Criterion for inductive compensation location to enhance systemsteady state stability

Huge reactive power surplus at light load operation may force system generators to operate in the under excited mode which reduces system stability margin. In this paper analytical expressions for generator reactive power sensitivities with respect to reactive compensation are derived. A criterion based upon these sensitivities with respect to reactive compensation are derived. A criterion based upon these sensitivities for choosing reactive compensation locations to improve system steady state stability is proposed. The effectiveness of this proposed criterion is demonstrated through application to the Saudi Consolidated Electric Company (SCECO)-Central Power system     

Impact of Postfault Active Power Recovery of Photovoltaic Power Generation on Transient Stability

Currently, Japanese grid codes require photovoltaic (PV) power generation systems to continue supplying power to the grid as soon as possible even if the systems temporarily stop their operation. Although the fault ride‐through capability was originally proposed for preventing a cascading frequency drop in the power system, the capability has the impact on other instability phenomena such as transient stability. In this study, we focus on the postfault active power recovery of the PV systems. The impact of the recovery speed on the transient stability is investigated under different load conditions, in particular static/dynamic load condition. Numerical examples are carried out for the one‐machine one‐load infinite‐bus system, and the effects of the recovery speed are evaluated by equal area criterion and critical clearing time. As a result, we have found both desirable and undesirable effects on the transient stability depending on the load condition.     

基于感应电动机的暂态电压稳定判据的研究

提出一种负荷采用感应电动机模型时的暂态电压稳定的判断方法.该判据通过比较扰动后感应电动机电磁转矩和机械转矩以及转差的变化情况来判断负荷的稳定性,以系统的最大传输功率与负荷功率需求的关系来确定负荷失稳是否会导致暂态电压失稳.以单机单负荷系统和IEEE39节点系统为例,用MATLAB软件进行仿真分析,仿真结果验证了所提出的方法的准确性.     

PERFORMANCE ANALYSIS OF SELF-EXCITED INDUCTION AND RELUCTANCE GENERATORS

ABSTRACT

The paper presents a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines. The proposed arrangement is adapted to use one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors. Operational and steady-state equivalent circuits for both types are developed and used to predict the dynamic and steadystate behaviours under load conditions. This analysis depends mainly upon the computation of the power angle for a given machine parameters, capacitor ratings, and load conditions at a constant speed. Further, stability limits of both generators are investigated by developing the active-reactive power (P-Q) diagram for each generator. Conditions required to achieve self-excitation are also given. Performances of the two generator types are evaluated theoretically and experimentally.     

AN EFFICIENT CONTINUATION POWER FLOW METHOD FOR VOLTAGE STABILITY ANALYSIS

ABSTRACT

This paper presents an efficient continuation power flow-method for determining voltage stability limit of interconnected power systems. Decoupled power-flow solutions are extremely popular because of lesser storage and faster solution speed as compared to coupled power flow solution. However, it is generally believed that decoupling cannot be used near critical loading conditions. This paper shows that decoupled power-flow solution is possible even under such adverse operating conditions, it is achieved by judiciously incorporating the effects of non-negligible off diagonal submatrices through a subiteration scheme. The load parameter is included in both sets of equations. Bus angle (other than slack bus) and load parameter are used as continuation parameters for solving real & reactive power equations respectively. Results for 5-bus, 14-bus and a practical 91 -bus test systems have been obtained with the coupled and proposed decoupled versions of continuation power-flow to demonstrate the validity and efficiency of the proposed algorithm.     

NEW APPROACH FOR PLANNING PRIMARY DISTRIBUTION NETWORKS

ABSTRACT

The paper presents a new and simple methodology for planning primary distribution networks. It enables distribution system planners to determine: optimum feeder routes, optimum wire sizes, optimum substation locations and optimum substation sizes. The objective is to achieve a reliable and efficient configuration to supply the given loads with an overall minimum investment.

A criterion is established to determine the best feeder routing directly from the topology or the served area and load locations. An accurate representation for feeder cost models is presented and an economic loading limits for each feeder type are introduced.

A sample planning study is presented to indicate that the proposed method is simple, fast, efficient, and hence, it can be very valuable for system planning engineers.     

Maximum Power Point Tracking Using Disturbance Observer-Based Sliding Mode Control for Estimation of Solar Array Voltage

Abstract

The output power of solar panel in photovoltaic systems is affected by changes in environmental and load conditions. Most currently developed MPPT control algorithms require measurements of panel output voltage, output current, and converter output voltage. In this paper, a new scheme that can cater to uncertainties in the environmental and load condition, is developed using a disturbance observer-based sliding mode control (DOSMC). The proposed DOSMC scheme obviates the need of using a panel output voltage sensor. The proposed scheme does not use a discontinuous control, thereby overcoming the problems of chatter normally associated with the conventional sliding mode control (SMC). The stability is proven in the sense of ultimate boundedness. The proposed scheme is validated by extensive simulation and laboratory experimentation under various scenarios of irradiation, temperature, and load conditions and compared with two existing popular schemes.     

Robust Control of the Brushless DC Motor with Variable Torque Load for Automotive Applications

Abstract

The design of an Active Disturbance Rejection Controller for the Brushless DC motor (BLDC) that compensates load torque variations in the rotor shaft without the measurement of the rotor shaft speed is presented. The reconstruction of the unknown load and motor speed is accomplished by the combination of a generalized Proportional Integral Control (PI) and a Luenberger observer, while the stator current regulation is designed around a passivity based controller. Using parameters of a commercial motor designed for a small electric vehicle under different driving conditions, numerical simulation results are included that validate the effectiveness of the proposed scheme both in terms of transient response to changes in set points and in tracking variable speed references.     

PERFORMANCE ANALYSIS OF A D.C. DRIVE ELECTROMECHANICAL SYSTEM WITH ELASTIC COUPLING AND PULSATING LOAD TORQUE

ABSTRACT

This paper presents the analysis of a d.c. motor drive with a pulsating load torque and elastic mechanical link between the motor and the load. A mathematical model of the system using State Space technique is given and the equations are solved to obtain closed-form solutions for motor speed and current under transient and steady state conditions. The analysis reveals that the system performance is significantly affected by elasticity of the shaft and the nature of pulsation of load torque     

Full-state Variables Control of a Grid-connected Pumped Storage Power Plant Using Non-linear Controllers

Abstract—In this article, a controller based on a multi-variable sliding mode is provided for pumped storage with four goals. (1) Full-state variables of the plant, generator, and hydro turbine are developed to improve transient responses under fault conditions by compensating the fast electrical dynamics. (2) The sliding-mode controller is designed for robustness against uncertainty in both the power system parameters and its topology. (3) Two surfaces (power angle and output voltage) are proposed to coordinate both the turbine and excitation inputs of the generator in transient conditions. (4) The decentralized method is used to decrease the complexity of the controller equations and cost of implementation. To show the effectiveness of the proposed controller, two other controllers—full-state variables feedback linearization and a generic power system stabilizer—are simulated by MATLAB/Simpower (The MathWorks, Natick, Massachusetts, USA). The simulation results show full-state variables feedback linearization cannot be robust against model uncertainty; it is also shown that the power plant with linear controller has unpleasant transient responses in both fault conditions and low-frequency oscillations. In contrast, the proposed method plays an effective role in solving the mentioned problems and limits the stator current magnitude and terminal voltage post-fault.     

DIRECT EVALUATION OF TRANSIENT STABILITY IMPROVEMENT WITH STATIC VAR COMPENSATORS USING A STRUCTURE PRESERVING ENERGY FUNCTION

Abstract

The ability of Static Vax Compensators (SVCs) to rapidly and continuously control reactive power in response to changing system conditions can result in the improvement of system stability and also increase the power transfer in the transmission system. This paper concerns the application of strategically located SVCs to enhance the transient stability limits and the direct evaluation of the effect of these SVCs on transient stability using a Structure Preserving Energy Function (SPEF). The SVC control system can be modelled from the steady- state control characteristic to accurately simulate its effect on transient stability. Treating the SVC as a voltage-dependent reactive power load leads to the derivation of a path-independent SPEF for the SVC. Case studies on a 10-machine test system using multiple SVCs illustrate the effects of SVCs on transient stability and its accurate prediction.     

Fast Evaluation of Transient Stability of Power Systems Using a Structure Preserving Energy Function

Abstract

In this paper, a fast method of evaluating the transient stability of power systems using a topological energy function is presented. This is applicable to the case when the load buses are uncoupled and for a class of nonlinear voltage dependent loads. A topological energy function (TEF), using centre of angle (COA) formulation, is used for computation of the stability region. A power Invariant transformation is presented which leads to the decoupling of load buses in a practical system with connected load buses. Although the load characteristics do not remain invariant under this transformation, approximations can be introduced to facilitate the analysis. A numerical example is precentod to illustrate the application of the method.     

基于感应电动机网荷互馈特性的暂态电压失稳机理探析

<正>确认识电压失稳机理是进一步对电力系统电压稳定问题进行深入研究的关键。分析了网络视在功率传输特性和感应电动机负荷特性,揭示了以感应电动机为核心的暂态电压失稳正反馈动态过程。将与滑差相关的感应电动机负荷及网络视在功率传输的相互作用关系定义为感应电动机网荷互馈特性,并据此进一步分析了含有感应电动机负荷的系统电压崩溃过程,明确了基于感应电动机网荷互馈特性的暂态电压失稳机理,提出了感应电动机负荷电压失稳判据,构建了简单系统算例验证分析结果。分析表明,以感应电动机为核心的电压失稳正反馈动态过程是系统暂态电压失稳的重要环节;将感应电动机故障切除时滑差对应的恢复电压作为判断感应电动机电压稳定的必要条件,能够提高暂态电压失稳判定的准确性与适用性。所述电压稳定判据为预防电压失稳现象的发生和制定电压失稳解决措施提供了有力的理论支撑。     

Reliability and economic evaluation of demand side management programming in wind integrated power systems

In this paper, security constrained unit commitment (SCUC) is employed for simultaneous clearing of energy and reserve markets. Spinning reserve of generation units and interruptible loads (IL) are assumed as system operating reserves. In the proposed method, the unit commitment program is done with considering the wind power uncertainty. So, modeling the wind uncertainty has been done by a two-stage stochastic programming. Also, the economic evaluation of wind power uncertainty is discussed and the impacts of IL and wind farm locations have been studied on the system reliability. Expected energy not supplied (EENS) is considered as criterion for undesirable load shedding of power system. Finally, the proposed model is applied to the IEEE reliability test system (IEEE-RTS) to demonstrate its effectiveness.     

Induction Motors Broken Rotor Bars Diagnosis Through the Discrete Wavelet Transform of the Instantaneous Reactive Power Signal under Time-varying Load Conditions

Abstract—In this article, a method based on the application of the discrete wavelet transform to the instantaneous reactive power signal, for diagnosing the occurrence of broken rotor bars in induction motors operating under time-varying load conditions, is presented. This method is based on the decomposition of the instantaneous reactive power signal, from which wavelet approximation and detail coefficients are extracted. The energy evaluation of known bandwidths permits to de?ne a fault severity factor. This method has been tested through the simulation of an induction motor using a mathematical model based on the winding-function approach. These simulation results are complemented by experimental tests conducted on an induction motor with several faulty rotors that can be interchanged and both simulation and experimental results have shown the effectiveness of the proposed method for broken rotor bars diagnosis in induction motors even under time-varying load conditions.     

EFFECTS OF INDUCTION MOTOR LOAD ON DYNAMIC STABILITY OF POWER SYSTEMS

Abstract

A study of the effects of induction motor load on the dynamic stability of power systems is presented in this paper. The power system is modelled as a multivariable system with load dynamics considered in the feedback path. The induction motor is represented by a transfer function matrix relating bus voltage magnitude and frequency to the active power and reactive power of the motor

Multivariable Nyquist criterion and eigenvalue analysis are used to investigate the effects of induction motor dynamics on system stability     

基于相量测量技术和模糊径向基网络暂态稳定性预测

提出一种新的基于模糊聚类的径向基神经网络及其训练算法,利用同步相量测量装置获得的故障后短时间内各发电机的功角,经简单运算后作为神经网络的输入,其输出为多机电力系统稳定性的分类结果。对４９机实际系统在不同接线方式和故障位置条件下,进行了有无切机控制两种情况下的数值仿真实验,结果表明所提出的方法对系统的失稳预测和切机控制决策是有效的,神经网络训练时间短,分类精度高。     

Optimal integration of DGs into radialdistribution network in the presence ofplug-in electric vehicles to minimize dailyactive power losses and to improve thevoltage profile of the system using bioinspiredoptimization algorithms

Purpose: The increase in plug-in electric vehicles (PEVs) is likely to see a noteworthy impact on the distribution system due to high electric power consumption during charging and uncertainty in charging behavior. To address this problem, the present work mainly focuses on optimal integration of distributed generators (DG) into radial distribution systems in the presence of PEV loads with their charging behavior under daily load pattern including load models by considering the daily (24 h) power loss and voltage improvement of the system as objectives for better system performance. Design/methodology/approach: To achieve the desired outcomes, an efficient weighted factor multi-objective function is modeled. Particle Swarm Optimization (PSO) and Butterfly Optimization (BO) algorithms are selected and implemented to minimize the objectives of the system. A repetitive backward-forward sweep-based load flow has been introduced to calculate the daily power loss and bus voltages of the radial distribution system. The simulations are carried out using MATLAB software. Findings: The simulation outcomes reveal that the proposed approach definitely improved the system performance in all aspects. Among PSO and BO, BO is comparatively successful in achieving the desired objectives. Originality/value: The main contribution of this paper is the formulation of the multi-objective function that can address daily active power loss and voltage deviation under 24-h load pattern including grouping of residential, industrial and commercial loads. Introduction of repetitive backward-forward sweep-based load flow and the modeling of PEV load with two different charging scenarios.     

Design and modeling of SMES based SAPF for pulsed power load demands

In this article, a Superconducting Magnetic Energy Storage (SMES) based Shunt Active Power Filter (SAPF) topology is proposed to compensate high power pulsating load demands in a power system. The SMES based SAPF is designed and modeled to realize as an efficient compensator for the compensation of pulsed power load demands. The conventional SAPF is efficient to mitigate the power quality problems in a power system unless there is high power pulsating load demands, transient conditions or power fluctuations. Particularly, a Modified Synchronous Reference Frame (MSRF) control algorithm has been implemented to generate proper switching signals for the three-phase Voltage Source Converter (VSC) of the SMES based SAPF. In the simulation, it has been seen that the SAPF is incompetent under high power pulsating load demands whereas the SMES based SAPF has shown excellent performance under such load conditions. Moreover, a comparative analysis has been made between the conventional SAPF and the SMES based SAPF under pulsating load conditions, to check the effectiveness of the SMES based SAPF. The performance of the proposed system is presented by using Sim Power System (SPS)/MATLAB Simulink and real-time digital simulator laboratory (RTDS-Lab).     

Decentralized coordinated control for large power system based on transient stability assessment

For the purpose of enhancing transient stability of large power systems, this paper focuses on an issue of decentralized coordinated control. A modified equal area criterion (MEAC) is firstly proposed as the transient stability judgment criterion of multi-machine power systems. Then, a hierarchical decentralized coordinated excitation control is designed, which consists of both upper level coordinated control and lower level decentralized control. Based on the transient stability assessment, the coordinated controller determines whether to send coordinated control signal to lower level decentralized controllers. Moreover, the decentralized coordinated controller is designed by using H_∞ robust control method so as to deal with the uncertainties of system. Finally, simulation studies test effectiveness of the proposed control.