Virtual Synchronous Power Converter Current Limiting During Grid Faults
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Solution Overview
Problem
Existing power converters connected to power systems lack effective countermeasures for preventing overloads and short-circuit faults, which can lead to system instability and failure.
Innovation Solution
A power converter designed to operate as a virtual synchronous generator, equipped with a control device that includes a voltage amplitude command calculation unit, a frequency command calculation unit, a current command calculation unit, and a voltage command calculation unit. This control device calculates and adjusts current command values to restrict the output current within an upper limit value, thereby preventing overcurrent conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter operates as a virtual synchronous generator without overcurrent protection, then the system can respond quickly to power system disturbances, but the converter may suffer from overcurrent damage during faults
Solution Approach 1:
The control device calculates a current command value in advance based on voltage amplitude command, frequency command, and output voltage, then restricts this command value before it can cause overcurrent damage. This preliminary calculation and restriction prevents overcurrent conditions before they occur during power system faults.
Solution Approach 2:
The control device continuously monitors the calculated current command value and compares it against safe operating limits. When the current command exceeds safe thresholds, the feedback mechanism triggers restriction of the current command, creating a closed-loop protection system that adapts to real-time operating conditions.
2Duration of action of stationary object
If the power converter restricts output current to prevent overcurrent, then the converter can continue operating during faults, but the current limitation may reduce power delivery capability
Solution Approach 1:
The current restriction is not a fixed limit but a dynamic control mechanism that adjusts the current command value based on real-time operating conditions including voltage amplitude, frequency deviations, and power system state. This dynamic adjustment allows maximum power delivery within safe operational boundaries.
Solution Approach 2:
The control device changes operational parameters (current command value) based on the calculated relationship between voltage amplitude command, frequency command, and actual output voltage. By dynamically adjusting these parameters, the system maintains optimal power delivery while preventing overcurrent conditions that would force shutdown.
Data Source
AI summary
A power converter having a power conversion circuit, a filter provided and a control device configured to control an output voltage of the power conversion circuit to a power system. The control device includes: a voltage amplitude command calculation unit configured to calculate an amplitude command value for the output voltage; a frequency command calculation unit configured to calculate a frequency command value for the output voltage; a current command calculation unit configured to calculate a first current command value for the output current; and a voltage command calculation unit configured to generate a command value for the output voltage. The current command calculation unit, responsive to a magnitude of the first current command value exceeding an upper limit value, calculates a second current command value as the current command value, by restricting the magnitude of the first current command value to the upper limit value.