Grid-connected large-scale power converter-based intermittent renewable energy sources (RES) reduce system inertia, increase frequency fluctuation, and increase the rate of change of frequency (RoCoF). An energy storage system (ESS) is an indispensable component of a smart grid, and is used to overcome low-inertia problems. However, the capital and maintenance costs of ESS are high and high RoCoF events are less frequent in power systems. Therefore, the introduction of a virtual energy storage system (VESS) to provide the function of a conventional ESS for power system ancillary services is an innovative and cost-effective method. This study investigated a VESS using photovoltaic (PV) generators and inverter air conditioners (IACs) to provide virtual inertia and frequency regulation for a low-inertia microgrid. A model predictive control (MPC)-based VESS regulates indoor temperature, microgrid frequency, and RoCoF. The impact of parameter variation, that is, the microgrid frequency weight, indoor temperature weight, virtual inertia gain, and number of IACs, was studied and selected by considering the ability of the parameters to provide virtual inertia and frequency regulation. Finally, the efficiency and robustness of the proposed MPC-based VESS technique are compared with those of a conventional VESS. Simulation results revealed that the proposed MPC-based VESS can improve the virtual inertia, reduce the frequency deviation, and reduce the RoCoF of the studied microgrid. In addition, the proposed method is robust to variations in the system parameters.

Local latency adversely affects the stabilising performance of damping controllers especially in the two‐level control scheme. By considering both wide area and local latencies, this study presents the two‐level coordinated control which consists of wide area centralised and local controls of power oscillation damper (POD) and power system stabiliser (PSS) for robust power oscillation damping. The PODs are equipped with the doubly fed induction generator (DFIG) wind turbine, the solar photovoltaic generator (SPV), and the static VAR compensator (SVC). The centralised PODs of DFIG, SPV, SVC, and the centralised PSSs act as the primary damping controllers. When the communication failure occurs, the local PODs of such devices and the local PSSs are activated and used as the backup damping controllers. To achieve the damping performance and robustness, the parameters of centralised and local controllers are individually optimised based on the worst scenarios determined by the lowest damping ratio of target inter‐area oscillation modes. Study results in New England and New York IEEE 68‐bus system demonstrate that the proposed two‐level coordinated controllers are superior to the conventional two‐level controllers in terms of damping performance and robustness against various operating conditions.

It is ubiquitously accepted that system latency causes a serious problem in an oscillatory stability, especially when it involves with the centralized damping controllers using wide-area input signals. Previously, the latency is assumed to be constant in the centralized controller design and nonlinear time simulation. However, variable latencies, which vary area-to-area depending on the distances between stabilizing devices and control center, inevitably occur in large power systems. Thus, the damping performance may be deteriorated when variable latencies are ignored in the control design. This paper presents an inter-area oscillation damping controller design considering the impact of variable latencies. Selection of suitable stabilizing devices and input signal is conducted by taking variable latencies into account. Stability studies are carried out in IEEE 50-machine 145-bus to analyze an influence of variable latencies on the oscillation damping and the signal selection. The proposed damping controller can achieve desired damping performance as well as robustness against variable latencies, various operating conditions, and severe disturbances.

Since operating conditions of power systems always change, the input and output signals of wide area damping controller (WADC) which are selected at an operating point may not be able to guarantee the damping effect at other operating points. This paper focuses on a new adaptive signal selection for WADC against several operating conditions such as various load demands, control signal failure, line and generator outages, and effect of communication latency. The joint controllability and observability is used to determine the best input and output pair of WADC at any operating points. Small signal and transient stabilities study in the IEEE 50-machine system including renewable sources, i.e. wind and solar photovoltaic generators is conducted to evaluate the effect of the proposed method. Study result demonstrates that the WADC with the adaptive signal selection yields superior damping effect to the WADC with the fixed signal selection over wide range operations.