Optimal PWM Strategy And Improved Filter Design For Medium Voltage Wind Power Converter

With the increase of the unit capacity of the wind power generators,the power of the converters with grid connected for wind turbines is also increasing.The medium-voltage and high-power wind power converters has become a new research hotspot.In order to reduce the switching loss of the device,the switching frequency of the device is usually low.If the conventional three-level modulation strategy is adopted,the low switching frequency will lead to the problem of excessive output harmonics and insufficient system control bandwidth.The Selective Harmonic Elimination Pulse Width Modulation(SHEPWM)is ideal for medium-voltage and high-power wind power converters due to its low switching frequency,small device loss and excellent output harmonics performance.In this paper,the demand of the modulation strategy on the generator-side converter and the grid-side converter of the medium-voltage wind power converter is analyzed first.For the generator-side converter,its dynamic performance requirement for current loop control is relatively low.The main problems of concern are common-mode voltage and fluctuating of neutral point potential.For the grid-side converter,modulation strategy need to take account of the grid-connected current quality and system switching losses,dynamic and steady-state performance,and adaptation to non-ideal grid conditions.This paper presents improved SHEPWM strategies can achieve the common mode voltage suppression,neutral point potential balance and grid adaptability,respectively.The LCL filter is compared with its derivative topology,and its advantages and disadvantages are analyzed.In order to improve the output harmonics of SHEPWM,the design principle and method of parameters based on the improved LCL filter are given.The damping resistance loss is significantly reduced while the higher harmonics are effectively suppressed.Finally,the system simulation model is built on the Simulink platform of Matlab software,and the proposed improved SHEPWM strategy and filter design method are analyzed and verified.The simulation results show the effectiveness and feasibility of the control strategy and the related methods.