Abstract
This paper presents a novel hierarchical framework for real-time, network-admissible coordination of responsive grid resources aggregated into virtual batteries (VBs). In this context, a VB represents a local aggregation of directly controlled loads, such as smart inverters, electric water heaters, and air-conditioners. The coordination is achieved by solving an optimization problem to disaggregate a feeder's desired reference trajectory into constraint-aware set-points for the VBs. Specifically, a novel, provably-tight, convex relaxation of the AC optimal power flow (OPF) problem is presented to optimally dispatch the VBs to track the feeder's desired power trajectory. In additionto the optimal VB dispatch scheme, a real-time, corrective control scheme is designed, whichis based on optimal proportional-integral (PI) control with anti-windup, to reject intra-feeder and inter-feeder disturbances that arise during operation of the power system. Simulation results conducted on a modified IEEE test system demonstrate the effectiveness of the proposed multi-layer VB coordination framework.
Highlights
2) A novel second-order conic AC optimal power flow (OPF) formulation of a multi-period optimization of virtual batteries (VBs) designed for tracking the desired power reference at the head-node of the feeder. In this formulation, the feeder structure is taken into account and the second-order cone relaxation is proven to be exact even under significant reverse power flow and with a non-monotonic cost function, which is an improvement over the present state-of-science in radial network OPF presented in [29]
It is reasonable to assume that the distribution system operator (DSO) has access to SCADA data and is aware of the grid topology and receives VB state of charge (SoC) estimates from the VB-distributed energy resources (DERs) interface to run the AC OPF
Analysis and simulation results have been presented in support of a novel framework for large-scale coordination of DERs to support deep penetration of renewable energy
Summary
C OORDINATED control of demand-side, distributed energy resources (DERs), such as grid-tied PV inverters, distributed battery storage, and thermostatically controlled loads (TCLs; e.g., water heaters and air conditioners) is part of the solution that supports a renewable energy future [1]–[4]. The real-time controller borrows concepts from wide-area control (WAC) [22], including (local) droop [23] and (regional) automatic generation control, and adapts them to dynamically managing VB power in distribution feeders This results in a VB coordination scheme that enables a feeder head-node to optimally track a power reference while correcting, in real-time, for unexpected small (local, intra-feeder) and large (regional, inter-feeder) disturbances. The convex OPF formulation is proven tight at optimality, which guarantees that the prediction of future physical operating states of the grid and the VBs are accurate This is achieved by decomposing the feeder head-node (i.e., substation) economic reference into the aggregate VB dispatch, net-demand, and approximated total feeder line losses. The only measurement necessary for this purpose is the head-node power from the feeders
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