Due to the problem of pollution of the power distribution system due to power conversion (rectification and inversion), nonlinear electrical equipment such as lighting control systems and switching power supplies generate harmonics, which can cause the power distribution system itself or the equipment connected to the system to fail.

Harm of Harmonics

The main hazards of harmonics to the power system are:

(1) Additional power loss and heat generation to rotating electrical machines, and may cause vibration.

(2) Amplification of resonance or harmonic current caused by the reactive power compensation capacitor bank, resulting in damage to the capacitor due to overload or overvoltage; it will also cause overload or overvoltage breakdown to the power cable.

(3) Increase the loss of the power grid. Losses can reach considerable levels when resonance or amplification occurs.

(4) Cause malfunction and interference to relay protection, automatic control device and information machine.

(5) Harmonics increase the error of the watt-hour meter itself, and the user absorbs both the fundamental wave reactive power and the harmonic power.

With the rapid development of power electronic technology, the application of switching power supply is becoming more and more extensive. On the one hand, the switching power supply is developing in the direction of high reliability and miniaturization; on the other hand, the power capacity and power density of the power electronic device itself are also constantly improving. High-order harmonics and electromagnetic interference will inevitably be generated during shutdown, which will be injected into the power grid and endanger the stability of the power grid and the system itself. At present, there are two main methods to suppress harmonics at home and abroad, passive filtering and active filtering.

At present, harmonics have become one of the main obstacles to the normal and reliable operation of switching power supplies and electronic systems in the application site. European and American countries have formulated relevant standards in 1996 and enforced them strictly, and electrical products that do not meet their standards are not allowed to enter the market. my country also formulated corresponding standards in 2003, and implemented a system of punishing users with excessive harmonic content in a few cities. Therefore, the research on switching power supply harmonics is particularly important at present.