Steam Valve Control Research Articles

A robust nonlinear backstepping control scheme for hybrid AC/DC microgrids to improve dynamic stability against external disturbances

In this work, robust nonlinear controllers are designed for converters interfacing power generation and energy storage including DC- and AC-sides in hybrid AC/DC microgrid for improving the dynamic stability against external disturbances. The robust switching control inputs for all these interfacing converters and excitation as well as steam-valving control laws for the synchronous generators are determined using a nonlinear backstepping approach. The dynamic elements of the hybrid AC/DC microgrid are modeled by considering the effects of external disturbances where these disturbances reflect the effects of modeling errors, measurement noises, and parametric uncertainties. The robust control inputs for different elements in the microgrid are determined by guaranteeing the convergences of all relevant states, associated with different elements, toward their desired values while properly bounding the effects of disturbances. Control Lyapunov functions (CLFs) are formulated, during the proposed controller design process, to assess the dynamic stability. Simulation studies are conducted on a hybrid AC/DC microgrid to validate the effectiveness by observing the overall power balance with changes in the system while comparing with an existing sliding mode controller (ESMC). Simulation results clearly indicate robustness of the newly proposed controller through the improvement in the overall dynamic performance of the hybrid AC/DC microgrid over the ESMC.

Design method of nonlinear adaptive controller for the main steam valve of turbogenerator set considering state constrain

Aiming at the main steam-valve control of turbine generator unit with amplitude constraint and parameter uncertainty, adaptive backstepping is implemented on the main steam valve controller. The controller not only has an adaptive ability to uncertain parameters of the system and a good transient response performance, but also does not linearize the system. Meanwhile, the problem of state limit in the main steam-valve control of turbogenerator is effectively solved by using the Lyapunov function with constraints. Simulation results are presented to show the performance of the adaptive backstepping control.

Continuous fixed-time convergent regulator for dynamic systems with unbounded disturbances

This paper presents a novel continuous fixed-time convergent control law for dynamic systems in the presence of unbounded disturbances. A continuous fixed-time convergent control is designed to drive all states of a multi-dimensional integrator chain at the origin for a finite pre-established (fixed) time, using a scalar input. The fixed-time convergence is established and the uniform upper bound of the settling time is computed. The designed control algorithm is applied to fixed-time stabilization of two mechatronic systems, a cart inverted pendulum and a single machine infinite bus turbo generator with main steam valve control.

The Coordinated Immersion and Variance Control of Power Systems With Excitation and Steam-Valve

Transient stability is the key problem for reliable and secure planning under the new deregulated market conditions. By using immersion and invariance (I&I) method, a nonlinear coordinated generator excitation and steam-valve controller is designed to improve transient stability of power systems. The proposed coordinated I&I controller can assure power angle stability, voltage, and frequency regulations, when a large disturbance occurs on the transmission line or a small perturbation to mechanical power. Compared with the Lyapunov method, the proposed method does not need to construct a Lyapunov energy function. Some numerical simulations are used to validate the proposed controller. Simulation results show that the nonlinear coordinated I&I controller has better control performance than the existing coordinated passivation controller (CPC).

Nonlinear Synergetic Governor Controllers for Steam Turbine Generators to Enhance Power System Stability

This paper proposes a decentralized nonlinear synergetic governor controller (NSGC) for turbine generators to enhance power system stability by using synergetic control theory and the feedback linearization technique. The precise feedback linearization model of a turbine-generator with a steam valve control is obtained, at first, by using a feedback linearization technique. Then based on this model, a manifold is defined as a linear combination of the deviation of the rotor angle, speed deviation, and speed derivative. The control law of the proposed NSGC is deduced and the stability condition of the whole closed-loop system is subsequently analyzed. According to the requirement of the primary frequency regulation, an additional proportional integral (PI) controller is designed to dynamically track the steady-state value of the rotor angle. Case studies are undertaken based on a single-machine infinite-bus system and the New England system, respectively. Simulation results show that the proposed NSGC can suppress the power oscillations and improve transient stability more effectively in comparison with the conventional proportional-integral-derivative (PID) governor controller. Moreover, the proposed NSGC is robust to the variations of the system operating conditions.

A Backstepping Sliding Mode Dual-Excitation and Steam-Valving Control of Synchronous Generators

A nonlinear dual-excited and steam-valving controller for synchronous generators based on a combination of backstepping and sliding mode control methods is presented in this paper. The proposed controller is designed to enhance the power system stability and voltage and frequency regulation of an electric power system. This strategy is capable of achieving the desired dynamic performances and guaranteeing that the closed-loop system is transiently stable. Simulation results show better transient behavior of the proposed nonlinear controller as compared with the conventional backstepping strategy and an immersion and invariance (I&I) strategy. In addition, they can accomplish transient stability enhancement together with frequency and voltage regulation despite large disturbances.

Non‐linear adaptive coordinated controller design for multimachine power systems to improve transient stability

Based on an adaptive backstepping approach, this study proposes a new coordinated control design where the coordination is done between the excitation controller of synchronous generators and steam-valve controller of turbine-governor systems in a multimachine power system by considering the critical parameters of both systems as unknown. This new coordinated control scheme can ensure the stability of multimachine power systems through the formulation of control Lyapunov functions (CLFs) and derive the adaptation laws to estimate the unknown parameters in the design process to prove the convergence of power systems using CLFs. The performances of the proposed control scheme are evaluated on a two-area four-machine 11-bus power system under different operating conditions such as three-phase short-circuit faults along with changes in loads. Simulation results are then compared with those of a similar controller where there is no coordination between the excitation and steam-valve controllers as well as with a coordinated sliding-mode controller. The results clearly show the effectiveness and superiority of the proposed control scheme.

Wide-range reliable stabilization of time-delayed power systems

Steam valve control is usually discarded in power system stability due to belief in its slow response. The present manuscript makes use of it as a backup control in the case of failure of the main fast excitation control. The model describing system dynamics as a function of the two controllers, with wide range loading conditions, is derived in a norm-bounded format. Linear matrix inequalities are derived as a sufficient condition to obtain reliable controllers that provide good oscillation damping when both controllers are sound or even in the case of failure of either one. The design scheme is robust in the sense that it keeps reliable stability against wide load changes as well. A single machine innite bus system is presented to illustrate the proposed design procedure and exhibit its performance. Results of excitation and governor controller testing show that the desired performance could be fullled from light load to heavy load conditions. System performance shows a remarkable improvement of dynamic stability by obtaining a well-damped oscillation time response even in the case of failure of either controller. Extension of the proposed controller to multiarea load-frequency control with time delay is also presented.

Coordinated excitation and steam valve control for multimachine power system using high order sliding mode technique

This paper presents a decentralized coordinated excitation and steam valve adaptive control combined with a high-order sliding mode differentiator. The aim is to obtain high performance for the terminal voltage and the rotor speed simultaneously under a sudden fault and a wide range of operating conditions. The methodology adopted is based on second order sliding mode technique using the supper twisting algorithm. The proposed scheme requires only local information on the physically available measurements of relative angular speed, active electric power and terminal voltage with the assumption that the power angle and mechanical power input are not available for measurement. It can be implemented locally and dispersedly for individual generators and is convenient for industrial applications. Simulation results in the case of the Kundur 4-machines 2-area power system show the effectiveness, robustness and superiority of the proposed scheme over the classical AVR/PSS controller and steam valve PI regulator.

Coordinated Switching Control of the Excitation and Steam Valve System Based on State and Input Constraints

A single unit infinite system of the excitation and steam valve control was proposed based on Barrier Lyapunov theory of restrictive log type. The input amplitude constraint of the steam valve control was considered, and the coordinated nonlinear backstepping controller was designed by switching mechanism. At the same time, the generator rotor effect was considered to be an external unknown large disturbance on the output system, and the conservativeness of the simple estimates for the upper and lower bounds and scaling disturbance was reduced by Minimax. The Minimax method also ensured that the output of the controller and the power angle were within the prescribed range and inhibited the system output effect of disturbance as much as possible. Finally, simulation results of the generator disturbance of mechanical power in the single unit infinite system show that the control scheme effectively improves the transient stability of the dynamic processes of power systems.

Sliding Mode Control for the Synchronous Generator

Based on the Lyapunov stability theorem and sliding mode control technique, a design of the nonlinear controller is proposed for the dual-excited and steam-valving control of the synchronous generators with matched and mismatched perturbations in this paper. By using some constant gains designed in the sliding surface function, the perturbations in the power system can be suppressed, and the property of asymptotical stability of the rotor angle and the voltage can be achieved at the same time.

Nonlinear adaptive control for multi-machine power systems with boiler-turbine-generator unit

Summary This paper studies the stability of multi-machine power systems via simultaneous design of boiler fuel flow control, turbine main steam valve control and generator excitation control for the boiler-turbine-generator unit. Because the whole system is coupled among generators and has multi-parametric uncertainties, the decentralized adaptive coordinated controller design is considered and is based on the adaptive backstepping method. Moreover, in addition to the transient stability of the power angle and power oscillation, the voltage regulation is also an important property in power systems. Thus, the global control technique is used to simultaneously ensure both the transient stability and the voltage regulation. Furthermore, we improve the transient performance of power systems greatly by introducing the state-constrained control. Simulation results show the effectiveness and advantage of the proposed controller. Copyright © 2014 John Wiley & Sons, Ltd.

Whole-Range Nonlinear Large Disturbance Attenuation Controller Design for Turbo Generator Steam Valve Systems

For a class of strongly nonlinear reheat-type turbo generator steam valve control problem, a whole-range nonlinear adaptive large disturbance attenuation control scheme is investigated based on the Minimax and adaptive Backstepping method. The effect of unknown external disturbances on the rotor angle and the rotor speed of the generator are considered. The Minimax method is used to reduce effectively the conservativeness of the disturbance treatment, which is brought by the estimation of the upper bound of the disturbance and the inequality scaling. The purpose is to ensure the robustness and insensitivity to effects of large disturbances of the closed-loop system. By considering the effect of the short-circuit ground fault and the mechanical power of disturbances, an application of the single-machine infinite-bus system is researched. Simulation results show that the control scheme can effectively improve the dynamic process of the transient stability of the power system. Compared with the conventional nonlinear controller, the control scheme has more advantages for large disturbances, and the process of controller design is simple and intuitive.

Immersion and invariance-based nonlinear dual-excitation and steam-valving control of synchronous generators

Summary This paper focuses on designing the nonlinear dual-excited and steam-valving control of synchronous generators to enhance the system stability and voltage regulation of an electrical power system. Based on the concept of immersion and invariance technique, the resulting nonlinear controller is used to not only achieve power angle stability, frequency, and voltage regulation but also ensure that the closed-loop system is transiently and asymptotically stable. In order to show the effectiveness of the proposed controller design, numerical simulation results are provided to illustrate the performance of the proposed controller capable of keeping the system transiently stable and simultaneously accomplishing the system stability and voltage regulation improvement in spite of large disturbances and network changes. Copyright © 2013 John Wiley & Sons, Ltd.

Sliding Mode Control for the Dual-Excited and Steam-Valving Control of Synchronous Generator

Based on the sliding mode control (SMC) technique, a design of the sliding surface for the dual-excited and steam-valving control of the synchronous generators with matched and mismatched perturbations is proposed in this paper. By utilizing some constant gains designed in the sliding surface function, not only are the mismatched perturbations overcomed during the sliding mode, but also the property of asymptotical stability of the rotor angle and the voltage is achieved at the same time. Simulations have demonstrated that the control scheme is robust against the disturbances.

A family of robust adaptive excitation controllers for synchronous generators with steam valve via Hamiltonian function method

Using the Hamiltonian function method, this paper proposes a family of robust adaptive excitation controllers for synchronous generators with steam valve control. First, a parameterization method of robust adaptive controllers is investigated for dissipative Hamiltonian systems. This method avoids solving Hamilton-Jacobi-Issacs inequalities. The parameters in the family of controllers thus obtained are determined by a locally positive semidefinite function, which has only 2n independent variables, twice as many as the one used to characterize the state feedback. Then, with the parameterization method and the structural properties of dissipative Hamiltonian systems, a family of robust adaptive excitation controllers is designed for synchronous generators with steam valve control, disturbances and unknown parameters. Simulations illustrate the effectiveness and feasibility of the excitation control strategy proposed in the paper.

A novel adaptive backstepping design of turbine main steam valve control

The problem of transient stability for a single machine infinite bus system with turbine main steam valve control is addressed by means of a novel adaptive backstepping method in this paper. The recursive design procedure of the proposed controller is much simpler than that of the existing controller based on conventional adaptive backstepping method. In the system, the damping coefficient is measured inaccurately, and the reactance of transmission line also contains a few uncertainties. A nonlinear robust controller and parameter updating laws are obtained simultaneously. The system does not need to be linearized, and the closed-loop error system is guaranteed to be asymptotically stable. The design procedure and simulation results demonstrate the effectiveness of the proposed design.

New Coordinated Control Design for Thermal-Power-Generation Units

A nonlinear model combining boiler-turbine-generator dynamic characteristics for a thermal-power-generation unit is first introduced. Based on the nonlinear model, a new coordinated control design is proposed using the backstepping method incorporating the coordinated passivation approach that considers the entire boiler-turbine-generator system as a whole. The control design consists of three subcontrollers, namely, a main steam valve controller, an excitation controller, and a fuel flow controller. It is shown that the proposed coordinated control design can ensure asymptotical stability of the closed-loop system and improve the electric power regulation performance. Simulation results based on a practical thermal-power-plant model are presented to show the effectiveness of the proposed control design.

Extended backstepping approach for a class of non-linear systems in generalised output feedback canonical form

In this study, an extended backstepping approach is developed for tracking control of a class of systems that are globally diffeomorphic into systems in generalised output feedback canonical form. Output-dependent non-linearities are allowed to enter such a system both additively and multiplicatively. The system contains unknown parameters multiplied by output-dependent non-linearities. This method relies on a parameter estimator and state observer design and standard backstepping construction. Compared with the traditional parameter estimation and state observation, the approach in this study has three distinct features due to adopting the new adaptive mechanism recently developed in literature. First, the parameter estimator and state observer does not follow the classical certainty equivalent principle. Second, the design treats the unknown parameter estimation and unmeasured state observation in a united way. Third, unlike the conventional observer-based backstepping, the design does not require the construction of Lyapunov function for every augmented sub-system. Furthermore, the method is applied to the stabilisation of single-machine-infinite-bus power systems with steam valve control using only measurements of the power angle as an illustrative example. A typical example is also given to show that the proposed method can be applied to more general systems which violate the cascading upper diagonal dominance conditions.

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.