Research On Single-stage Bridgeless AC-LED Driver System Based On Chaotic Analysis

In today’s world of energy scarcity, LED is developing rapidly as the fourth generation light source with the improvement and enhancement of its technology. In some fields, it has tendency to replace the traditional light source. Havi ng the unique advantages of small size, flexible using, easy integration and high stability, AC-LED driver has become an important research direction of LED driving technology.For the existing problems of traditional AC-LED driving topologies, A novel single-stage bridgeless AC-LED driving topological structure is proposed in this paper. The topology has advantage of few components, high efficient, great power factor and better regulation of output current. Besides, the brightness and flicker frequency issues caused by a low-frequency sinusoidal input are surpassed by the implementation of a high-frequency square-wave output current. However, because of the existing of nonlinear switching devices and the time-varying characteristic of input voltage, this converter is enriched with complicated nonlinear dynamic behaviors. These nonlinear behaviors will cause the system extremely unstable and the system may break down due to a small change of the circuit parameters. Therefore, it has important and profound guiding significance for improving the instablity of the system to research on the phenomena of bifurcation and chaos using nonlinear theory.Borrowing the idea from the stroboscopic map, the discrete iterated mapping model of the proposed single-stage bridgeless AC-LED converter under current mode control in the condition of variable sampling interval is established. Meanwhile, the expression of matrix form of the discrete model is given. Using circuits simulation and numerical calculation, a period-doubling bifurcation at the switching frequency occuring for some intervals of time during the line cycle is founded under circumstance of improper choice of system parameters. The fast-scale instability phenomenon occurs with time variation and it has the characteristic of intermittent bifurcation. Based on the analysis of the loci of eigenvalues of a Jacobian matrix, the stable boundary of the system is located. A comparison of the critical phase angles obtained from analysis and simulations is described. And the reason of the discrepancies between theoretical and simulation data is given.The piecewise switched model of the single-stage bridgeless AC-LE D converter under PI control is derived. The simulation is based on the state equations. As the load is changed,the slow-scale instability is observed and it usually manifests itself as local oscillations within a line cycle. The paper shows that power factor will be degraded when slow-scale instability occurs. Through theory analysis, it has been found that border collision ignited by the change of the state-space dimension makes the system undergo a nonsmooth Neimark-Sacker bifurcation, and then give rise to the quasi-periodic behavior. At last, the phenomenon of slow-scale instability appears.At last, using the PSIM software, the simulation module in accordance with the calculated parameters is set up. And a 100 W prototype of the proposed AC-LED driver is implemented. Both simulation results and experimental results are corresponded with the theorized expectations. Under the rated input voltage condition, the power factor of the system is measured as 0.967 and the efficiency is up to 92.01%.