In　this　paper,　an　equivalent　nonlinear　block　diagram　for　analysing　the　stability　of　diesel-generator　sets　operating　in　parallel　is　given.　Then　the　harmonic　linearized　transfer　function　of　the　nonlinearity　F(　delta　,D　delta　)　is　proved　to　be　the　cascade　of　two　blocks,　a　nonlinear　differential　block　with　frequency　omega　as　a　variation,　and　a　monovalue　nonlinear　block　with　amplitude　delta　//m　as　a　variation.　By　using　logarithmic　approach,　author　discusses　two　following　problems:　1.　The　stability　of　nonlinear　self-oscillations　for　diesel-generator　sets　with　stable　and　desirable　subsystems　operating　in　parallel;　2.　Forced　nonlinear　oscillations　and　nonlinear　resonances　of　diesel-generator　sets　with　stable　but　undesirable　subsystems　in　parallel　run.