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Voltage-controlled three-phase three-leg inverters are widely applied in various occasions. The inverters are generally switched to the current-controlled mode to limit the fault currents when short-circuit faults happen. Under symmetrical fault, the inverter can be controlled as a symmetrical, three-phase current source. However, the voltage limiting will happen under asymmetrical fault. As a result, the fault phase currents will be distorted and cannot be completely controlled. Considering that the voltage limiting is mainly caused by large load impedance of healthy phase under asymmetrical fault, the voltage limiting is avoided by paralleling the virtual impedance with the output filter capacitor in this paper. As a result, the current limiting loop is not broken and the fault phase currents can be effectively controlled. The implementation of virtual impedance in control system and the influence of virtual impedance on the stability of system are also analyzed in detail in this paper. The theoretical results are validated by experiments. [ABSTRACT FROM AUTHOR]

Various methods have been presented in the past to emulate the electrical behavior of modular multilevel converters (MMCs). To meet the demands for the reliability aspect study of MMCs, this paper proposes a viable setup to emulate the thermal behavior and to investigate its feasibility for reliability testing and thermal model validation of the power modules in the MMC. The proposed mission profile emulator has three distinctive features: 1) capable of emulating and measuring the thermal stresses of power modules; 2) capable of implementing practical switching profile as a full-scale MMC; and 3) having significantly reduced requirement for dc power supply compared to existing setups used for electrical studies. Theoretical discussions, and simulations as well as the experimental results are presented to demonstrate the capability of the mission profile emulator both electrically and thermally. Moreover, this paper is accompanied by a video demonstrating how to measure the junction temperature of the power devices using the optical fiber and the thermal camera. [ABSTRACT FROM AUTHOR]

The emergence of applications which require high-voltage switches has created a tendency to use semiconductor device series stacks. These series stacks permit operation at blocking voltages above semiconductor elements’ nominal voltage. Insulated-gate bipolar transistors (IGBT) are currently utilized for controllability and switching speed, when these topologies are employed. The main challenge therewith is guaranteeing voltage balance between IGBTs, both when blocked and when switching transistors. Most of the methods which have been proposed to mitigate static and dynamic voltage unbalances increase transistor losses. The series stack loss-less high voltage switch (LHVS) which mitigates voltage unbalances, thus reducing switching losses, is presented in this paper. LHVS consists of a circuit, which ensures soft IGBT switching, an energy recovery circuit, and a gate delay compensation circuit. Additionally, the insulation voltage level is guaranteed to be equal between control circuit and high-voltage side of each IGBT. The operating principle of the LHVS is detailed in this paper, as is experimental validation which has been performed for three series stack modules. Static unbalances are reduced to 1%, while the differences between collector–emitter voltage curves in switching “on” do not surpass 8 ns, and switching losses are reduced by 41%, as compared to the hard-switching topology. [ABSTRACT FROM AUTHOR]

In this paper, an overload and short-circuit protection method is proposed for voltage source inverter-based uninterruptible power supply (UPS) system. In order to achieve high reliability and availability of the UPS, short circuit and overload protection scheme are necessary. When overload or short circuit happens, using the proposed control method, the amplitude of the output current can be limited to a constant value, which can be set by the customer to avoid the destruction of the power converter, and to obtain a faster recovery performance as well. The detailed principle of the proposed protection method is discussed in this paper. It mainly contains three parts in the control diagram for current limit, first is the anti-windup in the voltage and current controllers, then the feedforward of the capacitor voltage to the current control loop, the last is the fast reset of the resonant part of the current controller when overcurrent happens. The procedure of developing the control method is also presented in the paper. Experimental results on a commercial UPS system are presented to verify the effectiveness of the control method. [ABSTRACT FROM AUTHOR]

This paper presents a novel seven-level inverter topology for medium-voltage high-power applications. It consists of eight active switches and two inner flying capacitor (FC) units forming a similar structure as in a conventional active neutral-point-clamped (ANPC) inverter. This unique arrangement reduces the number of active and passive components. A simple modulation technique reduces cost and complexity in the control system design without compromising reactive power capability. In addition, compared to major conventional seven-level inverter topologies, such as the neutral point clamped, FC, cascaded H-bridge, and ANPC topologies, the new topology reduces the dc-link voltage requirement by 50%. This recued dc-link voltage makes the new topology appealing for various industrial applications. Experimental results from a 2.2-kVA prototype are presented to support the theoretical analysis presented in this paper. The prototype demonstrates a conversion efficiency of around 97.2% ± 1% for a wide load range. [ABSTRACT FROM AUTHOR]

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion. [ABSTRACT FROM AUTHOR]

This paper describes a dc-link voltage control method of a single-phase back-to-back cascaded H-bridge inverter (SBCI) for a medium-voltage motor drive system. The main advantage of the SBCI topology over the conventional regenerative cascaded H-bridge topology with a three-phase active front-end (AFE) is a simple system structure, which is composed of an input transformer, a power cell, a current sensor, etc. However, the challenging points of the SBCI are larger voltage ripple in the dc-link capacitor and imbalance of dc-link voltages of each phase. The asymmetric dc-link voltage of each power cells could cause unstable operation such as over-modulation due to the lack of the dc-link voltage of a particular phase and result in over-voltage or under-voltage faults. In this paper, the control strategy of the dc-link voltage for the SBCI that uses the negative-sequence voltage of the converter is described. The proposed control method is verified with a computer simulation whose target is a 6.6-kV–1.25-MW medium-voltage drive system. Also, through the experimental setup with the prototype SBCI whose power rating is 16.2 kVA, the dc-link voltage of each AFE has been controlled within a 0.5% error of its reference value at the full load. [ABSTRACT FROM AUTHOR]

This paper proposes a control method for a switching power converter. This converter is connected to a dc-link of a dc microgrid system via an LC input filter. This control method is based on a Lyapunov stability analysis; all state variables are acquired for evaluating stability analysis, including the output current for calculating the load resistance. To reduce a number of sensor counts, the input current is estimated. Moreover, loss occurrence in the converter is observed to reduce static errors of the controlled state variables, especially the output voltage. The losses are modeled as a series input voltage source observed from the dc–dc converter and a parallel current source. The latter enables us to eliminate the output current sensor. Using information from the estimated current source, a load resistance can be calculated. A Lyapunov function candidate is chosen to ensure that the system, including the observer, operates in a stable manner. Based on evaluating the time-derivative of the chosen Lyapunov function, we obtain the switching command that makes the system operate stably in each sampling cycle. In this paper, the proposed technique is applied to a boost converter. The simulation and as well experimental results validate the proposed control. [ABSTRACT FROM AUTHOR]

This paper proposes a unified control based utility-interactive uninterruptible power converter (UIUPC). The proposed control enables the UIUPC to inherently transfer from a $ p-q$ control strategy in grid-connected mode to a voltage–frequency control strategy in autonomous mode and vice-versa. This happens seamlessly with the same control topology. The need to switch between two separate control architectures is thus eliminated. Critical islanding detection and synchronizing mechanisms are also not needed in the proposed control method. The unified controller proposed in this paper is derived from the concept of controlling the perturbations in the magnitude and speed of the point of common coupling (PCC) space vector. The PCC space vector is compared with a reference space vector applied in the direction of the PCC space vector on an instantaneous basis to extract the perturbations. The reference system of the proposed control is linked to the dynamics of the PCC space vector. This offers the ability of parallel operation of similar unified control UIUPC. Thus, in addition to the above said advantages, the proposed control also puts forth an alternative to paralleling approaches like conventional droop and master–slave configurations. The effectiveness of the proposed control is validated by simulation and experimentation. [ABSTRACT FROM AUTHOR]

A modular multilevel converter (MMC) is regarded as a promising topology in high-voltage direct current systems. However, the MMC consists of numerous submodules (SMs) and switching devices, which lead to a considerable switching loss, and increased cost and size of the heat sink. To mitigate these issues, this paper presents a novel modulation method composed of fundamental frequency modulation (FFM) and multicarrier-based sinusoidal pulsewidth modulation schemes. The main purpose of this modulation method is the reduction of switching loss while maintaining good harmonic performance. However, the FFM scheme leads to the unbalanced capacitor voltage of each SM in the MMC. Accordingly, this paper additionally proposes the rotation method and selective voltage balancing control for SMs to ensure effective performance of the method. Simulation and experimental results verify the effectiveness and performance of the proposed modulation scheme through switching loss and spectral analyses. [ABSTRACT FROM AUTHOR]

Nonregenerative pulsewidth-modulated (PWM) rectifiers are increasingly being considered for applications, where the power flow is unidirectional, such as power supplies for telecommunications, X-ray, the machine-side converter for wind energy conversion systems, etc. They use fewer active switches, which increase their power density and reduce cost. This paper proposes a novel reduced switch topology for a multilevel (five-level or higher) nonregenerative PWM rectifier. It uses only four controlled switches and eight diodes per phase for a five-level rectifier. Half of the diodes are naturally commutated (zero current switching) at the line frequency, which reduces switching losses. This topology has several other advantages compared to similar topologies reported in the literature, such as minimum voltage stress across the devices, elimination of transient voltage-balancing snubbers, no extra hardware for balancing the flying capacitors, the dc-link mid-point voltage, etc. In this paper, switching cycle average modeling and the carrier-based modulation strategy for this rectifier are also presented to maintain a balanced dc link and to regulate flying capacitor voltages, while achieving unity displacement factor at the rectifier input terminals. The overall performance of the rectifier is verified by experimental results. [ABSTRACT FROM AUTHOR]

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

Inductive power transfer systems deployed in material handling have traditionally used parallel-tuned (current-sourced) boost regulators to independently control and regulate the load on each secondary. This paper evaluates the current doubler as an alternative parallel-tuned secondary controller within this application to better match the current and voltage requirements in the secondary resonant tuning network in high-power applications. This enables designs that enable the secondary magnetic pickup to achieve a smaller profile and fit within typical space constraints of material-handling vehicles. This paper presents the design approach needed for this regulator and compares its operation and performance against a traditional boost controller using both the simulation and the measurement of two built 5-kW secondary regulators. The current doubler naturally achieves a lower output ripple due to its interleaved switching and is found to have a comparable efficiency to the boost controller but requires slightly more components. [ABSTRACT FROM AUTHOR]

A plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle's battery becomes low and reaches a predetermined state of charge (SOC). This paper provides a better solution by replacing the internal combustion engine of a PHEV with a small-size photovoltaic (PV) module located on the roof of the PHEV, and a micro wind turbine located in front of the PHEV, behind the condenser of the air conditioning system. Thus, this study proposes a novel battery/PV/wind hybrid power source to be utilized in PHEVs. The power source equipped with vehicle-to-grid (V2G) technology is composed of a 19.2-kWh Lithium (Li)-ion battery used as the main energy storage device, and a PV module and a wind energy conversion system. A prototype of the battery/PV/wind hybrid power source has been constructed and utilized in a PHEV. Experimental verifications are presented that demonstrate utilizing the PV module and micro wind turbine adds 19.6 km to the cruising range of a PHEV with the weight of 1880 kg during two sunny days, and provides higher power efficiency (91.2%) and speed (121 km/h). Highly accurate dc-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using pulse width modulation technique are the other contributions of this paper. [ABSTRACT FROM AUTHOR]

This paper proposes a new power decoupling control method for a direct ac-to-ac converter. The ac-to-ac converter consists of two half-bridge converters, two input filter capacitors, and a series-resonant circuit, which enables it to convert the single-phase line-frequency ac input to the high-frequency ac output directly. The proposed power decoupling control method stores input power pulsation at double the line frequency in the input filter capacitors. Thus, the proposed control method realizes a unity power factor in the line-frequency ac input and a constant amplitude current in the high-frequency ac output without any additional switching device or energy storage element. This paper theoretically discusses the principle and operating performance of the proposed control method and confirms the effectiveness of the proposed control method in experiments using an isolated ac-to-dc converter based on the direct ac-to-ac converter. As a result, the proposed power decoupling control method effectively improved the displacement power factor of the line-frequency ac input current to more than 0.99 and reduced the voltage ripple in the dc load to 4%. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-efficiency photovoltaic (PV) converter for grid connection through a high-leg delta transformer. The converter is composed of a symmetrically connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. As a result, this circuit configuration enables to reduce the power losses in both boost converter and inverters. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in the switching power loss. Experimental results confirm that the proposed circuit configuration makes it possible to improve its European efficiency from 91.6% to 94.5%. Moreover, system performance is evaluated on the assumption of maximum power point tracking operation. [ABSTRACT FROM AUTHOR]

This paper presents a unified framework for the modeling, analysis, and design of load-independent Class E and Class EF inverters and rectifiers. These circuits are able to maintain zero-voltage switching and, hence, high efficiency for a wide load range without requiring tuning or use of a feedback loop, and to simultaneously achieve a constant amplitude ac voltage or current in inversion and a constant dc output voltage or current in rectification. As switching frequencies are gradually stepping into the megahertz (MHz) region with the use of wide-bandgap (WBG) devices such as GaN and SiC, switching loss, implementing fast control loops, and current sensing become a challenge, which load-independent operation is able to address, thus allowing exploitation of the high-frequency capability of WBG devices. The traditional Class E and EF topologies are first presented, and the conditions for load-independent operation are derived mathematically; then, a thorough analytical characterization of the circuit performance is carried out in terms of voltage and current stresses and the power-output capability. From this, design contours and tables are presented to enable the rapid implementation of these converters given particular power and load requirements. Three different design examples are used to showcase the capability of these converters in typical MHz power conversion applications using the design equations and methods presented in this paper. The design examples are chosen toward enabling efficient and high-power-density MHz converters for wireless power transfer (WPT) applications and dc/dc conversion. Specifically, a 150-W 13.56-MHz Class EF inverter for WPT, a 150-W 10-MHz miniature Class E boost converter, and a lightweight wirelessly powered drone using a 20-W 13.56-MHz Class E synchronous rectifier have been designed and are presented here. [ABSTRACT FROM AUTHOR]

This paper introduces the comparison of four predictive torque control schemes for a permanent-magnet synchronous machine (PMSM). The first method is the finite-set model predictive control (FS-MPC). In FS-MPC, the optimal switching state is selected based on the evaluation and minimization of a cost function for all possible voltage space vectors (VSVs) of the inverter. The second method performs a simplified FS-MPC where the selection and evaluation of the possible VSVs are reduced to only three. The third method is based on the principle of predictive direct torque control (PDTC), where the duty cycle of the switching state is optimized for application in the inverter. Finally, a method that combines FS-MPC and PDTC named model predictive torque control is presented. This paper introduces the methodology and the results of a comprehensive comparison of the four predictive schemes based on different criterions. The control schemes are implemented on a field-programmable gate array and are applied to a PMSM. Experimental results are presented to validate the presented comparison and discussion. [ABSTRACT FROM AUTHOR]

This paper discusses dynamic behavior of a dual-active-bridge (DAB) dc–dc converter. Conventional phase-shift control methods for the DAB converter may cause dc offsets in both inductor current and transformer magnetizing current in transient states. The dc offset in the inductor current would introduce an excessive peak current through the switching devices. The dc offset in the magnetizing current may induce magnetic-flux saturation. Conventional methods simultaneously turn on and off the diagonal switches in each H-bridge converter and produce a square-wave voltage with a 50% duty ratio. In contrast, the proposed method in this paper independently controls each switch to modify the duty ratio in transient states. This paper clearly derives the requirements of each switch to eliminate the dc offsets in both currents with a settling time shorter than half the switching period. Experimental results using a 5-kW 20-kHz system verify the validity of the proposed control method, which is effective not only in a single step change, but also in a continuous change in the phase-shift reference. [ABSTRACT FROM AUTHOR]

This paper is introducing a new method of operation for a series resonant converter, with intended application in megawatt high-voltage dc wind turbines. Compared to a frequency controlled series resonant converter operated in subresonant mode, the method (entitled pulse removal technique) allows the design of the medium frequency transformer for highest switching frequency, while being operated at lower frequency without saturation. The main focus of this paper is to identify and analyze the operating modes of the converter with pulse removal technique. With the use of variable frequency and variable phase displacement in subresonant mode, the new method of operation promises transformer size reduction and facilitates soft-switching transition of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on rectifier side. Four modes of operation are identified, while equations for output power, voltage, and current stress are identified. Experimental results are concluded on a 1 kW, 250 V/500 V prototype. [ABSTRACT FROM AUTHOR]

This paper proposes generation of a 15-level (14 concentric) dodecagonal voltage space vector structure (DVSVS) for a star connected induction motor drive. The proposed multilevel DVSVS is obtained by cascading two inverters, namely a primary and secondary inverter. The primary inverter is a five-level (5L) structure formed by stacking two three-level flying capacitors with individual reduced dc sources and the secondary inverter is also a 5L structure formed by cascading two capacitor-fed cascaded H-bridges (CHB). The active power is supplied by the primary inverter, while the secondary inverter acts as switched capacitor harmonics filter, and capacitors in the secondary inverter are balanced naturally irrespective of load power factor for entire modulation index. The high-voltage dc supply fed primary inverter is operated in quasi-square wave mode, while the high frequency switching is applied to low voltage CHBs, thus, reducing the overall switching loss. The proposed scheme gives the advantages of both DVSVS and multilevel structure, thus, making it one of the solutions for battery or stacked dc-fed applications. The paper also presents the experimental results as well as comparison study with the existing topologies to support the advantages of proposed scheme. [ABSTRACT FROM AUTHOR]

The output voltage of power electronic converters is a very important quantity for dynamic control of power electronic systems. In electrical drives without electromechanical position or speed sensor, the terminal reference voltage is used to obtain the rotor position. Dead-time effects and semiconductor voltage drop lead to distortion in the actual output voltage and degrade the control performance when the back electromotive force magnitude is low. Thus, for stable low-speed operation, output voltage sensing becomes necessary. Due to the switching nature of power electronic systems, this is not a trivial task, especially when instantaneous measurement of the terminal voltage is required. In this paper, an instantaneous switching-period average voltage sensing technique is proposed that utilizes a combined approach of oversampling and filtering. Based on the theoretical analysis of the sampling- and filter-induced measurement distortion, a general solution for an optimal filter design is derived. The additional sensing circuit is integrated into the low-side gate driver of the converter outputs. This paper includes details about the hardware implementation and extensive verification measurements. [ABSTRACT FROM AUTHOR]

High-performance cloud computing enables many key future technologies such as artificial intelligence (AI), self-driving vehicle, big data analysis, and the Internet of things (IoT), using clustered CPU and GPU servers in the datacenter. To improve the power efficiency and the infrastructure flexibility, the computing industry is adopting 54 VDC to power the servers in the open compute racks. In this paper, a new modeling technique for a soft-switched dc–dc converter is presented and suitable to guide optimal design in different applications, for example, 54 V to point of load (PoL) for the new open compute rack. To improve the model accuracy and reduce the complexity, this paper proposes a reduced-order linear differential equation (LDE) based modeling technique to discover the following: 1) the tank resonance involving the output inductor; 2) the output current ripple and its impact on power efficiency; 3) the proper on-time control for soft switching; 4) the unique bleeding mode under the heavy load; 5) the output power capability of the converter; and 6) component tolerance analysis and impact on the performance of the converter. With the power loss estimation, design guidelines are provided for a reference design and design improvement based on this new modeling technique. Using the proposed method, great accuracy can be expected in the efficiency estimation. Simulation and experimental results are provided to verify the modeling technique in a 54–1.2 V 25 A dc–dc converter prototype. [ABSTRACT FROM PUBLISHER]

This paper proposes the application of a finite control set model predictive control (FCS-MPC) strategy in standalone ac microgrids (MGs). AC MGs are usually built from two or more voltage source converters (VSCs) which have the capability of regulating the voltage at the point of common coupling, while sharing the load power at the same time. Those functionalities are conventionally achieved by hierarchical linear control loops. However, they present severe limitations in terms of slow transient response and high sensitivity to parameter variations. This paper aims to mitigate these problems by first introducing an improvement of the FCS-MPC strategy for a single VSC that is based on explicit tracking of derivative of the voltage reference trajectory. Using only a single step prediction horizon, the proposed strategy exhibits very low computational expense, but provides steady-state performance comparable to carrier-based sinusoidal PWM, while its transient response and robustness to parameter variation is far superior to hierarchical linear control. These benefits are exploited in a general ac MG setting where a methodology for paralleling multiple FCS-MPC regulated VSCs is described. Such an MG is characterized by rapid transient response, inherent stability in all operating conditions, and fully decentralized operation of individual VSCs. These findings have been validated through comprehensive simulation and experimental verification. [ABSTRACT FROM PUBLISHER]

This paper presents a novel control method for multimodule photovoltaic microinverter (MI). The proposed MI employs a two-stage topology with active-clamped current-fed push–pull converter cascaded with a full-bridge inverter. This system can operate in grid-connected mode to feed power to the grid with a programmable power factor. This system can also operate in line-interactive mode, i.e., share load power without feeding power to the grid. In the event of grid power failure, the MI can operate in a standalone mode to supply uninterruptible power to the load. This paper presents a multiloop control scheme with power programmable capability for achieving the above multiple functions. In addition, the proposed control scheme embedded a multimodule parallel capability that multiple MI modules can be paralleled to enlarge the capacity with autonomous control in all operation modes. Finally, three 250-W MI modules are adopted to demonstrate the effectiveness of the proposed control method in simulations as well as experiments. [ABSTRACT FROM PUBLISHER]

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

In order to increase the efficiency of modern microprocessors power supplies used in data centers, the 48-V dc distribution bus is gaining growing attention. For such applications, voltage regulation modules (VRMs) are currently obtained using two-stage conversion systems with an intermediate 12-V dc bus. This paper presents an innovative single-stage approach for the 48-V VRM based on a quasi-resonant constant on-time (COT) operation. The proposed topology inherently integrates the multiphase approach, providing fast phase shedding and flat high-efficiency curves even at light load conditions. This is a unique advantage, usually not available in the two-stage approach, that is very important in server architectures, where high efficiency is required even at light load conditions. The paper analyses the circuit topology, and proposes a control architecture for fast transient response, including the current sharing capabilities, and a solution for implementing the integrated magnetics. The digital controller has been implemented in 0.16-$\mu$ m lithography together with a digital pulse-width-modulation with a 195 ps resolution, and a 40 MS/s, 7-bit ADC. Experimental results show an efficiency of 93.1% for a 250 A, 1.8 V VRM, and of 93.2% for a 102 A, 1.2-V double data rate (DDR) power supply. [ABSTRACT FROM PUBLISHER]

This paper proposes a single-phase power factor correction (PFC) rectifier to achieve high power factor, wide output voltage range, and ripple power decoupling without using electrolytic capacitors. It consists of two parts: PFC circuit and output voltage regulation circuit. The load side is involved in both parts, which is different from the regular two-stage conversion structure. The proposed rectifier can be directly applied to low voltage cases due to the wide output voltage range. And the decoupling capacitor voltage can be smaller than the peak grid voltage, which reduces the voltage stress. Besides, the low-frequency ripple power buffer is implemented without a dedicated power-buffering controller. This paper first introduces the circuit structure, operation principles, and control method. Then, the system design consideration is given. Finally, the effectiveness of the proposed topology is verified by the simulations and experimental results. [ABSTRACT FROM AUTHOR]

A switched-capacitor-based dual-switch dc–dc converter with a high-boost voltage gain is proposed in this paper. The proposed converter can obtain a high-voltage gain with a small duty cycle, which decreases the voltage stress and the conduction loss on the power switches. This paper presents the key waveforms, the operating principles at the continuous conduction mode and the discontinuous conduction mode, and the parameter design. Moreover, a comparison between the proposed converter and other nonisolated converters has been completed. To verify the operating principle, a 200 W prototype is constructed with an input voltage of 25–50 V and an output voltage of 200 V. The simulation and experimental results are shown. [ABSTRACT FROM PUBLISHER]

This paper proposes a current sensorless control strategy for the dual active bridge (DAB) converter with nonlinear disturbance observer (NDO)-based load current feedforward. The proposed method can regulate both the dc-bus voltage and the current of the DAB converter without current sensors. Several performance indexes are established for the parameter design and a detailed design method is presented in this paper. When a single-phase H-bridge inverter is connected, the double-frequency oscillation from the feedback path is suppressed by proper parameter design, while the transient response of dc-bus voltage can be further improved by the NDO-based load current feedforward with a notch filter in the feedforward path. The performance of the proposed control method and the effectiveness of the parameter design are verified in a prototype by experimental results. [ABSTRACT FROM PUBLISHER]

Sheppard–Taylor power factor correction (ST-PFC) rectifier could obtain a high power factor due to its capability of overcoming the control detuning issue. However, it needs a bulky electrolytic capacitor at the load side to buffer the double-frequency ripple power (DFRP), which reduces the reliability and power density significantly. This paper proposes a control method to divert the DFRP to the small energy transfer capacitor. Consequently, the bulky electrolytic capacitor is replaced with a small film capacitor. The proposed method is carried out by introducing the freewheel state (one switch is turned on and the other is turned off) into the control. So no extra hardware is added, which makes the proposed method cost-effective. A low electromagnetic interference emission is also achieved due to the continuous input–output currents. In addition, the proposed method can be extended to other topologies easily. This paper first gives the detailed analysis of the proposed control method, and then introduces the controller design. The selection of the passive components is also briefly discussed. Finally, the simulation and experimental results verify the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

These days, constant on-time current mode (COTCM) control scheme is widely used in the voltage regulator (VR) controllers because it has a higher light-load efficiency and a higher BW design capability while maintaining a simpler compensation requirement. One issue plaguing the COTCM control is its slow transient response which is caused by its fixed TON operation. During the heavy-load step-up transient, the duty cycle becomes saturated and the inductor current increment becomes limited by TON and the minimum off time (TOFF$\_$ MIN) ratio, which can create a large undershoot at load step up. On the other hand, in the load step-down case, if the load step down occurs at the beginning of TON, a large overshoot can be created at the output. To solve this issue, this paper presents a method designed to increase the TON at load step up and then very quickly, decrease at load step down in order to reduce the undershoot and overshoot at output or otherwise save the output capacitor. In this proposed method, the increase or decrease of T ON is proportional to the output change which eliminates the chance of any overcorrection or ring-back problem unlike the methods presented in prior forums. This feature enables the control to work seamlessly in a high-frequency load repetitive case in VR applications. Since this TON change occurs only in the transient period when duty cycle is saturated, it does not affect the small-signal property of the COT control. Moreover, the proposed methods are very much compatible with the state-of-the-art single and multiphase COT control structures. Simulation and test results in both single and multiphase operations are also presented in the paper to verify the proposed concept. [ABSTRACT FROM PUBLISHER]

A novel soft-switching interleaved coupled-inductor boost converter is proposed in this paper. Only a single active soft-switching module is needed to simultaneously achieve the soft-switching property of the two switches in the interleaved coupled-inductor boost converter. The better efficiency is achieved with the less components and cost. The two main switches can achieve the ZVT turn-on and smaller-current turn-off simultaneously when the single active soft-switching module is active. Due to the coupling characteristic of the inductors, the voltages across the two inductors are changed at the same time; therefore, the equivalent circuit is equal to the parasitic capacitors of the two main switches in parallel to resonate with the auxiliary inductor. By coupling two input inductors, the volume and cost of the circuit can be reduced. The interleaved coupled-inductor topology can also reduce the input and output current ripples and share the input and output currents. The operating modes, analysis, and design of the proposed circuit have been discussed in this paper. Simulation and experiments are finally conducted to verify the validity of the proposed circuit. [ABSTRACT FROM PUBLISHER]

DC electric springs (DCES) are emerging technologies for the (i) regulation of mains voltage against the intermittent renewable generations and (ii) harmonic cancellation in dc microgrids. When conventional converter topologies (e.g., half-bridge or full-bridge converter) are adopted as DCES, the battery storage of the DCES has to process both the dc power and the ac harmonic power. The pulsating ac power can severely reduce the lifetime of the battery. To address this issue, a hybrid-DCES (H-DCES) is proposed in this paper to perform (i) and (ii) in a decoupled manner. With a modified topology and control method, the H-DCES can divert the ac current to the ground and retains the function of manipulating noncritical load for dc voltage regulation. The immediate benefits of this H-DCES are the reduction of storage capacity and a prolonged lifetime of the battery. Both the operating principle and the mathematical model of the proposed H-DCES are analyzed in this paper. A prototype of the H-DCES is practically tested in a 48-V dc grid. The experimental results show that the H-DCES can realize the decoupled operation of dc voltage regulation and harmonic cancellation. Simulation studies further demonstrate that the H-DCES requires less storage capacity than its counterparts. [ABSTRACT FROM AUTHOR]

In this paper, direct torque control (DTC) of five-phase induction motor (FPIM) is implemented using three-level neutral point clamped (TL-NPC) inverter. One of the advantages of three-level inverter over two-level one for DTC operation is the low torque ripple. Also TL-NPC inverter through space vector modulation technique gives low $ dv/dt$ transition with better voltage waveform. By applying conventional lookup table for DTC, the TL-NPC inverter does not ensures lower $dv/dt$ transition. In this paper, a novel switching scheme for DTC of FPIM using TL-NPC inverter is proposed that ensures the low $ dv/dt$ transition and balancing of dc-link capacitor voltages of TL-NPC inverter. To form the lookup table for DTC operation, instead of using voltage vectors directly, virtual vectors (VVs) are utilized. Two switching states are used in one sample time to generate a VV in $\alpha \beta$ plane, which gives zero resultant voltage in $ xy$ plane. The switching strategy ensures low number of transitions to reduce the switching losses. The switching state redundancies are used in a novel way to balance the dc-link capacitor voltages without using any additional hardware. The proposed technique to balance the dc-link capacitor voltage gives lower switching frequency. The MATLAB/Simulink environment is used for the simulation and the results are validated through experiments. [ABSTRACT FROM AUTHOR]

This paper presents a new feed-forward strategy for suppressing low-order harmonic circulating currents in pulsewidth-modulated (PWM) based modular multilevel converters (MMCs). The approach is based on the new average model approach established in this paper, which identifies cross-coupling interactions between the system-level and submodule elements using decomposed dependent sources. As well as improving the damping of the system, the major advantage of this approach is that it maintains the natural DC bus balance property of a PWM modulated MMC by considering the upper and lower arms together (unlike existing feed-forward schemes which treat each MMC arm independently). Moreover, unlike existing direct control resonant strategies, which require careful gain tuning and are highly dependent on the ac system frequency, the proposed approach achieves wideband circulating current ripple suppression without requiring knowledge of the circulating current harmonic frequencies and needs only a simple proportional–integral (PI) controller to regulate the circulating current dc component for power balance. This makes it particularly suitable for use in multifrequency or variable-frequency ac systems. Extensive simulation and matching experimental results, including steady-state and transient responses compared against existing circulating current suppression approaches, validate the effectiveness and benefits of this new feed-forward compensation technique. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid seven-level converter based on T-type converter and H-bridge cascaded suitable for low-voltage and high-power-density applications. The operation principles and conduction paths are analyzed comprehensively. Voltage balance control of the floating capacitors is the key point of this paper. Mathematical expressions of capacitor voltage balance conditions are deduced based on sinusoidal pulse width modulation (SPWM). The results show that floating capacitor voltages are only balanced when the modulation index is below 0.82 under SPWM. In order to enlarge the modulation index ensuring the capacitor voltage balance, space vector modulation (SVM) is also applied to regulate floating capacitor voltages taking advantage of redundant switching vectors. Meanwhile, in SVM, there are no additional control requirements for the capacitor voltage. Taken both SPWM and SVM into consideration, the limit to the range of operation for this seven-level converter is presented, which is a function of the modulation index and the power factor. The merit of dc voltage utilization improvement in this topology is also analyzed based on simulation results. Simulations and experimental results under different modulation index and RL load are presented to verify the modulation strategies illustrated in this paper. [ABSTRACT FROM PUBLISHER]

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

Conventional single-phase power-factor-correction (PFC) rectifiers with active power decoupling capability typically require more than three active switches in their circuits. By exploring the concept of power-buffer cell, a new single-stage PFC rectifier with two active switches, one inductor and one small power-buffering capacitor is reported in this paper. The proposed converter can achieve high-power factor, wide output voltage range, and power decoupling function without using electrolytic capacitor. Additionally, an automatic power decoupling control scheme that is simple and easy to implement is proposed in this paper. The operating principle, control method, and design considerations of the proposed rectifier are also provided. A 100-W prototype with ac input voltage of 110 Vrms and a regulated dc output voltage ranging from 30 to 100 V has been successfully designed and practically tested. The experimental results show that with only a 15 μF power-buffering film capacitor, the proposed converter can achieve an input power factor of over 0.98, peak efficiency of 93.9%, and output voltage ripple of less than 3%, at 100-W output power. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel five-level nested neutral point piloted (NNPP) converter and analyzes the operating principle of five-level NNPP converter. This paper presents a novel space vector pulse width modulation (SVPWM) algorithm based on gh coordinate for five-level NNPP converter. First, the common-mode voltage is reduced by choosing the appropriate redundant switching states. After that, the floating-capacitor voltage balance control strategy is presented. The appropriate switch combinations of each phase are determined by the control requirements of floating-capacitor voltages respectively and the hardware mapping method of the switching states is presented. Furthermore, the neutral-point voltage balance control strategy is presented. In order to balance the dc-link capacitor voltages, the seven-segment switching sequence is selected according to the control requirements of dc-link capacitor voltages and the neutral-point voltage regulatory factor is introduced to regulate the durations of the redundant switching states in a switching cycle. Finally, the validity of the novel SVPWM algorithm with decoupling control strategies of floating-capacitor voltages and dc-link capacitor voltages is verified by the experimental results of five-level NNPP converter under steady-state and dynamic conditions. [ABSTRACT FROM AUTHOR]

This paper analyzes three different carrier-based modulation patterns applied to a three-phase high-power-factor-corrected (PFC) five-level buck+boost-type converter acting as an interface between dc distribution systems and an ac grid. The modulation is analyzed employing the space vectors theory so that the achievable performance is demonstrated. The main advantage of the analyzed modulation strategy is its simplicity, which makes it suitable for digital signal controller (DSC) implementations. This seems straightforward for voltage source converters, but is a challenge for current-multilevel converters that typically employ field-programmable gate array devices to achieve better harmonic distortion performance. This is due to modern power electronics DSCs being typically designed for other converter topologies. The power converter is constructed with two phase-shift-modulated six-switch buck-type PFC converters, paralleled by interphase transformers, and an inverting circuit. The system features: bidirectional current carrying capability; relatively low parts count; high utilization of the semiconductors; and low current and voltage ripple at its terminals. The principle of operation, detailed description, analysis of the modulation strategy, and dimensioning equations for three different power circuit realizations are described in this paper assuming the analyzed modulation patterns. The feasibility of the presented converter is demonstrated by means of a constructed hardware prototype. [ABSTRACT FROM AUTHOR]

An efficient power converter system plays a significant role in the design of battery charging systems for electric vehicles (EVs). In this paper, a new zero-voltage and zero-current switching (ZVZCS) full-bridge dc–dc converter is proposed to reduce the power conversion losses. The proposed converter incorporates a new asymmetrical pulse width modulation (APWM) gating technique for the dc–dc conversion stage in the battery charging system. The proposed dc–dc converter topology achieves zero-voltage switching (ZVS) for all the active switches and near zero-current switching (ZCS) for low-side active switches throughout the charging range of the battery. The proposed APWM technique can reduce the switching and conduction losses compared to the conventional phase-shift modulation (PSM) gating technique. The auxiliary inductance required to ensure ZVS with APWM can also be reduced compared to PSM. Analysis, design, and implementation of the proposed APWM ZVZCS full-bridge dc-dc converter are discussed in this paper. A 100-kHz 1.2-kW laboratory prototype is developed and the experimental results are presented. The results validate the analysis and performance of the proposed converter. [ABSTRACT FROM AUTHOR]

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

In this paper, a family of new step-up series–parallel dual resonant switched-capacitor converters (SP-DRSCs) is proposed to extend the conversion ratio for high step-up applications. The converters feature a wide gain range, continuously adjustable, and enhanced light-load voltage regulation. All flying capacitors operate in resonance, eliminating high transient current spikes and charge sharing losses. Thus, zero-current-switching (ZCS) turn-on for all transistors and ZCS turn-off for all diodes are achieved. A comprehensive analysis of the operation principle, voltage-gain curves, stable regulation range, and voltage and current stress is given. An analytical method to quantify the passive component volume for the group of step-up dual resonance switched-capacitor converters is presented. Further design considerations to optimize the passive component volume of the proposed SP-DRSC and the effect of bulky bypass capacitors on the volume are discussed. [ABSTRACT FROM AUTHOR]

The power efficiency and weight of present point-of-load (POL) dc–dc converters for drone applications are often compromised because they suffer from large switching losses at continuous conduction mode for heavy loads and excessive hardware overheads at discontinuous conduction mode for light loads. This paper presents a boundary conduction mode (BCM) control scheme for POL converters embodying a single operation mode. This is achieved by means of a hysteresis voltage controller to turn on/off the output power stage when necessary. The proposed BCM control scheme achieves high power efficiency (≥91.2%) over a wide load range (5 mA–1 A) by means of fully soft switching. Specifically, a hysteretic current controller is proposed to realize ZCS, and an adaptive dead time controller is proposed to realize ZVS. Further, the proposed BCM control scheme requires a small output inductor (0.82 μH) by means of designing the customizable peak inductor current. To verify the proposed BCM control scheme, we realize a BCM-based POL converter that features an input voltage range of 5–16 V, output voltage range of 2.5–8 V, switching frequency of 1.5 MHz, peak power efficiency of 96.8%, and ≤35 mV output voltage undershoot/overshoot for 1-A load step. When being benchmarked against state-of-the-art counterparts, the proposed design features the lowest voltage undershoot/overshoot, the highest switching frequency, ∼5.7× smaller inductor, and ∼11% higher power efficiency at light loads. [ABSTRACT FROM AUTHOR]

This paper describes the design, robustness analysis, and implementation of a zero average dynamics sliding mode control (ZAD–SMC) for a multiphase step-down converter. The ZAD–SMC operates at fixed switching frequency and allows to implement an interleaving technique providing current-ripple cancellation at the converter output. Moreover, the proposed control structure, which is based on a master–slave strategy, includes an equalization technique guaranteeing current sharing among the phases and avoiding undesirable power unbalance. Additionally, a stability analysis considering unmatched losses in the converter phases shows that the design provides asymptotic stability for the overall load range. The controllers are implemented in an FPGA, and all the expected features, such as fast transient response, robustness, fixed switching frequency, interleaving, and current equalization are sustained by the experimental results obtained from using a 1.5-kW prototype. [ABSTRACT FROM AUTHOR]

This paper employs a single-phase-shift modulated dual-active-bridge converter (DABC), and establishes a small-signal model, which involves its voltage transformation ratio. Then, through a voltage transformation ratio feedback loop, which is feedforward compensated by the port voltages and currents, closed-loop control of the transformation ratio of the DABC is realized. The proposed controller can make the DABC operate in constant transformation ratio mode, and act as an ideal dc transformer in an active dc distribution network. Based on the bidirectional voltage support capability of the proposed dc transformer, the different buses of an active dc distribution network can mutually provide voltage support for each other. Besides, the proposed dc transformer can realize the normalized decentralized power coordination between the energy storage systems at different buses of the active dc distribution network. The feasibility of the proposed dc transformer is verified by several hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

This paper proposes the design of gray wolf optimizer (GWO) algorithm-based fractional order proportional integral (FOPI) controller for power factor correction (PFC) using interleaved dc–dc single ended primary inductance converter converter with improved performance characteristics such as speed, accuracy, and stability. The detailed analysis and modeling of the proposed converter are presented. The optimal parameters of FOPI controller are obtained using GWO algorithm to improve the speed of response of the system. FOPI controller provides better performance in terms of robustness and stability since it has one more adjustable parameter than the conventional proportional integral (PI) controller. The cascade control strategy is implemented for the proposed converter with GWO-based FOPI controller as inner current and outer voltage controllers for PFC and load voltage regulation. The performance characteristics of the proposed system are analyzed and compared with conventional and other optimization techniques using MATLAB/Simulink software. A prototype of the proposed converter controlled by TMS320C2000 microcontroller for an output power of 200 W is tested and validated with the simulation results. The proposed system is used for powering devices like robots in critical applications such as military, space craft, etc., where stability, speed, and accuracy are major concerns. [ABSTRACT FROM AUTHOR]

A novel nine-level inverter topology for low-voltage applications is proposed in this paper. Each phase of the inverter is composed of a T-type three‐level cell and an active neutral point clamp three‐level cell. The operation principles and current conduction paths are analyzed in detail and phase-disposition sinusoidal pulsewidth modulation is used to balance voltages of flying capacitors and neutral point. The mathematical relationship between the capacitance and the desired ripple in the inverter output is established to select the intermediate capacitance value. Compared with other nine-level inverters suitable for low-voltage applications, the proposed inverter has advantages in a number of gate drivers, a number of dc sources, and efficiency. Simulation and experimental results under different settings of modulation index, power factor, output frequency, and load are presented to verify the effectiveness and performances of the proposed inverter. [ABSTRACT FROM AUTHOR]

As a combination of the switched-mode converter and linear amplifier, the switch-linear hybrid (SLH) envelope tracking (ET) power supply can achieve high efficiency and high tracking bandwidth simultaneously, and it can be classified into three types, namely, series-form, parallel-form, and series–parallel-form. In the SLH ET power supply, interaction may occur between the converters, and as a result, the controlled variable will deviate from its target. In this paper, the interaction in the series-form SLH ET power supply with different structures is analyzed first from the aspects of control and parasitic capacitances, and the feedforward control scheme and/or filter is adopted to eliminate the interaction. Then, for the parallel-form SLH ET power supply, four current control methods are introduced and compared from the current tracking and disturbance-rejection performances, and the method for suppressing the disturbance is presented. Since series–parallel-form SLH ET power supply contains at least three converters, the interaction is more complex. On the basis of the analysis of the series-form and parallel-form SLH ET power supplies, the interaction between the converters in series–parallel-form SLH ET power supply is analyzed and followed by the corresponding elimination method. Finally, one series-form, and one parallel-form SLH ET power supplies are implemented in the lab, and the experimental results verify the theoretical analysis. [ABSTRACT FROM AUTHOR]