Modular quasi-8-level inverter topology by binary voltage adding through transformers with test bench results

Standard multilevel inverters offer high quality output voltages at small voltage steps even without using additional filter equipment. Voltages of separate converter stages can be added by series connection of transformers. However, the number of individual switches to be controlled precisely and at given sequence is a heavy burden for control. The hardware expenditure of standard circuits is rather high, too. This proposal employs an inverter system composed of 4 identical standard 2-level inverter modules producing binary weighted voltages being added at output side windings of transformer. Eight levels of output voltage (for e.g. positive polarity, including zero) can be generated. This quasi-8-level inverter achieves high quality output voltage at low harmonics and small voltage steps at significantly lower expenditure in hardware and control set complexity than comparable standard multi-level inverters. All modules are operated at same power dissipation. Hardware is realized by modules enabling fault handling by one spare part out of four power components used (PWM circuit, transformer) for full power rating, or at power reduction by 50% through rearranging one module and setting aside the defective part. In order to generate the high quality output voltage a special yet simple pulse control set is introduced. This paper describes its analog and digital realization.