Voltage Source Model Research Articles

A DC fault current fast-computing method of MMC-HVDC grid with short circuit protection equipment

The multi-terminal modular multi-level converter-based high voltage direct current (MMC-HVDC) grid with short circuit protection equipment (SCPE) is so complex that it is difficult to estimate its fault current and analyze the performance of SCPE by conventional time-domain numerical calculation method, it meets three big obstacles. This paper has made significant progress in overcoming these obstacles. 1). By applying the modern electrical circuit theory, a systematic formulation of the differential equation set for fault current calculation is developed to avoid a lot of complex and cumbersome matrix manual calculations. 2). A novel Y-Delta transformation in the s-domain is proposed to develop an eliminating virtual node approach for a complex MMC-HVDC grid, including the ring, radial, and hybrid topologies. 3). It is difficult to solve the equivalent circuit of MMC-HVDC grid with SCPE since SCPE is a time-variable-nonlinear circuit. A canonical voltage source model of SCPE is established to transform the time-variable-nonlinear circuit into a piecewise linear circuit. Based on the three significant progresses, a DC fault current fast-computing method of MMC-HVDC grid with SCPE is put forward to deal with all kinds of MMC-HVDC grids with several kinds of SCPEs. Then, the performance of several kinds of SCPE is analyzed and compared by this method. Consequently, the proposed DC fault current fast-computing method is a new powerful tool to estimate the fault current of MMC-HVDC grid and analyze the performance of SCPE.

A two-phase power flow algorithm of traction power supply system based on traction substation-network decoupling

Power flow analysis of traction power supply system (TPSS) is an effective approach to assess supply capacity and power quality, serving the whole process of system design, operation and optimization. The coupling effect between adjacent power supply arms poses challenges for the accurate and efficient solution, especially with the penetration of power converters and energy equipment. This paper proposes a two-phase power flow decoupling algorithm. TPSS is divided into traction substation and two decoupled power supply arms by introducing current ratio coefficients and unit matrices. Specifically, the equivalent voltage source model of traction substation and the modified chain network model of arms are solved by using forward–backward sweep method and LU decomposition method, respectively. Then the TPSS power flow can be obtained by alternative iteration of two solving phases. Simulations verify the proposed algorithm exhibits great compatibility at various operation modes. Additionally, the power supply capacity is mapped to the algorithm convergence. Compared to conventional methods, the algorithm achieves superior performance on accuracy and efficiency.

Modelling and control of current full compensation system‐based controllable voltage source

AbstractCurrent active suppression technology of arc overvoltage in distribution network has small capacity of controllable voltage source and complex control and cannot flexibly adjust the zero‐sequence voltage of neutral point. This study proposes a controllable voltage source system to fully compensate the arc current of ground fault for solving these problems. A controllable voltage source model based on passive supply voltage converter is established, utilising Dyn transformer to carry unbalanced load for a long time. The model output voltage is the same amplitude and frequency as that of single‐phase ground fault phase, but opposite phase. The compensation switch is operated when a ground fault occurs. The output voltage amplitude of the controllable voltage source is controlled, the fault phase voltage is controlled to be 0 in the closed loop, the grounding fault arc current is eliminated and the arc grounding overvoltage is suppressed. The control strategy was verified by the PSCAD/EMTDC simulation model of single‐phase grounding fault arc in 10 kV distribution network and the real single‐phase fault experiment platform of 0.4 kV distribution network. Results proved the model and strategy's accuracy and effectiveness. It provides an engineering practical method for active suppression of arc grounding overvoltage in distribution network.

Reduction of Multi‐Port Water Distribution Networks Using the Generalized Thevenin Theorem

AbstractExpansion and reorganization of water distribution networks by connecting sub‐networks via single or multiple pipes are common practices in developing cities to serve newly developed areas. In that context, the existing large network is often replaced with its equivalent simplified network for the optimal design of the upcoming sub‐networks to avoid the computational burden. The reservoir‐pump model is frequently used by practicing hydraulic engineers to replace an existing one; however, such a model should be applied only when the networks are connected through a single pipe. In this study, a new network reduction methodology is developed for multi‐port connections utilizing the analogy between electrical circuits and hydraulic networks. The equivalent simple network is obtained by suitably applying the generalized Thevenin theorem for electrical circuits. The number of network elements in the equivalent network is significantly reduced compared to the ones obtained by the existing water distribution network (WDN) reduction methods. Therefore, it is possible to reorganize and expand a large existing network system from a prior knowledge of its most sensitive parts. The accuracy and robustness of the proposed methodology are investigated on realistic WDNs by comparing the results with EPANET, for both Demand Driven Analysis and Pressure Driven Analysis. However, as of now, an electrical simulator is required to implement the proposed methodology due to the absence of current dependent voltage source model in hydraulic simulators. The proposed network reduction method can be of enormous utility for hydraulic engineers and opens up an opportunity to implement new elements in hydraulic simulators.

A method for simplified modeling and capacity, state of charge, current distribution analysis based on arbitrary topology connection battery pack

To meet the electric energy requirements of electric vehicles (EVs), the battery cells in power battery pack are normally connected in series and parallel. During the process of battery manufacturing and storage, battery parameters of the same batch and type are inconsistent, which may lead to accelerated aging of power batteries. Because of the change of cell-to-cell parameters, varied battery system topology structure will result in different battery pack characteristics. For power battery pack system design and optimization, it is important to understand the relationship among inconsistent parameter distribution, topological connection and battery performance. The traditional bulk model is based on the external characteristics of the battery pack, ignoring the inconsistency of cell-to-cell parameters. In order to investigate the non-uniform characteristics of battery pack, a simplified modeling method for power battery pack is proposed in this paper, which takes into account the parameter inconsistency of the battery pack and is suitable for power batteries with arbitrary topology. Based on the equivalent circuit model (ECM), a parallel model of two-cells is established and extended to the ECM of arbitrary topology structure battery pack. The analytical solution of the battery model is simplified by s-domain analysis and the transformation of current source and voltage source model. Based on the simplified model of battery pack with arbitrary topology, the 104 times Monte Carlo simulations is used to analyze the capacity distribution, state of charge (SOC) difference and maximum current distribution of the battery pack under different topology structures and parameters. The Monte Carlo simulation solves the problem of complex analytical solution of battery system and greatly improves the simulation speed. The results show that the series connection increases the voltage, but it will reduce the capacity. The parallel connection increases the capacity of battery pack, but it will lead to the increase of SOC inconsistency, maximum current and standard deviation of capacity. This paper provides a theoretical basis for reducing the heterogeneity of battery pack and a reference basis for battery manufacturers.

Optimal Protection Coordination of Active Distribution Networks With Synchronverters

Synchronverters are inverters imitating synchronous generators (SGs) to curb adverse impacts of traditional inverters on power networks. However, synchronverters may generate unlimited currents during faults. In addition, limiting the synchronverter’s fault currents by hard limiters could malfunction directional overcurrent relays (DOCRs). Thus, this paper employs virtual-impedance fault current limiters (VI-FCLs) that preserve the synchronverter’s voltage source model to guarantee a reliable operation of DOCRs. Also, an optimal protection coordination (OPC) scheme is developed to size the VI-FCLs and determine the DOCRs’ settings in a decoupled manner. The proposed protection scheme determines the highest values of the VI-FCLs that correspond to bolted faults at the synchronverters’ terminals. These conservative values are then relaxed by adaptively varying the VI-FCL based on the fault severity to enhance the DOCR sensitivity. Further, a short circuit calculation algorithm is formulated to incorporate the developed synchronverter with VI-FCL into an OPC program to determine the optimal settings of DOCRs that minimize the total operating time of all primary and backup relays. Case studies ensure the proposed protection scheme’s effectiveness in reliably protecting a radial 9-bus Canadian distribution system and a meshed 14-bus system powered by synchronverters.

Voltage instability identification with modified L-index using synchrophasor data

<p>In the prevailing open-access environment, one of the limitations for power exchanges has been voltage stability. The study of voltage stability necessitates a complete network representation. In this paper, the advantage of the dynamic behavior of generators is considered by incorporating dynamic models for generators. It has been shown dynamic models resulted in more accurate results compared to the conventional PV buses or ideal voltage source models that are used in most of the voltage stability studies. Moreover, the traditional L-index is augmented by incorporating real-time and synchronized phasor data collected from the optimally located phasor measurement units (PMU) in a wide-area measurement system (WAMS) to estimate more accurate voltage stability margins. Simulation studies carried out on IEEE 9-bus and IEEE 14-bus systems under various system conditions. It has been demonstrated that the inclusion of dynamic models and synchrophasor data from WAMS significantly improves the precision with which voltage stability analysis results are obtained.</p>

Parameters Affecting the Polarity Inversion of the Vertical Electric Lightning Field to the CN-Tower

The aim of this paper is to perform a parametric study in order to analyze factors having an effect on the vertical lightning field polarization to the CN-Tower in Canada, and estimate with numerical simulation, the horizontal distance for which the reversed polarity will occur. The calculation is performed using the Finite-Difference-Time-Domain technique in two dimensions (2D-FDTD), the spatial-temporal current propagation through the lightning channel and through the high structure is represented by the lumped-series voltage-source model. The obtained results show that the vertical electric lightning field behavior has a dual polarity, the transition from a negative waveform to a positive one is observed at different observation points localized near the elevated object influencing by each modification made to the tower-parameters, the medium conductivity and the return stroke speed value. These results can contribute to the understanding of the lightning-phenomenon and allow to solve the problems of electromagnetic compatibility.

Fault Ride-Through Analysis of Current- and Voltage-Source Models of Grid Supporting Inverter-Based Microgrid

Withstanding fault is a crucial technical challenge for inverter-based systems. Evolving grid codes require microgrids to possess fault ride-through (FRT) capabilities and support the grid voltage recovery. The traditional grid forming and grid feeding models lack such abilities. Consequently, this article enhanced these traditional models with droop control-virtual impedance and secondary power reference generation to form two models of a grid-supporting system. The first is a current source for grid feeding control, and the second is regulated as a voltage source for grid forming control. The result presents grid fault impact and FRT compliance in the proposed and traditional systems. Furthermore, the fault current curtailment and FRT improvement of the virtual impedances in the grid forming control were investigated within the MATLAB/Simulink environment. These proposed systems achieved FRT under a dynamic period and reverted to appropriate power delivery control under a static period.

Analysis and Design of Capacitive Power Transfer Systems Based on Induced Voltage Source Model

Capacitive power transfer is a promising mid-range wireless charging technique. The existing induced current source model suffers from the coupling variation issue, which causes troubles in resonance design and compensation development. This article explores an induced voltage source model for the capacitive coupler. Using this model, the six coupling-dependent capacitors between each pair of plates are equivalently represented by the self-capacitors and induced voltage sources. The self-capacitance is verified to be coupling independent. Based on this model, the power transfer capability, the efficiency, and the influence of adding external shunt capacitors are easily analyzed. This model is very helpful in investigating the existing topology and developing new compensations, such as the CLL-L compensation. Finally, a capacitive coupler is built to verify the model, based on which a CLL-L compensation is implemented for constant output voltage application. The achieved system peak efficiency is 88%.

Power Flow Regulation by UPFC in Networks with Voltage Dependent Loads

In this paper calculations are made to find out the power flow regulation capabilities of Unified Power Flow Controller (UPFC) in load flow analysis with loads which are voltage dependent. New equations for load flow analysis are developed that includes the models of voltage sensitive loads and voltage sources model of UPFC. Newton Raphson algorithm is used to solve the power flow equations of the network. UPFC voltage source model when included in the power equations has unique advantages over other modeling approaches. Analysis is done for two types of Loads. In the first analysis Constant current, Constant Power and Constant Impedance type of loads are examined. In the second analysis Composite loads are analyzed. The results of analysis on standard 5 bus system is presented here as a case study.

Mechanism Model and Prediction Method of Common Mode Radiation for a Nonisolated Very-High-Frequency DC–DC Converter With Cables

Research on electromagnetic interference of high-frequency power converters remains a challenging and important topic, particularly in light of rapidly emerging wide band-gap power devices operating with ns level turn- on /turn- off times. Building on the substantial contributions that have been made on the formation mechanisms of common mode (CM) radiation, a new mechanism for an equivalent CM driving voltage source caused by imbalanced conductors or components is proposed. Applying this mechanism, the CM driving voltage source model of a nonisolated boost dc/dc power converter with input/output cables is introduced. The CM far-field electric strength algorithms of an asymmetric cable antenna are theoretically analyzed and derived in detail. Subsequently, a prototype for a low-power 30-MHz very-high-frequency boost power converter based on gallium nitride is built and its 10-m CM far-field radiation strength is predicted according to the proposed model. The radiation pattern characteristics are analyzed and several radiation suppression methods are also designed. The comparison with the measured radiation results shows that the proposed CM radiation model and the prediction method achieve good effect below 300 MHz.

Modeling and Simulation of Voltage Source Model of UPFC in an IEEE 9 Bus System for Power Flow Enhancement

Modeling and Simulation of Voltage Source Model of UPFC in an IEEE 9 Bus System for Power Flow Enhancement - written by Shradha N. Waghade , Chandrakala Gowder published on 2020/01/10 download full article with reference data and citations

DC-side harmonic analysis and DC filter design in hybrid HVDC transmission systems

Hybrid high-voltage direct current (HVDC) transmission is a new transmission structure that uses line commutated converter (LCC) at the rectifier side and voltage source converter (VSC) at the inverter side. This study proposes a method to calculate DC side harmonic currents of hybrid HVDC transmission systems and design filters to mitigate DC-side low-frequency voltage pulsations. First, an equivalent harmonic analysis model of modular multilevel converter (MMC) is deduced according to the relationship among different harmonic components. The harmonic voltage expressions at DC side of 12-pulse LCC are deduced by combining the three-pulse harmonic voltage source model and FFT decomposition. On this basis, the expressions for harmonic currents are derived by multiplying the harmonic voltage transfer function and transfer admittance equation of DC network and are solved for the inverse Laplace transform. Two different types of DC filters are designed according to the requirements of DC filter on decaying specific order harmonic currents. The influence of partial element decay on the transfer characteristic of filter is analyzed, and appropriate partial component dissipation parameters are applied. The decay pole near the harmonic resonance frequency is configured to achieve reasonable DC-filtering results. Simulation results of a hybrid HVDC transmission system demonstrate the effectiveness of the proposed analysis model and filter design method.

Spurious Power Losses in Modular Multilevel Converter Arm Equivalent Model

This paper demonstrates the presence of spurious power losses or generation in the Arm Equivalent Model (AEM) of Modular Multilevel Converters. Such power losses can occur if model equations are not solved simultaneously with surrounding power circuit equations, which is the case when the AEM is implemented using control system blocks in electromagnetic transient simulation software. Depending on operating conditions and simulation parameters, these additional losses can represent a significant part of the total converter station losses or even surpass them, thus making simulation results inaccurate. Analytical demonstration of the losses is presented, and several models that eliminate the losses are proposed. Based on simulation studies, only the variable resistance model and equivalent voltage source model can give accurate simulation results without significantly increasing simulation time and generating or consuming spurious power.

A Modeling Study of Narrow Electric Field Signatures Produced by Lightning Strikes to Tall Towers

AbstractThe lumped voltage source model proposed by Baba and Rakov (2005b, https://doi.org/10.1029/2004JD005202) for studying the interaction of lightning with tall objects was used to examine the origin of earlier zero crossings observed in electric field signatures produced by lightning strikes to towers. Different return stroke models of transmission line type were used, and model parameters were varied in wide ranges. Lightning channel was assumed to be straight and vertical. It was found that the observed narrow field signatures cannot be reproduced by traditional models and require a narrower input current waveform or/and its faster decay with height. Contribution to the total electric field peak from a tower whose height exceeds 100 m or so is greater than that from the lightning channel. At distances of 2 to 50 km, the electric field signature due to the tower current was found to be bipolar, while that due to the lightning channel current was unipolar. The narrow bipolar electric field waveforms produced by lightning striking the 257‐m tower in Florida were reproduced using two approaches. In the first one, we employed as input a typical channel base current waveform and the transmission line with exponential current decay with height model with a very small decay height constant. In the second approach, we used a narrow pulse followed by a steady‐level tail as the input current waveform and the transmission line with linear current decay with height model. In both approaches, the computed electric field waveforms matched well the corresponding measured waveforms, at least for the initial half‐cycle and opposite polarity overshoot.

Harmonic load modeling: a case study of 33 kV Abuja Steel Mill Feeder

An in-depth study of the harmonic orders inherent in a power system network is required before mitigation techniques are adopted. This paper studied the harmonic orders of the 33 kV Abuja Steel Feeder modeled as a harmonic source using measured data. Readings of kW, kVar, kV and Hz were obtained using power quality analyzer (PQube) to identify the trend and the harmonic unbalance on the feeder. Electrical Transient Analyzer Program (ETAP) software package was deployed to perform Discrete Fast Transform (DFT) while the input parameters were the resultant relative amplitudes and phase angles for both the current and voltage source models. The current source model spectrum of the feeder under study revealed that the 11 th and 13 th harmonic orders have the highest percentage of amplitude relative to the fundamental compared to the other harmonics. On the other hand, the voltage source model spectrum showed that the 14 th , 15 th , 16 th , 17 th , 32 nd , 33 rd and 34 th harmonic orders have higher percentage of relative amplitude. However, only the 3 rd and 5 th harmonic orders were found to cause severe harmonic distortion of voltage and current after harmonic analysis and frequency scan were performed on the ETAP platform. Keywords: Harmonic order; Power quality; Transmission grid; ETAP; Tuned filters

Influence of Unified Power Flow Controller on Flexible Alternating Current Transmission System Devices in 500 kV Transmission Line

Power system maintenance and reliability has become an important aspect of research. In this paper the performance of unified power flow controller to control the power flow on the transmission line has been discussed. The voltage source model was used to study the UPFC's behavior in regulating active power, reactive power and voltage curves. Summarized the different results to see the benefits of UPFC in the power system by installing the Power system modeling in MATLAB and installation of UPFC in transmission link.

Application of Unified Power Flow Controller to Improve Steady State Voltage Limit

<span>This paper utilizes the voltage source model of Unified Power Flow Controller (UPFC) and examines its abilities in mitigating the steady state stability margins of electric power system. It analyzes its behavior for different controls strategies and proposes the most efficient mode of controlling the controller for voltage stability enhancement. A systematic analytical methodology based on the concept of modal analysis of the modified load flow equations is employed to identify the area in a power system which is most prone voltage instability. Also to identify the most effective point of placement for the UPFC, a computer program has been developed using MATLAB. The results of analysis on 14 bus system is presented here as a case study.</span>

ENGLISH

A Unified Power Flow Controller (UPFC) in Multi machine system is proposed. The UPFC model is having a voltage source. The magnitude and angle of this voltage source depends on the UPFC control parameters. For the analysis of Eigen value, power system with linearized model was developed. Poorly damped electromechanical mode is controlled by stabilizing signal. The superior stabilizing signal is selected by approach based singular value decomposition. The UPFC with voltage source model incorporated into the generator output power equation simplifies the dynamic analysis of the system and this incorporation into the generators output power equation can be easily done. This proposed model will be used to compare and determine a simple system’s dynamic behavior, equipped with an adaptive UPFC.