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This paper proposes a high-efficiency two-stage three-level grid-connected photovoltaic (PV) inverter. The proposed two-stage inverter comprises a three-level step-up converter and a three-level inverter. The three-level step-up converter not only improves the power-conversion efficiency by lowering the voltage stress but also guarantees the balancing of the dc-link capacitor voltages using a simple control algorithm; it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of leakage current. The three-level inverter minimizes the overall power losses with zero reverse-recovery loss. Furthermore, it reduces harmonic distortion, the voltage ratings of the semiconductor device, and the electromagnetic interference by using a three-level circuit configuration; it also enables the use of small and low-cost filters. To control the grid current effectively, we have used a feed-forward nominal voltage compensator with a mode selector; this compensator improves the control environment by presetting the operating point. The proposed high-efficiency two-stage three-level grid-connected PV inverter overcomes the low efficiency problem of conventional two-stage inverters, and it provides high-power quality with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we have evaluated the performance of the model and proved its feasibility. [ABSTRACT FROM PUBLISHER]

In this paper, a power factor correction (PFC)-based switched reluctance motor (SRM) drive is proposed. Generally, the SRM drive is fed with a simple diode bridge rectifier followed by a bulky capacitor, which draws peaky current at low power factor and high-input-current total harmonic distortion (THD). Here, a dual output converter is proposed to control the SRM and to provide power quality improvement as well. This converter is a combination of Cuk and SEPIC converters, which produces two equal output voltages with neutral point N, to feed a midpoint converter of the SRM drive. The converter is designed to operate in discontinuous conduction mode of operation to obtain inherent PFC at supply side. The motor control is attained by regulating dc link voltage over a wide range. Test results on a prototype of the SRM drive demonstrate the excellent performance with high power factor and reduced input current THD. The observed power quality indices depict the improved power quality as per the standard IEC 61000-3-2. [ABSTRACT FROM PUBLISHER]

Three-level buck dc–dc converters have advantages over the traditional buck converters: half switch voltage stress, doubling effective switching frequency, smaller inductor size, and the higher power density. To benefit from those advantages, the flying capacitor voltage must be balanced at half of the input voltage. Most existing methods of balancing the flying capacitor voltage require current sensing, which increases the cost and noise sensitivity. This paper proposes a novel state-machine structure of second-order sliding-mode (SOSM) control for three-level buck dc–dc converters without sensing currents. With insensitivity to parameter variations of SOSM control, the proposed control approach tackles the strongly coupled problem of output voltage and flying capacitor voltage in three-level buck dc–dc converters. Compared to existing approaches, the controller achieves fast start-up without overshoots, fast load disturbances rejection, and robustness against parameter uncertainties for the output voltage, and balance of the flying capacitor voltage without sensing the current of flying capacitor. The proposed approach is verified with experimental results of a 1.25 V, 2.5 A prototype. [ABSTRACT FROM PUBLISHER]

In this paper, a new type of matrix converter (MC) also called a single-phase high-frequency transformer isolated (HFTI) buck MC is proposed. The proposed converter can provide step-down operation of the input voltage with various types of output voltages such as in-phase and out-of-phase output voltages, rectified (or positive) output voltage, and output voltage with step-changed frequency. By incorporating HFT isolation, the proposed MC saves an extra bulky line frequency transformer, which is required for the conventional MCs to provide electrical isolation and safety, when used in application such as dynamic voltage restorers, etc. Two different circuit variations of the proposed HFTI MC are presented with and without continuous output currents, with the latter having less passive components. The safe-commutation strategy is also employed for the proposed HFTI MC to provide current path for the inductor during dead-time, which avoids switch voltage spikes without adding any snubber circuits. The operation principle and circuit analysis of the proposed MC are presented, and switching strategies are also developed to obtain various output voltages. Moreover, a prototype of the proposed MC is fabricated, and experiments are performed to produce in-phase/out-of-phase and rectified output voltages, and output voltage with step-changed frequency. [ABSTRACT FROM PUBLISHER]

This paper proposes a digitally implemented charge control for LLC resonant converters. By analyzing the small-signal characteristics of the resonant capacitor, it is revealed that the resonant capacitor has exactly the same functionality as a resettable integrator in the charge control for a PWM converter. Based on the analyzed results, the proposed charge control is implemented simply by sensing the voltage across the resonant capacitor in a switching period. The proposed method features simple implementation with resistive voltage divider and suitability for digital control as well as good performance as other multiloop controls have. The design guideline for the charge controller is given based on the loop gain analysis. Finally, the operation and performance of the proposed method are verified with a 240-W LLC resonant converter. [ABSTRACT FROM AUTHOR]

Novel load regulation methods for switched-capacitor converter (SCC) system operating in parallel mode are proposed. SCCs are ready for integrated design which is ideal for mass production and also enables power conversion in compact footprint. At the same time, they are excellent candidates for parallel mode operation since the load current sharing among them is automatically allocated by the inherent droop characteristic, which is determined by the equivalent internal resistance. Instead of controlling the individual switching frequency of SCC units, this paper proposes a number of unit commitment schemes which regulate the output voltage by adjusting the number of activated SCC units. In addition to conventional discrete unit commitment, intermediate number of activated units is realized by employing pulse-dropping pulse width modulation. The proposed methods are verified by simulation and the experiment of a parallel SCC system consists of a number of double-mode zero-current switching SCC units. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a simple neutral point potential (NPP) regulator for a three-level diode-clamped inverter employing a sine-triangle regulator in conjunction with a closed-loop controller with reduced switching losses. The regulator principle is based on adding a continuous variable offset voltage which regulates the midpoint potential of the dc bus. The novelty of the proposed NPP regulator is in the determination of the magnitude of variable offset voltage based upon the average value, peak-to-peak amplitude, total harmonic distortions, and third harmonic content in NPP. Aside from maintaining dc-bus voltage balance, the proposed regulator leads to a significant reduction in the voltage distortion at the NP, resulting in the reduction of the required dc-bus capacitance. It also reduces the switching losses of the inverter by inserting the “no-switching” zone within each half cycle of the fundamental voltage wave. Analytical, computer simulation, and experimental results verifying the approach are presented in this paper for various load power factor angles. [ABSTRACT FROM AUTHOR]

This paper proposes a phase-shift interleaving control method for variable-phase switched-capacitor (SC) converters that can perform voltage conversions with little electromagnetic interference over a wide range of operating condition. This is achieved by having multiple units of SC converter connected in parallel and an N-state hysteresis unit selection control scheme which works along the interleaving control to vary the number of converters in operation. By having the capacitors of inactive units connected to the output and the converters operating with output interleaving operation, the output capacitor that is typically required in SC converters for maintaining a small voltage ripple is made redundant in this configuration. A three-unit SC converter of the proposed configuration is described in this paper. Experimental results show that the proposed solution works satisfactorily with good regulation, input and output interleaving operations, and dynamic response for a wide operating range. [ABSTRACT FROM PUBLISHER]

Single-phase power factor correction (PFC) ac–dc converters are widely used in the industry for ac–dc power conversion from single phase ac-mains to an isolated output dc voltage. Typically, for high-power applications, such converters use an ac–dc boost input converter followed by a dc–dc full-bridge converter. A new ac–dc single-stage high-power universal PFC ac input full-bridge, pulse-width modulated converter is proposed in this paper. The converter can operate with an excellent input power factor, continuous input and output currents, and a non-excessive intermediate dc bus voltage and has reduced number of semiconductor devices thus presenting a cost-effective novel solution for such applications. In this paper, the operation of the proposed converter is explained, a steady-state analysis of its operation is performed, and the results of the analysis are used to develop a procedure for its design. The operation of the proposed converter is confirmed with results obtained from an experimental prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation strategy for the modular multilevel converter (MMC) which provides the voltage balancing of the capacitors of different submodules comprising the converter. Not only is this modulation applicable to MMCs constructed with classic two level (2L) submodules, but it is also effective for arrangements with different submodule concepts, for instance, topologies like neutral point clamped (NPC), flying capacitors (FCs), neutral point piloted (NPP), etc. Therefore, firstly, the general modulation philosophy is explained applied to the two level (2L) submodule concept, and secondly, the extension to 3L-NPC and 3L-FC submodule topologies is analyzed. After that, the validation of the studied modulation strategy is carried out by means of successful simulation results, at different switching frequencies and number of submodules. The corresponding experimental results are shown in Part II of this paper after having implemented the aforementioned modulation strategy in a real test bench. In addition to this, a comparison based on thermal analysis and sizing of elements among the four studied submodule topologies is also included. [ABSTRACT FROM PUBLISHER]

In this paper, an immune algorithm (IA) is developed for optimization of the harmonic performance of a three-phase inverter under the space-vector pulsewidth-modulation (SVPWM) control strategy. The presented algorithm employs the immune approach as the search method for finding the best optimal control vectors and action time of the three-phase inverter. As a result, the optimal control vectors and action time are calculated to minimize the objective function of the weighted total harmonic distortion of the output voltage waveforms. In addition, an experimental platform based on DSP and field-programmable gate array is built. This paper provides a detailed performance analysis of the method with comparison to the conventional SVPWM. The simulation and experimental results verify the superiority of the best control sequences generated by IA compared with the existing conventional control strategies. [ABSTRACT FROM PUBLISHER]

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype. [ABSTRACT FROM PUBLISHER]

A new three-phase single-stage rectifier is proposed in this paper. The outstanding features of the proposed rectifier are that it can produce input currents that do not have deadband regions and an output current that can be continuous when the converter is operating from maximum load to at least half of the load. In this paper, the operation of the new converter is explained, its features and design are discussed in results, and its operation is confirmed with experimental results obtained from a prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a novel soft-switching galvanically isolated buck-boost dc–dc converter as a module-integrated converter for photovoltaic (PV) applications. It features three major operating modes: boost, normal, and buck mode. Their proper distribution over the input voltage range enables wide voltage regulation capabilities, i.e., close to those of nonisolated power optimizers. The proposed control algorithm requires only one buck-boost switching stage that performs voltage regulation by means of the switching stage reconfiguration with smooth transition between the modes. The design guidelines and the digital control system for PV applications are provided. The module-integrated converter was verified experimentally with a solar array simulator. The converter showed good maximum power point tracking performance and a peak efficiency of nearly 97%. [ABSTRACT FROM PUBLISHER]

A microconverter serves as a front-end dc–dc stage of a microinverter to convert the power from a photovoltaic module to a dc bus. These front-end microconverters require isolation, high-boost ratio, wide-input voltage regulation, and high efficiency. This paper introduces an isolated resonant converter with hybrid modes of operation to achieve wide-input regulation while still maintaining high efficiency. The proposed converter is designed as a series resonant converter with nominal-input voltage and operates under two additional modes: a boost converter with low-input voltage and a buck converter with high-input voltage. Unlike conventional resonant converters, this converter operates at discontinues conduction mode with a fixed frequency, simplifying the design and control. In addition, this converter can achieve zero-voltage switching (ZVS) and/or zero-current switching (ZCS) of the primary-side MOSFETs, ZVS and/or ZCS of the secondary-side MOSFETs, and ZCS of output diodes under all operating conditions. Experimental results using a 300-W prototype achieve a peak efficiency of 98.1% and a California Energy Commission efficiency of 97.6% including all auxiliary and control power at nominal-input voltage. [ABSTRACT FROM PUBLISHER]

This paper presents a new active capacitor voltage balancing control method for the flying capacitor multicell (FCM) converters which is fully implemented using logic-form equations. The proposed active capacitor voltage balancing control technique, measures output current and flying capacitor (FC) voltages to generate the switching states in order to produce the required output voltage level and to balance FCs’ voltages at their reference values. Output voltage of the FCM converter controlled with proposed active capacitor voltage balancing method can be modulated with any pulse width modulation (PWM) technique such as the phase-shifted-carrier PWM or level-shifted-carrier PWM. An advantage of the proposed active capacitor voltage balancing control method is its simplicity as it does not require any complex computations and tedious optimization calculations. Simulation results and experimental measurements of a three-cell four-level and four-cell five-level FCM converters are presented to verify the performance of the proposed active capacitor voltage balancing control technique. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active capacitor voltage balancing technique for stacked multicell (SM) converters. The proposed active capacitor voltage balancing control method detects the direction of the load current and measures the voltage of flying capacitors (FCs) to generate a proper switching state in order to form the required output voltage level and regulate the FC voltages at their desired reference levels. The proposed active capacitor voltage balancing control technique can modulate the output voltage through any of the pulse-width-modulation (PWM) techniques such as the phase-shifted carrier PWM or the level-shifted-carrier PWM. The foremost advantage of the proposed active control technique is that it does not demand any complex computations because it is not based on the optimization of the FC voltage-deviation cost functions. A thorough set of simulation results and experimental measurements for the five-level and seven-level SM converters are provided to validate the proposed active capacitor voltage balancing control method. [ABSTRACT FROM AUTHOR]

This paper proposes a unique carrier-based pulse width modulation strategy for a three-level neutral-point-clamped inverter that works satisfactorily and with uniform convergence time over the full power factor (PF) range of the load variation. It has excellent control over capacitor voltages and mitigates low-frequency oscillations in the neutral point for the full PF range. First, an investigation is made to see how the load currents get modulated to generate compensating neutral current causing charging and discharging of dc-link capacitors. It is observed that when an additional modulating voltage signal that is in phase with the corresponding phase current is added in each phase, a neutral current is produced in the right direction which can be used to compensate for any prior unbalance in capacitor voltages. It is demonstrated that the performance of this scheme is insensitive to the load PF variation (full range from zero to unity). It performs satisfactorily throughout the entire linear modulation range and eliminates any undesirable low-frequency harmonic component in the compensating neutral current. The effectiveness of the proposed scheme is verified through simulation and experimental results by varying load PF as well as modulation index with both passive and motor loads. [ABSTRACT FROM PUBLISHER]

The high number of power semiconductors in multilevel converters makes them susceptible to failure. Therefore, one of the main concerns in utilizing multilevel inverters is their reliability. This paper proposes a new simple fault-diagnosis and fault-handling method to increase the robustness and reliability of a flying capacitor multilevel inverter (FCMLI) which is one of the most prominent multilevel inverters. The proposed method is capable of diagnosing failed switch(es) and reconfiguring the switching sequence such that the output voltage is maintained similar to a normal operation condition. The proposed scheme identifies failed switch(es) by using the information about the charging state of the capacitors and the applied switching sequence. After identifying the failed switch(es), the algorithm bypasses the failed switch(es) and converts the control signals of the faulty leg from an M -cell L-level configuration to an (M-F)-cell L -level configuration (where F is the number of failed switches). The most attractive feature of the proposed control scheme is that any number of failed switches can be tolerated, as long as the number of functional switches is higher than the minimum number of cells required to build a full-binary L-level FCMLI. Simulation and experimental results are presented that verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

In this paper, the near-state pulse width modulation (NSPWM), adapted to be used in dual-voltage source inverter (VSI) fed open-end load, is introduced primarily aiming to appreciably minimize the voltage total harmonic distortion (THD). Within the framework of the proposed method, the active time of pulses at the second inverter is relatively adjusted within switching interval (compared to the first VSI). The phase voltage harmonics are formulated for dual-inverter modulated by NSPWM; then, optimal adjustment is identified via a three-dimensional curve of phase voltage THD versus modulation index (MI) and phase angle displacement (PAD). Due to the limitation of MI in NSPWM, the desired output voltage is synthesized with modifying not only MI but also PAD between references of two VSIs. Furthermore, NSPWM inherently takes advantage of better efficiency compared to conventional space vector modulation due to switching only two phases within an interval (by clamping one phase to positive/negative dc-rail). The dual-VSI supplied by two isolated dc sources is assembled in the laboratory to experimentally evaluate the THD reduction feature of the proposed method; also, the simulation results obtained by means of a MATLAB/Simulink environment show close agreement with experimental data. [ABSTRACT FROM PUBLISHER]

This paper presents a new multicell topology based on flying capacitor (FC) structure suitable for multilevel converters. The proposed topology employs the concept of phase-shifted carrier pulse width modulation (PWM) with modified modulating signals to generate appropriate PWM signals. The modulation strategy along with all possible switching states are explained. The implementation of the proposed PWM technique is shown by the help of illustrating waveforms. To show the advantages of the proposed structure, different performance criteria are compared with other FC multicell (FCM) structures. Simulation results are used to further evaluate the potential merits of the proposed topology. It is shown that the proposed structure is superior to other FCM-based structures from different standpoints. Specifically, it reduces the number of high-frequency switches, the number of FCs, and at the same time improves the quality of output voltage. A laboratory-type experimental setup is used to validate the modulation strategy and other theoretical findings. [ABSTRACT FROM AUTHOR]

This paper proposes a power-factor-corrected bridgeless (BL) switched-mode power supply (SMPS) for welding applications that possesses output voltage control and current limiting feature even during extreme overloading conditions at the output terminals. Eliminating an input diode bridge rectifier minimizes conduction losses and improves thermal utilization of semiconductor devices. The front-end of the proposed SMPS consists of a BL boost converter operating in a continuous conduction mode to attain unity power factor, while at the rear end a pulse width modulation isolated full bridge dc–dc converter is used to regulate the output voltage. The design and implementation of this BL arc welding power supply (AWPS) is presented showing its fast dynamic response to supply voltage and load variations. The performance of the proposed AWPS is examined in terms of power factor, total harmonic distortion of the supply current, efficiency, and output current limit over a wide range of line/load variations. Test results confirm the effectiveness of the proposed AWPS in maintaining an impeccable power quality at utility interface apart from achieving an excellent output voltage regulation and current limiting capability. [ABSTRACT FROM PUBLISHER]

This paper presents an adaptive observer (AO)-based model predictive control (MPC) for a multilevel flying capacitors inverter (FCI). The proposed system consists of a midpoint dc-link three-cell four-level FCI feeding an RL load. Using the actual load current, the proposed AO estimates accurately the capacitors’ voltages, which are fed to the MPC algorithm by means of a hybrid model considering both discrete and continuous variables. For real-time constraints, sufficient conditions are given to guarantee the practical stability of the proposed AO-based MPC. Theoretical analysis and experimental results are given to show that the proposed method is stable for all system configurations and has good performances even during disturbances (load change, input change, and parameters variations). [ABSTRACT FROM AUTHOR]

A novel flying-capacitor-clamped five-level inverter based on bridge modular switched-capacitor topology is proposed in this paper. The inverter features the switched-capacitor circuit with dc–dc boosting conversion ability and the multilevel inverter circuit with flying-capacitor-clamped performance. With the special composite structure, the number of components is cut down compared to the topology of the conventional cascaded multilevel inverter. Meanwhile, part of switches can be operated under line voltage frequency, resulting in switching loss reduction. Hence, the potential of system efficiency and power density is released due to embed switched-capacitor circuit. More importantly, the optimized carrier-based phase disposition pulse width modulation method is employed as a control strategy. Under this control strategy, the capacitor voltage self-balance can be realized and quality of output waveforms can be improved significantly. After simulation, the prototype is built to validate the correctness and practicability of the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a closed-loop space vector modulation (SVM)-based sliding mode controller (SMC) for a three-level grid-connected neutral point clamped (3L-NPC) inverter. The nonlinear SMC based on Gao's reaching law has been designed to control the grid current and inject desired amount of active and reactive power into the network. Due to using single dc source at the NPC inverter dc bus, neutral point voltage is controlled through redundant switching states and instantaneous dc voltage feedback integrated into SVM technique. Meanwhile, there is no external voltage controller involved, thus no associated fine tuning issues are existed. The performance of the proposed hybrid controller to inject a desired active/reactive power to the grid is investigated through external perturbations such as change in the line current amplitude/phase shift, ac voltage fluctuation, as well as dc voltage variation. Full converter state-space model was developed and simulated. Experimental results are provided to verify the fast dynamic performance, low content of line current THD%, and good voltage balancing of dc bus capacitors of the NPC inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a new configuration for static ground power unit (GPU) based on the novel 25-level hybrid active neutral-point-clamped (HANPC) converter. The superiority of the proposed converter, as compared with conventional and other suggested multilevel converters, is significant decreasing the number of switches and minimizing the number of flying capacitors (FC) in converter. This improvement is possible by using suggested low-voltage submodule converter to the ANPC converter and proposed modulation method. This results in reduction of the size and cost of converter and makes it more feasible and reliable. Applying the active voltage balancing method for FC in the proposed HANPC converter guaranties fast charging and voltage-level regulation of FC without using balance booster circuit. Improving output voltage spectrum leads to inductance reduction of output L–C filter which enhances static GPU performance. The simulation and experimental results verify the validity and feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology of six-level inverters for a medium-voltage high-power applications is proposed, which consists of inner flying-capacitor inverter (FCI) units and outer two-level inverter units. The proposed topology can reduce the number of devices, components, and isolated sources compared with the existing ones in the case of the same number of output voltage steps, which result in a reduction of the size and weight of the inverters. Also, the total power loss of the proposed topology is lower than that of the diode-clamped inverter (DCI) and FCI. Besides, the estimated cost of the proposed topology is about 60.5% and 81.3% compared with the DCI and FCI, respectively. In addition, the modulation technique and the control strategy for the dc-link capacitor and flying-capacitor voltages are developed for the proposed topology. The effectiveness of the proposed six-level inverter for the medium-voltage applications has been verified by simulation results. Also, the feasibility of the proposed inverter has been proved by experimental results for the prototype at the laboratory. [ABSTRACT FROM AUTHOR]

This paper presents a finite-control-set model predictive control (FCS-MPC) for grid-tied packed U cells (PUC) multilevel inverter (MLI). The system under study consists of a single-phase 3-cells PUC inverter connected to the grid through filtering inductor. The proposed competitive topology allows the generation of 7-level output voltage with reduction of passive and active components compared to the conventional MLIs. The aim of the proposed FCS-MPC technique is to achieve, under various operating conditions, grid-tied current injection with unity power factor and low total harmonic distortion while balancing the capacitor voltage. Parameters’ sensitivity analysis was also conducted. The study is conducted on a low-power case study single-phase 3-cells PUC inverter and with possible extension to higher number of cells. Theoretical analysis, simulation, and experimental results are presented and compared. [ABSTRACT FROM AUTHOR]

In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched-capacitor techniques is presented. Compared with the traditional cascade multilevel inverter, the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation strategy. The operation principle and the charging–discharging characteristic analysis are discussed in detail. A 1-kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

The model predictive control has an ability to achieve multiple control objectives for a modular multilevel converter. This approach has high computational complexity and causes the unwanted switching's leading to a higher ripple in output current and harmonic distortion in output voltage and current waveforms. To solve the issues of computational burden and unwanted switchings, this paper proposes a dual-stage model predictive control approach for a modular multilevel converter. In this approach, the primary objectives are evaluated in first stage corresponding to the redundancy of voltage vectors, while the secondary objectives are evaluated in second stage corresponding to the submodule redundancy. Therefore, the computational burden is significantly minimized without affecting the dynamic response. In addition, a discrete-time model of modular multilevel converter incorporating the common-mode voltage is proposed. The simulation and experimental studies are conducted on a three-phase modular multilevel converter to verify the dynamic and steady-state performance of the proposed approach. The performance comparison between the proposed and conventional model predictive control approach is also presented. [ABSTRACT FROM PUBLISHER]

This paper provides a characterizationr analysis for the voltage balance of modular cascaded converter in a medium-voltage direct-current distribution grid. Specifically, voltage stability and traditional auxiliary resistor solution are analyzed from the theoretical level. On this basis, a minimum voltage tracking balance (MVTB) control based on a switched resistor is proposed. The voltage balance during startup and normal locked processes can be adjusted effectively by MVTB control. Moreover, the resistor does not need to absorb power continuously; instead, it is just switched into operation for a while when a difference occurs, and the power loss can be decreased after the system recovers to a steady state. Finally, experimental results verify the effectiveness of the MVTB control. [ABSTRACT FROM PUBLISHER]

This paper presents a control scheme based on the predictive control theory and Petri nets (PNs) formalism to control a flying capacitor multilevel converter. The proposed scheme takes advantage of the benefits offered by the finite control set-model predictive control (FCS-MPC) methodology and the versatility of PNs to regulate the capacitor voltages and output current, simultaneously. The inclusion of PNs allows us to simplify the control scheme. A first PN is used to select, from a subset of switching states, the switching state that accomplishes both control objectives. This approach reduces the computational burden if compared with a typical predictive control scheme. Furthermore, a PN-based prediction scheme is used to predict the capacitor voltages. This prediction scheme uses only measurements of output voltage and current, which reduces the number of required sensors. This approach allows us to implement the internal capacitor voltages control independently if a multileg configuration is needed. The scheme is experimentally validated in a five-level flying capacitor multilevel converter. [ABSTRACT FROM PUBLISHER]

In this paper, a simple control method of the half-bridge (HB) LLC converter with one additional switch and capacitor in the primary side is proposed for wide-input-voltage applications with the hold-up time conditions. At nominal input, since the proposed method enables the HB LLC converter to operate with large transformer magnetizing inductance, it can reduce the conduction and switch turn-off losses in the primary side, which makes it highly efficient. On the other hand, during the hold-up time, since the proposed method increases the resonant capacitance by turning on one additional switch, the HB LLC converter can obtain high-voltage gain. To confirm the validity of the HB LLC converter with the proposed method, a 325–385 V input and 56 V/350 W output laboratory prototype is built and tested. [ABSTRACT FROM PUBLISHER]

This paper presents a new family of buck type power factor corrector rectifiers that operates in continuous-conduction mode (CCM) and generates a multilevel voltage waveform at the input. Due to CCM operation, commonly used ac-side capacitive filter and dc-side inductive filter are removed from the proposed modified packed U-cell rectifier structure. Dual dc output terminals are provided to have a five-level voltage waveform at the input points of the rectifier where it is supplied by a grid via a line inductor. Producing different voltage levels reduces the voltage harmonics which affects the grid current harmonic contents directly. Low switching frequency of the proposed rectifier is a distinguished characteristic among other buck type rectifiers that reduces switching losses and any high switching frequency related issues, significantly. The proposed transformerless, reduced filter, and multilevel rectifier topology has been investigated experimentally to validate the good dynamic performance in generating and regulating dual 125-V dc outputs terminals as telecommunication boards feeders or industrial battery chargers under various situation including change in the loads and change in the main grid voltage amplitude. [ABSTRACT FROM PUBLISHER]

In this paper, an improved model predictive control (MPC) of the modular multilevel converter (MMC) with reduced computational burden is proposed. A mathematical model of the MMC system based on the sum and difference of arm voltages are derived. Instead of determining the switching state of individual submodule (SM), the voltage levels of MMC are considered as control options based on the assumption that the SM capacitor voltages are well balanced. The further reduction of calculation effort is realized by using the tolerance band of capacitor voltages. The proposed MPC has a hierarchical structure. The cost function taking into account the ac-side current control, circulating current elimination and arm energy balancing is presented. The optimal voltage level, selected by the cost function, provides the voltage reference for the pulse width modulation modulator. The SM capacitor voltage balancing is done using a separate control loop. The proposed control strategy is investigated using an MMC high-voltage direct current system with 200 SMs in each arm in real-time simulation and hardware-in-the-loop tests. The performance of proposed method is verified by both steady-state and transient-state operations. [ABSTRACT FROM PUBLISHER]

For cascaded multilevel inverter topologies with a single dc supply, closed-loop capacitor voltage control is necessary for proper operation. This paper presents zero and reduced common-mode voltage (CMV) operation of a hybrid cascaded multilevel inverter with predictive capacitor voltage control. Each phase of the inverter is realized by cascading two- three-level flying capacitor inverters with a half-bridge module in between. For the presented inverter topology, there are redundant switching states for each inverter voltage levels. By using these switching state redundancies, for every sampling instant, a cost function is evaluated based on the predicted capacitor voltages for each phase. The switching state that minimizes cost function is treated as the best and is switched for that sampling instant. The inverter operates with zero CMV for a modulation index upto 86%. For modulation indices from 86% to 96%, the inverter can operate with reduced CMV magnitude (Vdc/18) and reduced CMV switching frequency using the new space-vector pulsewidth modulation (SVPWM) presented herein. As a result, the linear modulation range is increased to 96% as compared to 86% for zero CMV operation. Simulation and experimental results are presented for the inverter topology for various steady state and transient operating conditions by running an induction motor drive with open loop $V/f$ control scheme. [ABSTRACT FROM PUBLISHER]

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, phase-shifted schemes suffer from harmonic degradation when operated at the low carrier frequencies required in high-power high-level number applications. This paper develops a model predictive modulation (MPM) scheme that achieves superior harmonic performance, compared to phase-shifted modulation, while ensuring equal semiconductor loss distribution. With respect to complete-enumeration-based predictive techniques, the proposed modulation significantly reduces the number of times the system cost function is evaluated. Reducing the number of calculations by several orders of magnitude ensures computational feasibility. Simulation and experimental results are presented, which confirm correct operation of the modulation strategy. [ABSTRACT FROM PUBLISHER]

This paper presents the new implementation of the finite control states set model predictive control (FS-MPC) applied to three-level four-leg flying capacitor converter (FCC) operating as a shunt active power filter (SAPF). The three main issues regarding the algorithm development are described and the solutions are proposed. The first is addressed to modeling of the four-wire system, which for simplification is based on wire-to-wire voltage equations. The second relates to the control of FCC by MPC, i.e., a proper interpretation of the FCC switching states and control of flying capacitor (FC) voltages, which was moved from the prediction loop. Finally, the system restriction regarding undesirable switching states’ transitions is explained and the solution is presented. The control performance was tested in the simulation model in MATLAB–Simulink and validated experimentally by measurements on the 10-kVA FCC laboratory setup. [ABSTRACT FROM PUBLISHER]

A new resonant converter having low voltage stress and nearly constant efficiency against line variation for high- and wide-input-voltage applications is presented in this paper. It is similar to a three-level zero-voltage-switching pulsewidth modulation converter (TL ZVS PWMC) with two flying capacitors. In the proposed converter, however, two flying capacitors are used as the resonant capacitors, and the output voltage regulation is achieved by frequency modulation. The main advantages of the proposed converter are that, since the sum of the voltages of two resonant capacitors is constant and is equal to half of the input voltage, the voltage across each switch clamps to half of the input voltage and keeps the balance. Moreover, all main switches and rectifier diodes are softly switched under full-line and full-load conditions, and high efficiency can be constantly achieved over a wide input voltage range. These advantages solve the drawbacks on TL ZVS PWMCs. The features, operation principles, and relevant analysis results over a wide input voltage range of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results of a prototype converter with 400–600-V input, 48-V/10-A output, and 200-kHz resonant frequency. The experimental results show that the maximum efficiency of the proposed converter is 95.08% under a full-load and a 600-V input and slightly varies across the 400–600-V input voltage range. [ABSTRACT FROM AUTHOR]

The matrix converter can be used in a wide range of applications. Nevertheless, it does not yet represent a sufficiently mature option for industrialization. In order to resolve this problem, this paper examines the hardware of the matrix converter and identifies all the circuits that should be included in this. It also quantifies the operating conditions and provides practical guidelines for the step-by-step design of a matrix converter. These considerations are validated with experimental results. In this way, it can be said that this paper represents a step forward toward the development of reliable matrix converters for real applications. [ABSTRACT FROM AUTHOR]

This paper proposes a novel family of cascade three-level (TL) ac–ac direct converters based on ac switch cells, which transfer unsteady high ac voltage with distortion into regulated sinusoidal voltage with low total harmonic distortion (THD). The topological family includes buck TL–boost, buck–boost TL, and buck TL–boost TL modes. In order to achieve a reliable TL ac–ac conversion, a double transient voltage feedback control strategy of the output voltage and the voltage across the flying capacitor is introduced in this paper. A 500-VA 220-V \pm10% 50-Hz ac/220-V 50-Hz ac prototype is presented with the experimental results to prove that the converters have four improved advantages simultaneously, including lower voltage across power switches, bidirectional power flow, low THD of output voltage, and higher input power factor. [ABSTRACT FROM AUTHOR]

This paper proposes a new space-vector pulsewidth modulation (SV-PWM) strategy for a three-level neutral point clamped inverter. The presented SV-PWM strategy makes it possible to control the neutral point voltage by optimum choice of switch sequence for any position and length of output voltage vector. The proposed solution takes into consideration the unbalance of the dc-link voltages. It also analyzes the influence of vector sequences on the predicted unbalance of the dc-link voltage. The solution allows selecting optimum vectors and their on-time durations in order to reduce quickly the dc-link voltage unbalance. The calculation of the space vector area proposed in this paper takes into consideration voltage unbalance and its influence on the length and position of vectors. The proposed approach assures properly generating the voltage output vectors, even in the case of the existing large voltage unbalance in the dc-link. The results of the experimental investigation of the proposed modulation strategy are presented in this paper. [ABSTRACT FROM PUBLISHER]

Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis. [ABSTRACT FROM PUBLISHER]

In this paper, a cascaded H-Bridge (CHB)-multilevel converter (MC)-based photovoltaic (PV) system with no voltage or current sensors at the dc-side is proposed. Eliminating the dc-side sensors simplifies the hardware, leading to lower cost and higher reliability of the PV system. A novel scheme estimating the capacitors’ voltages from the ac output voltage of the inverter is developed. The scheme allows replacing all dc-side voltage sensors by a single-voltage sensor at the ac-side of the converter. Furthermore, the dc current sensors, conventionally required for the maximum power point tracking (MPPT), are also eliminated. Instead, the outputs from the capacitors’ voltage control systems are utilized for the MPPT. The effectiveness of the proposed dc-side sensorless system is experimentally demonstrated on a 2-kW single-phase seven-level CHB converter-based PV system. [ABSTRACT FROM PUBLISHER]

This paper presents a new dual-switch control structure for an ac/dc noninverting cascaded buck–boost power factor correction converter. The proposed converter operates at a discontinuous capacitor voltage mode providing an inherent high-power factor and a zero voltage turn-off switching. Additionally, the proposed control structure enables for a nondistorted sinusoidal current for a wide range of output voltage levels. Unlike the conventional methods, a mode detector is not required and consequently there is no hard transition between buck and boost modes. Although both converter switches are controlled, only one feedback control loop is required to obtain the desired power flow at a unity power factor. The principle of operation, theoretical analysis, simulation, and experimental results of a 1.6-kW prototype grid-connected converter are presented. The results confirmed the validity of the proposed system under various operating conditions. [ABSTRACT FROM PUBLISHER]

In this paper, a model-predictive control (MPC) has been designed and implemented on the packed U-cell (PUC) inverter, which has one isolated dc source and one capacitor as an auxiliary dc link. The MPC is designed to regulate the capacitor voltage at the desired magnitude to have seven voltage levels at the output of the inverter. Since grid-connected application is targeted by this application, the inverter should be capable of supplying requested amount of active and reactive power at the point of common coupling (PCC) as well. Therefore, MPC should also consider the line-current control to monitor the exchange of reactive power with the grid while injecting appropriate active power at low total harmonic distortion (THD). Various experimental tests including change in dc-source voltage, active power variation, and operation at different power factor (PF) have been performed on a laboratory prototype to validate the good performance obtained by the proposed MPC. The dynamic performance of the controller during sudden changes in dc capacitor voltage, supply current, and PF demonstrates the fast and accurate response and the superior operation of the proposed controller. [ABSTRACT FROM PUBLISHER]

Compared with constant duty cycle-controlled discontinuous conduction mode (DCM) boost power factor (PF) correction (PFC) converter, constant duty cycle-controlled quadratic DCM–DCM boost PFC converter features with much lower second-order line frequency output voltage ripple, and however, it suffers from low PF. To increase PF of quadratic DCM–DCM boost PFC converter, a variable duty cycle control technique for quadratic DCM–DCM boost PFC converter is presented in this paper. An approximation equivalent for the variable duty cycle is employed to simplify the implementation circuit. The corresponding expressions of PF and output voltage ripple are analyzed. For input voltage range of 100–240 Vac, quadratic DCM–DCM boost PFC converter with variable duty cycle control benefits with very high PF, and tradeoff between PF and output voltage ripple of this converter is analyzed. Experimental results from 100-W prototypes are given to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

Modular multilevel converter (MMC) is a promising new topology for high-voltage applications. The MMC is made of several identical submodules. For proper operation, each submodule can be considered as a controlled voltage source where capacitor’s voltage should be maintained at a certain level. Besides, the minimization of the circulating current, which does not flow to the load, is crucial for achieving stable and efficient operation of the MMC. The interrelations among the load current, circulating current, and capacitor voltages complicate the MMC control. This paper aims to achieve stable and balanced voltage and current control with reduced circulating current in various operating conditions. The proposed control uses weighted model predictive control based on a normalized cost function to select the inverter switching patterns, which control the load current, while minimizing voltage fluctuation and circulating current. The weighting factors were selected based on minimizing the load-current total harmonic distortion (THD) and circulating current. The analysis is conducted on a low-power case study of single-phase four-cells MMC with possible extension to higher number of cells. The low-power three-level prototype is designed and built to validate this proposed method. Theoretical analysis, simulation, and experimental results are presented and compared. Parameter sensitivity analysis was also conducted. They all confirm the effectiveness of the proposed control method. [ABSTRACT FROM PUBLISHER]

In recent years, modular multilevel converters (MMCs) are very popular in medium/high-voltage motor drive systems and high-voltage direct-current (HVDC) applications. The conventional model predictive control (MPC) strategies for the MMC are not practical due to their substantial calculation requirements, especially under high number of voltage levels. To solve this problem, a fast MPC strategy combined with a submodule (SM)-voltage sorting balancing method is proposed based on the discrete mathematical model derived for the MMC in this paper. By optimizing the implementation of the control objectives and simplifying the rolling optimization, the proposed strategy is simpler to expand to a system with larger number of SMs, with the amount of calculation reduced and the advantages of the conventional MPC algorithm reserved. In addition, the proposed control can minimize the $dv/dt$ of the output voltages. Both steady-state and transient performances are evaluated by a down-scaled three-phase MMC prototype under various experimental conditions, which validates the proposed fast MPC strategy. [ABSTRACT FROM PUBLISHER]

The flying capacitor multilevel inverter (FCMLI) is one of the well-known structures of multilevel inverters having attracted considerable attention because of its merits. In spite of its many advantages, it has some limitations such as high volume and complicated control method because of its bulky capacitors and their voltage balancing requirement. Moreover, the high number of power semiconductors required makes this structure susceptible to failure. To increase the ratio of the number of levels to the number of components, an uneven distribution of capacitor voltages has been suggested in previous reports; however, this approach complicates the control method. Up to now, almost all presented methods suffer from high computational load and/or structure-dependent algorithm. In this paper, a simple state-based and structure-independent method is proposed for capacitor voltage regulation. The proposed method is straightforward and can perform online computation of switching sequences in a computationally efficient manner without any need for stored information or look-up tables. The method is conveniently extendible to any number of cells and levels in an FCMLI structure with arbitrary dc link voltage distribution schemes. Simulation and experimental results show the effectiveness and simplicity of this method. [ABSTRACT FROM PUBLISHER]