Cascaded Bridge Staircase Modulation for Low-Loss Power Balance
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Solution Overview
Problem
Conventional medium-voltage solid-state transformer systems face challenges in optimizing switching losses, power balance, and dynamic performance due to inadequate modulation methods for cascaded bridge systems.
Innovation Solution
A power converter with n cascaded bridges, where each bridge outputs multilevel pulses that are phase-shifted by a consistent angle, resulting in a desired output pulse waveform. Each bridge includes 2k+1 sub-pulses, symmetrically distributed with increasing and decreasing pulse widths, and zero zones to optimize phase shift and pulse width differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional modulation methods are used for cascaded bridge systems, then the system structure is simple, but switching losses are high and power balance is poor
Solution Approach 1:
The output pulse of each cascaded bridge is segmented into multiple sub-pulses (2k+1 sub-pulses) with different pulse widths. This segmentation allows each bridge to contribute differently to the total output, enabling better power balance and reduced switching losses by optimizing the conduction time of each bridge module.
Solution Approach 2:
Different sub-pulses within each bridge output have different pulse widths, creating local quality variations. The pulse widths follow a specific distribution pattern (increasing then decreasing) centered around the (k+1)th sub-pulse, which optimizes the power contribution of each bridge segment while reducing overall switching losses.
2Productivity
If conventional modulation methods are used for cascaded bridge systems, then the control is simple, but dynamic performance is poor
Solution Approach 1:
The modulation method dynamically adjusts the pulse widths of different sub-pulses based on real-time power balance requirements. The pulse width distribution pattern allows the system to respond dynamically to load changes while maintaining optimal performance across varying operating conditions.
Solution Approach 2:
The modulation strategy incorporates power balance considerations through the structured pulse width distribution. By centering the pulse width variation around the (k+1)th sub-pulse and creating symmetric increase-decrease patterns, the system achieves inherent feedback-like behavior that maintains power balance without requiring complex external control loops.
3Object-generated harmful factors
If conventional modulation methods are used for cascaded bridge systems, then the harmonics are not effectively reduced, but the modulation scheme remains simple
Solution Approach 1:
The modulation method employs periodic pulse patterns with 2k+1 sub-pulses in each half cycle, creating a structured periodic waveform. This periodic structure with multiple pulses per cycle helps cancel out harmonic components through constructive and destructive interference patterns, effectively reducing total harmonic distortion.
Solution Approach 2:
The pulse width distribution follows an asymmetric pattern that increases then decreases around the center (k+1)th sub-pulse. This controlled asymmetry in pulse width modulation creates specific harmonic cancellation effects while maintaining the fundamental output voltage, effectively reducing unwanted harmonic content.
Data Source
AI summary
A power converter and a staircase modulation method therefor are provided. The power converter includes n cascaded bridges, where n≥2, the n cascaded bridges are each configured to output same multilevel pulses, the output n multilevel pulses are sequentially phase-shifted by a same angle, and the n multilevel pulses are superposed on each other to form a desired output pulse waveform of the power converter. Each of the n cascaded bridges is configured such that an output pulse of each cascaded bridge includes 2k+1 sub-pulses in each half cycle, where k≥1; and the 2k+1 sub-pulses are symmetrically distributed by using a (k+1)th sub-pulse as a center, pulse widths from a 1st sub-pulse to the (k+1)th sub-pulse sequentially increase, and pulse widths from the (k+1) sub-pulse to a (2k+1)th sub-pulse sequentially decrease.