Harmonics Mitigation Of Standalone Brushless Doubly-Fed Induction Generator Under Nonlinear Loads

As a new type of energy-saving power generation system,the ship shaft power generation system has a broad application prospect.Unlike conventional diesel fuel-generators,the main engine of a poorly burned fuel engine acts as a prime mover to drive the shaft generator to take full advantage of its redundant power.The brushless doubly-fed induction generator(Brushless Doubly-Fed Induction Generator,BDFIG),is an AC multi-port motor.It not only maintains the advantage of operating with the fractionly rated power converter same as the traditional doubly-fed induction generator system,but also enhances the reliability of the system by virtue of its brushlessness.Therefore,the BDFIG-based ship shaft power generation system has received extensive attention and research.With the rapid growth of various non-linear loads in the ship loads,the load current waveform in standalone power generation system deteriorates with the exsistence of a large amount of harmonic current components.The harmonic voltage drop of nonlinear load currents on the internal impedance causes the distorted output voltage,which results in the reducement of the power quality.Based on the detailed analysis of BDFIG standalone power generation system under nonlinear loads,three active control schemes of harmonic mitigation are proposed in this paper,which can be divided into three kinds of harmonic elimination strategies based on the motor side converter,the load side converter and the double side converter,according to implementation object of the control strategy.Firstly,based on the internal electromagnetic relationship of BDFIG,the harmonic voltage drop caused by the nonlinear load is compensated by the induced harmonic electromotive force,and the harmonic mitigation technology based on the motor side converter is proposed.Secondly,based on the concept of shunt filter,the PW harmonic voltage based control method is used to replace the harmonic component extraction from laod current.A low harmonics mitigation method based on the load-side converter without additional current sensor is proposed.Finally,based on the aforementioned control methods of harmonics mitigation in the two single-sided converters,in order to utilize the maximum capability of harmonic mitigation of the system and enhance the flexible system adjustment ability under various constraints,a unified control scheme of harmonic mitigation based on double-sided converter is proposed.The scheme can continuously adjust the contribution of the double-sided converter in the harmonic mitigation by changing the weight coefficient.Finally,the experimental datas of three control methods under nonlinear loads have been acquired through the 30 kVA BDFIG standalone experimental platform.Comprehensive experimental results have demonstrated the effectiveness of the control strategies.