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This paper presents a disturbance observer-based robust backstepping load-following control (DO-RBLFC) scheme for modular high-temperature gas-cooled reactors (MHTGRs) in the presence of actuator saturation and disturbances. Based on reactor kinetics and temperature reactivity feedback, the mathematical model of the MHTGR is first established. After that, a DO is constructed to estimate the unknown compound disturbances including model uncertainties, external disturbances, and unmeasured states. Besides, the actuator saturation is compensated by employing an auxiliary function in this paper. With the help of the DO, a robust load-following controller is developed via the backstepping technique to improve the load-following performance of the MHTGR subject to disturbances. At last, simulation and comparison results verify that the proposed DO-RBLFC scheme offers higher load-following accuracy, better disturbances rejection capability, and lower control rod speed than a PID controller, a conventional backstepping controller, and a disturbance observer-based adaptive sliding mode controller.

Waterjet propulsion is increasingly used in both combat and civil ships. In this study, a mechanism analysis-based modelling approach of a dual-waterjets propulsion steering system is presented. Experiments carried out on an experimental platform are used to validate the model system. Then a model-based synchronous control strategy for the dual-waterjets propulsion steering system is developed. The experiment results show that the model-based proportional–integral synchronous control strategy may reduce the synchronization error significantly compared with the reciprocal of the synchronization error driving synchronous control strategy practised on some small ships.

It is well known that the model of nuclear reactors features natural nonlinearity, and variable parameters during power tracking operation. In this paper, a disturbance observer-based adaptive sliding mode control (DOB-ASMC) strategy is proposed for power tracking of the pressurized-water reactor (PWR) in the presence of lumped disturbances. The nuclear reactor model is firstly established based on point-reactor kinetics equations with six delayed neutron groups. Then, a new sliding mode disturbance observer is designed to estimate the lumped disturbance, and its stability is discussed. On the basis of the developed DOB, an adaptive sliding mode control scheme is proposed, which is a combination of backstepping technique and integral sliding mode control approach. In addition, an adaptive law is introduced to enhance the robustness of a PWR with disturbances. The asymptotic stability of the overall control system is verified by Lyapunov stability theory. Simulation results are provided to demonstrate that the proposed DOB-ASMC strategy has better power tracking performance than conventional sliding mode controller and PID control method as well as conventional backstepping controller.

The uncertainty and disturbance estimator (UDE)-based robust control is extensively investigated for its merits of strong robustness and straightforward principle. However, the structural constrain...

Grid voltage parameters, including the amplitude, frequency and phase angle, are the essential information for the control and protection of power systems. The sinusoid-locked loop (SLL) is a novel approach to estimate the grid voltage parameters, which achieves accurate estimation and strong robustness in the presence of harmonic disturbances. However, the conventional SLL is sensitive to large voltage variations or computation errors, which may fail to achieve accurate estimation when the controller is trapped in the undesired equilibrium. In this paper, a modified sinusoid-locked loop (MSLL) is designed to improve the estimation performance with respect to large voltage variations. A virtual stator impedance is introduced to eliminate the undesired equilibrium, which mimics the armature reaction of a virtual synchronous machine (VSM). In addition, the closed-loop stability is investigated based on the small-signal model of the proposed MSLL. Following the idea of the VSM, the output voltage of the VSM is locked with the input grid voltage when the real power and reactive power are both driven to zero. Simulation and experimental results are presented to illustrate the effectiveness of the proposed MSLL, which achieves excellent estimation performance in the presence of large voltage variations and harmonic disturbances.

The boiler-turbine system (BTS) is usually subject to the tight input constraint, the strong nonlinearity and the complex disturbance, which makes the control a challenging task To this end, a disturbance observer based fuzzy model predictive control (DOBFMPC) scheme is proposed for the BTS in this paper. The generalized discrete-time nonlinear disturbance observer (GDNDO) is first developed to estimate the higher-order disturbance by systematically extending the conventional nonlinear disturbance observer. The GDNDO exhibits a series structure of the internal states, and can precisely estimate the disturbance if its order is equal to or greater than that of the disturbance In addition, a baseline fuzzy model predictive control (FMPC) law is synthesized on the fuzzy model. With FMPC, the asymptotic stability is guaranteed, and meanwhile the input constraints are satisfied by both the free control variables and the future control inputs in the form of the state feedback law. At last, the disturbance estimate and the FMPC are applied to constitute the DOBFMPC law. With the proper design of the disturbance compensation gain, the disturbance influence is removed from the output channels by the composite DOBFMPC law at the steady state. Simulations for a 300 MW subcritical BTS well demonstrate the effectiveness of the proposed control scheme.

This paper proposes a disturbance-observer-based fuzzy model predictive control (DOBFMPC) scheme for the nonlinear process subject to disturbances and input constraints. The proposed control scheme is composed of the baseline fuzzy model predictive control (FMPC) law designed on the Takagi–Sugeno fuzzy model and the disturbance compensation law. To build a fuzzy model of appropriate complexity and accuracy for the nonlinear process model, a systematic approach is developed via the gap metric to determine the linearization points. With FMPC, the asymptotic stability is theoretically proved, and the input constraints are satisfied by both the free control variables and the future control inputs in the form of the state feedback law. The disturbance compensation gain is designed such that the influence of the disturbance is removed from the output channels by the composite DOBFMPC law at the steady state. The application to a subcritical boiler–turbine system demonstrate the effectiveness of the proposed control scheme.

In thermal power plants, air preheaters are used to preheat the combustion air with residual thermal energy of the flue gas. The air leakage from air to flue gas has negative impact on the heat transfer efficiency of air preheaters and the unit thermal economy. This paper proposes an online applicable approach to estimate the direct leakage of the air preheater based on temperature distribution modeling. To describe the heat transfer process in the air preheater, energy balance equations are established after discretizing the air preheater into a number of heat transfer units, where the unstable heat transfer caused by the rotor rotation is considered. The temperature distribution of the air preheater is obtained through iterative calculation of these energy balance equations. By solving the optimization problems with the objective to meet the conservation laws of mass and energy, the direct leakage of the secondary air and the primary air is estimated. Pseudo-online simulations are carried out with the history data of a 300 MW subcritical unit to verify the approach. The updating period of the calculation results is set to 30 s so that the proposed approach may be applied for online monitoring purposes.

The uncertainty and disturbance estimator (UDE)-based robust control approach is widely investigated and applied due to its excellent performance and simple implementation. However, its stabilisability of unstable systems has not been documented. In this study, the sufficient and necessary stabilisability conditions of the UDE-based robust control are investigated. According to the stabilisability conditions, a systematical design method is presented for the reference model based on the controllable canonical transformation and pole placement. This is then applied to a magnetic levitation system (MagLev) subject to model uncertainties and external disturbance as an example. Simulation results are presented to illustrate the effectiveness of the proposed control approach with respect to matched uncertainties.

Grid voltage parameters are essential for the real-time control and protection in power systems. Current approaches mainly focus on the phase-locked loop methods, but which are slow and sensitive to voltage variations and disturbances. In this paper, the estimation of grid voltage parameters is recast as an observer design problem. A second-order sliding mode observer (SMO) is designed to estimate the grid voltage parameters based on the exosystem model. Moreover, the asymptotic stability of the closed-loop SMO is proved. Simulation and experimental results are presented to illustrate the effectiveness of the proposed approach, which achieves fast response and accurate estimation

The DC–DC power converter plays an important role in solar systems to provide the stable DC bus voltage, but which is easily subject to various uncertainties and disturbances in practical operation. In this paper, an uncertainty and disturbance estimator (UDE) based sliding mode control approach is applied to improve the performance of power converters. The UDE is designed for the estimation of both the matched and mismatched uncertainties. To address the mismatched uncertainties, an adaptive sliding mode function is constructed with the compensation of the estimated uncertainties, which renders a chattering-free robust control law. Simulation and experimental results illustrate that the proposed control scheme achieves good dynamic performance, strong robustness and chattering reduction in the presence of uncertainties and disturbances

Maneuverability is one of the most important sailing performances of vessels. In this article, a motion control model with three degrees of freedom (DoFs) for twin-waterjet propulsion vessel is proposed. The model is developed on the basis of maneuvering model group (MMG) maneuverability equations. A simulation environment is constructed on the Matlab Simulink platform. Standard turning tests and zig-zag tests are simulated by solving the motion control model, and the corresponding maneuverability parameters are calculated. Simulation results demonstrate that the maneuverability parameters are in accordance with the vessel maneuverability standard. The approach may be applied to the rapid prediction of vessel maneuverability.

As higher requirements are proposed for the load regulation and efficiency enhancement, the control performance of boiler-turbine systems has become much more important. In this paper, a novel robust control approach is proposed to improve the coordinated control performance for subcritical boiler-turbine units. To capture the key features of the boiler-turbine system, a nonlinear control-oriented model is established and validated with the history operation data of a 300 MW unit. To achieve system linearization and decoupling, an adaptive feedback linearization strategy is proposed, which could asymptotically eliminate the linearization error caused by the model uncertainties. Based on the linearized boiler-turbine system, a second-order sliding mode controller is designed with the super-twisting algorithm. Moreover, the closed-loop system is proved robustly stable with respect to uncertainties and disturbances. Simulation results are presented to illustrate the effectiveness of the proposed control scheme, which achieves excellent tracking performance, strong robustness and chattering reduction.

The T-junction configuration is a classical test case for thermal fatigue phenomena. Turbulent penetration and unsteady thermal stratification can occur when hot and cold fluids mix in T-junction pipes at NPPs, which may lead to time-varying thermal stress and even induce thermal fatigue failure. In this paper, mock-up experimental and analyses were conducted to develop a new method to calculate the wall temperature fluctuations of mixing T-junction pipes only by the temperature and velocity information of the fluid in branch and main pipe. The experimental results prove the effectiveness of this new method.

The flue gas temperature is an important parameter for safe and economic operation of thermal power plants. However, in high temperature areas, it is difficult to measure the temperature directly because the sensors are subject to flying ash erosion. This paper establishes a dynamic heat transfer model for the furnace and the semi-radiative heat exchangers, and proposes an estimation approach of the flue gas temperature in the boiler’s horizontal flue. The boiler-side heat absorption models, which cover the heat exchangers, the metal wall and the heat losses are established to calculate the heat absorption rate of the working fluid in the boiler. By solving the optimization problems which are developed based on the dynamic heat transfer models, the flue gas temperature at the outlet of the furnace and the semi-radiative heat exchangers are obtained. Pseudo-online simulations are performed with the history data of an ultra-supercritical unit to verify the approach. The relative errors between the calculated and the designed flue gas temperature with both designed and calibrated feed coal are found less than 3.5%. Additionally, the proportion of the convective heat in the total heat absorption for each semi-radiative heat exchanger is obtainable with the same approach.

The operation conditions of the cold-end system have significant impact on the unit thermal economy. However, due to the difficulty of online determination of some key parameters, the condenser pressure optimization has been a challenging task for a long time. This paper proposes an online applicable approach to optimize the condenser pressure with variable speed pumps, taking the mass flow rate of the circulating water as the manipulating variable, to achieve better thermal economy. After the exhaust steam wetness fraction is online identified, the condenser thermodynamic characteristics under varying working conditions are investigated based on the effectiveness and steady-state energy balance of the condenser. By maximizing the net power benefit, defined as the difference between the unit power increment and the pump power consumption increment, the optimal mass flow rate of the circulating water is derived. To validate the approach, pseudo-online simulations are conducted with the history data from an ultra-supercritical unit. The retention time during which the set value of the mass flow rate of the circulating water remains constant is studied in context with the implementation of the manipulation strategy under on-site scenario. Simulation results reveal the energy-saving potential of condenser pressure optimization with the proposed approach.

The load following of nuclear power plants (NPPs) has been a contentious issue in the control field. In this paper, we propose a chattering-free higher order sliding mode control scheme with a high-gain observer for the load following of a pressurized water reactor (PWR) in the presence of lumped disturbances owing to model uncertainties and external disturbances. The mathematical model of the PWR system is first set up in the form of an affine nonlinear equation. Subsequently, a high-gain observer, which achieves accurate estimations of the unmeasured state and lumped disturbances, is designed. Based on the outputs of the high-gain observer, we develop a chattering-free higher order sliding mode controller to improve the load-following performance while dealing with lumped disturbances and estimation errors of the high-gain observer. In contrast to some previous sliding mode controllers for the load following of NPPs, the proposed controller is completely free from chattering effects because the control input is obtained after integration. The asymptotic stability of the overall control scheme is demonstrated by combining the Lyapunov stability theory with backstepping technology. Finally, the simulation results reveal that the maximum absolute power error is less than 1 × 10 4 W with the proposed control scheme, 5 × 10 5 W with a PID controller, and 4 × 10 5 W with a conventional sliding mode controller. In addition, in contrast to the conventional sliding mode controller, the proposed control scheme produces smooth control input without the chattering phenomenon. Thus, the proposed chattering-free higher order sliding mode control scheme with a high-gain observer provides smoother control input, higher load-following accuracy, and stronger robustness against lumped disturbances than the PID controller and the conventional sliding mode controller.

Online performance monitoring is crucial for the safe and economical operation of thermal power plants. In this study, dynamic models of the whole process are established for the subcritical coal-fired power plant in terms of thermodynamic balances, which covers both boiler-side and turbine-side processes. Based on the whole process models, a monitoring platform is constructed with the functions of online estimation of key state variables and performance evaluation of the unit. The evaluation results of the unit efficiency with the time period of every 5 s may be provided. Model validations are carried out with the history operation data derived from the distributed control system (DCS) of a real 300 MW power plant. Comparisons between the simulation results and designed values of the unit demonstrate the high accuracy of the whole process models. The monitoring platform may also play the role as an offline simulator for the purpose of double check of the unit’s operation during specific time period and accidental cases.

The evaporation system of the ultra-supercritical power plant is characterized with a once-through steam generator. Modeling of such evaporation system is of extreme importance for the purpose of efficiency assessment and operation optimization. There still exist some major problems in the modeling because of the complexity of the phase transitions in the evaporation system at different loads. This paper establishes a moving segment model (including subcooled water, saturated two-phase and superheated steam segments) based on the mass and energy conservation principles under the subcritical and supercritical working conditions, and proposes a solution algorithm to deal with working condition switching in an automatic mode. Pseudo-online simulations are performed to test the model and the algorithm by using the geometric parameters and the history operation data of a real ultra-supercritical unit in China. The calculated heat absorption rate of the working fluid from the entire evaporation system agrees well with the reference value. The maximum absolute relative error is found as small as 0.54% in the time resolution of 30 min, which indirectly demonstrates the feasibility and accuracy of the presented model and the solution algorithm.

This paper proposes a practical data-driven method to model the nodal water pressure transfer of urban water distribution network (WDN) systems. The suitable upstream-downstream node pairs are found out by correlation analysis of the nodal water pressure measurements and corresponding wavelet coefficients at level 3. To quantify the pressure transfer relation of each pair, we construct a linear model respectively. This method could be used in large-scale WDNs for which there is incomplete pipe network information. Real pressure data of a big city in the east of China are used to validate the proposed method. The simulation results show that the MAPE is less than 4.1%, which supports the potential implementation of this method for real operation.

Efficient and stable operation of marine diesel engines is crucial both for navigation maneuverability and safety of waterjet propulsion vessels. In this paper, a piecewise linear model and an affine nonlinear model of marine diesel engines are established by applying mechanism analysis techniques. The models are validated with the experimental data collected from a 290 kW (maximum power) diesel engine equipped on a waterjet propulsion vessel. The relative error of engine speed between model simulation and the measurements is found less than 3%. To improve the performance of the speed regulation system of diesel engines, a sliding mode control strategy is developed on the basis of the affine nonlinear model utilizing the equivalent control method. Simulation results are presented to illustrate the effectiveness of the proposed control strategy regarding model mismatch, response speed, disturbance rejection, and engine speed tracking ability.

Load following is one of the basic control task for nuclear power plants. This paper proposes a RBF-based adaptive sliding mode control strategy with extended state observer (ESO) for load following of nuclear power plants in the presence of disturbances. The nonlinear mathematical model of the nuclear reactor system is firstly described. In order to recover unmeasured states including average fuel temperature and relative delayed neutron precursor density, an extended state observer is designed to reconstruct both unmeasured states and disturbances at the same time, and its asymptotically stability condition is analyzed. Based on the nuclear reactor model and estimation information from the ESO, a RBF-based adaptive sliding mode control strategy is proposed, which consists of a dual closed-loop integral sliding mode control scheme while taking into account disturbances simultaneously. In addition, the chattering phenomenon of sliding mode control is alleviated by replacing the sign function with a saturation function. Simulation results are provided to verify the effectiveness of the overall control scheme compared with conventional PID control and sliding mode control approaches in accordance to load following performance, states reconstruction accuracy, and disturbances rejection ability.

Grid voltage parameters, including the amplitude, frequency and phase angle, are crucial information for real-time control and protection in power systems. Currently, the phase-locked loop methods are widely used for voltage parameters estimation. However, they could hardly achieve accurate estimation in the presence of unbalanced grid voltage and harmonic disturbance. In this paper, a novel three-phase sinusoid-locked loop (SLL) approach is proposed to address the estimation issue of the unbalanced grid voltage parameters. Firstly, the unbalanced three-phase grid voltage is decomposed as the positive and negative sequences based on the instantaneous symmetrical components theory. Then, two SLLs based on the principles of the virtual synchronous machine (VSM) are developed for the positive and negative sequence grid voltages, respectively. Following the idea of SLL, the output voltage of the VSM is locked with the input grid voltage when the real power and reactive power are both driven to zero. Eventually, the unbalanced three-phase grid voltage is reconstructed with the estimated parameters of the positive and negative sequence voltages. Simulation results demonstrate that the proposed SLL approach achieves excellent estimation performance with respect to the unbalanced grid voltage.

T0620. The gap metric is applied to investigate the nonlinearity of the boiler-turbine system to determine the linearization points for nonlinear model such that a Takagi-Sugeno fuzzy model of appropriate accuracy and complexity is obtained. The FAMPC is then designed based on the fuzzy model that is online updated to well approximate the nonlinear dynamics. The fuzzy model is validated with the plant data of a 300 MW unit and the result shows good agreement. The simulation cases demonstrate the proposed controller has good tracking performance and strong robustness.

Grid voltage parameters, including the amplitude, frequency and phase angle of the grid voltage, are essential for real-time control and protection in power systems. Current approaches mainly focus on adopting a phase-locked loop or its derivatives for parameters estimation. However, they could hardly achieve fast response and are sensitive to voltage variations and disturbances. In this paper, the estimation of grid voltage parameters is recast as an observer design problem. An exosystem model of the sinusoidal voltage is established at first. Then, a framework for the observer-based methods is proposed for the robust estimation of single-phase grid voltage parameters. Moreover, a second-order sliding mode observer (SMO), which actually has the lowest order among all possible observers, is designed to estimate the parameters. Based on the Lyapunov theory, the asymptotic stability of the closed-loop SMO is proved. Compared with two other typical methods, simulations are carried out to illustrate the effectiveness and robustness of the proposed approach in the presence of voltage variations and external disturbances. In addition, the proposed estimation approach may also be valuable for online fault detection of voltage sag and low-frequency oscillation.

In this paper, a method to estimate the target value of terminal temperature difference of horizontal three-segment feed water heater under various working conditions is proposed. The temperature of the water at the outlet of the condensation segment is obtained through mass and energy balance on the basis of actual extracted steam flow rate. Then by means of energy balance equation and heat transfer efficiency equation, the temperature of the outlet water at maximum heat transfer efficiency is calculated, thus obtaining the terminal temperature difference target value. Results based on offline operation data of a real 1000 MW supercritical power plant are given and the difference between target value and actual operation value could be used to estimate the loss differential of the terminal temperature difference.

As more stringent requirements are proposed for the load and frequency regulation in modern power grid, the performance of load tracking and main steam pressure stability becomes more important for the safe and economical operation of thermal power plants. In this paper, a new nonlinear control-oriented model of drum boiler-turbine system is developed with a balance between fidelity and simplicity, and validated with history operating data from a real 300 MW subcritical coal-fired unit over wide range. Then, feedback linearization is applied to the nonlinear model, resulting in two independent linear subsystems. Moreover, a sliding mode tracking controller is constructed for coordinated control based on the linearized model. Simulation results are presented to demonstrate the good tracking performance and strong robustness of the proposed approach.