Model-based cascade control of three-level STATCOM with a tuned LCL-filter

This paper studies model-based cascade control of three-level STATCOM operating with low switching frequency. Due to low switching frequency it is difficult to achieve desired damping of switching current harmonics with a typical LCL-filter structure. Therefore a tuned LC-sink is included in the filter shunt branch to achieve better damping of the switching harmonics. The current control is implemented in the synchronous dq frame using model-based cascade control. For the control design, a discrete closed-loop model of the system is derived. The performance of the control method is demonstrated with hardware-in-the-loop tests. The results show that the control method studied provides fast response time and good output current waveform.