Multiport Converter Research Articles

Comparison of cascaded modular converter and central Multi-Port converter for modularization of battery packs

The modularization of battery packs for grid-scale applications reduces the number of series-connected cells, lightens the load on battery management systems, and improves their reliability. The complete modular structure can be achieved by connecting each battery module to its corresponding converter and connecting the converters in series. An alternative strategy is that the battery packs can be modularized with the help of complementary switches in a multi-port converter. In this paper, these two modularized battery energy storage systems will be investigated and compared in terms of the required number of components, their ratings, and the efficiency, reliability, and flexibility in power sharing.

A Nonisolated Multiport Converter Based on LLC and Bidirectional Buck/Boost for Low Power EH-Battery Systems

Concerning about integration and high efficiency of topology, nonisolated multiport converters are widely researched in low power Energy-Harvesting-battery (EH-battery) systems. However, the pulse width modulation (PWM) based nonisolated multiport converters usually have the shortages of larger number of switches, ports’ voltage restrictions, hard switching, time-sharing transmission of energy and poor compatibility of MPPT algorithms. Therefore, in this article, a transformer-less multiport converter based on LLC and bidirectional buck/boost converter is proposed, which has the ability to step up and down voltage and well compatibility of MPPT. Meanwhile, soft switching technology is applied so that the converter can work in higher frequency and has smaller size. In addition, the energy can be transmitted simultaneously with the control of PWM and pulse frequency modulation (PFM). Finally, the experimental results of the proposed topology and its comparison with several topologies are given to prove the characteristics of the proposed converter

Multiport Converter for CubeSat

Maximizing solar energy harvesting and miniaturizing DC-to-DC converters will be a difficult task for the CubeSat that operates in low earth orbit (LEO), where size and weight are limited. To maximize solar energy collection, the electrical power system (EPS) architectures use numerous separate DC–DC converters, which will be problem for miniaturization of whole model because several inductors will be used in each converter. The key purpose of this article is to demonstrate a topology of multiport converter that requires only one inductor and a small number of components, reducing the overall system size. The proposed system will have half-bridge modules with series connection, connected parallelly with PV panels will power the battery system through a DC-DC boost converter. On considering the 1U CubeSat standards a prototype is used to verify the performance of the proposed converter in numerous case scenarios.

Dual-AC-port modular multilevel converter for hybrid frequency integration of offshore wind power: Modeling and control

Low frequency AC transmission system (LFAC) is a potential solution for deep-sea offshore wind power utilization besides HVAC and HVDC. Multi-port converter is the key device for the interconnection of hybrid frequency wind farms and power grid. An improved multi-port modular multilevel converter with dual AC ports and single DC port (DASD-MMC) is proposed as the key device for the interconnection among HVAC/HVDC/LFAC. The in-depth topology and working principle analysis are presented. The partitioned nearest level modulation method is proposed for high-voltage applications providing submodule capacitor voltage self-balancing ability. The mathematical model and the corresponding decoupling control strategy are presented afterward to realize the free power transfer among the three ports. To solve the output performance issues for hybrid HVAC and LFAC scenarios, an output current distortion suppression strategy is proposed with a novel cross-decoupling harmonic extraction method. Circulating current control strategy is presented with consideration of essential component analysis and calculation. Experiment and simulation validation and discussion are given, which show that the proposed DASD-MMC could provide a high quality hybrid frequency solution for offshore wind power collection and transmission.

A Modular Multiport Converter to Integrate Multiple Solar Photo-Voltaic (PV) Modules With a Battery Storage System and a DC Microgrid

A modular multiport converter (MMPC), which is capable of interfacing multiple solar Photo-Voltaic (PV) modules, a battery bank, and a dc microgrid, is proposed in this article. The number of solar PV modules that can be interfaced with the proposed MMPC is equal to the number of converter modules present in the system. Furthermore, all these solar PV modules can operate at their respective maximum power point, thus increasing the power extraction capability. A high-frequency transformer facilitates the interfacing of low-voltage solar PV modules and the battery bank with a 380-V microgrid. However, the power from the solar PV modules to the battery bank does not flow through this transformer. The variation in the transformer utilization with changes in operating voltages of the solar PV modules is analyzed. Detailed simulation studies are carried out on a system having five solar PV modules to verify the performance of the proposed MMPC. A laboratory prototype of the proposed MMPC consisting of four numbers of 400-W converter modules is fabricated. The performance of the MMPC is analyzed and the experimental results are presented.

Topology synthesis and control of integrated three-port converter for renewable energy system

This paper presents topology synthesis and control of a non-isolated three-port dc-dc Cuk converter (TPCC) for a renewable energy system (RES). The proposed control structure is composed of a decoupling network to address the inevitable cross-coupling effect of multiport converters present due to various interacting control loops. In addition, a PI-lead compensator is designed to achieve improved steady-state and transient performance in each operating mode of TPCC. Furthermore, an autonomous mode selection (AMS) technique is proposed to achieve a seamless transition between different operating modes. The AMS technique automatically shifts the operating modes of TPCC by comparing the available instantaneous power at each port to maintain an uninterruptable power supply to the load. Moreover, a state-space averaging method is adopted for modeling different operating modes and transfer functions of TPCC. Finally, the feasibility and effectiveness of the proposed control algorithm are validated with the help of a laboratory prototype.

Dual Active Bridge Based Reduced Stage Multiport DC/AC Converter for PV-Battery Systems

Standalone power systems are significant for electrifying the remote areas where extending the grid connectivity is not feasible, either economically or logistically. Solar Photovoltaic (PV) systems with battery backup are among the most popular candidates to serve as an energy source in standalone systems. This article presents a novel multiport converter (MPC) for PV-battery systems powering standalone loads. The proposed converter is a reduced stage power converter based on current fed dual active bridge (CF-DAB) topology. CF-DAB offers galvanic isolation and a high voltage ratio without sacrificing efficiency. Switching losses are further reduced by a modified modulation scheme that reduces the average switching frequency of some of the switches. The proposed converter performs the functions of tracking maximum power point of the solar panel and regulating the load voltage while using fewer power conversion stages. This is done by sharing components among the various stages performing maximum power point tracking, voltage boosting, and dc/ac conversion. A small-signal model of the proposed MPC required for its closed-loop control is also proposed, which can also be utilized for other CF-DAB-based converters. A lab prototype of the proposed MPC has been fabricated and its operation has been validated under various static and dynamic conditions.

Development of Multi-Port Converter with Square-Wave-Voltage Multilevel Converter and Active Power Filter Connected in Series

Development of Multi-Port Converter with Square-Wave-Voltage Multilevel Converter and Active Power Filter Connected in Series

A Modular Multifunction Power Converter Based on a Multiwinding Flyback Transformer for EV Application

In this article, a revolutionary and novel single-stage, multiport power conversion block is proposed. The power conversion concept is based on a bidirectional flyback converter with four-quadrant switches that permit us to seamlessly control the direction of the energy flow and to select which ports are active. This approach, denominated as multicell multiport bidirectional flyback (M2BF), can be used as a modular and a multifunction building block interfacing ac and dc sources and loads in complex conversion systems like the one we can encounter in electric vehicle (EV) applications. The multiport property is obtained due to the multiwinding flyback transformer that interfaces different sources and loads in a simple and effective way. We present and analyze this concept in detail, focusing on different operation modes it can provide (multiport dc–dc conversion, ac–dc conversion, vehicle-to-grid, grid-to-vehicle, and so on) and their possible implementation in the energy distribution network of an EV, where this unique multifunction multiport converter could bring an important breakthrough. The operating principles of the M2BF for different operating modes are described and analyzed, placing emphasis on the modularity of the proposed concept. The overall concept is evaluated and quantified using a gallium nitride (GaN)-based prototype achieving efficiencies higher than 91% that additionally validates the proposed idea experimentally. The presented analysis and experimental results clearly identify the advantages and limitations of the presented concept leaving no doubt about its usefulness to the future EV distribution network.

Topological review of hybrid RES based multi‐port converters

Depletion of natural resources like gas, oil, coal along with environment pollution increased the popularity of the Renewable Energy Sources (RES). Power Electronic converters are utilized for conversion of power from RES to coordinate the stand-alone load and utility grid. MPPT control is also established by these converters to supply the standalone or grid-connected load despite of the RES's unpredictable nature. In order to reduce the number of switches used for integrating RES to drive loads, Multi-port converters are developed. These converters have the capability to supply more than one load simultaneously. Furthermore, more number of RESs are connected using these converters in order to drive common loads. Available literatures do not explain in detail regarding various types of multi-output converters, their advantages, disadvantages, application area and control techniques used in order to drive these converters. In this context, a review of recent advances in multi-port DC-DC converters for different application using hybrid RESs is carried out. Initially in literature, few DC-DC converters are connected in parallel, series configuration and used as multi-port converters. Multi-stage conversion is realized using DC-AC-DC conversion. Advantages of conventional converters are integrated in order to develop derived multi-output converters. These multi-port converters have the capability to drive both DC and AC loads from a single DC input source. The converters share common power electronics equipment while generating both DC and AC power simultaneously. Furthermore, these multi-port converters also use single step power conversion process which reduces the overall system loss. As these hybrid multi-port converters use lesser number of power electronic switches, the control complexity of these converters reduces compared to the conventional converters connected in cascaded or parallel manner to drive loads. A detailed review of these multi-port converters with respect to topologies, and operating principle, diverse reliability and effectiveness are presented in this paper. This survey helps designers to select the appropriate RES-based multi-port converters for their respective applications.

Multiport converter integrating automatic current balancing interleaved PWM converter and DAB converter with improved transformer utilization for electric vehicles

AbstractMultiport converters (MPCs) that integrate multiple converters into a single unit have been proposed to reduce the converter count in electric vehicle power systems where multiple batteries are employed. However, conventional MPCs comprising a dual active bridge (DAB) converter and an interleaved PWM converter require feedback control loops and current sensors to balance the inductor currents. Furthermore, the transformer utilization decreases as the duty cycle of the interleaved PWM converter drifts away from 0.5. This paper proposes a novel MPC that integrates a DAB converter and an interleaved PWM converter with an automatic current balancing capability and improved transformer utilization. A 1‐kW prototype with a half‐bridge or full‐bridge circuit on the high‐voltage side was built for the experimental verification, and loss analysis was performed. The results demonstrated the automatic current balancing capability, improved transformer utilization, and flexible power exchange among three ports.

A novel multiport converter switching scheme to integrate multiple renewable energy sources

SummaryIn this paper, an innovative switching scheme named simultaneous space vector modulation (SSVM) is proposed for integrating various AC sources in the energy industry using a unified multiport converter. The proposed SSVM technique is applied to the multileg topology of a multiport converter, which is an encouraging option for the grid integration of renewable energy sources and multimachine drives. Considering the shared leg in the multileg converter, the proposed SSVM can utilize the utmost simultaneous switching states between different ports, resulting in lower switching loss and better DC‐link voltage utilization compared with the conventional sequential space vector modulation approach. A novel decision matrix concept is introduced to identify the simultaneous switching states. For this aim, according to the number of ports of the multileg converter, decision matrices containing valid simultaneous switching states are first calculated. Then, they are defined as look‐up tables in the proposed SSVM to be retrieved and exploited in every sampling period. The effectiveness of the proposed SSVM for a seven‐leg version of the multileg converter is assessed using the simulation analysis and real‐time validation. The capability of the proposed SSVM‐based multiport converter in grid integration of AC renewable energy sources is also verified considering two permanent magnet synchronous generator (PMSG)‐based wind turbines with real wind speed patterns. The simulation results confirm that the proposed SSVM is properly able to manage the power flow between different ports and improve the DC voltage utilization and switching loss compared with the sequential SVM.

A gridded modular bidirectional high voltage gain soft‐switching DC–DC converter and its multiport expansion

Here, a novel modular bidirectional high voltage gain soft-switching DC–DC converter is proposed. The proposed converter named gridded modular high-gain soft-switching DC–DC converter (GMHSC) can achieve wide range expansion of port voltage and voltage gain by gridded filling of modules and achieve voltage and current sharing among these modules. In addition, all semiconductor devices also realize full-load soft-switching operation in both power directions by introducing a simple auxiliary zero-current transaction (ZCT) cell in each module. A distributed control system including a centre controller and localized module controllers is proposed to improve the converter's design flexibility and dynamic performance. Moreover, the GMHSC is able to provide multiple fixed voltage nodes, which makes it suitable to expend to a multiport converter. A 1.6 kW 200 kHz experimental prototype based on SiC device is provided to achieve an efficiency of 97.9% and 97.7% in boost and buck modes, respectively. Furthermore, the input current and output voltage ripples are greatly reduced through interleaved operation of the GMHSC.

Grid integration of multiple wind turbines using a multi-port converter—A novel simultaneous space vector modulation

In this paper, an innovative approach of integrating multiple doubly-fed induction generator (DFIG)-based wind turbines using a single multi-port converter unit, named as a unified expandable power converter (UEPC) is presented. A novel partial simultaneous space vector modulation (PSSVM) scheme, adopted to the unified structure, is proposed to enhance the operational efficiency and DC-link utilization. The unified configuration can integrate two or more DFIGs through a multi-port converter in a cost-effective and efficient way. The unified structure enjoys compactness, plug & play capability, fewer switches, and a lower installation cost. Comparing with the conventional sequential space vector modulation (SSVM), which only uses the individual active vectors, the proposed PSSVM can utilize common active vectors between different ports, which is the main salient feature of this method. The performance of PSSVM is also validated via an OPAL-RT real-time simulator. The real-time outcomes prove that the proposed PSSVM can improve the DC-link voltage utilization and switching loss compared with the SSVM. The effectiveness of the proposed PSSVM based unified configuration in both normal and faulty conditions are evaluated and compared with the conventional structure using MATLAB/Simulink. The simulation results endorse the finding that regardless of the shared switches in the unified expandable power converter, the independent control and maximum power extraction from the wind are guaranteed using the proposed PSSVM.

A Comprehensive Review of Power Converter Topologies and Control Methods for Electric Vehicle Fast Charging Applications

Wide-scale adoption and projected growth of electric vehicles (EVs) necessitate research and development of power electronic converters to achieve high power, low-cost, and reliable charging solutions for the EV battery. This paper presents a comprehensive review of EV off-board chargers that consist of ac-dc and dc-dc power stages from the power network to the EV battery. Although EV chargers are categorized into two types, namely, on-board and off-board chargers, it is essential to utilize off-board chargers for dc fast and ultra-fast charging so that volume and weight of EV can be reduced significantly. Here, we discuss the state-of-the-art topologies and control methods of both ac-dc and dc-dc power stages for off-board chargers, focusing on technical details, ongoing progress, and challenges. In addition, most of the recent multiport EV chargers integrating PV, energy storage, EV, and grid are presented. Moreover, comparative analysis has been carried out for the topologies and the control schemes of ac-dc rectifiers, dc-dc converters, and multiport converters in terms of architecture, power and voltage levels, efficiency, bidirectionality, control variables, advantages, and disadvantages which can be used as a guideline for future research directions in EV charging solutions.

Comparative Assessment of Multi-Port MMCs for High-Power Applications

Multi-port converters can interconnect different dc and ac systems while reducing semiconductor requirements and losses by eliminating redundant power conversion stages. Modular multilevel converter (MMC)-based multiport systems are well suited for application in mixed ac-dc grids containing high-voltage dc (HVDC) and medium-voltage dc (MVDC) systems. This paper conducts a detailed comparative assessment of multi-port dc-dc-ac MMCs for high power applications. Four representative topologies are chosen for study due to their contrasting internal power processing characteristics. Three different network scenarios are investigated that include HVDC and MVDC applications, covering several different power flow cases. The multi-port MMCs are compared in terms of losses, semiconductor effort, internal energy storage and magnetics requirements. The results are extensively discussed and general conclusions are summarized.

A multi-port non-isolated bidirectional DC-DC converter

A multi-port non-isolated bidirectional DC-DC converter

Integrated Multiport DC-DC and Multilevel Converters for Energy Sources

This paper presents a novel converter system for integrating multiple renewable energy sources for both dc and ac grids. The proposed converter system is formed by integrating a novel multiport dc converter topology with a multilevel inverter topology, aiming to achieve multiple source integration with low component count and higher efficiency on the multiport converter section and efficient dc to ac conversion on the multilevel inverter section. As compared to counterparts in literature, where each energy source requires its own dc converter and the dc to ac conversion is achieved using a two-level converter, the converter system proposed in this paper has more attractive features of buck-boost operation, better power quality characteristics and low part counts. Within the framework, an auxiliary circuit-based dc link voltage balancing technique is proposed to balance the voltage on the dc link as compared to the more complex control-based balancing scheme. Open and closed loop operations of the converter system are numerically verified using simulations and validated by a high-fidelity hardware-in-the-loop implementation platform.

A Qualitative Investigation on Multiport Converters for Renewable Energy Sourced DC Loads

A Qualitative Investigation on Multiport Converters for Renewable Energy Sourced DC Loads

A Novel Multiport Converter Interface for Solar Panels of CubeSat

Maximization of solar energy harvest and miniaturization of dc–dc converters are essential for low earth orbit (LEO) CubeSats, which are constrained by volume and weight restrictions. The state-of-the-art electric power system (EPS) architectures utilize several individual dc–dc converters to maximize solar energy harvest but it has a tradeoff with miniaturization as it requires several inductors. The main objective of this article is to propose a single-inductor-based multiport converter topology for the LEO CubeSat's EPS. The proposed topology interfaces the photovoltaic (PV) panels to the energy storage system and a control strategy have been developed to extract maximum solar power from each PV panel under wide varying irradiation conditions of the LEO CubeSat. The proposed topology consists of series-connected half-bridge modules fed by PV panels and their output is supplied to the energy storage system via a boost converter. The principle of operation is introduced followed by steady-state analysis and converter dynamics analysis. The performance of the proposed converter is verified for several case studies with an experimental prototype developed based on 1U CubeSat specifications.