Initial Excitation Issues of Synchronous Generator with VSI Inverter in Varying Rotational Speed Operation

Synchronous self-excited generators still are and probably will be the most popular 3-phase alternators installed in inland power stations so onboard of seagoing ships. Because of fuel savings and environmental restrictions Diesel, dual-fuel and gas propulsion engines for alternators of wide-range varying revolutions drives are increasingly used. There must be efficient way of creating 3-phase voltages of desired constant parameters ensured when generator produces variable amplitudes and frequencies of voltages because of changing rotational speed. As the control method modified field oriented control widely used with squirrel cage induction machines was chosen. This control method involves decoupling of currents and control voltages to flux and torque components and keeping them in optimal (orthogonal) condition. In order to obtain proper excitation and operation of such generator several factors have to be taken into account. Nonlinear dependence of voltage generated from rotational speed of self-excited synchronous generator is one of the factors that affects initial excitation process thus specific control method while generator startup. Theoretical background of synchronous generator excitation and voltage source inverter adopted FOC control method along with experimental results obtained in laboratory test bench of 5,5 kW generator and conclusions were presented.