Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Confused with the speed control of BLDC motor using PWM

Status
Not open for further replies.

sarathisme

Newbie level 4
Joined
Jul 8, 2016
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
44
Hi folks,
I am currently learning the bldc motor drive. I am not understanding how changing the terminal voltage across the motor affects the motor speed. As per my knowledge the speed depends only on the frequency at which we are energizing the coils. But using pwm we are not changing the rate at which the three coils are energized , but we are only giving a reduced excitation to the coils. Then how the speed gets affected? I am not getting the logic behind it. Please anyone provide me with a correct explanation.
 

srizbf

Advanced Member level 5
Joined
Apr 3, 2010
Messages
1,995
Helped
417
Reputation
840
Reaction score
328
Trophy points
1,363
Activity points
10,985
basic theory is a DC motor speed is controlled by varying armature voltage(or field excitation).
In BLDC , the the average voltage (DC) is
(Ton/T)*Vin.
By varying the Ton(PWM) you are varying the speed.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
19,460
Helped
4,302
Reputation
8,609
Reaction score
4,260
Trophy points
1,393
Activity points
129,045
Hi,

Sensorless commutation? Or do you use sensors?

Klaus
 

sarathisme

Newbie level 4
Joined
Jul 8, 2016
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
44
Thankyou. That I understood. But still something is missing. I need a correct explanation - we are energising the subsequent phases at regular periods rt? The rate at which we are energising the coils is not varying , yet the speed gets varied. Expecting a more detailed explanation (not in terms of equations). @srizbf , thanks for the reply.

sensored commutation . using hall signals
 
Last edited by a moderator:

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
19,460
Helped
4,302
Reputation
8,609
Reaction score
4,260
Trophy points
1,393
Activity points
129,045
Hi,

sensored commutation . using hall signals
Are you familiar with sensored commutation?

In short.
* Voltage is applied to a coil
* Current is rising according coil inductance and applied voltage
* current generates a magnetic field
* magnetic field generates a force to the permanent magnet
* magnetc force generates a torque
* shaft rotates
* ...until the next hall sensor gets activated
* then the same loop starts with another coil (this is called commutation)

****
Now assume the voltage is PWM´d
--> the effective voltage at the coil is less than before
* the time for the current to rise increases (everything becomes slower)
* ..magnetic field is delayed, magnetic force is delayed, torque is less and delayed, rotation is slower
* and the next hall senser gets activated delayed..

--> less voltage --> less current --> less torque --> less speed

Klaus
 

sarathisme

Newbie level 4
Joined
Jul 8, 2016
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
44
@Klaus Thanks for the explanation. Now I got it. :thumbsup:
 

sarathisme

Newbie level 4
Joined
Jul 8, 2016
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
44
Hey .. I have one more querry.
I have designed and setup the whole circuitry for the bldc motor drive. Thecontrl is implemented using FPGA.But it is not working.
I just want to know if the hall signal output from the motor will give a constant signal output if the motor is unexcited,. (By just connecting the Vcc and ground) . .
BLDC model no is 42BL61.004 Rev.A from Delta line.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top