Incremental Nonlinear Dynamic Inversion (INDI) has received substantial interest in the recent years as a nonlinear flight control law design methodology that features inherent robustness against bare airframe aerodynamic variations. However, systematic studies into the robust design benefits of INDI-based control over the classical divide-and-conquer philosophy have been scarce. To bridge this gap, this paper compares the setup of hybrid INDI with a standard industry benchmark that is based on two-degree-of-freedom gain-scheduled proportional-integral-derivative control. This is done on an architectural basis and in terms of achievable robust stability and performance levels with respect to a common set of design requirements. To this end, a non-smooth, multi-objective H_∞-synthesis algorithm is used that incorporates mixed parametric and dynamic uncertainties in the design objective and constraints. It is shown that close similarities exist between hybrid INDI design and gain-scheduled PID control, which leads to virtually equivalent robustness and performance outcomes in both linear time-invariant and linear time-varying contexts. It is therefore concluded that the main benefit of the hybrid INDI does not lie in improved robustness properties per se, but in the opportunity to perform modular robust design in an implicit model-following context. Specifically, this implies that the areas of flying qualities, robustness, and nonlinear implementation are directly visible and accessible in the control law structure.

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This paper proposes a Linear Parameter-Varying (LPV) controller design for the pitch channel dynamics of a new class of Long Range Guided Projectiles (LRGP). The grid-based approach is preferred since it provides advantages in terms of performance and conservatism. Differently from standard aerospace applications that limit the scheduling vector to the variation of the altitude and the Mach number, the investigated flight envelope is parameterized through a 3D grid, which includes the variation of the angle-of-attack, crucial for range optimization purposes. Thus, an extensive investigation of the grid design is required to minimize the computational complexity of the controller synthesis. The performances of the LPV controller are assessed by employing a nonlinear reference tracking simulation scenario.

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Promising results on LPV design have been recently proposed, concerning the modeling and control of missiles, rockets, and aircraft. However, very few investigations have been focused on the development of guided projectile applications. This paper presents a pure linear parameter varying (LPV) modeling and control design approach intended to improve the range capability of a new class of Long Range Guided Projectiles (LRGP). The investigated concept consists of an asymmetric 155 mm fin-stabilized projectile equipped with a reduced amount of control actuators and characterized by a predominant unstable behavior across the analyzed flight envelope. The main advantages of the LPV design in terms of guaranteed robustness and stability are compared to standard gain-scheduling-based linear time-invariant (LTI) control strategies. A nonlinear simulation scenario is performed in order to assess the reliability of a pure LPV autopilot design, based on the polytopic formulation, across the entire flight envelope, over a local modal control design related to a specific set of flight conditions.@en

This article covers the design of an L1-adaptive Incremental Nonlinear Dynamic Inversion (INDI) autopilot applied to the control of the ballistic trajectory of a 155mm dual-spin projectile supplied with a roll-decoupled course-correction fuze. Associated with a Zero Effort Miss guidance law, the discrete-time INDI baseline successfully controls the lateral load factors of the projectile, resulting in a ballistic dispersion reduced to metric precision. However, aerodynamic data for dual-spin projectiles are often not very accurate because they rely on simplified CFD simulation and time-consuming wind tunnel tests aren’t always possible. Therefore significant parametric uncertainties are present in the model. Even if INDI is a sensor-based control technique, this approach is still sensitive to model mismatch. For this reason, L1-adaptive control theory was used to compensate for the degraded inversion of the INDI autopilot under the presence of parametric uncertainties. Nonlinear simulation results show the interest of an L1-adaptive augmentation of an INDI autopilot where the performance of the autopilot is guaranteed under a large range of time-varying matched uncertainties@en

This article deals with the control design of a dual-spin projectile concept, characterized by highly nonlinear parameter-dependent and coupled dynamics, and subject to uncertainties and actuator saturations. An open-loop nonlinear model stemming from flight mechanics is first developed. It is subsequently linearized and decomposed into a linear parameter-varying system for the roll channel, and a quasi-linear parameter-varying system for the pitch/yaw channels. The obtained models are then used to design gain-scheduled H_∞ baseline autopilots, which do not take the saturations into account. As a major contribution of this paper, the saturation nonlinearities are addressed in a second step through anti-windup augmentation. Three anti-windup schemes are proposed, which are evaluated and compared through time-domain simulations and integral quadratic constraints analysis. Finally, complete guided flight scenarios involving a wind disturbance, perturbed launch conditions, or aerodynamic uncertainties, are analyzed by means of nonlinear Monte Carlo simulations to evaluate the improvements brought by the proposed anti-windup compensators.

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