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Reliability worth analysis is of great importance in the area of distribution network planning and operation. The reliability worth's precision can be affected greatly by the customer interruption cost model used. The choice of the cost models can change system and load point reliability indices. In this study, a cascade correlation neural network is adopted to further develop two cost models comprising a probabilistic distribution model and an average or aggregate model. A contingency-based analytical technique is adopted to conduct the reliability worth analysis. Furthermore, the possible effects of adding distributed generation units into the network are evaluated. The proposed approach has been tested on a radial distribution test network evaluating the reliability worth. The results show that the probabilistic distribution model provides a more realistic model for the reliability analysis. [ABSTRACT FROM PUBLISHER]

This paper investigates the optimal operation and management of micro-grids (MGs) considering the high penetration of different types of renewable energy sources (RESs) and plug-in electric vehicles (PEVs). Optimal operation of MG is a precious and economic strategy for improving the situation of MG from different aspects such as reducing power losses and total costs, improving the reliability and enhancing the voltage level of buses. In order to achieve these goals, a new formulation is proposed to model the stochastic and volatile behaviors of RESs as well as PEVs. Also, the idea of vehicle-2-grid (V2G) is employed to provide a bi-directional power exchange (either charging/discharging) between PEV and the main grid during the parking hours. In order to model the uncertainties of the problem, a new sufficient stochastic optimization framework based on unscented transform (UT) and krill herd algorithm (KH) is proposed too. The feasibility and performance of the proposed method are examined on a typical grid-connected MG considering different types of RESs including Photovoltaics (PVs), Fuel Cell (FC), Micro Turbine (MT) and Wind Turbine (WT). [ABSTRACT FROM AUTHOR]

In this paper, the optimal energy management of MGs (micro grids) including RESs (renewable energy sources), PHEVs (plug-in hybrid electric vehicles) and storage devices is studied by a new stochastic framework that considers the uncertainties in modelling of PHEVs and RESs using the well-known Monte Carlo simulation. In order to see the influence of different charging behaviours of PHEVs in the MG, three different charging patterns including uncontrolled, controlled and smart charging schemes are investigated. To study the optimal operation of the MG including the natural stochastic behaviour of the uncertain parameters, a new robust and powerful SOS (Symbiotic Organisms Search) algorithm is applied too. SOS simulates the interactions observed among natural organisms relying on other organisms to survive. In addition, a new modified version of the SOS algorithm is suggested to increase its total search ability in the local and global searches successfully. The performance of the proposed method is examined on two typical MG test systems with different scheduling time horizons. The results of applying the proposed method on the case studies are compared to other algorithms in different conditions with and without the PHEV charging effects. [ABSTRACT FROM AUTHOR]

This paper reports a frequency-adaptive robust technique for the accurate estimation of the single-phase grid voltage fundamental and harmonic parameters. The technique is based on the discrete Fourier transform and a cascaded delayed signal cancellation strategy. There is no stability issue in the technique, since it does not contain any type of feedback loop. It can also be flexibly configured to estimate the parameters of the fundamental and/or one/multiple harmonic(s) from the grid voltage waveform distorted by various harmonics. Moreover, it does not require evaluation of trigonometric and inverse trigonometric functions for implementing on real-time digital signal processor. However, it needs computationally demanding high-order finite-impulse-response filters. The simulation and real-time experimental results are provided to verify the performance of the proposed technique. [ABSTRACT FROM PUBLISHER]

Introducing distributed generation (DG) into distribution networks can affect the problem of optimal switch placement. A method for solving the problem of optimal placement of sectionalizing switches with a large number of DGs is presented. The primary objective is to minimize the total cost of achieving a certain level of reliability in the presence of DG. The problem is formulated using mixed-integer linear programming to determine the optimal number and location of sectionalizing switches. Allowing DG to operate in an island mode is also considered. The effectiveness of the proposed formulation is examined on a modified reliability test system. The presented results indicate that the proposed formulation can provide a global optimum solution for the problem of sectionalizing switch placement, while reliability, capital investment, and annual operation and maintenance costs are considered. Furthermore, DG can play a key role in providing a reasonable improvement in the reliability indices of the system. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase boost-inverter topology is used to condition a typical low output voltage fuel cell (FC) as a stand-alone power supply. The key benefits of the proposed power supply include ability to deliver both the boosting and inversion functions in a single stage, compactness, and low cost. Additionally, the power supply incorporates a battery storage unit through a bidirectional converter to support the slow dynamics of the FC and simultaneously protect the FC as it acts as a filter for the low-frequency harmonics. The three-phase output voltage of the boost-inverter is voltage-mode controlled and the battery unit is current-mode controlled. Analysis, simulation, and experimental results taken from a 1-kW laboratory prototype three-phase boost-inverter operating at 20 kHz and bidirectional converter with two 12 V-24 Ah lead acid batteries are presented to confirm the operational performance of the proposed power supply. [ABSTRACT FROM AUTHOR]

This letter defines selective harmonic elimination pulse width modulation (SHE-PWM) formulations for single-phase, interleaved converters. Through precalculated solutions, interleaved converters work at the same operating point while eliminating multiple low-order harmonics. It is shown that multiple continuous solutions can be acquired for three-level interleaved waveforms. Extending the method to multiple levels further complicates the problem and reduces both the number and continuity of the solutions. Searching for solutions when the maximum possible number of harmonics, that can be minimized using this PWM method, is reduced confirms that such compromise can provide additional solutions with a minimal effect on the waveform's harmonic distortion. The SHE-PWM considerations are verified with simulations and experimental results. [ABSTRACT FROM AUTHOR]

A dc hybrid power source based on the combination of ultracapacitor and lead-acid battery is considered in this paper. The various control systems for such hybrid power source reported in the technical literature thus far are rather complex. A low complexity control system for such hybrid power source is proposed in this paper. The key feature of the proposed control system is its capability to maintain operation of the hybrid power source within all important operational limits. The proposed control system allows one to allocate the high-frequency current demands to the ultracapacitor and specify the current limits for both the battery and the ultracapacitor. It also maintains operation of the battery within its state of charge limits and the ultracapacitor voltage at a predefined value while charging the ultracapacitor from the battery rather than from the common dc bus. Presented experimental results verify the satisfactory operation of the power source utilizing the proposed control system. [ABSTRACT FROM AUTHOR]

A model predictive control system for a hybrid battery-ultracapacitor power source is proposed and experimentally verified in this paper. The main advantage of the proposed system is that the battery current, the battery state of charge, and the ultracapacitor current and voltage are maintained within predefined limits during the operation. In addition, the controller allocates fast current changes to the ultracapacitor while the battery responds mainly to slow current changes which helps to increase the battery lifetime. The presented experimental results verify operation of the proposed system. [ABSTRACT FROM AUTHOR]

This study presents application of the decoupled recursive‐least‐squares (DRLS) technique for extraction of power system synchronised phasors under fault conditions. The proposed DRLS technique demonstrates robust performance during faults, subsequent operation of circuit breakers and reclosing of a transmission line. The proposed DRLS technique also significantly reduces the computational burden of the conventional RLS technique for implementation on digital signal processors (DSPs). The modification of decomposition of single‐phase into orthogonal components frequency estimation technique for three‐phase power systems is also applied to adapt the DRLS estimation with frequency drifts. The performance of the proposed DRLS technique has been evaluated through presetting selected simulation results in DigSilent Power Factory and MATLAB‐Simulink. DSP implementation of the DRLS technique also confirms considerable computational efficiency improvement when compared with that of the conventional RLS technique. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical basis to restructure the recursive-least-squares (RLS) technique for real-time implementations on digital signal processors (DSPs). The proposed decoupled RLS (DRLS) technique is adapted for real-time estimation of phasors and harmonics. The comparison between the proposed technique and the conventional RLS one shows considerable improvement in terms of reducing the turnaround time on two different off-the-shelf research and development DSP platforms. The DRLS technique also shows better computational efficiency than the adaptive linear combiner (ADALINE) and recursive discrete Fourier transform (RDFT) technique sin direct estimation of amplitude and phase angle when implemented on DSPs. The DRLS technique performance is also superior to that of the ADALINE and RDFT techniques under the presence of noise, subharmonics, and frequency variations. The performance of the proposed technique has been evaluated by simulations using MATLAB-Simulink and through real-time experiments. Selected results presented in this paper confirm the DSP turnaround time improvementand satisfactory performance of the proposed technique. [ABSTRACT FROM PUBLISHER]

This paper presents real-time implementation of a new frequency adaptive least-squares-Kalman (LSK) technique to monitor voltage flicker and fluctuations in power system. The proposed method is based on a two-level mathematical model of a voltage waveform. A simple low computation frequency tracking method is also introduced. The least-squares (LS) optimization algorithm extracts the fundamental frequency component of the voltage and updates its internal model based on the estimated frequency of the voltage waveform. The Kalman filter, which works in combination with the LS algorithm, is developed to predict the instantaneous voltage flicker level. The proposed method is robust and adaptive and is evaluated experimentally through real-time implementation with a widely available digital control board. [ABSTRACT FROM PUBLISHER]

Multimodule converter-based high-voltage dc (HVDC) power transmission incorporates numerous voltage-source converters (VSCs) connected in series/parallel to provide increased voltage/current and, hence, power ratings. When a selective harmonic elimination pulsewidth-modulation (SHE-PWM) technique is employed, the switching losses of the VSC modules are reduced but the voltages of the series-connected dc capacitors are not naturally balanced. In this paper, a voltage-balancing technique is reported. The technique relies on monitoring the voltage of each dc capacitor and when such voltage exceeds its preset band, the realization of the multilevel waveform reallocates the task to another VSC module to ensure that voltage balance between all capacitors is achieved. Three-phase bipolar VSC modules are considered in this paper and each one is modulated by a precalculated multilevel SHE-PWM waveform. The time-domain waveforms and their line-to-line voltage spectra are verified by simulation using PSCAD/EMTDC. The selected results are presented to confirm the viability of the proposed method. [ABSTRACT FROM PUBLISHER]

A five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter is an arrangement of a three-level ANPC converter and a two-level cell. In this paper, a control strategy is proposed to regulate the voltage across the FCs at their respective reference voltage levels by swapping the switching patterns of the switches based on the polarity of the output current, the polarity of the FC voltage, and the polarity of the fundamental line-to-neutral voltage under selective harmonic elimination pulsewidth modulation. The voltage across the FCs and the dc-link capacitors are simultaneously controlled at their reference voltage levels. The proposed control strategy is applied using power system computer aided design/electromagnetic transients including dc on a static synchronous compensator operating under a power-factor-correction mode to verify its performance. Experimental results are also presented for low and high number of angles per quarter period using a low-power laboratory prototype. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a modified gradient search (MGS) technique to estimate harmonics/interharmonics of power system voltages and currents. The proposed technique, which is applied to spectral estimation, consumes very low processing power and needs a few samples per cycle for real-time implementation in smart meters. The computational burden of the proposed technique is lower than the discrete Fourier transform (DFT) and fast Fourier transform (FFT) and can be implemented recursively on digital signal processors (DSPs). In addition, the effects of slow sampling on the accuracy and estimation latency have been investigated. Performance of the proposed method is evaluated by simulations in MATLAB-Simulink and confirmed by experimental results. [Copyright &y& Elsevier]

Control methods based on selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer the lowest possible number of switching transitions. This feature also results in the lowest possible level of converter switching losses. For this reason, they are very attractive techniques for the voltage-source-converter-(VSC) based high-voltage dc (HVDC) power transmission systems. The paper discusses optimized modulation patterns which offer controlled harmonic immunity between the ac and dc side. The application focuses on the conventional two-level converter when its dc-link voltage contains a mix of low-frequency harmonic components. Simulation and experimental results are presented to confirm the validity of the proposed switching patterns. [ABSTRACT FROM AUTHOR]

The ever increasing development and availability of power electronic systems is the underpinning technology that enables large scale integration of wind generation plants with the electricity grid. As the size and power capacity of the wind turbine continues to increase, so is the need to place these significantly large structures at off-shore locations. DC grids and associated power transmission technologies provide opportunities for cost reduction and electricity grid impact minimization as the bulk power is concentrated at single point of entry. As a result, planning, optimization and impact can be studied and carefully controlled minimizing the risk of the investment as well as power system stability issues. This paper discusses the key technologies associated with DC grids for offshore wind farm applications. [ABSTRACT FROM AUTHOR]

Renewable energy sources based on photovoltaic (PV) along with battery-based energy storage necessitate power conditioning to meet load requirements and/or be connected to the electrical grid. The power conditioning is achieved via a dc-dc converter and a dc-ac inverter stages to produce the desired ac source. This is also the case even when the load is of dc type, such as the typical portable electronic devices that require ac adaptors to be powered from the ac mains. The letter presents a hybrid PV-battery-powered dc bus system that eliminates the dc-ac conversion stage, resulting in lower cost and improved overall energy conversion efficiency. It is also shown experimentally that the switching ac adaptors associated with the various commonly used portable electronic devices can be reused with the proposed dc bus system. A novel high-gain hybrid boost-flyback converter is also introduced with several times higher voltage conversion ratio than the conventional boost converter topology. This arrangement results in higher dc bus levels and lower cable conduction losses. Moreover, the voltage stress on the hybrid boost-flyback converter power switch is within half the output voltage. Experimental results taken from a laboratory prototype are presented to confirm the effectiveness of the proposed converter/system. [ABSTRACT FROM AUTHOR]

The ever increasing progress of high-voltage high-power fully controlled semiconductor technology continues to have a significant impact on the development of advanced power electronic apparatus used to support optimized operations and efficient management of electrical grids, which, in many cases, are fully or partially deregulated networks. Developments advance both the HVdc power transmission and the flexible ac transmission system technologies. In this paper, an overview of the recent advances in the area of voltage source converter (VSC) HVdc technology is provided. Selected key multilevel converter topologies are presented. Control and modeling methods are discussed. A list of VSC-based HVdc installations worldwide is included. It is confirmed that the continuous development of power electronics presents cost-effective opportunities for the utilities to exploit, and HVdc remains a key technology. In particular, VSC-HVdc can address not only conventional network issues such as bulk power transmission, asynchronous network interconnections, back-to-back ac system linking, and voltage/stability support to mention a few, but also niche markets such as the integration of large-scale renewable energy sources with the grid and most recently large onshore/offshore wind farms. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a new variation of selective harmonic elimination pulse-width modulation (SHE-PWM) technique suitable for a high-power five-level converter used in constant frequency utility applications. The governing system of equations associated with the elimination of specific harmonics is defined based on an equal number of switching transitions when compared against the single-carrier sinusoidal PWM (SC-SPWM) technique. For this paper, it is assumed that the modulating signal (triangular carrier) of the equivalent SC-SPWM method has twenty per unit frequency. The switching transitions for every quarter period are therefore distributed between the converter levels according to the modulation index of SC-SPWM. It is confirmed that the proposed technique offers significantly higher converter bandwidth and higher dc bus utilization for the same switching transitions. Furthermore, the proposed SHE-PWM offers better harmonic performance compared to its SC-SPWM counterpart. Selected solutions for the switching transitions are presented and verified experimentally in order to confirm the effectiveness of the proposed technique. [Copyright &y& Elsevier]

This paper proposes a generalized formulation for selective harmonic elimination pulse-width modulation (SHE-PWM) control suitable for high-voltage high-power cascaded multilevel voltage source converters (VSC) with both equal and nonequal dc sources used in constant frequency utility applications. This formulation offers more degrees of freedom for specifying the cost function without any physical changes to the converter circuit, as compared to conventional stepped waveform technique, and hence the performance of the converter is greatly enhanced. The paper utilizes the merits of the hybrid real coded genetic algorithm (HRCGA) in finding the optimal solution to the nonlinear equation system with fast and guaranteed convergence. It is confirmed that multiple independent sets of solutions exist. Different operating points for both five- and seven-level converters including single. and three-phase patterns are documented. Selected experimental results are reported to verify and validate the theoretical and simulation findings. [ABSTRACT FROM AUTHOR]

Selective harmonic elimination pulsewidth modulation techniques are some of the control methods used in voltage/current source converters. However, challenges such as the task of finding all the multiple sets of solutions of the switching angles for a given problem may be difficult to deal with. In this paper, a direct minimization of the nonlinear transcendental trigonometric Fourier functions in combination with a random search is discussed. The unipolar (three-level) waveform is used to illustrate the proposed method confirming its ability to find multiple sets of solutions, including a case where 51 angles are sought for single- and three-phase applications. A simple harmonic distortion factor is studied for each set of solutions to assess their performance against the noneliminated harmonics. The results presented both at theoretical and experimental level are in close agreement and confirm the robustness of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an optimal solution for a selective harmonic elimination pulse width modulated (SHE-PWM) technique suitable for a high power inverter used in constant frequency utility applications. The main challenge of solving the associated non-linear equations, which are transcendental in nature and, therefore, have multiple solutions, is the convergence, and therefore, an initial point selected considerably close to the exact solution is required. The paper discusses an efficient hybrid real coded genetic algorithm (HRCGA) that reduces significantly the computational burden, resulting in fast convergence. An objective function describing a measure of the effectiveness of eliminating selected orders of harmonics while controlling the fundamental, namely a weighted total harmonic distortion (WTHD) is derived, and a comparison of different operating points is reported. It is observed that the method was able to find the optimal solution for a modulation index that is higher than unity. The theoretical considerations reported in this paper are verified through simulation and experimentally on a low power laboratory prototype. [Copyright &y& Elsevier]

A five-level symmetrically defined multilevel selective harmonic elimination pulsewidth modulation (MSHE-PWM) strategy is reported in this paper. It is mathematically expressed using Fourier-based equations on a line-to-neutral basis. An equal number of switching transitions when compared against the well-known multicarrier phase-shifted sinusoidal PWM (MPS-SPWM) technique is investigated. For this paper, it is assumed that the four triangular carriers of the MPS-SPWM method have nine per unit frequency resulting in seventeen switching transitions for every quarter period. For the proposed MSHE-PWM method, this allows control of sixteen harmonics and the fundamental. It is confirmed that the proposed MSHE-PWM offers significantly higher converter bandwidth in the standard range of the modulation indices. Moreover, when the bandwidth is reduced to be equal with the one offered with the MPS-PWM, the modulation index can be increased resulting in a higher gain and at a reduced switching frequency overall. Selected solutions for the switching transitions are presented and verified experimentally in order to confirm the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

A high-voltage direct current (HVDC) transmission system based on three-level flying capacitor (FC) multilevel converters with hybrid pulse-width modulation (PWM) is presented in this paper. Selective harmonic elimination PWM (SHE-PWM) is used during normal operating conditions and is switched to phase-shifted sinusoidal PWM (PS-SPWM) during an asymmetric network fault. The generation of the switching patterns under SHE-PWM control for each power device is described taking into account the natural balancing of the FC voltages. A new and simple control method for balancing the FC voltages when using SHE-PWM is proposed which is based on the small change of the firing angle according to the polarity of the load current. The FC voltage ripple under SHIE-PWM control is estimated and compared to that under PS-SPWM. A method to implement the proposed hybrid PWM with capacitor voltage balancing is also provided. Simulation studies on a 300-MW/±150 kV voltage-source converter transmission system are presented to confirm the satisfactory performance of the proposed system under active and reactive power variations and single-phase fault conditions. [ABSTRACT FROM AUTHOR]

A transmission system based on voltage-source three-level flying capacitor (FC) multilevel converters with selective harmonic elimination pulse-width modulation (SHE-PWM) control is presented in this paper. The generation of the switching patterns for each power device is described taking into account the natural balancing of the FC voltages. A new and simple control method for balancing the FC voltages of the FC converter when using SHE-PWM is proposed which is based on the small change of the firing angle according to the load current polarity. Implementation of the SHE-PWM with capacitor voltage balancing is provided. Simulation studies for a 300MW/+- 150kV transmission system are presented to confirm the satisfactory performance of the proposed system. [ABSTRACT FROM AUTHOR]

Selective harmonic elimination pulse width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It was shown recently that symmetry requirements can be relaxed as a constraint. This changes the way the problem is formulated, and different solutions can be found without a compromise. This letter reports solutions to the switching transitions of a five-level SHE-PWM when both the quarter- and half-wave symmetry are abolished. Only the region of high-modulation indices is reported since the low-modulation indices region requires a unipolar waveform to be realized. Selected simulation and experimental results are reported to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Multiple sets of solutions for the selective harmonic elimination pulse-width modulation method for inverter control exist. These sets present an independent solution to the same problem but further investigation reveals that certain sets may offer an improved overall harmonic performance. In this paper, a minimization method is discussed as a way to obtain these multiple sets of switching angles. A simple distortion harmonic factor that takes into account the first two most significant harmonics present in the generated waveform is considered in order to evaluate the performance of each set. The bipolar waveform is thoroughly analyzed and two cases are considered; single-phase patterns which eliminate all odd harmonics and three-phase counterparts which eliminate only the nontriplen odd harmonics from the line-to-neutral pattern but such harmonics are naturally eliminated from the line-to-line waveform. Experimental results support the theoretical considerations reported in the paper. [ABSTRACT FROM AUTHOR]

Discusses the influence of magnetic saturation on maximum torque to current controlled interior permanent magnet (IPM) synchronous motor drives. Basic equations governing the IPM synchronous motor performance; Effect of magnetic saturation on the IPM motor; Derivation of the maximum torque-to-current condition that considers magnetic saturation.

Presents information on a study of the different multilevel topologies and their suitability for single-phase grid connected photovoltaic (PV) systems. Contribution of grid connected PV systems to clean power generation; Leakage currents in transformerless PV systems; Discussion and conclusion.

Discusses the use of computer software in the enhancement of laboratory facilities in an electrical engineering undergraduate program. Advantages of using software tools in engineering education; Mathcad, a commercial software package and how it is used; A typical laboratory experiment enhanced with the assistance of Mathcad; Results achieved.

Discusses general characteristics of various discontinuous switching patterns for pulse-width modulated (PWM) converters and shows that they can yield better performance than their continuous counterparts in some operating regions. Definition of performance in power electronics; Three-phase converter; Reference/modulating signal harmonic analysis.

This study proposes a frequency estimation technique for single‐phase systems in the presence of harmonic pollution. The technique is based on three consecutive samples and has an infinite‐impulse response, thus being a relatively simple one. It is immune to harmonic distortion at both nominal and off‐nominal frequencies. In addition, it offers frequency step estimation with a settling time of one nominal fundamental cycle. Compared to the competing algorithm based on three consecutive samples, the proposed one offers a faster dynamic response and improved estimation at steady state, and is also computationally efficient, thus requiring less hardware and cost for implementation. Simulated and real‐time experimental results confirm that the proposed technique exhibits superior performance when compared to the considered similar algorithm. [ABSTRACT FROM AUTHOR]

High-voltage direct-current (HVDC) based power distribution networks have become an attractive alternative to classical ac distribution networks in more electric aircrafts (MEAs). This paper proposes a power flow management system for an isolated multiport power converter (MPC), which includes a high-frequency transformer, that controls the power flow between three HVDC electric networks in MEAs. The operation of the MPC system and the control stability analysis are presented. The proposed power flow management is tested under normal operation mode and different fault conditions of the power generators. The experimental results demonstrate that the isolated MPC reduces the effect of a power generator failure to the other networks, thus enhancing the fault tolerance of the entire power distribution network of the aircraft. [ABSTRACT FROM AUTHOR]

In the integrated reconfigurable converter (IRC) topology for high-voltage series-connected battery module systems, the converter can be reconfigured into a range of operating modes: “feeding a load” mode, “battery modules balancing” mode, “regenerative” mode, “charging” mode, and “backup” mode. In most battery applications, a battery-balancing system operates while another converter is used as a controllable power interface between the battery system and a load. However, during the conventional IRC operation, the “battery modules balancing” and “feeding a load” modes cannot be operated simultaneously. In this paper, a new balancing scheme is proposed that allows balancing the battery modules while they are powering the load. The proposed balancing strategy is able to distribute different amount of load between the battery modules based on their state of charge (SOC). When the load is disconnected, the battery modules can be still balanced using the conventional “battery modules balancing” mode. A scaled down prototype of the IRC is implemented with three series-connected battery modules. Experimental results are provided to verify the viability of the proposed balancing method. [ABSTRACT FROM AUTHOR]

Filter-based battery–supercapacitor hybrid energy storage systems (HESSs) are popular as a way of extending battery lifetime by diverging the high-frequency power variations to the supercapacitor. However, when a traditional supercapacitor voltage controller (SCVC) is employed in the filter-based HESS, precise sizing of the supercapacitor as well as finding filter parameters for the power allocation are challenging due to nonlinearities. These problems can be circumvented by using a supercapacitor energy controller (SCEC) proposed in this paper. The paper presents a method for selection of the SCEC and filter parameters as well as precise sizing of the supercapacitor for a given application. The proposed method is experimentally verified on a single-phase grid-connected HESS used to smooth the power delivered to the grid at the point of common coupling. It is also shown that the size of the supercapacitor when using the SCEC is significantly lower than the one estimated for the traditional SCVC. [ABSTRACT FROM PUBLISHER]

The boost-inverter-based battery-supercapacitor hybrid energy storage systems (HESSs) are a popular choice for the battery lifetime extension and system power enhancement. Various sliding mode (SM) controllers have been used to control the boost inverter topology in the literature. However, the traditional SM controllers for the boost inverter topology operate with a high and variable switching frequency which increases the power losses and system components design complexity. This can be alleviated by a pulse width modulation (PWM)-based fixed-frequency SM controller proposed in this paper. The SM controller is implemented using variable amplitude PWM carrier signals generated using the output capacitor voltage and inductor current measurements, thus eliminating the requirement of the output capacitor currents measurement. The battery-connected inductor reference currents for the SM controller are generated by a supercapacitor energy controller which is responsible for the HESS power allocation. First, the theoretical aspects of the SM controller, the operation and parameter selection of the supercapacitor energy controller, and the supercapacitor sizing for the HESS are discussed in the paper. Then, the proposed control system is experimentally verified, and it is shown that the HESS is able to satisfy the HESS output power requirements, while allocating the ripple current and the fast power fluctuations to the supercapacitor while maintaining operation of the supercapacitor within predefined voltage limits. The main advantage of the proposed SM controller, as compared with the traditional double-loop control method, is in eliminating possible DC current injection into the grid when the equivalent series resistance values of the boost inductors become unequal due to the tolerances and temperature variations. [ABSTRACT FROM AUTHOR]

The need for continuous temperature monitoring and thermal management is unquestionable as operating temperature is a critical factor affecting many electrical/electronic components and devices, including energy storage such as batteries and supercapacitors (SCs). On the other hand, many applications require the battery or SC cells to be stacked up to meet the required voltage or power level which introduces uneven temperature distribution among the cells. Hence, thermal-model-based temperature monitoring and management has been widely utilized, using state estimation to allow the use of minimum number of temperature sensors. This paper explores the performance of multiple-model-based abnormal overheating detection in a SCs string with minimum number of sensors based on simulation and experimental results. The performance of the estimator/detector system is evaluated for the case of an abnormally overheating cell as well as for different values of the estimator parameters. Preliminary indication from the experimental results shows satisfying performance of the estimator/detector system. [ABSTRACT FROM PUBLISHER]

Model predictive control (MPC) technologies could deliver numerous competitive advantages for power electronics converters and systems with varying impact and benefits. However, assessing the benefits of such advanced and relatively complex control methods at both converter and system level for specific industrial applications is a serious challenge. Moreover, industry must move these technologies from the research and development stage to a maturity level where integrating them into commercial products is relatively low risk and offers economic advantages to customers. First, a generic technology readiness and risk assessment framework is discussed in this paper. Key developments of MPC technologies in power electronics are mapped across their technology readiness levels. Two cases in the area of medium-voltage motor drives are outlined in more detail. Both steady-state and dynamic performance benefits are considered and an attempt to translate them into more tangible economic benefits is reported. [ABSTRACT FROM PUBLISHER]

We consider the task of forecasting the electricity power generated by a solar PhotoVoltaic (PV) system for forecasting horizons from 5 to 60 min ahead, from previous PV power and meteorological data. We present a new method based on advanced machine learning algorithms for variable selection and prediction. The correlation based variable selection identifies a small set of informative variables that are used as inputs for an ensemble of neural networks and support vector regression algorithms to generate the predictions. We develop two types of models: univariate, that use only previous PV power data, and multivariate, that also use previous weather data, and evaluate their performance on Australian PV data for two years. The results show that the univariate models performed similarly to the multivariate models, achieving mean relative error of 4.15–9.34%. Hence, the PV power output for very short-term forecasting horizons of 5–60 min can be predicted accurately by using only previous PV power data, without weather information. The most accurate model was univariate ensemble of neural networks, predicting the PV power output separately for each step of the forecasting horizon. [ABSTRACT FROM AUTHOR]

This paper proposes a multi-agent control strategy to coordinate power sharing between heterogeneous energy storage devices distributed throughout a DC microgrid. Without requiring a central controller, the proposed control strategy extends the benefits offered by hybrid energy storage systems to DC microgrids with batteries and ultracapacitors spatially distributed at different levels of the power distribution hierarchy. The proposed control strategy has the following advantages. 1) The high frequency microgrid load is provided by the ultracapacitors. 2) The low frequency load is provided by batteries used for bulk energy storage during islanded mode, and the main grid during grid connected operation. 3) The ultracapacitor voltages are regulated at a desired reference. 4) State of charge balancing is provided between the batteries. 5) The energy storage systems cooperate based on neighbor-to-neighbor output feedback over a sparse communication network. The only communication requirement is a spanning tree from the ultracapacitor leaders and battery leaders to their respective followers. Simulations are presented demonstrating the performance of the proposed control strategy for a 380 VDC datacenter during grid connected and islanded operation. [ABSTRACT FROM PUBLISHER]

In this paper, a cascaded H-Bridge (CHB)-multilevel converter (MC)-based photovoltaic (PV) system with no voltage or current sensors at the dc-side is proposed. Eliminating the dc-side sensors simplifies the hardware, leading to lower cost and higher reliability of the PV system. A novel scheme estimating the capacitors’ voltages from the ac output voltage of the inverter is developed. The scheme allows replacing all dc-side voltage sensors by a single-voltage sensor at the ac-side of the converter. Furthermore, the dc current sensors, conventionally required for the maximum power point tracking (MPPT), are also eliminated. Instead, the outputs from the capacitors’ voltage control systems are utilized for the MPPT. The effectiveness of the proposed dc-side sensorless system is experimentally demonstrated on a 2-kW single-phase seven-level CHB converter-based PV system. [ABSTRACT FROM PUBLISHER]

A boost DC/AC converter is popular in AC line-integrated energy storage systems (ESSs) based on low-voltage DC sources such as battery, fuel cell, or supercapacitor. The direct DC/AC power conversion in the boost inverter introduces a second-order harmonic ripple current at the DC side of the boost converter, which leads to internal heating of the energy storage devices and degradation of their lifetime. In this paper, a novel current feedback method is proposed to mitigate the second-order harmonic current component at the DC side. The proposed method is able to significantly reduce the second-order harmonic component in the DC-side current of the boost inverter without increasing other harmonic components. Performance of the proposed method is validated on a single-phase grid-connected DC/AC boost inverter-based battery ESS experimental prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a rule-based power management algorithm to enable the dispatch of a utility-scale PV power plant consisting of a hybrid energy storage system, in accordance with the Australian national electricity rules. This algorithm is purposely designed to regulate the instantaneous power of a PV plant with the same level of dispatchability as conventional power plants. Additionally, the proposed algorithm is robust under large forecasting errors (up to 60%) of solar irradiance and it can be easily implemented in practice. Specifically, this algorithm can be executed within seconds even when considering detailed market operation and model nonlinearities. A 30 MW PV plant, including a 7.5 MW/1.25 MWh vanadium redox battery and a 1.5 MW/0.25 MWh suppercapacitors bank, has been modeled using MATLAB/Simulink and PLECS software environment. The simulation results were based on various scenarios and confirmed the effectiveness of the proposed power management algorithm. It has been shown that even in the worst-case scenario of solar forecasting error of 60%, the proposed algorithm still managed to deliver over 94% of the available energy for a given solar irradiance profile of one month. [ABSTRACT FROM AUTHOR]

In series-connected battery systems, typically, separate converters for intramodule balancing bidirectional connection to a load and charging from an external power source are employed. In this paper, an integrated reconfigurable converter for high-voltage series-connected battery storage systems is proposed. The main advantage of the proposed converter is that it can be reconfigured to operate in different operating modes: feeding the load from the battery system, feeding the load from a backup power source, regenerative mode, intramodule balancing mode, and charging mode. Unlike conventional systems, the proposed topology shares the semiconductor devices and an inductor among the different operating modes which makes it compact. The proposed converter exhibits redundant modes which together with a backup mode increase its reliability. Additionally, the proposed topology minimizes stress on the batteries during the charging/discharging cycles. A scaled down experimental prototype of the proposed converter is implemented for a five-module battery system to verify its viability and demonstrate all operating modes. [ABSTRACT FROM PUBLISHER]

This paper proposes and evaluates an active voltage-balancing method for stacked multicell converters (SMCs) using phase-shifted pulse width modulation. The method is easy to implement and can be applied to SMCs with any number of levels. The proposed method balances the voltages of the capacitors by modifying the duty cycle of each switch of the SMC using a proportional controller. The direction of the output current and the crossed effect among the duty cycles of the switches is considered and used to improve capacitor voltage balance. The performance of the proposed voltage-balancing method is verified experimentally for different loads, such as linear and nonlinear loads, and under transient conditions. [ABSTRACT FROM PUBLISHER]

Single conversion stage DC/AC boost inverters are an attractive solution when integrating energy storage devices, such as a battery, fuel cell, or supercapacitor to a single-phase AC grid. However, a second-order harmonic current ripple appears at the DC side of the inverter increasing the internal heat and losses in the energy storage device and degrading its lifetime. In this paper, a rule-based controller is proposed to reduce such harmonic current ripple component. A key feature and advantage of the proposed controller is its ability to reduce the ripple current amplitude in all four inverter output power operating quadrants without being affected by the capacitor tolerances and the internal resistance of the inductors. Presented experimental results validate the performance of the proposed controller on a single-phase grid-connected DC/AC boost inverter-based battery energy storage system. [ABSTRACT FROM PUBLISHER]

In conventional control systems for a static synchronous compensator (STATCOM) based on a cascaded H-bridge multilevel converter, the action of individual voltage controllers that balance capacitor voltages can alter the output of a cluster voltage controller and a current controller due to a coupling effect. In this paper, first, the conditions that eliminate this coupling effect are derived, and then, a control system that enforces the derived decoupling conditions is proposed. It is also shown that an additional advantage of the proposed decoupled control system is that it enables the linearization of a cluster voltage control loop. Experimental studies on a single-phase seven-level STATCOM demonstrate the effectiveness of the proposed decoupled control system in improving the transient performance of the STATCOM. [ABSTRACT FROM AUTHOR]

The thermal model of energy storage elements such as batteries or supercapacitors (SCs) can be used as a platform to predict thermal behavior of the elements, which is essential from the point of view of monitoring and diagnostics. While the lumped thermal model for a single cylindrical SC cell and its extension to multicells string or module have been covered in technical literature, the multicells model has not been experimentally validated. This paper presents experimental validation of the existing lumped thermal model of multicylindrical cells based on an experimental setup of a forced cooled SC string consisting of eight 650 F cells. The determination of the parameters of such a thermal model is discussed and the validated model is used as a basis to design a closed-loop observer for estimating string temperature. Experimental results are presented to confirm its applicability for predicting instantaneous temperatures of each cell in the string. [ABSTRACT FROM AUTHOR]

Accurate prediction of the power generated from solar energy is required for the successful integration of solar energy into the power grid. In this paper we consider forecasting the electricity power produced by a photovoltaic solar system. While previous research has been concerned with point forecasts, we focus on interval forecasts which are more suitable for the highly variable nature of the solar data. We consider a special type of interval forecasts, called 2D-interval forecasts, where the goal is to predict a range of expected values for the solar power output, for a future time interval. We present a new approach called SVR2D which directly computes the 2D-interval forecasts from previous historical solar power and meteorological data, using support vector regression as a prediction algorithm. We evaluate its performance using Australian photovoltaic data for two years sampled every 1, 5 and 30 min, for various interval lengths. The results show that SVR2D provides accurate predictions, outperforming a number of baselines and other methods used for comparison. [ABSTRACT FROM AUTHOR]