Dynamic Three-Phase Voltage Balancing via Sequence Control
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Solution Overview
Problem
Existing three-phase power converters face challenges in maintaining balance when a cell fails, leading to voltage unbalance and increased output voltage ripple due to static balancing methods and unequal impedance in multi-output transformers.
Innovation Solution
A dynamic method for electrical balancing in three-phase systems, which involves calculating and adjusting line-to-neutral and line-to-line voltages using sequence voltages to achieve balanced output voltages, even in the presence of cell failures or impedance differences, by rotating and modifying voltage phases to ensure balanced operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cell fails and is short-circuited to maintain power generation, then the converter continues to generate power, but voltage unbalance is introduced in the converter output
Solution Approach 1:
The patent applies dynamics by transitioning from static pre-defined balancing tables to a dynamic control system that continuously measures output power and adjusts the balancing strategy in real-time based on actual operating conditions, allowing the system to adapt to different failure scenarios and load conditions
Solution Approach 2:
The patent changes parameters by modifying the power output of remaining healthy cells rather than simply short-circuiting failed cells. The control system adjusts the power generation parameters of surviving cells to compensate for the failed cell, maintaining voltage balance through parameter optimization rather than structural modification
2Adaptability or versatility
If static balancing based on pre-defined tables is used, then balancing can be achieved in some failure cases, but it cannot include all possible failure cases for all possible powers
Solution Approach 1:
The patent applies self-service by enabling the system to automatically detect its own state (through continuous power measurement), diagnose imbalance conditions, and self-correct by adjusting the output of healthy cells. The system serves itself by using real-time data to dynamically generate appropriate balancing actions without external intervention or pre-programmed scenarios
Solution Approach 2:
The patent implements feedback by continuously measuring the output power of each cell, comparing it against expected values, and using this feedback information to adjust the power output of healthy cells. This closed-loop control ensures the system adapts to any failure scenario within its operational range
3Reliability
If a cell is canceled due to failure, then the converter continues operation, but the number of available PWM voltage levels decreases and output voltage ripple increases
Solution Approach 1:
The patent changes parameters by optimizing the power distribution among remaining healthy cells to compensate for the reduced PWM voltage levels. By adjusting operating parameters such as duty cycles and power output levels, the system maintains voltage balance and reduces ripple effects despite having fewer active cells
4Adaptability or versatility
If multi-output transformers with unequal impedance are used, then the converter can handle different load requirements, but perfectly balanced voltage cannot be generated in all phases
Solution Approach 1:
The patent applies local quality by treating each phase independently with customized power adjustment strategies. Rather than applying a uniform balancing approach, the control system adjusts the power output of each healthy cell based on its specific phase conditions, transformer impedance characteristics, and load requirements, allowing localized optimization for each phase
Data Source
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AI summary
A method of electrical balancing in a three-phase system is disclosed. The steps are: obtaining the magnitude and phase of each line-to-neutral output voltage; aligning a first line-to-neutral voltage with the real axis; choosing two voltages and adding a third voltage complex conjugate of the greater of the two previous voltages; calculating the positive sequence, the negative sequence and the zero sequence; cancelling the negative sequence; calculating the positive sequence and zero sequence of the new line-to-neutral voltage system; adding positive sequence voltage and zero sequence voltage to the positive sequence and zero sequence; calculating the new line-to-neutral voltages from the new positive sequence voltage and the new zero sequence voltage, with negative sequence voltage equal to zero; repeating the two previous steps until the module of the new third line-to-neutral voltage is equal to the module of the line-to-neutral output voltage discarded in the third step.