1. Optimum power load line
At different wind speeds, the relationship between the output power of the wind turbine and the rotational speed of the wind turbine is shown in the figure below. It can be seen from the curve in the figure that under different wind speeds, there is a maximum output power in the characteristic curve of the relationship between the output power and the rotational speed of the wind turbine.
power value, such as points a, b.c...g, and connect these points to the power load line to get the optimal power output line of the wind turbine, that is, the optimal power load line, as shown by the dotted line in the above figure. The power coefficient Cp is the number of the high-speed coefficient (or tip speed ratio) λ of the wind turbine, that is, Cp=f(λ). When A=ω R/ν changes, the Cp value changes. At a certain λ value, the Cp value reaches the maximum value, and the λ value corresponding to this maximum Cp value(CP max)is called the optimal tip speed. Compare. Therefore, the so-called optimal power load line means that each point on this line is operating under the optimal tip speed ratio. That is to say, when the wind speed increases, the speed of the wind turbine should also increase (that is, ν increases, n increases), so as to maintain the tip speed ratio as the optimal tip speed ratio, that is, λ=ω R/ν does not In order to keep the wind energy utilization coefficient Cp =Cp max unchanged, the output power of the wind turbine will also reach the maximum value. From the perspective of maximizing the use of wind energy, the wind turbine should be run at the optimal power load. However, it can be seen from the above figure that if the wind turbine runs on the optimal power load line, the rotational speed of the wind turbine should vary within a wide range with the change of wind speed. In the power load line of the wind power generation system that operates independently, synchronous generators are generally used, and the output power rate of the synchronous generators has a fixed proportional relationship with its rotational speed, which will lead to the failure of the power supply quality to meet the requirements. During the operation of the wind turbine, according to the power quality requirements of the user's electrical equipment, the wind turbine should run as close to the optimal power load line as possible, rather than on the actual optimal power load line.
2. Determination of actual power load line and load adjustment
In order to ensure the quality of output power, it is impossible for wind turbines to operate completely according to the optimal power load line.
In the power load line in the above figure, n is the rotational speed of the wind turbine at the rated wind speed. And when the wind turbine operates at a wind speed of 4~12 m/s, the rotational speed of the wind turbine is ns ±Δn, and the frequency of the corresponding synchronous generator will be f(50 Hz) ±Δf.
From the power load line in the above figure, when the wind speed changes, in order for the wind turbine to run along the actual power line, the load must be increased or decreased accordingly, so that the output power of the wind turbine is equal to that absorbed by the load ( or consumption) power balance, which is load regulation. Load regulation can increase (input) or decrease (cut) the load correspondingly according to the change in the rotational speed of the wind turbine when the wind speed (or load) changes. reach stability. Therefore, it can also be considered that load regulation is to stabilize the rotational speed of the wind turbine by changing the load. It can be seen from the power load line in the figure that if the rotation speed change range selected by the actual load power line is very small, the power supply quality of the generator can obviously be improved, but the increase or decrease of the load required for the relatively small speed change is not enough. It appears to be large, which has an impact on the unit and affects the stability of the unit's operation.
OK, but it should be as close as possible to the optimal power load line, especially when the rated wind speed is close to the rated wind speed, the phoenix turbine should run on the optimal power load line or close to the optimal power load line, as shown in the figure below. For example, if the rated wind speed is 8m/s, the actual power load line should be selected as shown by the solid line in the figure below. It can be seen that when this choice is made, the actual power load line of the wind turbine will be It is close to the optimal power load line. It can also be seen from the figure below that when the wind turbine runs according to the selected actual power load, the change of the wind turbine speed is much smaller than when it runs according to the optimal power load line. In this way, The quality of output power can be guaranteed.