The Control Strategy Research And System Design Of Off-grid Photovoltaic Power Generation Equipment

Solar energy has the largest amount and most common distribution in all therenewable energy resources.Various countries have been pursuing its effectivedevelopment and utilization. PV power generation is an efficient use of solar energyresources, which is significant to ease power shortage and reduce environmentalpollution. Currently there are two kinds of PV forms (grid-connected and off-grid).Grid-connected PV has a larger capacity. Off-grid PV has broad application prospectsbecause of its easy installation, without power policy restrictions, relatively low costand other characteristics. Based on the background, the paper studied the off-grid PVdevice and control strategy, and designed a set of off-grid PV system with the ARMcontroller as the core.After analyzing the research status and technical difficulties of off-grid PVsystems’ design, the paper took into account the mutual cooperation issues betweenpower generation and energy storage devices, and designed the overall structure of thesystem, including solar panels, batteries, Boost converter, bidirectional Buck/Boostconverter and full-bridge inverter.In order to maximize the use of PV panels’ power, the paper focused on theMaximum Power Point Tracking (MPPT) algorithm. Matlab simulation proved theshortcomings of perturbation and observation method. After twice modificationprocess of the algorithm, this paper designed improved feasible variable stepdisturbance and observation method, which well alleviated the problem that MPPTprocess can’t taking into account the conflict of the steady-state accuracy and responsespeed. To prolong battery life, this paper analyzed the battery’s charge and dischargecharacteristics, compared the advantages and disadvantages of the battery chargingmethods which were commonly used in engineering. This paper selected thetwo-stage charging method, and proved its feasibility by simulation experiments. Inaddition, the paper also designed control strategy for each power converter in overallstructure, and designed six working modes matching for different running states of PVpanels, load and battery. After that, this paper designed a suitable energy managementcontrol strategy.System design is also an important part of this article. For the needs of small andmedium-power appliances, the paper formulated the power parameters and voltagelevel of system’s each module. This paper designed the detailed hardware circuit and calculated component parameters for three kinds of power converters in main circuit.Devices were selected according to the calculation results. After that, based onSTM32F103ZET6, this paper designed the system’s control circuit, including powersupply circuit, sensor circuit, sampling circuit, MOSFET drivers and protectioncircuits, full-bridge inverter control circuits and human-machine interface.To further validated the reasonableness of the system design, the paper built asmall power experiment platform of off-grid PV system, completed the controlcircuit debugging experiment and MPPT experiment, and got the relevantexperimental waveforms. In addition, this paper achieved the sine wave inverterfunction of full-bridge, proved that the full-bridge inverter and its control circuit werereliable.