You might know that motor-control applications have been using MCUs for years, but you might not know that the very earliest MCUs used for motor control were actually targeted at the industrial market for power inverters, designed for converting DC power to AC. Once it was recognized that waveform output functions like Pulse-Width Modulation (PWM) had potential for addressing motor-control designs, things rapidly took off. Today, MCUs are used in just about every motor-control application imaginable; and by using new control algorithms and power-factor correction in the accompanying power modules, motor efficiency has improved significantly.
With estimates for motor-related power making up well over 20 percent of world’s energy use, it is easy to see that improved efficiency is a major focus for all new motor-control designs. These new algorithms are much more complex than traditional approaches, however, so MCU manufacturers have created complete development kits and reference designs to speed the development of these important applications. This article will review a sampling of recently introduced motor-control development kits to give you a solid background in selecting the kit that is right for your next application.
A good place to start
You might not know it, but a good place to start your search for the right development kit for your next design is with the Hotenda Reference Design Library. The library, as shown in the screenshot (Figure 1) below, is organized by target application, such as AC/DC and DC/DC Conversion, Audio Amplifiers, Energy Harvesting, Lighting, and Motor Control. If you select an application, like motor control, the filter window comes up, as shown on the right side of the figure, with several columns of items you can specify during your 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 will get several hits showing kits from Texas Instruments, Microchip, and STMicroelectronics. You can look over a summary of the kits’ features, data sheets, and users’ guides to find the right one for your application. We’ll now use the Hotenda Reference Design Library to explore the available kits for some common motor-control applications.
Figure 1: Hotenda Reference Design Library search function – Motor Control. (Courtesy of Hotenda)
Motor-control development kits for a variety of applications
As a result of the wide variety of motor-control applications and algorithms, some development kits serve multiple target systems. You may want to select a reference design that targets multiple types of motors in case you have several different designs to consider and you want to try and use the same MCU in each to leverage your development costs. Using the Dig-Key Reference Design Library you can select multiple types of motors and see which kits can support all of them. For example, by looking at both Three-Phase Brushless DC (BLDC) motors and Three-Phase Permanent-Magnet Synchronous Motors (PMSM) you can find kits targeted for both of these applications. Let’s look at one in more detail.
The Microchip dsPICDEM MCHV Development System is intended for the rapid evaluation and development of Brushless DC (BLDC) motors, Permanent-Magnet Synchronous Motors (PMSM), and AC-Induction Motors (ACIM) in sensor or sensorless operation. The system can be configured in different ways for use with Microchip’s specialized Motor-Control DSCs, and offers a mounting option to connect either a 28-pin SOIC device or a generic 100-pin Plug-In Module (PIM).
The dsPICDEM system has a three-phase power module device that contains the motor inverter and the gate driver’s circuitry. The circuit drives a BLDC, PMSM, or ACIM motor using different control techniques without requiring any additional hardware. It also has Power-Factor Correction (PFC) circuitry to provide a complete solution for efficiency-oriented motor-control applications. Figure 2 illustrates the hardware associated with the kit, shown at the left, and the accompanying 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 rated continuous-output current from the inverter is 6.5 A (RMS). This allows up to approximately 2 kVA output when running from a 208 V to 230 V single-phase input voltage in a maximum 30°C ambient temperature environment. Therefore, the system is ideally suited for running a standard Three-Phase Induction Motor of up to 1.4 kW (1.8 HP) rating or a slightly higher rated industrial servo-motor. The power module is capable of driving other types of motors and electrical loads that do not exceed the maximum power limit and are predominantly inductive. Furthermore, single-phase loads can be driven using one or two of the inverter outputs. The unit is capable of operating from 90 V up to a maximum of 265 V.
Note that the dsPIC DSC MCU is involved in both the motor control and PFC portions of the design. A PFC PWM output and fault detection and response from the dsPIC MCU provide a wealth of information to simplify any design with power-efficiency requirements. The two modules are designed as separate boards making it convenient to use schematics, board layout, and the bill of materials for customization. The robust enclosure brings out all key interfaces to standard headers – USB, RS-232 and program/debug, sensors, switches, LEDs, and the three-phase inverter bridge connector – making the development system an ideal test platform for prototyping a motor-control design.
Stepper motor controllers
The control of a stepper motor uses one of the simpler algorithms, and as such can be implemented using a specialized peripheral that integrates more of the analog and power-control circuitry than is usually possible with an MCU. For example, when searching in the Hotenda Reference Design Library for Stepper Motor reference designs the Texas Instruments DRV8818EVM Bi-Polar Stepper Motor Controller reference design appears. This reference design features the DRV8818 stepper-motor controller that integrates microstepping indexer logic and two N-channel power MOSFET H-bridge drivers. A simple step/direction interface allows easy interfacing to controller circuits. Pins allow configuration of the motor in full-, half-, quarter-, or eighth-step modes. Decay mode and PWM off time are programmable.
The evaluation module hardware, shown on the left side of Figure 3, can be connected via a USB cable to a PC to control and evaluate the operation of the DRV8818 in a test system with an actual motor. The PC-based control software has a simple-to-use Graphic User Interface (GUI), shown on the right side of Figure 3, to allow the user to make changes to control parameters such as starting speed, desired speed, stopping speed, step settings, and acceleration rate. The effects on the motor can be immediately determined and the best settings captured for use in the final design.
Figure 3: Texas Instruments DRV8818 Stepper Motor-Controller reference design. (Courtesy of Texas Instruments)
GUI control systems, hosted on a PC, are typically included with most motor-control evaluation kits and reference designs. They accelerate the process of evaluating the target system for a variety of applications and often include code that can be used in a final design as part of a more extensive testing or development environment. Look for kits that feature libraries of code, both for motor control and for testing to get the biggest head start on your design.
Controlling high-powered motors
The Hotenda Reference Design Library even supports searches for designs based on power levels. For example, searching for designs with a power of 1 kW will call up the STMicroelectronics STEVAL-IHM025V1 demonstration kit. This kit, as illustrated in Figure 4, is very robust, as you would expect from a design that supports up to 1 kW motors.
Figure 4: STMicroelectronics 1000 W motor-control kit. (Courtesy of ST Microelectronics)
The kit is typically used in conjunction with an STMicroelectronics eval board, handling the overall control function with the IHM025V1 serving as the power supply and power block for the external motor. The eval board serves as a convenient target for the supplier’s STM32 Field-Oriented Control (FOC) motor-control firmware library1. This library provides the high-level algorithms and low-level drives needed to create your own FOC motor-control designs. This type of augment to a development kit can be of critical importance, in particular with motor-control algorithms that are very complex. A library of key functions that allows the designer to simply specify key parameters to create production ready code can provide a dramatic time savings over reference designs that just supply example code and leave it up to the designer to “fill in” the gaps by developing and testing their own routines. Look for a motor-control library as an element of a reference design for the most efficient and robust implementation.
In summary, as we have seen the Hotenda Reference Design Library is a powerful tool for engineers looking to get a head start on a motor-control design project.
For more information about the reference designs and parts discussed in this article, use the links provided to access information pages on the Hotenda website.References