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In a battery energy storage system (BESS) based on the cascaded H-bridge (CHB) converter or modular multilevel converter (MMC), the active power distribution among the submodules (SMs) can be highly unbalanced, especially when batteries with different power ratings are used. Meanwhile, there are certain limits for the unbalanced power distribution among the SMs. It is a challenge to determine whether the active power distribution is viable for cascaded multilevel converters with unequal capacitor voltages because the complexity grows exponentially as the number of SMs increases. This article proposes a generalized analytic solution to this problem, which reduces the complexity significantly and is readily applicable to converters with large number of SMs. The validity of this method is proved theoretically and verified with simulation and experimental results on both the MMC and CHB converter. [ABSTRACT FROM AUTHOR]

An inductive power transfer system is able to charge multiple receivers (RXs) through a single transmitter. In order to develop suitable control methods, this article explores and compares the influence of driving current and loading resistance on the efficiency and power distribution. It starts from a simple system with equal coupling and then extends the discussion to a general one. With proper simplification, an optimization problem is defined to derive several important factors, including the optimal driving current, optimal loading resistance, and the corresponding optimized efficiency under various application constraints. In the final experiments, the dynamic tuning of driving current is able to maximize the system efficiency to 92.1% for a general three-RX system. In another customized system with equal coupling, the maximum error between the achieved efficiency and the real maximum efficiency is 0.4% through the calculation-based current control. [ABSTRACT FROM AUTHOR]

In the operation of cascaded H-bridge converters and modular multilevel converters with energy storage or renewable power resources, unbalanced active power distribution among the submodules (SMs) is unavoidable. Depending on the operating conditions, there are certain upper and lower limits on the active power that can be processed by a single SM or a subset of SMs. The control system needs to restrict the SM power references to these limits, hence, accurate knowledge of the power limits is important. In existing methods to derive the power limits, the SM capacitor voltages are assumed to have negligible ripples, whereas in practice the ripples can be considerable. This article analyzes the effect of capacitor voltage ripples on the SM active power control limits and highlights the importance of considering the ripple effect. A methodology is proposed to accurately incorporate capacitor voltage ripples in the derivation of SM active power control limits. Simulation and experimental results are provided to evaluate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

A multitransmitter (multi-TX) inductive power transfer system would not only offer better spatial freedom but also improve the overall output capability. Under heavy-load condition, it is desirable to fully utilize the output power capability, and the overall input power needs to be balanced among the multiple TXs. This article proposes a simple and low-cost current sharing method to balance the input power. The current distribution is analytically studied for an example two-TX system, and the sharing path is proposed to balance the power under coupling variation and coil inductance mismatch. It also explores the influence of sharing path on the efficiency and zero-phase operation. Besides, the proposed method is valid for other compensations and can be extended for N-TX (N $>$ 2) systems. Finally, a two-TX system is implemented to verify the sharing effect. The current imbalance factor is effectively reduced from 37% to 2.7% under the worst coupling cases. [ABSTRACT FROM AUTHOR]

A dual-dc output three-phase three-level ac–dc converter is proposed for low-frequency pulsed power decoupling applications. One of the dc output is connected to the dc pulsed load, whereas the other one is used as power decoupling port and connected to the decoupling capacitor. The voltage of the power decoupling dc port can vary in a wide range to reduce the value and volume of the power decoupling capacitor. A buck/boost converter is employed to interface the power decoupling port with the dc pulsed load. A modified space vector pulsewidth modulation strategy is proposed for the ac–dc converter, based on which independent voltage and power regulation of the two dc outputs is achieved. The steady-state power is directly fed to the dc load with single power conversion stage, and the low frequency pulse power is fed to the power decoupling port. As a result, high-power quality and efficient power decoupling with reduced power conversion stages are achieved. Operation principles, modulation, and control strategies of the ac–dc converter are analyzed in detail. A prototype is built and tested to verify the effectiveness and feasibility of the proposed ac–dc converter for pulsed load. [ABSTRACT FROM AUTHOR]

Short-term household electricity load forecasting is important for utility companies to ensure reliable power supplies. Traditional methods for load forecasting relied on historical records from one single data source and have limitations with insufficient or missing data. Recently, an emerging family of machine learning algorithms, multitask learning (MTL), has been developed and has the potential for load forecasting. By MTL, the electricity consumption data from multiple communities can be fused to improve forecasting accuracy. However, appropriate modeling of the relatedness to enable the between-community knowledge transfer remains a challenge. This paper proposes an improved MTL algorithm for a Bayesian spatiotemporal Gaussian process model (BSGP) to characterize the relatedness among the different residential communities. It hypothesizes on the similar impacts of environmental and traffic conditions on electricity consumption in improving short-term load forecasting. Furthermore, this paper proposes a low-ranked dirty model along with an iterative algorithm to improve the learning of model parameters under an MTL framework. This paper uses a real-world case study from two residential communities in Tallahassee, Fl, USA, to demonstrate the method effectiveness. The proposed method significantly outperforms state-of-the-art forecasting methods and effectively captures the relatedness to provide between-community knowledge transfer compared with other MTL methods. [ABSTRACT FROM AUTHOR]

This article proposes a modular hybrid-full-bridge dc transformer (MHDCT) with full-process matching switching strategy MHDCT for MVdc power distribution application. The proposed MHDCT merges the advantages of DCTs based on dual-active-bridge and modular multilevel converter, it not only has good reliability, but also has good modularity and flexibility. Especially, full-process matching switching strategy has good voltage regulation ability to ensure the voltage match of high-frequency-link under various states, then circulating current can be decreased and efficiency can be improved. The universal operation and modulation, voltage, current, power, and switching characterizations of MHDCT are analyzed and the control strategy is proposed in this article. Finally, an MHDCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution. The MHDCT will be a practical scheme for MVdc distribution application. [ABSTRACT FROM AUTHOR]

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 cascaded H-bridge (CHB) converter has become a promising candidate topology for utility-scale photovoltaic systems thanks to merits like modular structure, distributed maximum power point tracking (MPPT), and direct distribution grid access without medium-voltage transformers. However, module mismatches arising from nonideal elements like partial shading and parameter variations pose a technical challenge for such systems. If not dealt with properly, module mismatches can lead to adverse effects like unbalanced dc-link voltages of the modules, distortion of grid current, and reduced power generation. Conventional methods, such as reactive power compensation and level-shifted pulsewidth modulation (LS-PWM) based compensation, can alleviate this issue, but their performances are still limited by the allowable modulation range of power converters. In this paper, a compensation strategy combining reactive power compensation with a novel modulation method is proposed to extend the operating range in terms of module mismatch. Experimental results on a 2.4 kW/208 V single-phase setup are presented and have demonstrated that the proposed method can not only ride through a larger range of module mismatches but also improve solar power utilization and system efficiency owing to reduced switching events, noncompromised MPPT, and less required reactive power. [ABSTRACT FROM AUTHOR]

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 proposes and implements autonomous control of a multiple-receiver wireless charging system. The charging control problem is challenging due to the decentralized nature of the system, possible changing numbers and types of energy storage devices as loads of the receivers, and complexity in wireless power distribution mechanism. The game-theory-based control is developed that fully respects the unique characteristics of the transmitter (i.e., charger) and receivers. The preferences of the individual devices are first quantified using utility functions. Then, the charging control problem is formulated as a generalized Stackelberg game considering the leader–follower relationship between the transmitter and receivers, and the limited total charging power. At each control instant, the generalized Nash equilibrium among the receivers, i.e., charging power distribution here, is reached by searching the Lagrange multiplier while the total charging power from the transmitter is updated in a step-by-step manner. Both simulation and experimental results show that the proposed charging control autonomously manages and updates the power distribution in the cases where the receivers with different energy storage devices quit or join the wireless charging. [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]

This paper gives the fundamental aspects of a power distribution scheme on railway power flow controller (RPFC) for the grid connection compatibility improvement in planning stage railway power system (RPS) via neatly adjusting the value and rotation direction of the primary three-phase current phasors for every given power factor and random load point. This method not only leads RPS to satisfy the relevant grid connection standards, but also can make RPFC have minimum designing capacity and high operating efficiency to decrease its costs in system planning stage. The analytic design method and the experimental results validate the correctness of the conception. The method of using this idea in more challenging serviced RPS will be discussed in another companion volume. [ABSTRACT FROM AUTHOR]

In current source inverter (CSI)-based series-connected configurations, recently proposed for offshore wind energy conversion systems, a number of medium-voltage CSIs are connected in series to form a centralized dc/ac inverter to transfer offshore wind power to the grid. In previous studies, the series-connected CSIs are controlled based on assumptions that all CSIs are ideal and identical and the power is evenly distributed among them. However, in practice, such assumptions are invalid as tolerance exists. This study therefore works on the investigation of power distribution among series-connected CSIs considering the tolerance. First, the possible imbalance of power among CSIs is unveiled, analyzed, and quantitatively defined. Second, a combined control scheme is proposed, based on which both conventional control objectives, which are dc-link current control and power factor control, and an equal power distribution among CSIs are ensured simultaneously. Finally, simulations and lab-scaled experiments are provided. [ABSTRACT FROM AUTHOR]

A power regulation algorithm was designed to address the load requirements of a power packet dispatching system of interest. The switch controller, to which the regulation algorithm is applied, was constructed and implemented in the prototype of the power packet dispatching system. This algorithm was designed by extending the optimal dynamic quantizer investigated in the context of control with a discrete-valued signal. In the controller, the prediction of the states for the controlled variable in one packet transmission time before is applied to support the term when the controlled load is insulated from the source. This predictive dynamic quantizer can realize the power regulation for multiple loads simultaneously through a common power line. The stability of the system with the predictive dynamic quantizer is verified analytically as a switched system. The performance of the controlled variable is verified with the series of results from both experiments and numerical simulations. From these results, it was possible to verify that simultaneous voltage demands from multiple loads in the power packet dispatching system are satisfied with the regulation method. [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 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]

Availability of more number of levels for the same number of switching devices has made asymmetrical topologies superior over symmetrical structures. While the 16 : 4 : 1 configuration is reported as an optimal asymmetry, a detailed performance is not available in literature. This paper presents the performance and control of the 16 : 4 : 1 asymmetrical topology. A new analytical approach is introduced to find the complete information of the available combination of space vectors for any asymmetric ratio. A limit chart is introduced, which represents the number of ways to generate a particular space vector. Asymmetrical hexagonal decomposition technique is used to select the switching devices from the high-, medium-, and low-voltage cells to realize a space vector. The converter is simulated in MATLAB/Simulink. Supporting results from a laboratory prototype have confirmed the usefulness of the 16:4:1 asymmetrical configuration. [ABSTRACT FROM PUBLISHER]

A single-objective predictive control method that deals with four main control objectives applied to a multivariable single-phase three-level neutral-point-clamped converter operating as an active power filter is proposed in this paper. The four control objectives are to self-support the dc-bus voltage under load variations, to compensate the reactive power and the current harmonics, and to balance the dc capacitor voltages by using a predefined combination of the redundant switching states of the converter. The main contribution of the proposed method is that these objectives are accomplished without using weighting factors in the cost function, which eliminates problems such as multiobjective optimization or additional empirical procedures for determination of these factors. As a result, the method is easy to implement and rapidly selects the optimal voltage to improve the dynamic-state performance. Experimental results from a 2-kVA prototype are presented to prove that the method is valid for single-phase compensation. The well-known effect of model parameter errors' issue, which is inherent in predictive control methods, is also tested to confirm that the harmonic distortion in the grid current is below 5% even when the predictive model has a 25% error between actual and theoretically estimated grid impedance values. [ABSTRACT FROM PUBLISHER]

This "Special Section on New Technique Trends for Power Converters in Distributed Power Generation Systems" of the IEEE Transactions on Industrial Electronics (TIE) 35 papers selected among 89 submitted papers. Therefore, this Special Section will be published in two parts. In Part I, all the papers are related to dc/ac grid-tied inverters. [ABSTRACT FROM PUBLISHER]

As the penetration of renewable energy resources proliferate, inverters have been employed as interface in distributed power systems. To achieve expanded power level and system redundancy, parallel connection of inverters has been widely used. This paper derives mathematical models to quantitatively evaluate the reliability of parallel inverters under different topologies and control strategies. A framework to determine the number of inverters in parallel in terms of reliability and cost optimization is proposed. Sensitivity analysis is carried out to identify the impact of parameter variation on system reliability and total cost. At last, power densities of different structures are analyzed for a fair comparison. [ABSTRACT FROM PUBLISHER]

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]

Modeling and simulation are powerful tools to design power distribution systems made up of multiple converters and loads, such as the system of the more-electric aircraft (MEA). However, a system designer usually has no access to detailed data of the power converters, due to confidentiality of manufacturers. Therefore, a black-box modeling approach is necessary. This paper proposes a large-signal black-box modeling technique of three-phase voltage source inverters. The resulting model is oriented to perform system-level analysis and is fully parameterized from the transient response of the converter, which is obtained through simple experimental tests based on low-cost equipment. Moreover, it does not represent the internal data of the converter, thus keeping the confidentiality of the manufacturer. The proposed method has been experimentally validated on a 5-kW actual inverter, which has been applied on the test bench of an MEA power distribution system. [ABSTRACT FROM AUTHOR]

Owing to deregulation, privatization, and competition, estimating financial benefits of electrical power system projects is becoming increasingly important. In other words, it is necessary to assess the project profitability under the light of new developments in the electricity market. In this paper, a detailed methodology for the least cost choice of a distribution transformer is proposed, showing how the higher price of a facility can be traded against its operational cost over its life span. The proposed method involves the incorporation of the discounted cost of transformer losses to their economic evaluation, providing the ability to take into account variable energy cost during the transformer operating lifetime. In addition, the influence of the variability in the energy loss cost is investigated, taking into account a potential policy intended to be adopted by distribution network operators. The method is combined with statistical and probabilistic assessment of electricity price volatility in order to derive its impact on the transformer purchasing policy. [ABSTRACT FROM PUBLISHER]

This paper studies the effectiveness of reactive power compensation using a multilevel, hexagram-converter-based STATic COMpensator (STATCOM) with one-cycle control (OCC) for a wind farm with fixed-speed turbines, and the interaction with the power system network. Comparison is made with several common types of multilevel voltage source converters used for STATCOM applications. A new voltage control method based on OCC principles for hexagram-based STATCOMs is proposed and proven by a wind farm power system simulation showing the improvement of voltage variations caused by wind speed changes. The experimental results from tests of a small-scale hexagram converter prototype have verified the proposed converter and control method. [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]

This paper deals with the problem of reactive power and harmonics in a standard medium-voltage (MV) distribution network. It proposes a simple and inexpensive solution to enhance power quality when a particular connection to the high-voltage transmission network is required. It presents the design of a hybrid active filter topology connected to the MV level of a power distribution system. Its main task is to regulate a 132-ky voltage level. Reconfiguration of the power delivery network imposes new constraints in a distribution substation so that the reactive compensation should be increased. The topology of a shunt hybrid active filter is analyzed. It is built with the series connection of a passive filter and a low-rated active filter. The proposed filter is directly connected to a 13.8-kV level with no need of a step-down transformer. The possibility of different levels of reactive power compensation is implemented. The proposal shows very good performance for different load demands. [ABSTRACT FROM AUTHOR]

The problem of reactive power and harmonics in the medium voltage level of a power distribution system is considered in this paper. Reconfiguration of the power delivery network imposes new constraints in a distribution substation so that the reactive compensation should be increased. The alternative of a shunt hybrid active filter connected to the 13.8-ky level to enhance the power quality is analyzed in this paper. This proposal uses the existing capacitor bank to build a hybrid filter in which the complementary compensation is performed by the active filter. The performance of the hybrid filter is evaluated with extensive simulations considering reactive power, harmonics, and unbalance compensation. It shows very good behavior in steady-state and transient conditions. [ABSTRACT FROM AUTHOR]

In this paper, an active-clamp forward converter with transient current build-up zero-voltage switching (ZVS) technique is proposed. The proposed converter is suitable for the low-voltage and high-current applications. The structure of the proposed converter is the same as that of the conventional active-clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during the very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve the high efficiency and low electromagnetic-interference noise resulting from the soft switching without any additional conduction losses and shows the high power density resulting from the high efficiency and no additional components added. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and a significant improvement in the efficiency for the 100-W (5 V, 20 A) prototype converter. [ABSTRACT FROM AUTHOR]

The voltage waveform on the electric power distribution system is distorted by harmonic-producing loads. Regardless of the terminal voltage waveform with or without harmonics, the conventional current waveform of the pulse width-modulated converter systems connected to the power distribution system is always controlled to be sinusoidal. For harmonic suppression of the voltage and current on the distribution system, the authors propose the distorted current waveform whose harmonic components are in phase with the terminal voltage harmonics. The effectiveness of the proposed current waveform has been verified by experiments. [ABSTRACT FROM AUTHOR]

Presents corrections to the paper, ?Multilevel MVDC Link Strategy of High-Frequency-Link DC Transformer Based on Switched Capacitor for MVDC Power Distribution,? (Wang, Y., et al), IEEE Trans. Ind. Electron. vol. 64, no. 4, pp. 2829?2835, Apr. 2017. [ABSTRACT FROM PUBLISHER]