Su-Won Lee

Transmission Loss Allocation Algorithm Using Path-Integral Based on Transaction Strategy

This paper presents a new algorithm of accurate bus-wise transmission loss allocation based on path-integrals. With rigorous theoretical analysis, a new path-integral method is developed by integrating the partial differential of the system loss along a path reflecting the transaction strategy. This path-integral enables us to remarkably enhance the accuracy in loss allocation with full consideration of nonlinearity. The accuracy has been further improved by using the ac power flow. Determining the integral path is discussed to reflect various situations of the power market. Given an integral path, the proposed algorithm provides a unique and accurate solution to the loss allocation.

A tranformerless grid-connected photovoltaic system with active and reactive power control

This paper presents a transformerless grid-connected photovoltaic (PV) system with active and reactive power control. The proposed system operations can be categorized into sunny mode and night mode. In night mode, it compensates for the reactive power demanded by nonlinear loads. In sunny mode, it not only supplies active power from the PV array to the grid or loads, but also performs power quality control (PQC), to improve the power factor and reduce the harmonic current. Simulation results are provided to demonstrate the effectiveness of the proposed system.

Calculation of stochastic generation costs considering wind power generation

This paper represents a calculation method of stochastic generation cost (SGQ taking into consideration the wind power generation expressed as random variables, and shows its necessity. As wind power generation is stochastically predictable, a system demand should be expressed to a random variable with its own probability density function (PDF) instead of a constant value in unit commitment (UQ and economic dispatch (ED) problems, etc. Assuming that the produced wind power generation is fully consumed in power systems, total generation distributed to thermal generators, which becomes a modified system load, is equal to the difference between total system demand and total wind power generation. Given that the total wind generation is based on normal distribution, the modified system load should be also based on normal distribution. The proposed method is applied to illustrative examples and simple UC problems.

Grid-connected peak-load compensation system based on lithium-polymer battery

The conventional battery energy storage system (BESS) has many limits due to weight, size and low energy utilization resulted from battery characteristics. To solve this problem, we proposed a grid connected peak-load compensation system with high discharging current characteristics based on lithium polymer battery for development of the next generation power station. The lithium-polymer battery has faster discharging current characteristics than conventional battery, so that can compensate high active power demanded by load in a short time using the low capacity battery bank. Therefore, it is possible to control power leveling of grid by measuring stored energy in battery and active power which is needed from load. The validity of proposed system is verified through the simulation and experiment.

A New High Efficient Bi-directional DC/DC Converter in the Dual Voltage System

This paper introduces a new high efficient bi-directional, non-isolated DC/DC converter. Through variations of the topology of the conventional Cuk converter, an optimum bi-directional DC/DC converter is proposed. Voltage and current in the proposed DC/DC converter are continuous. Furthermore, the efficiency in both step-up and step-down mode is improved over that of the conventional bi-directional converter. To prove the validation for the proposed converter, simulations and experiments are executed with a 300W bi-directional converter.

Parallel Resonant DC-link Soft Switching Inverter based on Delta-Modulation Method

In this paper, we have proposed a parallel resonant soft switching inverter based on delta-modulation method. A conventional full-bridge inverter generates switching losses due to a hard switching. The proposed inverter operates soft switching using a DC-link switch and resonant circuit. Therefore, all of the switches in the proposed inverter are operate with soft switching. As a result, the proposed circuit can reduce the switching loss. The proposed inverter is verified through the theoretical analysis, simulation and experiment.

Power quality control using the Goertzel algorithm for grid-connected system

In this paper, power quality control (PQC) using a Goertzel algorithm for single phase grid-connected photovoltaic power conditioning system (PV-PCS) is proposed. The Goertzel algorithm is a kind of discrete fourier transform (DFT) that extracts magnitude and phase of required frequency from the input signal, with minimum computation. The proposed PQC is formed based on the Goertzel algorithm. Also that allows us to define the active and reactive power control. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

Operational Characteristics of a Flux-Lock Type SFCL Integrated with Voltage-Controlled Voltage Source Inverter

In this paper, a flux-lock type superconducting fault current limiter (SFCL) integrated with a voltage-controlled voltage source inverter (VC- VSI) is proposed. The suggested equipment, which consists of a flux-lock type SFCL and a VCYSI, can perform the fault current limiting operation from the occurrence of a short-circuit, In addition, it can compensate the reactive power that the nonlinear load requires and also perform the un interruptible power supply (UPS) as well as the load voltage stabilization by controlling the amplitude and the phase of the inverters output voltage. The specification for a test model was determined and its various functions such as the fault current limiting and the power conditioning operations were presented and analyzed via computer simulation. Through the analytical results based on the computer simulation, the validity of the analysis was confirmed and its multi-operation was discussed.

Output voltage control of a synchronous generator for ships using compound type digital AVR

This paper deal with field current control method of a synchronous generator (SG) for ships using a compound type digital automatic voltage regulator (AVR) in order to control output voltage of the generator. The compound type digital AVR is composed of a control part to adjust output voltage and an auxiliary power unit to supply power to the field. The control part which generates the PWM switching pattern via the PI controller drives a power MOSFET for bypass to limit the synchronous generators field current. The auxiliary power unit is parallel connected to an output terminal of the generator through a reactor and power CT. The residual magnetic flux of synchronous generator provides field current to the exciter through the reactor during the initial driving or no-loading operation and load current supplies field current to the exciter flowing to the power CT when the load is connected on the system. Experimental results demonstrate the digital AVRs benefits.

Power loss analysis of two-stage PV-PCS using interleaved soft switching dc-dc converter

This paper presents a grid-connected PV-PCS (Photovoltaic Power Conditioning System) using interleaved, soft switching boost converter for efficiency increment. The numerical analysis about power loss on the proposed PV-PCS is performed. And this analysis is confirmed by the simulation results. It is expected that the analyzed results can be used in the efficiency improvement of PV-PCS.