Comparison between Process Model based Controllers

Process model based control (PMBC) refers to methods that use a nonlinear process model directly--without linearization--for process control. Nonlinear IMC and GCC have been compared on an idealized SISO CSTR. Both methods gave nearly the same performance throughout a wide range of reactor nonlinearity. A SISO heat exchanger was used to further study GMC. The CSTR was an open loop unstable, lumped parameter process without deadtime and with a large sample time to process time constant ratio. By contrast, the heat exchanger was an open loop stable, distributed parameter process with transport delay and a small sample to process time constant ratio. In spite of these differences, GMC gave robust control over a wide range of process nonlinearity while remaining relatively insensitive to process-model mismatch. Optimally tuned GMC parameters, performed equally well for both linear and nonlinear process extremes. By contrast, nonlinear IMC filter parameters must change with process nonlinearity. Additionally, it is illustrated that GMC can yield excellent results even with a steady state process model.