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type 1 and type2 compensator

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garimella

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Trying to academically understand type 1 and type 2 compensator, but with so many articles on the internet are confusing me. Is there any simple way to understand type2 compensator comparing with type 1. For instance if type 1 has cut off of 1KHz, how should I design type 2 to boost the bandwidth and yet maintain low ripple?
 

There's no one general solution to this, because the system you're trying to compensate may have any sort of transfer function. The method I prefer is the K factor method described here. Basically you pick a desired crossover frequency and phase margin, then measure the magnitude and phase of the system response at that frequency. That tells you what phase and gain your compensator needs to have at that frequency. The K factor method tells you what order of compensator you need, and where the poles and zeros need to be. However you must also check that the gain margin is acceptable as well.
 

Referring to the article on k factor, I am just trying to understand. I do not have transfer function of the whole system. What I know is that 1st order filter is providing phase lag for which i need to compensate. I tried to design type 2 compensator with your proposed method, but I ended up with the transfer function whose bode plot resembles as desired, but when used in the system (implementing in simulink) the output simply saturates without converging. kindly advice

eg: 1st order LPF TF= 1/.1s+1 (cut off - 1Hz)
type2 compensator TF = 1/s *(1+.025s)/1+.007s)
 

Referring to the article on k factor, I am just trying to understand. I do not have transfer function of the whole system. What I know is that 1st order filter is providing phase lag for which i need to compensate. I tried to design type 2 compensator with your proposed method, but I ended up with the transfer function whose bode plot resembles as desired, but when used in the system (implementing in simulink) the output simply saturates without converging. kindly advice

eg: 1st order LPF TF= 1/.1s+1 (cut off - 1Hz)
type2 compensator TF = 1/s *(1+.025s)/1+.007s)
If your error amplifier saturates then it's likely set up to provide positive feedback instead of negative feedback. Can you show your block diagram? Should be as simple as multiplying the transfer function of the EA by -1, or switching its inputs.
 

am simply simulating your proposed circuit in proteus. I guess there is some problem with Vref. What is the role of Vref?
 

Vref simply sets the DC operating point of the system. It shouldn't affect stability. Posting a block diagram would help.
 

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