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This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic. [ABSTRACT FROM AUTHOR]

The combination of high-frequency ac drive and capacitors offers an attractive passive current balancing solution for multistring light-emitting diodes (LED) lighting systems due to the advantages of compactness, high efficiency, and ease of modularity. Given that frequency-controlled resonant converters are commonly used as high-frequency ac drivers, the conventionally used switching frequency modulation could impair the effectiveness of capacitive balancing as the impedance of the balancing capacitors is a sensitive function of the switching frequency which is constantly varied for the purpose of output voltage regulation. In this paper, a constant-frequency capacitive impedance current balancing method is proposed. Compared to the conventional method, output voltage regulation of resonant converter is achieved by modulating the resonant frequency of resonant tank by switch-controlled capacitor (SCC) technique, which gives rise to constant balancing capacitor's impedance and constant LED current over a wide range of load conditions. Its implementation in an $LCC$ resonant network is studied in this paper and a systematic design procedure of a SCC-based constant-frequency $LCC$ resonant converter is presented. The effectiveness of the proposed method is experimentally verified by a 70-W experimental prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a transformerless bipolar multistring dc–dc converter based on series-connected submodules. It is intended for converting dc voltage and managing power flow for medium-voltage high-power dc networks. This new converter has a flexible structure of multistrings and each string consists of four valves with their middle points crossly connected through two cost-effect dc capacitors to form power balancing channels between valves. Its transformerless solution and single-stage configuration greatly reduce the converter volume, weight, cost, and power loss. In this paper, voltage ratio range and its influence on submodule design are analyzed. Moreover, a control strategy with focus on current sharing control and submodule capacitor voltage control is proposed. A simulation model rated at ±10 kV 2 MW verifies the feasibility of the proposed dc–dc converter. Experimental results obtained from a 100-V 1.5-kW laboratory setup also confirm the validation of the proposal. [ABSTRACT FROM PUBLISHER]

A family of bidirectional switched-capacitor (SC) converters with high-gain ratio of any positive integer is proposed in this paper for distributed energy resources applications. As compared with other existing SC converters achieving a same conversion gain, the main advantages of the proposed converters are that they require a relatively lower number of switches and capacitors, have a relatively lower switch's and capacitor's stress, and that their associated driver circuits are simpler to realize. Importantly, with the achievable conversion ratio being flexible and that the input and output of the proposed converters are of common ground, the proposed converters are widely suitable for many applications. Moreover, as the proposed converters do not possess magnetic component or any component that can severely degrade the converters’ performance at high temperature, they are especially useful for high-temperature applications. Besides, the proposed converters are capable of delivering bidirectional power, which is a key requirement for emerging applications with battery storages. Different aspects of the proposed converters, including a simple auxiliary power supply circuit for the MOSFETs’ drivers, will be discussed in this paper. A nine-time SC converter prototype that operates with 20-V input voltage, 100-W output, and at 75 kHz, is constructed and tested. Experiment results show that the maximum efficiency achievable with this prototype is over 98% (without driver's loss) and the efficiency over the entire load range between 25 and 100 W is over 95.5% including the driver's loss. The output voltage ripple of the SC converter is less than 1%. When the SC converter is open-loop controlled, the load voltage regulation is relatively well kept at less than 5% between full load and no load conditions. [ABSTRACT FROM PUBLISHER]

In this paper, the Z-source converter is introduced to power factor correction (PFC) applications. The concept is demonstrated through a wireless power transfer (WPT) system for electric vehicle battery charging, namely Z-source resonant converter (ZSRC). Due to the Z-source network (ZSN), the ZSRC inherently performs PFC and regulate the system output voltage simultaneously, without adding extra semiconductor devices and control circuitry to the conventional WPT system such as conventional PFC converters do. In other words, the ZSN can be categorized as a family of the single-stage PFC converters. In addition, the ZSN is suitable for high-power applications since it is immune to shoot-through states, which increases reliability and adds a boost feature to the system. The ZSRC-based WPT system operating principle is described and analyzed in this paper. Simulations and experimental results based on a 1-kW prototype with 20-cm air gap between the system primary and secondary sides are presented to validate the analysis and demonstrate the effectiveness of the ZSN in the PFC of the WPT system. [ABSTRACT FROM PUBLISHER]

This paper proposes a new control method of three-phase active power filters for reducing the dc capacitor voltage fluctuations in transient load change. The proposed control method introduces a new \boldsymbolk-step compensator, which maintains the mean active power flowing into the dc capacitor at zero every \boldsymbol1/(k-1) ac line period. Therefore, the compensator can suppress the transient voltage fluctuations across the dc capacitor even when a quick load change occurs. This paper theoretically reveals the relationship between the step number \boldsymbolk and the reduction effect of the dc voltage fluctuations. The experimental setup introducing the proposed seven-step compensator exhibits a good suppression effect of the dc voltage fluctuations and makes it possible to reduce the required capacitance value of the dc capacitor by a factor of seven. [ABSTRACT FROM AUTHOR]

In this paper, the application of an innovative transformer-less unified power flow controller (UPFC) for interconnecting two synchronous ac grids with large phase difference is presented. The proposed transformer-less UPFC is based on two cascaded multilevel inverters. As is well known, the real power flow between two generators is mainly determined by their phase difference. If two grids with large phase difference are initially separate from each other, once connected, there will be huge current flowing through the transmission line and will, thus, damage the generators or other supplementary equipments. Therefore, to connect two synchronous ac grids with each other without using an extra device is impossible. For decades, researchers have been investigating different approaches to this problem but still difficult to conquer, especially for real hardware implementation. An effective solution using the transformer-less UPFC is demonstrated in this paper. The transformer-less UPFC can realize grid interconnection, independent active and reactive power control, dc-link voltage balance control, etc. Furthermore, a 1-pu equipment can compensate system with phase difference as large as 30°. Experimental results based on the 13.8-kV/ 2-MVA transformer-less UPFC prototype are shown to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

A new boost-type multilevel inverter using switched capacitor structure is proposed. The main feature of the proposed inverter is boosting and multilevel output with small number of components. Due to the passive voltage balancing of each capacitor maintains a constant voltage without additional control. In this paper, the operation principle, the modulation method, the voltage/current stresses on switches and the determination of capacitances, the simulation results with MATLAB/Simulink R2015a, the experimental results, and the 2-kW simulation are shown. The simulation and the experiments were conducted under resistive load and inductive load conditions. In addition, the load variation was conducted in the experiment. Under both resistive load and inductive load conditions, the obtained waveforms by simulation and experiment agreed well with the theory. In the load variation experiment, the obtained waveforms were not distorted and the capacitor voltages maintained constant. [ABSTRACT FROM AUTHOR]

The widespread use of electronic devices increases the need for compact power factor corrected power supplies. This paper describes an isolated power factor corrected power supply that utilizes the leakage inductance of the isolation transformer to provide boost inductor functionality. The bulk capacitor is in the isolated part of the power supply allowing for controlled startup without dedicated surge limiting components. A control method based on switch timing and input/output voltage measurements is developed to jointly achieve voltage regulation and input power factor control. A prototype design is implemented with detailed measurements and waveforms shown to confirm the desired functionality. [ABSTRACT FROM AUTHOR]

This paper introduces a new configuration of bidirectional multilevel converter in electric vehicle (EV) applications. It has multilevel dc–dc converter with a dc link capacitor voltage balance feature. The multilevel dc–dc converter operates in a bidirectional manner, which is a fundamental requirement in EVs. Compared to the conventional configurations, the proposed one only implements two extra power switches and a capacitor to balance the voltage of the T-type multilevel inverter (MLI) capacitor over a complete drive cycle or at fault conditions. Therefore, no extra isolated sensor, control loops, and/or special switching pattern are required. Moreover, the proposed configuration due to the high-frequency cycle-by-cycle voltage balance between ${C_N}$ and ${C_P}$ , the bulky electrolytic capacitors used in T-type MLI, are replaced with more reliable longer life film capacitors. This will result in a size and weight reduction of the converter by 20%. This allows more real estate for the EV battery in the chassis’ space envelope to increase its capacity. The proposed configuration is tested and validated using a matlab/Simulink simulation model. A laboratory prototype of 1 kW is built to provide the proof of concept results as well. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear controller is presented for regulating an emerging class of high power density, high power-conversion efficiency, and high reliability (H3) single-phase power converters featuring small buffering capacitors. The proposed controller combines the best features of input–output feedback linearization and an automatic-power-decoupling (APD) control strategy, and achieves enhanced dynamic performances as compared to existing solutions based on linear control techniques. By feedback linearization, the plant models of H3 single-phase converters are fully linearized and decoupled, and thus fast dynamics, large-signal asymptotic tracking, and global stability can be achieved with simple linear controllers. Additionally, the APD strategy further strengthens the robustness of the closed-loop system as active pulsating power buffering (of the instantaneous power difference between the ac-port and the dc-port of the converter) of basically any form can be achieved. With the proposed nonlinear controller, we are able to further exploit the potential and unlock several new features intrinsic in H3 single-phase converters, e.g., active voltage holdup function, allowing extended holdup time (comparable to existing products with large dc-link capacitors) with only a small energy storage. The general theory, design procedures, and practical considerations of the nonlinear controller are detailed. A 100-W hardware prototype is also built to demonstrate the advantages of the proposed solution. New opportunities of H3 single-phase power converters with the aid of the proposed nonlinear control are also suggested for future research. [ABSTRACT FROM AUTHOR]

This paper proposes a novel dynamic ramp valley control in a current-mode adaptive on-time controller for the on-chip buck converter. It improves the system stability and reduces the output voltage under the load-dump. The proposed novel dynamic ramp valley control uses a sample and hold circuit, a comparator, and a ramp valley control to avoid the generation of an erroneous pulse signal while regulating the output voltage under the load-dump. Finally, a buck converter with 12 to 19 V input voltage range and 1.05 V output voltage with the novel dynamic ramp valley control is implemented in an integrated circuit. Based on the hardware experimental results, the output voltage under the load-dump with and without the proposed dynamic ramp valley control is 156 and 224 mV, respectively. Thus, the output voltage with the proposed dynamic ramp valley control is lower by 68 mV than that without the proposed dynamic ramp valley control, avoiding the potential damage of the output load, moreover, this performance has been verified with the SIMPLIS simulation and hardware experimental results. [ABSTRACT FROM AUTHOR]

A decentralized control method for power module (PM) capacitor voltage and switching frequency balancing in modular multilevel converter is presented in this paper. The proposed method is composed of a central controller, six arm controllers, and several group controllers. The group controller is only in charge of the PM capacitor voltage balancing within a corresponding group, and the arm controller is in charge of the PM capacitor voltage balancing and PM switching frequency balancing among groups within an arm. A control method based on a PI controller using the average PM capacitor voltage of each group to keep voltage balancing among groups is proposed. A dynamically adjusted extra exchange number strategy based on the voltage difference of each group is also developed to balance the PM switching frequency among groups. The key advantages of the proposed method are the reduction in the number of the PM capacitor voltages that need to be transmitted and sorted in each group controller as well as the reduction of the communication burden between the group and arm controllers. The proposed method is also highly effective under PM faults. The voltage ripple factor and the PM switching frequency of the proposed method are almost identical to the conventional centralized methods. The RT-LAB-based real-time control hardware in the loop test results of a ±350 kV/1000 MW MMC system verify the correctness and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Modular multilevel converters are increasingly being considered or used for various medium voltage applications. Multiple control methods have been proposed for the control of the direct to three-phase modular multilevel converter. They differ one from another in the way the capacitor voltage ripples are handled, i.e., either neglected, estimated, reconstructed by filtering or measured. This has implications on the performance level that can be obtained. This paper provides insights on the advantages and drawbacks of each control method, in inverter and rectifier mode, with a fair and thorough assessment supported by extensive simulations, with converter ratings that are realistic for medium voltage applications. Finally, this works highlights the impact of the higher dynamics for medium voltage direct current (dc) applications compared to high voltage dc ones on the choice of the control method. [ABSTRACT FROM AUTHOR]

This paper presents an active state-of-charge (SOC) balancing control strategy for modular super capacitor energy storage system (ESS). The strategy has a master–slave structure, including a common dc bus voltage loop and individual slave current loop for each submodule. The common voltage loop ensures the ability of the system to stabilize dc bus voltage cannot be affected by SOC balancing control, and provides a same original current reference for all submodules. SOC information is introduced into current loops to achieve SOC balancing control. The highest SOC is taken as a reference for low SOC modules, thus, the low SOC modules can regulate the submodule average operation current according to the SOC reference and their own SOC. In order to minimize system current deviation caused by the introduction of SOC, a current correction method is proposed to improve system current regulate performance. The proposed strategy can achieve SOC balancing control during ESS charging and discharging process dynamically, in addition, the modularity of the system is improved and the proposed strategy has favorable stability. A modular ESS prototype consisting of three half-bridge submodules is tested in the laboratory, and the experimental results verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a fully integrated energy harvesting (EH) system that even includes an input capacitor and a simplified ripple correlation control (RCC) maximum power point tracking (MPPT) method for low-power system-on-a-chip applications. The proposed system implements the RCC block with a charge pump (CP) that can be integrated into the chip, instead of the inductive switching converter that is commonly used for conventional RCC methods. The CP changes the input impedance by changing the size of the flying capacitor to ensure system reliability. The simplified RCC method is implemented using a low-power analog divider operated in a subthreshold region. A test chip fabricated in a 180 nm CMOS process achieves over 95% MPPT accuracy with a very small input capacitor of 5 nF and a low quiescent current of 2.6 μA. The chip size of the entire system is 8 mm2, and the harvested power range is from 6 μW to 1.4 mW. [ABSTRACT FROM AUTHOR]

High-voltage and high-power dc–dc conversion is key to dc transmission, distribution, and generation, which requires compact and efficient dc transformers with large step ratios. This paper introduces a dc–dc converter with the input-series–output-parallel arrangement of multiple high step ratio subconverter units. Each subconverter unit is an isolated modular dc–dc converter with a stack of half-bridge cells chopping the dc down to low voltage level. The transformer provides galvanic isolation and additional step ratio. The converter achieves a large step ratio due to the combination of the series-parallel configuration, the modular cells, and the isolation transformer. The proposed dc–dc converter is analyzed in a 30 kV–1 kV, 1-MW application to discuss the operation performance, tradeoffs, power efficiency, and selection of components. Finally, the converter is validated through a laboratory downscaled prototype. [ABSTRACT FROM AUTHOR]

This paper presents a modular multilevel series/parallel converter (MMSPC) with intermodule switched-inductor power transfer. The switched-inductor voltage conversion feature allows controllable and efficient transfer of energy between modules with nonnegligible voltage difference, providing both step-down and step-up functionalities. Thus, this converter can accurately control and rapidly adjust the voltage of each module to generate an ac output voltage waveform with a controllable number of levels, increasing the quality of the output. Moreover, the intrinsic dc–dc conversion feature can generate a dc controllable output voltage and enable new applications. In this text, we specifically demonstrate how the flexibility of obtaining both ac and dc output with the same setup renders the topology promising for battery energy storage systems and dc microgrid applications. Experimental results validate the topology and concept of an MMSPC with intrinsic switched-inductor conversion. [ABSTRACT FROM AUTHOR]

An LLC resonant converter would have light-load voltage regulation problems due to the effect of parasitic capacitances in a high-frequency range. In this paper, an energy feedback control method is proposed to improve the light-load regulation capacity by using synchronous rectifiers (SRs). The SR bridges are controlled ahead of the primary inverter bridges to deliver the energy from load to source, reducing the output voltage independent of the load. Then the desired voltage can be achieved even in no-load conditions by regulating the operation time of the energy feedback mode. The gain, voltage ripple, and efficiency performances of the proposed control method are discussed based on the precise analysis and an accurate model of the converter. Moreover, the light-load operations of the LLC resonant converter are analyzed deriving the critical load condition. Finally, the proposed control method is verified by the experiments of a 12 V/8 A LLC resonant converter prototype. [ABSTRACT FROM AUTHOR]

This paper presents new space vector pulsewidth modulation (PWM) strategies for a single-phase three-level buck-boost neutral point clamped inverter coupled with impedance-source (IS) network. These strategies can be implemented for systems with any IS network with neutral point. The case study system is based on the quasi-Z-source inverter with continuous input current. To demonstrate an improved performance, the strategies are compared with a traditional PWM strategy. The advantages lie in reduced switching number, without output voltage quality distortion. The simulation and experimental results confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

This paper presents a drive system based on a modular multilevel converter (MMC) with high-frequency magnetic channels between adjacent-arm submodules (SMs), suitable for medium-voltage, high-power three-phase variable-speed machines. The configuration employs chains of dual half-bridge (DHB) modules linking adjacent SMs of three-phase symmetrical arms. The DHB modules are operating as power channels enabling energy exchange to restore the power imbalance among the SM capacitors. This allows arms’ ripple-powers to be entirely decoupled through bidirectional power transfer between adjacent-arm SMs, resulting in a near ripple-free SM capacitor voltage profile. Therefore, the MMC common problem of wide voltage fluctuation across SM capacitors is comprehensively solved, independent of the operating frequency. Additionally, a significant reduction in the sizing requirement of SM capacitance is achieved. The configuration is able to drive multimegawatt machines from standstill to the rated speed at the rated torque operating condition. The operating principle of the proposed MMC configuration is explained and necessary mathematical analysis is derived. Features and viability of the proposed drive system are verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

This paper proposes an indirect input-series output-parallel (I2SOP) dc–dc full-bridge converter system based on asymmetric pulsewidth modulation (APWM) control strategy for high input voltage applications. When a short-circuit fault occurs in a high input voltage dc bus, the proposed I2SOP system can disconnect from the dc bus effectively and avoid the input filter capacitors of constituent modules discharge compared with the traditional ISOP system, facilitating fault handling and protecting the input filter capacitors. Moreover, with the proposed I2SOP structure, it is easy to achieve redundancy design when one or a few constituent modules fail. The APWM control strategy is introduced to the I2SOP system rather than the classical phase-shifted control strategy for the basic full-bridge module to reduce the voltage stress of power switch and the filter requirement. The characteristics of input voltage sharing and output current sharing of the I2SOP system are also analyzed. A three-module I2SOP system prototype was built, and the experimental results verify the correctness and effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of half-bridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N + 1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus, the converter performance is improved notably. Besides, with the redundant FBSMs, the converter can continue its operation even if a fault occurs in one of HBSM switches. All the control procedure is accomplished using model predictive control strategy and performance of the proposed converter is verified by several simulation and experimental studies. The obtained results confirm the feasibility of the proposed scheme in reducing the converter loss, improving its performance and fault-tolerant operation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control strategy for three-level neutral-point-clamped (NPC) power converter. The proposed control scheme consists of three control loops, i.e., instantaneous power tracking control loop, voltage regulation loop, and voltage balancing loop. First, in the power tracking control loop, a set of adaptive sliding mode controllers are established to drive the active and reactive power tracking to their desired values via radial basis function neural network technology. In the voltage regulation loop, an efficient but simple adaptive controller is designed to regulate dc-link output voltage where the load is considered as an external disturbance. Moreover, a composite controller is developed in the voltage balancing loop to ensure imbalance voltages between two dc-link capacitors close to zero, in which a reduced-order observer is used to estimate sinusoidal disturbance improving the converter performance. The effectiveness and superiority of the proposed control strategy for the NPC power converter are compared with other control schemes through experimental results. [ABSTRACT FROM AUTHOR]

A fast modularized multiwinding transformer balancing topology (MMTBT) for series-connected supercapacitors is proposed in this paper. With the proposed MMTBT, the voltage balancing inside modules and between modules are completely decoupled and the degree of modularization is high. This is different from the existing MMTBT, with the existing MMTBT, different modules share the same PWM drive. While with the proposed MMTBT, different modules can be driven by different PWM, then the variable frequency control strategy can be used to realize a fast balancing speed. With the proposed variable frequency control strategy, the average balancing current will be large and the balancing speed inside modules will be fast. With the proposed MMTBT, the balancing between modules is realized by discharging the higher voltage modules. The MMTBT of the higher voltage modules will act as a fly-back converter and the excitation current is in continuous current mode (CCM) to realize a great discharging power. First, the extra energy from the higher voltage module is transferred to the filter capacitor of the half-bridge converter. Then, the outputs of the half-bridge converters are connected in series to form a multilevel converter to act as the input of a boost converter. At last, the energy is transferred back to the supercapacitor energy storage system by the boost converter. The higher voltage module will be discharged with a great discharging power, then the balancing speed between modules will be fast. The fast balancing speed is realized inside modules and between modules, then the balancing speed of the whole system will be fast. The variable frequency control strategy and the control strategy of boost converter are analyzed in detail and the fast balancing speed of the proposed balancing topology is proved by experimental results. [ABSTRACT FROM AUTHOR]

Single-phase universal-input ac–dc converters are needed in a wide range of applications. This paper presents a novel power factor correction (PFC) architecture that can achieve high-power density and high efficiency for grid-interface power electronics. The multitrack PFC architecture reduces the internal device voltage stress of the power converter subsystems, allowing PFC circuits to maintain zero-voltage-switching at high frequency (1 MHz–4 MHz) across universal input voltage range (85  $\rm V_{\text{ac}}$ –265  $\rm V_{\text{ac}}$). The high performance of the power converter is enabled by delivering power in multiple stacked voltage domains and reconfiguring the power processing paths depending on the input voltage. This multitrack concept can be used together with many other design techniques for PFC systems to create mutual advantages in many function blocks. A prototype 150 W, universal ac input, 12  $\rm V_{\text{dc}}$ output, isolated multitrack PFC system with a power density of 50 W/in $^3$ , and a peak end-to-end efficiency of 92% has been built and tested to verify the effectiveness of the multitrack PFC architecture. [ABSTRACT FROM AUTHOR]

A 1-φ hybrid nine-level inverter (H9LI) topology has been proposed in this paper. The proposed H9LI topology uses a simple phase disposition pulsewidth modulation strategy to generate nine-voltage levels in the output. The main advantage of this topology is that it has a low switch count (ten switches) compared to the existing nine-level inverter topologies. To regulate the voltage across auxiliary capacitor, two innovative control techniques are proposed, which are integrated with the inverter modulation technique itself. Hence, it does not require any extra voltage balancing circuits to maintain the voltage across the auxiliary capacitor and input dc capacitors. A major advantage of these control techniques is that they eliminate the sensing of the coupled inductor current. Another significant advantage of H9LI is that loss distribution among all the power switches is more uniform compared to existing nine-level inverters. Due to low part count and absence of extra voltage balancing circuits, the H9LI achieves higher efficiency (η ≍ 94.5%) and lower cost. Furthermore, the requirement of filter size reduces due to the presence of coupled inductor in H9LI. The proposed 1-φ grid connected H9LI is verified through MATLAB/Simulink simulations and validated through experiments on a laboratory prototype of 400-VA rating. [ABSTRACT FROM AUTHOR]

This paper presents a five-level flying capacitor multilevel (FCML) converter with an integrated auxiliary power converter to supply power to the controller and gate drive circuitry. The auxiliary power converter is sourced from within the FCML converter at a naturally occurring low-voltage node, reducing the voltage rating requirements by 75% and thus the size of the auxiliary converter. The auxiliary load current drawn from the FCML converter induces an imbalance in the flying capacitors, which is detrimental to the capacitor and switch ratings if left unchecked. To compensate for this imbalance, an active-balancing method is proposed that adjusts the phase and duty cycle of the traditional phase-shifted pulsewidth modulated control signals. The active balancing requires only a single capacitor voltage measurement and proportional control with no additional hardware components. A start-up circuit is proposed to power the auxiliary power supply and soft-start the FCML converter. Experimental results have been demonstrated with an experimental prototype resulting in an excellent flying capacitor balancing and FCML start-up. [ABSTRACT FROM AUTHOR]

In this paper, capacitor current sensorless control by using an observer is applied in a seamless transfer single-phase inverter. The proposed control system is a multiloop control system. The control loop is composed of a capacitor voltage outer control loop and capacitor current inner control loop for stand-alone mode. For on-grid mode, the grid current outer loop controller is combined with the stand-alone control structure to form a simple controller structure for mode switching. The capacitor current feedback signal is calculated using the observer in the discrete-time domain and thus sensors are not required. Use of the proposed observer for the inverter with capacitor current control has many advantages, such as sensorless capacitor current calculation, one-sample-ahead data prediction for sampling delay compensation, and an average capacitor current without ripple components. Verification of the theoretical analysis is presented through simulation and experiment. A 5-kW single-phase inverter prototype combined with a Li-ion battery is set up with a digital controller using a TI TMS320F28377D microcontroller unit to confirm the feasibility of the system. [ABSTRACT FROM AUTHOR]

This paper describes a control algorithm based on modified enhanced phase-locked loop (MEPLL) in dynamic voltage restorer (DVR). It compensates distortions and unbalances in the supply voltage along with voltage sag/swell. Three-phase MEPLL extracts the fundamental positive-, negative-, and zero-sequence components from the distorted/unbalanced signals. Further fundamental positive-sequence components are used in the reference load voltage calculations. In addition to track the angle of the input signals similar to the conventional PLLs, the proposed algorithm (MEPLL) offers features of getting fundamental and sequential components in case of distorted or unbalanced grid voltage for all the three phases simultaneously. Optimization approach named as autonomous groups particle swarm optimization, a variant of PSO is used for the calculation of PI-controller gains. The integrated time square error is used as a cost function for optimization of an error between the reference and actual values. This approach of tuning PI gains improves the performance by eliminating the manual process. The proposed control algorithm is implemented in DVR system using MATLAB software and validated in a laboratory environment. The performance shows that the proposed control algorithm gives time effective and satisfactory solution for the unpredictable issues mentioned. [ABSTRACT FROM AUTHOR]

In this paper, a simple controller configuration for the decentralized parallel operation of single-phase inverters in stand-alone ac supply systems is proposed. The configuration is designed considering the unavailability of the filter capacitor voltage and grid current information to the controller. Due to the unavailability of voltage information, internally estimated voltage references and the measured value of the converter-side inductor current are used for the calculation of the active and reactive power. Frequency and voltage droop characteristics are used, and hence, communication is not required. The operation of the inverter at the reference voltage magnitude and frequency is achieved by the direct control of the modulating wave. Therefore, inability to implement closed loops caused by the absence of certain voltage and current information is mitigated. The proposed controller has the provision for protection of switching devices during overcurrent situation. The accuracy and feasibility of the proposed controller are validated using the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Transformerless photovoltaic (PV) grid-connected inverters have become more and more popular in distributed PV power generation systems due to the advantages on high efficiency, low cost, and small size. However, common-mode (CM) current in the transformerless PV inverters can result in serious electromagnetic interference and insecurity, which will further reduce the reliability of the PV inverter systems. In this paper, an improved H5 topology, namely H5-D topology, is proposed, in which a clamping diode is added on the basis of H5 topology to eliminate the CM voltage fluctuation in H5 topology. Further, the PSIM simulation results of the H5-D topology and H5 topology are given and compared, especially, the performance of H5-D topology for CM current suppression is presented and analyzed concretely. Finally, the experimental prototypes of the H5-D topology and H5 topology are built and tested, and the experimental results validate the advantages of the H5-D topology. The proposed H5-D topology provides a new practical topology for distributed PV grid-connected power generation systems. [ABSTRACT FROM AUTHOR]

Balanced issues of neutral-point (NP) voltage in the neutral-point-clamped (NPC) three-level photovoltaic converter have been studied in depth. Numerous algorithms for NP voltage control have been proposed and proven to be effective in normal operations. However, most of the previous studies fail to consider the effect of imbalanced loads on NP voltage, especially under low-voltage-ride-through (LVRT) condition, which faces problems of imbalanced grid voltages and low power factor. In this paper, through derivation of NP current model for different loading conditions, the behavior of NP voltage under LVRT condition is comprehensively analyzed for the first time. Then, theoretical limitations of NP voltage control based on two common space-vector-pulsewidth modulations (SVPWMs) that three-nearest-vectors and symmetric SVPWM are investigated, and additional low-frequency oscillation in NP voltage is analyzed. This oscillation is dominated by fundamental frequency and has different generation mechanisms under different imbalanced grid faults. Then, a novel method of selective hybrid SVPWM, as selective combinations of SVPWM and virtual SVPWM according to different imbalanced grid faults, is proposed to effectively suppress NP voltage oscillations in LVRT operation without any complex improvements and increase of dc-link capacitor values. Finally, the analytical result and performance of the proposed method are confirmed in an existing 300 kW NPC converter. [ABSTRACT FROM AUTHOR]

This paper presents a compact and fully integrated switched-capacitor voltage doubler for voltage boosting in photovoltaic-powered implantable devices. Gate-voltage boosting, nonoverlapping, and interleaving techniques are adopted to enhance the driving capability of the voltage doubler at low supply voltage with high efficiency. A dual-mode three-dimensional (3-D) digital control circuit is proposed to regulate the output voltage under the load current variation. The 3-D control on the number of active converter cells, operation frequency, and on-resistance enable fine output voltage regulation over a wide load current range without extensive device segmentation, thereby reducing the routing complexity and the associated parasitic losses. Other advantages are that the switching loss can be proportionally scaled with the load current for high power efficiency and the periodic charge transfer to the output can keep small for small voltage ripple. Pulse-skipping modulation is employed to allow the converter to operate under ultra-light load. The proposed voltage doubler is designed and implemented using 0.18 μm-CMOS process. The measurement results demonstrate that the proposed converter can generate a voltage of 0.9 V from an input of 0.6 V, with a power efficiency of more than 60% within the output current range of 30–440 μA. The peak efficiency is 73% and the active area is 0.33 mm2. These measurement results suggest that the proposed voltage doubler is suitable for voltage boosting at low voltage under the limited availability of power and area. [ABSTRACT FROM AUTHOR]

This paper explores the large-signal and small-signal dynamics of a series-capacitor (SC) buck-type converter and introduces an optimal closed-loop control scheme to accommodate both the steady-state and transient modes. As opposed to a conventional buck converter, where time-optimal control is realized by a single on–off cycle, in the SC-buck topology, there is a need to distribute the switching phases to satisfy the charge balance of the SC. The new control method merges a voltage-mode controller for the steady-state operation and a nonlinear, state-plane based transient-mode controller for load transients. A detailed principle of the operation of the SC-buck converter is provided and explained through an average-behavioral model and state-plane analysis. The operation of the controller is experimentally verified on a 20 W 12 V-to-1 V converter, demonstrating voltage-mode control operation as well as minimum-deviation and time-optimal responses for load transients. [ABSTRACT FROM AUTHOR]

Voltages of series-connected batteries gradually become imbalanced due to nonuniformity in terms of not only battery characteristics but also self-discharge rate that is significantly dependent on temperature. In large-scale energy storage systems, a large temperature gradient is very likely because of its huge geometry, and therefore, equalizers capable of relatively large equalization currents would be necessary to eliminate voltage imbalance originating from uneven temperature distribution. A two-switch string-to-battery voltage equalizer using a half-bridge converter with multistacked current doublers (MSCDs) is proposed for series-connected batteries in this paper. The proposed equalizer is capable of providing relatively large equalization currents without increasing ripple currents thanks to the interleaved operation of the MSCDs. Fundamental operational analysis for a discontinuous conduction mode, in which currents in the equalizer can be limited to desired levels without feedback control, is performed. The experimental results of equalization tests performed for four supercapacitor modules and lithium-ion batteries connected in series demonstrated the equalization performance of the proposed equalizer. [ABSTRACT FROM AUTHOR]

In this paper, analysis and design of a three-phase-isolated Cuk-based power factor correction (PFC) converter have been proposed. The proposed converter is operated in discontinuous output inductor current mode to achieve PFC at ac input. This avoids the inner current control loop which further eliminates the sensing of current. This makes the system more reliable and robust. The converter requires only one simple voltage control loop for output voltage regulation, and all the power switches are driven by the same gate signal which simplifies the gate driver circuit. The detailed operation of the converter and design calculations are presented. And also a small-signal model of the converter by using current injected equivalent circuit approach is presented to aid the controller design. The experimental results from a 2-kW laboratory prototype with 208-V line-to-line input voltage, 400-V output voltage are presented to confirm the operation of the proposed converter. An input power factor of 0.999, an input current total harmonic distortion of as low as 4.06%, and a high conversion efficiency of 95.1% are achieved from laboratory prototype. [ABSTRACT FROM AUTHOR]

The stability and small-signal analyses of the dual series-resonant dc–dc converter are investigated in this paper. The small-signal model of the converter is derived from the extended describing function analysis. Frequency-domain analysis is then employed to derive the small-signal transfer functions of the converter. This procedure establishes an insightful understanding about the effects of the converter parameters and operating conditions on the stability and transient behavior of the converter. The results are used to illustrate the development of the single-loop, voltage-feedback control scheme for the dual series-resonant dc–dc converter. It is demonstrated that the proposed control method enables the converter to regulate its output voltage in the case of abrupt changes in input voltage and output load, and it provides improvement in the transient response. An experimental prototype of the dual series-resonant dc–dc converter is built and the performance of the control scheme is experimentally evaluated by applying abrupt changes in the operating condition of the converter. Based on the experimental results, it is shown that the single-loop, voltage-feedback control scheme is effective in regulating the output voltage of the converter. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems containing a rechargeable battery as an energy buffer require multiple dc–dc converters for PV panel control and battery regulation, and hence, they are prone to be complex and costly. To simplify the system by reducing the number of converters, this paper proposes the nonisolated switched capacitor converter (SCC)-based multiport converter (SC-MPC) for standalone PV systems. The proposed SC-MPC can be derived by integrating a bidirectional pulsewidth modulation (PWM) converter, series-resonant converter (SRC), and an SCC with sharing switches. PWM and pulse frequency modulation (PFM) controls are employed for the PWM converter and SRC, respectively, to regulate either a battery voltage, output voltage, or input power from a PV panel, depending on power balance among the input, battery, and load. The 150-W prototype was built for an experimental verification, and the results demonstrated the output voltage could be regulated independently on the battery voltage or input port of PV panels. [ABSTRACT FROM AUTHOR]

In this paper, a novel space-vector pulsewidth modulation technique for a five-level active neutral-point clamped (5L-ANPC) inverter is proposed to eliminate the common-mode voltage (CMV). For the 5L-ANPC inverter, which produces a good output voltage performance and lowdv/dt, the total 125 voltage vectors can be generated, among which the proposed scheme employs only 19 voltage vectors producing a zero CMV. Due to the limitation of voltage vectors selected, the dc-link capacitor voltages of the 5L-ANPC inverter cannot be balanced by themselves. Therefore, the capacitor voltages of the inverter should be controlled by choosing the redundant switching states appropriately. The validity of the proposed modulation scheme has been verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

High step-down voltage conversion is necessary to bridge the voltage gap between main power converters and low-voltage auxiliary electronics in power conversion systems. Switched capacitor converters (SCCs) are an attractive candidate as a high step-down converter, but their poor voltage regulation capability may limit their applications. Pulsewidth modulation (PWM) SCCs with adjustable high step-down voltage conversion are proposed in this paper. The proposed PWM SCCs can be derived from traditional SCCs by replacing an energy transfer capacitor with a switched-capacitor-inductor (SCL) cell that comprises inductors, capacitors, and diodes to realize PWM-controllable voltage conversion. The voltage step-down ratio of the proposed PWM SCCs is not only PWM controllable but also adjustable with structures of SCCs and SCL cells. Two representative PWM SCCs were taken as examples to perform the operational analysis. The prototypes of both representative PWM SCCs were built and tested to demonstrate the proposed concept. [ABSTRACT FROM AUTHOR]

A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at the instant of a mode change as well as during clearing time while quickly detecting unintentional islanding. The indirect current control has been proposed to provide not only a stable voltage to critical loads during clearing time but also a seamless transfer of inverters at the instant of a mode change. However, the conventional islanding detection methods cannot be applied to the indirect current control based inverter since the magnitude and frequency of voltage do not vary when an islanding occurs. This paper proposes a reactive power P&O anti-islanding method for the indirect current control. The proposed islanding detection method generates a small reactive power perturbation at the output of the inverter and detects the islanding by observing reactive power mismatch during the islanding. Using the proposed method, the inverter can supply high quality power to critical loads without distorting the output current during the clearing time. The proposed anti-islanding method is validated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper details the design and implementation of an efficient 4-kW bidirectional converter with a wide load range, based on a three-phase LCC resonant converter operated in a continuous conduction model, which has a number of advantages pertaining to a bidirectional power supply. The voltage boost-up function yields a high voltage gain without increasing the transformer turn ratio. The high switching frequency, which is achievable by using the soft-switching condition and multiphase operation, decreases the output ripple and helps minimize the size of the output filter, as the requirement for a filter changes after the power flow. Moreover, this reduction in the size of the filters yields economic advantages. In addition, because of the synchronous rectifier operation employed during switching, the conduction loss in the rectifier diode of the proposed converter is low. The direction of the output power can be changed easily, using phase control. The implemented power converter is connected to a 320-V rated generator on one side and 28-V lead-acid batteries on the other side. The functionality of the proposed converter is verified in experiments. We confirmed the high performance of the developed converter in terms of efficiency (92.2%), operable load range (0–12.5 A in step-up, and 0–142 A in step-down), and voltage ripple (0.05%). [ABSTRACT FROM AUTHOR]

In this paper, a family of step-up resonant switched-capacitor converters (RSCs) with a continuously adjustable conversion ratio is proposed based on the Cuk dual-resonance core (DRC) featuring two resonant paths. By adopting the on-time fixed frequency modulation, the two resonant paths can conduct simultaneously and satisfy the charge balance of the flying capacitor during the overlapping period. As a result, the conversion ratio—upper bounded by two determined by the circuit configuration—can vary continuously and efficiently even at the light load condition (1/10 of the rated power). A comprehensive analysis—the operation principle, voltage-gain curve, and voltage/current stresses—about the DRC is given. In addition, the Cuk DRC was extended to the series–parallel switched-capacitor converter (SCC), Fibonacci SCC, and voltage doubler to form a family of step-up RSCs, whose voltage-gain curves of different topologies are derived. Moreover, a characteristic comparison between the Cuk DRC and the traditional “direct” and “indirect” resonant core is given. Then, a 48 to 62–94.6 V resonant core with peak efficiency 97.8% and maximum power 120 W under the open loop condition was built. The analyses were verified by both experimental and simulation results. [ABSTRACT FROM AUTHOR]

The five-level nested neutral-point-clamped (5L-NNPC) converter is one of the most promising topologies for medium-voltage (2.3–7.2 kV) high-power applications such as medium-voltage drives, wind energy conversion systems, and grid-connected systems. The 5L-NNPC requires a fewer number of switching devices, freewheeling and clamping diodes, and flying capacitors compared to the existing five-level multilevel converters. In the 5L-NNPC topology, each flying capacitor voltage is regulated at one-fourth of the dc-bus voltage to obtain the five-level operation. Due to the lack of redundant switching states, it is difficult to control the flying capacitor voltages by using the pulse-width-modulation-based classical control methods. This paper proposes a model-predictive current control (MPCC) approach to control the flying capacitor voltages along with the output currents of the 5L-NNPC converter. The discrete-time model of 5L-NNPC is developed to implement the MPCC scheme. The simulation and experimental studies are conducted to verify the dynamic and steady-state performance of 5L-NNPC with the MPCC scheme. The performance of the proposed MPCC approach is compared with the conventional space-vector-modulation-based voltage-balancing approach. Furthermore, the flying capacitor voltage control capability of MPCC is verified at different load power factors. [ABSTRACT FROM AUTHOR]

This paper proposes a control method for a five-level hybrid flying-capacitor (5L-HFC) inverter, of which structure stems from the conventional five-level active neutral-point-clamped (5L-ANPC) topology by dividing the dc-link stage into three series-connected capacitors. In this inverter, the voltage stress on the power switches connected to the dc link is reduced by a half compared with that of the 5L-ANPC topology, thus the lower number of equally voltage-rated power devices can be employed. Also, the power losses in the 5L-HFC inverter are more evenly distributed than in the 5L-ANPC. In order to balance the dc-link capacitor voltages, a third-order harmonic offset injection is applied. When a diode rectifier is used to supply the dc bus voltage, the balancing method is not effective if the modulation index is higher than 0.64. Thus, an auxiliary circuit is needed to support the balancing of the dc-link capacitor voltages. However, the unbalancing problem can be overcome in a full-range operation without the auxiliary circuit if the back-to-back configuration is utilized. Finally, simulation and experiment results have verified the performance of the 5L-HFC inverter with the proposed control method. [ABSTRACT FROM AUTHOR]

Small dc-link drive systems, built with film capacitors in the dc-link, present a new trend in many industrial applications and are obtaining increasing interests. It has the advantages of longer lifetime and the possibility to achieve a more compact design of the capacitor bank, especially at medium and high power rates. However, it could exhibit instability problems, mainly in the form of oscillations. The unexpected oscillation may result in overvoltage and shorten the lifetime of the power devices and the dc-link capacitors; increase the total harmonic distortion and also the partially weighted harmonic distortion of the grid supply current. Therefore, active damping methods are usually needed in order to stabilize such drive systems. This paper first analyzes the system characteristics and the principles of existing active damping methods. Then, a new voltage modulation based method named as “virtual positive impedance” method is introduced to guarantee the dc-link stability. This new approach is simple to apply and its implementation does not require the knowledge of system parameters and machine operating conditions. The proposed method is analyzed in details and verified by experiments. [ABSTRACT FROM AUTHOR]

The existing power decoupling control method of modular multilevel converter (MMC) was developed from that of conventional two-level voltage source converters. Therefore, it cannot fully realize power decoupling due to neglecting the coupling effects from submodule capacitor voltage, dc current, circulating current as well as control strategies of circulating current, which inevitably results in inaccurate regulation of active and reactive power, deteriorated system dynamic performance, possible overload operation and eventually threatens the safety and stability of MMC. This paper analyzes the intercoupling among all electrical quantities and corresponding control strategies in MMC. An accurate control model of active and reactive power/current with four coupling paths and influence factors in the rotating frame is also established. A full power decoupling control method has been proposed based on the developed model. The proposed control method can realize accurate and completely decoupled active and reactive power regulation, avoid overload operation, and significantly improve the dynamic performance of MMC. Moreover, it facilitates the parameters selection of MMC controller with no extra cost, which is of great significance for practical projects. The effectiveness and accuracy of the proposed analysis and control methods were verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Fault detection and isolation (FDI) is currently considered a crucial way to increase the reliability of modular multilevel converters (MMCs), which consist of a large number of power electronics submodules (SMs). This paper proposes a fast FDI approach to identifying single open-circuit faults of insulated-gate bipolar transistors in SMs for MMCs with model-predictive control (MPC). The fault detection approach is simply implemented by checking the voltage errors between the measured arm voltages and the estimated ones in the former control cycle. The fault isolation is achieved by checking the switching state directly. The proposed FDI scheme is straightforward, and no additional transducer or measurement is required. Compared with the phase-shifted pulse-width-modulation-based scheme, the MPC has a known and unchanged switching state in a sampling period, which can be utilized for fast location of open-circuit faults. Experimental results show that an open-circuit fault in the MMC can be accurately detected and located in several sampling periods. [ABSTRACT FROM AUTHOR]

This paper demonstrates a two-stage implementation of a step-down power factor preregulator design that achieves a high efficiency across the entire universal input voltage range ($\text{85}\text{--}\text{265}\,\textrm {V}_{\textrm {rms}}$) for an offline power supply application. In this implementation, a resonant LLC converter supplies power to a boost converter operating in a continuous conduction mode. A variable frequency multiplier technique is used in a resonant LLC converter stage to provide different dc gains and compress the effective input voltage range. The efficiency performance achieved is flatter and higher than other conventional offline power converter design consisting of a boost power factor correction circuit followed by a resonant LLC converter, whose efficiency tends to drop significantly at low-line input voltages. The proposed circuit allows MOSFETs with lower voltage ratings and better conduction/switching characteristics to be used in both converter stages. Both of the LLC stage and boost circuit can be better optimized due to the compressed operation range and better semiconductor switches. A scaling law of power losses versus breakdown voltage requirement for boost circuit under the condition of the same output power is presented. Experimental results demonstrated a flatter high efficiency performance across a wide input range. [ABSTRACT FROM AUTHOR]