In the demand for stepless speed regulation, using a frequency converter is a reasonable choice; However, in the practical application of motors, there are always some cases where power frequency motors are used for frequency conversion. For motor manufacturers, there will be strict differences in the design of power frequency and variable frequency motors, such as special treatment in terms of electromagnetic wire selection, cooling structure, and bearing system quality control. The reason why variable frequency motors are controlled in this way is mainly because when powered by frequency converters, the unique sinusoidal waveform of the power supply will form a regular square wave due to the frequency converter. Especially in high-frequency conditions, the motor will have a high inter turn voltage peak during operation, which has varying degrees of adverse effects on the vibration and noise of the motor, as well as the bearing system; Especially for frequency converters of different qualities, their impact on the motor varies.
Based on the practice of many motor users using variable frequency motors, some manufacturers have taken necessary measures from the design stage to meet the normal operation of the motor within a certain frequency range; In response to the temperature rise problem that occurs during the frequency conversion operation of power frequency motors, some users will take measures to strengthen heat dissipation and further improve the input power quality of the motor by adding a sine wave filter, which can effectively improve the operating quality of the motor.
By using a sine wave filter, the SPWM modulation wave can be filtered into an approximately sinusoidal voltage waveform, and remote control of frequency conversion can be achieved. For motors, effective measures include the quality and reliability of windings, protection of bearing systems, and extension of service life.
But after using a sine wave filter, the load capacity of the frequency converter will be lower than the rated value of the system, which must be considered in the power setting of the frequency converter; In addition, a sine wave filter will cause a certain proportion of voltage drop in the filtered voltage, with a voltage drop of approximately 10% at the fundamental frequency. Due to the fact that the filter filters out a large amount of high-order harmonic components during the process of filtering PWM waves into sine waves, it leads to an increase in the no-load current of the frequency converter during no-load operation.
In transmission systems such as elevators, fans, and water pumps, sine filters are widely used and have varying degrees of application in the fields of metallurgy, coal, petrochemicals, water treatment, and new energy.