Principle of commands*

BLDC Motor Controller Commands: Principles and Control Modes

The motor controllers ensure precise control of BLDC (Brushless DC) and PMSM (Permanent Magnet Synchronous Motors) by converting direct current (DC) from a battery or power supply (often 24 to 51.2 V) into alternating signals (AC) synchronised with the rotor position.

The quality of control depends on the control mode used, the type of position feedback, and the regulation parameters chosen.

PWM – Pulse Width Modulation

PWM (Pulse Width Modulation) is the basis of all modern control.

It involves chopping the direct voltage at a high frequency (usually between 10 and 20 kHz) to adjust the average voltage applied to the motor phases.

By modulating the pulse width, one regulates:

• The average voltage → thus the speed of the motor,

• The current → thus the torque delivered.

This principle ensures efficient control while limiting the absorbed current, which improves efficiency and reduces heating.

Six-step / Trapezoidal: Simple and Robust Control

The six-step (or trapezoidal) mode is the most common form of control for simple BLDC motors.

The controller successively powers the three phases of the motor according to six combinations distributed over a complete rotation of the rotor.

This switching is done from:

• Hall sensors, which detect the rotor position,

• Or, in sensorless version, via the measurement of back electromotive force (back-EMF).

Advantages:

• Simple and economical electronics,

• Fast response, few calculations needed,

• Sufficient for constant speed applications.

Limits:

• Slightly rippled torque (vibrations at low speed),

• Less suitable for very low speeds or precision applications.

FOC – Field Oriented Control (Vector Control)

FOC, or vector control, is the most advanced method for controlling BLDC/PMSM motors.

It consists of decomposing the motor current into two components:

• Axis d: rotor magnetic field,

• Axis q: motor torque.

The controller manages these two currents separately, allowing for a perfectly smooth torque and better efficiency, even at variable speed or fluctuating load.

This technique requires:

• A position sensor (Hall, encoder, resolver)

• Or a sensorless estimation by real-time calculations.

Advantages:

• Smooth and silent torque,

• Excellent energy efficiency,

• Precise control of speed and torque.

Disadvantages:

• More complex calculations,

• Requires a more powerful controller and careful configuration.

Control Loops: Speed and Torque

Modern controllers integrate several closed-loop controls, generally of the PID (Proportional – Integral – Derivative) type:

• Current loop (torque): instantly regulates the force produced by the motor.

• Speed loop: maintains the desired rotation regardless of the load.

• Position loop (optional): used in robotic or automation systems.

The configuration of the controller involves defining:

• The PID gains (reactivity and stability),

• The limits of current, torque, or speed,

• The acceleration and braking ramps,

• And sometimes the motion profiles (S-curve, controlled braking, position holding).

In Summary

Conclusion

The choice of control mode primarily depends on the desired level of performance:

• For simple or robust applications → Six-step is sufficient.

• For smooth, precise, and energy-efficient control → FOC is required.

In all cases, proper tuning of the control loops and appropriate configuration ensure stable, high-performance, and durable motor operation.

*: The technical information presented in this article is provided for guidance only. It does not replace the official manuals of the manufacturers. Before any installation, handling, or use, please consult the product documentation and follow the safety instructions. Torque.works cannot be held responsible for inappropriate use or incorrect interpretation of the information provided.