The input-parallel output-parallel (IPOP) dc–dc converters are suitable for low-voltage and high-current applications, especially using high-frequency isolation instead of traditional line-frequency transformer for ac–dc converters in dc distribution. Compared to the existing closed-loop control for IPOP dc–dc converters, the magnetic-coupling current-balancing (MC-CB) cells based IPOP LLC resonant converter modules are proposed in this paper, which can realize the IPOP system work under open-loop operating condition naturally. The LLC modules can be used as a high-frequency isolation dc transformer operating under the quasi-resonant mode, which can achieve zero-voltage switching (ZVS) for inverter side and zero-current switching (ZCS) for rectifier side ensuring high power density and high efficiency. The proposed MC-CB cells for IPOP LLC resonant converter modules can adaptively ensure both the input-current sharing (ICS) and the output-current sharing (OCS) among constituent modules to make the IPOP system operate stably. Additionally, the steady-state and dynamic-state current-sharing performance of MC-CB cells for the IPOP converter system are analyzed based on a magnetic model. In the end, a hardware prototype has been designed and tested. The experimental results have verified the validity and performance of the proposed MC-CB cells for the IPOP LLC resonant converter modules.

Magnetic-Coupling Current-Balancing Cells Based Input-Parallel Output-Parallel LLC Resonant Converter Modules for High-Frequency Isolation of DC Distribution Systems

This paper introduces a single-stage isolated 48V-to-1.8V point-of-load converter based on the impedance control network (ICN) resonant converter architecture. This point-of-load ICN converter achieves large step-down while maintaining high efficiency across a wide range of input voltage and output power. Large step-down is achieved using a novel immittance network transformer and a resonant current-doubler rectifier. High efficiency is achieved by utilizing the ICN architecture, which enables zero-voltage and near-zero-current switching across wide operating ranges. The power density of the converter is enhanced by combining its magnetic components into two integrated magnetic structures: one implementing the three inductors of the ICN using two coupled windings, and the other implementing the immittance network transformer and current-doubler magnetics on a common core. A systematic methodology is introduced to design and optimize the proposed ICN converter. A prototype 90-W ICN converter utilizing PCB-integrated magnetics, designed to operate over an input voltage range of 36 V to 60 V and an output voltage of 1.8 V is built and tested. The prototype ICN converter achieves a peak efficiency of nearly 90%, and maintains greater than 87.9% efficiency across its nearly 2:1 input voltage range.

Single-stage isolated 48V-to-1.8V point-of-load converter utilizing an impedance control network and integrated magnetic structures

Current-doubler rectifiers are well-known in conjunction with double ended buck-derived isolated converters One major purpose for its implementation is the reduction of power losses in the transformer secondary winding The topic of this paper is an extension to this approach and presents a detailed analysis of a current-doubler rectifier used in an LLC resonant converter The analysis uses the first harmonic approximation (FHA) approach, which tremendously simplifies the system model, leading to a linear circuit The design constraints are worked out, such that the converter behavior remains unaltered by adding the current-doubler By using this type of rectifier, the LLC efficiency can be improved over a traditional approach with a center tapped secondary winding The secondary side power losses are reduced significantly and the drawback of an unequal coupling between the primary and either one of the two secondary windings is eliminated Measurements on a prototype verify the analytical and simulation results

Detailed analysis of a current-doubler rectifier for an LLC resonant converter with high output current

Present study analyzed the efficiency characteristics of LLC converters having current doubler rectification circuits. A current doubler rectification circuit has a coupled inductor as rectification circuit on the secondary side output terminal of the converter. A current doubler rectification circuit generally requires inductors on the secondary side however, the characteristic of an LLC converter preclude the inclusion of inductors on its secondary side. This problem is resolved here by proposing, a circuit system that has very small inductance values and uses a coupled inductor on the secondary side output terminal. The proposed circuit system is advantageous compared to center tap systems typically used at present, as confirmed by analysis and verified through simulated analysis.

Analysis of the efficiency characteristics of an LLC resonant converter having a current doubler rectification circuit

This article presents a hybrid converter combining soft-charged switched capacitors and an autotransformer with dc current in the windings, optimized for 4:1 fixed voltage gain conversion (DCX) for high output current. By adding an additional output inductor, it can also regulate the output voltage to lower than ¼ of the input voltage by changing the duty cycle. The switched capacitors voltage and the two winding currents in the transformer are auto-balanced. Nonresonant operation of the circuit enables dc current in the windings and simplifies both transformer and circuit design. Experimental results for 48 V–12 V DCX operation achieve 98% peak efficiency and 97.7% full load (250W) efficiency. Regulation by using the output inductor is verified experimentally up to 48–6V (8:1) voltage step down.

A Switched Capacitor and Autotransformer Hybrid Converter With DC Current in the Windings

In this paper, LLC series resonant converter with current-doubler as a rectification circuit for secondary side is proposed. The current-doubler circuit is generally used for the high voltage input and low voltage output application to get high efficiency characteristics with reduced transformer turn ratio. However, an inductive circuit is not used in a secondary side for the LLC series resonant converter generally. When there is inductive circuit like current-double on the secondary side, the resonant characteristics are changed. In this paper, LLC converter with the current-doubler using coupled inductor is proposed. We verify that the secondary side current-doubler using coupled inductor is not affect to the resonant characteristic of primary LLC by the mathematical analysis. Finally, the analysis results are proved by the simulation and experiments.

Analysis of LLC Resonant Converter with Current- Doubler Rectification Circuit

This study proposes an LLC series resonant converter with a current doubler using a coupled inductor as a rectification circuit for the secondary side. The current doubler circuit is generally used for a high-voltage input and low-voltage output circuit to obtain high efficiency with small transformer turn ratio. However, an inductive circuit is not generally used in the secondary side of an LLC series resonant converter. If inductive components exist on the secondary side, the resonant characteristics are changed through the secondary inductive circuit. Mathematical analysis shows that the secondary-side current doubler with coupled inductor is not affected by the resonant characteristic of the primary LLC if leakage inductance occurs in the coupled inductor. Results of the analysis are proven by simulation; an experiment is also conducted for the proposed circuit.

http://koreascience.or.kr:80/article/JAKO201431057577382.pdf

Jung-Yoon Shin

Papers

Analysis of LLC Resonant Converter with Current- Doubler Rectification Circuit

Mathematical Analysis of LLC Series Resonant Converter with Current Doubler Rectifier using Coupled Inductor