getting a 0dB DC gain in DCDC boost converter?

Hello everyone, I have designed a DC-DC boost converter with peak current mode control. I have used the AC sweep and Impulse response Analysis tools from PLECS BLOCKSET to try to get the frequency response in bode plot. I have placed the output the AC sweep/Impulse response block in the input of the PI controller and the and the input of the block AC sweep analysis is the Vout of the boost converter. 1-for the AC sweep I got a nic bode plot but the DC gain is 0DB which I believe should be at least 40dB(Vin=4V and Vout=20).why am I getting the 0 gain? 2-I tried with Impulse Response Analysis because the first one took me one day to simulate it and get the bode plot. So, I tried to use the impulse response but It shows a an error saying this: cannot sweep frequencies above half of the fundamental system frequency. you can find the pics of the error and body plot attached. best regards, tarik