Stability margin-based PD attitude control tuning for unstable flight vehicle
Proportional-derivative (PD) attitude control is widely used for the flight vehicles, especially in boost phase. Some of the flight dynamics are open-loop unstable, which often limits the achievable closed-loop performance. Based on the intrinsic characteristics of the linear model obtained from the small perturbation theory, simple numerical analytical tuning formulae of PD attitude control are derived to meet the gain and phase margin specifications. According to Routh stability criterion, the decreasing gain margin is obtained by using the approximation of delay amid low frequency with the established tuning rule. Some numerical polynomial solving approaches are employed to seek the feasible stability margin region, which is explicitly plotted in the 2-D plane. Taking engineering practice into account, the maximum gain constraint is also imposed. Finally, several numerical examples are presented to validate the analysis result.
stability margin tuning routh stability criterion pd control