Closed-Form Optimal Current-Limiting Curve-Based Variable Duty-Cycle Soft Start-Up Strategy for the LLC DC Transformer

The {{LLC}} converter-based dc transformer is popular for its stiff voltage gain, very high efficiency, and simple control. To avoid excessive start-up inrush current and hardware overdesign, the fixed-frequency variable duty-cycle soft start-up strategy is often adopted. However, in this convention...

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Bibliographic Details
Published in:IEEE transactions on industrial electronics (1982) 2024-10, Vol.71 (10), p.12524-12538
Main Authors: Wang, Wei, Yin, Yanxiang, Liu, Tong, Wang, Nan, Ren, Qicai, Chen, Alian
Format: Article
Language:English
Subjects:
Capability
Closed form solutions
Constraining
dc transformer (DCT)
Discrete cosine transforms
duty cycle
Exact solutions
Inrush current
Iterative algorithms
Iterative methods
Mathematical models
Numerical models
optimal current-limiting curve (OCC)
Optimization
start-up
state trajectory
Switches
Switching circuits
Trajectory
Trajectory analysis
Transformers
Voltage control
Voltage gain
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Summary:The {{LLC}} converter-based dc transformer is popular for its stiff voltage gain, very high efficiency, and simple control. To avoid excessive start-up inrush current and hardware overdesign, the fixed-frequency variable duty-cycle soft start-up strategy is often adopted. However, in this conventional strategy, the optimal current-limiting curve (OCC) is derived by the challenging numerical model iterative algorithm, which is difficult to model, calculate online, and adapt to different operating conditions. To solve this problem, a closed-form OCC (COCC)-based soft start-up strategy is proposed. The COCC is derived by state-trajectory analysis and can be quickly calculated through the simple closed-form equation, providing greater practicality and flexibility while accurately maximizing the utilization of the allowable peak current. Furthermore, the closed-form equation makes it possible to estimate the start-up capability under the variable duty-cycle strategy. The calculation method of the maximum allowable start-up load is proposed, offering an important basis for the design of distribution system restoration schemes. Finally, a 50-kW dc transformer is built to verify the effectiveness of the proposed strategy under various conditions.
ISSN:0278-0046
1557-9948
DOI:10.1109/TIE.2023.3340206