Inverter Anti-Islanding Control via Phase-Shift Frequency Deviation
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Solution Overview
Problem
Inverters fail to detect island states effectively, leading to continued power supply to electrical networks during maintenance, posing risks to personnel and causing device damage due to voltage phase differences, and existing detection methods rely on over/undervoltage or over/underfrequency protection mechanisms that often exceed the stipulated protection time.
Innovation Solution
An inverter anti-islanding control system utilizing a phase-shift loop to deviate the frequency of the inverter's alternating current end voltage to a second frequency, triggering frequency protection and disconnecting the inverter from the electrical network, thereby exiting the island state within a specified time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If over/undervoltage or over/underfrequency protection mechanisms are used for island detection, then the inverter can detect abnormal frequency conditions, but the protection time exceeds the island protection time stipulated in grid connection standards
Solution Approach 1:
The phase-shift loop proactively introduces a phase shift to the voltage instruction before frequency protection is triggered, causing the inverter frequency to deviate rapidly toward the protection threshold. This preliminary action accelerates the frequency change process, ensuring the inverter disconnects within the required protection time rather than waiting for natural frequency drift.
Solution Approach 2:
The system dynamically changes the phase shift parameter in the voltage instruction through the phase-shift loop, which directly affects the inverter's output frequency. By adjusting this parameter, the frequency is forced to deviate from its normal value and move toward the protection threshold, enabling faster detection and disconnection.
2Productivity
If the inverter continues to supply power during island state, then power is provided to the load, but corrective maintenance personnel may be injured or device damage may occur due to voltage phase differences
Solution Approach 1:
The system continuously monitors the frequency of the inverter's output voltage and feeds this information back to the phase-shift loop. When the frequency deviates from the normal range, the feedback mechanism triggers the phase-shift loop to adjust the voltage instruction, causing further frequency deviation that rapidly pushes the system into the protection threshold range, ensuring timely disconnection and eliminating safety risks.
Data Source
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AI summary
An inverter anti-islanding control system includes a phase-shift loop (10) and a drive circuit (20). The phase-shift loop (10) includes a first input end (11), a second input end (12), a third input end (13), a fourth input end (14), a first output end (15), and a second output end (16). The drive circuit (20) includes a first input end (21), a second input end (22), a third input end (23), and an output end (24). The first output end (15) of the phase-shift loop (10) is connected to the first input end (21) of the drive circuit (20), and the second output end (16) of the phase-shift loop (10) is connected to the second input end (22) of the drive circuit (20). In the inverter anti-islanding control system, when an inverter is in an island state, a frequency of an inverter alternating current end voltage is deviated to a second frequency by using the phase-shift loop (10), so that the second frequency triggers frequency protection to disconnect the inverter from an electrical network, to be specific, the inverter is out of the island state.