Fu-Sheng Pai

A Detection Algorithm for Islanding-Prevention of Dispersed Consumer-Owned Storage and Generating Units

One of critical concerns in the operation of grid-connected dispersed generating units is the occurrence of islanding. Islanding may pose hazards to utility personnel and complicate the orderly reconnection of the grid. Hence, in this paper, a new algorithm based on the monitoring of the change in dfldPL to detect the islanding is proposed. By the proposed method, a detection index can be evaluated that serves as a useful reference to activate the protective relays. This approach has been applied to investigate different scenarios, including the loss of grid and the parallel operation. Effects of load change and power-quality disturbances to the detection performance are also examined. From these test results, they help solidify the feasibility and effectiveness of the approach for the applications considered.

A new approach to islanding detection of dispersed generators with self-commutated static power converters

In this paper, an islanding detection approach for dispersed generators with a self-commutated static power converter is proposed. This method is suggested based on the monitoring of the magnitude and sign change in /spl part/f/sub B//|/spl part/P/sub L/. To facilitate the detection process, a designated circuit for generating the output power deviation is also developed. The proposed method has been tested under various scenarios in order to examine the detection performance and operation reliability. It is found that the proposed method effectively detects the islanding event when different amount of power mismatch is considered. Moreover, by employing the simulated disturbances to the test system, the outcome reveals that the probability of false alarm is low. Test results solidify the feasibility of the method for the application considered.

Design of dynamic voltage restorer with disturbance-filtering enhancement

In this paper, a new approach for the design of dynamic voltage restorer is proposed. By installing the filtering scheme at utility side and load side, the designated dynamic voltage restorer not only effectively compensates the voltage disturbances, but also helps ensure the supplying power quality. To validate the effectiveness of the method, several disturbance scenarios including voltage sag, oscillatory transients and power surges were examined in the simulation study. This is further supported through the hardware realization of the proposed design, where experimental results obtained under load change and voltage distortion scenarios were both investigated. Test results revealed that the proposed method is able to withstand possible disturbances at a faster dynamic response, thereby consolidating the feasibility and practicality of the approach for the applications considered.

An Improved Utility Interface for Microturbine Generation System With Stand-Alone Operation Capabilities

In this paper, an alternative filter and control approach for the design of a microturbines utility interface is proposed. The new method employs a unified current-regulated controller to drive the system converter as a power conditioner for the grid-tied operation and an emergent generator for the stand-alone operation, where few current sensors are required to serve the controller for both operating modes. The proposed method had been examined under various scenarios, including the loss of grid and parallel operation. The results help consolidate the feasibility and practicability of the approach for the applications considered

Design and operation of burn-in test system for three-phase uninterruptible power supplies

In this paper, a new approach for the burn-in test of three-phase uninterruptible power supplies is proposed. This method can perform the energy recovery for reducing the test cost, while the current supplied from the utility can be steered to be more sinusoidal. When a large number of burn-in test systems are activated such that harmonic problems may become more serious, the proposed method is also suggested based on its immunity to possible harmonies infiltration coming from the tested product to the utility power supplies. This method has been tested through simulation study and hardware experiments. Test results help consolidate the feasibility of the approach for the applications considered.

A novel design of line-interactive uninterruptible power supplies without load current sensors

In this paper, a new approach for the design of line interactive uninterruptible power supplies (UPS) without load current sensors is proposed. Based on the interactive structure, this system is constructed that includes the power factor improvement capability in anticipation of increasing the quality of supplying power. With the employment of such an approach, the power converter can be adaptively operated at the active power filter mode or backup mode, by which the power can be supplied to the connected load very reliably. Moreover, as the proposed circuit needs only one current feedback signal where the load current sensors can be saved, the circuit design can be thus simplified significantly. In order to confirm the effectiveness of this proposed design, the approach has been tested through the theoretical analysis and experimental validation under different test scenarios. Test results help support the feasibility and practicality of the method for the application considered.

Design of an Inverter Array for Distributed Generations With Flexible Capacity Operations

In this paper, an inverter array structure for the distributed generation is proposed. In the method, the inverter array is organized by basic and extended units, in which basic units are grouped to evenly share the capacity of primary energy source while extended units are designated for online redundant services. Through this design, it is not only beneficial to improve the reliability of energy production but also owns high flexibility of capability extension. To validate the effectiveness of this method, both simulations and hardware realizations have been made and evaluated. Test results help support the proposed approach for grid-connected operations.

An active islanding-detection method for power conditioning subsystem of utility interactive photovoltaic system

Islanding is a scenario where dispersed generators could be severed off from the grid, but continue to operate after the utility supply is disconnected. The occurrence of islanding events may complicate the orderly reconnection of the utility network and pose a hazard to utility personnel. In this paper, a novel active islanding-detection method for utility interactive photovoltaic systems is proposed. In this approach, a control circuit is developed and implemented for producing the designated amount of deviation, which can be reflected appropriately to the output of the photovoltaic system. Then, by coupling with a proposed algorithm, this amount of deviation will be a crucial indicator to detect the islanding. Besides, this method is capable of reactive power control such that system power factor can be better ensured. The proposed approach has been tested through different scenarios. By case studies with numerical simulation, the method was verified with simplicity, feasibility and efficiency for power system protection applications.

Design of modular inverter for distributed power generation

The alternative energy power generator has emerged to be an important research topic in the modern energy study, among which the expansion of generation capacity has a crucially high importance. Therefore, this paper has configured a modular inverter system, where the flexible capacity design was realized within this configuration in anticipation of improving the system operation reliability of the power generations. In order to verify this proposed approach, the simulation tests have been performed. Through these test results, they have supported the feasibility of the method for capacity expansion of distributed generation systems, thus further consolidating the reference value of the overall developed system.

A new approach of circulating current method for UPS testing with energy recovery

The burn-in test has been regarded as a feasible approach for quality certification of new UPS products. In this paper, we proposed a new approach of circulating current method for UPS burn-in testing with energy recovery. With the application of this method, the testing power can be recycled for reuse such that the experimental cost can be largely reduced. Besides, the proposed method is useful to restrict the degree of harmonic pollution that may affect the utility grid. Therefore, electric power quality can be also better ensured. This method has been validated through the simulation study. Simulation results help consolidate the feasibility of the approach for the applications considered.