Practical Criterion for Voltage Stability of Substation

This paper presents a new practical criterion for voltage stability based on the real-time information at the substation and the quasi-time information from power system.By using the criterion,it is effective to predict the bus voltage stability margin.This is of great importance to raise the security operation level and prevent voltage collapse.The practical criterion for voltage stability is tested on the IEEE-14-bus test system.It needs less calculation time and is very suitable for real-time control of power systems.     

Recognizing the reliability non-coherence components ofdistribution substation typical configuration

Reliability non-coherence components (RNC) may exist in a power system due to the effects of distribution substation connection modes, components reliability performance, load level, and other factors. Recognizing RNCs and removing them from a power system can improve system reliability. The reliability non-coherence phenomenon is analyzed and the reliability non-coherence probability, frequency and energy indices, which can describe the degree of the system reliability non-coherence feature, are proposed. Based on the reliability evaluation theory of substation configuration, recognizing technique of RNCs of distribution substation is proposed. The theoretical analysis and example show that the breaker connects high voltage buses may be the RNC when the rated capacity of one transformer can meet the load requirement, and the reliability parameters of breakers have some effects on the reliability non-coherence features of the typical substation configuration.     

Voltage and Reactive Power Optimization of Main Electric Power Network in Chongqing

Based on the reactive surplus of Chongqing 220 kV main electric power network under low water and low load, and on state of higher system voltage, a thorough research is done on voltage and reactive power of the system power network by means of calculation,analysis and experiments. A main network calculating equivalence model of power network in Chongqing is constructed. And reactive power optimizing calculation is figured out on the Chongqing power network on condition that the loss minimum of the active power network is object function. Several optimizing compensatory schemes are put forward. Based on the calculation result and the analysis of all schemes, the most reasonable and feasible optimizing scheme could be achieved. Meanwhile, the feasibility that the system voltage could be adjusted when generator operating under excitation was demonstrated. According to the experience of under-excitation operation of the same type units , it decreases the system voltage, improves Chongqing power network running performance, and strengthens the coordination and stabilization of system.     

OPTIMAL REACTIVE POWER FLOW BY SENSITIVITY METHOD

A new approach based on sensitivity method for the optimal power flow is presented in the paper. This method has the following advantages: it is suitable to solve a 200-node power system on the microcomputer; the convergence is easy to reach and the computation speed is quick; it is possible to reduce 8-14% power loss and to get maximum economic benefit by using this method; in power system dispatch center it can be used as an on-line voltage and reactive power control program to keep good voltage level. The proposed method has been proved successful by IEEE 118-node test system and the several real power systems such as 49-node, 61-node, 99-node and 200-node systems.     

A new control design for grid integration ofDFIG wind farm with VSC-HVDC

This paper proposes a control scheme for a doubly-fed induction generator (DFIG) wind farm with VSC-HVDC grid integration to ensure secure and reliable operation of power system with fluctuated wind power penetration. The whole system dynamic models are respectively described. Based on vector control system with a virtual voltage orientation, a steady-state voltage control block and a dynamic voltage control block with a cross-product term of d-q currents are separately designed for WFVSC to control the corresponding parts of the wind farm voltage. Meanwhile, with the consideration of AC and DC side parameter variation and external disturbance, an improved backstepping control scheme with Lyapunov stability provement is also proposed for the GSVSC. The combination of the two schemes makes up the new control design of this study. Besides, to verify the performance of the proposed new control design, three different cases are suggested which contain the AC and DC side parameter variation and external disturbance such as local load cut off-in, grid voltage harmonics. Finally, numerical simulations using MATLAB/Simulink are presented for a 200MW DFIG wind farm with VSC-HVDC grid integration to validate the proposed control scheme and demonstrate the improved system operation performance. Moreover, the corresponding discussions are also presented for further illustrations.     

计及电网停电风险的输电线路动态融冰决策方法

电网发生大面积冰灾情况时，多条输电线路存在覆冰故障隐患，电网稳定运行受到严重威胁，需要提前制定输电线路融冰方案，合理安排融冰顺序。针对此问题，分析输电线路覆冰继续运行给电网带来的停电风险，将与待融冰输电线路相关联的变电站的电气主接线展开，将传统削负荷模型改进后应用于输电网与变电站主接线的组合网络，建立断路器可靠性模型，计算靠后融冰线路因继续运行的电网停电风险；利用计及风速及降雨影响的输电线路覆冰增长预测模型，计算输电线路的覆冰率，根据覆冰率门槛值确定待融冰线路集，基于覆冰严重度模型构建系统全局的覆冰指数指标；综合考虑电网停电风险及系统全局覆冰指数建立输电线路融冰紧迫度指标，动态更新待融冰线路并决策融冰顺序。最后，以IEEE RBTS系统进行算例分析，验证了所提方法的可行性与合理性。     

MPPT control of photovoltaic grid connected system

The high cost of grid connected photovoltaic (PV) system is an important reason that hinders its market application. The control cost can be partly cut down by using sensorless Maximum Power Point Tracking (MPPT). However, the sensorless MPPT control proposed by previous literatures has drawbacks of poor estimation accuracy, bad real time performance, and poor dynamic responses, which has great impact on the MPPT and the output performance of the whole system. Aiming at these problems, an Adaptive Sliding Mode Observer (ASMO) for estimation of photovoltaic array voltage is proposed. The external disturbance and modeling errors are suppressed while the real time performance and the estimation accuracy are improved greatly by the proposed method. The favorable performance of the output performance and MPPT performance of the PV system based on the ASMO are validated by simulation and experimental results.     

Voltage Stability Control of Local Power System

In this paper,the conception of bus voltage stability control area of local powersystem is presented,based on the practical criterion for voltage stability calculated by the real-timeinformation and the quasi-real time information form the power system.The method is test6d onIEEE-30-bus test system and results are satisfactory.     

Analysis of Loosely Coupled Inductive Power Transfer System

In LCIPT system, the selection of system operation frequency has a relationshi Pwith the cost and power transfer capability of the power supply. Due to the development of Power device and system efficiency requirement , it is restricted to increase the system operation frequency . This paper presentes a topology which transfers power through LC oscillation. When the voltage of the capacitor is less than reference voltage, the switch is turned off and the capacitor is charged, which makes the switching frequency far less than the syntonic frequency. Thus the system efficiency is improved, and the system cost is reduced. This is verified by the time domain and frequency domain simulations of Saber. This topology not only can be used in LCIPT, but also in other convertors.     

An asymmetric fault ride-through control method forPMSG wind turbine based onsuper-capacitors

With the rapid increasing interaction between wind turbines and power systems, wind turbines have to have the fault ride-through (FRT) capability to ensure the safe operation of power grid. In order to improve the asymmetric FRT capability of permanent magnet synchronous generator (PMSG) wind turbine, a novel control FRT method based on super-capacitors is proposed. In this method, super-capacitors are connected to the DC bus of AC-DC-AC converter via a bi-directional DC-DC converter, and the power processed by the super-capacitors is controlled to limit the increasing of the DC bus voltage of the AC-DC-AC converter in grid failure condition, and to reduce the 2nd order voltage ripple in the DC bus. Meanwhile, the proposed control method employs the grid voltage feed-forward approach to reduce the negative sequence current component in the grid side converter. According to the low voltage ride through (LVRT) standard, the selection of the super-capacitor capacity is also discussed, and then a mathematical model of the super-capacitor with the bi-directional DC-DC converter is established for designing the controller. Simulation results for a 1MW PMSG wind turbine by MATLAB show that the proposed control method reduces both the negative sequence current component in grid side converter and the 2nd order voltage ripple in DC link at the same time. The results also demonstrate that the asymmetric FRT capability of PMSG wind turbine is improved, which verifies the effectiveness of the proposed control method in this paper.     

An Attentive Problem of 35 kV Power Lines in Mountain Area on Protecting Against

To counteract capacitive current and resume power system, the neutral point of 35 kV power system at the mountainous area is grounding through the arc winding widely. In fact, there is great difficult in selecting the arc winding to satisfy the requirement of system. In a 35 kV power system which neutral point is grounding through the arc winding, the capacitance current are measured in site when a single-phase is grounding. From the measure data, the imbalance of three-phase voltage whether the arc winding exist or not and the operating situation of arc winding are discussed, and bring forward an attentive problem about operation of arc winding and decrease of lightning outage rates.     

基于无迹卡尔曼滤波神经网络的光伏发电预测

针对光伏发电系统在不同天气状况下发电功率预测精度不高的问题，在分析传统方法的基础上，提出一种无迹卡尔曼滤波神经网络光伏发电预测方法。该方法利用无迹卡尔曼滤波实时更新神经网络模型的权重，以直流电压和电流作为系统的输入，以有功功率和无功功率作为系统的输出，分别建立两个独立的双输入单输出功率预测模型。实验结果表明：所提出的方法对有功功率和无功功率的预测精度分别为97.3%和94.2%，并且对天气具有良好的鲁棒性。     

Voltage Fluctuation and Flicker Mitigation Using STATCOM

Voltage fluctuation and flicker is one of the main causation that imperils reliability of power supply. Steelmaking EAF with large load of distribution network produces large impact and interference on the public electric network in operation. So it is very important to control reactive power for voltage fluctuation and flicker mitigation. STATCOM possessing high response speed is an effective measure to mitigate voltage fluctuation and flicker of distribution network. Here, comparing to static var compensation, many advantages of STATCOM are analyzed. Operation principles COM mitigating voltage fluctuation and flicker, general control strategies and control method are introduced cussed. The researching pivot and trend in the future are also discussed. of STAT- and discussed. The researching pivot and trend in the future are also discussed.     

Analysis to On-off Voltage Wave and Its Parameter of Switched Power

To analyse the working parameter of switched power, this article introduces the circuit model of switched power and the shaping process of its on off voltage wave. Aiming at analyzing to the voltage wave and parameter, an "assistant compensation" method is put forward. Based on this method, the voltage wave and parameter of switched power are theoretically analyzed and imitated. The imitation results indicate that the method is afeasible and advance one.     

A preventive control model for static voltage stability considering the power constraints of weak branches

The voltage instability of power system often occurs when the active power on one or more weak branches exceeds its transfer capability. A preventive control model for static voltage stability is proposed using the active power transfer capability of weak branches as static voltage stability constraints. A local line based voltage stability index is used to determine the critical contingencies, weak branches and transfer capability of each weak branch. A static security analysis method, which is based on DC power flow equations, is used to establish the non linear active power flow expressions on weak branches following each critical contingency. The active power constraints on weak branches can be obtained from the active power flow expressions and transfer capabilities of weak branches. A quadratic optimal model for preventive control including the proposed active power constraints on weak branches is presented. The simulation results for IEEEE14 bus system and IEEE118 bus system demonstrate the correctness and effectiveness of the proposed preventive control model.     

APPLICATION OF OUT-OF-KILTER ALGORITHM TO ECONOMIC DISPATCH WITH SECURITY

This paper reports on the application of "Out-of-Kilter Algorithm" (OKA) to the real power economic dispatch with security constraints. The network flow programming is characterized by simple manipulation, fast and reliable convergence, while the OKA can treat nonzero lower bounds and may initiate with any set of flows (including infeasible flow) which satisfies Conservation of flow. The major procedure and numerical example of OKA are given in this paper. The calculating results for economic dispatch on test systems have shown that the method is feasible and effective.     

Operation Optimization of Ball Type Pulverizer Based on System Identification

The ball type pulverizer system is widely used in power plant in China because of its better coal adaptability, easy maintenanceand high reliability. However, its primary disadvantageis high power consumption. Itis not only the big consumer of power plant ,but also thebig latenteconomizer. Some existentresearches mostly focus on pulverizer, not on the ball type pulverizer system. An operation optimization method is presented in the disquisitionbased on the system identification. By selecting data upon orthogonal norm , acquiring the system model through Least Squares method, and according to the theory of optimization, the authors obtain the optimal values of controlledparameters.This method can avoid disadvantageboth of searching for the input-output specialty through mechanismmodeling and big data sample space for Manual Neural Network. It is valuable in practice for the ball type pulverizer system operation optimization and economizing energy in power plant.     

Processing Fault Data Method in Load Forecasting Based on Wavelet Analysis

The reliability and reality of load historical data is the foundation of load forecasting.But,the impact load in running power system,and the disturb data in collecting load data through the SCADA may cause much fault data in load historical data. Focusing on solving this problem, a method through adjusting amplitade of its wavele modulus maxima and processing the wavelet decomposed detail signal by soft threshold based on wavelet analysis and singularity theory, then fault date can be eliminated,so that,the real historical imformation and regulation data can be gained by load forecasting.     

Modeling and control of An LCL bi-directional inductive power transfer system

Since there exist high-frequency switching networks and complicated operating modes in bi-directional inductive power transfer (IPT) system, it is easy to result in high harmonics and EMI interference. An LCL filter network is introduced to effectively filter out the unwanted harmonics in track current and reduce EMI interference. Based on a mathematical model of the power transmission established by complex analysis of the AC variables, under the condition of maximum transmission efficiency, the phase angle differences between the primary input voltage and secondary output voltage U·so are ±90° and the energy is respectively transferred in forward or backward direction. Moreover, the power magnitude can be controlled by adjusting the modulus of U·pi and U·so. In addition, to keep the track current constant, different phase-shifting control strategies are designed in the primary and secondary parts. Simulation and experimental results show that these strategies can not only adjust track current to keep constant but also dynamically change the direction and magnitude of power transmission according to the working conditions and actual needs of the system load to improve the system operating efficiency.     

Theoretic analysis and verification of the closed-loopself-oscillation for an MEMS gyroscope

By analyzing the requirement of the closed-loop control for the vibratory gyroscope, the behaviour of the self-oscillation system with automatic gain control was analyzed with averaging method to achieve system stability and stable equilibrium. The theoretic analysis and experiment show that the reference voltage must be larger than a critical value; the larger the reference voltage is, the larger the signal-noise-ratio is; the system phase error will cause the resonance frequency drift and decrease the vibrating amplitude; different constants of the low pass filters result in different time to achieve the stable states. The experiment shows the frequency accuracy of the close-loop self oscillation system is about ±8ppm in 10 minutes and vibration amplitude is about 0.1% error in an hour.