FPGAs enable energy-efficient motor control

Designers can modify their motor control systems and increase performance using FPGAs.

3Motor control strategies vary according to the type of motor and the control algorithms used.
To build an adaptable motor controller, an FPGA provides a flexible platform as a starting point to which designers can add the necessary IP to suit their needs.

Motor control is at the heart of many of today’s industrial automation and motion/drive control applications. Industrial systems and applications are becoming increasingly complex, and designers must support a steadily growing number of features and options to be able to compete in the marketplace. For example, a product must support multiple Industrial Ethernet and fieldbus standards for maximum market coverage. Industrial systems designers can leverage the falling price of processing power to deliver higher-performance drives at lower costs, but competition is fierce and the pressure to reduce time to market is continually increasing.

These market pressures demand that designers implement flexible platforms to create more efficient factories. Factory-wide information systems, control networks, and manufacturing systems, especially those that deploy flexible motion/drive control devices, can be quickly and inexpensively reconfigured for new applications while maintaining a high degree of system interoperability using Ethernet and fieldbus technologies for efficient factory and office communications.

The case for FPGAs

For years, industrial motor control applications used general-purpose electronic devices such as microcontrollers (MCUs) and DSPs. These devices are designed with fixed hardware, leaving software as the only method for designers to update designs and limiting the development of application-specific functions.

In comparison, can integrate processor, Industrial Ethernet/fieldbus standards, custom motor interfaces, and functions in one device. FPGAs give designers the freedom to create custom functions completely adapted to their specific application requirements by enabling both hardware and software customization. FPGAs provide the capability to implement functions in hardware, accelerating performance and simplifying the software porting effort. This additional freedom opens up new avenues of enhanced system performance, especially for motor control energy efficiency.

The following examples show how industrial systems designers can take advantage of technology and motor control Intellectual Property (IP) to design the next generation of motor control applications with the required functions fully integrated on a single FPGA.

Motor control basics

The increase in industrial energy efficiency during the past few years is largely due to a change in motor control technology. Using a power converter-based variable speed motor drive makes it possible to save up to 88 percent more energy than the previous generation of motor control applications.

The function of the motor controller is to limit the motor’s output. A digital speed controller does this by controlling the motor’s electrical drive, minimizing overall and reducing wear and tear on the motor’s mechanical parts. The quality of the design in terms of energy consumption is fundamental to meet market expectations, be cost competitive over the product’s lifetime, and comply with environmental and power utility regulations.

Systems and techniques in industrial applications

Motor control systems are at the core of machine control, production, assembly, packaging, robotics, computer numeric control machine tools, and printing. Motor control techniques depend on the type of motor being used. The most common types of motors used in these applications are brushless DC, stepper, AC synchronous, and AC induction.

Two types of motor control systems are typically used in industrial applications today. In a distributed drive control system, the motor controller performs all the motion control calculations (speed, velocity, position) and implements a local feedback loop to control the associated motor. These (or drives) may communicate with a Programmable Logic Controller (PLC) across a fieldbus or non-real-time Ethernet bus. In a centralized drive control system, the motor controller communicates with the PLC using fast real-time Ethernet, making it possible to expand the feedback loop right back to the PLC. This means that a high-performance PLC can perform all the motion calculations, thus enabling the use of simpler and lower-cost motor controllers.

Benefits of using FPGAs and custom IP

Motor control is a nonlinear and time-varying parameter application. An efficient motor controller demands large amounts of computing power due to the inherently fast dynamics of current flow in the motor and control electronics. Many of today’s MCU/DSP devices implement motor control using a simplistic software control loop and a generic one-size-fits-all Pulse-Width Modulation (PWM) block. However, this kind of system architecture cannot provide the optimal power, performance, or integration needed for efficient motor control applications.

Using FPGA devices offers advantages in power efficiency, performance, safety, reliability, system cost, system integration, and implementation flexibility. Figure 1 shows an example of an FPGA-based integrated motor control system.

21
Figure 1: An FPGA-based motor control system allows designers to create custom functions fully integrated on a single FPGA.
(Click graphic to zoom by 1.9x)

Power advantages

A central part of any current control strategy is actuating the voltage command using one of many PWM techniques. A PWM technique controls the power-converter transistor states to meet the time-average value of the voltage command. These techniques can reduce losses in the motor and power converter while optimizing the voltage utilization of the DC bus.

The true advantage of using FPGAs is the ability to customize what was previously fixed generic hardware in MCUs or DSPs. In FPGAs the standard PWM block found in an MCU- or DSP-based motor control chip can be replaced by an application-specific PWM IP core optimized for performance and energy efficiency based on individual motor parameters.

Figure 2 shows a reduction of nearly 50 percent in the total harmonic distortion at a high modulation index using an optimized PWM in an FPGA instead of a standard PWM as used in MCUs or DSPs. This more accurate control reduces time-harmonic losses in the motor, reduces audible noise, and increases global motor reliability.

22
Figure 2: FPGA-based motor control reduces total harmonic distortion by 50 percent compared to MCU-based motor control. (Source: Alizem)
(Click graphic to zoom by 1.9x)

Performance, safety, reliability, and system cost advantages

The hardware programmability of FPGAs enables designers to easily implement dedicated high-performance logic circuits. Compared to software running on generic MCUs or DSP blocks, using dedicated logic circuits for motor current and torque control allows the motor control loop to operate at much higher frequencies. This also enables the motor controller to extract critical information about the motor’s health during its operation, which then can be sent to the main application controller to notify the user about the risk of motor failure.

FPGAs also provide system cost advantages. One benefit of using FPGAs to increase performance in motor control applications is their ability to provide greater flexibility in arranging components and additional functions, for example, integrating computing-intensive functions (such as DSP blocks) to run parallel to the main control scheme. Such functions may be adaptive, with real-time motor parameters and state estimations used to increase motor control performance and allowed to run either with a feedback loop or without speed or position transducers (sensorless operation). An example would be to use advanced DSP techniques in hardware for measurement , minimizing the effort to port optimized from one platform to the next.

Integration and implementation advantages

In FPGAs, the hardware system design process is completely different from that of discrete components. In the case of Altera’s devices, every step of integration is performed within the Quartus II development software, an electronics application that enables the designer to integrate and test system component operations in a completely virtual environment. In this way, the industrial systems designer can start a design from scratch and have a complete operational system in a matter of minutes. In addition, designers can reduce the number of components used, decrease system complexity, increase system reliability (due to less system components), and allow for customizable motor system configurations that fit every design’s performance and price point.

Motor control IP is designed to provide a very high-performance interchangeable platform. The practical motor control IP for an application is achieved by selecting and integrating the right combination of IP. FPGAs are flexible and can support many types of communications protocols, motor control IP, and industrial I/O interfaces on one device or platform.

Implementing such functions on MCUs or DSP devices may not be possible or might force the designer to compromise on either motor control performance or system performance. In comparison, these functions are completely independent on an FPGA as they can run in parallel in the programmable logic hardware. An FPGA-based motor controller offers completely deterministic performance and enhanced product reliability compared to the serial instruction-execution approaches of MCUs or DSPs.

Another advantage of implementing the motor control IP (and network connectivity) on the FPGA is that it mitigates the risk of product . With long product life cycles, FPGAs are built with industrial longevity, system flexibility, and reliability in mind. Designers can modify their systems or migrate to new generations of FPGAs with ease. Contrast this methodology to MCUs or DSPs, which require intensive software resources and involve long development cycles when moving to a new processor architecture to update any hardware features.

FPGAs mean more flexibility

FPGA-based systems offer industrial applications flexibility and productivity benefits that cannot be found in MCU- or DSP-based systems. These devices increase system performance by performing timing-critical tasks in hardware while adding system flexibility, leading to fewer redesigns and enabling designers to deploy their products sooner than traditional MCU- and DSP-based designs. Using FPGAs in motor control applications, designers can easily adapt to their specific application requirements.

Jason Chiang is a senior technical marketing manager for Altera’s Industrial and Automotive Business Unit, based in San Jose, California. In this role, Jason is responsible for developing marketing strategies and industrial solutions that facilitate the use of FPGAs in industrial applications. Prior to rejoining Altera in 2008, Jason held various product marketing management roles at P.A. Semi and -Sierra. He holds a BSEE from Cal Poly, San Luis Obispo.

Altera
408-544-8373
jchiang@altera.com
www.altera.com