The Great Migration of Automotive OEM’s, from Brushed DC to BLDC Motors
Brushed DC Motors have been serving several industries, for over a century. Likewise, even in the Automotive Industry, Brushed DC Motors were omnipresent in all types of vehicles.
But then the innovations in electronics ushered in the wave of electric motors, which are controlled by an electronic circuit (popularly known as motor controllers)el.
Traditionally, all the automotive components like power windows, wiper systems, electronic 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 its major drawback. Also, in the brushed DC motors, the system could control only change in direction of rotation of the motor and nothing else.
These, along with other reasons led to the great migration from Brushed DC Motors to Brushless DC (BLDC) Motors.
(P. S – Of course, the emergence of electronics based advanced motor control solutions and their advantages also contributed in expediting this migration to BLDC motors.)
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!
Let’s first talk about how BLDC and Brushed DC motors work?
How Does Brushless DC (BLDC) v/s Brushed DC Motors work? – A Comparison
Both types of Motors have 3 basic components- Stator, Rotor (also called armature) and Commutator.
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.
(P.S – In a brushed DC motor, brushes are present as additional components).
Understanding How a Brushed DC Motor works:
- Stator, a permanent magnet, generates a stationary magnetic field around the rotor.
- Rotor, when energized by applied voltage, produces magnetic field in the direction opposite to that of the field generated by stator.
- Opposite poles cause the motor to turn.
- A switching of field is required in the rotor that energizes the rotor in different sequences.
- This switching of the magnetic field in the rotor windings is called
- 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’s understand how Brushless DC motors helps an automotive engineer to overcome this issue of wear and tear.
How Does a BLDC Motor Work (without the wear & tear)?
Since there are no brushes (unlike in their brushed counterparts), a BLDC motor 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 three phase BLDC (Brushless DC) motor:
- In a three-phase BLDC Motor, the switching of current in motor phases (commutation) is done in a 6-step pattern.
- This commutation phases move the electromagnetic field. This in turn moves the rotor and the motor shaft.
- This entire commutation sequence between the EMF, rotor and the motor shaft, is also used by the motor control system to generate PWM signals.
- These PMW signal help in controlling the speed of the motor, as required by the system.
- BLDC motor systems can also be fitted with HALL sensors, in order to improve the overall efficiency of the motor.
- A HALL sensor helps define the accurate position of the stator w.r.t the rotor. This is essential for the optimum functioning of the motor.
A Snapshot of BLDC vs Brushed DC Motor
|Brushed DC Motor||Brushless DC Motor|
|Commutation is achieved by brushes and copper commutators||Commutation is achieved electronically using motor control system|
|Presence of Brushes causes wear and tear||Wear & tear is minimum as brushes are absent|
|Peak speed can be reached fast but not suitable for high torque application||Capable of producing high torque and constant speed|
|Used in basic automotive applications like wipers, power windows||Deployed in Electronic power steering, HVAC systems|
Why Automotive Industry Embarked on this Great Migration to the BLDC Motors
The difference in the construction and working of both motors, offer enough reasons for automotive industry to upgrade to BLDC Electric Motors.
Let’s look at some of these advantages offered by a BLDC Motor:
- An increase in efficiency (of about 15-20%), offered by the electronically controlled BLDC motors.
- Reduction in maintenance cost, as there are no brushes in Brushless DC (BLDC) Motors
- BLDC motors deliver a flat torque curve (same torque at different RPMs), at all speeds.
- BLDC motors are more cost-effective, when we take into consideration the need to periodically replace Brushed DC motor (due to wear and tear).
- Smaller size, lesser noise, enhanced heat dissipation, and higher speed ranges also make BLDC motor, a preferred choice for automotive applications.
- Since BLDC motors can be integrated with electronics based advanced motor control solution, BLDC motors are ideal solutions for modern automotive applications like EPS (Electronic Power Steering), HVAC Systems, Electric Vehicle Drivetrain etc.
Although the BLDC motors are more expensive and require design & development of a motor control system. But the advantages outweigh the proposed additional investment in motor control systems for automotive applications.
What challenges your Team may Face During the Migration from Brushed DC to BLDC Motors
Migration from a brushed DC motor to its brushless relatives comes with its own set of challenges.
Of all the challenges, that one may face, overcoming the challenge related to commutation is going to be most critical.
As we have already discussed, a brushed DC motor relies on mechanical commutation with brushes and copper commutator. Meaning that the commutation is being performed only by the brushes and commutator, just to control the direction of the rotation of the motor.
BLDC motor, in contrast, is more than just about controlling the direction. There are 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 motor commutation i.e. switching of magnetic field.
While in Brushed DC Motors, the switching of the magnetic field is only limited to 2-phases; theBLDC motors are mostly 3-phased. Hence the switching of the current has to be done for 3 phases
In fact, how to achieve the optimum commutation, is the biggest challenge for OEMs or suppliers when they plan to migrate their applications to BLDC motors.
The motor control system developers meet this challenge by adopting tried and tested ways of commutation.
The following are some of the suggested commutation, in this regard:
- The classical and simple Trapezoidal control (6 step commutation )
- The advanced FOC with Space vector PWM
For correct commutation in a BLDC motor, the motor position is very important. Components like the HALL sensors, Resolver and Encoder are deployed in the BLDC motor controller, as feed-back mechanisms, in order to achieve 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 the BLDC motors.
Integrating this 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 conditions apply*.
The underlying hardware platform and other hardware components like current sensors etc. have to be similar. If there are changes in the hardware components, some customizations may be required in the following software components.
- Hardware Abstraction Layer
- MCAL Layer
Vehicle Diagnostics and In-vehicle network protocol stacks can be easily reused without any change.
The motor drive logic and the application layers mostly remain unchanged while migrating from Brushed DC motor to BLDC Motors.
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, application like traction control, which was once synonymous with brushed DC motors is now being designed using BLDC motor controllers.
Electric Vehicle is another good example! The traction application is quite similar to the Electric vehicle drivetrain.
Ans how can we not talk about the seating control system. Many automotive OEMs are wanting more from the vehicle seats. A humble brushed DC motor is not capable of such feats and hence, the shift to Brushless DC motor controllers is inevitable!
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