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The software-assisted reliability assessment of power electronic converters is increasingly important due to its multi-domain nature and extensive parametric calculations. The rainflow counting algorithm is gaining popularity for its low relative error in device lifetime estimation. Nevertheless, the offline operation of the algorithm prevents most simulation software packages considering other parameters for the device under study, such as aging and the current state of health in the estimation, as it requires a complete loading profile to run recursive comparison. This also brings difficulties in realization in circuit simulators such as SPICE. To tackle the issue, an in-the-loop circuit-based rainflow counting algorithm is proposed in this paper, and applied to estimate the consumed lifetime of the MOSFET in a boost converter for illustration. Instantaneous electrical and thermal performances, and the accumulated stress of the device can be monitored. Not only does this assist in evaluating the state of health of a device, but also allows the possibility of integrating the aging into the lifetime evaluation. The method follows the four-point rainflow counting algorithms, which continuously compares three adjacent temperature fluctuations Δ T j to select full cycles for two rounds, and the remaining cycles are counted as half cycles. To validate the performance, a comparative analysis in terms of counting accuracy and simulation speed was performed alongside the proposed method, MATLAB® and also with a well-accepted half-cycle counting method. Reported results show that the proposed method has an improved counting accuracy compared to the half-cycle counting from 24% to 3.5% on average under different load stresses and length conditions. The accuracy can be effectively improved by a further 1.3–2% by adding an extra comparison round. [ABSTRACT FROM AUTHOR]

Malfunction of power semiconductor switches is the dominant cause of failure in power electronic converters. This article proposes a novel dual-switch dc–dc topology for high-reliability applications. The proposed converter is fault tolerant and supports operation under both step-down and step-up modes. The proposed topology can be reconfigured automatically under various switch-fault conditions in order to maintain normal operation. This is enabled by an affine-parametrization-based control design, which minimizes the transient impact of the faults. The reliability performance of the proposed converter is evaluated theoretically using a Markov model, demonstrating its superiority over conventional topologies. Finally, a laboratory prototype is developed and tested to verify the proposed design and control performance under switch faults. [ABSTRACT FROM AUTHOR]

In this paper, a new high voltage gain step-up dc–dc converter is proposed for interfacing renewable power generation. The configuration optimally integrates both the coupled-inductor and switched-capacitor techniques to achieve an ultra-high step-up gain of voltage conversion with low voltage stress and high efficiency. It consists of a voltage boost unit, a passive clamp circuit, and a symmetrical voltage multiplier network. The structure becomes modular and extendable without adding any extra winding for ultra-high step-up voltage gain. The proposed topology not only reduces the voltage stress on the main switch but also maintains it steady for the entire duty cycle range. Furthermore, the reverse recovery issue of the diodes is alleviated through the leakage inductance of the coupled inductor. The operation principle and steady-state analysis are presented in detail. Experimental evaluation validates the claimed advantages and demonstrates a well-distributed efficiency curve and the peak of 96.70%. [ABSTRACT FROM AUTHOR]

The recent trend in the design of the high-power density power converter generally reduces the rate of the device cooling process. As a result, increased thermal coupling among devices exists. Based on measurements, a thermal coupling resistances network (TCRN) model is proposed in this article. Considering different spacings and current values at a fixed value of case temperature (${T} _{\text {c}}$), the relationships between the case-to-ambient thermal resistance (${R} _{\text {ca}}$) of individual power devices and their thermal coupling resistance (${R} _{\text {cp}}$) to the adjacent device are established. The close correspondence of ${T} _{\text {c}}$ from the calculation of the different spacing and experimental results obtained from a thermal coupling measurement platform confirms the established TCRN model and the relationships. Traditional thermal models do not consider the changes of ${R} _{\text {ca}}$ and also ignore the effect of thermal coupling among the adjacent devices. Compared with these models, the proposed thermal resistances modeling approach provides a better understanding of the thermal behavior of power devices. [ABSTRACT FROM AUTHOR]

This paper proposes a novel isolated bidirectional two-switch flyback converter with two integrated non-dissipative inductor–capacitor–diode (LCD) snubbers. In the proposed topology, the main flyback transformer and the LCD snubbers are cross coupled to minimize circulating current that would occur in the non-cross-coupled case, in addition to recycle leakage energy and protect the power transistors. The same current circulation issue also occurs in the bidirectional flyback converter with conventional resistor–capacitor–diode (RCD) snubbers. The main objective of this paper is to illustrate this issue and propose an alternate circuitry to reduce the current circulation and improve the conversion efficiency. The experimental results of a laboratory prototype are reported to verify the design. [ABSTRACT FROM AUTHOR]

This paper presents a model-predictive sliding-mode control (MPSMC) scheme for a three-phase ac/dc converter to achieve better stability and dynamic performances. In the conventional model-predictive control method, a proportional–integral (PI) controller is used to generate the active power reference. This traditional model-predictive PI control (MPPIC) scheme, however, produces a large overshoot/undershoot, a long settling time, and a large steady-state error under disturbances. To overcome these deficiencies, a sliding-mode controller is employed to replace the PI controller. Since the control law and the controller are designed based on the system model, the proposed MPSMC scheme can reduce the effects of unexpected disturbances, such as the output voltage demand and the resistance load variations. Both methods have been simulated in MATLAB/Simulink during various disturbances. Compared with the performances of MPPIC, the results obtained from MPSMC show that the settling time of the dc voltage can be minimized by about 91%, and the overshoot can be eliminated from 9.13% during the steady-state progress. The active and reactive power from MPSMC can also be controlled to the desired values, respectively, with a much smaller overshoot/undershoot and a faster response speed. Similar dynamic improvements can be achieved with MPSMC when the dc voltage demand varies. The simulation results are validated by experimental results. [ABSTRACT FROM AUTHOR]

State of charge (SoC) imbalance among batteries in a battery energy storage system (BESS) degrades the system performance and may lead to safety issue. A bidirectional multiple-input Ćuk converter for the BESS is proposed to prevent batteries from SoC imbalance issue. Compared to the traditional BESS, the battery balancing and voltage/current regulation subsystems are combined into one. As a result, the overall system complexity is significantly reduced. Moreover, the current flow of each battery is self-adjusted according to its terminal voltage. Therefore, the system does not require sophisticated control algorithm for battery balancing. Moreover, the proposed system has no energy dumping and energy transferring between batteries, which avoids unnecessary energy lose. Due to the nature of multiple-input converter structure, the proposed system can handle certain component failure. The proposed approach of designing the BESS has been investigated through simulation and validated experimentally. [ABSTRACT FROM PUBLISHER]

Computational burden is a major hurdle for practical implementation of finite-state predictive torque control (FS-PTC) of motor drive fed by a multilevel inverter. One of the reasons of computational complexity is that all voltage vectors are evaluated for prediction and actuation. This paper proposes a reduced number of voltage vectors for the prediction and actuation, which are called prediction vectors in FS-PTC. The performance is investigated for a three-level neutral-point clamped inverter fed motor drive in terms of torque and flux response, stator current total harmonic distortion, robustness, average switching frequency, and neutral-point voltage variation. The number of prediction vectors is reduced based on the position of stator flux and the deviation in stator flux from its reference. Experimental results confirm that the computational burden could be reduced by 38%, while the dynamic performance is comparable with the conventional all voltage vectors based FS-PTC. [ABSTRACT FROM AUTHOR]

Iterative and complex prediction loop is a challenge for the implementation of finite-state predictive torque control (FS-PTC) of motor drive. The complexity is due to the complex torque calculations, number of available voltage vectors (which are called as prediction vectors), and weighting factor tuning for torque and flux errors in the cost function. One way to reduce the complexity is an equivalent reference stator flux vector calculation (RSFVC) from torque and flux references, which also solves the problem of weighting factor tuning. Along with a new stator flux based RSFVC technique, a reduced number of prediction vectors are proposed in this study to reduce the number of iteration of the prediction loop. The position of the stator flux and sign of the stator flux-error are considered to lessen the number of prediction vectors. Hence, the implementation challenges of FS-PTC algorithm are overcome. The performance of the proposed technique is investigated for two types of RSFVCs: one is based on the stator flux, and another one is based on the rotor flux. Experimental results verify that the proposed low complexity FS-PTC strategies retain the advantages of a conventional FS-PTC. [ABSTRACT FROM AUTHOR]

Iterative and complex prediction loop is a challenge for the implementation of finite‐state predictive torque control (FS‐PTC) of motor drive. The complexity is due to the complex torque calculations, number of available voltage vectors (which are called as prediction vectors), and weighting factor tuning for torque and flux errors in the cost function. One way to reduce the complexity is an equivalent reference stator flux vector calculation (RSFVC) from torque and flux references, which also solves the problem of weighting factor tuning. Along with a new stator flux based RSFVC technique, a reduced number of prediction vectors are proposed in this study to reduce the number of iteration of the prediction loop. The position of the stator flux and sign of the stator flux‐error are considered to lessen the number of prediction vectors. Hence, the implementation challenges of FS‐PTC algorithm are overcome. The performance of the proposed technique is investigated for two types of RSFVCs: one is based on the stator flux, and another one is based on the rotor flux. Experimental results verify that the proposed low complexity FS‐PTC strategies retain the advantages of a conventional FS‐PTC. [ABSTRACT FROM AUTHOR]

Coordinated control of distributed energy resources (DER) is essential for the operation of islanded microgrids (MGs). Conventionally, such coordination is achieved by drooping the frequency of the reference voltage versus active (or reactive) power. The conventional droop method ensures synchronized operation and even power sharing without any communication link. However, that method produces unwanted frequency fluctuations, which degrade the power quality. In order to improve the power quality of islanded MGs, a novel decentralized control method is proposed in this paper. In this method, the GPS timing technology is utilized to synchronize the DERs to a common reference frame, rotating at a nominal frequency. In addition, an adaptive Q–f droop controller is introduced as a backup to ensure stable operation during GPS signal interruptions. In the context of the common reference frame, even sharing of active ( id) and reactive ( iq) components of the current are achieved based on vd\,\-\,id and vq\,\-\,iq droop characteristics. The method has been tested on a laboratory-scale MG. Experimental results demonstrate the efficacy of the proposed method in terms of dynamics, power quality, and robustness with respect to GPS interruptions. [ABSTRACT FROM PUBLISHER]

Finite-state predictive torque control (FS-PTC) of an induction motor (IM) drive has been widely investigated for two-level voltage source inverter recently. This control method suffers from high and variable switching frequencies in a wide range, due to the limited number of available voltage vectors of the power converter. In order to take advantage of multilevel inverter drives which offer the benefits of low harmonic distortion of the stator currents, torque ripple, and low switching frequency, this paper proposes the integration of the FS-PTC with a three-level neutral-point clamped (3L-NPC) inverter driven IM drive. The drawback inherited from the topology of 3L-NPC voltage source inverter (VSI), such as neutral-point voltage, is easily handled by treating it as a variable to the cost function. Similarly, apart from the inverter topology itself, the average switching frequency is reduced further, and is maintained almost constant over a wide speed range. The effectiveness of the proposed FS-PTC in terms of torque and flux responses, capacitor voltage balancing, and low average switching frequency is validated through experimental results. [ABSTRACT FROM AUTHOR]

Cascaded converters are adopted in many power systems to manage sources and loads at different voltage levels simultaneously. DC bus capacitor is one of the key components in these converters due to its energy storage and fast response capabilities. However, the ripple current through the capacitor will influence its lifetime and the overall efficiency of the converter. Previous studies showed that the capacitor current of ac systems is optimized when the duty cycles are synchronized under in phase or antiphase condition. In this paper, the bus capacitor ripple current of cascaded two-stage converters for dc systems with different combinations of duty cycles is analyzed. It is found that the optimum capacitor current ripple varies depending on the values of individual duty cycles and the phase-shift angle between them. By properly adjusting the phase shift, the capacitor RMS current value can be reduced without affecting the converter normal operation or the need for extra sensing circuits, hence improving the energy conversion efficiency and prolonging the capacitor lifetime with relatively simple implementation. To illustrate, a case study of a two-stage dc/dc converter is carried out. A laboratory prototype converter confirmed a maximum efficiency improvement of 2.8% if the phase shift is adjusted properly when compared to the same converter with the worst case phase-shift angle. [ABSTRACT FROM AUTHOR]

This letter presents a method for selecting an appropriate rating of fuse and MOSFET in a fault-tolerant dc/dc converter to protect the circuit in a short-circuit operating condition. The proposed method is based on the Joule-integral principle to calculate the amount of energy associated with the fuse. Different fuse melting characteristics are used to select the appropriate melting time by comparing them with the thermal characteristics of the circuit. The tests performed demonstrate consistent behavior with simulation results and they show that the fuse current rating must be lower than the current rating of the switch in order to provide a safe and reliable operation of the converter. [ABSTRACT FROM AUTHOR]

This letter presents a graph-theoretic approach to deriving a family of dual-switch step-down dc/dc converters with fault-tolerant capability. The constraint sets in the derivation process ensure that minimum additional component is used to achieve fault-tolerant operation. The operation of converters derived is flexible. Under normal operating conditions, one of the two switches can serve as a main switch to control the power flow (i.e., single-switch converter operation) and the other switch is in stand-by mode. When a fault occurs on the main switch, the other switch will be activated to provide an alternate current path to continue converter operation and maintain output regulation. The fault-tolerant converters are derived by integrating a buck converter with a buck–boost converter. They share all the components except for the power switches. Due to different duty cycles required between the two operating conditions, a feedback controller is necessary to adjust the duty cycle for tight output regulation. The derivation procedure and experimental results on fault occurrence are reported. The converter derivation approach is able to identify reported topologies and can be extended to synthesize other topologies with fault-tolerant capability. [ABSTRACT FROM AUTHOR]

Finite-state predictive torque control (FS-PTC) is computationally expensive, since it uses all voltage vectors (VVs) available from a power converter for prediction and actuation. The computational burden is rapidly increased with the number of VVs and objectives to be controlled. Moreover, designing a cost function with more than two control objectives is a complex task. This paper proposes a simplified algorithm based on a new direct torque control (DTC) switching table to reduce the number of VVs to be predicted and objectives to be controlled. The new switching table also assists to reduce average switching frequency and its variation range. As a result, the cost function is simplified by not requiring to include the frequency term. Experimental results show that the average execution time and the average switching frequency for the proposed algorithm are greatly reduced without affecting the torque and flux performances achieved in the conventional FS-PTC. [ABSTRACT FROM PUBLISHER]

Unbalanced load currents not only give rise to unbalanced voltages but also adversely affect the performance of the conventional current-limiting mechanisms. The latter might result in overcurrent stress on the distributed energy resources (DERs) or current harmonics. In this paper, a novel decentralized control method is proposed to improve the power quality and protect DERs from overload. The proposed controller makes use of the model predictive control (MPC) technique to minimize the voltage unbalance, improve current limiting, and prevent active power overload. The MPC is combined with the V-I droop method to realize coordinated operation with fast dynamic response. The proposed method is tested on the CIGRE benchmark microgrid. Simulation results demonstrate that the proposed method improves power quality but also allows for operation close to the maximum load capacity without imposing DERs to overload. [ABSTRACT FROM PUBLISHER]

Single-stage power-factor-corrected (S2PFC) power supplies usually suffer from high voltage stress, due to lack of control on the intermediate bus capacitor voltage. In the past, analysis of such voltage stress was mostly based on steady-state condition without providing sufficient explanation during the transient circuit operation. This paper revisits the problem at circuit level and reports that the root cause is due to the inherent negative current feedback property of the output inductor or the transformer operating in continuous conduction mode (CCM). Based on the finding, this paper further proposes a new approach to reducing the voltage stress by adding an auxiliary circuit branch to existing S2PFC converters. The additional circuit branch limits the effect of negative current feedback by suppressing the change of output current slope due to change of load. This assists the pulsewidth modulation controller to track the change of load better such that the bus capacitor voltage range is reduced through duty cycle control. The auxiliary circuit branch also reduces reverse-recovery-related losses of the converter under CCM operation. A laboratory prototype using the popular boost PFC converter combined flyback dc/dc converter was built and tested to confirm the analysis and effectiveness of the approach. [ABSTRACT FROM AUTHOR]

A sensorless finite-state predictive torque control (FS-PTC) strategy uses stator current, estimated stator and rotor flux, and estimated rotor speed to predict stator flux and torque. Direct application of measured stator currents and using a noisy estimated speed in the prediction model degrade the steady-state performance in terms of higher current total harmonic distortion (THD), torque ripple, and flux ripple, particularly at low speeds. This paper proposes an extended Kalman filter (EKF)-based, which is a promising state observer, improved prediction model of sensorless FS-PTC for induction motor drives. The EKF has been used to estimate rotor speed, rotor/stator flux, and stator currents accurately. The estimated stator currents, instead of measured currents, are fed back to the prediction model, and thus, small stator current THD is confirmed. Depending on the commanded speed, either the rotor current model or the open-loop stator voltage model is proposed for the EKF to achieve better performance in a wide speed range, including the field-weakening region. The proposed control system has been verified experimentally, and excellent torque and flux responses, robustness, and stable operation at lower and higher speeds have been achieved. [ABSTRACT FROM PUBLISHER]

In this paper, the two-input buck converter is proposed as the dc/dc stage for photovoltaic (PV) cascaded converters. This converter is attractive for this application because it is cost effective and reliable and can achieve dual maximum power point tracking (MPPT) with only one power transistor. However, due to the simplified and integrated structure, the nonlinear characteristics of the converter and the two PV arrays complicate the control. By means of a small-signal modeling, the control theme of the two PV voltages is formulated, and the effect of the nonlinearities is presented. It is shown that, while fast voltage dynamics are achieved for the first input, the second-input voltage response depends on the second-stage converter control. Simulation and experimental results are reported to validate the theoretical analysis, showing the dual MPPT capability. [ABSTRACT FROM PUBLISHER]

In dc microgrids, it is common that constant power loads (CPLs) exhibit negative incremental resistance. They degrade the stability margin of operation with their LC input filters and, thus, the whole system. In traditional active-damping methods, the extra stabilizing current is injected into CPLs to modify its input impedance to fulfill stability criteria. However, this injected current may cause undesirable performance of the loads, e.g., fluctuation in rotating speed of tightly regulated motors. There is always a compromise between stability margin and load performances. In order to overcome this drawback, this paper proposes a method that stabilizes the system from source-side converters, instead of from CPL themselves. In the proposed method, a virtual resistance is built in the source-side converter. This virtual resistor is effective around the resonant frequency of the LC input filter and thus can indirectly reduce its output impedance to fulfill Middlebrook's stability criterion. This paper also proves, both analytically and experimentally, that, in dc microgrids, resonant frequencies of LC filters of paralleled CPLs have to be different to maintain system stability. Simulation and experimental results are reported to verify the effectiveness of the proposed idea. [ABSTRACT FROM PUBLISHER]

Existing bridgeless boost (BLB) converter with soft switching utilize more than two active switches and extra resonant networks. In this paper, a new zero-current-switching BLB rectifier with high power factor (PF) using only two active switches is proposed. The proposed BLB converter is based on a totem-pole BLB (TPBLB) configuration, which allows the current to flow from high side to low side and vice versa during resonance. Hence, no auxiliary active switch is needed to provide soft switching for all semiconductor devices. The soft switching also reduces the body diode reverse recovery problem, hence allowing the TPBLB to operate in continuous conduction mode. Standard components are used to prove that the proposed converter is working with an acceptable performance compared with other BLB converters with soft switching. In order to achieve smooth input current waveform, high PF, and wide soft-switching operations, a pulsewidth modulation controller is proposed and developed, which combines a conventional PF correction average current mode controller with several logic gates and a phase detector. A detailed analysis of the converter operation and control is presented. Design considerations and parameter values calculations are given. An experimental prototype is developed and tested to verify the converter performance. [ABSTRACT FROM PUBLISHER]

A single-switch nonisolated dc/dc converter for a stand-alone photovoltaic (PV)-battery-powered pump system is proposed in this paper. The converter is formed by combining a buck converter with a buck-boost converter. This integration also resulted in reduced repeated power processing, hence improving the conversion efficiency. With only a single transistor, the converter is able to perform three tasks simultaneously, namely, maximum-power-point tracking (MPPT), battery charging, and driving the pump at constant flow rate. To achieve these control objectives, the two inductors operate in different modes such that variable switching frequency control and duty cycle control can be used to manage MPPT and output voltage regulation, respectively. The battery in the converter provides a more steady dc-link voltage as compared to that of a conventional single-stage converter and hence mitigates the high voltage stress problem. Experimental results of a 14-W laboratory prototype converter with a maximum efficiency of 92% confirmed the performance of the proposed converter when used in a PV-battery pump system. [ABSTRACT FROM PUBLISHER]

This letter presents the design of a magnetically isolated gate driver with high immunity to leakage inductance. The proposed gate driver (PGD) is developed based on a bipolar totem-pole gate driver (noninverting) located on the secondary side of the coupling transformer. It is able to drive a MOSFET/IGBT from standard CMOS to TTL output and down to LSTTL level. It also achieves large duty cycle ratio and small input to output delay and provides reliable isolation. In this letter, the PGD is analyzed and verified experimentally. The design guidelines are also provided including design considerations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Passive network supplied by a VSC-HVDC system is subject to power quality problems. [•] Direct control fails to quickly eliminate voltage fluctuation under disturbances. [•] Inverter nonlinearities degrade the performance of the feed-forward compensation. [•] A compensation method for inverter nonlinearities is designed in d–q rotating axis. [•] The proposed method capably mitigates voltage fluctuation under disturbances. [ABSTRACT FROM AUTHOR]

Highlights: [•] Causes of the current harmonics are summarized. [•] The harmonic amplitude increases as PV output power level decreases. [•] Field measurement for current harmonics is carried out at a microgrid. [•] DC-link voltage ripple cause a series of odd harmonics in the output current. [•] A time-varying model is proposed to reveal the characteristics of the harmonics. [Copyright &y& Elsevier]

A thermoelectric generator (TEG) is a low-voltage high-current dc power source with a linear V–I characteristic, and therefore, it is desirable to create a power converter with a topology and control method suited to these attributes. Due to the TEG’s low voltage, a topology that produces a high step-up gain for a moderate duty cycle is required to reduce voltage and current stresses within the converter. The linear V–I characteristic produces a P–I characteristic with a flatter peak relative to other sources. This can result in large operating point variations while performing maximum power point tracking (MPPT); thus, an algorithm with low steady-state error is desired. This paper presents a novel high step-up dc/dc converter topology operating with a fractional short-circuit MPPT algorithm for use with a 4.2-V, 3.4-A (for matched load at \Delta T = \270\,^\circ C) TEG module and a converter output of 180 V. Compared to existing high step-up dc/dc converters, the proposed converter achieves higher gain with similar component count. Experimental results are reported to confirm the converter analysis and better performance of the short-circuit MPPT algorithm over the perturb and observe algorithm. [ABSTRACT FROM PUBLISHER]

This paper presents a novel input current shaper based on a quasi-active power factor correction (PFC) scheme. In this method, high power factor and low harmonic content are achieved by providing an auxiliary PFC circuit with a driving voltage which is derived from a third winding of the transformer of a cascaded dc/dc flyback converter. It eliminates the use of active switch and control circuit for PFC. The auxiliary winding provides a controlled voltage-boost function for bulk capacitor without inducing a dead angle in the line current. Since the dc/dc converter operates at high switching frequency, the driving voltage is also of high switching frequency, which results in reducing the size of the magnetic components. Operating principles, analysis and experimental results of the proposed method are presented. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a high step-down tranformerless single-stage single-switch ac/dc converter suitable for universal line applications (90-270 Vrms) . The topology integrates a buck-type power-factor correction (PFC) cell with a buck-boost dc/dc cell and part of the input power is coupled to the output directly after the first power processing. With this direct power transfer feature and sharing capacitor voltages, the converter is able to achieve efficient power conversion, high power factor, low voltage stress on intermediate bus (less than 130 V) and low output voltage without a high step-down transformer. The absence of transformer reduces the component counts and cost of the converter. Unlike most of the boost-type PFC cell, the main switch of the proposed converter only handles the peak inductor current of dc/dc cell rather than the superposition of both inductor currents. Detailed analysis and design procedures of the proposed circuit are given and verified by experimental results. [ABSTRACT FROM AUTHOR]

This paper discusses the major issues that exist in the single-stage ac/dc converters with power factor correction (PFC) and presents a novel converter based on a quasi-active PFC scheme. Two additional windings wound in the transformer of a conventional dc/dc flyback converter are used to drive and achieve continuous current mode operation of an input inductor. In addition, direct energy transfer paths are provided through the additional windings to improve the conversion efficiency and to reduce the dc bus capacitor voltage below 450 V for universal line applications. The proposed converter can be easily designed to comply with IEC 61000-3-2 Class D requirement and to achieve fast output voltage regulation. By properly tuning the converter parameters, a good tradeoff between efficiency, dc bus capacitor voltage stress, and harmonic content can be achieved. Operating principles, analysis, and experimental results of the proposed method are presented. [ABSTRACT FROM PUBLISHER]

This paper proposes a current control strategy with zero steady-state tracking error for grid-connected boost inverters. Two boost converters are controlled separately to achieve both output current tracking and balanced output voltages. Based on cascading control and feedback linearization, the inner- and outer-loop controllers are as the combination of the inversion of boost converter model and the output error compensation. After the boost converter model is linearized, proportional and resonant controllers are derived from the internal model principle to achieve zero tracking error. Experimental results confirm that the proposed control achieves good current tracking to meet stringent grid-connection harmonics standards. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a battery-integrated boost converter utilizing the distributed maximum power point tracking (DMPPT) configuration for a photovoltaic (PV) system is studied. Each PV module has its own battery and DC/DC converter. Due to the proposed topology and use of battery, the MPPT function is not affected by the load demand and input power from PV. Application of the proposed converter to DMPPT configuration can save the voltage amplification stage and maintain PV voltage during partial shading. Steady-state analysis of the converter to determine the power flow equations is presented. Comparison with the series-connected conventional boost converter is reported in this paper. Simulation and experiment results of a laboratory prototype are presented to verify the effectiveness of the proposed approach. System design considerations are also discussed. [Copyright &y& Elsevier]

A transformerless single-stage single-switch ac/dc converter is presented in this paper. The converter allows a portion of the input power to be processed once only, resulting in enhanced conversion efficiency. Additionally, due to the absence of a transformer, the size and manufacturing cost of the converter can be reduced. The intermediate bus voltage is well kept below 400 V while maintaining high power factor even at light load and high line-input conditions. Extended experimental results on a 100-W hardware prototype for universal input-voltage range (90–270 Vrms) are given to confirm the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM PUBLISHER]

Renewable energy sources based on photovoltaic (PV) along with battery-based energy storage necessitate power conditioning to meet load requirements and/or be connected to the electrical grid. The power conditioning is achieved via a dc-dc converter and a dc-ac inverter stages to produce the desired ac source. This is also the case even when the load is of dc type, such as the typical portable electronic devices that require ac adaptors to be powered from the ac mains. The letter presents a hybrid PV-battery-powered dc bus system that eliminates the dc-ac conversion stage, resulting in lower cost and improved overall energy conversion efficiency. It is also shown experimentally that the switching ac adaptors associated with the various commonly used portable electronic devices can be reused with the proposed dc bus system. A novel high-gain hybrid boost-flyback converter is also introduced with several times higher voltage conversion ratio than the conventional boost converter topology. This arrangement results in higher dc bus levels and lower cable conduction losses. Moreover, the voltage stress on the hybrid boost-flyback converter power switch is within half the output voltage. Experimental results taken from a laboratory prototype are presented to confirm the effectiveness of the proposed converter/system. [ABSTRACT FROM AUTHOR]

This paper presents a systematic topological study to derive all possible basic and non-isolated three-port converters (TPCs) using power flow diagrams. Unlike most reported TPCs with one bidirectional port, this paper considers up to two bidirectional ports and provides a comprehensive analytical tool. This tool acts as a framework for all power flow combinations, selection, and design. Some viable converter configurations have been identified and selected for further analysis. [ABSTRACT FROM AUTHOR]

To reduce the intermediate storage capacitor voltage stress in single-stage power-factor-corrected (S2PFC) converters due to the change of load, some effective approaches such as variable frequency control and negative bus voltage feedback have been proposed. However, this intermediate capacitor voltage still varies largely against the change of line voltage. This paper proposes a S2PFC converter which is constructed in a way such that the amount of energy to and from the intermediate storage capacitor can be varied when the line voltage is changed, hence narrowed the range of intermediate capacitor voltage fluctuation. This is achieved by an auxiliary bidirectional switch, which operates at zero-voltage-switching (ZVS) condition. A dual-loop voltage mode control is proposed for the converter to achieve power factor correction, output voltage regulation, and intermediate capacitor voltage control simultaneously. Simulation and experimental results show that the proposed approach is effective. [ABSTRACT FROM AUTHOR]

Unlike existing single-stage ac/dc converters with uncontrolled intermediate bus voltage, a new single-stage ac/dc converter achieving power factor correction (PFC), intermediate bus voltage output regulation, and output voltage regulation is proposed. The converter is formed by integrating a boost PFC converter with a two-switch clamped flyback converter into a single power stage circuit. The current stress of the main power switch is reduced due to separated conduction period of the two source currents flowing through the power switch. A dual-loop current mode controller is proposed to achieve PFC, and ensure independent bus voltage and output voltage regulations. Experimental results on a 24-V/100-W hardware prototype are given to confirm the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a new family of single-stage AC/DC power factor correction converters (S2PFCC), which possesses reduced voltage stress across the storage capacitor and no extra current stress on the power switch, is proposed. The converters are realized by reduced repeated power processing concept in which part of the input power is transferred to the load directly after the first power process. This results in lower storage capacitor voltage than that of previously developed S2PFCCs but maintaining high power factor. In addition, the inherent input current control allows the load current to reduce the input line current automatically when the load becomes light, preventing excessive amount of energy being stored in the storage capacitor. Although the proposed converters employed two power switches, a simple single-loop controller for the proposed S2PFCC to achieve power factor correction (PFC) and tight output regulation is also proposed. Experimental results are reported to verify the operation and concept of the new S2PFCC. [ABSTRACT FROM AUTHOR]

This article addresses the design of reconfigurable single-inductor multiport converters with bidirectional power flow, no cross regulation, and simple control. The design uses both the voltage-source-mode and current-source-mode cells, thus allowing a full range of connectivity. The proposed single-inductor converters offer high modularity and scalability while offering bidirectional power flow and no cross regulation. The single-inductor structure reduces the overall size. The adoption of voltage-source-mode and current-source-mode cells leads to high modularity. High scalability is achieved due to arbitrary ports being allowed to the derived converters. Moreover, the topology inherently achieves no cross regulation among the output ports. The ports of the derived converters are reconfigurable, permitting transformation among single-input multi-output mode, multi-input multi-output mode, and multi-input single-output mode. Through the transformation of operating modes, bidirectional power flow is achieved. Thus, regenerative loads can be integrated seamlessly. In terms of control, the absence of cross regulation permits the adoption of very simple control design, leading to high flexibility. Thus, the derived converters can integrate multiple and various kinds of terminating sources and loads simultaneously with simple control methods. A reconfigurable single-inductor four-port converter is presented for illustration. Finally, experimental results are presented to verify the analytical findings. [ABSTRACT FROM AUTHOR]

The conventional online battery impedance measurement method works by perturbing the duty cycle of the DC-DC power converter and measuring the response of the battery voltage and current. This periodical duty cycle perturbation will continuously generate large voltage ripples at the output of power converters. These large ripples will not easily be removed due to the high amplitude and wide frequency range and would be a challenge to meet tight output regulation. To solve this problem, this paper presents a new online battery impedance measurement technique by inserting a small switched resistor circuit (SRC) into the converter. The first contribution of this work is that the perturbation source is moved from the main switch to the input-side of the converter, so the ripples are reduced. The analysis and experimental results of the proposed method show a reduction of 16-times compared with the conventional method. The second contribution tackles the possible change of the battery state of charge (SOC) during the online battery measurement process, which will inevitably influence the impedance measurement accuracy. In this proposed method, battery impedance at multiple frequencies can be measured simultaneously using only one perturbation to accelerate measurement speed and minimize possible SOC change. The experimental impedance results coincide with a high-accuracy laboratory battery impedance analyzer. [ABSTRACT FROM AUTHOR]

This paper presents the four-quadrant operation modes of bidirectional chargers for electric vehicles (EVs) framed in smart car parks. A cascaded model predictive control (MPC) scheme for the bidirectional two-stage off-board chargers is proposed. The controller is constructed in two stages. The model predictive direct power control for the grid side is applied to track the active/reactive power references. The model predictive direct current control is proposed to achieve constant current charging/discharging for the EV load side. With this MPC strategy, EV chargers are able to transmit the active and reactive powers between the EV batteries and the power grid. Apart from exchanging the active power, the vehicle-for-grid (V4G) mode is proposed, where the chargers are used to deliver the reactive power to support the grid, simultaneously combined with grid-to-vehicle or vehicle-to-grid operation modes. In the V4G mode, the EV battery functions as the static var compensator. According to the simulation results, the system can operate effectively in the full control regions of the active and reactive power (PQ) plane under the aforementioned operation modes. Fast dynamic response and great steady-state system performances can be verified through various simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to controlling and optimizing a single-stage boost-integrated full-bridge dc–dc converter for a stand-alone photovoltaic-battery-powered dc motor system by combining pulse-frequency modulation (PFM), pulsewidth modulation (PWM), and phase angle shift (PAS). Unlike most of the existing multiport dc–dc converters, which aim at regulating the output voltage (first- or second-quadrant operation), the dc motor load requires both voltage and current reversals (four-quadrant operation). The converter is able to perform three tasks simultaneously: maximum power point tracking (MPPT), battery charging/discharging, and driving the dc motor at variable speeds including bidirectional and stall motions. To achieve these control objectives, the boost inductor and the motor inductance operate in different modes such that PFM and PWM can be used to achieve MPPT and a wide motor voltage range, respectively. By properly adjusting the PAS of the duty cycles, the capacitor and battery rms current value can be reduced, while the operation of the converter remains unchanged, hence improving the conversion efficiency. Experimental results of a 26-W laboratory prototype converter confirmed the proposed design and operation and the efficiency improvement by 2–6%. [ABSTRACT FROM AUTHOR]

This paper proposes a distributed control strategy for coordination of distributed energy resources (DERs) in low-voltage resistive microgrids. The proposed framework consists of two level structures; primary and secondary control. Unlike the existing distributed control solutions, the proposed method is based upon the practical assumption of network impedance being resistive. The primary control level consists of a V-I droop mechanism, where GPS timing is used to synchronize the control agents. A consensus-based distributed secondary control method is introduced to improve the voltage regulation and load sharing accuracy of the V-I droop method. In the proposed approach, the d-axis component of the voltage is altered so as to regulate the average microgrid voltage to the rated value while guarantying proper sharing of active power among the DERs. Additionally, the q-axis component of voltage is adjusted to perform proper current and, accordingly reactive power sharing. The proposed control methodology accounts for the distribution line impedances. It features a plug-and-play environment; prior system knowledge is not required, and an arbitrary DER can enter the microgrid without any need for additional synchronization. An ac microgrid is prototyped to experimentally demonstrate the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a grid-tied residential smart microgrid topology is proposed, which integrates energies of a photo-voltaic (PV), a fuel cell, and a battery bank to supply the local loads through a combination of electric and magnetic buses. In contrast to multiple-converter-based microgrids with a common electric bus, using a multiport converter with a common magnetic bus can effectively reduce the number of voltage conversion stages, size, and cost of the renewable energy system and isolates the conversion ports. The resultant topology utilizes a centralized system level control that leads to a faster and more flexible energy management. The proposed microgrid is able to operate in multiple grid-connected and off-grid operation modes. A fuzzy controlled energy management unit (EMU) is designed to select the appropriate operation mode considering both real-time and long-term predicted data of the energy generation and consumption. A mode transition process is designed to smooth the mode variation by using a state transition diagram and bridging modes. To improve the microgrid operation performance, appropriate control techniques, such as synchronized bus-voltage balance, are used. A prototype of the proposed microgrid and the EMU are developed and experimentally tested for three different energy management scenarios. Energy distribution and energy cost analysis are performed for each scenario to validate the proposed control method. [ABSTRACT FROM AUTHOR]

To support the development of high-frequency ac microgrids in terms of compact design, high-voltage gain and low total harmonic distortion (THD), a buck–boost dual-leg-integrated step-up inverter is proposed in this paper. The inverter is formed by integrating a buck–boost converter into a conventional single-phase full-bridge inverter by sharing the upper switch and the body diode of the lower switch in both bridge-legs. Consequently, the component count is significantly reduced over the step-up inverter counterparts. In addition, to address the drawbacks of hybrid modulation methods adopted by existing dual-leg-integrated inverters, such as double-variable control, and high THD of output voltage/current at high input voltage and heavy load conditions, unipolar frequency doubling sinusoidal pulse width modulation scheme is adopted in this inverter. As a result, the modulation ratio M becomes the only control variable to regulate the output voltage/current and the control is simplified. The THD of the proposed inverter output can remain low throughout the entire input voltage range and load power range. This paper presents the topology derivation procedure, operation principle, and steady-state characteristics of the proposed inverter. To validate the effectiveness of theory, experimental results of a 400 W hardware prototype, where the output voltage frequency is at 500 Hz, are reported. [ABSTRACT FROM PUBLISHER]

The reliability and safety of battery operations necessitate an efficient battery management system (BMS) with accurate battery state of charge (SOC) and capacity estimation techniques. This paper investigates the incremental capacity analysis (ICA) and differential voltage analysis (DVA) methods for onboard battery SOC and capacity estimation. Since the conventional cell terminal voltage based ICA/DVA methods are sensitive to the changed battery resistance and polarization during battery aging processes, the SOC based ICA/DVA methods are proposed to address this problem as so to accurately identify features of interest on incremental capacity (IC) and differential voltage (DV) curves for applications. Three feature points (FPs) that are potential to be easily identified by battery management systems are extracted from the SOC based IC/DV curves, and then the relations between FPs and cell SOCs/capacities are quantified and applied for battery SOC and capacity estimation. The robustness of the proposed approach against various aging levels and erroneous cumulative capacities is evaluated. Promising results with the maximum absolute error of 1.0% and the relative error of 2.0% can be achieved for battery SOC and capacity estimation, respectively. [ABSTRACT FROM AUTHOR]

In this article, a low computational burden model predictive control (MPC) strategy without weighting factor is proposed for the single-phase cascaded H-bridge CHB converters. To reduce the switching state candidates, a hierarchy control algorithm is proposed. The grid current is controlled by selecting a subregion from the designed 2-D control plane, instead of the entire area. Two vectors are chosen in one sampling period for more accurate tracking. Then, the voltage balancing is achieved by selecting the optimal switching state from the subregion candidates to form the above two vectors. The cost function can be constructed of one variable: load voltage. Therefore, the weighting factor can be eliminated. No tuning or retuning processes are required in the proposed method. To reduce the computational time further, the principle of eliminating the switching state candidates operating the same voltage balancing performance is proposed. Conventional and proposed MPC methods are verified by experimental tests via a laboratory setup of a three-cell connected CHB converter. Steady-state and transient operations demonstrate that the proposed method guarantees less distortion grid current and shorter execution time (reduced from 15 to 3 $\mu s$). Fast response speed to variations in voltage reference and load resistance can be achieved t. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hierarchical control strategy for improvement of load sharing and power quality in ac microgrids. This control framework is composed of a droop-based controller at the primary level, and a combination of distributed power sharing and voltage conditioning schemes at the secondary level. The controllers in the primary level use GPS timing technology to synchronize the local reference angles. The voltage reference of each distributed generation is adjusted according to a voltage–current (V–I) droop characteristic to enable proper current and power sharing with a fast dynamic response. The droop coefficient, which acts as a virtual resistance, is adaptively changed as a function of the peak current. This strategy not only simplifies the control design but also improves the current sharing accuracy at high loading conditions. The distributed power sharing scheme uses consensus protocol to ensure proportional sharing of average power. The voltage conditioning scheme produces compensation signals at fundamental and dominant harmonics to improve the voltage quality at a sensitive load bus. Experimental results are presented to validate the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, we present a family of multilevel converters with the single-stage dynamic voltage-boosting feature, reduced number of circuit components, modular structure, bidirectional operation, continuous input current, and acceptable overall efficiency. The proposed structure is based on a three-level single-stage boost integrated inverter with an embedded quasi-H-bridge (QHB) cell. It is comprised of five unidirectional power switches and a floating capacitor. By differential connection of two or three QHB cells and with the aim of a single inductor/input dc source, several derived topologies for both the single and three-phase applications with different multilevel output voltage performances have been achieved. The aforementioned advantages make this converter a suitable candidate for renewable energy applications. Theoretical analysis, design consideration, comparative study, and several experimental results for a 3-kW laboratory-built system are presented to validate the effectiveness and feasibility of this proposal. [ABSTRACT FROM AUTHOR]

This paper presents a new single-source three-phase seven-level inverter with an inherent three-time voltage boosting capability for medium-voltage applications. The proposed topology is comprised of series connection of two switched-capacitor (SC) networks with an added half-bridge module per phase. Each of such integrated SC networks requires a single capacitor associated with three active power switches. The three-time voltage boosting feature of the proposed topology can reduce the dc-link voltage requirements by 50% in comparison to the traditional neutral point clamped (NPC), flying capacitors, active NPC (ANPC), hybrid clamped ANPC, and cascaded H-bridge topologies, and 75% to advanced ANPC topologies. It can also reduce the number of required switches and capacitors as well as their voltage stresses compared to those state-of-the-art topologies reported in the literature. By integrating “n” number of added SC networks in the proposed seven-level basic topology, the number of output voltage levels can be extended to 2n+3 per phase. A finite control set model predictive control algorithm is also derived to control the converter in both the active and reactive power exchanges modes without distorting the generated grid current quality. The capacitor voltage balancing is inherent in the proposed topology, and thus, there is no need for any additional voltage balancing circuit, which further reduces the control complexity. The performance of the proposed topology and its control algorithm are validated by several measurement results. [ABSTRACT FROM AUTHOR]