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Microgrid Power-Hardware-in-the-loop Simulation Based on StarSim and PXI

This article describes a micorgrid power-hardware-in-the-loop simulation system developed by Tsinghua University and ModelingTech (info@modeling-tech.com).

Requirements:

A testing system is required for verifying the active power control strategy for a microgrid (MG) which contains doubly-fed induction generators (DFIG). For the traditional power system laboratory (the scale-down physical prototype), it is not easy to change the system topology and it is dangerous to conduct the fault test as well. Real-time simulation can solve these problems, however, in some cases, the model might be too ideal, for example, the magnetic field of the electrical machine is often assumed to have the ideal sinusoidal distribution. Therefore, a testing system with both the real DIFG and the real time simulator is required. This system combines the advantages of both real physical devices and the real time simulator. This kind of simulation method is often called as the power-hardware-in-the-loop simulation.

Power-Hardware-in-the-loop Simulation based on StarSim and PXI:

There are three components in Power-Hardware-in-the-loop (PHIL) real-time simulation system: the real time simulator, the real physical device and the interface between them, as shown in below.

Fig 1 The diagram of PHIL System.png

As shown in the figure, the real time simulator and the real physical device form a close loop through the interface. The real physical device is modeled as controllable current sources in the real time simulator; terminal voltages of current sources are sent out to voltage amplifiers through AO boards, voltage amplifiers amplifies signal level voltage signals to true high power voltages. Meanwhile, actual currents are measured by sensors and acquired through data acquisition boards to the real time simulator as the feedback to control current sources, in this way, the close loop is formed.

The real-time simulation software is StarSim. StarSim is the LabVIEW-based Power System Electromagnetic Transient Real-Time Simulation software developed by ModelingTech. StarSim seamlessly integrates with LabVIEW, which means, the power system topology built with StarSim can be run directly in the NI real-time PXI.

Project Description:

This project is done in the collaboration between Tsinghua University (the smart grid operation and optimization laboratory) and ModelingTech. The testing system is shown below.

Fig 2 PHIL Lab Photo.png

The white box is the StarSim and PXI-based power system real time simulator, which is used to simulate the microgrid. The black boxes on both sides are voltage amplifiers to supply the voltage to the real DFIG system. The white cabinet on the left side is the control box (containing back-to-back converters) for DFIG, the induction generator is nearby.

The Experiment about the relationship between the microgrid frequency and the DFIG active power output:

The equivalent model of the actual 3kW DFIG in the real-time simulator is a DFIG rated 90MVA, there are other four synchronous machines in the microgrid system, each rated 900MVA. The active power output of DFIG is changed to observe the influence on the frequency of the microgrid, the result is shown in the below figure, the curves from above are the system frequency (in p.u.), bus voltages (in V) and machine currents (in A), respectively.

Fig 3 Waveforms of Experiment I.png

Active power set points of DFIG are given from 1kw to 3kw, and then the set points become smaller till the DFIG is disconnected from the grid (the two glitches are grid-connection and grid-isolated moments). The first curve shows how the frequency of the microgrid changes with the active power of DFIG

Experiment of the asymmetric fault in the microgrid:

The voltages at the point of common connection (PCC) of DFIG become asymmetric due to the asymmetric fault in MG, three phase voltages and currents at the PCC are observed, as shown in below.

Figure 4. Waveforms of Experiment II.png

As shown in the figure, three phase voltages are asymmetric; one of the three phases is smaller than the others, which leads to asymmetric currents. Despite asymmetric voltages and currents, the DFIG still works properly.

Conclusion:

In this project, the smart grid operation and optimization laboratory of Tsinghua University and ModelingTech work together to accomplish the design of power-hardware-in-the-loop simulation system using StarSim and real-time PXI. Two experiments are conducted to verify the feasibility of involving the real DFIG system into the power-hardware-in-the-loop simulation system. This PHIL testing platform forms a good foundation for testing integrating other distributed energy sources into the microgrid.

Kevin.Wang | kevin.wang@modeling-tech.com

Business Development Manager

ModelingTech Energy Technology Co.,Ltd

Copyright © 2013 ModelingTech Energy Technology Co., Ltd

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This application has been published on the journal of Electric Power Systems Research:

Yu Zhou, Jin Lin, Yonghua Song, et al; A power hardware-in-loop based testing bed for auxiliary activepower control of wind power plants, Electric Power Systems Research, 2015(124):10-17.

This is the abstract of this article:

Auxiliary active power control (AAPC) of wind power plants (WPP) has been an emerging subject of modern power systems. However, there is currently lack of appropriate platform to test AAPC performances of an actual WPP. Under the background, this paper presents a testing bed for AAPC in both frequency regulation and damping control of WPP. The main novelty is that the platform is designed based on power hardware-in-loop (PHIL) technologies. PHIL technologies enable a physical WPP to integrate to a virtual real-time power system, which is simulated with StarSim software. The technologies combine the advantages of software and hardware simulations. Based on the testing bed, this paper compares the frequency regulation and damping control performances of an aggregated wind farm integrated to an isolated system. The PHIL simulation results demonstrate the strength of the platform, which extends the flexibility of system configurations of software simulation to an actual physical WPP experiment.

If you would like to know more about this applicaiton or StarSim-based Real-Time Simulation, please feel free to contact us

Kevin Wang

Kevin.Wang@modeling-tech.com

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