We are struggling in the creation of Process Performance Model (PPM) which are fit and working. Is it a requirement for ML4 QPM? What are other alternatives for PPM?
Actually, the Goals and Practices in Quantitative Project Management (QPM) don't specifically direct you to use PPMs at all, although it is mentioned in the informative material. So the simplistic, "answer in a vacuum" is "no." HOWEVER, if you're striving to be a ML4 organization, you must also be performing Organizational Process Performance (OPP), which DOES have a practice that expects process performance models to be developed.
The expectation is that QPM uses these PPMs to plan and manage the project. So the PPMs originate with OPP, but is used by those who execute QPM (which could be completely different people).
If the reference in OPP to models was only in the practice (SP1.5 - Establish Process Performance Models) then it would only be "expected" (practices are expected, goals are required right?) then I could suggest an alternative, but alas, the Goal (SG1 in OPP) does indeed state the baselines AND models need to be developed.
So, yes, PPMs are required.