Distributed Optimal Power Flow in Hybrid AC–DC Grids

Abstract

Distributed or multi-area optimal power flow (OPF) in alternating current (AC) grids is currently a subject undergoing intense study to cope with computational burdens in large-scale grids and to maintain self-control of a regional system operator. However, future power grids will most likely be hybrid grids consisting of the conventional AC transmission system combined with high voltage direct current (DC) technology. Thus, we reformulate the full AC-DC OPF problem such that it becomes separable and, therefore, accessible to distributed algorithms. Then, we show in detail two different approaches on the decomposition of a hybrid AC-DC grid. Finally, we implement an improved alternating direction of multipliers method (ADMM) as well as the most recently proposed augmented Lagrangian based alternating direction inexact Newton (ALADIN) method. Simulation results show that optimality gaps below 0.01% are reached with both decomposition approaches and algorithms for two different test systems (5-bus and 66-bus). Furthermore, convergence rates and wall clock times are reduced by around one order of magnitude from ADMM to ALADIN.Index Terms-Distributed optimal power flow, multi-area optimal power flow, AC-DC grid, ADMM, ALADIN.

Multi-area Coordination of Security-Constrained Dynamic Optimal Power Flow in AC-DC Grids with Energy Storage

“…Thus, the number and dimension of AC regions are historically known. However, responsibilities in overlaying DC networks are yet to be defined and various options are thinkable [15]. We choose a Shared-DC approach.…”

“…We use the illustrative AC-DC test system from [15], see Tables 1 and 2 for line and generator parameters, respectively. The generator at Node 5 is interpreted as a wind park and a PV park is connected to Node 3.…”

“…Penalty terms, which are calculated from the coupling variable deviation and Lagrangian multipliers, are added to the objective function to push two neighbors towards a common boundary solution. ADMM was applied to a hybrid AC-DC grid in [15]. Multiarea optimization is applied to D-OPF with storage in [16] using OCD, but to the best of our knowledge, no attempts have been made toward distributing SC-D-OPF.…”

State Estimation for Hybrid VSC Based HVDC/AC Transmission Networks

“…The same architecture is used with the HVDC stations and transmission grids, they are operated by separate SCADA systems as shown in Figure 1 [1][2][3][13][14][15]. As a result, the research on SCADA for hybrid HVDC/AC transmission (mainly VSC based) is divided into two main approaches, a distributed or decentralized approach such as in [16][17][18][19], and centralized or hierarchical structure such as in [1,2,[20][21][22]. In the centralized approach, both AC and DC sides are controlled by one unified SCADA, leading to several challenges and modifications have to be addressed such as:…”

“…Second, the coupling between the AC and DC sides has to be modeled (hence, the converter impact). Third, a robust estimation has to be guaranteed using an AC and DC bad data detection block [19,27,28] or using an estimation algorithm claimed to be robust (e.g., Least Absolute Value (LAV) [29,30]).…”