A tri-state 4 switch bi-directional converter for interfacing super-capacitors to DC nano-grids

Supercapacitors are energy storage devices that can contribute with a fast varying current for the regulation of DC grids. However, their power electronics interface should present fast dynamic response as well, what is not exactly the case for the conventional 2-switch buck-boost bi-directional DC-DC converter operating with conventional dual-state modulation scheme. Besides, if the DC grid voltage happens to fall below the supercapacitor voltage, the anti-parallel diodes of the converter conduct and one loses control of the current injected into the DC grid. The alternative considered in this thesis is a 4-switch bi-directional DC-DC converter with an intermediate inductor, which allows the implementation of a tri-state logic that eliminates the RHP zero of the transfer function Iout/D, thus allowing the design of a fast acting controller. However it does not provide a solution for the earlier problem of losing control when grid voltage falls below the supercapacitor voltage. One alternative is to use the same 4-switch converter in the buck-boost mode using tri-state logic, which allows the input voltage to be lower or higher than the grid voltage while eliminating the RHP zero at the same time. This work presents a dynamic model for the 4-switch tri-state converter operating in the boost and buck-boost mode and connected to a droop-controlled DC micro-grid. The tri-state has essentially 3 stages, wherein the Off state length is kept constant. Based on this control approach, there are 2 possible sequences, for which a thorough analysis has been done. Further, the component sizing, selection of various parameters and control loop design for a tri-state system operating with boost mode of operation for higher voltage gain requirement (supercapacitor voltage is significantly lower than DC bus voltage), and with buck-boost mode of operation for low voltage gain requirement (supercapacitor voltage is slightly lower than, equal to or higher than DC bus voltage), is discussed. The simulation result for both modes of operation is presented as well showing an improved performance when compared to the conventional dual-state scheme. Finally, an experimental implementation of the converter is done and results for the same are provided to verify those described by theoretical analysis as well as simulation results

Multi-mode tri-state operation of a 4-switch bidirectional DC-DC converter for interfacing a supercapacitor to a DC grid

Energy storage devices such as supercapacitors and batteries are frequently used to support DC nanogrids that employ renewable resources. They make the system more stable and reliable, by contributing to power balance with high charge/discharge rates. The 2-switch class C DC-DC converter with dual-state logic is widely used as the interface for supercapacitors to a DC nano grid. It presents slow dynamic response due to the Right-Half Plane (RHP) zero in the transfer function of Vo/D in Boost mode, when supercapacitors supply power to the DC grid. This converter also faces an issue of losing current control when the voltage of the supercapacitor is higher than that of the DC nanogrid. A 4-switch bidirectional DC-DC converter in the Buck-Boost mode that consists of two half-bridges and an intermediate inductor can be used as the interface. By using tri-state logic with fixed Doff, it can eliminate the RHP zero in the transfer function Io/ Don and control the current flow all the time. However, the voltage gain of the output voltage over the supercapacitor’s voltage decreases because of the fixed Doff, which is an issue when the converter only operates in one mode and the supercapacitor voltage changes between half voltage (24 V) to rated voltage (48 V). Thus, the mode must be changed between Boost and Buck-Boost modes as the voltage in the supercapacitor varies. The tri-state logic can present different sequences with the three states Don, Doff, and Dfw. Thus the traditional pulse width modulation (PWM) technique using one modulating signal Don cannot be used in the tri-state logic. This thesis proposes a flexible space vector modulation scheme, which concerns the modes of operation, the sequences of the tri-states, and the state of each switch. A smooth mode transition logic is presented to reduce the output current variation when the mode changes between the Boost and Buck-Boost modes. The main goal of this work is to regulate the output current at a set value, while the converter changes between the Boost and Buck-Boost modes as a function of the voltage gain (Vo/Vin) with the input voltage varying in a wide range. The analysis of the system and design of controllers are presented and verified. Simulation results iv with the proposed modulation scheme and smooth mode transition logic, as well as experimental implementation, are presented and discussed

Fault Ride-Through Power Electronic Topologies for Hybrid Energy Storage Systems

This work presents a fault ride-through control scheme for a non-isolated power topology used in a hybrid energy storage system designed for DC microgrids. The hybrid system is formed by a lithium-ion battery bank and a supercapacitor module, both coordinated to achieve a high-energy and high-power combined storage system. This hybrid system is connected to a DC bus that manages the power flow of the microgrid. The power topology under consideration is based on the buck-boost bidirectional converter, and it is controlled through a bespoke modulation scheme to obtain low losses at nominal operation. The operation of the proposed control scheme during a DC bus short-circuit failure is shown, as well as a modification to the standard control to achieve fault ride-through capability once the fault is over. The proposed control provides a protection to the energy storage systems and the converter itself during the DC bus short-circuit fault. The operation of the converter is developed theoretically, and it has been verified through both simulations and experimental validation on a built prototype

SIZING AND SIMULATING OF AN AUTONOMOUS PUBLIC LIGHTING SYSTEM

According to the current energetic situation of the world, it arises with a strong intensity, the need of researching and using new alternative energy sources in order to be used as a complement of the actual power supply system, combined with the aware of decreasing environmental impacts.This paper presents the sizing and the simulation of an autonomous led lighting system, composed of supercapacitors as energy storage elements to be used as street lighting for pedestrians. This system can be devised into two different blocks. The first block consists in a photovoltaic panel; a Buck DC/DC converter; supercapacitors and a MPPT controller, which has the main purpose of managing the functioning of the led lighting, using the algorithms of constant voltage in order to find the MPPT point of the photovoltaic panel. Furthermore, the second block contains a Boost DC/DC converter; an assortment of high efficiency led lights and a PWM controller.In this context, the aim of this paper consist of presenting the feasibility of the use of the supercapacitor as an energy storage element and the presentation of a new public lighting system, in order to achieve a better use of power supplied by a solar panel using a second Buck DC/DC converter.The results have been obtained by the use of the Matlab software, which led to a conclusion that the system is efficient and it meets all the needs proposed before.

Development of a Step Down DC-DC Converter for Power Grid Energy Harvesting

This work contains an analysis of multiple topologies of DC-DC voltage buck con verters. The main goal of this Thesis is to study and design a functioning Step Down converter for capacitive coupling devices used for energy harvesting from the power AC grid. In order to achieve this goal, multiple topologies and circuits of this type of converter are studied and analysed, so that the requirements for the intended application are met. Since the input is obtained from the AC power grid and the output is connected to a supercapacitor, this results in a large input voltage (over 150V) and a low output voltage (between 1V to 3V), therefore the converter requires a step down voltage conversion ratio of around 130. The DC-DC converter should also have a large input impedance (around 50Mohm) to maximize the energy transferred from the power grid. This mode of operation is not common for regular inductance based DC-DC converters, making this a challenging problem. Moreover, since the amount of energy available from the capacitive coupling is very small, it is also necessary to develop a controller circuit that is capable of created a clock with a very low duty cycle while dissipating less than 50uW.Este trabalho visa analisar várias tipologias de conversores de tensão DC-DC deno minados conversores Buck. O principal objectivo desta Tese é estudar e projectar um conversor DC-DC abaixador de tensão para sistemas de acopelamento electromagnético capacitivo utilizada em aplicações de Energy Harvesting a partir da rede AC. De forma a cumprir este objectivo, várias tipologias são estudadas ao longo deste trabalho, de forma a cumprir as especificações exigidas. Uma vez que o sinal de entrada é obtido a partir da rede AC, e que o output está ligado a um supercondensador, isto faz com que a tensão de entrada seja elevado (Acima dos 150V) e a tensão de saída seja baixa (entre 1V e 3V), como tal o conversor precisa de um rácio de abaixamento bastante elevado de cerca de 130 vezes. O conversor DC-DC deve também ter uma impedância de entrada elevada (cerca de 50MOhm) por forma a maximizar a energia transferida da rede de energia. Estas condições de funcionamento não são habituais para conversores DC-DC indutivos, o que torna este um problema muito desafiante. Adicionalmente, uma vez que a energia disponivel devido ao acopelamento capacitivo é muito reduzida, é necessário desenvolver um circuito controlador capaz gerar um sinal de relógio com um duty cycle reduzido enquanto dissipa menos de 50uW de potência

Nonlinear Control of a DC MicroGrid for the Integration of Photovoltaic Panels

New connection constraints for the power network (Grid Codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic arrays. The interconnection of such renewables with storage systems through a Direct Current (DC) MicroGrid can fulfill these requirements. A "Plug and Play" approach based on the "System of Systems" philosophy using distributed control methodologies is developed in the present work. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources like photovoltaic arrays, storage systems in different time scales like batteries and supercapacitors, and loads like electric vehicles and the main AC grid. The proposed scheme can easily be scalable to a much larger number of elements.Comment: arXiv admin note: text overlap with arXiv:1607.0848

Ultracapacitors for port crane applications: Sizing and techno-economic analysis

The use of energy storage with high power density and fast response time at container terminals (CTs) with a power demand of tens of megawatts is one of the most critical factors for peak reduction and economic benefits. Peak shaving can balance the load demand and facilitate the participation of small power units in generation based on renewable energies. Therefore, in this paper, the economic efficiency of peak demand reduction in ship to shore (STS) cranes based on the ultracapacitor (UC) energy storage sizing has been investigated. The results show the UC energy storage significantly reduce the peak demand, increasing the load factor, load leveling, and most importantly, an outstanding reduction in power and energy cost. In fact, the suggested approach is the start point to improve reliability and reduce peak demand energy consumption

Supercapacitor assisted LDO (SCALDO) techniquean extra low frequency design approach to high efficiency DC-DC converters and how it compares with the classical switched capacitor converters

Supercapacitor assisted low dropout regulators (SCALDO) were proposed as an alternative design approach to DC-DC converters, where the supercapacitor circulation frequency (switching frequency) is in the order of few Hz to few 10s of Hz, with an output stage based on a low dropout regulator stage. For converters such as 12–5V, 5–3.3V and 5–1.5V, the technique provides efficiency improvement factors of 2, 1.33 and 3 respectively, in compared to linear converters with same input-output combinations. In a 5–1.5V SCALDO regulator, using thin profile supercapacitors in the range of fractional farads to few farads, this translates to an approximate end to end efficiency of near 90%. However, there were concerns that this patented technique is merely a variation of well-known switched capacitor (charge pump) converters. This paper is aimed at providing a broad overview of the capability of SCALDO technique with generalized theory, indicating its capabilities and limitations, and comparing the practical performance with a typical switched capacitor converter of similar current capability

Cross-platform validation of notional baseline architecture models of naval electric ship power systems

To support efforts in assessing the relative merit of alternative power system architectures for future naval combatants, the Electric Ship Research and Development Consortium (ESRDC) has developed notional baseline models for each of the primary candidate architectures currently considered, medium-voltage DC (MVDC), conventional 60 Hz medium-voltage (MVAC), and high-frequency medium-voltage (HFAC). Initial efforts have focused on the development of a consistent set of component models, of which the system models can be comprised, and the basic definition of the system models. The broader objectives of the consortium, however, go beyond the definition of the baseline models. The focus is on the process by which the models are implemented in software and validated, the process by which the performance of the disparate system models are objectively and quantitatively assessed and compared, and, ultimately, the process by which the relative merits of the architectures may be assessed. This paper focuses specifically on cross-platform component validation.Center for Electromechanic

REGENERATIVE BRAKING SYSTEM USING SUPER CAPACITOR

Recently, a lot of people are concern on the environmental pollution that is getting worse day to day and energy crisis that would implicate to the global economy. Most organizations and car manufacturers are putting to a rest on the dependencies of natural resources and try to find a new solution to the problems. Therefore, Electric Vehicles (EVs) are seen to be a promising alternative to the current main energy resources, natural gases. Even though the electric vehicles are seen to be the perfect candidate for this problem, EV s are still suffering from the major problem of any EVs that is short driving range. Hence, a system to manage the energy consumption of an EV is should be developed. According to a study on electric car braking energy consumption, the energy consumed during braking is around 43% of the total energy of the whole process [1 ]. When an electric car running in urban city without regenerative braking system, a lot of energy is wasted through the braking, while on the other hand, during the acceleration the battery's current may reach as high as 450 ampere [1 ][2]. A regenerative braking system is comprised of hydraulic motor, hydraulic accumulator, electric controller and other components. During braking, the transmission shaft is still rotating which then will drive the hydraulic pump under the inertia. The rotation allows energy to be regenerated during the braking and will be stored, preventing from the energy to be wasted. During the accelerating, the energy stored from the braking will be used again to feed the energy consumption of the system [3]. Implementing the regenerative braking system allows the energy to be recycled. The energy that will be used during the decelerating and accelerating is merely from the energy used during braking