cycle would occur in about 20% of the total duty cycle time, significant amounts of energy would be lost as heat.
The matrix ac drive works for this application because of its control technology. It employs a system of nine bi-directional switches arranged in a matrix to convert the three-phase ac input voltage directly into a three-phase ac output voltage. The ac drive topology eliminates the need for a rectifying circuit, dc smooth circuit, and the optional dynamic braking components usually required for this type of application.
The converter uses all three input phases in pulse width modulation (PWM) switching to control output voltage and input current, and it provides regenerative motor control operation. This control is required when the carriage and vessel motors decelerate. This allows the drive to save energy by regenerating the motor’s overhauling energy directly back into Gallagher Asphalt’s power distribution system. This is much more efficient than releasing the motor’s regenerative energy as heat via a traditional ac drive’s dynamic braking option.
The motor control centers (MCC) for the transporter systems are installed in outdoor-rated enclosures. Considerations for the limited MCC panel space, dirty, and wet weather environments along with wide ambient temperature fluctuations are important design criteria for this motor control solution. MCC wiring complexity is simple with the direct ac to ac matrix drive topology. Wiring requires little panel or field installation labor. The drive provides a three-phase power supply input and three-phase output main power supply wiring.
The main motor power circuit component count is reduced from several components to one. Using the drive selected allows control panels to be about 70% smaller than the traditional drive with dynamic brake module(s) and resistor(s) solution or a traditional ac drive regenerative power supply. Gallagher Asphalt applied for a Commonwealth Edison utility grant because of the energy savings offered by the matrix drive.
Gallagher’s KWh costs are .076 cents/KWh. Operation cycle time is 8.5 hours per work day, five work days per week average with 40 weeks a year of operational time. Approximately 20% of the total run time is spent in regenerative mode. This is 340 hours/year. Assuming each motor is at 100% braking torque during regeneration, the 30 hp drive’s total motor load will yield approximately $500/year and the 60 hp drive’s total motor load will yield approximately $1,000/year of savings (based on $0.076/kwh) vs. the standard and typical solution of using a conventional ac drive solution with the dynamic braking resistor option.
Mike Grant is a regional drive specialist, Yaskawa America Inc. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, email@example.com.
- Matrix drives were used for a transporter system retrofit for Gallagher Asphalt to reduce energy and maintenance costs.
- The industrial matrix drives operated a multi-motor powered carriage and the transfer vessel power train.
- The matrix drives reduced energy and maintenance costs for Gallagher Asphalt.
How could your motion control applications reduce the energy costs?
Four more photos appear with this article online, along with links to related information. For more information from Yaskawa about the drives mentioned, available for 5 hp to 800 hp, go here.
See additional photos below.