Hawaii International Conference on System Sciences

https://escholarship.org/content/qt8755h7rn/qt8755h7rn.pdf?t=p0jvvs

Occupant behavior modeling for building performance simulation: Current state and future challenges:

The electric power system is currently undergoing a period of unprecedented changes. Environmental and sustainability concerns lead to replacement of a significant share of conventional fossil fuel-based power plants with renewable energy resources. This transition involves the major challenge of substituting synchronous machines and their well-known dynamics and controllers with power electronics-interfaced generation whose regulation and interaction with the rest of the system is yet to be fully understood. In this article, we review the challenges of such low-inertia power systems, and survey the solutions that have been put forward thus far. We strive to concisely summarize the laid-out scientific foundations as well as the practical experiences of industrial and academic demonstration projects. We touch upon the topics of power system stability, modeling, and control, and we particularly focus on the role of frequency, inertia, as well as control of power converters and from the demand-side.

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Foundations and Challenges of Low-Inertia Systems (Invited Paper)

Accurate occupancy detection of an office room from light, temperature, humidity and CO2 measurements using statistical learning models

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems.

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Virtual Inertia: Current Trends and Future Directions

The thermal storage potential in commercial buildings is an enormous resource for providing various ancillary services to the grid. In this paper, we show how fans in Heating, Ventilation, and Air Conditioning (HVAC) systems of commercial buildings alone can provide substantial frequency regulation service, with little change in their indoor environments. A feedforward architecture is proposed to control the fan power consumption to track a regulation signal. The proposed control scheme is then tested through simulations based on a calibrated high fidelity non-linear model of a building. Model parameters are identified from data collected in Pugh Hall, a commercial building located on the University of Florida campus. For the HVAC system under consideration, numerical experiments demonstrate how up to 15% of the rated fan power can be deployed for regulation purpose while having little effect on the building indoor temperature. The regulation signal that can be successfully tracked is constrained in the frequency band $[1/\tau_{0},1/\tau_{1}]$ , where $\tau_{0}\approx 3$ minutes and $\tau_{1}\approx 8$ seconds. Our results indicate that fans in existing commercial buildings in the U.S. can provide about 70% of the current national regulation reserve requirements in the aforementioned frequency band. A unique advantage of the proposed control scheme is that assessing the value of the ancillary service provided is trivial, which is in stark contrast to many demand-response programs.

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Ancillary Service to the Grid Through Control of Fans in Commercial Building HVAC Systems

Automated demand response can be a valuable resource for ancillary services in the power grid. This paper illustrates this value with the first experimental demonstration of frequency regulation from commercial building heating ventilation and air conditioning (HVAC) systems. The experiments were conducted in Pugh Hall, a 40000 sq. ft. commercial building located at the University of Florida. Detailed are the steps required to make this possible, including control architecture, system identification, and control design. Experiments demonstrate: that satisfactory frequency regulation service can be provided by the HVAC system without noticeable effect on the indoor climate, and the ancillary service provided by this system passes the qualification criteria for participating in the Pennsylvania-New Jersey-Maryland (PJM) interconnection's frequency regulation market.

Experimental Evaluation of Frequency Regulation From Commercial Building HVAC Systems

We propose a novel stochastic agent-based model of occupancy dynamics in a building with an arbitrary number of zones and occupants Simulation of the model yields time-series of the location of each agent (a software representation of an occupant) The model is meant to provide realistic simulation of occupancy dynamics in non-emergency situations Comparison of the model's prediction of distributions of random variables such as first arrival time of a building is provided against those estimated from measurements in commercial buildings We also propose a lower complexity graphical model of occupancy evolution in multi-zone buildings The graphical model captures information on mean occupancy and correlation among occupancy at various zones in the building The agent-based model can be used in conjunction with building performance simulation tools, while the graphical model is more suitable for real-time applications, such as occupancy estimation with noisy sensor measurements

Agent-based and graphical modelling of building occupancy

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Research Roadmap on Grid-Forming Inverters

There is significant recent interest in applying model-based control techniques to improve the energy efficiency of buildings. This requires a predictive model of the building's thermal dynamics. Due to the complexity of the underlying physical processes, usually system identification techniques are used to identify parameters of a physics-based model. We investigate the effect of various model structures and identification techniques on the parameter estimates through a combination of analysis and experiments conducted in a commercial building. We observe that a second order model can reproduce the input-output behavior of a full-scale model (with 13 states). Even a single state model has enough predictive ability that it may be sufficient for control purposes. We also show that the application of conventional techniques to closed-loop data from buildings (that are collected during usual operation) leads to poor estimates; their inaccuracy becomes apparent only when forced-response data is used for validation where there is sufficient difference among various inputs and outputs. The results of this investigation are expected to provide guidelines on do's and don'ts in modeling and identification of buildings for control.

Yashen Lin

Papers

Ancillary Service to the Grid Through Control of Fans in Commercial Building HVAC Systems

Experimental Evaluation of Frequency Regulation From Commercial Building HVAC Systems

Agent-based and graphical modelling of building occupancy

Research Roadmap on Grid-Forming Inverters

Issues in identification of control-oriented thermal models of zones in multi-zone buildings