Electrification of the transportation sector can play a vital role in reshaping smart cities. With an increasing number of electric vehicles (EVs) on the road, deployment of well-planned and efficient charging infrastructure is highly desirable. Unlike level 1 and level 2 charging stations, level 3 chargers are super-fast in charging EVs. However, their installation at every possible site is not techno-economically justifiable because level 3 chargers may cause violation of critical system parameters due to their high power consumption. In this paper, we demonstrate an optimized combination of all three types of EV chargers for efficiently managing the EV load while minimizing installation cost, losses, and distribution transformer loading. Effects of photovoltaic (PV) generation are also incorporated in the analysis. Due to the uncertain nature of vehicle users, EV load is modeled as a stochastic process. Particle swarm optimization (PSO) is used to solve the constrained nonlinear stochastic problem. MATLAB and OpenDSS are used to simulate the model. The proposed idea is validated on the real distribution system of the National University of Sciences and Technology (NUST) Pakistan. Results show that an optimized combination of chargers placed at judicious locations can greatly reduce cost from $3.55 million to $1.99 million, daily losses from 787kWh to 286kWh and distribution transformer congestion from 58% to 22% when compared to scenario of optimized placement of level 3 chargers for 20% penetration level in commercial feeders. In residential feeder, these statistics are improved from $2.52 to $0.81 million, from 2167kWh to 398kWh and from 106% to 14%, respectively. It is also realized that the integration of PV improves voltage profile and reduces the negative impact of EV load. Our optimization model can work for commercial areas such as offices, university campuses, and industries as well as residential colonies.

In wake of frequency stability challenges enhanced by the volatile renewable energy based generation, there is a renewed interest in the methods that can provide stability insights for broad range of operating conditions of the oscillating multi-machine systems such as power system. With this perspective in sight, this work proposes an analysis of transient stability with emphasis on the Gram-Schmidt and covariant Lyapunov vectors. Numerical accuracy of these Lyapunov vectors is validated by comparison with Floquet exponents obtained from the Jacobian matrix leading to an increased confidence in their potential application. In addition, a study of global stability using Lyapunov exponents and of local stability by Lyapunov vectors is performed. The assumptions necessary for the derivation of energy functions are avoided resulting in a broader stability perspective that is also applicable on the operating point outside the stability manifold. The methods are evaluated for the IEEE 9 bus system.

This paper presents a methodology that aims at identifying virtual inertia (VI) gain limitations from virtual synchronous generators (VSGs) while maintaining the frequency stability considering the delay associated with the frequency measurement process. The phase-locked loop (PLL) is typically used for frequency estimation that is used to calculate the rate of change of frequency (RoCoF) and it drives the VI loop. The PLL is generally accompanied by a low-pass filter that aims to suppress the impact of harmonics. This filter introduces a delay that when used with the VI control loop causes stability issues for high values of VI gain. A comparison of various PLL approaches suggests that certain variants tend to permit higher value of cut-off frequencies which can be utilized to increase the VI gain limit from VSG. This study presents a method by which the upper limit on VI gain can be quantified and related to the cut-off frequency of the PLL low pass filter that is indirectly representing the delay. It is performed using small signal frequency stability analysis on the frequency domain model of the grid with virtual inertia emulating VSG. The effective maximum VI gain from VSG is explored while satisfying the frequency measurement accuracy specification considering harmonics. The results show that the requirements of reaching a stable operation with sufficient stability margins can still be met with a faster PLL-based system and the potential increases in VI support from VSG can be quantified using the proposed method. The study has been first performed on a single machine single inverter bus (SMSIB) system and is generalized to the multi-machine and multi-inverter system.

This paper presents a novel approach of assessing the required reserve capability in order to meet the forecast uncertainty dynamics in microgrid. The historical data of forecast variables is used to generate energy balance scenarios. The dynamics of these scenarios are represented as instances between capacity, ramp-rate and ramp-duration variables. A polytopic model is used to enclose these instances with its surface defining the worst case scenarios. This approach captures the correlated nature of the dynamics and provides a compact representation. In relevance, the capability of the generators and the power import from the grid are modeled as convex envelopes. A vertex based method is proposed that allocates the polytope among the resource envelopes. During this process, the operational cost is minimized while considering the resource location and the network constraints. The proposed method is examined for a microgrid test case based on the CIGRE medium voltage network. The results show new insights in the allocated demand and reserve capabilities. As an additional result, it is observed that the reserve requirements can be decreased by allocating reserves for each time instance separately as compared to the fixed percentage of load approach.

The potential of demand side as a frequency reserve proposes interesting opportunity in handling imbalances due to intermittent renewable energy sources. This paper proposes a novel approach for computing the parameters of a stochastic battery model representing the aggregation of Thermostatically Controlled Loads (TCLs). A hysteresis based non-disruptive control is used using priority stack algorithm to track the reference regulation signal. The parameters of admissible ramp-rate and the charge limits of the battery are dynamically calculated using the information from TCLs that is the status (on/off), availability and relative temperature distance till the switching boundary. The approach builds on and improves on the existing research work by providing a straight-forward mechanism for calculation of stochastic parameters of equivalent battery model. The effectiveness of proposed approach is demonstrated by a test case having a large number of residential TCLs tracking a scaled down real frequency regulation signal.