[SOLVED] Type III Compensator

[Max01800]

Suppose I have a buck converter with an output voltage of 5 V and a maximum output current of 10 A. I need to send this signal into an ADC with a Type III Compensator.
This is the input voltage range for the ADC (i'm using the ADC3A)

Now i have to design a Type III compensator shown in the photo below

I'm using the biricha softwer to get positions of the poles and the zeros. My question is, what is the value that i should use for Vref? Should it be the value of the output voltage that i want?

 

[G4BCH]

Assuming a perfect op amp and with Ve connected to the rest of the working PSU to give Vo ,then Vref = Vo * R4 / (R1 + R4).

 

[FvM]

Driving an ADC by the PID circuit makes only sense when its used in a digital control loop. Unfortunately, output voltage setpoint would be still fixed to Vref*(R1/R4 + 1).

So what's the purpose at all? If you are designing a digital controller, you'll measure output voltage, may be with some preconditioning, but neither fix setpoint nor PID parameters by analog components. Using an analog PID controller with digital PWM generator only doesn't seem reasonable.

 

[Max01800]

Driving an ADC by the PID circuit makes only sense when its used in a digital control loop. Unfortunately, output voltage setpoint would be still fixed to Vref*(R1/R4 + 1).

So what's the purpose at all? If you are designing a digital controller, you'll measure output voltage, may be with some preconditioning, but neither fix setpoint nor PID parameters by analog components. Using an analog PID controller with digital PWM generator only doesn't seem reasonable.

yeah i'm actually designing a buck converter with digital control

 

[FvM]

At least integrative term could be implemented in software, giving you a software variable voltage setpoint, controlled soft start and precise anti-windup control.

 

[Max01800]

Assuming a perfect op amp and with Ve connected to the rest of the working PSU to give Vo ,then Vref = Vo * R4 / (R1 + R4).

With Vo, are you referring to the input voltage of the Compensator?

 

[KlausST]

Hi,

yeah i'm actually designing a buck converter with digital control

here you say digital control.

But what you show in post#1 is purely analog. Isn´t this a contradiction?

My idea (in agree with FvM): If you have an ADC and want to do digital control, why not just read the output voltage and do the PID on the digital side?

*****
In post#1 you also talk about 10A and you need to send this signal to ADC. I miss this part...

Klaus

 

[Max01800]

Hi,

here you say digital control.

But what you show in post#1 is purely analog. Isn´t this a contradiction?

My idea (in agree with FvM): If you have an ADC and want to do digital control, why not just read the output voltage and do the PID on the digital side?

*****
In post#1 you also talk about 10A and you need to send this signal to ADC. I miss this part...

Klaus

yeah exactly i've asked myself the same question and i don't know what to say. the guideline says to design a buck converter with a microcontroller which processes the output from an external ADC and generates a PWM signal for the MOSFET driver. The ADC requires output voltage data from type III analog circuit designed through Biricha software. I actually don't understand why we need this Type III compensator but whatever. But anyway i just wanted to know the relation between the output voltage of the compensator and the reference voltage. Or if there is any way to calculate the voltage reference of the Compensator.

 

[KlausST]

Hi,

why now "external ADC"? Why not using a microcontroller with ADC?

The ADC requires output voltage data from type III analog circuit designed through Biricha software.

Are you sure about this? It´s not impossible. But in my eyes it makes not much sense either.

If you have an analog compensator ... you could do without ADC at all and simply feed the signal to a comparator to generate the PWM.

*****

i just wanted to know the relation between the output voltage of the compensator and the reference voltage.

I understand. But it makes a big difference whether the compensator is analog or digital.
* if digital: you don´t need a compenser and thus the compenser needs no REF at all. It´s just a "constant digital value"
* if analog: The formula is already given in the posts#2 and #3 above. The absolute value rather depends on the used OPAMP and it´s power rails and output voltage range.

Klaus

 

[Max01800]

Hi,

why now "external ADC"? Why not using a microcontroller with ADC?

exaclty, i think he just want to see how we choose the different components, how we use the datasheets etc.

Are you sure about this? It´s not impossible. But in my eyes it makes not much sense either.

yeah pretty sure lmfao

If you have an analog compensator ... you could do without ADC at all and simply feed the signal to a comparator to generate the PWM.

*****

I understand. But it makes a big difference whether the compensator is analog or digital.
* if digital: you don´t need a compenser and thus the compenser needs no REF at all. It´s just a "constant digital value"
* if analog: The formula is already given in the posts#2 and #3 above. The absolute value rather depends on the used OPAMP and it´s power rails and output voltage range.

Klaus

 

[FvM]

The ADC requires output voltage data from type III analog circuit designed through Biricha software.

If you look at the digital PSU structure on Biricha advertising web site, they have compensator implemented purely in digital domain.

 

[KlausST]

Hi,

so this is a school project?

Klaus

 

[Max01800]

Hi,

so this is a school project?

Klaus

yeah

 

[KlausST]

With Vo, are you referring to the input voltage of the Compensator?

Your schematic of post#1 shows Vo.

Klaus