基于自抗扰控制技术的分段式虚拟阻抗改进下垂控制

Improved Droop Control With Segmented Virtual Impedance Based on ADRC

通过并联变换器进行增容扩容时,由于其线路阻抗间存在偏差,导致有功/无功耦合,影响下垂控制性能和效果,产生环流增大系统功率损耗。对此,提出基于自抗扰控制技术(active disturbance rejection control,ADRC)的分段式虚拟阻抗改进下垂控制策略,以正负序与额定电压、实时与额定无功功率的偏差为基础,分别设计关于虚拟阻抗的分段函数,构成基于电压偏差和无功偏差的改进下垂控制,跟踪监测电压和无功,实现对下垂控制系数实时更新以满足不同工况控制要求,并采用正负序电压有效防止谐波影响控制精度,减小环流,降低损耗;为阻止因虚拟阻抗接入引起的电压跌落,提出基于ADRC的电压二次补偿策略,通过跟踪直流母线参考电压和额定电压,实时更新二次电压补偿值。最后,选取两并联、四并联变换器系统为研究对象,基于Matlab/Simulink仿真分析,结果表明:所提改进下垂控制策略在改善环流和补偿电压跌落方面效果明显,具有较好的工程适用性。

When the parallel converters are used for capacity expansion,the deviation between their line impedances leads to active/reactive power coupling,which affects both performance and effect of droop control and causes the circulation that makes the power loss of the system increased.For this reason,based on active disturbance rejection control(abbr.ADRC)an improved droop control strategy with segmented virtual impedance was proposed.In the proposed control strategy the deviation between positive and negative sequence voltage and rated voltage as well as the deviation between realtime power and rated reactive power were taken as the basis,and the piecewise functions of virtual impedances were designed respectively to constitute the improved droop control strategy based on the voltage deviation and reactive power deviation to trace and monitor the voltage and reactive power to realize the realtime updating of the coefficient of droop control to satisfy the demand on the control of different operating conditions.Meanwhile,in the droop control the positive and negative sequence decomposition was utilized to prevent the harmonics affecting the control accuracy,reduce the circulation and decrease the loss.To prevent the voltage sag due to the connection of virtual impedance,a secondary voltage compensation strategy based on ADRC was proposed,and by means of tracking DC bus reference voltage and the rated voltage the compensation value of secondary voltage was updated in realtime.Finally,selecting two-parallel system and four-parallel converter system were taken as research objects,the simulation on Matlab/Simulink platform was conducted.Simulation results show that the proposed improved droop control strategy plays an obvious role in improving circulation and compensating the voltage sag,thus,it possesses a better engineering applicability.