Pyeong-Ik Hwang

Coordinated Control of a DG and Voltage Control Devices Using a Dynamic Programming Algorithm

This paper presents a new control method, in which a distributed generator (DG) actively participates in steady-state voltage control, together with an under-load tap changer (ULTC) and shunt capacitors (Sh.Cs). In the conventional DG control method, the integration of DGs into a distribution power system increases the number of switching operations of the ULTC and the Sh.Cs. To solve this problem, this paper proposes that the DG output voltage be dispatched cooperatively with the operation of the ULTC and the Sh.Cs, based on load forecasts for one day in advance. The objective of the proposed method is to decrease the number of switching device operations, as well as to reduce the power loss in the distribution lines, while maintaining the grid voltage within the allowed range. The proposed method is designed and implemented with Matlab, using two different dynamic programming algorithms for a dispatchable and a nondispatchable DG, respectively. Simulation studies demonstrate that the objective can be achieved under various grid conditions, determined by factors such as the DG output power characteristics, the location of the DG-connected bus on the feeder, and the load profile of the feeder containing the DG.

Modeling of the fixed speed wind turbine generator system for DTS

The dispatcher training simulator (DTS) provides a realistic environment for system dispatchers to practice operating tasks and experience emergency operation situations. In order to provide a realistic environment, the power system simulator which is a component of the DTS should include models of all devices that exist in real power system such as generating units, transmission devices and loads. As the penetration of the wind turbine generator system(WTGS) increases, the necessity of modeling the WTGS increases. However, the conventional WTGS model is not suitable for the DTS because of its computational complexity. This paper presents a new fixed speed WTGS model from conventional models, simplified models and the implementation method which can be used for DTS. Moreover, the presented model and the conventional model are compared by using MATLAB/SIMULINK tool.

A Steady-state Analysis for an Inverter-based DG to Determine the Optimal Capacity of an Inverter and Harmonic Filters

Electric power quality in power transmission/distribution systems has deteriorated considerably with the increase in the number and the capacity of inverter-based distributed generators (DGs). This is caused by inverters, connecting DGs to conventional power grids, tend to generate harmonic currents and voltages due to the switching operations of their transistors and diodes. Therefore, this paper presents new methods to adopt harmonic filters to an inverter-based DG, considering a system consisting of both an inverter-based DG and harmonic filters. In order to prove that the system proposed in this paper can be used generally, this paper describes the simulation results obtained by using PSCAD/EMTDC: the relationship between the total harmonic distortion (THD) of the output current and the output power of a DG, and the harmonic mitigation ability of passive and active filters. Furthermore, the system is obliged to satisfy the regulations made by Korea Electric Power Corporation (KEPCO). In the regulations, DG power factor needs to be maintained between 0.9 and 1 in a grid-connected mode. Thus, this paper suggests two methods for the system to control its power factor. First, the power factor should be controlled by the DG inverter rather than an active filter because this brings a dramatic decrease in the capacity of the active filter. Second, the DG should absorb reactive power only in the low output power range in order to prevent a useless increase in the inverter capacity. This method is expected to result in a variable power factor of the system according to its output power. With these control methods, the proposed DG system can successfully operate in a grid-connected mode with an optimally-reduced capacity of active harmonic filters and DG inverters while satisfying the regulations in terms of voltage variation, power factor, and THD.

Adaptive step size method for the power system model of dispatcher training simulator

Because it is almost impossible to train the dispatchers with real power system, the dispatcher training simulator (DTS) is used for the training. Among various components of the DTS, the power system model (PSM) emulates the dynamic behavior of the power system to calculate the frequency and voltage. In the PSM, the power plants are modeled as differential equations, so the mechanical power of the power plants is calculated by the numerical methods. Conventionally, the fixed step-size algorithm has been used in the PSM, however it has some drawbacks. This paper develops the prototype PSM using the Matlab, and analyzes the problems of the fixed step-size algorithm by comparing the results with those of PSCAD simulation considered as a real system. In order to overcome the limitations, the adaptive step size method for the PSM is proposed by modifying the general adaptive step size method. From the simulation using the proposed method, it is verified that the accuracy of the PSM is increased.

Fossil fuel plant modeling for the dispatcher training simulator of the K-EMS

The Korean energy management system (K-EMS) development project, which includes the development of the dispatcher training simulator (DTS), has been underway since 2005. The DTS provides a realistic environment for system dispatchers to practice operating tasks and experience emergency operating situations. In order to provide a realistic environment, the DTS includes many dynamic models of power plants, such as fossil fuel plant and hydro plants. In this paper, the fossil fuel power plant model for the DTS in K-EMS is introduced and verified through actual measurement data.