Application Of Dynamic Energy In Broadband Oscillation Of DFIG Wind Power Connected System

Based on power electronic converter,DFIG(Doubly-Fed induction generator)wind power connected system has multi time scale characteristics.After disturbed,Multi-form interaction between DFIG and synchronous generator and series compensated transmission line will be incurred,which is easy to stimulate multi-time scale broadband oscillation from electromechanical transient to electromagnetic transient,lead to large-scale wind power loss and threaten the safe and stable operation of the system.How to build an effective broadband oscillation stability analysis method and active damping technology to improve the safe and stable operation ability of DFIG wind power connected system has become a key problem to be solved.Therefore,starting from the physical essence,this paper describes the dynamic development process of broadband oscillation with energy flow,and constructs a broadband oscillation analysis method based on dynamic energy.Focusing on the coupling between generator and network under different time scales,the energy interaction path between DFIG control links and power grid is depicted,and the occurrence and development mechanism of broadband oscillation is revealed.On this basis,in order to optimize the system energy dissipation,the active damping control schemes of generator side energy remodeling and wind farm side energy coordination are constructed respectively,which can effectively damp the broadband oscillation of DFIG connected system.The main contents and achievements are as follows.1)Aiming at the problem that the existing analysis methods mainly rely on the balance point and electrical phasor to evaluate the stability of an oscillation frequency point or a static section,which is difficult to adapt to the dynamic analysis of multi time scale broadband oscillation,a broadband oscillation analysis method based on dynamic energy is constructed.The quantitative correlation between potential energy and dissipative energy and oscillation modes and eigenvalues in DFIG wind power grid connected system is deduced,and the on-line stability evaluation scheme of broadband oscillation based on dissipative intensity is proposed.The basic principle of dynamic energy analysis under broadband oscillation is clarified,which lays a theoretical foundation for dynamic energy analysis method.2)Aiming at the problem that the interaction path between generator and power grid of DFIG is unknown in the electromechanical oscillation scene,and the occurrence and development mechanism of low-frequency oscillation is difficult to be accurately revealed,the interaction energy channel between DFIG and power grid through PLL(phase-locked loop)and virtual inertia under electromechanical transient is deduced,the generator-power grid coupling effect is quantitatively characterized by the coupling dissipation intensity,the energy flow path when the generator-power grid coupling dissipation intensity is negative is tracked,and the mechanism of low-frequency oscillation divergence induced by generator-power grid coupling is clarified.3)Aiming at the problems of unclear conduction and interaction path of sub/super synchronous oscillation components between control links,which makes it difficult to track the occurrence and development process of oscillation and to reveal oscillation mechanism,the dynamic energy branches in each control link of DFIG under electromagnetic transient are described,and the contribution of each energy branch to potential energy and dissipation energy is analyzed.Then,the conduction accumulation dissipation process of dynamic energy in control links-equipment level-wind farm level is described,and the physical essence of the occurrence and development of sub/super synchronous oscillation is revealed.4)Aiming at the problem that it is difficult for the existing DFIG oscillation suppression strategy to adapt to different oscillation scenarios,and cannot take into account the stability of the full width frequency band and the response requirements of the fundamental frequency function,the potential energy and dissipated energy compensation branches are constructed in DFIG control links,and the multi branch energy remodeling technology is proposed.Then,taking into account the low-frequency stability requirements and the fundamental frequency response requirements of the DFIG,the full wide-band compensation energy coordination optimization scheme is designed to realize the broadband oscillation active damping control with adaptive oscillation scenario and effective compatibility with the fundamental frequency characteristics of DFIG.5)Aiming at the problem that the existing wind farm level control strategy is based on the single DFIG equivalent wind farm,which is difficult to take into account the coupling between multiple DFIGs in the wind farm and suppress the global oscillation,considering the differences of control parameters and operation status among multiple DFIGs,the inter-DFIGs circulating energy and inter-DFIGs induction energy functions reflecting the stability of inter-DFIGs oscillation modes and wind farm-grid oscillation modes are deduced,the interaction path of dynamic energy in wind farm and wind farm-grid is described,the influence law of DFIG parameters and operation status differences on the two oscillation modes is explored.On this basis,a multi-DFIG parameter collaborative optimization strategy considering the stability requirements of multiple oscillation modes is constructed,with which,the active damping control of wind farm level broadband oscillation is realized.