Nowadays, more and more distributed generations and renewable energy sources, such as wind, solar and tidal power, are connected to the public grid by the means of power inverters. They often form microgrids before being connected to the public grid. Due to the availability of high current power electronic devices, it is inevitable to use several inverters in parallel for highpower and/or low-cost applications. So, inverters should beconnected in parallel to provide system redundancy and high reliability, which are important for critical customers. In this paper, the modeling, designing and stability analysis of parallel-connected three-phaseinverters are derived for application in renewable energy systems. To enlarge voltage adjustability, the proposed inverter employs an improved switched inductor Z-source impedance network to couple the main circuit and the power source. Compared with the classical Z-source inverter (ZSI) and switched inductor Z-source inverter (SL-ZSI), the proposed inverter significantly increases the voltage boost inversion ability and also can increase the power capacity and the reliability of inverter systems. The proposed topology and its performances are validated using simulation results which are obtained in Matlab/Simulink.
Keyword:
Modulation index
Corresponding Author:Ali Zakerian, Departement of Electrical and Computer Engineering, Urmia University, Urmia, Iran. Email: zakerian.alii@gmail.com
INTRODUCTIONIn some renewable energy utilization applications, the input power source is a DC voltage source which has a wide voltage variation range, such as the grid-tied photovoltaic generation and fuel cell generation. In these cases, an inverter with boost capability is required to generate electricity at low input DC voltage. Different inverter topologies meeting the requirement can be found and classified into two categories: the isolated inverters and non-isolated inverters. The isolated inverters are usually equipped with a step-up transformer which makes the system bulky and low efficiency while the non-isolated inverter is considered high efficiency and high power density [1]. There are typically two popular non-isolated topology candidates for these applications. One is the traditional two-stage boost-buck inverter (BBI), and the other one is the newly proposed Z-source inverter (ZSI) [2].The ZSI presents a new single-stage structure to achieve the voltage boost/buck character in a single power conversion stage, which has been reported in applications to renewable energysystems. The ZSI has gained popularity as a single-stage buck-boost inverter topology among many researchers. However, its boosting capability could be limited and therefore it may not be suitable for some applications requiring very high boost demanding of cascading other dc-dc boost converters. This could lose the efficiency and demand more sensing for controlling the added new stages.