并网逆变器中延时环节对系统稳定性的影响

Influence of Time Delay on System Stability in Grid-connected Inverter

分析了模拟数字采样、脉宽调制装载模式、调制方式和硬件滤波等因素对数字控制系统稳定性的影响。以单电感滤波器的并网逆变器为对象,以逆变侧电感单电流环控制为例,建立系统模型并分析数字控制延时环节的构成,通过开环传递函数和波特图分析系统的稳定性,同时定量地给出系统的稳定条件以及系统失稳时的谐振频率。在此基础上,在一台10 kW单电感滤波器的并网逆变器上进行实验验证,功率器件采用第5代沟槽栅场截止型单管IGBT,逆变电感磁芯采用铁硅二代粉芯磁环,控制器采用32位浮点微控制器。通过实验验证了影响系统稳定性的环节包含计算延时、零阶保持器和硬件滤波等,当硬件滤波RC参数满足RC<<2/(πfs)时,临界稳定比例参数只与电感值、输入母线电压和开关频率相关,系统失稳后的谐振频率近似为1/4开关频率。同时给出了硬件滤波参数的工程设计方法,即取RC=0.2/fs,保证硬件采样滤波性能的同时,不产生系统相位的延时。

The influence of analog digital sampling,pulse width modulation(PWM)loading mode,modulation mode and hardware filter on the stability of digital-controlled system are analyzed.Taking the grid-connected inverter with single inductor filter as an example,the system model is established and the composition of digital control delay is analyzed.The stability of the system is analyzed through open-loop transfer function and Bode diagram,and the stability condition and resonant frequency of the system are given quantitatively.On this basis,a grid-connected inverter with 10 kW single inductance filter is tested.The power device uses 5th generation TRENCHSTOP IGBT,the inverter inductance core uses the second-generation powder core ring,and the controller uses the 32-bit floating point microcontroller.When the hardware filter RC parameter is RC<<2/(πfs),the critical stability ratio parameter is only related to the inductance value,input bus voltage and switching frequency,and the resonant frequency of the unstable system is approximately one-quarter switching frequency.At the same time,the engineering design method of hardware filtering parameters is given,that is,RC=0.2/fs,by which the performance of hardware sampling can be ensured and filtering without the delay of system phase.