| Abstract |
Several modulation methods may be used in high-power, medium voltage, multilevel converters
operating at low switching frequencies. This paper considers the application of Selective Harmonic
Elimination PWM (SHEPWM) for utility-connected converters where very tight control over
individual harmonic amplitudes is essential, and a restricted modulation index range is usually
sufficient. An alternative approach for the calculation of firing angles is outlined, in particular for 5-
and 7-level inverters switching at frequencies typically 3 to 5 times fundamental. A modification to
the method allows inherent equalisation of the power flow to/from the individual DC energy sources,
whilst still allowing elimination of specified harmonics. The modified method is used to generate
firing angles to enable closed loop current control of the multilevel converter. Results from computer
simulations are presented in this paper. |
