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With increasing photovoltaic (PV) penetration in low-voltage (LV) distribution networks, voltage violation during the peak PV generation period is one of the main power quality concerns. To minimize the PV power curtailment caused by voltage violations, this paper proposes a new approach utilizing one dynamic voltage restorer (DVR) at the secondary of an existing urban distribution transformer as a continuous voltage compensator with an accompanying control algorithm. The voltage compensation algorithm controls the DVR in real-time to prevent over-voltage and under-voltage at all network nodes, thereby maximizing PV injection and preventing equipment damage. The controller uses the equivalent line impedance of network to estimate the average voltage of load points without the need for any communication links for measuring load voltages. In this approach, the fixed tap changer of the distribution transformer is also optimally adjusted to minimize the DVR rating using a proposed offline optimization method. Simulation results on IEEE LV test feeder prove the ability of the DVR in maintaining all network node voltages within the allowable range in peak demand and peak PV generation periods with the benefit of injecting only a small amount of active and reactive power to the system, in contrast to alternative algorithms.

Demand for converter-fed distributed energy resources are rapidly growing in microgrids and these energy sources are mainly responsible for sharing loads in islanded mode of operation. In high voltage lines, sharing real and reactive load power requirements can be achieved by conventional droop control methods, nevertheless strong coupling between active and reactive power in medium voltage lines with low X/R ratio degrades rating-based load sharing among converters. A transformation matrix which incorporates the line impedance effect in droop parameter calculation by modifying droop coefficients can be used to overcome this drawback. However, inclusion of power decoupling term in reference voltage calculation, has found to be more powerful to overcome coupling effects in load power sharing. By utilizing lesser steady state frequency deviation of angle droop in comparison with frequency droop, this paper adopts angle droop in real power loop. Angle droop concept along with power decoupling factor has an added advantage of improved reactive power sharing with surplus accuracy in real power distribution, which in turn, allows harmonic power distribution based on converter rating under different load conditions. Moreover, discrete state feedback control together with third harmonic injection-based pulse width modulation scheme provides additional robustness to individual converters.

Bird survey was conducted in Bellary-Hospet region which has intensive iron ore mining activities. A total of 77 species of birds were observed of which 15 were aquatic/semi-aquatic. House crow was the most dominant species with 14.32% followed by laughing dove (11.85%) and house sparrow (10.32%). Species diversity index was calculated as 9.98. The birds were found to avoid core zone of iron ore mines, whereas no such finding occurred away from mining areas.

A two-level decentralized hierarchical control strategy is developed to cope with active power deficiencies in remote microgrid (MG) systems containing intermittent energy resources. The primary level consists of a multilayer droop-based scheme designed to dispatch the required loads to be shed amongst controllable loads (CLs). The dispatch is proportionally fulfilled through the appropriate assignment of each layer of the droop curves to its corresponding priority type of the CLs. If the primary level is unable to handle the shortfall, the secondary level of the scheme is invoked by coupling of the overloaded MG with a neighboring one. Appropriate criteria are accurately formulated to assure desirable interconnections and proper isolations of the MGs. By detecting an overloading condition, the primary level attempts to raise the frequency by managing the CLs, whereas the secondary level assesses the possibility of forming a system of coupled MGs (CMG). Depending on the level of support provided by the neighboring MG, the shed loads can be restored completely or partially once the system of CMG is formed. Implementation of the two levels is coordinated such that the power shortfall can be relieved with very low bandwidth communication systems. Validity of the proposed strategy is demonstrated through several PSCAD/EMTDC studies.

This paper proposes a supervisory control scheme to facilitate coupling of remote droop-regulated microgrids (MGs) during power shortfalls. In this scheme, instead of power converters, an instantaneous static switch is incorporated for the interconnection. Therefore a supervisory controller is essential to cope with the associated challenges, which are: 1) the level of supporting power provided by the neighboring MG and 2) isolation procedure of the coupled MGs (CMG) when the power deficiency condition is removed. Droop coefficients of distributed generators of the overloaded MG are dynamically updated by the controller according to the three operating modes defined to address the aforementioned challenges. The transit criteria, as well as the controlling signals, are accurately formulated based only on the local measurements to decrease the dependency on the communication systems. This enhances the reliability level of the coupled system. Effectiveness of the proposed strategy is validated through the results obtained from PSCAD/EMTDC simulations. Also, small-signal stability of the CMG operated by the proposed controller is examined using a developed model in MATLAB.

This paper endeavors to provide the reader with an overview of the various tools needed to forecast photovoltaic (PV) power within a very short-term horizon. The study focuses on the specific application of a large scale grid-connected PV farm. Solar resource is largely underexploited worldwide whereas it exceeds by far humans’ energy needs. In the current context of global warming, PV energy could potentially play a major role to substitute fossil fuels within the main grid in the future. Indeed, the number of utility-scale PV farms is currently fast increasing globally, with planned capacities in excess of several hundred megawatts. This makes the cost of PV-generated electricity quickly plummet and reach parity with non-renewable resources. However, like many other renewable energy sources, PV power depends highly on weather conditions. This particularity makes PV energy difficult to dispatch unless a properly sized and controlled energy storage system (ESU) is used. An accurate power forecasting method is then required to ensure power continuity but also to manage the ramp rates of the overall power system. In order to perform these actions, the forecasting timeframe also called horizon must be first defined according to the grid operation that is considered. This leads to define both spatial and temporal resolutions. As a second step, an adequate source of input data must be selected. As a third step, the input data must be processed with statistical methods. Finally, the processed data are fed to a precise PV model. It is found that forecasting the irradiance and the cell temperature are the best approaches to forecast precisely swift PV power fluctuations due to the cloud cover. A combination of several sources of input data like satellite and land-based sky imaging also lead to the best results for very-short term forecasting.

This paper proposes a cooperative control of battery energy storage (BES) units within a microgrid (MG) which includes two control subsystems for charge and discharge operation mode of the BES. In addition, the proposed cooperative control strategy provides accurate reactive power sharing among the BES units. During discharge operation, the proposed strategy utilizes a SoC-based droop control in order to avoid promptly depleting of the BES units, by dedicating the highest priority to their SoC level and respecting their power rating. This is achieved without any disturbance in the power balance of the MG. In addition, during charge operation of the BES units, the proposed control method uses a proportional-integral (PI) controller to limit the BES absorbing power and match it with the available surplus power from the renewable energy sources (RESs). This in turn avoids any power imbalance within the system. Finally, to utilize the extra capacity of the BES converters and also to avoid overloading of RESs, a new adaptive virtual impedance (AVI) strategy is proposed here which provides accurate reactive power sharing by imposing a virtual impedance in series with the coupling impedance of each BES and RES unit. The system performance is validated through extensive simulations carried out in PSCAD/EMTDC software.

This paper proposes a power exchange strategy for sustainable microgrids (MGs) of remote areas that have no access to a utility grid. This strategy manages the MG during power deficiencies under a decentralised approach (DA), which is the most probable case for remote MGs due to the lack of communication systems, or a centralised approach if a data communication system is available. Under each approach, a two-level (internal/external) control is established. The internal support is provided through power exchange with local energy storage while the external support is provided through power exchange with a neighbouring MG, after their temporary coupling. Appropriate conditions and constraints, under which the necessity and possibility of internal/external power exchange can be determined, are defined and formulated. These terms are based on local frequency measurements (for DA) and instantaneous power generation of the dispatchable distributed energy resources (for centralised approach). The dynamic performance of a remote system, composed of two MGs, operating with this strategy is evaluated by simulation studies in PSCAD/EMTDC. Furthermore, the small signal stability of such a system is investigated in MATLAB.

The present study has been carried out to determine the sources and distribution of fluoride (F−) contamination in the water of district Bijapur, Chhattisgarh, central India. For this study, 45 water samples were collected from surface and groundwater from shallow and deeper aquifers. It was observed that 50% of groundwater samples have elevated F− level and varies from 0.1 to 7.1 mg/L, though, F− level in water bodies was below the WHO maximum permissible limit (1.5 mg/L). The major ions of water samples reveal the dominance of Ca–Mg–HCO3 hydrochemical facies. This study suggests F− contaminated water shows a significant correlation with Cl− which further supported by statistical correlation. Analysis of rocks and sediments from the study area suggests leaching of minerals like biotite, hornblende, and richterite which are likely sources for elevated F− level in groundwater. Gibbs diagram reveals the dominance of the evaporative process for contaminated water by F− in the study area. Due to improper awareness, the local tribal population (≈2, 55,000) of the area is consuming F− enriched groundwater and vulnerable to dental and skeletal fluorosis. Thus, surface and uncontaminated water w.r.t F− should be developed for providing safe water to the inhabitants.

This paper discusses how two islanded microgrids, when connected together, can support each other during contingencies. Nominally, each microgrid supplies local loads connected to it. However, during any overloading in one of the microgrids, the other supplies power to support it, if possible. The microgrids are interconnected through a back to back converter so that each of them can operate independently. The power exchange through these converters takes place only when there is a shortfall in one of the microgrids. In this paper, it is shown how such a collaborative scheme can work satisfactorily. Some important strategies, such as overload detection and excess power calculation are required for this type of interconnection and are proposed in this paper. The proposals are validated through extensive PSCAD/EMTDC simulation studies.

Presence of large number of single-phase, customer-owned, distributed energy resources that are installed randomly in any phase of Low Voltage (LV) distribution feeders, may lead the generation, in a particular phase, to exceed its load demand. This may result in reverse power flow in that phase towards the upstream network while in the other phases, power flows from the upstream network to the LV feeder. To avoid such problems, this paper proposes the use of Distribution Static Compensators (DSTATCOM) to circulate the reverse flowing power from one phase to the other phases. In this paper, the installation of DSTATCOMs is considered in the medium voltage feeders. The DSTATCOM can be connected in either wye or delta, both of these connections are explored here. Different control strategies are developed for each connection. The main objective of the DSTATCOM is to provide a path for the power, to circulate among the phases, through its DC link. The DSTATCOM controller is further developed to balance its upstream powers and to supply the load reactive power demand. The proposed configurations and the developed control methods for the DSTATCOM are numerically validated through extensive computer simulation studies in PSCAD/EMTDC.

Low voltage feeders (LVFs) experience several voltage quality (VQ) issues such as voltage drop at network peak periods, voltage rise at middays when high number of rooftop photovoltaic cells (PVs) are existing in the feeder, rapid voltage fluctuations as the results of the clouds effects on the power generation of PVs, and voltage unbalance due to the inherent random characteristics of the single-phase loads and PVs. This study addresses these problems by proposing the concept of coupling the neighbouring LVFs. Based on this concept, two or more LVFs of the same distribution transformer or different distribution transformers are interconnected to support each other and minimise the VQ problems. First, the performance of LVFs in the existing form is discussed and three approaches of coupling the LVFs are presented. Among the presented techniques, coupling of LVFs through a distribution static compensator (DSTATCOM) at the end of the feeder is proposed and focused as an effective technique with minimal side effects such as power losses and cost. Proper dynamic control methods are also proposed for the DSTATCOM and the performance of such a system is investigated under steady-state and dynamic conditions via numerical analysis and simulation studies in MATLAB and PSCAD/EMTDC.

This paper presents dynamic analysis of a Modular Multi-Parallel Rectifier (MMR) based on state-space modelling. The proposed topology is suitable for high power motor drive or multi-parallel AC-DC applications, which can reduce line current harmonics emissions significantly. However, a proper controller is required to share and control current through each rectifier. Mathematical analysis and simulations have been carried out to verify the proposed controller under different operating conditions.

This study proposes a new method for stabilising disturbed power systems using wide-area measurement and controllable devices. A new control algorithm based on kinetic energy is proposed to be applied on the controllers to improve the first swing stability of power systems following large disturbances while also damping the subsequent inter-area oscillations. The wide-area controller is implemented by using the Kalman filter estimation of the area-based model of the system, to stabilise the inter-area dynamic and improve the stability margin of the system. The proposed approach is simulated on several test systems and the results show significant improvement in the first swing and damping stability of the test systems.

A wireless data communication system for future microgrids (MGs) is presented in this paper. It is assumed that each MG has a central controller and each distributed generation unit in the MG has a local controller. The communication system is responsible for transmitting and receiving data amongst these controllers. This communication system is based on ZigBee technology, which is a low cost and low power consumption device. However, its main limitation is the low data transfer rate. To reduce the number of data transactions, a data management scheme is presented in this paper. The required data to be transferred are defined and a suitable coding is proposed. Finally, the number of transmitted symbols and the processing time of the proposed data management scheme are numerically analyzed. In addition, the dynamic operation of an MG is evaluated considering the delays that are imposed by this communication system.

A hybrid NanoGrid (NG) can be considered as the power supply system, for future community houses. In this study, the operation and control of an NG are presented. The NG consists of an AC bus and a DC bus, interconnected through a tie-converter (TC). All AC loads and distributed energy resources (DERs) of the community houses are connected to the AC bus while all their DC loads and DERs are connected to the DC bus. The NG has an adequate generation capacity to supply its loads in off-grid status as well as the capability to exchange power with the grid. The TC exchanges the power between two buses and regulates the voltage in both buses, in the case of off-grid operation. The NG dynamics, with the proposed structure and developed primary and secondary control algorithms are validated through extensive computer simulations in PSCAD/EMTDC.

This paper suggests a supervisory control for storage units to provide load leveling in distribution networks. This approach coordinates storage units to charge during high generation and discharge during peak load times, while utilized to improve the network voltage profile indirectly. The aim of this control strategy is to establish power sharing on a pro rata basis for storage units. As a case study, a practical distribution network with 30 buses is simulated and the results are provided.

Electron-irradiation induced changes in structural and, magnetic properties of Co 57.6 Fe 14.4 Si 4.8 B 19.2 Nb 4 , Fe 72 Si 4.8 B 19.2 Nb 4 and, Co 72 Si 4.8 B 19.2 Nb 4 metallic glasses were studied using magnetic hysteresis and, synchrotron X-ray diffraction measurements. Results reveal composition dependent changes of magnetic properties in electron irradiated metallic glasses. A low electron irradiation dose (15 kGy) enhances saturation magnetization (up to 62%) in Fe-based alloy (Fe 72 Si 4.8 B 19.2 Nb 4 ). Synchrotron XRD measurements reveal that electron irradiation transforms the amorphous matrix to a more ordered phase, accountable for changes in magnetic properties.

This paper proposes a control strategy for sharing load requirements in a low voltage islanded microgrid with converter interfaced distributed energy resources. In high voltage lines with large X/R ratio, real and reactive power are decoupled and thus conventional droop control can effectively share the power needs of the load. However, the same strategy cannot be applicable in dominantly resistive remote microgrids where, X/R ratio is very small. In order to ensure accurate sharing of load power, this paper adopts cut in contrast of conventional angle droop control, where active power sharing is achieved by controlling voltage and reactive power by angle droop method. In addition, virtual resistive output impedance is utilized to effectively decouple real and reactive power. Moreover, this strategy includes influence of line impedance in load power sharing and offers an added advantage of effective overall system damping. Third harmonic injection based pulse width modulation scheme is used for each distributed generators(DGs), which provides better utilization of DC link voltage and suppress neutral currents under unbalanced conditions.

Keeping in view the vision “to become an integral part of the financial system and participate in the nation building'', the Royal Securities Exchange of Bhutan (RSEB) was established in August, 1993 as the only stock exchange in the small and beautiful country of Bhutan. Initially RSEB was set up under the control of Royal Monetary Authority (RMA), the central monetary authority of the country, but in 1996, it was delinked as an autonomous body. Since 1993, the exchange has registered a growth as far as number of listed companies, market capitalization and numbers of shareholders are concerned. But during a journey of twenty years, whether the growth ratio registered is satisfactory or not, is a cause of real concern. This paper aims to highlight the trend of growth in the performance of the stock exchange for the past decade from different angles. The paper also aims to critically emphasize in measuring the performance of RSEB to be able to popularize stock investment as an investment tool for personal finance. The contribution of capital formation into GDP of the country also will be analyzed. The paper will utilize both primary and secondary data to be collected through questionnaire and available on different Government publications, Journals, Reports and websites.

This paper proposes the use of a common DC link in residential buildings to allow customers to inject their surplus power that otherwise would be limited due to AC power quality violation. The surplus power can easily be transferred to other phases and feeders through common DC link in order to maintain the balance between generated power and load. PSCAD-EMTDC platform is used to simulate and study the proposed approach. This paper suggests that this structure can be a pathway to the future DC power systems.

A new approach is proposed for obtaining a non-linear area-based equivalent model of power systems to express the inter-area oscillations using synchronised phasor measurements. The generators that remain coherent for inter-area disturbances over a wide range of operating conditions define the areas, and the reduced model is obtained by representing each area by an equivalent machine. The parameters of the reduced system are identified by processing the obtained measurements, and a non-linear Kalman estimator is then designed for the estimation of equivalent area angles and frequencies. The simulation of the approach on a two-area system shows substantial reduction of non-inter-area modes in the estimated angles. The proposed methods are also applied to a ten-machine system to illustrate the feasibility of the approach on larger and meshed networks. © The Institution of Engineering and Technology 2014.

Voltage unbalance is a major power quality problem in low voltage residential feeders due to the random location and rating of single-phase rooftop photovoltaic cells (PV). In this paper, two different improvement methods based on the application of series (DVR) and parallel (DSTATCOM) custom power devices are investigated to improve the voltage unbalance problem in these feeders. First, based on the load flow analysis carried out in MATLAB, the effectiveness of these two custom power devices is studied vis-a-vis the voltage unbalance reduction in urban and semi-urban/rural feeders containing rooftop PVs. Their effectiveness is studied from the installation location and rating points of view. Later, a Monte Carlo based stochastic analysis is carried out to investigate their efficacy for different uncertainties of load and PV rating and location in the network. After the numerical analyses, a converter topology and control algorithm is proposed for the DSTATCOM and DVR for balancing the network voltage at their point of common coupling. A state feedback control, based on pole-shift technique, is developed to regulate the voltage in the output of the DSTATCOM and DVR converters such that the voltage balancing is achieved in the network. The dynamic feasibility of voltage unbalance and profile improvement in LV feeders, by the proposed structure and control algorithm for the DSTATCOM and DVR, is verified through detailed PSCAD/EMTDC simulations.

To minimise the number of load sheddings in a microgrid (MG) during autonomous operation, islanded neighbour MGs can be interconnected if they are on a self-healing network and an extra generation capacity is available in the distributed energy resources (DER) of one of the MGs. In this way, the total load in the system of interconnected MGs can be shared by all the DERs within those MGs. However, for this purpose, carefully designed self-healing and supply restoration control algorithm, protection systems and communication infrastructure are required at the network and MG levels. In this study, first, a hierarchical control structure is discussed for interconnecting the neighbour autonomous MGs where the introduced primary control level is the main focus of this study. Through the developed primary control level, this study demonstrates how the parallel DERs in the system of multiple interconnected autonomous MGs can properly share the load of the system. This controller is designed such that the converter-interfaced DERs operate in a voltage-controlled mode following a decentralised power sharing algorithm based on droop control. DER converters are controlled based on a per-phase technique instead of a conventional direct-quadratic transformation technique. In addition, linear quadratic regulator-based state feedback controllers, which are more stable than conventional proportional integrator controllers, are utilised to prevent instability and weak dynamic performances of the DERs when autonomous MGs are interconnected. The efficacy of the primary control level of the DERs in the system of multiple interconnected autonomous MGs is validated through the PSCAD/EMTDC simulations considering detailed dynamic models of DERs and converters.

Advancement in communication technology and its application to power systems have introduced a new era in power system scheduling. Demand Side Management (DSM) is one of the main outcomes of this combination. In this paper, a droop-based hierarchical control strategy has been proposed to execute automatic Demand Dispatch (DD). When the frequency of the system falls/rises below/above rated level, Balancing Authority (BA) issues droop-based signal to the aggregators to check the feasibility and availability of DD according to the capability of aggregated loads. Then, these signals will be sent to the Appliance Management Unit (AMU). According to the availability, priority, and features of appliances, the AMU sends these commands in form of deferral or interruptible signals to appliances. At the time of DD events, the proposed AMU algorithm keeps the total household power consumption within the required limit to maintain the system frequency at nominal level. A wide variety of residential loads has been considered in the DD applications. It will be demonstrated that the proposed AMU algorithm is capable of maintaining the total demand of a house below the limit determined by the BA. In the second part of this paper, the necessity of renewable energy resources and battery storage system to prevent load rebound is highlighted.

Plug-in electric vehicles will soon be connected to residential distribution networks in high quantities and will add to already overburdened residential feeders. However, as battery technology improves, plug-in electric vehicles will also be able to support networks as small distributed generation units by transferring the energy stored in their battery into the grid. Even though the increase in the plug-in electric vehicle connection is gradual, their connection points and charging/discharging levels are random. Therefore, such single-phase bidirectional power flows can have an adverse effect on the voltage unbalance of a three-phase distribution network. In this article, a voltage unbalance sensitivity analysis based on charging/discharging levels and the connection point of plug-in electric vehicles in a residential low-voltage distribution network is presented. Due to the many uncertainties in plug-in electric vehicle ratings and connection points and the network load, a Monte Carlo-based stochastic analysis is developed to predict voltage unbalance in the network in the presence of plug-in electric vehicles. A failure index is introduced to demonstrate the probability of non-standard voltage unbalance in the network due to plug-in electric vehicles.

Due to its efficiency, reliability and better channel and resource utilization, cooperative transmission technologies have been attractive options in underwater as well as terrestrial sensor networks. Their performance can be further improved if merged with forward error correction (FEC) techniques. In this paper, we propose and analyze a retransmission protocol named Cooperative-Hybrid Automatic Repeat reQuest (C-HARQ) for underwater acoustic sensor networks, which exploits both the reliability of cooperative ARQ (CARQ) and the efficiency of incremental redundancy-hybrid ARQ (IR-HARQ) using rate-compatible punctured convolution (RCPC) codes. Extensive Monte Carlo simulations are performed to investigate the performance of the protocol, in terms of both throughput and energy efficiency. The results clearly reveal the enhancement in performance achieved by the C-HARQ protocol, which outperforms both CARQ and conventional stop and wait ARQ (S&amp, W ARQ). Further, using computer simulations, optimum values of various network parameters are estimated so as to extract the best performance out of the C-HARQ protocol.

This paper proposes a distributed control approach to coordinate multiple energy storage units (ESUs) to avoid violation of voltage and thermal constraints, which are some of the main power quality challenges for future distribution networks. ESUs usually are connected to a network through voltage source converters. In this paper, both ESU converters active and reactive power are used to deal with the above mentioned power quality issues. ESUs' reactive power is proposed to be used for voltage support, while the active power is to be utilized in managing network loading. Two typical distribution networks are used to apply the proposed method, and the simulated results are illustrated in this paper to show the effectiveness of this approach.

• Consequence of abusive handling of bearing during assembly and maintenance are discussed (two case studies are presented).

Summary form only given. In this paper, a new comprehensive planning methodology is proposed for implementing distribution network reinforcement. The load growth, voltage profile, distribution line loss, and reliability are considered in this procedure. A time-segmentation technique is employed to reduce the computational load. Options considered range from supporting the load growth using the traditional approach of upgrading the conventional equipment in the distribution network, through to the use of Distributed Generators (DG). The objective function is composed of the construction cost, loss cost and reliability cost. As constraints, the bus voltages and the feeder currents should be maintained within the standard level. The DG output power should not be less than a ratio of its rated power because of efficiency. A hybrid optimization method, called Modified Discrete Particle Swarm Optimization, is employed to solve this nonlinear and discrete optimization problem. A comparison is performed between the optimized solution based on planning of capacitors along with tap-changing transformer and line upgrading and when DGs are included in the optimization.

An iterative based strategy is proposed for finding the optimal rating and location of fixed and switched capacitors in distribution networks. The substation Load Tap Changer tap is also set during this procedure. A Modified Discrete Particle Swarm Optimization is employed in the proposed strategy. The objective function is composed of the distribution line loss cost and the capacitors investment cost. The line loss is calculated using estimation of the load duration curve to multiple levels. The constraints are the bus voltage and the feeder current which should be maintained within their standard range. For validation of the proposed method, two case studies are tested. The first case study is the semi-urban 37-bus distribution system which is connected at bus 2 of the Roy Billinton Test System which is located in the secondary side of a 33/11 kV distribution substation. The second case is a 33 kV distribution network based on the modification of the 18-bus IEEE distribution system. The results are compared with prior publications to illustrate the accuracy of the proposed strategy.

A new control method for battery storage to maintain acceptable voltage profile in autonomous microgrids is proposed in this article. The proposed battery control ensures that the bus voltages in the microgrid are maintained during disturbances such as load change, loss of micro-sources, or distributed generations hitting power limit. Unlike the conventional storage control based on local measurements, the proposed method is based on an advanced control technique, where the reference power is determined based on the voltage drop profile at the battery bus. An artificial neural network based controller is used to determine the reference power needed for the battery to hold the microgrid voltage within regulation limits. The pattern of drop in the local bus voltage during power imbalance is used to train the controller off-line. During normal operation, the battery floats with the local bus voltage without any power injection. The battery is charged or discharged during the transients with a high gain feedback loop. Depending on the rate of voltage fall, it is switched to power control mode to inject the reference power determined by the proposed controller. After a defined time period, the battery power injection is reduced to zero using slow reverse-droop characteristics, ensuring a slow rate of increase in power demand from the other distributed generations. The proposed control method is simulated for various operating conditions in a microgrid with both inertial and converter interfaced sources. The proposed battery control provides a quick load pick up and smooth load sharing with the other micro-sources in a disturbance. With various disturbances, maximum voltage drop over 8% with conventional energy storage is reduced within 2.5% with the proposed control method.

Single phase nanocrystalline soft magnetic Mg 0.7-x Ni 0.3 Zn x Fe 2 O 4, ferrites with x = 0.0 − 0.7 were prepared by sol gel auto-combustion method. X-ray diffraction confirms the formation of single phase nano-crystalline cubic spinel ferrites with average grain diameter ranging between 12.9 nm to 23.9 nm. Formation of the ferrite phase without subsequent heat treatment makes sol-gel auto combustion technique especially suitable and economical for the large scale industrial production of the nano-crystalline ferrites for multilayer chip inductor applications (MLCI). Both, lattice parameter and X-ray density shows a linear increase with increasing Zn 2+ concentration, attributed to the difference in ionic radii and density of Mg and Zn . Increase in Zn content enhances the soft magnetic behavior, exhibiting linear decrease of coercivity from 122.34 Oe to 72.45 Oe, explained by increase of density with Zn addition. The maximum magnetization (Mmax)increases up to 0.106 Tesla (for x = 0.4) and. then decreases with increase of Zn content, discussed on the basis of increase of the occupancy of A-site in spinel ferrite by non-magnetic Zn 2+ ion.

Recent progress in power electronic converters has increased the number of distributed energy sources to the grid. These converters act as a source of harmonics which connected with other loads affect the stability of power grid. Parallel operation of converters is common in power grid depends on the power sharing needs and current rating of power semiconductor devices. Though, these connections improves power handling capability of grid, the dynamic interaction between converters can affect stability of system. This paper addresses the stability issues in parallel connected, high frequency voltage controlled converters with an output LC filter. Studies on interactions between control loops verifies that, harmonic instability introduced by parallel converters can't be stabilized by traditional PI controllers in real power control loop. A new damping algorithm is introduced to suppress these harmonic oscillations caused by the interaction of controllers in grid connected converters.

Coupling remote microgrids (MGs) is a promising technique to handle power deficiency in such systems. However, once the shortfall is removed, the coupled MGs (CMG) should isolate to carry on their operation autonomously. Due to the non-zero power still flowing through the tie-line, however, considerable voltage spikes may be imposed on the interconnecting static switch (ISS) during the isolation that may damage the device. This paper proposes a practical decentralized approach to efficiently alleviate the mentioned transients, facilitating a successful MG isolation procedure. Two auxiliary controllable loads (ACL) are to be considered at two sides of the ISS. When the necessity of applying the isolation action is detected, the ISS controller commands the ACL on the supporting MG side to connect. A droop-based scheme is formulated to derive the load should be demanded by the ACL such that the power passing through the ISS drops to zero, preventing any spikes across it at the opening moment. Once the isolation action is accomplished, the controller disconnects the ACL. Efficiency of the proposed algorithm is validated through various cases simulated using PSCAD/EMTDC.

This paper proposes a self-healing strategy for two neighboring islanded microgrids (MGs) that are connected together through a normally open interconnecting static switch (ISS). Each MG is expected to support the other during power deficiencies, which is facilitated by the developed self-healing agent. This agent operates based on either a centralized approach, when data communication system is available, or a decentralized approach, when data communication system does not exist or is temporarily unavailable. The necessity and possibility of the MGs interconnection or isolation is determined based on instantaneous power generation of the distributed energy resources in both MGs (in the centralized approach) and local frequency measurements at either side of ISS (in the decentralized approach). The dynamic performance of the MGs with the proposed strategies is evaluated by PSCAD simulation studies. Furthermore, the stability of the system of coupled MGs is investigated through small-signal stability and modal analyses in MATLAB.

Three types of offshore wind power collection topologies are studied for DC power systems in this paper. Permanent Magnet Synchronous Generator (PMSG) based Wind Energy Conversion System (WECS) is considered and the Optimal Power Control (OPC) is used for the Maximum Power Point Track (MPPT) control. The failure of a wind power unit is regarded as the fault condition in this paper. Voltage control strategies are proposed for series and series-parallel power collection topologies when such a fault happens. Input and output voltage references of the Grid-Side Converter (GSC) are modified for series power collection systems on fault conditions. For series-parallel collection systems, power switches are employed between wind power branches and different voltage control effects with different switch options are discussed. Simulation studies are conducted base on PSCAD/EMTDC to validate the proposed control strategies.

Common-mode voltage generated by a power converter in combination with parasitic capacitive couplings is a potential source of shaft voltage in an AC motor drive system. In this study, a three-phase motor drive system supplied with a single-phase AC-DC diode rectifier is investigated in order to reduce shaft voltage in a three-phase AC motor drive system. In this topology, the AC-DC diode rectifier influences the common-mode voltage generated by the inverter because the placement of the neutral point is changing in different rectifier circuit states. A pulse width modulation technique is presented by a proper placement of the zero vectors to reduce the common-mode voltage level, which leads to a cost-effective shaft voltage reduction technique without load current distortion, while keeping the switching frequency constant. Analysis, simulations and experimental implementation have been presented to investigate the proposed method.

The degree of proliferation of Distributed Energy Resources (DERs) and application of power electronics appliances are in demand. A microgrid can contain variety of sources such as diesel generator, wind turbine, PV arrays, micro-turbine and fuel cell. Usually these sources share power where the system frequency changes depending on the power supplied. On the other hand, the microgrid can contain harmonic loads that can affect the performance of the synchronous generators. These deleterious effects of distorting loads can be corrected using a distribution static compensator (DSTATCOM). In this paper, an isochronous control based droop strategy is employed that forces the microgrid to operate at the base frequency of 50 Hz. Therefore the DSTATCOM can be operated at 50 Hz. A closed-loop space vector pulse width modulation (SVPWM) technique is used for the DSTATCOM control. The scheme is validated through the extensive PSCAD/EMTDC simulation studies.

It is expected that a microgrid (MG) can supply its local loads independently; however the load and generation intermittency may lead an MG to experience overloading. This problem can be mitigated by coupling the overloaded MG to another neighboring MG that has surplus power. It is a challenge to select a suitable MG within a distribution network composed of several islanded MGs, to be coupled to the overloaded MG. This paper presents a new decision-making-based method to select the suitable alternative. This selection is based on different criteria including the available surplus power, reliability, supply security, power loss, electricity cost and CO2 emissions in the alternative MGs. Moreover, the frequency and voltage deviation in the system of coupled MGs are considered in the selection. The performance of the developed method is evaluated within a cloud theory-based probabilistic analysis in MATLAB.

A new technique for optimal planning of MV and LV segments of a distribution system is presented in this paper. The main goal is to find optimally distribution transformer and substation locations and ratings, as well as, the route and type of Medium Voltage (MV) and Low Voltage (LV) feeders. The proposed technique is applicable to both uniform and non-uniform load densities areas. In this method, the planning area is divided into regions with relatively uniform load density such as urban, semi-urban, sub-urban. Each of regions is divided into zones, called LV zone. Each LV zone is supplied by an MV/LV transformer. The dimensions of LV zones are found based on the average load of each region. The placement and rating of MV/LV transformers, the type and route of LV conductors in an LV zone all depend on its loads’ location and power. Regarding the placement and rating of MV/LV transformers in planning area and the space of regions, the dimensions of a zone which is supplied by a HV/MV transformer, called MV zone, is determined. Additionally, the location and rating of HV/MV transformers as well as the feeder's routes and types are calculated. Since the dimensions of an LV zone influence the associated length of MV feeder, the MV feeder cost needs to be included in the total cost associated with the LV zone. This requires the MV feeder type to be known to calculate the corresponding cost. However, the MV feeder type is determined as an output from MV zone planning. As a result, an iterative based method is proposed to consider this common element in computations to develop integrated planning of both LV and MV zones. It is observed that the iterative technique quickly converges to the same results as the exhaustive search method. Discrete particle swarm optimization (DPSO) method is employed for solving the planning problem. The results are compared with nonlinear programming, genetic algorithm and exhaustive search methods. It is observed that DPSO is as accurate as the exhaustive search method for integrated planning of MV–LV distribution systems while its computation time is significantly lower.

The installation of domestic rooftop photovoltaic cells (PVs) are on the rise due to feed-in tariff and changes driven by environmental concerns. Even though the increase in the PV installation is gradual, their locations and ratings are often random. Therefore, such single-phase bi-directional power flow can have adverse effect on the voltage imbalance of a three-phase distribution network. In this paper, a voltage imbalance sensitivity analysis and stochastic evaluation based on the ratings and locations of single-phase grid-connected rooftop PVs in a residential low voltage distribution network are presented. The stochastic evaluation, based on Monte Carlo method, predicts a failure index of non-standard voltage imbalance in the network in presence of PVs. Some improvement methods are discussed and a new improvement method based on PV converter control is proposed.

This paper presents a novel topology for the generation of high voltage pulses that uses both slow and fast solid-state power switches. This topology includes diode-capacitor units in parallel with commutation circuits connected to a positive buck-boost converter. This enables the generation of a range of high output voltages with a given number of capacitors. The advantages of this topology are the use of slow switches and a reduced number of diodes in comparison with conventional Marx generator. Simulations performed for single and repetitive pulse generation and experimental tests of a prototype hardware verify the proposed topology.

The flying capacitor multicell inverter (FCMI) possesses natural balancing property. With the phase-shifted carrier-based scheme, natural balancing can be achieved in a straightforward manner. However, to achieve natural balancing with the harmonically optimal phase-disposition (PD) carrier-based scheme, the conventional approaches require (n - 1) × (n - 1) trapezoidal carrier signals for an n-level inverter, which is ( n - 1) × (n - 2) times more than that in the standard PD scheme. This paper proposes two improved natural balancing strategies for FCMI under PD scheme, which use the same (n - 1) carrier signals as used in the standard PD scheme. In the first scheme, the on-line detections are performed of (i) the band in which the modulation signal is located, (ii) corresponding period number of the carrier, and (iii) rising or falling half cycle of the carrier waveform to generate the switching signals based on certain rules. In the second strategy, the output voltage level selection is first processed and the switching signals are then generated according to a rule based on preferential cell selection algorithm. These methods are easy to use and can be simply implemented as compared to the other available methods. Simulation and experimental results are presented for a five-level inverter to verify these proposed schemes.

The hysteresis modulation for power electronic converters is attractive in many different applications because of its unmatched dynamic response and wide command-tracking bandwidth. Its application and benefits for two-level converters are well understood, but the extension of this strategy to multilevel converters is still under development. This paper summarizes and reviews the various hysteresis modulation approaches available in the literature for multilevel converters. The pros and cons of various techniques are described and compared for tracking the reference signal in order to attain an adequate switching optimization, excellent dynamic responses and high accuracy in steady-state operation. By using the recently developed multilevel hysteresis modulation approaches, the advantages of using several accessible dc potentials in a multilevel inverter have been fully exploited. All of these hysteresis modulation approaches are tested for tracking a current reference when applied to a five-level inverter. The relevant simulation and experimental results are also presented. This study will provide a useful framework and point of reference for the future development of hysteresis modulation for multilevel converters.

PurposeMulti‐level diode‐clamped inverters have the challenge of capacitor voltage balancing when the number of DC‐link capacitors is three or more. On the other hand, asymmetrical DC‐link voltage sources have been applied to increase the number of voltage levels without increasing the number of switches. The purpose of this paper is to show that an appropriate multi‐output DC‐DC converter can resolve the problem of capacitor voltage balancing and utilize the asymmetrical DC‐link voltages advantages.Design/methodology/approachA family of multi‐output DC‐DC converters is presented in this paper. The application of these converters is to convert the output voltage of a photovoltaic (PV) panel to regulate DC‐link voltages of an asymmetrical four‐level diode‐clamped inverter utilized for domestic applications. To verify the versatility of the presented topology, simulations have been directed for different situations and results are presented. Some related experiments have been developed to examine the capabilities of the proposed converters.FindingsThe three‐output voltage‐sharing converters presented in this paper have been mathematically analysed and proven to be appropriate to improve the quality of the residential application of PV by means of four‐level asymmetrical diode‐clamped inverter supplying highly resistive loads.Originality/valueThis paper shows that an appropriate multi‐output DC‐DC converter can resolve the problem of capacitor voltage balancing and utilize the asymmetrical DC‐link voltages advantages and that there is a possibility of operation at high‐modulation index despite reference voltage magnitude and power factor variations.

This paper discusses the use of trajectory sensitivity analysis (TSA) in determining the transient stability margin of a power system compensated by a shunt FACTS device. The shunt device used is static synchronous compensator (STATCOM). It is shown that TSA can be used for the design of controller for the STATCOM. The preferable locations for the placement of the STATCOM for different fault conditions are also identified. The effects of STATCOM in maintaining different bus voltages in the post-fault condition are studied. The STATCOM is modeled by a voltage source connected to the system through a transformer. The systems used for the study are the WSCC 3-machine 9-bus system and the IEEE 16-machine 68-bus system.

In this paper, the performance of voltage-source converter-based shunt and series compensators used for load voltage control in electrical power distribution systems has been analyzed and compared, when a nonlinear load is connected across the load bus. The comparison has been made based on the closed-loop frequency resopnse characteristics of the compensated distribution system. A distribution static compensator (DSTATCOM) as a shunt device and a dynamic voltage restorer (DVR) as a series device are considered in the voltage-control mode for the comparison. The power-quality problems which these compensator address include voltage sags/swells, load voltage harmonic distortions, and unbalancing. The effect of various system parameters on the control performance of the compensator can be studied using the proposed analysis. In particular, the performance of the two compensators are compared with the strong ac supply (stiff source) and weak ac-supply (non-still source) distribution system. The experimental verification of the analytical results derived has been obtained using a laboratory model of the single-phase DSTATCOM and DVR. A generalized converter topology using a cascaded multilevel inverter has been proposed for the medium-voltage distribution system. Simulation studies have been performed in the PSCAD/EMTDC software to verify the results in the three-phase system.

An algorithm based on the concept of combining Kalman filter and Least Error Square (LES) techniques is proposed in this paper. The algorithm is intended to estimate signal attributes like amplitude, frequency and phase angle in the online mode. This technique can be used in protection relays, digital AVRs, DGs, DSTATCOMs, FACTS and other power electronics applications. The Kalman filter is modified to operate on a fictitious input signal and provides precise estimation results insensitive to noise and other disturbances. At the same time, the LES system has been arranged to operate in critical transient cases to compensate the delay and inaccuracy identified because of the response of the standard Kalman filter. Practical considerations such as the effect of noise, higher order harmonics, and computational issues of the algorithm are considered and tested in the paper. Several computer simulations and a laboratory test are presented to highlight the usefulness of the proposed method. Simulation results show that the proposed technique can simultaneously estimate the signal attributes, even if it is highly distorted due to the presence of non-linear loads and noise.

This paper proposes new droop control methods for load sharing in a rural area with distributed generation. Highly resistive lines, typical of rural low voltage networks, always create a big challenge for conventional droop control. To overcome the conflict between higher feedback gain for better power sharing and system stability in angle droop, two control methods have been proposed. The first method considers no communication among the distributed generators (DGs) and regulates the converter output voltage and angle ensuring proper sharing of load in a system having strong coupling between real and reactive power due to high line resistance. The second method, based on a smattering of communication, modifies the reference output volt-age angle of the DGs depending on the active and reactive power flow in the lines connected to point of common coupling (PCC). It is shown that with the second proposed control method, an economical and minimum communication system can achieve significant improvement in load sharing. The difference in error margin between proposed control schemes and a more costly high bandwidth communication system is small and the later may not be justified considering the increase in cost. The proposed control shows stable operation of the system for a range of operating conditions while ensuring satisfactory load sharing.