An Energy-Saving Control Strategy on Central Air-Conditioning System

An energy-saving control strategy based on predictive control for central air-conditioning systems is proposed in this paper. The cold load model is developed to describe the dynamic characteristics of temperature control systems, and then parameters in the cold load model and in the central air-conditioning system model are estimated. Generalized predictive control (GPC) is used to establish an optimization model to minimize the consumption of energy and the control error of temperature. The simulated annealing (SA) algorithm, combined with quadratic programming, is adopted to solve the optimal problem. Contrasted with the simulation of traditional PID control, the results prove the effectiveness of this proposed strategy.     

基于非线性时间序列分析的绝缘子污闪预测研究(英文)

To solve the problem of the flashover forecasting of contaminated or polluted insulator,a flashover forecasting model of contaminated insulators based on nonlinear time series analysis is proposed in the paper.The ESDD is the key of flashover on polluted insulator.The ESDD value of insulator can be forecasted by the method of nonlinear time series analysis of the ESDD time series and a forecasting model of polluted insulator flashover is proposed in the paper.The forecasting model consists of two artificial neural networks that reflect relationship of environment,ESDD and flashover probability.The first is used to estimate the ESDD time series of insulator and the second is employed to calculate the probability of the flashover.A series of artificial pollution tests show that the results of the forecasting model is acceptable.     

General Pattern and Neighborhood Search Algorithms for Non-Convex Unit Commitment

This paper presents a new approach to solve mixed-variable unit commitment （UC） problems with non-smooth cost functions based on a generalized pattern search filter （GPS-filter） algorithm. A GPS-filter algorithm does not require any information about the gradient of the objective function while searching for an optimum solution. At the same time, it is available for solving mixed-variable optimization problems, which is very suitable for UC. A new suitable discrete neighborhood structure with UC characteristics is proposed to improve GPS-filter efficiently. A lot of multiple units＇ states are fixed before search; hence, the polling search of discrete variable is efficient for a few uncertain units. Numerical experiments are included to demonstrate the proposed approach＇s ability to handle the highly nonlinear, discontinuous, non-smooth cost functions and mixed variables of the UC problem.     

中国电网近年来防雷技术发展及应用效果（英文）

In recent years,along with the rapid expansion of power grids,the increasing complication of grid structures,and the development of smart grids and energy technologies,the lightning protection of power grids becomes increasingly prominent.Power grids of China have acquired significant achievements on lightning protection technologies,which are reviewed in this paper.A technical route of lightning protection is introduced in detail; it allows us to find problems through detection and measurement of lightning,to analyze problems through evaluation and simulation of lightning,to solve problems through lightning protection measures,and to prevent problems through hazard risk warning of lightning.Following the route,the technical breakthroughs of these four aspects in China are presented,including the chinese lightning detection network(CLDN),natural lightning observations,lightning faults detection at transmission lines,lightning current measurements,progresses in lightning distribution maps,lightning fault replays,lightning hazard risk evaluations,and lightning simulated experiments,as well as novel lightning protection measures.The practical devices and systems corresponding to the technologies mentioned above are also introduced and discussed.Due to the progress of lightning protection technologies in recent years,despite the rapidly growing length of transmission lines in China,the lightning accident rate is controlled at a certain level.     

The Past, Present and Future of Electric Power Systems in China

(1) The revising of criteria of power system planning and operation are absolutely needed to adapt ever-changing conditions and to make the better coordination between security, quality and economy.(2) The main mission of the Ministry of Electric Power is to realize long distance and bulk power transmission from the west to the east and to solve the related technical, economic and organizational problems. To meet the mission, the Ministry of Electric-Power is preparing some planning and operating guides to promote regional interconnections and keeping stable and economic operation of interconnected systems.(?) There are many problems needed to be studied for the new market-oriented structure in power industry.     

Improved Location Algorithm of VIRE Based on RFiD

Using linear interpolation method, VIRE algorithm simply treats the signal strength value and distance of the reference tag as a linear relationship, leading to the inaccuracy of signal strength value for virtual reference tags. The threshold in VIRE algorithm is a fixed value that needs repeatedly adjustment through experiments, which results in the complicated algorithm. To solve these problems, an improved algorithm is proposed in this paper, including nonlinear interpolation algorithm, dynamic threshold setting and tag self-correction of fuzzy map, which builds an indoor positioning system based on reference tags. The experimental results show that the improved algorithm can improve the position- ing accuracy and improve the stability of positioning results under bad environmental conditions with- out increasing the number of reference tags.     

Parameter Test and Analysis for Dynamic Compensation Devices in Wind Power Farms

The dynamic reactive power compensation equipment in Jiuquan Wind Power Base of above 10 GW consists of three different types of compensation devices,including:static var generator(SVG),thyristor controlled compensator(TCR)and magnetically controlled reactor(MCR).The lack of experimental verif ication of performance is not conducive to voltage/var management or full utilization of device capacities.In order to solve the above problems,the compensation device performance test was performed.The test items and procedures were selected based on related national standards with the consideration for different grid structures and wind farm operation modes.The testing contents included dynamic regulating range, active power loss,dynamic response time,and harmonic voltage level.Three types of compensation devices installed in different wind farms,namely SVG,TCR and MCR,were chosen and tested.The performances were compared and analyzed according to the field test results.     

A NEW GA APPROACH FOR OPTIMAL CONTROL SETTING DETERMINATION OF UPFC IN POWER SYSTEM OPERATION

This paper presents a new, hybrid genetic algorithm (GA) approach to solve optimal power flow (OPF) in power system incorporating flexible AC transmission systems (FACTS). A versatile FACTS device, UPFC (unified power flow controller), is considered. In the solution process, GA, coupled with full AC power flow, selects the best regulation to minimize the total cost and keep the power flows within their security limits. The optimization process with GA is presented with case study examples using IEEE test system to demonstrate its applicability.The results are presented to show the feasibility and potential of this new approach.     

临近高压电气设备电缆局部放电脉冲的鉴别方法

On-line partial discharge(PD)diagnostics data are corrupted by various noise sources and this makes it more challenging to extract the PD signal contained in the raw data.Though the noise sources can be filtered out using signal processing techniques,PDs from neighboring cables and other high voltage equipment make the de-noising process more difficult due to the similar features of these signals with the PD signal of interest.Proposed in this paper is a double-ended partial discharge diagnostic system with dual sensors at each end which uses wireless time triggering using global time reference with the aid of global positioning system(GPS).Using the time of arrival method based on the velocity of propagation on the data,PD pulses originating from other sources can be discarded which reduces the volume of data to be stored and would eventually also reduce the hardware and software requirements of the denoising process thereby improving de-noising efficiency.System design,laboratory tests and on-site measurements are discussed.     

Adaptive coordination control strategy of renewable energy sources, hydrogen production unit, and fuel cell for frequency regulation of a hybrid distributed power system

The ‘mismatch losses’ problem is commonly encountered in distributed photovoltaic (PV) power generation systems. It can directly reduce power generation. Hence, PV array reconfiguration techniques have become highly popular to minimize the mismatch losses. In this paper, a dynamical array reconfiguration method for Total-Cross-Ties (TCT) and Series–Parallel (SP) interconnected PV arrays is proposed. The method aims to improve the maximum power output generation of a distributed PV array in different mismatch conditions through a set of inverters and a switching matrix that is controlled by a dynamic and scalable reconfiguration optimization algorithm. The structures of the switching matrix for both TCT-based and SP-based PV arrays are designed to enable flexible alteration of the electrical connections between PV strings and inverters. Also, the proposed reconfiguration solution is scalable, because the size of the switching matrix deployed in the proposed solution is only determined by the numbers of the PV strings and the inverters, and is not related to the number of PV modules in a string. The performance of the proposed method is assessed for PV arrays with both TCT and SP interconnections in different mismatch conditions, including different partial shading and random PV module failure. The average optimization time for TCT and SP interconnected PV arrays is 0.02 and 3 s, respectively. The effectiveness of the proposed dynamical reconfiguration is confirmed, with the average maximum power generation improved by 8.56% for the TCT-based PV array and 6.43% for the SP-based PV array compared to a fixed topology scheme.     

Power generation maximization of distributed photovoltaic systems using dynamic topology reconfiguration

The ‘mismatch losses’ problem is commonly encountered in distributed photovoltaic (PV) power generation systems. It can directly reduce power generation. Hence, PV array reconfiguration techniques have become highly popular to minimize the mismatch losses. In this paper, a dynamical array reconfiguration method for Total-Cross-Ties (TCT) and Series–Parallel (SP) interconnected PV arrays is proposed. The method aims to improve the maximum power output generation of a distributed PV array in different mismatch conditions through a set of inverters and a switching matrix that is controlled by a dynamic and scalable reconfiguration optimization algorithm. The structures of the switching matrix for both TCT-based and SP-based PV arrays are designed to enable flexible alteration of the electrical connections between PV strings and inverters. Also, the proposed reconfiguration solution is scalable, because the size of the switching matrix deployed in the proposed solution is only determined by the numbers of the PV strings and the inverters, and is not related to the number of PV modules in a string. The performance of the proposed method is assessed for PV arrays with both TCT and SP interconnections in different mismatch conditions, including different partial shading and random PV module failure. The average optimization time for TCT and SP interconnected PV arrays is 0.02 and 3 s, respectively. The effectiveness of the proposed dynamical reconfiguration is confirmed, with the average maximum power generation improved by 8.56% for the TCT-based PV array and 6.43% for the SP-based PV array compared to a fixed topology scheme.     

Designing of robust frequency stabilization using optimized MPC-(1+PIDN) controller for high order interconnected renewable energy based power systems

The challenge of controlling frequency becomes greater as the complexity of a power network increases. The stability of a power system is highly dependent upon the robustness of the controller. This paper presents automatic generation control (AGC) of a four-area interconnected power system along with integrated renewable energy sources of PV and wind energy. The designed model is a challenge given the increased penetration levels of PV and wind along with a thermal-hydropower system. The addition of a hydropower system as a fourth type results in the pole of the open loop system of the hydropower system being located at the right half side of the s-plan. This demands a robust control. A novel MPC-(1 + PIDN) is designed for high-order interconnected areas (HOIA) to stabilize the frequency in a robust way. The salp swarm algorithm is adopted to optimize the parameters of the PIDN controller. The performance of the proposed controller under HOIA is tested in a unbalanced load environment with uncertainty in the power system. The proposed controller can effectively handle the frequency disruption by stabilizing it in 0.86s for Area-1, 1.08s for Area-2, 0.81s for Area-3, and 0.84s for Area-4 with an average time of 0.89s for all the areas, whereas the average time for GWO: PI-PD, MPC/PI and GA-PI is 3.48s , 10.36s and 18.47s , respectively. The results demonstrate the effectiveness of the controller when compared to other controllers.     

Mach Number Prediction for a Wind Tunnel Based on the CNN-LSTM-Attention Method

The test section’s Mach number in wind tunnel testing is a significant metric for evaluating system performance. The quality of the flow field in the wind tunnel is contingent upon the system''s capacity to maintain stability across various working conditions. The process flow in wind tunnel testing is inherently complex, resulting in a system characterized by nonlinearity, time lag, and multiple working conditions. To implement the predictive control algorithm, a precise Mach number prediction model must be created. Therefore, this report studies the method for Mach number prediction modelling in wind tunnel flow fields with various working conditions. Firstly, this paper introduces a continuous transonic wind tunnel. The key physical quantities affecting the flow field of the wind tunnel are determined by analyzing its structure and blowing process. Secondly, considering the nonlinear and time-lag characteristics of the wind tunnel system, a CNN-LSTM model is employed to establish the Mach number prediction model by combining the 1D-CNN algorithm with the LSTM model, which has long and short-term memory functions. Then, the attention mechanism is incorporated into the CNN-LSTM predic-tion model to enable the model to focus more on data with greater information importance, thereby enhancing the model''s training effectiveness. The application results ultimately demonstrate the efficacy of the proposed approach.     

FPGA-based real-time simulation for EV station with multiple high-frequency chargers based on C-EMTP algorithm

The electric vehicle (EV) charging station is a critical part of the infrastructure for the wide adoption of EVs. Real- time simulation of an EV station plays an essential role in testing its operation under different operating modes. However, the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation. This paper proposes a compact electromagnetic transient program (C-EMTP) algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers. The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations, to fully utilize the high parallelism of FPGA. The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm, and so the simulation accuracy for high-frequency power electronics is improved. The EV chargers can be decoupled with each other and simulated in parallel. A CPU-FPGA-based real- time simulation platform is developed and the proposed simulation of the EV station is implemented. The control strategy is simulated in a CPU with 100μs time-step, while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step. In the case studies, the EV station consists of a two-level rectifier and five dual-active bridge (DAB) EV chargers. It is tested under different scenarios, and the real-time simulation results are validated using PSCAD/EMTDC.     

Db复小波在超高频局部放电测量中的应用(英文)

On-line partial discharge(PD)detection still remains a very challenging task because of the strong electromagnetic interferences.In this paper,a new method of de-noising,using complex Daubechies wavelet(CDW)transform,has been proposed.It is a relatively recent enhancement to the real-valued wavelet transform because of tow important properties,which are nearly shift-invariant and availability of phase information.Those properties give CDW transform superiority over other real-valued wavelet transform,and then the construction algorithm of CDW is introduced in detail.Secondly,based on the real threshold algorithm of real-valued wavelet transform,complex threshold algorithm is devised.This algorithm take the different characteristics of real part and imaginary part of complex wavelet coefficients into account,it modifies the real and imaginary parts of complex wavelet coefficients respectively.Thirdly,to obtain a real de-noised signal,new combined information series is devised.By applying different combination of real part and imaginary part of de-noised complex signal,a real de-noised signal can be restored with higher peak signal-to-noise ratio(PSNR)and less distortion of original signals.Finally,On-site applications of extracting PD signals from noisy background by the optimal de-noising scheme based on CDW are illustrated.The on-site experimental results show that the optimal de-noising scheme is an effective way to suppress white noise in PD measurement.     

基于粗糙集理论的配电网故障诊断规则提取方法(英文)

As the first step of service restoration of distribution system,rapid fault diagnosis is a significant task for reducing power outage time,decreasing outage loss,and subsequently improving service reliability and safety.This paper analyzes a fault diagnosis approach by using rough set theory in which how to reduce decision table of data set is a main calculation intensive task.Aiming at this reduction problem,a heuristic reduction algorithm based on attribution length and frequency is proposed.At the same time,the corresponding value reduction method is proposed in order to fulfill the reduction and diagnosis rules extraction.Meanwhile,a Euclid matching method is introduced to solve confliction problems among the extracted rules when some information is lacking.Principal of the whole algorithm is clear and diagnostic rules distilled from the reduction are concise.Moreover,it needs less calculation towards specific discernibility matrix,and thus avoids the corresponding NP hard problem.The whole process is realized by MATLAB programming.A simulation example shows that the method has a fast calculation speed,and the extracted rules can reflect the characteristic of fault with a concise form.The rule database,formed by different reduction of decision table,can diagnose single fault and multi-faults efficiently,and give satisfied results even when the existed information is incomplete.The proposed method has good error-tolerate capability and the potential for on-line fault diagnosis.     

A simple decision tree-based disturbance monitoring system for VSC-based HVDC transmission link integrating a DFIG wind farm

Fault detection and classification is a key challenge for the protection of High Voltage DC (HVDC) transmission lines. In this paper, the Teager–Kaiser Energy Operator (TKEO) algorithm associated with a decision tree-based fault classi f ier is proposed to detect and classify various DC faults. The Change Identification Filter is applied to the average and differential current components, to detect the first instant of fault occurrence (above threshold) and register a Change Identified Point (CIP). Further, if a CIP is registered for a positive or negative line, only three samples of currents (i.e., CIP and each side of CIP) are sent to the proposed TKEO algorithm, which produces their respective 8 indices through which the, fault can be detected along with its classification. The new approach enables quicker detection allowing utility grids to be restored as soon as possible. This novel approach also reduces computing complexity and the time required to identify faults with classification. The importance and accuracy of the proposed scheme are also thor oughly tested and compared with other methods for various faults on HVDC transmission lines.     

电力变压器介质响应的测量与分析(英文)

This paper discusses approaches to measure moisture in power transformers by analyzing the dielectric response of the main insulation. Dielectric diagnostic methods deduce moisture in the solid insulation from dielectric properties like polarisation depolarisation currents and dissipation factor vs. frequency. A new instrument "Dirana" combines time domain (PDC) and frequency domain (FDS) measurements and thus substantially shortens the measurement duration. New software was developed which bases on a new data pool,measured at new and aged pressboard samples with various moisture contents and oil impregnation. Its analysis algorithm compares measurements from a transformer to modelled dielectric responses,obtained from the so-called XY-model. To avoid overestimation of moisture for aged transformers,the analysis algorithm compensates for the influence of conductive aging by-products. Moisture especially increases the losses in the low frequency range of the dielectric response of pressboard. Thus,data on the left-hand side of the area dominated by interfacial polarization (insulation geometry) are required for reliable moisture determination. Case studies illustrate the application of moisture determination by dielectric response methods.     

EXCITATION CONTROL FOR POWER SYSTEMS WITH NO NLINEAR LOADS

The paper describes an approach of exact linearization for multi input power systems with nonlinear loads. The considered nonlinear differential algebraic systems (NDAS) are not in general state variable form. Some new definitions of M derivative and M bracket that are similar to the definitions of classic differential geometric theory and some related revised results are given. The definitions of M derivative and M bracket can be easily used to obtain the feedback control law of the NDAS. The conditions of exact feedback linearization are shown. When given NDAS satisfy the proper conditions of exact linearization, the multi-machine power systems with nonlinear loads can be transformed into Brunovsky standard form with constraint algebraic equations.     

高海拔地区±800KV特高压直流线路空气间隙操作冲击放电特性(英文)

This paper is concerning switching impulse air gap insulation characteristics of rod-to-plane and V-string 6-conductor bundle to tower body in ±800 kV transmission lines.The tests were performed in China Southern Power Grid Co.,Ltd.(CSG) Kunming outdoor UHV laboratory at an altitude of 2 100 m.The switching impulse strength performance were obtained at a rod-to-plane arrangement and a full-scale model of 6-conductor bundle to tower.The test gap length of the typical rod-to-plane arrangement is 1.5～10 m and 5.3～8.2 m for the conductor-tower model,and the range of test voltage is about 450～3 100 kV.The critical positive switching impulse strength of conductor-tower gap is 1 525 kV in the gap length of 6.2 m.Additionally,the influence of the wave front time(100～1 700 μs) on the 50% flashover voltage is discussed.According to the test data,the minimum air gap clearances of the conductor-tower model with V-insulators at the altitude of 2 100 m should be longer than 6.8 m(wave front time 250 μs) and 5.8 m(wave front time 1 000 μs),respectively.The results are useful to air gap insulation design in UHVDC systems with rated voltage of ±800 kV.