Using Snubber Circuits in a Brushless Exciter Will Reduce Voltage Commutation Spikes


  • Esnick Felissaint Esnick Felissaint is with Siemens-Energy, 4400 N Alafaya Trl, Orlando, FL. 32826
  • Kalpathy Sundaram Kalpathy Sundaram is with the University of Central Florida, 4000 Central Blvd, Orlando, FL. 32816


Brushless exciter, diode, rectifier, commutation spike, forward biased, reversed biased, P-N junction, cathode, forward voltage, repetitive peak reverse voltage, fuse, reverse recovery time, capacitor


In a brushless exciter with a multi-phase bridge rectification system, diodes open and close periodically. When a diode turns off, a commutation voltage spike is generated by the internal AC winding inductance of the machine.  Voltage spikes can be detrimental to the health of the diodes that are operating in the machine. A diode can fail short in the reverse direction if its reverse recovery voltage is exceeded, or it can fail open due to excessive current in the forward direction. Voltage commutation spikes are known to occur with various amplitude in shaft voltage to ground with static excitation systems and exciter field voltage to ground in brushless excitation systems. This paper evaluates the phenomena of voltage commutation spikes and presents a snubber circuit as a robust solution that can reduce the amplitude of the spikes. Consequently, prolonging the life of the diode and allows it to function as designed at optimal level.


IEEE Std. 421.1-2011, "IEEE Standard Definitions for Excitation Systems for Synchronous Machines"

S. M. Sze, Physics of Semiconductor Devices, 2nd ed. (Wiley, New York, 1981), Chap. 5.

B. J. Baliga, Silicon Carbide Power Devices, Singapore:World Scientific, 2005.

B. Van Zeghbroeck (2011). "P-n junctions: I-V characteristics of real p-n diodes". Retrieved 2020-11-02.

P. O. Lauritzen and C. L. Ma, "A simple diode model with reverse recovery", JEEE Trans. Power Electron., vol. 6, pp. 188-191,Apr. 1991

Kal, Santiram (2004). "Chapter 2". Basic Electronics: Devices, Circuits and IT Fundamentals (Section 2.5: Circuit Model of a P-N Junction Diode ed.). Prentice-Hall of India Pvt.Ltd.

Isaa Batarseh, Power electronics circuit analysis and design, 2nd ed., January 2018.

Somos, Istvan, “Commutation and destructive oscillation in diode circuits,” Transactions of the American Institute of Electrical Engineers, vol. 80, May 1961

Wei-Li, Dai, Hai-Hong, Qin, Guo, Hong-Hao et al, “Analysis of commutation in three-phase rectifier of doubly salient electro-magnetic generator,” Proceedings of the CSEE, vol 28,

Etto E. VonZastrow and James H. Galloway, “Commutation behavior of diffused high-current rectifier diodes,” IEEE Transactions on Industry and General Applications, vol. IGA-1965.




How to Cite

Esnick Felissaint, & Kalpathy Sundaram. (2024). Using Snubber Circuits in a Brushless Exciter Will Reduce Voltage Commutation Spikes. International Journal of Sciences: Basic and Applied Research (IJSBAR), 73(1), 139–153. Retrieved from