| Due to its small volume,light weight and high realibility,the wide-range variable frequency ac power system has become the major developing trend of the areo power supply system,and it has been already successfully applied in large-scale civil aircraft such as Boeing 787 and Airbus 380.However,there is a considerable part of airborne electric equipments that cannot be directly fed by variable frequency ac power,and plenty of power electric converters are demanded to match loads with power sources.Superior to traditional back-to-back converters,the two-stage matrix converter(TSMC)is free of electrolytical capacitors,and has tight construction,high I/O performance and the capability of bidirectional power flow.Besides,the TSMC has simpler commutation and feasibility of zero current switching of its rectifier-stage,in comparison with the conventional single-stage matrix converter.The TSMC will be a promising alternative application for aero converters in the variable frequency power system.The TSMC could help to reduce the volume and weight of electric facilities,improve the power density and effieciency,thus lowering maintenance cost for aircrafts.Therefore,the research of the application techniques of the TSMC in the aero power system is of important value.The main content of this thesis is centered on the operation characteristics and control strategies of the TSMC fed by wide-range variable frequency AC power.The research is directed by theorectical analysis,and is carried on via both computer simulation and hardware experiments.The correctness of theoretical derivation results and validity of the proposed modulation methods and control strategies are all verified in this thesis.The topology and basic operation principles of the TSMC are introduced.And the parameterdesigning criterions of the TSMC's input LC filter,particularly for the input condition of the wide-range variable frequency ac power system,are concluded: according to TSMC's operation characterics and its rated active and inactive power,the power range,which should be taken into consideration during filter-designing progess,is determinted;then the worst operation conditions for relevant requirements are found out,and a filter which satisfies the specifications under the worst status will satisfy them under any other status.The designed filter is verified by simulation.The conventional modulation of the TSMC is reconsidered for the wide-range variable frequency power system.In this application,the carrier frequency ratio is quite low,and the output voltage and input current will be distorted obviously if the TSMC is asymmetrically modulated.In aim to precisely explain the influence of asymmetric modulation upon waveform distortion,a novel concept,“pulse orthocenter”(PO),is proposed to describe the distribution pattern of an arbitrary pulse train.And the “PO theory” is then derivated that,the equivalent value of a pulse train differs from the average value per period by the differential of the product of the average value per period and the pulse orthocenter.Based on the PO theory,the spectra of TSMC's output voltages and input currents are then analyzed,indicating that asymmetric modulation causes 3n?in±(3m±1)?o harmonics in the output voltages and(3n±1)?in harmonics in the input currents,where ?in and ?o are input and output frequency respectively.On the basis of spectra analysis results,a duty ratio correction(DRC)algorithm is proposed to improve the waveform quality of the TSMC's output voltage and input current without increasing switching loss.The DRC formula are provided and the available range of related parameters discussed.The correctness of distortion analysis is testified via simulation and experiments,and the validity and feasibility of the DRC algorithm is verified via experiments.Despite of its effectiveness,the DRC algorithm is only an open-loop compensation,not capable to system parametes variation.Hence,a dual-loop control structure in synchronous rotating frame(SRF)system is proposed to regulate the output voltage of the TSMC.The controller is based on PI controller and self-tuning resonant controller(STRC).The DC components of the output voltage in SRF is controlled by PI controller,and the 3n?in±(3m±1)?o harmonics are suppressed by STRC.At the same time,a novel asymmetric modulation strategy for the rectifier stage is also proposed to improve the input-side performance of the TSMC.The stability problem of the TSMC is studied when it is connected with an LC filter on output-side and closed-loop controlled for its output voltage.In order to improve the stability,the drawbacks of the published active damping methods are analyzed,and a novel active damping method based on the feedforward of voltage derivative is proposed.The simulation and experimental results verified the vadility and feasibility.In the final,the developing scheme of the experimental platform of the TSMC-based power conversion utility is denmonstrated,and the flow diagram of control softwares is displayed.Last but not least,a multi-step protection strategy for the TSMC is proposed to safely shut down the platform in emergency.Using this method,the clamp circuit turns to be unnecessary,and the hardware circuits becomes conciser.In all the carried experiments,the proposed protection strategy is proved applicable and effective. |
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