Search

In wide voltage range applications, traditional LLC converters suffer from the following issues: (i) to cover a wide voltage gain operating range, the required switching frequency range is also large, which challenges the design and optimisation of magnetic components, gate driver circuitry, and electro-magnetic interference filter; (ii) a small magnetising inductance is preferred in wide voltage gain range application, which leads to the increase of circuit circulating current and corresponding conduction loss; (iii) passive elements are determined based on the minimum switching frequency, so bulky passive elements are required to satisfy the required operation range. To solve these problems, in this study, a full-bridge LLC (FBLLC) resonant converter with two operation modes, namely full-bridge operation and frequency doubler operation, is proposed for wide voltage gain range application. The FBLLC converter discussed in this study can be designed in half of the input voltage range when compared with the conventional method, so smaller switching frequency operating range and higher efficiency operation are guaranteed. In addition, the smooth mode transition is achieved by introducing switching frequency feedforward control and small output voltage overshoot or undershoot is observed. A 150 W experimental prototype was built to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

LLC resonant converter has been widely used in many applications due to its characteristics of high efficiency and high frequency characteristics. Analysis method plays great role in converter design and operation performance. For LLC resonant converter, the most frequently used analysis methods are frequency-domain analysis (FDA) and time-domain analysis (TDA). FDA assumes that only fundamental harmonics can deliver energy in the system, while TDA is obtained by solving circuit state equations. In this study, comprehensive and complete comparisons between FDA and TDA in terms of analysis methodology, parameter design, analysis accuracy, conduction loss, other power losses, and system efficiency are implemented. The analysis and comparison results show that under the same system specifications, by adopting TDA, a larger magnetising inductance value can be used when compared with FDA, which will reduce the resonant tank circulating current and increase the system efficiency. The comprehensive analysis can provide guidance for engineers when analysing and designing LLC resonant converter. Finally, a 200 W experimental prototype was built and tested to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

High‐temperature optical analysis of three different InGaN/GaN multiple quantum well (MQW) light‐emitting diode (LED) structures (peak wavelength λp = 448, 467, and 515 nm) is conducted for possible integration as an optocoupler emitter in high‐density power electronic modules. The commercially available LEDs, primarily used in the display (λp = 467 and 515 nm) and lighting (λp = 448 nm) applications, are studied and compared to evaluate if they can satisfy the light output requirements in the optocouplers at high temperatures. The temperature‐ and intensity‐dependent electroluminescence (T‐IDEL) measurement technique is used to study the internal quantum efficiency (IQE) of the LEDs. All three LEDs exhibit above 70% IQE at 500 K and stable operation at 800 K without flickering or failure. At 800 K, a promising IQE of above 40% is observed for blue for display (BD) (λp = 467 nm) and green for display (GD) (λp = 515 nm) samples. The blue for light (BL) (λp = 448 nm) sample shows 24% IQE at 800 K. [ABSTRACT FROM AUTHOR]