In recent years, with the widespread use of nonlinear loads represented by power electronic devices, various complex and precise electrical equipment represented by microcomputerization has become increasingly popular, and users' requirements for power quality have been continuously increasing. This issue has attracted high attention from power departments at all levels, and the country has also issued relevant technical standards. Qualified power quality refers to the electricity provided to sensitive equipment, as well as the grounding system set up for it, which is suitable forPower quality monitoringdeviceNormal operation of.

With the development of power electronics technology, power users have adopted a large number of nonlinear devices with time-varying control. The scope of electricity usage has expanded, and a large number of impacts, nonlinear loads, and unbalanced loads have flooded into power users. The promotion and use of new power generation and energy storage methods, high-voltage direct current transmission, new control methods, and the use of many nonlinear components continuously improve the requirements for power quality.

The above reasons have led to power quality issues, mainly including power outages, frequency deviations, voltage drops, voltage rises, instantaneous pulses, voltage fluctuations, voltage cuts, harmonics, inter harmonics, overvoltage, undervoltage, etc.Power quality issues can have serious impacts on the power grid and user equipment, mainly manifested as the following:

1. Voltage fluctuations:Causing uneven motor speed and endangering the normal operation of the motor, affecting product quality, causing lighting flicker, causing eye fatigue and reducing work efficiency. Voltage fluctuations and flickers can also cause interference to the digital system and cause misoperation.

2. Increased harmonic content in the power grid：This can shorten the lifespan of electrical equipment, even cause damage, increase network losses, and increase the likelihood of harmonic resonance in the system. At the same time, it may cause a series of problems such as misoperation of relay protection and automatic devices, inaccurate instrument indications and electrical measurement, and interference in communication.

3. Unbalanced three-phase voltage：It can cause additional vibration torque and heating of the motor, increase transformer leakage and local overheating, increase power grid line loss, interfere with communication, and malfunction of various protection and automatic devices.

4Voltage sag：Mainly affecting the normal operation of voltage sensitive electrical equipment (such as electronic equipment) in industrial production processes, and even causing serious economic losses. Therefore, voltage sag has become one of the serious electromagnetic interference problems faced by modern power users.