Rotor Speed Deviation Research Articles

Wide-Area-Based Adaptive Neuro-Fuzzy SVC Controller for Damping Interarea Oscillations

Low-frequency interarea oscillation is a major problem in interconnected power systems with weak tie-lines that causes several stability problems if not damped. Fuzzy logic controller can generate human knowledge-based control rules to solve complex nonlinear problems. Unlike a neural network, fuzzy systems cannot learn from data, and it takes a long time to modify the membership functions. The adaptive neuro-fuzzy inference system (ANFIS) is a robust and intelligent system that integrates the capabilities of fuzzy logic and neural networks with several advantages such as adaptability, robustness, rapidity, and flexibility. In this paper, an ANFIS-based controller is proposed for controlling the reactive power provided by static var compensator to damp interarea oscillations. The controller input is a remote signal provided by a wide-area measurement system, and it is calculated as the center-of-inertia difference of generator rotor speed deviations. Moreover, a proportional-plus-derivative time-delay compensator with adaptive parameters is added to the controller to reduce the influence of time delay. A two-area four-machine test system is used and simulated with a Simulink-based package developed for the work of this paper. The time-domain simulations and frequency response analysis demonstrate the capability of the proposed controller to effectively damp interarea oscillations, under a small- and large-scale disturbances and against a wide range of time delays and load uncertainty.

Improvement of energy conversion efficiency and damping of wind turbine response in grid connected DFIG based wind turbines

This paper examines dynamic performance of DFIG based wind turbine regarding torsional electromechanical oscillations when the wind turbine is controlled in power control mode. In the power control mode, the stator active power is set to its reference value, where the reference active power is determined based on a predefined power-speed curve. Torsional oscillations associated with the poorly torsional modes may reduce the aerodynamic efficiency, deteriorate the power quality and increase stresses on the drive train system. The paper indeed analytically investigates the drive train dynamics for different operating regions of the power-speed curve. It is shown that under some operating points, torsional oscillations are well damped and the DFIG control improves the damping of torsional modes. On the other hand, at some regions of the power-speed curve, the DFIG control does not provide significant damping action on the torsoinal modes. Then a wind turbine stabilizer (WTS) is implemented to suppress torsional vibrations in the drive train system. The role of the WTS is to add positive damping to the generator rotor oscillations by controlling the active power and providing a component of electrical torque proportional to the rotor speed deviations.

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.

Synchronizing Torque Impacts on Rotor Speed in Power Systems

Renewables are increasingly replacing power from conventional generators. Renewable power injected through power electronic converters lacks the fundamental electric torque components. Electric torque components have an important role in determining the behavior of conventional machines in the network. The influence of this factor becomes more notable in power systems with reduced inertia. Hence, questions arise on, how can synchronizing torque basically contribute to the rotor speed deviation and eventually the system frequency and if there is a potential for using the steady state synchronizing torque coefficient (STC) to achieve acceptable frequency operating points. This paper calculates the steady state STC matrix by using the multimachine Heffron-Philips model in conjunction with the network admitance matrix. Accordingly, it investigates the impact of the generator location and reactive power output on the STC matrix. It demonstrates how this impact manifests in the generator rotor speed deviation. Eventually, the significance of the STC from the system frequency perspective is assessed.

Power-Smoothing Scheme of a DFIG Using the Adaptive Gain Depending on the Rotor Speed and Frequency Deviation

In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction generator (DFIG) that significantly mitigates the system frequency fluctuation while preventing over-deceleration of the rotor speed. The proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while preventing over-deceleration of the rotor speed, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system clearly demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WPP under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

Decentralized Synergetic Power System Stabilizer

This paper presents a decentralized synergetic power system stabilizer (DSPSS). The nonlinear control law was synthesized by introduction of invariant manifolds into the state space of studied system, synchronous machine connected to infinite bus. The invariant manifold was defined as a linear combination of the generator terminal voltage, rotor speed and active power deviation to achieve coordination of the synchronous generator electromechanical oscillation damping and terminal voltage control. Compared to other synergetic power system stabilizers, this one uses real time Park’s transformation to calculate dq-components of generator currents and voltages. Also, a novel approach for calculation of a generator voltage derivative is presented, and the proposed stabilizer is less sensitive to sudden voltage changes and measurement noise. DSPSS control law was implemented on real-time hardware platform and experimentally tested on an 83kVA synchronous hydrogenerator. Experimental results for the power and voltage reference step change, loss of the transmission line and three phase short circuit were conducted using DSPSS and PSS2A stabilizers. Furthermore, the results showed that the proposed DSPSS stabilizer was robust to system parameter changes and has better dynamic response than the classic PSS2A in case of small and large disturbances.

Mitigation of SSR with STATCOM using Subsynchronous Damping Controller on Series-Compensated Transmission Line

Objective: The phenomenon of Sub Synchronous Resonance (SSR) on series-compensated long transmission line with steam turbine generator results into adverse oscillations. Therefore, occurrence of SSR should be reduced to the lowest possible level. Method/Analysis: In this paper, the use of STATCOM and subsynchronous damping controller (SSDC) is proposed to alleviate SSR. The rotor speed deviation of generator is being captured and given to the STATCOM. The IEEE second benchmark model (IEEE SBM) on SSR is adopted to analyze and validate the proposed controller. For this, the controller is applied on STATCOM, which in turn is regulating the line. Findings: SSR generates due to the presence of frequency other than the nominal frequency in the system. By calculating frequency response and FFT analysis, the resonant frequency present in the system, is calculated. Then conventional STATCOM is applied, which shows that STATCOM with no auxiliary control is not capable of damping the SSR oscillations. But with auxiliary SSDC on same STATCOM, effectively mitigate the SSR. Novelty/Improvement: The SSR alleviation is done by conducting transient simulations using MATLAB environment on detailed three-phase model, which is non-linear in nature. Fast Fourier Transform (FFT) analysis is also performed to demonstrate the capability of proposed controller.

Recurrent ANFIS-Coordinated Controller Design for Multimachine Power System with FACTS Devices

This paper proposes the design of auxiliary-coordinated controller for static VAR compensator (SVC) and thyristor-controlled series capacitor (TCSC) devices by adaptive fuzzy optimized technique for oscillation damping in multimachine power systems. The performance of the coordinated control of SVC and TCSC devices based on feedforward adaptive neuro fuzzy inference system (F-ANFIS) is compared with that of the adaptive neuro fuzzy inference system (ANFIS) structure based on recurrent adaptive neuro fuzzy inference system (R-ANFIS) network architecture. The objective of the coordinated controller design is to tune the parameters of SVC and TCSC fuzzy lead lag compensator simultaneously to minimize the deviation of rotor angle and rotor speed of the generators. The performance of the system is enhanced by optimally tuning the membership functions of fuzzy lead lag controller parameter of the flexible AC transmission system (FACTS) by R-ANFIS controller. The training data for F-ANFIS and R-ANFIS are generated by conventional linear control technique under various operating conditions. The offline trained controller tunes the parameter of lead lag controller in online. The oscillation damping ability of the system is analyzed for three-machine test system by calculating the standard deviation and cost function. The superior performance of R-ANFIS controller is compared with various particle swarm optimization-based feedforward ANFIS controllers available in literature.

Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current (HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Co-Ordinated Multiloop Switching Control of DFIG for Resilience Enhancement of Wind Power Penetrated Power Systems

This paper proposes a co-ordinated four-loop switching controller (SC) for the doubly fed induction generator (DFIG) to improve the transient stability of wind power penetrated power systems. A short-term resilience index is introduced, and it reflects the dynamics of both system frequency and load bus voltage. A four-loop SC is driven by the four outputs of a DFIG, namely, the rotor speed deviation, the reactive power output of stator winding, the reactive power transferred through grid-side converter, and the DC-link voltage, respectively. Referring to a state-dependent switching strategy, the four-loop SC switches between a logic-based bang–bang constant funnel controller (LBCFC) and a vector control theory-based conventional controller (CC) in each control loop. The LBCFC is robust to system nonlinearities, uncertainties, and external disturbances. The control signal of the LBCFC is bang–bang with the upper and lower limits of control variables. Simulation studies are undertaken in a modified IEEE 16-generator 68-bus power system, in which four DFIG-based wind farms are penetrated to provide 9.94% power supply. The performance of the four-loop SC is evaluated in aspects of the integral control of the DFIG and the resilience enhancement of the multimachine power system, respectively.

Oscillation Energy Analysis of Inter-Area Low-Frequency Oscillations in Power Systems

Low-frequency inter-area oscillation is a potentially dangerous phenomenon in power systems involving exchange of power among generators in different areas. In this paper, we study the characteristics of inter-area oscillation by analyzing the distribution of the oscillation energy. First, we introduce equations for the kinetic energy of generators and the potential energy of network branches, derived from the linearization of system dynamic equations. Then, we study the mode composition and the distribution of the generators' kinetic energy during low-frequency oscillations. A modal kinetic energy participation factor is proposed for evaluating the participation of each generator in the oscillation. The relationships among electromagnetic power oscillation distribution, rotor speed deviation, and generator kinetic energy are analyzed and compared to their modal parameter left eigenvectors, right eigenvectors, and linear participation factors, respectively. The bus voltage angle deviation, active power oscillation, and branch potential energy are calculated using the right eigenvector from modal analysis. The distribution characteristics of voltage angle oscillation and branch potential energy in inter-area oscillation is developed. The simulation results for a four-generator two-area system and the New England 10-machine 39-bus system illustrate the feasibility and validity of the proposed theory and method for analysis of inter-area oscillations.

Modeling, simulation, and optimal design of power system stabilizers using ABC algorithm

This paper introduces a methodological system for modeling, simulation, and optimal tuning of the parameters of power system stabilizer (PSS) controllers in a multimachine power system so as to enhance transient stability. The model of a multimachine power system with PSS controllers is developed in MATLAB/Simulink for the simulation design. Simulink is a software instrument related to MATLAB, which is employed for modeling, simulating, and analyzing dynamical systems. The PSS controllers' design problem is expressed as an optimization problem; and the artificial bee colony (ABC) algorithm is utilized so as to examine the optimal PSS controller's parameters. The power system's transient stability performance is enhanced through diminishing a time domain-based objective function, where the oscillatory rotor speed deviation of the generator is obtained. The results of the nonlinear simulations substantiate the efficacy of the proposed modeling and tuning approach for power system stability enhancement. These outcomes likewise indicate that the proposed PSS controllers are operative in damping low frequency oscillations. In addition, comparing the ABC algorithm with the genetic algorithm method shows that better performance is achieved.

Low‐order controller design using remotely measured time delayed signals for stabilisation of equivalent power grid

This study discusses the use of time-delayed remote signals available through phasor measuring units (PMUs) for low-order controller design in order to stabilise the power oscillations in the range of 0.3–0.42 Hz between two areas. In the proposed approach, first synchronisation measures are determined among the group of generators located in two areas. Then, an index that characterises the joint observability and controllability property in terms of Hankel singular values is defined as a criterion to preselect the remote feedback signal. Following this, a low-order controller design based on minimisation of H ∞ norm is considered. The measurement redundancy is taken into account in controller design using rotor angle, power flow or speed deviation as feedback signal from one of the generators. Additionally, if some specific PMU fails to provide measurements from a chosen generator, then controller effectiveness is guaranteed using signal from other generator in the same area. The performance of controller is verified considering single-step and multi-step disturbances applied to the reference voltage of exciter system. The comparison with design functions such as H 2 norm, complex stability radius and spectral abscissa are also presented. The analytical results confirm using H ∞ design algorithm provides better dynamic performance.

Dynamic Stability Improvement of Multimachine Power Systems using ANFIS-based Power System Stabilizer

Modern power system are very vurnerable to against load fluctuation during their operation. Load fluctuation identified as small disturbance is important to test dynamic (small signal) stability. This research is focused on improvement of multimachine dynamic stability by using ANFIS-based power system stabilizer (proposed PSS). ANFIS method is proposed because the ANFIS computation is more efective than Mamdani fuzzy computation. Simulation results show that the proposed PSS is able to maintain the dynamic stability by decreasing peak overshoot (Po) to the value -3,37´10 -5 pu/pu and accelerating settling time (St) to the time 4.01 s for rotor speed deviation Machine-2. Also, the Po is decreased to the value -3,37´10 -5 pu/pu and the St is accelerated to the time 3.98 s for rotor speed deviation Machine-3.

Application of Turbine Torsional Oscillation Damping Controller to Static Var Compensator

This paper proposes a new auxiliary turbine torsional oscillation damping controller (TTODC) for static var compensator (SVC) to dampen out subsynchronous oscillations in power systems containing series compensated transmission lines. A new TTODC algorithm on the basis of synchronized phasor measurements received from phasor measurement units (PMUs) is presented. The idea of using remote signals obtained from PMU to dampen subsynchronous resonance (SSR) presented, too. An auxiliary TTODC is proposed for a SVC, using the generator rotor speed deviation signal as the stabilizing and remote signal to dampen subsynchronous oscillations. The performance of the controller is verified in a detailed nonlinear system considering eigenvalue analysis and transient simulations. Sturdiness of the controller is examined by applying the disturbances in the system that causes significant changes in generator's operating point. The IEEE second benchmark (SBM) model is used for the analysis and the SVC is simulated using the power system blockset (PSB) in the matlab/simulink environment.

Coordinated and uncoordinated design of LFO damping controllers with IPFC and PSS using ICA and SFLA

A single machine-infinite-bus (SMIB) system including the interline power flow controllers (IPFCs) and the power system stabilizer (PSS) controller is addressed. The linearized system model is considered for investigating the interactions among IPFC and PSS controllers. To improve the stability of whole system again different disturbances, a lead-lag controller is considered to produce supplementary signal. The proposed supplementary controller is implemented to improve the damping of the power system low frequency oscillations (LFOs). Imperialist optimization algorithm (ICA) and shuffled frog leaping algorithm (SFLA) are implemented to search for optimal supplementary controllers and PSS parameters. Moreover, singular value decomposition (SVD) method is utilized to select the most effective damping control signal of IPFC lead-lag controllers. To evaluate the system performance, different operating conditions are considered. Reponses of system in five modes including uncoordinated and coordinated modes of IPFC and PSS using ICA and SFLA are studied and compared. Considering the results, response of system without controller shows the highest overshoot and the longest settling time for rotor angel at the different operating conditions. In this mode of system, rotor speed has the highest overshoot. Rotor angel in the system with only PSS includes lower overshoot and oscillation than system without controller. When PSS is only implemented, rotor speed deviation has the longest settling time. Rotor speed deviation in the uncoordinated mode of IPFC and PSS shows lower overshoot than system with only PSS and without controller. It is noticeable that in this mode, rotor angel has higher overshoot than system with only PSS. The superiority of the suggested ICA-based coordinated controllers is obvious compared with SFLA-based coordinated controllers and other system modes. Responses of coordinated PSS and IPFC SFLA-based supplementary controllers include higher peak amplitude and longer settling time compared with coordinated IPFC and PSS ICA-based controllers. This comparison shows that overshoots, undershoots and the settling times are reduced considerably in coordinated mode of IPFC based controller and PSS using ICA. Analysis of the system performance shows that the proposed method has excellent response to different faults in power system.

Devising the law of automatic compensation for a failed engine in a going around plane

The paper presents a numerical simulation of an automatic go-around of an aircraft with a failed engine. When an engine fails, it reveals additional resistance force as well as entails unbalanced forces and moments at a roll and a yaw rotation. To quantify an automatic go-around of an aircraft with a failed engine, the value of the steady climb full gradient should not be lower than its minimum set point. Thus, for a four-engine airplane the minimum set value of the full steady climb makes up 2.7 %. An automatic go-around of an aircraft with a failed engine (with no regard to the failure compensation) is characterized by a decreased full gradient of the steady climb and the current gradient as well as a “sluggish” acceleration of the aircraft speed and climb. The synthesis of the law of automatic compensation for a failed engine is based on the principle of direct measurement of disturbances and their application in a loop control of the rudder. The measured disturbances typical of an engine failure include deviation of the set rotor speed of low-pressure fans for the left and right engines as well as a lateral acceleration in the direction of the failed engine. The devised law of automatic compensation for a failed engine in the rudder channel allows to increase the supply of a complete steady gradient of an aircraft climb by 2.0-3.0 % and improve the dynamics of velocity acceleration and the aircraft climb.

Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

Abstract This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.

Power System Low Frequency Oscillation of Resonance Mechanism Induced by Disturbance of Turbine Governing System

According to the resonance mechanism, power system forced low frequency oscillations can be aroused by power disturbance of prime mover. Therefore, the causes of turbine power disturbance were analyzed. The coupling model between turbine-governing system and power system was established in MATLAB. The possibility of governing system disturbance inducing the variation of control valve position and turbine power was researched in detail. The simulation results indicate that high level variation of control valve can be induced by the rotor speed deviation disturbance, if the speed-droop ratio of turbine-governing system is too small in local running position; power system low frequency oscillations of resonance mechanism might be caused by the disturbance of rotor speed deviation, when it’s frequency is close to power system natural oscillations frequency. Oil-pressure pulsation is easily happened in hydraulic governing system. If the frequency of oil-pressure pulsation is near to power system natural oscillations frequency, power system low frequency oscillations of resonance mechanism can be induced.

Design of static synchronous series compensator based damping controller employing invasive weed optimization algorithm.

This paper proposes designing of Static Synchronous Series Compensator (SSSC) based damping controller to enhance the stability of a Single Machine Infinite Bus (SMIB) system by means of Invasive Weed Optimization (IWO) technique. Conventional PI controller is used as the SSSC damping controller which takes rotor speed deviation as the input. The damping controller parameters are tuned based on time integral of absolute error based cost function using IWO. Performance of IWO based controller is compared to that of Particle Swarm Optimization (PSO) based controller. Time domain based simulation results are presented and performance of the controllers under different loading conditions and fault scenarios is studied in order to illustrate the effectiveness of the IWO based design approach.