Modular Inverter Phase-Rotated Cells Harmonic Cancellation
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Solution Overview
Problem
Existing modular multi-level power converters, such as series H-bridge inverters, suffer from input current and voltage harmonics that degrade power quality due to single-phase loading of H-bridge inverters, leading to significant harmonic distortion and total harmonic distortion (THD) exceeding recommended levels.
Innovation Solution
A modular cascaded H-bridge-based drive system with phase-rotated power cells and transformers, where each slice has transformers with phase-shifted windings, and power cells receive phase-shifted reference signals to cancel harmonic currents at the input side, improving power quality by summing phase-shifted harmonic currents effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single large transformer or multiple modular transformers are used to power series H-bridge inverters, then voltage and power levels can be easily scaled, but input current and voltage harmonics significantly degrade power quality
Solution Approach 1:
The system divides the power conversion function into multiple independent H-bridge inverters connected in series, where each inverter processes a portion of the total power. This segmentation allows voltage and power scaling while distributing harmonic generation across multiple units, reducing overall harmonic distortion when properly controlled
Solution Approach 2:
The patent applies phase-shifted pulse width modulation (PWM) techniques where each H-bridge inverter operates with a different phase angle. By changing the temporal parameters of the switching signals and introducing phase shifts between inverters, the harmonic components cancel each other out, significantly reducing input current and voltage harmonics while maintaining the scalability benefit
2Temperature
If multiple H-bridge inverters are connected in series to achieve higher voltage levels, then voltage capability increases, but harmonic distortion and total harmonic distortion (THD) exceed recommended levels
Solution Approach 1:
The high voltage output is achieved by segmenting the system into multiple H-bridge inverters connected in series, where each inverter contributes a portion of the total voltage. This segmentation enables high voltage capability while allowing individual inverters to operate at lower voltage levels with reduced harmonic distortion
Solution Approach 2:
The patent employs phase-shifted PWM control where each H-bridge inverter is switched with different phase angles. This parameter change in the switching时序 causes the harmonic components from each inverter to cancel each other constructively at the output while minimizing input harmonics, thereby achieving high voltage capability with acceptable THD levels
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The phase-rotated control significantly reduces input harmonic content, improving power quality by minimizing harmonic distortion from 5.86% to 2.3% in test systems, adhering to IEEE 519-2014 standards and maintaining modular system efficiency.
Implementation Method 1
a transformer of each slice may include a primary winding to couple to an input power source and a plurality of secondary windings each to couple to one of a plurality of power cells of the slice
Implementation Method 2
each of the plurality of power cells of a first slice has an output that is phase rotated with respect to a correspondingly positioned power cell of a second slice... summing phase-shifted harmonic currents effectively to cancel harmonic currents at the input side
Data Source
AI summary
In one embodiment, a system includes a plurality of slices each having a transformer including a primary winding to couple to an input power source and a plurality of secondary windings each to couple to one of a plurality of power cells of the slice. Each of the power cells of a first slice may have an output that is phase rotated with respect to a correspondingly positioned power cell of a second slice.