Transient stability enhancement in multiple‐microgrid networks by cloud energy storage system alongside considering protection system limitations

Abstract

The gas turbine synchronous generators (GTSGs) are widely deployed as distributed generations (DGs) in countries with massive natural gas production owing to their low prices. However, due to the low inertia time constants of these synchronous‐based DGs, they are more susceptible to power grid faults which stands as a transient stability issue in networks with multiple microgrids (MGs). On the other hand, the cloud energy storage system (CESS) is a new concept that centralizes the individual distributed energy storage of one or more MGs. Here, the employment of CESS with synchronverter grid connections creates a suitable opportunity for improving the transient stability of the network by providing higher inertia. This is while the fault current contribution of the synchronverter‐based CESS imperils protection constraints in these networks. Therefore, a proper protection coordination index (PCI) is considered in the conducted study to identify the optimal size of the synchronverter‐based CESS through a two‐stage optimization algorithm that preserves the protection constraints among protective devices. Finally, the transient stability of the network with synchronverter‐based CESS is assayed by calculation of the critical clearing time (CCT) for faults. Numerical studies are carried out on the IEEE 33‐bus test system. Results are discussed in depth.

Design of Energy Recovery Control for General Virtual Synchronous Machines Based on Various Forms of Energy Storage

“…Across the studies, although some researchers noticed the importance of keeping a necessary energy reserve for continuous VSM operation [26], there is a lack of proper energy recovery control applied to the ESS-based VSM, especially for the one with small-sized ESS (i.e., energy capacity at the second-to-minute time scale, compared with the capacity at the hour time scale, for the rated discharging speed). Specifically, the parameter design of energy recovery control, and the impact of such control on system frequency control, were rarely studied.…”

“…(1) Current of VSM must be limited within the safe range in the faulty cases. As a voltage source intrinsically, VSM will experience overcurrent in the low-voltage or short-circuit fault, and may thus damage the converter or ESS associated with VSM, especially considering the overcurrent capability is smaller than conventional rotating generators [26]. There are no standard solutions at present, based on either software (for example, virtual impedance or saturation control) or hardware (overcurrent limiter or protection).…”

“…However, most studies are focused on frequency performance and stability improvement, while ignoring the energy constraints. A more practical VSM implementation by accumulating sufficient energy based on cloud energy storage is proposed in Ebrahimi et al's work [26], but the energy consumed in ESS for such VSM services is not quantified. The key literature related to the energy variation and management of ESS-based VSM is summarized in Table 1.…”

A new protection algorithm for tackling the impact of fault‐resistance and cloud energy storage on coordination of recloser‐fuse protection

“…An inverter called synchronverter mimics the behaviour of a synchronous generator; however, unlike such generators, its parameters can be tuned to serve a particular application [10,11]. The high inertial response of the synchronous generators against disturbances of the system can be employed by synchronverters in highly inverter-based distributed generations (IBDG) penetrated distribution systems to provide proper inertia in the network [12]. However, the connection of the CESS by synchronverters causes the highest fault current contribution for this energy source which should be investigated in terms of protection in emergent MGs.…”

“…The authors of [10] elaborate on the deployment of synchronverter in an RES-integrated system. Moreover, the employment of synchronverter as the connection interface of the CESS is surveyed in [12]. In this study, the protection viewpoint is also incorporated; however, the recloser-fuse scheme as the most prominent protection protocol for distribution systems is neglected.…”