**Background: **Using powerful static converters in a ship unified electric power system considerably distorts the voltage in the ship power network as the latter are a non-linear load and are comparable in power with the power supply sources. This factor has a negative effect on operation of many power plant components, in particular automation and control systems. This problem can be solved by installing a harbor diesel generator at the power plant. Such generators are now used as an emergency power supply source and a special power supply source ensuring ship survivability. That is why on some ships, harbor generators are expected to work continuously, with their load varying within a wide range: from the nominal value to the minimal one (20–30 % of *P _{n}*). It is quite urgent to develop and design diesel generator units in which the drive motor rotation speed depends on the generator load considerably saving fuel (by up to 10–20 %) in the ship power system. The problems of modeling and designing such units are being actively studied but the problem of maintaining constant output voltage and engine speed still remains unsolved.

**Materials and methods: **The mathematical calculations and modeling of variable and fixed speed generator units were made in the «SimPowerSystems» library of the MATLAB Simulink package, with the fixed step Runge-Kutta (ode4) method used for the calculations. The model accounts for the changes in the inductive components occurring with the voltage frequency changes at the generator output and simulates the magnetization curve including the saturation magnetization. The heat loss variations in different modes of diesel generator operation are left out of account.

**Results: **The authors have developed a flow chart and a model of a generator unit with automatic systems of rotation speed, synchronous generator voltage, frequency converter output voltage frequency and amplitude control. They have also determined the optimal operation and component adjustment parameters.

**Conclusions: **The suggested systems of output voltage parameters control in the load mode ensure high accuracy of static and dynamic amplitude and sinusoidal curve form by using a simple low-pass filter. As the modeling shows, variations in the active load of a synchronous generator change the diesel rotation speed, which saves fuel (the maximum economy reached 16–22 %), while the generator voltage remains nominal and is accurately maintained.

**Key words: **autonomous electric power plant, diesel generator, voltage control system, frequency converter, fuel economy, speed control.