Review of multiport power converters for distribution network applications

Multiport power converters integrate three or more energy devices into a single (potentially highly controllable and efficient) hub. These characteristics suggest that multiport power converters may be valuable for the decarbonisation of distribution networks, where the increase of converter-interfaced devices has degraded system reliability and efficiency. This review analyses the suitability of a wide range of multiport power converter solutions for four example distribution network applications (where previous studies have focussed on a limited range of topologies or applications) and the research areas that can progress their maturity. A review of grid codes and standards overviews the base capability that multiport power converters are likely to require, some of which are carried forward as requirements for a novel comparison tool. The comparison tool is developed to qualify and score reviewed topologies in terms of a range of features that are weighted for the applications. Isolated and partially-isolated topologies perform well due to their flexibility to be configured for the specifications and their operational capabilities (including modularity and voltage decoupling). Further research should focus on the complex control interactions between ports and scaling of these topologies for medium voltages. In contrast, many direct current non-isolated topologies do not qualify due to their low flexibility to be configured for the applications. This suggests that future research could focus on the development of a more flexible non-isolated multiport power converter configuration to take advantage of the high efficiency and low footprint that these topologies might otherwise offer for low voltage applications

A Four-Port Bidirectional DC-DC Converter for Renewable Energy System and Microgrid

Renewable energy has nowadays become important in electrical power applications. Power converters play an important role in integrating these distributed energy sources. However, due to their intermittence characteristics, e.g., the output power provided by the PV and wind turbine is not stable, either an energy storage system will be used or microgrid is formed between the main grid and the sources. To integrate these renewable energy sources and manage the power flow, a multiport converter is preferred because it is highly beneficial and cost-efficiently than the traditional solution that using multiple individual power converter for each source. This thesis proposed a novel four-port bidirectional DC-DC converter with a battery storage system, which uses phase-shift control of two active bridges connected through two transformers. Compared with the traditional multiport converters, the proposed four-port converter uses the least number of power switches and zero-voltage switching (ZVS) for all the switches can be realized. The design and effectiveness of controllers are validated by experimental results. The converter can work in different scenarios regardless of the availability of renewable energy and the state-of-charge of the battery. In addition, maximum power point tracking for renewable energy sources can be achieved for each renewable energy source while managing the power flow of the battery

A Comprehensive Review of DC-DC Converters for EV Applications

DC-DC converters in Electric vehicles (EVs) have the role of interfacing power sources to the DC-link and the DC-link to the required voltage levels for usage of different systems in EVs like DC drive, electric traction, entertainment, safety and etc. Improvement of gain and performance in these converters has a huge impact on the overall performance and future of EVs. So, different configurations have been suggested by many researches. In this paper, bidirectional DC-DC converters (BDCs) are divided into four categories as isolated-soft, isolated-hard, non-isolated-soft and non-isolated-hard depending on the isolation and type of switching. Moreover, the control strategies, comparative factors, selection for a specific application and recent trends are reviewed completely. As a matter of fact, over than 200 papers have been categorized and considered to help the researchers who work on BDCs for EV application

Design and implementation of multi-port DC-DC converters for electrical power systems

The thesis proposes developing, analysing, and verifying these DC-DC converters to improve the current state-of-the-art topology. Four new DC-DC converters for applications like light emitting diode, lighting microgrids DC, PV applications, and electric vehicles are as follows. In this study, the two-input converter is presented. The two-input converter that has been proposed serves as the interface between the two input sources and load. Using two switches and two diodes, the proposed converter minimises switching losses and contains eight components in total, making it compact and low volume. As a result, the highest average efficiency is 92.5%, and the lowest is 89.6%. In this research, the new three-port converter that has been proposed serves as the interface between the input source, a battery, and a load. In addition, the converter is suitable for use in standalone systems or satellite applications. A low-volume converter is designed with three switches and two diodes, thereby minimizing switching losses and ten components in total. Regarding efficiency, the highest average is 92.5%, and the lowest is 90.9%. Also, this study proposes a single-switch high-step-up converter for LED drivers and PV applications. A further benefit of the proposed converter over conventional classical converters is that it utilises only one active switch. These results align with simulation results, and its gain is 6.8 times greater than classical converters. Furthermore, stress across switches and diodes is smaller than the output voltage, approximately 50%. Semiconductor losses were limited with a low duty cycle of 0.7. This makes the highest average efficiency 95% and the lowest 93.9%. The new four-port converter is presented for applications such as microgrid structures and electric vehicles. As part of the integrated converter, two or three converters are combined by sharing some components, such as switches, inductors, and capacitors, to form a single integrated converter. As a result of the four-port converter proposed, battery power can be managed, and output voltage can be regulated simultaneously

Two new families of high-gain DC-DC power electronic converters for DC-microgrids

Distributing the electric power in dc form is an appealing solution in many applications such as telecommunications, data centers, commercial buildings, and microgrids. A high gain dc-dc power electronic converter can be used to individually link low-voltage elements such as solar panels, fuel cells, and batteries to the dc voltage bus which is usually 400 volts. This way, it is not required to put such elements in a series string to build up their voltages. Consequently, each element can function at it optimal operating point regardless of the other elements in the system. In this dissertation, first a comparative study of dc microgrid architectures and their advantages over their ac counterparts is presented. Voltage level selection of dc distribution systems is discussed from the cost, reliability, efficiency, and safety standpoints. Next, a new family of non-isolated high-voltage-gain dc-dc power electronic converters with unidirectional power flow is introduced. This family of converters benefits from a low voltage stress across its switches. The proposed topologies are versatile as they can be utilized as single-input or double-input power converters. In either case, they draw continuous currents from their sources. Lastly, a bidirectional high-voltage-gain dc-dc power electronic converter is proposed. This converter is comprised of a bidirectional boost converter which feeds a switched-capacitor architecture. The switched-capacitor stage suggested here has several advantages over the existing approaches. For example, it benefits from a higher voltage gain while it uses less number of capacitors. The proposed converters are highly efficient and modular. The operating modes, dc voltage gain, and design procedure for each converter are discussed in details. Hardware prototypes have been developed in the lab. The results obtained from the hardware agree with those of the simulation models. --Abstract, page iv

Topology Derivation and Development of Non-Isolated Three-port Converters for DC Microgrids

Currently, three-port converters (TPCs) are gaining popularity in applications which integrate renewable energies, such as photovoltaics and wind, and energy storage elements, such as batteries and supercapacitors with load. This is due to the advantages of a single power conversion stage between any two ports for better conversion efficiency and a highly integrated structure for compactness. Most of the reported TPCs focus on the consuming load. However, there are applications such as hybrid-electric vehicle braking systems and DC microgrids which have power generating capability. A typical example is battery charging in a DC microgrid. When the photovoltaics has inadequate power to charge the battery, the TPCs that consider only consuming load need an extra DC/DC converter for the DC bus to charge the battery. Three-winding transformers associated with full-bridge configurations as the basis for TPCs can fulfill the purpose of bi-directional power flow between any two ports. However, bulkiness of transformers and the need for more switches and associated control mechanisms increases the converter complexity, volume and cost. Solutions for integrating a regenerative load in NITPCs are still limited. This research work focuses on the development of non-isolated three-port converters (NITPCs), as they are capable of driving a regenerative load while offering a compact solution. The study includes a systematic approach to deriving a family of NITPCs. They combine different commonly known power converters in an integrated manner while considering the voltage polarity, voltage levels among the ports and overall voltage conversion ratio. The derived converter topologies allow for all possible power flow combinations among the sources and load while preserving the single power processing feature of the TPC. A design example of a boost converter based TPC with a bi-directional buck converter is reported. In addition, a novel single-inductor NITPC is proposed. It is a further integrated topology according to the aforementioned design example where only one inductor is required instead of two, and the number of power transistors remains the same. The detailed topological derivation, operation principles, steady-state analysis, simulation results and experiment results are given to verify the proposed NITPCs

Development of Multiport Single Stage Bidirectional Converter for Photovoltaic and Energy Storage Integration

The energy market is on the verge of a paradigm shift as the emergence of renewable energy sources over traditional fossil fuel based energy supply has started to become cost competitive and viable. Unfortunately, most of the attractive renewable sources come with inherent challenges such as: intermittency and unreliability. This is problematic for today\u27s stable, day ahead market based power system. Fortunately, it is well established that energy storage devices can compensate for renewable sources shortcomings. This makes the integration of energy storage with the renewable energy sources, one of the biggest challenges of modern distributed generation solution. This work discusses, the current state of the art of power conversion systems that integrate photovoltaic and battery energy storage systems. It is established that the control of bidirectional power flow to the energy storage device can be improved by optimizing its modulation and control. Traditional multistage conversion systems offers the required power delivery options, but suffers from a rigid power management system, reduced efficiency and increased cost. To solve this problem, a novel three port converter was developed which allows bidirectional power flow between the battery and the load, and unidirectional power flow from the photovoltaic port. The individual two-port portions of the three port converter were optimized in terms of modulation scheme. This leads to optimization of the proposed converter, for all possible power flow modes. In the second stage of the project, the three port converter was improved both in terms of cost and efficiency by proposing an improved topology. The improved three port converter has reduced functionality but is a perfect fit for the targeted microinverter application. The overall control system was designed to achieve improved reference tracking for power management and output AC voltage control. The bidirectional converter and both the proposed three port converters were analyzed theoretically. Finally, experimental prototypes were built to verify their performance