Catalogue:

1. What is a Motor Control Unit (MCU)?

2. Main Functions of an MCU

3. Typical Hardware Architecture of an MCU

4. Working Principle of an MCU

5. Future Trends in MCU Development 

   
   

 What is a Motor Control Unit (MCU)?

A Motor Control Unit (MCU) is an electronic module positioned between the battery and the motor in an electric vehicle, controlling the vehicle's speed and acceleration based on throttle input. This controller converts direct current (DC) from the battery to alternating current (AC) and regulates the power output from the battery to drive the motor. Additionally, during regenerative braking, it can reverse the rotation of the motor to recharge the battery. Motor controllers in electric vehicles vary in voltage, power, and current capabilities, and can be broadly categorized as follows:

Main Functions of an MCU

The Motor Control Unit acts as the central control hub for the electric vehicle's motor, performing multiple critical functions to ensure smooth and efficient driving. Its primary responsibility is to convert the direct current (DC) supplied by the battery into three-phase alternating current (AC) to drive the motor. Moreover, the MCU monitors key parameters like temperature, current, and voltage to optimize motor performance and prevent potential faults. It also precisely controls the motor's speed, torque, direction, and corresponding power output based on inputs from the driver or the vehicle control system. Key functions of the Motor Control Unit (MCU) include:

l Controlling motor torque and speed

l Starting/stopping the motor

l Preventing electrical faults

l Providing overload protection

l Changing motor rotation direction

l Regenerative braking

Typical Hardware Architecture of an MCU

The diagram below depicts the typical hardware architecture of an MCU, consisting mainly of a power section, current sensing circuit, Voltage Source Inverter (VSI), CAN transceiver, and a microcontroller (MCU) among others.

Microcontroller (MCU): The main control inputs for the microcontroller itself come from the throttle signal, which can be controlled by the vehicle's driver. This throttle signal determines how the PWM pulse duty cycle varies to achieve the desired speed and torque. For efficient and rapid control, the microcontroller implements Field Oriented Control (FOC).

Voltage Source Inverter (VSI): The primary function of the VSI is to convert DC to AC based on motor position feedback. Typically, VSI uses six IGBTs, although parallel combinations of IGBTs are used to increase the inverter's current capacity. Low voltage motors (typically below 100V) use MOSFETs, while high voltage motors use Gallium Nitride (GaN) power switches and Silicon Carbide (SiC)/Insulated Gate Bipolar Transistor (IGBT) drivers.

Current Sensing Circuit: To sense the phase currents of the motor, Hall effect-based current sensors are used. Typically, two current sensors are used to sense two phase currents, with the third phase current derived from these sensors.

Power Supply: Different voltage levels are required to power the microcontroller, motor temperature sensors, and position sensors. Additionally, since the microcontroller has built-in current sensors, the power supply must provide appropriate bias voltages for these sensors. To meet these requirements, the power section converts the battery's DC voltage into different voltages as needed.

Gate Drivers: Gate driver circuits are used to amplify the PWM pulse voltage levels produced by the microcontroller, which then drive the IGBTs.

CAN Transceiver: The function of the CAN transceiver is mainly to transmit and receive data on the CAN bus, facilitating communication between the MCU and other modules in the vehicle.

Working Principle of an MCU

The microcontroller (MCU) is responsible for executing complex control algorithms and managing the overall operation of the motor. It also provides an external communication interface (mainly CAN), allowing it to communicate with other ECUs in the system and receive control information from the VCU. The PWM signals generated by the MCU are amplified by gate drivers to control the power switches IGBT. The VSI inverter facilitates the conversion between DC and AC. Typically, six IGBTs configured in three half-bridges are used for this conversion, with additional parallel units added as needed to meet the motor's current requirements. Various sensing and sampling circuits provide feedback on motor parameters, such as position, phase current, temperature, etc., for precise control. The type of motor used in electric vehicles varies, including BLDC/PMSM DC motors and AC motors, thus the control algorithms employed by electric vehicles will depend on the type of motor and control method (open-loop or closed-loop).

Future Trends in MCU Development

Multi-motor control is becoming a significant advancement in the electric vehicle industry, with new developments focused on controlling multiple motors simultaneously.

Exploring hub-drive and mid-drive modes for motors.

With increasing demands for integration and efficiency in MCUs, third-generation semiconductor materials like SiC and GaN are being widely applied, offering advantages such as higher switching speeds, lower power losses, and better thermal performance compared to traditional silicon-based switches. This results in higher efficiency, lower energy consumption, and greater power density for motor control units. SiC and IGBT drivers provide higher operating temperatures and voltage capabilities, thereby enhancing performance and reliability in demanding electric vehicle applications.

The intelligence of MCUs is being enhanced with machine learning and artificial intelligence to protect data integrity and reduce human error.

As electric vehicles become more common, the role of the Motor Control Unit (MCU) in enhancing vehicle performance is increasingly crucial. With ongoing advancements in MCU architecture and technology, the future of electric vehicles looks more efficient, powerful, and sustainable.