Abstract : The working principle of the snubber circuit for power switching devices is analyzed, and the selection method of key component parameter values ​​for the snubber circuit is given. Simulation experiments of two snubber circuits are carried out using the circuit simulation software Multisim, and the similarities and differences between the two circuits are analyzed and their effectiveness is verified. Keywords : Power switching device, buffer circuit, simulation CLC number: TP319 [align=center]Analysis and Simulation of Buffer Circuit for Power Switching Device Zhang Yang Qu Yanbin Li Junyuan (Department of information science and engineering, Harbin Institute of Technology at Weihai, 264209) Zhang Yang Qu Yanbin Li Junyuan (School of Information Science and Engineering, Harbin Institute of Technology at Weihai, 264209)[/align] Abstract : The work principle of the buffer circuit for power switching device is studied. The choice of the main parts parameters is introduced. Schematic drawings of two kinds of buffer circuit are built in the Multisim format and simulated. The similarities and differences between them are analyzed and the validities are proved. Keywords : Power Switching Device, Buffer Circuit, Simulation 1 Introduction The buffer circuit, also known as the absorption circuit, has several functions including controlling the turn-off of power switching devices such as MOSFET and IGBT, restoring surge voltage of freewheeling diodes, reducing switching losses, limiting voltage rise rate, and eliminating electromagnetic interference[1]. In the application of power switching devices, with the continuous increase of voltage, current, and frequency, protection becomes particularly important, and the role of buffer circuits becomes even more significant. Therefore, this paper uses the circuit simulation software Multisim to analyze and compare the protection performance of the buffer circuit in a MOSFET inverter. 2. Working Principle and Improvement of Inverter Buffer Circuits Figure 1 shows three common buffer circuits in inverters. Their common characteristic is that the voltage of the absorption capacitor C_S is equal to the power supply voltage. Before the next turn-off, part of the energy from the capacitor voltage overshoot is fed back to the power supply, and the other part is consumed in the resistor. A brief analysis of the working process of the buffer circuit in Figure 1(c) is as follows: [align=center] (c) Figure 1 Schematic diagram of three common buffer circuits[/align] Theoretical analysis and practice show that the buffer circuit in Figure 1(a) is only very effective in suppressing transient voltages at low power levels. As the power level increases, this buffer circuit may oscillate with the parasitic inductance L_P of the DC bus. In the buffer circuit shown in Figure 1(b), the fast recovery diode D[sub]S[/sub] can effectively suppress transient voltage, thereby suppressing resonance. However, as the power level increases further, the parasitic inductance L[sub]S1[/sub] of this circuit becomes very large and cannot effectively suppress transient voltage. For high-current circuits, the buffer circuit shown in Figure 1(c) can be used, which can effectively suppress oscillation and has a small parasitic inductance. [align=center] Figure 2 A buffer circuit with variable capacitance[/align] 3 Buffer circuit turn-off waveform and component selection [sup][3][/sup] Figure 3 shows the typical turn-off waveform of the buffer circuit. Where: It should be noted that the buffer diode should be a fast soft recovery type to avoid severe oscillation during turn-off. The buffer resistor should be a non-inductive resistor to avoid oscillation during turn-on. 4. Simulation Analysis of the Buffer Circuit The simulation results are shown in Figure 5. The figure shows the turn-on and turn-off waveforms of the switching device without a buffer circuit and with the above two types of buffer circuits (represented by 1, 2, and 3 respectively). For ease of comparison, the MOSFET trigger signal in these three cases has been sequentially processed. [align=center] (b) Turn-on waveform Figure 5 MOSFET switching voltage waveform[/align] As can be seen from the figure above, under the condition that the simulation parameters are completely consistent, the buffer circuit shown in Figure 2 can effectively suppress transient overvoltage when the MOSFET is turned off. When the MOSFET is turned on, due to the presence of C[sub]S2[/sub] (C[sub]S5[/sub]) in the circuit, the charge in the buffer circuit can be released within a limited time, effectively avoiding the oscillation caused by the resonance of C[sub]S[/sub] and L[sub]S[/sub] (the area indicated by ○B in Figure 3). If the discharge time needs to be adjusted, simply change the value of C[sub]S2[/sub] (C[sub]S5[/sub]) (as shown in Figure 5(b), curve 4 is the waveform when the capacitor value is 10nF). Compared with the unbuffered circuit, the buffer circuit shown in Figure 1(c) can reduce the oscillation of the switching device during turn-on and turn-off to a certain extent, but it still has a large peak value. This is mainly because the value of C[sub]S[/sub] is too small. When C[sub]S[/sub] in Figure 1(c) is increased to 600nF, the turn-off waveform is shown in Figure 6, which effectively suppresses the generation of turn-off surge. In addition, through simulation analysis of the two buffer circuits mentioned above at different frequencies, it was found that their effects are basically the same. As the switching frequency increases, the two peak voltages show a decreasing trend[4]. This is because the resistive-inductive load has a suppressive effect on the change of bus current. When the frequency is high enough, the bus current has not reached a stable value before the switch is turned off. Both voltage spikes are related to the bus current. However, as the frequency increases, the turn-off waveform deteriorates and the output power decreases. Therefore, soft switching is generally used at high frequencies. [align=center] Figure 6 Turn-off waveform after increasing Cs in Figure 1(c)[/align] 5 Conclusion This paper analyzes the commonly used C-type buffer circuit and a variable capacitance buffer circuit through simulation. Both circuits can effectively suppress the transient voltage peaks when the switching device is turned on and off. In comparison, the buffer circuit proposed in reference [2] is relatively complex, but the effect is better. In summary, in practical applications, by effectively using simulation tools to analyze the buffer circuit for different circuit conditions, the circuit parameters can be optimized and a circuit that meets the design requirements can be found. References [1] Huang Shisheng. New type of arc welding power supply and its intelligent control [M]. Beijing: Machinery Industry Press, 2000. [2] Zhou Yueqing, Yin Zhongming. Design of a new type of IGBT buffer circuit [J]. Electric Welding Machine, 2004, 34 (10): 11-12. [3] Xu Xiaofeng et al. Research on absorption circuit of IGBT inverter. Power Electronics Technology, 1998, 32 (3): 43-47. [4] Sun Qiang, Yu Juan et al. Simulation analysis of buffer circuit of MOSFET inverter [J]. Electrical Application, 2005, 24 (5): 42-44. About the authors: Zhang Yang (1975.12-), male, from Qingdao, Shandong, lecturer, master, mainly engaged in research on artificial intelligence, computer control, etc. Qu Yanbin (1961-), male, from Muping, Shandong, professor, doctor, research direction: computer control, embedded system and application, control theory and application. Contact Information: Mailing Address: P.O. Box 5, Faculty and Staff Office, Harbin Institute of Technology (Weihai), Shandong Province, China Department: School of Information Science and Engineering, Harbin Institute of Technology (Weihai) Name: Zhang Yang Postcode: 264209 Telephone: 0631-5687204 E-mail: [email protected]