Abstract : AC excitation generators, capable of independent regulation of active power, reactive power, and speed, have broad application prospects in improving the stability of ultra-high voltage power systems and variable-speed constant-frequency power generation. AC-DC-AC voltage source inverters, with their excellent output characteristics, can be used as excitation power supplies for these generators. AC excitation generators have relatively low excitation voltages. Due to the inherent characteristics of the excitation main circuit components (such as IGBTs), the output voltage waveform of these inverters is severely distorted at low voltage output, leading to increased rotor current harmonics and increased stator output voltage and current harmonics. This paper analyzes in detail the mechanism of harmonic increase caused by component characteristics and proposes a method for compensating for transistor voltage drop. Simulation and experimental results demonstrate the correctness of the analysis and the effectiveness of the proposed compensation method. Keywords : AC excitation generator; harmonics; tube voltage drop; compensation 1 Introduction AC excitation generators, due to their symmetrical AC excitation of the rotor and the controllability of the excitation voltage amplitude, frequency, phase, and phase sequence according to operating requirements, can achieve independent regulation of active power, reactive power, and speed, giving them unparalleled advantages over traditional synchronous generators. To fully utilize these superior characteristics, a high-performance variable frequency power supply is essential for their excitation power. When the excitation current contains harmonics, the stator voltage and current of the AC excitation generator will contain abundant harmonics. Therefore, reducing excitation current harmonics has become a major concern. Currently popular variable frequency power supplies mainly include AC-AC converters and AC-DC-AC converters. Since AC-DC-AC converters can employ SPWM technology, they can theoretically completely eliminate low-order high-order harmonics (mainly the 5th, 7th, 11th, and 13th harmonics), a fact that has been widely applied and verified in variable frequency speed control systems. However, when considering the voltage drop of the inverter's power devices, output voltage errors occur. These errors cause voltage waveform distortion and generate harmonic currents. In traditional variable frequency speed control, because the inverter's output voltage is high, the proportion of harmonic voltage is relatively small and is often ignored. Therefore, there are no research reports on the relationship between the voltage drop of the transistors and the output voltage waveform when the devices are turned on. [b][align=center]For details, please click: Research on Harmonics Caused by Voltage Drop of Excitation Power Transistors in AC Excitation Generators and Their Elimination Methods[/align][/b]