BLDC - PPT

Brushless DC Motor

Cross sectional view of BLDC Machine

Components of BLDC Machine

Permanent magnet rotor

Hall sensors

Stator windings

BLDC Drive scheme

Electronic Commutator is used for switching currents in windings

D1, D2, D3, D4, D5, D6 - Diodes Q1, Q2, Q3, Q4, Q5, Q6 - npn Transistors

P.S.(Hall position sensor) is used to sense the position of the rotating rotor in BITS

Components of BLDC Drive scheme

Switching sequences in electronic commutator

SwitchingIntervals

Seq.Numbr

Position Sensor

Switch Closed

Phase Current

H1 H2 H3 A B C

0 ° - 60° 0 1 0 0 Q1 Q4 + - Off

60 ° - 120 ° 1 1 1 0 Q1 Q6 + off -

120 ° - 180 ° 2 0 1 0 Q3 Q6 Off + -

180 ° - 240 ° 3 0 1 1 Q3 Q2 - + Off

240° - 300° 4 0 0 1 Q5 Q2 - Off +

300° - 360° 5 1 0 1 Q5 Q4 off - +

Realization of PI/PID controller for BLDC motor

P = Kp*e(t)

Σ Σ Process

e(t)

PV

SP —

++

+

MV

PI Controller block diagram

Δ = SP - PV.whereG = KP = proportional gain

G / τ = KI = integral gain

Setting a value for G is often a trade off between decreasing overshoot and increasing settling time.

The control output is

Δ is the error or deviation of present measured value (PV) from the set-point (SP).

Advantages & Disadvantages of PI Controller

• The integral term in a PI controller causes the steady-state error to reduce to zero, which is not the case for proportional-only control in general.

• The lack of derivative action may make the system more steady in the steady state in the case of noisy data. This is because derivative action is more sensitive to higher-frequency terms in the inputs.

• Without derivative action, a PI-controlled system is less responsive to real (non-noise) and relatively fast alterations in state and so the system will be slower to reach setpoint and slower to respond to perturbations than a well-tuned PID system may be.

Simulink model of BLDC motor (PI controller)

Brushless DC motor fed by six step inverter

Speed regulator

Reference speed (RPM)

rad2rpm

K-

Discrete,Ts = 5e-006 s.

is_a e_a

PI

v+-

v+-

Vdc

Vab

g

A

B

C

+

-

Te (N.m)

Step

Permanent MagnetSynchronous Machine

Tm

mA

B

C

N (rpm )

Gates

emf_abc Gates

Double click here for more info

?

Decoder

Hall emf _abc

3000

<Stator current is _a (A)>

<Stator back EMF e _a (V)>

<Rotor speed wm (rad/s)>

<Electromagnetic torque Te (N*m)>

Simulation results

1. Stator currents & emf waveforms

2. Rotor speed

3. Electromagnetic torque

PID Controller

Process

D = Kp*e(t)

I = Kp*e(t)

P = Kpe(t)

Σ Σerror OutputSP

—

+

Block diagram of a PID controller

Proportional term

Integral term

Derivative term

Simulink model of BLDC Motor