Dr. Espinosa-Neira, Eduardo

Small grid-connected inverters are not friendly to the electrical grid, in the sense they do not take any action to support the grid when contingency events occur. For example, because of their relatively low power capacity, small grid-connected inverters are not designed to provide dynamic frequency support to the grid. On the other hand, it is well known that microgrids and weak grids including distributed generation would benefit significantly if all of the grid-connected converters could support and help against grid frequency disturbances. Within the family of small grid-connected converters, single-phase quasi-Z-source inverters (QZSI) have become an attractive topology, because they represent a reliable and economical alternative, and can be very efficient in applications that demand small or medium powers. However, a major disadvantage is that the control strategy must manage both direct current and alternating current variables through the same group of switches. The latter is a challenging task when implementing predictive control schemes. This paper proposes a finite control set model predictive control (FCS-MPC) strategy for a single- phase grid-supporting QZSI. The proposed predictive scheme can be easily integrated with a complementary control block to provide grid frequency support. Experimental results show evidence of the inverter operating under the proposed control strategy and providing grid frequency support, which demonstrates the feasibility of the proposal

Cascaded H-bridge drives require using a significant-size capacitor on each cell to deal with the oscillatory power generated by the H-bridge inverter in the DC-link. This results in a bulky cell with reduced reliability due to the circulating second harmonic current through the DC-link capacitors. In this article, a control strategy based on a finite control set model predictive control and a proportional-resonant controller is proposed to compensate for the oscillatory power required by the H-bridge inverter through the cell’s input rectifier. With the proposed strategy, a DC-link second harmonic free operation is achieved, allowing for the possibility of reducing the capacitor size and, in consequence, the cell dimensions. The feasibility of the proposed control scheme is verified by experimental results in one cell of a cascade H-bridge inverter achieving an operation with a capacitance 141 times smaller than required by conventional control approaches for the same voltage ripple.