This paper presents a modified power factor correction (PFC) ON/OFF control and three-dimensional (3D) printed circuit board (PCB) design for a high-efficiency and high-power density onboard charger (OBC). By alternately operating one of two boost modules of the PFC stage at a 50% or less load condition, the proposed PFC control can reduce the load-independent power loss of the PFC stage, such as core loss and capacitor charging loss of switches. It enables OBCs to have high efficiency across a wide output power range and better thermal performance. The 3D-PCB design decouples a trade-off relationship of the PCB trace design and heat spreader design, increasing the power density of OBCs. A 3.3 kW prototype composed of an interleaved totem-pole bridgeless boost PFC converter and full-bridge (FB) LLC converter has been built and tested to verify the proposed PFC control and 3D-PCB effectiveness design. The prototype has 95.7% full power efficiency (98.2% PFC stage efficiency) and 52 W/in³ power density.

Server power supply has to maintain output power even under abnormal input voltage conditions for stable operation of the server. Input-voltage-based current reference control has been widely used for power factor correction converter in server power supply because it can instantly generate a current reference and maintain a stable output. However, because harmonics and noise in the input voltage directly influence the current reference, the input current total harmonic distortion (THD) increases. On the other hand, phase-locked loop (PLL) based control can achieve lower current THD due to its excellent noise and harmonic filtering capabilities, but it cannot respond to sudden changes in the input voltage. In this letter, a hybrid current reference control method is proposed to achieve stable operation of the server power supply. The proposed method ensures continuous operation under abnormal input voltages by utilizing input-voltage-based control. Therefore, in normal input condition, the PLL bandwidth design can be alleviated to achieve a lower current THD. To determine the effectiveness of the proposed control method, steady-state operation and abnormal input condition operation were confirmed through a 47–64 Hz/90–264 V _rms 3-kW prototype converter.

A fault-tolerant converter is widely used in high-reliability applications. To satisfy the high-reliability requirements, fault tolerance is an essential feature and can be achieved by redundant converters. However, a large number of redundant converters degrade the overall power density and cost. This paper proposes a novel fault-tolerant LLC converter, which can reduce the number of redundant converters. Its structure is based on the input-parallel, output-series two half-bridge LLC converters and a midpoint connection on the secondary side. The proposed converter can withstand double short-circuit faults (SCFs) by utilizing only two converters instead of three converters. The redundant converter is used to achieve a single fault-tolerant capability against an SCF. When a second SCF occurs in the switch, the proposed converter is reconfigured to regulate the output voltage without additional semiconductor components. By analyzing the proposed converter, it is demonstrated that the proposed converter achieves high power density and low cost without degradation of efficiency. In addition, it can be easily extended to have multiple fault-tolerant capabilities. Finally, the performance and feasibility of the proposed converter were confirmed with a 100 V/12 A 1200 W prototype.

This article proposes a novel offset current modulation technique, which can add a new degree of freedom to the dual active bridge dc–dc converter. The concept of the proposed technique is to inject offset currents into the primary- and secondary-sides of the transformer. If the same offset currents are injected into both sides, dc bias does not occur in the magnetizing current of the transformer. Therefore, the offset current can be used as a new control variable without any adverse effects. When the proposed technique is applied to single phase shift (SPS) modulation, zero voltage switching (ZVS) characteristics can be further improved by realizing the ZVS of two more switches, leading to higher efficiency. Furthermore, the proposed control system can be configured with simple modification of the conventional control system. The optimal SPS modulation with the proposed technique is derived through theoretical loss optimization considering a tradeoff between conduction loss and switching loss. The feasibility of the proposed technique is verified using a 3.3 kW prototype with a 400 V input and 280–420 V output conditions.

The two-phase LLC resonant converter is widely used in high-power applications. It can reduce the conduction losses and prevent the thermal runaways by sharing the overall output currents. In addition, the converter can operate in single-phase mode by turning off one of the two phases during phase-shedding or fault situations. Consequently, the two-phase LLC resonant converter can achieve high efficiency and high reliability across a wide operating range. However, this topology suffers from a significant unbalanced current caused by component's tolerance. Thus, this article proposes a novel LLC resonant converter to alleviate the unbalanced current. The structure of proposed converter is based on the variable voltage sources and secondary-side point connection. The proposed converter can achieve natural current sharing without multiple current sensors, load share ICs, and complex current control. In addition, it has small current sharing errors and excellent phase-shedding performance through variable voltage sources. The small capacitance of voltage variable sources acts as a current balancer, allowing voltage gain differences caused by the component's tolerance. As a result, the proposed converter can achieve high efficiency and high reliability without any additional components. The feasibility of proposed converter is demonstrated by the experimental results with 100 V/20 A 2000 W lab prototype converters.

The electromagnetic interference (EMI) filter is essential for industrial products to comply with EMI standards. It can reduce the EMI noise, which may cause harmful effects on other electronic devices or human health. However, the EMI filter typically occupies a large volume, around one-third of the entire power supply volume, leading to a deterioration in power density. Among previous studies, the winding cancellation method is an attractive approach for reducing the volume of EMI filter. It can reduce the common-mode (CM) noise by canceling the CM voltages of the transformer without requiring shielding layers. However, the winding cancellation method is only applicable to specific topologies. Particularly, in topologies with an output inductor, the implementation of winding cancellation method requires additional components such as reset windings or capacitors. Therefore, this article proposes a novel coupled inductor rectifier that enables the winding cancellation method without any additional components. The proposed rectifier ensures that the voltages generated at the primary and secondary nodes of the transformer have the same dv/dt directions. Consequently, the CM voltages of the transformer cancel each other, leading to the significant mitigation of CM noise. Furthermore, the proposed rectifier can be implemented simply by replacing the existing output inductor with a coupled inductor. It does not require additional components and has the same circuit characteristics as conventional converters. Finally, the proposed rectifier can be extended to different converter topologies with an output inductor. As a result, the proposed rectifier can achieve high power density by reducing the volume of EMI filter. To verify the performance of the proposed rectifier, laboratory prototypes of forward and asymmetric half-bridge converters were built and tested. The proposed prototypes reduced CM noise by 9.7 and 15.4 dB, respectively, compared to conventional prototypes through winding cancellation. Consequently, the volume of EMI filter in the proposed prototypes was reduced by 55.7% and 75.9%, respectively.