This paper presents a comprehensive review of multiport converters for integrating solar energy with energy storage systems. With recent development of a battery as a viable energy storage device, the solar energy is transforming into a more reliable and steady source of power. Research and development of multiport converters is instrumental in enabling this transformation in an efficient manner. The high efficiency of conversion in comparatively smaller footprint makes a multiport converter very attractive in this application. Most of the recently reported multiport converter topologies are discussed here. A breakdown of isolated and nonisolated topologies is presented along with the comparison of converter architectures and features such as operating conditions, device count, efficiency, etc. Each group of multiport converters is subdivided into different smaller groups based on their architecture. Detailed specifications are presented for important topologies. Finally, a performance comparison is carried out featuring the advantages and disadvantages of the various topologies leading to suggestions for the direction of future research.

Review of Multiport Converters for Solar and Energy Storage Integration

In this paper, a dual-transformer-based asymmetrical triple-port active bridge converter (DT-ATAB) is proposed to interface two different dc-sources and a load. DT-ATAB consists of three active power electronic converters and two high-frequency transformers. All switches of these converters can be turned on with zero-voltage switching to reduce the switching losses. The bidirectional power flow operation is possible between the ports. The DT-ATAB also reduces the circulating powers between the ports for well-matched transformer turns ratios as compared to those in the other existing triple-port active bridge converters (TAB). Furthermore, the magnetic short-circuit conditions arising in the three-winding transformer of the TAB are mitigated in DT-ATAB. The principle of operation, steady-state analysis, various modes of operation (three-port and two-port modes), and a closed loop controller of DT-ATAB are presented. The theoretical analysis of this paper is verified using both simulation and experimental studies. The illustrated results show that DT-ATAB can be used as a promising multiport converter to interface the multiple sources and load to achieve wide-ranging outputs with the minimal losses.

Dual-Transformer-Based Asymmetrical Triple-Port Active Bridge (DT-ATAB) Isolated DC–DC Converter

In this paper, the contemporary development in multiple input dc-dc converters are identified and examined. The quest to mitigate the difficulties associated with employing renewables in distribution systems and electric vehicles (EVs) has yielded many new converter topologies. These new topologies have easier control, lower parts count, are cheaper and are worthy alternatives to the typical series or parallel connection of converters. The converters are identified by three divisions that bother on the isolation between the respective ports. The electrically connected converters do not have isolation between the ports, and thus, a dc link connects the ports. Electromagnetically connected converters use a dc-link to connect input ports, but the input ports and output port are isolated. In magnetically connected converters, input ports are separated by multiple winding transformer, just as the output port is isolated from the input ports by the winding. The formation, structure, characteristics, operation, merits and demerits of the converters will be presented. Thereafter, comparisons will be done based on the distinct features of the converters. This review identifies that converter properties depend on the specific application requirement and thus, no converter fulfills all demands in the industry. Prospective future research trends are suggested. This work aims to update on research done during the time gap since the last comprehensive reviews.

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A review of multiple input DC-DC converter topologies linked with hybrid electric vehicles and renewable energy systems

In this paper, a family of three-port three-level converters (TPTLC) composed of asymmetrical bidirectional half-bridge modules is proposed, which offers the benefits in terms of a simple control scheme, extended soft switching over a wide range of operating conditions, and reduced voltage stress across switches. The proposed converters take advantage of a pulsewidth modulation plus phase shift control technique to regulate the output voltage as well as to control the power flow between different ports independently. A stacked TPTLC is taken as an example to be introduced in detail to gain a thorough insight into the proposed family of converters. The stacked TPTLC can provide a high voltage gain along with a wide voltage gain range without using any transformer, resulting in the improvement in the power density. In order to minimize the conduction loss and reduce the current stress of switches, the root-mean-square current of the inductor and the boundary condition of the phase-shift controller in different operation scenarios are studied. Finally, the feasibility of the proposed concept and effectiveness of the design approach are validated based on the experimental results of a 1-kW, 100-kHz prototype of the stacked TPTLC using gallium nitride switches.

A Family of Three-Port Three-Level Converter Based on Asymmetrical Bidirectional Half-Bridge Topology for Fuel Cell Electric Vehicle Applications

This article proposes modeling and two controller design techniques for a triple active bridge (TAB) three-port dc–dc converter comprising of fuel cell, battery, and load. The sources are integrated, employing boost interleaved full-bridge converters in order to get smoother source current profile. The converter is a nonlinear multi-input multi-output (MIMO) system with a large number of control variables. Moreover, a high degree of coupling among the control variables makes its modeling and control system design quite cumbersome and complex. To overcome the complexity of analysis in a higher order system like TAB, a generalized frequency-domain modeling technique is introduced in this article. A new decoupling matrix-based proportional-integral controller design method is also proposed. It reduces the design complexity and improves the system dynamic performance (lower settling time, overshoot/undershoot in the controlled variables) in comparison to similar three-port converters reported in the literature. Further, the performance of the proposed controller is compared by simulation with another popular MIMO system controller design technique, namely the state feedback control. A 1-kW laboratory prototype is built and tested to verify the system performance during dynamic load changes, source current variation, and battery charging/discharging operation.

Small Signal Modeling and Decoupled Controller Design for a Triple Active Bridge Multiport DC–DC Converter

A conventional transformer can withstand multiple electrical, mechanical and thermal faults which enables it to have a long lifetime. However, its inability to control the power flow through it has led researchers to look for alternate options such as the solid-state transformers. With the Silicon Carbide (SiC) semiconductor devices, it is now possible to go to high switching frequencies in medium voltage applications, which helps in reducing the overall size and weight of the transformer. The advent of medium voltage (MV) SiC devices has enabled the use of simple two-level and three-level topologies for medium voltage power transfer. This paper discusses a basic power topology for a medium voltage mobile utilities support equipment based solid state transformer (MUSE-SST) with the new 10 kV SiC MOS-FETs. A design of the MUSE-SST is presented followed by some of the practical considerations that needs to be taken, including gate driver design and heat sink configurations. Simulation results for a 100 kW, MV MUSE SST system is presented. Experimental results are provided validating the operation of these 10 kV devices in double pulse tests, buck and boost operation. This research helps in providing an overview regarding the usage of the 10 kV SiC devices in grid-interconnection and also discusses various challenges that comes along with it.

Design of a Medium Voltage Mobile Utilities Support Equipment based Solid State Transformer (MUSE-SST) with 10 kV SiC MOSFETs for Grid Interconnection

With the increasing maturity of Silicon Carbide (SiC) semiconductor devices at medium voltage (MV) level, high switching frequencies and low conduction losses in MV applications is possible. Higher switching frequency operation enables the reduction in size and weight of transformers. In an application such as MV-MV or MV-LV grid-interconnection, a solid state transformer offers a multitude of advantages compared to conventional transformers. A reduction in size and weight, in addition to having active and reactive power flow control have made SSTs a lucrative replacement to conventional low frequency (LF) transformers. Lower conduction losses exhibited by SiC devices (as compared to their silicon counterparts) have made it possible to achieve similar efficiencies as compared to conventional LF transformers. This paper aims at providing an overview of a MV MUSE-SST topology. A brief idea on control and monitoring is also provided. Practical design considerations that are required to build a MV system is provided to aid researchers in designing converters for MV applications. The protection aspects of the MV MUSE-SST system is also highlighted. Basic experimental results for the gate driver is also shown. Initial testing results with the Gen3 10 kV SiC MOSFETs and the challenges associated with it are also discussed. This research aims at being a building block for implementation and testing of the medium voltage converter systems.

Mobile Utility Support Equipment based Solid State Transformer (MUSE-SST) for MV Grid Interconnection with Gen3 10 kV SiC MOSFETs

Several applications such as power supplies for electric precipitators, ozone generation, partial discharge, etc., require ac superimposed dc (ACsDC) voltage supply. Most of such applications use intransigent systems for producing ACsDC voltages. In this paper, three different kinds of flexible power electronic converters are proposed for producing ACsDC voltages. These converters have two power conversion stages: input and output. In the input stage, two isolated dc voltages are obtained by using an isolated three-port dc–dc converter or two isolated two-port dc–dc converters. In the output stage, one of the input-stage dc voltages is used to generate an ac voltage and the obtained ac voltage is added to the remaining input-stage dc voltage to obtain an ACsDC voltage. Based on the converters used in the input stage, the proposed ACsDC converters are named as a dual active bridge (DAB) converter-based ACsDC converter (DAB-ACsDC), triple port active bridge (TAB) converter-based ACsDC converter (TAB-ACsDC), and dual transformer-based asymmetrical triple port active bridge (DT-ATAB) converter-based ACsDC converter (DTATAB-ACsDC). A detailed analysis of these ACsDC converters and their verifications using simulations and experimental studies are presented, which depict that the proposed converters can be used effectively for producing ACsDC voltages.

Flexible Power Electronic Converters for Producing AC Superimposed DC (ACsDC) Voltages

Integration of multiple power sources using power electronic converters and high-frequency isolation links to supply the sustainable electricity is expected to have a significant impact on the future power system. In this paper, a triple port active bridge converter (TAB) based multi-fed power electronic transformer (TMF-PET) is proposed. The proposed PET consists of three ports having the flexibility to connect the power generating units, grid, and loads. The TMF-PET have three power conversion stages: input, isolation, and output. The input stage consists of two active rectifiers for integrating two different ac sources. The isolation stage consists of a triple port active bridge, and the output stage consists of an inverter. A detailed analysis of the principle of operation and the control techniques used for the converters of these stages are presented. The efficacy of the proposed system is verified using the simulation and experimental studies. The illustrated results show that the discussed controllers of TMF-PET are able to maintain the desired powers and voltages at the inputs and outputs of different power conversion stages. As a result, the proposed system can be used as an efficient energy router to interface different sources and loads in the modern power distribution systems.

Venkat Nag Someswar Rao Jakka

Papers

Dual-Transformer-Based Asymmetrical Triple-Port Active Bridge (DT-ATAB) Isolated DC–DC Converter

Design of a Medium Voltage Mobile Utilities Support Equipment based Solid State Transformer (MUSE-SST) with 10 kV SiC MOSFETs for Grid Interconnection

Mobile Utility Support Equipment based Solid State Transformer (MUSE-SST) for MV Grid Interconnection with Gen3 10 kV SiC MOSFETs

Flexible Power Electronic Converters for Producing AC Superimposed DC (ACsDC) Voltages

A triple port active bridge converter based multi-fed power electronic transformer