Bench Talk

Image Source: Mouser Electronics

Motors are everywhere—from air conditioners and vacuum cleaners to power tools and industrial equipment. As globalisation and urban infrastructure advance, familiar products are evolving to offer higher performance, better energy efficiency, and compact sizes. Power tools need to be smaller yet deliver higher torque and longer battery life, while home appliances emphasise quieter operation and faster rotation.

Central to achieving these innovations is the motor control system. It ensures precision, efficiency, and safety in applications ranging from everyday devices to high-end industrial drives. To address these challenges, Renesas Electronics offers a scalable portfolio of microcontroller units (MCUs) that enable advanced control methods and real-time performance.

Motor control systems are composed of many elements, and while requirements vary depending on the application, real-time performance is one of the key factors. It ensures precision, improves efficiency, and prevents failures by completing a specific process within a set time, with minimal variation.  

Brushless motors are increasingly used in home and industrial applications for their efficiency, maintainability, and controllability. Two common control methods offered by brushless motors are 120-degree conduction and vector control. The former requires fewer MCU operations but can cause vibration and noise, while vector control offers precise speed regulation at the cost of higher computational load.

Renesas’ RL78 family provides an entry point for motor control. These 8/16-bit MCUs feature low power consumption and analog peripheral functions. MCU groups such as the RL78/G1F, RL78/G14, and RL78/G24 support vector control, while others handle 120-degree conduction. Renesas offers sample software for both methods, including sensorless speed control and initial position detection, as well as solutions for high-speed rotation and high-voltage applications. Development tools such as Renesas Motor Workbench and Configuration File Generator simplify evaluation and parameter tuning, helping designers move quickly from concept to production.

Size, efficiency, and quiet operation are critical factors in power tools and home appliances. Brushless motors controlled with simpler methods, like 120-degree conduction, often face issues such as torque ripple and vibration. Vector control addresses these challenges by keeping torque constant, but it requires more MCU processing power to bring vector control to compact, cost-sensitive applications. Renesas’ RA2T1 MCU helps with this requirement by using a single-shunt current detection method that leverages the existing DC link current sensing circuit, minimising extra components. Its analog-to-digital converter (ADC) conversion starts request linkage function with general PWM timers (GPTs), enabling precise current detection, while built-in comparators and Port Output Enable for GPT (POEG) functionality quickly shut off PWM outputs during abnormalities for safety.

For fan applications, the RA2T1 integrates a dedicated 3-channel sample-and-hold ADC circuit, ensuring simultaneous current sampling without timing discrepancies—critical for high-speed motors operating above 100,000 RPM. Powered by a 64 MHz Arm^® Cortex^® M23 core, the RA2T1 simplifies system design with optimised analog and timer functions, compact packages as small as QFN24, and broad voltage support.

Moving to high-end motor control applications, such as AC drives and servo motors, conventional MCUs can easily guarantee real-time performance because the central processing unit (CPU) and memory frequencies are similar. Microprocessor units (MPUs), however, use faster CPUs and shorter control cycles, which can be limited by slower external flash memory. To overcome this, programs are often placed in high-speed static random access memory (SRAM) or tightly coupled memory (TCM), but capacity constraints make this challenging.

Renesas’ RA8T2 MCU solves this by combining the best features of MCUs and MPUs. Equipped with a 1 GHz Arm® Cortex® M85 core, built-in cache, TCM, and SRAM, it also includes Magnetoresistive RAM (MRAM) for programs. MRAM operates at 100 MHz—much faster than external flash—making real-time performance easier to achieve. Additionally, RA8T2 offers an optional Cortex M33 core for system control, enabling parallel processing and improving overall responsiveness.

From basic conduction control to advanced vector control and real-time industrial performance, Renesas delivers a complete motor control portfolio: RL78 provides a cost-effective starting point, RA2T1 brings advanced techniques to compact devices, and RA8T2 enables deterministic, high-speed control for demanding applications. Explore Renesas Motor Workbench, sample software, and motor control kits to accelerate your next design.

Author

Yuki Ueno is an engineer and product marketing manager of semiconductor products, specifically planning and developing MCUs and solutions for motor control applications, including Renesas' RL78/RA family of motor control MCUs. He is well-versed in embedded motor control technologies such as brushless DC motors (BLDC) and vector control, also known as field-oriented control (FOC).