| The invisibility and non-controllability of the distributed renewable energy generation system have brought great challenge to the reliable operation of distribution network.While the unique network form of microgrids can solve the above problem effectively.As the mainstream of micro-grid,the AC microgrids can be divided into low frequency micro-grid?The frequency of the bus voltage is 50/60Hz.?and high frequency microgrids?The frequency range of the bus voltage is from500Hz to 1kHz.?.Compared with the former,the high frequency AC?HFAC?microgrids can effectively reduce the size and weight of the filter elements in the interfacing converter,improve the energy density and power quality of the system,decrease the audible noise of equipments and cut down the current harmonic of some particular loads?such as fluorescent lamp,high-frequency induction motor and etc.?to improve the operating efficiency.Therefore,in recent years,there has been a resurgence of interest in the HFAC microgrids among researchers.The HFAC microgrids are the small power distribution system,which is mainly composed of distributed power,energy storage devices,energy conversion devices?They are mainly DC/DC converters and inverters.?,relevant load and monitoring,protector.The inverters are the key devices,which can make the renewable energy access into the HFAC microgrids.They must meet the performance requirements of high integration and high gain.Accordingly,a novel single-stage Buck-Boost integrated step-up inverter was proposed in this issue,which integrates two Buck-Boost dc converters with the voltage-type full-bridge inverter by sharing the body diodes of the lower bridge arm(DS1,DS2)and the upper bridge arm?S2,S4?of the full bridge inverter.The inverter proposed in this issue can realize the functions of boosing and inverting with single stage which reduces the cost and improves the integration.It is more suitable for the application of HFAC microgrids with the advantages of using less components,simple structure and high integrationcomparedwithotherones.Basedonthe unipolar-frequency-doubling?UFD?SPWM modulation and hybrid SPWM modulation,the operating principle,the steady characteristics and the small signal model and closed-loop control of the proposed inverter are analyzed in detail.And then,the parameters of a 500W prototype was designed and achieved.At last,the correctness of the theoretical analysis is verified by simulation and experiment.The simulation and experimental results demonstrate that two modulation approaches can both boost DC link voltage and achieve sinusoidal output voltage.But under different control schemes,there are some differences in the performances of the boosting inductor current ripple,the output-voltage harmonic and the electric stress.Compared with the hybrid SPWM modulation,The UFD-SPWM modulation has the advantages of low output voltage THD,easy control method,good rapidity,besides,there is higher 2nd harmonic ripple of the boosting inductor current and the value of the boosting inductor current is also higher.In addition,for low input voltage applications,the voltage stress of power devices is relatively small under UFD-SPWM modulation. |
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