Xin Jianbo

Study of brushless excitation system parameters estimation based on improved genetic algorithm

For estimating the parameters of brushless excitation system including nonlinear blocks, in this paper, a new optimization method based on improved genetic algorithm (IGA) is developed. A practicable test method which performs the linear block parameters and nonlinear parameters estimation respectively is presented. First, the model of brushless excitation system of AC1A developed by IEEE is presented. Then an improved GA based on real-coding is detailed. In this method a modified linear cross operator is used whose merits lies in both of child generation are feasible and one must be in the vicinity paternal generation so the convergence and precision of new method are improved. Finally, the single unit simulation system and AC1A excitation system are built in Matlab/Simulink. Utilizing the improved GA the linear block parameters and nonlinear block parameters of AC1A excitation system are estimated respectively using M serial pseudo random binary signal (PRBS) and reference voltage step signals. Compared with results received from simple GA the conclusions can be obtained that the improved GA is effective and the test method is practicable.

Effect of the coupling between hydraulic turbine set and power grid on power grid dynamic stability

With the proportion of hydroelectric power station in power grid and the single-turbine capacity larger and larger, the effect of hydraulic turbine set on power system dynamic stability will be more significant. The power oscillation phenomenon, which affects the safe and stable operation of power system, occurred many times in China. For example, on October 29th, 2005, low frequency oscillation occurred in Central China Power Grid. The most of researches on the hydraulic turbine system and power system were carried out independently in the past. First, according to the physical characteristics of the draft tube hydraulic system, the hydraulic turbine set model considering the draft tube hydraulic pressure dynamic was established in this paper. Secondly, based on the single machine infinite bus system, the effect of draft tube hydraulic pressure pulsation on the power grid dynamic security and stability was studied and the coupling between the hydraulic turbine set and power grid was investigated. Thirdly, taking Zhelin Hydropower Plant in Jiangxi Power Grid as an example, the influence of the draft tube hydraulic pressure pulsation to power grid stability was illustrated in this paper. The loads of unit 5, 6 at Zhelin hydropower station have a wide range of vortex operating conditions, about 20~100MW. In this case, the vortex frequency will enhance as the loads of vortex operation conditions increase.

Energy analysis of power system low frequency oscillation of resonance mechanism

Some power oscillations occurring in the actual power system, which are not induced by negative damping mechanism, has been explained well using this resonance mechanism of power system low frequency oscillation. The resonance mechanism in power system is explained from the energy point of view in this paper. The rotor energy functions of two-machine system and multi-machine system were deduced, and then the low frequency oscillation resonance mechanism of two-machine system was established. The energy characteristics of low frequency oscillation of resonance mechanism in two- machine system were analyzed through the simulations in Matlab. Finally, Southern Power Grid of Hebei province was taken as a multi-machine case. Its electromechanical oscillation modes were obtained using Small Signal Analysis Tool (SSAT), the relative rotor speed and generator power angle were obtained from the Power System Simulator/Engineering (PSS/E) simulation results and the energy of generator rotor was calculated using deduced energy function of multi-machine system. Its result causes the physical process of power oscillation to be clearer, and is helpful to well understand the power system low frequency oscillation of resonance mechanism.