Why are Brushless DC Motors the Preferred Choice of Automotive OEMs Today?

Why are Brushless DC Motors the Preferred Choice of Automotive OEMs Today?

Brushed DC Motors have been omnipresent in the Automotive Industry for a very long time. However, the innovations in automotive electronics have ushered in a wave of electric motors that are controlled by electronic circuits (popularly known as motor controllers).

The advantages offered by these advanced motor control systems have also expedited the migration of Automotive OEMs from Brushed DC Motors to Brushless DC Motors.

A Sneak-Peek into the History of Automotive DC Motors

Traditionally, all automotive components like power windows, wiper systems, power steering, seating control, traction control system, etc. relied heavily on Brushed DC Motors.

Reason- Brushed DC Motors had the ability to reach peak speed in a matter of seconds.

However, wear and tear in Brushed DC Motors was a major drawback. Also, controlling the speed in such a motor was not easy. These, along with several other reasons, led to the widespread adoption of Brushless DC (BLDC) Motors in the automotive industry.

Sounds like an interesting piece of technology-related history, right? We will delve deeper into this topic, but before that, let’s brush up our basics a bit.

Brushed Vs Brushless DC Motors

Brushed and Brushless DC Motors have 2 basic components- Stator and Rotor (also called armature).

In a Brushed DC Motor, brushes are present as additional components.

While both Brushed DC Motors and BLDC Motors are driven by permanent magnets or electro-magnets as the stator, the difference lies in the commutation.

How Does a Brushed DC Motor Work?

• Rotor, a permanent magnet, generates a stationary magnetic field around the stator.
• When DC power is applied to a phase of the stator coils, the coils become energised and function as an electromagnet.
• The force interaction between this permanent magnet and the electromagnet is what drives the BLDC Motor.

 

Motor Rotation – Energising of the Stator Coils and Movement of the Rotor   In the above diagram, when coil A is energised, the opposite poles of the stator and rotor are attracted to each other. This causes the rotor to move towards coil A. As the rotor comes close to coil A, then coil B is energised. Subsequently, the rotor moves towards coil B. When the rotor nears coil B, coil C is energised. Then the rotor moves towards coil C. As the rotor nears coil C, coil A is energised with opposite polarity. This makes the rotor move towards coil A. This process is repeated and causes continuous rotation of the rotor. The switching of current to energise the appropriate coil is called commutation. Commutation is brought about by carbon brushes and commutator (preferably made of copper).

As brushes and commutator come in contact with each other and the rotor winding, it gets worn out very frequently.

Now, let us understand how Brushless DC Motors help in overcoming this issue of wear and tear.

How Do Brushless DC Motors Work Without Wear and Tear?

Since there are no brushes in a BLDC Motor, it relies on an electronic system (external motor control system) for commutation.

For ease of understanding, let’s discuss the working of the most commonly deployed 3 phase Brushless DC Motor:

• In this motor, the switching of current in the motor phases (commutation) is done in a 6-step pattern.
• These commutation phases move the electromagnetic field. This, in turn, moves the rotor and the motor shaft.
• The motor control system generates PWM signals that assist in energising the motor phases at the right time.
• BLDC Motor systems can also be fitted with Hall Effect sensors, in order to improve the overall efficiency of the motor.
• A Hall Effect sensor helps define the accurate position of the stator with respect to the rotor. This is essential for the optimum functioning of the motor.

A Snapshot of Brushed Vs Brushless DC Motors

Parameter	Brushed DC Motor	Brushless DC Motor
Commutation	Commutation is achieved by brushes and copper commutators	Commutation is achieved electronically using motor control system
Wear and tear	Presence of brushes causes wear and tear	Wear & tear is minimum as brushes are absent
High torque	Peak speed can be reached fast but not suitable for high torque application	Capable of producing high torque and constant speed
Use cases	Used in basic automotive applications like wipers and power windows	Deployed in electronic power steering, HVAC systems
Efficiency	Moderate	High
Regular maintenance	Periodic maintenance required	Limited/none
Dynamic Response	Slow	Low rotor inertia; hence fast
Electric Noise	High	Low, due to the absence of arcs from brushes that generate noise

Why Did the Automotive Industry Embark on This Great Migration to BLDC Motors?

The difference in the construction and working of brushed and brushless motors offer enough reasons for the automotive industry to upgrade to BLDC Motors.

Let’s look at some of these advantages in detail:

• An increase in efficiency of about 15-20% is offered by electronically controlled Brushless DC motors.
• There is a marked reduction in maintenance cost, as there are no brushes in BLDC Motors
• Brushless DC motors are more cost-effective, when we take into consideration the need to periodically replace brushes in Brushed DC Motors (due to wear and tear).
• Smaller size, lesser noise, enhanced heat dissipation and higher speed also make BLDC Motor a preferred choice for automotive applications.
• Since BLDC Motors can be integrated with electronics-based advanced motor control systems, these are ideal solutions for modern automotive applications like EPS (Electronic Power Steering), HVAC Systems,Electric Vehicle Drivetrain.

Point to note – BLDC Motors are more expensive as far as initial investment is concerned. This is primarily due to the need for design and development of motor control systems. However, the advantages offered by these motors far outweigh the additional investment.

What Challenges Would Your Team Face During the Migration from Brushed DC to BLDC Motors?

Migration from Brushed DC Motors to its brushless relatives comes with its own set of challenges.

Of all the issues that one may face during the migration process, overcoming the challenge related to commutation is the most critical.

A Brushed DC Motor relies on mechanical commutation with brushes and a copper commutator, and this controls the direction of the motor rotation.

A BLDC Motor, in contrast, has several other capabilities. This includes features like soft start/stop, diagnostics capability, FOC algorithm for better efficiency and various other software-level functionalities.

Most of these features are facilitated by the BLDC motor controller.

While in Brushed DC Motors, the switching of the magnetic field is only limited to two phases, BLDC Motors are mostly 3-phased. Hence, the switching of current is done for three phases.

While migrating to Brushless DC Motors, either of the following commutation sequences can be adopted:

• The classical and simple Trapezoidal Control (6-step commutation)
• The advanced FOC with Space Vector PWM

For accurate commutation in a BLDC Motor, the motor position is very important. Components like Hall Effect sensors, Resolvers and Encoders are deployed in the BLDC motor controller as feed-back mechanisms. This helps in achieving the required accuracy of the motor position.

Sensor-less option for commutation of BLDC Motor is also used in some applications. The back EMF provides the feedback mechanism in such cases. However, FOC algorithm (Vector Current Handling) is a more efficient method of commutating BLDC Motors.

Integrating Vector Current Handling requires a great deal of experience and expertise in Control Systems and motors.

Software Components That Can Be Reused During Migration to a BLDC Motor

Certain software components like communication stacks can be reused in the process of migration from Brushed to Brushless DC Motor. However, there are certain aspects to be considered while doing so.

The underlying hardware platform and other hardware components like current sensors must be similar. If there are changes in the hardware components, some customisations may be required in the following software components:

1. Hardware Abstraction Layer
2. MCAL Layer

The motor drive logic and application layers mostly remain unchanged while migrating from Brushed DC Motor to BLDC Motors. Vehicle Diagnostics and In-vehicle Network Protocol Stacks can be easily reused without any change.

How is the Migration to BLDC Motors Manifesting Itself in the Automotive Industry?

The migration has been quite fast paced. The modern automotive industry is experimenting with a lot of new technologies and BLDC Motors seem to fit the bill.

In fact, applications like traction control, which were once synonymous with Brushed DC Motors are now being designed using BLDC motor controllers.

In the case of an automotive seating control system, the humble Brushed DC Motor would not be able to efficiently perform all the operations. Hence, the shift to Brushless DC Motors with BLDC motor controllers for accurate operations is inevitable.

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