A Study on a Carrier Based PWM having Constant Common Mode Voltage and Minimized Switching Frequency in Three-level Inverter

  • Ahn, Kang-Soon (Willings Co. Ltd) ;
  • Choi, Nam-Sup (Div. of Electrical, Electron. Communication and Computer Engineering, Chonnam National University) ;
  • Lee, Eun-Chul (Willings Co. Ltd) ;
  • Kim, Hee-Jun (Dept. of Electronic Systems Engineering, Hanyang University)
  • Received : 2015.07.01
  • Accepted : 2015.11.10
  • Published : 2016.03.01


In this paper, a carrier-based pulse with modulation (PWM) strategy for three-phase three-level inverter is dealt with, which can keep the common mode voltage constant with minimized switching frequency. The voltage gain and the switching frequency in overall operating ranges including overmodulation are investigated and the analytic equations are presented. Finally, the leakage current reduction effect is confirmed by carrying out simulation and experiment. It will be pointed out that the leakage current cannot be perfectly eliminated because of the dead time.


Transformerless photovoltaic system;Three-level inverter;Carrier-based PWM;Leakage current elimination;Medium Vector PWM


  1. Ziya Ozukan and Ahmet M. Hava, “Classification of Grid Connected Transformerless PV Inverters with a Focus on the Leakage Current Characteristics and Extension of Topology Families,” Journal of Power Electronics, Vol. 15, No. 1, pp. 256-267, Jan. 2015.
  2. T. Kerekes, R. Teodorescu and U. Borup, “Transformerless Photovoltaic Inverters connected to the Grid”, Conf. Record on APEC 2007, pp. 1733-1737, Anaheim, USA, Feb. 25-Mar. 1, 2007.
  3. H-. J. Kim, H-. D. Lee, S-. K. Sul, “A new PWM strategy for common-mode voltage reduction in neutral-point-clamped inverter-fed AC motor drives,” IEEE Trans. on Industry Applications, vol. 37, no. 6, pp.1840-1845, Nov/Dec 2001.
  4. A. Videt, P. Le Moigne, N. Idir, P. Baudesson and J. Ecrabey, “A new carrier-based PWM for the reduction of common mode currents applied to neutral-point-clamped inverters”, Conf. Record on APEC 2007, pp. 1224-1230, Anaheim, USA, Feb. 25-Mar. 1, 2007.
  5. M. C. Cavalcanti, K. C. Oliveira, A. M. Farias, F. A. S. Neves, Gustavo M. S. Azevedo and F. C. Camboim, “Modulation Techniques to Eliminate Leakage Currents in Transformerless Three-Phase Photovoltaic Systems,” IEEE Trans. on Industrial Electronics, vol. 57, no. 4, pp. 1360-1368, Apr. 2010.
  6. K. Zhou and D. Wang, “Relationship between space-vector modulation and three-phase carrier-based PWM: A comprehensive analysis,” IEEE Trans. on Ind. Electron., vol. 49, no. 1, pp. 186-196, Jan 2002.
  7. M. C. Cavalcanti, A. M. Farias, K. C. Oliveira, F. A. S. Neves and J. L. Afonso, “Eliminating Leakage Currents in Neutral Point Clamped Inverters for Photovoltaic Systems,” IEEE Trans. on Industrial Electronics, vol. 59, no. 1, pp.435-442, Jan. 2012.
  8. J-. S. Lee and K-. B. Lee, “New Modulation Techniques for a Leakage Current Reduction and a Neutral-Point Voltage Balance in Transformerless Photovoltaic Systems Using a Three-Level Inverter,” IEEE Trans. on Power Electronics, vol. 29, no. 4, pp.1720-1732, April 2014.
  9. X. Guo, M. C. Cavalcanti, A. M. Farias and J. M. Guerrero, “Single-Carrier Modulation for Neutral-Point-Clamped Inverters in Three-Phase Transformerless Photovoltaic Systems,” IEEE Trans. on Power Electronics, vol. 28, no. 6, pp.2635-2637, June 2013.
  10. Nam-Sup Choi, Eun-Chul Lee and Kang-Soon Ahn, “A Carrier-Based Medium Vector PWM Strategy for Three-level Inverters in Transformerless Photovoltaic Systems”, Conf. Record on ICPE2015-ECCE Asia, July 1, 2015.