Inverter design for brushless AC motor control with Renesas RX111 MCU kits

September 02, 2014 // By Graham Prophet
RX111 motor control kits are inverter reference solution kits designed to drive any 3-phase permanent magnet synchronous motors (PMSM), also called brushless AC motors. The RX111 inverter kits enable engineers to save time by eliminating the need to tune their motor parameters and evaluate the best tuning algorithm coefficients.

RX111 inverter kits, says Renesas, revolutionise the integration of 3-phase motors in equipment. Based on Renesas' 32-bit RX family of MCUs running at 3V, they deliver 50 DMIPS at 32 MHz. The RX111 reference kits are designed for equipment requiring medium and high dynamics and a low-cost bill of materials. The kits provide up to 7 A(max) at 24 VDC and have been tested with more than 30 different motors. An external power stage is available that is fully-compatible with the existing RX220 and RX62T inverter kits. The new RX111 solution kits provide the dynamics required to drive motors with a high level of accuracy.

Renesas has developed the two design tools based on RX111 MCUs to respond to a challenge encountered by engineers: tuning the embedded software to the application requirements, especially for sensorless field oriented control algorithms. The inverter kits provide:

  1. Auto-tuning of the current proportional-integral (PI) coefficients: Kp, Ki
  2. Identification of intrinsic motor parameters: Rs, Ls, Lm
  3. Real-time visualisation of the motor phase, current and step response
  4. Dynamic modification of the PWM frequency and control loop

The kits include an intuitive PC graphical user interface (GUI), providing engineers with a ready-to-use inverter reference prototype that enables them to drive their own motors in a few clicks. The solution kits also feature a sensorless vector control algorithm, which is used to accurately control the speed and the torque. This algorithm uses flux weakening to achieve rotation speeds higher than the nominal speed of the motor. Finally, two flux estimator blocks are implemented to ensure high flexibility in terms of motor types and application requirements.

Each kit contains the YROTATE-IT inverter board, a 24 VDC permanent magnet AC motor, a CD-ROM including the embedded software source code, the PC GUI, the board schematics, the bill of materials, Gerber files, user manual, quick start guide and the power stage schematics/Gerber files.

A video demonstration of the kits is available at