harmonicIt refers to the amount of electricity contained in the current with a frequency that is an integer multiple of the fundamental frequency. Generally, it refers to the Fourier series decomposition of periodic non sinusoidal electricity. Except for the electricity at the fundamental frequency, the electricity generated by currents greater than the fundamental frequency is called harmonics. The harmonic frequency is the ratio of the harmonic frequency to the fundamental frequency (n=fn/f1).

There are a large number of nonlinear loads in the power system, including large-scale power electronic application devices (energy-saving devices, frequency conversion equipment, etc.), high-power power drive equipment, DC output devices, electrochemical industrial equipment (rectification in chemical and metallurgical enterprises), electrified railways, steelmaking arc furnaces (AC and DC), rolling mills, elevators, calcium carbide furnaces, induction heating furnaces, and other nonlinear loads. In addition, there are many rapidly changing impact loads, such as large motors and motor groups, high-speed elevators in high-rise buildings, electric cars in large entertainment venues, welding machines in automobile manufacturers, high-speed railways, high-speed maglev trains and subways, cranes in ports, and other rapidly changing loads.

New types of power equipment containing nonlinear and impactful loads inevitably generate non sinusoidal waveform currents while implementing power control and processing, injecting harmonic currents into the power grid, causing severe distortion of the voltage waveform at the point of common connection (PCC), and load fluctuations and impacts leading to various power quality disturbances such as voltage fluctuations and instantaneous pulses. According to data analysis, more than 50% of the load in developed countries needs to be powered by electronic devices. Currently, about 30% of the load in China is supplied to users after various power conversions. With the increasing awareness of energy conservation and environmental protection among people, this type of load will rapidly increase in China. With the widespread use of these nonlinear and impactful loads, power quality issues will become more prominent, and the impact and harm to power grid operation and sensitive electrical equipment will become more apparent. The possibility of power accidents will gradually manifest as being caused by substandard power quality.

Benefits of harmonic control:

Directly connected benefits：1. Protect capacitors from interference, 2. Reduce losses, 3. Reduce heating of lines and busbars; 4. Protect electrical equipment;

Indirect benefits:Improve the power quality of the system, reduce the capacity burden of the distribution system, and protect the safe and stable operation of electrical equipment;

social results:Eliminating harmonics from the source of each low-voltage harmonic source, preventing harmonic currents from flowing into the upper level power grid, and contributing to the construction of a perfect power quality power grid.