Isolated and Bidirectional two-stage DC/AC converter with grid-forming virtual inertia and high ripple on the DC bus for Single-Phase Grid applications

The increasing utilization of electronic converters to interface distributed energy resources (energy storage units and renewable energies) with the grid, has decreased the inertial spinning reserves of the power system. In this context, an isolated and bidirectional two-stage DC-AC converter with grid-forming virtual inertia capability and film capacitor on the DC-Link is presented. The proposed converter allows to interface energy storage units (ESU) with the single-phase grid. The two-stage DC-AC converter is composed of a dual active bridge series resonant (DABSR) DC-DC converter cascaded with a single-phase voltage source inverter (VSI), linked by a film capacitor. In the proposed control strategy, the DABSR controls the DC-Link voltage allowing the power decoupling on the DC-side while the VSI is controlled to emulate a virtual synchronous machine (VSM) when the ESU are connected to the grid. Therefore, the proposed converter has the following advantages: (1) high durability with reduced volume due to film capacitor instead of electrolytic capacitor on the DC-Bus, (2) high efficiency due to ZVS in the DC-DC converter and, (3) virtual inertia provided by VSI controlled as a VSM, increasing inertial energy reserves in the grid. The converter functionality and control strategy are validated by simulation of a 3.3kW system.