With the needs of industrial development, in order to reduce the load of the system and save energy, a large number of variable frequency inverter are used in industrial occasions. The use of frequency converter can indeed achieve energy-saving effects, but it also brings other problems such as harmonics. We encountered a very typical site where a large number of high-power inverters were used in the control of the water pump. The operation of a large number of inverter equipment leads to serious harmonic distortion in the system, which seriously affects the safe and stable operation of the system.
From the field test waveform, the main harmonic distortion order is 5, 7 harmonics. Before the operation of APF, the total harmonic distortion rate of the system has reached 39.5%. After the operation of active harmonic filter, the total harmonic distortion rate of the system is reduced to about 6%, the waveform is restored to normal, and the harmonics of each order are significantly reduced. From figure 1 to figure 4, we can see very clearly that the effect of harmonic control after using active filteris very obvious and effective.
The harm of harmonics is very serious. Harmonics reduce the efficiency of the production, transmission and utilization of electric energy, overheat the electrical equipment, produce vibration and noise, and make the insulation aging, shorten the service life, and even malfunction or burn. Harmonics can cause local parallel resonance or series resonance in the power system, which magnifies the harmonic content and causes the capacitor and other equipment to burn. Harmonics can also cause misoperation of relay protection and automatic devices, causing confusion in electric energy measurement. Outside the power system, harmonics can cause serious interference to communication equipment and electronic equipment.
The active power filter is connected to the power system in parallel, through external current transformer to sample the three phase current. The main control unit calculate the required compensation current value and send a command to IGBT, The IGBT dynamically adjust the switching frequency to optimize the performance and AHFto offset harmonic current.
Post time: Jul-28-2023