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This paper proposed a simple strategy for parameters identification of switched reluctance motor (SRM) direct instantaneous torque control. This strategy without rotor locking includes measuring and calculating steps. In the measuring step, flux linkage curves with current at three critical positions are obtained. At the intermediate position, flux linkage curve is measured under current chopper control (CCC). At the aligned and unaligned position, flux linkage curves are measured when the winding is given a voltage pulse. In the calculating step, the whole flux-linkage characteristics with current and position can be calculated based on the measured critical curves. Then torque curves are calculated for direct instantaneous torque control. Meanwhile, the i-Ψ loci curves during CCC operation are analyzed for identifying adjusting advance angle. In this way, the entire flux linkage characteristics and adjusting advance angle parameters under different operating area are obtained. This strategy is applied to a 7.5 kW 12/8 SRM for direct instantaneous torque control (DITC). Experiments have been carried out to verify the effectiveness and accuracy of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper presents a robust control strategy to improve dc-link voltage control performances for grid-connected converters (GcCs). The proposed control strategy is based on an adaptive proportional integral (PI) controller and is aimed to ensure fast transient response, low dc-link voltage fluctuations, low grid current total harmonic distortion, and good disturbance rejection after sudden changes of the active power drawn by the GcC. The proportional and integral gains of the considered adaptive PI controller are self-tuned so that they are well suited with regard to the operating point of the controlled system and/or its state. Several simulation and experimental results are presented to confirm and validate the effectiveness and feasibility of the proposed dc-link voltage control strategy. [ABSTRACT FROM PUBLISHER]

This paper presents the framework for the applications of double-source wireless systems in charging for movable electronic devices. To acquire the real-time mutual inductances between the receiving coil and the transmitting coils, a detection strategy on the basis of primary parameters (currents and voltages) is introduced, which can replace the wireless communications between the receiving side and the transmitting side. Coordinated control of two source voltages is employed to deal with the power fluctuation of load, which is caused by load position variations. In specific, the constraint of two source voltages, which can maintain the output power stable, is derived. Based on these feasible combinations of source voltages, numerical calculations are further carried out to identify the optimized voltage combination, which can achieve high power transfer efficiency. Finally, an experimental prototype is built up and the results show that the proposed coordinated control strategy can minimize power fluctuation and maintain relative high efficiency at the same time. [ABSTRACT FROM PUBLISHER]

This paper proposes a simplified small-signal model for output voltage control of a single-phase asymmetrical cascaded H-bridge multilevel inverter (ACHMI). The ACHMI is an n-series connected H-bridge converter, each one with a unique value at the dc link and usually scaled at 1:2:6:… or 1:3:9:…. By assuming that the small-signal variation component is equal in all n converter terminal ports, a simplified small-signal model is obtained. This assumption is carefully described and justified. To verify the veracity of the proposed model, two distinct control strategies are applied. One is a single-loop control scheme based on a modified proportional-integral (PI) controller. The other one is a double-loop control scheme based on a PI controller with feedforward action of the load current. Both controllers are tuned based on the dynamic behavior of the proposed model. Since the designed controllers based on the simplified model make the ACHMI output voltage to follow the reference without steady-state error, the proposed simplified model truly represents the inverter. Experimental results show the efficacy of the simplified model of the ACHMI through the two mentioned control strategies as well as the ACHMI installed in a microgrid. [ABSTRACT FROM PUBLISHER]

Switched capacitor converters with ideal switches exhibit discontinuities in the electrical variables, i.e., state jumps at the switching time instants. This feature introduces some difficulties for the determination of compact dynamic models for these power converters. In this paper, we tackle the issue by considering a switched model where the dynamics of the modes are represented through differential algebraic equations. For this class of systems the classical averaged model fails. By including a suitable jump mode that approximates the state discontinuities, a generalized frequency-dependent averaged model is proposed. The effectiveness of the switched and averaged models is numerically and experimentally verified by analyzing the ladder, series–parallel, Fibonacci, and Dickson topologies, and by considering different switching frequencies, voltage sources, and circuits parameters. [ABSTRACT FROM PUBLISHER]

This paper proposes a star-channel modular multilevel converter (MMC). It overcomes the zero/low-fundamental-frequency operation issues of conventional MMC while not injecting the common-mode voltage (CMV). The proposed converter is characterized by the cross connections of upper three arms and lower three arms through two sets of star-channel branches. These star-channel branches rebalance the power among three phase legs, resulting in minimized submodule capacitor voltage ripples even at zero/low-fundamental-frequency operation without CMV injection. This feature enables the proposed converter to interface medium/high-voltage DC and variable-frequency AC systems. A 4160-V 1-MW simulation model is performed in MATLAB/Simulink, and a 208-V 5-kW experimental setup is constructed in the lab. Both of the simulation and experimental results verify the feasibility of the proposal. [ABSTRACT FROM PUBLISHER]

Direct torque control (DTC) has been recently used for the development of high-performance five-phase induction motor (IM) drives, where normal operation of the system has been usually considered and the ability of DTC to manage the situation has been analyzed in comparison with different rotor-field-oriented control (RFOC) strategies. The exploitation of fault-tolerant capabilities is also an interesting issue in multiphase machines, where the utility of RFOC controllers has been stated when the open-phase fault operation is considered. In this paper, the performance of DTC and RFOC controllers based on proportional resonant regulators and predictive control techniques is compared when an open-phase fault appears in a five-phase IM drive. Experimental tests are provided to compare the performance of the system using these control alternatives. [ABSTRACT FROM PUBLISHER]

This paper proposes a simple control method of induction motors (IMs) with improved dynamic response and steady-state performance by using a model-based predictive control algorithm. The predictive torque control (PTC) method analyzes the relationship between the electrical torque and stator voltage of IMs by using the stator voltage vector magnitude to obtain the reference voltage vector angle and accurately control the electrical torque. However, the conventional PTC method has a fixed reference voltage vector magnitude and thus has a large torque ripple in the steady state and slow dynamics in the transient state. The proposed PTC method is based on mathematical equations, which allow minimization of torque error and calculation of a relevant reference voltage to establish a better dynamic response in the transient state and accurate control performance in the steady state. Excellent steady-state performance and a quick dynamic response of the proposed method are proved by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the thermal models which can physically reflect the heat-flow paths in a lightweight three-phase half-bridge two-level SiC power module with six MOSFETs and can be used for coupled electrothermal simulation. The finite-element (FE) model was first evaluated and calibrated to provide the raw data for establishing the physical resistor–capacitor (RC) network model. It was experimentally verified that the cooling condition of the module mounted on a water cooler can be satisfactorily described by assuming the water cooler as a heat exchange boundary in the FE model. The compact RC network consisting of 115 R and C parameters to predict the transient junction temperatures of the six MOSFETS was constructed, where cross-heating effects between the MOSFETs are represented with lateral thermal resistors. A three-step curve fitting method was especially developed to overcome the challenge for extracting the R and C values of the RC network from the selected FE simulation results. The established compact RC network model can physically be correlated with the structure and heat-flow paths in the power module, and was evaluated using the FE simulation results from the power module under realistic switching conditions. It was also integrated into the LTspice model to perform the coupled electrothermal simulation to predict the power losses and junction temperatures of the six MOSFETs under switching frequencies from 5 to 100 kHz which demonstrate the good electrothermal performance of the designed power module. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel sensorless speed estimation for an induction motor (IM) based on a new stator-voltage model reference adaptive system (Vs-MRAS) scheme. This is utilized for torque-controlled drive (TCD) based on indirect rotor field oriented control technique in limp-home mode operation of electric vehicles (EV) applications. The Vs-MRAS scheme uses the error between the reference and estimated stator-voltage vectors and estimates the synchronous speed. Unlike existing MRAS schemes, the proposed sensorless scheme does not require the measured nominal values of stator resistance, stator inductance, and rotor resistance. This scheme is insensitive to variations of the aforementioned parameters. Moreover, using the proposed scheme eliminates the need for slip calculation. The proposed scheme is implemented and experimentally tested in a lab environment, on a 19-kW IM, and also applied on an electric golf buggy, powered by a 5-kW IM. The experimental results show that the proposed scheme is immune to parameter variations and is consistent in vehicle-starting from standstill and hill-starting tests. This scheme is also free from drift problems associated with a pure integration and is stable in the field weakening region. The test-drive results from the golf buggy confirm suitability of the proposed Vs-MRAS scheme over a wide range of speeds for the purpose of TCD in EV applications. [ABSTRACT FROM PUBLISHER]

Detailed thermal dynamics of high-power IGBT modules are important information for the reliability analysis and thermal design of power electronic systems. However, the existing thermal models have their limits to correctly predict these complicated thermal behavior in the IGBTs: The typically used thermal model based on one-dimensional RC lumps have limits to provide temperature distributions inside the device; moreover, some variable factors in the real-field applications like the cooling and heating conditions of the converter cannot be adapted. On the other hand, the more advanced three-dimensional (3-D) thermal models based on finite-element method (FEM) need massive computations, which make the long-term thermal dynamics difficult to calculate. In this paper, a new lumped 3-D thermal model is proposed, which can be easily characterized from FEM simulations and can acquire the critical thermal distribution under long-term studies. Meanwhile, the boundary conditions for the thermal analysis are modeled and included, which can be adapted to different real-field applications of power electronic converters. Finally, the accuracy of the proposed thermal model is verified by FEM simulations and experimental results show a good agreement. [ABSTRACT FROM PUBLISHER]

Silicon carbide (SiC) power metal–oxide–semiconductor field-effect transistors (mosfets) have been applied in high-power and high-frequency converters recently. To effectively predict characteristics of SiC power mosfets in the design phase, a simple and valid model is needed. In this paper, a simple improved SiC power mosfet behavioral model is proposed using SPICE language. Key parameters in the model are analyzed and determined in detail, including parasitic parameters of the power module, steady-state characteristic parameters, and nonlinear parasitic capacitances. The effect of negative turn-off gate drive voltage is considered and a continuously differentiable function is proposed to describe the gate–source capacitance. Experimental validation is performed under a double pulse circuit employing an N-channel power mosfet half-bridge module CAS300M12BM2 (Cree Inc.) rated at 300 A/1200 V. The main switching dynamic characteristic parameters of the model have been compared with those of the measured results. The results show that taking gate–source capacitance as a linear value as most previous models do will cause significant turn-on deviations between experiment and simulation results, while the improved model is more accurate compared with the measured results. [ABSTRACT FROM AUTHOR]

In this paper, a new duty cycle control method is proposed to reduce torque and flux ripples of the conventional direct torque control (DTC). In the proposed method, a new approach is initially introduced to select the appropriate active voltage vector (VV) precisely. Then by inserting the zero VV along with the selected one, a finite set of new candidate VVs with different duty cycles are synthesized. Finally, the model predictive control method is employed to select the appropriate VV among the candidate ones to reduce flux and torque errors. Simulation and experimental studies are conducted to show the good performance and the superiority of the proposed method over classical DTC and model predictive control methods. As a result, lower torque and flux ripples are achieved in the proposed method. Furthermore, the proposed method works with almost a fixed switching frequency for all speed ranges. [ABSTRACT FROM PUBLISHER]

A main design constraint of the digitally controlled power electronics converters is the time delay of control systems, which may lead to the reduced control loop bandwidth and even unstable dynamics. Numerous time-delay compensation methods have been developed, of which the model-free schemes are independent to model accuracy whereas the model-based alternatives are sensitive to system modeling. This paper first presents a graphical illustration of four model-free delay compensation techniques, where their principles and performances are intuitively elaborated and compared by means of the impulse area equivalence method. An improved time-delay compensation approach is then proposed based on additional area insertion, which provides a wider frequency of phase compensation. Finally, the dynamic response of an LCL-filtered grid-connected inverter was tested with the studied delay compensation methods. Simulations and experimental test results validate the effectiveness of the graphical comparisons and the proposed approach. [ABSTRACT FROM PUBLISHER]

A phase-locked loop (PLL) is a closed-loop feedback control system that estimates the frequency as well as phase of an input signal. The most commonly deployed synchronization method in three-phase applications is a type-2 synchronous reference frame PLL. With pre/in-loop selective harmonic filtering stage, type-2 PLLs can obtain good detection speed, decent stability margins, and better disturbance rejection. However, it suffers from the finite steady-state phase error during ramp change in input signal frequency. To tackle this challenge type-3 PLLs have been developed recently, either by adding a feed-forward path to the PLL structure, or by using a second-order controller as the loop filter. However, recent analysis carried out of type-3 PLLs show that they aggravate stability problem and compromise the performance in terms of detection speed and disturbance rejection. A new concept of synchronization is proposed in this paper that obtains the performance of type-3 PLL but retains all the advantages associated with type-2 PLL. Extensive experimental results are provided to validate the proposed work. [ABSTRACT FROM AUTHOR]

This paper proposes a unified impedance model of grid-connected voltage-source converters for analyzing dynamic influences of the phase-locked loop (PLL) and current control. The mathematical relations between the impedance models in the different domains are first explicitly revealed by means of complex transfer functions and complex space vectors. A stationary (αβ-) frame impedance model is then proposed, which not only predicts the stability impact of the PLL, but also reveals its frequency coupling effect. Furthermore, the impedance shaping effects of the PLL on the current control in the rotating (dq-) frame and the stationary ( αβ-) frame are structurally comapred. The frequency-domain case studies on a three-phase grid-connected converter are next presented, and subsequently validated in time-domain simulations and experimental tests. The close correlations between the measured results and theoretical analysis confirm the effectiveness of the stationary-frame impedance model. [ABSTRACT FROM AUTHOR]

This paper presents a current sensorless technique for current-driven full-bridge dc/dc converters. The proposed technique is able to precisely estimate the transformer current and in turn input/output current of the converter. Since the high-frequency current is estimated, different current-based modulations schemes (e.g., self-sustained oscillating control (SSOC), modulators for synchronous rectifications, etc.) can be implemented using the proposed current sensorless technique. In the proposed technique, the current is estimated using the precise model of dc/dc converters instead of the averaged model. Thus, the accurate current waveform is derived within a switching cycle. The mathematical analysis of the system observability and the practical concerns related to the implementation of the proposed technique are also described in detail. Experimental results on a current-driven dc/dc converter are presented to show the feasibility of the proposed technique and verify its performance. [ABSTRACT FROM AUTHOR]

The modular multilevel converter is one of the most attractive converter topologies for high-voltage dc transmission systems, but it needs at least 10 min during the system uncontrolled precharge stage to verify the stability and reliability of submodules (SMs), making the capacitor static voltage balancing a key issue. This paper proposes a novel method based on self-power supply control for balancing capacitor static voltage. Because of the influence of self-power supplies on capacitor voltages, the method can keep the capacitor static voltage balanced by controlling the input characteristic of SMs self-power supplies. The control signals of self-power supplies have a fixed frequency and duty ratio, and they can be determined based on capacitor voltage sorting results and self-power supply output support capacitor. Compared with previous works, this method has less computation, and it does not rely on IGBTs and additional complex circuits except for the self-power supplies. This can save on the software and hardware costs. The proposed method also leads to improved equalizing resistances and reduced active power losses of the SMs. Simulations and experimental studies were conducted, and the results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a detailed power loss model for a microinverter with three different zero voltage switching boundary conduction mode (BCM) current modulation methods. The model is used to calculate the optimum peak current boundaries for each modulation method. Based on the power loss model, a dual-zone modulation method is proposed to further improve the microinverter efficiency. The proposed modulation method provides two main benefits: the addition of one more soft switching transition and low inductor peak current. The additional soft switching transition reduces switching losses by means of zero current switching. The lower peak current boundary reduces inductor rms current and conduction losses as well as allowing the output filter inductor to be smaller and more efficient. An improved BCM peak current control method was proposed and implemented on a microinverter prototype. The control circuit provides a highly accurate representation of the filter inductor current waveform and also provides galvanic isolation that simplifies control circuit design. The experimental results on a 400-W three-phase half-bridge microinverter validate the theoretical analysis of the power loss distribution and demonstrate that further improvement in efficiency can be achieved by using the proposed dual-zone modulation method. [ABSTRACT FROM AUTHOR]

LLC resonant converter is a nonlinear system, limiting the use of typical linear control methods. This paper proposed a new nonlinear control strategy, using load feedback linearization for an LLC resonant converter. Compared with the conventional PI controllers, the proposed feedback linearized control strategy can achieve better performance with elimination of the nonlinear characteristics. The LLC resonant converter's dynamic model is built based on fundamental harmonic approximation using extended describing function. By assuming the dynamics of resonant network is much faster than the output voltage and controller, the LLC resonant converter's model is simplified from seven-order state equations to two-order ones. Then, the feedback linearized control strategy is presented. A double loop PI controller is designed to regulate the modulation voltage. The switching frequency can be calculated as a function of the load, input voltage, and modulation voltage. Finally, a 200 W laboratory prototype is built to verify the proposed control scheme. The settling time of the LLC resonant converter is reduced from 38.8 to 20.4 ms under the positive load step using the proposed controller. Experimental results prove the superiority of the proposed feedback linearized controller over the conventional PI controller. [ABSTRACT FROM PUBLISHER]

The series connection of IGBTs is essential for high-voltage applications where fast switching performances need to be maintained. However, unbalanced voltage sharing is a major resistance to the converter application of this structure. There are a number of causes leading to voltage unbalance, such as different signal delays, parasitic parameters, tail currents, and so on. A temporary clamp scheme performed by active voltage control (AVC) has been proven to be effective in solving the unbalanced voltage-sharing issue. However, the basic physics has not been investigated. In this paper, the physical principle of voltage unbalance within IGBTs series operation is discussed. The carrier storage region differences are concluded to be the intrinsic cause of unbalanced voltage sharing. By using an accurate Fourier-series-based IGBT simulation model with appropriate assumptions, a physical explanation for temporary clamp is provided in detail. At the end of the tail current period when the excess carrier concentration becomes close to the intrinsic doping density, the temporary clamp is able to achieve satisfactory equal voltage sharing. [ABSTRACT FROM PUBLISHER]

A discrete time domain modeling and analysis for the current-mode-controlled (CMC) buck LED driver with slope compensation is presented in this paper. The discrete time domain equation representing the buck LED driver is derived and linearized about the equilibrium state. Also, the switching control law, the proportional-integral compensator is used here as an example of the error amplifier, is linearized about the equilibrium state. The linearized buck LED driver and the control law are then combined to arrive at a linearized CMC buck LED driver. The root-locus method is employed to analyze the closed-loop system. The design guidelines and experimental results for the CMC buck LED driver are presented. [ABSTRACT FROM PUBLISHER]

Power electronic systems are prone to instability. The problem, generally attributed to the constant power load (CPL) behavior of their power electronic controlled loads, can become more acute when the systems are subject to parametric uncertainties. The structured singular value (SSV) based $\mu$ method has proven to be a reliable approach for assessing the stability robustness of such uncertain systems. Despite its numerous benefits, the $\mu$ method is not often applied to electrical power systems (EPS) with multiple uncertainties. This may be due to the mathematical complexity underlying the $\mu$ theory. This paper aims to make the $\mu$ approach more application-friendly by providing clearer insights into the meaning and usefulness of the robust stability measure $\mu$ for EPS with multiple parametric uncertainties. This is achieved by presenting a methodology for translating $\mu$ analysis results from the frequency domain to the more perceivable uncertain parameters domain. The method directly demonstrates dependences of system stability on uncertain system parameters. Further, it clearly identifies robust stability domains as subsets of the much wider stability domains. The work is based on a representative EPS connected to an ideal CPL. $\mu$ analysis predictions are evaluated and validated against analytical results, for example, CPL system. [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 power electronic applications, aging of the electric double layer capacitors (EDLCs) is considered as a serious issue since it may lead to failure. Their degradation is usually evaluated by an increase of the internal resistance or a decrease of the equivalent capacitance. These aging indicators have a good correlation with the supercapacitor's state-of-health (SoH). Generally, SoH is measured by electrochemical impedance spectroscopy (EIS). However, this technique must be performed offline and requires interruption of the system's operation. In this paper, a sliding mode observer is designed to estimate online the EDLC's aging indicators. Unlike several online estimators, the supercapacitor's parameters are considered as a nonlinear random distribution with external noises which yields accurate estimation. In addition, the relationship between the capacitance and the bias voltage is considered to be nonlinear. Lyapunov stability analysis is also provided. The proposed approach is validated experimentally using a standardized dynamic current profile. Furthermore, comparison against EIS is carried out for different aging phases and under different environmental temperature conditions. [ABSTRACT FROM PUBLISHER]

The objective of this paper is to propose an efficiency model to evaluate the impact of the pulse width modulation (PWM) duty cycle jitter on the efficiency of switching-mode power converter. By taking the product of two perturbation terms into consideration, which is ignored in the conventional average small-signal model, the average efficiency model is proposed first. Due to the nonlinear characteristic of the PWM generator, the multifrequency efficiency model is also developed by considering the sideband frequency. Three different perturbation waves are induced to the control loop of the converter to generate the jitter to observe its impact on the efficiency. The mathematical expression of the efficiency drop based on the proposed multifrequency model is derived. The reason of control-to-output gain's magnitude spike on the Bode plot can be explained by the derived equations. Eventually, the methods to reduce the efficiency drop caused by the jitter are suggested. In spite of various perturbation frequencies, amplitudes, and waveforms, the mathematical calculation, the computer simulation, and the hardware measurement of the efficiency drop are consistent which validate the accuracy of the proposed multifrequency efficiency model. [ABSTRACT FROM AUTHOR]

To maximize solar photovoltaic (PV) output under dynamic weather conditions, maximum power point tracking (MPPT) controllers are incorporated in solar PV systems. However, the occurrence of multiple peaks due to partial shading adds complexity to the tracking process. Even though conventional and soft computing techniques are widely used to solve MPPT problem, conventional methods exhibit limited performance due to fixed step size, whereas soft computing techniques are restricted by insufficient randomness after reaching the vicinity of maximum power. Hence, in this paper, a new flower pollination algorithm (FPA) with the ability to reach global peak is proposed. Optimization process in FPA method performs global and local search in single stage and it is a key tool for its success in MPPT application. The ruggedness of the algorithm is tested with zero, weak, and strong shade pattern. Further, comprehensive performance estimation via simulation and hardware are carried out for FPA method and are quantified with conventional perturb and observe and particle swarm optimization (PSO) methods. Results obtained with FPA method show superiority in energy saving and proved to be economical. [ABSTRACT FROM AUTHOR]

Inverters and loads can freely connect to any node in a meshed parallel inverters system, leading to variations of line impedance between two nodes and the structure of the electric network. More challenges exist for proportional load-sharing control in such a system. An improved proportional load-sharing strategy for a meshed parallel inverters system with complex impedances is proposed in this paper. The RL-type droop method is modified through injecting the power droop information of all other inverters, which can improve the load-sharing accuracy to some extent and completely compensate the voltage amplitude and frequency deviations caused by droop equations under accurate load-sharing conditions. Besides, an adaptive virtual resistance tuned by the integral of the linear combination of output active and reactive powers, is added to eliminate load-sharing errors. In addition, the central controller broadcasts the control variables to all inverters. This improves the simultaneity of control data and minimizes the mismatch of control delay. Three modified droop methods are compared with the small-signal analysis and simulation. Experimental results are presented to investigate the performance of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

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]

Predictive torque control (PTC) is based on the prediction of motor torque and stator flux for all possible voltage vectors of power converter. These predictions are derived from a mathematical model of the motor that depends on the motor parameters. But, these parameters may not match with their actual values. These parametric uncertainties lead to inaccurate predictions of torque and stator flux and affect the performance of the predictive algorithm. This paper presents a modified PTC for a permanent magnet synchronous motor to reduce the torque ripple at the presence of parametric uncertainty by improving the prediction accurateness. Simulation and experimental results are provided to show the effect of the proposed method. [ABSTRACT FROM PUBLISHER]

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]

Recently, riding through grid faults and supporting the grid voltage by using grid-connected converters (GCCs) have become major requirements reflected in the grid codes. This paper presents a novel reference current generation scheme with the ability to support the grid voltage by injecting a proper set of positive/negative active/reactive currents by using four controlling parameters. Analytical expressions are proposed to obtain the optimal values of these parameters under any grid voltage condition. The optimal performances can be obtained by achieving the following objectives: first, compliance with the phase voltage limits, second, maximized active and reactive power delivery, third, minimized fault currents, and fourth reduced oscillations on the active and reactive powers. These optimal behaviors bring significant advantages to emerging GCCs, such as increasing the efficiency, lowering the dc-link ripples, improving ac system stability, and avoiding equipment tripping. Simulation and experimental results verify the analytical results and the proposed expressions. [ABSTRACT FROM PUBLISHER]

This paper presents the method of modeling single-inductor dc–dc converters with thermal phenomena in the inductor taken into account. The electrothermal models of an inductor and semiconductor devices in the form dedicated for SPICE are proposed. Using the proposed models, the electrothermal analysis of buck and boost converters was performed for the inductor with cores made of different ferromagnetic materials. It was proved that nonlinearity of the inductor characteristics and thermal phenomena occurring in this element should be taken into account when the converter operates at high frequency range (over 200 kHz), especially for the inductor with the powder core. [ABSTRACT FROM PUBLISHER]

Wireless power transfer using near-field inductive coupling is the predominating technology to power up wireless devices such as radio frequency identification tags, sensors, and medical implants. Miniaturization is a new key requirement for the application in the internet of things and implantable medical devices. Realization of efficient RF power transfer using conventional techniques based on 900 MHz and 2.4 GHz is difficult, mainly due to the relatively large wavelength in these bands. On the other hand, conventional inductive coupling is very inefficient as the device becomes very small, limited by the small coupling factor and operating frequency. In this paper, we utilize a multicoil transmitting (Tx) array to power up very small receiving (Rx) devices in the near field by boosting the power gain to a much higher level. The power gain boosting is achieved by operating the array close to its self-resonance frequency and optimizing the phase relationship of the array elements. To validate the proposed technique, we implemented a prototype printed circuit board (PCB) to power a 1 cm  $\times$  1 cm small Rx coil at a distance of 20 cm. To demonstrate the improvement on power gain, we designed a 3  $\times$  3 Tx coil array composed of nine 3 cm  $\times$ 3 cm elements, as well as an individual large Tx coil with the same dimension of the array for fair comparison. Measured results show that the transducer power gain can be increased by 16.4 dB with the proposed technique. [ABSTRACT FROM PUBLISHER]

Inductive power transfer power supplies for electric vehicle charging in dynamic applications need to tolerate large variations in coupling and tuning with varying loads. This paper investigates the use of a buck converter to regulate the input voltage to a fixed frequency unidirectional switch push–pull converter to meet the requirements of dynamic charging. The presented circuit is optimized to remove some of the additional components introduced. A mathematical model is presented that shows the circuit is capable of operating while extremely mistuned in both the inductive and capacitive regions while maintaining sinusoidal currents. A controller design is also presented allowing constant primary current operation, safe start up, and operation under no load conditions. A 5-kW prototype was built and validated when operated with a dynamic load under severely mistuned conditions. [ABSTRACT FROM PUBLISHER]

Traditionally, the current control of grid-tied converters with LCL filter is based on proportional-resonant or proportional-integral controllers, which often need an additional active damping method to achieve stability. These solutions do not permit to place the closed-loop poles in convenient locations when dealing with such high-order plants. This constraint results in degraded reference-tracking and disturbance-rejection responses. On the other hand, the existing methods based on direct pole placement or other modern control strategies, do not control with zero steady-state error both positive and negative sequences of the grid current, but only the positive one. This limitation is undesirable under unbalanced grid conditions. This paper presents a current controller for grid-tied converters with LCL filters based on direct discrete-time pole placement. The proposed controller makes it possible to control both positive and negative sequences of the grid-side current with zero steady-state error. Contrarily to the classical resonant controllers, the closed-loop poles can be placed in convenient locations, yielding a fast response with negligible overshoot and low controller effort. Moreover, no additional damping methods of the resonance are necessary to achieve stable operation, regardless of the switching frequency and LCL filter used. Simulation and experimental results that validate the proposal are presented. [ABSTRACT FROM PUBLISHER]

This paper presents a feedback/feed-forward control strategy to improve the voltage balancing of modular multilevel converters (MMCs) under unbalanced grid conditions. The inclusion of a feed-forward compensation improves the disturbance rejection capability against asymmetrical faults and sudden voltage imbalances in the ac grid. The floating capacitor voltages of the MMC are controlled in two stages. The first one equally distributes the voltages in each arm, and the second one balances the energy among the six arms. This last control stage is also divided into the called horizontal and vertical balancing. Based on a detailed analysis of the power terms disturbing the MMC arm energies, the control strategy is tailored to improve the voltage transient response by adding feed-forward terms to both horizontal and vertical balancing controls. In addition, various approaches to manage the MMC under unbalanced grid conditions are compared regarding several aspects, such as capacitor voltage ripple, balancing performance, and negative-sequence current injection. Advantages and disadvantages of both the proposed and the conventional energy-based control schemes are also studied, showing that the voltage control performance can be improved by enhancing the existing MMC control systems. [ABSTRACT FROM AUTHOR]

Averaged modeling is a commonly used approach used to obtain mathematical representations of VSC-based systems. However, essential characteristics mainly related to the modulation process and the harmonic distortion of the signals are not able to be accurately captured and analyzed. The extended harmonic domain (EHD) has recently been seen as an alternative modeling framework since it allows us to consider the harmonic interaction explicitly. However, there is not a clearly established methodology to derive the EHD models in the presence of power electronic switches. This paper presents a generalized methodology based on the switching instants to obtain large-signal EHD models of VSC-based power systems. Three model order reduction approaches are also proposed to address the increased size of the resulting EHD models. Analytic formulas of three modulation techniques: sinusoidal pulse-width modulation, third harmonic injection pulse-width modulation, and space vector pulse-width modulation are provided to obtain the open-loop large signal EHD models. A performance assessment of the proposed modeling approach in respect to model size, the computational time and the accuracy is presented based on simulations and experimental case studies. The obtained results show that the resulting EHD models are accurate and reliable, while the memory and computation time are improved with the proposed model order reductions. [ABSTRACT FROM AUTHOR]

Diode–capacitor-based dc–dc converters provide a simple and low cost solution for high step-up voltage regulation in solar and fuel cell generation. Transient modeling analysis reveals their worse influence of nonlinear and nonminimum-phase system characteristic due to right-half-plane (RHP) zero, especially in high voltage gain application. However, the process of energy transfer for diode–capacitor-based dc–dc converter is different from basic dc–dc converter. Based on the unique feature, this paper proposes an improved main circuit structure with parallel connection of resistive–capacitive damping network across the intermediate capacitor to achieve good dynamic performance. By optimal parameter design according to Routh–Hurtwitz criterion, all the RHP zeros in the transfer function of control-to-output voltage are eliminated completely. Then, by the case of diode–capacitor-based boost converter, the adaptive PI controller is designed to deal with nonlinear characteristic of voltage gain. It gets good dynamic performance under wide range output voltage. All the theoretical findings and design approaches are verified by simulation and experiment results. The existing diode–capacitor-based high step-up dc–dc converters with slight main circuit modification are more promising in renewable energy application. [ABSTRACT FROM AUTHOR]

Like any electric energy storage system, supercapacitors have a limited lifetime. Indeed, they degrade with time because of parasitic reactions between electrodes and electrolyte. Porous electrodes are complex structures and pores have size dispersion because of manufacturing processes. This paper proposes to study the specific impact of supercapacitor floating ageing on different pore sizes using a multipore model. The multipore model is an equivalent electrical circuit model, capable of representing impedance behavior of supercapacitor in full range of its operating frequencies and classifying different sized pores by their impedance parameters. This paper first presents a link between pore sizes and impedance parameters of the modeling circuit. Then, floating ageing experiments are carried out using three samples from two different manufacturers. Multipore model impedance parameters evolution is monitored and discussed. Finally, a new representation of ageing processes is proposed by pore size and for different ageing phases. [ABSTRACT FROM AUTHOR]

Distributed energy resources (DERs) are expected to provide ancillary functions including reactive power generation and harmonics compensation. Meanwhile, multilevel inverters and two-level converters with optimal pulsewidth modulation (OPWM) will be commonly used for DERs at high power levels. The challenge is to realize harmonic compensation with limited switching angles. This paper presents an online solution to realize the selective harmonics compensation (SHC), and power generation with DERs. For harmonics compensation, the selective harmonic components in the load current are detected. Then, the harmonic voltages are provided with DERs to cancel out these detected components. Since the power converter is requested to realize both harmonics filtering and power generation, limitations on harmonics compensation at the given power are discussed. Power hardware-in-the-loop-based online verifications are shown at the end of the paper. [ABSTRACT FROM AUTHOR]

Recent uninterruptible power supply (UPS) systems, in the medium power range (a few 100 kW), are based on a three-power stage topology including a rectifier, an inverter, and a dc-dc converter. The dc-dc converter ensures the charger/discharger function necessary for battery management. The monolithic intercell transformer (ICT) described in this paper is dedicated to such a charger/discharger, of which the nominal power is 137 kW. This dc-dc converter is comprised of eight interleaved cells that are interconnected by the ICT. The first part of this paper briefly presents the full UPS system and the topology of the eight-cell charger/discharger arranged around the eight-phase monolithic ICT. The second part suggests a model and emphasizes the design specificities of the monolithic ICT. The final design is provided by an optimization routine, checked in the end by different 2-D and 3-D finite-element simulations, both electromagnetic and thermal. The third part describes the construction of the ICT prototype. It is then placed in a test bench that reproduces the conditions of future operations and provides current balance conditions. Finally, the experimental results obtained for the 137-kW nominal power validate design parameters and confirm the interest of the ICT solution. [ABSTRACT FROM AUTHOR]

The transmission-line busbar filter is an innovative high-density electromagnetic interference (EMI) containment solution for power electronics systems. It uses the concept of the transmission-line EMI filter as a part of the power interconnection to eliminate the EMI noises in power converters. This paper presents a systematic study of the transmission-line busbar filter in a motor drive system, which includes its design, modeling, and improvement using a hybrid approach. The paper investigates the relationship between the busbar filter's in-circuit attenuation and its geometry, and then derives a general design guideline for the transmission-line busbar EMI filters. To improve the performance of the transmission-line busbar filter, the paper proposes a hybrid busbar filter combining a transmission-line busbar filter and a one-turn inductor. This improvement provides much higher attenuation than the traditional transmission-line busbar filters. These proposed concepts have been verified experimentally not only with small-signal measurement but also with in-circuit tests in a medium-power motor drive system. [ABSTRACT FROM AUTHOR]

Bidirectional inductive power transfer (BD-IPT) systems are high-order resonant circuits, which are complex in nature and sensitive to variations in system parameters and control variables. Consequently, modeling and design of BD-IPT systems are relatively difficult in comparison to unidirectional IPT systems. An accurate model that predicts the behavior of BD-IPT systems under different operating conditions is invaluable but yet to be reported. This paper, therefore, proposes a generalized steady-state model through which the behavior of BD-IPT systems can be accurately characterized. The proposed mathematical model is comprehensive and includes the effects of harmonics and sensitivity to variations in system parameters and control variables. Using the model, this paper investigates the behavior and sensitivity of BD-IPT systems under a range of practical operating conditions. The validity of the proposed generalized model, which is verified using the results of a 1-kW prototype system, provides a clear insight into BD-IPT systems and is expected to be useful at both design and implementation stages. [ABSTRACT FROM AUTHOR]

This paper presents a method for design and control of dc-bus capacitance and transients in a renewable single-phase grid-connected converter. Conventionally, a proportional (P) or proportional-integrating (PI) controller is commonly used and the design stage is performed using trial-error or using a simplified analysis that does not take the dynamics of the current control loop into consideration. This paper proposes 1) a systematic and efficient method for design of dc-bus PI controller gains; and 2) an accurate method for the design of the dc-bus controller gains without neglecting the dynamics of the current control loop. Two main objectives are to have control over the amount of output current harmonics and over the level of bus fluctuations caused by random input power swings. The proposed method is transparent and it provides a convenient and rigorous insight for the designer to properly select the size of dc-bus component and to determine the controller gains. [ABSTRACT FROM PUBLISHER]

This paper proposes an improved strategy for the optimization of dynamic photovoltaic arrays (DPVAs) utilizing the “irradiance equalization” (IEq) reconfiguration strategy. This type of reconfigurable array is already very robust as it amalgamates the flexibility of dynamic reconfiguration with the averaging ability of total cross-tied array architecture. This paper identifies four areas to further increase the power yield and significantly reduce the time for a return on investment. Results indicate potential efficiency improvements of more than 10% in some cases, and between 4% and 10% across a number of random and abrupt shading conditions. As in any DPVA system, the proposed approaches require additional hardware and advanced control algorithms compared to a static PV array, but anyone implementing a dynamic array has already committed themselves to including the majority of this infrastructure. This investigation supports the idea of a fully dynamic IEq-DPVA with the ability to resize its array dimensions while implementing a rapid sorting algorithm based on information gathered using a novel precision irradiance profiling technique. [ABSTRACT FROM AUTHOR]

The resonant converter (RC) is finding wide applications in many space and radar power supplies. Among various RCs LCL, LCC, and LCL-T topologies are broadly used. This manuscript presents a comparative evaluation of steady-state stability of LCL, LCC, and LCL-T resonant configurations. Careful analysis favors LCL RC among the aforementioned three configurations since the stability region is good for the LCL RC over the other configurations. Also, this paper presents a comparative evaluation of proportional integral (PI) controller and fuzzy logic controller for a modified LCL RC. The aforementioned controllers are simulated using MATLAB and their performance is analyzed. The outcome of the analysis shows the superiority of fuzzy control over the conventional PI control method. The LCL RC is proposed for applications in many space and radar power supplies. Design, simulation, and experimental results for a 133-W, 50-kHz LCL RC are presented in this manuscript which provide high efficiency (greater than 89%) even for 50% of load. Efficiencies greater than 80% are obtained at significantly reduced loads (11%). In this paper, the applicability of the Philips advanced RISC machine processor LPC 2148 is also investigated for implementing the controller for an RC. [ABSTRACT FROM AUTHOR]

In this paper, a new energy management strategy (EMS) for a dc distribution system in buildings is being proposed. The dc distribution system is considered as a prospective system according to the increase of dc loads and dc output type distribution energy resources (DERs) such as photovoltaic (PV) systems and fuel cells. Since the dc distribution system has many advantages such as feasible connection of DERs and electric vehicles (EVs), reduction of conversion losses between dc output sources and loads, no reactive power issues, it is very suitable for industrial and commercial buildings interfaced with DERs and EVs. The establishment of an appropriate EMS based on the economic point of view can reduce energy costs of buildings and provide benefits to participants in energy management. Applicable elements for the dc distribution system are identified and the real-time decision-making-based algorithm for minimizing operating costs is proposed in this paper. The EV service model for the EMS to offer incentive to EV owners who participate in battery discharging is described. To verify the performances of the proposed algorithm, computer simulation and economic analysis are being performed where the results show that the proposed EMS reduces energy costs, motivates EV owners, and can be applied to the dc distribution buildings. [ABSTRACT FROM AUTHOR]

Planar electromagnetic interference (EMI) filter has good application prospect in power electronics system with the advantages of small volume and good high-frequency performance. However, a complete theoretical system for the design of planar EMI filter has not been proposed yet. In this paper, an integrated structure formed by an annular “inductor–capacitor” (LC unit) is proposed first, which can be used as the basic cell of the planar EMI filter. A general arc transmission theory is also proposed, based on which the distributed-parameter model of the LC unit is established. Then, this LC unit can be equivalent to the two-port network by employing the model transformation method. Besides, the turn-to-turn electromagnetic parameter is extracted using finite element method, which provides the foundation for the research of LC unit and electromagnetic performance of the filter. The design method and the implementation of the whole planar EMI filter are elaborated in details, and the empirical initial values of the related structural sizes are also presented in this paper. In order to verify the proposed design theory, several EMI filters formed by LC units are designed according to the specifications. Common-mode insertion losses of the EMI filter are calculated and measured, respectively. The results verify the feasibility of the design theory. [ABSTRACT FROM AUTHOR]

This paper presents a new three-phase phase-locked loop (PLL) system that primarily estimates the phase angles, frequency, and magnitudes of the a three-phase input signal and also provides a filtered version of the input. It is then extended to the estimation of sequence components, their magnitudes, and phase angles. As compared with the conventional three-phase PLL, this method does not suffer from errors that are caused by signal unbalance and dc offset. It also provides estimate for several other variables which are not included in the conventional three-phase PLL. As compared with the method of using three independent single-phase enhanced PLLs, the proposed method offers a simpler structure. Moreover, the estimated frequency is more accurate and smoother because it uses the information from all three phases to estimate a single value for frequency. The paper also presents a modification that makes the PLL parameters independent from the input signal amplitude. The same modification is applicable to existing methods such as conventional three-phase PLL. Simulation and experimental results are presented to confirm desirable performance of the proposed method. [ABSTRACT FROM AUTHOR]