Optimization-based transient control of turbofan engines: a sequential quadratic programming approach

Engine transient control has been challenging due to its stringent requirements from both performance and safety. Many methodologies have been proposed such as conventional schedule-based methods, linear parameter varying, multiobjective optimization and evolutionary computations etc. These approaches have been well-established and led to a series of significant results. However, they are either not providing limit protection or requiring exhaustive computational resources, particularly when generating results into full flight envelope applications. Consequently a compromise between limit protection and computational complexity is necessitated. This note considers a sequential quadratic programming (SQP)-based method for full flight envelope investigations. The proposed method can provide important design guidance and the corresponding claims are validated through detailed analysis and simulations.

Multi-Parameter Quadratic Programming Explicit Model Predictive Based Real Time Turboshaft Engine Control

The traditional model predictive control (tMPC) algorithms have a large amount of online calculation, which makes it difficult to apply them directly to turboshaft engine–rotor systems because of real time requirements. Therefore, based on the theory of the perturbed piecewise affine system (PWA) and multi-parameter quadratic programming explicit model predictive control (mpQP-eMPC) algorithm, we develop a controller design method for turboshaft engine–rotor systems, which can be used for engine steady-state, transient state and limit protection control. This method consists of two steps: controller offline design and online implementation. Firstly, the parameter space of the PWA system is divided into several partitions offline based on the disturbance and performance constraints. Each partition has its own control law, which is in the form of piecewise affine linear function between the controller and the parameters. The control laws for those partitions are also obtained in this offline step. After which, for the online control implementation step, the corresponding control law can be obtained by a real-time query of a corresponding partition, which the current engine state falls into. This greatly reduces the amount of online calculation and thus improves the real-time performance of the MPC controller. The effectiveness of the proposed method is verified by simulating the steady-state and transient process of a turboshaft engine–rotor system with a limit protection requirement. Compared with tMPC, an mpQP-eMPC based controller can not only guarantee good steady-state, dynamic control performance and limit protection, but can also significantly improve the real-time performance of the control system.

Research on Optimal Coordination and Algorithms of Microprocessor-based Inverse Time Backup Protection

Backup protection plays an important role in the safe operation of power grid, and it has important research value in the field of power system relay protection. Firstly, the research status and development opportunities of inverse time limit protection are analyzed, and then the best cooperation between inverse time limit protection and distance protection is discussed theoretically. According to the time constraint relationship in the protection range, an objective function satisfying the selectivity and speed is proposed. Secondly, in view of the difficulty in calculating the inverse time characteristic curve, a processing algorithm combining Taylor expansion method and look-up table method is proposed. Finally, the effectiveness and practicability of the method are verified by simulation experiments.

Design of Linear Parameter-Varying Based Sliding Mode Regulator for Limit Protection of Aero-Engines

In aircraft engine control, replacing linear regulators by sliding mode control (SMC) regulators is considered as an effective approach to reducing the conservatism in the traditional treatment for limit protection. However, most of the relevant studies are based on linear descriptions, which cannot represent the nonlinear systems directly due to their limited valid range. Even if gain scheduling techniques are employed, the stability of the nonlinear systems cannot be theoretically guaranteed. In this paper, a sliding mode strategy for a class of uncertain linear parameter varying (LPV) systems is studied. LPV descriptions are applied to extend the valid range of the linear models covering the entire operation envelope with guaranteed performance and stability. The mismatch between LPV and the real systems is considered as uncertainties. With a sliding surface defined by the tracking errors, system properties on the surface are proved to be satisfactory. After that, a reaching law is designed to ensure global invariance of SMC. Based on a reliable model turbofan, simulation results show that the SMC method can fully exploit the limit margin and, compared to the traditional proportional-integral-derivative (PID) control, has a faster response. In addition, stability and effectiveness of the proposed method are verified in a temperature protection case.

Conservation of terrestrial invertebrates: a review of IUCN and regional Red Lists for Myriapoda

Red Listing of Threatened species is recognized as the most objective approach for evaluating extinction risk of living organisms which can be applied at global or national scales. Invertebrates account for nearly 97% of all animals on the planet but are insufficiently represented in the IUCN Red Lists at both scales. To analyze the occurrence of species present in regional Red Lists, accounts of 48 different countries and regions all over the world were consulted and all data about myriapods (Myriapoda) ever assessed in Red Lists at any level assembled. Myriapod species assessments were found in eleven regional Red Lists; however, no overlap between the species included in the global IUCN Red List and the regional ones was established. This means that myriapod species considered threatened at regional level may not be eligible for international funding specific for protection of native threatened species (more than US$ 25 million were available in the last decade) as most financial instruments tend to support only threatened species included in the IUCN Red List. As the lack of financial resources may limit protection for species in risk of extinction, it is urgent to increase the possibilities of getting financial support for implementation of measures for their protection. A Red List of all Myriapoda species recorded in Red Lists at national or local (596) and global (210) scales totaling 806 species is presented. This list shows for the first time an overview of the current conservation status of Myriapoda species. Here, the urgent need of establishing a Myriapoda Specialist Group in the Species Survival Commission of IUCN is also stressed.

An Output-Based Limit Protection Strategy for Turbofan Engine Propulsion Control with Output Constraints

To accomplish the limit protection task, the Min-Max selection structure is generally adopted in current aircraft engine control strategies. However, since no relationship between controller switching and limit violation is established, this structure is inherently conservative and may produce slower transient responses than the behavior by engine nature. This paper proposes an output-based limit management strategy, which consists of the safety margin module and the parameter prediction module to monitor system responses, plus the switching logic to govern switches between the main controller and limiters, and, in this way, a faster transient performance is achieved, and the limit protections in transient states become more effective. To realize smooth switching control, the linear-quadratic bumpless transfer method is developed. The design principle of the multi-loop switching control and bumpless compensator is detailed, and the effect—on limit protection control performance—of the design parameters in the safety margin and parameter prediction modules are also analyzed. The proposed approach is tested using simulations covering the whole flight envelope on the nonlinear component-level model of a turbofan engine, and the superiority over the Min-Max architecture is also validated.