Current Status

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The GridLAB-D system currently implements modules to perform the following functions:
 * Power and energy flow and control
 * Load electric, thermal, and control behavior
 * Economic behaviors
 * Data collection and analysis
 * Physical and economic boundary condition management
 * Integration with other software

= Power Flow =

The power flow component of GridLAB-D is separated into a distribution module and a transmission module. While the distribution systems are the primary focus of GridLAB-D, the transmission module is included so that the interactions between two or more distribution systems can be simulated.

Transmission System
The transmission system is included to allow for the interconnection of multiple distribution feeders. If a transmission module was not included each distribution system could only be solved independently of other systems. While distribution systems can be solved independently, as is common in current commercial software packages, GridLAB-D will have the ability to generate a power flow solution for multiple distributions systems interconnected via a transmission or sub-transmission network. Traditionally the ability to examine interactions at this level has been limited by computational power. To address this limitation, GridLAB-D is being developed for execution on multiple processor systems. In the current version of GridLAB-D the AC power flow solution method used for the transmission system is the Gauss-Seidel (GS) method, chosen for its inherent ability to solve for poor initial conditions, and to remain numerically stable in multiprocessor environments.

Distribution System
In order to accurately represent the distribution system the individual feeders are expressed in terms of conductor types, conductor placement on poles, underground conductor orientation, phasing, and grounding. GridLAB-D does not simplify the distribution system component models. The distribution module of GridLAB-D utilizes the traditional forward and backward sweep method for solving the unbalanced 3-phase AC power flow problem. This method was selected in lieu of newer methods such as current injection methods for the same reasons that the GS method was selected for the transmission module; converging in the fewest number of iterations is not the primary goal. Just as with the transmission module the distribution modules will only start with a flat start at initialization and all subsequent solutions will be derived from the previous time step.

Metering is supported for both single/split phase and three phase customers. Support for reclosers, islanding, distributed generation models, and overbuilt lines are anticipated in coming versions.

The following power distribution system components are implemented and available for use:


 * Overhead and underground lines
 * Transformers
 * Voltage regulators
 * Fuses
 * Switches
 * Shunt capacitor banks

= Buildings =

Commercial and residential buildings are implemented using the Equivalent Thermal Parameters model. These are differential models solved for both time as a function of state and state as a function of time. Currently implemented residential end-uses are:
 * Water heaters
 * Refrigerators
 * Stand-alone freezers
 * Dishwashers
 * Clothes washers and dryers
 * Electric ranges
 * Microwaves
 * Electric plugs and lights
 * Internal gains
 * House loads (including air conditioning, heat pumps, and solar loads)

Commercial loads are simulated using an aggregate multi-zone Energy Technology Perspectives (ETP) model that will be enhanced with more detailed end-use behavior in coming versions.