alternator o/p voltage control

[ckdckd]

hi everyone

recently i have a project regarding controlling the rectified o/p voltage of an 3 phage alternator with varying load and rpm. the system parameters are as follows

controlled o/p = 130V
max o/p current = 0-200A
rpm = 0-2500 (0 - 500hz)
field current vary frm 0-10A to provide the desired o/p power.
i have to do this by varying the field current of the stator. the field voltage is get frm rectifying the two of the 3 phage. I want to control this by a microcontroller based PWM which ON/OFF the field voltage accordingly(varying field current) to maintain a constant voltage at o/p with varying loads. I design the h/w. A simplified block diagram is attached.

I need some topology(s/w based) to control this. any PI control code assistance.
if you need any further information please fill free.

thanks

 

[MikeMl]

Without the uController, this is the way hundreds of millions of automobiles do it. Not sure you need the extra diodes to rectify the field. The original Motorola automotive alternators had the extra diodes, but it hasn't been common since the late sixties. It is ok just to power the field from the main output. You will find that the inductance of the field is so high that a PWM rate of 40 to 100Hz is sufficient. If all you wanted to do is regulate the output voltage, a simple voltage reference, opamp, and gate driver for the IGBT is sufficient; just a bang-bang on-off field controller with no PID required.

 

[ckdckd]

thanks

but there must be some logic to control the ON/OFF period of pwm according to the reference. because there are two variable (rpm,o/p load).at high rpm, required low field current and vice verse. and extra factor is load. so max field cur is required at min rpm(say 350) and max load (200A) & min field curr is required at max rpm(2500) and min load(no load).
so give some bigger picture to do this. any related h/w and s/w also.
thanks

 

[MikeMl]

You will learn a lot about your task if you understand this simulation of a standard 50A 14V automotive alternator and charging system. If you like, I can upload the running LTSpice simulation so that you can modify it to match the characteristics of your alternator. Study the alternator model; note the important parameters.

The sim shows how a simplistic bang-bang voltage regulator controls the field voltage/current which in turn adjusts the output of the alternator to match the load condition. Note that the average field current results from PWM; but notice that this is not a fixed frequency PWM, rather both the period and on-time adapt automatically. The PWM is largely dependent on the field inductance; not the VR.
The important parameters of the VR are the trip point (14.25V) and hysteresis (4mV), typical of automotive voltage regulators. Note that the VR is a bang-bang system, not a linear regulator.

The sim shows the VR initially charging a battery, then stabilizing with a light load, then a big load is applied, and finally the big load is turned off. Note how the feed back loop keeps the battery voltage more-or-less constant, and look at the PWM frequency/duty cycle that produces that. This is typical of charging systems in hundreds of millions of automobiles built since the 1960s.

 

[ckdckd]

thanks

with this topology how i do this in microcontroller??

as i understand i have to take some feedback of o/p voltage(for voltage regulation) and o/p current (for current limit) to the uc. continuously checking these two whenever o/p voltage above set value, just OFF the field and when below just ON the field. If i am right please a idea of voltage and current ripple,efficiency (desired volt ripple within 2% & for current 10%, efficiency about 95%).

If i am wrong please give idea for implementing the control algorithm in the microcontroller.

thanks

ckdckd

 

[MikeMl]

Well, the voltage regulation for my example is as simple as:

do
      If V(Bat)<=14.23 Then FIELD = 1
      If V(Bat)>=14.27 Then FIELD = 0
forever

 

[ckdckd]

thank you

i will inform you after field trial according to your suggestion.it will take some time.please keep in touch if you have any further assistance.

 

[caitoc]

You will learn a lot about your task if you understand this simulation of a standard 50A 14V automotive alternator and charging system. If you like, I can upload the running LTSpice simulation so that you can modify it to match the characteristics of your alternator. Study the alternator model; note the important parameters.

The sim shows how a simplistic bang-bang voltage regulator controls the field voltage/current which in turn adjusts the output of the alternator to match the load condition. Note that the average field current results from PWM; but notice that this is not a fixed frequency PWM, rather both the period and on-time adapt automatically. The PWM is largely dependent on the field inductance; not the VR.
The important parameters of the VR are the trip point (14.25V) and hysteresis (4mV), typical of automotive voltage regulators. Note that the VR is a bang-bang system, not a linear regulator.

The sim shows the VR initially charging a battery, then stabilizing with a light load, then a big load is applied, and finally the big load is turned off. Note how the feed back loop keeps the battery voltage more-or-less constant, and look at the PWM frequency/duty cycle that produces that. This is typical of charging systems in hundreds of millions of automobiles built since the 1960s.

Hello, I am also very interested in this model. Is it possible for you to upload this simulation file so that I can download and study it. Thank you!

 

[MikeMl]

Hello, I am also very interested in this model. Is it possible for you to upload this simulation file so that I can download and study it. Thank you!

caitoc :Enjoy

 

[caitoc]

Thank you Mike.

I am going to study it. This will help