Modularized Bidirectional Grid-Connected Inverter With Constant-Frequency Asynchronous Sigma-Delta Modulation

The objective of this paper is to propose a modularized bidirectional single-phase grid-connected inverter (BGI) with constant-frequency asynchronous sigma-delta modulation (CF-ASDM) control for the renewable energy (RE)-supplied dc power system. The proposed BGI can be operated either in the inverter mode (IM) or rectified mode (RM); both are necessary features for the RE-supplied dc power system. By comparing to the conventional ASDM with variable switching frequency, the proposed CF-ASDM can simplify the filter design and can reduce the computational burden of the digital signal processor while maintaining the merit of quick dynamic response. Moreover, the proposed BGI has a redundant central controller which can increase the system reliability. The major contribution of this paper includes developing the modularized BGI with CF-ASDM control scheme for IM and RM operations thoroughly and applying it to the RE-supplied dc power system successfully. In this paper, the mathematical equations to achieve the constant switching frequency operation for the CF-ASDM will be derived. Computer simulations and hardware experiments are shown to verify the performance of the proposed modularized BGI with CF-ASDM control.