Controle de tensão adaptativo para sistemas de distribuição com geração fotovoltaica distribuída operando com nuvens

Abstract

The operation of distribution systems with photovoltaic distributed generation units on cloudy days is an increasing challenge. Photovoltaic generation operating under cloud conditions may result in fast power and voltage variations that affect the power quality and performance of step voltage regulators typically used in medium voltage networks. In the context of ancillary services for photovoltaic generation, this work proposes a voltage control approach for photovoltaic distributed generation units operating under shading conditions caused by clouds, which is a typical operating condition. The proposed control uses the variable reactive power margin of the units to determine an adaptive voltage reference. The voltage regulation margin of each photovoltaic generation unit is determined in real-time through a mathematical formulation developed in this work. The proposed volt-var control is local, coordinated with step voltage regulators, and incorporates a dynamic model that takes into account realistic shading conditions. The results show that the control is effective in mitigating voltage fluctuations caused by stochastic power variations in photovoltaic generation and system load, outperforming the conventional fixed reference approach. The proposed control enabled voltage regulation even in conditions with reduced reactive power availability caused by high solar irradiance. Additionally, the formulation to determine the voltage regulation margin was effective to support the voltage regulation process by providing a feasible range of values for the voltage reference of the photovoltaic generation units. This work also proposes an analysis of the rapid power and voltage variations in a distribution system with photovoltaic distributed generation units operating under cloud conditions. The use of realistic operational assumptions, such as control loop modeling, cloud conditions, and dynamic simulations, which are typically not considered simultaneously in other works, constitutes one of the innovative contributions of the performed analyses. The evaluation of the proposed control approach and the analysis of rapid voltage and power variations are carried out through time-domain computer simulations, considering the typical control loops of generation units and different weather conditions synthesized using a fractal geometry-based approach. The IEEE 34-bus distribution system is used as the test system.