Scheduling and Pricing for Expected Ramp Capability in Real-Time Power Markets

Abstract

Higher variable renewable generation penetrations are occurring throughout the world on different power systems. These resources increase the variability and uncertainty on the system which must be accommodated by an increase in the flexibility of the system resources in order to maintain reliability. Many scheduling strategies have been discussed and introduced to ensure that this flexibility is available at multiple timescales. To meet variability, that is, the expected changes in system conditions, two recent strategies have been introduced: time-coupled multi-period market clearing models and the incorporation of ramp capability constraints. To appropriately evaluate these methods, it is important to assess both efficiency and reliability. But it is also important to assess the incentive structure to ensure that resources asked to perform in different ways have the proper incentives to follow these directions, which is a step often ignored in simulation studies. We find that there are advantages and disadvantages to both approaches. We also find that look-ahead horizon length in multi-period market models can impact incentives. This paper proposes scheduling and pricing methods that ensure expected ramps are met reliably, efficiently, and with associated prices based on true marginal costs that incentivize resources to do as directed by the market. Case studies show improvements of the new method.Index Terms-Economic dispatch, electricity markets, power system economics, power system operations, variable generation. NOMENCLATUREGenerator index/number of generators . Interval index/number of intervals . Also for interval indexing for look-ahead intervals. Bus location index/number of buses.Interval index between models (i.e., lining up time intervals when resolutions are not the same.) Piecewise block index/number of blocks .

A Flexible Ramping Capacity Model for Generation Scheduling with High Levels of Wind Energy Penetration

“…The uncertainty is represented by (A) in Figure 2, and can be expressed as the difference between the forecast wind power and the actual wind power output. It is very difficult to predict by how much the actual wind power output will deviate from the forecast wind power output [21]. Therefore, the uncertainty caused by the forecast error requires operating reserve in order to control the balance between generation and load [14].…”

“…The Constraints (21) and (22) describe minimum and maximum power constraints of each generator considering the FRC. Constraint (21) limits the sum of the awards of energy schedule, operating reserve and upward flexible ramping capacity to be less than or equal to the unit's maximum power.…”

Analysis of Wind Ramping Product Formulations in a Ramp-constrained Power Grid

“…Recently, the substantially increasing integration of variable renewable energy sources, such as wind power, has significantly changed the generation portfolios of many electric power systems [1][2][3][4]. To operate power systems with high penetration levels of variable renewables, the systems need more flexible resources to mitigate the variability and uncertainty [5][6][7][8][9][10]. In realtime operations with high penetration of renewables, one of the major challenges is ensuring sufficient ramping capability.…”

Wind Power Providing Flexible Ramp Product

“…In some markets, the frequency of price spikes is indeed increasing due to the changing generation portfolio [4]. In the US, RT markets are usually cleared every 5 minutes by the RT economic dispatch (RTED) tool, which considers a single time interval or multiple intervals [5]. When there are significant variations in load, interchange transactions or variable generation, the system could be in lack of flexible capacity to move from one RT dispatch point to the next.…”