Di Chen Liu

Hydro Turbine Nonlinear Model Parameter Identification Based on Improved Biogeography-Based Optimization

The nonlinear model of hydro turbine considering the elastic water column was proposed, and the improved biogeography-based optimization (IBBO) algorithm was applied to identify parameters of this model. The cosine species migration model and the elitist reservation strategy were introduced into the algorithm to improve operating efficiency. Based on measured data, comparison of the effects of different identification methods was presented, including the IBBO algorithm, genetic algorithm (GA) and particle swarm optimization (PSO). The results demonstrated that the IBBO algorithm can be applied in parameters identification of hydro turbine nonlinear model, and it has the advantages of faster convergence and higher precision.

The Balance of Power System Peak Load Regulation Considering the Participation of Nuclear Power Plant

Nuclear power plants (NPP) have to face urgent requirement of participating in peak load regulation of power grid. The peak load regulation performances of NPP were researched. Based on the calculation and analysis on peak load regulation cost and benefit of NPP, the location, criterion and peak balance algorithm of NPP participating in peak regulation were proposed. Results of the actual research show that NPP possesses better ability of peak load regulation and the cost is lower, so NPP can participate in daily peak load regulation, which will improve both security and flexibility of power grid and enhance the efficiency of resource configuration. However, the depth and speed of peak load regulation by NPP are restricted by security and economy.

Fast Computation of Sample Entropy in Forced Oscillation Detection

Forced power oscillation in power systems has a serious influence to the safe and stable operation of power systems. A fast dynamic sample entropy algorithm is proposed based on sample entropy in this paper. The change of dynamic sample entropy of the tie-line power is analyzed to determine whether the forced power oscillation happened. Case study on the 4-machine 2-area system shows the effectiveness and efficiency of the proposed methodology.

Risk Assessment of a Line Outage Based on Fuzzy Membership

There are many uncertainties in power system. It is significant to consider the impact of uncertainties when comparing the importance of lines. The fuzzy set theory was applied and the fuzzy load flow calculation on the basis of line outage which had taken into account the generator output and load uncertainties were deduced. Overload, low voltage, and load shedding were selected as risk indexes. Then combined with the severity functions in the risk theory, the risk assessment models based on fuzzy membership have been put forward. Finally, the results of the three indexes and their comprehensive risk index about IEEE 118-bus system were given, and then the importance of each line in the system was compared, which confirms the value of the approach introduced in this paper.

Identification of Power Quality Disturbances Based on EEMD and TEO

The empirical mode decomposition (EMD) is a good time-frequency analysis method, which can deal with nonlinear and non-stationary signals. Aiming at improving modal aliasing problem brought by the traditional EMD, white noise is introduced into the improved aided analysis algorithm namely ensemble empirical mode decomposition (EEMD), instantaneous amplitude and frequency can be obtained by using teager energy operator (TEO), which is adopted to identify the type of power quality disturbance. The anti-aliasing of EEMD and real-time detection of TEO are verified by the signal simulation in Matlab. Simulation and experimental results show that the proposed algorithm can detect and locate power quality disturbances accurately and quickly, with excellent detection effects.

A New Method for Capturing Oscillation Center Based on Reactive Power Integral

The construction and development of power system have made our country form interconnected power grid. When oscillates occurs without timely disconnected control, accident may spread which will cause stability damage and uncontrollable chain reaction. So, how to guarantee the system to make effective out-of-step separation in the critical moment is the significant task in current power system. This paper analyzes the characteristics of electrical quantity after out-of-step, proposes a criterion based on reactive power integral, and does simulation in CEPRI-36-node system. The experimental results show that this control can start from the comprehensive situation, adopt multiport electrical parameter, locate and capture oscillation center accurately, monitor system state timely, adapt to system network structure and operation mode change automatically, recognize condition of out-of-step rapidly.

Analysis of Static Frequency Characteristics Based on Curve Fitting

Identification and calculation of static frequency characteristics is of great significance for power system to maintain its stability. In this paper, coefficient of static frequency characteristics is fitted by the least squares method. Frequency deviation restriction point under different capacitances is forecasted by the fitted trend of coefficient of static frequency characteristics. Moreover, the new method is simulated and its calculation error is also compared.

Static Security Risk Assessment Based on Outage of Line

From the risk theoretical point of view, static security risk indicators of the transmission grid are built on the basis of the probability theory, grid static security risk indicators, including overload risk indicators and voltage-limit risk indicators. For both risk indicators, the probability of the outage of one line is considered, as well as in the case of the uncertainty of the power system the serious consequences caused by the outage of one line. And the overload risk assessment model and voltage-limit risk assessment model are built. Finally, quantitative assessment and calculation are done through the standard system examples of these two static safety risk indicators, then assess and sort the transmission lines of the importance based on the simulation results.

Study on 3-Phase PWM Rectifier Controlled by Direct Power

Based on the analysis on shortcomings of controlling strategies of direct power on the traditional 3-phase Boost-type PWM Rectifier through space vectors, a new controlling strategy is proposed in this paper. With this new strategy, the space vector is divided into 12 basic space vectors to form a new switching table. The instantaneous power controlling technology is realized through the control of instantaneous active power and reactive power by choosing the best switching state of PWM Rectifier. This new controlling strategy can put the input side unit power into operation, improve the efficiency of power and reduce harmonics of the input current. The effectiveness and feasibility of this controlling strategy have been justified through the simulation and experiment.

Distinction of the Property of Low Frequency Oscillation Based on ARMA Mode Identification

Aiming at how to solve the question of quantitatively distinguish negative damping low frequency oscillation and forced power oscillation, the difference in frequency and damping ratio between the two kinds of oscillations have been discovered through mechanism analysis, and a new quantitative distinction criterion for the property of the low frequency is proposed. The oscillation data is windowing identified by ARMA model based on weighted recursive least squares algorithm dynamically, and low frequency type can be distinguished according to the changes of oscillation frequency and damping ratio during the oscillation. The simulative results have shown that the method is feasible and effective.