Abstract
The main weakness of the brushless excitation system in a synchronous generator (SG) is the slow de-excitation response obtained during a load rejection. That is why voltage overshoots may be observed on the generator terminals. This behavior is mainly due to the exciter machine response time and the rotating diode bridge which is not able to quickly de-excite the generator by negative excitation voltages. This paper presents a new brushless de-excitation structure able to perform a quick de-excitation of the generator by providing controlled negative excitation voltage to the generator main field winding. The proposed structure is based on a new brushless de-excitation machine, called a control machine, and mounted on the same shaft of the generator and the brushless exciter. The brushless control machine is a low power one and used to transfer the orders from the voltage regulator to the discharge system located on the rotor side of the main generator. The dynamic performance of the proposed de-excitation system is evaluated in terms of system stability, voltage regulation response times and voltage overshoots during different load rejection tests. The proposed system is compared to the conventional brushless excitation system without the proposed de-excitation structure. In addition, a comparison is done with the static excitation system. The simulation tests are realized on an experimentally validated model of 11kVA synchronous generator developed in Matlab/Simulink.
Highlights
Synchronous generators (SGs) are the most used machines in power generation
In the static excitation (SE) system, the thyristor bridge is able to deliver negative excitation voltages by controlling the firing angle to be around 155°
The performance of each structure is presented by performing a sudden variation of the load connected to the main synchronous generator (SG)
Summary
Synchronous generators (SGs) are the most used machines in power generation. They are used in hydro, gas, steam and nuclear power plants. Voltage regulation with advanced digital controllers, sliding mode control, fuzzy logic controllers, H∞ controllers, and neural network controllers achieves good performance and improves the transient stability of the closed loop system [10,11,12,13,14]. These advanced controllers have a minor effect in reducing the voltage overshoot and the response time during a load rejection. Authors in [16, 17] proposed an excitation structure based on a rotating thyristor bridge This solution allows controlling the generator field winding by negative and positive excitation voltages. A comparison is made with the static excitation system
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