Coordination Control Of Doubly-fed Wind Power Generation System Under Harmonically Distorted Voltage Conditions

Fossil energy created current industrial civilization, while inevitably it brings about a series of environmental problems such as haze. The rise of wind power generation technology can provide an effective scheme to solve environmental problems. With the rapid development of double-fed wind power generation technology, power-generating capacity is increasing as well, while strict grid codes are proposed to make sure a nice operation. In this paper, the mathematical models of grid-side converter and rotor-side converter for DFIG are derived and relevant control strategies are analyzed under the low-order grid voltage harmonic conditions. The possibility of coordinated control for grid-side and rotor-side converter, resonance on grid-side converter, is considerated, and additional operational control of DFIG is researched.Firstly mathematical model of DFIG grid-side converter is derived under the harmonic grid voltage conditions, including expression of GSC output current, active and reactive power,and four control targets are analyzed. The insufficient ability to achieve the targets for traditional control strategies is analyzed, resonance mechanism caused by gird-side converter filter and line impedance is discussed and the corresponding control strategy is analyzed.Then mathematical model of DFIG rotor-side converter is derived under the harmonic grid voltage conditions, including expression of rotor and stator output current, stator active and reactive power and electromagnetic torque, and five control targets are analyzed. The insufficient ability to achieve the targets for traditional control strategies is analyzed as well, and corresponding harmonic suppression strategy is adopted and the validity is proved with line impedance changed.DFIG grid-side and rotor-side converter can be used independently to achieve the control objectives respectively, and can cooperate with each other to achieve total control targets. According to the actual situation, several coordinated control objectives are listed in this paper.Phase-locked loop is the basis of vector control, principle of frequency-locked and phase-locked loop based on the second-order generalized integrator is introduced in detail under low-order grid harmonics conditions in this paper.Simulations and experiments prove the feasibility and effectiveness of the control strategies mentioned above.