Investigation of anti-islanding schemes for utility interconnection of distributed fuel cell powered generations

The rapid emergence of distributed fuel cell powered generations (DFPGs) operating in parallel with utility has brought a number of technical concerns as more DFPGs are connected to utility grid. One of the most challenging problems is known as islanding phenomenon. This situation occurs when a network is disconnected from utility grid and is energized by local DFPGs. It can possibly result in injury to utility personnel arriving to service isolated feeders, equipment damage, and system malfunction. In response to the concern, this dissertation aims to develop a robust anti-islanding algorithm for utility interconnection of DFPGs. In the first part, digital signal processor (DSP) controlled power electronic converters for utility interconnection of DFPGs are developed. Current control in a direct-quadrature (dq) synchronous frame is proposed. The real and reactive power is controlled by regulating inverter currents. The proposed digital current control in a synchronous frame significantly enhances the performance of DFPGs. In the second part, the robust anti-islanding algorithm for utility interconnection of a DFPG is developed. The power control algorithm is proposed based on analysis of a real and reactive power mismatch. It continuously perturbs (??5%) the reactive power supplied by the DFPG while monitoring the voltage and frequency. If islanding were to occur, a measurable frequency deviation would take place, upon which the real power of the DFPG is further reduced to 80%; a drop in voltage positively confirms islanding. This method is shown to be robust and reliable. In the third part, an improved anti-islanding algorithm for utility interconnection of multiple DFPGs is presented. The cross correlation method is proposed and implemented in conjunction with the power control algorithm. It calculates the cross correlation index of a rate of change of the frequency deviation and (??5%) the reactive power. If this index increases above 50%, the chance of islanding is high. The algorithm initiates (??10%) the reactive power and continues to calculate the correlation index. If the index exceeds 80%, islanding is now confirmed. The proposed method is robust and capable of detecting islanding in the presence of several DFPGs independently operating. Analysis, simulation and experimental results are presented and discussed.