LCL Filter Damping During Start-Up of Grid Converters
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Solution Overview
Problem
Electronic appliances with LCL filters, such as low harmonic drives and grid converters, face issues with excessive DC-voltages during start-up due to voltage distortion at resonance frequencies, leading to potential overvoltage trips and capacitor degradation.
Innovation Solution
Incorporating damping components, such as resistors or secondary windings with switches, in parallel with the grid side inductors of the LCL filter, which are connected during start-up and disconnected once synchronization with the grid is achieved, to mitigate voltage amplification and minimize losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the LCL filter is designed with low resistive losses for efficient cooling and high efficiency, then the filter efficiency is improved, but the immunity against grid disturbances deteriorates leading to excessive DC-voltages during start-up
Solution Approach 1:
The damping components are connected in advance during the start-up phase before the active front end rectifier begins modulating. This preliminary action prevents voltage amplification at resonance frequencies from occurring in the first place, rather than attempting to correct it afterward. The damping resistors are strategically activated only when needed (during start-up) and disconnected during normal operation to maintain filter efficiency.
2Reliability
If damping components are permanently connected to the grid side inductors, then the immunity against grid disturbances is improved, but the filter losses increase reducing efficiency
Solution Approach 1:
The damping components are made dynamically controllable through switches that connect them during start-up and disconnect them during normal operation. This dynamic configuration allows the system to adapt its damping characteristics based on operational requirements, maintaining high efficiency during steady-state operation while providing adequate protection during the vulnerable start-up phase.
Solution Approach 2:
The damping components are activated periodically only during the start-up phase and deactivated during normal operation. This periodic action pattern matches the specific temporal requirement for damping - needed only transiently during start-up when the active front end rectifier is not yet modulating, but unnecessary during steady-state operation where it would only cause power losses.
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
This solution effectively prevents excessive DC-voltage spikes during start-up, ensuring safe operation and extending the lifespan of DC-link capacitors by actively damping resonances in the LCL filter, while minimizing thermal and power losses.
Implementation Method 1
damping components are provided in parallel to the grid side inductors... to actively damping resonances in the LCL filter
Data Source
AI summary
An electronic appliance such as a low harmonic drive, an active rectifier, a grid converter or any active front end or grid converter with an LCL filter. The converter is a two-level, a three-level or a multilevel inverter. The electronic appliance includes an LCL filter on a grid side of the electronic appliance and an active front end rectifier provided on a load side of the electronic appliance. The LCL filter includes grid side inductors and an active front end rectifier is connected to the LCL filter. A method for damping a corresponding electronic appliance is also disclosed.