采用功率坐标变换的微网并联逆变器控制方法

A Control Strategy for Parallel Inverters in Microgrid by Power Coordinate Transformation

下垂控制是微网中逆变器并联运行常用控制方法,但P-f下垂会导致稳态频率偏差,减小下垂系数虽可减小频率偏差但会影响控制性能。针对上述问题,本文将虚拟阻抗、下垂控制和功率坐标变换相结合提出新的控制方法,利用虚拟阻抗对有功P和无功Q进行坐标变换,得到广义有功Pd和广义无功Qd,并证明Pd和f存在下垂关系,Qd可通过虚拟阻抗的大小进行调节。然后根据负荷功率因数选择虚拟电阻和虚拟电抗的比值,使Pd在稳态时趋于零,从而使稳态频率偏差趋于零,再按照逆变器额定容量的反比选择下垂系数以及虚拟阻抗大小从而实现P和Q的按比例分配。本文所提方法可以使稳态频率偏差趋于零,并能实现有功和无功负荷的按比例分担,Matlab仿真证明了本文方法的有效性。

Droop control is widely used in parallel operation of inverters in microgrid. This control method will lead to frequency deviation and decreasing the deviation by diminishing droop coefficient will influence control performance. This paper proposes a new control method by combining the droop control , virtual impedance and power coordinate transformation. Coordinate transformation is carried out for the active power P and reactive power Q by virtual impedance, by which general active Pd and general reactive power Qd are got. Droop characteristics between Pd and f is proven while controlling Qd by adjusting virtual impedance is also exhibited. By choosing ratio between virtual resistance and virtual reactance according to power factor of load, Pd will be bear zero and thus the steady state frequency will be near zero. The P and Q sharing is adjusting by choosing proper droop coefficient and the impedance amplitude inversely in inverse proportion to inverters＇ rated capacity. The proposed method can achieve near-zero steady state frequency deviation and proportional sharing of active power and reactive power. Simulation by Matlab confirms the effectiveness of the proposed control method.