A Convex Approximation Method for Smoothing Out Control of Voltage Profile at a Critical Distribution Bus Under Sharp PV Power Fluctuations

The high penetration of photovoltaic (PV) panels in a distribution system could cause sharp fluctuations in bus voltages. This phenomenon could induce abnormal operations in high-precision equipment or result in erroneous computer memory functions. To handle this issue, this paper proposes a voltage control to smooth out a critical bus voltage, without utilizing the local controllable devices, while maintaining the bus voltages across the distribution system within the allowable range. First, a smoothing out control of voltage is proposed and theoretically proved to mitigate the voltage fluctuations at the critical bus by the first-order inertia. Second, an optimization model is proposed for the coordinated voltage control, which coordinates the actions of discrete control devices with the smoothing out control of PV inverters. A novel convex approximation method is proposed to transform the nonconvex model into an approximate convex model. It is theoretically proved that the solutions obtained by solving the approximation model can control the bus voltages across the distribution system within the allowable range. Last, the proposed voltage control is simulated in 15-bus and 51-bus distribution systems. The 6-minute and 24-hour simulations show that a single voltage fluctuation and the sum of squared voltage fluctuations at a critical bus are reduced by 22.4% and 36.5%, respectively, as compared to the results offered by using the existing benchmark control method.