Mostafa Sahraei-Ardakani

A study of electricity market dynamics using Invasive Weed Colonization Optimization

A method based on the novel optimization algorithm of Invasive Weed colonization Optimization (IWO) is used to study electricity market dynamics. Dynamics of such a multi agent system is analyzed using aspects both from Game theory and IWO. The method is integrated with a power system simulator to consider all the constraints of a realistic power system to make sure that the results are reliable. The IWO has also been introduced briefly and it is discussed why this method is supposed to be appropriate in such problems. Several simulation studies are presented to show how the method works. These outputs are compared with what exist in the literature. It is shown that making use of search based optimization algorithms such as IWO is necessary for consideration of all the constraints and details.

Real-Time Contingency Analysis With Transmission Switching on Real Power System Data

Transmission switching (TS) has shown to be an effective power flow control tool. TS can reduce the system cost, improve system reliability, and enhance the management of intermittent renewable resources. This letter addresses the state-of-the-art problem of TS by developing an AC-based real-time contingency analysis (RTCA) package with TS. The package is tested on real power system data, taken from energy management systems of PJM, TVA, and ERCOT. The results show that post-contingency corrective switching is a ready to be implemented transformational technology that provides substantial reliability gains. The computational time and the performance of the developed RTCA package, reported in this letter, are promising.

A Fast LP Approach for Enhanced Utilization of Variable Impedance Based FACTS Devices

Transmission systems are under stress and need to be upgraded. Better utilization of the existing grid provides a fast and cheap alternative to building new transmission. One way to improve the utilization of the transmission network is power flow control via flexible ac transmission system (FACTS) devices. While FACTS devices are used today, the utilization of these devices is limited; traditional dispatch models (e.g., security constrained economic dispatch) assume a fixed, static transmission grid even though it is rather flexible. The primary barrier is the complexity that is added to the power flow problem. The mathematical representation of the DC optimal power flow, with the added modeling of FACTS devices, is a nonlinear program (NLP). This paper presents a method to convert this NLP into a mixed-integer linear program (MILP). The MILP is reformulated as a two-stage linear program, which enforces the same sign for the voltage angle differences for the lines equipped with FACTS. While this approximation does not guarantee optimality, more than 98% of the presented empirical results, based on the IEEE 118-bus and Polish systems, achieved global optimality. In the case of suboptimal solutions, the savings were still significant and the solution time was dramatically reduced.

Performance of AC and DC based transmission switching heuristics on a large-scale polish system

Optimal transmission switching (OTS) has demonstrated benefits both in terms of reliability and cost savings for bulk power systems. OTS is a mixed-integer program (MIP) with binary variables representing the status of the transmission elements. Due to the computational complexity of this MIP, implementation of OTS is limited. Therefore, different heuristics have been proposed to find good, suboptimal solutions fast. The heuristics are often tested on small test cases with restricted analysis on actual systems. This work tests two of the recently developed fast heuristics on the Polish system to show their performance. The results suggest that the best solutions are among the top twenty candidates identified by the heuristics if they are based on the ACOPF solution. If the heuristics are calculated based on the DCOPF solution, the performance may be poor. The correlation between estimated benefits and actual benefits is not very promising in either of the cases.

Day-Ahead Corrective Adjustment of FACTS Reactance: A Linear Programming Approach

Reserve requirements serve as a proxy for N-1 reliability in the security-constrained unit commitment (SCUC) problem. However, there is no guarantee that the reserve is deliverable for all scenarios (post-contingency states). One cheap way to improve reserve deliverability is to harness the flexibility of the transmission network. Flexible AC transmission system (FACTS) devices are able to significantly improve the transfer capability. However, FACTS utilization is limited today due to the complexities these devices introduce to the DC optimal power flow problem (DCOPF). With a linear objective, the traditional DCOPF is a linear program (LP); when variable impedance based FACTS devices are taken into consideration, the problem becomes a nonlinear program (NLP). A reformulation of the NLP to a mixed integer linear program, for day-ahead corrective operation of FACTS devices, is presented in this paper. Engineering insight is then introduced to further reduce the complexity to an LP. Although optimality is not guaranteed, the simulation studies on the IEEE 118-bus system show that the method finds the globally optimal solution in 98.8% of the cases. Even when the method did not find the optimal solution, it was able to converge to a near-optimal solution, which substantially improved the reliability, very quickly.

Market Equilibrium for dispatchable transmission using FACT devices

Traditionally system operators would minimize generation cost considering transmission as a passive system. Having the smart grid technology transmission network topology can be optimized simultaneously with the generation system. This can be done either by switching lines on and off, or by continuously controlling the admittance of the lines. FACTS devices make adjustment of a transmission lines admittance possible. Here we study a market design for operation of such FACTS devices based on Supply Function Equilibrium (SFE). We model the variable cost associated with utilization of the FACTS devices as the relative additional cost of losses. The owners are being paid the market clearing price for the additional transfer capacity they provide. The problem is formulated for a simple two-node two-transmission line system. It is shown that the marginal cost functions are increasing and it is not clear that FACTS devices are natural monopoly. Our simulation study shows that a market-mechanism can be employed for operation of the devices. Under the market mechanism that we consider, owners of FACTS devices are permitted make supply offers to the market alongside generators. Market-clearing consists of determining nodal prices for generators and admittance-based pricing for transmission or FACTS device owners. Such a market would be beneficial to the device owners by providing revenue for them and the system by increasing the social welfare.

Transfer Capability Improvement Through Market-Based Operation of Series FACTS Devices

Traditionally, electric system operators have dispatched generation to minimize total production costs, ignoring the flexibility of the transmission system. Implementation of smart-grid systems could allow operators to co-optimize flexible transmission alongside generation dispatch; the technologies that would enable such co-optimization are still regulated as part of the monopoly transmission system. One particular flexible transmission asset is variable impedance flexible AC transmission system (FACTS). This paper 1) points out the positive externality problem existing in a recent market design proposal with active transmission participation, and 2) proposes a sensitivity-based method to estimate the marginal market value of FACTS adjustments to overcome this positive externality problem. The marginal value would suggest efficient impedance adjustments to the operator and provide the right financial incentives for the FACTS owners to operate their assets in a socially optimal way. Revenue adequacy is demonstrated under specific conditions and more broadly investigated through simulation studies. An analytical example on a two-bus system as well as a numerical study on the IEEE 118-bus system are presented. The results suggest that inclusion of a price signal for FACTS devices would lead to significant social welfare improvements in competitive power markets.

Harnessing Flexible Transmission: Corrective Transmission Switching for ISO-NE

Despite the significant attention transmission switching (TS) has gained over the last decade, important challenges remain. This paper addresses the state-of-the-art challenges of TS by studying the benefits of corrective switching using authentic Independent System Operator of New England (ISO-NE) data and software. Thus, the results and analyses presented in this paper are more convincing than any other study conducted to date. TS is successfully implemented for reliability applications as a corrective mechanism. ISO-NE maintains N -1 reliability based on the preventive dispatch and enforcing proxy reserve requirements along with N - 1 - 1 reliability based on reserves and interface limits. This paper incorporates TS as a corrective mechanism in response to both the N - 1 and N - 1 - 1 events. Not only does this paper investigate the capability of corrective switching to alleviate thermal overloads but also the economic benefits of corrective switching with actual market data and in-house market software at ISO-NE. The results show that corrective TS can improve the reliability of the system and save millions of dollars each year by providing a cheaper corrective action alternative for ISO-NE. The results also suggest that TS would provide more significant benefits for systems with more transmission congestion such as Pennsylvania New Jersey Maryland, Midcontinent Independent System Operator, and Electric Reliability Council of Texas.

Computationally Efficient Adjustment of FACTS Set Points in DC Optimal Power Flow With Shift Factor Structure

Enhanced utilization of the existing transmission network is a cheaper and paramount alternative to building new transmission lines. Flexible ac transmission system (FACTS) devices are advanced technologies that offer transfer capability improvements via power flow control. Although many FACTS devices exist in power systems, their set points are not frequently changed for power flow control purposes, which is mainly due to the computational complexity of incorporating FACTS flexibility within the market problem. This paper proposes a computationally efficient method for adjustment of variable impedance-based FACTS set points, which is also compatible with existing market solvers. Thus, the method can be employed by the existing solvers with minimal modification efforts. This paper models FACTS reactance control as injections to keep the initial shift factors unchanged. Next, the paper formulates a dc optimal power flow that co-optimizes FACTS set points alongside generation dispatch. The resulting problem, which is in a nonlinear program, is then reformulated to a mixed-integer linear program. Finally, an engineering insight is leveraged to further reduce the computational complexity to a linear program. Simulation studies on IEEE 118-bus and Polish 2383-bus test cases show that the method is extremely effective in finding quality solutions and being very fast.

Real-Time Contingency Analysis With Corrective Transmission Switching

Transmission switching (TS) has gained significant attention recently. However, barriers still remain and must be overcome before the technology can be adopted by the industry. The state-of-the-art challenges include AC feasibility, computational complexity, the ability to handle large-scale real power systems, and dynamic stability. This paper investigates these challenges by developing an AC corrective TS (CTS) based real-time contingency analysis (RTCA) tool that can handle large-scale systems within a reasonable time. The tool quickly proposes multiple high-quality corrective switching actions for contingencies with potential violations. To reduce the computational complexity, three heuristic algorithms are proposed to generate a small set of candidate switching actions. Parallel computing is implemented to further speed up the solution time. Moreover, time-domain simulations are performed to check for dynamic stability of the proposed CTS solutions. The promising results, tested on the Tennessee Valley Authority (TVA) system and actual energy management system snapshots from the PJM Interconnection (PJM) and the Electric Reliability Council of Texas (ERCOT), show that the tool effectively reduces post-contingency violations. It is concluded that CTS is ripe for industry adoption for RTCA application.