Power talk is a method for communication among voltage control sources (VSCs) in DC microgrids (MGs), achieved through variations of the supplied power that is incurred by modulation of the parameters of the primary control. The physical medium upon which the communication channel is established is the voltage supply level of the common MG bus. In this paper, we show how to create power talk channels in all-to-all communication scenarios and implement the signaling and detection techniques,

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... sing on the construction and use of the constellations or arbitrary order. The main challenge to the proposed communication method stems from random shifts of the loci of the constellation symbols, which are due to random load variations in the MG. We investigate the impact that solutions that combat the effects of random load variations by re-establishing the detection regions have on the power talk rate. due to the availability and reliability requirements and advocate the use of the capabilities of the power electronic interfaces, foremost the capability to perform digital signal processing, as potential communication enablers. Notable examples are the bus signaling solutions that have been proposed to address specific aspects of distributed control in DC and AC MGs [8] [9] [10] [11] [12] . Figure 1. Architecture of a single bus DC microgrid (MG) system. In this paper, we present a novel communication method designed for DC MGs termed power talk [13, 14] that exploits the flexibility of the power electronic converters, enables a general digital communication interface to support optimal MG control without necessitating external hardware and has the same reliability and availability as the MG system itself. The main idea behind power talk is to modulate information in the parameters of the primary control loops that are implemented in the power electronic converters that regulate the voltage of the MG buses. This incurs bus voltage deviations that can be detected by other MG units, resulting in information transfer; the effective physical medium used for communication is bus voltage level, jointly maintained by all units in the system through primary control. As a result, the induced power talk channel exhibits some challenging properties from the communication perspective. The achievable rates of the power talk are limited by the response times of primary control loops, which are at the order of tens of milliseconds. Nevertheless, such rates may prove sufficient for the communication requirement of the MG control applications. On the other hand, power talk is, in essence, as reliable as the MG power control system itself, since all units connected to the same bus measure the bus voltage. Unlike existing bus signaling solutions whose application is limited to a narrow set of predefined coordination strategies, power talk offers a generic digital communication interface, able to support the communication demands of the majority of optimization and coordination mechanisms. As an example, the core mechanism in standard bus signaling solutions [8-12] relies on assigning several predefined bus voltage/frequency thresholds; whenever the thresholds are crossed, the units in the system performed predefined and coordinated actions (e.g., back up generators are turned on when the bus voltage falls beneath a predefined threshold, signaling that the system is overloaded). Evidently, the bus signaling solutions are not actually designed to transmit information messages. Thus, their implementation is application specific; this is the main limitation of existing bus signaling solutions that power talk aims to alleviate. Finally, since power talk is implemented in primary control loops, it only demands software modifications in the power electronic converters, a major advantage over other communication solutions, including standard off-the-shelf power line communications that require the installation of additional hardware. Power talk has been introduced in [13, 14] , in a basic setup with two MG units and in a one-way communication scenario. The focus of [13] is on enabling reliable communication without precise knowledge of the system configuration and of the load; it is shown that using a special input symbol in the role of a pilot transforms the MG bus into some of the known communication channels. The work in [14] represents the unknown system configuration and load variations through a Thevenin