| With the increasing installed capacity of wind power,the permeability in some areas has reached a high level,forming power systems with high-proportion wind energy.Wind speed fluctuations may cause the active power imbalance,and the reserve capacity and control speed of synchronous generators are hardly to meet the reserve demands,which may cause the frequency over-limit.In addition,the voltage of the point of common connection vulnerable to wind power,causing problems such as the voltage fluctuations.Scheduling plans based on the wind speed prediction can alleviate the grid frequency problems,while the wind power prediction errors bring new challenges to the active power balance and frequency stability.Installing reactive compensation equipments can suppress the voltage change to some extent,but they cannot balance the response speed and compensation capacity.Variable speed wind turbines have fast and flexible power control abilities,while they are usually controlled at the maximum power tracking mode and operate at the unit power factor,which cannot provide the active and reactive power supports for power systems.Therefore,the characteristics of grid frequency and voltage variations under wind speed fluctuations are studied,the reserve capacity and reactive capacity of wind turbines and their dunamic change rules are analyzed,the relationship between unit capacity and system demand are coordinated from the grid level through the multi-time scale optimal models,and wind turbines participate in the frequency and voltage control through the deloading is achieved.The main contents are as follows:(1)When the high-proportion wind power integration causing the system reserve demand cannot be met,the effects of the wind power prediction errors,the load variations,the deloading control constraints of wind turbines,the rotating reserve of synchronous generators and the system operating costs are considered,and the idea of frequency control based on the optimal deloading of wind power is proposed.The dynamic characteristics of the system reserve demand and the reserve capacity of wind turbines under wind speed fluctuations are considered,the optimal model considering wind power participation in the frequency regulation is established.The grid frequency can be maintained within an acceptable range by a small amount of wind abandoning,which is verified by simulation studies.(2)When the voltage of point of common connection exceeds the limits due to the insufficient reactive capacity under wind speed fluctuations,the dynamic characteristics of the system reactive demand and the reactive capacity of wind turbines under wind speed fluctuations are considered,and the idea of voltage control based on the dynamic reactive demand is proposed.According to the constraints of the reactive capacity and active power of wind turbines,the optimal model considering dynamic reactive demand is established.The effects of wind speed fluctuations and the limited reactive capacity of wind farms are effectively solved by a small amount of wind abandoning,and the voltage of can be maintained within an acceptable range,which is verified by simulation studies.(3)If the effects of the reduced active power of wind farms on the point of common connection cannot be ignored,the idea of voltage control based on the active and reactive power coordination is proposed.The influences of the reduced active power on the reactive power of wind farms and the voltage of point of common connection are fully considered,and the active and reactive power coordination optimization model considering wind power regulating voltage is established.With a smaller amount of wind abandoning,the output scheme of wind farms is layout which maximizes the system operating economy under the prerequisite for voltage stability. |
