Due to climate changes, planetary efforts are conducted towards energy saving by increasing equipment efficiency. Especially the high efficiency not only under full load conditions but also under light load conditions is required in the applications such as personal and server computer, display devices, and so on. Also system requirements often dictate the need for most switching power supplies to provide regulated and isolated multiple outputs. Among the regulation schemes for multiple outputs, the synchronous switch post regulator (SSPR) is one of the methods that can achieve high efficiency. The SSPR is basically a simplified version of a buck converter in which the buck switch is placed directly in series with the pre-regulator rectifier, and this will reduce the costs. Also, it is easy to implement the protection functions and achieves good regulation over a wide range of line and load variations. However, it has many components for auxiliary output and the regulation switch is hard switching. To overcome these problems, the proposed SSPR circuits are derived. The proposed ones have simple structure with low component counts and ZVS capability by modulating the gate signal of regulation switch. Thus, the multi-output converter with proposed SSPR circuits can have higher efficiency.
Firstly, a new asymmetric half-bridge multi-output flyback converter is proposed. It consists of two synchronous switches in the secondary side for two outputs with same ground. The primary switches control the main output voltage and the synchronous switches in the secondary side control the auxiliary output voltage. The main advantages of the proposed converter are that the primary switches have low voltage stress, the secondary regulation switch for auxiliary output can achieve the zero-voltage switching (ZVS) under entire load conditions, and the low conduction loss can be obtained by using the synchronous switches.
Secondly, a new active clamp multi-output forward converter is proposed. It consists of four synchronous switches in secondary side for two outputs with same ground. The primary switches control the main output voltage and the synchronous switches in transformer secondary side control the auxiliary output voltage. The main advantages of the proposed converter are that the secondary regulation switch for auxiliary output can achieve the zero-voltage switching (ZVS) at entire load conditions and the secondary rectified voltage is a three-level waveform, which can reduce the output filter.
Thirdly, a new standby structure where the standby flyback converter is integrated with the ZVS multi-output full-bridge DC-DC converter is proposed. In standby mode, the standby power is generated from the conventional flyback converter. However, in normal mode, the auxiliary output of high efficiency full-bridge converter provides the standby power. Thus, the proposed structure shows higher efficiency under entire load conditions, especially light load conditions in normal mode, due to the ZVS of all switches and lower conduction and core loss from the CCM operation of the standby transformer.
Finally, the proposed SSPR circuits is generalized to ‘ZVS buck cell’ which is applied for non-isolated multi-output converters and isolated multi-output rectifiers. Also, to further reduce the output filter of auxiliary output, ‘modified ZVS buck cell’ is proposed by using one additional diode and tapped winding.
In this doctoral dissertation, to improve the conventional SSPR circuits, new SSPR converters capable of ZVS are proposed, applied to sever power applications, and generalized to ‘ZVS buck cell’ and ‘modified ZVS buck cell’. As a result, it is expected that proposed works can provide to improve the overall efficiency in multi-output applications.
지구 온난화 등의 환경 문제로 인해 에너지 절약에 대한 관심이 높아지고 있는 상황에서 고효율 제품에 대한 수요가 크게 증가하고 있다. 특히, 우리 주변의 여러 전자기기들을 살펴보면, 출력에 여러 전압 레벨을 갖은 전원 장치를 요구하고 있다. 이는 일반적으로 트랜스포머의 multi-winding을 이용한 다중 출력 컨버터로 구현이 된다. 다중 출력 컨버터에서는 각 출력 전압의 제어와 효율적인 면이 중요한 요소가 된다. 각 출력 전압을 제어하기 위한 여러 가지 방식들이 제안되어 있고, 그 중에서 메인 출력과 병렬로 MOSFET 스위치를 이용해서 보조 출력들을 얻는 SSPR(Synchronous Switch Post Regulator) 방식이 효율 면에서 가장 장점이 있는 방식이라 할 수 있다.
가장 일반적인 SSPR 방식은 전압 또는 전류 소스로부터 단방향 스위치나 양방향 스위치를 활용하여 보조 출력으로 에너지를 전달하는 것이다. 크게 flyback-type 이나 forward-type으로 구분이 될 수 있으며, 특히 forward-type 에 대한 연구가 많이 이루어져 왔다. 이는 대부분 출력 인덕터 전압을 제어하는 방식들로서 conduction loss를 매우 키우거나 추가적인 소자들로 인해 회로가 매우 복잡해지고, 보조 출력 제어스위치가 hard switching 하는 단점을 가진다.
본 논문에서는 기존의 forward-type SSPR 회로를 개선하여 보다 단순하고, zero-voltage switching(ZVS)이 가능한 SSPR 회로를 제안한다. 기존의 일반적인 forward-type SSPR 방식을 각각 flyback converter나 forward converter를 가진 메인 출력에 적용하여 제안하는 SSPR 회로를 유도한다. 제안하는 회로는 기존에 회로에 비해 단순한 구조를 가지고 있고 보조 출력 제어스위치의 ZVS가 가능하다. 제안하는 SSPR 회로들을 여러 converter에 적용해보고, 실험으로 그 성능을 검증하며, 일반화된 switching cell을 유도하여 family를 구성한다.
본 논문에서 제안된 SSPR을 이용한 다중출력 컨버터는 단순한 구조에 고효율 특성을 가짐으로써 다중 출력을 요구하는 여러 전자기기에서 적용되어 효율 개선을 할 수 있을 것으로 기대한다.
