Frequency Load Control of Seamless Connection with Shore Power for Dual Generators

Connection of ship diesel power system with shore power can reduce the ship's energy consumption and realize environmental protection in the port. Difference in voltage, frequency and phase between the ship's power system and the shore power system generates the voltage difference envelope, and this paper, by testing of the lowest point of the envelope, controlled the switch to realize seamless and impulse current-free connection between the ship's power system and the shore power system. The envelope simulation model of frequency and phase variety is established to analyze the lowest point control performance of envelope. Besides, it established the synchronous-generator grid-connection operation equation under difference conditions of frequency difference and load changes. Under the classic load, when the frequency difference Δf between the ship's power system and the shore power system is a constant and the envelope reaches the lowest point, the switch is turned on, and then ratio control between the frequency difference and the power changes is established, the source of power supply is turned from the ship's power to shore power, and the load of the ship's power generator reduces to 10% Rated load - in this scenario, ideal synchronized control of the switch and load transfer is realized. Simulation and model tests confirmed the conclusion above. The simulation model is built to prove that the ship power generator's rotational inertia and frequency tracking coefficient have significant impact on the frequency, while difference adjustment characteristics have little impact. This paper solves the key problems in realizing seamless connection with the shore power and load transfer.