Fault-Tolerant Control for a Modular Generator–Converter Scheme for Direct-Drive Wind Turbines

Abstract

Abstract-A modular power electronic converter, with a cascaded H-bridge multilevel inverter, has been proposed as the grid interface for a large direct drive wind turbine generator. The present study is to investigate the potential and requirement of fault tolerant operation in such a system. As each module is connected to isolated generator coils, tolerance to a module or coil fault is possible if the affected module can be bypassed while the control of the healthy modules can be adjusted accordingly. A boost rectifier scheme on the machine side of the power conversion stage has been developed for this purpose, featuring control of the coil current without measuring the EMF. A coordinated DC-link voltage controller has been developed which can rapidly raise the DC-link voltage of the remaining modules to compensate for the loss of a module, while ignoring the ripple in the DC-link due to low-frequency inverter switching. The ability of the resultant system to tolerate module faults has been demonstrated on a small scale laboratory prototype.

Grid fault ride-through of an LCC-VSC tandem converter, used as a grid interface for a multi-MW wind turbine.

“…A proportional controller is used to regulate the current on a phase by phase basis, and mainly operates during thyristor commutation and transient changes in current demand. A similar system has successfully been used in an active rectifier scheme, in which similar discontinuities occur around the current zero crossings [15].…”

“…While the conventional 3-level NPC converter was considered adequate for the application, and is proposed by GE for their generator design [12], the tandem converter design shown in Figure 1 was found to have several advantages. As well as potential cost and efficiency benefits, the use of a cascaded multilevel VSC and multiple series thyristors allows for tolerance of switching device faults [14,15], reducing the chances of a generator short circuit and improving reliability compared with the NPC converter. The tolerance of device faults could also be achieved using a modular multilevel converter (MMC) [16], but the low generator frequency means that the DC-link capacitance requirement is high.…”

Model prediction-based approach to fault-tolerant control with applications

“…In most practical applications of interest, the process and/or measurement dynamic models are described by non-linear equations, represented in system (1). This means that the nonlinear behavior can affect the process operation at least through its own process dynamics or measurement equation.…”

“…Because of the poor health of the system, the operation continues certainly at a reduced level, rather than failing completely. Moreover, the performance is proportional to the severity of the failure, as compared to a conventionally-designed system Area of tank i γ 1 QTS: tank 1 and tank 4 water diverting ration γ 2 QTS: tank 2 and tank 3 water diverting ration k 1 Gain of Pump 1 in QTS k 2 Gain Heat capacity ρ Fluid density in reactor f (. ), g (.…”

“…The problem of fault tolerance is of extreme importance when it comes to mission critical systems and life-critical systems and several approaches have been adopted to implement a reliable fault tolerant control scheme. Result on FTC for a direct-drive wind turbines and five-phase permanent-magnet motors are reported in [1] and [2], respectively. A scheme for optimal torque FTC is proposed in [3].…”