Sang-Kyoo Han

Compared to a basic buck converter, the 3-level buck converter operates with the output inductor at twice the switching frequency. Additionally, the voltage across its flying capacitor contributes to reducing the slope of the inductor current. These factors can result in a reduction in the maximum output current ripple by up to four times, enabling the use of a smaller output inductor. Moreover, the voltage stress on the switches is only half of the input voltage. Therefore, the 3-level buck converter is advantageous for achieving high efficiency and high power density. To maintain these advantages, the voltage across the flying capacitor must be kept at half of the input voltage. Conventionally, this condition is usually ensured by using peak or valley current mode control methods. However, these methods have complex control circuits or algorithms and are vulnerable to noise interference because their operation is based on instantaneous peak or valley current sensing. Additionally, different control configurations must be employed for M < 0.5 and M > 0.5, where M is the input-to-output voltage conversion ratio. In this paper, we propose a two independent single-loop voltage mode control method that can guarantee the flying capacitor voltage remains at half of the input voltage. The proposed control method is simple to implement and does not require current sensing or complex control algorithms, allowing the use of simple and low-cost digital or analog controllers. The method is also robust to noise interference because it only operates based on the output and flying capacitor voltage. Furthermore, this method ensures normal operation across all values of M without changing the control configuration. The experimental results from a 500 W-rated prototype confirmed the validity of the proposed control method.

The conventional Weinberg converter, owing to its high efficiency; continuous input and output current; and the soft switching of its switches and diodes, is essentially utilized in battery discharge regulators (BDR) – components that make up the overall electrical power system for geostationary satellites. However, this converter faces a crucial drawback in that the output current ripple is considerably high during the commutating operation of its output diodes. Consequently, the output root mean square (RMS) current and output voltage ripple are high. This may directly influence the lifetime and overall capacitance of the bus capacitors, ultimately affecting the longevity and size of the geostationary satellite. Therefore, reducing the BDR’s output current ripple is essential in designing a geostationary satellite’s electrical power system. As a result, this paper proposes an improved Weinberg converter to reduce the output current ripple and output voltage ripple. Specifically, the proposed converter not only has a lower output current and voltage ripples compared to the conventional converter but also reduces the magnetizing current offset of the coupled inductor. Furthermore, similar to the conventional converter, it is capable of soft switching operation of all switches and achieving high efficiency without the reverse recovery problem of diodes. Overall, the proposed converter is verified with experimental results from a 750 W-rated prototype.

The conventional power factor correction (CPFC) converter suffers from excessive heat generation due to high conduction loss from the input bridge diode. Various bridgeless PFCs (BPFCs) have been proposed to overcome this drawback. Among them, the conventional BPFC (CBPFC) features the significantly reduced conduction loss but has very poor conducted electromagnetic interference (EMI) noise. Further, the semi-BPFC features the reduced input diode loss and good EMI, but the input diode loss is too significant to ignore. Although another solution, totem-pole BPFC, features high efficiency and good EMI, it usually requires expensive current sensors and microprocessor. A BPFC with the integrated magnetics common mode coupled inductor (ICC) is proposed to overcome the drawbacks of traditional BPFCs. The ICC can significantly reduce the system size by integrating three inductive components into a single magnetic core. Moreover, the small magnetizing current of the ICC, not the main input current, flows through input diodes; thus, experimental results from a 600 W rated prototype prove that the input diode loss can be significantly reduced by about 10 W compared to the CPFC, and the input diode exhibits a low heat generation of 49.8 °C despite the absence of a heat sink. In particular, with the help of input diodes, the EMI noise spectra of the ICC BPFC can meet the EMI standard with a sufficient margin. The detailed analysis, design guide and experimental results from a 600 W rated prototype are provided to confirm the validity of the ICC BPFC.

Recent studies on compact and lightweight electronic devices have demonstrated that the LLC resonant converter (LRC) can facilitate achieving high efficiency and high power density. Moreover, employing a planar transformer can further improve the overall system power density. Although the planar transformer can assist in reducing the size of the converter, its high magnetic coupling makes the leakage inductance too small for a resonant inductor in the LRC. Therefore, an extra inductor must be employed separately, leading a considerable decrease in the power density. From this reason, significant research on integrated magnetics has been conducted to combine a transformer and external inductor into a single core. However, they require additional wires or magnetic sheets, and their structures are complex and costly. To overcome these limitations, the integrated magnetics planar transformer (IMPT) for a high power density LRC is proposed in this paper. In the proposed approach, since the primary wire is split into each side leg of the EE-type magnetic core and each operates as a transformer and a resonant inductor alternatively, an external inductor or additional wires are unnecessary. In addition, since the magnetic flux density of the IMPT is approximately equivalent to that of conventional transformer, the core size and the number of turns are almost the same. Therefore, the proposed IMPT features higher efficiency and power density without additional size and costs. To confirm the validity of the proposed IMPT, the operational principles, theoretical analysis, design considerations, and experimental results from a 350 W prototype are presented.

In this paper, we propose a lossless snubber cell for a soft-switched bidirectional buck–boost converter (BBC). The proposed snubber cell provides all switches with soft-switching conditions in both the bidirectional power flows of the BBC. In addition, the cell also achieves a relatively low circulating current for the snubber operation over a wide load range. In particular, the reverse recovery problem of the synchronous rectifier can be eliminated with the aid of the snubber inductor. Accordingly, the snubber cell enables high-frequency switching of approximately 60 kHz for all power switches and achieves high efficiency and high power density. Moreover, the proposed snubber cell does not have any auxiliary switch; therefore, complex auxiliary circuits or driving algorithms for the auxiliary switch are not required. Therefore, the proposed snubber cell has a simple structure with high reliability. To confirm the validity of the proposed lossless snubber cell, we provide detailed analyses, design guidelines, and experimental results using a 3-kW laboratory prototype.

A novel asymmetric current-fed energy-recovery circuit (ERC) for a plasma display panel (PDP) is proposed. Two ERCs composed of single switch and different resonant inductors, ERC-Y and ERC-X, are used for both sides of the PDP, and slow discharging and fast charging times can be employed. The ERC-Y discharging C_p to zero employs the slow discharging time, which reduces a current stress on ERC-Y compared with ERC-X. The ERC-X charging C_p to V_s employs the fast charging time, which ensures a stable light emission. Furthermore, inductor currents are built up before the PDP is charged and discharged. These built-up inductor currents help to fully charge and discharge the PDP, achieve the zero voltage switching (ZVS) of main switches, reduce an electromagnetic interference (EMI) noises, and compensate for a large gas-discharge current. Therefore, it features the ZVS, low EMI noises, low current stress, and high energy-recovery capability. The operation of the proposed circuit, design considerations, and experimental results are presented to show the validity of the proposed circuit.