Backfeeding

Abstract: In this paper, a dc-link voltage protection (DCVP) control method is proposed to address the dc-link overvoltage issue due to power backfeeding in a parallel uninterruptible power supply (UPS) system. The proposed control method is able to protect the inverter against the excessive dc-link voltage, which increases the system reliability and robustness. Moreover, a current sharing control strategy is proposed by online regulating the virtual resistance of each UPS module. The proposed current sharing control strategy is able to address the circulating fundamental and harmonic currents caused by the line impedance mismatching or power backfeeding issue in the UPS system. In addition, an improved consensus-based distributed controller is proposed to alleviate the overshoot issue during the transient process in voltage amplitude and frequency restoration. Finally, the feasibility of the proposed methods is verified by experimental results from the parallel UPS prototypes.

Abstract: An automatic transfer switch system controls switching of power from a main source (utility power) to a backup source (generator) by using a state machine controller and low cost relay switches housed in a single electrical panel. The low power automated transfer switch system is well-suited for residential use and is less expensive and easier to install than conventional automatic transfer switches. The key to a low cost transfer switch is delivering power with low cost relays. This is accomplished by employing relay drive techniques that enable these devices to survive rigorous standards compliance testing. Preferably, the state machine controller measures utility and generator source compliance using an optical coupling arrangement, rather than a transformer. The automated transfer switch disconnects the utility and generator means through a circuit breaker providing for fast protection. The relay drive techniques disclosed provide a form of an electrical interlock. This is a key feature when seeking compliance standard approval. Essentially, an automated transfer system should not continuously be capable of backfeeding power from generator to utility, and the electrical interlock of the relays as taught by this invention prevents any such backfeeding.

Abstract: Three-phase reclosers with single-phase tripping are being more widely employed on utility distribution feeders They have the advantages of increasing reliability for the customers on the feeders, because the majority of distribution feeder faults are single-phase However, certain difficulties may occur when three-phase industrial and commercial loads, with three-phase transformers and motor loads are interrupted on one phase only These include overheating of motors, ferroresonance of transformers, tripping of power electronic drives and backfeeding of distribution lines This paper examines these effects, their severity and mitigation techniques

Abstract: This paper analyzes long duration overvoltages due to backfeeding currents from the low-voltage network to the medium-voltage network through network protectors in heavily meshed underground distribution networks. Overvoltages above 3 p.u. may be developed as a result of a simultaneous occurrence of three phenomena: neutral displacement, Ferranti effect, and current chopping. A detailed model of a typical distribution network is utilized for the study. Time-domain simulations are performed using an Electromagnetic Transients Program-type program. The results demonstrate that overvoltages due to backfeeding last longer during peak load operating conditions, and the largest peak overvoltages occur at no load.