A motor side harmonic suppression method based on cascaded self disturbance rejection control and improved particle swarm optimization algorithm is proposed to address the problems of severe stator current harmonic distortion,intensified torque ripple, and insufficient dynamic disturbance rejection capability in distributed photovoltaic power generation systems connected to the grid through inverters. Establish a mathematical model for the coupling system between photovoltaic grid connected inverters and motor,and design a cascaded self disturbance rejection control structure.The outer loop uses a linear self disturbance rejection controller to robustly track the motor speed,while the inner loop uses an extended state observer to estimate and compensate for internal disturbances such as motor winding resistance,inductance changes,and inverter nonlinearity in real time. It actively suppresses the conduction of harmonics from the grid side to the motor side, reducing the total harmonic distortion rate of the motor current. Furthermore, an improved particle swarm optimization algorithm was designed to synergistically optimize the key parameters of the controller. Experimental results showed that the proposed method greatly reduced the harmonic distortion rate of the motor stator current,reduced the torque ripple coefficient, and maintained excellent dynamic response during grid frequency fluctuations and load changes. This effectively improved the stability and energy utilization efficiency of grid connected motor,laying an important foundation for the safe and stable operation of distributed photovoltaic system driven motor.