Nonlinear and Variable Structure Excitation Controller for Power System Stability

A new nonlinear variable structure excitation controller is proposed. Its design combines the differential geometry theory and the variable structure controlling theory. The mathematical model in the form of ＂an affme nonlinear system＂ is set up for the control of a large-scale power system. The static and dynamic performances of the nonlinear variable structure controller are simulated. The response of system with the controller proposed is compared to that of the nonlinear optimal controller when the system is subjected to a variety of disturbances. Simulation results show that the nonlinear variable structure excitation controller gives more satisfactorily static and dynamic performance and better robustness.

Robust excitation control of multi-machine multi-load power systems using Hamiltonian function method

Using an energy-based Hamiltonian function method,this paper investigates the robust excitation control of multi-machine multi-load power systems described by a set of uncertain differential algebraic equations.First,we complete the dissipative Hamiltonian realization of the power system and adjust its operating point by the means of pre-feedback control.Then,based on the obtained Hamiltonian realization,we discuss the robust excitation control of the power system and put forward an H1 excitation control strategy.Simulation results demonstrate the effectiveness of the control scheme.

Nonlinear excitation controller design for power systems:an I&I approach

The Immersion and Invariance （I＆I） methodology provides a novel approach for nonlinear system control, which is distinct from the traditional feedback linearization and backstepping method. In this paper, a new excitation controller is designed for single machine infinite bus system （SMIBS） based on the I＆I approach. Firstly the dynamic model of SMIBS is homeomorphously transformed to a specific form for which a stable lower-order target system is selected. Then the I＆I excitation controller is designed by immersing the transformed system into the target system. Simulation results from PSCAD/EMTDC demonstrate that the proposed controller guarantees transient stability of the system after large disturbances.

Nonlinear variable structure excitation and steam valving controllers for power system stability

A set of novel nonlinear variable structure excitation and steam-valving controllers are proposed in this paper. On the basis of the classical dynamic equations of a generator, excitation control and steam valving control are simultaneously considered. Design of these controllers combines the differential geometry theory with the variable structure controlling theory. The mathematical model in the form of ＂an affine nonlinear system＂ is set up for the control design of a large-scale power plant. The dynamic performance of the nonlinear variable structure controllers proposed for a single machine connected to an infinite bus power system is simulated. Simulation results show that the nonlinear variable structure excitation and steam-valving controllers give satisfactory dynamic performance and good robustness.

Observational linearization and tracking objective excitation control strategy based on phasor measurement unit

To improve the transient stability of multimachine power systems,observational linearization and tracking objective excitation control laws were derived from the phasor measurement unit(PMU),observational linearization,and tracking objective control theory based on synchronized coordinates and reference generator coordinates.The control strategies utilized real-time state variables obtained by PMU to linearize the state equations of the system,and then the linear optimal control strategy was used to design excitation controllers.The inaccuracy of the local linearization method and the complexity of the system models designed in the exact linearization method for nonlinear systems were avoided.Therefore,the control strategies were applied in real time.Simulation results show that the proposed method can improve the transient stability of power systems more efficiently than nonlinear optimal excitation control.

Adaptive H-infinity control of synchronous generators with steam valve via Hamiltonian function method

Based on Hamiltonian formulation, this paper proposes a design approach to nonlinear feedback excitation control of synchronous generators with steam valve control, disturbances and unknown parameters. It is shown that the dynamics of the synchronous generators can be expressed as a dissipative Hamiltonian system, based on which an adaptive H-infinity controller is then designed for the systems by using the structure properties of dissipative Hamiltonian systems. Simulations show that the controller obtained in this paper is very effective.

Photo-Doped Active Electrically Controlled Terahertz Modulator

We demonstrate an electric-controlled terahertz（THz） modulator which can be used to realize amplitude modulation of terahertz waves with slight photo-doping. The THz pulse transmission was efficiently modulated by electrically controlling the monolayer silicon-based device. The modulation depth reached 100% almost when the applied voltage was 7V at an external laser intensity of 0.6W/cm2. The saturation voltage reduced with the increase of the photo-excited intensity. In a THz continuous wave（CW）system, a significant fall in both THz transmission and reflection was also observed with the increase of applied voltage. This reduction in the THz transmission and reflection was induced by the absorption for electron injection. The results show that a high-efficiency and high modulation depth broadband electric-controlled terahertz modulator in a pure Si structure has been realized.

Control of cardiac excitability and arrhythmias by microRNAs

Recent studies revealing the important roles of microRNAs（miRNAs） in regulating expression of ion channel genes have opened up a research field for extending and deepening our investi- gation into the cardiac excitability and the associated arrhythmogenesis.Cardiac excitability,the fundamental property of the cardiac myocytes,defines the cardiac conduction,repolarization,automaticity,intracellular calcium handling,and their regional heterogeneity. Our previous and ongoing studies and the work from other laboratories have demonstrated the significant involvement of miRNAs in regulating every aspects of cardiac excitability.We have found earlier that the muscle-specific miRNA miR-1 boosts up the arrhythmogenic potential through targeting gap junction channel connexin 43 in myocardial infarction.A subsequent study revealed that miR-1 can also cause arrhythmias by impairing Ca2+ handling by targeting phosphatase.We then identified another muscle-specific miRNA miR-133 promotes abnormal QT prolongation by repressing HERG K+ channel expression in diabetic cardiomyopathy. Subsequently,we discovered that both miR- 1 and miR-133 are involved in the reexpression of pacemaker channels HCN2/HCN4 to enhance abnormal automaticity in cardiac hypertrophy.Recently, we further identified miR-328 as an important determinant for atrial fibrillation（AF） and the associated adverse atrial electrical remodeling via targeting L-type Ca2+ channels.While all the above-mentioned miRNAs are proarrhythmic,we have newly identified for the first time a natural antiarrhythmic miRNA miR-26.We found that all three members of the miR-26 family is downregulated in their expression in AF tissues and this downregulation increases AF vulnerability as a result of removal of an endogenous antiarrhythmic factor.miR-26 downregulation shortens atrial action potential favoring AF by increasing inward rectifier K+ current（IK1） density. This is caused by an upregulation of Kir2.1 K+ channel subunit due to derepression of its encoding gene KCNJ2 as we have validated KCNJ2 as a target gene for miR-26.Administration of a LNA-modified antimiR-26 antisense through tail vein injection increases AF vulnerability as indicated by increased number of mice with AF induction by intracardiac pacing.And this effect is blunted by co-injection of either an adenovirus vector carrying miR-26 precursor sequence or a LNA-modified miR-26 mimic to specifically target KCNJ2.We further discovered that the activity of NFAT transcription factor is enhanced in AF which represses the transcription of miR-26. We characterized the promoter region of the host genes of all three members of the miR-26 miRNA family and identified a common cis-acting element for NFAT binding.Thus,our study unraveled a novel miRNA signaling pathway AF NFAT miR-26 KC-NJ2 /Kir2.1/IK1 AF as a positive feedback loop favoring AF and the remodeling process.

A Nonlinear Coordinated Approach to Enhance the Transient Stability of Wind Energy-Based Power Systems

This paper proposes a novel framework that enables the simultaneous coordination of the controllers of doubly fed induction generators(DFIGs) and synchronous generators(SGs).The proposed coordination approach is based on the zero dynamics method aims at enhancing the transient stability of multi-machine power systems under a wide range of operating conditions. The proposed approach was implemented to the IEEE39-bus power systems. Transient stability margin measured in terms of critical clearing time along with eigenvalue analysis and time domain simulations were considered in the performance assessment. The obtained results were also compared to those achieved using a conventional power system stabilizer/power oscillation(PSS/POD) technique and the interconnection and damping assignment passivity-based controller(IDA-PBC). The performance analysis confirmed the ability of the proposed approach to enhance damping and improve system’s transient stability margin under a wide range of operating conditions.

Fast and Robust Control of Excitation Systems: A Finite-time Method

Using finite-time control approach, this paper proposes a new design method for nonlinear robust excitation control of a widely used 5th-order model of synchronous generators. The finite-time excitation controller achieved here can improve the system′s behaviors in some aspects such as quick convergence and robustness for uncertainties. Simulations demonstrate that the finite-time excitation controller is more effective than some other excitation controllers.

Wide-area nonlinear robust voltage control strategy for multi-machine power systems

This paper presented a novel wide-area nonlinear excitation control strategy for multi-machine power systems. A simple and effective model transformation method was proposed for the system's mathematical model in the COI (center of inertia) coordinate system. The system was transformed to an uncertain linear one where deviation of generator terminal voltage became one of the new state variables. Then a wide-area nonlinear robust voltage controller was designed utilizing a LMI (linear matrix inequality) based robust control theory. The proposed controller does not rely on any preselected system operating point, adapts to variations of network parameters and system operation conditions, and assures regulation accuracy of generator terminal voltages. Neither rotor angle nor any variable's differentiation needs to be measured for the proposed controller, and only terminal voltages, rotor speeds, active and reactive power outputs of generators are required. In addition, the proposed controller not only takes into account time delays of remote signals, but also eliminates the effect of wide-area information's incompleteness when not all generators are equipped with PMU (phase measurement unit). Detailed tests were conducted by PSCAD/EMTDC for a three-machine and four-machine power systems respectively, and simulation results illustrate high performance of the proposed controller.

Analysis and Design of Switching Surface for Nonlinear Variable Structure Control Systems

One of the main problems in variable structure control systems is finding the switching surface on which the controlled plant has a desired specific behaviour.This paper presents a new method for finding switching surfaces of nonlinear variable structure systems. Using this method, the designer first presents a system with the desired properties, then finds the switching function σ(x) such that the switching surface S∶={x∈R n|σ(x)=0} is coincident with the sliding motion in the given system. This method is applied to the design of the variable structure controller in a power system and the highest transient stability limitations are attained.

Robust control of exciting force for vibration control system with multi-exciters

Due to the dynamical character of electromagnetic exciter and the coupling between structure and exciter(s),the actual output force acting on the structure is usually not equal to the exact value that is supposed to be,especially when multi-exciters are used as actuators to precisely actuate large flexible structure.It is necessary to consider these effects to ensure the force generated by each exciter is the same as required.In this paper,a robust control method is proposed for the multi-input and multi-output(MIMO)structural vibration control system to trace the target actuating force of each exciter.A special signal is designed and put into the coupled mul-ti-exciter-structure system,and the input and output signals of the system are used to build a dynamic model involving both the dynamical characters of the exciters and the structure using the subspace identification method.Considering the uncertainty factors of the multi-exciter/structure system,an H-infinity robust controller is designed to decouple the coupling between structure and exciters based on the identified system model.A MIMO vibration control system combined with a flexible plate and three electromagnetic exciters is adopted to demonstrate the proposed method,both numerical simulation and model experiments showing that the output force of each exciter can trace its target force accurately within the requested frequency band.

Bifurcations and Stability Boundary of a Power System

A single-axis flux decay model including an excitation control model proposed in [12,14,16] is studied. As the bifurcation parameter P m (input power to the generator) varies, the system exhibits dynamics emerging from static and dynamic bifurcations which link with system collapse. We show that the equilibrium point of the system undergoes three bifurcations: one saddle-node bifurcation and two Hopf bifurcations. The state variables dominating system collapse are different for different critical points, and the excitative control may play an important role in delaying system from collapsing. Simulations are presented to illustrate the dynamical behavior associated with the power system stability and collapse. Moreover, by computing the local quadratic approximation of the 5-dimensional stable manifold at an order 5 saddle point, an analytical expression for the approximate stability boundary is worked out.