Abstract : This paper briefly describes the working principle of a composite photoelectric encoder, analyzes the shortcomings of existing rotor position detection methods for permanent magnet synchronous motors (PMSMs), and proposes a method for detecting the initial rotor position and starting the PSM using a composite photoelectric encoder. Finally, experiments are conducted on an experimental platform based on a digital signal processor (DSP). The experimental results show that this method can meet the requirements of practical use and achieves reliable motor starting and operation. Keywords : Composite photoelectric encoder; Permanent magnet synchronous motor; Rotor initial position 1. Introduction Permanent magnet synchronous motors (PMSMs) are increasingly widely used due to their high efficiency, compact structure, small size, and good speed regulation performance. In PMSM drive systems, rotor position detection and initial positioning are fundamental conditions for system configuration and operation, and also necessary conditions for vector control decoupling. Only by accurately detecting the rotor position of the PMSM can the motor be started smoothly, and with the help of vector control technology, the PMSM can be controlled according to the control method of a separately excited DC motor, achieving the same performance indicators as a separately excited DC motor drive system. Starting a PMSM when the rotor position information is unknown has always been a challenge. Currently, the main methods for rotor position detection in permanent magnet synchronous motors include photoelectric encoders, rotary transformers, motor-embedded position sensors, and sensorless position detection. Among these methods, only rotary transformers and absolute photoelectric encoders contain initial rotor position information, enabling initial positioning of the motor upon system power-up. (Full text available for download: Research on Starting Methods for Permanent Magnet Synchronous Motors Based on Composite Photoelectric Encoders)