Li-Jun Cai

Simultaneous coordinated tuning of PSS and FACTS damping controllers in large power systems

This work deals with the simultaneous coordinated tuning of the flexible AC transmission systems (FACTS) power oscillation damping controller and the conventional power system stabilizer (PSS) controllers in multi-machine power systems. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among FACTS controller and PSS controllers are considered. Furthermore, the parameters of the damping controllers are optimized simultaneously. Simulation results of multi-machine power system validate the efficiency of this approach. The proposed method is effective for the tuning of multi-controllers in large power systems.

Simultaneous coordinated tuning of PSS and FACTS controller for damping power system oscillations in multimachine systems

This work deals with the simultaneous coordinated tuning of the FACTS (flexible AC transmission systems) POD power oscillation damping) controller and the conventional PSS (power system stabilizer) controllers in multimachine power systems. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among FACTS controller and PSS controllers are considered. Furthermore, their parameters are optimized simultaneously. Simulation results of multimachine power system validate the efficiency of this new approach. The proposed algorithm is an effective method for the tuning of multicontrollers in large power systems.

Coordination Between Transient and Damping Controller for Series Facts Devices Using ANFIS Technology

Abstract This paper deals with the control of the series FACTS (Flexible AC Transmission Systems) devices for the coordination between their transient stability controller and POD (Power Oscillation Damping) controller in multi-machine power systems. The design aspects and their implementation in form of fuzzy-logic coordination controller are presented. Furthermore, ANFIS (Adaptive Neuro-Fuzzy Inference System) is employed for the training of the proposed fuzzy-logic controller. The local signals of the FACTS devices are applied to achieve the coordination objectives. Digital simulations of multi-machine power system subjected to a wide variety of disturbances validate the efficiency of this approach. The proposed control scheme is not only robust, but also simple and easy to be realized in power systems.

Wind turbine modeling, LVRT field test and certification

The need to validate wind turbine models for the use in grid integration studies is addressed in an increasing number of grid codes. In several countries (Spain, Australia, UK, Germany) requirements for simulation models are now required for the grid access of wind turbines. In Germany, triggered by the new renewable energy law (EEG), a guideline for validating electrical simulation models of wind turbines has been designed. The model validation approach chosen will be described. The aim of this validation approach is to quantify the error between measurement and simulation. This is necessary in order to give a reliable figure for the model uncertainty for the use of the model in studies. Results of FRT-measurements with balanced and unbalanced faults will be compared to the results of an RMS DFIG model. It can be shown that the validation approach can be applied with success both to balanced and unbalanced faults.

Dynamic Voltage Stability Analysis for Power Systems with Wind Power Plants using Relative Gain Array (RGA)

Abstract This paper concerns the use of relative gain array (RGA) for analyzing the interactions among the wind power plant voltage controller and power system traditional voltage stability controllers. RGA analyses for both static and dynamic voltage stability controls are carried out based on the multi-input multi-output (MIMO) transfer function matrix J v (s). By means of the singular value and RGA, the dynamic voltage stability and their controller interactions are analyzed and the dynamic voltage stability control loop selection can be realized. A multi-machine power system with a wind power plant is simulated for the demonstration of the proposed approach. The proposed approach takes the advantages of the classical static voltage stability analysis and the modern multi-variable feedback control theory. This proposed approach is simple and can be easily implemented into large power systems with distributed wind power plant voltage controllers.

Dynamic voltage stability assessment and control by computational intelligence

This paper presents a novel approach for the assessment of dynamic voltage stability. The power system dynamic voltage stability problem is modeled as a multi-input multi-output (MIMO) transfer function. By means of singular value analysis, interactions between properly defined input and output variables affecting dynamic voltage stability can be analyzed for different frequencies. The output singular vectors provide information about the level of risk at the observed nodes and the input singular vectors show which control variables are most effective for taking counter measures. Since the modal analysis and singular value analysis required for MIMO systems are very time consuming, this paper proposes using computational intelligence (CI) to predict the input and output singular vectors, which are of interest in an on-line power system operation. In this study, a neural network (NN) is used for the prediction of singular vectors. Moreover, in order to reduce the extremely high number of the NN outputs, the principal components (PC), instead of the full singular vectors, are suggested as NN outputs. After calculation of the PCs by the NN, the full vectors can be obtained by a simple matrix multiplication

Transient interaction study for VSC-HVDC connected offshore wind park considering original controls

The work presented in this paper describes an electromagnetic transient interaction study performed for an offshore wind park connected by a high voltage DC transmission link based on modular multilevel voltage sourced converter technology. Since original controls are considered highly confidential for all manufacturers and typically not open and available to all parties, the controls are integrated into the simulation program as dynamic link libraries without disclosing the original content and structure. Studies considering original controls from different manufacturers in the same network model are extremely unique and the results highly beneficial for design, control, and operation of equipment from different manufacturers. Main focus of this study is to analyze and understand possible controller interactions in the wind park network. The study results indicate stable and robust operation for REpower wind turbines operated together with a Siemens DC transmission link in modular multilevel voltage sourced converter technology for all analyzed conditions.

Control of wind power plant for cooperation with conventional power generation unit and HVDC classic link

This paper focuses on the control of wind power plant equipped with doubly-fed induction generators (DFIG) for its cooperation with conventional generation unit and HVDC classic link. DFIG wind turbine and wind power plant voltage control are presented in detail. Also their influences on power system voltage stability are analyzed. Besides DFIG wind power plant, synchronous generators and monopolar HVDC classic link are also considered. For synchronous generator, conventional controllers are employed: governor, exciter and power system stabilizer (PSS). For the HVDC classic converters, the V-I controllers are applied. In this paper, the capability of DFIG wind power plant to improve power system dynamic behavior is presented. Simulation results show that the DFIG wind power plant and wind turbine voltage control strategy will reinforce the power system voltage stability.