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In this paper, single-stage LCL inductive power transfer (IPT) system is proposed in low voltage vehicle charging applications to minimize the system complexity, and its reduced-order modeling and design approach is presented. To deal with the high-order resonant tank, the reduced-order methodology is applied throughout the paper, with which the behavior of resonant tank is investigated under multiple scales. Using the reduced-order time-domain model, the resonant waveform within switching period is accurately described with only one cycle's numerical computation. A novel parameter design principle for realizing ZVS condition and high averaged efficiency within full load range is then proposed and serves as parametric basis. Next, the low-order linear frequency-domain model is deduced using Extended Describing Function (EDF). It is found that six-order LCL-type system behaves as second-order underdamped system within frequency range of interest. Compared to existing models, the proposed reduced-order model features much more simplicity as it provides intuitive understanding into both steady and dynamic characteristic of the converter while facilitating the parameter and controller design. Through above work, the overall design consideration towards a single-stage LCL IPT system is elaborated. Finally, experimental results are given to verify accuracy of the models as well as the effectiveness of designed parameters and controller. [ABSTRACT FROM AUTHOR]

In this paper, we investigate multilayer tubular conductor for multi-MHz Wireless Power Transfer systems high- Q (quality factor) resonators. The conductor layers’ thicknesses and current sharing between them are optimized at 13.56 MHz, showing significant reduction in conductor ac resistance R{AC}. Capacitive ballast is used as a practical method for current sharing between layers and operation of coil near resonance. A two-layer conductor is designed, fabricated, and characterized at 27.93 MHz, showing 18.1% and 12.8% reduction in R{AC}, compared with an identical conductor without capacitive ballast and a same size solid conductor, respectively. [ABSTRACT FROM PUBLISHER]

Substantial induced eddy-current losses and the need for skin-depth-size strands leave litz wire out as an option for inductive applications at multi-megahertz frequencies. To address this, we analyze and minimize the litz-wire eddy-current losses by adding a coating layer to each strand while keeping the wire dimensions and packing factor constant. The skin and proximity effects of isolated and in-bundle coated strands are studied for various coating properties and dimensions. A new method is proposed for calculation of proximity losses inside coated-strand litz wire, which enables simple systematic approach for proximity loss and ac resistance ( R \mathrm{ac} ) determination. Three types of pure copper (Cu), silver-coated copper (Ag/Cu), and nickel-coated copper (Ni/Cu) strands are studied in isolation and inside a litz wire. The litz wires associated with these strands are fabricated and their power dissipations are measured. Analytical results followed by finite-element modeling and experimental results show 26% reduction in Ni/Cu litz wire R \mathrm{ac} , and 3% reduction in Ag/Cu litz wire R \mathrm{ac} at 13.56 MHz compared with same-size Cu litz wire. [ABSTRACT FROM PUBLISHER]

A network of fast-charging stations is of great importance for widespread adoption of electric vehicles (EV) if the so-called range anxiety issue is to be resolved. As with petrol stations, we expect that multiple chargers will be co-located to form charging stations. This layout allows for the fast-charging station to make use of a common rectifier stage and several dc/dc stages to charge multiple EVs. This paper builds on our previous work where we proposed a novel dc-side filter for the 12-pulse rectifier and investigated the power profile for a MW fast-charging station. In this paper, we propose a novel control approach for the filter, based on the virtual resistor injection, which results in further reduction in dc ripple, ac-side harmonics, and filter VA ratings. We also demonstrate that, with the proposed topology and control, the filter stage can be used as dc-side energy storage system. [ABSTRACT FROM AUTHOR]

The 12-pulse rectifier is often used to supply high-power industrial loads. Its ability to effectively and cheaply mitigate the harmonics on the ac side has ensured its dominance in the industry even as active front ends become cheaper and more reliable. Despite its many benefits, the 12-pulse rectifier is not able to reduce the ac-side harmonics to a level acceptable by the pertinent IEEE standards without additional filtering. In this paper, we outline a novel method to profile the rectifier output current to be triangular which results in low ac-side harmonics. The novelty in the proposed approach is that we exploit the dc-side filter design to minimize the volt-amperes (VA) rating of the current source used to profile the dc-side rectifier current. Additional benefits of the proposed method include lower VA rating of the dc filter, simple integration of dc energy storage, and effective ac harmonic control even when the initial rectifier current is discontinuous. [ABSTRACT FROM PUBLISHER]

The series resonant dc–dc converter with clamped capacitor voltage exhibits excellent characteristics in forward operating mode, including simple control, high reliability, soft switching, high power density, and inherently limited load fault current. However, the conventional single angle phase-shift modulation that works well in the forward mode cannot reverse the power flow. In this paper, we propose a modulation strategy for reverse-mode operation by utilizing three phase-shift angles afforded by the two active full bridges of the circuit. We identify the optimal modulation trajectories in 3-D modulation space and implement a lookup-table-based modulator for power flow control. A high-fidelity simulation model of a 35-kW 750-V input, 300–600-V output, and 50-kHz insulated-gate bipolar-transistor-based converter was used for verification. The proposed modulation scheme and efficiency calculations were validated on a scaled-down (15-kW) prototype. The power loss distribution was analyzed for further converter efficiency optimization. [ABSTRACT FROM PUBLISHER]

Energy storage systems (ESSs) are enabling technologies for well-established and new applications such as power peak shaving, electric vehicles, integration of renewable energies, etc. This paper presents a review of ESSs for transport and grid applications, covering several aspects as the storage technology, the main applications, and the power converters used to operate some of the energy storage technologies. Special attention is given to the different applications, providing a deep description of the system and addressing the most suitable storage technology. The main objective of this paper is to introduce the subject and to give an updated reference to nonspecialist, academic, and engineers in the field of power electronics. [ABSTRACT FROM PUBLISHER]

Switched reluctance motors (SRMs) exhibit advantageous features such as low inertia, fault tolerance, high efficiency, and simple design. However, its control is fairly complex due to nonlinear characteristics of the magnetic flux linkage seen on the stator windings. Several memory and/or processor intensive solutions have been proposed to deal with the control problem, constraining the use of the motor to high-cost and high-performance applications. The focus of this paper is to develop a simple controller for the SRM based on state-switching digital control. The concept of state-switching digital control is to control the motor state (speed) by applying a high or a low energy pulse—above and below the desired steady state of the motor. Such a controller can be implemented in low-complexity analog circuitry. This paper presents two methods of motor control: one for single-speed applications and another for variable speed applications. In addition, this paper derives the control equations and disturbance rejection response. Simulation and experimental results for various operating modes are presented. [ABSTRACT FROM PUBLISHER]

Auto rickshaws are three-wheeled vehicles that are extensively used in many Asian countries as taxis of people and goods. Although the vehicle design is well suited to the environment in which it operates, it is a crude and inefficient design. Due to poor vehicle maintenance and the use of inefficient two-or four-stroke engines with very little pollution control, auto rickshaws present a grave pollution problem in major Indian cities. This paper details the overall development of an advanced solar-assisted electric auto rickshaw. Research on the conventional auto rickshaw is presented, as well as future conceptual infrastructure designs for electric rickshaws and the recent design research, simulations, and experimental validation of the next auto rickshaw. The proposed solar/battery electric three-wheeler is meant to match and exceed the conventional vehicle's performance but with a more intelligent and efficient design. We introduce the next overall design of the rickshaw in this paper as Auto Rickshaw 2.0, where the conventional vehicle is version 1.0. The technical development aim for Auto Rickshaw 2.0 is to decrease the total electric power needed for propulsion with an optimized battery system and a more efficient motor and inverter. Four system drive-train options are covered, a rickshaw prototype is built, and several configurations are simulated and analyzed in the Advanced Vehicle Simulator (ADVISOR) software. Additionally, conceptual infrastructure designs are modeled and optimized in the Hybrid Optimization Model for Electric Renewables (HOMER) software. [ABSTRACT FROM AUTHOR]

The fuel efficiency and performance of novel vehicles with electric propulsion capability are largely limited by the performance of the energy storage system (ESS). This paper reviews state-of-the-art ESSs in automotive applications. Battery technology options are considered in detail, with emphasis on methods of battery monitoring, managing, protecting, and balancing. Furthermore, other ESS candidates such as ultracapacitors, fly-wheels and fuel cells are also discussed. Finally, hybrid power sources are considered as a method of combining two or more energy storage devices to create a superior power source. [ABSTRACT FROM AUTHOR]

From the point of view of overall hybrid electric vehicle (HEV) and fuel cell vehicle (FCV) drive train efficiency, the research focus is mainly on the efficiency analysis of the power train components, which prove to be an integral part of modern HEV and FCV drive trains. The critical portion of any HEV electrical system consists of a power electronic converter (inverter) and a suitable traction motor. Thus, the efficiency analysis of the inverter/motor is of prime importance for the calculation of the overall efficiency of the drive trains. This paper aims at modeling the efficiencies of the traction motor/controller through efficiency maps. Efficiency maps are a convenient way to represent motor drive systems of large and complex systems, like that of a HEV. The paper uses the advanced vehicle simulator (ADVISOR) software for the simulations of a large-sized car, similar to a Chevy Lumina, over the urban dynamometer-driving schedule and highway fuel economy test drive cycles. Furthermore, the paper investigates the traction motor efficiency maps and consequent overall drive train efficiencies of commercially available Honda Insight and Toyota Prius HEVs. In all the case studies, the aim is to analyze the overall drive train efficiency over the city and highway drive cycles based on the inverter/motor efficiency maps. [ABSTRACT FROM AUTHOR]

The 15 papers in this special section focus on energy storage systems. [ABSTRACT FROM PUBLISHER]

The output characteristic of an inductive power transfer (IPT) system is highly susceptible to variations in magnetic coupling. In this article, a primary-side X-type compensation topology is proposed to acquire stable output characteristics against a wide range of magnetic coupling without resorting to tight control and coil design. By introducing the concept and derivation principle for the coupling-insensitive compensation topologies, the X-type network is presented to provide self-regulation ability for primary coil current against variable coupling, thereby enabling steady power transfer in a highly dynamic environment. The design considerations for the passive parameters are elaborated, followed by the comparison with regular compensation methods. Owing to its unique structure and design flexibility, the X-type compensation exhibits a stable output characteristic that is beneficial in enhancing the tolerance to position shifts. Moreover, it also features a wide soft-switching range and more flexible design for the output level range than previous topologies. Experimental results show stable power transfer over a coupling factor of 0.14–0.28, where the power fluctuation is less than 20%. The presented method is seen as a potential solution for low power IPT systems, where high mobility is demanded. [ABSTRACT FROM AUTHOR]

In dynamic wireless charging applications, segmented transmitter coils transfer power to a moving receiver coil. This article proposes a method in which the field strength in coupled transmitter coils automatically adjusts based on the position of the receiver. Specifically, a saturable inductor is applied to provide a high uncompensated inductive reactance in the uncoupled condition. By exploiting the reflected reactance as the system approaches the maximum coupled condition, the inductor saturates and the field strength in the coupled transmitter coils automatically increases. The field strength is at its peak when the transmitting and receiving coils reach their maximum coupling and sharply decreases when the receiver is decoupled from the transmitter. Consequently, the difference between the coupled and uncoupled currents in the transmitter coil is maximized, resulting in a near six-fold improvement in field containment performance compared to previously reported findings. This allows for system-level efficient power transfer and compliance with electromagnetic emission standards without complex shielding circuits and auxiliary active position detection approaches. We present the analysis, design criteria of the compensation network, and experimental validation for the proposed method. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge (CHB) converters are receiving growing attention in battery energy storage systems (BESS) due to their modularity and flexibility. However, direct generation of ac output in CHB-BESSs incurs large second-order current ripple in the batteries, which causes additional loss and might accelerate battery aging. Existing methods for ripple-current suppression usually require bulky passive components due to the high energy content of the ripple components. This paper presents a class of current injection methods for delta-configured CHB-BESSs. The injected currents flow through the CHB arms and transfer the original second-order oscillating power to the fourth or the sixth order, or even to an arbitrarily high-order frequency. As such, the battery current ripple appears at much higher frequencies with lower oscillating energy and can be easily filtered by small passive components. In the laboratory setup, the proposed methods reduced the battery root-mean-square current ripple to less than 10% of the dc component with negligible distortion in the loads. The proposed methods and the filter implementations show good tolerance to load frequencies and to the control error of the injected currents. [ABSTRACT FROM AUTHOR]

Momentary power disruptions commonly occur in many industrial settings, and can trip large electric machines, which must then be brought to zero speed before the machine can be restarted. The resulting frequent interruptions in industrial processes can have negative effects on productivity. A restart algorithm brings the machine back to the original speed as soon as power is restored, without waiting for the machine to reach zero speed. This paper proposes an approach for implementing a restart algorithm for synchronous reluctance machines (SynRMs) that use a simple identification algorithm to determine the speed and position of the machine so that the appropriate voltage vector can be applied, thus minimizing the inrush current during the restart. The proposed method only requires nameplate machine parameters and needs no machine-specific tuning, making the approach suitable for implementation with both high-inertia vector and scalar-controlled SynRM. [ABSTRACT FROM AUTHOR]

Reliable protection of distribution systems is becoming increasingly challenging with growing distributed energy resources (DERs) and microgrids. Existing adaptive overcurrent relaying (AOCR) schemes are vulnerable to DER ride-through and generally focus on only grid or islanded modes. This paper presents a dynamic AOCR scheme independent of external controllers to estimate relay pickup that ensures significantly less communication overhead. Existing and emerging challenges for the state-of-the-art are discussed and resolved using the proposed scheme. The reliability is tested using transient system models in Simulink for all combinations of state and fault types/impedances in a 15-bus distribution system. [ABSTRACT FROM AUTHOR]

This paper presents a universal flying restart strategy for scalar (V/f) controlled induction machines. The proposed method performs a frequency search to estimate the rotor speed, and applies the correct frequency and voltage to minimize the inrush current during the restart. This method uses the measured phase current and the motor nameplate parameters, thus making the approach ideal for scalar-controlled motor drives. In addition, the restart algorithm provides controllable restart dynamics, independent of the motor parameters. The main advantages of this method include simple and cost effective implementation without the need for additional sensors, and controllable restart dynamics independent of the motor parameters. Beyond the development of the algorithm, we consider implementation issues to provide a general guideline for the application of the developed algorithm. [ABSTRACT FROM PUBLISHER]

In many industrial settings, momentary power disruptions commonly occur, resulting in tripping of large electric machines, which then have to be brought to zero speed before the machine can be restarted. This can result in frequent interruptions in an industrial process, which can have negative effects on productivity. A more practical approach would restart the machine back to the original speed as soon as power is restored, not having to wait for the machine to be at a standstill. This concept is known as flying restart. In this paper, we propose an approach to implement the flying restart for permanent magnet synchronous machines (PMSM) by using an identification algorithm that determines the speed and position of the machine back-electromotive force so that the correct voltage vector can be applied, thus minimizing the inrush current during the restart. The novelty of the proposed method is that its implementation only requires nameplate machine parameters and needs no machine-specific tuning, making the approach suitable for implementation with both vector- and scalar-controlled PMSM. [ABSTRACT FROM PUBLISHER]

This paper presents a generalized analysis of an inductive power transfer system where multiple frequencies are used to transfer power through the magnetic link. Specifically, we consider a system that amplifies both the fundamental and the third harmonic generated by a full-bridge inverter in order to transfer power to a receiver at both frequencies. The system is analyzed in a generalized manner, by looking at the transconductance function at the transmitter and the receiver for each of the harmonics. Using this approach, the emitted field strength, inverter losses, combined transmitter and receiver coil conduction losses, and VA ratings are compared to a reference single-frequency system. The analysis shows that the dual-frequency system can outperform the single-frequency equivalent for all metrics considered; however, in practice, a tradeoff between the performance criteria is necessary, since the optimal operation points for each criterion cannot be attained with a single design. [ABSTRACT FROM AUTHOR]

The total harmonic distortion (THD) of a waveform is a standard way to quantify its deviation from a sinusoid. In three-phase systems, we are interested in minimizing 3THD: the component of THD produced by odd nontriplen harmonics. However, its definition involves an infinite sum, making it difficult to evaluate and analyze. This paper solves the problem of finding equivalent closed-form expressions for the 3THD of a staircase waveform. In particular, two expressions are rigorously derived, which reveal 3THD to be a piecewise differentiable function. One expression is shorter but describes the pieces implicitly. The other is longer but describes the pieces explicitly. We minimize 3THD using the closed-form expression and provide a comparison with previous techniques. Finally, we provide experimental results that show close agreement with the theoretical results. [ABSTRACT FROM AUTHOR]

We present a new topology appropriate for “dynamic” wireless charging. Possible applications include charging of electric vehicles or robots moving in a large, predesignated area. We propose a system with a transmitter made from multiple coils commensurable with the moving receiver(s), and powered by a single inverter. The proposed system uses the reactance reflected by the receiver to automatically increase the field strength in coupled portions of the transmitter-receiver system, thus allowing efficient power transfer and adherence to electromagnetic field emission standards without complex shielding circuits, switches, electronics, and communication. The power transfer is at its peak when the transmitting and receiving coils approach their maximum coupling (as defined by the geometrical constraints of the system), resulting in improved system-level efficiency. The presented analysis is supported with simulations and experiments. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) is commonly used to transmit power from an extended loop (track) to a number of galvanically isolated movable pick-ups. To maximize the power transfer and minimize converter requirements, various compensation circuits have been proposed for both the track (primary) and the pick-up (secondary). This paper investigates the suitability of the LCC series–parallel compensation for IPT primary design. A new compensation-circuit design procedure is proposed that considers high-order current harmonics and results in inverter zero-current switching. The proposed compensation is compared with the classical compensation designed for zero phase angle between the inverter voltage and current fundamental components. Expressions for the bifurcation boundary, voltampere rating of reactive-compensation elements, and the current at the moment of switching are derived and analyzed. Analytical results are verified both via PSpice simulations and experimentally using a 1-hp MOSFET-based prototype. [ABSTRACT FROM PUBLISHER]

Cascaded multilevel converters have been gaining popularity in static compensators (STATCOMs) owing to their excellent modularity, output quality, and fault tolerance. However, cascaded multilevel converters require a large number of galvanically isolated voltage sensors and complex communication systems in order to balance the module dc-link voltages. This article proposes a reduced series/parallel module (RSPM) that intends to replace H-bridges in cascaded multilevel STATCOMs. Any adjacent RSPMs can be configured in series, bypass, or parallel. Cycling the parallel state through all modules balances all capacitor voltages in a sensorless manner. Since the RSPM-balancing process occurs at the hardware level, H-bridges can be easily replaced by RSPMs without changing higher-level control loops. Compared to existing series/parallel modules, the RSPM has the same functionalities but uses 25% fewer transistors. Despite the reduced switch count, the RSPM is shown to achieve even better efficiency under certain load conditions. The RSPM also attains similar semiconductor utilization ratio as H-bridge modules. The features of the RSPMs are verified on simulations and a down-scaled experimental setup. [ABSTRACT FROM AUTHOR]

Virtual oscillator control (VOC) is a nonlinear grid-forming controller that simultaneously achieves the functionality of output voltage control and primary control layers in a power electronics interfaced distributed generation (DG) unit. Unlike conventional phasor-based primary control methods such as the droop control and virtual synchronous machine control, VOC is a time-domain controller that can guarantee almost global asymptotic synchronization. However, the high-frequency dynamics has largely been ignored in the analysis of VOC in prior art; as a result, VOC-based DGs fail to suppress harmonic current in the presence of harmonic distortion in the network-side voltage. In this work, we demonstrate that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current. We propose a virtual impedance-based selective harmonic current suppression method, and demonstrate that it is better to use the network-side current feedback rather than that of the converter-side current for VOC implementation with virtual impedance control. Established harmonic rejection strategies for grid-following and conventional grid-forming converters are compared with the proposed method for VOC. Through impedance-based analysis, we demonstrate that the proposed method augments the passivity range of the converter terminal response with a much simpler implementation. The proposed harmonic suppression strategy is validated through hardware experiments using a single-phase inverter prototype. [ABSTRACT FROM AUTHOR]

Virtual oscillator control (VOC) is a nonlinear time domain controller that achieves significantly faster primary control response in islanded microgrids, compared to droop or virtual synchronous machine (VSM) control. Despite its superior performance, adoption of VOC is limited due to the lack of compatible secondary regulation or grid synchronization techniques. This is attributed to the nonlinear nature of VOC that complicates secondary control design, and the third-harmonic component in VOC output voltage that severely restricts grid-tied operation. To leverage the faster primary control response characteristics of VOC, we propose a compatible hierarchical control structure that enables operation and seamless transition between islanded and grid-connected modes. In the islanded mode, the controller achieves voltage and frequency regulation and grid synchronization; in the grid-tied mode, notch filters are used to suppress harmonic currents and tertiary level power reference tracking is achieved. The proposed controllers are validated through a series of real-time hardware-in-the-loop tests and hardware experiments using laboratory inverter prototype and state-of-the-art controls and communications hardware. [ABSTRACT FROM AUTHOR]

This paper presents an isolated auxiliary power supply for medium-voltage power electronics systems. The proposed converter comprises two stages: a non-isolated ac/dc stage that connects directly to the medium-voltage line, and an isolated dc/dc stage that provides 100-W output power at 24 V, with 10 kV isolation. The proposed modular ac/dc stage uses just one active semiconductor device per module, features an internal capacitor voltage balancing, and achieves power factor correction by employing predictive current control. High switching frequency operation of both converter stages enable a reduction in system size and weight when compared to traditional low-frequency transformer-based approach. The proposed converter is simulated and its operation is validated experimentally on a 100-W prototype. [ABSTRACT FROM AUTHOR]

This paper presents a new predictive power-factor-correction (PFC) controller for series-interleaved three-level boost (TLB) converters. Compared to the state-of-the-art TLB PFC controllers, where a two-cycle prediction and a detection of an operating region are necessary, the proposed controller achieves a low total harmonic distortion of the input current by using a single equation to predict the input current in all operating regions of the converter, in just one operating cycle. The average current control is achieved by sampling at the peak of the triangular carrier. The proposed PFC controller significantly reduces the distortion of the input ac current near the zero-crossing points, resulting in a low total harmonic distortion of the input current. The operation of the proposed controller was evaluated, and its stability and robustness to parameter changes was confirmed analytically. The controller operating principles were verified in simulations and validated by experiments on a medium-voltage 50-kW converter prototype. [ABSTRACT FROM AUTHOR]

This paper presents a multiobjective real-time controller for a modular multilevel converter capable of parallel module connectivity, the so-called modular multilevel series parallel converter (MMSPC). The MMSPC topology allows the batteries to be dynamically rewired in various series–parallel configurations, generating a wide range of output voltage levels. The novel control method parallelizes the modules to balance their voltages without the need for individual module voltage monitoring. Additionally, the controller optimizes across the large number of feasible system configurations to minimize switching and conduction losses. Finally, the controller efficiently encodes the system configuration with module interconnection states rather than the module switch states, which substantially simplifies control. Furthermore, this work experimentally validates the MMSPC topology and concept. In the prototype, the parallel mode reduced the system losses at 5 kW output power by 18% and 24% for load power factors of 1.0 and 0.8, respectively. Sensorless balancing via parallelization maintained well-matched module voltages (standard deviation = 0.045 V) over a 5-h battery discharge with highly variable load current. The reduced conduction losses and simple balancing capability of the MMSPC can enable new applications at medium and low voltages that benefit from its high-quality output, elimination of filtering magnetics, fast response, and modularity. [ABSTRACT FROM AUTHOR]