Stability analysis of a flatness-based controller driving a battery emulator with constant power load

This contribution deals with the control of a battery emulator used in automotive testbeds for electric drivetrains. The battery emulator, which is realized as a DC-DC converter, is connected to a unit-under-test (UUT), e.g., an electric motor inverter. To accurately emulate the dynamic impedance of a battery, a highly dynamic output is required. Additionally, battery emulators should be applicable for a large variety of UUTs, hence robust performance in a large operating range is also required. This is especially challenging when the UUT behaves like a constant power load, as this can cause stability issues. To meet the requirements, a flatness-based control concept is presented that establishes feedback equivalence between a nonlinear and a linearized system representation. By examining the stability of the concept, an estimation of the region of attraction is found.