混合导通模式并网逆变器的直接电荷量控制方法

Direct Charge Control Method for Mixed Conduction Mode Grid-connected Inverters

逆变器的不连续导通模式(discontinuous conduction mode,DCM)所需滤波电感量小,可以实现开关管的软开通,因而能够有效地提高逆变器的效率及功率密度。但是,DCM下电流应力较高。针对这一问题,该文采用T型三电平电路构建LCL型并网逆变器,并使逆变侧电感工作于混合导通模式(mixed conduction mode,MCM)。逆变器在负载电流较小时工作于DCM,在负载电流较大时工作于梯形导通模式(trapezium conduction mode,TPCM),从而在实现软开关的同时,有效地减小了电流应力。DCM与TPCM都可以实现固定开关频率,但基于传统的状态平均模型难以实现控制器的设计。该文提出一种以桥臂输出的电荷量作为控制变量的电荷量模型。该模型为线性化的二阶模型,大大简化控制器的设计。基于该模型,该文提出了一种定开关频率的直接电荷量控制方法。最后,通过仿真和实验,验证所提出的建模与控制方法的优越性。

Discontinuous conduction mode(DCM) for inverters requires a small size of inductor and can realize soft switching for switches.Therefore,DCM can effectively improve the efficiency and power density for inverters.However,the current stress under DCM is relatively high.Targeting this issue,T-type three-level circuit was used to construct the LCL-filtered grid-connected inverter in this paper.And the inverter-side inductor worked under mixed conduction mode(MCM) combined by DCM when the load current was small and trapezium conduction mode(TPCM) when it was high,so as to realize the soft switching and reduce the current stress.Both DCM and TPCM could realize the fixed switching frequency,but it was difficult to design the controller based on the conventional state average model.Therefore,a charge quantity model which takes the charge quantity output from the bridge as the control variable was proposed in this paper.This model was a linear two-order model,which greatly simplified the design of controller.Based on the proposed model,a direct charge control(DCC) method with fixed switching frequency was proposed.Finally,the good performance of the proposed model and control method was verified by the simulations and experiments.