Table of Contents
BLDC Motor Full Form – BRUSHLESS DC MOTOR, Permanent magnet brushless dc motor
What is BLDC Motor
A permanent magnet-based rotor and polyphase armature windings-based stator make up a brushless DC motor. It differs from a typical dc motor in that it lacks brushes and commutation is carried out electrically with the aid of an electronic drive that supplies the stator windings.
In essence, there are two ways to build a BLDC motor: one is to place the rotor outside the core and the windings inside, and the other is to place the windings outside the core. In the first configuration, the rotor magnets function as an insulator, slow down the motor’s rate of heat dissipation, and draw little current. It is frequently employed in fans. The motor produces less heat in the latter configuration, which increases its torque. It is a component of hard drives.
4 Pole 2 Phase Motor Operation
An electronic drive that alternates the supply voltage between the stator windings as the rotor. Rotates powers the brushless DC motor. So The stator winding that needs to be energised is chosen based on the rotor position as monitored by the transducer (optical or magnetic), which provides information to the electronic controller. The transistors in this electronic drive—two for each phase—are controlled by a microprocessor.
The magnetic field generated by the permanent magnets interacts with the field induced by the current in the stator windings, creating a mechanical torque. An angle between the interacting fields that is always between 0 and 90 degrees is maintained by the drive or electronic switching circuit. The stator or the rotor are where Hall Sensors are typically mounted. Depending on whether the rotor passes through the North or South Poles of the hall sensor, a high or low signal is produced. The winding to be energised is determined by the combination of these signals. The magnetic field generated by the windings should move as the rotor moves to catch up with the stator field in order to keep the motor running.
In a 4 pole, 2 phase brushless dc motor, a single hall sensor is used, which is embedded on the stator. As the rotor rotates, the hall sensor senses the position and develops a high or low signal, depending on the pole of the magnet (North or South). A resistor connects the transistors and the hall sensor. The transistor connected to coil A begins to conduct when a high voltage signal is present at the sensor’s output, creating a path for the current to flow and energising coil A. To reach the full supply voltage, the capacitor begins to charge. The transistor 1 is in cutoff condition when the hall sensor detects a change in the rotor’s polarity because this causes a low voltage signal to develop at its output. The second transistor’s supply voltage, Vcc, which has built up around the capacitor, is now powered on as current flows through coil B.
BLDC motors do not have any issues with current flowing to the moving armature because they have fixed permanent magnets that rotate and a fixed armature. Additionally, the rotor may have more poles than the stator or reluctance motors do. The latter could only have poles. That are induced on the rotor and then pulled into a configuration by timed stator windings, without any permanent magnets. The brushed DC motor’s brush/commutator assembly, which alternately switches the phase to the windings to keep the motor turning, is replaced by an electronic controller. Instead of using a brush/commutator system, the controller performs comparative timed power distribution using a solid-state circuit.
Advantages of Brushless DC Motors
- Better speed versus torque characteristics
- High efficiency
- High dynamic response
- Noiseless operation
- Long operating life due to a lack of electrical and friction losses
- Higher speed ranges
Because of advancements in materials and design, the BLDC Motor price has decreased since its introduction. The Brushless DC Motor is a popular component in numerous unique applications due to its lower cost as well as its many advantages over the Brush DC Motor. Applications for BLDC motors may include, but are not limited to:
- Consumer electronics
- Heating and ventilation
- Model engineering
- Industrial engineering
BLDC Motor Working Principle
Similar to brushed DC motors, BLDC motors operate on the same principles of internal shaft position feedback. A mechanical commutator and brushes are used to implement feedback in the case of brushed DC motors. It is accomplished with the help of numerous feedback sensors in BLDC motors. In BLDC motors, a Hall-effect sensor is frequently used. When the magnetic poles of the rotor approach the sensor, they produce a HIGH or LOW-level signal that can be used to calculate the position of the shaft. The voltage generated will change if the magnetic field’s direction is reversed.
Controlling a BLDC Motor (BLDC Motor controller)
There are several high-tech options available for the Control unit, which is implemented by microelectronic. A microcontroller, a special microcontroller, a hardwired microelectronic unit, a PLC, or a comparable device may be used to implement this.
Although the analogue controller is still in use, it is unable to process feedback messages and adjust control. High-performance control algorithms, like vector control, field-oriented control, and high-speed control, all of which are related to the electromagnetic state of the motor, can be implemented with this kind of control circuits. Additionally, conventional outer loop control is implemented for a variety of dynamics requirements, including sliding motor controls, adaptive control, predictive control, etc.
In addition to all of these, high-performance PIC (Power Integrated Circuit), ASIC (Application Specific Integrated Circuits), and other components can greatly simplify the construction of the control and the power electronic unit. Today, for instance, we have a complete PWM (Pulse Width Modulation) regulator in a single IC that can take the place of the system’s entire control unit. A three-phase converter’s six power switches can be driven entirely by a compound driver IC. Similar integrated circuits are widely available, and each day, more and more are being added. At the end of the day, system assembly may only require a piece of control software because all of the hardware will have reached the proper shape and size.
The PWM wave, also known as pulse width modulation, can be used to regulate the motor’s speed. Here, the average voltage or average current through the motor is given. So The duty cycle of the wave, which determines the speed of the wave, controls the speed of the motor. We can alter the speed by adjusting the duty cycle (ON time). It will actually change the motor’s direction by switching the output ports.
For the BLDC motor to operate at the desired rate, speed control is crucial. By altering the input dc voltage, a brushless DC motor’s speed can be managed. The speed increases with increasing voltage. The PWM model changes the input voltage of the armature when the motor is operating normally or when it is operating below rated speed. The flux is weakened by advancing the exiting current when a motor is run above its rated speed.
- The speed control can be closed-loop or open-loop speed control.
- Closed Loop Speed control – It involves controlling the input supply voltage through the speed feedback from the motor. Thus the supply voltage is controlled depending on the error signal.
- Open Loop Speed Control – It involves simply controlling the dc voltage applied to motor terminals by chopping the dc voltage. However, this results in some form of current limiting.
The closed-loop speed control consists of three basic components.
- A PWM circuit to generate the required PWM pulses. It can be either a microcontroller or a timer IC.
- A motor drive to control the motor operation.
- A sensing device to sense the actual motor speed. It can be a hall effect sensor, an infrared sensor, or an optical encoder.
This technique of changing the supply voltage based on the error signal can be either through the pid controlling technique or using fuzzy logic.
Application to Speed Control of Brushless DC Motor
An optocoupler and MOSFET arrangement is used to control the motor’s operation,. With the microcontroller’s PWM technique controlling the input DC power. Due to the presence of a white spot on the motor’s shaft. That reflects infrared light, the infrared led located at its shaft becomes illuminated with white light as the motor rotates. This infrared light strikes the photodiode, changing its resistance and, in turn, the supply voltage to the connected transistor. The microcontroller is then given a pulse to determine the number of rotations per minute. On the LCD, this speed is shown.
The keypad connected to the microcontroller accepts the required speed as input. The error signal is the difference between the sensed speed and the desired speed,. And the microcontroller generates the PWM signal in accordance with the error signal. Using fuzzy logic to supply the motor with dc power. The brushless dc motor can be made to rotate at any desired speed. So By using closed-loop control to regulate its speed.