Study On Transient Aggregation Model Of Permanent Magnet Direct Driven Synchronous Wind Turbine Generator

Wind power is renewable,pollution-free,and relative economic.This naturally makes the wind power industry,including permanent magnet synchronous wind power generator(PMSG),a significant increase in installed capacity and power generation in the past twenty years.So Strong is the growth of wind power that it will inevitably bring about rising penetration rate in the grid,and the interaction between the wind farm and the grid is no longer a problem to be ignored,especially when under fault conditions.Therefore,based on the existing research on the results of the transient conditions of the PMSG unit and then PMSG model of the wind farm,Some specific work had been carried out and briefly described as follows:At first,the PMSG air dynamics model,the mechanical model,the converter and DC bridge model were established.And the wide acceptance of the flux oriented zero d-axis current vector control at the machine side converter,the positive d-axis voltage oriented active reactive power vector control of grid side converter,and Bridge DC voltage control strategy was also introduced later on.After introducing the mathematical model of PMSG unit and the conventional control strategy,this paper modeled the PMSG unit under symmetrical voltage drop in which case the conventional control strategy can still handle.Then put forward a new method by looking on the PMSG under symmetrical faults as a controlled current source which depends on the depth of the voltage sag and the active power of the moment before voltage sag,and demonstrated their mathematical relationship.Considering the probability of symmetrical voltage sags is indeed small,most often the faults PMSG unit faces are asymmetric faults and the two order fluctuation of active power it induce makes power blocking problem even worse for asymmetric faults than under symmetrical voltage sags.After a detailed deduction of the relationship between the power components and current components under dual current loop control strategy.This paper again modeled the PMSG under asymmetrical voltage sags as a controlled current source which is controlled by the depth of the voltage sag and the active power of the moment beforevoltage sags.However,getting the exact setpoint of active and reactive power was not a standard practice in real world,which was not a good news for modelling PMSG.To get round that,this paper originally choose to simulate the PI controller with amplitude constraints by optimization method.Usually,there is a reactance between PMSG and the grid,and it inevitably causes a dilemma of making the active power at the output port of PMSG constant and making the power injected into the grid constant when there is asymmetrical element in the voltage of the grid.Considering that the unbalance or the asymmetry of gird voltage is a common occurrence even in normal operation.Hence when the voltage is moderate,people usually choose to keep the active power at the output port of PMSG constant.At this time,the power component equation becomes a nonlinear equation.Again this paper chose to use optimization to simulate the control process and gave its results.Through the in-depth analysis of the PMSG unit under symmetrical and unsymmetrical voltage sags of electrical characteristics,this paper concludes that the under transient conditions of electromagnetic power grid PMSG can be equivalent to voltage sag depth and pre fault controlled current source active power control of the conclusion.After the comparison of the modelling of the doubly fed induction generator wind farm,a simple method is proposed to solve the problem of the current source vector summation,which is the direct equivalent of the current source vector.Finally,based on the assumption that the controlled current source is equivalent to the PMSG,the dynamic process of PMSG was qualitatively analyzed.