Abstract
The nine-arm inverter integrates two modular multilevel converters (MMCs) into one compact inverter to diminish the number of power semiconductor devices. It can be used for dual-motor driving or connecting two AC power sources in a multi-terminal high voltage direct current (HVDC) system, etc. Although the half-bridge based modular multilevel converter has the fewest components, it is generally not resistant to the DC-side faults. In order to achieve a DC fault blocking capability with high efficiency and low cost, this paper proposes a hybrid nine-arm high-voltage inverter, which is consists of a full-bridge sub-module (FBSM) and a half-bridge sub-module (HBSM). Firstly, the topology, operation modes, and modulation strategy of the proposed hybrid inverter are presented. Then, by analyzing the potential short-circuit current paths between different ports, the ability of the proposed hybrid inverter to block the DC faults is described and the appropriate ratio of HBSM and FBSM is determined to further reduce the number of devices and the losses of the proposed hybrid inverter. Finally, simulation results based on MATLAB/Simulink are provided to demonstrate the effectiveness and feasibility of the proposed hybrid nine-arm high-voltage inverter under normal operation and DC fault condition.
Highlights
In recent years, the power system is gradually comprising more and more power sources, such as renewable energy sources and energy storage systems
NA-modular multilevel converters (MMCs), a reverse voltage can be generated by the capacitors to block sub-module (FBSM) in the nine-arm multilevel converter (NA-MMC), a reverse voltage can be generated by the full-bridge sub-module (FBSM) capacitors the short-circuit current subsequent to the DC-side fault
The voltage difference between two output ports is 1 = ψ2 =that there are m half-bridge sub-module (HBSM) and n FBSMs in the middle arm, based on Figure 5, the voltage formed by the capacitors in series 1will be h (m + n)U when the fault current flows ifrom a to a, or u
Summary
The power system is gradually comprising more and more power sources, such as renewable energy sources and energy storage systems. Multi-terminal converters have become increasingly attractive, as they can connect multiple distributed power sources instead of using several individual converters [1,2,3,4]. In order to realize further reductions in complexity and capital cost, multi-terminal inverters with a reduced number of power semiconductor devices have been developed for the multi-motor drive systems over the past two decades [7,8]. Among multi-port inverters, a nine-switch inverter is a typical three-port system that can connect one DC supply to two AC loads and has the advantage of saving 25% of the number power semiconductor devices compared to using two independent inverters [9].
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