Hybrid System Approach Research Articles

Stability analysis of periodic triggering reset control systems

In most literature related to reset control, the reset actions are triggered by continuous monitoring triggering reset conditions, which is not suitable for computer-based implementation. This paper considers periodic triggering reset control, where the reset actions are only triggered at periodically sampling instants. Hybrid system approach is given to analyze the asymptotic stability and L2 gain property, and less conservative switched system approach is presented for asymptotic stability analysis. The comparison of the two approaches is discussed. Moreover, novel reset conditions are given to improve the overshoot performance. Simulations are presented to support our results.

Advanced control approach for hybrid systems based on solid oxide fuel cells

Abstract This paper shows a new advanced control approach for operations in hybrid systems equipped with solid oxide fuel cell technology. This new tool, which combines feed-forward and standard proportional–integral techniques, controls the system during load changes avoiding failures and stress conditions detrimental to component life. This approach was selected to combine simplicity and good control performance. Moreover, the new approach presented in this paper eliminates the need for mass flow rate meters and other expensive probes, as usually required for a commercial plant. Compared to previous works, better performance is achieved in controlling fuel cell temperature (maximum gradient significantly lower than 3 K/min), reducing the pressure gap between cathode and anode sides (at least a 30% decrease during transient operations), and generating a higher safe margin (at least a 10% increase) for the Steam-to-Carbon Ratio. This new control system was developed and optimized using a hybrid system transient model implemented, validated and tested within previous works. The plant, comprising the coupling of a tubular solid oxide fuel cell stack with a microturbine, is equipped with a bypass valve able to connect the compressor outlet with the turbine inlet duct for rotational speed control. Following model development and tuning activities, several operative conditions were considered to show the new control system increased performance compared to previous tools (the same hybrid system model was used with the new control approach). Special attention was devoted to electrical load steps and ramps considering significant changes in ambient conditions.

A hybrid systems approach to global synchronization and coordination of multi-agent sampled-data systems

A global synchronization algorithm for a network of resetting clocks is presented. Each clock signals its neighbors when it resets to zero after reaching the end of its period. Based on where a neighbor is located at the time of the signal, the neighboring clock adjusts its value instantaneously to synchronize with the signaling clock. Subsequently, the sychronization algorithm is used in the context of networked, multi-agent sampled-data systems. Here, agents update their internal state, based on the values of the internal states of their neighbors, when their clock variable resets to zero. The synchronization algorithm, together with additional sampling of the internal states of neighbors, is used to synchronize and coordinate the agents of the networked sampled-data system. These actions enable achieving the stability property that would result if the agents performed their state updates simultaneously. The models associated with these algorithms are presented in terms of hybrid dynamical systems. Well-posed models are developed that exhibit robustness properties, including robustness to small communication delays and to small mismatch in the natural frequency of each clock, and for which extensive analysis tools are available, including an invariance principle and a reduction principle.

Set-membership parity space hybrid system diagnosis

In this paper, diagnosis for hybrid systems using a parity space approach that considers model uncertainty is proposed. The hybrid diagnoser is composed of modules which carry out the mode recognition and diagnosis tasks interacting each other, since the diagnosis module adapts accordingly to the current hybrid system mode. Moreover, the methodology takes into account the unknown but bounded uncertainty in parameters and additive errors (including noise and discretisation errors) using a passive robust strategy based on the set-membership approach. An adaptive threshold that bounds the effect of model uncertainty in residuals is generated for residual evaluation using zonotopes, and the parity space approach is used to design a set of residuals for each mode. The proposed fault diagnosis approach for hybrid systems is illustrated on a piece of the Barcelona sewer network.

Fuzzy Predictive Control of Step-Down DC-DC Converter Based on Hybrid System Approach

In this paper, a fuzzy predictive control scheme is proposed for controlling output voltage of a step-down DC-DC converter in presence of disturbance and uncertainty. The DC-DC converter is considered as a hybrid system and modeled by Mixed Logical Dynamical modeling approach. The main objective of the paper is to design a Fuzzy Predictive Control to achieve desired voltage output without increasing complexity of the hybrid model of DC-DC converter in various conditions. A model predictive control is designed based on the hybrid model and applied to the system. Although the performance of the model predictive control method is satisfactory in normal condition, it suffers from lack of robustness in presence of disturbance and uncertainty. So, to succeed in facing up to the problem a fuzzy supervisor is utilized to adjust the main predictive controller based on the measured states of the system. In this paper it is shown that the proposed fuzzy predictive control scheme has advantages such as simplicity and efficiency in normal operation and robustness in presence of disturbance and uncertainty. Through simulations effectiveness of the proposed method is shown.

Multi-storage Hybrid System Approach and Experimental Investigations

The paper presents a new multi-storage hybrid system concept for the improvement of self-consumption rate, conversion efficiency and storage lifetime in photovoltaic (PV) hybrid systems. Main idea is the smart combination and control of short- and long-term storage technologies with supplementary operating characteristics. The paper discusses a typical application example of a PV-hybrid system with lithium-ion battery, hydrogen and heat storage path. A dynamic lithium-ion battery model is presented. The power electronic and control structure of the multi-storage experimental test-bed is explained. Investigation results for a typical application example demonstrate the functionality and benefits of the proposed concept.

A hybrid-system approach for W state and cluster state generation

Here we demonstrate an efficient scheme for W state and cluster state generation based on the hybrid-system where nitrogen-vacancy centers are coupled to microcavities. In our proposed scheme, entanglement between solid-state qubits can be generated with the assistance of an ancillary photon. We also discuss the efficiency of the entanglement generation protocols and generalize them to multi-qubit cases. With current and near-future technology, the entanglement of nitrogen-vacancy centers can be achieved and our scheme can further be used for quantum information processing and long-distance quantum communication.

Hydrogen atom as a quantum-classical hybrid system

Hydrogen atom is studied as a quantum-classical hybrid system, where the proton is treated as a classical object while the electron is regarded as a quantum object. We use a well known mean-field approach to describe this hybrid hydrogen atom; the resulting dynamics for the electron and the proton is compared to their full quantum dynamics. The electron dynamics in the hybrid description is found to be only marginally different from its full quantum counterpart. The situation is very different for the proton: in the hybrid description, the proton behaves like a free particle; in the fully quantum description, the wave packet center of the proton orbits around the center of mass. Furthermore, we find that the failure to describe the proton dynamics properly can be regarded as a manifestation of the fact that there is no conservation of momentum in the mean-field hybrid approach. We expect that such a failure is a common feature for all existing approaches for quantum-classical hybrid systems of Born-Oppenheimer type.

Hybrid-system approach to fault-tolerant quantum communication

We present a layered hybrid-system approach to quantum communication that involves the distribution of a topological cluster state throughout a quantum network. Photon loss and other errors are suppressed by optical multiplexing and entanglement purification. The scheme is scalable to large distances, achieving an end-to-end rate of 1 kHz with around 50 qubits per node. We suggest a potentially suitable implementation of an individual node composed of erbium spins (single atom or ensemble) coupled via flux qubits to a microwave resonator, allowing for deterministic local gates, stable quantum memories, and emission of photons in the telecom regime.

On Trajectory Tracking Model Predictive Control of an Unmanned Quadrotor Helicopter Subject to Aerodynamic Disturbances

AbstractIn this article a model predictive control (MPC) strategy for the trajectory tracking of an unmanned quadrotor is presented. The quadrotor's dynamics are modeled using a hybrid systems approach and, specifically, a set of piecewise affine (PWA) systems around different operating points of the translational and rotational motions. The proposed control scheme is dual and consists of an integral MPC for the translational motions, followed by an MPC scheme for the tracking of the quadrotor's attitude motions. By the utilization of PWA representations, the controller is computed for a larger part of the quadrotor's flight envelope, which provides more control authority for aggressive maneuvering. The proposed dual control scheme is able to calculate optimal control actions with robustness against atmospheric disturbances (e.g. wind gusts) and with respect to the physical constraints of the quadrotor (e.g. maximum lifting forces or fixed thrust limitations in order to extend flight endurance). Extended simulation studies indicate the efficiency of the MPC scheme, both in trajectory tracking and aerodynamic disturbance attenuation.

Detection of Cardiovascular Anomalies: Hybrid Systems Approach

In this paper, we propose a hybrid interpretation of the cardiovascular system. Based on a model proposed by Simaan et al. (2009), we study the problem of detecting cardiovascular anomalies that can be caused by variations in some physiological parameters, using an observer-based approach. We present the first numerical results obtained.

Bio-inspired Synchronization of Non-Identical Pulse-Coupled Oscillators Subject to a Global Cue and Local Interactions

Pulse-coupled oscillators (PCOs) comprise a class of limit cycle oscillators coupled in an impulsive rather than smooth manner. Their importance in biology and engineering motivated the analysis of the basic properties and design principles of PCO networks. In this work, we address synchronization of non-identical PCO networks with a global cue by using a hybrid systems approach. Using phase response curves as a design element, we characterize solutions and give conditions under which frequency synchronization is achieved. Numerical experiments are provided, which confirm the theoretical findings.

Fault Detection and Isolation of Hybrid Systems using Diagnosers that Reason on Components

In this paper, a design methodology and implementation architecture for diagnosers in the framework of hybrid systems is proposed. The design methodology is based on the hybrid automata model that represents the system behavior, in which each mode relates to a set of components. The architecture includes a set of modules which achieve mode recognition and diagnosis tasks both based on residuals generated by structural analysis. The two tasks interact each other since the diagnosis module adapts accordingly to the current mode of the hybrid system. Mode recognition involves detecting mode change and identifying the set of residuals that are consistent with the current mode of the hybrid system. On the other hand, diagnosis involves detecting and isolating the fault by interlinking the components underlying the inconsistencies reported by the residuals, along the DX approach. As an application case study to illustrate the proposed fault diagnosis approach for hybrid systems a partial model of the Barcelona sewer network is used.

Fault Diagnosis in Hybrid Systems using Possible Conflicts

Hybrid systems, whose behavior exhibit continuous and discrete event dynamics, are present in many industrial environments. The complexity of such behavior makes the online fault diagnosis task very challenging. In this work we propose an accurate and timely online fault diagnosis approach for hybrid systems. Our approach uses the Hybrid Bond Graph modeling methodology to avoid the precompilation of all possible modes in the system. Structural decomposition of Hybrid Bond Graph models, obtained by means of Possible Conflicts, together with its implementation using Block Diagrams, allows the diagnosis system be quickly reconfigured when a mode change occurs. Moreover, this diagnosis approach has the ability to track the behavior of the system during the transitory states caused by mode changes. Diagnosis results using a four-tank system demonstrate the capabilities of the proposal.

A Hybrid System Approach for High Consumption Industrial Furnace Control

In this paper we describe a hybrid system approach for high consumption industrial furnace control. The problem is observed in systematic way starting from the need for modeling this system as hybrid. For description of this behavior we use the Hybrid System Description Language. After that, we design an optimal controller for the furnace and we simulate and compare the controller with other relevant predictive controllers. We have shown that using the hybrid approach for control of industrial furnaces leads to significant improvement of the control system performances.

A Hybrid System Approach to the Analysis and Design of Power Grid Dynamic Performance

In this paper, we describe an approach to the analysis and design of power grid dynamic performance based on hybrid systems theory. Power grid is a large-scale cyber-physical system for transmission of electrical energy. The joint dynamics of physical processes and cyber elements in power grids are typical of a mixture of continuous and discrete behaviors, that is, hybrid dynamics. We address problems on stability that are basic concerns in the performance of current and future power grids with the hybrid dynamics. Measures for stability of power grids are interpreted as safety specifications in hybrid system models and are translated into restrictions on the systems' reachable sets of states. Algorithmic reachability analysis of hybrid systems enables analysis of safe initial states and hence quantitative estimation of stability regions. Also it contributes to synthesis of safe initial states as well as switching conditions in order to satisfy safety specifications in a power grid. We demonstrate the approach for two problems on transient stability of the single machine/infinite bus (SMIB) system and on fault release control of a multimachine power grid.

Discontinuities and hysteresis in quantized average consensus

We consider continuous-time average consensus dynamics in which the agents’ states are communicated through uniform quantizers. Solutions to the resulting system are defined in the Krasowskii sense and are proven to converge to conditions of “practical consensus”. To cope with undesired chattering phenomena we introduce a hysteretic quantizer, and we study the convergence properties of the resulting dynamics by a hybrid system approach.

Stability Analysis of Recurrent Fuzzy Systems: A Hybrid System and SOS Approach

This paper presents a new approach to the stability analysis of recurrent fuzzy systems (RFSs). RFSs are rule-based dynamic fuzzy systems that are usually obtained from heuristic or data-driven modeling. In the presented approach, the stability of both continuous-time and discrete-time RFS can be analyzed in a common framework. It is based on the representation of an RFS as a hybrid polynomial system. Due to the polynomial structure, the recently developed method of sum-of-squares (SOS) decomposition along with semidefinite programming can be employed to derive sufficient conditions for the stability of equilibrium points. We consider stability analysis for known equilibrium points as well as unknown equilibrium points. The latter results in a two-step procedure. In the first step, a polynomial is constructed. In the second verification step, this polynomial is proven to be a Lyapunov function for the RFS. The applicability of the approach is shown by two systems formulated as a rule-based RFS.

A Hybrid System Approach to Robust Fault Detection for a Class of Sampled-data Systems

A Hybrid System Approach to Robust Fault Detection for a Class of Sampled-data Systems

Quantized average consensus: Discontinuities and hysteresis

It is well known that the consensus problem can be formulated in terms of a stabilization problem. In this note we consider continuous-time average consensus dynamics: We discuss how quantization can be included in the system, and focus on one model in which the agents’ states are communicated through uniform quantizers. Solutions to the resulting system are defined in the Krasowskii sense, and results are given proving their convergence to conditions of practical consensus. To cope with potential chattering phenomena, which may be undesired in the applications, we propose the use of a hysteretic quantizer, and study the convergence properties of the resulting dynamics by a hybrid system approach.