Optimal Capacity of a Battery Energy Storage System based on Solar Variability Index to Smooth out Power Fluctuations in PV-Diesel Microgrids

Battery energy storage systems can be integrated with photovoltaic (PV)-diesel microgrids, as an enabling technology to increase the penetration of PV systems and aid microgrid stability by smoothing out the power fluctuations of the PV systems. The aim of this paper is to derive correlations between the optimal capacity of the smoothing batteries and variabilities in daily solar irradiance. Two commonly used smoothing techniques of moving average and ramp rate control are applied on a real solar irradiance dataset with a 1-minute resolution for a full calendar year across 11 sites in Australia. The paper then presents the developed empirical model, based on linear regressions, to estimate the optimal capacity of the batteries without requiring the use of detailed simulation studies. The performance of the developed technique is validated by numerical simulation studies in MATLAB. The study demonstrates that the empirical model provided reasonably accurate estimates when using the moving average smoothing technique, but had limited accuracy under the ramp rate control technique

Sensitivity of Electric Vehicles Demand Profile to the Batteries Departure State-of-Charge

This paper focuses on the impacts of considering batteries state-of-charge (SOC) at the departure time on thedemand modeling of plug-in electric vehicles (PEVs). Almost all of the previous researches assumed that PEVs batteries at the departure time are fully charged; however, this assumption is highly questionable because it is probable for a PEV to not be charged every day. The probability density function of a vehicle owners’ willingness to fulfill the daily charging is extracted according to the initial SOC of a PEV and the estimated distance of its next trip. Afterwards, with the aim of considering the uncertainties with the associated random variables as well as properly adjusting vehicles SOC at the departure time, a Monte Carlo based multi loop (MCML) algorithm is developed which is composed of two loops, namely the inner loop and the outer loop. In order to implement the proposed stochastic method, a case study has been conducted employing the gathered datasets related to the ICE vehicles in Tehran. Appropriate Student’s t copula functions have been fitted to the datasets in order to take into account the correlation structure among them as well as to generate the required random samples

Contributions of Single–Phase Rooftop PVs on Short Circuits Faults in Residential Feeders

Sensitivity analysis results are presented to investigate the presence of single–phase rooftop Photovoltaic Cells (PV) in low voltage residential feeders, during short circuits in the overhead lines. The PV rating and location in the feeder and the fault location are considered as the variables of the sensitivity analysis. The single–phase faults are the main focus of this paper and the PV effect on fault current, current in distribution transformer secondary and the voltage at each bus of the feeder are investigated, during fault. Furthermore, to analyze the bus voltages and fault current in the presence of multiple PVs, each with different rating and location, a stochastic analysis is carried out to investigate the expected probability density function of these parameters, considering the uncertainties of PV rating and location as well as fault location

Distributed Battery Storage Units for Overload Prevention in an Islanded Microgrid

In an islanded microgrid, the load demand must be met by the distrusted generators (DGs) connected to it. Usually this can satisfactorily. However load growth increases, especially the peak load. In such a case, more DGs are to be connected to cater to the load growth. Alternatively if the overloading conditions occur infrequently or remain for shorter periods, storage units can be employed. In this paper, distributed battery storage units (BSUs) are employed for the overloading prevention in an islanded microgrid. It has been assumed that the microgrid only contains inertial DGs and ordinarily they share power in a frequency droop control. When an overloading is detected, the BSUs come on line and share power with the DGs using the same frequency droop control. The detection of overloading condition and when overload has been removed are crucial for this operation. An algorithm is proposed for this purpose. Through simulation studies, it has been demonstrated that the BSUs can be switched on and off seamlessly

Improving the Learning Experience of Power System Protection Students using Computer-based Simulations and Practical Experiments

This paper presents a survey on the activities carried out to improve the learning experience of electrical engineering undergraduate students in power system protection unit in Curtin University, Australia. The unit was conducted initially based on lectures and tutorials where only two sessions on computer simulation and one session of laboratory demonstration were conducted. In academic year of 2013, to improve the learningexperience of students, several computer-based simulations and laboratory experiments were prepared. The students are introduced with two power system analysis software, namely ETAP and PSCAD/EMTDC which are used to demonstrate the overcurrent relays performance and their coordination as well as the time transient analysis of different faults in an electric network where some protection relays are applied. A practical setupcomposed of LabVolt electrical modules and SEL relays is used to simulate an electric network. Several tests are built up to simulate fault and protection layout for transformer and induction motor. Finally, a secondary injection test set is used to introduce the concepts of relay testing and commissioning

Multi-level supervisory emergency control for operation of remote area microgrid clusters

Remote and regional areas are usually supplied by isolated and self-sufficient electricity systems, which are called as microgrids (MGs). To reduce the overall cost of electricity production, MGs rely on non-dispatchable renewable sources. Emergencies such as overloading or excessive generation by renewable sources can result in a substantial voltage or frequency deviation in MGs. This paper presents a supervisory controller for such emergencies. The key idea is to remedy the emergencies by optimal internal or external support. A multi-level controller with soft, intermedial and hard actions is proposed. The soft actions include the adjustment of the droop parameters of the sources and the controlling of the charge/discharge of energy storages. The intermedial action is exchanging power with neighboring MGs, which is highly probable in large remote areas. As the last remedying resort, curtailing loads or renewable sources are assumed as hard actions. The proposed controller employs an optimization technique consisting of certain objectives such as reducing power loss in the tie-lines amongst MGs and the dependency of an MG to other MGs, as well as enhancing the contribution of renewable sources in electricity generation. Minimization of the fuel consumption and emissions of conventional generators, along with frequency and voltage deviation, is the other desired objectives. The performance of the proposal is evaluated by several numerical analyses in MATLAB (R)

Overload Prevention in an Autonomous Microgrid using Battery Storage Units

A new control strategy for smooth transition of a battery storage unit (BSU) is proposed in this paper to prevent overloading in an autonomous hybrid microgrid. The BSU is controlled to come online to prevent overloading to the distributed generators (DGs) in the autonomous microgrid and to go offline when the load demand is less than the total rating of the DGs in the microgrid. The microgrid can contain either inertial DG or non–inertial DGs, which are controlled in a frequency droop. The sensing of switching on and switching off of the BSU depends on the frequency signal, which is developed in the paper. The proposed strategy is validated through PSCAD/EMTDC simulation studies

Motivating Power System Protection Course Students by Practical and Computer-Based Activities

This paper presents several methods for motivating students taking a power system protection (PSP) course. The paper reviews the laboratory activities developed for the PSP course at Curtin University, Australia; these methods are applicable and can be used for PSP course instruction at any institution. These activities were developed to improve the learning experience of the electrical engineering undergraduate and postgraduate students enrolled in this course. Initially, the PSP course at Curtin University consisted of lectures and tutorials accompanied by two sessions of software-based simulations and one session of laboratory demonstration. To motivate the students, several computer-based simulations and practical laboratory experiments were developed. PSCAD and ETAP power system analysis software tools are introduced and used to demonstrate the performance and coordination of different protection relays from steady-state and dynamic points of view. Also, a practical setup composed of a LabVolt power system simulator and industrial relays is used to carry out several practical experiments. The experiments help students observe the performance of protection systems for transformers and induction motors during faults and abnormal operating conditions. Finally, the concept of relay testing and commissioning is introduced by relay standalone experiments using a secondary injection relay test set. The results of these activities were evaluated according to the students’ satisfaction, comments, total scores, and interest in PSP

Market model for clustered microgrids optimisation including distribution network operations

This paper proposes a market model for the purpose of optimisation of clustered but sparse microgrids (MGs). The MGs are connected with the market by distribution networks for the sake of energy balance and to overcome emergency situations. The developed market structure enables the integration of virtual power plants (VPPs) in energy requirement of MGs. The MGs, internal service providers (ISPs), VPPs and distribution network operator (DNO) are present as distinct entities with individual objective of minimum operational cost. Each MG is assumed to be present with a commitment to service its own loads prior to export. Thus an optimisation problem is formulated with the core objective of minimum cost of operation, reduced network loss and least DNO charges. The formulated problem is solved by using heuristic optimization technique of Genetic Algorithm. Case studies are carried out on a distribution system with multiple MGs, ISP and VPPs which illustrates the effectiveness of the proposed market optimisation strategy. The key objective of the proposed market model is to coordinate the operation of MGs with the requirements of the market with the help of the DNO, without decreasing the economic efficiency for the MGs nor the distribution network. © The Institution of Engineering and Technology 2019

Coordination of single-phase rooftop PVs to regulate voltage profiles of unbalanced residential feeders

Installation of single-phase rooftop Photovoltaic (PV) systems in low voltage distribution networks is gaining increasing popularity in many countries including Australia. Utilization of rooftop PVs in residential feeders without controlling their ratings and locations may deteriorate the overall grid performance including power flows, losses and voltage profiles. This paper investigates the effectiveness and limitations of two different methods for regulating the voltage profile at low voltage residential feeders with single-phase rooftop PVs. These methods are based on the availability of voltmeters at each phase at each bus along the low voltage feeder which transmit their measurements to the controllers of the PV inverters. The main objective is to regulate the voltage profiles and reduce the voltage unbalance using drool control. The algorithm considers reactive power exchange and active power curtailment of the single-phase rooftop PVs. MATLAB-based simulation results demonstrate effectiveness of the proposed approach