The three-phase CLLC resonant converter has attracted widespread attention due to its high efficiency, high capacity, and low device stress. However, the large number and volume of magnetic components in multi-phase structures are the main factors limiting the size of power converters. With the development of wide band gap devices, the switching frequency of power converters has significantly increased, providing favorable conditions for the utilization of PCB windings. The flat characteristics of PCB windings are more suitable for planar magnetic components. Additionally, the low inductance demand brought about by high frequencies also makes PCB-based planar magnetic components more advantageous for integration. Some integrated schemes have achieved the integration of all magnetic elements and the controllability of leakage inductance, but their structure resulted in the asymmetry of magnetic resistance. Some other studies have proposed a symmetrical integrated scheme that achieved the complete symmetry of magnetic resistance, but the leakage inductance obtained by the integration method was restricted.
In this paper, a “cylindrical” planar magnetic core structure based on a three-phase CLLC resonant converter is proposed to realize the integration of magnetic elements and improve the power density of the system. The magnetic core structure is entirely symmetrical in space, achieving the symmetry of magnetic resistance and enhancing the stability of the system. Fig.A1 shows our topology structure and integrated magnetic core structure (including the planar structure diagram). The proposed integrated magnetics consists of the magnetic lid, magnetic plate, PCB winding, and magnetic base.
Fig.A1 Structure of the topology and integrated magnetics
Firstly, according to the equivalent circuit of the three-phase CLLC resonant converter, its gain characteristics are derived, and the prototype parameters are reasonably designed according to the relationship between the gain curve and K, Q values. Then, based on the proposed integrated magnetic core structure, a magnetic circuit model is established. The relationship between the resonant inductance Lr, the excitation inductance Lm, the inductance coefficient K, the winding turns N1 and N2, and the magnetic resistance Rg is analyzed. Next, a loss model and an optimization procedure of the transformer is built to achieve the lowest loss of the transformer. Finally, an 800 V/10 kW prototype platform was built. Comparative experiments were conducted with the “square” integrated magnetics and the proposed “cylindrical” magnetics, as shown in Fig.A2.
Fig.A2 “square” integrated magnetics and the “cylindrical” magnetics
The following conclusions can be drawn from the experiments. (1) Compared to the “square” integrated magnetics, the proposed integrated magnetics shows smaller imbalances among the three-phase resonant currents, achieving better system stability. (2) The proposed integrated magnetics maintains higher efficiency than the “square” integrated magnetics, even with a smaller volume and footprint. It demonstrates that the proposed structure possesses high power density and efficiency. (3) The proposed integrated magnetics achieves an efficiency of 97.5% at full load, validating the rationality and feasibility of the proposed magnetic core structure.
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