The Design And Development Of Low-power Single-phase Grid-connected Inverter Control System

With the concept of "Green and Environmental Protection" was proposed, all kinds of new energy exploitation program are in the rapid promotion, which is in order to solve the power shortage, pollution and other issues. It makes exploring renewable energy feedback the grid technology has a very important practical significance. How to deliver power into the grid reliably and quality is an important problem, the inverter that can transform the electrical energy in the system of the renewable resource to be fed into the grid is becoming one of the hot points in international research. This paper focuses on single-phase grid-connected system. The topology, control strategy, parameter selection and grid-connected experiment of grid-connected system are analyzed and studied in detail. The main contents are as follows:Firstly, the research current situation of grid-connected inverter and the development prospect of renewable energy are introduced, and then analyses main circuit topologies structure and principle of grid-connected inverter. The designing ideas and processes of the filters on both DC and AC sides are studied in this paper, and the formulas of the key parameters of the main circuit are derived and given out.Secondly, this paper aims at the character of grid-connected inverter, has proposed an improved SPWM current tracking control strategy based on DSP. The mathematical model of control system are established, it has ascertained PI closed-loop regulation for controlling core. Meanwhile, in order to control the output current to good effect, the system adopts a series of advanced and assistant control algorithms. Voltage feedforward compensation offsets the influence of the grid for the output current of the inverter. Prediction algorithm eliminates the errors of sampling process and designing principle, so that the sampling result and the real value are more approximation. Asynchronous varying-frequency modulation algorithm can enable the output current of the inverter and the Voltage of the grid with the same frequency and phase, it ensures that the inverter output in high power factor.Thirdly, this paper designs software and hardware of grid-connected inverter system respectively. It distributes sub-block resource and IPRI of the main control chip TMS320LF2407A properly, uses inner CAP capture interface of DSP to design a fast and reliable software PLL of inverter system. Otherwise, it uses SCI asynchronism serial communication interface to perform man-machine interaction function and uses the embedded CAN control block to perform muti-system communication function. In addition, it analyses and designs the PWM output interface, inverting drivers, A/D change, protected control and self-checking of the inverter system. The programs of different function block in control system are given at last.Finally, under the system design requirements, and developed an inverter prototype, its hardware and software were experimented and debugged, and the experimental results and data were given out.Through the inverter prototype tests show that its DC input, AC output, power factor, inverter efficiency, the THD of the grid-connected current, and other areas of technical indicators are attained or better than design standards require, the inverter accomplishes the feedback of the renewableenergy to the utility line in high power factor. The prototype can work stably and achieve the expected goals.