How commutation happens in Bldc?

Put simply, commutation is the process of switching the current in the motor phases to generate motion. Brushed motors have physical brushes to achieve this process twice per rotation, while BLDC motors do not, hence the name. Due to the nature of their design, they can have any number of pole pairs for commutation.

How do you sense the back EMF of a BLDC motor?

There are several techniques for measuring the back EMF. The simplest is to compare the back EMF to half the DC bus voltage using a comparator. Figure 4a shows a schematic of such a system. In this case, the comparator is connected to coil B; a complete system would have a comparator connected to every coil.

What type of commutation does a brushless DC motor use?

The widely used commutation methods for the BLDC motor are trapezoidal (or six-step), sinusoidal, and field oriented control (FOC) (or vector control). Each commutation method can be implemented in different ways, depending on control algorithms and hardware implementation to provide their own distinct advantages.

How does a sensorless BLDC motor work?

A typical sensorless brushless motor has permanent magnets fixed on the rotor with the electro-magnets mounted around the edge of the motor. As the motor picks up speed it starts to generate electro-motive force in the stator coils.

How many commutation sequences do you know about a BLDC motor have?

A control circuit called an inverter*2 is used to drive a BLDC motor. There are two major commutation techniques: 120° square-wave commutation and 180° sinusoidal (sine-wave) commutation.

What is motor commutation?

In order to generate motion in a three-phase linear motor there must be switching between the phases to energize appropriate windings. The process of switching between the phases is called commutation.

What is the difference between BLDC and PMSM?

In simple terms, a BLDC motor has trapezoidal back-emf, whereas a PMSM has sinusoidal back-emf. PMSM has reduced torque ripple and current-ripple than BLDC motors. BLDC motors have concentric windings whereas PMSM has distributed winding. PMSMs are expensive, and highly efficienct.

How do you control a BLDC motor?

One of the simplest methods of control for dc brushless motors uses what is termed Trapezoidal commutation. In this scheme, current is controlled through motor terminals one pair at a time, with the third motor terminal always electrically disconnected from the source of power.

How is commutation accomplished in a brushless DC motor?

Commutation is done by determining the angular position and then applying current to the stator which creates a magnetic field that attracts the rotor to a new position. This would cause the rotor to rotate and the state of the hall switches would change to; 1 on, 2 off, 3 off.

How is BLDC motor controlled?

The brushless DC (BLDC) motor is also referred as an electronically commuted motor. The most common way to control a BLDC motor is to use Hall sensors to determine the rotor position. The control system senses the rotor position and the proper voltage pattern is applied to the motor.

What does a BLDC motor controller do?

A BLDC motor controller detects the position of the rotor either by using sensors (for example, a Hall-effect sensor) or sensorlessly. The sensors measure the rotor’s position and send out this data.

Which motor uses electronics commutation?

The process is called electronic commutation, borrowing on terminology used for the mechanism in dc motors, called a commutator, that switches current from winding to winding, forcing the rotor to turn. The rotor in a typical brushless motor incorporates a four-pole permanent magnet and a smaller “sensor” magnet.

What are the zero crossing points on a BLDC motor?

A combination of all three zero crossing points for the coils is used to determine the coil energizing sequence. Note that there is a phase difference between an individual Hall sensor changing output in a conventional BLDC motor, and the back EMF zero crossing point for an individual coil in a sensorless unit of 30 degrees.

How is the PWM used for BLDC commutation?

In addition, the PWM provides the six-step BLDC commutation control (where one motor phase is left unpowered so the Back-EMF can be detected). The PWM duty cycle can be set asynchronously to the commutation of the motor phases event using the channel swap feature.

Which is an example of a BLDC motor control system?

The concept of the application is th at of a speed-closed loop drive using an AD converter for Back-EMF Zero Crossing technique position detection. It serves as an example of a sensorless BLDC motor control system using Freescale’s Digital Signal Processor (DSC) with SDK support.

How can I control a sensorless BLDC motor?

In Figure 2, the short-dashed lines indicate the current in the coils. Figure 3 shows a control circuit for a sensorless three-phase BLDC motor. In this case, the circuit uses a Microchip PIC18FXX31 8-bit MCU to generate the pulse width modulated (PWM) outputs to trigger the IGBTs or MOSFETs in the three-phase inverter bridge.