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A space vector modulation (SVM) technique of a dual-inverter system for an open-end winding motor drive is described in this paper, where one inverter has a battery power source and the other has an only capacitor across the dc bus. The SVM must be achieved to operate the motor with field-oriented control and simultaneously to control the capacitor voltage at a constant value by using redundant switching states of the dual-inverter system. The control of the capacitor voltage is carried out by selecting a charging or a discharging mode in each redundant switching state, taking the instantaneous motor power factor into account. In addition, it is also required to reduce the error voltage pulses, which are generated in output multilevel voltage waveforms during the dead time. The compensation method of the existing dead-time scheme and the improved SVM sequence to reduce the error voltage vectors are proposed in this paper. The proposed methods are examined through several experimental tests and are confirmed to generate superior output voltage waveforms from the viewpoint of the measured total harmonic distortion and dv/dt. [ABSTRACT FROM AUTHOR]

In this paper, a single-inductor dual-output (SIDO) dc–dc converter is proposed. The significant feature of the proposed converter is feeding a constant power load in low-voltage side (LVS) port, where even feeding a variable load at LVS does not have any cross regulation to high-voltage side port with the desired approximation. Magnificently, both merits are obtained in open-loop manner, which is an outstanding characteristic in comparison with that of the existed converters. In this paper, soft commutation and soft switching of switches and diodes are investigated along with the aforementioned main novelty. Moreover, detailed theoretical analyses of the proposed SIDO dc–dc converter in continuous conduction mode are presented besides the comparisons with some other structures. Finally, theoretical analyses are verified through a 1500 W experimental prototype results. [ABSTRACT FROM AUTHOR]

This paper proposes a capacitor voltage regulation method for the dual converter with a floating bridge for aerospace applications. This topology has previously been reported, but with a constrained voltage utilization factor due to the need for capacitor voltage regulations. In this paper, the effect of switching states on the voltage variation of capacitor is quantitatively modeled and an enhanced space vector modulation scheme with current feedback is proposed to achieve an active control of the floating capacitor voltages. This proposed method also allows further exploitation and utilization of converter voltage. The relationship between the allowed modulation index of dual converter and load power factor is obtained and expressed using a fitted polynomial equation. The advantages of the proposed method include boosted voltage utilization and superior performance in term of capacitor voltage balance. These advantages have been proven through simulation and experimental results on RL loads as well as with an open-end winding induction motor. The proposed modulation scheme can boost the converter voltage utilization by at least 10% while achieving full four-level operation. More importantly, the higher available voltage allows extending the constant torque region of the motor, the further beginning of field weakening operation could be postponed. [ABSTRACT FROM AUTHOR]

A trinary multilevel converter uses a few heterogeneous H-bridge submodules (SMs) to synthesize an output voltage with multiple levels. Two major limitations of this converter are that it needs multiple dc sources and it cannot operate under pulsewidth modulation (PWM). This paper addresses these limitations by adding a low-voltage H-bridge SM to this converter and proposing a new switching algorithm. The resulting PWM-based asymmetric cascaded H-bridge converter uses only one dc source and synthesizes a high-quality output voltage. This improved converter can be a potential choice for real and reactive power support in power system applications. This paper also proposes methods for stability analysis and design of this converter. Experimental case studies evaluate the performance of the proposed converter for both standalone and grid-connected modes of operation. [ABSTRACT FROM AUTHOR]

This paper develops a modulation based fault-tolerant (FT) strategy for restoring the operation of three-phase modular multilevel converters (MMCs) with faulty switches. This FT strategy is based on a proposed modified space vector modulation (SVM) technique that generates balanced line-to-line (line) voltages even in the case of a fault occurrence. In the postfault operation, the proposed strategy is able to restore the fundamental amplitude of the line to the neutral (load) voltages to that of the normal operation condition with a slightly increased voltage stress over the switches in the faulty phase. In this paper, first a brief background about MMCs and SVM technique is provided. Then, the proposed FT strategy and the modified SVM technique are presented. Finally, several simulation and experimental results are provided to validate operation of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents two capacitor voltage balancing (CVB) strategies for modular multilevel converter (MMC) applications. Both balancing schemes are based on model predictive control and are designed to efficiently solve a constrained optimal control problem, where the predicted capacitor voltage errors are included in the cost function with the demanded output voltage of a cluster being forced through an equality constraint. The first method proposed in this paper computes specific modulation indexes for each module using the explicit solution of a relaxed version of the original optimization problem. The second approach proposed in this paper reduces the complexity of the original problem by linearizing the objective function and using an optimal sorting network based on a greedy algorithm to solve this approximation. Considering the structures of both solution approaches, they are integrated into modulation schemes based on phase-shifted and level-shifted pulsewidth modulation algorithms, respectively. Experimental results obtained from a nine-cell single-phase MMC prototype demonstrate the good performance achieved with the proposed methodologies, as well as the implementation simplicity offered by the proposed CVB algorithms. [ABSTRACT FROM AUTHOR]

This paper analyzes the combination in a cascaded H-bridge multilevel inverter (CHBI) based on transformers with the different turn ratios for increasing the voltage level and proposes the switching method for achieving the output voltage distribution among H-bridge cells (HBCs). The transformers used in this paper are connected to the output of the respective HBCs, and the secondary sides of all the transformers are connected in series for generating the final output voltage. Only one of the transformers, in particular, has a different turn ratio for increasing the output voltage level. In this paper, the possible turn ratio of the special transformer with a different turn ratio is discussed in detail, and a switching method based on the level-shifted switching method for the topology used in this paper is proposed. To verify the effectiveness of the proposed method, a three-phase 21-level CHBI is experimentally tested. [ABSTRACT FROM PUBLISHER]

This paper presents three unidirectional step-up ac–dc converter topologies with voltage multiplication on their outputs. The first topology is the hybrid boost rectifier and the other two are novel bridgeless structures, all based on the integration of boost rectifier and the ladder switched-capacitor (SC) cell. The new hybrid structures provide high voltage gain with low voltage stress across the switches, high-power factor, and output voltage regulation. This paper presents the principle of operation, steady-state and dynamic analysis, design methodology, and experimental verification. A different approach is also presented for the design methodology of the SC cell and for the analysis of its influence on the dynamic model. Three 1000-W prototypes with a 220-V input voltage, 800-V output voltage, and 100-kHz switching frequency were designed to corroborate the theoretical study. The best efficiency was 97.1$\%$ in the proposed bridgeless versions and the voltage stress across the switches stands around 400 V. Furthermore, a comparison between the proposed structures and previous topologies is also presented. [ABSTRACT FROM PUBLISHER]

In this paper, a novel current fed hybrid dual active bridge dc–dc converter is proposed, which is suitable for a low-voltage fuel cell power conditioning system. The high-frequency input current ripple can be reduced to minimum because the input side switches are always switched at 50% duty cycles in spite of the fuel cell voltage and the load variation. Notch filter is used in the voltage feedback path to reduce the low-frequency input current ripple when interfaced with a single-phase inverter load. All of the power devices can achieve zero voltage switching by the proposed control strategy. The mode analysis, the operation principle, zero-voltage switching (ZVS) conditions, and parameter design are given in this paper. A 1 kW prototype has been fabricated to verify the effectiveness of the proposed converter and control strategy. [ABSTRACT FROM PUBLISHER]

This paper proposes an effective sliding mode controller (SMC) for a grid-connected 7-level packed U-cell (PUC7) inverter. The aim is to design a simple controller that deals effectively with the complex control problem of the PUC7 inverter (multiobjective control problem). The selection of the control actions is achieved according to the system state error at every sampling time, regardless of the previous values, which makes the control technique model-independent. The control algorithm evaluates online two cost functions (one for each state error), which are derived on the basis of sliding mode theory, and it selects the optimal control input in order to satisfy the reaching conditions of the two cost functions. Compared with the existing solutions, the proposed SMC technique ensures lower average switching frequency by tuning the hysteresis bandwidth of the capacitor-voltage error. The fast implementation, needless of gains tuning, and simple design procedure are the main features of the proposed algorithm. Simulation and experimental results are presented to prove the effectiveness of the proposed technique in controlling the PUC7 inverter with high dynamic performance and robustness against disturbances and parameters mismatch. [ABSTRACT FROM AUTHOR]

In this paper, a voltage sensorless controller is developed for a two-switch single-phase rectifier that involves power factor correction and active pulsating power buffering without electrolytic capacitors. While a two-switch rectifier normally requires four sensed signals for control, only one current sensor is required in this proposal, thereby offering advantages such as low cost, high compactness, isolation between control and power circuits, and improved reliability. While the basic operating principle follows that of a conventional voltage sensorless controller for single-switch converters, several critical design considerations are the key to the success of the implementation which is explained in detail. The feasibilities of the controller are experimentally testified with a 100-W rectifier prototype regarding both steady state and dynamic performance. [ABSTRACT FROM AUTHOR]

For an LLC converter, it is difficult to realize the wide output range with conventional pulse frequency modulation control because of the limited operating frequency. This paper proposes a new hybrid control method. The proposed strategy combines the burst-mode control and phase-shift control methods for the LLC converter. The burst-mode control can regulate the output voltage from zero to its maximum value, and the phase-shift control can reduce the increased resonant current during burst-on time. By using this method, the wide output voltage range is realized with the low resonant current during burst-on time and zero-voltage switch (ZVS) for all switches. The reliability and efficiency of the converter can be improved accordingly. The burst duty ratio is regulated by the reference output voltage, and the phase-shift angle is derived when realizing ZVS for lagging-leg switches. Moreover, the resonant parameters and the maximum phase-shift angle are optimized under the constraints of current stress and ZVS condition. This method is easy to be implemented in a low-cost microcontroller because high-frequency real-time calculations are not necessary. A 1.5-kW prototype is built to verify the feasibility and validity of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents the current control design procedure of a single-phase grid-tied five-level packed U-cell inverter (PUC5) with an LCL output filter. The PUC5 inverter is used as an interface of renewable energy sources, such as solar applications. The LCL filter is calculated according to the grid-tied operation and converter ratings. An optimal controller, based on a linear quadratic regulator with integral action, is designed to inject a sinusoidal current with low harmonic distortion at unity power factor. For that design, the PUC5 inverter is modelled in the D–Q frame. The sensorless voltage control is incorporated into the switching technique to balance the PUC5 capacitor voltage and generate a five-level waveform at the output. Experimental tests are performed on a laboratory benchmark to confirm the theoretical design. The results prove the efficiency and accuracy of the adopted control strategy in a steady state and under transients of grid current, grid inductance, ac and dc voltage amplitudes. [ABSTRACT FROM AUTHOR]

For photovoltaic applications, the flyback microinverter with pseudo-dc-link is popular as a simple topology but brings large transformer turns ratio and thus large leakage inductance, which would deteriorate the converter efficiency. To solve this issue, based on the nonisolated pseudo-dc-link structure, this paper proposed a hybrid boost–flyback/flyback (BF/F) microinverter. This new topology is operated at the BF mode for the most segment of a half grid cycle and the F mode for the rest. During the BF mode, high voltage gain with low voltage stress is easily available in minimized transformer turns ratio. Besides, the leakage energy is recycled and the turn-off voltage spike of the main switch is clamped, as a result of a passive snubber inherently contained in this mode. Given that the BF mode is lack of step-down function, the F mode is developed to regulate the output voltage even for values lower than the input voltage. The operation and characteristic of the hybrid BF/F microinverter in boundary conduction mode are analyzed in detail, and the mathematical expression of reference current is derived theoretically to guarantee high power quality. Finally, a 240 W prototype was implemented to validate the theoretical analysis and the benefits of the proposed topology. [ABSTRACT FROM AUTHOR]

Power flow control in multiterminal HVdc (MTdc) grids is essential to restrict operation within permissible limits. A current flow controller (CFC) can achieve this. In this paper, the modeling, control, and simulation of resistive, RC-circuit-based, and capacitive CFCs is carried out. CFC prototypes have been developed and an MTdc grid test-rig has been employed for experimental validation. Results show that all devices achieve an effective power flow management. The impact of CFC deployment in future MTdc grids is assessed on droop-controlled converters. A voltage compensation-based method is proposed to minimize power deviations during unscheduled line current control. A protection scheme has been assessed under faults. [ABSTRACT FROM AUTHOR]

In this paper, a resonant current-mode receiver is studied to charge low-voltage batteries wirelessly for supplying medical implantable systems. To increase efficiency, the root-mean-square (rms) current in the LC tank of the receiver (RX) is reduced by using a voltage-boosted current-mode (VBCM) receiver. This receiver combines the conventional current-mode receiver with a switched-capacitor converter to boost the voltage instantaneously at the switching node ($V_{X}$) of coil. Owing to the suggested technique, the receiver directly charges a low-voltage battery while maintaining a small rms current without using a complex voltage regulator. The receiver achieves an efficiency as high as 84.7% with a 1.1 V battery while operating at the resonant frequency ($f_{{\text{reso}}}$) of 6.78 MHz. The power delivered to the output ($P_{O}$) is in the range from 1.5 to 50 mW. The VBCM receiver was fabricated by 180 nm CMOS technology with a total active area of 0.22 mm2. [ABSTRACT FROM AUTHOR]

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging, as voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques, such as using redundant vectors in space vector modulation (SVM). The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., SVM. The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes unified non-inverting and inverting ac–ac converter (UNI-AC) using pulse width modulation (PWM) for the utility voltage compensation. It offers four effective switching states to regulate the output voltage in bipolar manner, facilitating versatile modes of operation with different number of switching states being modulated. Each mode of the proposed UNI-AC is able to compensate both the grid voltage sag and swell problems due to its bipolar voltage gain. The operational principle and comparison for all these modes are investigated in details. Also, the UNI-AC is reversible and compatible with full range of power factor. Other technical merits offered by the proposed approach include the compact hardware installation, reduced switch voltage stress (also low dv/dt) and decreased control complexity. Detailed analysis and experimental verification are presented in this paper. [ABSTRACT FROM AUTHOR]

In a conventional finite control set model predictive control (FCS-MPC) formulation, active and reactive power control loops rely on the predictive controller, whereas the dc-bus voltage is usually governed by a PI-based control loop. This originates from fact that the dynamic equations for describing the predictions of these variables are heavily coupled. In this paper, a cascade-free FCS-MPC for single-phase grid-connected power converters is presented. The proposed control algorithm is formulated in terms of established dynamic references design, which was originally proposed to directly govern active and reactive power, and dc-voltage in three-phase power converters. In this paper, the dynamic reference design concept is extended to control single-phase grid-connected power converters. The proposed control algorithm does not use instantaneous ac-power calculations; instead, it directly formulates the optimal control problem on the grid-current in the original stationary reference frame. The experimental results obtained with a single-phase grid-connected neutral point clamped (NPC) converter confirm a successful design, where system constraints, e.g., maximum power and weighted switching frequency, are easily taken into account. [ABSTRACT FROM PUBLISHER]

Zero-common-mode-voltage (CMV) operation of multilevel inverters results in reduced dc-bus utilization and reduced linear modulation range. In this paper, a method to increase the linear modulation range for zero-CMV operation without increasing the dc-bus voltage using a cascaded multilevel inverter with a single dc supply is presented. Using this method, the peak fundamental output voltage can be increased from 0.499 to 0.637  \textV\text{dc} with zero CMV inside the linear modulation range. Also, various pulse width modulation (PWM) switching sequences are analyzed in this paper, and the PWM sequence that gives minimum current ripple is used for the zero-CMV operation of the inverter. The inverter topology with single dc supply is realized by cascading a two-level inverter with two floating-capacitor-fed full-bridge modules. Simulation and experimental results for steady-state and dynamic operating conditions are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a model predictive control technique applied to a dual-active bridge inverter where one of the bridges is floating. The proposed floating bridge topology eliminates the need for isolation transformer in a dual inverter system and therefore reduces the size, weight, and losses in the system. To achieve multilevel output voltage waveforms, the floating inverter dc-link capacitor is charged to the half of the main dc-link voltage. A finite-set model predictive control technique is used to control the load current of the converter as well as the floating capacitor voltage. Model predictive control does not require any switching sequence design or complex switching time calculations as used for space vector modulation; thus, the technique has some advantages in this application. A detailed analysis of the converter as well as the predictive control strategy is given in this paper. Simulation and experimental results to validate the approach are also presented. [ABSTRACT FROM PUBLISHER]

This paper presents a three-phase open-end winding induction motor drive. The drive consists of a three-phase induction machine with open stator phase windings and dual-bridge inverter supplied from a single dc voltage source. To achieve multilevel output voltage waveforms, a floating capacitor bank is used for the second of the dual bridges. The capacitor voltage is regulated using redundant switching states at half of the main dc-link voltage. This particular voltage ratio (2:1) is used to create a multilevel output voltage waveform with three levels. A modified modulation scheme is used to improve the waveform quality of this dual inverter. This paper also compares the losses in the dual-inverter system in contrast with a single-sided three-level neutral point clamped converter. Finally, detailed simulation and experimental results are presented for the motor drive operating as an open-loop v /f controlled motor drive and as a closed-loop field-oriented motor controller. [ABSTRACT FROM PUBLISHER]

The interleaved bidirectional buck–boost converter dual active half-bridge (IBBC-DAHB) dc–dc converter consists of two converters IBBC and DAHB and a coupled inductor. The IBBC-DAHB converter has significant features such as low ripple current at the low-voltage side, low current stress on the input inductors, voltage stress across the switches less than the high-voltage side, high voltage gain, and zero-voltage soft switching. The converter offers high efficiency using phase-shift modulation when it operates at a nominal design operating point. However, the efficiency decreases due to high circulating current, high current stress, and limited soft-switching range when the source and load voltages deviate from their nominal values. This paper employs both duty cycle and phase-shift modulation methods to improve the above mentioned shortcomings using voltage matching for the DAHB converter. The proposed converter is analyzed and a 500-W experimental prototype with 40–60 V input voltage and 400 V output voltage under 100 kHz switching frequency is implemented to verify the theoretical results. The maximum efficiency of 97.15% is achieved at 60 V and 400 W. A flat efficiency characteristic for the converter is derived by the proposed control method, where the efficiency at 20% of nominal load is 91% and much higher than the phase-shift control, which is 70.8%. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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

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

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

This paper proposes a novel 11-level improved active-neutral-point-clamped (11L-IANPC) converter for ground power unit (GPU) application. This hybrid topology consists of the 5L-ANPC and the proposed low-voltage submodule. The proposed 11L-IANPC converter possesses only one flying capacitor (FC) and reduced number of high-frequency switches. Hence, voltage diversity and ratings, stored energy, and the number of costly and bulky FCs are significantly decreased. Moreover, operating the augmented submodule at the low voltage and power leads to doubling the number of output voltage levels, whereas the low extra cost and size are imposed on the proposed converter. In addition, suggested sensorless switching method leads to self-balancing of FC and significantly amends the output voltage frequency spectrum. These improvements cause significant reduction in control complexity of the proposed 11L-IANPC converter, remarkable decrease in size of the bulky and costly output LC filter, and improving the dynamic and steady-state performance of the proposed static GPU. The simulation and experimental results validate the feasibility of the proposed converter as well as its suggested modulation and control method. [ABSTRACT FROM AUTHOR]

The conventional design of voltage-source power converters is based on a two-level half-bridge configuration and the selection of power devices designed to meet the full application specifications (voltage, current, etc.). This leads to the need to design and optimize a large number of different devices and their ancillary circuitry and prevents taking advantage from scale economies. This paper proposes a paradigm shift in the design of power converters through the use of a novel configurable device consisting on a matrix arrangement of highly optimized switching cells at a single voltage class. Each switching cell consists of a controlled switch with antiparallel diode together with a self-powered gate driver. By properly interconnecting the switching cells, the switching-cell array (SCA) can be configured as a multilevel active-clamped leg with a different number of levels. Thus, the SCA presents adjustable voltage and current ratings, according to the selected configuration. For maximum compactness, the SCA can be conceived to be only configurable by the device manufacturer upon the customer needs. For minimum cost, it can also be conceived to be configurable by the customer, leading to field-configurable SCAs. Experimental results of a 6 × 3 field-configurable SCA are provided to illustrate and validate this design approach. [ABSTRACT FROM AUTHOR]

This paper proposes a novel nonisolated single-input dual-output three-level dc–dc converter (SIDO-TLC) appropriate for medium- and high-voltage applications. The SIDO-TLC is an integration of the three-level buck and boost converters, whose output voltages are regulated simultaneously. Reducing voltage stress across semiconductor devices, improving efficiency, and reducing inductors size are among the main merits of the new topology. Moreover, due to the considerably reduced volume of the step-down filter capacitor, a small film capacitor can be used instead, whose advantages are lower equivalent series resistance and a longer lifespan. A closed-loop control system has been designed based on a small-signal model derivation in order to regulate the output voltages along with the capacitors’ voltage balancing. In order to verify the theoretical and simulation results, a 300-W prototype was built and experimented. The results prove the aforementioned advantages of the SIDO-TLC, and the high effectiveness of the balancing control strategy. Furthermore, the converter shows very good stability, even under simultaneous step changes of the loads and input voltage. [ABSTRACT FROM AUTHOR]

In this paper, a three-level quasi-switched boost T-type inverter (3L qSBT2I) is proposed. A new pulse-width modulated (PWM) control method is presented to reduce the inductor current ripple of the qSBT2 I. In the introduced PWM technique, the shoot-through duty cycle is maintained constant to keep the modulation index as high as possible. Then, the only control parameters of the qSBT2I are the duty cycles of the two additional switches. By controlling the duty cycles of the two additional switches, the voltage gain of the proposed qSBT2 I can be improved to a value larger than that of the conventional 3L impedance source inverters. The steady-state analysis, operating principles, and comparisons with the impedance source-based 3L inverters are presented. A 1-kW prototype is constructed to verify the operating principle of the 3L qSBT2I. An indirect dc-link voltage regulator and a capacitor voltage-balance controller are applied to the proposed qSBT2I. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

Microinverters operating into the single-phase grid from new energy source with low-voltage output face the challenges of efficiency bottleneck and twice-line-frequency variation. This paper proposed a multilevel inverter based on bridge modular switched-capacitor (BMSC) circuits with its superiority in conversion efficiency and power density. The topology is composed of dc–dc and dc–ac stages with independent control for each stage, aiming to improve system stability and simplify the control method. The BMSC dc–dc stage, which can be expanded to synthesize more levels, not only features multilevel voltage gain but also partially replaces the original bulk input capacitor and functions as an active energy buffer to enhance power-decoupling ability between dc and ac sides. In dc–ac stage, the control strategy of optimized unipolar frequency doubling sine-wave pulse width modulation is proposed to improve the quality of output waveform. Meanwhile, the multilevel voltage phase has been optimized to further reduce the power loss. Finally, a prototype has been built and tested. Associated with the simulation, the experimental results validate the practicability of these analyses. [ABSTRACT FROM PUBLISHER]

A new pulsewidth modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is proposed in this paper. A three-level NPC inverter is completely mature and very well-established topology in high-power applications. However, the three-level NPC inverter has an inheritance problem of the neutral-point voltage unbalancing due to the split dc-link capacitors. This structure can cause large neutral-point voltage ripple. Furthermore, output currents of the three-level NPC inverter are distorted by the neutral-point voltage ripple. Therefore, the neutral-point voltage must be controlled. In this paper, a new DPWM method using two different offsets for the neutral-point ripple reduction is proposed and the effectiveness of the proposed DPWM method is verified by using the simulation and the experimental results. [ABSTRACT FROM PUBLISHER]

Single-stage power-factor-corrected (S2PFC) power supplies usually suffer from high voltage stress, due to lack of control on the intermediate bus capacitor voltage. In the past, analysis of such voltage stress was mostly based on steady-state condition without providing sufficient explanation during the transient circuit operation. This paper revisits the problem at circuit level and reports that the root cause is due to the inherent negative current feedback property of the output inductor or the transformer operating in continuous conduction mode (CCM). Based on the finding, this paper further proposes a new approach to reducing the voltage stress by adding an auxiliary circuit branch to existing S2PFC converters. The additional circuit branch limits the effect of negative current feedback by suppressing the change of output current slope due to change of load. This assists the pulsewidth modulation controller to track the change of load better such that the bus capacitor voltage range is reduced through duty cycle control. The auxiliary circuit branch also reduces reverse-recovery-related losses of the converter under CCM operation. A laboratory prototype using the popular boost PFC converter combined flyback dc/dc converter was built and tested to confirm the analysis and effectiveness of the approach. [ABSTRACT FROM AUTHOR]

Filters for switching ripple attenuation are essential at the input, and sometimes at the output for certain applications, for the deployment of matrix converters (MCs). Due to the absence of inertial elements in the MC structure and the consequent tight input–output coupling, the filter parameters significantly affect its dynamic behavior. This paper presents an exhaustive filter design method for synchronous applications of the MC in power systems. Apart from the usual considerations of ripple attenuation, voltage regulation, reactive current loading, and internal losses, this paper also addresses additional constraints which may be imposed by requirements of dynamic performance and reliable commutation. Rigorous analytical justification of each design step is provided and the sequential design process is summarized. Relevant experimental results are presented to validate the proposed design tool. [ABSTRACT FROM PUBLISHER]

Due to the relatively low output voltage of photovoltaic (PV) source, a high step-up converter with high efficiency is needed when the PV source is connected to the power grid. A novel high step-up converter based on two switched capacitors and a coupled inductor is proposed in this paper. The operating principle is analyzed and the voltage gain is derived. A 100-W prototype is fabricated in the laboratory to verify the theoretical analysis, and the highest efficiency is 96.4%. [ABSTRACT FROM PUBLISHER]

This paper proposes the combination of a novel modified quasi-Z-source (MqZS) inverter with a single-phase symmetrical hybrid three-level inverter in order to boost the inverter three-level output voltage. The proposed single-phase MqZS hybrid three-level inverter provides a higher boost ability and reduces the number of inductors in the source impedance, compared with both the single-phase three-level neural-point clamped quasi-Z-source inverter and the single-phase quasi-Z-source cascaded multilevel inverter. Additionally, it can be extended to obtain the nine-level output voltage by cascading two three-level pulse width modulation switching cells with a separate MqZS and a dc source, which herein is called a single-phase MqZS cascaded hybrid five-level inverter (MqZS-CHI). A modified modulation technique based on an alternative phase opposition disposition scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS. The performances of both the proposed MqZS-CHI and the modulation techniques are verified through simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a nine-level active-neutral-point-clamped (ANPC) based multilevel inverter (MLI) topology for grid-connected applications requiring only ten switches. The envisaged structure comprises two parts, namely five-level ANPC unit, and a two-level converter leg whose midpoint is used as another ac terminal. An ad hoc switching state redundancy based modulation strategy is used to ensure that the voltage across the flying capacitor is tightly balanced and is implemented using a look-up table further simplifies the control complexity. The performance and effectiveness of the proposed topology with its control scheme are validated through simulations and experimental tests. Comparison with other MLIs is included to highlight the merits of the proposed topology. From the results, it will be shown that the proposed inverter requires the least part count as compared to other topologies with the same performance and output quality. [ABSTRACT FROM PUBLISHER]

In this paper, a priority sorting approach based on simplified model predictive control (MPC) is proposed for modular multilevel converter (MMC). It aims at reducing the computational burden of conventional MPC method while maintaining the system performance, especially under high voltage levels. The proposed approach mainly consists of three parts, i.e., grid-side current control (GCC), circulating current control (CCC), and capacitor voltage balancing control (CVBC). The GCC and CCC are separately designed with simplified MPCs, avoiding the weight factor. Meanwhile, the redundant calculations are eliminated in GCC by considering the desired predicted output voltage of equivalent MMC model. To further minimize the optional combinations of the switching states, the CCC is constructed by utilizing the output of GCC and the arm current. Besides, a novel priority sorting approach is proposed for the CVBC to alleviate the sorting operation. The submodules are divided into three groups according to the detected capacitor voltages. Moreover, the groups are assigned with different priorities based on the arm current, and only one group needs the sorting process. Additionally, a reduced frequency approach is introduced to decrease the power loss in the steady state. The effectiveness of the proposed approach is validated by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Cascaded H-bridge (CHB) multilevel inverters (MLIs) have been widely used for power electronics systems. While high-voltage blocking across power switches is not a constraint for low voltage applications, the research trend has been oriented to the design of more compact module topologies as an alternative for CHB. Despite the generation of more voltage levels with reduced switch count, the existing module topologies in recent literature take no account of the freewheeling current path during dead-time, thus, inducing multistep jumps in voltage levels and giving rise to undesirable voltage spikes. Addressing this concern, this paper proposes two symmetrical compact-module topologies for cascaded MLI, where freewheeling current path during dead-time is provided for smooth transition between voltage levels to prevent voltage spikes. The proposed 7-level and 13-level compact-modules demonstrated low number of conducting switches for all voltage levels. Comprehensive analysis and comparison with the latest module topologies are conducted. To validate the operation of the proposed compact-module topologies, simulation and experimental results are presented. [ABSTRACT FROM PUBLISHER]

This paper proposes a multiloop framework for current control of grid-connected voltage source inverters (VSIs) with LCL output filter. The discrete-time model is of third-order with a nonminimum phase zero when controlling the grid side current. This poses some difficulties on the design of most types of controllers. Motivated by this problem, the inner loop is implemented by a discrete-time sliding mode control law to ensure the tracking of the converter side current. This can be achieved regardless the grid impedance and voltage, making the converter to behave like a current source inverter with a capacitive+inductive (CL) filter. Thus, the problem of current control falls from a third-order system to a second-order system. Several types of controllers can be designed to implement the outer loop based on the equivalent CL circuit. In this work, a resonant controller with a virtual resistor was applied. Simulations and experimental results are presented to validate the proposal. [ABSTRACT FROM PUBLISHER]

This paper extends the trans-Z-source concept to ac–ac power conversion and proposes a novel single-phase trans-Z-source ac–ac converter. The proposed converter retains the advantages of its existing Z-source/quasi-Z-source counterparts in which the output voltage can be boosted and in-phase with the input voltage or bucked/boosted and out-of-phase with the input voltage. Meanwhile, a coupled inductor is introduced into the proposed converter, and the turns ratio of the coupled inductor become another control variable beside the duty cycle to obtain extreme voltage gain. Importantly, the input voltage and output voltage share the same ground, and the input current could be continuous, which is a benefit for reducing input current harmonics. Most important of all, the safe-commutation strategy for the proposed converter is deep developed, and analytic expression between the switches state and loop circuit voltage/current condition is derived out. Hence, the current/voltage ripple can be avoided without a loss snubber circuit, which benefits a reduced cost and enhanced reliability. The performance analysis is discussed in consideration of parasitic resistance, and system parameter design is optimized based on theoretic calculation. A laboratory prototype is fabricated, and experiments are performed to verify the validation of the proposed converter. [ABSTRACT FROM PUBLISHER]

The control loop stability in boost converters operating in continuous conduction mode has been restricted due to its nonminimum phase nature: the presence of a positive zero (right-half plane zero) in the control to output voltage transfer function. This paper proposes a method to mitigate the effect of the zero on the control loop by shifting the position of the zero to the left-half plane and hence leading to increased stability for the control loop of the boost converter. Superior performance of the proposed method has been clearly demonstrated using simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Compared with multilevel space vector modulation, level-shifted multicarrier sinusoidal pulsewidth modulation (SPWM) for nested neutral point-clamped (NNPC) inverters requires much less calculations and implementation efforts, but the existing conventional SPWM cannot suppress the severe flying-capacitor (FC) voltage ripples under low output-frequency conditions. In order to solve this problem, a multicarrier-based PWM strategy with complete voltage balance control (VBC) capacity is proposed in this paper. For NNPC inverters operating under low output-frequency conditions, two preprocessing steps, the zero-sequence injection and the modulation-signal rearrangement, are proposed before the comparisons between level-shifted carriers and modulating signals. These preprocessing steps make the average currents flowing through FCs zero, which is beneficial to greatly reduce the FC voltage ripples under low output-frequency conditions. Together with additional VBC, the proposed modulation can assure the FC voltages balanced under the entire output-frequency conditions. Principles and implementation processes of proposed modulation techniques and VBC methodsare elaborated in detail and compared with conventional modulation methods. Both simulation results from a 5-MVA system and experimental results based on a 5-kVA platform are presented to verify the effectiveness. [ABSTRACT FROM AUTHOR]

Two main problems, including unbalanced grid input and circuit parameters uncertainty in the three-phase soft-switching converter control system, are considered in this paper. First, the constant-switching-frequency model-predictive control (CF-MPC) is improved for application in compound active-clamp zero-voltage-switching three-phase power factor correction converter. Second, a robust-constant-frequency model-predictive control (RCF-MPC) method is proposed for current loop; the novel contributions are: 1) the negative-sequence current component is introduced into the cost function of the model-predictive control to decrease the influence of unbalanced grid input; and 2) a robust item is added into the predictive model to reduce the influence of the circuit parameter uncertainty. Third, a robust variable structure controller is proposed for voltage loop considering the capacitor and load uncertainty. The simulation and experiment results show that, compared with the original CF-MPC method and the traditional proportional–integral control method, the proposed RCF-MPC method decreases the total harmonic distortion under the unbalanced grid condition. Meanwhile, the voltage loop robust variable structure controller has better transient and steady-state performance with respect to the load perturbation. [ABSTRACT FROM PUBLISHER]