A SIMPLIFIED LOSSLESS PASSIVE SOFT- SWITCHING SNUBBER FOR PWM HALF-BRIDGE INVERTERS 2009 Second International Conference on Intelligent Computation Technology and Automation Yuanyuan Yang School of Electronics and InformationTongji University Shanghai, Xu Weisheng School of Electronics and Information Tongji University Shanghai, China 班級 : 控晶四乙 學號 :4a02c076 姓名 : 王鈺傑 指導老師 : 王明賢

I. INTRODUCTION  Soft-switching methods can be broadly classified into two groups: active one and passive one. In recent years, passive soft-switching has been given renewed notice as having a better price/performance ratio than their active counterparts [1]. And snubber technique is the only possible way to achieve soft-switching through passive means. The snubber technique is having an inductor and capacitor placed in series and parallel with each power switch to reduce its di/dt and dv/dt, achieving ZCS turn-on and ZVS turn-off or ZCS turn-off and ZVS turn-on for each switch. Fig 1 shows the McMurray Snubber [2], which had been widely used in PWM inverters. Although it can partly return the snubber energy into DC rail, it is still lossy, dissipating the recovered energy in resistors. Recently, many lossless passive snubber circuits have been proposed, but they almost use transformers, whose parameters such as their associated diode stress and leakage inductance problem still remain to be studied

. There have been great improvements in this field such as [3, 4], which have an idea that takes advantage of transformer as a part of resonant circuitry. In [5] the authors present a method adding additional voltage stress to provide higher efficiency and larger duty ratio range

II. SIMPLIFIED LPSSS CIRCUIT ANALYSIS  Fig 2 shows the proposed simplified LPSSScircuit, which consists of two IGBT switches 1 S,2 S, and two diodes 1 D, 2 D that are reversely paralleled to the main switches, and a snubberinductor s L which reduces the rate of turn- oncurrent(di/dt) to achieve ZCS turn-on and restrains the reverse recovery current of diodes,and a larger capacitor b C which has two functions: one is, as a passive voltage source connected across the two snubber capacitors s1 C, s2 C,guarantying the sum of both snubber capacitors’ voltages constant and equal to the DC link voltage; the other is, as a transient energy storage, recovering the snubber energy into the DC rail through the resonant inductorr L. The simplified LPSSS circuit also includes asnubber diode s1 D and a snubber capacitor s1 C for the upper main device 1 S and symmetrically s2 D and s2 C for the lower main device 2 S, which can reduce dv/dt to achieve ZVS turn-off for

each main switch and remain the circuit free from parasitic oscillation. Because the upper and lower main devices always operate complementarily to each other during normal PWM operation, to further guarantee the sum of both snubber capacitor’ voltage constant, the two snubber capacitor are connected to the midpoint of the phase leg.

Fig 3 [6] shows the ideal voltage operating waveforms of s1 C and s2 C during 1 S turns off and 2 S turns on. In this time, cs1 V increases, cs2 V decreases and the sum of both capacitors’ voltage remains constant.

3.1 幾個假設受僱於 分析 [7] ：  在這個電路中的所有元件都是理想的 ;  提供感性負載，等效  電流源需要的負荷的地方  在減刑的研究 ;  為了簡化分析， S L 是等於 r L ，  B C ，作為無源電壓源 E ，大  夠了。 Ë= D U （直流電源電壓）。 3.2 符號說明  1 （ ω ） =1/1 的  b  L  ç  是諧振角  次數 11 / B Z = L C 是  諧振特性阻抗  電路，其包括電感器。 S L ， R L 和  電容器 B C ， 1 / R S R 。 S L= L L L+ L;

CONCLUSION 簡化的無源無損軟開關緩衝電路已被本文提出。它由導通 / 關斷緩衝電路再生電路，它包括一個較大的電容器和諧振電感器回收 存儲在此緩衝能量緩衝電容器為直流軌道，實現緩衝技術和共振的結合 技術。這種簡化的電路可以工作井具有高性能，低成本和無需額外的開 關或控制電路，它適合任何 PWM 逆變器。從仿真結果，這 LPSSS 電路可 以實現 ZVS 關斷 / ZCS 導通主開關和最小化開關損耗和應力。然而，由於 簡單的拓撲的，這在大型提出的電路不能正常工作功率範圍有限的負載 電流和輸出功率。

References  tp%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F %2F % 2F pdf%3Farnumber%3D tp%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F %2F % 2F pdf%3Farnumber%3D 