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In this paper, an input-series flyback converter with the coupled-inductor-based passive snubber is proposed, where the input-series converter is based on transformer integration, and the passive snubber is composed of inductors, capacitors, and diodes. The inductors of the snubber in various series modules are made on a common magnetic core, and the coupled-inductor scheme is adopted. With the help of the coupled inductor, active input voltage sharing of the input-series converter can also be achieved after the switches are turned off, and voltage sharing of the switch in each series module can be ensured, which overcome the shortcomings of the existing input-series flyback converter. Active voltage sharing processes caused by the coupled inductor are analyzed in detail. Furthermore, the design guideline of the passive snubber is discussed. Finally, the experimental study has been done on a 1500 Vdc/60 W laboratory-made prototype composed of three flyback series modules, and the feasibility of the proposed method and the theoretical analysis is verified by the experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with torque ripple estimation and reduction in a vector controlled double-inverter-fed wound rotor induction machine (DI-WRIM) drive by employing different pulsewidth modulation (PWM) techniques applied to stator and rotor side voltage source inverters (VSIs). The influence of PWM switching sequences on torque ripple is studied in terms of stator and rotor flux ripples. A novel rotor speed independent transformation has been proposed to visualize the nature of stator and rotor flux ripples from a common frame of reference. The expression for instantaneous torque ripple is formulated and a PWM combination is proposed resulting in lower root mean square (rms) and peak–peak torque ripple. The estimated instantaneous, rms, and peak–peak torque ripple is verified through simulation and experimental results from a 3-kW vector controlled DI-WRIM drive. [ABSTRACT FROM AUTHOR]

This paper proposes a single-vector-based model predictive control (MPC) for an induction motor drive supplied by a three-level neutral-point-clamped inverter operating at a low switching frequency. Unlike the torque and flux control in the conventional MPC, the proposed MPC tries to minimize the error between the applied voltage vector and a reference voltage vector obtained based on the principle of deadbeat control, thereby reducing the number of weighting factors in the cost function. To reduce the computational burden and restrict the high jumps in both phase and line voltages, two switching tables are proposed and compared for the preselection of candidate voltage vectors. The neutral point potential fluctuation and switching frequency are also included in the cost function to achieve the balance between the upper and lower dc voltages and a relatively low switching frequency. Furthermore, a speed adaptive stator flux observer with a novel gain matrix is proposed to achieve speed-sensorless operation, which has a higher speed and flux estimation accuracy than conventional fixed gains. Finally, the proposed MPC is extended to the field-weakening operation by adjusting the torque and stator flux references online, which significantly widens the speed range and improves the practical value of the MPC. The effectiveness of the proposed method is confirmed by the experimental results obtained at an average switching frequency of less than 600 Hz. [ABSTRACT FROM AUTHOR]

This paper proposes a solid-state pulsed power modulator (PPM) with fast rising/falling time and high repetition rates to drive pockels cells. Since the proposed circuit is based on the modular structure using silicon carbide (SiC) metal–oxide silicon field-effect transistors (MOSFETs) for bypass devices as well as for main switches, it can achieve fast switching speed and high reliability. In addition, by a control scheme employing the voltage difference, the proposed circuit can accomplish a high repetition rate and short pulsewidth. Design and implementation of 1.8-kV PPMs with repetition rate of 1 MHz and rising/falling time below 6 ns are presented. Also, important issues for the practical use of the SiC-based PPM are discussed. Experimental results from the developed PPMs are shown to verify the proposed works. [ABSTRACT FROM AUTHOR]

In this paper, an expandable single-input three-output high step-up dc–dc boost converter is proposed. The voltage conversion ratio of the output ports of the converter can be increased by inductor-diode-capacitor and diode-capacitor cells. The proposed converter can be applied in renewable energy conversion systems, such as in photovoltaic and fuel cells. Also, due to the three output ports of the converter, it can be utilized in portable devices which require high voltage conversions. The main advantage of the proposed converter is supplying loads with different voltages and current ranges due to the expandable structure of the converter. Besides, the proposed converter has the merit of achieving high voltage gains at high frequencies without preselecting wide duty cycles. Furthermore, the proposed converter is able to achieve higher voltage ranges without having any transformer or coupled inductors in its structure; consequently, the related drawbacks are avoided. The switching pattern of the converter is simple and both switches are on and off simultaneously. In this study, a single switching period of the proposed converter, the voltage conversion ratios of the output ports and the expanded form of the structure are analyzed theoretically. Finally, to verify the theoretical results, the experimental results for 40-V input/200-V, 100-V and 360-V outputs with total 600-W output power are extracted and compared with each other. [ABSTRACT FROM AUTHOR]

Series–parallel forward dc–dc converter system is a good option in high-voltage high-power applications. A switch fault, in this converter, should be detected as soon as possible, to avoid further damage and save maintenance cost. In this paper, a new switch fault diagnosis method, which treats output inductor voltages as diagnostic criteria, is proposed for this system. With the proposed method, expensive sensors are needless, since diagnostic signal can be easily acquired by adding a small auxiliary winding into inductor magnetic core. Based on the feature of diagnostic signals in such a system, a low-cost diagnostic circuit is designed. The failed module caused by open-circuit fault or short-circuit fault could be detected within one switching period, allowing for an immediate fault-tolerant action. This method also shows generality for different connections and buck-type isolated topologies. Besides, it works reliably under input-voltage variation and load step, and no misdiagnosis will occur during normal dynamic process. Finally, experimental result verifies the effectiveness of this method. The proposed scheme has a good potential to be applied in real applications for its simplicity and robustness. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

This paper presents the design, analysis, and verification of a novel reaching law for discrete-time sliding-mode control. The control gains of the reaching law are automatically regulated by the power function and the exponential term that dynamically adapts to the variation of the switching function. The reaching law also employs the perturbation estimation and the difference function to redefine the change rate as the second-order difference of the uncertainty. Compared with previous methods, the proposed reaching law has the capability to amend the control gains in a wise manner, further mitigate chattering, and guarantee a smaller width of the quasi-sliding-mode domain (QSMD). In order to describe the system dynamics in the reaching phase and the sliding phase with respect to control gain values, both the decrement band and the QSMD (ultimate band) of the proposed reaching law are theoretically analyzed. The reaching steps for the switching function to converge toward the sliding surface are also obtained. The effectiveness of the proposed method is verified through numerical simulations and experimental investigations on a piezoelectric actuator. [ABSTRACT FROM AUTHOR]

This paper presents a hierarchical Markov model to assess the reliability of a double-sided linear switched reluctance generator (DLSRG) system. The proposed reliability model can be applied to find the balance point of reliability assessment accuracy and model complexity. First, the dominant fault modes of the DLSRG system are highlighted to quantitatively obtain the operation states, survival or failure, with a novel failure criterion. Second, a hierarchical Markov model is adopted to build a systematic reliability model of the DLSRG system, wherein a state transition diagram can be built in the detailed description to constitute the graphical Markov reliability model. And then the solving process to get state probability matrix P(t) is intensively investigated. Notably, a reliability block diagram model is also built to compare with the hierarchical Markov model, whose results verify that the Markov model can capture the effect of fault-tolerance capability on system reliability. Moreover, it is expected that the one-level Markov model is the most suitable model for the DLSRG system for its ability of decreasing the model complexity and improving the assessment accuracy. Analytic investigation in conjunction with simulation and experimental measurements demonstrates the feasibility and validity of the proposed model. [ABSTRACT FROM AUTHOR]

A nonisolated bidirectional dc–dc converter with high voltage gain, low voltage stress, low component count, and soft-switching features is presented in this paper. In this topology, coupled inductors and voltage multiplier cells are merged to achieve high step-up/down voltage gain. Also, due to using active clamp circuits, the voltage stress of power switches is relatively low. Thus, the low voltage switches with low on-resistance can be employed to reduce the conduction losses. Furthermore, zero-voltage switching is accomplished in both high step-up and high step-down modes for all power switches, and due to zero-current switching operation of all antiparallel diodes, the reverse recovery losses are reduced. In order to verify the theoretical analysis and the converter performance, a 200 W prototype circuit of the proposed converter is implemented in the laboratory. [ABSTRACT FROM AUTHOR]

Due to the pulsating power at the inverter output terminals, the passive storage elements of the boost stage of the current-fed switched inverter (CFSI) contain a power frequency harmonic component (100 Hz), apart from dc and switching frequency components. In prior designs, the second harmonic component is suppressed by increasing the size of the input filter inductor and capacitor or by using additional circuits. This paper presents a complete characterization of a control-based approach to suppress the power frequency harmonic component in the input inductor current of a CFSI. It also presents a comprehensive characterization of the harmonic power redistribution. Using the proposed approach, it is demonstrated that the inductor value of a CFSI is reduced by 61% for the same peak-to-peak ripple. This leads to an improvement in the conversion ratio, efficiency, and power density of the overall converter. A SiC MOSFET-based CFSI with 75-kHz switching frequency is used to verify the proposed design philosophy. [ABSTRACT FROM AUTHOR]

Model-predictive current control (MPCC) is a promising candidate for modular multilevel converter (MMC) control due to its advantages of direct modeling and fast dynamic response. The conventional MPCC, which obtains the optimal control input by evaluating a cost function for all the possible switching states, may make the MPCC impractical due to the exponentially increasing computation burden with the increasing number of submodules (SMs). On the other hand, the MPCC experiences high load current and circulating current tracking errors, since only one switching state is selected and applied during one control period. To address these issues, this paper proposes an MPCC with phase-shifted pulsewidth modulation (PS-PWM) for improving the steady-state control performance. The arm voltages are considered as a whole to implement the proposed MPCC. The optimal duty cycle is obtained based on the load and circulating current tracking error minimization and applied using the PS-PWM. As a result, the computation burden is unrelated to the number of SMs by avoiding the exhaustive evaluation process for all the possible switching states. A better steady-state performance with smaller tracking errors is achieved with the similar switching frequency, and the tedious tuning process of the weighting factor is eliminated. Experimental results are presented to demonstrate the effectiveness of the proposed MPCC. [ABSTRACT FROM AUTHOR]

This paper presents a high-efficiency inverter with the aid of the soft-switching technology, which is accomplished by the resonance of the in-series inductance with the snubber capacitance. The equivalent circuit of the quarter-phase ultrasonic motor is initially deduced, based on which the topology along with the operations of the novel inverter is subsequently presented. The configuration of the new quarter-phase inverter shows its uniqueness in terms of the shared arms and the especially designed snubber capacitance in comparison with the existing inverters. The circuit analysis infers that the dead time of the inverter is the key factor to arrive at the zero-voltage-switching or the zero-current-switching operations. Experimental measurements have demonstrated that the efficiency of the whole drive increases by a factor of 1.25 after replacing the traditional inverter with the proposed one. It should also be noted that the proposed inverter in association with the design method of the dead time not only can work for the quarter-phase ultrasonic motor, but also can be applicable for other kinds of quarter-phase devices. The soft-switching operations are achieved in the quarter-phase inverter for the first time, whose amplitudes of the output voltage and switching frequency are not required to be constant any more. [ABSTRACT FROM AUTHOR]

Two parallel interleaved two-level (2L) three-phase voltage source inverters (VSIs) can be analyzed as a single three-level (3L) VSI. A generalized carrier-based method is proposed in this paper for implementing different 3L pulsewidth modulation (PWM) techniques using two parallel interleaved 2L VSIs. The proposed method modifies the given three-phase reference signals of 3L VSI for implementation of the PWM technique using two parallel interleaved 2L VSIs. The influence of nonidealities on the equivalent 3L PWM switching sequences is also discussed. To overcome the effect of nonidealities, a new modified discontinuous PWM technique (MDPWM1) is proposed. The analysis of different performance indices is carried out for different 3L PWM techniques, and the key advantages of different PWM techniques are identified. Simulation and experimental results are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) dc–dc converter using triple phase shift (TPS) control to enable closed-loop power regulation while minimizing current stress. The key new achievements are a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e., Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed-loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter ac rms current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the rms current in the entire bidirectional power range of –1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool, which is carefully analyzed to derive simple useful relations. Such relations enable a generic closed-loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate the precision of the proposed closed-loop controller under various operating conditions. An experimental prototype also substantiates the results achieved. [ABSTRACT FROM AUTHOR]

In this paper, a high step up converter consisting of an integrated quadratic-boost converter and a voltage doubler is proposed. The integration of the quadratic-boost converter makes the system easier to lift up its voltage gain through slightly increasing the duty ratio of the single switch. The voltage doubler further increases the voltage gain of the system as the turn ratio rises. The voltage stresses on the switch and the diodes are decreased for such cascaded topology. Different operation modes are analyzed and mathematical analysis of the converter is presented in detail. The leakage inductance contributes to realizing zero current switching of the diodes in the second boost stage and the doubler and the energy can be recycled to the load. A 38-W prototype is built to work as a vehicle LED driver. Experiments are conducted to verify the advantages of the proposed converter and the efficiency is 90% at the nominal operating point. [ABSTRACT FROM AUTHOR]

This paper explores a power-conversion system for single-phase transformerless ac module application. A nonisolated high-gain dc–dc stage is coupled with a doubly grounded dynamic dc-link inverter to implement the microinverter topology. The front-end boost stage steps up the single-module voltage to a higher dc voltage, typically to 200 or 400 V as required for the following inverter stage. It is a hybrid of an interleaved boost and switched capacitor concept capable of achieving high gain while simultaneously maintaining reduced voltage and current stress, and thus lowering switching and conduction loss for most of the switches. By directly connecting the grid neutral to the photovoltaic (PV) negative, the doubly grounded voltage swing inverter has the advantage of zero capacitive-coupled common-mode ground currents, critical for transformerless PV inverters. The two dc links of the inverter stage share the double-line frequency power decoupling with a combination of higher value of mean voltage and relatively large 120-Hz ripple component–the dynamic dc-link approach. Through an optimization algorithm, the decoupling capacitance is minimized enabling an all-film capacitor implementation while satisfying the converter's operating constraints over a wide range of power factors. The simulation as well as experimental results from a GaN-based hardware prototype validate the converter's performance. [ABSTRACT FROM AUTHOR]

In recent years, modular multilevel converter (MMC) is considered for medium-voltage variable speed drives (VSD) due to its modularity and higher reliability. However, the major drawback of the MMC-based VSD is the higher capacitor ripple voltage at lower operating speeds. In literature, this ripple voltage is reduced by injecting a high-frequency circulating current into each arm. This additional circulating current increases the overall current rating of the devices, inductors, and capacitors. Alternatively, the capacitor ripple voltage can be reduced at the lower output frequency by reducing the dc-bus voltage. This paper proposes a new configuration using a multipulse diode-bridge rectifier to reduce the dc-bus voltage when the drive is operated at lower speeds. Therefore, the capacitor ripple voltage decreases without injecting any circulating current. In addition, a new technique is proposed to maintain the peak-to-peak value of the submodule capacitor ripple voltage constant at near-zero speed. The proposed converter with 24-pulse rectifier configuration is simulated in MATLAB/Simulink, and the experimental validation is carried out on a prototype with 12-pulse rectifier. [ABSTRACT FROM AUTHOR]

The development of a photovoltaic ac module composed of a high static gain nonisolated dc–dc converter with current source output characteristic followed by an unfolding low-frequency inverter is presented in this paper. The operation of the dc–dc converter with high static gain and with reduced switch voltage is obtained using the Cuk converter integrated with the switched-inductor technique. The nonisolated structure allows the elimination of the volume and losses of the power transformer and leakage inductance, and an output filter configuration is proposed to reduce the high-frequency ground leakage current. The grid-tied inverter operating in a discontinuous conduction mode (DCM) allows a sinusoidal output current with low harmonic distortion (THD = 3.72%) to be obtained without current control loop and without the use of a current sensor at the output. The maximum power point tracking operation is obtained without the use of the current sensor. The DCM operation increases the current stress, but the proposed converter presents two switches and two input inductors sharing the input current in these components. The theoretical analysis, design procedure, and experimental results are presented for a prototype with a dc input voltage Vi = 30 V, an ac output voltage Vo = 127 V, and output power Po = 180 W. [ABSTRACT FROM AUTHOR]

This paper presents a five-phase dual random space vector pulsewidth modulation (FPDR-SVPWM) strategy with an optimized probability density function (PDF) for a five-phase voltage-source inverter, and its performance and evaluation are also analyzed. Based on the nearest four vectors modulation method, the FPDR-SVPWM strategy, combined with random switching frequency and random zero vector, is investigated to significantly reduce the amplitude of high-order harmonics near the switching frequency and its integer multiples. For the nonsinusoidal power supply, third harmonic injection is introduced in this modulation strategy as well. Considering the effect of random numbers on the performance, an optimized Beta distribution is studied in detail. In order to analyze harmonic dispersion degree qualitatively and quantitatively, the power spectral density and the harmonic spread factor are both employed to assess the performance of the FPDR-SVPWM strategy. A series of results of simulation in MATLAB and experiments based on field programmable gate array demonstrate that the proposed modulation strategy is correct and valid, and it distributes high-order harmonics into a wide range without affecting the fundamental wave and third harmonic. [ABSTRACT FROM AUTHOR]

In this paper, the averaged small-signal model of the dual-interleaved buck converter is extended to include the phase interaction effects that arise from the interleaved sampling of the phase currents. Sampler decomposition techniques are used to extend the averaged model, revealing a slow-scale instability that can place significant restrictions on the choice of controller parameters. The model is confirmed by simulations and measurements using a 60-kW dual-interleaved prototype with an interphase transformer; however, the analysis is equally applicable to interleaved converters without magnetic coupling. [ABSTRACT FROM AUTHOR]

To reduce the common-mode voltage (CMV) and eliminate the CMV spikes for two-level voltage source inverters (2L-VSIs), an improved model predictive control (MPC) based CMV reduction method is proposed in this paper considering dead-time effects. First, an improved voltage vector (VV) preselection strategy is proposed to reduce the CMV spikes caused by the dead time. Second, a new hybrid VV preselection strategy based on a delay compensation strategy and a modified current sector division strategy is proposed to completely eliminate the CMV spikes. As the proposed hybrid VV preselection based MPC strategy makes full use of the six nonzero VVs of the 2L-VSI, the current total harmonic distortions and ripples are reduced. The simulation and experiments are carried out to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this paper, a new modified single-switch single-ended primary inductor converter (MS2-SEPIC)-based high step-up dc–dc converter is presented. The proposed topology uses the coupled-inductor (CL) technique and a voltage tripler rectifier, which results in a high voltage gain for the converter. Here, the switching loss has been reduced significantly owing to the quasi-resonance operation of the circuit created by the leakage inductance of the CL along with circuit capacitors. The operational principles and steady-state analysis are discussed. Experimental results based on a 100 W laboratory prototype verify the validity of theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a fixed switching frequency model predictive current controller is designed and implemented on a sensorless five-level packed U-cell (PUC5) inverter interfacing the utility. The predictive control methodology is based on a voltage vector generation technique for the cost function optimization by nullifying its derivative. The aim of the controller is to allow a fixed-frequency operation with no iterations while operating as a utility line current regulator. A pulsewidth modulator based on employing PUC5 redundant switching states fixes the PUC5 auxiliary dc bus capacitor voltage to its desired level with no necessity of a regulator; the overall technique reduces system complexity with less sensors and no loops in the predictive algorithm making it suitable for industrial applications. System discrete model is developed and experimental results verify the performance of the designed controller in making a fast response in regulating the grid current and balancing the capacitor voltage. [ABSTRACT FROM AUTHOR]

To solve the problem of poor robustness due to the high dependence of model predictive control (MPC) on the three-phase inverter model, the influence mechanism of the mismatch of circuit parameters R and L, the model discretization error, and sampling errors on MPC prediction error are analyzed in this paper. A feedback self-correction is proposed, which the next current errors are predicted and used to modify the model, based on the previous prediction errors. This proposed method involves simple structure and a small amount of calculation. Steady-state effects of the proposed method are quantized to prove a good inhibitory ability on multifactorial prediction errors. Finally, experimental results in a three-phase inverter are presented to support the theoretical analysis and demonstrate the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

MR16 lighting system with a high-frequency step-down electronic transformer is widely used in commercial lighting. In this paper, a single-switch quadratic boost light emitting diode (LED) driver compatible with electronic transformers for the MR16 lighting system is proposed and analyzed. It combines a prestage boost power factor correction (PFC) converter and a second-stage boost dc–dc converter with a single switch. The effect of the dc link voltage ripple of the prestage boost PFC converter on the output of the second-stage boost dc–dc converter is eliminated by a fast voltage mode control loop of a second-stage circuit. Therefore, flicker-free low ripple LED current is achieved. With a small dc link voltage ripple of prestage, the turn-on time of the active switch is almost constant in a half-line cycle. Therefore, PFC can be achieved with inductor current of prestage operating in a discontinuous conduction mode. With small input capacitance, the proposed LED driver presents a good compatibility performance with different kinds of electronic transformers. Furthermore, the proposed LED driver needs only one active switch and one control loop, which makes circuit volume small and low cost. Finally, a 4 W LED driver for a small-size MR16 lighting system is provided to verify the studied results. [ABSTRACT FROM AUTHOR]

When the selected harmonic elimination pulsewidth modulation (SHEPWM) is adopted to three-level neutral-point-clamped converters to reduce the switching frequency, the neutral-point potential (NPP) problem becomes more severe compared with other modulations. It is because there is no degree of freedom for SHEPWM to control the NPP. SHEPWM realizes a better harmonic performance by calculating the switching angles offline based on harmonic requirements. Since it is harsh to solve the angles online, we cannot change the angles to control the NPP. Aiming at the low-frequency NPP fluctuation minimum, a novel current harmonic minimum method based on the optimal third-order/ninth-order harmonic is proposed in this paper. The optimal third-order/ninth-order harmonic is derived based on the relationships among the third-order/ninth-order harmonic and the NPP. They can be utilized to realize the low-frequency NPP fluctuation minimum without changing any switching angle online. Moreover, some comparisons, such as the solution ranges, weighted total harmonic distortion, the initial value of iteration calculation, show that the proposed method has a good output performance. Finally, the experimental results are given to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

A 1-MHz-modified single-ended primary-inductor converter (SEPIC) circuit is presented in this paper as an LED driver for automotive headlights. On the basis of traditional SEPIC, only a diode and two capacitors are added; therefore, the circuit structure is relatively simple and the volume is relatively small. High step-up capability is obtained with moderate duty cycle. Compared with traditional step-up circuit such as boost, low-voltage stress is gained which is beneficial to device selection. Zero-voltage switching is achieved at the same time to reduce switching loss. Planar inductors are used with the advantages of low profile and good thermal characteristic. Operational principle and parameters design process are introduced in detail. A 36-W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 90.91% at full load. [ABSTRACT FROM AUTHOR]

Multilevel inverters are now-a-days being applied in electric vehicles (EV). Considering the dynamic operating conditions of an EV propelled by an induction motor, this paper proposes a flexible discontinuous modulation strategy for three-level neutral-point-clamped (NPC) inverter that can shift modulation pattern seamlessly from sinusoidal pulsewidth modulation (SPWM) to discontinuous PWM (DPWM). The modulation scheme is generalized at each degree of discontinuity to ensure minimum switching losses for variable load power factors. Additionally, a hybrid voltage balancing strategy, which comprises two sets of compensating offset signals with complementary features, has been introduced to mitigate voltage deviation problem at neutral point of the inverter. The unique feature of the proposed hybrid balancing approach is that it generates uniform compensating neutral current regardless of the level of discontinuity. This results in identical and predictable voltage balancing dynamics for the entire modulation transition covering SPWM and DPWM. It has been shown that the proposed hybrid balancing strategy does not lose its unbalance compensation strength even during transition from one modulation pattern to another. The effectiveness of the proposed scheme for wide variations in operating conditions is studied through extensive simulation, and validated in experimentation using a prototype NPC inverter with induction motor loads. [ABSTRACT FROM AUTHOR]

Switched-capacitor converter (SCC) featuring high efficiency and power density has attracted industry interest, but weak output voltage regulation hinders its application. This paper presents an optimized phase-shift (PS) control strategy for a bridge modular SCC, utilized in energy storage system, to obtain continuous conversion ratio and high-efficiency operation. By employing a small inductor as current buffer, the control strategy could be implemented to regulate output voltage conveniently with excellent steady and dynamic performance in step-down mode as well as step-up mode. Most importantly, the high-efficiency operation mechanism never reported before is revealed here. Correspondingly, the active circumfluence could be controlled through optimizing the range of PS time, which will avoid the loss in circuit self. Meanwhile, the soft-switching conditions of all the switches are comprehensively analyzed and soft-switching operations are achieved according to the logic timing control of the power devices, improving efficiency further. Finally, the prototype of the proposed converter was built and the experimental results validated the principle and features of the conversion method. [ABSTRACT FROM AUTHOR]

In photovoltaic systems, dc–dc converters have been identified as one of the most critical and challenging subsystem in terms of failure rate. Thus, this paper proposes fault-tolerant operation of a two-stage buck/buck–boost converter under open-circuit switch failure. Remedial actions are efficient in any failure of one of the two switches of the converter. Here, a new unified approach is considered, for the overall fault-tolerant operation of the two stages of the converter. The fault-tolerant circuit we propose lies on performing redundancy by implementing the equivalent synchronous switch for the two main switches of the two stages, in offline mode. The fault-tolerant circuit results from the basic two-stage buck/buck-boost converter and its equivalent circuit with a synchronous switch, merged together to form the new dc–dc fault-tolerant circuit. Therefore, postfault operation at full power can also be performed. By using a switch fault management unit with reduced complexity, inserted between the control block and the switches, we have designed an unified, efficient, and optimized fault-tolerant control, suitable in both healthy and postfault operations. Some selected experimental tests, which all confirm the good performances of the proposed fault-tolerant approach, are presented and discussed. [ABSTRACT FROM AUTHOR]

Wireless power transfer with a self-tuning LCC inverter using pulsewidth modulation (PWM) controlled switched capacitor is proposed in this paper in order to compensate for the variations of Tx inductance. Usually, receivers contain magnetic and conductive materials for shielding and mechanical support. The inductance of the Tx coil is sensitive to the variation of Tx–Rx alignment because the interaction between the Tx coil and the Rx magnetic–conductive materials is also varied. It is shown that the detuning of the Tx inductance value exacerbates the losses in the LCC inverter. In the proposed method, the PWM duty ratio of a single capacitor adjusts the effective output impedance of the LCC inverter. The PWM feedback loop is designed such that the power factor and the real-part impedance of the LCC inverter are maximized. The PWM switch is turned on at zero voltage and turned off with low dv/dt, minimizing switching losses. Such a soft-switching tunable capacitor can handle higher power compared to the traditional hard-switching capacitor, p-n junction capacitor, or an analog IC capacitor. Another advantage of the proposed technique is the continuity in achievable capacitance value using only one capacitor. The feedback can be fully implemented by analog components, obviating the necessity of digital samplings, ADC/DACs, and microcontrollers. The power of 54 W is transferred at 76.6% and 60.7% with and without the proposed method, respectively. [ABSTRACT FROM AUTHOR]

High step-up converters are required for distributed photovoltaic generation systems, due to the low voltage of the photovoltaic source. In this paper, a new hybrid high voltage gain dc–dc converter is created by merging the standard boost converter with a coupled inductor and different switched-capacitor techniques. With a single switch and no requirement of higher duty cycle values, the proposed converter achieves a high voltage gain and high efficiency, in addition to lowered voltage and current stresses of the components. A 200-W prototype was implemented experimentally to evaluate the converter, which reached a maximum efficiency of 97.6%. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid switched-capacitor/switched-quasi-Z-source bidirectional dc–dc converter is proposed for electric vehicles (EVs) with hybrid energy sources, which has a wide voltage gain range in the bidirectional energy flows. Compared with the traditional quasi-Z-source bidirectional dc–dc converter, the proposed converter only changes the position of the main power switch and employs a switched-capacitor cell at the output of the high-voltage side. Therefore, the advantages of the wide voltage gain range and the lower voltage stresses across the power switches can be achieved. The operating principle, the voltage and current stresses across the power switches, and the comparisons with other converters are analyzed in detail. Furthermore, the parameter design of the main components, the dynamic modeling analysis, and the voltage control scheme are also presented. Finally, the experimental results obtained from a 400 W prototype validate the characteristics and the theoretical analysis of the proposed converter. [ABSTRACT FROM AUTHOR]

Soft-switching inverters can achieve high efficiencies and low switchdv/dtanddi/dt, but often impose additional stress on the switches due to their resonant behavior. Multicell converters, on the other hand, can process high voltages by arranging the switches to share the stress. This paper proposes a buck–boost multicell soft-switching inverter with inherent cell voltage balancing. Both the current and voltage stresses are shared by the cells. Soft-switching conditions are achieved for all switching transitions without any need for auxiliary circuitry or clamps. A multiple-winding transformer transfers energy between the terminals and provides galvanic isolation. An analytical study and experimental results on a 1200-W prototype verify the operation of the inverter. [ABSTRACT FROM AUTHOR]

In this paper, a novel buck–boost converter with low electric stress on components and negative output voltage is proposed. The operational principle, steady-state analysis, and small-signal modeling of the proposed buck–boost converter in continuous conduction mode are presented. Comparisons among another five buck–boost converters and the proposed buck–boost converter are presented. It is found that the proposed converter's voltage gain is smaller than the other converters’ in step-down mode. Also, based upon the comparisons among the same kind and same number of components, the voltage and current stresses on the power switch of the proposed buck–boost converter are less than or equal to those of the comparative converters, and the voltage stress on the charge pump capacitor and the switching device power rating of the proposed buck–boost converter are always lower than those of other comparative converters. The efficiency of the proposed buck–boost converter is highest among those converters having the same number of elements. These advantages make component selection for the proposed converter much easier, and it can be used directly in applications needing a negative voltage source. Finally, simulation results and circuit experiments are given for validating the effectiveness of the proposed buck–boost converter. [ABSTRACT FROM AUTHOR]

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared with the existing fast OC FD techniques in three-phase voltage source inverters, this method is more cost-effective since no ultrafast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification. When both stages of the OC FD algorithm are done, a redundant leg is activated and utilized instead of the failed leg. The accuracy of the proposed method is confirmed by the experimental results from a low-voltage q-ZSI prototype. [ABSTRACT FROM AUTHOR]

Condition monitoring (CM) has been considered as a promising technique to improve the reliability of insulated gate bipolar transistors (IGBTs). Among various condition parameters, switching time is a good health status indicator to detect IGBT failures. However, on-line monitoring of the IGBT high-speed switching time is still difficult in practice due to the requirement of the extremely high sampling rate for signal acquisition. To overcome the technical difficulty, this paper provides an innovative compressed sensing (CS) method to achieve equivalent sampling performance for high-speed IGBT switching time monitoring with a lower sampling rate. By utilizing the sparse characteristics of an IGBT switching signal, the sampling rate in the CS method could be far less than the traditional Nyquist sampling rate. To clarify the method, the CM mechanism using IGBT switching time is first analyzed. Then, three key points in the CS method are studied, i.e., the selection of sparsifying basis, the design of a measurement matrix, and the implementation of a reconstruction algorithm. Finally, experiments are carried out to investigate the performance of the CS method for on-line CM. Experimental results show that the IGBT turn-offtime at different temperatures can be accurately monitored with a highly compressed sampling rate, which validates the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a sequence switching control (SSC) scheme based on an auxiliary parallel inductor is proposed to improve the transient performance of buck converters. The proposed SSC scheme introduces a small controlled inductor in parallel with the output inductor, so as to increase the inductor-current slew rate when it is activated during a load transient. Furthermore, an “n+ 1” sequence switching strategy is proposed to control the auxiliary parallel inductor. The proposed scheme divides the transient event inton+ 1 periods. In the formernperiods, the same small output voltage deviations are designed, while in the last period, a smaller deviation is done for a smooth transition from the transient to the steady state. The switching sequence is derived applying the capacitor–charge balance principle for each ofn+ 1 periods. For a given buck converter in the experiment, the settling time and the output voltage deviation of the proposed SSC scheme enhance more than 50% and 67%, respectively, over those of the time-optimal control for a 3-A load step. [ABSTRACT FROM AUTHOR]

A new light emitting diode (LED) driver circuit is presented in this paper based on the buck converter with coupled inductors for automotive applications. Soft-switching condition is provided for the switch via a passive resonant circuit incorporating the leakage inductance of the coupled inductors. Also, the leakage inductance energy is recycled to the output. The proposed converter has a very simple structure as well as high efficiency, which makes it a good candidate for battery-operated applications. The proposed converter only applies one magnetic element and the leakage and magnetizing inductances are used as resonant elements. Also, during the resonance, a resonance capacitor is approximately charged to the input voltage, and therefore, the capacitor voltage stress and semiconductor devices voltage stress are low. These are the main advantages of the proposed converter over other similar converters. The theoretical analysis is provided and the operating principles and design considerations are explained. An 8 W laboratory prototype is implemented in order to prove the validity of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Series connection of individual semiconductors is an effective way to achieve higher voltage switches. However, the inherent unequal dynamic voltage sharing problem needs to be solved, even when well-matched gate drivers and semiconductors are used. A majority of the existing voltage balancing schemes are developed for slow-switching silicon (Si)-based semiconductors, and are also associated with a significant amount of additional losses in the control circuit or on the switches. In this paper, a novel method is proposed for balancing the dynamic voltages among series-connected silicon carbide (SiC) MOSFETs with highdv/dtrates. The method takes advantage of a small capacitor to provide additional current to the gate of the MOSFETs at turn-off, meaning the switching speed (and thus, the device voltage after turn-off) is controlled. The proposed method generates negligible losses in the control circuit, and also does not significantly increase the switching losses of the semiconductors. Experimental results are provided to prove the effectiveness of the proposed voltage balancing scheme on two SiC MOSFETs inside a module connected in series. In order to do so, an active gate driver is designed embedding the activedv/dtcontrol scheme as well as other essential functionalities needed for operation of SiC MOSFETs. [ABSTRACT FROM AUTHOR]

Gallium nitride high electron mobility transistor has been seen as a power semiconductor devices with lots of potential since it has been commercialized. However, the advantages of fast switching speed with low conduction resistance always have to compromise to the fast switching on evoked overvoltage. Though it has been realized that the overvoltage problem arises from the joint effect of fast switch speed and parasitics, there is a lack of ways for quantitative analysis. This paper proposes a reliable circuit model based on a quantitative way to analyze the cause of overvoltage and finds optimized parameters to suppress. A normalized method is adopted to make the analysis more general, and the voltage and current stress determined safe operation area during the switchingonprocess under the constraint of maximum overvoltage is detailed. The analysis is verified by a double pulse test experiment, with the calculated and measured maximum overvoltage matching very well. The analysis can help us to choose reasonable turn-onspeed and power loop parasitic inductance before the printed circuit board (PCB) manufacture with an acceptable maximum overvoltage guaranteed. [ABSTRACT FROM AUTHOR]

Recently, a few fault-tolerant control strategies have been proposed for T-type three-level inverters to improve the reliability of the inverter system. However, the neutral-point (NP) voltage oscillations suppression is never considered in the previous fault-tolerant control strategies. In order to suppress the NP voltage oscillations when open-circuit fault occurs to NP switches, this paper proposes two novel fault-tolerant control strategies named as improved two-level switching tolerant control and hybrid switching tolerant control (HS-TC). Both methods are implemented by adding an optimal time-offset to the three-phase turn-ontimes. The corresponding time-offset value of each method is simply calculated considering the phase current and dwell time of [O] state. Moreover, an NP voltage balancing algorithm to eliminate the dc deviation and a dc bias to further reduce the NP voltage oscillations are used in the HS-TC. The performance and comparison of the tolerant controls with respect to the NP voltage oscillations, current total harmonic distortion, and dynamic response are illustrated and analyzed through the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has become a promising topology applied in medium/high-voltage applications due to its advantages. However, there are several challenges in the MMC, such as the appearance of harmonic circulating current. In this paper, a novel two-stage model predictive control (TSMPC) is proposed to suppress the harmonic circulating current. First, the mathematical model of the MMC is discretized to describe steady-state objectives including output currents, circulating currents, summation, and imbalance of capacitor voltages. Then, an optimal control options set consisting of inserted numbers is built by the front stage of TSMPC, while the inserted number applied to the MMC ultimately is selected from the above-mentioned set by the back stage of TSMPC. The proposed TSMPC can not only improve the control performance of harmonic circulating current but also ensure the overall control performance of the MMC system. In addition, a simplified rolling optimization method is proposed to reduce computation from the aspect of simplifying each control option prediction. An optimized search space method is also proposed to design the control options set to be evaluated from the aspect of ensuring the output current tracking and harmonic circulating current suppression. Finally, the effectiveness of the proposed method is validated by experiment results. [ABSTRACT FROM AUTHOR]

For dc–ac modular multilevel converters (MMCs) in double-star configuration, this paper proposes a fast closed-loop control method based on optimized pulse patterns (OPPs). Thanks to the direct manipulation of the OPP switching instants, OPPs with discontinuous switching angles can be used, and the intrinsic cell capacitor voltage ripple is compensated for to preserve the OPPs’ superior harmonic performance. This model predictive pulse pattern controller is combined with a fast acting dead-beat circulating current controller and linked to an upper layer voltage balancing control scheme. The proposed control and modulation method is particularly suitable for medium voltage MMCs with a low number of cells. Despite operation at very low switching frequencies close to and including the fundamental frequency, a superior harmonic performance can be achieved. [ABSTRACT FROM AUTHOR]

Discontinuous modulation applied to modular multilevel converters is an effective method for reducing the capacitor voltage ripples. In this paper, the discontinuous modulation is adapted and used in a motor drive application. For proper operation of the converter, a new energy controller is presented, which is suitable for operation with nonsinusoidal reference signals. Experimental results comparing the discontinuous modulation with other techniques operating at low motor speeds are shown. The results demonstrate the effectiveness of the discontinuous modulation on reducing capacitor voltage ripples and power losses. [ABSTRACT FROM AUTHOR]

This paper presents a modified modular multilevel converter with the three-terminal middle-cells inserted between arms and ac-side for medium voltage applications. It is intended to reduce the submodule capacitor voltage ripples by controlling the high-frequency powers flowing among arm branches for low-frequency output operations without common-mode voltage injected in ac-side. Due to the physical connection among the upper arm, the lower arm and ac-side, the middle-cell can be regarded as the excess degree of freedom to modify the dc-side and ac-side characteristics. Therefore, the common-mode voltage in ac-side can be eliminated by the inverse common-mode voltage produced by the middle-cell in ac-side. Moreover, owing to the unique structure of the middle-cell, the middle-cell capacitor voltage also results in a small ripple due to the high-frequency current flowing into it by proper control. The operation principle and control strategy of the middle-cell has been proposed in detail. Simulation and experimental results have verified the effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

Traditional control strategy for a power decoupling circuit typically involves a dedicate ripple power control loop, which makes it hard to achieve satisfied transient performance. Meanwhile, traditional single-phase ac–dc converters achieve active power decoupling function with extra power switches, which inevitably increased the cost of the system. In this paper, a controller based on automatic power decoupling concept is proposed for a dependent power decoupling circuit with no extra switches. Compared with the existing methods, the system controlled by the proposed controller has superior transient performance with simplified controller's structure. The controller parameter's design procedures will also be illustrated step by step with the help of the bode diagram. In comparison with traditional control methods, simulations and experiments verify the feasibility of the proposed control methods on the dependent power decoupling circuit. [ABSTRACT FROM AUTHOR]

A fully digital driving circuit for thin-film transistor liquid crystal display can offer benefits, including less power consumption and a shortened design schedule. Using the pulsewidth signal to control the moment to stop the ramp voltage, the pixel voltage can be set accurately. In this paper, the possible issues of power consumption, device nonuniformity, and parasitic capacitance are well-studied to prove the feasibility and advantages of the digital driving method. It is prospectively expected to substitute for the conventional analog driving method in the future. [ABSTRACT FROM AUTHOR]

A new approach to performance validation of finite control set model predictive control (FCS-MPC) regulated power electronics converters is presented in this paper: statistical model checking (SMC). SMC is an established method used in various sectors of industry to provide solutions to problems that are beyond the abilities of classical formal techniques. The method is simple for implementation and requires only an operational system model that can be simulated and checked against properties. The approach will be presented on a standard two-level voltage source converter regulated by the FCS-MPC algorithm. In UPPAAL SMC toolbox, the converter system and controller are modeled as a network of stochastic timed automata. To assess the quality of the model, an equivalent Simulink model is used as a benchmark model. Using the model created in UPPAAL SMC toolbox the performance of the FCS-MPC algorithm is verified. The control algorithm is also tested on an experimental setup. During the evaluation, no significant degradation of reference tracking was found during transients nor under model parameter uncertainty. [ABSTRACT FROM AUTHOR]