Excitation System Model Research Articles

Dynamic theory and experimental testing in ipsilateral offset dual-motor excitation system

This paper addresses unbalanced trajectories of dual-motor vibrating screens by proposing a dynamic theory and experimental testing. First, based on the Lagrange equation, the dynamic model of ipsilateral offset dual-motor excitation system is established. Subsequently, the steady response is worked out by solving the differential equation of motion of the vibrating body. Then, the synchronization condition and synchronization stability criterion of the system are determined employing the small parameter method and the Routh–Hurwitz criterion. Numerical analysis methods are given to reveal the relationship between structural parameters and synchronization characteristics of the vibration system. Moreover, an mechanical–electric coupling model is developed to study dynamic characteristics. The results demonstrate that synchronization condition can be described with capture torque and difference of output torque between motors. The synchronization ability is enhanced by improving installation distance of the motors. Additionally, increasing angle β or decreasing angle θ of the motors is in favor of optimization of centroid trajectory; swing oscillation of the box can be controlled by adjusting the main inclination angle of motors; in such a condition, equilibrium of motion trajectory of system is enhanced. Finally, the validity method for designing vibrating screen is verified through theoretical calculations, simulation analysis, and experiments.

Analysis of random induced dynamic response of rural roads considering friction effect and nonlocal effect under the load of construction vehicles

Abstract The objective of this paper is to propose a novel computational model for solving the problem of accurately evaluating the randomly induced road vibration response of engineering vehicles traveling on rural roads. The computational model, first, focuses on the unique pavement characteristics of rural roads, constructs a tire grounding function model and innovatively introduces a dynamic friction factor, and successfully develops a coupled stochastic excitation system model for the interaction between the dynamic loads of 1/4 vehicle tires and the pavement of rural roads by applying the power spectral density function of the rural roads and combining it with the elastic roller model of the vehicle tires. Second, considering the nonlocal superposition effect of the soil skeleton of the roadbed, a coupled vibration response model of a 1/4 automobile rural road is successfully developed, and a validation method is given. Finally, the coupled vibration response characteristics of engineering vehicles and rural roads under random excitation at different speeds are analyzed. The analysis results show that the model proposed in this paper can well predict the degree and influence the range of rural road vibration caused by random excitation of construction vehicles traveling at any speed.

Emulation of IEEE STD 421.5/Industrial Excitation Systems Using a Micro-Alternator's Exciter

Micro-alternators, having similar parameters as turbo-alternators, play a significant role in the experimental evaluation of power system dynamics. Early thyristor excitation systems of micro-alternators have limited re-configurable options. Three possible control structures, two closed-loop control structures proposed in the literature and one open-loop control structure proposed in this paper, including a time constant regulator to mimic large machine time constants, are evaluated to emulate any IEEE 421.5 standard excitation system model or interface an industrial excitation system controller hardware in the loop (CHIL). It is shown that the communication delay introduced in CHIL does not impact the closed-loop stability within the bandwidth requirements of the excitation systems. One of the closed-loop structures, which is more generalized, and the open-loop structure performances are compared for emulating IEEE AC4C, DC1C, and ST1C excitation systems on a laboratory micro-machine based single machine infinite bus test system with buck exciter and H-bridge chopper (HBC) exciter using EMTP simulations under small and large disturbances. HBC exciter is used in the experimental validation with both the closed-loop and the open-loop control structures. The proposed open-loop structure is easy to implement and performs better than the closed-loop structure.

Research on Modeling Method for Excitation System of One Million-Kilowatt Unit in Nuclear Power Plant based on Real-Time Digital Simulation System

The excitation system is an important link between the generator set and the power grid. It is not only the key system to stabilize the operation of the generator set but also an important element related to the network. The accurate modeling and testing of the excitation system clarify and analyze the characteristics of the system. The traditional simulation software can only simulate the excitation system without the ability to test the control device and protection equipment. However, the real-time digital simulation system (RTDS) can realize real-time closed-loop tests of the hardware, which provides a new means for the excitation system analysis. This paper builds a detailed excitation system model of nuclear power units based on RTDS. The under-excitation limitation model is proposed based on the actual test data. Furthermore, the stability of the stator current limitation is improved by adding restriction conditions. Finally, the excitation system model is validated based on the measured data.

A Novel Field Current Estimation Method for Brushless Wound-Field Synchronous Machine

Compared with other electric machines, wound-field synchronous machines (WFSMs) have the advantage of having three control variables (stator <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents and rotor current). Determining the optimum combination of field and armature currents is necessary for ensuring the high-performance control of the WFSM. Two methods are usually employed to supply the field winding of the WFSM. The first one uses brushes and slip rings, while the second one uses a brushless excitation system. Concerning the WFSM with a brushless excitation system, a dc field current is provided by a rotating diode bridge rectifier fed by an exciter machine. Therefore, direct measurement of the field current is not possible. As a solution, field current needs to be accurately estimated. Previously, field current estimation methods proposed in the literature have been based on modeling the brushless exciter machine and the rotating rectifier. Using the brushless exciter machine model, these methods estimate electric quantities of the exciter rotor (currents and voltages); then, through the rotating rectifier model, the rectified field current is estimated. Accordingly, any inaccuracy in the models leads to estimation errors. The effectiveness of the techniques relying on the brushless excitation system model is not clearly justified, especially because the nonlinearity of the brushless system has been intensified by the existence of the rotating uncontrolled diode bridge rectifier. This article proposes an accurate online field current estimation method for WFSMs without the need neither to estimate exciter rotor voltages or currents nor to use a rotating rectifier model. The accuracy and effectiveness of the proposed field current estimation method are demonstrated by experimental validation tests.

Design Improvement and Tuning of Excitation System ST5B With PSS3B and Coordinated OEL in Hydropower Plant

The article analyzes and suggests the tuning and design improvement in the excitation system for the 1400 MW Tehri–Koteshwar hydropower plant (HPP) to mitigate the severe issues of active power oscillations leading to tripping of generating units. The static excitation system model ST5B, power system stabilizer model PSS3B, and over excitation limiter (OEL) are designed for each synchronous machine in the power plant. The coordination of ST5B, PSS3B, and OEL during critical transient operating conditions is analyzed. The proper coordination of these components of excitation system provides better transient and voltage stability. A new thermal-based OEL and modified power system stabilizer (PSS) designs are implemented to enhance the system's voltage and transient stability. The advantage of improved transient response by using different transient gain reduction (TGR) blocks formed by the lead-lag filter in ST5B during normal and limiting excitation operating conditions is presented. The ST5B and PSS3B dynamic analysis and tuning are performed using bode frequency response in offline mode. The robustness of the modified excitation system and limiters together with the added advantage of different TGR blocks in ST5B are verified using real-time digital simulator. A PSS-improved design and thermal-based OEL implemented for this HPP offer better transient and voltage stability as compared to the existing excitation system.

Improvement of Dynamic Reactive Power Characteristics of New-type Condenser by Excitation Parameters

The new-type condenser has the capability of dynamic reactive power compensation under subtransient, transient and steady-state, which could effectively solve the problem of insufficient dynamic reactive power reserve under the background of large-scale development of UHVDC transmission. In this paper, the excitation system parameters of the condenser are taken as the research object. First, the basic principle of new-type condenser and the excitation system model are introduced. Then, an effective gain of reactive current is defined as the quantitative index of the dynamic reactive power characteristics of the new-type condenser, and the effect of excitation system parameters on the dynamic reactive power characteristics of new-type condenser is studied by frequency domain trajectory sensitivity analysis. Finally, the simulation model of the condenser grid connected system is built based on PSCAD/EMTDC, the steady-state reactive power output level and transient response characteristics of new-type condenser with different excitation parameters are studied, and the optimization direction of the condenser excitation system parameters is determined. The simulation results show that reducing k A, k p, k D, T m and increasing k I T D, T Z are beneficial to improve the steady-state reactive power output of the condenser. Decreasing k A, k p, k D and increasing k I, T D, T m, T Z are beneficial to improve the transient response characteristics of the condenser.

Simulation test and parameter optimization of fast cut back of large thermal power plant in the condition of synchronization of large-scale wind power

Fast cut back (FCB) is an important condition in power control of steam turbine generator unit, which is closely related to the flexibility, safety and stability of thermal power unit. In this paper, the traditional single reheat steam turbine model were optimized and improved by adding the key links such as medium pressure control valve and bypass, and further adding the once through boiler, bypass control system, FCB action signal, excitation system and other models. A thermal power unit model suitable for FCB large disturbance condition simulation was established. The simulation results verify the effectiveness of the model, and meet the requirements of power system electromechanical transient simulation and FCB simulation. And then, this paper improved the PSO (Particle Swarm Optimization) algorithm, and combined the advantages of each algorithm in the aspects of calculation difficulty, convergence speed, accuracy, ability to jump out of local optimum, etc., puts forward and verifies the GA-PSO (Genetic Algorithm-PSO) optimization method. Finally, considering the stability and regulation performance of the system, the GA-PSO optimization algorithm was used to obtain the optimal values of the system component parameters. The simulation results indicated that the characteristics of optimized system damping was improved, which enhanced the regulation performance and stability of the system.

Coordinated control of energy storage electric brake device and generator

The application of Super Capacitor energy storage Brake Device (SCBD) in the electrical braking system of Hydrogenerator can not only assist the rapid shutdown of hydrogenerator, but also significantly provide the ability to resist large disturbance of the system, which is conducive to the improvement of the transient stability of the system. Based on the principle of capacitor energy storage, the differential algebraic model of SCBD and generator excitation and speed regulation system is derived in this paper, and the multi index nonlinear control is used to design the coordinated controller. In order to verify the effect of SCBD on generator system, three-phase short circuit simulation with and without SCBD and voltage regulation disturbance simulation are carried out. The simulation results show that the SCBD braking effect is obvious and the transient stability of the system is improved significantly.

Analysis of Model-Based Tuning Method of PID Controller for Excitation Systems Considering Measurement Delay

In this paper, a model-based tuning method for a PID controller of excitation systems based on a simplified model that considers measurement delay is proposed. The conventional model-based tuning method, which has been studied previously, uses a simplified excitation system model that ignores all the delay components. However, since the rms voltage measurement can take hundreds of milliseconds to calculate depending on the system settings, this delay cannot be ignored when the required response needs to be as fast as the measurement delay. Furthermore, the linearity of the measurement method is not taken into account because the measurement delay has already been ignored. Therefore, in this paper, a simplified model that considers measurement delay and its linearity is proposed, and a model-based tuning method of PID controllers for two kinds of excitation systems is proposed and compared with the conventional method by analysis. To verify the analysis and proposed tuning method, experiments are conducted for both excitation systems.

Analysis of the Interturn Short Circuits of Stator Field Windings in Multiphase Angular Brushless Exciter at Nuclear Power Plant

An excitation system with a multiphase angular brushless exciter is the preferred nuclear power excitation scheme because of its low output voltage ripple. However, interturn short circuits of the stator field windings (ISCFW) often occur in the brushless exciter, affecting the normal operation of the system. To study this type of fault, this paper presents research on theoretical analysis, simulation calculation, and model machine experiments. First, through the analysis of the magnetomotive force produced by windings and their interaction in the air gap under fault, the frequency domain characteristics of the postfault steady-state current are obtained. A general multiloop-method-based mathematical model of multiphase angular brushless excitation system with ISCFW is established. Correlated simulations and experiments with ISCFW are carried out, verifying the result of the theoretical analysis: m / P times harmonics are in the field current, while all harmonics are in the armature current. The general theoretical analysis method and mathematical modeling method proposed in this paper provide a basis for the protection scheme to rapidly remove ISCFW that occurs in the multiphase angular brushless exciter.

Passivity-Based Control of Power Systems Considering Hydro-Turbine With Surge Tank

This paper proposes an interconnection and damping assignment passivity-based control (IDA-PBC) for multimachine power systems including hydro-turbine governing systems (HTGS) with surge tank. The main objective is to stabilize the rotor speed and regulate the terminal voltage of each synchronous machine in a power system. The proposed control is decentralized, thus avoiding challenges of communication between generators. Passivity theory is used since the open-loop of the HTGS presents a port-Hamiltonian structure. IDA-PBC allows a control law that maintains the passive structure in closed-loop, guaranteeing its asymptotic stability using Lyapunov's theory. The dynamics of each HTGS are described by an eleventh-order model, which can be reduced to a tenth-order. The proposed control is tested in a 12-bus test system and compared to a standard control, which considers a voltage regulator and exciter based on the IEEE type ST1A excitation system model and power system stabilizer IEEE-PSS1A. The governing system based on a PID control with static and transient droop is also employed. Additionally, the proposed controller is compared to a sliding mode controller. Time-domain simulations demonstrate the robustness and appropriate performance of the proposed decentralized control under different large disturbances.

Excitation procedure for brushless wound‐rotor synchronous starter generator with seamless transitions

An analytical model of excitation system of brushless wound-rotor synchronous starter generator for aircraft applications is developed and presented in this study. During engine start-up process, the starter generator operates as a motor to start the aircraft turbine and to assist it up to the self-sustaining speed. On the basis of rotation speed of the starter generator in the engine start-up process, there are three excitation modes for the exciter and two transient modes for the field current of the main generator (MG). In this study, for each excitation mode, the relationship between the excitation current (field current of the exciter) and the field current of MG is investigated by taking into account the influence of power electronic parts. This study also proposes a control method for the generator field current in all excitation modes which can detect optimum operating points for transition between excitation modes. Furthermore, a seamless transient control strategy is proposed for the transient modes of the generator field current. Simulation and experimental results are provided to demonstrate the feasibility of the proposed solution.

Synchronous condenser excitation system parameter identification based on improved artificial bee colony algorithm

The quality of excitation control of the synchronous condenser directly determines the reactive power regulation ability and control support performance of the power grid.Aiming at parameter identification of non-linear links such as limit and saturation in the synchronous condenser excitation system, a parameter identification method of the synchronous condenser excitation system based on improved artificial bee colony algorithm is proposed.Firstly, the order of the phase modulation operation is deduced, and the mathematical model of the synchronous condenser excitation system is established based on it.Then the artificial bee colony algorithm is improved and applied to the parameter identification of the synchronous condenser excitation system. A parameter identification strategy based on sensitivity analysis is proposed for the unstable and multi-solution situation of multi-parameter identification results. Analysis of parameter sensitivity and identification based on parameter sensitivity. Finally, the identification parameters and the overall identification results obtained after sensitivity analysis are compared and analyzed. The results show that the proposed method can effectively identify the parameters of the non-linear link and has strong robustness. It can provide accurate models and parameters for power system stability analysis.

Modeling and Simulation of Excitation System for Third Harmonic Brushless Synchronous Generator

The excitation system of third harmonic excitation brushless synchronous generator (HESG) can improve the voltage stability and is widely used in small and medium generator set. In order to establish the model of harmonic brushless excitation system, the formula of third harmonic EMF is derived. Then, based on the traditional synchronous generator model, the influence of harmonic windings is counted in. Finally, the simulation model of closed-loop excitation system is analyzed with the automatic voltage regulator (AVR) as the core. On the basis of theoretical analysis, simulation and comparative analysis are carried out according to parameters from actual system. The results show that compared with normal synchronous generator, HESG has the advantage of excellent dynamic characteristics and automatic voltage adjustment.

Application of Multi-Stage Homotopy Analysis Method for Power System Dynamic Simulations

Homotopy analysis method (HAM) is a popular semi-analytical method used widely in applied sciences. It stands out from the rest of the semi-analytical methods as it provides a family of solutions to nonlinear equations, including ordinary differential equations (ODEs), partial differential equations, etc. The convergence characteristics of the solutions can be varied by changing an auxiliary parameter ( $\hbar$ ) in HAM. The convergence region of solution of ODEs using HAM can be improved by applying it over multiple intervals of time, which is referred to as multi-stage HAM (MHAM). In this paper, MHAM models for the IEEE Model 2.2 synchronous machine, IEEE Type-1 excitation system, first-order governor and first-order turbine models have been developed. The applicability of MHAM for power system dynamic simulations has been investigated in this paper using seven widely used test systems ranging from 10 generators 39 bus systems to 4092 generators 13 659 bus systems. The effect of number of terms, $\hbar$ and the time step on the accuracy and stability of the solution has been studied. The effectiveness of MHAM has been compared with the modified Euler (ME) and midpoint Trapezoidal (TrapZ) methods. The accuracy of MHAM has been found to be comparable with ME and TrapZ methods for the values of $\hbar$ between $-$ 1.05 and $-$ 0.95. The best accuracy is obtained for $\hbar$ = $-$ 1.0, which is a special case of MHAM called multi-stage homotopy perturbation method (MHPM). In this paper, it is also shown that MHPM is equivalent to multi-stage adomian decomposition method, which has been recently explored for large power system simulations.

Improved niche genetic algorithm based parameter identification of excitation system considering parameter identifiability

In order to obtain the parameters of excitation system accurately, and improve the accuracy and efficiency of parameter identification much further, an improved niche genetic algorithm was adopted, which can overcome local convergence of genetic algorithm by the fitness sharing mechanism that could increase population diversity. Moreover, the proposed algorithm could avoid the disadvantage of usual niche genetic algorithm that is difficult in determining the niches. By using the method of fuzzy clustering, niche groups can be created dynamically. In addition, regarding the problem that the partial parameters of excitation system cannot identify stably because of the relevance among these parameters, this study analysed the identifiability of excitation system model primarily, separated associated parameters into several parameter sets then. This type of relevance would be removed by assigning typical values to representative parameters, which belong to different sets. Identifiability analysis can not only avoid identifying parameters blindly, but also increase the credibility of the results. The test study shows that the proposed method can acquire accurate and reliable parameter values.

A Theoretical and Practical Approach for Underexcitation Protection and Control Studies of Hydrogenerators in a Real-Time Environment

The installation and settings of protection devices and excitation control systems require experience since a failure can cause damage to the synchronous generator and negative impact on the power grid. A test bed implemented in a real-time digital simulator (RTDS) is presented in this paper as an alternative for the training and learning process that involves the knowledge of an effective coordination between such protection and control systems of synchronous generators. A complete generation system is implemented in a RTDS, including an excitation system model with its limiters. These limiters are coordinated with the protection functions implemented in a physical relay. The contributions of this work are the demonstration of the importance of this type of study (i.e., real-time simulations results through hardware-in-the-loop tests), the consolidation of the impedance (R-X) and admittance (G-B) planes as the more appropriate ones to analyze the coordination between the ANSI 40 function and the underexcitation limiter, and the presentation of a study focused on hydrogenerators (including novel settings for the ANSI 40 protection).

Numerical Average-Value Modeling of Rotating Rectifiers in Brushless Excitation Systems

Brushless excitation systems are widely used for synchronous machines. As a critical part of the system, rotating rectifiers have a significant impact on the system behavior. This paper presents a numerical average-value model (AVM) for rotating rectifiers in brushless excitation systems, where the essential numerical functions are extracted from the detailed simulations and vary depending on the loading conditions. Open-circuit voltages of the brushless exciter armature are used to calculate the dynamic impedance that represents the loading condition. The model is validated by comparison with an experimentally validated detailed model of the brushless excitation system in three distinct cases. It has been demonstrated that the proposed AVM can provide accurate simulations in both transient and steady states with fewer time steps and less runtime compared with detailed models of such systems and that the proposed AVM can be combined with AVM models of other rectifiers in the system to reduce the overall computational cost.

An Optimal Robust Excitation Controller Design Considering the Uncertainties in the Exciter Parameters

This paper develops a novel framework to design an optimal robust excitation system controller considering the uncertainties in the parameters of the model of the excitation system. The uncertainties may cause the parameter values to vary from their nominal values within a specified upper and lower limit. These uncertainties can have a significant influence on the dynamic characteristics of the power system, that is, the variations in the parameters of the excitation controller model due to the uncertainties in the parameters can cause the system to change from being stable to unstable. It is, therefore, important to design a robust excitation system controller that can ensure that irrespective of the values of the parameters within the boundary of the uncertainties, the power system will not have any variation from its stability. The proposed framework decomposes the uncertainties in the parameters of the excitation system model into two components: matched and unmatched. To eliminate the uncertainties from both components, a linear quadratic regulator problem is constructed to deal with the matched component, while an augmented control is used to cope with the unmatched component. The robustness of the resulting controller is verified using time-domain dynamic stability simulations of a single-machine test system and the IEEE 39-bus New England system.