Capacitor Voltage Balancing for Single-Phase Asymmetric Cascaded H-Bridge Inverters

Capacitor Voltage Balancing of a Grid-Tied, Cascaded Multilevel Converter with Binary Asymmetric Voltage Levels Using an Optimal One-Step-Ahead Switching-State Combination Approach

“…The suggested algorithm uses an optimal, one-step-ahead switching-state combination approach to balance the capacitor voltages as quickly as possible. In comparison to that of the methods available in [14][15][16][17][18]24,[28][29][30], the presented algorithm utilizes a low switching frequency (couple of kHz) and it achieves a quick dynamic response without requiring any additional hardware. Moreover, it can be easily applied to higher level asymmetric MLCs operated with nearest-level control (NLC).…”

“…Thus, considering a variation of the converter's displacement power factor and current amplitude, a large, intricate array of switching-state sequences would be required in theory. Although, when considering the illustration of the cell-voltage combinations in [24] [Figure 4], it becomes obvious that both the current-second and the applied voltage-second areas at steady state for any discrete output voltage become zero, if the EMMC itself is operated with a unity displacement power factor. Therefore, to reduce the required computational effort and the memory for the lookup table, the output current should be controlled to be in phase with the converter's output voltage, as depicted in Figure 5 for grid-feeding mode, which slightly reduces the actual power factor cos(ϕ).…”

“…This approach requires a rectifier stage or a DC converter for each H-bridge module, introducing additional system costs. The authors of [24] suggest to replace only a limited selection of capacitor modules by additional isolated voltage sources, acting as charge buffers. Similarly, in [14,25,26] it is suggested to combine a number of redundant high and low resolution cells, which help to maintain the capacitor charge balance, whereas the number of output levels is reduced.…”