Partial-retuning of decentralised PI Controller of nonlinear multivariable process using Firefly algorithm

This work aims to retune the controller parameters of decentralised PI controller of Alstom gasifier using Firefly algorithm. Coal gasifier is a highly nonlinear, multivariable process involving many complex reactions, and it seems to be difficult to control. The performance of the existing decentralised PI controller of Alstom gasifier does not able to satisfy the requirements at 0% load condition for sinusoidal pressure disturbance except which it seems to be good enough to meet the constraints at 50% and 100% load conditions. This is due to improper tuning of decentralised PI controllers and here we attempt to retune the PI controller responsible for pressure loop, using Firefly Algorithm (FA). Existing parameters of PI controller for pressure loop is replaced by the retuned parameters and pressure disturbance test (both sinusoidal and step), load change test and coal quality test are conducted and compared with the existing results. Results shows that the process satisfies the performance requirements at 0%, 50% and 100% load conditions without violating the constraints.