Behavior Of Synchronous Machine Research Articles

Harmonic Sequence Component Model-Based Small-Signal Stability Analysis in Synchronous Machines during Asymmetrical Faults

Power systems are complex and often subject to faults, requiring accurate mathematical models for a thorough analysis. Traditional time-domain models are employed to evaluate the dynamic response of power system elements during transmission system faults. However, only the positive sequence components are considered for unbalanced faults, so the small-signal stability analysis is no longer accurate when assuming balanced conditions for asymmetrical faults. The dynamic phasor approach extends traditional models by representing synchronous machines with harmonic sequence components, making it suitable for an unbalanced condition analysis and revealing dynamic couplings not evident in conventional methods. By modeling electrical and mechanical equations with harmonic sequence components, the study implements an eigenvalue sensitivity analysis and participation factor analysis to identify the variable with significant participation in the critical modes and consequently in the dynamic response of synchronous machines during asymmetric faults, thereby control strategies can be proposed to improve system stability. The article validates the dynamic phasor model through simulations of a single-phase short circuit, demonstrating its accuracy and effectiveness in representing the transient and dynamic behavior of synchronous machines, and correctly identifies the harmonic sequence component with significant participation in the critical modes identified by the eigenvalue sensitivity to the rotor angular velocity and rotor angle.

Canay Inductance Impact Characterization on Dynamic Behaviour of Synchronous Machines

Canay Inductance Impact Characterization on Dynamic Behaviour of Synchronous Machines

Inertia Estimation Through Covariance Matrix

This work presents a technique to estimate on-line the inertia of a power system based on ambient measurements. The proposed technique utilizes the covariance matrix of these measurements and solves an optimization problem that fits such measurements to the synchronous machine classical model. We show that the proposed technique is adequate to accurately estimate the actual inertia of synchronous machines and also the virtual inertia provided by the controllers of converter-interfaced generators that emulate the behavior of synchronous machines. We also show that the proposed approach is able to estimate the equivalent damping of the classical synchronous machine model. This feature is exploited to estimate the droop of grid-following converters, which has a similar effect of the swing equation equivalent damping. The technique is comprehensively tested on a modified version of the IEEE 39-bus system as well as on a dynamic 1479-bus model of the all-island Irish transmission system.

Low-frequency Oscillation Damping Control for Large-scale Power System with Simplified Virtual Synchronous Machine

This study focuses on a virtual synchronous machine (VSM) based on voltage source converters to mimic the behavior of synchronous machines (SMs) and improve the damping ratio of the power system. The VSM model is simplified according to some assumptions (neglecting the speed variation and the stator transients) to allow for the possibility of dealing with low-frequency oscillation in large-scale systems with many VSMs. Furthermore, a virtual power system stabilizer (VPSS) structure is proposed and tuned using a method based on a linearized power system dynamic model. The linear and nonlinear analyses examine the stability of two modified versions of a 16-machine power system in which, in the first case, partial classical machines are replaced by VSMs, and in the second case, all SMs are replaced by VSMs. The simulation results of the case studies validate the efficiency of the proposed control strategy.

EIGENVALUE METHOD AND LINEARIZATION FOR THE STEADY STATE STABILITY ANALYSIS OF JAMSHORO THERMAL POWER PLANT (JTPP)

Electrical power system without interruption is the need of every consumer. Therefore, supplying electrical power which must be efficient, reliable and secure from any disturbance is the priority of power supply companies. But, due to changes in weather conditions and continuous load variations, small disturbances arise which may lead to severe disturbance. All electrical generating stations are interconnected, so a failure in any one unit can affect other generating units, therefore analysis is compulsory to solve the problem in the least time, and avoid a further big loss. Analysis of steady-state stability or transient stability plays a key role in a power system which helps to understand the behavior of a dynamic system. The stability problem is concerned with the behavior of the generating station when the system puts on either small or large disturbance. In this work, the steady-state stability (SSS) analysis of the Jamshoro thermal power plant (JTPP) is analyzed by using the eigenvalue method and linearization technique at four different reheat gain values. We develop a nonlinear mathematical model of JTPP and discuss its linearized form, and examine the behavior of the system stability using eigenvalues. The eigenvalue method analyzes the behavior of synchronous machine when system load varies continually. Numerical values of eigenvalues consist of either real part or real as well as imaginary parts. These eigenvalues help to understand the stability of the system, as to whether the system is stable or not.

Validating grid‐forming capabilities of hybrid power park technologies in future OFTO networks

In recent years, there has been considerable interest in convertor-based generating solutions which to a greater or lesser extent mimic the behaviour of synchronous machines, thus overcoming many of the disadvantages of the existing technologies which are potentially destabilising at high penetration. Such solutions are frequently referred to as grid-forming convertors (GFCs). This study focuses on the application of GFC technologies in offshore windfarms, where installation, maintenance and/or modification of any offshore equipment is very expensive and carries greater commercial risks, requiring extensive testing and confidence building prior to deployment in real applications. This is time consuming and particularly significant for GB and where there are large quantities of offshore generation. Onshore solutions to stability are therefore desirable for off-shore transmission owners (OFTOs), especially, if they could be applied by retrofitting to existing conventional converter plant. Consequently, this study proposes and investigates the performance of hybrid solutions for offshore networks where the conventional STATCOM onshore unit is replaced by alternative options such as synchronous compensator and virtual synchronous machine converter of similar (or appropriate) rating with the aim of achieving grid-forming capability. A laboratory-scale implementation of the proposed control algorithm is also presented with selected validation test results.

Improving synthetic inertia provision by Power Electronic Interfaced Power Sources to support future system stability

Increasing penetration of power-electronics-converter-interfaced generation and loads raises several challenges for the operation, control and protection of power systems. This paper investigates the impact of high penetration of Power Electronic Interfaced Power Sources (PEIPS) on frequency control, and aspects of provision of synthetic inertia (SI) by PEIPS. Contrary to directly connected conventional synchronous machines, which provide inertia to the system inherently, thus effectively counteracting large gradients in the system frequency (rate of change of frequency, RoCoF), PEIPS need to be operated under specially designed control schemes in order to provide synthetic inertia by varying their power output proportionally to the RoCoF. Implementing such control schemes for current-controlled PEIPS requires both accurate and fast frequency measurement and can rather approximately reproduce physical inertia added to the system by directly connected synchronous machines. While the transient behavior of conventional synchronous machines is defined by their well-known electromechanical properties, the dynamic behavior of PEIPS is mostly dictated and limited by their control strategy and pertinent measurements. Under this setup, it is worth contemplating strategies that go beyond mimicking the dynamic capabilities of synchronous machines. A synchronous machine provides inertia to the system inherently due to its rotating mass. However, current-controlled PEIPS implement synthetic inertia by measuring frequency, calculating the frequency gradient and providing power accordingly. The delays due to frequency measurement, RoCoF computation and current control reflect an inherent difference and disadvantage of synthetic inertia compared to real inertia and must be properly studied to avoid deterioration of system stability under a large penetration of PEIPS. While the behavior of synchronous machines is determined by their physical properties, the behavior of PEIPS may be altered by modifying their control regime in order to improve their transient behavior under higher RoCoF values. Furthermore, it is possible to implement non-linear strategies that do not depend only on the frequency gradient but also on the frequency deviation. One option to achieve this is to implement different activation areas for different signs of both frequency deviation and RoCoF. Such a zone-selective implementation of synthetic inertia, realized by an activation function, could avoid that synthetic inertia counteracts the effect of other control reserves during recovery from frequency deviations, i.e., after the frequency nadir has occurred. This paper investigates such options and their impact on the frequency stability of the power system when synthetic inertia is provided by PEIPS.

Steady State Stability Analysis and Improvement using Eigenvalues and PSS: A Case Study of a Thermal Power Plant in Jamshoro, Pakistan

The efficient handling and distribution of electrical power consist one of the most complex and appealing research problems. Due to the interconnection of different power plants and intensity of load, which gradually changes due to continuous change in load on generating units, careful treatment of the small disturbances in a power system which may lead to severe disturbance is necessary. Stability is an essential part in electrical power system operation and control. The stability problem is related with the behavior of synchronous machine after the power system is subjected to trouble. This work presents Steady State Stability (SSS) analysis of a Jamshoro Thermal Power Plant (JTPP) by using eigenvalue analysis of the different cases by varying load at three different positions. A mathematical model has been used for the JTPP with real data in order to examine the behavior of the system and to find the eigenvalues. A Simulink model of the JTTP for waveform analysis in MATLAB/Simulink has been used without and with Power System Stabilizer (PSS). Numerical quantification of the eigenvalues under the examined cases categorizes the stability of the system. The waveforms of the system are analyzed, and in cases of instability, the proposed procedure utilizing PSS helps in maintaining the system’s usual working conditions. The eigenvalue analysis and simulation results show the behavior of synchronous machines when loading changes gradually. The existing system becomes stable after more swings, whereas by using PSS in the existing system, stable regimes are attained in less time. The obtained results demonstrate the effectiveness of the proposed solution for SSS examination and securing of the disturbances of the JTPP.

DYNAMIC CONDITIONS OF COMPENSATED SYNCHRONOUS MACHINE

The dynamic behavior of synchronous machine with longitudinal-transverse excitement by maintenance of the rotor overhang corner as equal zero are considered. The given condition is named as compensated and correspond with full compensation of transverse armature reaction by magnetizing force of transverse excitement winding. In such machine is absented the limit of steady-state overload, but active and reactive components of load current are concurrent as projections of load current image vector on orthogonal axes of machine inductor. The research aim is a determination of steady-state stability criterion of compensated synchronous machine working on powerful electrical system. The researches are organized in assumption of inductor current invariance and at neglect of stator windings time constant. The electromagnetic moment expression of longitudinal-transverse excitement synchronous machine in compensated work condition is received as a result of analysis of the spatial vector diagrams and equations. The expression analysis has allowed to find the criterion of rotor creepage stability and to examine the steady-state stability of the machine in different work conditions. It is shown that machines stability factor is defined by not only the reactive power of machine short circuit, but also associated reactive power.

Placement and Implementation of Grid-Forming and Grid-Following Virtual Inertia and Fast Frequency Response

The electric power system is witnessing a shift in the technology of generation. Conventional thermal generation based on synchronous machines is gradually being replaced by power electronics interfaced renewable generation. This new mode of generation, however, lacks the natural inertia and governor damping which are quintessential features of synchronous machines. The loss of these features results in increasing frequency excursions and, ultimately, system instability. Among the numerous studies on mitigating these undesirable effects, the main approach involves virtual inertia emulation to mimic the behavior of synchronous machines. In this work, explicit models of grid-following and grid-forming virtual inertia (VI) devices are developed for inertia emulation in low-inertia systems. An optimization problem is formulated to optimize the parameters and location of these devices in a power system to increase its resilience. Finally, a case study based on a high-fidelity model of the South-East Australian system is used to illustrate the effectiveness of such devices.

Anomalous Stability Behavior of Synchronous Machine With High Impedance Faults

It is generally believed that following a fault, the system remains stable as long as the fault is cleared within a “critical clearing time” or CCT. This letter shows that when there is a high impedance resistive fault, there are later intervals such that if the fault is cleared within these intervals of time, the system is still stable notwithstanding that the clearing time is now larger than the conventionally calculated CCT. The results are obtained precisely using digital simulation and explained qualitatively using the equal area criterion.

Active Voltage Feedback Control for Hybrid Multiterminal HVDC System Adopting Improved Synchronverters

In this paper, we propose an idea to integrate more renewable energy into the existing China power grid and to provide remote islands with a reliable power supply. The idea is to expand the existing point-to-point line-commutated converter (LCC) HVDC transmission link into a hybrid multiterminal HVDC (hybrid MTDC) system, which contains LCC stations and voltage-source converter (VSC) stations. Accordingly, this paper proposes a novel control strategy for this system called active voltage feedback control, which does not need any high-speed communication system under various disturbances, such as wind speed variations, load fluctuations, faults, etc. This paper also adds secondary frequency regulation to the synchronverter, which is one way of combining the VSC converter with synchronous machine behavior. Then, this paper applies an approach to limit its current under fault conditions. Finally, the entire hybrid MTDC system is modeled in PSCAD/EMTDC. Simulation results show that the improved synchronverter is able to achieve secondary frequency control, and the presented active voltage feedback control works very well when exposed to various disturbances.

Novel Comprehensive Control Framework for Incorporating VSCs to Smart Power Grids Using Bidirectional Synchronous-VSC

This paper presents a new control strategy for voltage-source converters (VSCs) in the frequency-angle domain which enables dc-link voltage regulation via frequency and load angle adjustment. A major advantage of the proposed controller is emulating the behavior of synchronous machines (SMs) with proper regulation of dc-link voltage which eases integration of VSCs interfacing distributed and renewable generation units into ac systems in the presence of conventional SMs. A cascaded frequency, angle and virtual torque control topology is developed to emulate the mechanical behavior of an SM which offers synchronization power to eliminate the need for a phase-locked-loop after initial converter synchronization, and damping power dynamics to damp power oscillations; and presents frequency dynamics similar to SMs, thus it introduces some inertia to the grid. The controller presents high stability margin and fast dc-link voltage regulation, whereas it can provide frequency support in the ac-side during contingencies. Frequency and voltage amplitude are adjusted by two separate loops. Two different variants are proposed for dc-link voltage control; namely direct dc-link voltage control and indirect dc-link voltage control via a dc-link voltage controller. Small-signal dynamics, analysis, and design process are presented. Both simulation and experimental results are provided to validate the controller effectiveness.

A state space synchronous machine model with multifunctional characterization of saturation using Levenberg–Marquardt optimization algorithm

Performance of electrical machines is critically affected by the saturating nature of ferromagnetic materials. In order to have a reliable and accurate estimation of the steady-state behavior of synchronous machines, it is important to have a precise machine model that includes saturation. This paper aims to develop a new synchronous machine model incorporating an accurate saturation model. The algorithm used in this paper to represent magnetic saturation calculates the coefficients in several real function expressions for the saturation characteristics of a synchronous machine. The new synchronous machine model proposed in this paper has been used in the investigations to calculate the machine behavior in various operating conditions.

Generalized Gain Scheduling for Deloaded Wind Turbine Operation

The ability to produce less power than what is available from a wind source, a condition known as deloaded operation, is needed for a wind turbine to reproduce synchronous machine behavior in terms of inertial response and frequency droop regulation. Deloaded operation requires the ability to regulate both power production and rotor speed under any wind speed conditions. In this paper, a novel controller for deloaded wind turbine operation is presented. This controller is made possible by a Cp table inversion procedure allowing generalized gain scheduling for linearization of the pitch response. After introducing the wind turbine models, a review of classical turbine control principles and the proposed deloaded wind turbine control architecture is presented. A discussion of wind turbine non linearity and linearization principles follows. Simulation results are shown for stability, immunity to icing and performance. The advantages of generalized gain scheduling over classical gain scheduling are demonstrated by simulation results.

Anisotropy Comparison of Reluctance and PM Synchronous Machines for Position Sensorless Control Using HF Carrier Injection

Position sensorless control of reluctance and permanent magnet synchronous machines at zero and low speed is possible using HF voltage injection and proper demodulation. The so-called saliency position, which is tracked by the HF sensorless scheme, is different from the actual rotor position: the difference contains both offset and rotor-position-varying components, which may be explained by carefully considering the HF behavior of the machine and the effect that fundamental excitation and rotor position have upon it. This paper gives insight into the HF behavior of synchronous machines and serves as a practical guide for implementation of stable and robust position estimation at zero and low speed.

Behavior of Synchronous Machines Subjected to Voltage Sags of type A, B and E

Voltage sags and voltage interruptions are huge power quality problems for many industries. Voltage sags cause apart from eventual tripping, large torque peaks, which may cause damage to the shaft or equipment connected to the shaft. This paper illustrates how the stator flux in a synchronous machine changes during voltage sags. These changes result in torque peaks. An analytical time dependent expression of the stator flux during voltage sags explains the behaviour of synchronous machines and why there are high torque and current peaks during voltage sags. Simulations verify the expressions, and illustrate the dependence of torque and current peaks on voltage sag duration and magnitude.

A developmental package of interactive software for illustrating power-system protection principles in educational and industry training programs

This paper describes the philosophy, development and use of a series of microcomputer-based software packages which assist in the analysis and demonstration of some fundamental concepts associated with power system protection and related areas. These easily-used, interactive programs employ extended screen color graphics capabilities to demonstrate fundamentals of steady-state synchronous-machine behavior, instrument transformers, time-overcurrent relay operation, directional relaying, percentage differential protection of a generator, and distance relaying. They include the display of instructions and tutorials, parameter values and numerical results, phasor diagrams, one-line diagrams, circuit diagrams, and device animation as appropriate. The software described is representative of what the authors envision to ultimately form a very comprehensive but expandable set of training modules for the power-system protection area. The modules are applicable to both academic power programs and industry training efforts. >

Preliminary results on neural net based simulation of synchronous machine dynamic response

Synchronous machine analysis has been the subject of investigation for a long time. For the reliable prediction and evaluation of the dynamic performance of power systems, it is essential to use a comprehensive mathematical model. In practice, however, such detailed knowledge is rarely available. This paper describes an application of artificial neural networks in studies of unmodeled synchronous machine dynamics. The goal is to examine the extrapolation and interpolation capabilities of neural networks within the scope of being able to learn synchronous machine behavior and to predict the time response of a synchronous generator for new initial conditions.

Considerations on natural frequency and transient behavior of synchronous machines.

Considerations on natural frequency and transient behavior of synchronous machines.