Zheng Qunru

Research on nonlinear phenomena of single-phase H-bridge inverter

In this paper, the bifurcation and chaos in the operation of H-bridge inverter modulated by bipolar SPWM is studied. The one-dimensional discrete iterated mapping model under proportional control is established. Effects of the input voltage E on the system performance are analyzed by using bifurcation diagram, folded diagram. The time-domain waveforms with different proportional coefficients are obtained by Mat-lab/Simulink, which verify the correctness of theoretical analysis. Finally, the nonlinear behavior in the inverter caused by the variation of other circuit parameters like proportional coefficient k, load resistance R, and inductance L is investigated through bifurcation diagrams. The results have important guiding significance and application value for designing and debugging the single-phase H-bridge inverter.

Strategy research of low voltage photovoltaic microgrid protection

In recent years, with rapid development of low voltage photovoltaic(PV) microgrid, control and protection technology associated with low-voltage microgrid has been the focus of research. Microgrid with its power can flow in both directions and fault current differs in the grid-connected mode and islanded mode, takes a great challenge to the traditional protection technology. To solve this problem, this paper proposes a new strategy to protect microgrid using the fault direction information, determines the switchs fault direction through the energy function, locates the external fault, common bus fault and feeder fault using fault direction information based on stratification searching thought. For the feeder fault location, this article creates direction information matrix, switch-branch matrix and branch-switch matrix, to achieve fast feeder fault location and action through the matrix operation. The Simulation results show that, the micro-grid protection strategies propose to achieve fast fault location and isolation, effectively protect the security and stability of low voltage photovoltaic microgrid.