| A car inverter is a device that can convert a battery voltage into a conventional household AC voltage allowing us to use electronic devices such as portable notebook, charger for cells phone and refrigerator when an AC voltage is not available. The common inverter on the consumer market today is the type of modified sine wave. It is suitable for most electronic loads except for the inductance loads like devices with motor, which confines its application occasion. Pure sine wave inverters produce AC voltage with low total harmonic distortion. It can be used when there is a need for clean sinusoidal output which remedies the defects of modified sine wave inverters. Many commercially manufactured models use the same basic two-stage concept: Push-Pull step-up converter with a high frequency transformer and full-bridge SPWM inverter configuration. Due to the high input current ripple, hard switching conditions of switches and serious recovery problem of the diode in Push-Pull converter, it is hard to achieve high efficiency and high reliability.To solve these problems, this dissertation has a review of low input voltage high step-up DC/DC converters, and a input-parallel output-series active clamped Flyback-Forward high step-up converter and a full-bridge SPWM inverter configuration is adopted to fulfill high efficiency high step-up high power density power conversion. The operation principle and performance of the step-up converter is analyzed, and detailed design guidelines are presented in section 3. The influence of current sharing performance of the converter due to the parameter differences is analyzed by simulation. As the converter has the ability of auto current sharing, it can work properly if the difference of duty cycle is limited in a certain extent.To obtain good performance under steady and dynamic situation, the small signal model of DC/DC converter is deduced, and the output voltage outer-loop and input current inner-loop control method is adopted in the DC/DC converter. Further more, the DC bus feed-forward control is employed in the full-bridge SPWM inverter. To ensure the system work in safe region, accordance protect circuit is designed, such as input under/over-voltage protection, overload protection, the DC bus over-voltage protection and thermal protection. Besides, the loss of the system is analyzed to provide the basis for the heat sink design and system optimization. Finally a 12V-input 220V-50Hz 500VA output prototype is built and tested to demonstrate that the inverter has high efficiency, smart size and low noise compared to conventional inverter. |
