Description:
IEEE This paper presents a new compact three-phase cascaded multilevel inverter (CMLI) topology with reduced device count and high frequency magnetic link. The proposed topology overcomes the predominant limitation of separate DC power supplies, which CMLI always require. The high frequency magnetic link also provides a galvanic isolation between the input and output sides of the inverter, which is essential for various grid-connected applications. The proposed topology utilizes an asymmetric inverter configuration that consists of cascaded H-bridge cells and a conventional three-phase two-level inverter. A toroidal core is employed for the high frequency magnetic link to ensure compact size and high-power density. Compared with counterpart CMLI topologies available in the literatures, the proposed inverter has the advantage of utilizing the least number of power electronic components without compromising the overall performance, particularly when a high number of output voltage levels is required. The feasibility of the proposed inverter is confirmed through extensive simulation and experimentally validated studies.
Description:
IEEE This paper presents a new compact three-phase cascaded multilevel inverter (CMLI) topology with reduced device count and high frequency magnetic link. The proposed topology overcomes the predominant limitation of separate DC power supplies, which CMLI always require. The high frequency magnetic link also provides a galvanic isolation between the input and output sides of the inverter, which is essential for various grid-connected applications. The proposed topology utilizes an asymmetric inverter configuration that consists of cascaded H-bridge cells and a conventional three-phase two-level inverter. A toroidal core is employed for the high frequency magnetic link to ensure compact size and high-power density. Compared with counterpart CMLI topologies available in the literatures, the proposed inverter has the advantage of utilizing the least number of power electronic components without compromising the overall performance, particularly when a high number of output voltage levels is required. The feasibility of the proposed inverter is confirmed through extensive simulation and experimentally validated studies.
Description:
One of the key challenges in multilevel inverters (MLIs) design is to reduce the number of components used in the implementation while maximising the number of output voltage levels. This paper proposes a new concept that facilitates a device count reduction technique of existing cascaded MLIs. Moreover, the proposed concept can be utilised to extend existing single phase cascaded MLI topologies to three-phase structure without tripling the number of semiconductor components and input dc-supplies as per the current practice. The new generalized concept involves two stages; namely, cascaded stage and phase generator stage. The phase generator stage is a combination of a conventional three-phase two level inverter and three bi-directional switches while the cascaded stage can employ any existing cascaded topology. A laboratory prototype model is built and extensive experimental analyses are conducted to validate the feasibility of the proposed cascaded MLI concept.
Description:
One of the key challenges in multilevel inverters (MLIs) design is to reduce the number of components used in the implementation while maximising the number of output voltage levels. This paper proposes a new concept that facilitates a device count reduction technique of existing cascaded MLIs. Moreover, the proposed concept can be utilised to extend existing single phase cascaded MLI topologies to three-phase structure without tripling the number of semiconductor components and input dc-supplies as per the current practice. The new generalized concept involves two stages; namely, cascaded stage and phase generator stage. The phase generator stage is a combination of a conventional three-phase two level inverter and three bi-directional switches while the cascaded stage can employ any existing cascaded topology. A laboratory prototype model is built and extensive experimental analyses are conducted to validate the feasibility of the proposed cascaded MLI concept.
Description:
IEEE Frequency response analysis (FRA) has recently been developed as a widely accepted tool for power transformer winding mechanical deformation diagnosis, and has proven to be effective and powerful in many cases. However, there still exist problems regarding the application of FRA. FRA is a comparative method in which the measured FRA signature should be compared with its fingerprint. Small differences of FRA signatures in certain frequency bands might be produced by external disturbance, which hinders fault diagnosis. Additionally, the existing correlation coefficient indicator recommended by power industry standards cannot reflect key information of signatures, namely the extreme points. This paper proposes an improved FRA based on binary morphology and extreme point variation. Binary morphology is first introduced to extract the certain frequency bands of signatures with significant difference. A composite indicator of extreme point variation is adopted to realize the diagnosis of fault level. A ternary diagram is constructed by the area proportions of the binary image to identify winding faults, which has a potential to realize cluster analysis of fault types.
Description:
On 4 August 1888, Reefton became the first town in New Zealand to have its own public electricity supply powered by hydrogeneration. In Australia, the first supply of electricity to the public at large was in two small country towns in New South Wales. Tamworth, with a population of 3,000, switched on arc and incandescent street lighting on 9 November 1888. In April 1889, the smaller town of Young switched on its incandescent street lighting and shortly thereafter went on to connect shops, offices, and homes within reach of its lines. However, the history of electricity supply in Australia traces back earlier, with Brisbane as one of the first cities in Australia to use electricity commercially, in 1882. Thus, electricity utilization down under coincided with the history of its emergence among the countries of the Northern Hemisphere.
Description:
Online impulse frequency response analysis (IFRA) has proven to be a promising method to detect and diagnose the transformer winding mechanical faults when the transformer is in service. However, the existing fast Fourier transform (FFT) is actually not suitable for processing the transient signals in online IFRA. The field test result also shows that the IFRA signature obtained by FFT is easily distorted by noise. An improved method to obtain the online IFRA signature based on multi-scale complex continuous wavelet transform is proposed. The electrical model simulation and online experiment indicate the superiority of the wavelet transform compared with FFT. This paper provides guidance on the actual application of the online IFRA method.
Description:
Online impulse frequency response analysis (IFRA) has proven to be a promising method to detect and diagnose the transformer winding mechanical faults when the transformer is in service. However, the existing fast Fourier transform (FFT) is actually not suitable for processing the transient signals in online IFRA. The field test result also shows that the IFRA signature obtained by FFT is easily distorted by noise. An improved method to obtain the online IFRA signature based on multi-scale complex continuous wavelet transform is proposed. The electrical model simulation and online experiment indicate the superiority of the wavelet transform compared with FFT. This paper provides guidance on the actual application of the online IFRA method.
Description:
In a modern power system network having multiple interconnected High Voltage (HV) substations, communication amongst Intelligent Electronic Devices (IED) becomes an important feature in an automation system. Time critical information, such as feeder faults, overcurrent, under frequency messages between multiple geographically isolated substations have opened up number of issues related to reliability in protection, automation and control. There are problems related to latency, data loss and transfer of Sampled Value (SV) packets transmitted to these inter-connected substations on radio wireless and Ethernet mode linked up in a Wide Area Network (WAN) configuration. Few other key area of concerns in a digital protection scheme are packet losses, errors in packet arrival at destination, latency in transmission, End to End delay in packet transfer due to flooding of the network, out of sequence packet arrival etc. Error prone packets could seriously compromise the protection scheme and endanger the safety of primary plant assets in a transmission substation. This paper investigates performance of SV packet transmission between two interconnected substations]. Practical simulations were performed to evaluate the performance of SV packets in a laboratory set up to assess the performance of digital protection scheme based on Parallel Redundancy Protocol (PRP) topology involving digital equipment such as Merger Units (MUs), switches, IEDs and Redundant boxes (Red box), etc.
Description:
IEEE This paper addresses the time delay effects of the wide area monitoring and control systems (WAMCS) in smart power grids which may critically impact system stability. The main purpose is to conduct a detailed delay analysis of the WAMCS in case of grid contingences. This analysis is performed via an advanced WAMCS testbed where a wide area controller (WAC) for a flexible AC transmission system (FACTS) device is implemented. The real-time measurements for the WAC are collected using phasor measurements units (PMU). The testbed is resulted from an interface of four main segments known as the WAC, the actual FACTS device, the local area controller, and the power grid system along with the PMUs are simulated via real time digital simulator (RTDS). To mimic the real case scenario both hardware-in-the-loop (HIL) and software-in-the-loop (SIL) schemes are adopted in the experimental testbed, considering time delay effects. The results obtained clarify the effect of delay in WAMCS in case of smart grid contingences.
Description:
Cascaded multilevel inverters (MLI) have recently received much attention due to its ability to perform well in various high voltage and high power applications with high efficiency. Cascaded inverters are able to generate high voltage output by utilizing a number of low voltage DC supplies and switches of low blocking voltage rating, which make cascaded MLI a cost effective choice for high voltage/power applications. The main drawback of cascaded MLI is the requirement of large number of isolated DC sources particularly, for three phase applications where the number of required input DC sources is three times that of single phase structure. In addition to the extra cost it will incur, the use of large number of DC supplies within the inverter will significantly increase its physical size, and complicate the management of such large number of DC sources. This paper presents a new topology for three phase MLI with a minimum number of input DC supplies. Symmetric and asymmetric input DC supply modes are developed for the proposed topology. Simulation and experimental results are provided to assess the performance of the proposed MLI topology.
Description:
Thermographic scanning of electrical installations is sometimes conducted as part of electrical safety audits. This scanning is mostly considered based on the present temperature identified on a particular device or location and according to a pre-specified temperature category. But in most of the cases the recommended temperature of the particular devices cannot be considered during temperature categorization. There are many electrical audits using Thermographic scanning and recommend solution based on normal category of temperature rather than manufacturer's suggestion or specified standard for particular electrical device. Now a days, thermographic scanning is being used in Readymade Garments (RMG) industries in Bangladesh in such simple way where details analysis are not in practice and hence exact recommendation is absent in reports. The importance of this topic is focused on the 4.2 million people working in more than 5,000 factories in Bangladesh, where 80% of the fire incident are caused by inappropriate electrical installation or short circuits (as per Fire Service and Civil Defense statistics of Bangladesh). Recently many violent industrial accidents caused death of more than 1,500 people in the last 3 years. Among these, majority of the incidents were due to unsafe electrical system and inappropriate maintenance. The paper will further explore the importance of thermal scanning on electrical devices and compare the temperature considering manufacturer's recommendation for identifying system errors. The paper is written based on previously published recommendations and based on conducting an experimental sample audit aimed to develop a thermography based auditing standard. Based on the statistical and systematic analysis of the obtained data (e.g. temperature values, visual abnormalities, comparative differences) the paper will further discuss the possible area(s) that can be improved by introducing the thermal reports for the safety audits. This paper is aimed to develop an auditing structure proposed to implement identified areas within a standard electrical safety audit process.
Description:
Online impulse frequency response analysis is a recently-developed diagnostic method for in service transformer with a promising outlook. This paper aims to detect the impact of external interferences including pulse shaped interferences from switching operations and other phenomena in the power system on the frequency response of the transformer. For modeling the transformer for online IFRA, a simulation approach based on finite element analysis (FEA) and circuit analysis is used. In this approach, instead of using a linear model with static parameters, 3D finite element model of the transformer is calculated in Maxwell Software and then exported into an external Maxwell Spice circuit which allows for study the terminal behaviors of the transformer. A modified S transform is then applied to the recorded input and output signals in healthy and faulty conditions to construct the electrical impedance as well as the time-frequency contours of the transient responses.
Description:
This paper presents a sinusoidal ripple current (SRC) emulator which superimposes an ac ripple current frequency into a dc charging current in order to produce a sinusoidal ripple current without a ripple current controller. It can be used for several purposes:1) to analyze the impact of ac ripple current magnitude and frequency on the battery internal characteristics; 2) to determine the parameters related to thermal rise and lithium plating; 3) to obtain more updated parameter information for improved utilization of a battery; 4) to determine the optimal ripple current frequency at the minimum impedance point by sweeping the ripple current frequency; 5) to utilize the obtained impedance data for estimating the battery circuit parameters and SOC level. The internal characteristics of batteries are complex and dynamic; therefore, it is beneficial to use the SRC emulator to validate SRC performance in a battery stack before integrating a SRC algorithm into a battery charger. This paper describes the development procedure of a SRC emulator to produce the electrochemical impedance spectroscopy (EIS) measurement for measuring the battery internal impedance. In order to validate the performance of the SRC emulator, a 12.8 V, 40 Ah Li-ion battery was charged at C/8 rate in CC mode with ± 1 App ac ripple current perturbation with an impedance from 20 Hz to 2 kHz.
Description:
This article evaluates the effect of randomly distributed, residential single-phase rooftop photovoltaic systems in the low voltage residential networks, during short-circuit faults on the overhead lines. The important parameters such as the fault current, the current sensed at the distribution transformer secondary, and the voltage profile along the feeder during the fault are examined. A sensitivity analysis is carried out in which the rating and location of the photovoltaic systems in the feeder, as well as the fault location and type, are the considered variables. Moreover, to demonstrate the effect of multiple photovoltaic systems with different ratings and penetration levels when distributed unequally among three phases of the network, a stochastic analysis is carried out. The article summarizes the outcomes of these two analyses to provide a better understanding of the impact of single-phase rooftop photovoltaic systems on the residential feeders during short-circuit faults.
Description:
This article evaluates the effect of randomly distributed, residential single-phase rooftop photovoltaic systems in the low voltage residential networks, during short-circuit faults on the overhead lines. The important parameters such as the fault current, the current sensed at the distribution transformer secondary, and the voltage profile along the feeder during the fault are examined. A sensitivity analysis is carried out in which the rating and location of the photovoltaic systems in the feeder, as well as the fault location and type, are the considered variables. Moreover, to demonstrate the effect of multiple photovoltaic systems with different ratings and penetration levels when distributed unequally among three phases of the network, a stochastic analysis is carried out. The article summarizes the outcomes of these two analyses to provide a better understanding of the impact of single-phase rooftop photovoltaic systems on the residential feeders during short-circuit faults.
Description:
This paper investigates the impact of time delay in the control of a grid-connected microgrid with renewable energy resources. The considered microgrid has a critical load that needs to be powered and protected in the event of grid voltage disturbance while the microgrid maintains connection to the grid. Three case studies are performed considering three different time delays to indicate the advantages of fast communication system in the performance of renewable microgrids. Detailed simulation results illustrate that the proposed communication system using IEC 61850 substation automation standard provides better voltage and current quality to the critical local load with larger phase and gain margins while keeping the microgid connected to main grid.
Description:
This paper investigates the impact of time delay in the control of a grid-connected microgrid with renewable energy resources. The considered microgrid has a critical load that needs to be powered and protected in the event of grid voltage disturbance while the microgrid maintains connection to the grid. Three case studies are performed considering three different time delays to indicate the advantages of fast communication system in the performance of renewable microgrids. Detailed simulation results illustrate that the proposed communication system using IEC 61850 substation automation standard provides better voltage and current quality to the critical local load with larger phase and gain margins while keeping the microgid connected to main grid.
Description:
Large remote area networks normally have self-suffi-cient electricity systems. These systems also rely on non-dispatchable DGs (N-DGs) for overall reduction in cost of electricity production. It is a fact that uncertainties included in the nature of N-DGs as well as load demand can cause cost burden on islanded microgrids (MGs). This paper proposes development of power exchange strategy for an interconnected MGs (IMG) system as part of large remote area network with optimized controls of dispatchable (D-DGs) which are members of master control unit (MCU). MCU analysis includes equal cost increment principle to give idea about the amount of power exchange which could take place with neighbor MGs in case of overloading situation. Sudden changes in N-DGs and load are defined as interruptions and are part of analysis too. Optimization problem is formulated on the basis of MCU adjustment for overloading or under loading situation and suitability of support MG (S-MG) in IMG system for power exchange along with key features of low cost and minimum technical impacts. Mixed integer linear programming (MILP) technique is applied to solve the formulated problem. The impact of proposed strategy is assessed by numerical analysis in MATLAB programming under stochastic environment.
Description:
Large remote area networks normally have self-suffi-cient electricity systems. These systems also rely on non-dispatchable DGs (N-DGs) for overall reduction in cost of electricity production. It is a fact that uncertainties included in the nature of N-DGs as well as load demand can cause cost burden on islanded microgrids (MGs). This paper proposes development of power exchange strategy for an interconnected MGs (IMG) system as part of large remote area network with optimized controls of dispatchable (D-DGs) which are members of master control unit (MCU). MCU analysis includes equal cost increment principle to give idea about the amount of power exchange which could take place with neighbor MGs in case of overloading situation. Sudden changes in N-DGs and load are defined as interruptions and are part of analysis too. Optimization problem is formulated on the basis of MCU adjustment for overloading or under loading situation and suitability of support MG (S-MG) in IMG system for power exchange along with key features of low cost and minimum technical impacts. Mixed integer linear programming (MILP) technique is applied to solve the formulated problem. The impact of proposed strategy is assessed by numerical analysis in MATLAB programming under stochastic environment.
Description:
Predictive maintenance offers substantial benefits for detecting the early signs of power transformer faults before they burgeon into catastrophic failures. Online impulse frequency response analysis is a recently-developed diagnostic method for in service transformer with a promising outlook. This paper aims to propose an online partial discharge detection method the online IFRA test. To emulate the dynamic performance characteristics of in service transformer, 3D finite element model of the transformer is calculated in Maxwell Software. In post processing, the FEM sub-circuit model is exported into an external Maxwell Spice circuit to study the terminal behaviors of the transformer. A pulse signal simulating PD is injected between sections of the LV winding. The S transform is then applied to the recorded input and output signals in healthy and faulty conditions to construct the electrical impedance as well as the time-frequency contours of the transient responses. Also, a mechanical deformation is imposed on the transformer to compare its impact on online IFRA to the impact of internal partial discharge.
Description:
This paper investigates the performance of a recently proposed online transformer internal fault detection technique and examines impact of harmonics through detailed nonlinear simulation of a transformer using three-dimensional finite element modelling. The proposed online technique is based on considering the correlation between the instantaneous input and output voltage difference (ΔV) and the input current of a particular phase as a finger print of the transformer that could be measured every cycle to identify any incipient mechanical deformation within power transformers. To precisely emulate real transformer operation under various winding mechanical deformations, a detailed three-dimensional finite-element model is developed. Detailed simulations with (non)sinusoidal excitation are performed and analysed to demonstrate the unique impact of each fault on the ΔV-I locus. Impact of harmonic order, magnitude and phase angle is also investigated. Furthermore, practical measurements have been performed to validate the effect of winding short circuit fault on the proposed ΔV-I locus without and with the impact of system harmonics.
Description:
This paper investigates the performance of a recently proposed online transformer internal fault detection technique and examines impact of harmonics through detailed nonlinear simulation of a transformer using three-dimensional finite element modelling. The proposed online technique is based on considering the correlation between the instantaneous input and output voltage difference (ΔV) and the input current of a particular phase as a finger print of the transformer that could be measured every cycle to identify any incipient mechanical deformation within power transformers. To precisely emulate real transformer operation under various winding mechanical deformations, a detailed three-dimensional finite-element model is developed. Detailed simulations with (non)sinusoidal excitation are performed and analysed to demonstrate the unique impact of each fault on the ΔV-I locus. Impact of harmonic order, magnitude and phase angle is also investigated. Furthermore, practical measurements have been performed to validate the effect of winding short circuit fault on the proposed ΔV-I locus without and with the impact of system harmonics.
Description:
Large remote areas normally have isolated and self-sufficient electricity supply systems, often referred to as microgrids. These systems also rely on a mix of dispatchable and non-dispatcha- ble distributed energy resources to reduce the overall cost of electricity production. Emergencies such as shortfalls, overloading, and faults can cause problems in the operation of these remote area microgrids. This paper presents a power transaction management scheme amongst a few such microgrids when they are coupled provisionally during emergencies. By definition, power transaction is an instance of buying and selling of electricity amongst problem and healthy microgrids. The developed technique aims to define the suitable power generation from all dispatchable sources and regulate the power transaction amongst the coupled microgrids. To this end, an optimization problem is formulated that aims to define the above parameters while minimizing the costs and technical impacts. A mixed- integer linear programming technique is used to solve the formulated problem. The performance of the proposed management strategy is evaluated by numerical analysis in MATLAB.
Description:
Large remote areas normally have isolated and self-sufficient electricity supply systems, often referred to as microgrids. These systems also rely on a mix of dispatchable and non-dispatcha- ble distributed energy resources to reduce the overall cost of electricity production. Emergencies such as shortfalls, overloading, and faults can cause problems in the operation of these remote area microgrids. This paper presents a power transaction management scheme amongst a few such microgrids when they are coupled provisionally during emergencies. By definition, power transaction is an instance of buying and selling of electricity amongst problem and healthy microgrids. The developed technique aims to define the suitable power generation from all dispatchable sources and regulate the power transaction amongst the coupled microgrids. To this end, an optimization problem is formulated that aims to define the above parameters while minimizing the costs and technical impacts. A mixed- integer linear programming technique is used to solve the formulated problem. The performance of the proposed management strategy is evaluated by numerical analysis in MATLAB.
Description:
Conventional power converters control pulse width modulation (PWM) signals based on the directly sensed feedback signals or estimated state signals. Recently, information and communication technologies are beginning to integrate power converters into smart grid applications. This paper presents a Hardware-In-The-Loop Testbed using a WirelessHART network for smart home applications in a case study. The main components of the testbed are OP4510 RT-LAB-RCP/HIL systems, Texas Instruments Digital Signal Controllers and AwiaTech wireless modules. In this testbed, wireless based controller is integrated with conventional digital controller. OP4510 is used to simulate power stages of the power converters in real time. Texas Instruments Digital Signal Controllers provide PWM signals from the control loop and communication loop. AwiaTech wireless modules are used to build a WirelessHART network to communicate with power converter from a supervisory program. The case study is to support reactive power in smart home applications using 3 bridgeless unidirectional power factor correction (PFC) converters. For this scenario, supervisor collects reactive power measurement data from the input power node and wirelessly transfers reactive power command values to the home appliances driven by PFC converters. Thus, reactive power demand can be minimized. The experimental result demonstrates the performance of the testbed in different communication delays.
Description:
This chapter presents a preliminary study conducted to improve photovoltaic (PV) cell conversion efficiency using MATLAB/Simulink platform. The study uses multi-junction solar cell and investigates the maximum performance compared with a conventional silicon PV cell. Maximum Power Point Tracker (MPPT) is applied to assess the conversion efficiency of the PV system. Study integrates thermoelectric generator (TEG) with PV modules because the PV cells work by converting high frequency irradiation where as a TEG has the ability to convert wasted low frequency heat to the electricity. The combination delivers more power and contributes to enhance the conversion efficiency of a PV system. The simulation results show that a tandem cell can provide a considerable higher power with a conventional PV cell operation.
Description:
This paper presents a hardware design for a Travelling Wave (TW) Detector and data recorder for a three phase Medium Voltage (MV) distribution network. The proposed pole mounted platform consists of a capacitively coupled receiver system, a GPS receiver and a Texas Instruments Delfino 28377 processor based travelling wave detection unit. The data recording system uses an Intel Atom base single board computer, a four channel 10Ms/s analogue to digital converter card along with Wi-Fi and GORS communications links. The proposed system is capable of recording three phase voltages simultaneously with the ability to trigger remotely. The platform is mounted in an IP56 enclosure and can be mounted on the MV distribution poles. The paper provides a brief review of hardware and software developed for the TW detector.