An Accurate Power Research Of Microgrid Based On Improved Decoupling Control

In recent years, due to the rapid advancement of power electronics technologies, a large number of distributed generation (DG) units based on the inverters powered by the renewable energy resources have been integrated into the power generation systems. For the autonomous operation of distribution generation system, multiple DG units normally need to provide efficient and reliable energy to the loads at the same time. So it is important to achieve precise power sharing for the parallel DG units. Therefore, the power sharing of DG units in islanding operation is the key of this paper.Considering the low voltage level of the most microgrid, the line impedance is mainly resistive, then the traditional P-V droop control is employed. This paper firstly proposes a precise feeder impedance estimation strategy by imposing a small perturbation to its voltage magnitude without phase varying in grid-connected operation. Due to its variation of the local load, the impedance characteristic of the transmission line can be changed, then the total equivalent impedance can be obtained in this method. The locations of DG units in a microgrid are decentralized, so the impedance from each DG to the point of common coupling (PCC) is inconsistent. The traditional method can not realize accurate power sharing in multiple DG units. Based on the estimated results, this paper proposes an improved decoupling control—a decoupling droop coefficient correction control. Secondly, with the help of the proposed low bandwidth communication method, the impedance parameters of each DG and the real-time power signal of the DG units are then sent to the central controller. Afterwards, a simple adaptive droop coefficient update algorithm is implemented in the central controller. Based on the DG unit which has the smallest impedance, the accurate power sharing is realized by modifying the droop coefficients of the other DG units.Finally, the small signal stability analysis, simulation and experimentation results have been obtained from the laboratory prototype to validate the feasibility of the proposed method. Both simulation and experiment prove that the impedance can be precisely detected and the power sharing error is eliminated by the droop coefficient modification, and this is favorable for the system stability.