Studies On Active Power Coordinated Control With Large-Scale Wind Power Integralion

Along with the economic development, the growing problem of resources environmental stimulates the integration of wind power in power system. Currently, the mainly wind turbines integrated are variable speed wind turbines (including Doubly Fed Induction Generator and Permanent Magnet Synchronous Generator wind turbines). The active output power of variable speed wind turbines is decoupled with power system frequency, and the active output of wind turbines can’t change to decrease the system frequency deviation under power system fault condition. Unlike conventional generators, the maximum active output power of wind turbines depends on wind speed, and the volatility of net load is strengthened, which aggravates the operating stress and increases the operating cost of AGC (automatic generation control) units. Particularly in the case of high wind speed, the wind turbines may be cut out from power grid if the wind speed is higher than Cut-off wind speed, which will cause severe active power disturbance on power system. Especially the power grid with large-scale centralized wind power connected as in china, wind power ramp event may bring great operating risk to power system.Aims at the active power balance problems brought by wind power integration, several problems are studied according to the order of primary frequency regulation, secondary frequency regulation and dispatching schedule in this thesis. Including analysis of frequency control characteristics of variable speed wind turbines and the coordination frequency control strategy of wind farm, distributed coordinated control of wind farm and AGC units, risk assessment of power system with wind power ramp event based on prospect theory, reserve demand analysis and preventive controls to deal with wind power ramp event. The main contributions and innovations are described as follows.(1) The frequency control characteristics of VSWT (variable speed wind turbines) are analyzed and a coordination frequency control strategy of wind farm is proposed for the weakly coupling between wind turbine active output power and system frequency. VSWT with additional frequency control was studied. The dynamic characteristics of input mechanical power and output active power of VSWT during frequency response process are analyzed, and the relationships between the active power incremental and the duration of VSWT participating in system frequency regulation is analyzed, based on which, a coordination frequency control strategy of wind farm is proposed. According to the control strategy, the VSWTs can participate in frequency regulation depending on the coordination of wind speed, power incremental and duration. The simulation results demonstrate the effectiveness of the proposed control strategy, which can make full use of the frequency regulation ability of VSWTs as well as avoid the negative effects of wind turbines participating in system frequency regulation.(2) A distributed coordinated control of wind farm and AGC units is proposed for the large predication error of wind power aggravates the operating stress and increases the operating cost of AGC units. A minutely distributed coordinated control model of wind farm and AGC units are constructed, and a distributed incremental consistent algorithm apply to the control process with high wind power penetration are proposed. In order to reduce the power system operating cost and the curtailed amount of wind power, the minutely net-load increment are allocated between the wind farm and conventional AGC units according to the law of equal marginal costs. The simulation results validate the effectiveness of the proposed control strategy, and the regulation capacity of AGC units can be guaranteed as well as reducing the curtailed amount of wind power and power system operating cost.(3) A risk assessment model of power system with wind power ramp event based on prospect theory is proposed for the impact of wind power ramp event on power system becomes more and more serious. The characteristic and development process of wind power ramp event is analyzed, and a time-dependent outage model of conventional generators which is appropriate to wind power ramp event is constructed based on Monte-Carlo method. The time-sequence of ramp event and outage of conventional generators is considered by sampling the possible outage time and state of conventional generators separately. The simulation results with IEEE RTS 24 system validate the effectiveness of the proposed model.(4) The predicition information of wind power ramp events has significant time sequence characteristic, which is normally expressed as the start time, the duration and ramp amplitude of wind power ramp event, and it is difficult for conventional power system reserve setting and preventive control. A reserve demand analysis and preventive control model to deal with wind power ramp event is proposed to solve the above problems. The probability distributions of wind power ramp event predication information in time series is converted to the probability distributions in single time sections, and the reserve demand to deal with ramp event is analyzed based on it. A preventive control model is proposed, the dispatching schedule is adjusted according to the newest predication information with it, and the adjustment includes the curtailed amoumt of wind power, the output power and reserve capacity of conventional generators. The conclusion is demonstrated with the simulation on IEEE RTS 24 system.