Power electronics simulation is a vital aspect of the RTDS Simulator, with users worldwide performing closed-loop testing on various aspects of converter controls in order to validate behaviour prior to deployment on the grid. The RTDS Simulator must therefore provide a high-fidelity electromagnetic transient representation of all aspects of power electronics-based systems in real time. The approach that has been taken to do so has changed over time with the availability of processing hardware and research in converter simulation.
The release of the innovative, proprietary Universal Converter Model (UCM) in 2021 has significantly improved the accuracy, flexibility, and accessibility of real time power electronics simulation.
The RTDS Simulator’s UCM is a significant development in the field of real-time power electronics simulation. It overcomes many of the challenges associated with the various other modelling approaches used by the RTDS Simulator (described in the above sections) and other real-time simulation tools.
The UCM based on a Descriptor State-Space modelling approach, which allows both sides of the converter to be represented by controlled sources with no delay introduced between them. The UCM is not decoupled at the DC bus, with no numerical interface between the converter model and surrounding network. The result is improved numerical stability. The UCM utilizes the same predictive switching technique that the Substep resistive switching converter models are based on, so it maintains the accurate and clean performance of those models.
The UCM is currently available for the following fixed converter topologies: two-level, NPC and T-type three-level, boost, and buck.
The UCM also considers both blocked and deblocked modes, so users can now more precisely model the charging and discharging of their circuit. The UCM represents the transition between blocked and deblocked states with improved accuracy and smoothness.
The UCM has three input options:
With Improved Firing, the UCM can accurately represent:
• Switching at >100 kHz in the Substep environment
• Switching at 3 kHz in the Mainstep environment
Using the Improved Firing input, the performance of the UCM is equivalent to that of offline electromagnetic transient program models (such as those available in the PSCAD software), which can take advantage of interpolation techniques. This is a milestone for real-time simulators, which are subject to much more stringent demands on calculation speed and efficiency due to the real-time requirement.
The unique advantages of the UCM (particularly with Improved Firing) have tangible benefits for RTDS Simulator users. The ability to represent converter performance with PWM firing at over 100 kHz – without compromising stability or accuracy, which can occur when a decoupled approach or L/C switching are used – sets a new industry standard for hardware-in-the-loop testing for converter controls.
Additionally, users with more limited simulator hardware configurations will now have significantly improved opportunities for power electronics simulation and testing. When used in the Mainstep environment, the UCM requires only 10 load units, making it computationally light. Several UCM components could easily be represented using a NovaCor system with a single licensed core, meaning that entry-level simulators are now capable of running power electronics studies and closed-loop testing of converter controls in a more detailed way than ever before – with full switching represented in the 3 kHz range.
Sample cases involving the UCM are now available in RSCAD V5.014 and RSCAD FX (V1.0 and up). For more information, please email firstname.lastname@example.org.
Did you miss our recent webinar and demonstration on the UCM?
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