Multisampling Method for Single-Phase Grid-Connected Cascaded H-Bridge Inverters

This article proposes a multisampling method for single-phase grid-connected cascaded H-bridge (CHB) multilevel inverters with the phase-shifted carrier pulsewidth modulation in order to reduce the time delay involved in the control loop and increase the control bandwidth. In this method, the controlled variables are sampled not only at the peak and the valley of all triangular carriers, but also at the intersection points of all phase-shifted carriers and inverted ones, which enables a minimum unity sampling interval without detecting the current ripple caused by the switching action and breaking the voltage-second balance in the modulation process. The bandwidth of the current control loop based on the proposed sampling method is illustrated and compared to other traditional sampling methods. The analysis shows that the system effectively reduces the time delay involved in the control loop and improves the bandwidth of the control loop. Finally, a downscale test platform of the single-phase grid-connected CHB multilevel inverter with an inductance (L)-filter is built to verify the effectiveness of the proposed method.