Design of grid connected PWM converters considering topology and PWM methods for low-voltage renewable energy applications

This paper assesses the feasibility three-phase PWM three-level voltage source converters (VSCs), namely NPC-type VSC (3L-NPC) and T-type VSC (3L-T) as alternatives to standard three-phase PWM two-level VSC (2L-VSC) for low-voltage grid interface applications. The topological performances are compared through a design algorithm regarding varying switching frequency, load condition, modulation index, and converter side inductance under distinct pulse-width modulation methods. Design of the LCL filter is also addressed. With the proposed design algorithm, a wide range of power levels (100kW-7MW) can be spanned and in the end the optimum topology and its design details are determined by comparing the return on investment (the pay-off time of total cost of ownership) of each design in the major energy markets.