Powerline noise is a severe interference source in urban or mine transient electromagnetic (TEM) surveys. TEM systems generally adopt the synchronous detection scheme to suppress powerline noise. However, considerable powerline noise residue still remains even after synchronous detection when the powerline frequency fluctuates differing from its nominal value (50/60Hz).

In order to solve this problem, Jang Chol Jin, a researcher at the Institute of Nano Science and Technology, has proposed a quantitative suppression method for powerline noise taking into account the instability of powerline frequency. The method is based on the adjustment of base frequency and optimal choice of stacking-times.

He mathematically represented a sufficient condition for powerline noise suppression by synchronous detection. It consists of two equations; one is related to base frequency and the other is connected with stacking-times. He first derived the mathematical relationship between frequency estimation accuracy and residual noise amplitude and stacking-times. Based on it, he developed an efficient algorithm to determine the optimal stacking-times. The algorithm takes as input the powerline noise estimates and the noise tolerance limit. By adjusting base frequency and determining the optimal stacking-times, he reduced the powerline noise residue after synchronous detection to below the desired tolerance limit.

The experimental results show that the method achieves quantitative suppression of unsteady powerline noise and prevents measurement time loss due to excessive stacking without any damage to effective signals.

You can find the details in his paper “Quantitative suppression of unsteady powerline noise in transient electromagnetic surveys: Adjustment of base-frequency and optimal choice of stacking-times” in “Review of Scientific Instruments” (SCI).

Microgrids, which have been developed to cope with the penetration of renewable energy systems, can provide a promising solution to integrate renewable and distributed energy resources and distributed energy storage systems. Microgrids now play an important role in the improvement of the stability, reliability and power quality of power systems. In microgrids with nonlinear loads, current harmonics may induce voltage distortion of the point of common coupling (PCC).

Load power sharing and voltage quality are more challenging in islanded microgrids with nonlinear loads. Distributed generations (DGs) can be used to improve the power quality in microgrids. However, the conventional droop control can cause poor harmonic power sharing among the DGs due to mismatched line impedance.

Kim Sung Hyok, a researcher at the Faculty of Electrical Engineering, has proposed a harmonic power-sharing control method using the adaptive regulation of virtual harmonic impedance. He used consensus algorithm to regulate the virtual harmonic impedance with mismatched line impedance in consideration. The consensus-based distributed control does not require prior knowledge of line impedance.

The simulation results show that the proposed method is appropriate for achieving accurate harmonic power sharing while reducing the voltage distortion at the point of common coupling (PCC).

For more information, you can refer to his paper “Voltage Harmonic Compensation Using Virtual Harmonic Impedance Regulation in Islanded Microgrids” in “Journal of Electrical Power & Energy Systems” (EI).

Environmental pollution and depletion of fossil energy have made the research for the exploitation and use of natural energy more and more intensive in the world, and wind power resources find wide application day by day because it is free of depletion and environmentally friendly.

Precedence has been given to the research on developing high-efficiency wind turbines, and as a result, various types of wind turbines have been developed to provide maximum wind energy.

As well known in the general momentum theory, the performance of wind turbines is characterized by the power coefficient, which is defined as the ratio of mechanical energy to kinetic energy of wind passing through the rotating blade face per unit time.

However, the total kinetic energy of wind mentioned above is not generated by the real wind flowing into the blade inlet because the nearer it gets to the face of blade, the lower the upstream velocity gets due to the pressure caused by the blade of wind turbine.

Kim Mun Hui, a researcher at the Faculty of Electrical Engineering, has presented the theoretical consideration results from the new concept on the rotor swept area.

She applied optimization theory of multivariate functions to describe the power characteristics of wind turbines by the relationship between the upstream area and the rotor swept area. She predicted that the upstream area is 1/1.125 times the rotor swept area and the value of the maximum power coefficient increases to 0.667.

In addition, she confirmed that the maximum value of the power coefficient is kept as 0.667 even in the case of rotors installed in several rows on one axis, and that the total power is not distributed to the rotors in each row, but depends on the rotor in the last row.