Determination of the Number of Cells in a Stepped Sine Wave Inverter for Equal Charge Transfer

The synthesis of an inverter sine wave output voltage by a staircase wave shape of low level voltage sources (cells) is accomplished by combining the cells in series at specific time intervals. Different cells of the inverter are then connected to the load for different time durations which results in unequal discharging of the cells. In order for the cells to transfer equal charge during the system operation, each voltage step should consist of a different number of cells in a parallel combination (module), the number of which depends on the time along the wave shape. The number of cells in each module is determined from the circuit current analysis and the appropriate switching time intervals, and is performed for a resistive and an inductive load. This number depends on the number of inverter voltage steps, the cell internal resistance, and the type of the load. The proper number of cells in the modules ensures identical state of charge of the cells, and equal cell recharging, and simplifies cell inspection, maintenance, and replacement.