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Provides instructions and guidelines to prospective authors who wish to submit manuscripts. [ABSTRACT FROM AUTHOR]

This paper proposes a variable off-time control method for a single-phase microinverter operating in the discontinuous conduction mode (DCM) for efficiency improvement. First, the fixed off-time control method is analyzed. The concept is to fix the off-time of the active switch throughout a line cycle for all output powers and scale the on-time of the active switch to shape a sinusoidal output current. Then, based on the fixed off-time control method, a variable off-time control method is proposed to modulate the preset fixed off-time in order to decrease the switching frequency during ac line zero-crossings and light load conditions. Compared with existed fixed-frequency DCM control or boundary conduction mode control, the variable off-time control is more flexible to optimize the efficiency under different load conditions as the switching frequency range can be automatically adjusted according to the output power. The switching frequency is high at heavy loads to limit the maximum peak current and is low at light loads to increase the light load efficiency. In addition, a predictive on-time method is adopted to simplify inverter control and reduce hardware costs. The parameter design principle is detailed in this paper. A 300 W prototype is built to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

In addition to field-oriented control and direct torque control, the model predictive control (MPC) is another typical control method for permanent-magnet synchronous machine (PMSM) drives. In some critical applications, fault-tolerant controls are usually required. The faults of PMSM drives in this paper are limited as a single-phase open-circuit fault, which may be caused by open circuit or short circuit of one power switch. In the postfault operation, the neutral point of the PMSM is connected to a redundant leg. As is known, MPC is a model-based control method. Since the PMSM has different mathematical models in both normal and postfault operations, two different MPCs (MPC-I and MPC-II) should be, respectively, designed for both normal and postfault operations according to traditional thinking. However, it is first found in this paper that the faulty PMSM drive can be treated as an equivalent healthy PMSM drive, and MPC-I can be shared by both normal and postfault operations without any modification. The major contribution of this paper is to find this fact, and verify it with theoretical analysis and experimental validation. Obviously, this finding will simplify the whole control method of PMSM drives considering single-phase open-circuit fault. [ABSTRACT FROM AUTHOR]

A recent paper by Hoffmann et al. presents a discrete-time model in a rotating $dq$ reference frame of an R-L filter and its current control. The purpose of this note is, first, to show that the discrete model presented in the paper behaves differently to the sampled continuous-time model of the plant, formulated in the stationary $\alpha \beta$ reference frame; second, to find the proper discretization of the plant in $dq$ coordinates; and third, to verify that there is cross coupling between axes $d$ and $q$ in the closed-loop system if the original model is used, and that this coupling is not present when using the model found in this note. In the note, it is verified that having a precise model of the plant allows us to fulfill the control objective of obtaining the complete decoupling between axes. [ABSTRACT FROM AUTHOR]

In a hybrid ac/dc grid, the ac-side unbalance voltage introduces adverse effects on dc grids and interfacing converters (IFC) (active power oscillations, dc-link voltage oscillations, and IFC peak current increase at the same average power production). For parallel IFCs, these adverse effects can be easily aggregated. In this paper, two new control strategies are proposed for parallel IFCs to improve both ac and dc subgrids power quality. The proposed control strategies focus on canceling active power oscillations of parallel IFCs that provide oscillation-free dc link and sharing collective peak current of parallel IFCs. In the first proposed control strategy, IFCs’ power coefficients are controlled by solving a set of nonlinear equations, and this method is called as coefficient-based strategy, whereas, in the second proposed control strategy, peak currents of IFCs are controlled directly through the derived relationship of IFCs' peak currents under zero power oscillation in this paper, and this method is named as peak current based strategy. This peak current based strategy features much simplified calculation and could be easy to implement. To achieve control objectives, thorough study on parallel IFCs' peak currents is conducted. Based on the study, it is shown that the collective peak current of all IFCs is a constant under zero total active power oscillation, and therefore, keeping all IFCs' peak currents in the same phase and in-phase with collective peak current optimizes the utilization range of parallel IFCs. The numerical examples and experimental results are provided to verify the validity of the proposed control strategies under different operating conditions. [ABSTRACT FROM AUTHOR]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

This paper presents a fault diagnosis technique for high-resistance connection (HRC) in a nine-phase flux-switching permanent-magnet (FSPM) machine based on zero-sequence voltage components (ZSVC), where the neutral-point connection mode is considered. A nine-phase FSPM machine topology is first introduced and no-load back electromotive force waveforms are analyzed. Moreover, the topologies of the nine-phase FSPM drive with different neutral-point connection modes are studied. Then, the mathematical model of a nine-phase FSPM machine with HRC is established with the consideration of the neutral-point connection mode and then the influence of the HRC on the ZSVC is analyzed based on the established model. It is shown that the HRC may be diagnosed by monitoring the change of the spectral contents of the ZSVC. Furthermore, this paper focuses on the situation of the nine-phase FSPM machine with one neutral point. In this case, to remove the influence of the FSPM machine operating point, an effective fault indicator is defined and used for HRC fault detection. Finally, the simulation and the experiment are carried out to validate the proposed method. Both the results show that the proposed method can be applied for the HRC fault diagnosis in a nine-phase FSPM machine. [ABSTRACT FROM AUTHOR]

This paper presents a specific architecture for a low-side/high-side gate driver implementation for power devices running at high switching frequencies and under very high switching speeds. An electromagnetic interference (EMI) optimization is done by modifying the parasitic capacitance of the propagation paths between the power and the control sides, thanks to a specific design of the circuit. Moreover, to reduce the parasitic inductances and to minimize the antenna phenomenon, the paper studies which elements of the drivers’ circuitry must be brought as close as possible to the power parts. This is important when the ambient temperature of the power device becomes critical, for instance, in automotive and aeronautic applications. Simulations and experiments validate the advantages of the proposed architecture on the conducted EMI problem. [ABSTRACT FROM AUTHOR]

This paper proposes a new methodology to control a three-phase boost power factor correction (PFC) using a single dc output voltage sensor. Typically, a PFC control technique requires measurement from five independent sensors, i.e., two input voltages, one output dc voltage, and two input phase currents. Elimination of four sensors in the control system of a PFC converter is theoretically feasible and implementable without compromising stability and power quality of the converter, as analyzed and presented in this paper. The proposed control technique uses the ripple information of the measured dc-link voltage, converter dynamics, and switching states at a preceding sample in order to estimate the present state of four other unknown state variables and, thus, establishes the control method. A 2.2-kW experimental prototype of a three-phase boost PFC is developed and tested to verify the accuracy and applicability of the proposed control logic at different line and load conditions. According to the experimental measurements, conversion efficiency more than 98%, total harmonic distortion as low as 4.3%, and an output voltage ripple of ±2% are achieved at 2.2-kW output power. [ABSTRACT FROM AUTHOR]

This paper presents, initially, a systematic derivation of extended first harmonic approximation (FHA) analysis and, later, a comprehensive time-domain (T-D) analysis to study series–series compensated inductive power transfer (IPT) systems with a diode bridge rectifier. Further, the paper shows that both FHA and T-D methods predict four mutually exclusive and collectively exhaustive modes of operation. Explicit criteria for each operation mode and formulae for mode boundaries are derived and it is concluded that FHA can explain three of four modes. The proposed T-D analysis is capable of describing the quantitative behavior of the system in all four operation modes with closed-form equations for all the mode boundaries. This analysis provides an objective basis to assess the accuracy of FHA predictions under the entire operating conditions. Quantitative comparison of key variables revealed that the FHA results can be unacceptably inaccurate for certain operating points. It is shown that the T-D approach provides a comprehensive design base for series–series compensated IPT without a need to know the load value. The T-D predictions are validated by experiment. A mathematical design calculator tool is also provided to the reader to visualize the mode boundaries, all the waveforms and the numerical results from both methods. [ABSTRACT FROM AUTHOR]

This part of the paper illustrates the use of the expression derived in Part I for predicting subharmonic oscillation in switching regulators. Six case studies with different control schemes from the recent literature are used to validate the novel approach and the new derived expression, which is benchmarked for these case studies against results obtained using the discrete-time modeling approach or Floquet theory combined with Filippov method. Numerical simulations from the circuit-level switched models, implemented in PSIM software, are used to demonstrate the correctness of the derived closed-form condition. A procedure is presented to apply the approach of the paper to power converters with nonlinear sources, such as photovoltaic (PV) arrays or fuel cells. Experimental measurements from a boost converter prototype for PV applications are also provided to validate the theoretical predictions and the numerical simulations showing a remarkable agreement. [ABSTRACT FROM AUTHOR]

A three-phase three-level (TPTL) converter is an optimal alternative for high-input and high-power dc/dc conversion system. The voltage stress on the primary switch is only half of the input voltage due to its three-level (TL) structure, and the current rating of power devices can be reduced by the three-phase configuration. To achieve soft switching and improve efficiency, the resonant tank can be introduced to optimize the performance of the converter. In this paper, a novel TPTL LC-type series resonant converter with few switches and simple configuration is proposed. The voltage stress on all switches can be reduced to the half of the input voltage, and the voltage across output rectifiers is clamped to the output voltage; as a result, the proposed converter is suitable for high-input/output applications. Meanwhile, the ripple frequency of the output current can be increased significantly, resulting in a reduced filter requirement. Variable frequency control strategy is adopted in order to obtain zero-voltage switching for all switches and zero-current switching for all rectifier diodes in wide input voltage and load range. In this paper, the comprehensive analysis on the proposed converter is carried out, including the operation mode classification, the operating mechanism under different operation mode, along with the circuit model, and gain characteristics of the converter by the fundamental harmonic analysis. Experimental results from a 440–590 V input and 400 V/5 A output are presented to verify the theoretical analysis and the performance of the converter. [ABSTRACT FROM AUTHOR]

Nowadays, active-front-end rectifiers are increasingly used as grid connected devices. Their efficiency and performances have become relevant for reducing the overall grid losses. This paper thus introduces a predictive hybrid pulse-width-modulation (PH-PWM) technique, adaptable to any space-vector PWM (SVPWM) controller. As opposed to hybrid PWM techniques based on sector partitioning, the PH-PWM technique selects the appropriate PWM sequence online with the help of a predictive algorithm. This selection is based on a cost-function where users can define a tradeoff between various criteria, such as the reduction of current distortion and switching losses, as presented in this paper. The use of the PH-PWM technique increases performances in comparison with the conventional PWM techniques. The simulation and experimental results are presented to confirm the effectiveness of the proposed PH-PWM technique. Aside from the tradeoff capacity of the proposed PH-PWM technique, the simulation results validate a reduction of the switching losses for the converter up to 23$\%$ as compared with the conventional SVPWM technique. [ABSTRACT FROM AUTHOR]

This paper further develops the concept of very large size flash-memory-based pulsewidth-modulated (PWM) algorithms for three-phase inverters. Such algorithms differ from the conventional counter-based implementation, and they follow a preprogrammed optimal PWM pattern that is read from a very large size memory with magnitude and phase as coordinates. Any sequence of states is thus possible within a PWM sampling interval. A novel digital structure has been built around the newly released flash memory integrated circuits. The paper demonstrates the feasibility of operation at any PWM sampling frequency up to 20 kHz when using gigabit-size flash memory integrated circuits along any low-cost microcontroller with an SPI peripheral. To empower the concept, a multioptimal PWM has been proposed and implemented on a 2-Gbit memory table. The harmonics of the phase currents are reduced by more than 40% while a constant PWM sampling frequency is maintained in order to comply with the conventional vector control methods for grid or motor applications. [ABSTRACT FROM AUTHOR]

This paper presents a coupling method of power supplies to improve power density, efficiency, and dynamic response by taking the case of heater supply, ignitor supply, and keeper supply for hollow cathode of an all electric propulsion (AEP) Hall thruster. The working principle and timing characteristic of the coupled supply, as well as the three-loop control, current sampling and chopping switch control are also illustrated. With the proposed coupling method, the power density is improved since three supplies are coupled into one supply. Additionally, the test on the coupled supply prototype with 200 W maximum output power shows that the efficiency of the coupled supply could reach up to 89.7%, increasing by 3.9%–14.2% as being compared with that of traditional three supplies with heater current between 4 and 10 A, and the joint test of the coupled supply with an AEP hall thruster proves the achievement of fast dynamic response and the ability to extend useful life of hollow cathode. Hence, the coupling method proposed in this paper could achieve the power supply system with high power density, efficiency, and fast dynamic response. [ABSTRACT FROM AUTHOR]

To achieve high-performance control of modern dc–dc converters, using direct digital design techniques, an accurate discrete model of the converter is necessary. In this paper, a new parametric system identification method, based on a Kalman filter (KF) approach is introduced to estimate the discrete model of a synchronous dc–dc buck converter. To improve the tracking performance of the proposed KF, an adaptive tuning technique is proposed. Unlike many other published schemes, this approach offers the unique advantage of updating the parameter vector coefficients at different rates. The proposed KF estimation technique is experimentally verified using a Texas Instruments TMS320F28335 microcontroller platform and synchronous step-down dc–dc converter. Results demonstrate a robust and reliable real-time estimator. The proposed method can accurately identify the discrete coefficients of the dc–dc converter. This paper also validates the performance of the identification algorithm with time-varying parameters, such as an abrupt load change. The proposed method demonstrates robust estimation with and without an excitation signal, which makes it very well suited for real-time power electronic control applications. Furthermore, the estimator convergence time is significantly shorter compared to many other schemes, such as the classical exponentially weighted recursive least-squares method. [ABSTRACT FROM AUTHOR]

Rotor position estimated with high-frequency (HF) voltage injection methods can be distorted by voltage errors due to inverter nonlinearities, motor resistance, and rotational voltage drops, etc. This paper proposes an improved HF square-wave voltage injection algorithm, which is robust to voltage errors without any compensations meanwhile has less fluctuation in the position estimation error. The average position estimation error is investigated based on the analysis of phase harmonic inductances, and deduced in the form of the phase shift of the second-order harmonic inductances to derive its relationship with the magnetic field distortion. Position estimation errors caused by higher order harmonic inductances and voltage harmonics generated by the SVPWM are also discussed. Both simulations and experiments are carried out based on a commercial PMSM to verify the superiority of the proposed method and the investigations in this paper. [ABSTRACT FROM AUTHOR]

In transformerless high-power pulse width modulation (PWM) current-source drives, common-mode inductor is implemented to attenuate the common-mode voltage (CMV). However, the common-mode inductor is bulky and costly, so that scaling down the size of the common-mode inductor can achieve the system size reduction and efficiency enhancement. The size of the common-mode inductor is mainly related to the maximum common-mode current, which occurs at the resonant frequency of the common-mode circuit when motor speed is low. Previous research demonstrates that 3-segment average-value-reduction (AVR) space vector modulation (SVM) has good common-mode resonance suppression performance by attenuating the third-order CMV from the inverter. However, as studied in this paper, when modulation index of the inverter is lower than 0.4, the performance of 3-segment AVR SVM is affected as the dwell time of zero vector becomes too long to effectively compensate the CMV introduced by the active vectors. To overcome this problem, three modified AVR SVM schemes are proposed in this paper, where the single long zero vector is separated into two segments in the PWM sequence. The working principles, CMV reduction performance, harmonic performance, and switching frequency analysis of the proposed SVM methods are presented in detailed. Experiments are conducted to verify the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

This paper proposes grid current shaping method using dc-link shunt compensator for three-phase diode rectifier system without electrolytic dc-link capacitor. In the proposed method, the diode rectifier system can satisfy the grid regulation IEC61000-3-12 without any power factor correction circuit or heavy grid filter inductor. The proposed grid current shaping method can be realized by applying DSC with reduced-rating components and without electrolytic capacitor, which is connected parallel to the dc link. Since DSC has no electrolytic capacitor, the system with DSC has high circuit reliability. Furthermore, DSC can enhance the system efficiency, especially in flux-weakening area, since the motor drive inverter recovers the reduced modulation index, which has been spent in the additional control for small passive components. This paper presents the control method for DSC and analyzes the effect of proposed method. The feasibility of proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized design procedure for repetitive current controllers in distorted distribution grids to obtain good disturbance rejection properties and well behaved and robust system dynamics. Different implementation options for repetitive controllers (RCs) are discussed based on an accurate discrete time model. A simple control design is derived, which allows any desirable dynamics to be adjusted by one single parameter. Even a deadbeat design is possible. The impact of model inaccuracies and numerical errors on the dynamic and stability of the system is investigated. It is shown that the RC leads to low damping or even instability at high switching frequencies caused by modeling errors or numerical inaccuracies. Based on the stability analysis, it is discussed how to handle these design challenges, which exist especially for RCs of high order. The proposed control structure and control design concept is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

Flying-capacitor modular multilevel converter (FC-MMC) overcomes the zero/low-fundamental-frequency operation issues of conventional MMC without injecting common-mode voltage. However, the FC-MMC suffers from high current stress due to the large amplitude of inner high-frequency current. The square-wave design for the inner high-frequency components could effectively reduce the current stress, but the per-phaseLCcircuit (formed by arm inductor and flying capacitor) challenges the square-wave current control. This paper investigates the equivalentLCcircuit in FC-MMC, and proposes a control method to improve the performance of inner current control. Accordingly, the desired square wave is achieved for inner high-frequency current. The current stresses on semiconductor switches and flying capacitor are reduced by around 25% and 45%, respectively. Simulation and experimental results prove the effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

In this paper, it is shown how to obtain a low-cost, high-resolution, and fault-robust position sensing system for permanent-magnet synchronous motor drives operating in safety-critical systems, by combining binary Hall-effect sensors with high-frequency signal injection. It is shown that the position error signal obtained via signal injection can be merged easily into the quantization-harmonic-decoupling vector-tracking observer that is used to process the Hall-effect sensor signals. The resulting algorithm provides accurate, high-resolution estimates of speed and position throughout the entire speed range; compared to the state-of-the-art drives using Hall-effect sensors alone, the low-speed performance is greatly improved in healthy conditions and also following position sensor faults. It is envisaged that such a sensing system can be successfully used in applications requiring IEC 61508 SIL 3 or ISO 26262 ASIL D compliance, due to its extremely high mean time to failure and to the very fast recovery of the drive following Hall-effect sensor faults at low speeds. Extensive simulation and experimental results are provided on a 3.7-kW interior permanent-magnet drive. [ABSTRACT FROM AUTHOR]

A single-stage high-frequency resonant ac/ac converter converts the ac-line input voltage into the high-frequency sinusoidal output voltage, which consists of two power conversion units, i.e., a power factor correction (PFC) unit and a high-frequency resonant dc/ac unit, and it can be used to derive a modular multichannel constant current LED driver. By adopting a totem-pole bridgeless PFC boost rectifier to reduce conduction losses, a single-stage bridgeless high-frequency resonant ac/ac converter is proposed in this paper. The operating principle is described, and the performance analysis is presented in detail. Moreover, the quantitative parameter design method of the main circuit is presented, which is suitable for other single-stage ac input converters, such as a single-stage PFC rectifier. Finally, a 130-W prototype has been built and tested to verify the correction of related theoretical analysis and parameter design. [ABSTRACT FROM AUTHOR]

This paper presents the digital implementation of a boundary controller with unipolar switching characteristic for single-phase voltage source full-bridge inverters. This paper expands the application of a second-order switching surface-based control method to unipolar switching of single-phase voltage source inverters (VSIs) using a finite-state machine. The finite-state machine has been formulated considering four different states of the inverter; positive,zero1, negative, andzero2. The second-order boundary control governs the current state of the system and provides proper switching action to keep the system within the desired reference. The control law is implemented digitally in F28m35x digital control card. A full-bridge inverter topology is used to achieve the three-level voltage switching. Various simulations and experiments were performed in a 550 VA, 120 V, 60 Hz VSI with a digitally implemented controller to verify the theoretical predictions. A high-quality voltage output was obtained for various loading conditions. The transient performance of the controller was investigated using a reference and load changes. A comparison of the implementation was made with the existing classical controllers to verify the fast-dynamic response of the system. [ABSTRACT FROM AUTHOR]

For the purpose of increasing the reliability in a hostile environment, techniques of fault diagnosis have been reported for a three-phase voltage-source inverter (VSI). Based on the average current Park's vector method, this paper proposes a fuzzy-based fault diagnosis method for the VSI in the three-phase permanent-magnet synchronous motor drive. By utilizing the phase current information, the fault symptom variables are calculated by using the average current Park's vector method. The fuzzy logic approach is applied to process the fault symptom variables and obtain the faulty information of power switches. Compared with other fuzzy logic methods, the fuzzy logic design, fuzzy inputs, and fuzzy rules are different. The proposed fault diagnosis method can detect and locate not only the single or multiple open-circuit faults, but also the intermittent faults in power switches, which can improve the reliability of the motor drive system. The effectiveness of the proposed method is validated by both simulation and experiments. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of three aspects of the supercapacitor physics on its charge capacity: porous electrode structure, charge redistribution, and self-discharge. The relationship between the delivered charge and the discharge current is examined for both the upper and lower bounds of the utilized charge capacity, which refers to the amount of charge delivered during a constant-current discharge process. In the upper bound case, Peukert's law applies when the discharge current is above a certain threshold and does not apply anymore if the discharge current is below the threshold. In the lower bound case, if the discharge current is above a specific threshold, the delivered charge increases when the discharge current decreases although the increase rate is lower compared to that in the upper bound case. The individual and combined effects of the three supercapacitor mechanisms are studied. The porous electrode structure and the charge redistribution process result in an increase in the delivered charge when a smaller discharge current is applied. The impact of self-discharge is negligible when the discharge current is relatively large. If the discharge current is sufficiently small, self-discharge results in a significant energy loss and consequently a drop in the delivered charge. [ABSTRACT FROM AUTHOR]

Switching power supplies are sources of noise for sensitive circuits. Converters should comply with electromagnetic compatibility (EMC) rules so that the electromagnetic interference (EMI) caused by switching cannot interfere with the normal operation of adjacent circuits and also the converter itself. The produced interference can be in the form of conduction or radiation. In this paper, some techniques are used in switching converters to suppress EMI with emphasis on the conduction form. EMI analysis and evaluation of a conventional flyback converter and a proposed zero-current transition (ZCT) flyback converter is achieved by simulation and experimental results. In addition to evaluating some EMI suppression techniques, the main objective of this paper is to improve EMI in the topology design stage. The operating modes of the improved ZCT flyback are discussed. In addition to the efficiency improvement, the amount of EMI reduction of this ZCT flyback and the effectiveness of some EMI reduction techniques are shown by practical implementation. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid pulsewidth modulation (PWM) scheme is proposed to suppress the LC resonance for the high-power current-source inverter (CSI) fed drives with low switching frequency. In CSI drive systems, the selective harmonic elimination (SHE) is selected due to the better performance of harmonics, but the LC resonance cannot be effectively damped due to the lack of control flexibility of SHE. In this paper, SHE is only used for the steady-state operation. The modulation scheme is then switched to space vector modulation with dynamic capacitor voltage control when the transient event occurs. The smoothed transitions between different modulation schemes are proposed. The proposed hybrid method effectively solves the resonant issues in CSI drives, while maintaining the power quality. Both simulation and experiments verify the performance of the proposed hybrid PWM scheme. [ABSTRACT FROM AUTHOR]

This paper presents a study on the gate driver circuitries that need to be implemented to drive several power devices when associated in series connection. More specifically, the propagation paths of parasitic currents through the gate driver circuitries, exited under high switching speeds, are studied in different configurations trying to minimize common mode currents generated. In a gate driver circuitry for a regular low side–high side switching cell configuration with one upper switch and one lower switch, the voltage transient dv/dt at the middle point applied across the primary-secondary parasitic capacitance of gate driver supplies, and control signal isolation units are the reasons for the generation of conducted electromagnetic interference (EMI) perturbations. In complex power converters, multicell, multilevel, or even series connection of power devices, many driver circuits are required and implemented. Similarly, in such converters, there are several dv/dt sources generated at different floating points producing conducted EMI perturbations from the power part to the control part through many gate driver circuitries. Based on previous works, this paper analyzes the best configuration to minimize parasitic currents, especially reducing the conducted common mode currents in series connected transistors topologies. Simulations and practical results validate the analysis for two power devices in series connection, and then the extrapolations for more power devices in series connection, up to six are discussed and analyzed with the help of simulations results. [ABSTRACT FROM AUTHOR]

Dual active bridge (DAB) based converters offer the benefit of smaller volume due to high-frequency isolation and controllability of active power flow, making them attractive for various applications, such as renewable energy generation, plug-in hybrid vehicles, and distribution systems. This paper presents a novel converter topology along with a modulation strategy for a DAB-based three-phase ac to dc converter. The major benefits are single-stage conversion, no unreliable intermediate dc-link capacitor, reduced number of switches, i.e., only two active switches on the ac side, simple control scheme, open-loop unity power factor operation, bidirectional power flow, and partial soft-switching. This paper presents the analysis of all the operating modes of the converter, resulting in the analytical estimation of power transfer and rms winding current and investigation of soft-switching conditions for the power devices. Simulation and experimental results have been presented to demonstrate the advantages of the proposed technique and accuracy of the analysis.1 [ABSTRACT FROM AUTHOR]

This paper describes a multiphase pulsewidth modulation (MPWM) technique used for controlling the luminance of a solid-state lamp (SSL). For a SSL consisting of multiple high-brightness LEDs (HBLEDs) that are electrically connected as a series-parallel network, the desired output luminance is obtained by modulating the average current through each parallel HBLED string. In conventional pulsewidth modulation (PWM) and pulse code modulation techniques, the average HBLED string current is controlled by simultaneously varying the "ON" time duration of each current regulator circuit, resulting in large current transients and pulsating light output. The proposed MPWM technique operates by uniformly time-shifting the individual ON/OFF control signal pulses, thus avoiding large current transients. When compared to conventional PWM dimming, MPWM dimming reduces the risk of visible flicker and lowers the magnitude of audible noise. The reduced magnitude of output current transients results in lower electromagnetic interference and enables optimization of the size of passive components. In this paper, the operation of the MPWM technique is explained in detail. Experimental results are presented for a 27 W boost converter powering 64 HBLEDs with digital MPWM and digital voltage loop implemented using a Virtex-4 field programmable gate arrays. [ABSTRACT FROM AUTHOR]

This paper presents a simple voltage balancing scheme for m-level diode-clamped multilevel converters (DCMC). This paper first introduces a novel and simple current flow model for general m-level DCMCs. The superiority of the proposed model is its independence from the modulation scheme and its simplicity. It also provides a new perspective for voltage sharing accessibility among the dc link capacitors. The proposed current flow model, a cost function, and a space vector modulation (SVM) switching strategy are then used to balance the capacitors' voltages of the DCMCs in a very simple and optimized manner. Such a voltage balancing scheme was not developed for converters of five levels or greater due to the complexity of the converter and its modeling approaches. To validate the feasibility of the proposed voltage balancing scheme, this paper presents analytical and simulation results obtained from a five-level DCMC. In particular, this paper introduces a stability region within which the voltage balancing strategy converges. The impact of the cost function on the stability margins and converter performance is examined and discussed by means of comparison with different cost functions, and it is shown that the proposed cost function will improve the stability margins. The performance of the strategy for unbalanced and polluted loads shows that, unexpectedly, in some specific cases output current harmonics will improve the stability margin. [ABSTRACT FROM AUTHOR]

This paper explores the issue of balancing the inter- mediate inductor currents of a multilevel current source inverter (CSI). The paper begins by identifying that single-phase multi-cell CSIs and flying capacitor voltage source inverters (FCVSIs) form a topological dual pair. This allows the established understanding of the natural balance process of the FCVSI intermediate capacitor voltages to suggest that the intermediate inductor currents of the CSI should also settle to their target balance values when phase-shifted carrier (PSC) pulse width modulation (PWM) is used. This concept is confirmed by full switched simulations. Next, an analytic model is developed to explore the dynamic response and robustness of the balancing process, using a double Fourier series representation of the converter switching signals to linearise a nonlinear transient circuit model. The model is verified against simulations, and predicts that the resistance of the intermediate inductors can perturb the steady state balancing point. The model further predicts that the resistance of the inductance must be small compared to the load resistance to minimize this effect. Results obtained on a five-level experimental CSI precisely match the theoretical model and hence support these conclusions. [ABSTRACT FROM AUTHOR]

While the matrix converter has many advantages that include bidirectional power flow, a size reduction, a long lifetime, and sinusoidal input currents, it is vulnerable to the input voltage disturbances, because it directly exchanges the input voltage to the output voltage. The instantaneous effective power control (IEPC) method has been proposed to compensate the input voltage disturbances, in which the instantaneous effective power is kept constant by controlling input current. However, to date, no method has been proposed to maintain the stability of the system with the IEPC. The purpose of this paper is to propose a method to control the stability of the system with IEPC. First, this paper explains the IEPC theoretically. Next, a model of the system with the IEPC is developed, and stability analyses are conducted. Then, based on the results of the analyses, a stability control method for the system with the IEPC is proposed. Furthermore, the validities of the proposed method are demonstrated by simulation and experiments. Finally, a restart performance of the system after momentary power interruption is discussed. Because the IEPC does not need phase-locked-loop to detect the phase angle of the input voltage, fast restart is expected. [ABSTRACT FROM AUTHOR]

This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive electromagnetic interference (EMI) filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper. [ABSTRACT FROM AUTHOR]

This paper compares the many fault tolerant three-phase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of dq components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon over-rating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter. [ABSTRACT FROM AUTHOR]

A comprehensive literature review shows that transformer-based solutions are superior for the mitigation of inrush currents than external (to the transformer) solutions. The use of air gaps and low-permeability (iron) materials are known techniques for this purpose. This paper investigates the effectiveness of these approaches for reducing inrush and phase-hop currents. Studies are carried out on toroidal transformers, due to their broad application in power electronics devices. Contrary to common belief, this paper demonstrates that air gaps do not reduce the inrush currents when a transformer is fully demagnetized. However, inrush currents can be mitigated by the use of low-permeability iron materials. It is also demonstrated that air-gaps significantly reduce inrush currents when transformers have residual flux, e.g., for phase-hop conditions. Analytical expressions are derived to compute the mitigation factor for a specific gap length. The results and formulae presented in this paper are verified with laboratory experiments, transient simulations with validated circuit models, and 2-D finite element simulations. [ABSTRACT FROM AUTHOR]

In order to balance the light-emitting-diode (LED) current in each channel, many active and passive methods have been investigated. Among the various methods, the passive method using the LLC converter with a blocking capacitor or flyback converter with a current-sharing transformer (CST) in the secondary side is one of the simplest methods because it does not use any active component. However, the LLC driver requires two main switches and external resonant inductor to obtain a wide output voltage range. Also, flyback with a CST requires an additional magnetic component for CST and high-voltage rated diodes, resulting in the limitation of the cost and system volume. In this paper, a single-switch forward-flyback driver for a two-channel LED is proposed. The most powerful advantage of the proposed driver is the cost effectiveness, since it eliminates additional magnetic component. Furthermore, due to the reduced-voltage stress on rectifier diodes compared to the flyback driver, the proposed driver achieves a higher efficiency. The prototype of the 150–100-V/0.3-A two-channel LED verifies the effectiveness of this paper. [ABSTRACT FROM PUBLISHER]

This paper proposes an inductors coupling technique to cancel input current ripples of a quasi-Z-source inverter (ZSI) without adding any additional components. The source input filter thus might be suppressed. This remains valid whatever the boost factor value. This cancellation property is made possible by a suitable coupling of the two existing quasi-Z-source inductors according to mathematical condition. The considered system in this paper is an electric drive system composed of a motor fed by the proposed coupled quasi-ZSI. An experimental prototype to validate both the theoretical and simulation analyses has been developed. The results have validated the proposed coupling strategy and show that it does not degrade the global efficiency of the system. [ABSTRACT FROM PUBLISHER]

This paper presents an alternative approach to address the control and modulation problem of single-phase three-level converters applied in the high-speed railway electrical traction drive system. Following the principle of deadbeat predictive direct torque control of ac motors, this paper discusses an improved direct power control (DPC) method based on a deadbeat active and reactive power prediction technique. Comparing with the conventional PI-based DPC scheme, the proposed deadbeat predictive DPC scheme can provide these advantageous features: lower current harmonics and THD index, lower active and reactive power ripples, and fewer adjusted parameters. Moreover, compared with PI-based DPC with the PI parameters optimization, this approach can also easily obtain fast dynamic response but without the main voltage orientation. A single-phase three-level space vector pulse width modulation (SVPWM) with inherent neutral-point voltage balancing capability is adopted, which can be combined with DPC scheme as an overall control and modulation system. A series of simulation and experimental tests have been conducted to demonstrate an excellent performance of the deadbeat predictive DPC. In addition, the neutral-point-voltage balancing ability of the adopted SVPWM method has been verified. [ABSTRACT FROM PUBLISHER]

This paper has presented a stability analysis of a LCL-type grid-connected inverter in the discrete-time domain. It has been found that even though the system is stable when the resonance frequency fr is higher than one-sixth of the sampling frequency ( fs/6), an effective damping scheme is still required due to the potential influence of the grid impedance. With a conventional proportional capacitor-current-feedback active damping (AD), the valid damping region is only up to fs/6. This however is not sufficient in the design process for obtaining a high quality output current and the system can easily become unstable due to the resonance frequency shifting. Considering the resonance frequency design rules of the LCL filter, this paper proposes an improved capacitor-current-feedback AD method. With a detailed analysis and proper parameter design, the upper limit of the damping region is extended to fs/4, which can cover all the possible resonance frequencies. Then, the damping performance of the proposed AD method is studied. It shows that the optimal damping is obtained when the actual resonance frequency is (fr + fs/4)/2. Moreover, an approximate calculation for the optimal damping coefficient R is given. Finally, the experimental results have validated the effectiveness of the proposed AD method. [ABSTRACT FROM AUTHOR]

A DFIG connected to a dc bus by a diode rectifier and a unique reduced-power PWM converter is considered in this paper. With respect to the traditional ac-grid connected DFIG, such a layout avoids the grid-side PWM converter and is an interesting solution to integrate the DFIG in a dc microgrid together with other generating units, loads as well as storages. The peculiarity of the DFIG, which allows the control of the rotor current space vector independently of the mechanical position, offers two important benefits when the stator is connected to a constant voltage dc grid by a diode bridge: it avoids the need to boost the flux amplitude at low speed, and it allows to considerably reduce the torque ripple due to the diode commutation. This last issue is developed in this paper by using a field-oriented control scheme based on proportional-integral and resonant Controllers. The proposed control is validated through simulation and experiments. [ABSTRACT FROM AUTHOR]

This paper presents an intensive discussion on a transformerless back-to-back (BTB) system using modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). It is expected to be applied to a power distribution system with many distributed power generators. This paper designs, constructs, and tests a three-phase 200-V, 10-kW DSCC-based BTB system installed on a 200-V, 40-kW power distribution simulator consisting of two radial feeders. Experimental results show that the BTB system can mitigate power-flow imbalance between the two feeders. Moreover, the zero-sequence current circulating between the two feeders can be suppressed to be as small as 10 mA (0.02%) in rms by connecting a common-mode choke to the common dc link of the BTB system. [ABSTRACT FROM AUTHOR]

Two-stage single-phase inverters have been widely used as they can achieve voltage matching and galvanic isolation between the input and output. Due to the pulsating output power of the downstream inverter, an ac current at twice the output frequency, which is called second harmonic current (SHC), arises in the input side of the downstream inverter. This SHC will penetrate to the front-end dc-dc converter, leading to reduced conversion efficiency. This paper first analyzes the propagation mechanism of the SHC and load transient response of two-stage single-phase inverters from the viewpoint of output impedance. Then, based on the current mode control and load current feed forward, two control methods to achieve low SHC in the front-end dc-dc converter and fast dynamic performance during load transient are proposed in this paper. Finally, a 2-kW two-stage single-phase inverter prototype has been constructed and tested, and the experimental results are provided to verify the effectiveness of the proposed control methods. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is an emerging and highly attractive multilevel converter topology for high-voltage and high-power applications. This paper proposes the control method of parallel-connected modular multilevel converters (parallel-MMCs), which assumes that the multiple MMCs are directly connected at both ac and dc sides to effectively enhance the power rating as expected. Two key problems were first solved for the parallel-MMCs under the normal operation conditions: voltage balancing of submodules and mitigation of circulating currents, where the novel transformed third-order harmonic resonant controller in the synchronous reference frame was employed to mitigate the dominant second-order and fourth-order circulating currents and a sixth-order harmonic resonant controller is used to attenuate the zero-sequence sixth-order circulating current existed in all phase currents per MMC. Considering the high risk of switches fault in the parallel-MMCs, the fault-tolerant operation schemes were then proposed in this paper to address the major concerns of open-circuit and short-circuit switch fault in a submodule, respectively. Carefully controlling the healthy submodules and the corresponding phase arms, the parallel-MMCs can successfully maintain their balanced capacitor voltages and mitigate the circulating currents with the qualified output waveform obtained. In addition, the parallel configuration of MMCs provides the unique solution for the short-circuit switch fault operation which was seldom discussed in the published literature works with respect to the MMC fault-tolerant operation schemes. MATLAB simulations and the constructed experimental prototype have verified the performance of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Adaptive linear neuron (ADALINE) is widely used in parameter estimation due to its algorithmic simplicity and parallel computing nature. One of the most popular training schemes for ADALINE is the least-mean-squared (LMS) rule, which can be implemented online to reduce the computation and storage requirements greatly. In this paper, an optimal current harmonic extractor based on unified ADALINEs for the shunt active power filter (APF) is proposed to achieve a better dynamic performance and reduced computation burden. The proposed control algorithm consists of three ADALINEs. Two ADALINEs are used for frequency estimation and supply voltage synchronization, while the third ADALINE is used to extract the fundamental active component of the load current. The main factor that affects the estimation speed and accuracy is the learning rate involved in LMS weight-update rule. Generally, this learning rate is selected by trial and error. In this paper, the learning rate of each ADALINE is tuned using particle swarm optimization to achieve the best dynamic performance. Furthermore, an adaptive learning rate for the frequency-ADALINE is proposed to enhance the estimation speed. The proposed ADALINE-based control structure is validated with a detailed experimental study. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of charge redistribution on supercapacitor charge capacity by experimentally estimating the charge capacity bounds. An analysis of a physics-based $RC$ ladder circuit model for supercapacitors reveals the theoretical bounds and provides guidelines for designing experiments to estimate the bounds. The upper bound corresponds to a long time constant voltage charging process and the lower bound is established using a charging process with the largest possible current. Bounds of two types of supercapacitor charge capacity are estimated: the total charge stored in the supercapacitor that can be released during multiple discharging processes and the utilized charge delivered during one discharging action. The relationship between the utilized charge capacity and the discharge current is examined and different patterns are observed depending on the supercapacitor state of charge. For a fully charged supercapacitor, the utilized capacity increases when the discharge current decreases. For a supercapaictor partially charged by a relatively large current, the utilized capacity is dependent on both the discharge current and the supercapacitor operation voltage range. The difference between the bounds is significant for both types of charge capacity. These observations provide guidelines for optimizing the supercapacitor charging and discharging policies for different applications. [ABSTRACT FROM AUTHOR]

This paper presents a low-dropout (LDO) regulator structure that is aimed at rechargeable battery powered systems where direct sensing of the load voltage is not available. The cable connecting the regulated output to the load may create a voltage drop and cause error to the load voltage. Conventional methods address this issue by increasing the LDO output voltage to compensate the cable voltage drop. The proposed architecture extends this idea by including a calibration block that updates the required compensation voltage to track the cable resistance shift due to cable length or temperature change. The measured cable-drop error was reduced from 2.4% to ∼0.1% by iterating the proposed calibration process three times. Under the condition of time-varying temperature, the measured calibration process effectively reduced the cable-drop error due to the temperature-coefficient of the cable resistance. The proposed system also includes a current management block, by which the priority is set between the load current and the battery charging current. This paper proposes two architectures, the two-cable and the three-cable structures, to implement both the cable-drop calibration and the current management functions. Other functions such as input under-voltage-lockout and output current-limiting are also included and have been verified by experiment. [ABSTRACT FROM AUTHOR]

Constant output current is desirable for some wireless power transmission applications such as charging batteries and driving light-emitting diodes. Converters having an inherently small output current fluctuation versus variations of load and coupling are attractive solutions since such converters can be controlled to achieve constant current with minimum control efforts. In this paper, the impedance conditions and the output current characteristics for different compensation types are presented. It is shown that the types of compensation producing load- and coupling-independent output current at the designed operating point as well as having a unimodal dependence of the output current on coupling would achieve better output current performance against variations of load and coupling. The sensitivities of the output current to parameter variation of typical compensation types are quantitatively analyzed and compared. Analytical results indicate that the primary parallel–series and secondary series compensation, which produces output current that exhibits a unimodal relationship with coupling and is nearly immune to coupling variation at the designed operating point, has the smallest output current fluctuation versus variation of the coupling coefficient. Finally, a comparison of experimental results of different types of compensation is presented for verification. [ABSTRACT FROM AUTHOR]

This paper presents the active capacitor voltage-balancing (ACVB) methods based on the dynamic model for a five-level nested neutral-point piloted (NNPP) converter using hybrid carrier modulation. The traditional hybrid carrier modulation provides natural voltage balancing of floating capacitors and dc-link capacitors. First, the natural voltage-balancing ability under steady-state and ideal conditions is theoretically proved. However, there are accumulated errors and deviations of capacitor voltages in practical applications, especially under dynamic conditions. In order to address the accumulated errors and deviations of capacitor voltages, the dynamic models of floating-capacitor voltages and neutral-point voltage are established. Moreover, the ACVB method based on the dynamic model of the neutral-point voltage is proposed by injecting the zero-sequence voltage. And the ACVB method based on the dynamic model of floating-capacitor voltages is proposed by introducing the adjustment variables. The proposed ACVB methods have the advantages of simple formula, definite physical meaning, and high accuracy. Furthermore, the output voltage quality and current quality are evaluated in term of total harmonic distortion and the effect of model parameter mismatch on the proposed ACVB methods is presented. Finally, the comparative simulation and experimental results verify the correctness of the proposed ACVB methods based on the dynamic model under different conditions. [ABSTRACT FROM AUTHOR]