A Control Concept for Battery Emulators Using a Reference Governor With a Variable PT1-Element for Constraint Handling

Abstract

This paper presents a method for highly dynamic nonlinear control of DC-DC converters with constraints used in battery emulators. Controlling this system is particularly challenging as the connected units-under-test often behave like constant power loads (CPLs), which introduce unstable system dynamics and render the system nonlinear. In order to achieve fast output dynamics with the DC-DC converters over a large operating range, a special control architecture is proposed where feedback equivalence is established between a nonlinear system description and a linear description. The nonlinear system dynamics can then be transformed into linear ones for controller synthesis by exploiting the flatness property of the system. Additionally, constraints have to be met at any time during operation to prevent damage to components. In order to satisfy the constraints, a reference governor (RG) is added to the loop. This novel RG concept uses a low-pass filter in the shape of a PT1-element to modify the voltage reference. By changing the time constant of the PT1-element, the RG is able to generate smooth constraints-aware trajectories for setpoint changes. Finally, the capabilities of the control concept are demonstrated and discussed based on high-fidelity simulations.

Keywords

• Constant power load
• constraints handling
• DC-DC step-down converter
• reference governor
• flatness-based control