Introduction to BLDC Motors

INTRODUCTION:

BLDC motors are very popular in a wide array of applications. Compared to a DC motor, the BLDC motor uses an electric commutation, replacing the mechanical commutator and making it more reliable than the DC motor. In BLDC motors, rotor magnets generate the rotor’s magnetic flux, allowing BLDC motors to achieve higher efficiency. Therefore, BLDC motors may be used in high-end white goods such as refrigerators, washing machines, dishwashers, etc., high-end pumps, fans, and other appliances that require high reliability and efficiency.

TARGET MOTOR THEORY:

A BLDC motor is a revolving electric machine with surface-mounted permanent magnets on the stator and a traditional three-phase winding with focused coils on the rotor. Figure 2 shows the situation.

The BLDC motor is analogous to a reversed DC commutator motor in this regard, with the magnet rotating while the conductors remain still. The commutator and brushes of a DC commutator motor change the current polarity.

Unlike brushless DC motors, polarity reversal is accomplished using power transistors that switch in time with the rotor position. To sense the actual rotor position, BLDC motors always include external position sensors known as Hall sensors, or the position can be determined without sensors using the BEMF zero cross detection method.

DIGITAL CONTROL OF A BLDC MOTOR:

The BLDC motor is pushed through square voltage strokes coupled with the given rotor position, as depicted in Figure 3. The stator flux and the rotor flux, generated by a rotor magnet defines the torque and thus, the velocity of the motor.

The voltage strokes should be applied to 2 phases of the three-segment winding machine primarily based totally at the rotor position, so that the angle between the stator flux and the rotor flux is close to 90°, to get the highest possible torque. Therefore, the motor calls for digital manipulation for efficient operation.

In a three-phase BLDC motor, a preferred three-phase power storage is used. See Figure 4. The strength level makes use of six power transistors that function both in an unbiased or complementary mode.

In both modes, the three-section power stage utilises two phases to run the motor. The third phase isn’t powered and left behind. Thus, six different voltage vectors can be implemented to the BLDC motor using the pulse-width modulation (PWM) technique.

There are simple varieties of power transistor switching schemes: unbiased and complementary. Both the switching modes are capable of working in bipolar or unipolar mode. The current application makes use of the unipolar complementary / unbiased combine PWM mode.

COMMUTATION:

Commutation helps to produce a rotational field. As noted earlier, for correct operation of a BLDC motor, it is essential to hold the angle between the stator and rotor flux close to 90 degrees. Total six stator flux vectors are achieved with a six-step control. The stator flux vector is changed at specific positions. These positions are detected by the Hall sensors. The Hall sensors can generate 3 signals that also have six states. Each of the Hall sensors’ states correspond to a sure stator flux vector. All the Hall sensor states, with corresponding stator flux vectors, are illustrated in Figure 5.

The subsequent figures depict the commutation method. The real rotor role in Figure 6 corresponds to the Hall sensors state ABC[110]. Phase A is attached to the positive DC-bus voltage through transistor Q1; Phase B is attached to the floor through transistor Q6, and Phase C is unpowered.

When the rotor arrives at a specific position, the Hall sensor state changes its values from ABC[110] to ABC[100]. See Figure 7 another voltage design is chosen and applied to the BLDC engine.

As displayed in Figure 6 and Figure 7, it is hard to keep the point between the rotor transition and the stator motion definitely at 90° in a six-venture control strategy, while utilizing the six-venture control procedure. The real point differs from 60° to 120°.

The substitution interaction is rehashed per every 60 electrical degrees and is basic to change the exchanging design as quick as conceivable after a Hall sensor edge is recognized. Any deviation causes force swells, bringing about speed variety.

COMMUTATION TABLE FOR HALL SENSORS PLACED AT 60 AND 120 DEG

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When the Hall sensor styles are defined, the corresponding commutation vectors also can be defined. For every of the sectors I-VI, the corresponding commutation vector A-F and Hall sensor sample are defined. Table three suggests the vectors for a clockwise path of rotation that guarantees the variant of actual attitude from 60° to 120°. The Hall sensor sample, taken into consideration as a binary variety, outcomes in a decimal variety from 1 to 6. For example, one zero one in binary form corresponds to the decimal variety 5. From Table 3, it could be seen that commutation vector B corresponds to the decimal Hall sensor sample 4, commutation vector A corresponds to variety 5, and so on. The graphical interpretation of commutation vectors is illustrated in Figure 14.

This blog has been submitted by KRSSG under the Robocraze club outreach program.

Author:- Siddharth & Rudrajyoti

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