Reverse active-reactive optimal power flow in ADNs: Technical and economical aspects

Abstract

Since 1880s unidirectional power flows in electrical distribution networks (DNs) have been known as the usual case. But after 1990s due to the installation of new entities such as distributed generation (DG) units and battery storage systems (BSSs) bidirectional power flows would be the future case. Recently, a combined problem formulation for active-reactive optimal power flow (A-R-OPF) has been developed to utilize the economical benefits of operating both low-and medium-voltage active DNs (ADNs). In this paper, some technical and economical aspects of allowing reverse A-R-OPF in ADNs are highlighted. This is achieved by considering a real medium voltage ADN with a high penetration of wind and battery stations. The results show that considering a price for reactive energy in ADNs will lead to a huge amount of reverse reactive energy. This new phenomenon needs to be considered in operating and planning future ADNs. Keywords: Active distribution networks (ADNs), optimization, reverse active-reactive optimal power flow (A-R-OPF). I. INTRODUCTIONThe dynamics of demand, distributed generation (DG), energy prices, and governmental regulations make the operation/planning of distribution networks (DNs) highly complicated. The increasing installation of DG units will lead to the situation that a part of the generated renewable energy has to be curtailed [1], [2], [3], [4]. One measure of avoiding curtailments is to allow exporting the surplus energy to the upstream network, i.e., reverse power flow [5], [6], [7]. Another measure is to use storage systems for energy accumulation [8]. However, even by using both measures, it may be impossible to address the curtailment problem, if there are bottlenecks inside the DN due to capacity limitations of existing feeders. Thus, for an optimal operation/planning, it is necessary to examine the effects of reverse power flow, distribution feeder layout, and storage systems for the reduction of curtailment.Reverse active power flow was considered in [6] and [7] for determining the optimal location and sizing of DG units, where a predefined limit on the maximum allowed reverse active power flow was taken. But reverse reactive power flow was not considered.In [8], a method for sizing and allocating battery storage systems (BSSs) in a DN with a high penetration of wind energy was proposed, where a maximum allowed reverse active power flow was assumed. In addition, fixed locations of wind stations and a fixed lowest feeder capacity were taken.

On Variable Reverse Power Flow-Part I: Active-Reactive Optimal Power Flow with Reactive Power of Wind Stations

“…In summary, the issue of metering bidirectional power [26] due to possible reverse active and reactive power flows [27][28][29][30] in a transformer (TR) [31] which is typically used to connect different voltage levels in power systems, as seen in Figure 1, is of high interest and major importance for the society of power and energy systems. This represents a combined technical and economical complex problem, and, therefore, more studies are required in this area.…”

“…As depicted in Figure 1, a downstream network is being supplied by an upstream network via a TR which allows the flow of powers in two directions. For the MV network, the forward direction means import while the reverse direction means export [26][27][28][29][30]. Basically, the apparent power at bus S 1 is described as:…”

On Variable Reverse Power Flow-Part II: An Electricity Market Model Considering Wind Station Size and Location

“…The forward reactive energy is to be minimized based on a reactive energy price model Cpr.q, while the reverse reactive energy (e.g., from WSs) is not allowed, in contrary to [21], in order to avoid any possible charge (payment) for capacitive reactive energy, e.g., as the case in Norway [3].…”

“… In this paper, we consider the situation that an operating point in the gray quadrants (i.e., quadrants 3 and 4) should be avoided to minimize charging costs for reverse reactive energy [3]. However, if reverse reactive energy is being remunerated, as in the practice in some countries, a huge amount of reverse reactive energy could be observed as shown in [21]. [1].…”

“…However, if reverse reactive energy is being remunerated, as in the practice in some countries, a huge amount of reverse reactive energy could be observed as shown in [21].…”