Epoxy, with excellent electrical insulation properties, processing performance, and low price, is commonly used for transformers (110kV and below) and power electronic transformers (high-frequency transformers) as the...
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ISBN:
(数字)9798350308976
ISBN:
(纸本)9798350308983
Epoxy, with excellent electrical insulation properties, processing performance, and low price, is commonly used for transformers (110kV and below) and power electronic transformers (high-frequency transformers) as the primary insulating material. Since the thermal conductivity of epoxy resins is only 0.2 W/(m·K), the electrical insulation properties decline significantly at high frequency. Preparing epoxy composites with high thermal conductivity and excellent electrical insulation at high frequencies is a great challenge for industrial production. It is considered that SiO
2
(9 eV), BN (5.9 eV), and Al
2
O
3
(7.2-8.8 eV) are thermally conductive particles with good electrical insulation properties. The materials filled with different micron-scale particles have higher thermal conductivity than the nanofilled materials. In this study, 5 μm SiO
2
, 25 μm BN, and 40 μm Al
2
O
3
were used as fillers, and the filler ratios were calculated according to the Dinger-Funk model, focusing on the effects of the variation of filler content on thermal conductivity and electrical insulation properties. The thermal conductivity of the epoxy composites improved with the increase of filler content up to 1.003 W/(m·K), while the AC breakdown field strength gradually decreased. However, the breakdown time at 20 kHz, 35 kV/mm bipolar square wave appeared to increase and then decrease with the increase of content. Therefore, the optimum content of fillers allows the preparation of efficient epoxy composites as insulating materials for power electronic transformers. This study provides ideas for designing thermally conductive composites operating at high frequency and high voltage fields.
CLLC converters are broadly used in battery energy storage systems (BESS), where the capabilities of bidirectional operation and voltage regulation are desired. In the existing bidirectional power transfer scheme, pul...
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ISBN:
(数字)9798350376067
ISBN:
(纸本)9798350376074
CLLC converters are broadly used in battery energy storage systems (BESS), where the capabilities of bidirectional operation and voltage regulation are desired. In the existing bidirectional power transfer scheme, pulse frequency modulation (PFM) is used to realize the reciprocal gain of forward and backward directions. It leads to not only large frequency modulation range but also asymmetric transfer characteristics. In this paper, a novel modulation scheme of CLLC converters for bidirectional power transfer is proposed. In the proposed backward power transfer scheme, the driving signals of primary and secondary-side switches are aligned at the falling-edge, which brings about symmetrical characteristics as forward scheme. This symmetry further ensures the identical switching frequency in both directions, which simplifies parameter design, minimizes switching frequency range, and improves efficiency. A 10-kW prototype is built and the experimental results validate the effectiveness of the proposed scheme, offering potential for cost-effective and efficient applications.
The voltage support capability of renewable resources (RES) is emphasized by grid codes for stable and secure operation faced with grid faults. However, there is another problem occurs when the penetration of RES is b...
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ISBN:
(数字)9781665464543
ISBN:
(纸本)9781665464550
The voltage support capability of renewable resources (RES) is emphasized by grid codes for stable and secure operation faced with grid faults. However, there is another problem occurs when the penetration of RES is boosting. The capability occupation due to injected power for voltage support leads to the decrease of output power for loads, which may result in frequency issues when the inertia of the system decreases. To guarantee the voltage and frequency security during fault ride through (FRT) process, this paper proposes an optimal scheduling scheme for PV-BES system considering voltage support and frequency regulation. In the optimal model, in order to map the voltage and frequency constraints into power constraints, the evaluation model of required injected power for voltage support is formulated firstly. Based on center of inertia theorem and time scale characteristics of FRT, the frequency deviation is represented by distributed generator (DG) adjustment. The voltage and frequency constraint are incorporated into the optimal scheduling model and the quasi-steady-state of the PV-BES system during FRT can be analyzed. The proposed method is fully tested, and the results demonstrate that with the proposed method, the voltage and frequency security can be well guaranteed.
Flexible powercontrol (FPC) for distributed PV-BESS systems has been presented in the past years to extend the service life of the energy storage unit. The photovoltaic(PV) works with the flexible power tracking mode...
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ISBN:
(数字)9798350361001
ISBN:
(纸本)9798350361018
Flexible powercontrol (FPC) for distributed PV-BESS systems has been presented in the past years to extend the service life of the energy storage unit. The photovoltaic(PV) works with the flexible power tracking mode to control the DC bus voltage, which can reduce the work of the energy storage unit. The existing FPC method works well with slow-changing irradiance. However, the DC voltage will be unstable when the irradiance changes fast or there is a change in the load. So, an advanced FPC method for PV is proposed in this paper. The proposed FPC keeps the DC voltage moving around the voltage reference with a limited wave. Compared with the existing FPC method, the proposed FPC for PV systems is much more effective under various working conditions. Followed by theoretical analysis, the simulation results validate the claimed advantages of the proposed solution.
Traditional time-domain simulation method has long calculation time on transient voltage stability margin prediction problem, the direct method is difficult to adapt to the complex power grid model, and the deep neura...
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power loss measurement and evaluation form the foundation of loss modeling and optimization. This paper proposes a method for evaluating power loss in high-frequency (HF) transformers operating under forced air-coolin...
power loss measurement and evaluation form the foundation of loss modeling and optimization. This paper proposes a method for evaluating power loss in high-frequency (HF) transformers operating under forced air-cooling conditions, simply based on surface temperature measurement with a thermal camera. A direct correlation is established between power loss and surface temperature, utilizing a simplified thermal network. This method enables the measurement of both total loss and individual core loss and winding loss directly for HF transformers operating within the whole range of normal working conditions. simulations are conducted to validate the practicality and accuracy of the proposed method. Experiments are carried out on a HF transformer prototype, following the proposed loss evaluation process, validating the accuracy of the evaluated power loss within wide operation range in loaded tests.
The integration of renewable energy sources (RES) into the powersystem has surged, posing significant challenges due to their inherent volatility and unpredictability. This paper examines the economic feasibility of ...
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With the incorporation of more renewable energy sources, distribution networks are shifting from passive to active. The enhanced coupling of transmission and distribution networks is enhanced and bidirectional tides a...
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Current risk assessment ignores the stochastic nature of energy storage availability itself and thus lead to potential risk during operation. This paper proposes the redefinition of generic energy storage (GES) that i...
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Remote operation of protective setting value can enhance the adaptability of protection to real-time operating conditions. As centralized solutions, existing models face information security risks. The decentralized n...
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ISBN:
(数字)9798350359558
ISBN:
(纸本)9798350359565
Remote operation of protective setting value can enhance the adaptability of protection to real-time operating conditions. As centralized solutions, existing models face information security risks. The decentralized nature of blockchain is advantageous for addressing reliability issues in remote operations. This paper treats the control center and protection relay system sub-stations as nodes in blockchain, proposing a Proof-of- Reliability (PoRel) consensus mechanism based on node reliability. The paper first defines sub-station node types and classification criteria, achieving optimal sub-station node grouping based on 0–1 integer programming. Next, it provides a method for evaluating sub-station node reliability and outlines the consensus mechanism process. Finally, using the IEEE 39-bus system as an example, a blockchain system with 27 sub-station nodes is built using Python software, and the proposed consensus mechanism is simulated and verified. The results indicate that the proposed consensus mechanism improves efficiency, achieves decentralization, and helps ensure reliable relay setting remote operations.
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