“You may know that motor control applications have been using MCUs for years, but you may not know that the earliest MCUs for motor control were actually aimed at the industrial market for power inverters, designed to convert DC power to AC. Once it was recognized that waveform output capabilities such as pulse width modulation (PWM) had the potential to address motor control designs, things happened quickly. Today, MCUs can be used for nearly every motor control application imaginable; motor efficiency is significantly improved by using new control algorithms and power factor correction in the included power module.
You may know that motor control applications have been using MCUs for years, but you may not know that the earliest MCUs for motor control were actually aimed at the industrial market for power inverters, designed to convert DC power to AC. Once it was recognized that waveform output capabilities such as pulse width modulation (PWM) had the potential to address motor control designs, things happened quickly. Today, MCUs can be used for nearly every motor control application imaginable; motor efficiency is significantly improved by using new control algorithms and power factor correction in the included power module.
With electric motors estimated to account for more than 20% of the world’s energy use, it’s easy to see that improving efficiency is a major concern for all new motor control designs. However, these new algorithms are much more complex than traditional methods, so MCU manufacturers have created complete development kits and reference designs to accelerate the development of these important applications. This article will review a sample of recently introduced motor control development kits to give you a solid background for choosing the right kit for your next application.
a good starting point
As shown in the screenshot below (Figure 1), the library is organized by target applications such as AC/DC and DC/DC conversion, audio amplifiers, energy harvesting, lighting, and motor control. If you select an application, such as motor control, the filter window appears, as shown on the right, and you can specify several columns of items during the search. For example, if you want a motor control reference design for a three-phase induction motor with overcurrent protection and power factor correction, you’ll get several showing kits from Texas Instruments, Microchip, and STMicroelectronics. You can review a summary of toolkit features, datasheets and user guides to find the right tool for your application.
Figure 1: Digital Key Reference Design Library Search Function – Motor Control. (Courtesy of Digi-Key)
Motor Control Development Kits for Various Applications
Several development kits are available with multi-objective systems due to various motor control applications and algorithms. You may want to choose a reference design for multiple types of motors in case you are considering multiple different designs and want to try to use the same MCU in each motor to get the most out of the development costs. Using the Dig-Key Reference Design Library, you can choose from many types of motors and see which kits can support all of them. For example, by looking at three-phase brushless DC (BLDC) motors and three-phase permanent magnet synchronous motors (PMSM), you can find target kits for both applications. Let’s take a look in more detail.
The Microchip dsPICDEM MCHV Development System is designed to rapidly evaluate and develop Brushless DC (BLDC) motors, Permanent Magnet Synchronous Motors (PMSM) and AC Induction Motors (ACIM) for sensor or sensorless operation. The system can be configured in different ways for use with Microchip’s dedicated motor control DSCs and offers a mounting option for interfacing with 28-pin SOIC devices or a generic 100-pin plug-in module (PIM).
The dsPICDEM system has a three-phase power module device containing the motor inverter and gate driver circuits. This circuit uses different control techniques to drive BLDC, PMSM or ACIM motors without any additional hardware. It also features power factor correction (PFC) circuitry, providing a complete solution for efficiency-oriented motor control applications. Figure 2 shows the hardware associated with the kit as shown on the left and the block diagram on the right shows the main components of the system – the PFC power module on the left and the motor control module on the right.
Figure 2: Microchip dsPICDEM MCHV Motor Control Development Kit. (Courtesy of Microchip)
The inverter is rated for a continuous output current of 6.5 A (RMS). This allows outputs up to about 2 kVA when operating from a single-phase input voltage of 208 V to 230 V in ambient temperature environments up to 30°C. Therefore, the system is ideal for running standard three-phase induction motors rated up to 1.4 kW (1.8 HP) or industrial servo motors with slightly higher ratings. Power modules are capable of driving other types of motors and electrical loads, which do not exceed the maximum power limit and are mainly inductive. Additionally, one or two inverter outputs can be used to drive single-phase loads. The device is capable of operation from 90 V up to 265 V.
Note that the dsPIC DSC MCU is involved in the design of the motor control and PFC parts. The dsPIC MCU’s PFC PWM outputs and fault detection and response provide a wealth of information to simplify any design with power efficiency requirements. The two modules are designed as separate boards for easy access to schematics, board layouts and custom bills of materials. The rugged housing brings all the key interfaces of standard headers – USB, RS-232 and program/debug, sensors, switches, LEDs and a three-phase inverter bridge – making the development system an ideal testbed for motor prototyping – Control Design .
Stepper motor controller
The control of stepper motors uses a simpler algorithm, so circuits typically available on MCUs can be implemented using specialized peripherals that integrate more analog and power control. For example, when searching for a stepper motor reference design in the Digi-Key reference design library, the Texas Instruments DRV8818EVM bipolar stepper motor controller reference design will appear. This reference design features the DRV8818 stepper motor controller with integrated microstepping indexing logic and two N-channel power MOSFET H-bridge drivers. A simple step/direction interface makes it easy to interface with controller circuits. Pins allow the motor to be configured in full-step, half-step, quarter-step or eight-step mode. Decay mode and PWM off time are programmable.
The evaluation module hardware shown on the left side of Figure 3 can be connected to a PC via a USB cable to control and evaluate the operation of the DRV8818 in a test system with an actual motor. The PC-based control software features an easy-to-use graphical user interface (GUI), shown on the right side of Figure 3, allowing the user to change control parameters such as start speed, desired speed, stop speed, step settings, and acceleration. Immediately determine the impact on the motor and capture optimal settings for final design.
Figure 3: Texas Instruments DRV8818 stepper motor controller reference design. (Courtesy of Texas Instruments)
A PC-hosted GUI control system is typically included with most motor control evaluation kits and reference designs. They speed up the process of evaluating target systems for a variety of applications and often include code that can be used in the final design as part of a wider test or development environment. Look for a suite with a codebase, including motor control and testing, to get the biggest head start on your design.
Control high power motors
For example, a search for a 1 kW design will invoke the STMicroelectronics STEVAL-IHM025V1 demo kit (now obsolete). As you can see in Figure 4, the kit is pretty solid and, as you’d expect, supports motors up to 1 kW.
Figure 4: STMicroelectronics 1000 W Motor Control Kit. (Courtesy of ST Microelectronics)
This kit is typically used with STMicroelectronics evaluation boards to handle the overall control functions, the IHM025V1 is used as a power supply and power module for external motors. The evaluation board is a convenient target for the vendor’s STM32 Field Oriented Control (FOC) motor control firmware library1. This library provides the high-level algorithms and low-level drivers needed to create your own FOC motor control designs. This enhancement to the development kit can be critical, especially for very complex motor control algorithms. A library of key functions that allows designers to create production-ready code simply by specifying key parameters can save a lot of time over reference designs that only provide example code, and let designers test their own conventions by developing and “filling in” the gaps. Look for a motor control library as an element of a reference design for the most efficient and robust implementation.