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Smart buildings form an integral part of the smart grid that lowers electricity cost. This objective can be achieved by using suitable enhanced algorithms and techniques. The motivation of this paper is the request for an economical decision-making system from a commercial company in Singapore. This paper presents an economical building management system (EBMS) concept inspired by the building management system and machine learning. EBMS improves the decision-making process through rule-based algorithm within the system. Machine learning algorithm is included as part of EBMS to enhance the computational calculation for the electricity distribution. It includes the function of self-making decision for purchasing electricity based on forecasting system for electricity price or real-time electricity price data when facility managers are not present. EBMS uses multiagent system to communicate, interact, and negotiate with multiple agents for energy supply and demand in the building. Simulation studies have shown the potential of EBMS concept to provide a cost reduction solution up to 61.42% savings for smart buildings. Better electricity purchasing contract option can be decided based on the forecasting system for building power consumption. [ABSTRACT FROM AUTHOR]

Reactive power planning has always been a key research area in power distribution engineering; technically and economically. However, the problem needs to be revisited to consider several aspects of modern distribution systems, such as a high penetration level of renewable resources with intermittent nature; the microgrid concept and the possibility of system operation in grid-connected or isolated single microgrid mode, or isolated multiple microgrids; and probabilistic or hourly load profile. Motivated by these needs and considering all these aspects, this paper presents a generalized approach for probabilistic optimal reactive power planning in modern distribution systems. A new index is defined to probabilistically assess the success of microgrids in terms of real and reactive power adequacy and voltage limit constraints. Afterward, the reactive power planning is performed to reduce the annual energy losses of the grid-connected system and increase the defined microgrid success index. The problem formulation and solution algorithms are presented in this paper. The well-known PG&E 69-bus distribution system is selected as a test case, and through several sensitivity studies, the effect of optimization coefficients on the design and the robustness of the algorithm are investigated. A cost–benefit case study is also presented to determine the optimum total size of distributed reactive sources for the system under study. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel control method for an asymmetrical-cascaded-multilevel-converter-based hybrid energy storage system (HESS), which includes one battery and several electrical double-layer capacitors (EDLCs). Traditionally, it is challenging to control the power distribution between different cascaded H-bridges by using different energy storage components as dc sources. In this paper, a feedforward space-vector-modulation (FFSVM) technique is used to distribute the active power between the battery and EDLCs. With the proposed voltage feedforward mechanism, the HESS can flexibly operate in the normal operation mode, the high-power output mode, and the reverse power absorption mode. The principle and effectiveness of the improved FFSVM technique are analyzed. Meanwhile, the state-of-charge-balancing mechanisms are introduced. The simulation results obtained in MATLAB/Simulink as well as the experimental results of a hybrid energy storage test bed based on the proposed system are presented to verify its performance. [ABSTRACT FROM PUBLISHER]

This paper describes a systematic procedure using power flow graphs for generating all possible double-input single-output (DISO) dc/dc converters. To maximize the generality of applications, the input ports can possibly be connected with voltage source(s) or current source(s), and the output port can be connected with a voltage load or current load. The control methods are described in this paper. A DISO converter with two voltage sources and one voltage load is taken as an example to analyze a few key properties of practical relevance, including input voltage range, efficiency, power distribution, and switching stress. A popular application of DISO converters involves the use of a battery as storage element, and for this specific case, possible choices for the converters, the control method, and the attainable efficiency are discussed. Finally, experimental results are presented to verify the analytical results. [ABSTRACT FROM PUBLISHER]

This paper proposes an interleaved buck converter (IBC) with continuous input current, extremely low output current ripple, low switching losses, and improved step-down conversion ratio. Unlike the conventional IBC, the proposed converter has a continuous input current, and its output current ripple is extremely low. The proposed converter has a lower voltage stress in comparison to the conventional IBC and can also provide a high step-down ratio, which makes it a proper choice for high-power applications where a nonisolated step-down converter with low output current ripple and continuous input current is required. Also, the proposed converter can provide current sharing between two interleaved modules without using additional current-sharing control method. All of these benefits are obtained without any additional stress on the circuit components. A prototype converter with 200-V input and 24-V–10-A output is implemented to verify the theoretical analysis. Operational principles and experimental results are presented in this paper. [ABSTRACT FROM PUBLISHER]

A quasi-Z-source modular cascaded converter (qZS-MCC) is proposed for dc integration of high-power photovoltaic (PV) systems. The qZS-MCC comprises series-connected front-end isolated qZS half-bridge (HB) dc–dc converter submodules (SMs). With the front-end isolation, the qZS-MCC achieves high-voltage dc capability, while maintaining modularity and PV panel grounded. The post-stage qZS-HB handles the PV voltage and power flows, dc-link voltage balance, and output-series power integration. Whereas, the front-end isolation converters of all SMs perform a constant duty cycle, lowing the control complexity. There is no double-line-frequency power flowing through the dc-side PV panels, qZS inductors, and qZS capacitors in the qZS-MCC, so small qZS impedance is possible compared to the existing qZS cascaded multilevel inverter. The configuration, operating principle, power loss evaluation, and passive components design of the proposed system are investigated in this part of the paper. The system control, modeling, and corresponding verifications are stated in Part II of this paper. [ABSTRACT FROM PUBLISHER]

The operation of more electric aircraft is dependent on the embedded power grid. Therefore, the on-board power-distribution system must be reliable, having a high level of survivability, and promptly respond to any change in aircraft's operation. Recent studies have presented a number of frequency-response-based tools with which to analyze both single- and multiconverter systems. The methods can be efficiently applied for on-board system analysis, stability assessment, and adaptive control design. Most often, wideband measurement techniques have been applied to obtain the frequency response from a specific converter or a subsystem required for the analysis. In the methods, a broadband excitation such as a pseudorandom binary sequence (PRBS) is used as an external injection, and Fourier techniques are applied to extract the spectral information. This paper presents implementation techniques of the wideband methods using power-hardware-in-the-loop measurements based on OPAL-RT real-time simulator. The presented methods make it possible to modify the system characteristics, such as impedance behavior, in real time, thereby providing means for various stability and control design tools for on-board power distribution systems. Experimental measurements are shown from a high-power energy distribution system recently developed at DNV GL, Arnhem, The Netherlands. [ABSTRACT FROM AUTHOR]

The closed-loop distribution system has become a trend, owing to increasing demands of electric power reliability in high-tech parks or in metropolitan areas. Harmonic propagation caused by power-factor correction capacitors and system inductors may lead to significant harmonic amplification throughout a closed-loop distribution feeder. This paper proposes a novel equivalent model of a closed-loop distribution feeder that a closed-loop distribution feeder can be equivalent to a radial feeder. This paper analyzes the harmonic propagation in a closed-loop distribution feeder and proposes a long-feeder simulator-based active power filter (LFS-APF) to damp out the harmonic propagation, based on the novel equivalent model. The proposed LFS-APF is installed at the middle point of a closed-loop feeder. The LFS-APF has better capability of harmonic damping than the resistive APF (RAPF), especially in response to variation of both nonlinear loads and power-factor correction capacitors or even if the installation location has to deviate from the middle point. Both simulation and experiment results are provided to validate the correctness and effectiveness of the novel equivalent model and the proposed LFS-APF. [ABSTRACT FROM PUBLISHER]

This paper proposes an improved performance interactive distribution static compensator (DSTATCOM) to address the limitations of conventional current control mode (CCM) and voltage control mode (VCM) operations. The proposed interactive scheme provides smooth transfer of modes of operation while remaining connected in the distribution system. In normal operation, the DSTATCOM operates in CCM to make source currents balanced, sinusoidal, and at a unity power factor. During voltage disturbances, the CCM operation cannot improve load voltage. In that case, DSTATCOM operation is changed to VCM, which maintains a constant voltage across the sensitive loads. Hence, this interactive DSTATCOM ensures continuous, flexible, and robust operation of the load. Moreover, the filter current requirements are reduced in the proposed scheme, which reduces the losses in the filter and feeder, improves inverter efficiency, and requires a reduced-rating inverter for sag mitigation. The principle of operation and control for both operating modes is analyzed. The detailed process of the flexible transfer between the two modes is derived. Deadbeat predictive control algorithms for CCM as well as VCM operation are developed for fast operation during mode transfers. The performance of the proposed scheme is validated by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

A stability study of distribution networks with a high penetration of distributed generators (DGs) actively supporting the network is presented in this paper. A possible way of mitigating the voltage rise caused by DGs is the local control of reactive power. Among the different possible options, the Q(U) control (reactive power as a function of the voltage) is one of the commonly suggested solutions. However, the Q(U) control can, under certain conditions, lead to instability. This paper summarizes the results of a stability study conducted on a single-inverter system and on a multiinverter system. It shows that the requirements for reaching a stable operation can easily be met for integrated systems but could be a significant constraint for systems relying on communication. [ABSTRACT FROM PUBLISHER]

In the hybrid ac–dc microgrid, the ac and dc subgrids are connected by bidirectional power converters (BPCs) that play an important role in the load power sharing and power interaction between the ac and dc subgrids. The coordination control and circulating current suppression for the parallel BPC system are very challenging. In this paper, a decentralized coordination control method is proposed for parallel three-phase BPCs, which can suppress the circulating currents, realize proper power interaction, and achieve overall load power sharing in both the grid-connected mode and the islanded mode. The performance of the proposed control methods is verified by the real-time hardware-in-loop tests. [ABSTRACT FROM PUBLISHER]

Energy storage systems (ESSs) are becoming indispensable components in electric power systems. They are used for energy scheduling, power/voltage smoothing, load shifting, as well as for emergency power supply. The most common control method for power/voltage smoothing is based on a high-pass-filter (HPF) structure. It generates the power reference according to the fluctuating power and provides a stabilization effect. The power and energy supplied by ESSs are majorly configured by the cutoff frequency and gain of the HPF. Considering the operational limits on ESS state-of-charge (SoC), this paper proposes an adaptive cutoff frequency design method to realize communication-less and autonomous operation of a system with multiple distributed ESSs. The experimental results demonstrate that the SoCs of all ESS units are kept within safe margins, while the SoC level and power of the paralleled units converge to the final state, providing a natural plug-and-play function. [ABSTRACT FROM PUBLISHER]

Dual active bridge (DAB) converter is the most suitable converter to transfer high power with bidirectional power flow capability and isolation. However, it has the drawbacks of circulation power flow (CPF) and limited range of zero voltage switching (ZVS). To overcome these drawbacks, several modulation strategies have been proposed; however, the CPF can be eliminated either at input or output voltage ends. In order to eliminate the CPF at both input and output sides, a novel front and rear end switch DAB (FRS-DAB) bidirectional dc–dc converter has been proposed in this paper. It has the advantages of lower current stress, extension of ZVS range, higher power transfer capacity, and improved efficiency compared to the conventional DAB converter. The paper presents the detailed operating modes and analysis of power flow control for the proposed FRS-DAB converter. The operation and analytical results of the proposed converter have been verified through the experimental results using an FPGA Spartan 3AN processor. [ABSTRACT FROM PUBLISHER]

A smart and autonomous integration concept for dc microgrids into the legacy ac grid is proposed based on the virtual synchronous machine (VSM) concept. It utilizes a dc–ac converter as a universal VSM-based interface (VSMBI) between the ac grid and various distributed energy resources (DER) connected on the dc side. The control strategy of it includes: 1) a frequency regulation improved from previous VSM works, which is suitable for the microgrid integration; 2) an improved dual droop control between the ac frequency and the dc side energy storages; 3) a power system stabilizer to enhance the system stability. Under this concept, the VSMBI integrates the DERs, loads and energy storages in the dc microgrid into a VSM. The VSMBI and the dc microgrid together will respond to short-term and long-term requirements of the grid frequency regulation, and achieve autonomous power management for the ac grid and the dc microgrid. It is therefore an important step forward in supporting high DER penetration. The concept, its design and small-signal analysis are presented in this paper. Its effectiveness and functions are verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

In a conventional finite control set model predictive control (FCS-MPC) formulation, active and reactive power control loops rely on the predictive controller, whereas the dc-bus voltage is usually governed by a PI-based control loop. This originates from fact that the dynamic equations for describing the predictions of these variables are heavily coupled. In this paper, a cascade-free FCS-MPC for single-phase grid-connected power converters is presented. The proposed control algorithm is formulated in terms of established dynamic references design, which was originally proposed to directly govern active and reactive power, and dc-voltage in three-phase power converters. In this paper, the dynamic reference design concept is extended to control single-phase grid-connected power converters. The proposed control algorithm does not use instantaneous ac-power calculations; instead, it directly formulates the optimal control problem on the grid-current in the original stationary reference frame. The experimental results obtained with a single-phase grid-connected neutral point clamped (NPC) converter confirm a successful design, where system constraints, e.g., maximum power and weighted switching frequency, are easily taken into account. [ABSTRACT FROM PUBLISHER]

The temperature of electrolytic capacitor in light-emitting diode (LED) drivers continuously increases under operation conditions, thus the capacitors degrade faster than that with constant temperature assumption. In this paper, a physics-of-failure (PoF)-based reliability prediction methodology is developed for LED drivers to consider the temperature change of electrolytic capacitor. SPICE simulation, compact thermal modeling, and Monte Carlo simulation are integrated to predict the failure rate distribution of an electrolytic capacitor of given LED driver systems. The simulation results agree well with the accelerated test results for an RC linear AC–DC converter. Furthermore, a single inductor buck–boost DC–DC converter is simulated to understand the degradation behavior of electrolytic capacitor. It has been found that the temperature of an output stage capacitor increases significantly during operation time. The capacitor's performance without taking temperature change into account results in an overestimated driver lifetime by more than 38% for the selected case study. [ABSTRACT FROM AUTHOR]

Power Electronic Building Block-based power converters are the ideal solution for interfacing different portions of the network in power distribution systems. Flexibility is the feature that makes them suitable as power routing devices, load drives, active filters, and interfaces for energy storage devices. Standardization is the key to actual realization. The flexibility and standardization of the hardware components must be paired with the standardization of the control architecture to achieve full plug-and-play capabilities. The recent work of IEEE standardization bodies is fully supporting this direction. This paper shows how these concepts can find immediate application, with significant benefit of robustness of power systems. In this paper, the authors focus on the higher layer of the architecture that is not covered by the standards. This paper provides a proposal for the list of functionalities that could exploit the characteristics of the standardized hardware. Most of the examples presented herein are derived from experience in the area of ship power systems and could be applied immediately to terrestrial systems. [ABSTRACT FROM PUBLISHER]

The increased penetration of nonlinear loads and power-electronics-based distributed generation (DG) systems may introduce power quality issues to the distribution power system. However, if controlled and regulated properly, the DG–grid interfacing converters are able to improve the distribution system efficiency and power quality. This paper focuses on the distribution system harmonic control through the DG–grid interfacing converters. Two alternative DG systems, namely, current-controlled DG and voltage-controlled DG, are considered. While most of the previous works on harmonic compensation are based on the current-controlled method, a novel harmonic control scheme using a voltage-controlled method is developed in this paper. The voltage-controlled method is more flexible and has similar compensation performance compared to the conventional current-controlled method. In addition, by avoiding the implementation of a harmonic current tracking loop, the proposed voltage-based method can be seamlessly incorporated into a voltage-controlled DG unit, which is important to provide direct voltage and frequency support in a microgrid. Moreover, the possible harmonic circulating current among multiple DG systems is also investigated in this paper. Simulations and experimental results from a three-phase 5-kVA laboratory DG prototype are provided to validate the discussion. [ABSTRACT FROM AUTHOR]

This paper presents a new synchronous-reference-frame (SRF)-based control method to compensate power-quality (PQ) problems through a three-phase four-wire unified PQ conditioner (UPQC) under unbalanced and distorted load conditions. The proposed UPQC system can improve the power quality at the point of common coupling on power distribution systems under unbalanced and distorted load conditions. The simulation results based on Matlab/Simulink are discussed in detail to support the SRF-based control method presented in this paper. The proposed approach is also validated through experimental study with the UPQC hardware prototype. [ABSTRACT FROM AUTHOR]

Industrial distributed control continues the move toward networks at all levels. At lower levels, control networks provide flexibility, reliability, and low cost, although perhaps the simplest but most important advantage is the reduced volume of wiring. Powered fieldbuses offer particular notable benefits in system wiring simplification. Nevertheless, very few papers are dealing with the potentials and limitations in power distribution through the bus cable. Only a few of the existent fieldbus standards consider this possibility but often simply as an option without enough technical specifications. In fact, nobody talks about it, but power distribution through the bus and conducted noise disturbances are strongly related. This paper points out and analyzes these limitations and proposes a new low-cost fieldbus physical layer that enlarges power distribution capability of the bus and improves system robustness. We show an industrial application on water desalination plants and the very good results obtained owing to the fieldbus. Finally, we present electromagnetic compatibility test results that verify improvements against electrical fast transients on the sensor/actuator connection side as disturbances usually encountered in harsh-environment industrial applications. [ABSTRACT FROM AUTHOR]

The local DC power distribution system of More Electric Aircraft is one of the cores of the electric power transmission. Because the mechanical source (turbine engine) is unidirectional, the system is not totally reversible. Some storage and dissipation systems are necessary to store or/and dissipate the returned energy to maintain the dc bus voltage. Different power-management strategies are proposed and compared. The development of experimental test benches is necessary to validate these strategies. In this paper, we present a 3-kW test bench, emulating a unidirectional source that supplies a bidirectional load with the help of a hybrid system using supercapacitors and a dissipation system. The experimental validation of the power-management strategies is presented in this paper, too. [ABSTRACT FROM PUBLISHER]

Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control. [ABSTRACT FROM AUTHOR]

A simple ac-dc pulsewidth-modulation (PWM) converter that can perform isolated dc-dc conversion while shaping the input current to improve power factor is proposed in this paper. The converter is almost the same as a standard PWM full-bridge converter with a diode rectifier/LC low-pass filter input except for some slight modifications. The converter topology is, therefore, very simple, as is the method of control used to achieve both power-factor correction and dc-dc conversion. In the paper, the operation of the converter is explained and analyzed, and the converter's steady-state characteristics are discussed. A design procedure for the selection of components is presented, and then demonstrated with an example. The feasibility of the converter, and its ability to meet EN61000-3-2 Class P standards for electrical equipment is shown with results obtained from an experimental prototype. [ABSTRACT FROM AUTHOR]

Dynamic wireless power transfer (WPT) is a practical method to solve electric vehicle (EV) range anxiety and reduce the cost of on-board batteries. This paper presents a novel dynamic WPT system that combines the advantages of pads array and segmental long coils coupler. In the proposed circuit, several paralleled LCC reactive power compensation networks (RPCNs) in the primary side were excited by a sole inverter and the power distribution was realized automatically; an auxiliary LCC network was proposed to regulate current in the primary coil to minimize the electromagnetic interference (EMI) and reduce the system’s power loss. A scaled-down prototype of a dynamic wireless charging system was developed to prove the validity of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper deals with the combined least mean square–least mean fourth (LMS–LMF)-based control algorithm for distribution static compensator (DSTATCOM) in three-phase distribution system to alleviate the power quality problems caused by solid-state equipments and devices. The combined LMS–LMF-based algorithm is simulated using Sim Power System (SPS) toolbox in MATLAB for obtaining the corresponding active and reactive weights and supply reference currents. The proposed control algorithm has advantages of both LMF- and LMS-based control algorithms, which helps in fast and accurate response with a robust design. Depending on the value of error signal obtained in any of the phases either of LMS- or LMF-based control is used to minimize the error. The developed combined LMS–LMF-based algorithm is implemented on the prototype of the proposed system and responses obtained are found satisfactory with harmonic spectra of the supply currents meeting the power quality standards. [ABSTRACT FROM PUBLISHER]

Differences in the thermal and electrical switching time constants between parallel-connected devices cause imbalances in the power and temperature distribution, thereby reducing module robustness. In this paper, the impact of electrothermal variations (gate and thermal resistance) between parallel-connected devices on module robustness is investigated for 900-V-CoolMOS and 1.2-kV-SiC MOSFETs under clamped inductive switching (CIS) and unclamped inductive switching (UIS). Under CIS, the difference in the steady-state junction temperature (\bm \Delta \bm T\bm {J}) and switching energy (\bm \Delta \bm E{\bf SW}) between the parallel-connected devices for a given difference in the gate and thermal resistance (\bm \Delta \bm R\bm {G} and \bm \Delta \bm R{\bf TH}) is used as the metric for determining robustness to electrothermal variations, i.e., how well the devices maintain uniform temperature inspite of switching with different rates and thermal resistances. Under UIS conditions, the change in the maximum avalanche current/energy prior to device failure as a function of the \bm \Delta \bm T\bm {J} and \bm \Delta \bm R\bm {G} between the parallel-connected devices is used as the metric. Under both CIS and UIS, SiC devices show better performance with minimal negative response to electrothermal variations between the parallel-connected devices. Finite-element models have also been performed showing the dynamics of BJT latch-up during UIS for different technologies. [ABSTRACT FROM AUTHOR]

Local secondary control has been successfully used to regulate the frequency of inverter-based islanded microgrids without using communications. In this scenario, noticeable steady-state deviations have been observed in active power sharing caused by the inherent clock drift of the digital processors that implement the local control of inverters. This paper presents a control scheme that performs frequency regulation and improves the active power sharing under high-load conditions, thus alleviating the impact of clock drifts in this situation. The study introduces a theoretical analysis that quantifies the steady-state deviations in active power sharing. It also includes a design procedure for the control parameters based on static and dynamic specifications. Experimental tests validate the expected features of the proposed control. The experimental setup is based on a laboratory microgrid equipped with three independent digital signal processors with different clock drifts. [ABSTRACT FROM AUTHOR]

In this paper, a decentralized switched current control is presented for dc microgrids. The dc microgrid is modeled considering dc–dc converters as controlled current sources instead of traditional voltage sources in droop control schemes. The proposed current control consists of switching between two current reference signals while keeping the voltage level at the loads and with proper current distribution. It is shown that the closed-loop system is stable through passivity analysis. Experimental tests are performed to illustrate the effectiveness of the proposed control strategy using a laboratory microgrid. [ABSTRACT FROM AUTHOR]

The extensive use of grid-connected power electronics converters in the most different conditions, e.g., grid voltage quality, power level and grid codes, requires a robust synchronization method in order to properly feed other converter controllers with reliable and exact information, namely the phase-angle and the magnitude of the grid voltage. The grid phase-angle is a vital variable used in almost any single- or three-phase converter. The paper proposes a synchronizer based on the Least Squares approach: using the sampled grid voltages to fit a straight line corresponding to the grid phase-angle estimation. An extensive set of simulation results, including comparative results with three other methods, covering steady state and transient conditions, is provided and demonstrates the feasibility of the proposed method. Also, a set of experimental results, obtained with a field programmable gate array platform, complements the validation of the synchronizer and its very good performance in all conditions. [ABSTRACT FROM PUBLISHER]

There is increasing interest in the evaluation of the capability of power-electronic-interfaced distributed generators (DGs) connected to weak medium-voltage (MV) feeders, to provide ancillary services. Classic simulations using simplified DG models have their limitations and may prove insufficient due to the complexity of adequate modeling of power electronic interfaces. Moreover, conventional testing does not allow the investigation of the real generator with the distribution system interactions. Therefore, a scaled-down physical DG (i.e., inverter and dc source) with exactly the same functionalities can be used to evaluate the network integration of the actual DG, by means of power hardware-in-the-loop (PHIL) testing. In this paper, suitable scaling of the power rating and voltage level of the hardware is performed, and an interfacing approach is proposed that achieves stability of simulations without compromising accuracy. The PHIL tests successfully demonstrate potential problems in the coordination of the on-load tap changer controlling the MV feeder with the voltage controller of the DG, such as recurring tap changes, increased reactive power flows, and opposing actions. Moreover, recurring oscillations of the voltage controller of the hardware model are observed at certain system configurations. These inverter control instabilities, which are not visible in purely digital simulations, demonstrate the added value of employing PHIL testing for current and future power system analysis and testing. [ABSTRACT FROM PUBLISHER]

A microgrid is a promising approach to provide clean, renewable, and reliable electricity by integrating various distributed generations and energy storage systems into power systems. However, highly intermittent renewable generations and various load demands pose new challenges to the optimal resource management in a microgrid. This paper proposes a fully distributed control strategy based on the consensus algorithm for the optimal resource management in an islanded microgrid. The proposed strategy is implemented through a multiagent system framework, which only requires information exchange among neighboring agents through a local network. The objective is achieved through a two-level control strategy. The upper control level is a consensus-based optimization algorithm that discovers the reference of optimal power generation or demand while maintaining the supply–demand balance. The lower control level is responsible for reference tracking of the associated component. Simulation results in the IEEE 14- and 162-bus systems are presented to demonstrate the effectiveness of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

In this paper, a distributed convex optimization framework is developed for energy trading between islanded microgrids. More specifically, the problem consists of several islanded microgrids that exchange energy flows by means of an arbitrary topology. Due to scalability issues and in order to safeguard local information on cost functions, a subgradient-based cost minimization algorithm that converges to the optimal solution in a practical number of iterations and with limited communication overhead is proposed. Furthermore, this approach allows for a very intuitive economics interpretation that explains the algorithm iterations in terms of a “supply–demand model” and “market clearing.” Numerical results are given in terms of the convergence rate of the algorithm and the attained costs for different network topologies. [ABSTRACT FROM PUBLISHER]

Distributed networked control systems (D-NCSs) are more vulnerable to malicious attacks with the adoption of distributed control strategies. The misbehaving agents in the D-NCS can disrupt the distributed control algorithms and gradually compromise the entire system. In this paper, a multirobot system using the linear consensus algorithm for formation control is studied where parts of the robots are compromised. A reputation-based secure distributed control methodology with built-in defense is proposed to achieve accurate consensus computation in the presence of misbehaving robots. It embeds four phases (i.e., detection, mitigation, identification, and update) into the distributed control process. The effectiveness of the proposed method is illustrated through simulation analysis and experimental results. [ABSTRACT FROM PUBLISHER]

Near-future green and intelligent buildings will likely have multiple and modularized distributed energy resource devices incorporated into their power distributed networks, e.g., modularized uninterruptible power supply (MUPS), to provide energy storage or modularized solar photovoltaic systems to provide renewable energy. However, the issue of unwanted active power circulation among parallel MUPS modules may cause dc bus overvoltage problems under no-load condition, leading to protective system activation and affecting normal system operation. Causes of the overvoltage are first investigated with detailed analysis of multiple parallel MUPS modules in this paper. The investigation is started with two parallel modules and is then extended to multiple modules. A novel method based on shifting carrier wave frequency is proposed to suppress the dc bus overvoltage. Experimental results show that the proposed solution is effective without any negative impact on the normal operation of a MUPS network. [ABSTRACT FROM PUBLISHER]

The electrical frequency in high-speed machines leads to more pronounced parasitic effects such as skin and proximity effects. In low-voltage machines, a low turn count is needed, requiring individual strands to be connected in parallel and further enhancing these adverse effects. This results in an uneven distribution of the current across the strands and circulating currents. This paper presents a simple yet flexible method to estimate this distribution, based on finite-element simulations and basic circuit equations. The effects of strand displacements or twisting can be accounted for in the actual machine geometry using a 3-D finite-element method, without requiring excessive computer memory or time. Experiments are performed to confirm the modeling method. Straight and twisted windings are compared, clearly showing the effectiveness of twisting the strands. [ABSTRACT FROM AUTHOR]

Voltage flicker is one of many serious power quality disturbances, which would deteriorate the stability and operation efficiency of a power system. Effective evaluation of flicker severity plays an important role in the monitoring and control of developing advanced metering infrastructure. Since the evaluation process for voltage flicker is complicated, some inaccurate intermediate results may give rise to the propagation of estimation errors. Therefore, an accurate solution procedure for the calculation of voltage flicker components is proposed in this paper. With the extraction technique for envelope signal and high-frequency resolution mechanism for flicker spectral analysis, the superior performance to achieve the instantaneous flicker severity evaluation can be obtained. [ABSTRACT FROM PUBLISHER]

The inverter control plays a critical role in microgrid (MG) hierarchical control structure. In this paper, a dominant dynamic elimination control is studied for the voltage-controlled MG inverter. A compact control structure is designed to include separated static state feedback and feedforward terms. Benefitting from the designed control structure, the dominant dynamic can be canceled by the static feedforward control via the fundamental zero-pole cancelation principle. Thanks to the cancelation of the dominant dynamic, the load disturbance-rejection performance is improved, and the approximate unity gain from the reference to output is also achieved from the perspective of the application control layer, thereby the performance of power control for the upper application is improved. Furthermore, the strong robustness to parameter variations and low total harmonic distortion are also achieved. Comparative simulations and experiments are adopted to verify the effectiveness and superiority of the designed approach. [ABSTRACT FROM PUBLISHER]

This paper investigates the optimal resource management in a microgrid under various operating conditions. A two-level optimization system is proposed for the distributed optimal resource management based on a multi-agent system framework. The proposed strategy generates a reference of the optimal power output at the top level through local communication. This strategy only requires the information among neighboring participants without a central control coordination, and simultaneously accomplishes resource optimization in a finite time while maintaining the supply–demand balance. The bottom-level control is responsible for the reference tracking of each corresponding participant in a microgrid. The convergent rate of the proposed algorithm is compared with other consensus-based algorithms through simulation studies. Simulation results in the IEEE 14-bus system and an actual islanded system are also presented to demonstrate the overall effectiveness of the proposed strategy. [ABSTRACT FROM PUBLISHER]

The recycled batteries can be assumed for the cost-effective grid energy storage (ES) applications, where the state of health (SOH) of recycled batteries are hard to make equal when reassembling them in one ES system. Therefore, when implementing the traditional state-of-charge balancing control methods, the batteries integrated into the same ES system will demonstrate the SOH deviation characteristics during the long-term operation due to the different degradation they suffered, which will reduce the mean time to repair, increase the maintenance duty, and shorten the life time of the ES system. Alternatively, this paper proposes an SOH balancing control method for the modular multilevel-converter-based battery energy storage system (MMC BESS) by fully using the unique modular configuration. The relationship among SOH, depth of discharge, and life cycles is analyzed in the theory, which builds the criteria for power distribution among battery packs in the MMC BESS. In addition, instead of estimating the specific SOH value, a relative SOH evaluation method is presented for easier practical implementation. And then, multiple control loops are designed for achieving the expected operational performance. MATLAB simulation and experimental results are presented to verify the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper presents a novel power distribution system (PDS) algorithm to be employed in a hybrid energy storage system (HESS). PDS is responsible for sharing the demand power between energy storage modules, which are battery and ultracapacitor (UC) in this study. The challenge in designing PDS is in assigning the power-share between these modules. A state of available power technique is proposed based on the prediction of the power limitations for a predefined time frame in the future. Another PDS based on the UC state of charge is developed. Various design variables are defined that affect the performance of the PDS. The genetic algorithm optimization technique is employed to determine the design variables. The proposed PDS techniques along with an energy storage system (ESS) consisting of a single battery and a basic PDS system is studied on a 12-kW electric motorcycle during the standard FTP and the New York City Cycle (NYCC) driving cycles. Battery lifetime, vehicle range, and regenerative braking energy recovery functions for the proposed methods compared with the ESS are improved by 2.6 times, 25%, and 29%, respectively. The results suggest that employing the proposed novel PDSs improves the performance of the HESS significantly. [ABSTRACT FROM PUBLISHER]

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid voltage and current control method to improve the performance of interfacing converters in distributed generation (DG) units. In general, current-controlled methods have been widely adopted in grid-connected converters nowadays. Nevertheless, in an islanded system, the voltage control of DG units is desired to provide direct voltage support to the loads. Due to the absence of closed-loop line current controller, the voltage control scheme can hardly regulate the DG unit's line current harmonics. Furthermore, if not addressed properly, the transfer between the grid-connected operation and autonomous islanding operation will introduce nontrivial transient currents. To overcome the drawbacks of voltage- and current-controlled DG units, this paper develops a hybrid voltage and current control method (HCM). The proposed method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents. With the HCM, local harmonic loads of the DG unit can even be compensated without using harmonic current extraction. In addition, the HCM guarantees smooth transition during the grid-connected/islanding operation mode transfer. Simulated and experimental results are provided to verify the feasibility of the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel control design for the unified power quality conditioner (UPQC). This design, enabled by a control framework that employs the output regulation (OR) theory, is also made up of an exogenous Kalman filter used to extract the state components of the distorted supply voltage and load current, and a plant Kalman filter as a state observer. In addition, the same framework integrates the major functions of the UPQC with ease to unify the treatments of several power quality problems including system harmonics in the supply voltage and load current, sags/swells in the supply voltage, variations in the load demands, and poor power factor at the supply side. A linear quadratic regulator-based self-charging circuit is also incorporated into the control design so that the UPQC operates without relying on an external dc source. Simulation and experimental studies on a single-phase power distribution system are used to verify the performance and real-time implementation of this control design with the UPQC. [ABSTRACT FROM PUBLISHER]

Smart microgrids offer a new application domain for power electronics. In fact, every distributed energy resource includes an electronic power processor (EPP) to control the power exchange with the grid. If such distributed EPPs perform cooperatively, all the available energy sources and energy storage units can be fully exploited, resulting in reduced power consumption from the utility, high power quality, and increased hosting capability by the utility. This paper shows that, even in low-voltage meshed microgrids, where the electrical distribution pattern is complex and sources and loads may vary during daytime, such cooperative operation can be achieved by a proper selection of the local control algorithms and by allowing narrow-band communication capability among neighbor EPPs. In particular, this paper describes a token ring control approach which allows full exploitation of the microgrid capabilities with marginal investment in the information and communication technology infrastructure. [ABSTRACT FROM PUBLISHER]

Universal, intelligent, and multifunctional devices controlling power distribution and measurement will become the enabling technology of the Smart Grid ICT. In this paper, we report on a novel automation architecture which supports distributed multiagent intelligence, interoperability, and configurability and enables efficient simulation of distributed automation systems. The solution is based on the combination of IEC 61850 object-based modeling and interoperable communication with IEC 61499 function block executable specification. Using the developed simulation environment, we demonstrate the possibility of multiagent control to achieve self-healing grid through collaborative fault location and power restoration. [ABSTRACT FROM PUBLISHER]

In order to properly suppress the harmonic current in a power system, the harmonic similarity metric is developed in this paper and used to establish an efficient strategy for harmonic filter placement. To validate the strategy, an industrial distribution system is analyzed under two harmonic current injection scenarios. It is demonstrated that the proposed strategy has a robust ability to successfully determine the most efficient and effective location for placing a harmonic filter bank based upon the desired objectives. The two harmonic current injection scenarios serve to validate the proposed strategy regardless of the power distribution level at which harmonic current is injected. [ABSTRACT FROM PUBLISHER]

The progress in the field of wireless power transfer in the last few years is remarkable. With recent research, transferring power across large air gaps has been achieved. Both small and large electric equipment have been proposed, e.g., wireless power transfer for small equipment (mobile phones and laptops) and for large equipment (electric vehicles). Furthermore, replacing every cord with wireless power transfer is proposed. The coupled mode theory was proposed in 2006 and proven in 2007. Magnetic and electric resonant couplings allow power to traverse large air gaps with high efficiency. This technology is closely related to electromagnetic induction and has been applied to antennas and resonators used for filters in communication technology. We have studied these phenomena and technologies using equivalent circuits, which is a more familiar format for electrical engineers than the coupled mode theory. In this paper, we analyzed the relationship between maximum efficiency air gap using equivalent circuits and the Neumann formula and proposed equations for the conditions required to achieve maximum efficiency for a given air gap. The results of these equations match well with the results of electromagnetic field analysis and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a generic and comprehensive distribution optimal power flow (DOPF) model that can be used by local distribution companies (LDCs) to integrate their distribution system feeders into a Smart Grid. The proposed three-phase DOPF framework incorporates detailed modeling of distribution system components and considers various operating objectives. Phase specific and voltage dependent modeling of customer loads in the three-phase DOPF model allows LDC operators to determine realistic operating strategies that can improve the overall feeder efficiency. The proposed distribution system operation objective is based on the minimization of the energy drawn from the substation while seeking to minimize the number of switching operations of load tap changers and capacitors. A novel method for solving the three-phase DOPF model by transforming the mixed-integer nonlinear programming problem to a nonlinear programming problem is proposed which reduces the computational burden and facilitates its practical implementation and application. Two practical case studies, including a real distribution feeder test case, are presented to demonstrate the features of the proposed methodology. The results illustrate the benefits of the proposed DOPF in terms of reducing energy losses while limiting the number of switching operations. [ABSTRACT FROM AUTHOR]

Classical wind energy conversion systems are usually passive generators. The generated power does not depend on the grid requirement but entirely on the fluctuant wind condition. A dc-coupled wind/hydrogen/supercapacitor hybrid power system is studied in this paper. The purpose of the control system is to coordinate these different sources, particularly their power exchange, in order to make controllable the generated power. As a result, an active wind generator can be built to provide some ancillary services to the grid. The control system should be adapted to integrate the power management strategies. Two power management strategies are presented and compared experimentally. We found that the “source-following” strategy has better performances on the grid power regulation than the “grid-following” strategy. [ABSTRACT FROM AUTHOR]

This paper presents a solution to the control of a unified power quality (PQ) conditioner (UPQC) for PQ improvement in power distribution systems. The problem formulation allows not only harmonic compensation but also voltage sags/swells, load demand changes, and power factor correction to be tackled in a unified framework. The proposed controller combines the multivariable regulator theory with H∞ loop shaping, so that zero steady-state error, robustness to modeling uncertainties, and insensitivity to supply frequency variations can be accomplished simultaneously, thus providing a complete theoretical solution to all the aforementioned PQ problems. The effectiveness of the proposed controller is, in practice, verified by experimental studies on a single-phase power distribution system. [ABSTRACT FROM AUTHOR]