Robust Controller Design for UAM Using Incremental Nonlinear Dynamic Inversion With Double-Loop Structure

This article discusses the design of a control system for urban air mobility (UAM) using incremental nonlinear dynamic inversion (INDI). The INDI controller offers advantages, such as robustness and the absence of a requirement for gain scheduling, making it a suitable candidate for the UAM controller. However, there are limited INDI studies focused on UAM applications. Therefore, this article aims to analyze the applicability of INDI to UAM by designing an INDI controller for a quadcopter-type UAM aircraft. The INDI controller is designed sequentially from attitude control (single-loop INDI) to position control (double-loop INDI). The frequency response analysis of the INDI and PID attitude controllers confirms that the INDI exhibits a larger phase margin and bandwidth compared to the PID. A larger bandwidth implies that the INDI has a faster response but contains high-frequency signals in the output. However, numerical simulations demonstrate that this issue can be mitigated by implementing the double-loop INDI. Furthermore, through disturbance simulations, a comparison of robustness between single- and double-loop INDIs and PID reveals that the double-loop INDI maintains robustness even in the presence of disturbances introduced during attitude changes.