by Mike Donnelly
31 July 2014
PartQuest Explore provides the perfect collaboration environment for Power System Engineers, whether they work on Generation, Transmission or Distribution Systems, or if they design Power Converters or complex end-user Load Systems. On-line access, with nothing to install or license, allows many participants to effectively work together on a “virtual grid” model. The participants may include component and sub-system application engineers, consultants, industry experts and educators, as well as utility system planning and development engineers.
The "Live-View Design" below shows an example power distribution system model, with an ideal 3-phase voltage source and a network of transmission lines and transformers, feeding a variety of different load types. Go ahead, move the waveform probes around to see any voltage, current, power or any other aspect of the system that is of interest to you.These loads represent important static and transient operating conditions, such as currents with high harmonic content and time-varying loads that cause unbalanced power flow. They include a constant power load, a switched lighting load, a variable heater element, and an induction motor operating through a line-start transient while driving a non-linear mechanical load.
Power distribution system with a variety of complex load models
The models provide not only the characteristic behavior of each component, but they also internally track the instantaneous power inputs and outputs, per phase and in total, so that power flow can be easily monitored. This system can be used, for example, to assess the potentially destabilizing “negative impedance” effect of a constant power load.
Although not shown here, models of protection elements can be included and various fault conditions inserted. Development engineers can use this to assess failure modes and the system’s ability to prevent or mitigate any resulting damage.
While PartQuest Explore provides many power system component models already, this is just the beginning. Because new models can be created by anyone, and used by everyone, the potential for effective collaboration is immense. And because the underlying model format is IEEE Standard 1076.1, there is minimal risk of losing any investment in modeling effort, as can happen with proprietary tool- or vendor-specific formats.
EV Charging System – A Case Study
In a recent project conducted by researchers at Portland State University (PSU), a new model was created to represent the load current draw of an Electric Vehicle (EV) charger. It can be calibrated by specifying the load current’s harmonic content, but it runs in time-domain simulations. Harmonic data was collected from different types of EV chargers, and while they were operating at different charging-state conditions. This data was added to the model, so it is ready for use by utility planning engineers evaluating proposed EV charger installations. They can verify the power system’s capability to handle expected maximum load currents, TDD (Total Demand Distortion) and power flow under various usage scenarios.
For example, the following measured harmonic data was entered in to the "AC_Load_5_Harmonic" time-domain simulation model:
constant load_data : load_state_array := (( 27.41516, 3.92103, 1.31469), -- Load State 1 Magnitude
(-52.20925, -163.50319, -40.79310), -- Load State 1 Phase
( 20.19034, 4.14641, 1.25855), -- Load State 2 Magnitude
(-50.4735, -138.8609, 6.8535), -- Load State 2 Phase
( 13.16234, 3.64058, 0.80223), -- Load State 3 Magnitude
(-51.3602, -114.0323, 68.840 )); -- Load State 3 Phase
Load State 1 represents the maximum charging rate, Load State 2 a medium rate and Load State 3 the minimum rate. The triple valued vectors are the magnitudes and phase angles of the fundamental, 3rd and 5th harmonics, as measured for a specific EV charger. The following simple "distribution system" was simulated, and the resulting time-domain and corresponding FFT (frequency-domain) results are shown below. Note the close fit between the magnitude of the Load State 1 measured current harmonics, and the correponding spectral magnitudes shown in the FFT graph.
EV-charger installation simulation model, using multiple calibrated “AC Harmonic Load” models
EV-charger current dB magnitude of odd harmonics of 60 Hz, at maximum charge state
A technical paper summarizing this research work is available here:
IEEE.org: Modeling Harmonic Impacts of Electric Vehicle Chargers on Distribution Networks
The Future of Power System Simulation is Here!
PartQuest Explore is a multi-discipline simulation platform, supporting analog, digital and even non-electrical aspects of the power system. Renewable energy system manufacturers, such as wind or solar, can provide models of their components and sub-systems and study the interaction with the utility’s “virtual grid”. End-user sub-system models, such as motors and drive electronics, advanced lighting systems, UPS, etc., can also be included.
PartQuest Explore is poised to revolutionize the way Power System Engineers Learn, Explore, Collaborate and Innovate. Smart Grid, anyone?
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