Synergetic Allocation and Operation of Hybrid Energy Storage System and Unified Power Quality Conditioner for Power Quality Enhancement of Distribution Networks with Renewables

With the penetration of renewable power generation (RPG) in the distribution network (DN), power quality issues caused by RPG fluctuations have become more prominent than ever, let alone the integration of new types of power loads like electrified trains and electric vehicles that are major harmonic sources. Traditional power quality enhancement approaches are mostly dedicated to the smoothing of RPG power output or active compensation of harmonics, but fail to incorporate both routines into one single power quality enhancement scheme. Out of this research motivation, this paper aims to propose a synergetic allocation scheme for the hybrid energy storage system (HESS) and the unified power quality conditioner (UPQC) to achieve superior power quality enhancement. Firstly, a novel comprehensive vulnerability index of the DN suited for the power quality issues is presented to reflect the key factors that may impact the bus voltage security. Afterwards, the capacity specifications of HESS and UPQC for power smoothing and load side harmonic compensation are deduced with variational mode decomposition and inverter capacity configurations. Subsequently, the synergetic allocation method of HESS and UPQC are proposed by formulating an optimization problem, with the former obtained capacity specifications acting as the main constraints. After that, a dynamic hourly network reconfiguration approach is proposed to enhance the vulnerability level of the DN by dynamically changing its topology, and ensuring better power quality with the optimally allocated HESS and UPQC. Finally, simulation tests and comparative studies are conducted to evaluate the effectiveness and performance of the proposed scheme by comparing with existing methods. The comparative study has shown that the proposed method can reduce bus voltage deviation by 2.63%; meanwhile, it can reduce the total harmonic distortion by 1.83%.