基于自适应下垂控制的柔性能源变换器

Flexible Energy Converter Based on Adaptive Droop Control

采用传统下垂法控制的柔性能源变换器能够实现并离网的无缝切换,但是由于缺乏惯性导致其在输出指令突变时系统容易产生频率突变从而影响系统的稳定性。对基于下垂控制的柔性能源变换器加入低通滤波器使频率平滑转变,等效达到了同步发电机的惯性效果。低通滤波器的截止频率越低则模拟的惯性效果越大,但也使逆变器调节速度越慢,从而产生能量过冲以及导致调整时间过长。为使柔性分布式能源变换器不仅具有抑制输出功率指令突变时所需要的惯性,而且能够减小惯性导致的功率过冲,并更快地达到稳定状态,充分利用逆变器灵活的参数调节能力,提出了根据逆变器输出情况对低通滤波器时间常数T进行自适应变化的自适应下垂控制。同时将该方法用于并网前同步,使并网前同步既具有惯性又能够快速完成同步过程。最后对柔性能源变换器输出功率指令突变时的自适应下垂控制进行了暂态能量的推导,从理论上分析了所提方法的有效性和可行性,并通过仿真和实验进行了验证。

The flexible energy converter(FEC)based on the traditional droop control method can realize seamless switching between islanding and grid-connection.However,due to the lack of inertia,the system is easy to generate frequency mutations when the output power command has a sudden change,which affects the stability of the system.In this paper,a low-pass filter(LPF)is added to the FEC to make the frequency change smoothly,realizing the inertia effect of a synchronous generator equivalently.If the cutoff frequency of LPF is lower,then the simulated inertia effect will be bigger;nevertheless,the slower adjusting speed of the inverter will generate energy overshoot and make the adjusting time longer.Based on the inverter’s flexible parameter adjusting capability,an adaptive droop control is proposed,with which the time constant T of LPF can change adaptively according to inverter output situation.In this way,the FEC not only has the inertia that is needed to suppress the sudden change of output power demand,but also can reduce the overshoot of power and thus converge to a steady state more quickly.Meanwhile,this method is used in synchronization before gridconnection to keep the inertia and finish quickly.Finally,a transient energy analysis is performed for the proposed adaptive droop control when the output power command from the FEC has a sudden change,which verifies the feasibility and effectiveness of the proposed method theoretically;moreover,simulations and an experiment also verified the novel method.