Qiang Zang

Robust Load Frequency Controller Design Based on a New Strict Model

Abstract This article presents an approach to design robust load frequency controllers. In view of the drawbacks of the conventional load frequency control model, a new strict model is derived from the detailed area model. Based on the derived model, the robust load frequency controllers are designed to restrain the disturbances. Since the robust controllers with high order are adverse to practical application, the balanced truncation method is adopted to reduce the order of the controllers. Finally, the designed controllers are tested on a typical two-area four-machine system, and the results verify the validity of the presented approach.

Backstepping control for a class of nonlinear differential-algebraic equations subsystems with application to power systems

Backstepping control method of nonlinear ordinary differential equations (ODE) systems is extended to a class of nonlinear differential-algebraic equations (DAE) subsystems, which are put forward for decentralized control analysis of power systems. The differential equations and underlying constraints of the DAE subsystems involve the interconnection inputs generated by the rest of the large-scale systems. Equivalent systems are obtained through a local differomorphism and a feedback, and then the well-known Backstepping method for nonlinear ODE systems can be extended. An asymptotic stabilization controller is designed based on such a recursive approach. Based on the design scheme proposed in this paper, a speed governor is designed for one synchronous generator set in multi-machine power systems. The simulation results illustrate the utility of the proposed scheme.

A New Output Feedback Control for Nonlinear Differential-Algebraic-Equation Systems

Abstract This note considers the problem of stabilization by output feedback for a class of nonlinear Differential-Algebraic-Equation systems. The output feedback controller is constructed which ensures the closed-loop systems asymptotically stable. Not based on separation-principle that is commonly adopted in the literature, the output feedback controller design is coupled with that of the non-initialized linear high gain state observer. The numerical simulation results illustrate the effectiveness of the proposed scheme.

Decentralized Control for Large-Scale Systems with Uncertain Missing Measurements Probabilities

For large-scale systems which are modeled as interconnection of networked control systems with uncertain missing measurements probabilities, a decentralized state feedback controller design is considered in this paper. The occurrence of missing measurements is assumed to be a Bernoulli random binary switching sequence with an unknown conditional probability distribution in an interval. A state feedback controller is designed in terms of linear matrix inequalities to make closed-loop system exponentially mean square stable and a prescribed performance is guaranteed. Sufficient conditions are derived for the existence of such controller. A numerical example is also provided to demonstrate the validity of the proposed design approach.

A Nonlinear Excitation Controller Design Method for Terminal Voltage Regulation and Transient Stability Enhancement

Abstract This paper proposes a cascade control method to design a nonlinear excitation controller to guarantee the terminal voltage regulation and the transient stability. Firstly, a nonlinear automatic voltage regulator (NAVR) in the inner loop is designed to control the terminal voltage exactly. Secondly, the generator model including the NAVR is transformed to be a reduced one. Subsequently, based on the reduced generator model, the nonlinear power system stabilizer in the external loop is designed to enhance the transient stability of the power systems. Furthermore, a coordination strategy is presented to improve the performances of the terminal voltage regulation in the steady state and the stability in the transient state. Finally, the proposed method is verified by numerous simulation results.

Invertibility of Nonlinear Differential-Algebraic-Equation Subsystems with Application to Power Systems

For nonlinear differential-algebraic-equation subsystems, whose index is one and interconnection input is locally measurable, the problem of invertibility is discussed and the results are applied to the power systems component decentralized control. The inverse systems’ definitions for such a class of differential-algebraic-equation subsystems are put forward. A recursive algorithm is proposed to judge whether the controlled systems are invertible. Then physically feasible α-order integral right inverse systems are constructed, with which the composite systems are linearizaed and decoupled. Finally, decentralized excitation and valve coordinative control for one synchronous generator within multimachine power systems are studied and the simulation results based on MATLAB demonstrate the effectiveness of the control scheme proposed in this paper.

Output feedback adaptive maneuvering for a class of MIMO nonlinear systems

The output maneuvering problem is defined as solving the geometric and dynamic tasks. Based on the backstepping approach with vector form, a new output feedback adaptive control scheme is presented to solve an output maneuvering problem for multi-input and multi-output (MIMO) nonlinear systems with parametric uncertainty. The geometric and the dynamic tasks are solved meanwhile the global stability of the closed loop systems is guaranteed through the control scheme. The simulation results illustrate the effectiveness of the proposed scheme.

Decentralized Nonlinear Control Method of Components in Power Systems Based on Differential-Algebraic Sub-System Models

Abstract Complete nonlinear differential-algebraic equation (DAE) sub-system models are considered in the paper when designing controllers of components in power systems. First-principle models are nonlinear DAE sub-system models, but they use non-local measurable variables to describe the mutual relation (interconnection) between component and the AC grid, and thus they are not suitable for designing decentralized controllers. In the paper, component structural models are constructed, in which the local-measurable interface variables are used to describe the mutual relation between component and the AC grid. Thus, the proposed models are equivalent to the first-principle models in essence, and have two characteristics: with local measurable interconnections and index 1. These two characteristics make it possible to transform the component structural models to nonlinear ordinary differential equation (ODE) sub-system models with measurable interconnections. Thus, traditional nonlinear control methods which are suitable for nonlinear ODE systems could be developed and expanded to be suitable for designing component controllers.