Research on Control Strategy of AC-DC-AC Substation Based on Modular Multilevel Converter

Table 1

Comparison of the circuit topology of advanced cophase power supply device.

Topology type	Diode clamped cascaded AC-DC-AC topology; (ABB)	MMDC circuit topology; (Siemens)	H-bridge cascaded multiple AC-DC-AC topology; (Japan Toshiba)	MMC AC-DC-AC topology; (studied in this paper)
Input/output decoupling performance	Excellent	Good	Excellent	Excellent
Input/output transformer	Special single-phase input/output transformer, complex structure and large quantity	Normal three-phase input transformer, no need single-phase output transformer	Special single-phase input/output transformer, complex structure and large quantity	Normal three-phase input transformer, no need single-phase output transformer
Input/output filter	Need	No need	Need	No need
Converter efficiency (excluding transformers)	About 95%	≥99%	About 96%	≥98%
Area covered	Larger	Larger	Large	Larger
Manufacturing cost	Higher	Higher	High	Higher