Aggregating DERs VAR Capability Curve to Support the Grid in an Integrated T-D System

The multitudes of inverter-based distributed energy resources (DERs) can be envisioned as geographically distributed reactive power (var) devices (mini-SVCs) that can offer enhanced var flexibility to a future grid as an ancillary service. To facilitate this vision, a systematic methodology is proposed to construct an aggregated var capability curve of a distribution system with DERs at the substation level, analogous to a conventional bulk generator. Since such capability curve will be contingent to the operating conditions and network constraints, an optimal power flow (OPF) based approach is proposed that takes curtailment flexibility, unbalanced nature of system and coupling with grid side voltage into account along with changing operating conditions. Further, the influence of several other factors such as revised integration standard 1547 on the capability curve is thoroughly investigated on an IEEE 37 bus distribution test system. Finally, a T-D cosimulation is employed to demonstrate how DER aggregated flexibility can potentially enhance the decision domain for the transmission grid leading to improved performance

Real-Time Local Volt/VAR Control Under External Disturbances with High PV Penetration

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.Comment: IEEE Transactions on Smart Grid, 201