How to choose a suitable motor control scheme

Different applications have very different requirements for motor controllers. Current controller / driver solutions on the market each have their strengths, including standard controllers / drivers for specific simple applications, and MCUs, DSPs, and FPGAs that use external buffer gate drivers and power stages.

MCU is the current mainstream motor control solution in the market, suitable for high, medium and low-end motor control. Through the internal integrated motor control module, it can simplify the development of the customer's motor control; compared with the stronger control function of DSP, the servo control and protection functions of the motor can be better achieved. In addition, in the 32-bit processor, by increasing the speed of calculation processing, it can also achieve complex control of space vector, magnetic field positioning and PD closed-loop adjustment.

For simple low-power motor control applications such as small BLDC cooling fans, a dedicated standard motor control IC can achieve low cost. But for demanding applications, it is more suitable to use DSP, MCU and FPGA, because other system management functions can be added, such as monitoring motor parameters and status, and communication with the host system. "However, DSP, MCU, and FPGA require external gate drivers and power devices," said Khagendra Thapa, global strategy marketing manager for Diodes.

"At present, 8-bit MCUs are mainly used for low-cost and low-performance occasions, and 16-bit and 32-bit DSP / MCUs are used for medium / high-performance occasions. Among them, the price-performance ratio of DSC is relatively high." Freescale microcontroller business Charlie Wu, senior system engineer of the Ministry, pointed out that "FPGA is mainly used in conjunction with DSC / MCU to generate special PWM signals, which is mainly used in high-power applications."

"Regarding motor control schemes, DSP, MCU and FPGA have their own unique characteristics. DSP is suitable for high-end and complex motor system control because of its strong data processing ability and fast operation speed, such as space vector control algorithm for AC induction motor and sensorless. Spatial positioning, etc., but it depends on the maturity and stability of the software algorithm, and has higher requirements for developers. In addition, because the core voltage and interface level are mainly 3.3V or 1.8V, the relevant level of the motor driver needs Drive circuit support. "Peng Tao, product manager of Fujitsu Microelectronics (Shanghai) Co., Ltd. pointed out," FPGAs can be well adapted to customized motor drives by integrating logic circuits and special motor drive circuits, but they are generally used in motor control. There is a slight lack of sexuality. "

"The function of single chip microcomputer with DSP is generally used in more high-end applications that require faster speed. Infineon's 16-bit single-chip microcomputer and 32-bit single-chip microcomputer are both single-chip microcomputer with DSP function, 32 of which support floating-point arithmetic." Infineon Mr. Shi Jingyan, Senior Director of Sales and Business Development, Industrial and Diversified Electronics Market Division, Ling Technology (China) Co., Ltd. pointed out, "FPGA has its own characteristics, it is flexible, but the entry threshold is high and the unit price is high. It is generally used for a small amount. field."

What is the opinion of FPGA vendors? This article invited two FPGA manufacturers to talk about the current status of their products in motor control.

Zhang Yuqing

Director of Marketing and Applications, Xilinx Asia Pacific

The current motor control needs high performance and high efficiency, which puts forward higher requirements on control accuracy and response time. The technology based on asynchronous motor vector control has been widely used since it was invented in the 1970s. This control method is now relatively mature, has been commercialized and the product quality is stable. However, because this method uses a more complex coordinate transformation, it has higher performance requirements on the controller's computing speed and processing power. In addition, in some places where cost and surrounding environment are considered, speed sensorless technology has also received extensive attention. This undoubtedly also puts forward higher requirements on the processing power of the chip. With the rapid development of modern control theory, MCU / DSP / FPGA and other semiconductor devices and power electronic switching devices, the realization of high-performance sensorless vector speed control system is the future development trend of the motor control market.

The MCU usually focuses on the number of I / O interfaces and the size of the programmable memory, which is very suitable for occasions with a large number of I / O operations, so it is widely used in low-cost, low-power and low-precision systems. However, due to its limited processing capacity, the application occasions are subject to relatively large restrictions. The DSP chip integrates interfaces such as analog-to-digital conversion, digital input / output, serial port communication, and motor control PWM signal output. Therefore, the hardware design of the motor control system is flexible and simple, and the DSP is good at high-speed computing, so it is generally used for relatively high-end Control system, such as servo motor control. FPGA shows excellent performance in high-end motor applications. It implements fast response, multi-axis simultaneous processing, flexible and diverse peripheral interfaces, and support for multiple industrial buses.

For the different requirements of motor control, the inherent programmability and parallel processing characteristics of FPGA chips are very suitable for mid-to-high-end motor control applications. Because it performs parallel processing in a pure hardware manner, and does not occupy CPU resources, it can make the system achieve high performance. The current development of motor control is more and more diversified and complicated, and more and more demanding performance requirements are put forward on site. Therefore, customers may consider developing their own dedicated control chips. The programmability of FPGA can meet this demand.

At present, most products consider current loop control as a DSP co-processing, while speed or position loop control is implemented by the DSP chip. In general, because the position control is more flexible and the difference is relatively large, it is difficult to achieve versatility, so the position loop is generally completed directly by the DSP; but the speed and current loops are relatively versatile and closely related to each other, so that the high Speed ​​control of performance is inseparable from current control, so they can be integrated into a chip for processing, so that both speed servo control can be achieved, current control can be performed separately, and a position servo system can be formed together with DSP. Xilinx FPGA also provides a 32-bit MCU Microblaze, which can further realize the three control of position, speed, current by a single FPGA, customers can completely customize a SOC chip to meet special needs. And once the trial production is successful, such as mass production, you can also directly customize the ASIC chip according to the FPGA design to reduce costs. In addition, FPGA also serves as the co-processing function of MCU / DSP on many occasions, and also plays a very important role in the combination of logic, bus and interface expansion.

In addition, with the improvement of process technology level, FPGA chips also show more and more obvious advantages in power consumption and cost. Xilinx ’s recently launched Spartan-6 series is based on 45 nanometer technology and is very suitable for industrial control applications. It integrates advanced technologies such as DSP hard core, memory controller hard core, PCIe hard core, etc., and customers can implement vector control Algorithms, high-speed interconnection to meet the requirements of complex servo systems.

As the MCU / DSP coprocessor function, FPGA has been widely used in most motor control products, providing functions such as logic, interface expansion and bus. At the same time, third-party Xilinx, such as Xilinx authorized agent Avnet, also provides a large number of peripheral interfaces and industrial bus IP cores, which enriches the application of motor control.

Xilinx will launch a reference design based on AC motor vector control in the near future, and provide a demo board and FPGA source code. Customers can develop products suitable for their applications on the basis of this platform. We also plan to provide motion control engine and direct torque control algorithm implementation to provide customers with more choices to meet the needs of higher performance on site.

Our FPGA chips have been widely used in high-end CNC machine tools, high-end servo systems, high-end inverters, laser marking machines, and robot products. Most large foreign companies such as Siemens, GE, ABB, etc. use FPGA as the core processing platform to implement a SOC solution. At present, the research and development level of domestic enterprises in high-end servo products is still far behind foreign countries, but we believe that under the industrial policy of the Chinese government to encourage domestic enterprises to develop their own intellectual property rights, FPGAs will definitely play an increasingly important role.

Mike Brogley

Actel company IP and solution product marketing manager

Now, the market has appeared a wide range of emerging market applications that use motor control, so it also puts forward different requirements for motor controllers / drivers. The new design for AC and DC motor control must have the following characteristics: high efficiency, as low power consumption as possible; long working time without affecting performance.

Traditionally, designers of embedded systems have always considered MCU + ASSP solutions. However, by using solutions that combine MCUs, analog peripherals, embedded flash memory, programmable logic, and true single-chip operation (such as SmartFusion), designers can now achieve a high level of integration that was previously only possible with custom solutions .

SmartFusion intelligent mixed-signal FPGA has an important impact on system operation. Since the ARM Cortex-M3 processor is a standard unit module separate from the FPGA architecture, the two can operate independently. Therefore, when reprogramming the FPGA architecture, there is no need to interrupt the operation of the processor. This also allows the user logic to be updated as needed while the processor is processing critical system functions. Similarly, during the processor firmware update, the user logic can continue to operate.

The intelligent mixed-signal FPGA provides the following performance advantages: customizable and robust PWM to achieve more sophisticated control algorithms; compared to software solutions, it has a faster and more deterministic control system, which reduces current ripple and Noise; immediate response to user I / O (such as emergency braking alarms); hardware acceleration of control algorithms; high-speed flash memory enables faster access to lookup tables, etc.

Actel's DSP design flow allows designers to use Matlab and Simulink with complete DSP blocksets and Actel IP sets to evaluate algorithms at a high level of abstraction. DSP designers can now use our industry-leading toolset to run a seamless and intuitive design flow to interpret, optimize, and verify RTL-level, logic-gate-level, and physical-level designs.

The use of smaller, more cost-effective motors in traditional motor applications has gradually become an important factor in the use of electronic motor control technology in the industrial sector. SmartFusion FPGA can provide embedded system designers who need a true system-on-chip (SoC) solution with greater flexibility than traditional fixed-function microcontroller solutions, and the cost is much lower than traditional FPGA solutions with embedded soft-core processors .

SmartFusion FPGA provides a low-power, single-chip solution to optimize slip frequency control in AC induction motors. It integrates CPU, NVM, ADC, and analog interfaces, enhances the control loop, and improves efficiency, reliability, and energy-saving performance, making the motor have higher efficiency and lower power consumption. In addition, large-capacity embedded non-volatile memory can provide the required security to protect customized control algorithms. Actel is actively developing a multi-axis motor control solution based on SmartFusion for permanent magnet synchronous motors, featuring the unique advantages of SmartFusion for sophisticated control algorithms.

Actel also meets the requirements of low power consumption and handheld applications through the IGLOO ultra-low power FPGA series, and is an ideal solution for micro motor control. In brushless DC or stepper motors, the IGLOO series can be used for sensored or sensorless applications.

The SmartFusion and IGLOO series are popular because of their following characteristics and advantages:

* Realize high-performance precision active control of multiple motors in a single-chip solution, reduce bill of materials and assembly costs, and reduce footprint and improve system stability.

* Manage power, direction, speed, torque, and provide protection against overload or failure

* Using FPGA to achieve ultra-fast closed-loop algorithm, while Cortex-M3 manages the rest

* Motor control development tool kit with five reference designs for demonstration and laboratory development

* The development cycle is very short, and the product can be quickly listed

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