This study focused on the brushless phase-compounding excitation synchronous generator for ships. First, the working principle and excitation characteristics of the generator were introduced, and the output current calculation formula for compound excitation was derived. Then, to address the issue of the generator’s regulation characteristics being unable to fully compensate for the excitation system’s output, an appropriate overcompensation coefficient for the excitation current was designed. The system stabilized the port voltage by coordinating with the unique working mechanism of the shunt resistor. Next, the calculation method for the main component parameters based on this design was provided, and a simulation model was established for verification under both steady-state and dynamic load conditions. Finally, a 25 kVA experimental prototype was manufactured based on the proposed design and the parameters of the existing machine. The test results showed that the designed controllable excitation system could adjust the excitation current by switching the shunt resistor, ensuring stable port voltage despite load fluctuations. A comparison of the calculation, simulation, and experimental results showed an error of less than 1%, confirming the validity of the derived formulas. The simulation error was less than 3.5%, demonstrating that the model effectively reflected both the steady-state and dynamic characteristics of the prototype, verifying the rationality of the overcompensation design.