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Summary Inductive power transmission (IPT) and capacitive power transmission (CPT) are currently the two main wireless power transfer technologies. Hybrid power transmission (HPT) systems that combine IPT and CPT can improve transmission performance and are more attractive for some charging applications such as electric bicycles (e‐bikes). However, HPT systems are more sensitive to parameter variations, and the coupling mechanism is prone to misalignment during wireless charging. Therefore, achieving stable output power and constant transfer efficiency over a wide range of coupling coefficient variations is still a major challenge for HPT systems. In this work, the parity–time (PT) symmetry theory is applied to an SS‐type HPT system, and a circuit model of the PT‐based HPT system is developed by using coupling capacitance and coupling inductance. The effect of connecting the plates to the homonymous end or heteronymous end of the coupling coils on the PT symmetry range of the HPT system is discussed. It is found that the heteronymous end connection of the coils can effectively increase the range of constant output power and stable transfer efficiency. Finally, a prototype is built to verify the feasibility and effectiveness of the proposed PT‐based HPT system. The transfer power and efficiency remain constant in the PT‐symmetric range, and the inductive and capacitive coupling coefficients are smaller compared to IPT and CPT systems with the same parameters. [ABSTRACT FROM AUTHOR]

Electric spring (ES), which has been widely discussed in recent years, is a new demand response method. By adjusting the power of noncritical load (NCL), ES can adaptively improve power quality of the grid containing a high proportion of renewable energy sources. Most of the existing ESs is connected in series with NCLs, but this structure limits the compensation power range of ES. In this article, a new ES topology based on LCL filter is proposed, where NCL is paralleled with the capacitor branch as the shunt damper. Compared with other types of ES, the proposed LCL-ES has the advantages which can extend the adjustable power range, improve the voltage regulation performance, and suppress the inherent resonance spikes effectively. Finally, the feasibility of LCL-ES has been verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

For a multiload wireless power transfer (WPT) system, it has always been a challenge to maintain constant output power with constant efficiency for each load when the coupling conditions change. Besides, the unbalanced power distribution and cross-coupling among loads are also the key issues. In order to solve these problems, a novel multiload WPT system combining the parity-time (PT) symmetry principle and time-sharing control strategy is proposed. First, the multiload PT-symmetric WPT (PT-WPT) system with single natural resonant frequency is modeled and analyzed based on the circuit model. Then, a multiload PT-WPT system with time-sharing control strategy is constructed by adding a controllable resonant capacitor array at the transmitter. The time-sharing control strategy is realized by periodically turning on/off a controllable resonant capacitor selectively, which enables a single transmitter to supply power to multiple loads with different natural resonant frequencies, and each load realizes PT transmission characteristics. Further, using the time-sharing control strategy, the power distribution among multiple loads is realized by only controlling the duty cycle of each load. Finally, two dual-load PT-WPT experiments are designed and carried out. Experimental results show that each load can maintain constant output power with constant transfer efficiency about 90% in a wide coupling range, and realize power distribution at desired values simultaneously. [ABSTRACT FROM AUTHOR]

In the multi-load wireless power transfer (WPT) system, the output power and transfer efficiency will drop significantly with the change of distance between transmitter and receiver. Power distribution among multiple loads is also a major challenge. In order to solve these problems, a novel multi-load WPT system based on parity–time symmetry (PT-WPT) is proposed in this paper. Firstly, the multi-load PT-WPT system is modeled based on the circuit model. Then, the transmission characteristics of the multi-load PT-WPT system are analyzed. It is found that constant output power with constant transfer efficiency can be maintained against the variation of coupling coefficient, and the power distribution relationship among loads is only related to the coupling coefficient. Further, power distribution under different coupling situations is analyzed in detail to meet different power demands. Finally, taking a dual-load PT-WPT system as an example, the system parameters are designed and the circuit simulation is carried out. The simulation results are consistent with the theoretical analysis, which shows that PT symmetry can be applied to the multi-load WPT system to achieve constant output power, constant transfer efficiency, and power distribution simultaneously. [ABSTRACT FROM AUTHOR]

The nine-arm inverter integrates two modular multilevel converters (MMCs) into one compact inverter to diminish the number of power semiconductor devices. It can be used for dual-motor driving or connecting two AC power sources in a multi-terminal high voltage direct current (HVDC) system, etc. Although the half-bridge based modular multilevel converter has the fewest components, it is generally not resistant to the DC-side faults. In order to achieve a DC fault blocking capability with high efficiency and low cost, this paper proposes a hybrid nine-arm high-voltage inverter, which is consists of a full-bridge sub-module (FBSM) and a half-bridge sub-module (HBSM). Firstly, the topology, operation modes, and modulation strategy of the proposed hybrid inverter are presented. Then, by analyzing the potential short-circuit current paths between different ports, the ability of the proposed hybrid inverter to block the DC faults is described and the appropriate ratio of HBSM and FBSM is determined to further reduce the number of devices and the losses of the proposed hybrid inverter. Finally, simulation results based on MATLAB/Simulink are provided to demonstrate the effectiveness and feasibility of the proposed hybrid nine-arm high-voltage inverter under normal operation and DC fault condition. [ABSTRACT FROM AUTHOR]

The mechanism of a ZVT PWM boost converter is analyzed in detail in this study. In addition, the comprehensive parasitic parameters are taken into consideration. It is discovered that some unexpected modes, referred to as sneak circuit modes, occur during the operation of the converter, when certain excitation conditions are applied. Parasitic parameters and dynamic sneak paths impact the converter operating performance, causing both positive and negative effects. The effects of sneak circuits and excitation conditions are analyzed so that those with negative effects can be eliminated, and those with positive effects can be utilized. In contrast to previous works, sneak circuit phenomena are utilized to optimize the converter performance. Furthermore, parasitic circuit elements are identified and quantitatively determined to estimate their impact on the switching performance of the converter. Combining parameter optimization and topology optimization, soft switching is achieved in both the main power switch and the auxiliary power switch, and waveform distortion is reduced. Finally, simulation and experimental results are included to verify the theoretical analyses. [ABSTRACT FROM AUTHOR]

Summary: Ultra‐high voltage inverters are widely used as grid‐connected devices in new energy grids, and the state‐space average model is the most practical modeling method for the inverter. However, the accuracy of this modeling method is significantly reduced because it ignores the high‐frequency switching process, which contains overshoot voltage and other factors that affect system stability. Moreover, the amplitude of the overshoot voltage in the ultra‐high voltage inverter will be huge, which may lead to the damage to switching devices, circuit overheating, and even the collapse of the system. Therefore, the wavelet decomposition and reconstruction methods are used in this paper to extract the transient characteristics of the inverter and integrate them into the state‐space average model. Compared with the traditional state‐space average model, the improved model method can obtain a more accurate overshoot voltage peak value with the same simulation step size. Then, it can provide a more precise reference for the withstand voltage in the device selection of a high voltage level system. The single‐phase full‐bridge inverter is taken as an example to illustrate the construction process based on the wavelet decomposition and reconstruction method. Finally, the simulation waveform is verified to be in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

State-space modeling is often used to design power converters so that the performance of the closed-loop control system can meet design requirements. However, single-phase DC-AC converters based on constant state feedback control have some issues, including long response times and unpredictable robustness. To solve these problems, a novel control strategy based on state feedback control (SFC), called the smooth projection adaptive strategy (SPAS), is developed by adaptively changing the state feedback coefficient according to the projection value of the system. First, a state space model of the DC-AC converter with the adaptive state feedback control law is established. Then based on the SPAS and considering parameters perturbation, two control laws named current-mode control (CMC) and voltage-mode control (VMC) are proposed, and their robustness are further discussed. Furthermore, the design method of the proposed control system in the digital control framework is presented. Finally, experiments on a 400 W prototype, and comparative analyses among the proposed control laws and the conventional PI control method are carried out. The results show that the proposed CMC has apparent superiority in terms of both static and dynamic performance. [ABSTRACT FROM AUTHOR]

Summary: The transmission distance and the output load of wireless power transfer (WPT) system are particularly prone to change, which results in higher requirements for the robustness and dynamic performance of the control. In order to reduce the influence of these characteristics, an H∞ loop shaping controller based on generalized state space averaging (GSSA) method is proposed in this paper. Based on the GSSA model, an appropriate compensation function is constructed for the WPT system to the target loop transfer function. The nominal coprime factorization of WPT system is carried out, and on this basis, H∞ controller is achieved by Riccati equation to minimize the infinite norm from disturbance to error output. The designed controller meets the requirements of robust. Furthermore, the obtained high‐order controller is discretized by a reasonable discretization method, and the details and limitations of its practical application are discussed based on the hardware computational capacity. The experimental results show that the proposed controller has better robustness and dynamic performance and flexibility than the mixed sensitivity H∞ controller and the Z‐N PI controller. [ABSTRACT FROM AUTHOR]

In this letter, a new half-bridge impedance source inverter (HBISI) with high voltage conversion ratio is developed. Compared with other well-known existed HBISIs (HB-qZSIs/HB-qSBIs), the proposed HBI can increase the voltage boost factor significantly. Only a very small shoot-through (ST) duty cycle (Dsh) is required to produce a higher voltage gain. The upper and lower switches of the inverter bridge can be turned on simultaneously, and no dead time is needed for the control scheme. So the reliability of the inverter system can be improved. The produced square-waveform output voltage not only has positive and negative voltage levels like the traditional HB-ZSI but also has a zero voltage level, and the nth harmonic of the output voltage can be eliminated by choosing Dsh = 1/n, which implies that it would be applicable for the electrochemical and electroplating applications. The topological configuration, operating principle, power loss analysis, and performance comparison with other high-boost HBISIs are presented. Finally, both simulations and the experimental results are presented to validate the effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

Summary: Very‐high‐frequency (VHF) resonant converters have the advantages of small volume, light weight, and high power density. However, under the operating frequency of tens of megahertz, the nonlinear characteristics of the power semiconductor devices intrinsic capacitances will affect the analysis accuracy of VHF converters and increase the difficulty of parameter design of these converters. Thus, this paper proposes a method to obtain the equivalent capacitances of power semiconductor devices. Taking the VHF resonant boost converter as an example, the process of obtaining the equivalent capacitances of power semiconductor devices is elaborated first. And then a prototype with operating frequency 17.30 MHz, input voltage 3–6 V, and output voltage 9–18 V is built to verify the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

It is found in the latest research works that there are sneak circuit phenomena in power converters, which would normally be ignored but finally cause various problems. Therefore, it is necessary to find out and analyze sneak circuits. Under certain conditions, sneak circuit phenomena caused by parasitic parameters are first found in a Boost converter operating at discontinuous conduction mode (DCM). A detailed investigation into the impacts of sneak circuits on the operation performances of the DCM Boost converter is achieved. It is found that the operation performances of the DCM Boost converter will be adversely affected when the sneak circuits appear. Then, the conditions of the sneak circuits are derived. Furthermore, design guidelines for reducing or eliminating the sneak circuit phenomena are presented. Finally, the theoretical analyses are demonstrated with both simulation and experimental results. [ABSTRACT FROM AUTHOR]

By the logical statements and linear inequalities, a new modeling method named bi-switching status modeling (BSM) method is presented to model the dc–dc converters in this paper. Compared with other modeling methods, such as the state-space averaging method and the mixed logical dynamical (MLD) method, first, the BSM method can describe continuous conduction mode and discontinuous conduction mode operations of the dc–dc converters as a unified bi-switching status model. Second, the BSM method is more precise than the state-space averaging method because there is no approximate assumption. Third, the constrains of the operating modes in the BSM method can be simplified as a consolidated inequality, which means that the model obtained by the BSM method is more concise than that obtained by the MLD method. Simulation and available experiments of a buck converter verify the effectiveness of the proposed BSM method. [ABSTRACT FROM PUBLISHER]

This paper presents a new family of hybrid Z-source boost dc–dc converters intended for photovoltaic applications, where the high step-up dc–dc converters are demanded to boost the low-source voltages to a predefined grid voltage. Because the boost capabilities of the traditional Z-source networks are limited, the proposed converters are composed of combine traditional Z-source networks in different ways to enhance the boost abilities of the traditional Z-source networks. The new version of the proposed Z-source converters is termed as hybrid Z-source boost dc–dc converters to satisfy the traditional benefits of Z-source networks with stronger voltage boost abilities which can also be applied to dc–ac, ac–ac, and ac–dc power conversions. The performances of the proposed converters are compared with other Z-source networks behaviors. The simulation and experimental results of the proposed converters are validated at different operating conditions. [ABSTRACT FROM PUBLISHER]

In recent years, very high frequency (VHF) converter has attracted much attention. However, with rich parasitic parameters and complex resonance links, there are some great difficulties to the modeling of such systems. Taking the on-off controlled VHF resonant boost converter as an example, this paper presents an accurate modeling and analysis method that considers multiple parasitic parameters. First, the closed-loop VHF converter system is divided into a main network and a parasitic oscillation network. Then, based on the operation analysis, an equivalent circuit model characterized by a time-varying input voltage source and two variable duty-cycle controlled switches is proposed. It worth noting that both the time-varying input and the controlled switches take into account the influences of the parameters. Furthermore, the periodic approximate analytical solution of the output voltage in the on stage is obtained by using the equivalent small parameter method to the proposed circuit model. And then combining the solution of the parasitic oscillation network and on-off state switching conditions, the steady-state waveform of output voltage can be obtained quickly. Finally, a prototype with operating frequency of 21.44 MHz is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In power electronic equipment, magnetic devices are important parts, and their working condition and reliability are closely related to turn‐to‐turn insulation. With the increasing application of high‐frequency square wave voltage in the fields of frequency conversion technology and motor control, the high voltage stress on magnetic devices will accelerate insulation aging, so it is necessary to monitor the aging state of turn‐to‐turn insulation. At present, researchers mainly detect insulation aging by detecting partial discharge signal. However, this method cannot realize the early monitoring of aging, and the measurement cost is high and the accuracy is low. Therefore, for the dry‐type core reactor with epoxy resin as the insulation medium, this paper proposes a turn‐to‐turn insulation aging state detection method under high‐frequency square wave voltage excitation. According to the relationship between the turn‐to‐turn insulation aging state of the reactor and its parasitic capacitance, the turn‐to‐turn insulation aging degree of the reactor is predicted by measuring and analyzing the phase information of high‐frequency components of the current signal. Finally, the measuring principle and method are introduced and verified by experiments. [ABSTRACT FROM AUTHOR]

The min-projection strategy (MPS) is a switching rule with better convergence speed, which can improve the dynamic characteristics of three-phase grid-connected inverters. However, the grid-connected current harmonics of the system are large when the MPS is used directly in the digital control framework due to the limitations of the sampling frequency. To solve this problem, an improved min-projection strategy is proposed in this paper by introducing a zero voltage vector to the control. First, the non-zero voltage vector is selected through the switching law function of the MPS. Then the time occupied by the non-zero voltage vector and the zero voltage vector can be obtained through an error function, which is established by the principle of minimum current error. Finally, the switching signal can be obtained for control, based on the method of duty cycle modulation. This method can realize fast current tracking and current decoupling control, reduce the grid-connected current harmonics, and improve the steady state performance of the system without increasing costs. The effectiveness of the proposed method is verified by simulations and experimental results. [ABSTRACT FROM AUTHOR]

Switched‐capacitor (SC) technique is widely used in high step‐up DC‐DC converters. Yet the unwanted high spike current in the SC‐based loop deteriorates the converters performances. To find a solution to this issue, this paper devises a general method of constructing topologies that can prevent high spike current and obtain additional voltage pumping as well. By inserting a VSL unit, which consists of an inductor, an active switch, and a voltage source, into a typical SC‐based converter, a series of improved topologies can be obtained systematically. Based on the proposed rule of inserting VSL units, the operating modes and sequence of the SC‐VSL‐based loop are first discussed to explain the principle of preventing current spike. Then, performances are analyzed in detail, and experiments are carried out for further verification of the proposed rules and the converters derived from these rules. Results from theoretical analysis and experiments show that the proposed converters can produce an additional voltage pumping capability while suppressing the spike current in the SC loop and thus have a higher efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a common grounded Z-source dc–dc converter with high voltage gain is proposed for photovoltaic (PV) applications, which require a relatively high output–input voltage conversion ratio. Compared with the traditional Z-source dc–dc converter, the proposed converter, which employs a conventional Z-source network, can obtain higher voltage gain and provide the common ground for the input and output without any additional components, which results in low cost and small size. Moreover, the proposed converter features low voltage stresses of the switch and diodes. Therefore, the efficiency and reliability of the proposed converter can be improved. The operating principle, parameters design, and comparison with other converters are analyzed. Simulation and experimental results are given to verify the aforementioned characteristics and theoretical analysis of the proposed converter. [ABSTRACT FROM PUBLISHER]

Lifting operating frequency can effectively reduce the size of energy‐storage components and increase the power density of converters, thus the very high frequency (VHF) resonant converters can find wide applications in practice. In order to further study the characteristics of VHF converters, a modeling method is presented for solving the state variables. First, according to the analysis of a typical VHF converter's operating modes, a unified equivalent circuit is established, which contains nonlinear controlled current sources. Then the mathematical model of the equivalent circuit is derived and solved by using the equivalent small parameter (ESP) method. And the approximate analytical solutions of state variables can be finally obtained, which are composed of a DC component and various harmonics. It is shown that the obtained solutions are accurate enough as the results from the proposed method agree well with the simulations and experimental results. Furthermore, the approximate analytical expressions for harmonics of state variables can be used as a guide for circuit design and stability analysis of the converter. [ABSTRACT FROM AUTHOR]

In magnetic resonant coupling wireless power transfer (WPT) system, the frequency splitting phenomena have a vital influence on the output power. This paper mainly focuses on the frequency splitting of two-coil and three-coil WPT. First, the frequency characteristics of transfer power and system efficiency of the two-coil WPT are analyzed by circuit theory. In addition, the magnetic field distribution of the two splitting frequencies is simulated to analyze which frequency is better for the operating frequency. Second, considering the reference resistance of RF power, the frequency splitting of two-coil and three-coil WPT is analyzed. Finally, the critical coupling, which determines the over coupled region, of two-coil and three-coil WPT is derived. Meanwhile, we propose a tuned frequency method according to the numerical results. In addition, the transfer power can be kept at a relatively constant level in the over coupled region. [ABSTRACT FROM AUTHOR]

A novel Cuk-based bridgeless rectifier is proposed for receiving side of wireless power transfer (WPT) system. The proposed converter can not only help improve overall efficiency but also is with features of wide power modulation range and very low output current ripple. In terms of the output current source characteristics of series-series-compensated WPT system, a bridgeless rectifier and a Cuk converter are combined and an input inductor of Cuk converter is cut down to form the proposed single-stage converter. Besides, a synchronization operation method is derived for the proposed converter to realize the optimal working point of transmission power and efficiency. Operation principles of the converter and its impact on performance of WPT system are analyzed. Also, design methods for system parameters are given. A prototype is built up to verify the feasibility of the proposed topology and the operation method. It is noted that the proposed converter can well adjust the output power of WPT system to realize the desired working point via adjusting the duty cycle at different transfer distances and loads. [ABSTRACT FROM AUTHOR]

In the paper by Jin et al. (IEEE Trans. Ind. Electron., vol. 62, no. 3, pp. 1363–1371, Mar. 2015), the authors present an expansion of Ohm's law in the nonsinusoidal ac circuit, based on which a distinct instruction for analyzing and designing nonsinusoidal circuit including ac/dc link circuit is provided. This paper is very interesting and a good work. However, some equations and expressions may be improved. In this paper, they are discussed and modified. [ABSTRACT FROM AUTHOR]

In this article, a time-invariant polynomial model of fixed-frequency pulsewidth modulation dc–dc converter is proposed. Through normalized coordinate transformation, the time-varying model of the converter is transferred into a time-invariant model, whose state matrix and input matrix are obtained by the addition and multiplication of matrices simply and expressed by the polynomial of duty cycle concisely. The proposed model has the following advantages. Compared with the state-space average (SSA) model, the ripple of the state vector and the switching period are considered, thereby improving the accuracy. Contrary to other time-invariant models, the state matrix and input matrix instead of the state vector are expanded into series. Therefore, neither the number of state vectors nor the order of the matrices increases, and the proposed model has a simple structure similar to the SSA model. In addition, as a time-invariant polynomial model, the calculation and analysis of the proposed model are much simpler than the time-variant exact model. In order to prove the above advantages of the proposed model, the general expression of the proposed model is derived and the proposed model is compared with other models. These analyses and comparisons are verified through the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this letter, the authors put forward a symbolic approach to analyze the nonlinearities of switching power converters. This proposed method can be used to describe bifurcation and chaos behavior by means of coarse-grained symbols. First, the period-doubling structure of a symbolic series is studied in symbolic dynamics. Second, the block entropy, which is the related statistics of subsequences of a symbolic series, is introduced. Finally, two Boost converters are studied as examples to illustrate the applications of the proposed symbolic dynamics method. Via block entropy, both period-doubling and border collision bifurcations are identified and quantified, and initial value sensitivity is successfully used to distinguish chaos from periodic motions. [ABSTRACT FROM AUTHOR]

Abstract-In this paper, a system description of the spectrum of different pulsewidth modulation (PWM) schemes based on time- frequency and wavelet transforms is developed for electromag- netic interference (EMI) suppression in a converter. The wavelet reconstructions of different PWM schemes are obtained exactly. The wavelet coefficients of periodic PWM and of constant PWM have the property of being analogous. The wavelet coefficients of chaotic PWM lack resemblance. The peak of wavelet power spec- trum of chaotic PWM fell off sharply at frequency domain and en- ergy transfer to the low-frequency belt. Based on time, frequency transforms, Renyi information, marginal characteristics, and time torque of different PWM schemes are obtained. At last, conduct EMI of an adapter was tested in the case of constant PWM, pe- riodic PWM, and chaotic PWM, respectively, and experimental results testify the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this article, we propose an enhanced one-cycle control (EOCC) strategy for high-voltage gain multicell converters, aiming to resolve the existing issues that exist in the conventional one-cycle control techniques, such as intolerance to load disturbances and inapplicability to multicell converters. The proposed EOCC method is able to overcome these limitations while effectively suppressing input voltage fluctuations and having great responsiveness. Simulation and experimentation on an improved four-cell switched inductor with the proposed EOCC are conducted, which agree well with the theoretical analyses and demonstrate a range of favorable features of the EOCC method, revealing its great feasibility and wide applicability. [ABSTRACT FROM AUTHOR]

This paper proposes a family of single-stage converters consisting of three different converters, each of which is able to produce a variety of waveforms through the waveform-subtraction technique. We brand this converter family as waveform-subtraction based single-stage converter (WSSC). By using only a single-stage converter, the proposed waveform generation technique is able to realize dc–dc–ac conversions and suppress input current ripple, meeting the needs of modernized power grid with renewable energy sources. At the same time, converters in this WSSC family are capable of generating a range of shapes, such as triangular, rectangular, and sawtooth waveforms, with simple structures, demonstrating its suitability of being applied in the electrochemical industry, e.g., in the electroplating process. Furthermore, the proposed family converters also realize substantially better input current ripple suppression compared to other conventional converters. In order to prove the validity and efficacy of the proposed WSSC and the theory underpinning it, in this paper, extensive simulations and analyses are conducted to verify the theoretical foundation of the proposed WSSC strategy, and the prototype of a converter from the proposed converter family is built and tested in our laboratory, which validates the functionality of the WSSC. [ABSTRACT FROM AUTHOR]

Designing of power electronics converters seldom considers multiscale coupling relationship between components and circuits. Although macroscale is computationally efficient, it barely contains the micro implications about aging, deterioration, transient performance, etc. Conversely, the microscale obtains multiple observation scope, however, with computational disaster. In this paper, the multiscale method is applied in the power electronic modeling which provides a qualitative methodology to combine the scales appropriately, and to obtain the dynamic response under the action of multiphysics accurately. Firstly, the concept of multiscale and the scale division of power electronic system are expounded. Considered the dynamic behavior of components and converters with different complexity, the framework of multiscale converters and modeling method is proposed. Afterwards, a scalable coupling separation method is presented, providing interfaces for the multiphysics and dielectric physics. Additionally, a multiscale conversion algorithm considering both efficiency and accuracy is designed. In the end, a DC/DC converter is taken for the verification. The feasibility and advantages of multiscale method and conversion algorithm have been demonstrated in accuracy, consistency and multiple analysis. By filling in the microscale observation, it is plausible to provide theoretical guidance for reducing margin, accurate analysis and reliability estimation of electronic components. [ABSTRACT FROM AUTHOR]

The magnetic resonant wireless power transfer (WPT) system with a class E inverter has wide application in mid-range power transmission, especially for several megahertz scenario. However, it is cumbersome for the existing modeling and analysis methods to obtain the analytical solution to the system variables, which limits the evaluation of system characteristic. This paper proposes a nonlinear mathematical model for the WPT system with a class E inverter. The equivalent small parameter method (ESPM) is first adopted to solve the proposed six-order nonlinear model, and symbolic-form steady-state periodic solutions are yielded. During the whole solving process, only three iteration steps are needed for the proposed method. Compared with other existing modeling and analysis methods, the symbolic periodic results acquired by the ESPM exhibit sufficient accuracy by virtue of the combination of more higher harmonics. Meanwhile, the calculation complexity is simplified remarkably. Simulation and available experiments validate the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Conventional parameter designs of two-stage grid-connected photovoltaic (PV) system relied on its mathematical model of the cascade structure (CS), but the procedure is excessively cumbersome to implement. Besides, for a two-stage converter system, the coupling interaction between the power converters can directly lead to a poor parameter design. To overcome this drawback, this paper uses a simplified structure (SS) of single-phase two-stage grid-connected PV system to better design the parameters of the front-stage dc-dc converter. After establishing the small-signal model for SS and CS in the PV system, the relative eigenvalue sensitivity is used as the criterion for judging the influence of some parameters on the stability of the two structures. The stable boundary of MPPT control parameters is compared and discussed in SS and CS, respectively. In addition, the relationship between the front-stage dc-dc converter and the rear-stage dc-ac inverter is analyzed by the modal participation factor calculated in CS. An experiment is also performed at the end of this paper to further verify the feasibility of using SS to design the parameters of the dc-dc converter in the PV system. [ABSTRACT FROM AUTHOR]

Nowadays, it is a trend to update electronic products by replacing the traditional wire charging with emerging wireless charging. However, other features of the products must generally be left unchanged, which limits the options in receiving coil design. As a result, asymmetric coil designs should be adopted in wireless charging systems. In this paper, a wireless power transfer system with asymmetric transmitting and receiving coils is modelled using circuit theory. The output power of the asymmetric system is analyzed, and the conditions of the maximum power splitting phenomenon are addressed in detail. Cases for different resonant frequency conditions are elaborated. The splitting frequencies and critical coupling coefficient are obtained, which are different and more complicated compared with the symmetric counterparts. Asymmetric coil designs can be adopted based on the proposed method, so that adequate and efficient output power transfer can be realized. Finally, the asymmetric coils design is utilized in an experimental prototype in order to contactlessly charge a portable power tool lithium-ion battery pack with 18 V DC and 56 W output through 220 V AC input, without altering its original configuration, and the correctness of proposed analysis can thus be verified. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

A high step-up DC–DC converter with active switched LC-network is proposed in this paper, which can be used in the photovoltaic system as the front-end stage to generate the required DC bus voltage. Based on the transformerless DC–DC converter with an active switched inductor (ASL) network, this proposed converter introduces an active switched capacitor (ASC) network, where only one capacitor and one diode are added, while the voltage gain is efficiently increased by a compound of ASL and ASC networks. The structure of the proposed converter is simple and voltage stresses on the additional diode and capacitor are low. In addition, unlike other voltage-boosting structures that utilized switched capacitor, the proposed converter avoids the extreme instantaneous currents of capacitor. The detailed analysis of the proposed converter and performance comparison with recently published ASL network-based converters are presented. Finally, a 100 W, 20/200 V prototype circuit is operated to verify its performance. [ABSTRACT FROM AUTHOR]

• Nonlinear Model and Characteristic Analysis of Fractional Order High Frequency Oscillator Yixuan Li, Yanfeng Chen, Fan Xie, Bo Zhang, Dongyuan Qiu, Chao Cheng. • Combined with the mechanism model of transistors, nonlinear mathematical model of the fractional-order oscillator is built in this manuscript. • The equivalent small parameter method is used to solve the nonlinear model, and an approximate analytical expression of the oscillator output voltage is obtained. • According to the properties of inductors and capacitors in the frequency selective network, the fractional-order capacitive feedback LC oscillators are classified and the influence of fractional orders on the characteristics of different types of fractional oscillators is revealed. Recently, fractional calculus theory has been widely used in various fields, including the design of oscillators. However, there are still some issues that need to be studied in depth. Firstly, it is necessary to classify the fractional-order oscillators according to the properties of the frequency selective network components, and analyze the influence of the fractional order of components on the characteristics of different types of fractional-order oscillators. Secondly, for fractional-order oscillators with nonlinear devices such as transistors, the traditional linear models cannot describe them accurately. Thirdly, due to the complexity of fractional differential equation, it is difficult to obtain the general analytical solution of the fractional-order oscillator. For these reasons, this paper takes the fractional-order capacitive feedback LC oscillator as an example, and establishes a nonlinear model of this oscillator based on the transistor characteristic mechanism. With the help of the equivalent small parameter method, the influence of the fractional-order characteristics of the components on the output waveform is analyzed. It is revealed that for the fractional-order capacitive feedback LC oscillator, the order of capacitance C 1 has the most significant effect on frequency and amplitude, followed by the order of inductance L 2 , and the order of the feedback capacitor C 2 has very little effect on the oscillator. In addition, although the introduction of fractional order increases the oscillation frequency, it will also lead to an increase in THD in some cases. Simulation and experimental results verify the correctness of the proposed nonlinear model and characteristic analysis of fractional-order high frequency oscillator. [ABSTRACT FROM AUTHOR]

This paper proposes a modeling and analysis method for fractional-order dc–dc converters operating in continuous conduction mode (CCM). As an example, a fractional-order boost converter is studied in detail. Instead of using fractional calculus, the method presented here uses a general state vector differential equation to describe the converter. By combining the principle of harmonic balance and equivalent small parameter method, an approximate analytical steady-state solution of the state variables could be obtained. Subsequently, the CCM-operating criterion of the converter is discussed based on the proposed method, and the appropriate parameters are provided to make sure that the fractional-order converter operates in CCM. In addition, a statistical analysis of harmonics is performed, from which the effects of fractional orders on harmonics can be observed. Moreover, numerical simulations are performed using the Adams–Bashforth–Moulton-typed predictor–corrector method and the Oustaloup's-filter-based approximation method. Both the dc components and ripples of the state variables obtained from these two methods are combined with those obtained by the proposed method, and they are in good agreement. Finally, the fractional-order capacitor and inductor are designed and verified by simulations, and on the basis of which experiments of the fractional-order boost converter are carried out to further verify the proposed method. [ABSTRACT FROM PUBLISHER]

In recent years, several large blackouts have drawn much attention to security problems in electric power transmission systems all over the world, which were triggered by initial minor disturbances and caused by cascading failures. Many models for cascading failures in power grids based on node attacks have been proposed, where only one kind of load is involved. In real power systems, however, strict measures are normally taken to protect the nodes, i.e. the power stations, so that failures at the nodes can hardly occur. It is much easier for transmission lines to break down, which may lead to cascading failures in entire power systems. Hence, a newmodel involving active and reactive loads and considering transmission line failures instead of node failures is proposed to understand cascading failures of power grids. When a transmission line breaks down, its load is redistributed to its neighbouring lines according to their respective capacities. It is well known that a power grid's topology and connectivity play a key role in determining its dynamic behaviour. Therefore, cascading failures of power grids with typical topologies, i.e. random, small-world and scale-free networks, are investigated using the model proposed and considering transmission line breakdowns. Finally, the model's effectiveness is validated employing real data of the European power grid. [ABSTRACT FROM AUTHOR]

A novel boost converter is proposed in this paper, which consists of three active Z-networks and is then named as a 3-Z-network boost converter. A distinct advantage of this proposal is that it can reach a high-gain voltage and well fulfill the stringent requirements from industry, particularly renewable power systems, to boost low voltage from clean sources such as photovoltaic (PV) arrays and fuel cells to high voltages for grid-connected converters. Corresponding to different states of the diodes and currents of the capacitors, six operational cases of the proposed converter, including two continuous-current modes (CCMs) and four discontinuous-current modes (DCMs), are analyzed. It is then followed with the parameters design. Finally, simulations and experiments are conducted to verify the effectiveness of the proposed converter. [ABSTRACT FROM PUBLISHER]

Applying an LC network into a half-bridge converter, a novel Z-source half-bridge converter is presented, in which less LC components are needed compared to the conventional one. This Z-source half-bridge converter can solve not only the problems of the shoot-through and limited voltage but also the problem of imbalance at the midpoint voltage of input capacitors. Furthermore, it can generate a broader range of output voltage values and much more kinds of waveforms, such as the varied positive or negative output voltages and the varied time ratio between positive and negative voltages, which are particularly desirable for some special power supplies, like the electrochemical power supply. Finally, the proposed converter is implemented in a prototype, and the experimental results can verify the effectiveness of the proposed converter. [ABSTRACT FROM PUBLISHER]

Quantifying nonlinear dynamic behaviors, such as bifurcation and chaos, in nonlinear systems are currently being investigated. In this paper, permutation entropy is used to characterize these complex phenomena in nonlinear direct current-direct current (DC-DC) converter systems. A mode switching time sequence (MSTS), containing the information from different periodic states, is obtained in a DC-DC converter by reading the inductor current when altering the switching mode. To obtain the nonlinear characteristics of this system, the concept of permutation entropy of symbolic probability distribution properties is introduced and the structure of the chaotic system is reproduced based on the theory of phase space reconstruction. A variety of nonlinear dynamic features of the DC-DC converter are analyzed using the MSTS and permutation entropy. Finally, a current-mode-controlled buck converter is reviewed as a case to study the quantification of nonlinear phenomena using permutation entropy as one of the system parameters changes. [ABSTRACT FROM AUTHOR]

A foreign metal object will deteriorate the performance of wireless power transfer (WPT) systems and cause insecurity issues. Therefore, the influence principles and rules of foreign metal objects on soft-switching conditions of Class-E inverters and the performance of WPT systems are developed in this paper. The effects of different metal materials on coil parameters at different frequencies and positions are analyzed first, then the effects of foreign metal objects on soft-switching conditions of Class-E inverters and the power transfer capability of WPT systems are investigated. Principle analyses and simulation results demonstrate that there are significantly different effects on the soft-switching conditions and power transfer when a foreign metal object is placed near the transmitter coil or the receiver coil. In addition, the monotonicity of the variation in power transfer also depends on the position of the foreign metal object. Finally, a WPT experimental prototype with a Class-E inverter is implemented to verify the influence principles and rules of foreign metal objects. The experimental results are highly consistent with the principle analyses and simulation results. [ABSTRACT FROM AUTHOR]

An omnidirectional magnetically coupled resonant wireless power transfer (WPT) system based on rotary transmitting coil is presented. The proposed scheme can ease the variations of the transfer efficiency and output power caused by the deviation of transfer direction, and improve the unbalanced power distribution phenomenon between the receivers, which are still not fully achieved in current WPT systems. The modified coupled-mode model is built first to describe the non-rotary multi-receiver WPT system. The analysis indicates that the transfer efficiency and output power of the system can be expressed as functions of the deviation angle between the transmitting coil and receiving coil, which has a non-negligible influence on the system performances. Then, the modified high order coupled-mode model containing time-varying parameters about the deviation angle is derived for the proposed omnidirectional WPT system. Theoretical analysis and simulated results indicate that this system can transfer power to multiple receivers around the transmitter synchronously and evenly, which is very suitable for wireless charging for household appliances indoors. The scheme feasibility and theoretical analysis are verified by experimental results. [ABSTRACT FROM AUTHOR]