After AC-DC electric locomotives receive 25 kV power frequency single-phase voltage from the OCS, the voltage is stepped down to 1500 V via on-board transformers and rectified before being supplied to the traction motors, as shown in Fig. 2.1. These locomotives are equipped with semi-controlled bridge rectifiers and regulate output by controlling the conduction angle of the thyristors. However, this control mode results in low power factors for AC-DC locomotives and the generation of significant high-order harmonics during operation. In response, various countries hastened to develop new types of AC drive electric locomotives to effectively address the shortcomings of AC-DC electric locomotives. In 1979, Germany successfully introduced the world’s first high- and medium-power single-phase AC drive heavy-duty electric locomotive for operation on high-speed trunk railways. This locomotive model was quickly adopted and popularized in many developed countries.