Real-Time Local Volt/Var Control Under External Disturbances With High PV Penetration

Abstract

Volt/var control (VVC) of smart PV inverter is becoming one of the most popular solutions to address the voltage challenges associated with high PV penetration. This work focuses on the local droop VVC recommended by the grid integration standards IEEE1547, rule21 and addresses their major challenges i.e. appropriate parameters selection under changing conditions, and the control being vulnerable to instability (or voltage oscillations) and significant steady state error (SSE). This is achieved by proposing a two-layer local real-time adaptive VVC that has two major features i.e. a) it is able to ensure both low SSE and control stability simultaneously without compromising either; and b) it dynamically adapts its parameters to ensure good performance in a wide range of external disturbances such as sudden cloud cover, cloud intermittency, and substation voltage changes. A theoretical analysis and convergence proof of the proposed control is also discussed. The proposed control is implementation friendly as it fits well within the integration standard framework and depends only on the local bus information. The performance is compared with the existing droop VVC methods in several scenarios on a large unbalanced 3-phase feeder with detailed secondary side modeling.

Review of Challenges and Research Opportunities for Voltage Control in Smart Grids

“…The droop curve allows var injection/absorption for low/high voltages [100]. Due to its simple design and easy implementation, it has been explored by [101]- [104] and recommended by integration standards.…”

Reducing the Unfairness of Coordinated Inverter Dispatch in PV-Rich Distribution Networks

“…Let V nom be the nominal voltage at the secondary side of the distribution transformer and Q min be the maximum reactive power absorbed by inverters with the given solar PV output P av that can maintain the minimum power factor requirement cos θ. Following [4], we use Volt/VAr control with no deadband…”

A Framework to Utilize DERs’ VAR Resources to Support the Grid in an Integrated T-D System

“…Where L p and L q are vectors of real and reactive loss factors. Using (5), (7) and (8), voltages in form of net injections can be written as following:…”

“…Much of the extant literature focuses on utilizing the var control potential of DERs to improve the distribution system performance. For instance [7]- [9] demonstrate the benefit of local volt/var control in mitigating voltage challenges. Several optimization techniques are employed to minimize distribution system losses [10], [11], real power consumption [12] and var absorption [13] by the feeder etc.…”

“…We call the DER coordinating entity as distribution system operator (DSO). our assertion is founded on following reasonings: 1) The inverter based DERs can inject/absorb var via fast local volt/var controls [7], [9], thus can provide a significant amount of fast and continuous capacitive/inductive var support, if aggregated; 2) The proposition of DERs' var provision is gaining strength with recently revised DER integration standards such as IEEE1547-2018 [14], California Rule 21, Hawaii Rule 14 [15] and Germany grid codes [4] that have made it obligatory for DERs to provide var support for grid requirements; 3) We argue that the local and distributed nature of the var flexibility provided by DERs makes it a suitable contestant for var provision. In fact, an assessment study for East Denmark identifies DERs var provision scheme technically and economically competitive to conventional dynamic var devices i.e.…”