Influence of wind power generation on power grid operation and countermeasures
In recent years, with the increasing shortage of global petroleum energy and the nuclear power warnings brought about by the earthquake in Japan, it has become a general trend to accelerate the development of a safe clean energy industry including wind power. Large-scale wind power generation needs to be connected to the grid. Although foreign wind power countries have accumulated some experience in wind power generation and power grid operation, due to the particularity of China's power grid structure, how to coordinate the development of wind power generation and grid operation has become the planning and design of wind farms. The most important issue that cannot be avoided in operation.
I. Impact of wind power generation on power grid operation in China
In the enriched areas of wind resources in China, the power grids are relatively weak. The impact of wind power generation on grid operation is mainly reflected in grid dispatching, power quality and grid security and stability.
1.1 Impact on grid dispatching
Wind energy resource-rich regions are characterized by sparse population, small load, and weak power grid structure. The input of wind power must change the power flow distribution of the power grid, and it will have a greater impact on the node voltage of the local power grid. Wind energy itself is an uncontrollable energy source. Whether it is in the state of power generation and the amount of electricity generated depends on the wind speed condition. The instability and intermittentness of the wind speed determine the large fluctuation and intermittentness of the wind turbine generating capacity. The latter wind farm is equivalent to the random disturbance source of the power grid. It has anti-regulation characteristics, and requires more backup power and peak-shaving capacity on the grid side. Due to the instability of wind power generation, the difficulty of wind power dispatching is increased.
1.2 Impact on power quality
The fluctuation of the output power of the wind turbine makes the wind turbines suffer from turbulence, wake and tower shadow effects during operation, causing voltage deviation, fluctuation, flicker, harmonics and periodic voltage pulsation, especially Voltage fluctuations and flicker have a serious impact on grid power quality. The asynchronous motor in the wind turbine does not have an independent excitation device. There is no voltage in the front of the grid, and it is accompanied by an inrush current of 5-6 times higher than the rated current when the grid is connected, resulting in a large drop in the grid voltage.
Power electronic frequency conversion devices widely used in variable speed wind turbines generate harmonics and interharmonics, harmonics and interharmonics that can cause distortion of the voltage waveform.
1.3 Impact on grid security and stability
When the grid was originally designed and planned, it did not take into account that the wind turbines connected to the end of the grid would change the one-way flow of the distribution grid power, which would change the tidal current flow and distribution, causing the grid voltage near the wind farm to exceed the safety range, and even lead to The voltage has collapsed. The injection of large-scale wind power into the grid will inevitably affect the transient stability and frequency stability of the grid. The short-circuit current exceeds the breaking capacity of nearby substation busbars and switches, which affects the safety of the power grid.
Second, the reasons for the inconsistency between wind power generation and grid operation
2.1 The pace of wind power generation and power grid construction is not uniform
The preliminary work flow of the wind power project is relatively simple, the approval progress is fast, and the construction period is relatively short. The grid access system is relatively complicated in project review, program determination and project construction. The 220kV power grid can be approved by all provinces (autonomous regions), all of which are above 330kV. It needs to be reported to the National Energy Administration for approval, and the approval procedure for the power grid is complicated. After each village has to obtain supporting documents for townships, counties, cities, and provinces, it will take a long time, making it difficult to complete the access system project and wind farm construction. The construction period cannot be matched. In China, the construction period of the first unit of a wind farm is usually 6 months. It takes only one year for all wind farms to be built, and the construction period of the power grid project is much longer. Especially for the construction of transmission lines, it is difficult to coordinate work. . The reasonable construction period of the 220kV transmission project is about 1 year, and the reasonable construction period of the 750kV transmission project is about 2 years.
2.2 Wind power peaking capacity is insufficient
From the perspective of power balance, the power grid cannot completely eliminate wind power resources. A good power supply structure and sufficient backup are the basis for full utilization of wind power. Wind power has the characteristics of randomness, intermittentness and fast fluctuation, and needs a certain scale. Flexible adjustment of the power supply to match it. Taking Inner Mongolia as an example, the power supply structure of the power grid is single, the proportion of thermal power units accounts for 84% of the total power generation installed capacity, and the heat supply units account for 40% of the thermal power units, accounting for 64% of the highest power generation load of the power grid. After entering the heating period in winter, the peaking depth of coal-fired units is about 50%, and the peaking depth of gas and pumped storage units can reach 100%. The heating unit does not participate in peak shaving at all. Although the power grid has been optimized and dispatched, in order to meet the heating demand, the load margin left for wind power is very small, and the power grid cannot meet the requirements of full-scale access to wind power, and the power balance is difficult.
