Voltage Source Inverter Island Detection Using Phase-Power Correlation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Voltage source inverters maintain island networks undesirably when disconnected from a superordinate network, posing a safety risk, and existing methods for island network detection are not applicable to them.
Innovation Solution
A method for voltage source inverters to detect island networks by generating a voltage curve with a phase variation and determining the correlation between this variation and power exchange, using active power or apparent power, to identify a predefined degree of correlation for detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If voltage source inverters maintain voltage in subnetworks, then power stability is improved, but unintended island network formation occurs creating safety hazards
Solution Approach 1:
The inverter performs preliminary island network detection by superimposing a test voltage with a distinct frequency component before normal operation. This preliminary action allows the system to identify island network conditions in advance and switch from voltage maintenance mode to island operation mode, preventing unintended island formation while maintaining power stability during normal grid-connected operation
Solution Approach 2:
The system continuously monitors the subnetwork conditions by measuring current flow and power exchange. When the inverter detects that the subnetwork is disconnected from the superordinate network through feedback signals indicating zero or minimal current flow, it automatically switches operation modes to prevent unintended island network formation, thus resolving the contradiction between maintaining power stability and preventing harmful island effects
2Measurement precision
If existing island network detection methods are used, then detection capability is improved, but they are not applicable to voltage source inverters
Solution Approach 1:
The patent adapts island network detection to voltage source inverters by changing the detection parameter from current-based measurement (used in line-commutated inverters) to voltage-based measurement. The inverter superimposes a test voltage with a specific frequency offset on the network voltage and measures the resulting current response, making the detection method suitable for voltage source inverter topology while maintaining high detection precision
Solution Approach 2:
The detection method is designed to be universal for voltage source inverters by using the inverter's inherent voltage generation capability to create test signals. The same voltage source that normally provides power to the network is used to generate detection test voltages, allowing the inverter to perform both power delivery and island network detection functions through a single integrated system, thereby improving adaptability
3Measurement precision
If a test voltage is superimposed on the network frequency, then island network detection is improved, but the test frequency must be less than the network frequency limiting flexibility
Solution Approach 1:
The system dynamically adjusts the test frequency offset based on the operating conditions. The frequency offset is not fixed but can be varied within a range to optimize detection accuracy for different network conditions. This dynamic approach allows the inverter to maintain high detection precision while adapting to various frequency scenarios, reducing the practical impact of the frequency constraint
Data Source
AI summary
The disclosure is directed to an island network detection method using a voltage-impressing converter, and includes determining the frequency and phase of a voltage curve of a sub-network connected to a network connection point of the converter, and generating a voltage curve using a bridge circuit of the converter with the determined frequency. The method also includes determining a correlation between a first temporal variation and a second temporal variation of an output exchanged by the converter with the sub-network, and detecting an island network if the determined correlation undershoots a specified correlation measurement.