Motor control

Realized brushless motor control

Two main types of motor control and how they are used.

There are many products with built-in motors around us, such as air conditioners, vacuum cleaners, and electric fans. As robots, drones and electric vehicles, which are expected to bring great change to society in the future, become more widespread, more motors will be used.

Motors, which are familiar to us as described above, are classified into several types according to the structures. Among them, brushless motors are increasingly used in domestic/industrial applications. The characteristics of brushless motors are high efficiency, maintainability and controllability. With the increasing concern for environmental issues in recent years, the use of brushless motors that can be driven with high efficiency is desired. As the name “brushless” motor implies, there are no brushes in contact with the rotor, so there is no need to worry about brush wear, reducing the frequency and cost of maintenance. Brushed motors have the brush and commutator constantly exerting torque without a drive circuit due to their structural mechanism, while brushless motors do not have such brushes and commutators. Instead, the torque is generated by the MCU adjusting the direction and magnitude of the current in response to the position of the rotor, and high controllability can also be achieved, such as maintaining a constant speed even if the load exchange.

There are two types of control methods often used for brushless motors: 120 degree driver control and vector control. The 120 degree driver drive uses six voltage patterns to drive the motor. This control method requires relatively less operation on the MCU, but can cause vibration and noise because the angle of the torque acting on the rotor is not constant. On the other hand, vector control is a control method in which the torque acting on the rotor is constantly in the vertical direction. This method requires a large number of operations on the MCU, but it is characterized by low speed ripple. From there, vector control tends to be used in applications that require precise control.

RL78 is an 8/16 bit low power consumption microcontroller. In the RL78 series, RL78/G1F, RL78/G14, RL78/G1G and RL78/G1M are often used for motor control. Here are the features of each MCU.

  • RL78/G1F: Multifunctional MCU with enhanced functionality for motor control
  • RL78/G14: General purpose MCU with a wide range of pins, memory sizes and package types
  • RL78/G1G: Small system microcontroller with integrated analog peripheral functions
  • RL78/G1M: Compact MCU with the minimum functions required for motor control

A 120 degree conductive control, which requires a small amount of calculation, can be used with these four microcontrollers. On the other hand, vector control, which requires large computing load, is realized by RL78/G1F and RL78/G14, which have relatively high computing power among the above MCUs. In addition to these control methods, we are also developing solutions using the analog peripheral functions of the RL78/G1F, such as initial position detection, which estimates the rotor angle without sensors before rotation begins, and a high-speed rotation solution that performs 120 degree conductive control using a dial gauge.

We provide sample software that implements each of these control methods. With the sample software for 120 degree drive control, speed control can be performed using Hall sensors or without sensors. Additionally, for vector control, we prepare two kinds of software examples that perform sensorless speed control using one or three shunt resistors for current sensing. We also offer the above-mentioned home position and high-speed rotation sensing solutions as an example of software that can be used in specific applications. Additionally, we plan to release new sensorless vector control sampling software for high voltage applications. This sample software runs on the “T1003-A” high voltage inverter board (input voltage range: AC 85 – 265 [Vrms]rated output current: AC 1 [Arms]) manufactured by Desk Top Laboratories Inc., and can be used for developing high voltage applications such as refrigerators, ceiling fans, and conveyor belts.

We also provide a variety of development assistance tools to support the development of motor control solutions. Renesas Motor Workbench (RMW), a motor control evaluation tool, can measure the motor characteristic parameters and display the variable information saved in the internal RAM of the MCU in wave form, etc. Additionally, by using a porting support tool called Configuration File Generator (CFG), it is possible to automatically redesign motor control parameters when training the motor using the development environment prepared by the customer. look please the tutorial video learn how to use these development aid tools.

For more information, please visit the RL78 motor control solutions web page.

Akasaka Yuta

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Akasaka Yuta is an application engineer at Renesas.