Cascaded Control Architecture Research Articles

Avoiding contingent incidents by quadrotors due to one or two propellers failure.

With the increasing impact of drones in our daily lives, safety issues have become a primary concern. In this study, a novel supervisor-based active fault-tolerant (FT) control system is presented for a rotary-wing quadrotor to maintain its pose in 3D space upon losing one or two propellers. Our approach allows the quadrotor to make controlled movements about a primary axis attached to the body-fixed frame. A multi-loop cascaded control architecture is designed to ensure robustness, stability, reference tracking, and safe landing. The altitude control is performed using a proportional-integral-derivative (PID) controller, whereas linear-quadratic-integral (LQI) and model-predictive-control (MPC) have been investigated for reduced attitude control and their performance is compared based on absolute and mean-squared error. The simulation results affirm that the quadrotor remains in a stable region, successfully performs the reference tracking, and ensures a safe landing while counteracting the effects of propeller(s) failures.

On the control allocation of fully actuated multirotor aerial vehicles

The present work deals with the optimal control allocation of fully actuated multirotor aerial vehicles (MAVs) equipped with fixed (non-vectoring and constant-pitch) rotors. To tackle the problem, a cascaded control architecture is considered in which the control allocation is separated from the control law itself. The latter provides the resulting control efforts (three-dimensional force and torque) from the desired state trajectory, while the former is entrusted to distribute the resulting control efforts among the available actuators. The control allocation is formulated as a convex optimization problem, which, on the one hand, unifies the previous methods and, on the other hand, extends the literature by rigorously considering the rotors' dynamics and bounds, thus resulting in a novel constrained optimal control allocation algorithm suitable for quite general fixed-rotor fully actuated MAVs. Moreover, a control-allocation feasibility analysis based on the control allocator admissible set is presented. It provides a necessary and sufficient condition for the existence of a solution to the control allocation problem. We argue that this condition can be explicitly used in the design of the control law, thus improving its synergy with the control allocator. The proposed control allocation method is mathematically analyzed and widely illustrated by the computer simulation of two non-planar omnidirectional MAVs.

Capacitor Voltage Ripple Suppression in a Modular Multilevel Converter Using Frequency-Adaptive Spatial Repetitive-Based Circulating Current Controller

In this article, a new circulating current control architecture is proposed to suppress the submodule capacitor voltage ripple in a modular multilevel converter (MMC). The proposed cascaded control architecture uses the spatial repetitive controller (SRC) in both the outer voltage loop and the inner current loop, and can effectively suppress the second harmonic component of the submodule capacitor voltage ripple even under variable line frequency conditions. The dual SRC-based circulating current controller injects a second harmonic component into the circulating current to suppress the submodule capacitor voltage ripple. The SRC, which is a frequency-adaptive periodic digital controller, incorporates a phase sampling technique to achieve dynamic change in the sampling frequency, can adaptively tune its gain characteristics according to operating line frequency of the MMC. Unlike the existing techniques, the proposed controller uses the submodule capacitor voltage information for circulating current harmonic reference generation and, hence, does not require additional sensing of the output current. Detailed mathematical analysis and architecture of the proposed controller are presented in this article. A 400-V, 1-kW MMC laboratory prototype is developed and experimental results demonstrating the performance of the proposed circulating current control architecture for variable frequency and load conditions are also presented.

Real-Time Path Generation and Obstacle Avoidance for Multirotors: A Novel Approach

Multirotors, among all aerial vehicles, are fundamental instruments in many situations, i.e. video recording of sport events, leisure, environmental monitoring before or after a disaster. In particular, in the context of environmental monitoring, the possibility of following a predetermined path while avoiding obstacles is extremely relevant. In this work, we propose a novel method for path definition in presence of obstacles, which describes a curve as the intersection of two surfaces. The planner, based on that path definition along with a Cascaded control architecture and utilizing a nonlinear control technique for both control loops (position and attitude), creates a framework to manipulate the multicopters’ behaviors. The method is demonstrated to be able to generate a safe path taking into account obstacles perceived in real-time and avoids collisions. These algorithms are embedded in a software package to control the flight of a fully autonomous AscTec Firefly hexacopter with two cameras and onboard processing capabilities.

Control system design and testing for a small‐scale autonomous helicopter

PurposeThe purpose of this paper is to conduct the design, development and testing of a controller for an autonomous small‐scale helicopter.Design/methodology/approachThe hardware in the loop simulation (HILS) platform is developed based on the nonlinear model of JR Voyager G‐260 small‐scale helicopter. Autonomous controllers are verified using the HILS environment prior to flight experiments.FindingsThe gains of the multi‐loop cascaded control architecture can be effectively optimized within the HILS environment. Various autonomous flight operations are achieved and it is demonstrated that the prediction from the simulations is in a good agreement with the result from the flight test.Research limitations/implicationsThe synthesized controller is effective for the particular test‐bed. For other small‐scale helicopters (with different size and engine specifications), the controller gains must be tuned again.Practical implicationsThis work represents a practical control design and testing procedures for an autonomous small‐scale helicopter flight control. The autonomous helicopter can be used for various missions ranging from film making, agriculture and volcanic surveillance to power line inspection.Originality/valueThe research addresses the need for systematic design, development and testing of controller for a small‐scale autonomous helicopter by utilizing HILS environment.