Fault tolerance of a 10 MW, 100 kV transformerless offshore wind turbine concept with a modular converter system

Abstract

This paper presents the investigation of fault tolerance for a transformer-less generator/converter concept suitable for 10 MW offshore wind turbines. The fault tolerance is necessary to achieve good availability for the turbine, since the accessibility can be sparse for turbines located far offshore. Based on the identified opportunities, changes to the control of the converter and turbine are proposed to exploit the inherent fault tolerance possibilities in the converter system. The transient response to faults, bypass and continued operation of the turbine was investigated through simulations. An estimate of the availability of the turbine with and without fault tolerance is presented. The estimate indicates that the redundancy will be beneficial, despite increased cost.

Operation under fault conditions of the stacked polyphase bridges converter

“…It was verified that with a suitable motor design, when a short-circuit fault occurs at the motor terminals, the short-circuit current is less than the rated current. This motor design allows us to eliminate the breakers that are suggested in [17]. The control method proposed in this paper allows the faulty submodule to be bypassed without any crowbar.…”

“…The former fault type is considered here; the latter will be studied in further research. In [17], a similar converter (for wind-turbine applications) during an unspecified submodule fault is studied. It is recommended that, in order to bypass the fault, a crowbar should be installed across each submodule.…”