Super-Twisting Control: An Alternative to PI Control in Practical Applications
Abstract
This contribution shows that super-twisting control (STC) can be an interesting alternative to PI control in practical applications, even if the practical problem is not in the "classical form" (relative degree one with matched disturbance). To that end, temperature control of the process air of a fuel-cell test bed is considered. The temperature dynamics involve heat transfer from the heater to the process air and heat convection along a pipe to the device under test, hence the dynamics heavily depend on the mass flow rate. Nonetheless, it is shown that by exploiting physical insights the plant model can be simplified to a first-order lag element with parameters depending on the mass flow rate. Due to these simplifications, however, one has to deal with unmodelled dynamics—as is usually the case in practical applications. Both a STC and a PI controller are designed for a nominal case and are then used in the nominal and an uncertain case. While "classical" STC cannot replace PI control, since it exhibits chattering due to the unmodelled dynamics, it is shown for this example that a low-chattering modification of the STC yields a better transient behaviour than PI control in both the nominal and the uncertain case, i.e. virtually no overshoot, while showing a similar steady-state behaviour. To further promote the practical use of STC, this contribution provides practical insights and intuition.