Guowei Cai

A new control strategy to improve voltage stability of the power system containing large-scale wind power plants

In this paper, the control strategy to improve voltage stability of power system was studied after large scale wind power plants integrated. And the strategies to improve the transient voltage stability of wind power plants were introduced firstly. Based on the analysis of characteristics that voltage stability of the fix speed wind generator, a new control strategy that can improve the voltage stability of the power system containing large-scale wind power plants was proposed by employing permanent magnet synchronous generators(PMSG) together with static compensator(STATCOM). The stability of transient voltage can be improved by using full power wind turbine close to generators to provide reactive power. STATCOM control model, fixed-speed wind turbine model and the model of permanent magnet were established, the voltage stability of wind power plants can be improved using full power permanent magnet synchronous generator with together STATCOM to provide reactive power compensation to constant speed wind during disturbance. The simulation carried out on the test system verify the proposed control strategy can effectively enhance the transient voltage stability of the power plants containing large scale wind generators.

Rotor current control for a doubly-fed induction generator using a novel nonlinear robust control approach based on extended state observer–backstepping

The doubly-fed induction generator (DFIG) has been widely applied in wind power generation systems. However, the applications of DFIG are limited by the failure of power system and inefficient fault ride-through (FRT) strategy, which lead to overcurrent in rotor windings. The overcurrent that results from continuous operation of DFIG may cause a serious tripping accident in wind turbine generators. The occurrence of overcurrent at the rotor side of DFIG must be prevented to ensure safe operation of the rotor-side converter. Preventing overcurrent can enhance the control ability of rotor current and the FRT capacity of DFIG. A novel rotor current controller for DFIG is designed to overcome its strong nonlinearity. The controller combines extended state observer (ESO) with backstepping theory. ESO is used to dynamically estimate and eliminate the model error and the uncertain external disturbance of the rotor current of DFIG. The controller is designed on the backstepping method, and then the feedback of ESO is used to eliminate the nonlinear factor. As a result, computation complexity is reduced. The controller has both superior static, dynamic performance, and strong robustness. The effectiveness of the proposed control approach is verified.

Design nonlinear robust damping controller for static synchronous series compensator based on objective holographic feedback–H∞

Considering the strong nonlinearity of power oscillation in power system containing static synchronous series compensator and nonlinear factors, a novel power oscillation damping controller that exhibits nonlinearity and robustness is proposed to reduce power oscillation in such systems. First, use objective holographic feedback on the system state equation to obtain system model. Second, nonlinear factors and external disturbances are estimated using direct feedback linearization to achieve linearization of the nonlinear model. Third, HN equation should be selected. Finally, a power oscillation damping controller of static synchronous series compensator is designed on direct feedback linearization, objective holographic feedback theory–HN. The controller exhibits good dynamic performance and robustness. Simulations on four-generator two-area system are conducted under various disturbances to prove the effectiveness and robustness of the proposed damping control method.

Large-scale power system small signal stability analysis based on matrix exponential

A new method for small signal stability analysis of large-scale power system is presented in this paper. The task of the eigenvalue analysis method which is the most common method used in the small signal stability analysis is to obtain the eigenvalue of the state matrix. However, it is very difficulty for the exiting mathematic method to solve the eigenvalue of the studied system when the orders of system reaches thousands or more. In this paper, the numerical solution of matrix exponential by employing the precise time-step integration and the numerical curve of the trace of matrix exponential are used to solve the linearization and high-order state matrix of system. For the numerical curve of the trace, the impact of the positive real part of eigenvalues will be extended of the corresponding period while the impact of the negative real part of eigenvalues will be diluted. The mode parameters, such as frequency, damp, can be obtained by using the HHT method to analyze the sections divided according to time-domain characteristics the numerical curve. Then the small signal stability is analyzed by employing the mode parameters. The results carried out on the 16 machine-68 buses test system show that the proposed method is effective for the small signal stability analysis for the large power system. The analysis process is shown in Figure 1.