Research And Implementation On Key Technologies Of Three-phase Photovoltaic Inverter Based On DSP

Photovoltaic(PV)power generation,as one of the easiest way to implement renewable energyapplication,has great significance on promoting the transformation of human energy supply and improving the ecological environmentin the future.This article combines the actual situation of PV grid-connected inverter application,in order to develop 50 k Wpower level of two-stage three-phase PV grid-connected inverter as the goal.Based on the analysis of the main topology of two-stage three-phase photovoltaic inverters,the Maximum Power Point Tracking(MPPT)scheme for partial blocking of photovoltaic arrays is studied.The inverter control strategy is analyzed in detail,and the dynamic detection of grid impedance scheme is studied.The software architecture is designed withthe digital signal processor(DSP)of multi-core,and a prototype machine is developed and tested in conjunction with the requirements.Power generation is a key indicator of measuring the economic benefits of grid-connectedinverters.It’s critical that it can output power with maximum capacity and run stably.In terms of maximum output power,due to the ’multi-peak’ characteristic of the PV array output curve in the case of partial occlusion,the classic MPPT algorithm cannot track to the highest power point,and misjudgment often occurs at the local highest point.This paper proposes an optimized scanning area scheme based on the characteristics of isopower lines,which can effectively shorten the scanning time and operate at more than99.2% MPPT efficiency.Grid impedance is an important parameter to analyze the stability of inverter operation.The grid impedance detection scheme based on the q-axis component perturbation proposed by vector relationship analysis can conveniently and efficiently detect impedance dynamically,and it is easy to implement in DSP.The prototype has verified that the impedance detection error is within 5%,which is suitable for engineering applications.In terms of inverter hardware and software implementation,this thesisselects a multi-core DSP and designs the software architecture from the perspectives of physical,logical,and data structures.So that key functions can be executed in parallel,which provide a basis to improve the intrinsic performance of the inverter.In order to improve the defects caused by modulation delay and current interruption in digital control,a high-frequency sampling scheme based on direct memory access(DMA)is proposed.The main research contents of this article are listed as below:(1)Analyzethe structure and principle of the front stage boost circuit and the back stage T-type three-level circuit of the three-phase photovoltaic inverter.Establish the photovoltaic panel engineering model and analyze the curve characteristics.Establish partial occlusion simulation model of photovoltaic array and propose the global scanning MPPT optimization method by using the bimodal P-U curve as an example.Proposed photovoltaic array power prediction method so as to achieve the purpose of accurately turning on the inverter and increasing the system operation time.(2)Analyze the control strategy of the inverter part in detail.Investigate the decoupled double synchronous reference frame software phase locked loop(DDSRF-SPLL)with the space-vector-pulse-width-modulation(SVPWM),and establish the switching cycle model of the inverter circuit.Focus on the algorithm and execution process from grid signal acquisition to power tube drive output.According to the stability margin of the inverter impedance,a scheme of power grid impedance detection based on q-axis component micro disturbance is proposedand the simulation is validated.(3)Perform the hardware main circuit component selection,driving and sampling circuit design according to the requirements and specifications analysis.Optimize the digital control and propose a DMA-based high-frequency sampling scheme.The multi-core chip TMS320F28379 D selected to enhance the system performance,combine the chip characteristics for function module allocation and data interaction processing to achieve a multi-core-based software architecture design.(4)The system validation process includes the establishment of a system simulation model,a hardware in-loop simulation validation platform,and build the experimental prototype for testing to complete the implementation of 50 kW power level inverter.