Active Frequency Drift Islanding Detection Method for Photovoltaic Grid-Connected Power Generation Systems

Islanding effect in photovoltaic grid-connected power generation systems refers to the phenomenon where the PV system continues supplying power to local grids after main grid failure. This condition poses safety risks to maintenance personnel and may disrupt normal equipment operation. The Active Frequency Drift (AFD) method is an active islanding detection technique that identifies islanding status through intentional frequency disturbance injection.

The core principle involves PV inverters injecting minor frequency disturbance signals into output currents during grid-connected operation. Under normal grid conditions, the strong grid force-locks the system frequency, absorbing disturbance signals without effect. When grid power loss creates an islanding condition, these frequency disturbances accumulate continuously, causing persistent PV output frequency deviation beyond normal ranges until protection mechanisms trigger grid disconnection. Code implementation typically involves configuring disturbance injection parameters through DSP/FPGA controllers using phase-locked loop (PLL) frequency modulation algorithms.

The AFD method offers advantages including rapid detection speed, high reliability, and minimal power quality impact. Critical implementation consideration involves appropriate disturbance magnitude setting - insufficient amplitude may cause detection failure while excessive values could compromise system stability. Practical applications often combine AFD with passive detection methods (e.g., voltage/frequency protection) to establish multi-layer protection systems, ensuring PV grid-connected system safety under various operating conditions. Programming typically incorporates hysteresis comparison algorithms and frequency threshold checks in the protection logic module.