Equal load sharing modulation technique for series-connected H-bridge multilevel converters

A modulation scheme for multilevel inverters, which ensures equal loading of the power modules is presented. The scheme uses two-to-three transformation to calculate duty-cycles of each phase directly from the reference vector expressed in the Cartesian coordinate system. There is no need for trigonometric functions, which makes the applicability of the algorithm very effective in a DSP or an FPGA. The pulse formation with module circulation is also introduced. The module circulation ensures equal load sharing and balanced DC-link voltages. The methods are verified with simulations and with experimental tests on a seven-level 100 kVA, 3 kV prototype induction motor drive.