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In this paper, a direct torque control using a four-dimensional switching-table (4D-ST) is proposed for the voltage source inverter–permanent magnet synchronous motor drive system. The proposed strategy takes a number of virtual vectors, of which magnitude and angle can be configured freely, as candidate vectors. By taking advantage of the variety of the virtual vector, the proposed strategy can obtain superior steady-state and dynamic performance. To choose the optimal vector from all of virtual vectors, first quantify the change rule of the torque and stator flux generated by each different virtual vector, and then take the magnitude and angle of the virtual vector, stator flux angle, and the quantificational factor as four dimensions to establish 4D-ST; by analyzing the distributed laws of quantificational factors in 4D-ST, we can compress 4D-ST and propose a quarter selector to choose the optimal vector accurately and rapidly. By taking the step function instead of the hysteresis comparator as the torque and flux controller, the direct torque control using 4D-ST can be realized. Finally, numerical simulations and experiments with prototype are carried out to validate the feasibility and effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this paper, the performance of the new three-dimensional space vector-based switching signal generation technique for a grid-connected four-leg voltage source inverter used as a shunt compensator is proposed. The shunt compensator can be used for reactive power compensation, harmonic elimination, load balancing, and neutral current elimination in a three-phase four-wire grid-connected system. It is shown through experimental studies that switching losses in the four-leg voltage source inverter are appreciably reduced to a maximum of 33% in three-dimensional space vector modulation without NULL vector as the number of switches controlled at any instant of time is six out of eight. The new proposed technique is compared with three-dimensional space vector modulation with null vector. Experimental results are given to show the validity of the proposed switching control strategy. [ABSTRACT FROM AUTHOR]

This paper revisits the switched flow graph (SFG) technique. A general and unified equivalent SFG model of a three-terminal switcher encountered in regular and tapped inductor converters operating in the continuous conduction mode is proposed. The model can be applied to most PWM topologies and facilitates construction of a complete flow graph of a given converter. The approach can be helpful in theoretical analysis and derivation of analytical expressions of converter's small-signal transfer functions. The suggested methodology extends the previously proposed SFG analysis technique and alleviates the principal difficulties involved. Furthermore, the approach is straightforward and expeditious. Application guidelines and examples are presented and compared to simulation and earlier theoretical results. [ABSTRACT FROM PUBLISHER]

A new method for deriving isolated buck-boost (IBB) converter with single-stage power conversion is proposed in this paper and novel IBB converters based on high-frequency bridgeless-interleaved boost rectifiers are presented. The semiconductors, conduction losses, and switching losses are reduced significantly by integrating the interleaved boost converters into the full-bridge diode-rectifier. Various high-frequency bridgeless boost rectifiers are harvested based on different types of interleaved boost converters, including the conventional boost converter and high step-up boost converters with voltage multiplier and coupled inductor. The full-bridge IBB converter with voltage multiplier is analyzed in detail. The voltage multiplier helps to enhance the voltage gain and reduce the voltage stresses of the semiconductors in the rectification circuit. Hence, a transformer with reduced turns ratio and parasitic parameters, and low-voltage rated MOSFETs and diodes with better switching and conduction performances can be applied to improve the efficiency. Moreover, optimized phase-shift modulation strategy is applied to the full-bridge IBB converter to achieve isolated buck and boost conversion. What's more, soft-switching performance of all of the active switches and diodes within the whole operating range is achieved. A 380-V output prototype is fabricated to verify the effectiveness of the proposed IBB converters and its control strategies. [ABSTRACT FROM PUBLISHER]

This paper describes the control of an isolated multiphase high-frequency-link (HFL) matrix inverter by controlling the time evolution of its switching states (or, switching sequences). It is referred to as the optimal-switching-sequence-based control (OSBC). Unlike several conventional control schemes, where, typically the control is based on averaged model of the inverter and the modulation scheme sets a predetermined switching sequence, OSBC synthesizes the fundamental switching sequence depending on the control needs on the fly. For instance, OSBC can seamlessly play with the inverter switching sequences if the input voltage of the inverter changes as evident in solar or wind-based energy systems. This necessitates that OSBC use a switching-sequence-based discontinuous (instead of averaged) modeling approach. Further, the stability of the closed-loop inverter is determined in OSBC using an advanced composite Lyapunov-function based approach, which also enables one to predetermine the reachability of the inverter dynamics for a given switching sequence. Thus, optimal control in OSBC is ensured under stability bound of the switching sequence. This provides a fundamental difference between OSBC and model predictive control for inverters. This also implies that in a multiobjective OSBC, one can shift the weights of the individual cost functions to yield better inverter performance without compromising the stability. [ABSTRACT FROM PUBLISHER]

A single-phase four-switch rectifier with considerably reduced capacitance is investigated in this paper. The rectifier consists of one conventional rectification leg and one neutral leg linked with two capacitors that split the dc bus. The ripple energy in the rectifier is diverted into the lower split capacitor so that the voltage across the upper split capacitor, designed to be the dc output voltage, has very small ripples. The voltage across the lower capacitor is designed to have large ripples on purpose so that the total capacitance needed is significantly reduced and highly reliable film capacitors, instead of electrolytic capacitors, can be used. At the same time, the rectification leg is controlled independently from the neutral leg to regulate the input current to achieve unity power factor and also to maintain the dc-bus voltage. Experimental results are presented to validate the performance of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation strategy for n-phase neutral-point-clamped (NPC) converters. The proposed modulation strategy is able to control and completely remove the low-frequency neutral-point (NP) voltage oscillations for any operation point and load types. Even when unbalanced and/or nonlinear loads are considered, the NP voltage remains under total control. Consequently, the strategy is very attractive for n-phase active filters. In addition, it enables the use of low-capacity film capacitors in NPC converters. The proposed modulation takes the carrier-based modulation strategy as a basis. It is formulated following a generalized approach that makes it expandable to n-phase NPC converters. In addition, the NP voltage is controlled directly using a closed-loop algorithm that does not rely on the use of the linear control regulators or the additional compensators used in other modulation algorithms. Therefore, no tuning of parameters is required and it performs optimally for any operating conditions and kind of loads, including unbalanced and nonlinear loads. Although the high-frequency harmonic content of the output voltages may increase, the weighted total harmonic distortion generated by the proposed strategy is similar to that of a standard sinusoidal pulse width modulated strategy. The proposed modulation algorithm has been tested in a four-leg NPC converter prototype performing as a three- and four-phase system and operating with balanced and unbalanced loads. [ABSTRACT FROM AUTHOR]

Z-source inverters have become a research hotspot because of their single-stage buck–boost inversion ability, and better immunity to EMI noises. However, their boost gains are limited, because of higher component-voltage stresses and poor output power quality, which results from the tradeoff between the shoot-through interval and the modulation index. To overcome these drawbacks, a new high-voltage boost impedance-source inverter called a switched-coupled-inductor quasi-Z-source inverter (SCL-qZSI) is proposed, which integrates a switched-capacitor and a three-winding switched-coupled inductor (SCL) into a conventional qZSI. The proposed SCL-qZSI adds only one capacitor and two diodes to a classical qZSI, and even with a turns ratio of 1, it has a stronger voltage boost-inversion ability than existing high-voltage boost (q)ZSI topologies. Therefore, compared with other (q)ZSIs for the same input and output voltages, the proposed SCL-qZSI utilizes higher modulation index with lower component-voltage stresses, has better spectral performance, and has a lower input inductor current ripple and flux density swing or, alternately, it can reduce the number of turns or size of the input inductor. The size of the coupled inductor and the total number of turns required for three windings are comparable to those of a single inductor in (q)ZSIs. To validate its advantages, analytical, simulation, and experimental results are also presented. [ABSTRACT FROM AUTHOR]

Contactless power transfer systems require compensators to improve power factor degradation caused by significant leakage inductance in the contactless power transformer. The most commonly used compensators are LC series- and parallel-resonant compensators. In this paper, we present a comparison between the characteristics of the compensators with a focus on transfer efficiency. Based on these characteristics, a compensator capable of switching between the LC parallel- and series-resonant topologies is proposed, and its changeover algorithm is explained. The proposed compensator was experimentally examined and was found to perform efficiently over a wider range of output power than conventional LC resonant compensators. [ABSTRACT FROM AUTHOR]

This paper presents a method for a reconfigurable magnetic resonance-coupled wireless power transfer (R-MRC-WPT) system in order to achieve higher transmission efficiency under various transmission distance and/or misalignment conditions. Higher efficiency, longer transmission distance, and larger misalignment tolerance can be achieved with the presented R-MRC-WPT system when compared to the conventional four-coil MRC-WPT (C-MRC-WPT) system. The reconfigurability in the R-MRC-WPT system is achieved by adaptively switching between different sizes of drive loops and load loops. All drive loops are in the same plane and all load loops are also in the same plane; this method does not require mechanical movements of the drive loop and load loop and does not result in the system volume increase. Theoretical basis of the method for the R-MRC-WPT system is derived based on a circuit model and an analytical model. Results from a proof-of-concept experimental prototype, with transmitter and receiver coil diameter of 60 cm each, show that the transmission efficiency of the R-MRC-WPT system is higher than the transmission efficiency of the C-MRC-WPT system and the capacitor tuning system for all distances up to 200 cm (∼3.3 times the coil diameter) and for all lateral misalignment values within 60 cm (one coil diameter). [ABSTRACT FROM AUTHOR]

An online steady-state load identification method is proposed to solve the problems related to frequency drift, system robustness deterioration, difficulties in controller design due to the uncertainties in load and mutual inductance variations of an inductive power transfer (IPT) system. Take a Series-Series-type IPT system as an example, an additional capacitor is added into the system to make the system work in two operating modes, and a mathematical model is established according to the two modes for the system identification. Simulation and experimental results have verified the proposed online load identification method. It has demonstrated that the method is accurate and reliable for identifying uncertain loads and magnetic coupling variations if other system parameters are known. The method can be used to improve the system performance with precise control. [ABSTRACT FROM AUTHOR]

Recently, several researches have been progressed on the primary-side control (PSC) methods which decrease the size and cost of the control stage. However, most of the researches have been applied to the flyback converter, and they have some challenges in applying them to the half-bridge (HB) LLC converter due to the large voltage across the secondary leakage inductor of the transformer. In this letter, a new PSC method for the HB LLC converter is proposed to obtain accurate output voltage. In the proposed method, the output voltage is regulated by obtaining the voltage across the primary side of the transformer when the external resonant inductor voltage becomes 0 V. At this time, since the voltage across the transformer secondary leakage inductor is small, the proposed method can accurately regulate the output voltage. A 400 V input and 20 V/85 W output laboratory prototype is built and tested to verify the effectiveness of the proposed PSC method. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of the periodical. [ABSTRACT FROM AUTHOR]

In this paper, various types of discontinuous space vector pulse-width modulation techniques for a three-leg voltage source inverter supplying balanced two-phase loads are proposed. The main objectives of the paper are to analyze switching loss characteristics associated with semiconductor devices and to reduce output current ripple by dealing with various types of zero space vector time in each switching sequence. Capabilities of reductions in switching losses and current ripple for both balanced and unbalanced output phase voltages at high modulation index and load power factor angle of 30° lagging are focused. The validity of the proposed techniques is verified by simulation and experimental results in terms of voltage spectrum, current waveforms, reductions in switching losses, and output current ripple at high modulation index when compared to a continuous space vector pulse-width modulation technique. [ABSTRACT FROM AUTHOR]

This paper proposes a nonsuperconducting fault current limiter (NSFCL) topology and control strategy. The switched impedance transformer-type NSFCL topology is optimized to protect against short transients and to work in conjunction with other fuses or circuit breakers, hence has the merits of being simple, low cost, and compact. A prototype has been designed and built for a three-phase 600-VRMS,L-L system. It has been tested in a UL-certified high-power test lab with 5-A normal current and 100-kA potential fault current. [ABSTRACT FROM AUTHOR]

This paper proposes a simple power control scheme in order to convert the conventional nonadjustable self-oscillating half-bridge series-resonant inverter into an adjustable one. The proposed topology, based on a self-oscillating structure, can automatically ensure the turning on and the turning off of the switches without any external control. A simple modification in one of the gate drivers side circuit allows one to adjust the output power without compromising the simplicity, reliability, and low cost, which characterize the self-oscillating half-bridge inverter. Moreover, this topology achieves a stable and efficient zero-voltage switching over the entire operating range with a constant switching frequency; as a consequence, the inverter overall efficiency is significantly improved. Experimental results are proposed to validate the analysis and to demonstrate the performance of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper presents a power converter and its control circuit for high-frequency-fed ac to dc conversion. Based on the resonant technique, the input current is shaped to be sinusoidal and is forced to follow the high-frequency sinusoidal input voltage so as to achieve unity power factor. With the proper selection of the characteristic impedance of the resonant tank, the converter is able to perform the function of a buck, boost, or buck-boost converter. The initial condition of the resonant tank is used to control the output voltage gain of the converter. Since all the switches are operated at the fundamental frequency of the input ac source, the switching loss of the converter is small. A control scheme is also proposed for the converter. A proof-of-concept prototype operating at 400 kHz is constructed and its performance is experimentally measured. Results show that the proposed converter operates as theoretically anticipated. [ABSTRACT FROM AUTHOR]

This paper presents novel single-phase pulse width modulation (PWM) ac-ac converters that can solve the commutation problem in single-phase direct PWM ac-ac converters without sensing the input voltage polarity. By using a basic switching cell structure and coupled inductors, the proposed ac-ac converters can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor dedicated soft commutation strategy is required in the proposed converter. By replacing the conventional phase-leg of the PWM ac-ac converters with the switching cell structure and the coupled inductor, three novel buck, boost, and buck-boost type PWM ac-ac converters are developed. Although two coupled inductors are required for the proposed converter, the input inductor of the proposed converter can be much smaller than that of the conventional PWM ac-ac converters. The volume of the magnetic components can be further reduced by increasing switching frequency of the converter because very fast recovery diodes can be selected externally. In order to verify performance and robustness of the proposed converter, a 200-W boost type prototype converter was built and tested with both mismatched gate signals and highly distorted input voltage. [ABSTRACT FROM AUTHOR]

A paralleled multilevel inverter topology consists of n three-phase three-level current-fed inverters (CFIs) connected in parallel on ac side. AC currents with (2n+1) levels can be generated utilizing redundant switching states when all three-level inverters have equal dc-link currents. However, the multilevel space vector diagram gets modified, redundancy in the switching states is lost and the multilevel current pattern changes when the dc-link current of all inverters is not the same. This introduces low-frequency harmonics in output current, thereby deteriorating total harmonic distortion (THD). The presence of low-frequency components in the output current could be avoided by selecting suitable switching state vectors and ensuring proper time sharing among these vectors. Two methods to select such switching state vectors are proposed in this paper. In the first method, a reference current space vector is realized using the nearest switching state vectors. However, this method results in low-frequency pulsation in dc-link voltage of each inverter. In the second method, the switching state vectors are chosen to eliminate this low-frequency pulsation. Effectiveness of these methods is experimentally validated for a five-level CFI. Further, performance of these methods is compared based on efficiency, THD, and dc-link voltage ripple for various inequality ratios in dc-link currents. [ABSTRACT FROM AUTHOR]

This paper presents a three-phase multilevel power factor correction (PFC) rectifier employing multistate switching cells. A generalized converter structure is presented based on the connection of switching networks of Vienna-type rectifier topologies through multiinterphase transformers (MIPTs). The resulting rectifier presents the intrinsic benefits to the employed building blocks and the ones added by a modular construction that enables the reduction of passive components and overall losses. The operation of the PFC rectifier is described, including appropriate modulation and control strategies. Design guidelines for the magnetic components are derived for the MIPTs, boost inductors, and power semiconductor devices. Finally, a lab prototype is used to present experimental results. This prototype is rated at 7.5 kW and uses a modular structure to assemble a four legs per phase rectifier. Efficiency above 98% from 40% load and IEC61000-3-2 requirements are observed. [ABSTRACT FROM AUTHOR]

This paper describes a dimming method for hot cathode fluorescent lamp (HCFL) using a resonant inverter operating at fixed switching frequency. The proposed method is based on burst dimming and decreases the inverter output voltage during the burst-off period by changing the switching pattern of the inverter. Consequently, the lamp can be turned OFF, while the filaments of lamp are kept preheated without adding an inverter for preheating. Once the lamp is turned OFF, N-times resonant mode (where N means a natural number) occurs because the characteristic of the resonant circuit (which depends on lamp impedance) changes drastically. This mode keeps the root mean square of filament currents large enough to ensure long lamp life. Moreover, the inverter operates in zero-voltage-switching resonant mode during both the burst-on and burst-off periods. Experimental results showed that stable burst dimming and preheating characteristics were attained. The proposed method thus contributes to achieving long lifetime, small size, and low cost of lighting system for HCFLs. [ABSTRACT FROM AUTHOR]

High-frequency copper losses, or copper losses produced during switching in switching-mode power supplies, are very much related to variations of the magnetic field distribution within the core window. When operating at high frequency, the current flowing through the windings of a magnetic component experiences redistribution across the section of the conductor due to skin and proximity effects. Current redistribution depends not only on actual frequency, but also on conductor size and layer distribution. While previous works aim to optimize windings size by considering just the current flowing through that winding, this paper shows that, in most of the cases, current redistribution is strongly affected by the currents at the other transformer windings, which should also be taken into account. This paper derives a mathematical expression to calculate the evolution, in the time domain, of the magnetic field during the switching, which will be later used to obtain the current density distribution and copper losses in the component. An easy-to-calculate expression will be derived that allows magnetic windings to be analyzed and/or optimized, because losses are expressed as a function of the winding geometry and position. An application example is also included. All the equations derived are verified by comparing them with the results obtained from a differential equations solver, and with previous works when applicable. Experimental results are also provided. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage balancing method for flying capacitor multilevel converters based on phase-disposition pulse width modulation (PD-PWM) using optimal transitions between converter switching states. The optimal transitions between converter switching states are possible due to the converter states' redundancy and are decided with the continuous evaluation and minimization of a cost function. Simulation and experimental results verify the robustness of the proposed voltage balancing method against different load conditions. A significant reduction of the average switching frequency is achieved, when compared to the use of the optimal state voltage balancing method, where the optimal states are decided independently for each voltage level ignoring how transitions impact on the converter switching frequency. Moreover, the line-to-line output voltages are compared with the ones obtained with other modulation techniques in terms of total harmonic distortion values, and PD-PWM with the proposed voltage balancing method produces the best results. [ABSTRACT FROM AUTHOR]

In this letter, an approach to eliminate the mutual flux effect on the rotor position estimation of switched reluctance motor drives without a priori knowledge of mutual flux is proposed, while operating in both linear and saturated magnetic regions. Considering magnetic saturation, the incremental-inductance estimation using the phase current slope difference method can be classified into three modes: Modes I-III. At positive-current-slope and negative-current-slope sampling point of one phase, the sign of current slope of the other phase changes in Modes I and II, but does not change in Mode III. Theoretically, the incremental-inductance estimation error introduced by the mutual flux is both rotor position and phase current dependent, which is ±1% to ±7% for the studied motor in Modes I and II. However, in Mode III, the mutual flux effect does not exist. Therefore, two methods are proposed to ensure that the incremental-inductance estimation is working in Mode III exclusively. The first one is variable-sampling incremental-inductance estimation for the outgoing phase and the other is the variable-hysteresis-band current control for the incoming phase. Simulation and experimental results show that the proposed method improves position estimation accuracy by 2° compared with the conventional method without variable-sampling and variable-hysteresis-band current control. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of this publication. [ABSTRACT FROM AUTHOR]

This letter presents a modular naturally clamped snubberless bidirectional soft-switching current-fed dual 6-pack (CFD6P) dc/dc converter to interface two dc buses of large voltage difference such as 24 V and 380 V. It is therefore suitable for energy storage, uninterruptible power system, renewable energy system, vehicle, and micro-grid applications. The proposed novel secondary modulation technique forces the currents through the primary-side (low-voltage side) devices to reverse its direction resulting in zero-current switching (ZCS) or natural commutation of current-fed low-voltage side devices. Secondary-side (high-voltage side) devices are turned-on with zero-voltage switching (ZVS). In addition, the resonance between the device parasitic capacitance and transformer leakage inductance achieves ZVS turn-on of the primary-side devices. Thus, the converter maintains a zero-voltage zero-current switching of the current-fed devices and ZVS of high-voltage devices. High-current applications needs short-circuit protection and that is built-in the converter inherently. It limits the peak current and circulating current through the devices resulting in low kVA rating devices. Steady-state operation, analysis, and design of the proposed converter have been studied and explained. Experimental results for 1-kW laboratory prototype have been demonstrated as a proof of concept to validate the claims. [ABSTRACT FROM AUTHOR]

A pulse-width modulation modulator for a noninverting bidirectional buck-boost converter is analyzed and a corresponding average-mode current controller design is revealed. The main feature of the modulator is the ability to create switching sequences for both converter legs without requiring any information regarding either operation mode or the direction of power flow. The modulator receives a control signal generated by the current controller, and a triangular carrier and generates driving signals with two different duty cycles, allowing tight control of the inductor current throughout the entire operating range. The underlying circuitry is thus relatively simple; moreover, the proposed method greatly simplifies the outer loop controller design. The revealed findings are supported by simulations and experiments. [ABSTRACT FROM AUTHOR]

Nonlinear, voltage-dependent capacitances of power semiconductor devices are capable of having significant impact on the operation of switched-mode power converters. Particularly at high switching frequency, these nonlinearities play a significant role in determining switching times, losses, and converter dynamics during switching transitions. In order to accommodate the well-established design and analysis techniques commonly used for linear circuits, this paper examines the nonlinear voltage-dependence of switching device capacitances and proposes a circuit-oriented analysis technique that allows the parasitic capacitances to be replaced with linear equivalents. The multitude of developed equivalents are verified through full nonlinear simulation in both MATLAB/Simulink and SPICE, as well as through experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a Bang-Bang Charge Control (BBCC) method for LLC resonant converters. Instead of switching frequency control, the BBCC method utilizes the series resonant capacitor voltage level to trigger the MOSFETs' switching actions. Advantages of the proposed method include fast dynamic performance and simple implementations. Small-signal analysis shows that the loop bandwidth can achieve around 1/6 of the switching frequency in all operating conditions. Experimental results show that 5 to 25 A load step transients are completed within only seven switching cycles at both 400- and 300-V input-voltage conditions. Practical considerations are also discussed in detail. [ABSTRACT FROM AUTHOR]

Unique pitfalls in parallel three-level T-type inverters (3LT2 Is) are potential zero-sequence circulating currents (ZSCCs) which are more complex than parallel two-level inverters and can cause current discrepancy, current waveform distortion, power losses, etc. In this paper, the ZSCC paths in the parallel 3LT2Is are first presented, and an equivalent model of the ZSCCs is developed. It is seen from this model that the ZSCCs consist of conduction, switching, and hybrid components. Based on the aforementioned analysis, an original sharing neutral bus structure is proposed to eliminate the conduction ZSCCs. With regard to the switching ZSCCs composed of high-frequency and low-frequency harmonics, modified LCL filters are proposed to eliminate the former, and zero-sequence control loops are put forward to suppress the latter. Furthermore, the proposed schemes are also proven to be effective to elimination of the hybrid ZSCCs. Experimental results validate the developed models and the proposed ZSCC elimination schemes. [ABSTRACT FROM AUTHOR]

For high-power PWM current-source drive systems, the distortion of dc-link current cannot be ignored due to the low converter switching frequency and the relative small dc choke for reduced cost/weight. The distorted dc-link current may introduce interharmonics in the grid side and the motor side through the rectifier and the inverter, and may give rise to the system resonance at certain motor speeds. When resonance occurs, significant interharmonics are introduced in the drive system, which will degrade the grid-side power quality and produce the excessive torque ripples on the motor side. In this paper, the harmonics interaction in a high-power PWM current-source drive system is investigated, and a method for the system resonance estimation is proposed. Based on the estimation of resonance conditions, a dc-link virtual impedance-based control method is developed to mitigate the resonance resulted from the harmonics interaction. The investigation of harmonics interaction, the proposed resonance estimation method, and the dc-link virtual impedance-based suppression method are verified through both simulations and experiments. [ABSTRACT FROM AUTHOR]

Switch fault diagnosis and remedial actions are an important design aspect for isolated full-bridge dc-dc converters, and they can highly improve reliability of the whole system. In this paper, a fast switch short-circuit fault (SCF) diagnostic method is proposed for the phase-shifted full-bridge (PSFB) converter. The dc-link current and transformer primary voltage are treated as diagnosis criteria. Based on the combination of real-time criteria and switch gate-driver signals, the switch SCF can be identified rapidly, and thus further damage can be avoided. Besides, a remedial action for the faulty PSFB converter is introduced to keep the continuity of the system. The converter under fault can be reconfigured into an asymmetrical half-bridge converter. Moreover, a boost unit, including a switch and a diode, is inserted into between the output rectifier and filter capacitor to compensate the output voltage. The operational principle, design considerations, and implementation are discussed in this paper. Experimental results are shown to verify the validity of theoretical analysis. [ABSTRACT FROM AUTHOR]

With the increase in the switching speed and power level in the bridge-leg configuration, the spurious triggering pulse in the synchronous switch is prone to exceed the threshold voltage and cause spurious turn-on. Eliminating the spurious turn-on phenomenon plays an important role in preventing excessive switching loss, self-oscillation, and shoot-through in the bridge-leg configuration. A novel resistor-capacitor-diode ( RCD) level shifter is proposed to generate a negative gate voltage so that the spurious triggering pulse can be shifted below the threshold voltage, and thereby, the spurious turn-on can be avoided. The merits of the devised auxiliary circuit lie not merely in that it consists only of passive components and can easily be co-packaged with the existing gate driver, but also in that the negative voltage level is tunable and independent of the duty cycle of the converter. The effectiveness of this circuit has been verified by the experimental results. It is shown that when the spurious turn-on occurs in a bridge-leg configuration, the adoption of the proposed circuit can eliminate the spurious turn-on and reduce the turn-off switching loss by more than 40%. [ABSTRACT FROM AUTHOR]

This paper presents an optimal lowest-voltage-switching technique for boundary mode power factor correction (PFC) converters. The proposed approach minimizes the switching loss of the power MOSFET without additional discrete components. Optimal zero-voltage-switching or valley-switching can be achieved for universal input range. The gate driver delay can also be taken into account. A boundary mode boost PFC converter with the proposed optimal switching technique has been implemented using a 0.5-μm N-well process. Experimental results show that the proposed approach can realize optimal soft switching, and improve the efficiency of the boost PFC converter. The proposed lowest-voltage-switching technique can be applied to other resonant converters as well. [ABSTRACT FROM AUTHOR]

High efficiency and high power density can be achieved with a dc-dc transformer by operating all the switches at a fixed 50% duty cycle. However, the output voltage of the dc-dc transformer cannot be regulated. Novel rectifiers named active boost rectifiers (ABRs) are proposed in this paper. Basically, an ABR is composed of a traditional diode rectifier and a bidirectional switch. By adopting phase-shift control between the primary- and secondary-side switches, the output voltage regulation can be achieved when introducing the ABR to a dc-dc transformer. As a result, a family of novel soft-switching dc-dc converters is harvested. When the proposed converter operates in the soft-switching continuous conduction mode, zero-voltage-switching (ZVS) performance for all the primary- and secondary-side switches is achieved. When the converter operates in the discontinuous conduction mode, zero current switching (ZCS) for the primary-side switches and ZVS for the secondary-side switches are achieved. Furthermore, the diode reverse-recovery problem is alleviated by employing the ABR and phase-shift control scheme. As an example, the full-bridge converter with voltage-doubler ABR is analyzed to verify the proposed ABR concept and converters. The operation principles, voltage conversion ratio, and output characteristics are analyzed in depth. Finally, experimental results are provided to verify the feasibility and effectiveness. [ABSTRACT FROM AUTHOR]

This paper proposes an improved bidirectional LLC resonant topology with a new control scheme. All the switches in the proposed topology can achieve soft switching. Compared with traditional isolated bidirectional dc-dc converters such as dual active bridge converter, the reverse energy and turn-off loss are reduced dramatically, and the conversion efficiency can be much improved. With the proposed new control scheme, the power flow direction and output power of the proposed converter can be changed automatically and continuously, which is attractive for energy storage systems to balance the energy and to keep the dc-bus voltage constant. Performance of the proposed circuit is validated by the experimental results from a 1-kW prototype. Over 97% efficiency is achieved at full load condition based on the prototype. [ABSTRACT FROM AUTHOR]

In a modular multilevel converter (MMC), the interaction between switching actions and fluctuating capacitor voltages of the submodules results in second- and other even-order harmonics in the circulating currents. These harmonic currents will introduce extra power loss, increase current stress of power devices, and even cause instability during transients. Traditional methods for circulating current harmonic suppression have problems such as limited harmonic rejection capability, limited application area, and complex implementation. This paper presents a plug-in repetitive control scheme to solve the problem. It combines the high dynamics of PI controller and good steady-state harmonic suppression of the repetitive controller, and minimizes the interference between the two controllers. It is suitable for multiple harmonic suppression, easy to implement, and applicable for both single-phase and three-phase MMCs. Simulation and experimental results on a single-phase MMC inverter proved the validity of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation and capacitor voltage control method for the modular multilevel converter (MMC) allowing the fixed switching frequency of 50 Hz. In the proposed modulation method, the switching angles are calculated through a new approach with reference to the nearest voltage level control. And then, every four pulse patterns are grouped together for averaging the dc and fundamental ac components in the output voltage of individual submodules. Accordingly, the absorbed power of each submodule could be self-balanced during few line periods simply by periodically swapping the pulse patterns. Moreover, the different power losses or different initial energy states of the submodules may also cause the dc capacitor voltage deviation although the absorbed power is equally distributed. Therefore, a closed-loop-based method of exchanging the leading or falling edges of pulse patterns is developed for dc capacitor voltage control. Simulation results show that the MMC circuit together with the proposed method functions very well in both rectifier and inverter modes. Experimental results on a single-phase MMC-based inverter with four submodules in one arm show the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a simplified nearest level control balancing method for modular multilevel converter is presented. The proposed method neither requires individual sorting of the submodule voltages nor the redundancy of the switching states. Once the sorting of the submodules is done on the basis of the number of the submodules to be switched on, the identifications of the submodules can be carried out throughout the stages of the implementation of the this method. The proposed method also does not require the individual submodule status in the gate pulse generation stage. The gate logic in the presented method can be implemented with the help of the switching states of the voltage levels. Those simplifications and removing of the some of the stages by the proposed balancing method may ease and lead to the less processor time at the implementation level. The pictorial presentation further helps in consolidating the understanding of the different stages of the method. Rigorous simulations are carried out for open and one of the prominent closed-loop applications, i.e., modular multilevel converter-based high-voltage direct current to demonstrate the validity and effectiveness of the proposed simplified balancing method under normal and emergency conditions. [ABSTRACT FROM AUTHOR]

In this paper, by investigating the topology derivation principle of the phase-shift-controlled three-level dc/dc converters, the modular multilevel dc/dc converters, by integrating the full-bridge converters and three-level flying capacitor circuit, are proposed for the high step-down and high power dc-based systems. The high switch voltage stress in the primary side is effectively reduced by the full-bridge modules in series. Therefore, the low-voltage-rated power devices can be employed to obtain the benefits of low conduction losses. More importantly, the voltage autobalance ability among the cascaded modules is achieved by the inherent flying capacitor, which removes the additional possible active components or control loops. In addition, zero-voltage-switching performance for all the active switches can be provided due to the phase-shift control scheme, which can reduce the switching losses. The circuit operation and converter performance are analyzed in detail. Finally, the performance of the presented converter is verified by the simulation and experimental results from a 2-kW prototype. [ABSTRACT FROM AUTHOR]

Low-switching frequency modulation of multilevel inverters for medium-voltage high-power industrial ac drives is essential to reduce switching losses and, thus, improve the overall energy efficiency of the system. However, minimizing the switching frequency increases the total harmonic distortion (THD) of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging technique for controlling multilevel inverters at low-switching frequency without compromising on the THD of machine currents. The goal of our experiment was to implement SOP technique for controlling seven-level cascade inverter for an induction motor drive at an average device switching frequency limited to rated fundamental frequency. First, optimal seven-level waveforms were obtained by ofline optimization assuming steady-state operating conditions. Then, the switching angles for each semiconductor device were obtained that ensure equal distribution of switching losses as well as minimal unbalance in dc-link capacitor voltages. The proposed SOP technique is validated by experimental results obtained from the seven-level cascade inverter feeding a 1.5-kW induction motor. [ABSTRACT FROM AUTHOR]

This paper introduces a novel modular multilevel series/parallel converter that allows switching modules dynamically not only in series, as in the traditional modular multilevel converter (M2C), but also in parallel. As in M2C, the semiconductor voltages do not exceed the module capacitor voltage for any module state. While the new topology is a generalization of M2C and could, therefore, be operated identically to it, the additional states provide degrees of freedom that the controller can dynamically employ to achieve several advantages. Whereas in M2C many modules are bypassed if the instantaneous converter voltage is lower than the system's peak voltage, the parallel connectivity enables these modules to contribute to the current load, thus reducing conduction losses. In addition, the parallel configuration of modules can be used for balancing the modules' state of charge (SOC). The parallelization losses are moderate or negligible, dependent on the switching rate. Since the parallel connection of capacitors can ensure balancing, it enables stable operation of a multilevel converter without the need for monitoring the module SOCs. While such economical control hardware may be appropriate for low-power systems, we also present more sophisticated control that uses the additional degrees of freedom to minimize losses. Finally, we point to further extensions of the circuit topology to multipole module connectivity that could enable additional functionality and applications. [ABSTRACT FROM AUTHOR]

The balancing of the capacitor voltages in modular multilevel converters becomes increasingly difficult when the switching frequency is reduced. Typically, a reduced switching frequency will increase the spread in the capacitor voltages and, thus, the voltage ripple in the individual submodules. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor-voltage ripple. This is done by a predictive algorithm that controls the converter in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltages in the submodule capacitors at switching frequencies as low as 2-3 times the fundamental switching frequency. The proposed capacitor voltage balancing strategy is validated by both simulations and experimental results with 130-Hz and 140-Hz switching frequency. In the simulations, the capacitor voltage ripple was reduced by 24% compared to the case when a conventional sorting algorithm is used, and the experimental results show that it is possible to combine the proposed voltage balancing strategy with a circulating-current controller. [ABSTRACT FROM AUTHOR]

In this paper, a novel bidirectional modular multilevel dc-dc converter is proposed. The proposed topology, named the triangular modular multilevel dc-dc converter (TMMC), can achieve equal power sharing among its modules over a broad range of conversion ratios. The proposed control algorithm provides localized control of modules which enhances the converter's dynamic performance and design flexibility. A 1.7-kW experimental implementation of the converter is shown to achieve an efficiency of 95.9% and 96.2% in step-up and step-down modes, respectively. Significant reductions in the input current and output voltage ripples are observed through the interleaved operation of the converter. The TMMC also provides multiple fixed voltage nodes which makes it suitable as a multiple-input multiple-output converter. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (M2Cs) are increasingly used in high-voltage direct current (HVDC) systems. The efficiency of M2Cs is influenced by the modulation and cell selecting methods, which determines the switching frequency and capacitor voltage ripple in the converter station. A new approach to modulation of the M2C is presented in this paper. Tolerance band methods are employed to obtain the switching instants, and also cell selection. The proposed methods overcome the modulation problem for converters with few cells on one hand and also reduce the sorting efforts for cell balancing purposes of many cells converter on the other hand. Three different algorithms are also proposed to balance the cell capacitor voltages. The evaluation is done in time-domain simulation by which the performance of each method is studied in both the steady-state and transient cases. It is observed that using tolerance band methods not only reduces the switching frequency but also allows for handling severe fault cases in a grid-connected system. Eventually, the most promising tolerance band method has been implemented and verified in a real-time digital simulator, RTDS®. The average switching frequency of 70 Hz has been achieved for the system under study, while the capacitor voltage ripple is limited to 10% of the nominal cell voltage. [ABSTRACT FROM AUTHOR]

Synchronous optimal pulsewidth modulation (SOP) permits low switching frequency modulation of multilevel inverter for medium-voltage high-power industrial ac drives without compromising on total harmonic distortion (THD). An aim of our experiment was to operate a nine-level cascade inverter of an induction motor drive at an average device switching frequency limited to rated fundamental frequency by using SOP technique. To reduce the number of separate dc sources, a three-level diode clamped converter was used as a cell in the nine-level cascade inverter. Using SOP technique, optimal nine-level waveforms were obtained by ofline optimization assuming steady-state operation of the induction machine. The switching angles for each semiconductor switch are then obtained from optimal nine-level waveforms based on the criteria to minimize the switching frequency as well as unbalance in dc-link capacitor voltages. Experimental results obtained from the 1.5-kW induction motor drive show THD 5% for stator currents. The results indicate that SOP technique reduces the switching frequency of operation without compromising on THD. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) structures are composed of several hundreds to thousands of half-bridge converters. Such large numbers of power switches and electrical nodes introduce important numerical challenges for the computation of electromagnetic transients. The problem becomes particularly more complex for the real-time simulations. This paper presents a feasibility study on the real-time simulation of the MMC models. CPU-based and field-programmable gate array-based implementations are proposed and evaluated for the MMCs having up to 401 levels. The study also provides guidelines for the real-time simulation platform requirements to simulate these MMC models. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of the periodical. [ABSTRACT FROM AUTHOR]

Switched capacitor (SC) converters are becoming quite popular for use in dc-dc power conversion. The concept of equivalent resistance in SC converters is frequently used to determine conduction losses that occur as a result of the load current. A variety of methodologies have been presented to predict the equivalent resistance in hard-switched SC converters. These works, however, did not consider the effect of stray inductance on equivalent resistance. Current power converter design practices favor higher switching frequencies, moving hard-switched SC converters into operating areas in which stray inductance affects converter performance. This paper presents an analytic equation that can be used to evaluate the effects of stray inductance on the equivalent resistance of SC converters. The concepts proposed here were verified by both digital simulation and a prototype converter. The equations presented can be used to evaluate the effects of stray inductance on SC converter performance, thereby helping designers set a maximum operating frequency to limit those effects. [ABSTRACT FROM AUTHOR]