分频输电系统交—交变频器触发脉冲实时生成方法

A Real-time Control Pulse Generating Method for Cycloconverter in Fractional Frequency Transmission System

分频输电是一种适用于大规模风电接入系统的新型输电方式,其核心部件为交—交变频器。当分频输电系统用于风电并网时,系统对交—交变频器提出了尽量减少谐波含量和低频侧频率可随风速变化2点要求。为了适应这一要求,文中提出一种利用多指针法实时生成交—交变频器触发脉冲的方法。该方法避免了传统余弦交点法中需要实时计算三角方程的问题,同时解决了直线近似余弦交点法中谐波偏大和离线计算时低频侧输出电压频率无法变化的问题。文中对该算法进行了详细的推导,并给出了硬件电路和程序框图。实验结果表明,该方法可在无需增加存储数据的情况下实现脉冲实时触发,且低频侧电压频率可实时变化,精度满足工程需求。该方法硬件电路简单,易于在工程中加以应用和推广,并可在分频输电系统中加以利用。

Fractional frequency transmission system（FFTS）is a new approach for large capacity wind power integration into a power system.The cycloconverter is the key equipment for FFTS.Because of the large capacity of a power system,the harmonics generated by cycloconverter must be suppressed to reduce the costs of filters.Meanwhile,in order to capture more wind power,the frequency of the lower frequency side（LFS）of the system should be changed according to the wind velocity.To satisfy these requirements,a new method,namely multi-pointer method,is proposed.With this method,the time-varying sequences of pulses could be generated in real-time to trip the thyristors of the cycloconverter.This method does not need solving of the triangular equations and can produce output voltage with less total harmonic distortion（THD）than other methods,such as the linear approximation method.Meanwhile,the frequency of LFS could be changed online.The principle,hardware design layout and flow chart of this method are illustrated.The validity of this new method is proved by the experimental results.Furthermore,the hardware circuit and the program of this method are easy to realize,thus make it suitable for industrial applications,especially in FFTS.