适应于直流新能源/储能接入的三电平Buck-Boost变换器建模及控制器设计

为实现大功率直流新能源/储能系统的接入,以一种级联同相三电平Buck-Boost变换器为研究对象,该拓扑可在宽电压波动范围内可升、可降,能适应大功率、宽范围电压的直流新能源/储能的接入和变换。首先,对级联同相三电平Buck-Boost变换器的工作原理进行分析,基于储能充放电控制均存在Buck模态和Boost模态2种工作模式,分别推导级联三电平Buck-Boost变换器的小信号平均模型,其次,考虑到中点电压平衡问题,分析占空比差值ΔD对系统的影响,并通过Bode图,得出ΔD只对Boost模式低频段时影响较大,而对Buck模式和Boost模式高频段影响不大。然后,根据系统的小信号模型,对控制器进行设计,对比了传统控制器与TypeⅢ控制器的差异,得出TypeⅢ控制器有更大的控制带宽及稳定性。最后,通过仿真验证2种控制器的效果及特性。

MODELING AND CONTROLLER DESIGN OF THREE-LEVEL BUCK-BOOST CONVERTER ADAPTED TO DC NEW ENERGY AND ENERGY STORAGE ACCESS

In order to solve the access of new energy generation/energy storage devices, in this paper a cascaded three-level Buck-Boost converter is taken as the research object. The topology can achieve the access of new energy generation/energy storage devices with high power and wide range of input voltage. Firstly, the working principle of cascaded three-level buck-boost converter is analyzed. Based on the charging and discharging of energy storage devices, there are two operating modes： Buck mode and Boost mode, and the small-signal average model of cascaded three-level buck-boost chopper is deduced respectively. Secondly, considering the midpoint voltage balance problem, the influence of the duty-cycle difference ΔD on the system is analyzed, and through the Bode diagram, it is concluded that the influence of ΔD is great only in the low frequency band of Boost mode, but not in the high frequency band of Buck mode and Boost mode. Then, according to the small signal model of the system, the controller is designed, and the differences between the PI controller and the TypeⅢ controller are compared. It is concluded that the TypeⅢ controller has greater control bandwidth and stability. Finally, the effect and characteristics of two controllers are verified by simulation.