Cascaded H-Bridge Converter Based on Current-Source Inverter with DC Links Magnetically Coupled to Reduce the DC Inductors Value

The main drawback of the Cascaded-H Bridge converter based on three-phase/single-phase current-source inverters is the large DC inductors needed to limit the variation of the DC current caused by the single-phase inverter oscillating power. If the oscillating power is somehow compensated, then the DC inductor can be designed just as a function of the semiconductors’ switching frequency, reducing its value. This work explores the use of three-phase/single-phase cells magnetically coupled through their DC links to compensate for the oscillating power among them and, therefore, reduce the DC inductor value. At the same time, front ends controlled by a non-linear control strategy equalize the DC currents among coupled cells to avoid saturating the magnetic core. The effectiveness of the proposal is demonstrated using mathematical analysis and corroborated by computational simulation for a 110 kVA load per phase and experimental tests in a 2 kVA laboratory prototype. The outcomes show that for the tested cases, coupling the DC links by a 1:1 ratio transformer allows reducing the DC inductor value below 20% of the original DC inductor required. The above leads to reducing by 50% the amount of magnetic energy required in the DC link compared to the original topology without oscillating power compensation, keeping the quality of the cell input currents and the load voltage.

Multivariable Model Predictive Control for a Virtual Synchronous Generation-Based Current Source Inverter

Three-phase current-source inverters are an alternative solution for interfacing photovoltaic modules to the utility thanks to its voltage boosting ability. This paper presents a virtual synchronous generator strategy for a three-phase current-source inverter using a multivariable model predictive control. The proposed method can ensure operations in both grid-connected and islanded modes while achieving virtual inertia features to stabilize the grid frequency and active damping to reduce grid current distortions caused by an output CL filter included on the grid side of the system. The obtained simulation results in the PSCAD/EMTDC environment software verify the effectiveness and the excellent performance of the proposed method.