Am I obliged to explain where I am going, where I live, and what I am doing?
police-stopright-to-silenceidentity-check
No. Under Art. 19 of the Law "On Police", answering an officer's questions during questioning is voluntary (with narrow exceptions under Art. 17, cl. 8 — threat to life/health, etc.). What you are obliged to provide is your name and your document.
If you don't want to answer, don't answer. A polite "I'd prefer not to answer" or "that question is outside the scope of an ID check" is enough. Silence is not evidence of guilt; it is your right.
Caveat: if the check has already escalated into detention (an administrative-offence protocol is being drafted, arrest is being processed), the rules change — procedural norms kick in, and silence must be combined with a demand for a lawyer.