Abstract
A three-phase multi-level multi-input power converter topology is presented for grid-connected applications. It encompasses a three-phase transformer that is operated on the primary side in an open-end winding configuration. Thus, the primary winding is supplied on one side by a three-phase N-level neutral point clamped inverter and, on the other side, by an auxiliary two-level inverter. A key feature of the proposed approach is that the N-level inverter is able to perform independent management of N − 1 input power sources, thus avoiding the need for additional dc/dc power converters in hybrid multi-source systems. Moreover, it can manage an energy storage system connected to the dc-bus of the two-level inverter. The N-level inverter operates at a low switching frequency and can be equipped with very low on-state voltage drop Insulated-Gate Bipolar Transistor (IGBT) devices, while the auxiliary inverter is instead operated at low voltage according to a conventional high-frequency two-level Pulse Width Modulation (PWM) technique and can be equipped with very low on-state resistance Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices. Simulations and experimental results confirm the effectiveness of the proposed approach and its good performance in terms of grid current harmonic content and overall efficiency.
Highlights
The number of electricity generators powered by renewable energy sources (RESs) is continuously increasing because of concerns about environmental pollution and the limited reserves of fossil energy sources such as oil, coal, and gas [1]
Hybrid renewable energy systems (HRESs) combining more than one energy source are a viable solution to this problem [5] because they are effective in enhancing the reliability of power supply and in reducing the size of energy storage systems [6,7]
The effectiveness of the proposed topology was first evaluated through a simulation, taking into account a scaled model of a hybrid renewable energy generator tailored around an open-end winding 5 kVA-230/400 V three-phase transformer, a three-level neutral point clamped (NPC) inverter exploiting a 1 kHz SVM strategy with a 400 V dc-bus voltage, a two-level inverter (TLI) Pulse Width Modulation (PWM) operating at 10 kHz, and a three-phase grid
Summary
The number of electricity generators powered by renewable energy sources (RESs) is continuously increasing because of concerns about environmental pollution and the limited reserves of fossil energy sources such as oil, coal, and gas [1]. Grid-connected photovoltaic (PV) and wind turbine (WT) generators are the most widely diffused types of RES power plants and their specific cost is continuously decreasing [2,3,4]. A power plant relying only on a single form of RES and without an energy storage capability can hardly cope with the requirements for a reliable electric power generation unit. Hybrid renewable energy systems (HRESs) combining more than one energy source are a viable solution to this problem [5] because they are effective in enhancing the reliability of power supply and in reducing the size of energy storage systems [6,7]. In HRESs, a specific dc–dc power converter is normally used to manage each input power source, leading to a quite complex and expensive structure [8,9]
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