| As the application of power electronic converters becomes more and more critical,people’s requirements for their reliable operation are getting higher and higher.Capacitor is one of the most age-affected components in converters,and the characteristic parameter C or ESR reflects it’s healthy condition.By estimating C or ESR online,it’s possible to know the aging process of capacitor in real time,and then replace the failed one in time,which is of great significance for improving the reliability of converters.In this paper,a AEC-used Boost PFC converter is taken as the research object,and two online estimation methods for it’s output capacitor’C and ESR are proposed.The main contents are as follows:1 Based on the traditional signal-injection method,this paper proposes an online C and ESR estimation method using power balance and capacitor’s frequency characteristics.First,a harmonic current is injected at the input side of the Boost PFC converter to generate corresponding harmonic components on the output side.Then,using power balance and fast Fourier transform(FFT)algorithm to extract the harmonic components in capacitor current and output voltage respectively,and further deriving the calculation model of C and ESR with the frequency characteristics of capacitor.Besides,the amplitude and frequency of the injected harmonic current is determined.Finally,a scheme of the online estimation is given,and a simulation model is built.The impacts of three variable factors on the accuracy of estimation results are discussed,which include the input voltage,the load resistor and the capacitor with different Cs and ESRs,and the estimation accuracy is less than 10%.In this method,only the output voltage needs to be sampled,and no addition hardware circuit is used.2 An online ESR estimation method based on time-frequency analysis is proposed.In Boost PFC converter,ESR causes a small jump in the output voltage at switching moments,especially at turn-off moments.The jump is hardly observed either using traditional time-domain analysis or frequency-domain analysis,because the double line-frequency component contained in the output voltage is larger than the switching ripple.However,the small jump is very prominent in time-frequency analysis due to its singularity.In this,the wavelet transform(WT)is used to analyze the small jump contained in the output voltage.First,the operating characteristics of Boost PFC converter are analyzed,and the relationship between ESR and the jump amount of output voltage at turn-off moments is derived.Then,transforming the output voltage into time-frequency domain to derive the WT-based ESR calculation model.Moreover,an appropriate sampling interval for the output voltage and the inductor current is determined.Finally,a scheme of the online estimation is given,and an experimental platform is built.The impacts of four variable factors on the accuracy of estimation results are discussed,which include the capacitor with different ESRs,the inductor,the MOSFET and the load resistor,and the estimation accuracy is less than 10%. |
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