Zhongwei Lin

ℋ∞ stabilisation of switched linear stochastic systems under dwell time constraints

Based on the determination of a minimum dwell time, this article addresses the problem of characterising a switching strategy for ℋ∞ stabilisation of switched linear stochastic systems with adapted external inputs. Sufficient conditions that assure exponential mean square stability and an ℋ∞ performance index are established by analysing the time evolution of the second-order moment of the state and a recursive dynamic programming inequality, respectively. Alternative conditions are derived for numerical implementations. The proposed method is illustrated by numerical simulations.

A geometric approach to H∞ control of nonlinear Markovian jump systems

This paper first discusses the H∞ control problem for a class of general nonlinear Markovian jump systems from the viewpoint of geometric control theory. Following with the updating of the Markovian jump mode, the appropriate diffeomorphism can be adopted to transform the system into special structures, which establishes the basis for the geometric control of nonlinear Markovian jump systems. Through discussing the strongly minimum-phase property or the strongly γ-dissipativity of the zero-output dynamics, the H∞ control can be designed directly without solving the traditional coupled Hamilton–Jacobi inequalities. A numerical example is presented to illustrate the effectiveness of our results.

Mixed H2/H∞ Pitch Control of Wind Turbine with a Markovian Jump Model

ABSTRACT This paper proposes a Markovian jump model and the corresponding H2/H∞ control strategy for the wind turbine driven by the stochastic switching wind speed, which can be used to regulate the generator speed in order to harvest the rated power while reducing the fatigue loads on the mechanical side of wind turbine. Through sampling the low-frequency wind speed data into separate intervals, the stochastic characteristic of the steady wind speed can be represented as a Markov process, while the high-frequency wind speed in the each interval is regarded as the disturbance input. Then, the traditional operating points of wind turbine can be divided into separate subregions correspondingly, where the model parameters and the control mode can be fixed in each mode. Then, the mixed H2/H∞ control problem is discussed for such a class of Markovian jump wind turbine working above the rated wind speed to guarantee both the disturbance rejection and the mechanical loads objectives, which can reduce the power volatility and the generator torque fluctuation of the whole transmission mechanism efficiently. Simulation results for a 2 MW wind turbine show the effectiveness of the proposed method.

Decentralized adaptive controller design for large-scale power systems

In this paper, a novel decentralized adaptive excitation control scheme is proposed for improvement of transient stability of large-scale power systems. The key feature of this control scheme is that by introducing two smooth functions and a bound estimation approach, the obstacle caused by time-varying interactions and unknown plant parameters is circumvented. We show that without the utilization of remote information and the bounds of interconnections, all signals of the overall closed-loop large-scale power system are globally uniformly bounded. The proposed control scheme is tested on a three-machine power system, and simulation results show transient stability enhancement of the power system in the face of a large sudden fault.

Regional pole placement of a Markovian jump model for wind turbine generator system

This paper discusses the regional pole placement problem for Markovian jump system, and the corresponding application on wind turbine generator system (WTGS). Through sampling the low-frequency wind speed datas into separate intervals, the dynamic process of WTGS can be modelled into Markovian jump system. The traditional operating points of wind turbine are divided into separate subregions correspondingly, where the model parameters and the control mode can be fixed in each mode. However, the control designed for each operating subregion can not guarantee the whole dynamic response performance of WTGS, which is caused by the stochastic switchings between different system modes. Hence, the pole placement problem is discussed for linear Markovian jump systems, and applied on improving the dynamics response of WTGS.

Passivity and feedback design of nonlinear Markovian jump systems

This paper is an attempt to combine the passivity theory with geometric control theory for nonlinear Markovian jump systems. The key-point concretes on taking the appropriate coordinate changes following with the Markovian switchings. Based on this concept, we investigate the passivity, feedback equivalence and global stabilization problems, which implies that feedback equivalence to a passive Markovian jump system requires a strongly minimum-phase condition.

Stabilization of continuous-time switched linear stochastic systems

This paper addresses the problem of characterizing a switching strategy for stabilization of switched linear stochastic systems with state-dependent noise. The strategy is based on the determination of a minimum dwell time. Sufficient conditions that assure exponential mean square stability and a guaranteed cost-to-go performance index are established by analyzing the time evolution of the second-order moment of the state and constructing a novel cross-monotonicity condition at the switching instants, respectively. Alternative conditions are derived for numerical implementations. The proposed method is illustrated by numerical simulations.