Research On Grid-Connected PV System With APF

A solution of single phase grid-connected PV power generation system with APF is proposed in this paper, which is applicable to the small and medium power applications, such as roof PV system. Besides the function of converting the power of PV cells to the grid, the system can also compensate the reactive power and harmonic power of the local load in this solution so as to improve the power quality. Thus the PV power generation system becomes multifunctional and utilization of the device is increased.This paper introduces harmonics compensation algorithm based on Fryze reactive power theory and proves this method does not have longer latency than instantaneous reactive power theory. Because of the clear physical meaning of Fryze reactive power theory, the algorithm can be simplified and applied to power generation system with APF application in easy calculation, which is verified by formula derivation and simulation in this paper.In the power generation system, the PLL method is used to detect the grid voltage phase and frequency. This paper proposes a novel software algorithm that can detects the frequency, phase and amplitude of the grid voltage simultaneously. Through a delay loop, the signal of the sampled input voltage is converted to an orthogonal signal, which together with the input voltage signal is then sent to a phase control loop to control the output phase and amplitude. After the algorithm steps into the neighborhood of steady status, the algorithm adopts phase indirectly control method and finally outputs the amplitude, frequency and phase of the input signal steadily. Moreover, with the advantage of sample frequency diversity, this algorithm shows practical to be planted in MCU and DSP. Simulation and experimental results verify this proposed algorithm. This paper adopts string mode as the system structure and in this structure, the main circuit is composed by two parts: DC/DC converter and DC/AC inverter. DC/DC converter can serve as a MPPT controller as well as to boost voltage. The related theory and parameter calculation are studied.The paper also studies the control circuit, writes the program, and does experiments. The results of the experiment verify the feasibility of this solution.