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This paper proposes a resonant switching cell model to analyze and design the single-ended resonant dc–dc converters. The single-ended zero-voltage switching (ZVS) converters such as the Class E converter are efficient for megahertz switching because they feature low turn-on and turn-off switching losses. Also, they use only a ground-referenced switch, allowing a simple gate drive circuit. In this paper, we investigate the single-ended resonant converter with the small input inductance, whereas the conventional Class E converter has a large input inductance. The main contribution of this paper is to propose the resonant switching cell as an analytic model that simplifies the analysis and the design of the resonant dc–dc converters. Furthermore, this paper presents the design method of the resonant switching cell model for minimizing the resonant current magnitude and conduction loss while the converter maintains ZVS property. The experimental results from a 10-MHz GaN-based prototype demonstrate the feasibility and effectiveness of the analysis and design based on the proposed resonant switching cell model. [ABSTRACT FROM AUTHOR]

This paper is concerned with control-oriented modeling of a class of wireless power transfer systems with a phase-shift-controlled inverter. Two methods are investigated: the analytical modeling method, which is based on physical laws, and the refined instrumental variable method, which is based on sampled data. It shows that the former provides physical insights into the system, and that the resulting models will be accurate if the true circuit component parameters are a priori known. Otherwise, the model accuracy may decline. By contrast, the latter provides a cheap solution for accurate modeling, based only on a set of sampled input–output data, and the resulting model can capture very well the dynamic behavior of the system within a defined operating range. In real applications, it is always hard to know the actual circuit component parameters, since they may drift from the nominal values, due to some reasons such as the aging of circuit components and the variation of coil placement, making the analytical modeling method not very accurate. Therefore, to preserve the virtues of both methods, it is suggested to use them as a combination, that is, using the analytical modeling method to determine the model structure while using the data-driven modeling method to estimate the model parameters. All results derived in this paper are verified by means of both numerical simulation and experimental validation. [ABSTRACT FROM AUTHOR]

Miniature power semiconductor devices mounted on printed circuit boards (PCBs) are normally cooled by means of PCB vias, copper pads, and/or heatsinks. Various reference PCB thermal designs have been provided by semiconductor manufacturers and researchers. However, the recommendations are not optimal, and there are some discrepancies among them, which may confuse electrical engineers. This paper aims to develop analytical thermal resistance models for PCB vias and pads, and further to obtain the optimal design for thermal resistance minimization. First, the PCB via array is thermally modeled in terms of multiple design parameters. A systematic parametric analysis leads to an optimal trajectory for the via diameter at different PCB specifications. Then, an axisymmetric thermal resistance model is developed for PCB thermal pads where the heat conduction, convection, and radiation all exist; due to the interdependence between the conductive/radiative heat transfer coefficients and the board temperatures, an algorithm is proposed to fast obtain the board-ambient thermal resistance and to predict the semiconductor junction temperature. Finally, the proposed thermal models and design optimization algorithms are verified by computational fluid dynamics simulations and experimental measurements. [ABSTRACT FROM AUTHOR]

This paper proposes a predictive speed and current control with multi-timescale optimization in a cascade architecture for a permanent-magnet synchronous motor. Considering the difference of timescale characteristics for speed loop and current loop, different sampling times are assigned to the respective subsystem. In the prediction step of the conventional two-timescale system, the coupling between slow and fast sampling models is ignored and the output of the slow-sampling model at asynchronous sampling period is missing, which both weaken the prediction performance of the system. In this paper, the predictions of both slow and fast models for all the prediction instants are analyzed in detail. Besides, a linear estimation method based on virtual instants is proposed to improve the performance of the slow-sampling model for fast prediction instants. The data stream of the proposed method is designed based on the cascaded structure. The strategies are implemented on a field-programmable gate arrays taking advantages of parallel and pipeline processing techniques. Experimental results show that the proposed strategies have a better dynamic performance compared to the conventional method. [ABSTRACT FROM AUTHOR]

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]

One promising topology for solid state transformer (SST) is a modular multilevel cascaded converter, in which submodule is composed of dual active bridge (DAB) and H-bridge. For SST application in PV system, the efficiency could be severely affected especially for DAB due to the wide voltage and power range of PV panels. Thus, the motivation of this paper is to deal with the control strategy to improve DAB efficiency inside SST for PV application. Instead of utilizing time-domain based analysis method, which requires complex modeling process, this paper models DAB under frequency domain by fully considering the effect of both fundamental and harmonic frequency component. To achieve high efficiency operation, a multiorder reactive-current suppression (MRS) strategy is proposed by controlling phase shift angle as well as the duty cycles of primary and secondary side H-bridges. In terms of DAB controller design inside SST, the small signal model under MRS is established and a notch filter is implemented to suppress the second order line frequency fluctuation in the control loop. Finally, a 10 kV/1 MW SST prototype is introduced along with the system control structure and implementation method. The experiment of the submodule and SST confirms the effectiveness of proposed method. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of phase-locked loop (PLL) on the stability of LCL-type single-phase grid-connected asymmetrical cascaded H-bridge multilevel inverter (ACHMI) with synchronous reference frame proportional-integral (SRF-PI) grid current control under weak grid scenarios. The ACHMI system is composed of power stage circuit and control system, where the control system contains the dual-loop current control strategy established in the hybrid reference frame, the SRF-PLL, and the hybrid modulation method employed to synthesize the multilevel output voltage. The small-signal model of the whole ACHMI system is first established by using a simple step-by-step derivation method, and then, the small-signal analysis method is adopted to linearize the ACHMI, which is then utilized to derive the impedance model of the ACHMI system. Furthermore, an improved impedance stability criterion is derived, which is then employed to analyze the system stability. By using this criterion, the stability of the ACHMI can be evaluated with the variation of the bandwidth of PLL, the output power factor angle of the ACHMI, and the amplitude of the grid current reference signal under weak grid conditions. In this paper, a systematic design procedure for the optimal selection of the PI controller of the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system. With this design method, the dual-loop current control and PLL can be taken into account simultaneously when analyzing the stability margin of the ACHMI. Finally, the simulation and experimental results from a down-scaled grid-connected ACHMI prototype system are provided to confirm the validity of theoretical analysis. [ABSTRACT FROM AUTHOR]

In dc distribution networks, the parallel H-bridge dc/dc converters (HBDCs) are widely adopted to convert voltage levels with the higher power rating and reliability, in which the parallel HBDCs are naturally connected in input-parallel output-parallel (IPOP) form. However among IPOP HBDCs, there are complicated circulating currents that will influence the safe and steady operation of dc distribution networks. This paper focuses on the suppression of these circulating currents. First, the detailed mathematic models of circulating currents among IPOP HBDCs are derived. Through the model, it is found that various types of circulating currents exist in the system, including the circulating currents within the single HBDC and the circulating currents among the multiple HBDCs. Hence, the suppression of circulating currents among IPOP HBDCs is a multiobjective control problem. In this paper, it is proven that the conventional one degree of freedom control based on the bipolar modulation cannot eliminate all the circulating currents. Second, a novel two degrees of freedom control method is proposed to suppress all kinds of circulating currents based on the improved modulation way of HBDCs, which consists of two parts. The droop based control is used to suppress the circulating currents among the multiple HBDCs, whereas the common mode control is used to control the circulating currents within the single HBDC. All the theoretical analyses are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

This paper analyzes the limitations of a reduced-order model for modular multilevel converters (MMCs) by elucidating the relation between its accuracy, operating frequency, and converter parameters. A reduced-order simplifies the analysis of the MMC and thereby may provide additional information about the converter behavior. However, the accuracy of such model depends on several factors. In this paper, the effect of approximating the converter as a continuous system by neglecting quantization issues associated with having a finite number of modules is studied in detail. The analysis is done based on Fourier-series approximations with which it is possible to elucidate the relationship between the resonant frequencies of the MMC and the error of the reduced-order model. With the Fourier approximation, it is also possible to characterize resonant frequencies of the converter, both numerically and analytically, in terms of the converter parameters. The results can serve as a tool to identify situations when the reduced-order model produces good and also less accurate approximations especially when a low number of modules is available. [ABSTRACT FROM PUBLISHER]

An analytical steady-state model of the modular multilevel converter (MMC) can be used for component sizing and assessment of the impact of different parameters on the MMC performance. Thus, this paper proposes an enhanced steady-state model for the MMC, which enables one to calculate the amplitudes of the harmonic components of MMC arm currents, submodule capacitor voltages, and arm voltages. In addition, the proposed model allows for the calculation of the amplitude and phase angle of the modulating signal, and it also presents a criterion for resonance of the arm currents. This is achieved by means of a polynomial function of the modulation index, and through checking the stability criteria established by the proposed model. The capability of formulating the modulating signal enables a more accurate calculation of the steady-state amplitudes of the variables, as compared to the previously published models. This paper also presents an accurate method of submodule capacitor sizing, based on the proposed steady-state model. The proposed method gives the exact value of the submodule capacitance (i.e., the capacitance that results in dc voltage fluctuations within a desired range) for a prespecified submodule capacitor voltage variation and a given circulating current amplitude. The stability criterion given by the proposed steady-state model, used for sizing the arm inductance, and the submodule capacitor voltage variation given by the proposed capacitor sizing method, used for sizing the submodule capacitor, allows for the determining of the operating limits of the MMC in terms of its parameters. Extensive simulation results are presented to demonstrate the efficacy of the proposed steady-state model and the capacitor sizing method. Further, the results obtained from the proposed capacitor sizing method are compared with experimental results from the literature. [ABSTRACT FROM AUTHOR]

This paper proposes a decentralized current-sharing control strategy to endow fast transient response to paralleled dc–dc converters systems, such as dc microgrids or distributed power systems. The proposed controller consist of two main control loops: an external voltage droop control for current-sharing proposes and an internal current loop. The external droop control loop is designed as a voltage loop with embedded virtual impedance, which avoids the use of a slow voltage loop and a separate extra virtual impedance loop that may limit the system bandwidth. The internal current loop, thanks to the external control loop simplification, plays a major role in the system bandwidth, so that an adaptive proportional-integral (PI) controller is proposed for this matter. In the paper, two different droop control methods have been modeling, designed, simulated, and tested: The conventional virtual-impedance-loop based V–I droop and the proposed embedded-virtual-impedance based I–V droop. In order to compare the dynamic response performances between two droop controllers, their state-space models have been developed and analyzed in this paper. The results show that the dynamic response of the I–V droop control is faster than that of the conventional V–I droop control. Furthermore, by analyzing the effects from I–V droop control parameters, the errors can be reduced faster by enlarging the proportional terms, but with no fluctuations, and then completely eliminated by restoring back to small proportional values. Meanwhile, there exists a tradeoff phenomenon between the fast dynamic response and good steady-state performance; thus, an adaptive PI controller is proposed to both improve dynamic response and guarantee good steady-state performance simultaneously. Experimental results are shown to verify the accuracy of the models and the effectiveness of the proposed control framework. [ABSTRACT FROM PUBLISHER]

The modeling and control of a buck–boost and stacked dual half-bridge (DHB) integrated bidirectional dc–dc converter have been studied in this paper. This converter features high-voltage transfer ratio, high efficiency, and the minimum number of switches. In this paper, an extended, continuous, full-order, state-space averaging modeling method is proposed. Compared with existing methods, the proposed method exhibits higher coincidence with the switching circuit simulation, in steady and especially dynamic states. Due to its high dynamic accuracy and low complexity, the proposed modeling method provides a better theoretical analysis and a fast simulation tool for transient process and control design of converters with dual-active-bridge units, especially with DHB units. By using this method, the high-frequency transformer series inductance current is directly divided into a sampled dc component and a fluctuant component. Only the sampled dc one is included into state variables, but both components are considered into state equations. Besides, this method regards the entire converter as a linear superposition of its subsections, which provides a stepwise modeling based on linearization of subsections. Moreover, a decoupled proportional-integral control method is proposed to enhance the stability and dynamic response of the converter. This control method is analyzed by the proposed models, which can be regarded as an application of the proposed modeling method. Simulation and experiments have validated both the proposed modeling and the decoupled control strategy. [ABSTRACT FROM PUBLISHER]

Generally, battery-fed capacitive loads are charged to high voltages in series of switching cycles with smaller fragments of energy delivered to the load in every cycle to ensure an efficient charging process. In high voltage low power (HVLP) flyback charging circuit, significant portion of input energy drawn from the source in a cycle is utilized by the effective parasitic capacitance of the HV transformer and semiconductor devices and circulated back to the source at the end of the cycle. This reduces the energy delivered to the load per cycle and hence the net energy delivered in the charging process. In this paper, an energy-based analysis and simplified energy-based model for HVLP charging circuits is derived. An energy-based approach is appropriate to describe and define the HVLP converter behavior in terms of load energy component and circulating energy component. The derived energy-based model is extended to obtain analytical closed-form expressions governing the essential parameters of the charging circuit. The proposed energy-based model and analytical formulation of essential parameters are experimentally validated on a 0–2.5 kV programmable high voltage charging circuit prototype fed from 12 V input battery source. [ABSTRACT FROM AUTHOR]

Design optimization of magnetic components, which considers both electrical and thermal performance, can help in designing power converters with a high power density. This paper proposes an approximate analytical model for thermal resistance of inductor and transformer windings, including litz wire, which only requires knowledge of thermal properties of constituent materials and geometric dimensions. The model is based on regular square and hexagonal packing of insulated wires and is derived by integration of infinitesimal thermal resistances along a specified heat flow path. The model closely agrees with finite-element analysis (FEA) and can be used in place of time-consuming FEA as part of larger thermal network models for magnetic components. The model is also experimentally validated using a toroidal inductor with a litz-wire winding; the model has less than 12% error compared to the experimental measurement. Application of the model for practical windings, including litz-wire windings, is also discussed. The model can be used during the design process of magnetic components of a switching power converter to evaluate the temperature and potential hot spots. The model provides closed-form results, hence fast computation times, and so can be used in design optimization procedures. [ABSTRACT FROM AUTHOR]

EMC spectrum analyzers are popularly used for electromagnetic interference (EMI) measurement in power electronics systems. Depending on the specifications of EMI standards, the EMI measurement could be very time consuming. Conventionally, the fast Fourier transform is used to derive the EMI spectrum from the measured time-domain waveforms. However, these results may not agree with the measurement results from spectrum analyzers, and sometimes the difference could be significant. In this paper, a technique to quickly and accurately predict and analyze the EMI spectrum from time-domain waveforms is proposed. The technique is developed based on the spectrum analyzer's operating principle and the requirements of EMI standards. The EMI spectra of three modulation schemes are also analyzed. Theoretical analysis, simulations, and experiments were all conducted. The predicted peak, quasi-peak, and average EMI matches the measured EMI in whole conductive frequency range. The developed technique can accurately predict EMI using much shorter time than conventional EMC spectrum analyzers and it saves cost of expensive spectrum analyzers. [ABSTRACT FROM AUTHOR]

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology can fulfill the requirements of time-varying spatial positions of loads in mid-range applications, as it can generate a rotating magnetic field around sending coils, and effectively reduce the limits of spatial positions on transfer characteristics including output power and transfer efficiency. Nevertheless, the design of coils parameters and control strategies put a great influence on the realistic transfer characteristics, which should be considered elaborately in practice. In this paper, a three-phase MCR WPT system with cylinder-shaped coils is investigated, the equivalent circuit model is built to carry out the theoretical analysis. Based on that, the influence on zero-voltage-switching (ZVS) conditions of power switches and the output power of the system, resulting from different phase-shifted angles between each phase, coil turns and angular misalignments of the receiving coil, is analyzed comprehensively. Detailed discussions on relationships among coil turns, the angular misalignment, ZVS conditions, and the output power are completed under different phase-shifted angles. Furthermore, the parametric optimization of coil turns, as well as phase-shifted angles, are proposed to ensure the power switches realize ZVS and ensure the system realize stable output power within the full range of angular misalignment. Finally, experiments are carried out to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed optimal design. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) systems in dynamical applications, such as roadway-powered electrical vehicles, require dynamical models for the analysis and control. Conventional modeling methods for WPT systems lead to high-order models as each resonant voltage or current is described by two slowly varying real-valued variables. Other modeling methods may reduce the order but suffer from disadvantages, such as the lack of analytical expressions, loss of generality, and incomplete modeling. This paper develops a systematic and intuitive modeling approach using time-domain dynamic phasors and proposes reduced-order models by applying appropriate s-domain approximations to the linear parts of the system. A dual-side pulse-density-modulation WPT system is completely modeled as an example. Both the equivalent circuits and the mathematical descriptions are presented. The derived models are verified by large-signal step responses and small-signal frequency responses measured during experiments. As compared with the full-order models, the proposed reduced-order models have much more concise formulae while retaining high accuracy. [ABSTRACT FROM AUTHOR]

Recent studies have shown how synchronization units of converters operating nearby may interact with each other, affecting the stability of the system. Synchronverters are able to self-synchronize to the grid without the need of a dedicated unit because they can reproduce the power synchronization mechanism of synchronous machines. Recently, the robust stability of a synchronverter has been investigated by means of structured singular values (commonly called $\mu$ -analysis). In this paper, $\mu$ -analysis is performed to investigate how the robust stability of a synchronverter is affected by the presence of another converter of the same type operating in parallel. It is demonstrated that the parallel operation of synchronverters reduces their robust stability and a possible solution is proposed, based on the implementation of virtual impedances in the control algorithm. An accurate state-space model of the system under study is developed by adopting the component connection method and the robust stability analysis is validated against time-domain simulations in MATLAB/Simulink/PLECS and experimental results with a power-hardware-in-the-loop test bench. [ABSTRACT FROM AUTHOR]

To analyze the radiated electromagnetic interference generated by isolated power converters, this paper proposes a technique to develop a general radiation model for the converters. The radiated electric field can be predicted from the developed model. The interaction between the impedance of the converter and the undesired antenna in the converter's power delivery paths is explored in detail based on the developed model. Moreover, a dual active bridge converter is taken as an example to demonstrate the developed modeling technique based on the converter's topology. The radiated electric field of the dual active bridge converter is predicted from the developed model. Experiments are conducted to validate the developed model and the predicted interaction between the converter impedance and the undesired antenna impedance in the power delivery paths. [ABSTRACT FROM AUTHOR]

Owing to the high operation frequency and fast switching speed, gallium nitride (GaN) devices are prone to the false turn-on phenomenon, causing high switching loss, shoot through, and even sustained oscillation. However, most of research on false turn-on aims at the enhancement-mode GaN devices, whereas there is still little published research on GaN devices in cascode configuration due to the comparatively complicated structure and various parasitic components. This paper conducts a comprehensive and in-depth study for the problem of false turn-on in cascode GaN devices based half-bridge circuits, which has a great guiding significance in the device selection, printed circuit board (PCB) design, and debugging of cascode GaN converters. In this paper, a novel analytical model of the device suffering false turn-on is first developed, with all the parasitic parameters being fully considered. Based on the model, the quantitative and accurate expression of the induced gate-to-source voltage is derived, which can serve as a precise and significant reference for judging and evaluating the false turn-on problems. Then, the influences of device and circuit parameters on the peak value of induced voltage are first investigated in detail, providing a reliable guidance for the usage and PCB design of cascode GaN devices based half-bridge converters. What's more, guidelines to effectively suppress the false turn-on phenomenon are also given, which can be adopted both in the design and debugging process of cascode GaN applications. Finally, all the theoretical calculations and analysis are verified by experiments with satisfying results and performances. [ABSTRACT FROM AUTHOR]

This paper presents new analytical equations, parametrized with respect to the number of converter phases, for multiphase isolated dc–dc topologies. This paper describes five multiphase isolated converter models, as well as their level of accuracy. Based on these new parametric models, a thorough comparative among various common high-power converter topologies is carried out, highlighting the best topology regarding efficiency, cost, and power density. The analytical results are firstly compared and verified using PLECS simulation software, and validated finally by experimental measurements with a 10-kW/20-kHz/500-V configurable laboratory prototype. Due to the low computation cost and accuracy, the developed analytical models provide important insights for optimization-based design methodologies. Furthermore, this paper highlights, depending on the targeted application and objectives, the benefits of each analyzed converter configuration. [ABSTRACT FROM AUTHOR]

Nowadays, the use of mathematical optimization techniques to design power converters has become more and more attractive. This paper goes a step further in studying the influence of some specifications (e.g., the input voltage of the converter) or model parameters (e.g., the transformer heat-transfer coefficient) on the multiobjective optimal design of isolated dc-dc converters. A response surface methodology (RSM) approach is used in combination with a multiobjective optimal design tool dedicated to such power converters and using genetic algorithms. At each time, two factors are studied while two response variables are of interest, namely, the power loss and the weight of the converter. The pairs of factors are: the input voltage and the output power, the current and voltage ripples (through the inductor and across the capacitor of the output filter), and, finally, the convection heat-transfer coefficient and the maximal isolation transformer temperature. It should be pointed out that the full-bridge topology is considered in this paper but the proposed methodology is easily applicable to other topologies. It can also be extended to study other factors or other responses of interest. [ABSTRACT FROM AUTHOR]

The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion. [ABSTRACT FROM AUTHOR]

Multiple loops have been used extensively to enhance the system performance in various applications. However, the increasing complexity of multi-loop systems also makes them much more difficult to analyze and implement. In this paper, a new methodology to analyze multi-loop system is proposed. In the proposed framework, multi-loop systems are regarded to be built upon of sub-modules of cascade, parallel adding, and feedback units, and then, they are simplified following a certain procedure based on the correlation of the Bode characteristics of the segmented sub-modules. Applying this methodology, the Bode plot and the transfer function of the system can be easily obtained with the system properties of gains, zeros, and poles. Two examples are provided as demonstrators, including a multi-loop low-dropout regulator (LDO) from literature, and a newly designed multi-loop LDO aiming at enhancing the stability over a wide load range, which show that the Bode plot and the transfer function can be obtained more intuitively and rapidly. Excellent agreements among theory, simulations, and measurements are confirmed, which verify the proposed method. It can help designers to gain more intuitions and insights on multi-loop systems from both circuit and device perspectives, which is also an effective tool for both stability analysis and circuit design. [ABSTRACT FROM AUTHOR]

Models that accurately predict the output voltage ripple magnitude are essential for applications with stringent performance target for it. Impact of the dc input ripple on the output ripple for a frequency-controlled series resonant converter (SRC) using a discrete-domain exact discretization modeling method is analyzed in this paper. A novel discrete state-space model along with a small-signal model for the SRC considering three state variables is presented. The audiosusceptibility (AS) transfer function that relates the input-to-output ripple is derived from the small-signal model. Analysis of the AS transfer function indicates a resonance peak and an expression is derived connecting the AS resonance frequency for the input ripple based on the SRC component values. Further analysis is done to show that a set of values for the SRC parameter exists, which forms a design space, for which the normalized gain offered by the SRC for the input ripple is less than unity at any input ripple frequency. A test setup to introduce the variable frequency ripple at the input of the SRC for the experimental evaluation of the AS transfer function is developed. Influence of stray parameters on the AS gain, AS resonance frequency, and on the SRC tank resonance frequency is evaluated. An SRC is designed at a power level of 10 kW. The analysis using the derived analytical model, simulations, and experimental results are found to be closely matching. [ABSTRACT FROM AUTHOR]

For a general multi-coil magnetic coupling wireless power transfer (MC-WPT) system with different coil properties and non-negligible cross couplings, there is no analytical solution that connects the resonant frequencies of the system to its electric parameters. Establishing such a generalized analytical solution not only permits quantitative analysis of resonant points but also provides a generic platform for the physical interpretation of resonance. For this purpose, a novel modeling and analysis method of integrating time domain and frequency domain is proposed in this paper, with that all possible resonant points of arbitrary coil MC-WPT systems can be quickly and accurately determined. First, an accurate state-space model of a general MC-WPT system with arbitrary number of transmitters, repeaters, and receivers is established and the analytical current response on each circuit is derived. Then, several key system concepts about resonance are elucidated, based on which the generalized analytical expressions of resonant points of MC-WPT systems, including resonant frequencies and corresponding powers and efficiencies, are derived. Furthermore, the physical interpretation along with the mathematic relationships of several key easy-confusing concepts are deduced, which provides a systematic theoretical criteria for the selection of operating frequency to achieve the resonant states for MC-WPT systems. [ABSTRACT FROM AUTHOR]

Taking switching transients of switching devices into consideration in design and simulation of power electronic systems has long been a huge obstacle. Sufficient accuracy has to be ensured, meanwhile more significantly the transient model has to be practical, i.e., providing a convergent result with an acceptable solving speed and a convenient parameter extraction technique. Aiming at both targets, this paper proposes a piecewise analytical transient (PAT) model for switching device commutation unit, taking an IGBT–p-i-n diode pair as an example. A piecewise time-varying voltage source-current source pair is utilized to model the IGBT–p-i-n diode pair. With sufficient accuracy, PAT modeling methodology noticeably increases the solving speed and improves the convergence of converter simulations. Model expressions and datasheet-driven parameter extractions are illustrated in detail. Experimental and simulated results are presented and compared to validate both the accuracy and the practicability of the proposed PAT model, expected to be employed in transient simulations of power electronic systems. [ABSTRACT FROM AUTHOR]

The small-signal impedance modeling of a modular multilevel converter (MMC) is the key for analyzing resonance and stability of MMC-based power electronic systems. The MMC is a power converter with a multifrequency response due to its significant steady-state harmonic components in the arm currents and capacitor voltages. These internal harmonic dynamics may have great influence on the terminal characteristics of the MMC, which, therefore, are essential to be considered in the MMC impedance modeling. In this paper, the harmonic state-space (HSS) modeling approach is first introduced to characterize the multiharmonic coupling behavior of the MMC. On this basis, the small-signal impedance models of the MMC are then developed based on the proposed HSS model of the MMC, which are able to include all the internal harmonics within the MMC, leading to accurate impedance models. Besides, different control schemes for the MMC, such as open-loop control, ac voltage closed-loop control, and circulating current closed-loop control, have also been considered during the modeling process, which further reveals the impact of the MMC internal dynamics and control dynamics on the MMC impedance. Furthermore, an impedance-based stability analysis of the MMC-high-voltage direct current connected wind farm has been carried out to show how the HSS-based MMC impedance model can be used in practical system analysis. Finally, the proposed impedance models are validated by both simulation and experimental measurements. [ABSTRACT FROM AUTHOR]

In this paper, the third quadrant behavior of a high-voltage superjunction mosfet (SJ-FET) in cascode configuration (CC) with a low-voltage silicon mosfet is deeply studied by means of an analytical model and experimental data. The third quadrant dynamic behavior of the SJ-CCs is compared to the standalone counterparts by evaluating their reverse recovery time (tRR), reverse recovery peak current (IRRM), and reverse recovery charge (QRR). An analytical model and experimental results show that the SJ-CC avoids or mitigates the activation of the SJ-FET body diode during the third quadrant operation. As a consequence, the SJ-CC strongly improves the widely used figure-of-merit RON·QRR, which considers the on-state resistance of the transistors (RON). In addition, the results obtained using an SJ-CC are similar or better than those achieved by SJ-FETs with enhanced reverse recovery (i.e., irradiated SJ-FETs). This paper also includes a comparison with commercial wide bandgap switches, concluding that the RON·QRR value provided by the SJ-CC is around eight times higher than that provided by a commercial GaN cascode. [ABSTRACT FROM AUTHOR]

This paper presents a detailed analysis of short-circuit current behavior during interturn short-circuit faults in permanent magnet synchronous machines (PMSMs) by considering the short-circuit contact resistance. For this purpose, an finite element analysis (FEA)-based equivalent circuit model is developed to understand the circulating current behavior in the shorted turns. Various fault resistance and number of shorted turn combinations are examined at different torque and speed levels. To include saturation due to high fault currents, the inductance matrix of faulty machine is created in FEA environment and incorporated into the equivalent circuit model as four-dimensional lookup tables. In order to take loop responses into account, the model is controlled through field oriented control (FOC) with closed speed and current loops. An experimental setup is built to verify the simulation results using a PMSM with several winding taps. It is shown that the experimental results and the simulations are quite consistent with each other. The findings from this study are essential to predict fault severity, develop mitigation techniques and determine the safe operating area for faulty machines. [ABSTRACT FROM AUTHOR]

LLC resonant converters have gained popularity in a wide number of industrial applications due to their high efficiency and power density. Common applications of these converters are battery chargers, electric vehicles, and high-efficiency power supplies, which require tight output voltage regulations. However, traditional averaging techniques employed in pulse width modulation converters cannot be employed for LLCs. As a consequence, designing linear controllers for these types of converters requires complex analysis or applying empirical methods. This paper proposes a simple and straightforward methodology for designing linear controllers for LLC resonant converters. A dual-loop control scheme including an inner current loop and an outer voltage loop is introduced. A simplified second-order equivalent circuit is employed to derive all the relevant equations for designing the compensators. Simulations and experimental results using a 150-W platform are employed to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Stability analysis of average value models (AVMs) of vector-controlled modular multilevel converters (MMCs) is the subject matter of this paper. Stability analysis of fundamental frequency phasor-based AVMs of MMCs can be conducted in a traditional linear time-invariant framework through eigenvalue computation. This class of models does not consider circulating current control loop and hence fails to capture system instability that occurs in a certain range of gains of the circulating current controller. We propose stability analysis in a linear time-periodic (LTP) framework to solve this issue. To that end, a nonlinear AVM is presented that considers the submodule capacitor insertion dynamics and takes into account the output and the circulating current control schemes in the vector control approach. Upon linearization, an LTP model is derived from this averaged model. It is shown that the Poincar \acutee multipliers are indicative of system instability corresponding to a certain range of gains of the circulating current controller. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth critical discussion and derivation of a detailed small-signal analysis of the phase-shifted full-bridge (PSFB) converter. Circuit parasitics, resonant inductance, and transformer turns ratio have all been taken into account in the evaluation of this topology's open-loop control-to-output, line-to-output, and load-to-output transfer functions. Accordingly, the significant impact of losses and resonant inductance on the converter's transfer functions is highlighted. The enhanced dynamic model proposed in this paper enables the correct design of the converter compensator, including the effect of parasitics on the dynamic behavior of the PSFB converter. Detailed experimental results for a real-life 36 V-to-14 V/10 A PSFB industrial application show excellent agreement with the predictions from the model proposed herein. [ABSTRACT FROM AUTHOR]

V2Ic control provides very fast dynamic performance to the Buck converter both under load steps and under voltage reference steps. However, the design of this control is complex since it is prone to subharmonic oscillations and several parameters affect the stability of the system. This paper derives and validates a very accurate modeling and stability analysis of a closed-loop V2Ic control using the Floquet theory. This allows the derivation of sensitivity analysis to design a robust converter. The proposed methodology is validated on a 5-MHz Buck converter. The work is also extended to V2 control using the same methodology, showing high accuracy and robustness. The paper also demonstrates, on the V2 control, that even a low bandwidth-linear controller can affect the stability of a ripple-based control. [ABSTRACT FROM AUTHOR]

Stability analysis of power converters in ac networks is complex due to the nonlinear nature of the conversion systems. Whereas interactions of converters in dc networks can be studied by linearizing about the operating point, the extension of the same approach to ac systems poses serious challenges, especially for single-phase or unbalanced three-phase systems. A general method for stability analysis of power converters suitable for single-phase or unbalanced ac networks is presented in this paper, based on linear time periodic theory. A single-phase grid-connected inverter with phase-locked loop (PLL) is considered as case study. It is demonstrated that the stability boundaries can be precisely evaluated by the proposed method, despite the nonlinearity introduced by the PLL. Simulation and experimental results from a 10-kW laboratory prototype are provided to confirm the effectiveness of the proposed analysis. [ABSTRACT FROM PUBLISHER]

Flying capacitor photovoltaic (PV) inverters have been widely discussed in the literature. However, the relevant leakage current issues have not received much attention. In this paper, the modulation techniques for a transformerless three-phase flying capacitor PV inverter are investigated for the leakage current suppression. First, the theoretical analysis of the system common mode model and leakage current is presented. Second, three kinds of conventional carrier-based modulation techniques are evaluated, and results indicate that they fail to effectively suppress the leakage current. Third, a new carrier modulation and logic function is presented. It is able to maintain the constant common mode voltage, and consequently, the leakage current can be significantly reduced. Finally, the experimental tests are conducted on a transformerless three-phase flying capacitor PV inverter to verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper presents a simple method to analyze the behavior of feedback loops that contain a naturally-sampled single-edge pulse-width modulator. A small-signal model is derived by means of simple geometric arguments. It is shown how this small-signal model can be used to analyze the stability of the continuous-time pulse-width modulated feedback loop by using standard $z$-domain techniques. The strategy relies on familiar concepts like transfer functions and small-signal gains and does not require any in-depth knowledge of nonlinear systems. A simple design process, where the continuous-time compensator is designed directly in the $z$-domain, is developed and detailed design equations are derived for a PI current regulator. It is shown how the proposed strategy can accurately predict instability that cannot be explained by means of the well-known average model of the pulse-width modulator. The theoretical analysis is confirmed by means of detailed time-domain simulations. The mechanisms that lead to instability are discussed and an equation for the critical loop gain is derived. [ABSTRACT FROM PUBLISHER]

In high-power applications, parallel operation is required to improve both efficiency and reliability. In an LLC converter, it is difficult to achieve parallel operation due to the gain sensitivity to component tolerance. This paper proposes a new structure of a common resonant capacitor for a multiphase LLC converter, which can achieve very good current-sharing performance with no additional components or control. To evaluate the current-sharing performance, a new first harmonic approximation (FHA) model is built in this paper to analyze the LLC converter with coupled resonant tanks. Both FHA analysis and powersim (PSIM) simulation results demonstrate the load-sharing improvement of the proposed common capacitor LLC resonant converter over the conventional two-phase LLC converter. The current-sharing performance from the FHA analysis and the PSIM simulation are compared, and the error of the FHA analysis is evaluated and explained. A 600 W two-phase LLC converter prototype based on the proposed method is also built to verify the feasibility. Excellent current-sharing performance (6% resonant current sharing error at a wide load range) has been achieved. [ABSTRACT FROM PUBLISHER]

For isolated dc–dc power converters, the interwinding parasitic capacitance of the transformer is usually one of the main paths for common-mode (CM) noise. In order to simplify the CM noise analysis, this paper proposes a two-capacitor transformer winding capacitance model. The model is derived based on general conditions so it can be applied to different isolated converter topologies. A measurement technique is also proposed to obtain the lumped capacitance for the model. The CM noise models of several isolated converter topologies are analyzed with the proposed two-capacitor transformer winding capacitance model to achieve simplicity. Finally, the proposed transformer winding capacitance model and measurement technique are verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

Dual active bridge (DAB) converters have been widely used in distributed power systems and energy storage equipment. However, the inherent nonlinearity of the DAB converters can cause stability problem, such as output voltage oscillation. In this paper, the dynamic behavior and stability of a digitally controlled DAB converter with a closed-loop controller are studied. First, to accurately study the nonlinear dynamics and stability in a DAB converter, a bilinear discrete-time model considering the output capacitor equivalent series resistance (ESR) and the digital control delay in circuit is established. Based on the model, the nonlinear dynamic characteristic and stability of the DAB converter versus the control parameter are studied. Furthermore, extensive analyses are performed to study the effect of the transformer leakage inductance and the output capacitor ESR on the stability boundaries of the control parameter. The accuracy of the model and the theoretical analyses are validated by simulation and experimental results. The proposed model of the digitally controlled DAB converter can accurately predict the stability boundaries, which can be effectively applied to the design of the system parameters and guarantee stable operation of the converter. [ABSTRACT FROM AUTHOR]

An increasing number of power-electronic-based distributed generation systems and loads generate not only characteristic harmonics but also unexpected harmonics. Several methods, such as impedance-based analysis, which are derived from the conventional average model, are introduced to perform research about the harmonic interaction. However, it is found that the linear-time-invariant-based model analysis makes it difficult to analyze these phenomena because of the time-varying properties of the power-electronic-based systems. This paper investigates a grid-connected converter by using the harmonic state-space (HSS) small-signal model, which is based on a linear time-varying periodically theory. The proposed model can include the switching behavior of the model, where it makes the model possible to analyze how harmonics are transferred into both the ac-side and dc-side circuits. Furthermore, a harmonic matrix of the grid-connected converter is developed to analyze the harmonic interaction at the steady-state behavior. Besides, the frequency-domain results are compared with time-domain simulation results by using the HSS modeling to verify the theoretical analysis. Experimental results are finally discussed to verify the proposed model and study. [ABSTRACT FROM PUBLISHER]

A comprehensive method of electromagnetic emission interference (EMI) reduction in dc/ac inverters through periodic dithering of the pulse-width modulated (PWM) switching frequency is presented in this paper. The periodic dithering is the process of changing the switching frequency of the PWM signal that drives the switches of the power electronics inverter. The effects of the various parameters involved in the PWM dithering process have been analyzed in this paper. The important parameters involved in the dithering process are the frequency range used for dithering, the periodic time of the dithering signal, and the phase of the dithering signal. The effect of each of these parameters has been studied to determine their values that minimize the EMI. Additionally, analytical expressions for theoretical prediction of the EMI levels at different frequencies have been derived for performance analysis during the design stage. The theoretical predictions for the dithering signals have been found to accurately correlate with both the simulation and experimental results. [ABSTRACT FROM AUTHOR]

All the interconnected regulated systems are prone to impedance-based interactions making them sensitive to instability and transient-performance degradation. The applied control method affects significantly the characteristics of the converter in terms of sensitivity to different impedance interactions. This paper provides for the first time the whole set of impedance-type internal parameters and the formulas according to which the interaction sensitivity can be fully explained and analyzed. The formulation given in this paper can be utilized equally either based on measured frequency responses or on predicted analytic transfer functions. Usually, the distributed dc–dc systems are constructed by using ready-made power modules without having thorough knowledge on the actual power-stage and control-system designs. As a consequence, the interaction characterization has to be based on the frequency responses measureable via the input and output terminals. A buck converter with four different control methods is experimentally characterized in frequency domain to demonstrate the effect of control method on the interaction sensitivity. The presented analytical models are used to explain the phenomena behind the changes in the interaction sensitivity. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) devices enable more compact and efficient design of applications such as traction inverters and rectifiers. With miniaturization of power electronics, the volume and weight of heatsink or cold plate occupies a significant portion. So, thermal design, especially power loss evaluation, is crucial to the whole system. Analytical switching model based on datasheet parameters is usually adopted to evaluate devices’ switching loss due to its convenience. However, when applied on SiC metal-oxide-semiconductor field-effect-transistors (mosfets), turn-on waveforms of conventional analytical switching model show obvious discrepancy from experiments at both current rising and voltage falling stages. The transfer and capacitance characteristics from datasheet are responsible for that. Due to short channel effect and drain-induced barrier lowering, transfer characteristic during turn on period varies with different drain-to-source voltage vds. Cgd during actual turn on period is also different from that on the datasheet. So, considering the actual turn on process, dynamic transfer characteristic and Qgd are proposed and measured in this paper. After these modifications, switching-on waveforms of the analytical switching loss model match the experiments very well, and error of the estimated loss is less than 5%. [ABSTRACT FROM AUTHOR]

The wind power generation techniques are continuing to develop and increasing numbers of doubly fed induction generator (DFIG)-based wind power systems are connecting to the on-shore and off-shore grids, local standalone weak networks, and microgrid applications. The impedances of the weak networks are too large to be neglected and require careful attention. Due to the impedance interaction between the weak network and the DFIG system, both subsynchronous resonance (SSR) and high-frequency resonance (HFR) may occur when the DFIG system is connected to the series or parallel compensated weak network. This paper will discuss the SSR and the HFR phenomena based on the impedance modeling of the DFIG system and the weak networks, and the cause of these two resonances will be explained in details. The following factors will be discussed in this paper: 1) transformer configuration; 2) different power scale of DFIG system with different parameters; 3) L or LCL filter adopted in the grid side converter (GSC); 4) rotor speed; 5) current closed-loop controller parameters; and 6) digital control delay. On the basis of the analysis, active damping strategies for HFR using virtual impedance concept will be proposed. [ABSTRACT FROM AUTHOR]

The impedance-based model of doubly fed induction generator (DFIG) systems, including the rotor part (rotor side converter (RSC) and induction machine), and the grid part (grid side converter (GSC) and its output filter), has been developed for analysis and mitigation of the subsynchronous resonance (SSR). However, the high-frequency resonance (HFR) of DFIG systems due to the impedance interaction between the DFIG system and parallel compensated weak network is often overlooked. This paper, thus, investigates the impedance characteristics of DFIG systems for the analysis of HFR. The influences of the rotor speed variation, the machine mutual inductance and the digital control delay are evaluated. Two resonances phenomena are revealed, i.e., 1) the series HFR between the DFIG system and weak power grid; 2) the parallel HFR between the rotor part and the grid part of DFIG system. The impedance modeling of DFIG system and weak grid network, as well as the series HFR between DFIG system and parallel compensated weak network has been validated by 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]

In this paper, average modeling and analysis of a dual-supercapacitor bank, actively balanced by a bidirectional buck–boost converter, is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed-loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Therefore, dynamical equations of the system are developed in order to derive the switching-cycle-averaged model and reveal the tradeoff between current limit level, balancing time and efficiency for the worst case of imbalance. Simulations and experiments support the presented findings. [ABSTRACT FROM PUBLISHER]

Through coupling the impedance network between the grid and the conventional indirect matrix converter (IMC), the LC-filter-integrated quasi-Z-source (qZS) IMC overcomes the 0.866 voltage gain limitation of the conventional IMC and also avoids the input filter that is required to mitigate current harmonics of the conventional qZS matrix converters. This paper further investigates the voltage boosting and LC filtering function of the LC-filter-integrated qZS IMC. The voltage gain, the filtering function, and qZS network parameters design are presented using a small-signal model and circuit analysis. Simulation and experimental results validate the built model, the voltage gain analysis, and the parameters design of this type of qZS IMC. The input current of the LC-filter-integrated qZS network is compared to the conventional Z-source and qZS IMCs to investigate the integrated LC filtering capability. The experimental results verify that the LC-filter-integrated qZS network provides the necessary filtering function. Thus, the traditional input filter can be eliminated, which reduces the cost, power loss, volume, and weight for the overall system, when compared with the other conventional topologies that require the input filter, even those with impedance-source networks. [ABSTRACT FROM PUBLISHER]

The layout of power modules is one of the key points in power module design, especially for high power densities, where couplings are increased. In this paper, along with the design example, automatic design processes by using a genetic algorithm are presented. Some practical considerations and implementations are introduced in the optimization of module layout design. [ABSTRACT FROM AUTHOR]