bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparator hysteresis compensation for decision feedback equalisers
Authors: Mattia O.E. , Guermandi D. , Torfs G. , Wambacq P.
Published: October 2018

High‐speed comparators are extensively used in serial link receiver designs. Some comparator architectures can show significant hysteresis that degrade the sensitivity of the receiver, increasing the bit error rate. In this Letter, a comparator hysteresis compensation strategy that re‐uses the first tap of a decision feedback equaliser to shift the comparator input voltage, increasing the decision margin is proposed. An updated equaliser coefficient adaptation scheme is also introduced. The proposed technique can be used for binary and multi‐level modulations.
Substrate integrated waveguide FPWD with quasi‐elliptic response
Authors: Gao Yi‐Qiang , Shen Wei , Wu Liang , Sun Xiao‐Wei
Published: October 2018

A novel filtering power divider (FPWD) with a quasi‐elliptic response based on the multilayer substrate integrated waveguide is presented. The odd‐symmetric fact of the TE102 mode is applied to accomplish two contrary couplings with equal strengths. On the basis of the specially coupling topology, the FPWD can realise quasi‐elliptic response. An experimental sample is measured to verify the design methods, and the measured results account with the simulated ones well.
Trapezoidal recursive convolution‐based FDTD method for arbitrary‐shaped dispersive materials
Authors: Shibayama J. , Suzuki K. , Yamauchi J. , Nakano H.
Published: October 2018

A trapezoidal recursive convolution (TRC) technique is one of the simple ways to incorporate dispersive models into the finite‐difference time‐domain (FDTD) method. The authors newly develop the TRC–FDTD method for the analysis of arbitrary‐shaped dispersive materials using a dispersive contour‐path algorithm. The accuracy of the present method is found to be the same as that using the Z‐transform technique with reduced computational requirements.
Multi‐beam receive scheme for millimetre wave wireless communication system
Authors: Chen Weicong , He Shiwen , Xu Qinzhen , Yang Luxi
Published: October 2018

Different from the conventional receive scheme for millimetre wave (mmWave) communication, this study proposes a multi‐beam receive scheme to improve the quality of the received signal and enhance the robustness of the system. The authors proposal is firstly formulated as an optimisation problem, where each signal received by different beams is combined through phase compensation to harvest more transmission energy. Then the original problem is divided into a series of sub‐problems and an analytical solution is further obtained for each sub‐problem. Furthermore, considering the spatial sparsity of the mmWave channel, they propose further a low‐computational complexity algorithm by choosing a few candidate codewords with non‐negligible receive signal power. Numerical results show that their proposal achieves remarkable performance improvements even with a small size codebook and is more robust for different scenarios, especially for a non‐line of sight scenario. Compared with doubling receive antennas to obtain diversity gain, their proposal obtains larger signal‐to‐noise ratio gain while using fewer hardware resources.
Frequency‐domain channel equalisation for LTE‐based uplink narrowband Internet of Things systems
Authors: Ali Md Sadek , Jewel Md Khalid Hossain , Li Yu , Lin Fujiang
Published: October 2018

An emerging narrowband radio technology named narrowband Internet of Things (NB‐IoT) based on cellular communications has been standardised by the 3rd Generation Partnership Project in release‐13. It is specifically designed to provide low‐power wide‐area connectivity for the IoT. In this study, the authors derive an analytical signal model for Long Term Evolution (LTE)‐based uplink NB‐IoT systems. The problem of channel equalisation for the uplink NB‐IoT systems having mismatched baseband processing and sampling rate between transmitter and receiver is addressed. A relation between the channel impulse response and the channel frequency‐domain equalisation coefficients is derived under imbalanced baseband processing and sampling rate environment. Accordingly, a novel one‐tap frequency‐domain channel equalisation algorithm specific to NB‐IoT uplink systems is proposed based on the resultant channel coefficients. Comprehensive link‐level simulations are carried out to validate the potentiality of the proposed equalisation method, compared with other conventional techniques like zero forcing and minimum mean square error equalisers in terms of symbol error rate and throughput against signal‐to‐noise ratio. Simulation results indicate that the proposed equaliser outperforms the existing linear equalisers for all cases of evaluation.
Moving horizon shared steering strategy for intelligent vehicle based on potential‐hazard analysis
Authors: Liu Jun , Chen Hong , Guo Hongyan , Song Linhuan , Hu Yunfeng
Published: October 2018

The collaboration between a human driver and an automation system will serve as an effective measure before the autonomous driving technology is fully implemented. To discuss the driving authority between a human driver and an automation system, a novel moving horizon shared steering framework is proposed, in which the controller assists the driver when the vehicle is in danger. First, a potential‐hazard analysis is presented based on the potential steering operation error and lane departure distance to predict the degree of a hazard and to determine the driving authority between the human driver and the automation system. Then, the minimum collaborative steering operation is determined using a moving horizon optimisation approach with safety constraints. Thus, the automation system shares steering with the driver protect the vehicle from risks in a non‐invasive manner. To demonstrate the effectiveness of the proposed strategy, simulations with different types of drivers and scenarios are conducted. The results of these simulations demonstrate that the proposed approach can enhance the driving ability of drivers with different skill levels in dangerous situations. The approach can also guarantee the safety of the intelligent vehicle to some extent when drivers lose focus for a period of time.
Multi‐functional distributed generation control scheme for improving the grid power quality
Authors: Ali Zunaib , Christofides Nicholas , Hadjidemetriou Lenos , Kyriakides Elias
Published: October 2018

Renewable sources are expected to be a key element of future power systems. With many challenges ahead, thinking out of the box is necessary in order to equip the power system with additional advanced functionalities and capabilities to combat the anticipated challenges. The associated equipment of distributed generation can be seen as a grid asset upgrade because of the increased number of elements connected to the grid, such as grid side converters (GSC) of photovoltaics and battery storage systems. It therefore makes sense to think of ways to diversify the role of distributed renewables in a way that benefits the grid, consumers, and prosumers in terms of power quality. The work proposes an advanced, multi‐function GSC control technique for improving the distribution grid power quality by enabling the injection of asymmetric, DC and harmonic currents in case it is needed. Injecting for example such currents locally through the GSC of a residential photovoltaic system can compensate undesired characteristics of the prosumer loads in order to allow the flow of symmetric and high quality currents between the prosumer and the distribution grid. Experiments and simulation results are presented to validate the performance of proposed control technique.
Research on transformerless dual‐buck full‐bridge grid‐connected inverter with H5‐type for PV systems
Authors: Dai Yunzhong , Li Wenzhu , Zhou Chunhua , Zhuang Shengxian
Published: October 2018

To eliminate the common‐mode leakage current in the transformerless grid‐connected photovoltaic (PV) system, inspired by the newly‐developed embedded‐switch H5 topology and dual‐buck full‐bridge grid‐connected inverter (GCI), a novel transformerless dual‐buck full‐bridge GCI with H5‐type (TDFGI‐H5) topology for PV systems is firstly presented. Then, the operating modes and common‐mode leakage current of TDFGI‐H5 modulated by unipolar sinusoidal pulse‐width modulation are analysed. The analysis result shows that TDFGI‐H5 has the advantages of the three‐level output, no shoot‐through problem, high reliability, and can completely meet the condition of eliminating common‐mode leakage current. Aim at the problem of the common‐mode leakage affected by the switches’ junction capacitances, the effect of switch's junction capacitance is explored in detail when TDFGI‐H5 is in the transient process that converts from non‐decoupling states to decoupling states. Finally, the results of experiment verify the correctness of the theoretical analysis.
Elimination of zero sequence circulating currents in paralleled three‐level T‐type inverters with a model predictive control strategy
Authors: Wang Xiaodong , Zou Jianxiao , Peng Ying , Xie Chuan , Li Kai , Guerrero Zapata Josep Maria
Published: October 2018

The configuration of modular paralleled three‐level T‐type inverters (3LT2Is) has been widely utilised to extend the system power rating. However, zero sequence circulating currents (ZSCCs) are generated when sharing the common DC‐link and the AC side without isolated transformers. This study presents a novel model predictive control (MPC) based strategy to eliminate the ZSCC in parallel operating 3LT2Is. Both the differences of common‐mode voltages (CMVs) and neutral point potentials (NPPs) between paralleled 3LT2Is are investigated to be the potential exciting sources of the ZSCC based on the developed model of the ZSCC. According to this conclusion, an MPC‐based zero CMV method which adds an additional term to the cost function is used to reduce the differences of CMVs between paralleled 3LT2Is. Besides, a closed‐loop ZSCC feedback control method is further introduced to compensate the ZSCC by modifying the cost function. With the proposed MPC‐based ZSCC elimination strategy, the ZSCC between the paralleled 3LT2Is can be effectively eliminated in both steady and dynamic states. Besides, good performances can be achieved for both load current tracking and NPP balance control. Simulation and experimental results validate the effectiveness of the proposed ZSCC elimination strategy.
Unified discrete‐map modelling and dynamical behaviour analysis of current mode controlled tri‐state dc–dc converters
Authors: Zhou Guohua , Zeng Shaohuan , Zhou Shuhan , Mao Guihua , Xu Shungang
Published: October 2018

Through analysing the operating principle of current mode controlled (CMC) tri‐state dc–dc converters, the inductor current borders are obtained and a unified discrete‐map model of CMC tri‐state dc–dc converters with ramp compensation is established. According to this model, the dynamical behaviour of the tri‐state dc–dc converters is analysed by utilising bifurcation diagram. In addition, the boundary equation of tri‐state dc–dc converters from stable pseudo‐continuous conduction mode (PCCM) period‐1 state to unstable state is derived. The expressions of the minimum slope of ramp compensation for the converter shifting from unstable state to stable PCCM period‐1 state are also obtained. Meanwhile, the operating regions are divided effectively by the boundary equation. The research results indicate that border collision bifurcation could occur when the circuit parameters vary, including a bifurcation from one periodic orbit to another periodic orbit, such as period‐1 to period‐2 or period‐2 to period‐4 and so on, or a bifurcation from a period orbit to chaotic orbit. By using ramp compensation, the stable working range of the CMC tri‐state dc–dc converter could be broadened. Finally, an experimental circuit is built and the experiment results verify the theoretical analysis.
Flexibility of controllable power transformers for managing wind uncertainty using robust adjustable linearised optimal power flow
Authors: Nikoobakht Ahmad , Aghaei Jamshid , Farahmand Hossein , Lakshmanan Venkatachalam , Korpås Magnus
Published: October 2018

As renewable energy sources (RESs) penetration increases in the power system, the transmission system operators face new challenges to ensure system reliability and flexibility while ensuring high utilisation of uncertain RES generation. Controllable transformers with on‐load tap changers and phase shifting capability are the promising flexibility tools to keep the system acceptable security and flexibility levels by controlling the voltage levels and energy flow. The AC optimal power flow (AC OPF) with detailed modelling considerations such as the bus voltage magnitude by including these devices is challenging. This study develops the AC OPF model to propose a robust flexibility optimisation framework for daily scheduling problem with uncertain wind energy sources. Nevertheless, the proposed formulation representation is an intractable mixed integer nonlinear programming (MINLP) while it includes AC grid constraints and the augmented modelling of the mentioned transformers. Accordingly, the proposed MINLP problem has been converted into a mixed‐integer linear program where a certain level of solution accuracy can be achieved for the available time budget. The effectiveness of the proposed method is demonstrated using a modified 6‐bus and IEEE 118‐bus test systems.
Ground vehicle target signature identification with cognitive automotive radar using 24–25 and 76–77 GHz bands
Authors: Tan Qinling Jeanette Olivia , Romero Ric A.
Published: October 2018

The authors present cognitive automotive radar (CARr) as a significant capability to the sensing technology suite of autonomous driving vehicles. CARr is a closed‐loop intelligent radar system utilising the automotive frequency bands of 24–25 and 76–77 GHz for the purposes of ground vehicle target signature identification. The authors consider specific cases of ground vehicle recognition and ground vehicle class identification in the presence of aspect angle uncertainty using forward‐looking automotive radar. The transmit‐adaptive waveforms are based from signal‐to‐noise ratio and mutual information optimisation metrics. In this study, two new adaptive waveform techniques with the flexibility to accommodate angular uncertainty probability distributions are introduced. The classification performance of these new waveforms is compared against the receive‐adaptive wideband pulsed and other transmit‐adaptive waveforms in the presence of angular uncertainties characterised by the uniform and truncated normal distributions. To ensure the validity of results, high‐fidelity electromagnetic simulated radar cross‐section signatures generated from scaled‐to‐true‐physical‐size ground vehicle computer‐aided design models are utilised.
Revisiting the methodological approach to some application oriented unipolar corona investigations focusing interfacial properties of the ionised region
Authors: Lattarulo Francesco
Published: October 2018

This study gives new insight into unipolar coronas with special regard to the governing parameters, of practical value, for the outer edge of the ionisation region. The shape and local radius of that interface are fully determined according to a capillary‐based scheme, whose original application can be explained by a long‐range collective containment effect presumably exerted by internal streamers. Properly implemented indirect experiments furnish supportive features, especially used to reconstruct interfacial anomalies. The adopted cross‐sectorial approach allows traditional pre‐breakdown Townsend/Meek criteria to be circumvented for the benefit of computational simplification, other than precision when strongly non‐uniform fields are, as usual, involved. This represents a genuine disruptive paradigm change whose additional advantages are reflected in clearer interpretations of both Kaptsov hypothesis and maximum thrust density impressed, next to the interface, to air neutrals. Even the corona current–voltage characteristic has been called into play to sustain the capillary model with convincing arguments. These claims existence of a unifying theoretical substrate for a number of pre‐breakdown interfacial phenomena, whatever the state of matter.
Research on commutation failure of Jinsu DC transmission project caused by a complex AC fault
Authors: Peng Wei , Jian‐Kun Liu , Qian Zhou , Ning‐Yu Zhang
Published: October 2018

Commutation failure is an important factor on safe and stable operation of the receiving‐end power grid for high voltage direct current (HVDC) project. A commutation failure event in Jinsu DC transmission project caused by a complex AC failure was taken as background, process of fault and action sequences of protection was introduced, and the reason of the commutation failure and protection action was analysed from principle. Real‐time digital simulation (RTDS) was connected to the true‐type device of ultra‐high voltage direct current (UHVDC) control and protection to form a closed‐loop simulation platform. The commutation failure event was inversed, and the simulation result was compared with the actual recorded wave. The results show that abnormal AC voltage leads to the commutation failure.
Restart progress of fault in UHVDC after blocking
Authors: Wei Peng , Zhou Qian , Liu Jian‐kun , Wang Cheng‐gen
Published: October 2018

In order to reduce the impact of bipolar blocking on grid stability of restoration and restart process, a unipolar blocking caused by fires in Jin Su ultra‐high voltage direct current (UHVDC) as background was taken, using real time digital simulator (RTDS) built a model of DC and AC power grid on both sides, forming closed‐loop simulation platform together with UHVDC control and protection true‐type device. Based on the simulation platform, unipolar blocking fault caused by wildfire was inversed, and line protection action principle and restarting logic are studied. Protection action and restart during unipolar blocking were studied. Based on simulation platform on RTDS of UHVDC control and protection, the unipolar blocking event was inversed and the simulation result was compared with the actual recorded wave. The results show: operation of the protection device does reflect the line fault.
Double‐port network model with fault slag based on multi‐terminal DC system
Authors: Fu Yuan , Liu Jingyan , Xu Yan
Published: October 2018

According to the actual requirements of the project, when the pole‐to‐pole fault occurs in the DC system, the fault must be cleared during the capacitor discharge phase, so the requirements of the calculation of the current transient expression at the fault point are made. To solve this problem, this study proposes a dual‐port network model with fault flags. First, analyse the equivalent circuit diagram of the tree and ring DC system after fault, and compare it with the dual‐port network model. The relationship between the parameters of the original system and the parameters of the proposed model is given. Second, put the relationship expression into the short‐circuit current expression of the dual‐port network model and obtain the final transient expression for multi‐ended systems. Finally, the 3‐end tree and ring DC system model are set up on the MATLAB/Simulink software platform. The simulation of the model is verified. The error is below 5%, which proves the reliability of the model.
Discussion on infrared accurate temperature‐measuring technology of composite insulators for overhead lines
Authors: Liu Rong , Shen Qinghe , Liu Hui , Duan Yubing , Zhang Yang , Zhou Chao
Published: October 2018

Through analysing the infrared temperature measurement data obtained from composite insulators for overhead lines in actual operation state and atmospheric environment, detection requirements of infrared accurate temperature‐measuring technology of composite insulators for overhead lines were discussed, such as the detector, detection environment, and position. According to the local detection, two kinds of insulators' local heating, caused by insulation deterioration and damp contamination on the surface, were researched. A judgment method was proposed, and overheat of the electric equipment, which was caused by voltage effect, should be judged from both the contrast of similar equipment and the thermal image characteristic. This method can greatly reduce the insulators overheat error rate, improve the detection efficiency of composite insulators, and enhance the accuracy of composite insulators' insulation defects judgment.
Identification method based on correlation analysis for SPTG fault in MMC‐MVDC system
Authors: Zeng Yu , Zou Guibin , Sun Chenjun , He Shan , Jiang Lingtong
Published: October 2018

Due to the labyrinthine topology of the MMC‐MVDC system, identification of the faulty feeder especially for a single‐pole‐to‐ground (SPTG) fault is a challenging task. Based on the characteristics analysis of capacitance charge–discharge, this article obtains the typical characteristics of the faulty feeder. To improve the sensitivity, the characteristic frequency band of capacitance current is extracted by S‐transform which has excellent time–frequency resolution. According to the analysis, S‐transform characteristic frequency band (STCFB) of positive and negative differential current of faulty feeder is negatively correlated while the healthy feeders are positively correlated. To distinguish the faulty feeder, an identification method based on Pearson correlation coefficient (PCC) is constructed. In terms of the energy difference between the positive and negative differential current, the faulty pole can be verified. Finally, a typical radial flexible DC distribution grid model is constructed in PSCAD, and the simulation results confirm the reliability and sensitivity of the identification method.
Energy storage‐based control of multi‐terminal DC grid to eliminate the fluctuations of renewable energy
Authors: Nan Jiajun , Yao Wei , Wen Jinyu
Published: October 2018

DC grid technology is an effective approach to implement large‐scale renewable energy integration and accommodation. However, because of randomness and volatility of renewable power generation, the stability and efficiency of the power grid with high penetration integration will be weakened. This study proposes an energy storage‐based control for the multi‐terminal DC grid, and a way of integration in photovoltaic stations and wind power generators. The energy storage unit will be inputted into the multi‐terminal DC grid to provide power support so as to eliminate the fluctuations of renewable energy and stabilise power flow of AC grids. Firstly, the four‐terminal DC grid topology is established, which includes wind power generation, photovoltaic power generation and energy storage unit. Also, the corresponding system control strategy is designed. Then, by using the PSCAD/EMTDC platform, the equivalent simulation model of DC grid is built and the simulation studies are carried out under different conditions. Simulation results show that the proposed control strategy based on energy storage unit can eliminate the fluctuations of renewable power effectively.
Operation characteristics of DC transmission system with large‐scale renewable energy integration
Authors: Qian Minhui , Zhao Dawei , Ma Jin , Zhu Lingzhi , Ju Rongrong , Chen Mei
Published: October 2018

Marked with flexible interconnection and control, the high‐voltage direct current (HVDC) gird has captured much attention of industries and academics. Hybrid dual‐infeed or multi‐infeed HVDC composed of line‐commutated‐converter HVDC (LCC‐HVDC) and voltage source converter HVDC (VSC‐HVDC) will form the main pattern in a further power grid; meanwhile, the new gird pattern will bring new opportunities and challenges to security and stability control in the power system. First, research works on the control strategies and operation performances of LCC‐HVDC and VSC‐HVDC are stated in this paper; then, a model of wind power integration into a dual‐infeed DC transmission system is established in PowerFactory, and case studies are conducted in both steady and transient states. On this basis, a new control strategy for variable‐speed constant‐frequency wind power generators to promote voltage characteristics of the DC network is designed in this paper, and two additional active power control segments are designed in the traditional control system; thus, DC voltage stability can be improved by fast regulation of active power output due to quick power adjustment of wind power generators; simulations are implemented and the results will lay a foundation for safe and stable operation in the DC transmission system with renewable energy integration.
Reliability and economy assessment of offshore wind farms
Authors: Huang Qihang , Wang Xiuli , Fan Jiajie , Zhang Xiaoliang , Wang Yifei
Published: October 2018

Offshore wind power resource, which is relatively stable, abundant, and with modest impact on the environment, is a kind of clean and renewable energy suitable for large‐scale development. Offshore wind farms have different topological structures of the collection system, such as AC parallel type, DC parallel type, DC series type, single‐ring type, and double‐ring type. The purpose of this paper is to analyse reliability and economy for various topologies and provide an insight into wind farm construction. In this study, the topology structure of various offshore wind farms is introduced firstly. Then, the reliability assessment methods are proposed. The reliability of the chain wind farm is analysed with the reliability block diagrams, while the reliability of the ring wind farm is analysed by using the classification method. In addition, the economy is evaluated considering investment costs. The investment cost for each type of component is calculated separately, which contributes to assessing the investment cost of the whole offshore wind farm. Detailed results from a case study, which includes 96 wind turbines, demonstrate that the DC series–parallel wind farm has superiority in reliability and economy, as well as in terms of its potential applications.
Reliability assessment of DC series–parallel offshore wind farms
Authors: Huang Qihang , Wang Xiuli , Qian Tao , Yao Li , Wang Yifei
Published: October 2018

The remarkable benefits of wind power as an environmentally friendly renewable energy resource have led to an increasing penetration of offshore wind energy in modern power systems. Since the DC series–parallel connection system does not need large capacity DC/DC converters, it can reduce the construction costs of wind farms to some extent. In this study, the models of wind speed, wind direction and the wind turbine output power characteristic are developed. Based on this, the output power of each turbine considering the wake effect can be estimated. Then, the reliability block diagrams are drawn according to component relationships in reliability. Moreover, indexes like the probability of all wind turbine string failure, system unavailability and the average available output power of the power system are proposed to assess the reliability of the DC series–parallel offshore wind farm. A case study is presented to calculate the reliability indexes of different situations, where the amount of wind turbines remains the same while the number of turbine strings varies. It can be concluded that the DC series–parallel offshore wind farm is more reliable when increasing turbine string number, and reference is provided for DC series–parallel wind farm structure optimisation.
Calculation of main circuit steady state parameters for S‐MTDC transmission systems
Authors: Yu Shiyou , Wen Jun , Li Jiaqi , Liu Helin
Published: October 2018

Multi‐terminal high voltage direct current (MTDC) has many features including multiple sending ends, multiple receiving ends, and high transmission capacity. These make it highly competitive in both technical and economic terms. In designing a MTDC system, the calculation of the main circuit steady‐state parameter plays a fundamental role. However, existing researches mainly focus on parallel multi‐terminal DC transmission systems (P‐MTDC), few looks into series multi‐terminal DC transmission systems (S‐MTDC). Therefore, this study researches into the calculation of the main circuit steady‐state parameters for S‐MTDC transmission systems. First of all, the two types of MTDC transmission systems, S‐MTDC and P‐MTDC, are briefly introduced and compared. Then, the calculation of the steady‐state parameter of the main circuit for two‐terminal high voltage direct current (HVDC) transmission systems is explained. Based on this calculation method, research on the main circuit steady‐state parameter for S‐MTDC transmission systems is conducted and the design of calculation of steady‐state parameter of the main circuit is presented in detail. Finally, this study designs a series four‐terminal HVDC systems and verifies the calculation method of the steady‐state parameter of the main circuit.
Study on the resonance stability problem of the wind power base with the MMC–HVDC system
Authors: Xing Facai , Wang Shijia , Zhang Feng , Wang Heng , Xu Zheng , Xiao Huanqing
Published: October 2018

Considering the negative resistance effect of power electronic equipment, unstable resonance problems may occur between wind farms and converter stations. This paper focuses on the resonance stability problem of a wind power base coupling with a multi‐level converter−high‐voltage direct‐current transmission (MMC–HVDC) system. Firstly, the s‐domain impedance models of the doubly‐fed induction wind generator, the permanent magnet synchronous wind generator, and the modular MMC are built, through the theoretical derivation and simulation test. Secondly, based on the s‐domain nodal admittance matrix method, the resonance structure of the wind power base coupling with an MMC–HVDC system is analysed, including the resonance mode frequencies, the resonance mode damping factors, the nodal participation factors, and the nodal voltage mode shapes. Thirdly, the main factors influencing the resonance structure are studied, including the topology of the wind power base, the capacity of the wind turbines, and the operation mode of the MMC station. Finally, a brief conclusion ends the paper.
Transient stability analysis of one special type of AC microgrids with a gas reciprocating generator unit
Authors: Jun Liu , Hui‐wen Sun , Can Su , Jun‐hui Wu , Gui‐quan Han , Jian He
Published: October 2018

More and more gas reciprocating generator units are integrated into offshore platforms, due to their compact structure and high efficiency. This paper concentrates on the transient stability analysis of one special type of AC microgrids containing a gas reciprocating generator unit. Firstly, the operation principle for the gas reciprocating generator unit is presented, which mainly consists of a reciprocating internal combustion engine and a linear synchronous alternator (LSA). Afterwards, the mathematical model for the core part of the gas reciprocating generator unit LSA is proposed, based on the principle of armature reaction in traditional synchronous and asynchronous machines. Finally, the simplified model of the independent offshore power system with a gas reciprocating generator unit is derived, and numerical simulations on the transient stability of this typical AC microgrid are performed, from which the effectiveness and correctness of the LSA model are validated. The transient stability analysis method of the independent offshore power system and the mathematical model of LSA can provide beneficial guidance for the stable operation of other types of stand‐alone AC microgrids.
Grid‐connected control strategy of modular multilevel converter–battery energy storage system based on VSG
Authors: Zhang Dan , Jiang JianGuo , Zhang Liang , Zhou ZhongZheng
Published: October 2018

Modular multilevel converter‐battery energy storage system (MMC‐BESS) has a good engineering application. When MMC‐BESS is connected to the grid, the real‐time phase angle of grid is an important parameter. When MMC‐BESS is connected to the grid, a simulation model based on virtual synchronous generator (VSG) is built in MATLAB. The results show the control algorithm based on VSG can improve the dynamic response of the system and stably detect the phase angle of the grid.
Novel methodology solving distribution network reconfiguration with DG placement
Authors: Gong Zhiyun , Chen Qing , Sun Kongming
Published: October 2018

This paper proposes an effective and accurate methodology to solve the smart distribution network reconfiguration problem considering distributed generation (DG) placement, whose objective is to minimise power loss and enhance voltage stability. An intelligent optimisation algorithm using the electromagnetism‐like mechanism (ELM) is used to effectively find the best configuration of the network and placement of the DG units simultaneously. ELM is a novel global optimisation algorithm referring to the electromagnetic interaction among the electric charge to search a best location of an individual. To secure the radial nature of the network and avoid creating non‐feasible solutions, a novel encoding and decoding method is designed based on an exchanging tie switch sequentially, thereby accelerating the calculation speed. The rationality of codification is theoretically certified thereafter. To assess the performance of the proposed method, simulations are carried out on the IEEE 33‐ and 69‐bus distribution network. The simulation results demonstrate the validity and effectiveness of the proposed method.
Improved sensitivity analysis method and decision error discussion for limiting short‐circuit current of power grid
Authors: Qi Shixiong , Wang Xiuli , Tian Shijun , Wang Ruogu
Published: October 2018

This study mainly focuses on the method of limiting short‐circuit current of a power grid by partial transmission switching. The restrictive effect of short‐circuit current and the integrality of the power grid should be considered before the choosing the transmission lines. By analysing the relationship between transmission switching and self‐impedance of bus with increasing short‐circuit current magnitude, a sensitivity matrix can be derived. Based on sensitivity analysis, a set of the least transmission switching is chosen, which can limit short‐circuit current to the maximum. This study improves the method of transmission lines selection by sensitivity analysis. The improved sensitivity analysis method directly selects a set of transmission switching lines by the maximum value of weighted sensitivity coefficient instead of selecting lines one by one. It requires less calculation and has a high‐computation speed, but there are engineering errors. This work also studies the error influencing the decision of lines selection in different power grid scales. The effectiveness of the improved sensitivity analysis method is verified by several case studies. The cases of different power system scales are utilised for discussing the impact of error on decision of lines selection and for drawing the scope of the improved sensitivity analysis method.
Analysis for DC transmission line harmonics originated from AC transformer inrush current and improved method for DC harmonic protection
Authors: Cao Wenbin , Yin Xinaggen , Qi Xuanwei , Wang Yuxue , Liu Wei , Pan Yuanlin
Published: October 2018

Large‐scale electricity has fed into Central and Southern China through DC transmission lines. Any one of the DC transmission lines suddenly outage will result in a large proportion of power‐shortage. Recently, there are many DC harmonic protection misoperations caused by AC disturbance, resulting in DC transmission line exit operation. Therefore, it is necessary to analyse the effect of AC disturbance on DC harmonics and study methods for DC harmonic protections. In this study, based on the theory of switching function, the harmonics interaction in AC–DC systems is studied. The cause of DC line harmonic protection misoperation during unusual AC disturbances, such as inrush current and short circuit, is revealed. The DC line 50 Hz harmonic protection misoperates frequently due to inrush current on site. Taking it for example, an improved method using the second harmonic voltage in AC system bus is proposed. In this method, the 50 Hz harmonics generated by inrush current can be accurately identified by judging the correlation between the AC harmonic voltage and the DC line harmonic current. By automatically adjusting the threshold value of protection, the misoperation can be prevented effectively without affecting the original protection performance. The simulation results verify the correctness of the method.
Dual‐loop SFC scheme for BTB‐VSC‐HVDC interconnecting asynchronous AC grids
Authors: Zeng Lingkang , Li Dahu , Yao Wei , Sun Jianbo , Wen Jinyu
Published: October 2018

This study proposes a dual‐loop supplementary frequency control (SFC) scheme for back‐to‐back voltage source converter high‐voltage DC (BTB‐VSC‐HVDC) interconnecting asynchronous AC grids, to provide frequency support for each other after a large disturbance. The proposed dual‐loop SFC consists of the frequency‐active power (f–P) loop and the frequency‐reactive power (f–Q) loop. The former deployed on the P ‐loop of VSC‐HVDC can provide frequency support for the disturbed grid during the primary frequency regulation and improve the steady‐state characteristics of the frequency response, while the latter attached to the Q ‐loop of VSC‐HVDC supports virtual inertia to ameliorate the transient characteristics of the frequency response. Simulation studies are conducted based on the equivalently simplified model of Southwest Power Grid and Hubei Power Grid interconnected by Chongqing‐Hubei BTB‐VSC‐HVDC. Simulation results show that the proposed SFC scheme can effectively improve the transient and steady‐state characteristics of the system frequency response under a wide range of operating condition.
Characteristics of electrostatic discharges between metallic objects in the ion‐flow field under HVDC lines
Authors: Li Xueshan , Wang Donglai , Lu Tiebing
Published: October 2018

Metallic objects under high‐voltage direct current (HVDC) transmission lines will produce certain induced voltages due to the charging of ion flow. Electrostatic discharge (ESD) may occur between two objects at different potentials when they are close enough to spark under HVDC transmission lines. With a view to investigating such events in the ion‐flow field generated by HVDC transmission lines, a laboratory study on the ESD characteristics of two metallic objects in a close approach to each other under HVDC line is conducted. Discharge current and induced voltage are monitored to analyse the effect of experimental parameters. The ground‐level electric field without objects was measured, and the relationship between it and the voltage on objects was explored.
Hybrid ultra‐HVDC system with LCC and cascaded hybrid MMC
Authors: Yang Ruizhang , Xiang Wang , Lin Weixing , Wen Jinyu
Published: October 2018

Nowadays, the hybrid high‐voltage direct current (HVDC) system consisting of line commutated converter (LCC) and modular multilevel converter (MMC) has become the most competitive candidate in multi‐infeed power systems. Owing to the limitation of insulated‐gate bipolar transistor's withstand voltage, the DC voltage rating of MMC is not compatible with the LCC valve. To increase the DC voltage level, the number of sub‐modules of each arm should be increased drastically, leading to many technical problems in communication design, optical fibre instalment, cooler system design and so on. To overcome the above problems, a hybrid HVDC system consisting of LCC and cascaded hybrid MMC valves is proposed to realise ultra‐HVDC transmission. It can switch two operating modes (single valve/double valve) according to the conditions so that the system can maintain a certain power transmission when one of the valves quit operation during faults or maintenances. Meanwhile, by implementing the hybrid MMC, the system can ride through DC faults. The design of the topology and controllers, the DC fault ride‐through strategy and the online switching strategy for MMCs will be presented in this study. Finally, the performance during DC faults and online switching is verified by extensive simulations.
Dynamic modelling and long‐term simulation of ultracapacitor‐type ESS integration in power grid
Authors: Tang Yanan , Ye Hua , Liu Yao , Pei Wei , Kong Li
Published: October 2018

A novel dynamic average‐value model (AVM) of energy storage systems (ESS) integration in power grid for long‐term control is developed and validated. It is expected to greatly improve the computational speed of power system dynamics in a long‐term simulation. To end this, the development of the dynamic AVM of ESS integration including ultracapacitor, DC–DC converter, and voltage source converter is elaborated upon. A new control strategy which uses digital logic circuit is proposed to keep the ultracapacitors from overcharging without significantly increasing the charging time. To validate the proposed dynamic AVM and control strategy, case studies are carried out to perform the dynamics as affected by sudden changing of charging/discharging of ESS. The accuracy of the proposed model and controller is verified by the simulation results with that obtained from the detailed model implemented in MATLAB/Simulink. Moreover, the time‐step size is enlarged greatly without sacrificing the accuracy, therefore the computational speed is improved significantly.
Characteristics of sub‐synchronous interaction among D‐PMSG‐based wind turbines
Authors: Liu Yuming , Wang Long , Sun Haishun , Huang Biyue
Published: October 2018

With the development of wind energy conversion system (WECS), sub‐synchronous oscillations (SSO) phenomena have occurred in direct‐drive permanent magnetic synchronous generators (D‐PMSGs)‐based wind farms. There are several studies on the analysis of the SSO worldwide. However few researchers are concern about the interaction among D‐PMSGs. Considering the interaction among D‐PMSGs, especially in the weak grid condition, some researches are conducted in this study. The model of D‐PMSG is shown firstly. Then the simulations are carried out to research the characteristics of interaction among D‐PMSGs. Control parameters of grid side converter and wind turbine (WT) operating conditions are taken into consideration. At last, a proper mitigation method is introduced. Meanwhile, the impact of interaction among WTs on the effect of mitigation method is studied. The simulation result shows that there are distinct interactions among D‐PMSGs. The interactions among D‐PMSGs need to be considered when coordinating the SSO mitigation control among D‐PMSGs.
Novel control strategy of grid‐connected photovoltaic power supply for frequency regulation
Authors: Yang Bingdeng , Wang Xitian , Xie Da , Guo Yufeng
Published: October 2018

The maximum power point tracking (MPPT) mode is widely applied in photovoltaic (PV) power generation system. In this article, instead of MPPT, a novel control strategy of grid‐connected PV power supply for frequency regulation is proposed. First, the static frequency characteristic curve of PV plant is proposed, and a method of synthesising the PV power output power–voltage characteristic curve and static frequency characteristic curve into frequency regulation curve of PV power supply is introduced. So the PV plant can participate in frequency regulation of the system. Through simulation analysis in power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC), PV plant realises the function of frequency regulation when load changes, so the variation of system frequency can be reduced and the frequency stability of power system can be improved, and the effectiveness of the strategy is verified.
Study on the lightning overvoltage protection of a 500 kV unified power flow controller station
Authors: Ding Ting , Tao Fengbo , He Hengxin , Zhong Jiqun , He Junjia , He Huiwen
Published: October 2018

The unified power flow controller (UPFC) is the third generation of flexible AC transmission systems. It can control the power flow and voltage of the power system quickly and flexibly that has an advantage in compensating the AC transmission system in real time. The world's first 500 kV UPFC project is under construction in Jiangsu Province of China. On the paralleled converter side, it is connected to the 500 kV Mudu substation by using a gas insulated transmission line, and the series converter side is connected to the 500 kV Meili substation through a 500 kV double‐circuit overhead transmission line. In order to optimise insulation design of the UPFC system and ensure the safety operation of the power system, it is essential to analyse the characteristics of lightning overvoltage. Considering the invaded path of lightning surges in the UPFC system, a detailed model was established by using Electro‐Magnetic Transient Program/Alternative Transients Program in this study. The lightning overvoltage level at key nodes of the UPFC system was presented. The check calculation for the configuration and protection level of ZnO arresters were also carried out. The obtained results can provide a reference for insulation coordination design of the 500 kV UPFC project.
Novel correction control approach for an AC/DC hybrid network considering the PQ decoupling property
Authors: Lin Yi , Li Meng , Qi Zhi‐Nan , Qiu Liu‐Qing , Zhang Yong‐Hua
Published: October 2018

With the maturity and wide application of the voltage‐source converter‐based high‐voltage direct current (VSC‐HVDC) technology in the power grid, the fast‐response characteristic of VSC helps to improve the speed of corrective control for the AC/DC hybrid system. This paper presents a corrective control model for AC/DC hybrid grids based on VSC‐HVDC. The model is expressed as a typical optimisation model with both the features of the equipment and security constraints of a power network. The corrective control model is dived into an active power sub‐model and a reactive power sub‐model in order to improve the calculation speed. Case studies of a modified IEEE testing system have been carried out. The results demonstrate the effectiveness of the approach.
Simulation research on the LVRT the module of wind turbines in renewable energy integration
Authors: Huang Ruanming , Guo Mingxing , Zhang Mengyao , Fei Fei , zhu Hang , Zhu Miao
Published: October 2018

As a powerful power system simulation software package, PSS/E has great advantage in large‐scale power system simulation. However, in the PSS/E dynamic model, there is no low voltage ride through (LVRT) the model for the wind turbine generator, and that is why for engineering practice it less referred with regard to wind power simulation. According to the analysis of the principle of the PSS/E second generation generic model wind generator, this paper built the LVRT a model‐based PSS/E second generation generic model for the wind generator with the help of Fortran, and the model has been verified. The model this paper has built enriches the dynamic model of PSS/E and has led to more reference to PSS/E in engineering practice for the study of power system simulation with fluctuant wind power.