Unipolar Spwm Control Sine Wave Inverter

Based on the power supply for railway signal system, this dissertation investigates an inverter controlled by the strategy of unipolar modulation. The very power supply consists of three stages, which are respectively the circuit of PFC, full-bridge phase-shifted DC/DC circuit and unipolar inverter. The first stage, PFC, can increase the power factor of front end and simultaneously reduce the harmonic pollution brought by the power supply. Moreover, the steady DC voltage is obtained in this very stage. The second stage, isolated DC/DC, separates the DC input from the DC output. The last stage is an inverter, whose outputs are desired AC voltages.This dissertation analyzes the respective operation principle of the bipolar and unipolar SPWM inverters. Furthermore, two generation schemes of SPWM for the later modulation type and their respective control technique are introduced, and detailed analysis is followed. Both simulation and experiment are implemented. The circumstance of oscillation occurring at their zero cross point of sine wave for the two control technique is definitely compared. Finally, both the simulation and experimental results are given to verify the concept presented in this dissertation, i.e. dual-side SPWM generation scheme is more preferable.Moreover, this dissertation analyzes waveform distortion provided that load of the inverter is inductive and design consideration of circuit for suppressing magnetic deflection is presented. According to requirement of the product and consideration of the application of saturable inductor, the suppression function of diode reverse recovery current existing in PFC stage is emphasized.