**Background:** The known research results describe the nature of power exchange fluctuations in case of parallel operation of AC diesel generator units and prove the need to determine the criterion of stability of parallel operation by the active power exchange fluctuations. The accumulated information, technical expertise and research findings on power exchange fluctuations give grounds to say that the recommendations usually reduce the optimization measures to some design changes in diesel-generator units (mainly diesel ones), which is natural for mechanics experts. However, the seemingly profound studies of the nature and causes of metabolic power fluctuations provide no information about the successful implementation of innovations and elimination of exchange fluctuations, or specific methods which would give a real effect. On the contrary, even the ultra-modern electro-service vessels with automation class A1 are affected by the negative consequences of such fluctuations. Therefore, it is quite urgent now to find out the reasons for power exchange fluctuations.

**Materials and methods: **The study employed the results of a computational experiment of parallel operation of generating units in a ship electrical complex conducted by mathematical modeling methods. To determine the «backlash» as the reason for power exchange fluctuations, we used a mathematical model of the ship electrical complex as it takes into account the «backlash» in the systems of automatic control of diesel rotation speed.

**Results: **The obtained experimental results have confirmed the presence of power exchange fluctuations in case of parallel operation of synchronous generators of the electrical complex as there is a «backlash» in the automatic control systems of diesel rotation speed. The mathematical modeling results have proved that the power exchange fluctuation amplitude increases with the increase in the width of the gaps of the generators running in parallel whether their values are different or equal.

**Conclusions: **«Backlashes» are among the main reasons for exchange fluctuations of power in ship synchronous generator units operating in parallel. The obtained results allow us to exclude different design parameters of ship diesel generator units from the list of causes of power exchange fluctuations in case when the units run in parallel.

**Key words: **power exchange fluctuations, experimental studies, mathematical model, parallel operation, electrotechnical equipment, synchronous generator, generating unit, generator current, generator power.