Research On High Availibility Long Lifetime Parallel Converter For Wind Power Application

As environmental pollution and energy shortages become progressively serious, windenergy, as a clean energy, has been fully developed and widely used in recent years, windpower technology has been had a great development worldwide. Because of landresources, the availability of on-shore wind energy is limited, and due to nonrestraint ofnoise, Effect of wind shadow, space, and abundant wind resources on the sea, offshorewind power will make rapid development. However, due to the large offshore wind powercapacity, harsh environment, difficulties in the maintenance of wind turbines have putforward higher requirements for reliability. The full-scale power of the wind turbine withSCIG (Squirrel Cage Induction Generator) is research foundation of this paper. This isaccording to the high reliability and strong robustness of the squirrel-cage induction motor.Furthermore full-scale power converter decouples electrical grid and generator, to acertain extent, decouples mechanical transmission part and the grid, this will help toimprove the mechanical parts’ reliability. Based on this kind of wind turbine,reliability-oriented of wind power converter topology, modulation and control strategiesare proposed in this paper. Here are the main works:1) With reliability evaluation method based on physical failure mechanism of powersemiconductors, for wind’s stochastic and fluctuation, analysis and evaluate the reliabilityof wind power converter. It provides a theoretical basis for the study of the reliability ofwind power converter.2) High availability-based design, System-level parallel wind power convertertopology is proposed, so is reliability assessment of the topology, Combined with theeconomic optimization, N+X parallel design method is presented. For this type ofcomplex large-scale parallel power electronic devices, this paper proposes a kind ofhighly reliable distributed control system. This paper research on parallel inverters’ faultdiagnosis, location, isolation, reconstruction; study on power-limitation control strategy of wind turbine to achieve wind power converters N-1operation after fault isolation.3) From the average junction temperature of the device to reduce the power convertercan extend the life of the reliability mechanism, the interleaved modulation with DPWMis put forward to minize the power switching loss, thereby reducing its average junctiontemperature and improve reliability of converter. This paper has analyzed the highharmonic distortion and high zero-sequence circulating current problems, for this issues,optimization modulation and control strategies are propoed, thus ensuring the performanceof wind power converter, the reliability of the converter power increases substantially.4) Two kinds of thermal control strategies based on reactive circulating current andorthogonal circulating current are proposed, two kinds of state control method based onthe thermal control strategies are studied. Firstly, from the reliability mechanisms thatsmoothing power device’s junction temperature fluctuations can extend the life ofconverter, smoothing fluctuations in the junction temperature based on circulation thermalcontrol technology is proposed. Secondly, The method that slowing down the rate ofdecline of the junction temperature by thermal control technology based on circulatingcurrent is presented to prevent condensation phenomena, thereby reducing the failure rateof the converter, the converter also enhanced the its reliability.The control strategies and modulation methods proposed in this paper are verified bytheoretical analysis, mathematical modeling, simulations and experiments.