• Proceedings of the KIEE Conference
• /
• 2001.04a
• /
• pp.174-177
• /
• 2001

The dependence of modern life upon the continuous supply of electrical energy makes system reliability and power quality topics of the utmost importance in the power systems. Power quality is the combination of voltage quality and current quality. But in this paper, voltage quality and harmonic distortion are focused. Transient phenomena and current quality are not included. Voltage quality is split into voltage sags. voltage swells, and short interruptions. These voltage variations are studied on their definitions, origins, the effect on electric equipment. Related industrial standards and guidelines are summarized. Harmonic voltage and current distortion are strongly linked. The concepts and contributions of harmonic distortions are studied. Typical symptoms of harmonic problems and a summary of the trends and guidelines are given.

• Proceedings of the KIPE Conference
• /
• 2013.07a
• /
• pp.1-2
• /
• 2013

In this paper, we inject input currents having $3^{rd}$ harmonic to reduce the capacitance of DC link capacitors in single-phase converters. If the input current with third harmonic is injected, the required capacitance can be reduced by minimizing the difference between the input and output power. To control the input current, instead of PI control done in rotating frame, PR controller is used with the proposed separate current control method for fundamental and $3^{rd}$ harmonic components. The validity of the proposed method has been demonstrated by simulation results.

• 전기의세계
• /
• v.15 no.1
• /
• pp.1-13
• /
• 1966

The harmonic components of a current in the power system have been known to be harmful to the sound operation of the system. Their occurrence is mainly due to the nonlinear characteristics of magnetic materials which are used in the system. This paper has, therefore, numerically analyze the harmonics from the relation between the magnetic characteristic curve and the harmonic components of a current in the R-L-C circuit. It also has suggested a new method of calculating the magnitudes and phase angles of the harmonic components by means of approximate formulas derived here. The method is expected to apply to the determination of harmonics-limiting conditions in case of the design of such power equipments as transformer, reactor and so on.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.1
• /
• pp.1-7
• /
• 2014

This paper proposes a current harmonic compensation method for the grid-connected inverter, especially caused by the grid impedance. Grid impedance causes low order harmonics in the grid current and deteriorates power quality. This paper analyzes the negative impact of the grid impedance, and proposes an active feedforward compensation method. Proposing method verified through simulation and experiment with 3-phase 1.5kW voltage source inverter prototype.

• Proceedings of the KIEE Conference
• /
• 2004.11b
• /
• pp.217-219
• /
• 2004

The second harmonic component could be decreased by magnetizing inrush when there have been changes to the material of the iron core or its design methodology. The higher the capacitance of the high voltage status and underground distribution, the more the differential current includes the second harmonic during the occurrence of an internal fault. Therefore, the conventional second harmonic-restrained RDR needs modification. This paper describes an advanced numerical algorithm that utilizes terminal voltage, differential current harmonics, harmonic ratio, and flux-differential current slope. Based on the results of testing with WatATP99 simulation data, the proposed algorithm was proven to be faster and more reliable.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.38 no.6
• /
• pp.441-450
• /
• 1989

A control technique for current-fed filters is proposed which not only eliminates the harmonic current, but also controls the reactive power at the ac sides of PWM inverter-induction motor drive system. Injecting the proposed PWM current enables the harmonic components of orders not greater than the number of pulses per half-cycle to be removed completely. Also it enables the input fundamental power factor to become unity and hence total input power factor can be improved greatly. Digital simulation is performed to investigate the theoretical output characteristics of the current-fed filters by the proposed control technique.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.1
• /
• pp.6-14
• /
• 2014

A new method to determine the total harmonic contributions of several customers and the utility at the point of common coupling is presented. The proposed method can quantify the individual harmonic impact of each suspicious harmonic source at the point of common coupling. The individual harmonic impact index is then used to assess the total harmonic contribution of each harmonic source. This index can be calculated by the results processed from instantaneous harmonic voltage and current phasor values. The results demonstrate the performance of the proposed method in terms of steady-state accuracy and response to time-varying operating conditions. The proposed index can be used for billing purposes to control harmonic distortion levels in power systems.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.10
• /
• pp.1856-1861
• /
• 2010

To reduce a high fault current, neutral ground reactors (NGR) were installed in the Korean substation. Current with several harmonic components flows in a NGR due to load unbalance in normal steady state and magnetic fields with several harmonic components are also generated around a NGR. As results of study, we found magnetic fields around a NGR in Korean substation included two harmonics, 180Hz and 540Hz. Magnetic fields of 180 Hz increased 3 times more current density inside a worker near a NGR than same magnitude magnetic fields of 60 Hz. We know a worker near a NGR may not meet ICNIRP guideline of 10(mA/$m^2$) due to several harmonic components.

• Journal of Power Electronics
• /
• v.13 no.4
• /
• pp.712-718
• /
• 2013

This paper proposes a control method for reducing the total harmonic distortion (THD) of the grid current of three-phase grid-connected inverter systems when the grid voltage is distorted. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for the minimum point of the THD. Both the gain and angle of the compensation voltage at the minimum point of the THD of the grid current are derived with the variation of cut-off frequencies of the hardware LPF. Simulation and experimental results show the validity of the proposed control methods.

• Proceedings of the KIEE Conference
• /
• 2000.07b
• /
• pp.1236-1238
• /
• 2000

This paper considers the problem of eliminating harmonics in the inverter output waveforms. The approach is based on the minimization of the current harmonics in the induction motor by space vector modulation method. Reference voltage is compensated with injection of controlled current harmonics which are calculated to reduce current harmonics through sampled current harmonic analyzing algorithm. The theoretical analysis is carried out using computer simulation. It is verified that proposed SVM technique could reduce current harmonic component and improve THD.