This paper presents the design and optimisation of a suitable topology for an isolated DC-DC auxiliary power supply with high isolation voltage and low coupling capacitance. The converter consists of a GaN HEMT inverter operating at 6.78 MHz, an LCC resonance tank and a class E low dv/dt rectifier. Furthermore, the galvanic isolation is implemented using a coreless planar transformer that enables higher insulation voltage with similar or better converter efficiency compared to designs using magnetic material. An analytical design methodology is developed, however, SPICE investigations show that optimal designs might lie outside the validity of the design equations. Consequently, a virtual prototyping tool is developed based on a genetic algorithm with numerical simulations and, in turn, is used to optimise the converter. The optimisation algorithm maximises the converter efficiency while minimising the transformer size. Prototypes are constructed based on the resulting Pareto front. Experimental results show the validity of the simulated results. Prototypes transferring power up to 15 W with a peak efficiency of 81% are shown. The selected topology enables insulating voltages exceeding 40 kV and coupling capacitances below 10 pF.
This paper describes a modelling approach suitable for assessments of future scenarios for renewable energy integration in large and interconnected power systems, based on sequential optimal power flow computations that take into account variability in power consumption, in renewable power production, energy storage, and flexible demand. The approach and the implementation as an open source Python package called Power Grid And Market Analysis is described in some detail. Particular emphasis is put on the modelling of energy storage systems, and the use of storage values as a means to define storage utilisation strategies. A case study representing a 2030 scenario for the Western Mediterranean region is then analysed using this approach. The main aim of this study is to assess the benefit for the system of adding flexibility in terms of storage associated with concentrated solar power or flexible demand. But other results are also presented, such as the resulting energy mix, generation costs, price variations, and grid congestion.
This review investigates different aspects of the realization of a North Sea offshore grid. The North Sea region has several characteristics that make large-scale integration of renewable energy sources attractive, such as large wind resources and huge hydro reservoirs in the North. A meshed offshore grid with underwater storage can contribute to facilitate sufficient flexibility in the system. The technical review reveals some aspects that need more research, particularly regarding the protection schemes. Furthermore, offshore storage solutions are under development. However, most other aspects are covered by readily available solutions. The greatest challenges seem to lie within standardization, cost-benefit sharing and harmonization of regulatory regimes of the surrounding countries. Nevertheless, several studies have shown highly promising economic benefits of establishing an offshore grid in the North Sea compared to traditional planning of point-to-point connections only.Keywords: offshore grid, HVDC, grid integration, renewable, energy storage, North Sea IntroductionThe integration of renewable power generation implies new challenging issues for the grid such as variability of energy input, frequency response, system power balancing and power market design. Moreover, renewable resources are often located far from the load centers. For future scenarios new transmission infrastructure and energy storage is needed. Consequently, the grid will be more flexible and the security of supply will be ensured. Depending on the grid layout, distance from load centers and geography, few power grids today will support renewable integration above 10%-30% without an elevated risk of outages [1][2][3][4]. To increase the renewable penetration either grid extensions or storage should be added to the system. Optimally, a combination of the two are implemented [4]. The North Sea region could very well be a first mover towards integrated grid and storage planning for high renewable penetration levels. The grid will connect the Northern European mainland, the UK and Scandinavia, with the goals of:• Harvesting offshore wind • Interconnect Europe's energy markets to enhance security, stabilize prices and increase cost efficiency • Provide large scale hydro balancing power to markets with high penetration of variable renewable production • Implement deep-water energy storage to balance fluctuations In addition, the offshore grid can connect to energy consuming facilities in the North Sea, such as oil and gas platform at the Norwegian sector, and thus reduce regional CO 2 emissions further. For reference, the total emission for the power generation of the Norwegian oil and gas sector equaled more than 9 million tons CO2-eqvuivalents for 2010. The power comes mainly from open cycle gas turbines with an average efficiency of approximately 33%, about half of what a modern onshore gas plant can achieve today [5].
Abstract-This paper investigates a method for quantifying the additional losses in high-voltage GaN enhancement mode HEMTs (eHEMT) employed in converter applications. The additional losses stem from the phenomenon known as current collapse or dynamic on-state resistance. The goal of this work is to investigate how these losses contribute to the total power loss in converter application. Measurement and modelling methods in the literature are reviewed. Changes to the measurement circuit are made to improve measurement accuracy. Measurements of dynamic on-state resistance are made on a commercial GaN eHEMT. The experimental results shows that the resistance depends on both dc-link voltage and blocking time. The resistance waveform and initial attempts at modelling the dynamic onstate resistance indicate that the suggested model is suitable for modelling the losses in LTSPICE software.
This paper investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2D axial-symmetry, the transformer circuit parameters and electric field distribution are modelled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimisation results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the PCB windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.
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