Distributed Generation System Controlled in Voltage and Power Modes for Stand-alone or Grid-tie Operation

Abstract

This work presents a control strategy to manage the power delivered to or absorbed from the grid, independently of the local load characteristics. To achieve this goal, a voltage source inverter (VSI) will work as a distributed generation system (DG) or like an active filter. The VSI will be controlled by means of a double cascade classical controller, where the inner loop is used to stabilize the VSI output current and the outer loop controls the DG terminal voltage. To improve the response of the VSI, resonant filters are placed in parallel. Additionally, resonant filter dynamic responses are enhanced through the use of a proper discretization method, where the coefficients are changed dynamically by means of the synchronism frequency produced by the phase-locked loop (PLL) algorithm. This study also exhibits two closed-loop structures: one to control the reactive power through the grid by adjusting the DG voltage amplitude, and the other to control the active power by modifying the angle of displacement between the grid and the DG voltages. Both power control structures operate adequately in decoupled operation mode, so that one has a faster dynamic response than the other. To verify all statements proposed in this tesis, a set of simulations and experimental results are presented.