微电网是相对于大电网来说的，但微电网并不等同于早期低电压等级的大电网，

The microgrid is relative to the large grid, but the microgrid is not equivalent to the large grid of the early low voltage level. The microgrid has its distinctive characteristics. The microgrid uses distributed power generation as a power source: and has an energy storage system as Regulation; there are two modes of operation: ① parallel operation with the distribution network, ② island operation. Therefore, the research on the power quality of the microgrid can also be equivalently analyzed separately for its two operating modes, that is, the impact of the operation changes of the distribution network on the power quality of the microgrid during grid-connected operation; and The influence of micro power supply and power electronic equipment on the power quality in the micro grid. When the microgrid is switched from the island operating mode to the grid-connected operating mode, since the voltage amplitude of the microgrid and the large grid is different before grid-connected operation, the energy storage device needs to regulate and stabilize the microgrid voltage, but this process often makes the microgrid voltage The fluctuation exceeds 5%, which affects the power quality of the microgrid. On the other hand, the three-phase imbalance and harmonics in the distribution network during grid-connected operation will penetrate into the microgrid from the common connection point PCC (Point of Common Coupling) and affect it. Microgrid power quality. In the micro-grid island operating mode, due to the relatively small capacity of the micro-grid, it cannot be regarded as an infinite power supply with constant voltage and frequency like the large grid, so its anti-interference ability is also very weak and more susceptible to nonlinear The influence of external factors such as load and voltage mutation, which affects the stability of the microgrid voltage, frequency and waveform.

The microgrid is relative to the large power grid, but the microgrid is not equivalent to the early low voltage level of the large power grid, the microgrid has its distinct characteristics, the microgrid is distributed power generation as a power source: and has the energy storage system as regulation; Therefore, the study of the power quality problem of microgrid can also be equivalent to the analysis of its two modes of operation, that is, the impact of grid-connected operation on the power quality of microgrid due to the operation of the grid, and the impact of the island operation on the power quality of the microgrid due to micro-power supply and power electronic equipment. When the microgrid is switched from an island operating mode to a grid-connected mode, because the microgrid and large grid voltage amplitude are different before grid-connected operation, it is necessary to adjust the voltage of the microgrid through the energy storage device, but this process often causes the microgrid voltage to fluctuate by more than 5%, thus affecting the power quality of the microgrid, on the other hand, the three-phase imbalance in grid-connected operation and the harmonics will be from the common connection point (Point of common) Infiltrating into the microgrid affects the power quality of the microgrid. In the operation mode of microgrid island, because the microgrid itself has relatively small capacity, it can not be regarded as an infinite power supply with the same voltage and frequency as a large power grid, so its anti-jamming ability is also very weak, more vulnerable to nonlinear load and voltage mutation and other external factors, thus affecting the stability of the microgrid voltage, frequency, waveform.

Micro grid is relative to large grid, but micro grid is not equal to the early low-voltage level of large grid, micro grid has its distinctive characteristics, micro grid is distributed generation as the power source, and has energy storage system as the regulation; there are two operation modes: ① grid connected operation with distribution network, ② island operation. Therefore, the research on the power quality of microgrid can also be equivalent to the analysis of the two operation modes, that is, the impact of the operation changes of the distribution network on the power quality of microgrid in grid connected operation, and the impact of the micro power supply and power electronic equipment on the power quality of microgrid in island operation. When the micro grid is switched from island operation mode to grid operation mode, because the voltage amplitude of the micro grid and the large grid is different before grid operation, it is necessary to adjust and stabilize the micro grid voltage through energy storage device, but this process often makes the micro grid voltage fluctuate more than 5%, thus affecting the power quality of the micro grid. On the other hand, the three-phase imbalance and harmonic in the distribution network during grid operation The power quality of microgrid will be affected by the penetration of PCC (point of common coupling) into microgrid. In the islanding operation mode of microgrid, because the capacity of microgrid is relatively small, it can not be regarded as an infinite power source with constant voltage and frequency, so its anti-interference ability is also very weak, and it is more vulnerable to the influence of nonlinear load and voltage mutation and other external factors, thus affecting the stability of voltage, frequency and waveform of microgrid.<br>