Power Converter Control for DC Link Capacitor Ripple Reduction
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Solution Overview
Problem
Power converters experience reduced capacitor lifetime due to voltage unbalances in AC power distribution networks, leading to ripple currents and voltages that cause additional heating and premature failure.
Innovation Solution
A control system estimates voltage unbalances and compensates by controlling electronic switches in the rectifier to reduce ripple currents and voltages, extending the lifetime of capacitors and the power converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage unbalance compensation control is implemented, then capacitor lifetime is extended and reliability is improved, but device complexity and control system complexity increase
Solution Approach 1:
The control system performs preliminary estimation of voltage unbalance metrics and negative sequence voltage components before the ripple currents affect the capacitor. By calculating compensation signals in advance based on predicted voltage disturbances, the system proactively mitigates capacitor stress rather than reactively responding to already-damaging conditions, thus extending capacitor lifetime while maintaining manageable control complexity
Solution Approach 2:
The control system continuously monitors intermediate node voltages, estimates unbalance metrics in real-time, and adjusts electronic switch control signals dynamically. This closed-loop feedback mechanism allows the system to adapt to varying voltage unbalance conditions, optimizing capacitor protection while using algorithmic efficiency to prevent control complexity from becoming prohibitive
2Duration of action of stationary object
If voltage unbalance compensation is implemented to reduce ripple currents, then capacitor lifetime is extended, but manufacturing complexity and implementation difficulty increase
Solution Approach 1:
The patent replaces physical capacitor protection mechanisms with electronic control and software-based voltage unbalance estimation algorithms. Instead of using larger capacitors, additional filtering hardware, or mechanical protection devices, the system uses digital signal processing to estimate negative sequence voltage components and adjust switch control signals, significantly reducing manufacturing complexity while extending capacitor lifetime
Solution Approach 2:
The control system dynamically changes control parameters (electronic switch timing and duty cycles) based on estimated voltage unbalance metrics. By adjusting these electrical parameters in response to measured conditions, the system achieves capacitor protection without requiring physical hardware changes, simplifying manufacturing and implementation
Data Source
AI summary
A power converter includes: a filter system including a plurality of input nodes, each input node configured to electrically connect to one phase of a multi-phase AC electrical power distribution network; an electrical network including a plurality of intermediate nodes, each intermediate node electrically connected to one phase of the filter system, the electrical network configured to convert alternating current (AC) to direct current (DC), the electrical network including a plurality of electronic switches; a DC link electrically connected to the electrical network and configured to receive the DC current from the electrical network; and a control system configured to: estimate an unbalance metric at the intermediate nodes; and control the electronic switches to compensate for the estimated unbalance metric to thereby reduce an amplitude of a ripple current in the DC current.