Modified bus split aggregation and control of residential loads
University of New Brunswick
Over the past few years, power systems around the world, including Canadian ones, have reported significant progress in implementing smart grid functions (passive and active demand response, direct load control, and peak-load management). One of the key requirements for implementing smart grid functions is the accurate, reliable, and non-intrusive aggregation and control of the power delivered to a certain point-of-supply (a distribution transformer or a substation). Such a requirement is justified by load types and behaviors, as well as, growing levels of de-regulated operation of power systems. In general, the conventional bottom-up aggregation of power demands and generation has been widely used as an effective tool for the planning, control, and operation in power systems. However, the implementation of smart grid functions require new methods to achieve the aggregation of the power injected (delivered or generated) at a certain point-of-supply. In order to meet such a requirement, the bottom-up, coordinated and bus-split aggregation approaches have been introduced, and have shown good abilities to accurately aggregate the power delivered at load buses. Nonetheless, these aggregation approaches have been facing challenges due to their formulation that may become complicated, when combined with a generic power (active and reactive) delivery. In addition, existing aggregation approaches are highly dependent on collecting and processing significant amount of data in order to create and update energy profiles at points-of-supply with possible bi-directional power flows. The bus-split aggregation approach has demonstrated a unique feature of creating state matrix-based models for aggregated power injection at buses that feed industrial loads. Such a state matrix can be formulated using load models and/or load energy profiles. The capabilities of the bus-split aggregation approach can be utilized in implementing smart grid functions for residential and commercial loads (RCLs). Such an employment can be achieved by expressing the power demands of RCLs in terms of orthogonal components, which can be defined using the new ZIP-phaselet load model. The ZIP-phaselet load model defines the power demands of any load as a combination of the power demands of constant-impedance, constant-power, and constant-current load components. The power demands of these load components are independent and constitute an orthogonal set. The first objective of this research work is to generalize the formulation of the bus-split aggregation approach for combinations of industrial, commercial, and/or residential loads. The desired bus-split formulation can be founded on the ZIP-phaselet load modeling, thus aggregating power demands of specific load classes that have energy storage capabilities (water heaters, heating units, and HVAC units). The second objective of this research work is to utilize the generalized bus-split aggregation for developing a unit commitment-based controller to operate water heaters for maximizing their energy storage during off-peak-demand hours. The performance of the generalized bus-split aggregation and unit commitment-based controller is tested for different residential loads during different seasons. Test results demonstrate the accuracy, reliability, and applicability of the proposed aggregation and control methods for implementing smart grid functions in residential loads.