Parallel AC/DC Converter Control for Resonant Current Suppression
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Solution Overview
Problem
High-voltage AC/DC converters in modular multilevel converters (MMC) systems face issues with ground fault failures and noise propagation due to uninsulated input and output terminals, and existing solutions like multi-stage converters and resonance suppression reactors increase converter size and complexity.
Innovation Solution
A power conversion device with parallel-connected power conversion units, incorporating current sensors and a control unit to manage variable resistance switches, which detect and mitigate resonant currents between capacitors, thereby reducing converter size and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-stage converters or resonance suppression reactors are used to suppress resonant currents, then reliability is improved, but device size and complexity increase
Solution Approach 1:
The control unit automatically detects resonant currents through current sensors and suppresses them by controlling the switching elements, eliminating the need for external resonance suppression reactors. The system serves itself by using its own control capability to resolve the resonance issue, thereby improving reliability without adding external components.
Solution Approach 2:
The invention extracts the resonance suppression function from external components (reactors) and transfers it to the control system. By using the control unit to detect and suppress resonant currents through switching element control, the patent removes the need for separate resonance suppression reactors, reducing device complexity while maintaining reliability.
2Reliability
If multi-stage converters or resonance suppression reactors are used to suppress resonant currents, then reliability is improved, but converter size increases
Solution Approach 1:
The resonance suppression function is extracted from physical components (reactors) and implemented through control algorithms. The control unit detects resonant currents and suppresses them by adjusting switching element operations, eliminating the need for bulky resonance suppression reactors and thereby reducing converter size while maintaining reliability.
Solution Approach 2:
The converter uses its own control system to suppress resonant currents without requiring external resonance suppression reactors. This self-service approach eliminates additional components that would increase converter size, achieving reliability improvement through intelligent control rather than physical expansion.
3Loss of energy
If power conversion units are connected in parallel to increase withstand voltage, then system efficiency is improved, but resonant currents between capacitors increase
Solution Approach 1:
The control unit uses current sensors to detect resonant currents generated by parallel-connected power conversion units and implements feedback control to suppress these currents. By continuously monitoring and adjusting switching element operations based on detected resonant currents, the system maintains high efficiency while eliminating harmful resonant effects.
Solution Approach 2:
The control unit acts as an intermediary between the parallel-connected power conversion units, detecting resonant currents through current sensors and mediating their suppression through switching element control. This intermediary function allows efficient parallel operation while preventing harmful resonant current interactions between unit capacitors.
Data Source
AI summary
A plurality of power conversion units, a current sensor that detects a current at an output terminal of the power conversion unit, and a control unit that measures a frequency component in a predetermined frequency range of a current detected by the current sensor are included, the power conversion unit includes an AC/DC converter that outputs AC power at an input terminal to an output terminal, a smoothing capacitor that is connected in parallel to the output terminal and smooths an output voltage, and a variable resistance switch connected between one end of the smoothing capacitor and one end of the output terminal, the control unit controls a resistance value of the variable resistance switch according to a magnitude of a predetermined frequency component detected by the current sensor, and the output terminals of the plurality of power conversion units are connected in parallel to constitute output terminals.