High frequency isolated resonant converters have found widespread application in the field of EV charging, solar inverters, switch mode power supplies, and aircraft power supplies, due to their higher power density and superior conversion efficiency. Specific applications include auxiliary power units used in more electric aircrafts that use fuel cell-based system at 400 DC to serve battery loads at 24-28V DC voltage levels at low load conditions, that in turn support the main supply during heavy loading conditions, thus demanding bidirectional power flow. In that context, bidirectional capacitor-inductor-inductor-capacitor (CLLC) resonant converter topology has proved to provide various advantages, such as reduced losses due to soft switching in the primary bridge and synchronous rectification in the secondary bridge, no-load voltage regulation and wider gain range over narrow frequency modulation zone. Further, in such applications, high frequency planar transformers (HFPT) have found wide acceptance due to their advantages pertaining to lower profile, increased reliability, and modularity. However, these advantages can only be redeemed by precise design and analysis of the equivalent parameters based on the physical design of the transformer winding arrangement, to obtain the desired gain characteristics, yet achieving the targeted efficiency and power density.
Current HFPT models focus on aspects of reduced winding losses with interleaved arrangements, issues pertaining to electromagnetic interference occurring due to stray capacitances and ways to reduce them. These models portray generalized models to characterize the HFPT with assumptions pertaining to uniform winding arrangements and correspondingly are unable to correlate the obtained equivalent parameters with the physical constraints of a printed circuit board such as its thickness and corresponding insulation layer distribution, air gaps, and the conductor trace thickness. Thus, there is a need for a CLLC converter for a charging application and model for designing said CLLC converter for said application.
Researchers at Arizona State University have developed a bidirectional resonant asymmetric capacitor-inductor-inductor-capacitor (CLLC) converter for charging applications and a model for obtaining a winding configuration of a high frequency planar transformer (HFPT) employed in a CLLC converter. The model parameterizes the R-L-C components of a HPFT for any isolated DC/DC converter topology, thus eliminating the need for accommodating the computational burden of a finite element analysis (FEA) solver software. In addition to precisely characterizing the parasitic components, this model provides several design guidelines and trade-offs of selecting the required PCB specifications and correlation between various air gaps.
Related publication: Fabrication Tradeoff Based Optimal Synthesis of Winding Configurations for Planar Transformer in CLLC DC–DC Converter
Potential Applications:
- Wireless charging
- EV onboard and wireless charging
- More-electric-aircrafts
- Naval power supply
Benefits and Advantages:
- Ease of use and significant time saving when compared to a typical FEA software
- Considers (1) PCB design specifications, (2) comparisons of various winding configurations and their effects on system performance, and (3) corelates air gaps and their effect on parasitic components
- Accepts design specifications and target performance metrics from user and provides (a) the best possible winding configuration, and (b) optimum choice of PCB fabrication specifics while ensuring crucial operational limitations like soft switching capabilities of any circuit topology and transformer winding/core loss minimization, thus yielding maximum efficiency