This study attempts to offer an alternative to the problem
of implementing
model predictive controllers (MPC) in conditions where the timescale
multiplicity of the process model is not accounted for when incorporated
into the MPC. Modeling methods that do not account for the timescale
multiplicity in system’s dynamics tend to become ill-conditioned
and stiff when inversed in model-based controllers, thus requiring
high computational loads to solve the equations. Therefore, this study
proposes an alternative approach to the control of multi-timescale
processes based on the use of multiple timescale recurrent neural
network (MTRNN)-based neural network predictive controllers (NNPC).
The effectiveness in handling setpoint tracking scenarios by the proposed
method is evaluated using a benchmark nonexplicit two-timescale continuous
stirred tank reactor (CSTR). After undergoing controller parameter
optimization, the optimum configuration is found to be at 110, 37,
and 0.2 for the cost horizon, control horizon, and control weighting
factor, respectively. Results show that the MTRNN-based NNPC is able
to track the reference trajectory with stable response and minimal
error with a root mean square error of 0.0642. The optimized MTRNN-based
controller is tested for its robustness under plant-model mismatch
and is compared for its setpoint tracking abilities with a nonlinear
autoregressive exogeneous (NARX)-based NNPC which showed that the
proposed controller can satisfy the desired setpoint, resulting in
an error that is 1.8 times lower than NARX-based NNPC.