Ning Lu

A state-queueing model of thermostatically controlled appliances

This paper develops a state-queueing model to analyze the price response of aggregated loads consisting of thermostatically controlled appliances (TCAs). Assuming a perfectly diversified load before the price response, we show that TCA setpoint changes in response to the market price will result in a redistribution of TCAs in on/off states and therefore change the probabilities for a unit to reside in each state. A randomly distributed load can be partially synchronized and the aggregated diversity lost. The loss of the load diversity can then create unexpected dynamics in the aggregated load profile. Raising issues such as restoring load diversity and damping the peak loads are also addressed in this paper.

Modeling uncertainties in aggregated thermostatically controlled loads using a State queueing model

To study the impacts of price responsive demand on the electric power system requires better load models. This paper discusses the modeling of uncertainties in aggregated thermostatically controlled loads using a state queueing (SQ) model. The cycling times of thermostatically controlled appliances (TCAs) vary with the TCA types and sizes, as well as the ambient temperatures. The random consumption of consumers, which shortens or prolongs a specific TCA cycling period, introduces another degree of uncertainty. By modifying the state transition matrix, these random factors can be taken into account in a discrete SQ model. The impacts of considering load diversity in the SQ model while simulating TCA setpoint response are also studied.

Pumped-storage hydro-turbine bidding strategies in a competitive electricity market

This paper develops optimal pump-hydro unit bidding strategies in a competitive electricity market. Starting from a weekly forecasted market clearing price (MCP) curve, an algorithm to maximize the profit of a pump-hydro unit considering reserve bids is developed. A comparison between the optimal bidding strategy and a fixed-schedule weekly generating and pumping strategy is provided.

Control strategies of thermostatically controlled appliances in a competitive electricity market

This paper discusses setpoint-control strategies for thermostatically controlled appliances (TCAs) in a competitive electricity market, with the electric water heater load used as an example. By varying the TCA thermostat settings, the TCA power consumption can be shifted from the high-price period to the low-price period to reduce the peak-load and energy cost. Economic benefits and impacts on distribution feeder load shapes when applying different setpoint-control strategies are studied.

Climate Change Impacts on Residential and Commercial Loads in the Western U.S. Grid

This paper presents a multidisciplinary modeling approach to quickly quantify climate change impacts on energy consumption, peak load, and load composition of residential and commercial buildings. This research focuses on addressing the impact of temperature changes on the building cooling load in ten major cities across the Western United States and Canada. Our results have shown that by the mid-century, building yearly energy consumption and peak load will increase in the Southwest. Moreover, the peak load months will spread out to not only the summer months but also spring and autumn months. The Pacific Northwest will experience more hot days in the summer months. The penetration levels of air-conditioning (a/c) systems in this region are likely to increase significantly over the years. As a result, some locations in the Pacific Northwest may be shifted from winter peaking to summer peaking. Overall, the Western U.S. grid may see more simultaneous peaks across the North and South in summer months. Increased cooling load will result in a significant increase in the motor load, which consumes more reactive power and requires stronger voltage support from the grid. This study suggests an increasing need for the industry to implement new technology to increase the efficiency of temperature-sensitive loads and apply proper protection and control to prevent possible adverse impacts of a/c motor loads.

The Wide-Area Energy Storage and Management System – Battery Storage Evaluation

This report presents the modeling approach, methodologies, and results of the sodium sulfur (NaS) battery evaluation study, which was conducted by Battelle for the California Energy Commission (CEC).

Modeling Power Systems as Complex Adaptive Systems

Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of todays most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This report explores the state-of-the-art physical analogs for understanding the behavior of some econophysical systems and deriving stable and robust control strategies for using them. We review and discuss applications of some analytic methods based on a thermodynamic metaphor, according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwise understood. We apply these methods to the question of how power markets can be expected to behave under a variety of conditions.

Smart meter data analysis

This paper presents a thorough analysis of 15-minute residential meter data sets to identify possible value propositions of smart meter measurements. Meter measurements of 50 houses were used to derive a few key data signatures for several target applications such as identifying demand response potentials, detecting abnormal load behaviors, and fault diagnosis. Results showed that for different applications, the communication needs from meters to control centers, data storage capabilities, and the complexity of data processing intelligence varies significantly. Therefore, it is important to build a dynamic data signature database and optimize the distribution of data processing capability between local devices and control centers to avoid communication congestion and to identify problems early. This paper also demonstrates that highresolution smart meter data can make distribution power grids more economical, reliable, and resilient.

A multi-layer Petri net model for deregulated electric power systems

This paper proposes a hybrid multilayer Petri net model for electric power systems. The base layer is the physical layer, which represents the physical flow in a power system. On top of it are information layers to model information flows, which schedule the physical flow via discrete tokens. In between, there is an interface layer coded as programs and functioning as a control agent. An extension of continuous Petri nets, called a variable arc weighting Petri net (VAWPN), is introduced to simulate the physical layer, in which vector tokens are used to match the information flows to the physical flows. The operation of a VAWPN is presented. A three-zone example of a power system dispatch model is used to illustrate the concepts.

The potential of thermostatically controlled appliances for intra-hour energy storage applications

This paper investigates the potential of providing a variety of energy storage services by directly control the thermostatically controlled appliances (TCAs) from a centralized controller. Dispatch algorithms for the controller to arrange the turn-on and turn-off time and duration of individual TCAs are presented. The control goal is to operate each TCA within the customer-desired temperature range and maintain the TCA load diversity, and make the aggregated TCA load at the target load level. Methods to minimize the communication needs by reducing the monitoring and control data flows between the central controller and the end devices are also discussed. A thousand space heating units are modeled to demonstrate the control algorithms to provide load shifting and load balancing services for a period of 24 hours. The results demonstrate that the energy and ancillary services provided by the TCA loads meet the performance requirements and can become a major source of revenue for load-serving entities where the two-way communication smart grid infrastructure enables direct load control over the TCA loads.