Dynamic integral sliding mode control for interconnected delayed power systems

Robust tracking of the heating value in an underground coal gasification process using dynamic integral sliding mode control and a gain-scheduled modified Utkin observer

Conventional control techniques such as proportional integral (PI) control and proportional integral derivative (PID) control are widely used as the load frequency controller in power system control applications; however, the increase in complexity of the power system is degrading the performance of classical control. Therefore, in this paper a new control approach using fractional calculus has been proposed for the load frequency control problem of two-area hydro-thermal power system. The paper presents an interconnected hydro-thermal power system working under different operating conditions introduced in the form of various nonlinearities. Four case studies have been presented in this paper considering transient analysis with (i) different loading conditions, (ii) parameter variations, (iii) different nonlinearities (governor dead band nonlinearity, time delay and generation rate constraints), and (iv) superconducting magnetic energy storage (SMES) device. A tilt integral derivative (TID) control has been presented as a secondary controller to stabilize the frequency deviations occurring in the two-area power system with the above-mentioned different operating conditions. The parameters of TID controller have been optimized using a differential evolution algorithm which solves an optimization problem formulated using the integral of time-weighted absolute error (ITAE) performance index. In addition, a comparison of dynamic system response obtained using TID control and PID control has been presented, which focusses on the better performance of TID control over PID control in an interconnected power system.

In industry or any area increasing load is a vast problem for power generation plants due to increase in demand for power. So making balance between generation and demand is the operating principle of load frequency control (LFC). The reliable operation of a large interconnected power system necessarily requires an Automatic Generation Control (AGC). The objective of AGC is to regulate the power output of Generators within a specified area in response to change in the system frequency, tie line power or relation of the two to each other, so as to maintain the scheduled system frequency and power interchange in the other are within the prescribed limits. This paper presents the use of conventional PI controller and artificial intelligence to study the load frequency control of interconnected power system. In the proposed scheme, a control methodology is developed using conventional PI controller and Fuzzy Logic controller (FLC) for interconnected hydro-thermal power system. The control strategies guarantees that the steady state error of frequencies and inadvertent interchange of tie-lines power are maintained in a given tolerance limitations. The performances of the controllers are simulated using MATLAB/SIMULINK package. A comparison of Fuzzy controller and PI controller based approaches shows the superiority of proposed Fuzzy logic controller for step change in loading conditions. The simulation results also tabulated as a comparative performance in view of settling time and peak over shoot.

The load frequency control (LFC) problem in interconnected multiarea power systems is facing more challenges due to increasing uncertainties caused by the penetration of intermittent renewable energy resources, random changes in load patterns, uncertainties in system parameters and unmodeled system dynamics, leading to a compromised reliability of power systems and increasing the risk of power outages. In responding to this problem, this paper proposes a decentralized disturbance observer-based sliding mode LFC scheme for multiarea interlinked power systems with external disturbances. First, a reduced power system order is constructed by lumping disturbances from tie-line power deviations, load variations and the output power from renewable energy resources. The disturbance observer is then designed to estimate the lumped disturbance, which is further utilized to construct a novel integral-based sliding surface. The necessary and sufficient conditions to determine the tuning parameters of the sliding surface are then formulated in terms of linear matrix inequalities (LMIs), thus guaranteeing that the resultant sliding mode dynamics meet the <i>H</i>_&#x221E; performance requirements. The sliding mode controller is then synthesized to drive the system trajectories onto the predesigned sliding surface in finite time in the presence of a lumped disturbance. From a practical perspective, the merit of the proposed control method minimizes the impact of the lumped disturbance on the system frequency, which has not been considered to date in sliding mode LFC design. Numerical simulations are illustrated to validate the effectiveness of the proposed LFC strategy and verify its advantages over other approaches.

A new cyber-security approach for load frequency control of hybrid interconnected renewable power systems

This paper proposes a novel load frequency control (LFC) approach formulated on an optimal structure of the coefficient diagram method (CDM) in a two-area thermal power system. As part of a realistic analysis, nonlinearities related to governor dead band (GDB) and generation rate constraint (GRC) have been considered. In this article, a hybrid CDM method is combined with the optimization of its mathematical equations to achieve an innovative controller. Furthermore, a new metaheuristic optimization technique called the water cycle algorithm (WCA) is used to determine the optimal coefficients of the CDM controller. For the purpose of demonstrating the validity of the proposed scheme, a wide range of uncertainties in the dynamic parameters of a nonlinear power system were tested. In addition, a comparative study is presented between the results obtained from a classical integral, CDM alone, optimized fuzzy, optimized PID, and the suggested controller. In this new approach to improved control, algebraic support provides a robust and responsive controller that can provide fast and stable dynamic responses and effectively overcome the detrimental effects of nonlinearities and uncertainties in the parameters of the power system.

The FACTS device like TCPAR can be used to regulate the power flow in the tie-lines of interconnected power system. When TCPAR is equipped with power regulator and frequency-based stabiliser it can also significantly influence the power flow in the transient states occurring after power disturbances. In the case of simple interconnected power system, consisting of two power systems the control of TCPAR can force a good damping of both power swings and oscillations of local frequency. In the case of larger interconnected power system consisting of more than two power systems the influence of the control of TCPAR on damping can be more complicated. Strong damping of local frequency oscillations and power swings in one tie-line may cause larger oscillations in remote tie-lines and other systems. Hence, using devices like TCPAR as a tool for damping of power swings and frequency oscillations in a large interconnected power system must be justified by detailed analysis of power system dynamics.

Stress on the generation and transmission capability of the power system increased as the energy demand increases. Distributed generation (DG), which is usually placed near the load centre has the capability to meet these energy increment in demands. Hence, for making the power system highly durable and reliable, Distributed generations are interconnected with the existing power system. Based on the nature of the primary source of generation and the energy conversion technology these types of generation have important impacts on power system voltage stability. One of the most significant threats considered for a secure operation of the power system is voltage instability problem. Voltage collapse might occur in an interconnected power system due to voltage instability and thus lead to power blackouts. Hence in an interconnected power system it is essential to know the strength of the buses to monitor and improve the stability of the system. This paper focuses on voltage stability analysis of an interconnected distributed photovoltaic system with IEEE 30 bus system. The voltage stability of the system assessed by evaluating voltage stability indicators at each bus of interconnected power systems. Fast Voltage Stability Index value of each bus is evaluated under normal and critical load conditions. The index value helps to identify the weakest or the bus which is likely to get voltage collapse due to voltage instability problem in the interconnected system.

In this paper, a robust high voltage direct-current (HVDC) wide-area time-delay damping control strategy is proposed to prevent the potential low-frequency power oscillation and enhance the power stability of HVDC/AC interconnected power systems. Firstly, the basic design concept and the related design flow are presented. Then, the general wide-area power system model with the time-delay characteristic is described by the linearization modeling method. The practical reduced-order algorithm is introduced to further obtain the reduced system state-space model that maintains the low-frequency oscillation mode. Furthermore, considering the inevitable time delay in the wide-area feedback control signals transmitted by the wide-area measurement system (WAMS), the improved linear matrix inequality (LMI) method is applied to design the robust supplementary damping controller associated to the HVDC converter pole-control. Such controller can efficiently suppress the negative effect of time delay of the wide-area control signals on the oscillation damping performance. In addition, the iterative algorithm is proposed to search the optimal overall gain matrix for the state feedback control, and the state observer is also designed based on the classic pole-placement method to realize the observability on the state variables of the reduced system. Finally, a case study on a benchmark system of small signal stability study is performed to validate the proposed HVDC wide-area time-delay damping control strategy.

Frequency control in interconnected electrical power systems is nowadays realized using the networks' conventional thermal power plants. With the ongoing changes in power systems worldwide the share of these conventional power plants is decreasing while renewable resources such as wind power and photovoltaics are increasing their share continuously. Up to now a contribution of renewable sources to primary frequency control is not realized in interconnected power systems. This paper describes possibilities to support the frequency of power systems using wind turbines with enhanced active power functionalities such as primary frequency control and synthetic inertia. The effects of these functionalities are analyzed in the IEEE 39 bus system. Different simulations with an implementation of these functionalities in a doubly fed induction generator wind turbine model show promising results. The frequency behavior of a 50 % penetrated system with standard wind power plants shows unfavorable frequency behavior compared to the original system, whereas a system with additional frequency supporting functionalities by wind power plants improves the frequency behavior significantly.

Power system oscillation is an unavoidable threat to the stability of an interconnected modern power system. The reliable operation of a modern power system is widely related to the dampening of electromechanical low‐frequency oscillations (ELFOs). These ELFOs must be dampened appropriately to maintain the stability and reliability of the system. However, it is relatively difficult to resolve the problem of ELFOs completely with traditional power system stabilizers (PSSs). Consequently, research should be directed towards the development of efficient damping controllers, or PSSs, for power oscillation damping. Motivated from the aforementioned fact, this article presents the design of a proportional integral derivative power system stabilizer (PID‐PSS) via a long short‐term memory neural network (LSTM) based deep neural approach for damping power system oscillations in interconnected power systems. LSTM is used to train the parameters of PID‐PSS. To evaluate the performance of the proposed LSTM based PID‐PSS, diverse test cases under different operating conditions are examined. Further, the performance of the proposed LSTM based PID‐PSS is compared with traditional PSSs through time‐domain simulations. The test cases reveal the desired efficiency achieved by the proposed LSTM based PID‐PSS under diverse loading conditions.

In this paper, the dynamical response of the load frequency control problem in an interconnected power system is improved with a pragmatic viewpoint. In practice, access to all the state variables of system is not possible and also their measurements are not feasible. Usually only a reduced number of state variables or linear combinations thereof, are available. To resolve this difficulty, in this paper optimal output feedback method is proposed which uses only the measurable state variables. The optimal control is determined by minimizing a performance index under the proposed output feedback conditions. The effectiveness of the method is demonstrated on the two equal area interconnected thermal power system. The results indicate that the proposed controller exhibits better performance. In fact, the control system designed on this method satisfies the load frequency control requirements with a reasonable dynamic response. The proposed method has several desirable properties such as good sensitivity and robustness behavior.

This study presents the application of non‐linear disturbance observer (NDO) for automatic generation control of interconnected thermal area power systems considering generation rate constraints. In this work, any change in electrical power arising in the system due to either load change or change in power output of intermittent renewable energy sources is called a disturbance. This disturbance is estimated using an NDO and the same is rejected by giving an equivalent command to the governor of thermal power units to maintain a power balance in the system; thereby maintaining frequency and tie‐line power flows in each area of an interconnected power system. The analysis is presented on a two‐area power system and it is shown that the proposed control scheme effectively mitigates any active power imbalance in the system not only for normal operations but also when there is large communication delay in the system. The key advantages of the proposed scheme not only include faster frequency and tie‐line power control but also reduced control efforts as compared to other established control schemes. Furthermore, the proposed scheme requires the optimisation of only one control parameter in each area. Therefore, the scheme gives away the requirement of complex optimisation algorithms.

In the category of small signal stability problem, one of the major causes of unpredictability of power transfer in the inter-connected power system is due to low frequency oscillations (LFO). These oscillations in the inter-connected power system, affects the power transfer capability and thereby, needed to be suppressed. To damp the oscillation and protect the power system, power system stabilizers are used. In this study, a Kho-Kho optimization (KKO) based proportional integral derivative (PID) power system stabilizer is put forward which can suppress the LFO in the inter-connected power system. Optimization methods are widely being used to solve number of optimization problem. Therefore, in this work the specification of the stabilizer are calibrated using KKO technique by optimizing a objective function constructed using the Integral time square error (ITSE) of the speed deviation. To test the effectiveness of the designed optimal controller, a one machine infinite bus (OMIB) with IEEE type DC-1 exciter unit is also taken into consideration. The superiority of the proposed technique is examined by comparing the obtained results with some other existing techniques.

Decentralized optimal controller design for multimachine power systems using successive approximation approach