A modified switching scheme for a new multi level inverter topology for fuel-cell microgrid

Recently the use of multilevel inverters (MLIs) in modern drives and for interfacing the renewable generation systems to grid have given wide scope for designing new topologies of MLIs. Fuel cell generation systems are expected to see practical usage due to several advantages over conventional generation systems. This paper introduces a new switching scheme for a new topology of MLI with reduced number of switches for interfacing Fuel-cell with the grid. The unipolar pulse width modulation (PWM) technique is used for the switching of H-bridge switches, while for the outer switches sinusoidal modulating wave is compared with DC component. With this modified switching scheme the Total Harmonic Distortion (THD) in the output voltage of MLI decreased. It is also observed from the simulation results that the THD of output voltage of 21-level MLI is within limits as specified by IEEE 519 standard. A comparative analysis of proposed switching scheme with the reported switching scheme is carried out for the seven and thirteen levels of new topology in terms of the THD in the output voltages. Moreover, a comparison of new topology with conventional reported MLI topologies is also made in terms of the number of switches and required DC sources for different levels. It is also observed from simulation results that during the integration of the Fuel-cell with the grid, the grid requirements such as phase angle, frequency and amplitude of grid voltage are also satisfied.