Abstract
For the full-bridge LLC converter, it is necessary to establish a large signal model with low-complexity and high-precision when the current of filter inductor works under the continuous conduction mode (CCM) situation. In terms of low complexity, peak values of resonant state variables and average values of slow state variables are taken as the measured indexes between models and actual converter. Models based on the first harmonic approximation (FHA) are studied in depth because they have lower complexity than the existing models. From prospective of high precision, deficiencies of typical FHA model are explained in the light of harmonic generation mechanism of primary current and influence of Fourier series on the typical equivalent circuit. Therefore, transient process of each metallic oxide semiconductor field effect transistor (MOSFET) and its related fast recovery diode, transient process of Schottky rectifier diodes, piecewise equivalent circuit, appropriate selection of variables, and simplified modified dynamic equations are all considered. Furthermore, the unified proposed model is achieved according to the equivalent principle of indexes between aforementioned improved analyses and proposed model. Numerical results of typical FHA model and proposed model are given in accordance with the key indexes. Then, corresponding experimental results are also presented. Differences of indexes between the two models and the actual converter are compared respectively. Though complexity of proposed model is the same as that of typical FHA model, precision of proposed model is higher than that of typical FHA model.
Highlights
With the popularity of renewable energy generation, kinds of DC-DC converters play important roles in the power conversion system
When the algebraic equations presented from (40a) to (40i) are solved and the equivalent principle of indexes is applied to the large signal model from (44a) to (44f) under the steady state, correction coefficients and Ro(eq), ton shown in Fig 3, and key indexes under different working conditions can be obtained respectively
According to the two points, complexity of both typical first harmonic approximation (FHA) model and proposed model is five and it is lower than the Table 2
Summary
With the popularity of renewable energy generation, kinds of DC-DC converters play important roles in the power conversion system. A large number of advanced maximum power point tracking (MPPT) algorithms have been successfully implemented in the DC-DC converter. In the electric vehicle (EV) system, DC-DC converter is intermediate link between different energy storages and DC bus. In [5], high voltage battery-supercapacitor and DC motor are connected to the two ports of a kind of typical bidirectional DC-DC converter respectively. Proposed power-split strategy is developed to track real-time load profiles and determine cutoff frequency. In [6], dual battery energy source and DC-bus of different voltage levels are connected to the interfaces of proposed bidirectional DC-DC converter respectively. In the modern electric ship medium voltage DC power system such as [7], DC-DC modular multilevel converter with a medium-frequency transformer is the promising transmission device. The proposed control strategy based on single phase pq theory is developed to ensure stable and robust operation
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