Planning and Operation Key Technologies for Source-Network-Load-Storage New Distribution System ·Hosted by DONG Xuzhu,SHANG Lei,LI Hongjun·
CAO Xiaoqing, LI Te, LI Lin, CHEN Di, ZHOU Zhengxu, SHI Xiaojie
[Objective] With the integration of large-scale distributed photovoltaics,issues such as reverse power flow and overvoltage arise,posing challenges to the safe and stable operation of power systems. To address this issue,both domestically and internationally,regulations mandate that PV systems must have grid support capabilities,such as voltage-reactive control,which actively regulates reactive power based on voltage deviations. However,such regulations are typically designed for balanced voltage scenarios and unbalanced voltage conditions are rarely considered. [Methods] Therefore,using voltage-reactive power control(volt-var control,VVC)as an example,this study analyzes the influence of voltage imbalance on the reactive power output and proposes an improved voltage-support control method aimed at minimizing three-phase voltage deviation. Based on instantaneous power theory,the mathematical relationship between voltage imbalance and active/reactive power is derived,demonstrating the voltage regulation effect of reactive power and the existence of the minimum voltage point. Then,with the three-phase voltage deviation as an index,the positive sequence voltage and reactive power corresponding to such point are calculated,and dynamic adjustments to the voltage-support control curve are made using this point,voltage limits,and reactive power capacity of PV inverters. [Results] Matlab/Simulink simulation results demonstrate that the proposed improved voltage-support control method ensures that three-phase voltages remain within limits while achieving minimal deviation from the nominal voltage under the lowest reactive power output. This ensures economical and efficient regulation of the three-phase voltage in unbalanced scenarios. [Conclusions] The proposed control strategy effectively coordinates the traditional VVC control with negative-sequence current/power control. It maintains three-phase voltages within grid-connected standard limits despite changes in irradiance,temperature,or other factors causing photovoltaic power fluctuations or voltage-unbalance variations,significantly enhancing the adaptability of conventional VVC control functions.