روش تشخیص جزیره ای شدن مستقل ولتاژ و سوئیچ ولتاژ پایین از طریق یک مبدل PV دو مرحله ای A voltage independent islanding detection method and low voltage ride through of a two stage PV inverter

I. INTRODUCTION Distributed Generation (DG) and microgrids are getting increased attention day by day for their flexible power controlling capability in renewable energy applications. Photovoltaic (PV) is one of the most popular renewable energy sources. A popular approach for integrating PV panels to the grid is to use a two-stage inverter with a front-end boost (DC/DC) converter followed by an inverter [1]. The basic block diagram of such a system is shown in Fig.1. As can be seen, there are two breakers, one on the load side and the other on the utility supply side. In the event of grid nonavailability due to an upstream fault in the power system, it is likely that the utility-side breaker trips under the action of grid-side control. Under such a scenario, the inverter continues to pump power into the local load, resulting in islanding operation [2-3]. Sometimes islanding is desirable, but other times it is not. Islanding can create safety problems for workers and equipments that are not under direct control of the utility. Therefore, islanding condition should be detected, and the inverter should be tripped [4-6]. The inverter side breaker also needs to be opened to isolate the system from the grid. This operating mode of a grid connected inverters is known as anti-islanding. It is clear that in the event of opening of the grid side breaker following a grid outage, the grid-side voltage sensors start sensing the inverter output voltage. Thus inherent detection of islanding condition is not possible by merely monitoring the grid-side sensors, and specific detection mechanisms are necessary. Sensing signal from grid side breaker is difficult as generally grid side breaker is positioned far away and there also can be many breakers in series. Sensing all signals will also increase cost and complexity of the system. Generally, two approaches are adopted for this purpose. They are classified as – passive methods [1-8] and active methods [2- 9]-[17-19].