Hi,  

      I am difficulty in finding the Kp and Ki values for the PI controller i wish to use for the inverter system.I had derived the transfer function of the plant which includes the inverter and the filter. i had tried in MATLAB/SIMULINK  . There's a tuning method in the PID controller.But i am getting the same values of Kp and Ki even if i change the input signal.                  I had also developed the closed loop control law equations,but without proper design of the controller,i am not able to simulate the whole system.

   For  example, for the voltage controller the transfer funtion is 1/S*Cdc, where Cdc is the capacitance of the DC Link. i am calculating the error from a reference DC signal and the DC signal from the DC link side and passing it to the PI controller. The output from the PI will be the reference current for the current controller. how to find the Kp and Ki values for this .  

 Similarly for the current controller i use the transfer function of the plant which includes the inverter and the filter.                  It would be a great help if anyone can guide me to solve this problem.