Three level voltage inverter using synchronized SVPWM and DSP

Abstract

Three level inverters have certain advantages over the two level inverters and hence they find applications especially in medium voltage high power applications. Three level inverters can synthesize double the voltage levels using the devices of similar voltage rating. Hence, the power handling capacity can be doubled. For a given switching frequency, three level voltage can have double the bandwidth. Three level inverters have improved total harmonic distortion (THD) compared to two level inverters. In high power inverters the switching frequency is limited to low values in order to reduce the switching power losses. In the field of high performance applications, the three-level inverter is the most promising alternative. In this work a simplified space-vector PWM method for three-level inverter is proposed and described in detail. The proposed SVPWM method has the following features. The switching sequence is determined without a look-up table, so the memory of the controller can be saved. The dwelling times of voltage vectors are calculated in the same manner as two-level inverter SVPWM. Thus the proposed method reduces the excution time of three-level SVPWM. The theory of space vector based synchronized PWM method with half-wave symmetry and three phase symmetry for three-level VSI is explained. The proposed algorithm is implemented using TMS320F2812 DSP processor. The experimental results are also presented. The experimental wave-forms show HWS and TPS for any integer value of number of samples per sector. The absence of triplen harmonics from the line voltage shows that the inverter output voltages have three-phase symmetry. The theory about TMS320F2812 DSP processor is also presented.