The star-switched MMC (SSMMC) - a hybrid VSC for HVDC applications

Abstract

This paper presents a new hybrid VSC topology (the StarSwitched MMC) -suitable for HVDC applications. The basic structure and operating principles of the topology are described. Control strategies that regulate the power exchanged between the VSC, the AC network and the DC network are presented. A modulation strategy ensuring appropriate switching of the individual chain-link submodules and a capacitor voltage balancing algorithm that ensures the capacitor voltages are maintained within the required tolerance are discussed. Results from a simulation model are presented to validate the expected performance of the converter and the proposed control schemes.

Experimental verification of bidirectional modular multilevel cascaded converter suitable for applying 120‐degree discontinuous pulse width modulation maximum

“…There are also proposals of two-phase modulation (DPWM: discontinuous PWM) MMCC also using high-voltage switching elements. [13][14][15] Such MMCC configuration is illustrated in Figure 2. Here, cell modules in the upper arm of DSCC are replaced with high-voltage switching elements so that the number of cells is halved without changing cell capacitor voltage.…”

“…However, a very strong surge occurs due to magnetic energy of the buffer reactor L B to destroy IGBT. This is the reason why the previous studies 13,14 verified only AC-DC conversion that does not require HV-IGBT to shut off current. Thus, in reference 15, we demonstrated via simulations that bidirectional conversion is possible when snubber capacitors C P are connected in parallel to HV-IGBT, and verified operation using a mini-model of reactive power input/output.…”