Studies On Solar Photovoltaic Grid-connected Inverter And Islanding Detection Technology

As the energy crisis and the pollution are serious, the exploitation of renewable and green energy sources has received more and more attention. Solar energy has been paid a lot of attention in many countries, because it’s inexhaustible and clean. With the technological progress of photovoltaic (PV) cell and power electronics, PV generation has become not only an important supplement of current energy consumption, but also the potential main energy source in the future. The solar energy is transformed to electric energy, and the electric energy is fed to the grid by the grid-connected PV system, which is the most common form of the exploitation of solar energy.This paper focuses on the control strategies in grid-connected PV systems, which includes modeling of grid-connected PV systems, maximum power point tracking (MPPT) methods for PV arrays, integration of reactive power compensation function and islanding detection methods in PV systems. Through analyzing the I-V characteristic of PV cells, its output power is nonlinear and is influenced by the solar radiation and environment temperature. In order to transforming the solar energy into electric energy with greatest efficiency, the maximum power point tracking should be adopted. Anti-islanding protection is mandatory feature for grid-connected inverters. Islanding detection method should not only detect islanding within acceptable duration, but also can minimize undesirable influence to power quality. This paper presents the detection principle and the criterion of islanding effect, and analyzes its happened causations. Considering the advantages and disadvantages of common islanding detection methods, this paper proposes an active current amplitude drifting methods in PV grid-connected converters to detect islanding. This method not only has little desirable influence to power quality, but also doesn’t contain non-detected zone in theory and convenient to implement with good results. The simulation results prove that this method is effective and fast. According to the characteristics of PV systems, a three-phase grid system including control of PV cells, maximum power point tracking (MPPT) and reactive power compensation function is set up in this paper, and the simulation results testify the feasibility of the design.In order to simplify hardware design and reduce debugging cost, this paper tries to emulate a real PV inverter by employing an op-amp analog circuit. The working principle of the op-amp circuit model is first analyzed and then derived in more detail. Based on the dual current loop inverter model, the op-amp circuit model has been built to simulate the real inverter system in PSIM software, and the simulation results validate that the op-amp circuit model is effective. The schematic and PCB board of op-amp analog circuit are therefore designed and built, and together with DSP control board, which employs TMS320F28335as CPU, compose the whole emulating hardware. The DSP codes are edited, compiled and debugged under the CCS studio platform. The hardware experiment is finally finished, and the experimental results verify that the op-amp circuit model is effective and practical.