Analysis and Parameter Design of LCL-Based Parallel T-type Inverters

For medium and high power applications, parallel converters are commonly utilized to boost the power capacity of system. Meanwhile, interleaved operation of pulse width modulation (PWM) is a common and effective method to increase the number of output levels and reduce current ripples. Nevertheless, due to asynchronous switching operation, the problem of circulating current inevitably emerges. To suppress circulating current, this paper aims to analyze the principle of circulating current generation and design the parameters of the inductors for suppression. A 100kW grid-connected system with two T-type inverters parallel connected is built, applying phase opposition disposition (POD) modulation for decreasing circulating current. The LCL filter is designed to achieve low harmonics. Simulation validations are provided to prove the feasibility of the analysis and design.