Exponentially increasing "vref" waveform likely indicates instability in the control loop, here are the checks that can be performed to troubleshoot:
- Control Loop Gain: Ensure that the gains in your current controller are not too high, which can cause instability. Try reducing the "Ki" (integral) and "Kp" (proportional) gains. For more information refer to this link on desigining a current controller: https://www.mathworks.com/help/mcb/ug/design-current-controller.html
- PLL Stability: Verify that your Phase-Locked Loop (PLL) is correctly tuned and stable, providing an accurate phase angle. Refer to the a documentation on "PLL testbench": https://www.mathworks.com/help/msblks/gs/DesignAndEvaluateSimplePLLModel.html
