Wide Area Frequency Protection And Control Scheme For Interconnected Power System With Significant Wind Energy Penetration

Frequency, which is an important index of AC power systems, reflects the balance between active power generation and load. Given the implementation of global energy strategy, large-scale energy resource bases and electric power transmission capability have increased gradually, thereby leading to a high probability of power deficit. In addition, the scale of wind power-integrated power systems that use flexible technology has continually expanded as energy crises occur and electronic power technology improves. The active power balance of power systems that use large amounts of wind power is greatly affected by fluctuations in wind power. To ease the transition from conventional power systems to complex power systems with a high penetration of wind power, research still needs to be conducted on the effect of intermittency and wind power ramp events on frequency dynamics and frequency stability.Based on research on the dynamic frequency characteristics of interconnected power systems, wide-area frequency protection and control are discussed in this study, followed by theoretical analysis and numerical simulation. The main research work and innovative results of this thesis are as follows.(1) First, the model used to estimate the active power deficit based on local measurements is established in this paper. The dynamic characteristics of the complex interconnected power system after active power disturbance are investigated based on the frequency response characteristics of multi-machine power systems. Abrupt changes in the active power flow in the tie line and the rate of frequency change of the generators are used to identify the fault region. The area-decoupled expression of the active power deficit is derived from frequency dynamics analysis. It makes use of the rate of frequency change of the reginal center of inertia. The load voltages and their changes as well as the tie line active power changes within the fault region are used tp estimate the magnitude of the active power deficit.(2) Once the active power deficit is estimated, a quantitative security assessment method for transient frequency is proposed by analyzing the dynamic frequency response of the system frequency response model.(3) Considering the error of the estimation method and the uncertaintes in the load shedding control process, a two-stage control scheme with basic control and corrective load shedding control is presented in this thesis. In the basic control stage,0.9times the estimated active power deficit is shedded to prevent unnecessarily large amounts of load shedding. The second control stage is used to prevent frequency hover in case the frequency can not recover to acceptable limits after the first control stage is activated.(4) Given that conventional frequency load shedding (UFLS) cannot position the shedding location and distribute the active power deficit, the proposed load shedding sensitivity is based on the characteristics of frequency dynamics. The schemes for positioning the shedding location and distributing the active power deficit are then presented according to the load shedding sensitivity. The simulation results indicate that the proposed UFLS scheme based on load shedding sensitivity results in excellent control under the same load shedding amount compared with conventional UFLS.(5) Given fluctuations in wind power, more requests are brought up for load frequency control (LFC). To design LFC controllers for high wind power-penetrated power systems, an LFC model that takes wind power fluctuations into consideration is first developed. Multivariable decentralized model predictive control is then proposed for use in designing LFC controllers that can adapt to wind power fluctuations based on the wide-area measurement system.