Junjie Tang

Trade-Offs in PMU Deployment for State Estimation in Active Distribution Grids

Monitoring systems are expected to play a major role in active distribution grids, and the design of the measurement infrastructure is a critical element for an effective operation. The use of any available and newly installed, though heterogeneous, metering device providing more accurate and real-time measurement data offers a new paradigm for the distribution grid monitoring system. In this paper the authors study the meter placement problem for the measurement infrastructure of an active distribution network, where heterogeneous measurements provided by Phasor Measurement Units (PMUs) and other advanced measurement systems such as Smart Metering systems are used in addition to measurements that are typical of distribution networks, in particular substation measurements and a-priori knowledge. This work aims at defining a design approach for finding the optimal measurement infrastructure for an active distribution grid. The design problem is posed in terms of a stochastic optimization with the goal of bounding the overall uncertainty of the state estimation using heterogeneous measurements while minimizing the investment cost. The proposed method is also designed for computational efficiency so to cover a wide set of scenarios.

Adaptive load shedding based on combined frequency and voltage stability assessment using synchrophasor measurements

Under frequency load shedding (UFLS) and under voltage load shedding (UVLS) are attracting more attention, as large disturbances occur more frequently than in the past. Usually, these two schemes work independently from each other, and are not designed in an integrated way to exploit their combined effect on load shedding. Besides, reactive power is seldom considered in the load shedding process. To fill this gap, we propose in this paper a new centralized, adaptive load shedding algorithm, which uses both voltage and frequency information provided by phasor measurement units (PMUs). The main contribution of the new method is the consideration of reactive power together with active power in the load shedding strategy. Therefore, this method addresses the combined voltage and frequency stability issues better than the independent approaches. The new method is tested on the IEEE 39-Bus system, in order to compare it with other methods. Simulation results show that, after large disturbance, this method can bring the system back to a new stable steady state that is better from the point of view of frequency and voltage stability, and loadability.

Dimension-Adaptive Sparse Grid Interpolation for Uncertainty Quantification in Modern Power Systems: Probabilistic Power Flow

In this paper, the authors firstly present the theoretical foundation of a state-of-the-art uncertainty quantification method, the dimension-adaptive sparse grid interpolation (DASGI), for introducing it into the applications of probabilistic power flow (PPF), specifically as discussed herein. It is well-known that numerous sources of uncertainty are being brought into the present-day electrical grid, by large-scale integration of renewable, thus volatile, generation, e.g., wind power, and by unprecedented load behaviors. In presence of these added uncertainties, it is imperative to change traditional deterministic power flow (DPF) calculation to take them into account in the routine operation and planning. However, the PPF analysis is still quite challenging due to two features of the uncertainty in modern power systems: high dimensionality and presence of stochastic interdependence. Both are traditionally addressed by the Monte Carlo simulation (MCS) at the cost of cumbersome computation; in this paper instead, they are tackled with the joint application of the DASGI and Copula theory (especially advantageous for constructing nonlinear dependence among various uncertainty sources), in order to accomplish the dependent high-dimensional PPF analysis in an accurate and faster manner. Based on the theory of DASGI, its combination with Copula and the DPF for the PPF is also introduced systematically in this work. Finally, the feasibility and the effectiveness of this methodology are validated by the test results of two standard IEEE test cases.

A modified Taylor-Kalman filter for instantaneous dynamic phasor estimation

This paper proposes a modified Taylor-Kalman filter (TKF) for instantaneous phasor estimation based on an improved dynamic model describing the complex trajectory of dynamic phasors. The improved dynamic model is obtained thanks to a revised state transition equation of the rotating phasor and its derivatives. The proposed approach is assessed with dynamic compliance tests defined in the synchrophasor standard and in a power system test case. As the results show, the modified TKF can track the time-varying behavior of dynamic phasors under non-steady state conditions in power systems. It achieves good estimation performance without manually adjusting the Kalman gain as in the existing solution. Thus, the modified TKF fully exploits the self-adaptive nature of the Kalman filter principle.

Impact of synchrophasor measurement uncertainty on detecting voltage stability margin in power systems

Phasor Measurement Units (PMUs) provide synchronized phasors (synchrophasors) of voltage and current, usually together with measurements of frequency and rate of change of frequency. One of the main characteristics of the PMUs is to provide synchronized and accurate measurement of all these quantities with a reporting rate much higher than that of traditional measurement systems. Also for this reason, PMUs have been shown have a lot of potential in different applications in power systems, including voltage stability monitoring. As the uncertainty of the PMUs impacts the monitoring performance, it is necessary to perform a thorough analysis before the monitoring system can be designed and its outcome used for control, particularly of critical applications. Hence, this paper presents the analysis of the effect of the uncertainty introduced by the PMUs, on a global method for voltage instability detection. In particular, the Load Margin Index based on wide-area phasor measurements is considered as reference method. Several tests and results obtained on the IEEE 39-bus system are presented and discussed.

Impact of PMU sychronization on wide area state estimation

This paper investigates the impact of the PTP (Precision Time Protocol) synchronization method, used to synchronize different Phasor Measurement Units (PMUs), on a state estimation application. As a case of study, the output data of the PMUs, synchronized by means of a software-only implementation of the PTP, have been used to estimate the state of an IEEE 57-bus power system.

Probabilistic Power Flow for AC/VSC-MTDC Hybrid Grids Considering Rank Correlation Among Diverse Uncertainty Sources

A new, unscented transformation (UT) based probabilistic power flow method for Alternate Current/Voltage Source Control-Multiple Terminal Direct Current hybrid grids is presented herein. The method is able to accurately tackle various random variables, including renewable energy sources with uncertainties such as wind speeds and solar radiations, which are rank correlated and are likely to follow different types of probability distributions. The concept of Gaussian copula is adopted to transform the rank correlated random variables into a group of standard Gaussian distributions with Pearson correlation coefficients, so that the UT method can be later applied to select the critical sample points from Gaussian distributions in a proper and uniform way. The effectiveness of the proposed method is validated using a set of test results on the modified IEEE 39-bus system and IEEE 300-bus system.

Integration of a large-scale research facility into the grid: Case study of a real project

Pursuing 2020 and 2050 energy and emission goals also the large-scale research facilities must reduce energy consumption and contribution to greenhouse gas (GHG) emission, as well as behaving like good citizens of the smart grid. These new requirements are currently being integrated in the design process of these facilities. Hence, extensive verifications and tests must be carried out before a facility with very heavy power demand is deployed into the grid. In particular, how it impacts the regional grid and how the regional grid impacts the facility. In this paper, we present the simulation results of these mutual impacts, based on the real world project of a spallation source. As a meaningful contribution, the uncertainty quantification is applied to handle with stochastic nature of renewable energy in this project, by RTDS simulation and Monte Carlo simulation together.