Influences Of ODD Harmonics On Doubly-fed Induction Generator Performances

This thesis was supported by Technology Project of State Grid (DKYKJ[2012]001-1)and Program of Shenyang Science (F11-238-1-00), studied the performance impact ofmachine-side converter odd harmonics to power system, pointed out the influenceharmonics to DFIG active power, electromagnetic torque and loss extent. Analysisfocused the impact of5th,7th,11th and13th harmonics on electromagnetic torque, bythe method of harmonics as independent power-supply and combined with the equivalentcircuits of stator and rotor. Furthermore, thesis discussed the situation thatelectromagnetic torque ripple with inverter output waveforms contains even harmonics,when the operating status of DFIG changes. Simulation results show that harmonicimpact on generator performance is correct.Firstly, the thesis expounded basic structure and operation principle of DFIG system,showed DFIG equivalent circuit and space vector illustration, transform equivalentcircuit to circuit with stator and rotor separated according to the superposition principle.Calculation formula of active power, reactive power in stator and rotor sides andelectromagnetic torque under ideal sine wave were deduced, relation of power flow andsteady-state performance of DFIG was analyzed.Secondly, double fourier series expressions of two-level single-phase half-bridgeinverter SPWM, single-phase full-bridge and three-phase full-bridge were deduced.Harmonic spectrum of voltage waveform outputted with single-phase and three-phaseinverter is analyzed. According to results of analyzed harmonic spectrum, the rule ofinfluence of frequency modulation F and amplitude modulation M on inverter outputtedwaveform was summed.Finally, starting from the effects of harmonics on magnetic motive force(MMF) and slip, calculation formula for active power and electromagnetic torque were deduced. Onthis basis, the rules of influence of different harmonics on output power and torque ripplewere deduced. Torque ripple waveforms of each harmonics were analyzed by matlabsimulation. The simulation results verify the correctness of the analysis and calculationmethods in this thesis.