Abstract
At the present time, there is a worldwide tendency to clustering the electrical power systems at LV and MV levels – creating the micro-grids. In this connection, numerous of technical issues appear in control approaches in general and in particular in emergency and post-emergency control. As micro-grids are meant to operate both in interconnected and islanded modes, the ability to steadily island and backward synchronize with an upper grid provides reduction of the negative impact of failure rate of electrical power system’s elements, as well as power quality parameters influence toward operation regime of the loads. The consequence of previously described features is particular requirements for the following emergency automatics: overload-preventing automatics for overhead lines, cables and transformers; out-of-step automatics and under-frequency load shedding. Low inertia constants of some distributed generation units and low time constants of electromagnetic transients of generating units and ESS, interconnected with a grid by means of power-electronics, provide an ability to realize additional (fast) control signals in overload-preventing automatics, dispatching generating units and ESS with an aim to prevent considered elements tripping.
Highlights
Error penalization should be considered for combined regulators, as continuation to operate in power control mode in case of micro-grid islanding likely to lead to power outage, whereas, only inaccuracy of power dispatch occur in the opposite situation, when gas turbines operate with frequency droop in parallel regime
If generator covers entire reactive load, the voltage drop is minimal; the loads are within their transient stability margins; the active power deficit is reflected in frequency reduction (Fig. 5a)
The deep under-excitation of micro-grid generators can lead to significant voltage reduction, motor’s slip rise and further process progress up to voltage collapse
Summary
Generation capacity decentralization forced by distinctive factors, including evolving of economically justified low-power energy generation and storage technologies (installed capacity less than 670 kW), added by electricity market liberalization, reflecting in price-responsive demand as a measure of consumer’s involvement, end up with the formation of physical and virtual (consumption reduction) lump generation capacities in MV/LV distribution grids. Energy storage deployment is always coupled with automatic control system tying, which can be used for implementation of demand response. Аn aggregation of DG units, energy storage units and controllable loads, forming together so called DERs, by control integrity leads to the origin of controllable distribution grid’s concept with the following objectives: Reduction of uncontrollable influence of commissioned and future DG objects towards both steady-state and transient regime parameters, Creation of the technological basis of nondiscriminatory access for dispatched and non-dispatched «heterogeneous» DERs (comprising renewable energy sources),.
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