This paper presents a methodology for generating restoration sequences in distribution systems and microgrids with emphasis on deriving optimal switching times for remote control switches (RCS). Microgrid architecture considered are assumed to be operating in islanded single master mode. Control methods for handling the unbalance inherent in distribution systems using single-phase controlled PQ inverters were developed and incorporated in the proposed method. The problem of considering simultaneously both energy optimization and dynamic stability of the system, which is lacking in existing methods, was addressed by studying the transient behavior of microgrids based on extended EMTP simulations and then approximate and incorporate these behaviors into the optimization formulation for restoration. The approach is based on multi-objective optimization of final restored load and total restoration time. The methodology was studied on modified IEEE 123 node test feeder. An EMTP simulation in PSCAD of the formed microgrids was used to validate the accuracy of the dynamic and steady-state characteristics of the resulting systems. By considering the transient behavior of DGs during restoration, a better restoration sequence that does not trigger protection relays could be realized.

The electricity grid faces the possibility of outages due to extreme weather events, cyber-attack, and unexpected events. When these unwanted events occur, it is desired that electricity be restored as soon as possible to meet the power demands of critical loads. The microgrid approach to power restoration holds a lot of promise, since microgrids can operate in island mode. This paper presents a novel sequential restoration methodology for microgrid black start. The microgrid architecture considered is assumed to be operating in multi-master mode. The master distributed generators (DGs) are coordinated to operate together through droop control. Several operational constraints are formulated and linearized to realize a mixed-integer linear programming (MILP) problem. The method is studied on an islanded microgrid based on a modified IEEE 13 node test feeder. Detailed transient simulation in PSCAD was used to verify the accuracy of the restoration methodology. The developed restoration method can maximize the energy restored while ensuring good voltage and frequency regulation, and ensure that power scheduling mismatch is shared in the desired proportion.

The need to restore and keep the grid running or fast restoration during emergencies such as extreme weather conditions is quite apparent given the reliance of other infrastructure on electricity. One promising approach to electricity restoration is the use of locally available energy resources to restore the system to form isolated microgrids. In this paper, we present a black start restoration method that forms islanded microgrids after a blackout. The master DGs in the formed microgrids are coordinated to work together through droop control. Several constraints, including incentive-based demand response (DR) with direct load control (DLC) and distributed generator (DG) operation constraints, were formulated and linearized to realize a mixed-integer linear programming (MILP) restoration model. To improve compactness and to ensure that the model is neither under-sized nor over-sized, a pre-processing graph analysis approach was introduced which helps to characterize the least number of restoration steps needed to optimally restore the microgrid. Studies were performed on a modified IEEE 123 node test feeder to evaluate the effects of demand response, non-dispatchable DGs, and choice of restoration steps on the quality of the restoration solution. When possible, the proposed method yields an interconnected multi-master microgrid with improved redundancy.

For a three-phase islanded microgrid with non-stiff grid-supporting or grid-forming distributed generators (DGs), unbalance power dispatch from these DGs can negatively influence the voltage quality, stability, and lifespan of the DGs. One way to solve such unbalance is to have DGs that can compensate for the load unbalance by being able to dispatch unbalance power. In this work, single-phase controlled PQ inverter interfaced DGs are modeled for this purpose. A detailed control model of the single-phase PQ inverter is derived from which we approximate the power stage of the inverter to a voltage-controlled source. Simulation studies in PSCAD showed that the voltage-controlled model gives an accurate representation of the elaborate switching model of the single-phase PQ inverter. Coordination of unbalanced power dispatch is realized by stacking the single-phase inverter in a manner similar to the three-bridge four wire shunt active filter and dispatch setpoint are sent to the PQ inverters from the secondary and tertiary control level of the microgrid for load compensation purpose. Case studies of balanced, unbalanced and load compensated systems are presented and evaluated with two unbalance indices: phase voltage unbalance rate (PVUR) and true voltage unbalance factor (VUF). The studies showed that in an islanded microgrid with a non-stiff reference source, the primary source of voltage unbalance across three phase nodes is unbalanced loading and that by dispatching unbalanced power to the PQ inverters to compensate for load unbalance, a significant improvement in system balancing could be realized.

Developing a test environment for smart grid forms an indispensable stage to the realization of the next generation of the electricity grid. The coupling of the physical power system and its associated communication network makes modern power grid a typical cyber-physical system. In this paper, a real-time power system was simulated in RTDS and the communication network in NS-3. This test bed includes a wide area control scheme that employs the speed difference of generators in two areas of a simple 11-bus power system to dampen down local and inter-area oscillations. Different network conditions were tested and compared with cases that made use of only local input to dampen oscillations and another case that assumes a perfect communication network. The test bed showed that wide area control implementation with extremely unfavorable network conditions could introduce delays beyond the tolerable limit and lock the power system into a continually unstable mode, while favorable network conditions enhance damping of the local and inter-area oscillations of the power system.