A large number of harmonic is mainly produced by with the discrete variable frequency soft starter. The harmonic during the motor soft starting is characterized by the high energy consumption and signal interference. Therefore, harmonic analyzing and filtering of motor discrete variable frequency soft starter is presented in this paper to achieve low energy consumption and ensure the motor soft starting stably. The following works have been done in the study: introduce the reason of harmonics appearance, analyze the harmonic, and present the filtering approach. The motor soft starter developed with this filtering approach has been successfully applied to filter out harmonic and to improve the starting performance when the motors draw the heavy-loads. It saves energy, stabilize the voltage of the power supply network.

The started motors are characterized by the low staring torque and large currents when the motors draw the heavy-loads. Therefore, a method of motor discrete variable frequency soft starting based on the variable reactance is presented in this paper [1,2]. According to the topological structure and working principle of motor discrete variable frequency soft starting based on the variable reactance, the simulation model of the system has been set up by the Matlab/Simulink tool. Simulation results show that the motor starters developed with this method have been successfully applied to the loads of the drive equipment in the kiln, coal grinding mill or the mine. It can improve the starting performance when the motors draw the heavy-loads., save energy, stabilize the voltage of the power supply network.

The started motors with the discrete frequency converter are characterized by high staring torque and a large number of harmonics when the motors draw heavy-loads. It may pull down the voltage of the power supply network; it will severely influence the other electrical devices in the same power network. Furthermore, it increases the motor temperature, which may lead to motor damage. Therefore, a novel integrated method of motor discrete variable frequency starting and harmonic filtering is presented in this paper, to achieve quick and smooth motor starting, to produce high staring torque, to keep the harmonics in permitted ranges. The following works have been done in the study: analyze the principle, design the structure of the integrated device, and present the implementation steps. The motor starter developed with this method has been successfully applied to the loads of the drive equipments in the kiln, coal grinding mill or the mine. It can improve the starting performance when the motors draw the heavy-loads, save energy, stabilize the voltage of the power supply network.

The started motors with the discrete frequency converter are characterized by high starting torque and a large number of harmonics when the motors draw heavy-loads. It may pull down the voltage of the power supply net work and influence the other electrical devices. Furthermore, it increases the motor temperature, which may lead to motor damage. Therefore, an integrated device of motor discrete variable frequency starting and harmonic filtering was developed. In this paper, a controller is designed to control the motor during the soft starting/stopping and keep the harmonics in permitted ranges by harmonic filtering. The following works have been done in the study: the needs analysis of the controller, design the hardware based on the PLC and the software design of the controller. The motor starter developed with this controller has been successfully applied to the loads of the drive equipments. It can improve the starting performance when the motors draw the heavy-loads, save energy, stabilize the voltage of the power supply network.