Showing papers on "Maximum power transfer theorem published in 2019"

A Misalignment-Tolerant Series-Hybrid Wireless EV Charging System With Integrated Magnetics

Abstract: Electric vehicles (EVs) are becoming increasingly popular as a mean of mitigating issues associated with fossil fuel consumption in transportation systems. A wireless inductive power transfer (IPT) interface between EV and the utility grid has several key advantages, such as safety, convenience, and isolation. However, physical misalignments between the pads of IPT charging systems used in EVs are unavoidable and cause variations in key system parameters, significantly increasing losses and affecting power throughput. This paper presents a novel series-hybrid topology in which the series inductors of the primary and pick-up inductor–capacitor–inductor ( LCL ) networks are integrated into polarized magnetic couplers to improve the system performance under pad misalignment. A mathematical model is developed to investigate the behavior of the proposed system under misalignment. To demonstrate the viability of the proposed method, the results of a 3.3-kW prototype series-hybrid IPT system are presented, benchmarked against a conventional IPT system. Experimental results clearly indicate that the proposed system maintains the output power within ±5% of its rated power despite the pad misalignment. The proposed system is efficient, reliable, and cost effective in comparison to conventional LCL- and CL -compensated IPT systems.

Nonlinear Parity-Time-Symmetric Model for Constant Efficiency Wireless Power Transfer: Application to a Drone-in-Flight Wireless Charging Platform

Abstract: A major challenge for practical wireless power transfer (WPT) applications is to attain stable power transfer with high and constant transfer efficiency under a dynamic change of coupling condition. In order to address the issue, this paper proposes a novel nonlinear parity-time (PT) symmetric model, wherein the nonlinear saturable gain is provided by a self-oscillating controlled inverter. In this paper, the transfer performance and stability criterion of the nonlinear PT-based WPT system are analyzed based on the coupled-mode theory. The theoretical analysis shows that the proposed system automatically achieves constant output power with constant transfer efficiency against the variation of coupling coefficient. Moreover, based on the gain saturation mechanism, the control strategy for the inverter needs to detect only the current in the transmitter, which eliminates auxiliary circuits of wireless communication for feedback control from the receiver. As a case study of dynamic charging, a drone-in-flight wireless charging platform is improved by applying the nonlinear PT-symmetric model. Experimental results show that when the flying drone hovers in a confined three-dimensional volume of space above the WPT platform, a stable output power is maintained with approximately constant transfer efficiency of 93.6%.

Analysis, Design, and Implementation of Accurate ZVS Angle Control for EV Battery Charging in Wireless High-Power Transfer

Abstract: To acquire high efficiency and reduce electromagnetic interference in wireless high-power charging for electric vehicles (EVs), it is of great importance to realize accurate zero voltage switching angle (ZVSA) control of the inverter. However, the traditional zero-crossing detection cannot be applied in high power because of considerable noise and poor accuracy in wide power range applications. In this paper, to suppress the noise in high power, a current hysteresis comparator is adopted, and an enhanced phase detection methodology is proposed to measure the phase of resonant current by using a reference signal produced by a processor. Meanwhile, to improve the accuracy of ZVSA, a uniform time delay compensation method (UTDCM) by considering the whole time delays synthetically is proposed, and a uniform time delay equation can be obtained to guarantee the high accuracy of phase detection, especially in the wide power range. Finally, a novel control strategy with the ZVSA loop based on UTDCM is proposed for battery charging in wireless high-power transfer system. A 500-W wireless power transfer prototype is built to verify the accuracy of ZVSA based on UTDCM and the system efficiency can achieve 94.17% with $k$ = 0.22.

Load-Independent Wireless Power Transfer System for Multiple Loads Over a Long Distance

Abstract: In this paper, a novel long-distance wireless power transfer (WPT) system using repeater coils is proposed to provide power supplies for the driver circuits in high-voltage applications, such as flexible alternative current transmission systems. Different from most of the existing wireless repeater systems where the load is only connected to the last coil and the repeater coils function solely as power relays, in the proposed system, multiple loads are powered by the repeaters. The repeater coils transfer power not only to the subsequent coils but also to the loads connected to them. Dual coil design is proposed for the repeaters with which load-independent characteristics are obtained with a suitable design of coupling coefficients. As a result, the load power can be easily adjusted without affecting each other. Load current characteristics and system efficiency have been analyzed in detail. The power transfer capability of the proposed system is illustrated for different coil quality factors and coupling coefficients. An experimental setup with 10 loads has been built to validate the effectiveness of the proposed long-distance WPT system. The maximum reachable system efficiency is about 84%.

Dynamic Capabilities of Multi-MHz Inductive Power Transfer Systems Demonstrated With Batteryless Drones

Abstract: This paper presents the design of a multi-MHz inductive power transfer (IPT) system showcasing lightweight and energy-efficient solutions for non-radiative wireless power transfer. A proof of concept is developed by powering a drone without a battery that can hover freely in proximity to an IPT transmitter. The most challenging aspect, addressed here for the first time, is the complete system-level design to efficiently provide uninterrupted power flow while allowing for variable power demand and highly variable coupling factor. The proposed solution includes the design of lightweight air-core coils that can achieve sufficient coupling without degrading the aerodynamics of the drone, and the design of newly developed resonant power converters at both ends of the system. At the transmitting-end, a load-independent Class EF inverter, which can drive a transmitting-coil with constant current amplitude and achieves zero-voltage switching for the entire range of operation, was developed; and at the receiving-end, a hybrid Class E rectifier, which allows tuning for large changes in coupling and power demand, was used. For the demo, the range of motion of the drone was limited by a 7.5 cm nylon string tether, connected between the center of the transmitting-coil and the bottom of the drone. The design of the IPT system, including all the power conversion stages and the IPT link, is explained in detail. The results on performance and specific practical considerations required for the physical implementation are provided. An average end-to-end efficiency of 60% was achieved for a coupling range of 23%–5.8%. Relevant simulations concerning human exposure to electromagnetic fields are also included to assure that the demo is safe, according to the relevant guidelines. This paper is accompanied by a video featuring the proposed IPT system

Robust Circuit Parameters Design for the CLLC-Type DC Transformer in the Hybrid AC–DC Microgrid

Abstract: CLLC-type dc transformer (CLLC-DCT) is very popular in the hybrid ac–dc microgrid thanks to its high-power density advantage and good bidirectional power transfer capacity. In the hybrid ac/dc microgrid, the open-loop control is always utilized by the CLLC-DCT to cooperate with the bidirectional interlinking converter to realize the power and voltage conversion between the ac and dc bus. This paper first studies the circuit parameters design of the open-loop controlled CLLC-DCT with consideration of such a realistic problem: The real inductors/capacitors values are actually different with their theoretically designed values due to the operation power and temperature variation. To solve this problem, a robust circuit parameters design scheme is proposed for the CLLC-DCT in this paper. With the proposed scheme, the designed CLLC-DCT exhibits good power transmission and voltage regulation ability in the hybrid ac/dc microgrid even when its actual inductors/capacitors values vary with the practical power and temperature. The robust design method is experimentally verified in a hybrid ac/dc microgrid prototype.

Pulse Density Modulated ZVS Full-Bridge Converters for Wireless Power Transfer Systems

Abstract: Pulse density modulation (PDM) is an advanced technique for maximum efficiency point tracking of wireless power transfer (WPT) systems. By using PDM, both voltage regulation and efficiency maximization can be achieved without dc/dc converters. PDM is also compatible with the dual-side soft switching technique that utilizes resonant tanks and synchronous rectification. However, this soft switching technique depends on coupling and load conditions. Hard switching may occur when the coupling of coils gets stronger or the equivalent load is not properly controlled. To eliminate the dependence and ensure the soft switching under various operating conditions, this paper proposes a PDM zero-voltage-switching (ZVS) full-bridge converter for WPT systems. The converter employs a ZVS branch between switching nodes to provide a ZVS current, and uses a specially designed modulator to obtain the valid ZVS current waveforms. Experimental results verified the proposed operating principles and showed that the additional power loss caused by the ZVS current is insignificant. The overall efficiency of the WPT prototype was 93 ∼ 73% when the power transfer distance was 0.1 ∼ 0.4 m, among which up to 85% efficiency was observed when the distance equaled the coil diameter.

Compensation Topologies in IPT Systems: Standards, Requirements, Classification, Analysis, Comparison and Application

Abstract: Wireless power transfer devices are becoming more relevant and widespread. Therefore, an article is devoted to a review, analysis and comparison of compensation topologies for an inductive power transfer. A new classification of topologies is developed. A lot of attention is paid to the problems of the physical fundamentals of compensation work, standards, safety, and five main topology requirements. It is determined, that topologies with the series primary compensating are the most effective in the IPT for charging devices among the four classical schemes. The series-parallel solution is recommended in case of the low output voltage, minimum size of a secondary side coil is achievable. The series-series solution does not depend on the magnetic coupling coefficient and the load on the resonance frequency. For the convenience of displaying and understanding the information, the comparison results are listed in the tables, graphs and dependencies. The main suitable topologies for a certain application are defined. The given conclusions provide a “one-stop” information source and a selection guide on the application of compensation topologies both in terms of devices and in terms of power level that is the main value of this paper. During literature analysis and recent trends in the market for wireless power transmission devices, the main possible further ways of developing topologies are underlined. First of all, it concerns increasing the frequency of resonance of compensation topologies, the use of multilevel / multi-pulse / multicoils structures, the study of existing high-frequency semiconductors and the development of the semiconductor and magnetic materials.

Adaptive Reactive Power Control of PV Power Plants for Improved Power Transfer Capability Under Ultra-Weak Grid Conditions

Abstract: This paper analyzes the power transfer limitation of the photovoltaic (PV) power plant under the ultra-weak grid condition, i.e., when the short-circuit ratio (SCR) is close to 1. It explicitly identifies that a minimum SCR of 2 is required for the PV power plant to deliver the rated active power when operating with the unity power factor. Then, considering the reactive power compensation from PV inverters, the minimum SCR in respect to power factor (PF) is derived, and the optimized coordination of the active and reactive power is exploited. It is revealed that the power transfer capability of PV power plant under the ultra-weak grid is significantly improved with the low PF operation. An adaptive reactive power droop control is next proposed to effectively distribute the reactive power demands to the individual inverters, and meanwhile, maximize the power transfer capacity of the PV power plant. Simulation results of a 200-MW PV power plant demonstrate that the proposed method can ensure the rated power transfer of PV power plant with the SCR of 1.25, provided that the PV inverters are operated with the minimal PF=0.9.

Design and Control of Inductive Power Transfer System for Electric Vehicles Considering Wide Variation of Output Voltage and Coupling Coefficient

Abstract: In this paper, a design and control scheme of the inductive power transfer (IPT) system for electric vehicles are proposed, considering a wide variation in output voltage and coupling coefficient. The characteristics of the proposed IPT system and a design method for the resonant network are suggested. By utilizing the battery management converter at the secondary side, the design and control can be simplified while managing the output voltage and power of the battery. In order to achieve high efficiency by reducing the voltage–ampere rating, zero phase angle tracking control is proposed. In addition, a phase-shift control is applied to the primary side to ensure the stable system operation by limiting output voltage. A 3.3-kW laboratory prototype with magnetic power pads is manufactured, and the validity of the proposed design and control is verified through experimental results using the laboratory prototype.

Robust Beamforming Design in a NOMA Cognitive Radio Network Relying on SWIPT

Abstract: This paper studies a multiple-input single-output non-orthogonal multiple access cognitive radio network relying on simultaneous wireless information and power transfer. A realistic non-linear energy harvesting model is applied and a power splitting architecture is adopted at each secondary user (SU). Since it is difficult to obtain perfect channel state information (CSI) in practice, instead either a bounded or Gaussian CSI error model is considered. Our robust beamforming and power splitting ratio are jointly designed for two problems with different objectives, namely, that of minimizing the transmission power of the cognitive base station and that of maximizing the total harvested energy of the SUs, respectively. The optimization problems are challenging to solve, mainly because of the non-linear structure of the energy harvesting and CSI errors models. We converted them into convex forms by using semi-definite relaxation. For the minimum transmission power problem, we obtain the rank-2 solution under the bounded CSI error model, while for the maximum energy harvesting problem, a two-loop procedure using a 1-D search is proposed. Our simulation results show that the proposed scheme significantly outperforms its traditional orthogonal multiple access counterpart. Furthermore, the performance using the Gaussian CSI error model is generally better than that using the bounded CSI error model.

An IPT Battery Charger With Near Unity Power Factor and Load-Independent Constant Output Combating Design Constraints of Input Voltage and Transformer Parameters

Abstract: Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC – LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.

Improving Misalignment Tolerance for IPT System Using a Third-Coil

Abstract: To improve misalignment tolerance for an inductive power transfer (IPT) system, a third-coil is employed to reversely connect with the primary coil of the loosely coupled transformer (LCT) in series The LCT with a third-coil (LCT-TC) not only can improve the misalignment performance in x - and y -directions, but also does not affect the inherent output characteristics (such as constant current or voltage output) of original compensation topologies In addition, the proposed approach can keep the IPT system operating with relatively high efficiency against misalignment Then, a detailed design method of LCT-TC is presented Finally, a double-side LCC-compensated IPT system is chosen as an example to verify the feasibility of proposed LCT-TC A 34-kW prototype is constructed, and experimental results show that the proposed method has a good misalignment performance The LCC-LCC IPT system with LCT-TC can retain 96% of the well-aligned power at 40% misalignment, and the end-to-end (dc–dc) overall system efficiency is at least 92% Besides, the fluctuation of the output current is [–2%, 5%] while the load varies from 15 to 34 Ω within 40% misalignment

A Control Strategy for Efficiency Optimization and Wide ZVS Operation Range in Bidirectional Inductive Power Transfer System

Abstract: The efficiency of bidirectional inductive power transfer (BIPT) systems is strongly dependent on the load. Besides, the soft-switching operation of power switches is critical to high-frequency converter in the BIPT systems. In this paper, a triple-phase-shift (TPS) control strategy is proposed to achieve load matching while realizing zero voltage switching (ZVS) for all power switches within the entire power range. The load matching condition of the BIPT system with double-sided LCC compensation network is analyzed. And a dual side phase shift control is proposed to adjust power flow while realizing load matching. To realize ZVS operation, the third phase shift between primary and secondary side is introduced as an extra control variable. A time domain model of double-sided LCC compensation network is established to analyze the ZVS range. With the proposed TPS control, wide ZVS operation range of the system can be achieved while maintaining load matching. At last, a scale down prototype of 1 kW BIPT system is developed. The experimental results show good agreement with theoretical analysis, all switches realize ZVS within the entire power range and a peak efficiency of 94.83% is achieved.

On-Board Deep Q-Network for UAV-Assisted Online Power Transfer and Data Collection

Abstract: Unmanned Aerial Vehicles (UAVs) with Microwave Power Transfer (MPT) capability provide a practical means to deploy a large number of wireless powered sensing devices into areas with no access to persistent power supplies. The UAV can charge the sensing devices remotely and harvest their data. A key challenge is online MPT and data collection in the presence of on-board control of a UAV (e.g., patrolling velocity) for preventing battery drainage and data queue overflow of the devices, while up-to-date knowledge on battery level and data queue of the devices is not available at the UAV. In this paper, an on-board deep Q-network is developed to minimize the overall data packet loss of the sensing devices, by optimally deciding the device to be charged and interrogated for data collection, and the instantaneous patrolling velocity of the UAV. Specifically, we formulate a Markov Decision Process (MDP) with the states of battery level and data queue length of devices, channel conditions, and waypoints given the trajectory of the UAV; and solve it optimally with Q-learning. Furthermore, we propose the on-board deep Q-network that enlarges the state space of the MDP, and a deep reinforcement learning based scheduling algorithm that asymptotically derives the optimal solution online, even when the UAV has only outdated knowledge on the MDP states. Numerical results demonstrate that our deep reinforcement learning algorithm reduces the packet loss by at least 69.2%, as compared to existing non-learning greedy algorithms.

AI Algorithm-Based Two-Stage Optimal Design Methodology of High-Efficiency CLLC Resonant Converters for the Hybrid AC–DC Microgrid Applications

Abstract: Thanks to the advantages of high power density and the capacity of bidirectional power transfer, the CLLC resonant converter is widely used in the hybrid ac–dc microgrid as a dc transformer to interlink the ac and dc bus. Since the voltages of ac and dc bus are controlled by the energy management system, the CLLC resonant converter operates under open-loop condition, which means the switching frequency and duty cycle are fixed. As a result, in the hybrid ac–dc microgrid applications, for the CLLC converter, the main concern is not the voltage regulation but the conversion efficiency. This paper focuses on the total power loss optimization and the magnetic design of the CLLC resonant converter based on artificial intelligence (AI) algorithm. In order to optimize the total power loss, an AI algorithm-based two-stage optimal design method is proposed. In the first stage, the total power loss, including the driving loss, turn- off loss, conduction loss of the switches, the power loss of the resonant capacitances, and copper and core loss of the transformer are optimized by the proposed AI algorithm, GA+PSO, and the optimal parameters, including the leakage inductances ( Lr 1 and Lr 2), magnetizing inductance ( Lm ), and resonant capacitances ( Cr 1 and Cr 2) are derived. In the second stage, the optimal leakage inductances and magnetizing inductance are realized by setting proper distance between the primary winding and the secondary winding ( dw ), and the thickness of the air gap ( da ). As for the magnetic design, in this paper, the leakage inductances of a planar transformer are used as the resonant inductances. The equations of dw and da to achieve the optimal leakage inductances and magnetizing inductance are derived. Both the proposed optimal design method and the equations of dw and da are validated by simulations and experiments.

An Inductive-Power-Transfer Converter With High Efficiency Throughout Battery-Charging Process

Abstract: An inductive power transfer (IPT) converter usually has an optimum efficiency only at a matched load. Because of wide load range variation during battery charging, it is challenging for an IPT converter to achieve the required output and maintain high efficiency throughout the charging process. In this paper, a series–series compensated IPT converter with an active rectifier is analyzed and implemented for battery charging. Appropriate operations are employed for constant-current charging and constant-voltage (CV) charging. A novel operation approach is proposed to achieve constant output voltage and to ensure load impedance matching during CV charging without the help of an extra dc–dc converter, which incurs loss. Both a frequency modulated primary inverter and a phase-angle modulated secondary active rectifier can achieve soft switching. High efficiency can be maintained during the whole battery-charging profile.

Wireless Power Transfer With Magnetic Resonator Coupling and Sleep/Active Strategy for a Drone Charging Station in Smart Agriculture

Abstract: Drones can be used in agriculture applications to monitor crop yield and climate conditions and to extend the communication range of wireless sensor networks in monitoring areas. However, monitoring the climate conditions in agriculture applications faces challenges and limitations, such as drone flight time, power consumption, and communication distance, which are addressed in this study. Wireless power transfer (WPT) can be used to charge drone batteries. WPT using a magnetic resonant coupling (MRC) technique was considered in this study because it allows high transfer power and efficiency with tens of centimeters, power transfers can be achieved in misalignment situations, charging several devices simultaneously, and unaffected by weather conditions. WPT was practically implemented based on a solar cell using a proposed flat spiral coil (FSC) in the transmitter circuit and multiturn coil (MTC) in a receiver circuit (drone) for the alignment and misalignment of two coils at different distances. FSC and MTC improved power transfer and efficiency to 20.46 W and 85.25%, respectively, at 0 cm with the loaded system under alignment condition. In addition, the two coils achieved appropriate transfer efficiencies and power for charging the drone battery under misaligned conditions. The maximum power transfer and efficiency were 17.1 W and 71% for the misalignment condition, at an air gap of 1 cm between two coils when the system was loaded with the drone battery. Moreover, the battery life of the drone was extended to 851 minutes based on the proposed sleep/active strategy relative to the traditional operation (i.e., 25.84 minutes). Consequently, a 96.9% battery power saving was achieved based on this strategy. Comparison results showed that the proposed system outperformed some present techniques in terms of the transfer power, transfer efficiency, and drone battery life. The proposed WPT technique developed in this study has been proven to solve the misalignment issue. Thus it offers a great opportunity as a key deployment component for the automation of farming practices toward the Internet of Farming applications.

A New Design Approach to Mitigating the Effect of Parasitics in Capacitive Wireless Power Transfer Systems for Electric Vehicle Charging

Abstract: This paper introduces a new design approach to mitigate the effect of parasitic capacitances and achieve high performance in large air-gap capacitive wireless power transfer (WPT) systems for electric vehicle (EV) charging. In a capacitive WPT system for EVs, the vehicle chassis and roadway introduce multiple parasitic capacitances that can overwhelm the coupling capacitance and severely degrade power transfer and efficiency. The proposed approach addresses this challenge by employing split-inductor matching networks, which allow the complex network of parasitic capacitances to be simplified into an equivalent four-capacitance model. The shunt capacitances of this model are directly utilized as the matching network capacitors, hence, absorbing the parasitic capacitances and eliminating the need for discrete high-voltage capacitors. A systematic procedure is developed to accurately measure the equivalent capacitances of the model, enabling the system’s performance to be reliably predicted. The proposed approach is used to design two 6.78–MHz 12-cm air-gap prototype capacitive WPT systems with capacitor-free matching networks. The first system transfers up to 590 W using 150-cm2 square coupling plates and achieves an efficiency of 88.4%. The second prototype system transfers up to 1217 W using 118-cm2 circular coupling plates, achieving a power transfer density of 51.6 kW/m2. The measured output power profiles of the two systems match well with their predicted counterparts, validating the proposed design approach.

Survey on magnetic resonant coupling wireless power transfer technology for electric vehicle charging

Abstract: Wireless power transfer (WPT) technology makes it possible to supply power through an air-gap, without the need for current-carrying wires. One important technique of WPT technology is magnetic resonant coupling (MRC) WPT. Based on the advantages of MRC WPT, such as safety and high power transfer efficiency over a long transmit distance, there are many possible applications of MRC WPT. This study provides a comprehensive, state-of-the-art review of the MRC WPT technology and wireless charging for electric vehicle (EV). A comparative overview of MRC WPT system design which includes a detailed description of the prototypes, schematics, compensation circuit topologies (impedance matching), and international charging standards. In addition, this study provides an overview of wireless EV charging including the static wireless EV charging and the dynamic wireless EV charging, which focuses on the coil design, power transfer efficiency, and current research achievement in the literature.

Unified Load-Independent ZPA Analysis and Design in CC and CV Modes of Higher Order Resonant Circuits for WPT Systems

Abstract: This article proposes a general unified methodology for arbitrary higher order resonant circuits. With the proposed methodology, the equivalent circuits and the general resonant methods of the higher order resonant circuit are presented to realize the load-independent constant current (CC) and constant voltage (CV) outputs at two different load-independent zero phase angle (ZPA) frequencies. In addition, the corresponding regularized mathematical models of the constant output current and voltage and the purely resistive input impedances in CC and CV output modes are derived. All compensation topologies in both inductive and capacitive power transfer (CPT) systems have the essence of higher order resonant circuits. It means that the proposed methodology can be applied to investigate the load-independent output and input characteristics of any inductive power transfer (IPT) and CPT topologies. A 3.3-kW $LCC$ -series-compensated IPT system for electric vehicles (EVs) was designed and manufactured to verify the theoretical analysis. The system operating frequencies in both the CC output with ZPA and the CV output with ZPA are in compliance with the SAE J2954 standard.

Load-Independent Voltage and Current Transfer Characteristics of High-Order Resonant Network in IPT System

Abstract: Load-independent output characteristics of an inductive power transfer (IPT) system are of increasing interest in electric vehicle and LED lighting applications. All compensation networks in the IPT system are actually high-order resonant circuits. In a high-order resonant network, there are multiple resonant frequencies to get load-independent voltage output and current output. It is critical to analyze the resonant conditions to achieve high efficiency in both load-independent voltage output and current output modes. This paper proposed a general modeling method for arbitrary high-order resonant networks to get both the load-independent voltage and current transfer characteristics. A high-order circuit can be modeled as a combination of an LC network, a multistage T-circuit, and/or multistage $\Pi $ -circuit in series. The proposed method is verified by applying to voltage-fed double-sided inductor–capacitor–capacitor (LCC), series–series (SS), S-SP, LCC-S, and current-fed CLC-LC compensation networks in the IPT system. The MATLAB simulation and the experimental prototype of a constant voltage-fed double-sided LCC compensated IPT system with up to 3.3-kW power transfer are built. The efficiency of the double-sided LCC compensated IPT system is up to 92.9% and 90.6% when the IPT system operates at resonant frequencies that achieve constant current output and constant voltage output, respectively, which are compliance with the frequency requirement by SAE J2954 standard.

PV Solar System Control as STATCOM (PV-STATCOM) for Power Oscillation Damping

Abstract: This paper presents a novel control of photovoltaic (PV) solar system as a FACTS device STATCOM, termed PV-STATCOM, for power oscillation damping (POD) in transmission systems. In the proposed control, as soon as power oscillations due to a system disturbance are detected, the solar farm discontinues its real power generation function very briefly (few tens of seconds) and makes its entire inverter capacity available to operate as a STATCOM for POD. As soon as power oscillations are damped, the solar farm restores real power output to its pre-disturbance level in a ramped manner, while keeping the damping function activated. This results in much faster restoration than that specified in grid codes. During nighttime, the solar farm performs POD with its entire inverter capacity. It is shown from EMTDC/PSCAD simulations that the proposed control provides significant increase in power transfer capacity on a 24/7 basis in systems that exhibit both local inertial and interarea oscillatory modes. The proposed PV-STATCOM is about 50–100 times cheaper than an equivalent STATCOM for providing POD at the same location. This novel control can potentially bring large savings for transmission utilities and open up a new revenue making opportunity for solar farms for providing POD.

Robust Resource Allocation and Power Splitting in SWIPT Enabled Heterogeneous Networks: A Robust Minimax Approach

Abstract: Heterogeneous network (HetNet) with energy harvesting is a promising technique to provide perpetual power supplies and ubiquitous coverage as well as high data rate for next-generation wireless communications. In this article, we consider a robust power allocation and power splitting (PS) problem for downlink simultaneous wireless information and power transfer (SWIPT)-enabled HetNets. The robust energy-efficiency (EE) maximization problem of femtocell users (FUs) is formulated under the outage-probability interference power constraint of macrocell user (MU), the maximum allowable transmission power of FU, and the EE-based outage constraint of each FU. The originally fractional optimization problem with the probabilistic constraint is NP-hard and difficult to solve. Without knowing the distribution of uncertain parameters, a min–max probability machine approach is first introduced to convert the semi-infinite optimization problem into a deterministic one which is transformed into a deterministic convex one by using the Dinkelbach method and the quadratic transformation approach. An iterative power allocation and PS scheme is obtained based on convex optimization methods. Finally, the effectiveness of the proposed algorithm is demonstrated by simulation results from the perspective of EE and robustness.

Design of the Pacific DC Intertie Wide Area Damping Controller

Abstract: This paper describes the design and implementation of a proof-of-concept Pacific dc Intertie (PDCI) wide area damping controller and includes system test results on the North American Western Interconnection (WI). To damp inter-area oscillations, the controller modulates the power transfer of the PDCI, a ±500 kV dc transmission line in the WI. The control system utilizes real-time phasor measurement unit (PMU) feedback to construct a commanded power signal which is added to the scheduled power flow for the PDCI. After years of design, simulations, and development, this controller has been implemented in hardware and successfully tested in both open and closed-loop operation. The most important design specifications were safe, reliable performance, no degradation of any system modes in any circumstances, and improve damping to the controllable modes in the WI. The main finding is that the controller adds significant damping to the modes of the WI and does not adversely affect the system response in any of the test cases. The primary contribution of this paper, to the state of the art research, is the design methods and test results of the first North American real-time control system that uses wide area PMU feedback.

Analysis and Optimized Design of Compensation Capacitors for a Megahertz WPT System Using Full-Bridge Rectifier

Abstract: The spatial freedom of wireless power transfer (WPT) systems can be improved using a high operating frequency such as several megahertz (MHz). In the conventional compensations the load of the coupling coils is usually assumed to be pure resistive. However, in MHz WPT systems this assumption is not accurate anymore due to the nonneglectable rectifier input reactance. This paper discusses the impedance characteristics of the full-bridge rectifier at MHz and their influence under the series–series, parallel–series, series–parallel, and parallel–parallel compensation topologies. An undesirable nonzero phase (i.e., none unity power factor) is shown to exist at the primary input port, which leads to decreased power transfer capability. In order to minimize this negative effect, the compensation capacitors are optimally designed, and the series–series topology is found to have the smallest phase under load and coupling variations. Finally, an experimental 6.78 MHz system is built up to verify the optimized design of the compensation capacitors. The results show that the average nonzero phase is effectively reduced together with the improved power factor from 0.916 to 0.982.

A review on miniaturized ultrasonic wireless power transfer to implantable medical devices

Abstract: Wireless power transfer has experienced a rapid growth in recent years due to the need for miniature medical devices with prolonged operation lifetime. The current implants utilize onboard batteries as their main source of power. The use of batteries is not, however, ideal because they have constrained lifetime requiring periodic replacement. Energy can be supplied to the implantable devices through wireless power transfer approaches including inductive, ultrasonic, radio frequency, and heat. The implantable devices driven by energy harvesters can operate continuously, offering ease of use and maintenance. Inductive coupling is a conventional approach for the transmission of power to implantable devices. However, the inductive coupling approach is affected by tissue absorption losses inside the human body. To power implantable devices such as neural, cochlear, and artificial heart devices, the inductive coupling approach is being used. On the other hand, ultrasonic is an emerging approach for the transmission of power to implantable devices. The enhanced efficiency and low propagation loss make ultrasonic wireless power transfer an attractive approach for use with implantable devices. This paper presents a study on the inductive and ultrasonic wireless power transfer techniques used to power implantable devices. The inductive and ultrasonic techniques are analyzed from their sizes, operating distance, power transfer efficiency, output power, and overall system efficiency standpoints. The inductive coupling approach can deliver more power with higher efficiency compared to the ultrasonic technique. On the other hand, the ultrasonic technique can transmit power to longer distances. The advantages and disadvantages of both techniques as well as the challenges to implement them are discussed.

Generic Closed-Loop Controller for Power Regulation in Dual Active Bridge DC–DC Converter With Current Stress Minimization

Abstract: This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) dc–dc converter using triple phase shift (TPS) control to enable closed-loop power regulation while minimizing current stress. The key new achievements are a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e., Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed-loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter ac rms current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the rms current in the entire bidirectional power range of –1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool, which is carefully analyzed to derive simple useful relations. Such relations enable a generic closed-loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate the precision of the proposed closed-loop controller under various operating conditions. An experimental prototype also substantiates the results achieved.