Floating-Cell Converter Switching for DC Intermediate Voltage Balance
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Solution Overview
Problem
Existing power electronic converter devices face challenges in maintaining stable operation due to fluctuations in DC intermediate circuit voltages, which can lead to inefficiencies and harmonic distortion in output voltages.
Innovation Solution
The method involves using optimized pulse patterns and carrier-based pulse width modulation to switch semiconductor devices in both the main converter and floating cells, while generating a fundamental voltage component to balance the DC intermediate circuit voltage, thereby maintaining it within a reference range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If floating cells are used in the converter circuit to add or subtract DC voltages, then the voltage flexibility and power conversion capability are improved, but the stability of operation deteriorates due to fluctuations in DC intermediate circuit voltages
Solution Approach 1:
The patent implements a control device that continuously monitors the DC intermediate circuit voltage and adjusts the switching instants of semiconductor devices based on feedback signals. This closed-loop control ensures that voltage fluctuations are detected and corrected in real-time, maintaining operational stability while preserving the voltage flexibility provided by floating cells.
Solution Approach 2:
The control device dynamically adjusts switching parameters (switching instants and pulse patterns) in response to changing voltage conditions. By modifying these parameters based on actual voltage levels, the system maintains stable operation across varying load conditions while utilizing the full range of voltage flexibility offered by the floating cell configuration.
2Device complexity
If conventional switching methods are used without optimized pulse patterns, then the device complexity is reduced, but the harmonic distortion in output voltages increases
Solution Approach 1:
The patent employs periodic pulse patterns with optimized switching sequences that are applied cyclically to the semiconductor devices. These periodic control signals are designed to minimize harmonic content in the output voltage while maintaining relatively simple control logic, thus reducing harmonic distortion without significantly increasing device complexity.
3Ease of operation
If DC intermediate circuit voltage is not balanced, then the ease of operation is improved, but the efficiency of the system deteriorates due to increased switching losses
Solution Approach 1:
The control device automatically balances the DC intermediate circuit voltage through intelligent selection of switching instants and pulse patterns without requiring manual intervention. The system self-regulates by detecting voltage imbalances and adjusting switching sequences to equalize voltages across floating cells, thereby minimizing switching losses while maintaining ease of operation.
Data Source
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AI summary
A power electronic converter device (36) for an electrical power conversion system comprises a converter circuit (10) including an input side (12) with input terminals (14), an output side (16) with at least one AC output terminal (18), a first converter (20) with semiconductor devices (26) connected to the input terminals (14) and at least one second converter (22) connected between an AC output of the first converter (20) and the AC output terminal, said second converter (22) comprising at least one floating cell (28) with a DC intermediate circuit (32) and semiconductor devices (30). A method for operating the power electronic converter device (36), comprises: switching the semiconductor devices (30) of the floating cell (28) at switching instants determined with optimized pulse patterns or carrier based pulse width modulation; determining a fundamental voltage component for the floating cell, which fundamental voltage component depends on a difference between an actual voltage V C AF of the DC intermediate circuit of the floating cell and a reference value V C AF* for the voltage of the DC intermediate circuit; and generating the fundamental voltage component in the actual voltage of the floating cell by modifying the switching instants, such that a voltage V C AF of the DC intermediate circuit (32) is lying in a given reference voltage range for balancing the DC intermediate circuit of the floating cell.