Power Electronics

Smart Motor Controllers Take Charge of Expanding Applications

Advances in packaging and performance spawn a variety of low-cost, intelligent motor controllers for an expanding range of consumer and industrial applications

Find a downloadable version of this story in pdf format at the end of the story.

Take a look at a modern motor controller and one of the first things you'll notice is that the control circuit is about the same as the motor it controls. That ís a far cry from the 10X or size bigger sizes of just a few years ago. It's also less expensive and smarter. Credit IC chip advances in the form of more powerful and lower-cost DSPs, microcontrollers, amplifiers, encoders, power ICs, etc., for this.

This comes against a background of increasing demand for motor controls in many more sectors like the automotive, computer, industrial, medical, toys, as well as emerging white goods, power tools, and vacuum cleaner consumer appliances.

Motor control is a complex task involving not only understanding for the designer of complex operations, but also advanced hardware and software algorithms. Thus, it is not surprising to see field-programmable gate array (FPGA) vendors and vendors of intellectual property (IP) algorithms entire this field more recently. IC microcontroller unit (MCU) and DSP vendors are actively working with these aforementioned suppliers to present complete system development kits and platforms, particularly for users of embedded MCU and DSP users who are more software knowledgeable than hardware oriented.

In using stepper motors, engineers are challenged to maximize control algorithms for greater efficiency. This means boundary conditions of the complete electro-mechanical system must be mapped. This can be daunting since all system variables such as temperature, mechanical degradation, acceleration, velocity, supply voltage, vibrations, etc. must be accounted for.

The types of motor drives are widespread in both ac and dc varieties. These include universal ac and dc motors, high-frequency pulse-width modulated (PWM) universal types, brushed and brushless motors, induction motors, scalar variable frequency drives (VFD) motors, vector drive motors, as well as stepper motors.

Intelligent motor control ICs provide advanced control capabilities for multi-phase motors, most commonly brushless dc motors and three-phase induction motors. Microprocessors and DSPs are providing relatively inexpensive intelligent field-oriented control (FOC), or vector control, a math-intensive technique for controlling brushless dc and ac induction motors more efficiently. It reduces motor size, cost and power consumption. It achieves this by directly measuring the field position within the motor.

Another variant technique being used is indirect FOC. Here, the motor's field position is measured indirectly via slip calculations using a mathematical model of the motor.

A big push is on for more energy efficient motor control and the key to this is smart control. Smart motor control is indeed helping boost energy savings. This is particularly the case with the use of VFD circuits. These circuits optimize motor acceleration and deceleration ramps, slow down the motor, and turn it off when not in use.

A VFD is a system for controlling the rotational speed of ac electric motor by controlling the frequency of the electrical power supplied to the motor (Fig. 1). VFDs are also known as adjustable-frequency drives (AFD), variable-speed drives (VSDs), ac drives, micro-drives or inverter drives. Since the voltage is varied along with frequency, they are sometimes also called variable-voltage variable-frequency (VVVF) drives.

A VFD can also be used to save regenerated energy. For example, when a motor is trying to stop a high-inertia load, it acts as a generator by dynamically converting the kinetic energy in a motor into useful heat energy using high-wattage braking resistors. Many modern motors feature VFD capabilities.

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A SYSTEM LOOK

Texas Instruments (TI) was one of the first to offer a new line of scalable motor driver evaluation platforms for brushed dc stepper motor with its DRV8412-C2-KIT (Fig. 2). It provides all the hardware and software needed for driving brushless dc stepper motors running up to 6 A continuous and 12 A peak at 50 V. It is aimed at medical pumps, gate openers, stage lighting, textile manufacturing tools, and industrial and consumer robotics applications.

The platform includes the DRV8412 motor driver, a real-time C-200 Piccolo MCU control-card module, a quick-start graphical-user interface (GUI), full development source code, Code Composer Studio integrated development environment (IDE), as well as motors.

Microchip Technology Inc. recently announced two new low-cost development boards, one for the control of high-voltage motors (the dsPICDEM MCHV) and another for stepper motors (the dsPICDEM MCSM). Along with related application notes and free source-code FOC software, they enable rapid designs using Microchip Technology's dsPIC33 motor control digital signal controller families.

“These development tools jumpstart our customers' advanced high-voltage motor control and stepper motor control designs, and brings the benefits of high-efficiency control to their products quickly,” explains Sumit Mitra, vice president of Microchip Technology's high-performance motor control division. “They provide our customers with a winning combination of price, features and reduced time to market for the motor-control applications,” he adds.

The dsPICDEM MCHV is said to be the industry's most cost-effective tools for the rapid evaluation and design of a wide variety of high-voltage closed-loop control applications using ac induction motors, brushless dc motors, or permanent-magnet synchronous motors. The board includes in-circuit debugging circuitry, eliminating the need for a separate debugger for development with Microchip Technology's dsPIC33 product. The board also combines a proven motor-control system and power factor correction(PFC) for regulatory requirements.

The dsPICDEM MCSM is said to be the industry's most cost-effective tool for creating unipolar and bipolar stepper motor applications. This board enables the development of both open-loop and current closed-loop micro-stepping routines using the dsPIC product. It also provides designers with a GUI, which allows them to focus on integrating the other application features and fine-tuning the motor's operation.

Typical of modern motor control processors is the 58000 series Magellan motion processor from Performance Motion Devices Inc. (Fig. 3). This IC provides an oscilloscope-style trace of 64 separate motion variables for high-performance control applications. It captures and stores real-time signals from eight different functional areas such as trajectory generation, encoder feedback, servo control, commutation, motor output, general-purpose input, signal status and system clock into hardware buffers for future retrieval.

The IC works with the company's ProMotion software which facilitates servo tuning and trace-capture analysis via a graphical user interface. Trace and display can be tailored to the motion applications by programming trace start, trace stop, data-capture frequency, external signal triggers and other relevant parameters.

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Motor drivers are available for a wide range of stepper motor type fractions. For example, the BD638xxEV series of micro-step motor drivers from Rohm Semiconductor offer selectable excitation modes - from full step to 1/16th step with 1.0 or 2.0 of output current at full step and 2.5A at 1/8th step. Available in ultra-thin HTSSOP-B28 packages, they feature a unique ghost-supply prevention feature that eliminates motor malfunctions, as well as built-in voltage, current and thermal protection.

Galil Motion Control, an industry pioneer in motion control technology, recently introduced the DMC-41x3 motion controller series boards and packages for Ethernet applications. Part of Galil's Econo series of controllers, the new product offers many enhancements over previous products including operation over 100Base-T Et Ethernet, a USB 2.0 port, higher-speed performance, larger program memory, analog inputs and an optically isolated I/O.

“Compared to the older DMC-21x3, the new DMC41x3 controller offers many speed improvements and can accept encoder inputs up to 15 MHz and close the loop in as quickly as 62 µs,” claims Lisa Wade, vice president of sales and marketing at Galil. “It also offers twice as much memory for user programs and arrays,” she adds.

The DMC-41x3 operates in a standalone mode or interfaces to a PC with Ethernet 10/100-Base-T or USB connectivity. An auxiliary RS232 port is also provided. The product is available in one- through eight-axis formats each of which is user configurable for stepper or servo motor operation. It can be connected with external drives or any power range or with Galil's multi-axis (500 W/axis) servo drives or 60-V, 3-A micro-stepping drives. Standard I/O includes 16 optically isolated I/Os for the four-axis models and 32 I/Os for the five- to eight-axis models. Eight analog inputs are provided in addition to optically isolated forward and reverse limits and home input for each axis.

The DMC-41x3 comes in an 8.1-by-7.25-by-1.5-in. package for the one- through four-axis model and 11.5-by-7.25-by-1.5-in. package for five- through eight-axis models.

A ROLE FOR FPGAS

Increasingly, low-volume OEMs are turning to FPGAs together with IP ICs for motor control development. FPGAs allow specific one-size fits-all/generic PWM blocks and transducer interfaces (to be configured by the system designer) to specific pre-configured motor control blocks including software drivers on an FPGA embedded processor. Unlike a DSP or microcontroller where each device has its own tools that must be learned and much time is invested in component integration, an FPGA provides motor control designers with a single design environment where the complete system - hardware and software - can be developed.

The key to an FPGA's advantage is to use motor control IP from companies like Alizem. This company offers a complete range of advanced control and fault-diagnosis IP for motors designed to provide very high energy efficiency and safety in home appliances. The company offers three products: Zem-PWM IP for integrating high-performance PWM for voltage actuation, ranging from standard space-vector PWM to custom-optimized PWM; Zem-CC IP for enabling the correct cost/performance compromise for motor current regulation, ranging from standard scalar control to adaptive sensor-less vector control; and Zem-Diag IP to monitor measurement signals and machine states to proactively detect and diagnose faults in the motor, power converter, sensors and the load.

Marc Perron, Alizem's president, likens the shift toward FPGAs for motor control to the evolution from mobile cell phones to smart phones like the iPhone. “Apple has decoupled the phone's platform and functionality which allows me to apply third-party applications that customize the iPhone,” Perron said.

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Altera found the kind of IP that Alizem makes very helpful working with them in developing a motor control approach for home appliances using Altera's Cyclone III FPGA (Fig. 4). It found that all Alizem motor-control IP cores are designed with a proprietary DSP algorithm that offers the best compromise of performance and FPGA resources such as logic elements. A complete motor drive for a permanent-magnet synchronous motor including PWM and current control includes less than 500 logic elements on an Altera Cyclone III low-cost FPGA.

Actel (now part of Microsemi) uses its SmartFusion intelligent mixed-signal FPGAs for embedded motor control. The company says they are the only devices that integrate an FPGA, ARM Cortex-M3 processor, and programmable analog functions, offering full customization, IP protection, and ease-of-use. The SmartFusion mixed-signal FPGA is based on Actel's proprietary flash process (Fig. 5).

SmartFusion FPGAs are ideal for hardware and embedded designers who need a true system-on-chip (SoC) solution that gives more flexibility than traditional fixed-function microcontrollers - without the excessive cost of soft processor cores on traditional FPGAs.

Another FPGA supplier, Xilinx, is using its FPGAs to develop what it considers is the most advanced FPGA-based motor control system. The Targeted Design Platform is scheduled to be unveiled this quarter.

IMPROVED ENCODERS, POWER DEVICES

Key motor control components are also making performance improvements. Take the AM4096 12-bit magnetic encoder chip from Renishaw, for example. The chip (Fig. 6.) takes Renishaw's OnAxis encoder technology a step further with more functionality and lower costs. The encoder ( provides UVW outputs with 16 poles (8 pole pairs), incremental, absolute, linear (potentiometer), tacho generator and sinusoidal outputs. Resolution is 12 bits (4096 steps/turn) with a programmable zero position. The encoder operates from 3.3 V or 5 V and features a sleep mode for battery operation. It can be supplied pre-programmed or customer-programmed with settings stored in its on-chip EEPROM. The encoder can operate up to 60,000 rpm and withstand operating temperatures of -40°C to +125°C.

Rohm Semiconductor has used silicon-carbide (SiC) technology to develop the industry's first SiC trench MOSFET and Schottky barrier modules for automotive vehicle motor control. The 600-V 450-A devices take up less than 50% of equivalent-performance silicon modules and can operate at up to 200°C.

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