After energy sources such as wind and solar energy enter the grid, the number of power generation ends increases exponentially, but the power generation state of these power generation terminals is unstable, and the current generated is large and small, intermittent. As the installed capacity of wind and solar energy continues to expand, the impact on the power grid is increasing.

The power quality problems caused by photovoltaic grid connection are:

1. Large demand for reactive power

With the increase of installed capacity of photovoltaic power plants, the power fluctuation of photovoltaic power generation is large, and the high power factor operation of the inverter poses a threat to the stability of the power grid.

When the active power is unchanged, the reactive power can hardly be adjusted; Reactive power demand changes greatly, wind power systems are greatly affected by wind speed, active output fluctuates greatly, reactive power demand is large and changes rapidly, and additional reactive power is required to maintain voltage.

2. Voltage fluctuation and flicker

The output power of photovoltaic wind power generation devices changes with natural factors such as sunshine, weather, season, temperature, etc., and the output power is not stable, especially when the output power changes are small, it will cause voltage fluctuations and flicker to the system access point.

3. Generate harmonics

The power system has introduced a large number of new power electronic equipment such as converters, inverters, and unified power flow controllers, and the power grid has shown obvious characteristics of high penetration rate and high power electronics, and the problem of power grid harmonics has also undergone fundamental changes compared with the past, and is no longer a local problem on the load side.

The photovoltaic power generation system converts solar energy into DC power through photovoltaic modules, and then changes to AC energy through the inverter, and a large number of harmonics will be generated during the switching process.

After the generated harmonic current is injected into the power system

(1) it will cause grid voltage distortion;

(2) It will cause power system relay protection and automatic devices to malfunction;

(3) Harmonic current increases power loss;

(4) Accelerate the aging of equipment, which may cause equipment damage accidents in serious cases.

It threatens the safe and stable operation of the power system.

4. Island phenomenon

When the power grid loses voltage, the grid-connected wind power generation and photovoltaic power generation system still maintain the state of supplying power to a certain part of the lost voltage power grid, and connect with the local load to form an independent operation state. At this time, the voltage and frequency in the island are not controlled by the grid:

(1) If the voltage and frequency exceed the allowable range, it will cause damage to the user's equipment;

(2) If the load capacity is greater than the inverter capacity in the island, the inverter will be overloaded and the inverter may be burned;

(3) It will cause danger to maintenance personnel;

(4) If the island is reclosed, it will cause the line to trip again.

Solution

The existence of power quality problems has brought serious harm to the power grid and load, for this reason, Bowo provides a complete set of solutions, as follows: