Wanmin Fei Bin Wu Qin Wu A novel SHE-PWM method for five level voltage inverters with quarter-wave symmetry. 1034-1038 2009 CCECE http://dx.doi.org/10.1109/CCECE.2009.5090287 conf/ccece/2009 db/conf/ccece/ccece2009.html#FeiWW09