Multi-mode Control Strategies For A Inverter Of Grid-connected Photovoltaic Generation System

Grid-connected photovoltaic(PV) generation is main mode of utilizing of the solar energy. No matter for the large electrical network or Micro Grid, the instability of the PV generation restricts the consumption of the solar electricity in transmission and distribution network. At the same time, if the PV Company didn’t gain the support of the national industrial policy, the benefit is difficult to be guaranteed because the PV generation cost is enormous.In the grid-connected PV system, the inverter plays an important role because it can realize the function of DC-AC. The control strategy of the inverter is discussed from two key aspects of power control and electricity quality. In this paper, the capacity of inverter is 20 k W, the switch element is IGBT, and the grid voltage connected with PV is 380 V, frequency is 50 Hz.In the aspect of power control, the thesis focuses on the Maximum Power Point Tracking(MPPT). In the aspect of electricity quality, active power control and reactive power control are also analyzed. The active power control works when Grid is in imbalance fault, the influence of harmonic current and active vibration is reduced by negative sequence compensation. Moreover, the detection method of power harmonic is also analyzed in this paper, the power network quality can be guaranteed by reactive power control and negative sequence compensation.In the whole system, the discus based on an particular PV cell and the given 20 k W capacity, the series-parallel structure of the PV Array is calculated, and the influence of PV Array output power brought by light intensity is explicitly introduced. Moreover, the structure of filter circuit and the capacitance of filter inductance are clearly analyzed. Meantime, function of the capacitor on the DC side is introduced, the calculation steps for the capacitor is also detailed to introduced and the IGBT is designed.The adding value of the output reference currents of MPPT, active current, reactive current and harmonic current is taken as the given reference value of the current hysteresis control.Based on the function of the current hysteresis control, the trigger control of IGBT is controlled by the output of controller.At last, the simulation model for a single-stage grid-connected PV system of 20 k W is established on the platform. Simulation results show that under the conditions of whole day variable illumination, the multi-mode control strategy can track illumination changes fastly and achieve zero error maximum power point tracking(MPPT), detect the harmonic current promptly and unity power factor control so that the system has obtained excellent dynamic and static performance.