Ning Lu

Appliance Commitment for Household Load Scheduling

This paper presents a novel appliance commitment algorithm that schedules thermostatically controlled household loads based on price and consumption forecasts considering users comfort settings to meet an optimization objective such as minimum payment or maximum comfort. The formulation of an appliance commitment problem is described using an electrical water heater load as an example. The thermal dynamics of heating and coasting of the water heater load is modeled by physical models; random hot water consumption is modeled with statistical methods. The models are used to predict the appliance operation over the scheduling time horizon. User comfort is transformed to a set of linear constraints. Then, a novel linear-sequential-optimization-enhanced, multiloop algorithm is used to solve the appliance commitment problem. The simulation results demonstrate that the algorithm is fast, robust, and flexible. The algorithm can be used in home/building energy-management systems to help household owners or building managers to automatically create optimal load operation schedules based on different cost and comfort settings and compare cost/benefits among schedules.

An Evaluation of the HVAC Load Potential for Providing Load Balancing Service

This paper investigates the potential of providing intra-hour load balancing services using aggregated heating, ventilating, and air-conditioning (HVAC) loads. A directload control algorithm is presented. A temperature-priority-list method is used to dispatch the HVAC loads optimally to maintain customer-desired indoor temperatures and load diversity. Realistic intra-hour load balancing signals are used to evaluate the operational characteristics of the HVAC load under different outdoor temperature profiles and different indoor temperature settings. The number of HVAC units needed is also investigated. Modeling results suggest that the number of HVAC units needed to provide a ±1-MW load balancing service 24 hours a day varies significantly with baseline settings, high and low temperature settings, and outdoor temperatures. The results demonstrate that the intra-hour load balancing service provided by HVAC loads meets 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 HVAC loads.

Design Considerations of a Centralized Load Controller Using Thermostatically Controlled Appliances for Continuous Regulation Reserves

This paper presents design considerations for a centralized load controller to control thermostatically controlled appliances (TCAs) for continuous regulation reserves (CRRs). The controller logics for setting up the baseline load, generating priority lists, issuing dispatch commands, and tuning the simplified forecaster model using measurement data are described. To study the impacts of different control parameter settings on control performance and device lifetimes, a system consisting of 1000 heating, ventilating, and air-conditioning (HVAC) units in their heating modes is modeled to provide a CRR 24 hours a day. Four cases are modeled to evaluate the impact of forecasting errors, minimum HVAC turn-off times, response delays, and consumer overrides. The results demonstrate that a centralized TCA load controller can provide robust, good quality CRRs with reduced communication needs for the two-way communication network and inexpensive load control devices. Most importantly, because the controller precisely controls the aggregated HVAC load shapes while maintaining load diversity, the controllable and measurable load services that it provides can be used for many other demand response applications, such as peak shaving, load shifting, and arbitrage.

Evaluation of the flywheel potential for providing regulation service in California

Flywheel energy storage can provide ancillary services including regulation and frequency response to power grids. This study presents the technical characteristics, modeling approach, methodologies, and results for providing regulation services in the California Independent System Operator market. Breakeven cost analyses were developed for two cases: 1) the flywheel provides the regulation service alone and 2) the flywheel provides the regulation service aggregated together with a hydro power plant. For both cases, two payment methods were evaluated: pay-by-energy and pay-by-capacity. Based on the results of the technical and cost analyses, the opportunities for providing regulation services are discussed, field test results for the flywheels physical characteristics are presented, and performance metrics to evaluate the flywheels capability to provide the regulation services are proposed and evaluated.

An evaluation of the water heater load potential for providing regulation service

This paper investigates the possibility of providing aggregated regulation services with small loads, such as water heaters or air conditioners. A direct-load control algorithm is presented to aggregate the water heater load for the purpose of regulation. A dual-element electric water heater model is developed, which accounts for both thermal dynamics and users water consumption. A realistic regulation signal was used to evaluate the number of water heaters needed and the operational characteristics of a water heater when providing 2-MW regulation service. Modeling results suggest that approximately 33 000 water heaters are needed to provide a 2-MW regulation service 24 hours a day. However, if water heaters only provide regulation from 6:00 to 24:00, approximately 20 000 will be needed. Because the control algorithm has considered the thermal setting of the water heater, customer comfort is maintained. Therefore, the aggregated regulation service provided by water heater loads can become a major source of revenue for load-serving entities when the smart grid enables the direct load control.

Coordinated control algorithm for hybrid energy storage systems

Energy storage is an essential element of future power systems to integrate high level of variable renewable energy resources. Earlier studies have found that energy storage can compensate for the stochastic nature of intermittent energy sources by absorbing the excessive energy when generation exceeds predicted levels and providing it back to the grid when generation levels fall short. However, earlier economic studies have shown that battery energy storage and flywheel energy storage is not economically competitive comparing to traditional generation units. An optimal control algorithm has been developed to coordinate the slow unit (having respond time greater than 1 minute) and fast energy storage unit (having response time less than 1 minute) to maximize the revenue (or minimize the total cost) of the hybrid energy storage system. The fast energy storage unit, (which can be a flywheel or battery bank) is tuned to pick up the fluctuations of regulation signal while the slow unit, (which can be a traditional generation unit or slow energy storage system) is adjusted less than once per hour to provide regulation service. Simulation models of hydro, combined cycle, and flywheel unit have been developed and implemented in MATLAB. Extensive simulations demonstrate the effectiveness of the control algorithm. The value of the algorithm has been shown from power plant wear and tear aspect and reducing system balancing reserve aspect.

Integration of uncertainty information into power system operations

Contemporary power systems face uncertainties coming from multiple sources, including forecast errors of load, wind and solar generation, uninstructed deviation and forced outage of traditional generators, and unscheduled loss of transmission lines. With increasing amounts of wind and solar generation being integrated into the system, these uncertainties have been growing significantly. It is critically important to build the knowledge of major sources of uncertainties, learn how to model them, and then incorporate this information into decision-making processes and power system operations, for better reliability and efficiency. This paper gives a comprehensive overview on the sources of uncertainties in power systems, their important characteristics and models, and approaches for integrating uncertainty information into system operations. It is primarily based on previous works conducted at the Pacific Northwest National Laboratory (PNNL).

Parameter Selection for a Centralized Thermostatically Controlled Appliances Load Controller Used for Intra-Hour Load Balancing

This paper presents a novel dynamic parameter selection process to optimize the performance of a centralized load controller designed to provide intra-hour load balancing services using thermostatically controlled appliances (TCAs). An optimal set of control parameters for the controller are selected by exhaustive simulations of control variables such as the sampling time of the forecaster, the magnitude of the load balancing signal, and the temperature deadband. The effects of TCA lock-off times, ambient temperatures, heat gains, and two-way communication delays on the controller design are also modeled. Customer comfort, device life cycles, and control errors are used as metrics to evaluate the performance. The results demonstrate that the optimized controller offers satisfactory performance considering all the operational uncertainties.

An evaluation of the NaS battery storage potential for providing regulation service in California

Sodium sulfur (NaS) batteries can provide energy storage, real-time dispatch, regulation, frequency response, and other essential services to the power grids. This study presents the technical characteristics, modeling approach, methodologies, and results for providing regulation services in the California Independent System Operator (CAISO) market. Two different scenarios were studied and compared: a scenario without intermittent renewable-energy resource penetration (base case) and a scenario with significant renewable-energy resource penetration (including wind) reaching 20% of CAISOs energy supply. In addition, breakeven cost analyses were developed for four cases. Based on the results of the technical and cost analyses, the opportunities for the NaS battery providing the regulation services are discussed, design improvements for the batterys physical characteristics are recommended, and modifications of the regulation signals sent to NaS batteries are proposed.

Unit commitment considering generation flexibility and environmental constraints

This paper proposes a new framework for the power system unit commitment process, incorporating generation flexibility requirements and environmental constraints into the existing unit commitment algorithm. The generation flexibility requirements are to address the uncertainty and variability associated with large amounts of intermittent resources as well as with load, which cause real-time balancing requirements to be variable and less predictable. The proposed flexibility requirements include capacity, ramp-rate and energy (or ramp duration) for both upward and downward balancing reserves. The environmental constraints include emission limits for fossil fuelfired generators and ecological regulations for hydro power plants. The calculation of emission rates is formulated. Unit commitment under this new framework will be critical to the economic and reliable operation of the power grid and the minimization of its negative environmental impacts, especially when high penetration levels of intermittent resources are being approached, as required by the renewable portfolio standards in many states.