基于调制比自然过渡的多模式同步调制策略

Multi-mode synchronous modulation strategy based on modulation index natural transition

轨道交通牵引变流器通常运行在低开关频率下,随着电机转速逐渐上升,传统空间矢量脉宽调制(Space Vector Pulse Width Modulation,SVPWM)由于开关频率恒定,其载波比会随着逆变器输出基波频率的增大而下降,造成输出电压脉冲数减少,导致其含有大量低次谐波,畸变严重,最终影响整个系统的控制性能。此时系统需要切换至脉冲数对称且固定的同步调制,保证逆变器输出波形的同步性与对称性,以实现谐波优化。现有同步调制策略需要涉及众多脉冲数之间的切换,且最终需要进入3脉冲调制才可自然进入方波工况,实现过程考虑因素较多、难度较大。基于开关角的方法,提出一种随着调制比增大,可由15脉冲同步调制平滑过渡至各脉冲数且最终能自动过渡至方波工况的同步调制策略。首先,根据SVPWM原理,将各矢量作用时间转换为0~2π范围下的角度,并计算传统空间矢量策略(Conventional Space Vector Strategy,CSVS)的15脉冲调制下对应的所有开关角。其次,对调制比进行分段,改变开关角随调制比变化的斜率,进而在调制比逐渐增大的同时,使得相邻开关角逐渐向所划分的扇区边界合并,窄脉冲成对消失,实现在设定调制比下平滑过渡至不同脉冲数并最终进入方波单脉冲。最后,通过仿真与硬件实验对所提方法和传统方法进行对比,验证了所提方法的自然过渡能力。

Rail transit traction converters usually operate at low switching frequencies.As the motor speed gradually increases,the carrier ratio of traditional space vector pulse width modulation(SVPWM)decreases with the increase of the inverter output fundamental frequency due to the constant switching frequency.This can result in a decrease in the number of output voltage pulses,which contains a large amount of low-order harmonics and severe distortion,ultimately affecting the control performance of the entire system.At this time,the system needs to switch to a synchronous modulation with symmetrical and fixed pulse numbers to ensure the synchronization and symmetry of the inverter output waveform,in order to achieve harmonic optimization.The existing synchronous modulation strategy requires switching between numerous pulse numbers,and ultimately requires entering 3-pulses modulation before naturally entering the square wave condition,making the implementation process more complex and difficult.Based on the switching angle method,this article proposed a synchronous modulation strategy that can smoothly transition from 15-pulses synchronous modulation to various pulse numbers as the modulation index increases.This could eventually automatically transition to square wave operation.First,according to the SVPWM principle,the action time of each vector was converted to an angle in the range of 0~2π,and the corresponding switching angles under the 15-pulses modulation of the conventional space vector strategy(CSVS)are calculated.Secondly,the modulation index was segmented,and the slope of the switch angle as a function of the modulation index was changed.As the modulation index gradually increases,adjacent switch angles gradually merge towards the boundaries of the divided sectors,and the narrow pulses disappear in pairs,achieving a smooth transition to different pulse numbers at a set modulation index and eventually entering the square-wave single pulse.Finally,the proposed method was compared with traditional methods through simulation and hardware experiments,verifying its natural transition ability.