Showing papers on "Converters published in 2016"
TL;DR: In this paper, several passive filter topologies used to interface voltage-source converters with the utility grid are reviewed and evaluated in terms of damping capability, stored energy in the passive components, and power loss in the damping circuit.
Abstract: In order to reduce size and cost, high-order passive filters are generally preferred in power converters to cancel out high-frequency harmonics caused by pulsewidth modulation. However, the filter resonance peaks may require the use of passive dampers to stabilize the interactions between the load and source impedances. Furthermore, the stabilizing effect is more difficult to be guaranteed for cost-optimized filters, which are characterized by low-inductance and high-capacitance passive components. In this paper, several passive filter topologies used to interface voltage-source converters with the utility grid are reviewed and evaluated in terms of damping capability, stored energy in the passive components, and power loss in the damping circuit. In addition, the influences of different switching frequencies of power converters on the passive filter design are discussed in the range 1–15 kHz. Illustrative design examples of the passive filters and experimental data are also provided.
369 citations
TL;DR: In this article, the authors provide an introduction, review, and framework for the category of high-step-up coupled-inductor boost converters, which are categorized into five groups according to the major topological features.
Abstract: High-step-up, high-efficiency, and cost-effective dc–dc converters, serving as an interfacing cell to boost the low-voltage output of renewable sources to the utility voltage level, are an important part in renewable energy systems. Over the past few years, there has been a substantial amount of studies devoted to high-step-up dc–dc converters. Among them, the category of coupled-inductor boost converters is widely researched and considered to be a promising solution for high-step-up applications. In this paper, these converters are categorized into five groups according to the major topological features. The derivation process, advantages, and disadvantages of these converters are systematically discussed, compared, and scrutinized. This paper aims to provide an introduction, review, and framework for the category of high-step-up coupled-inductor boost converters. General structures for the topologies are proposed to clarify the topological derivation process and to show potential gaps. Furthermore, challenges or directions are presented in this paper for deriving new topologies in this field.
325 citations
TL;DR: In this article, a family of nonisolated high-voltage-gain dc-dc power electronic converters is proposed, which can be used as multiport converters and draw continuous current from two input sources.
Abstract: A family of nonisolated high-voltage-gain dc–dc power electronic converters is proposed. The suggested topologies can be used as multiport converters and draw continuous current from two input sources. They can also draw continuous current from a single source in an interleaved manner. This versatility makes them appealing in renewable applications such as solar farms. The proposed converters can easily achieve a gain of 20 while benefiting from a continuous input current. Such a converter can individually link a PV panel to a 400-V dc bus. The design and component selection procedures are presented. A 400-W prototype of the proposed converter with $V_{\text{in}} = 20$ and $V_{\text{out}} = 400$ V has been developed to validate the analytical results.
281 citations
TL;DR: In this paper, a two-port network composed of two capacitors and two inductors connected in an X shape is employed to provide an impedance source (Z-source) network, coupling the inverter main circuit to the dc input source.
Abstract: One of the most promising power electronics converter topologies is the Z-source inverter (ZSI). The ZSI is an emerging topology for power electronics dc?ac converters with interesting properties such as buck-boost characteristics and single-stage conversion. A two-port network, composed of two capacitors and two inductors connected in an X shape, is employed to provide an impedance source (Z-source) network, coupling the inverter main circuit to the dc input source. The ZSI advantageously uses the shoot-through (ST) state to boost the input voltage, which improves the inverter reliability and enlarges its application fields. In comparison with other power electronics converters, it provides an attractive single stage dc?ac conversion with buck-boost capability with reduced cost, reduced volume, and higher efficiency due to a lower component number. For emerging power-generation technologies, such as fuel cells, photovoltaic (PV) arrays, and wind turbines, and new power electronic applications such as electric and hybrid vehicles, the ZSI is a very promising and competitive topology [1]-[4].
242 citations
TL;DR: In this paper, a comparison of the features of different topologies of three-port DC-DC converters that have been proposed by different research groups is reviewed briefly, which can be used as a guide for the appropriate selection of the suitable topology to meet the particular requirement of a system.
Abstract: The application of renewable energy such as solar photovoltaic (PV), wind and fuel cells is becoming increasingly popular because of the environmental awareness and advances in technology coupled with decreasing manufacturing cost. Power electronic converters are usually used to convert the power from the renewable sources to match the load demand and grid requirement to improve the dynamic and steady-state characteristics of these green generation systems, to provide the maximum power point tracking (MPPT) control, and to integrate the energy storage system to solve the challenge of the intermittent nature of the renewable energy and the unpredictability of the load demand. In order to improve the efficiency and the power density of the overall circuit, the use of a three-port DC–DC converter, which includes a DC input port for the renewable source, a bidirectional DC input port for the energy storage system, and a DC output port for supplying the load, is a preferable solution to the traditional method using two DC–DC converters: one for the renewable sources and another for the energy storage system. In recent years, many DC–DC three-port converters have been proposed and reported in the literature. Each of these converters has its own topology and operating principle, which results in different complexities, different numbers of components, different reliability and efficiency. In this paper, a comparison of the features of different topologies of three-port DC–DC converters that have been proposed by different research groups is reviewed briefly. This review can be used as a guide for the appropriate selection of the suitable topology to meet the particular requirement of a system. The paper also discusses the potential research extension of the topologies from three-port DC–DC converters to three-port DC–AC inverters and how the voltage gain of the non-isolated three-port DC–DC converter can be improved.
169 citations
TL;DR: In this article, different state feedback approaches of finite control set model predictive control (FCS-MPC) applied to a grid-connected voltage-source converter (VSC) with an LCL filter are compared.
Abstract: This paper presents different state feedback approaches of finite control set model predictive control (FCS-MPC) applied to a grid-connected voltage-source converter (VSC) with an LCL filter. Besides converter-side current feedback, two multivariable control approaches and line-side current control are introduced and compared based on theoretical and experimental evaluation. As the LCL filter introduces an additional resonance frequency to the system, the use of different active damping (AD) methods in combination with FCS-MPC is discussed. Furthermore, practical control implementation issues are discussed. The presented methods reveal the great potential, high dynamic performance, and flexibility of FCS-MPC, enabling multivariable control as well as both reduced switching losses and low harmonic current distortion at the same time. Eventually, the feasibility of the theoretical control concepts is shown in a laboratory environment.
166 citations
TL;DR: In this article, the authors classified all the topologies of the impedance-source galvanically isolated dc-dc converters according to the element that transfers energy from the input to the output: a transformer, a coupled inductor, or their combination.
Abstract: Impedance-source converters, an emerging technology in electric energy conversion, overcome limitations of conventional solutions by the use of specific impedance-source networks. Focus of this paper is on the topologies of galvanically isolated impedance-source dc–dc converters. These converters are particularly appropriate for distributed generation systems with renewable or alternative energy sources, which require input voltage and load regulation in a wide range. We review here the basic topologies for researchers and engineers, and classify all the topologies of the impedance-source galvanically isolated dc–dc converters according to the element that transfers energy from the input to the output: a transformer, a coupled inductor, or their combination. This classification reveals advantages and disadvantages, as well as a wide space for further research. This paper also outlines the most promising research directions in this field.
161 citations
TL;DR: In this article, the generalized theory of phase-shifted carrier pulsewidth modulation (PSC-PWM) for cascaded H-bridge (CHB) converters and modular multilevel converters (MMCs) was discussed.
Abstract: This paper discusses the generalized theory of phase-shifted carrier pulsewidth modulation (PSC-PWM) for cascaded H-bridge (CHB) converters and modular multilevel converters (MMCs), provides a reasonable classification of the PSC-PWM, and extends the possible phase-shift angles to full range. First, the PSC-PWM for CHB converter is classified into two categories by phase-shift pattern. In addition, by rigorous mathematical derivation, the impact law of the full-range phase-shift angles on harmonic minimization is obtained. And then, it is proved that the generalized theory is equally applicable to MMC, which also merges the former proposed PSC-PWM for MMCs into itself. Moreover, the harmonic analysis of the dead-time error voltage is discussed, which is found to have the same harmonic distribution as the ideal voltage, except for the emerging of odd-order harmonics. In summary, this generalized theory offers a general perspective of the PSC-PWM for CHB converter and MMC, and builds up a scientific and comprehensive understanding for researchers from both academia and industry. Finally, the analytical findings are sufficiently validated by simulation and experimental results.
160 citations
TL;DR: An improved circulating current injection method is proposed, which does not completely eliminate the capacitor voltage ripple, but maintains it bounded within reasonable values, leading to converter efficiency improvement and reduction of semiconductor current ratings.
Abstract: Modular multilevel converters (MMC) represent an interesting and emerging topology in medium-voltage motor drive applications. The main challenge of using such a topology in variable-speed drives is the large voltage ripple of submodule capacitors at low speed with constant torque. In this paper, an improved circulating current injection method is proposed, which does not completely eliminate the capacitor voltage ripple, but maintains it bounded within reasonable values. As a result, magnitude of injected circulating current is reduced, leading to converter efficiency improvement and reduction of semiconductor current ratings. Dimensioning of submodule capacitance is also discussed, which is an important consideration when designing the MMCs in variable-speed drives. The proposed method has been successfully validated by simulation and experimental results.
159 citations
TL;DR: In this paper, a zero-sequence injection method was proposed to optimize the converter power balance, extending the converter operation with severe power imbalance in multilevel-cascaded H-bridge converters.
Abstract: Multilevel-cascaded H-bridge converters are promising candidates for next generation photovoltaic power converters. They feature reduced switching losses and higher conversion efficiency with modular structure; characteristics vital for large-scale photovoltaic power plants. However, the stochastically-variable nature of irradiance levels and ambient temperatures affects the normal operation of this topology, because power levels in the three phases can be unequal. The existing zero sequence injection method can deal with the power imbalance problem, but it is limited in its application. The paper proposes a zero sequence injection method to optimize the converter power balance, extending the converter operation with severe power imbalance. Based on the proposed optimal method, a simplified optimal zero sequence injection method requiring less calculation effort is derived and compared with the optimal method. Simulation and experimental results validate the effectiveness and feasibility of the proposed methods.
156 citations
TL;DR: In this paper, the authors present a comprehensive review of high-power dc-dc converters for high-voltage direct current (HVDC) transmission systems, with emphasis on the most promising topologies from established and emerging DC-DC converters.
Abstract: This study presents a comprehensive review of high-power dc-dc converters for high-voltage direct current (HVDC) transmission systems, with emphasis on the most promising topologies from established and emerging dc-dc converters. In addition, it highlights the key challenges of dc-dc converter scalability to HVDC applications, and narrows down the desired features for high-voltage dc-dc converters, considering both device and system perspectives. Attributes and limitations of each dc-dc converter considered in this study are explained in detail and supported by time-domain simulations. It is found that the front-to-front quasi-two-level operated modular multilevel converter, transition arm modular converter and controlled transition bridge converter offer the best solutions for high-voltage dc-dc converters that do not compromise galvanic isolation and prevention of dc fault propagation within the dc network. Apart from dc fault response, the MMC dc auto transformer and the transformerless hybrid cascaded two-level converter offer the most efficient solutions for tapping and dc voltage matching of multi-terminal HVDC networks.
01 Jan 2016
TL;DR: In this article, the authors present a review on the improvement of reliability of dc link in power electronic converters from two aspects: reliability-oriented dc-link design solutions; and conditioning monitoring of DC-link capacitors during operation.
Abstract: DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.
TL;DR: In this paper, the authors proposed a new modular multilevel converter with embedded electrochemical cells that achieves very low cell unbalancing without traditional balancing circuits and a negligible harmonic content of the output currents.
Abstract: New advanced power conversion systems play an essential role in the extension of range and life of batteries. This paper proposes a new modular multilevel converter with embedded electrochemical cells that achieves very low cell unbalancing without traditional balancing circuits and a negligible harmonic content of the output currents. In this new topology, the cells are connected in series by means of half-bridge converters, allowing high flexibility for the discharge and recharge of the battery. The converter features a cell balancing control that operates on each individual arm of the converter to equalize the state of charge of the cells. The paper shows that the proposed control does not affect the symmetry of the three-phase voltage output, even for significantly unbalanced cells. The viability of the proposed converter for battery electric vehicles and the effectiveness of the cell balancing control are confirmed by numerical simulations and experiments on a kilowatt-size prototype.
TL;DR: An improved control method for multiple bidirectional power converters is proposed to reduce the circulating current and power-sharing deviation among converters when the hybrid ac/dc microgrid operated in island mode, which can enhance the security of parallel converters.
Abstract: In this paper, an improved control method for multiple bidirectional power converters is proposed to reduce the circulating current and power-sharing deviation among converters when the hybrid ac/dc microgrid operated in island mode, which can enhance the security of parallel converters. First, a unified detection method for circulating current and power-sharing deviation is described. Then, the improved control method for bidirectional converters in hybrid microgrid operated in island mode is presented to reduce circulating current and power-sharing deviation, which includes the droop controller used to achieve automatic power sharing and the improved virtual impedance controller used to further reduce circulating current and power-sharing deviation. At last, simulation and experiment results verified that the proposed control method can simultaneously achieve circulating current reduction and automatic power sharing, and does not decrease the output power capability of converter. The proposed control method is suitable for the configuration that has a specific bus between bidirectional power converters, and the ac bus connected to ac loads and the host grid.
TL;DR: In this article, a modular dc-dc bypass converter is proposed to perform active battery cell balancing and to supply current to auxiliary loads, eliminating the need for a separate HV-to-LV high step-down DC-dc converter.
Abstract: Electric-drive vehicles, including hybrid, plug-in hybrid, and electric vehicles, require a high-voltage (HV) battery pack for propulsion and a low-voltage (LV) dc bus for auxiliary loads. This paper presents an architecture that uses modular dc–dc bypass converters to perform active battery cell balancing and to supply current to auxiliary loads, eliminating the need for a separate HV-to-LV high step-down dc–dc converter. The modular architecture, which achieves continuous balancing of all cells, can be used with an arbitrary number of cells in series, requires no control communication between converters, and naturally shares the auxiliary load current according to the relative state-of-charge (SOC) and capacities of the battery cells. Design and control details are provided for LV low-power dual active bridge (DAB) power converters serving as the bypass converter modules. Furthermore, current sharing is examined and worst-case SOC and current deviations are derived for mismatches in cell capacities, SOCs, and parasitic resistances. Experimental results are presented for a system consisting of 21 series 25 Ah Panasonic lithium-ion NMC battery cells and 21 DAB bypass converters, with combined outputs rated to supply a 650-W auxiliary load.
TL;DR: A review of past studies on synchronization methods for grid-connected converters together with their control and modeling techniques is presented in this paper, where key challenges for a smart and efficient synchronization are briefly overviewed and possible future works are also recommended.
Abstract: Recent interest in the integration of renewable energy sources (RES) into the power grid has raised concerns in synchronization of the various RES. Grid variables such as voltage, phase angle and frequency should be continuously monitored to guarantee correct operation and synchronization of power converters connected to the power grid. Numerous synchronization methods have been presented over the years to address issues such as unbalanced condition and frequency variation. This paper presents a review of past studies on synchronization methods for grid-connected converters together with their control and modeling techniques. Various estimation techniques for phase angle, frequency and harmonic are discussed and examined. Key challenges for a smart and efficient synchronization are briefly overviewed and possible future works are also recommended. A consolidated review is the particular focus of this paper, as is the provision of information on the best method for synchronizing grid-connected converters.
TL;DR: In this paper, the authors proposed a split-source inverter (SSI) topology, which requires the same number of active switches of the VSI, three additional diodes, and the same eight states of a conventional space vector modulation.
Abstract: In several electrical dc–ac power conversions, the ac output voltage is higher than the input voltage. If a voltage-source inverter (VSI) is used, then an additional dc–dc boosting stage is required to overcome the step-down VSI limitations. Recently, several impedance source converters are gaining higher attentions [1] , [2] , as they are able to provide buck-boost capability in a single conversion stage. This paper proposes the merging of the boost stage and the VSI stage in a single stage dc–ac power conversion, denoted as split-source inverter (SSI). The proposed topology requires the same number of active switches of the VSI, three additional diodes, and the same eight states of a conventional space-vector modulation. It also shows some merits compared to Z-source inverters, especially in terms of reduced switch voltage stress for voltage gains higher than 1.15. This paper presents the analysis of the SSI and compares different modulation schemes. Moreover, it presents a modified modulation scheme to eliminate the low frequency ripple in the input current and the voltage across the inverter bridge. The proposed analysis has been verified by simulation and experimental results on a 2.0-kW prototype.
TL;DR: Experimental results show the desired fixed switching behavior in the steady-state condition and the intrinsic fast dynamic provided by MPC during transients and the test outcomes demonstrate the robustness of the proposed controller under large system parameter deviations.
Abstract: In this paper, a model predictive control (MPC) based on optimal switching sequences (OSSs) for a single-phase grid-connected full-bridge neutral-point-clampled (NPC) power converter is presented. The predictive control algorithm is formulated in terms of OSSs, which was originally proposed to govern three-phase power converters. In this paper, the OSS concept is extended to control single-phase power converters. The proposed MPC algorithm belongs to the continuous control set MPC and is able to provide fixed switching frequency while handling system constraints. The proposed algorithm has been experimentally tested in an NPC power converter prototype. Experimental results show the desired fixed switching behavior in the steady-state condition and the intrinsic fast dynamic provided by MPC during transients. Furthermore, the test outcomes demonstrate the robustness of the proposed controller under large system parameter deviations.
TL;DR: In this article, the authors present an assessment of current and future trend of non-isolated DC-DC converters with various parameters and are analyzed using MATLAB Simulink.
Abstract: At present, power shortage became a huge problem in many countries, due to cumulative load demand which cannot be met by Conventional Energy Power Generation. These challenging situations lead researchers to focus on non-conventional energy sources to extract Electric Power. In order to extract the electric power, DC–DC converters are adopted at the primary stage to increase the efficiency Power Conversion. This paper presents an assessment of current and future trend of non-isolated DC–DC converters (Such as Buck–boost, Cuk and Sepic) with various parameters and are analyzed using MATLAB Simulink. Based on the simulation result, the performances of non-isolated converters are evaluated and are helps to determine the suitable converter with a particular power rating for renewable energy based applications. In addition, the state space mathematical modeling of DC–DC converters are also presented which will be useful in the design of controllers for different non isolated DC–DC converters.
TL;DR: In this paper, a split-phase control scheme was proposed to enable the Dickson converter to achieve complete soft-charging (or resonant) operation, which is not possible using the conventional two-phase controller.
Abstract: Switched-capacitor (SC) converters are gaining popularity due to their high power density and suitability for on-chip integration. Soft-charging and resonant techniques can be used to eliminate the current transient during the switching instances, and improve the power density and efficiency of SC converters. In this paper, we propose a split-phase control scheme that enables the Dickson converter to achieve complete soft-charging (or resonant) operation, which is not possible using the conventional two-phase control. An analytical method is extended to help in the analysis and design of split-phase controlled Dickson converters. The proposed technique and analysis are verified by both simulation and experimental results. An 8-to-1 step-down Dickson converter with an input voltage of 150 V and rated power of 36 W is built using GaN FETs. The converter prototype demonstrated a five fold reduction in the output impedance (which corresponds to conduction power loss) compared to a conventional Dickson converter, as a result of the split-phase controlled soft-charging operation.
TL;DR: In this paper, the authors consider the integration of multiphase machines and converters into a single-phase charging process of electric vehicles and propose a control scheme applicable to all topologies and which includes current balancing and interleaving strategy.
Abstract: The paper considers integration of multiphase (more than three phases) machines and converters into a single-phase charging process of electric vehicles (EVs) and, thus, complements recently introduced fast charging solutions for the studied phase numbers. One entirely novel topology, employing a five-phase machine, is introduced and assessed jointly with three other topologies that use an asymmetrical nine-phase machine, an asymmetrical six-phase machine, and a symmetrical six-phase machine. In all topologies, both charging and vehicle-to-grid (V2G) mode are viable. Moreover, all are capable of unity power factor operation. A torque is not produced in machines during charging/V2G process so that mechanical locking is not required. Hardware reconfiguration between propulsion and charging/V2G mode is either not required or minimized by using a single switch. Theoretical analysis of operating principles is given, and a control scheme, applicable to all topologies and which includes current balancing and interleaving strategy, is developed. Finally, operation of all topologies is compared by means of experiments in both charging and V2G mode, with a discussion of influence of current balancing and interleaving strategy on the overall performance.
TL;DR: In this paper, a simplified space vector modulation (SVM) scheme for multilevel converters is proposed, which simplifies the detection of the nearest three vectors and the generation of switching sequences, and therefore is computationally more efficient.
Abstract: This paper proposes a simplified space vector modulation (SVM) scheme for multilevel converters. Compared with earlier SVM methods, the proposed scheme simplifies the detection of the nearest three vectors and the generation of switching sequences, and therefore is computationally more efficient. Particularly, for the first time, the proposed scheme achieves the same easy implementation as phase-voltage modulation techniques. Another superior characteristic of the proposed scheme over earlier methods is its potential for multiphase multilevel applications. The proposed scheme also offers the following significant advantages: 1) independence of the level number of the converter; 2) more degrees of freedom, i.e., redundant switching sequences and adjustable duty cycles, to optimize the switching patterns; and 3) no need for lookup tables or coordinate transformations. These advantages make the proposed scheme well suited to large level-number applications, such as modular multilevel converters and high voltage direct current systems. Simulation and experimental results verify this new concept.
TL;DR: In this article, the authors proposed a LCL filter design method and its current control for grid-connected converters, where the resonance frequency of the filter was set to be higher than the Nyquist frequency, i.e., half of the system sampling frequency.
Abstract: This paper proposes a novel LCL filter design method and its current control for grid-connected converters. With the proposed design method, it is possible to set the resonance frequency of the LCL filter to be higher than the Nyquist frequency, i.e., half of the system sampling frequency, and this observation is so far not discussed in the literature. In this case, a very cost-effective LCL filter design can be achieved for the grid-connected converters, whose dominant switching harmonics may appear at double the switching frequency, e.g., in unipolar-modulated three-level full-bridge converters and 12-switch-based three-phase pulsewidth-modulated converters. Moreover, a single-loop current control strategy is proposed for the designed LCL filter, and the control system is inherently stable without introducing any passive or active damping. Based on the new stability region, two LCL filter design examples are given, with one of them optimizing the utilization of passive filter inductors, and another one being robust against grid impedance variation. Comprehensive experimental results, showing the high-quality output current and excellent resonance attenuation, are presented in this paper, which are also in very good agreement with those of the simulated ones. These results successfully verify the feasibility of the proposed LCL filter design and its current control.
TL;DR: In this paper, a hybrid boosting converter with collective advantages of regulation capability from its boost structure and gain enhancement from its voltage multiplier structure is proposed, which makes it suitable for front-end PV system and some other renewable energy applications.
Abstract: A hybrid boosting converter (HBC) with collective advantages of regulation capability from its boost structure and gain enhancement from its voltage multiplier structure is proposed in this paper. The new converter incorporates a bipolar voltage multiplier, featuring symmetrical configuration, single inductor and single switch, high gain capability with wide regulation range, low component stress, small output ripple and flexible extension, which make it suitable for front-end PV system and some other renewable energy applications. The operation principal, component stress, and voltage ripple are analyzed in this paper. Performance comparison and evaluation with a number of previous single-switch single-inductor converters are provided. A 200-W 35 to 380 V second-order HBC prototype was built with peak efficiency at 95.44%. The experimental results confirms the feasibility of the proposed converter.
01 Oct 2016
TL;DR: In this article, a comprehensive review of non-isolated bidirectional dc-dc converter topologies is presented based on the features and applications of each type and the most promising converters in terms of their simplicity, flexibility, and high efficiency are singled out.
Abstract: There is a growing interest in bidirectional dc-dc converters for interface battery with energy source and load. This paper provides a comprehensive review of non-isolated bidirectional dc-dc converter topologies. The classification and description of each type presented is based on the features and applications. This review paper is intended as a convenient reference to future non-isolated converter users. The most promising converters in terms of their simplicity, flexibility, and high efficiency are singled out.
TL;DR: In this article, a soft switching operation scheme for isolated modular dc/dc converters based on modular multilevel converter technology is proposed, where the chain-links generate quasi-square terminal voltages with reduced dv / dt.
Abstract: High-voltage dc/dc converters play an important role in HVDC grids. Isolated modular dc/dc converters (IMDCCs) based on modular multilevel converter technology provide a good solution to high-voltage applications. In order to reduce the size of the system, the IMDCC is required to be operated with a high ac-link frequency, but this will lead to increased switching loss and thus degraded efficiency. This paper proposes a soft-switching operation scheme for such an IMDCC. In this scheme, a quasi-square-wave (QSW) modulation method is employed, where the chain-links generate quasi-square terminal voltages with reduced dv / dt . With such chain-link terminal voltages, the arm currents which provide good condition for the soft-switching operation of the QSW-IMDCC can be obtained. Since soft switching can be achieved for the power switches, the proposed scheme will suffer less switching loss, thus improving the efficiency of the converter. Moreover, a capacitor voltage-balancing control strategy is proposed. This strategy does not need any arm current sensors, thus reducing the cost. The proposed soft-switching operation scheme and capacitor voltage-balancing control strategy are verified by the simulation results.
TL;DR: This paper presents the idea of phase-locked-loop-less (PLL-less) operation of grid-connected voltage source converters (VSCs) under new concept of inducverter, which offers a simpler and more reliable control strategy compared to the conventional methods.
Abstract: Inspired by induction machines working principles, this paper presents the idea of phase-locked-loop-less (PLL-less) operation of grid-connected voltage source converters (VSCs) under new concept of inducverter. The proposed controller eliminates the need for a dedicated synchronization process and the related PLL, and therefore it offers a simpler and more reliable control strategy compared to the conventional methods. In addition, it represents an improved performance, as it provides real and true auto-start and auto-synchronization with a grid without the need for grid voltage information. A current damping/synchronization unit enables grid auto-synchronization by using local current information and can track grid voltage frequency, angle, and amplitude variations while feeding constant amount of power, which is of high-interest in frequency varying grids and also in the case of grid voltage angle jump. Another advantage of the inducverter is that it introduces virtual inertia to the grid to regulate frequency, which enhances frequency dynamics of smart grids. Beside the current synchronization unit, the proposed strategy has a single-loop controller core with control over both power and current, which is implemented in a hybrid dq and abc frame using a virtual adaptive lead or lag impedance. The controller also offers stable and high-performance synchronization and operation under unbalanced and/or distorted grid conditions. The work beside synchronous current converters gives a bird’s eye view to research in the new area of PLL-less and virtual inertia-based operation of VSCs and fulfill a unified set of controllers for the smart grid integration. Simulation, hardware-in-loop, and experimental results are presented to validate effectiveness of the controller.
TL;DR: In this article, the conduction and switching power loss in an active neutral-point-clamped (ANPC) flying capacitor multicell (FCM) converter is investigated.
Abstract: Multilevel converters are mainly used in medium-voltage high-power applications. Active neutral-point-clamped (ANPC) flying capacitor multicell (FCM) converter is a well-known type of multilevel converters which is commercially available in high-power medium-voltage motor drive market. Since power loss investigation can be very advantageous in the design phase of multilevel converters, this paper presents an analytical approach to calculate and investigate the conduction and switching power loss in ANPC-FCM converter. First, the RMS and average currents of insulated-gate bipolar transistors (IGBTs) and antiparallel diodes are analytically calculated by considering the associated duty cycle of each IGBT and diode, converter modulation index, load current, and load power factor. Numerical results of the derived closed-form equations to calculate the RMS and average currents of IGBTs/diodes are compared with simulation results and experimental measurements. Numerical results match the simulation results and experimental measurements which validates the derived closed-form equations. Afterward, the obtained equations for RMS and average current computations are utilized to calculate the conduction power losses in a 12.1-MVA 6.6-kV nine-level (line-to-line) ANPC-FCM multilevel converter. For this purpose, a 4.5-kV 1.2-kA IGBT module from ABB is considered as a power switch and its parameters are employed in analytical computations and simulation of the ANPC-FCM multilevel converter for conduction power loss determination. Moreover, closed-form equations are derived for analytical determination of switching power losses for ANPC-FCM converter using Kapteyn (Fourier-Bessel) series. Based on the derived closed-form equations for conduction loss and switching loss calculation, a method is presented to determine the junction temperature in IGBTs and diodes for ANPC-FCM converter.
TL;DR: In this paper, a small-footprint differential power processing (DPP) converter is integrated into a micro-inverter system to improve its energy capture by recovering power losses due to sub-module mismatch.
Abstract: Differential power processing (DPP) is a power electronics system architecture that configures dc–dc converters in parallel with the PV string to improve its power yield. The parallel nature of the DPP architecture brings a number of benefits, such as low converter power rating and low power losses, all of which make DPP especially suitable for submodule-level maximum power point tracking (MPPT). Meanwhile, microinverters typically perform only module-level MPPT and do not address power losses due to uncompensated submodule mismatch. In this paper, we introduce DPP converters into a microinverter system to improve its energy capture by recovering power losses due to submodule mismatch. The control method to interface DPP converters with a microinverter for submodule MPPT is presented and the tradeoff between tracking accuracy and control overhead is analyzed. A small-footprint DPP converter is designed. A digitally assisted windowed sensing technique is also implemented to address the challenge of precise current sensing. Altogether, the proposed solution seamlessly integrates DPP into the existing microinverter design. To demonstrate the effectiveness of the proposed solution, a hardware prototype has been built and tested with an off-the-shelf commercial microinverter. The improvement in energy capture with DPP converters has been experimentally verified.
TL;DR: A new method for deriving isolated buck-boost (IBB) converter with single-stage power conversion is proposed in this paper and novel IBB converters based on high-frequency bridgeless-interleaved boost rectifiers are presented.
Abstract: A new method for deriving isolated buck-boost (IBB) converter with single-stage power conversion is proposed in this paper and novel IBB converters based on high-frequency bridgeless-interleaved boost rectifiers are presented. The semiconductors, conduction losses, and switching losses are reduced significantly by integrating the interleaved boost converters into the full-bridge diode-rectifier. Various high-frequency bridgeless boost rectifiers are harvested based on different types of interleaved boost converters, including the conventional boost converter and high step-up boost converters with voltage multiplier and coupled inductor. The full-bridge IBB converter with voltage multiplier is analyzed in detail. The voltage multiplier helps to enhance the voltage gain and reduce the voltage stresses of the semiconductors in the rectification circuit. Hence, a transformer with reduced turns ratio and parasitic parameters, and low-voltage rated MOSFETs and diodes with better switching and conduction performances can be applied to improve the efficiency. Moreover, optimized phase-shift modulation strategy is applied to the full-bridge IBB converter to achieve isolated buck and boost conversion. What's more, soft-switching performance of all of the active switches and diodes within the whole operating range is achieved. A 380-V output prototype is fabricated to verify the effectiveness of the proposed IBB converters and its control strategies.