Location

This example model can be found in the RTLAB under the category "MMC" example model with the file name "CPU_TSB_acac_2Lvl_withGND.mdl".

Description

This model simulates a back to back two-level voltage source converter (VSC) connecting an ac grid and an induction machine as shown below. The midpoint of dc link is connected to ground in this model.

The VSC is modelled by equivalent circuit method presented in [1] and defined as OPAL model in this demo. A model with detail switches is built in SPS and used as the reference. The subsystem "SM_SPS" contains the SPS model, while the subsystem "SS_OPAL" contains the OPAL model.

The DC link voltage is controlled by the rectifier and variable voltage and variable frequency (VVVF) control is adopted for the motor drive as presented in Control System.

The carrier frequency is 4878 Hz. The simulation time-step of the circuit is 50 us and time-step of the control block is 50 us. 

Simulation and Results

To illustrate the accuracy of the modeling method, the OPAL model (SWF) with 50 µs is compared with the SPS model with 50 µs and 1 µs. The comparison results are presented. The results validate that the OPAL model with 50 µs has matched performance as the SPS detail model with 1 µs.

The CPU usage in real-time simulation is presented as

Control System

Rectifier control system

Inverter control system

References

[1] W. Li and J. Bélanger, "An Equivalent Circuit Method for Modelling and Simulation of Modular Multilevel Converters in Real-Time HIL Test Bench," in IEEE Transactions on Power Delivery, vol. 31, no. 5, pp. 2401-2409, Oct. 2016.

[2] Bose, B. K., Power Electronics and AC Drives, Prentice-Hall, Englewood Cliffs, N.J., 1986.