Small distributed generation (DG) systems provide standby service during utility outages and, when operated during peak load hours, potentially reduce energy costs. The connection of a generation system to the utility grid requires a robust phase locked loop (PLL) and continuous detection of utility grid status (such as outage, over-/under-voltage and over-/underfrequency). This paper details a flexible control strategy to operate a small/micro single-phase DG in both stand-alone and grid-connected modes. The described system is effectively an extended line-interactive uninterruptible power supply (UPS). In particular, a high-performance PLL for single-phase inverters is proposed. The PLL uses a transport delay method to generate a virtual quadrature signal, thereby emulating a balanced threephase system. Furthermore, an orthogonal filter is incorporated to improve the PLL performance when the grid voltage is distorted. To achieve zero steady-state error and to implement selective harmonic compensation, resonant controllers are proposed, for both the voltage regulation in stand-alone control mode and the current regulation in grid-connected control mode. Simulation and experimental results from a 3.5 kW prototype with a fuel cell as the primary source are included to prove the effectiveness of the proposed methods.
|Title of host publication||Proceedings of the 42th Industry Application Society conference and annual meeting (IAS’07), 23-27 September 2007, New Orleans, USA|
|Place of Publication||New Orleans, USA|
|Publisher||Institute of Electrical and Electronics Engineers|
|Publication status||Published - 2007|