1. Baker RH. Electric power converter. US Patent 03-867-643; February 1975.
2. Baker RH. High-voltage converter circuit. US Patent 04-203-151; May 1980.
3. Nabae A, Takahashi I, Akagi H. A new neutral-point clamped PWM inverter. In: Proceeding of the industry application society conference; 1980. p. 761–6.
4. Fracchia M, Ghiara T, Marchesini M, Mazzucchelli M. Optimized modulation techniques for the generalized N-level converter. In: Proceeding of the IEEE power electronics specialist conference, vol. 2; 1992. p. 1205–13.
5. Meynard TA, Foch H. Multi-level conversion: high voltage choppers and voltage source inverters. In: Proceedings of the IEEE power electronics specialist conference, vol. 1; 1992. p. 397–403.