P. Ju

Dynamic equivalent modeling of FSIG based wind farm according to slip coherency

This paper applies the idea of coherency to induction generator, then presents a method called slip coherency to obtain the equivalent model of the wind farm with FSIGs. A criterion has been derived for slip coherency identification. A transformation of the entire internal network in the wind farm is discussed. This transformation should be carried out before aggregating the wind turbine generators, so that the entire internal network can be taken into account in equivalent model of the wind farm. Simulation results show that the transformation provides a satisfactory accuracy in both steady-state and dynamic process. The results also show that the equivalent model obtained by slip coherency method provides excellent accuracy as the detailed model.

Application of the battery energy storage in wave energy conversion system

The output power of the Wave Energy Conversion (WEC) system, such as AWS, varies, which may not satisfy the requirements of the grid code for the integration of wave generation into power grids. To deal with this issue, in this paper the Battery Energy Storage (BES) is applied to smooth the output power of the WEC. The BES is integrated to the converters of the WEC, and the controllers for the battery energy storage systems and the back-to-back converters of WEC are designed, respectively. The power quality of the wave farm (WF) using BES is tested, and the effectiveness of the controllers proposed is demonstrated under the system disturbances.

The application of ANN in fault diagnosis for generator rotor winding turn-to-turn faults

When turn-to-turn faults occurred to rotor winding of the generator, the terminal parameters of the generator will change. The condition of the rotor winding can be reflected by the terminal parameters, but itpsilas difficult to describe the relationship of fault information and terminal parameters by accurate mathematics expressions. Applying artificial neural network in rotor winding fault diagnosis can obtain a good result, and when there are faulty samples in the training samples of artificial neural network, the severity information of the generator faults can be obtained directly. But it is difficult to gain the faulty samples in practical applications. Through the analysis of magnetic motive force of the generator and application of artificial neural network for faulty samples, the fault diagnosis of turn-to-turn fault on generator rotor winding can be carried out.

Control strategy for AWS based wave energy conversion system

The controller for Archimedes wave swing (AWS) based wave energy conversion (WEC) system is designed in this paper. Based on the model of the AWS based WEC system in the d-q frame of reference, the control strategy of the WEC system under the irregular wave is derived. The AWS based WEC is regulated to be in resonance with the wave by the stiffness control of the linear permanent magnet generator, so that the power extracted from the wave can be improved. Using the control strategy proposed, it is demonstrated that the dynamic performance and the accuracy of the control are improved.

Parameter Tuning for Wind Turbine with Doubly Fed Induction Generator Using PSO

The rotor of the doubly fed induction generator (DFIG) is fed back from the grid via back-to-back converters. Under the disturbance, the rotor current increases to maintain the terminal voltage and the rotor rotating speed of DFIG, while the current in the grid side converter also increases to keep the DC-Link voltage constant. In this situation, the overshoots of the currents flowing through the converters stress the operation condition of the back-to-back converters, even destroy the converters. The controllers of the back-to-back converters have significant impact on the dynamics of the rotor current. In this paper, the parameters of back-to-back converter controller are tuned with the objective of reducing the maximum value of the currents using particle swarm optimization. Using the parameters optimized, the overshoot of the currents can be decreased.

Feasibility research on DC generator based wind power generation system

The biggest difference between wind turbine generating units and other traditional ones (hydro and thermal generating sets) is its frequent variation of the prime mover output power and difficulties in control, due to the volatility and the uncontrollability of wind speed. In consideration of the characteristics of wind power system and Direct Current (DC) generator, a wind power generation system based on DC generator is developed, and the feasibility and advantages of this system are analyzed theoretically, with emphasis placed on its control strategy. Then, a simulative system of wind power generation system based on DC generator is built in the power system dynamic simulative laboratory. At last the feasibility and advantages of the system are verified by elaborate experiments. Both theoretical analysis and the studies prove the excellent regulating characteristics on the voltage fluctuation caused by the frequently variable wind speed and load changes for the system which working with the variable pitch parts to satisfy the requirement of the dynamo in the wind power system.

Integrated diagnosis techniques of high voltage induction machine with rotor winding faults

This paper analyzes the novel techniques adopted to diagnose machine rotor winding fault. In order to accurately extract the fault characteristic in stator-steady current, frequency subdivision is used to enhance the frequency resolution of the signal and self-adapting filtering is used to enhance the magnitude resolution of the signal. Particular frequency component in the starting current is used for fault diagnosis, this greatly simplify the fault diagnosing technique based on starting current and make it applicable. Residual voltage after AC dump of the stator winding is used for fault diagnosis, this can effectively eliminate the effects caused by unsymmetrical source, load fluctuation, and iron saturation. The application of all these techniques can effectively diagnose the incipient faults of high voltage induction machine. Finally this paper introduces the basic structure and the main performance of the realized high voltage machine fault diagnosis system

Deterministic and probabilistic analysis of static voltage stability in power systems

The mechanism of static voltage stability was examined by a visual explanation, in that way, the static voltage stability criterion was obtained. It was indicated that the static voltage stability is determined by both characteristics in generation side and characteristics in load side. Then each kind of two-dimensional plane analysis can be unified in three-dimensional space. It is pointed that both critical voltage and voltage stability margin should be use for indexes. The impact of load model on static voltage stability is discussed by both deterministic and probabilistic analysis method.

Transient analysis of synchronous generator with stator winding faults based on starting process

Multi-loop theory is the most common and effective method used for analyzing stator winding internal faults of synchronous generators. Based on the current analysis methods, this paper modifies the existing models and introduces the motion equation of rotor into the multi-loop analysis model to describe the associated relations between main parameters (e.g. current, voltage, torque, speed of rotation) of generator. Since the starting process of motor contains abundant information, this paper analyzes the influence of internal faults to relevant parameters, during the starting process from zero to rated speed. Through analysis some conclusions can be obtained as follow: when stator winding internal faults occur, since the influence of space harmonic is stronger, electromagnetic torque is on oscillatory regime. All waves are distorted when turn-to-turn faults occur. The starting current is bigger than normal, and the current will fluctuate after stabilization. The changing trends of short circular current and neutral-point current are the same. The currents are both small when starting, then gradually decay and go stabilization after an obvious increasing. The amplitudes of currents are far bigger than every branch current of stator. After faults, the electromagnetic torque of motor changes a lot and there is still an oscillation with certain amplitudes after stabilization. More short turns would cause bigger amplitudes of oscillation.