Power Stabilization Control For Grid-connected Photovoltaic Power System

As one of the most prospective new energy source, grid-connected photovoltaic (PV) power generation is being developed widely. However, the PV power fluctuates seriously when radiation changes fast and may result some problems for the grid planning, operation and dispatching. In this paper, an energy storage-based grid-connected PV power generation system is proposed to overcome the power fluctuation problem. This paper focus on power stabilization control strategy basing on Maximum Power Point Tracking (MPPT) and DC/AC conversion. Simulation and experiments are carried out to validate the proposed strategy.Firstly, an energy storage-based grid-connected PV power generation system is proposed for power stabilization control. The two-stage grid-connected PV inverter is composed with a BOOST circuit for MPPT control and a bridge-inverter for DC/AC conversion control respectively. A bi-directional DC/DC couples the DC link bus to control the charging and discharging of battery bank for power stabilization.Secondly, MPPT control and DC/AC conversion is studied. An improved MPPT method is proposed to overcome the shortcomings of existing strategies. The proposed method is a combination of Perturb&Observe Algorithms, Quadratic Interpolation Method and Constant Voltage Tracking. Simulation and experiments are carried out to validate the method. For DC/AC conversion, a system with double-loop control is designed on the basis of synchronous vector current PI controller. The two loops are used to control the DC link voltage and AC currents respectively. The AC current components id and iq are decoupled and the space vector PWM is used to improve the AC power quality. Also, simulation is carried out and the results show the good performance of the method.Thirdly, power stabilization control strategy is studied. The potential impacts on the grid caused by power fluctuation are analyzed. The system operations are discussed in detail. The PV array actual power PPV is filtered through a low-pass filter and the high-frequency components will be cut. The filter result is used as reference power Pref injected into the grid. Low-pass filter design and bi-directional DC/DC converter operation are discussed. Simulation results validate the proposed strategy.Lastly, a bi-directional DC/DC converter is designed, including hardware and software. An experiment platform is made and experiments are carried out to validate the proposed power stabilization control strategy.