Dimitra Apostolopoulou

Automatic Generation Control and Its Implementation in Real Time

In power systems, the control mechanism responsible for maintaining the system frequency to the nominal value and the real power interchange between balancing authority areas to the scheduled values is referred to as automatic generation control (AGC). The purpose of this paper is to present a systematic way to determine, in real time, the power allocated to each generator participating in AGC by taking into account the cost and quality of the AGC service provided. To this end, we formulate the economic dispatch process and gain insights into the economic characteristics of the generating units. We value the quality of AGC service by taking into consideration the ramping constraints of the generating units. The proposed methodology is illustrated in the WECC system and is compared with other allocation methods.

An Assessment of the Impact of Uncertainty on Automatic Generation Control Systems

This paper proposes a framework to quantify the impact of uncertainty that arises from load variations, renewable-based generation, and noise in communication channels on the automatic generation control (AGC) system. To this end, we rely on a model of the power system that includes the synchronous generator dynamics, the network, and the AGC system dynamics, as well as the effect of various sources of uncertainty. Then, we develop a method to analytically propagate the uncertainty from the aforementioned sources to the system frequency and area control error (ACE), and obtain expressions that approximate their probability distribution functions. We make use of this framework to obtain probabilistic expressions for the frequency performance criteria developed by the North American Electric Reliability Corporation (NERC); such expressions may be used to determine the limiting values of uncertainty that the system may withstand. The proposed ideas are illustrated through the Western Electricity Coordination Council (WECC) 9-bus 3-machine system and a 140-bus 48-machine system.

The Interface of Power: Moving Toward Distribution System Operators

The Deployment of a Distribution System Operator (DSO ) is becoming a necessity as a result of the distribution grids increasing roles and functionalities to ensure an efficient and reliable delivery of electricity to emerging proactive customers. The preferences of customers have evolved as they are willing to have more control over their energy use and transactions with the utility grid. In parallel, there is a potential need for an intermediate entity between the independent system operators (ISO s) or regional transmission operators (RTOs) and distributed energy resource (DER) owners due to the limited visibility and control over the meter resources. A DSO may efficiently utilize DERs to improve system reliability and resiliency and reduce emissions and greenhouse gasses by resource diversification.

Optimized FTR Portfolio Construction Based on the Identification of Congested Network Elements

This paper focuses on the construction of an optimized financial transmission rights (FTR) or congestion revenue rights portfolio for an FTR market participant given his assessment of the frequency and economic impacts of binding constraints in the transmission network. We overcome the data handling and heavy computing demands of locational marginal price (LMP)-difference-based methods for FTR selection by recasting the problem into one that focuses on the underlying product of “binding constraints”, which are physically observable phenomena, based on the mathematical insights into the structural characteristics of the model used for the clearing of the hourly day-ahead markets. Differentials in the LMPs are due to system congestion and so are merely manifestations of binding constraints in the transmission network. In addition, we exploit extensively the salient topological characteristics of large-scale interconnections. The market participant specifies the subset of “focus” constraints and the position he is willing to take on them. Our approach builds on the mathematical insights and topological characteristics with the effective deployment of the orthogonal matching pursuit algorithm to construct the optimized FTR portfolio characterized by the minimum number of node pairs for the specification of the FTR elements. We apply the proposed approach to a test system based on the PJM ISO network and markets to illustrate its capabilities for solving the FTR market participants problem in realistic large-scale systems.

Effects of various uncertainty sources on automatic generation control systems

In power systems, the automatic generation control (AGC) system is responsible for maintaining the nominal system frequency and the scheduled real power interchange between balancing areas. This paper proposes a framework to evaluate the effects of uncertainty arising from renewable-based electricity generation and noise in communication channels on the AGC system performance. To this end, we introduce a unified stochastic differential equation (SDE) model that includes power system dynamics and the AGC system (including the communication network on which its operation relies). We propagate the uncertainty from renewable-based resources and communication channel noise through the SDE model and investigate the resulting effect on AGC system performance. The proposed ideas are illustrated through a 4-bus test system.

Assessing Demand Response Resource locational impacts on system-wide carbon emissions reductions

Demand Response Resource (DRR) curtailments are generally triggered in response to economic signals, such as the locational marginal prices (LMPs). However, consideration of only the economic signals leaves out important information about the impact of the location of DRR curtailments on the system-wide carbon emissions. In this work, we use the marginal carbon intensity (MCI), the carbon emissions analogue of the LMP, to develop a metric which may be used by the Independent System Operator ISO to identify nodes at which DRR curtailments have the greatest impact on both LMP (and thereby consumer payments) and system-wide carbon emissions. Through illustrative simulations, we compare the outcome of various DRR cases and show the usefulness of the identification metric.

Balancing Authority Area Model and its Application to the Design of Adaptive AGC Systems

In this paper, we develop a reduced-order model for synchronous generator dynamics via selective modal analysis. Then, we use this reduced-order model to formulate a balancing authority (BA) area dynamic model. Next, we use the BA area model to design an adaptive automatic generation control (AGC) scheme, with self-tuning gain, that decreases the amount of regulation needed and potentially reduces the associated costs. In particular, we use the BA area model to derive a relationship between the actual frequency response characteristic (AFRC) of the BA area, the area control error, the system frequency, and the total generation. We make use of this relationship to estimate the AFRC online, and set the frequency bias factor equal to the online estimation. As a result, the AGC system is driven by the exact number of MW needed to restore the system frequency and the real power interchange to the desired values. We demonstrate the proposed ideas with a single machine infinite bus, the 9-bus 3-machine Western Electricity Coordinating Council (WECC), and a 140-bus 48-machine systems.

Distributed optimal load frequency control and balancing authority area coordination

This paper proposes a distributed optimal load frequency control (OLFC) scheme that replicates the behavior of the economic dispatch process in a multi-area power system. Power systems are divided in balancing authority (BA) areas that exercise their own load frequency control to restore the system frequency and real power interchange to desired values. In this paper, we use a simplified model to describe the power system dynamic behavior and propose a coordination scheme between BA areas in an interconnected power system that decreases the regulation amount needed as well as the associated costs by formulating a distributed OLFC system. The proposed control scheme is compared with traditional automatic generation control (AGC) systems, as well as the economic dispatch process. The proposed distributed OLFC system is illustrated through the Western Electricity Coordination Council (WECC) 9-bus 3-machine system.

Closure of ‘effects of various uncertainty sources on automatic generation control systems’

In power systems, the automatic generation control (AGC) system is responsible for maintaining the nominal system frequency and the scheduled real power interchange between balancing areas. This paper proposes a framework to evaluate the effects of uncertainty arising from renewable-based electricity generation and noise in communication channels on the AGC system performance. To this end, we introduce a unified stochastic differential equation (SDE) model that includes power system dynamics and the AGC system (including the communication network on which its operation relies). We propagate the uncertainty from renewable-based resources and communication channel noise through the SDE model and investigate the resulting effect on AGC system performance. The proposed ideas are illustrated through a 4-bus test system.

Balancing authority area coordination with limited exchange of information

In this paper, we propose a coordination scheme between balancing authority (BA) areas in an interconnected power system that decreases the regulation amount needed as well as the associated costs. Our approach aims at mimicking the behavior of the automatic generation control (AGC) system in a scenario where the whole interconnected system is assumed to be operated by a single BA area. To this end, we modify the area control error (ACE), which is fed into the AGC system of each BA area, and determine the AGC allocation based on a distributed algorithm that identifies the least expensive generators, with the mismatch of the total regulation needed being the only information exchanged between BA areas. We demonstrate the proposed ideas with the 3-machine 9-bus Western Electricity Coordinating Council (WECC) system, and compare the performance of our method with other three existing coordination approaches.