Magnetic Analysis And Digital AVR Study Of Synchronous Generator By The Third Harmonic Excitation

Synchronous generator by the third harmonic excitation,with the characteristics of self-excited constant-voltage and superior economy,owns a wide range of attention and development. Based on the finite element method.this paper has analyzed the magnetic field and the process of self-excitation constant voltage,on the foundation of this, then designed the excitation control system,mainly including the following content:Firstly, introduces the basic structure and working principle of the third harmonic generator,including the excitation way, the arrangement and placement of these three windings in stator core. According to the maximum principle of harmonic output power, the calculation method of the turns of the third harmonic winding is given, and finally gives the No-load calculation waveforms of main winding and third harmonic winding using2-dimensional finite element.Secondly,deduces the function expression between the magnetic potential including excitation and armature, and the air gap flux density including the fundamental wave and third harmonical wave.In-depth studies on the No-load excitation magnetic and load armature magnetic field have been done, the calculation results and corresponding curves are given at the same time. Magnetic field analysis is consistent with theoretical analysis, and also provides a basis for the design of synchronous generator by third harmonic excitation.Thirdly, because of the absence of remanence in the finite element analysis software, the terminal voltage can’t be established. Based on the above contradiction, this paper puts forward a new method, then verifies the feasibility of this method. According to this method, has discussed the external characteristics of harmonic generator in different loads and different power factor, after that a comparative study with the external characteristics of ordinary small synchronous generator is carried out.Finally, based on the microcontroller PIC16F877A a digital excitation regulator(digital AVR) which matches with the synchronous generator by third harmonic excitation is designed. Based on the control algorithm of segmented incremental PID and the hardware circuit,laboratory debugging and field test are carried out.The test results show that:the digital AVR could meet the design requirements and be able to make the terminal voltage of harmonic generator stabilize within1%.