Shortening Time-to-Market with Advanced Auto-Characterization

Shortening Time-to-Market with Advanced Auto-Characterization

By Hugh Burns, Senior Systems Engineer &
Kerry Green, European Support Manager, Curtis Instruments, Inc

It’s a deceptively simple question: what gives AC-powered electric vehicles their “get-up-and-go”? The key factor of any electric vehicle powered by Alternating Current is the drive-system, comprised of two primary components: the AC Induction motor and the AC motor controller. Together, these two components determine the vehicle’s performance and power. Like partners in a marriage, they must work in perfect harmony to achieve the vehicle’s maximum operating potential.

Call it a marriage of brain and brawn. The AC Induction motor is the “muscle”, converting electrical energy into the mechanical energy that enables vehicle movement. The motor controller is the primary electronic “brain” of the power train. It converts the DC voltage of the vehicle’s battery into a 3-phase sinusoidal AC voltage and, upon receiving commands from the throttle, varies the amplitude, frequency and phase angle to provide the desired motor direction, speed and torque.

Characterization: A Hard Chore

One of the formidable tasks facing the vehicle design team is to tune the controller to the electric motor, as these components are most often provided by separate suppliers.
Usually, it’s the obligation of the controller supplier to assure that the controller is matched to the various motors offered in the international electric vehicle market.

Vehicle OEMs have to plan for the time required to “characterize” the motor in their development time schedule, as this process can typically take several weeks. During the characterization process, the electric motor’s key properties (electrical, electromechanical and magnetic) are determined and an accurate mathematical model of the motor is created and stored in the controller’s memory. The more accurate the motor model, the higher the performance that can be delivered by the controller’s software algorithms. Optimum performance demands superb accuracy.

In pursuit of this challenging accomplishment, the motor is usually shipped to the controller manufacturer. There, it will be mounted on a dynamometer and undergo a series of performance tests. Once the motor properties are analyzed, mathematical calculations will determine the numerical entries required for the controller’s algorithm.  Done this way, the traditional characterization process slows time-to-market and delays product introduction for the vehicle OEM.

A Better Way

Curtis Instruments, Inc., a world-leading specialist in electric motor control for the past 50 years, has developed a line of AC controllers that feature a unique, proprietary process to quickly and efficiently achieve “auto-characterization”. The Curtis approach allows the controller to capture the electric motor characteristics on-site, directly on the vehicle, substantially reducing development time. What used to take many weeks now takes less than an hour and the results achieve maximum motor efficiency for a given torque.

Curtis AC controllers with indirect field orientation (IFO) vector control and auto-characterization significantly outperform other AC controllers, by enabling higher levels of motor torque over an extended speed range with less heating due to their minimization of phase current to achieve the demanded torque.

Curtis “Auto-Characterization” = Self-Learning by the Smart Controller

The Curtis AC controller is set to an automatic test mode: the controller injects test currents at specific frequencies and measures the responses of the motor. From these measurements an advanced algorithm calculates the motor model, including detailed saturation characteristics, which is then stored in memory. The Curtis AC controller also learns the speed encoder pulses per revolution and direction. The slip gain test optimizes the controller to provide the best stall torque. As a final step, the base speed and field-weakening tests determine the amount of torque and efficiency provided at high speeds.

Proven, Fast and Easy

Curtis AC controllers with auto-characterization can be tuned by Curtis support engineers, or the vehicle OEMs -- with training from Curtis. The Curtis auto-characterization process does not rely on the theoretical data supplied by the motor manufacturers. This data often does not support perfect tuning. In contrast, Curtis auto-characterization algorithms achieve superior harmonization between the controller and motor, establishing optimum vehicle performance and efficiency.

Various other companies claim to achieve optimized auto-characterization through different methods, but do not quite achieve it.  Curtis abandoned the flawed portions of these approaches years ago in favour of actual vehicle performance measurements during the commissioning process.  The Curtis process measures real torque performance, rather than inferring it solely from potentially erroneous parameter determination. Through a proprietary combination of parameter determination and torque production optimization, the final motor model is forced to converge on the optimum solution.  This guarantees optimized controller tuning.

The Curtis auto-characterization feature also allows vehicle OEMs the flexibility to quickly switch from one motor to another, if desired or necessary. And, getting operational is a snap. The complete tuning process takes less than an hour -- saving valuable time-to-market and assuring peak operating efficiency.

Controller Auto-Characterization in Action: Aisle-Master

One recent example of the benefits of auto-characterization is Aisle-Master Ltd, Clontibret, Co Monaghan, Ireland. Aisle-Master chose the Curtis method to tune their Narrow Aisle Articulated Fork Lift Truck.

This customer had a unique challenge: their truck had limited space for the traction and pump motors. The electric motor supplier, Advanced Motors Inc, was able to supply three different motor designs for evaluation on the truck, under full performance conditions over various terrains. Trying out three different motors would have taken an inordinate amount of time with traditional tuning methods.  But Curtis auto-characterization allowed a very fast turnaround on the motor controller tuning while ensuring optimum performance. Three different motor types were tuned and evaluated on the vehicle within 6 working days. This literally saved many weeks of valuable time and allowed Aisle-Master to bring the vehicle to market quickly.

The Aisle-Master truck has a dual motor application utilizing a Curtis 1238 AC controller for traction; a Curtis 1236 controller for the hydraulic pump motor; a Curtis FP6 throttle pedal and a programmable display enGage® III.  The vehicle also utilizes Curtis VCL logic with the 1238 AC master controller to provide full multimode speed selection to suit the wide variety of applications. Additionally the 12V ancillary power is taken from the Curtis 1400 DC-DC converters which changes the 48V traction battery to a regulated 12V supply.

The system uses CANopen to achieve full integration of all components. Auto-characterization was used for the hydraulic pump motor and for the evaluation of three pairs of traction motors. Curtis support engineers performed the auto-characterization and performance tuning of the vehicle at the customer’s premises in Clontibret, Ireland.
Aisle-Master Managing Director, Gerry McHugh, stated, “We were very impressed with the auto-characterization feature and this is one of the reasons we chose Curtis as a partner to supply controllers for the electric powered trucks in the Aisle-Master range. The auto-characterization helped us greatly in terms of speeding up the development of the model, and thereby enabling us to launch it more quickly on to the market.”

About Aisle-Master

Aisle-Master manufactures a range of articulated forklifts which are able to work both inside in the warehouse within very narrow aisles as well as outside for off-loading. This versatility enables them to replace a combination of other forklifts such as counterbalance and traditional VNA (Very Narrow Aisle) trucks, offering customers vastly improved storage density, reduced operating costs and enhanced productivity. The company manufactures both AC electric and Liquid Propane Gas powered trucks, with 12.5 m lift heights and capacities of up to 2.5 tons. All models are manufactured in Clontibret, Ireland, and exported across the globe. 

Controller Auto-Characterization in Action: Taylor-Dunn

One recent example of the benefits of auto-characterization is Taylor-Dunn, in Anaheim, California, one of the leading manufacturers of industrial electric vehicles in the United States. Taylor-Dunn chose the Curtis method to tune a range of vehicles, including a new tow tractor named “Tiger” TC-50E and several classic Taylor-Dunn utility vehicles -and tow tractors. This customer had a unique challenge: Two different electric motors, AMD Motors and ABM, were compared to determine the best performance, according to criteria defined by Taylor-Dunn. Curtis auto-characterization was able to quickly and accurately conduct the comparison and to achieve the efficient control of the motors, resulting in low motor and controller heating and more distance per battery charge. Andrew McNiven, Senior Engineer for Taylor-Dunn, stated. “This saved us a lot of time. What we did in a half a day with Curtis would have taken us 5 days with an alternative approach.”

About Taylor-Dunn

Since 1949, Taylor-Dunn has been a leading manufacturer of commercial, industrial and ground-support vehicles. Taylor-Dunn vehicles are world renowned for their sheer dependability and performance, built to last in the toughest and most rugged work applications. Predominately used to move personnel, equipment, and materials, Taylor-Dunn vehicles are marketed internationally. For nearly sixty years, they have built reliable standard and custom vehicles - burden carriers, personnel carriers, stock-chasers, electric carts, tow tractors & more. Taylor-Dunn vehicles utilize a wide range of Curtis controllers, displays and accessories.

About Curtis Instruments, Inc.

Curtis Instruments, Inc., established in 1960, is a world renowned supplier of motor controls, instrumentation, battery management, and integrated vehicle systems for electric vehicles. Headquartered in Mount Kisco, New York, the company serves worldwide vehicle manufacturers and operates major R&D centers in Livermore, California; Mt. Kisco, New York; Biberist, Switzerland and Suzhou, China. Curtis products are manufactured in the company’s flagship facilities in Carolina, Puerto Rico; Sofia, Bulgaria; and Suzhou, China. Curtis products drive some of the best known electric vehicle brands globally, including all types of vehicles such as: material handling, industrial, aerial lift, recreational, sweeper/scrubber, light-on-road, airport, construction and medical mobility.