DSP based PWM control of Switched Boost Inverter for DC nanogrid applications

Switched Boost Inverter (SBI) is a buck-boost type dc to ac converter derived from Inverse Watkins Johnson (IWJ) Topology. This converter can supply both DC and AC loads simultaneously which makes it suitable for DC nanogrid applications. In order to invoke the boost operation, the SBI utilizes shoot-through state of the inverter bridge. So, the traditional Pulse Width Modulation (PWM) techniques of Voltage Source Inverter (VSI) have to be modified to incorporate the shoot-through interval in each switching cycle, so that they are suitable for SBI. This paper presents a PWM control strategy developed for SBI, and describes its implementation in digital domain using the enhanced PWM (ePWM) modules of TMS320F28335 Digital Signal Processor (DSP). This paper also presents a soft start method of SBI to limit the inrush current at the start-up. The PWM signals generated by the DSP are used to control a laboratory prototype of SBI supplying both DC and AC loads. The steady state and start-up waveforms of the converter are presented for verification of the DSP based PWM control technique and the soft-start method described in the paper. The experimental results show good correlation with the theoretical analysis given in the paper.