Hi Xin,
Your PLL drift using RTU box 204 likely stems from the unit delay or PI parameters.
- Unit Delay: Ensure the unit delay is placed correctly to break algebraic loops without unintended delays.
- PI Parameters: Start with a low P gain and adjust the I gain for settling time. High P gain can cause drift.
- Review Configuration: Verify RTU box settings match your PLL application (reference frequency, scaling).
- Hardware Check: Look for loose connections, component tolerances, or noise issues.
Consider monitoring the phase error signal for troubleshooting.