| Abstract |
Although fundamental frequency switching has been
the preferred method for high-power medium-voltage multilevel
converters, the technology of current generation power
semiconductors has made it possible to use higher rates. In
utility-connected applications, where a restricted modulation
index range is usually sufficient, a main requirement is for very
tight control over individual harmonics. For these reasons, this
paper considers the application of Selective Harmonic
Elimination PWM (SHEPWM) with 5- or 7-level converters
switching at low multiples of the fundamental frequency. An
alternative approach for the calculation of multiple solutions of
the firing angles is outlined, and is then applied in a modulation
scheme that inherently equalizes the power flow from and to the
individual DC energy sources. Computer simulation results for
a 7-level medium-voltage converter are presented in this paper.
A 3 kVA, 380VAC laboratory prototype was designed using the
same operating principles as the high-power converter,
constructed and tested. Experimental results confirming the
expected performance are included. |
