Reach On Key Issues Of Photovaltaic Grid-tied Generation System

The issue of energy shortage has become the main obstacle restricting the rapid development of today’s society. The development and utilization of renewable and clean energy has played a prominent role in easing the energy shortage and environmental pollution. Solar photovoltaic(PV) power generation which has the virtues of clean, efficient, and easy-to-large-scale application has gained highly attention by the government and research institutions. However, owing to some bottlenecks in technology, the large-scale reliable use of the conventional photovoltaic power generation is restricted.For instance, traditional PV grid-connected inverters adopt the voltage and current double closed-loop PI control method, yet the inherent control path coupling problem seriously affecting the quality of the inverter output current waveform, increasing the total harmonic distortion(THD) of the network current. The photovoltaic system employing non-isolated structure with no transformer has caused some problems such as the DC bias current(DCI), ground fault current injection(GFCI, also called leakage current), leading to further deterioration of power quality.As a result, this paper focuses on the three-phase PV grid-connected inverter control strategy, experiments are also conducted. The research mainly includes the following contents. First, this study introduces the topology of the PV power generation system that applied and the maximum power tracking(MPPT) technology. Second, based on the analysis of space vector pulse width modulation(SVPWM) algorithm and voltage and current double closed-loop PI control method, a new multi-internal model control(MIMC) strategy is proposed in order to achieve the decoupling and performance optimization. And, a detailed analysis of the anti-islanding protection, the DC bias current and leakage current is presented, and the corresponding improvements are advanced. Third, experimental prototype of20kW three-phase grid-connected PV system was established, which is used to testify the effectiveness of the proposed methods.