UDM for Load Shedding Scheme

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Hi everyone! I tried to implement dynamic load shedding scheme which detects ROCOF and shed equal amout of load to match the power imbalance during simulation using python script (other than using load relay models LVSHBL, DLSHBL etc.) but it didn't work. It sheds loads but frequency not come to stable range as it gradually decreases with time. Therefore I'm trying to implement UDM. But I'm not familiar with Fortran or creating UDMs. I read the POM chapter but I don't know how to start with this. Can someone assit me with an example UDM for this it'll be a big help for me. Thanks in Advance