Research and Simulation of Three-phase Grid-connected Photovoltaic System
|Course||Pattern Recognition and Intelligent Systems|
|Keywords||photovoltaic grid-connected system reactive power compensation cascaded converter phase shifted carriers pulse width modulation (PSPWM) proportion resonant (PR) controller|
As the development of social economy we are facing more and more series serious energy and environment problems. It has become hot topic how to explore regenerative energy effectively. Among many kinds of regenerative energy solar power attracts much attention because of its unique advantages. Photovoltaic grid-connected generation has become an effective way to use it. This article which focuses on photovoltaic grid-connected system, discusses the character of photovoltaic array, maximum power point tracking (MPPT), the control strategy of photovoltaic grid-connected generation with reactive power compensation, high voltage photovoltaic grid-connected system based on cascaded converter and constructs two simulation models of PV system.It is the foundation to study the character of PV array. This article puts forward a simulation model of PV array based on the equivalent circuit of PV cell, and finds them theoretic bases by jointing the MPPT of PV array.This article researches how the active power filter (APF) works, and the character of electric circuit of the PV system. I find that there are common parts for the two of them. So I put forward that it is reasonable to joint the power control of the PV system and APF to get a harmonic suppression and reactive compensation photovoltaic (HRPV) system. The HRPV system can not only generate electricity grid-connected, but also compensate the load current dynamically, which solves the problem of the low quality of power supply and saves the use of the additional filter device. This design reduces the cost of a PV system a lot. The calculation of the harmonic wave and the reactive power is obtained by the harmonic wave current detection algorithm based on the instantaneous reactive power theory, which is jointed with active power command current of the grid-connected power generation and realizes the double closed loop control to voltage and current of the HRPV system. The simulation shows that the HRPV system can suppress the harmonic wave and compensate the reactive power effectively. It is valid and practical to use this method to construct a PV system. The cascaded H-bridge converter can output a multilevel high voltage. It is possible to replace usual converter in PV system, because it make possible to connect the grid without many step-up voltage devices such as booster stations. Meanwhile, the PV array will be the independent source of those cascaded H-bridge. I use the phase shifted carriers pulse width modulation (PSPWM) method to control the cascaded H-bridge converter. Proportion resonant (PR) controller is used which can follow the AC signal accurately and track the grid-connected command current in real-time. To get a 10KV high voltage grid-connected PV system, I put together a five-cell cascaded H-bridge converter with PV array. The simulation of this design shows that the current could track without steady state error in real-time, and output a high voltage which could be used to connect with the grid directly to generate electricity.