Three-Level Inverter Modulation for Unbalanced Half-Bus Voltages

The patent segments the bus voltage measurement into two independent half-bus voltages (positive half-bus voltage and negative half-bus voltage) instead of treating the bus as a single unit. This segmentation allows the control system to independently account for voltage imbalances on each side of the neutral point, enabling accurate output voltage control even when the overall bus voltage is unbalanced. The segmentation principle resolves the contradiction by allowing adaptability to unbalanced conditions while maintaining precision through separate measurement and compensation of each half-bus voltage.

The patent introduces an intermediary measurement approach by measuring the half-bus voltages relative to the neutral point rather than measuring the full bus voltage directly. This intermediary measurement serves as a mediator between the unbalanced bus voltage condition and the control system, providing accurate voltage information that accounts for neutrality point shifts. The intermediary measurement enables precise duty cycle calculation without requiring complex compensation algorithms, thus maintaining control simplicity while improving voltage accuracy.

The patent implements a self-service control approach where the control system automatically adapts to bus voltage imbalances by using the measured half-bus voltages to calculate appropriate duty cycles. The system serves itself by internally compensating for voltage imbalances without requiring external intervention or complex coordination with other system components. The controller automatically adjusts the switching duties of positive and negative bridge arms based on the measured half-bus voltages, eliminating the need for manual calibration or complex external control mechanisms, thus achieving high precision with manageable complexity.