Three methods for suppressing harmonics

Absorbing harmonic current at the harmonic source is a method for effectively suppressing harmonics. This is a widely used harmonic suppression method in the current power system, and there are mainly three main methods:

1. Preventing the amplification of harmonics by parallel capacitor banks
Parallel capacitor banks in the power grid serve to improve power factor and regulate voltage. When harmonics exist, under certain parameters, the capacitor banks will amplify the harmonics, posing a threat to the safety of the capacitors themselves and nearby electrical equipment. Measures such as using series reactors, converting certain branches of the capacitor banks into filters, or limiting the input capacity of the capacitor banks can be taken to avoid the amplification of harmonics by the capacitors.

2. Passive Filter
The passive filter is installed on the AC side of the power electronic equipment. It consists of L, C, and R components and forms a resonant circuit. When the resonant frequency of the LC circuit is the same as the frequency of a certain high-order harmonic current, it can prevent this harmonic from flowing into the power grid. Due to its advantages such as low investment, high efficiency, simple structure, reliable operation, and convenient maintenance, passive filtering is currently the main method used to suppress harmonics and provide reactive power compensation. However, passive filters have many disadvantages, such as being susceptible to the influence of system parameters; having the potential to amplify certain harmonic frequencies; being costly, large in size, etc. Therefore, with the continuous development of power electronic technology, the research direction of filtering is gradually shifting towards active filters.

3. Active Power Filter
Compared with passive power filters, APF has high controllability and rapid response capability. It can compensate for various harmonics, suppress flicker, compensate for reactive power, and has the feature of multiple functions in one device. It has a reasonable cost-performance ratio; its filtering characteristics are not affected by the system impedance, and it can eliminate the risk of resonance with the system impedance; it has an adaptive function and can automatically track and compensate for the changing harmonics. It is currently an excellent power quality product for harmonic control, and has been widely applied in various industries, making outstanding contributions to the improvement and enhancement of power quality in these industries.