Step-Current-Approximation Modulation of Multilevel-CSC With Near-Power-Frequency Switching for High-Current Variable-Voltage Application

High-current variable-voltage rectifiers with continuously adjustable output are widely applied in industrial manufacturing, such as electrolysis, electrowinning, and dc arc furnaces. Multilevel current-source converter (MCSC) is a potentially feasible solution in these scenarios. In this article, a step-current-approximation modulation (SCAM) for MCSC is proposed. First, the topological constraint of the current-source converter is analyzed to obtain the feasible stepping-current approximation method, which is further optimized based on the gradient of reference current. Moreover, the current balancing algorithm is designed to achieve the dc current balance between modules with the least additional switching behavior. The proposed SCAM and traditional SPWM are compared by simulation, which indicates that SCAM reduces the switching frequency to less than 1/3 of SPWM and realizes the near-power-frequency switching. Finally, the feasibility of SCAM is verified in the hardware-in-the-loop experiment platform. The proposed SCAM is expected to bring the reverse-blocking devices with low
on
-state voltage into the application of MCSC. Therefore, the conversion efficiency will be greatly improved, meeting the energy conversion requirements of large-scale industrial manufacturing.