giovaniluigi
Member level 1
Hi everyone,
I don't know if this is the best place to post this topic but I'm desperate.
I have a BLDC motor from Maxon. (EC 22 100W)
I'm driving this motor with a 3-phase bridge with discrete MOSFETs, and using PIC18F2431 as MCU.
I'm running a closed loop with speed feedback.
Based on error I increase or decrease PWM duty.
This PWM is used to drive the MOSFETs and change motor speed trying to reach desired value.
The problem is that I need to maintain constant speed, but the performance is very bad.
The main problem, is that without load, a very small change in PWM increases a lot the motor speed.
When a considerable load is inserted, it is needed a very large change in PWM duty for a small change in current/torque of motor.
-
I'm using a PID controller (PI only) so that change in response of the actuator makes impossible to have a well stable and responsive at the same time for different loads.
I have an industrial equipment wich controls a BLDC motor.
It is impressive how it works perfectly.
It seems that motor never stops rotating, even inserting a huge load it keeps running stable till triggers the current protection.
The circuit from this system is very basic and was designed in 1995.
I compared the waveforms of my system with the industrial system.
The result:
Industrial system have a linear actuation on the same motor.
For example: 10% of PWM means 10% of motor max. speed.
In my system, with 2% of PWM I reach the same speed, but I need a lot of change to correct torque when inserting a load.
Someone have some idea about what could be happening ?
Both systems (mine and industrial one) works with 36V.
The motor is the same.
The circuits are very similar and simple.
PWM frequency is almost the same for both systems around 20Khz.
The performance is very different
Please, someone help me!
I don't know if this is the best place to post this topic but I'm desperate.
I have a BLDC motor from Maxon. (EC 22 100W)
I'm driving this motor with a 3-phase bridge with discrete MOSFETs, and using PIC18F2431 as MCU.
I'm running a closed loop with speed feedback.
Based on error I increase or decrease PWM duty.
This PWM is used to drive the MOSFETs and change motor speed trying to reach desired value.
The problem is that I need to maintain constant speed, but the performance is very bad.
The main problem, is that without load, a very small change in PWM increases a lot the motor speed.
When a considerable load is inserted, it is needed a very large change in PWM duty for a small change in current/torque of motor.
Resuming the problematic behavior:
Without load:
1% ~ 5% of PWM duty means 0 ~ 80% speed
With load:
PWM must be increased in large steps in order to maintain speed.
Problem: Instability.
Without load:
1% ~ 5% of PWM duty means 0 ~ 80% speed
With load:
PWM must be increased in large steps in order to maintain speed.
Problem: Instability.
-
I'm using a PID controller (PI only) so that change in response of the actuator makes impossible to have a well stable and responsive at the same time for different loads.
I have an industrial equipment wich controls a BLDC motor.
It is impressive how it works perfectly.
It seems that motor never stops rotating, even inserting a huge load it keeps running stable till triggers the current protection.
The circuit from this system is very basic and was designed in 1995.
I compared the waveforms of my system with the industrial system.
The result:
Industrial system have a linear actuation on the same motor.
For example: 10% of PWM means 10% of motor max. speed.
In my system, with 2% of PWM I reach the same speed, but I need a lot of change to correct torque when inserting a load.
Someone have some idea about what could be happening ?
Both systems (mine and industrial one) works with 36V.
The motor is the same.
The circuits are very similar and simple.
PWM frequency is almost the same for both systems around 20Khz.
The performance is very different
Please, someone help me!