Converter Current Control During Grid Fault Recovery
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Solution Overview
Problem
When a grid experiences a fault and is subsequently recovered, the converter in a photovoltaic power generation system continues to inject reactive and active currents, leading to increased voltage amplitudes that can damage devices and disrupt normal operation.
Innovation Solution
A power conversion apparatus with a controller that detects the output voltage of the converter and adjusts the active and reactive currents output by the converter. When the output voltage rises above a second threshold after a grid fault, the controller reduces the currents to specific values and adjusts them based on a preset rate until they reach target values within normal operational ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter continues to inject reactive current and active current after grid recovery, then the converter supports voltage recovery of the grid, but the voltage amplitude increases excessively causing device damage
Solution Approach 1:
The controller continuously monitors the output voltage of the converter and uses this feedback to dynamically adjust the reactive current and active current. When the output voltage exceeds the second threshold after grid recovery, the controller reduces the currents to prevent excessive voltage amplitude, thereby resolving the contradiction between supporting grid recovery and preventing device damage.
Solution Approach 2:
The converter operates in different modes dynamically: during grid faults, it injects large reactive and active currents to support voltage recovery; after grid recovery, it transitions to a controlled reduction mode where currents are gradually decreased based on voltage thresholds and adjustment rates. This dynamic operation allows the system to adapt to changing grid conditions and avoid excessive voltage amplitudes.
2Object-affected harmful factors
If a snubber circuit is added to reduce output voltage amplitude, then device safety is improved, but system cost increases
Solution Approach 1:
The converter uses its own control system to monitor its output voltage and automatically adjust its current injection accordingly. The controller reduces reactive current and active current when voltage thresholds are exceeded, allowing the converter to self-regulate and protect itself without requiring external snubber circuits or additional hardware modifications.
Solution Approach 2:
The controller changes the operating parameters (reactive current and active current) of the converter based on the detected output voltage. By adjusting these parameters dynamically according to voltage thresholds and preset adjustment rates, the system achieves voltage amplitude control through parameter modulation rather than hardware addition.
Data Source
AI summary
A power conversion apparatus and a control method for a power conversion apparatus to reduce an amplitude of an output voltage of a converter when a grid is recovered from a fault, to ensure device safety. The power conversion apparatus includes a controller and a converter, and the controller is connected to the converter. The controller is configured to: after the output voltage of the converter is less than a first threshold, when the output voltage of the converter rises to be greater than a second threshold, reduce an active current output by the converter to a first current value, and reduce a reactive current output by the converter to a second current value, where the second threshold is greater than the first threshold.