• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.1
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• pp.52-60
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• 2005

Generally, a voltage difference or voltage distortion exists between the reference voltage and the practical voltage applied to a motor in a pulse width modulated(PWM) voltage source inverter(VSI). This voltage distortion varies with the operating conditions such as the temperature, DC link voltage, and phase current level. Also the voltage distortion affects the machine current distortion, torque pulsations, and control performance. In this paper, the voltage distortion in a PWM VSI is analyzed and a new on-line estimation method based on the model reference adaptive system(MRAS) is proposed to compensate the time varying voltage distortion, while considering the parameter variations for a permanent magnet synchronous motor (PMSM). The simulation and experimental results show the effectiveness of the proposed voltage difference observer and the compensation method.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.228-234
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• 2012

This paper presents the algorithm of the compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it sugest simple method to solve the problem. PSIM simulation is used to validate the proposed algorithm.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.2
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• pp.155-161
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• 2014

Industrial Static Var Generator (SVG) is typically applied at or near the load center to mitigate voltage fluctuation, flicker, phase unbalance, non-sine distortion or other load-related disturbance. Special attention is paid to the influence of grid voltage quality on SVG current, the non-sine distortion and unbalance of grid voltage causes not only the AC current distortion and unbalance but also the DC voltage fluctuation. In order to let the inverter voltage contain the fundamental negative sequence and harmonic component corresponding to the grid voltage, a new dual-loop control scheme is proposed to suppress the influence in this paper. The harmonic and negative sequence voltage decomposition algorithm and DC voltage control are also introduced. All these analyses can guide the practical applications. The simulation results verify the feasibility and effectiveness of the present control strategy and analyses.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.2
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• pp.161-168
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• 2013

This paper presents an algorithm of a compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it suggest simple method to solve the problem. Simulation and experiment is used to validate the proposed algorithm.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.2
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• pp.115-121
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• 2015

Stand-alone inverter supplies constant voltage to loads. However, when a three-phase stand-alone inverter supplies unbalanced load, the generated output voltages also become unbalanced. The nonlinear characteristics of inverter dead time cause a more serious distortion in the output voltage. With unbalanced load, voltage distortion caused by dead time differs from voltage distortion under balanced load. Phase voltages in the stationary reference frame include unbalanced odd harmonics and then, d-q axis voltages in the synchronous reference frame have even harmonics with different magnitude, which are mitigated by the proposed multiple resonant controller. This study analyzes the voltage distortion caused by unbalanced load and dead time, and proposes a novel dead time compensation method. The proposed control method is tested on a 10-kW stand-alone inverter system, and shows that total harmonic distortion (THD) is reduced to 1.5% from 4.3%.

• Journal of Power Electronics
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• v.15 no.1
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• pp.10-17
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• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1833-1842
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• 2016

In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter's grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.342-348
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• 2021

The PV module of solar power systems requires maximum power point tracking (MPPT) technique because the power-voltage and current-voltage characteristics vary depending on the surrounding environment. In addition, the 120 Hz ripple voltage on the DC-Link is caused by the imbalance of the system voltage and current. The effect of this 120 Hz ripple voltage reduces the efficiency of the power generation system by increasing the output current distortion rate. Increasing the capacity of DC-Link can reduce the 120 Hz ripple voltage, but this method is inefficient in price and size. We propose a technique that detects 120 Hz ripple voltage and reduces the effect of ripple voltage without increasing the DC-Link capacity through a controller. The proposed technique was verified through simulations and experiments using a 1 kW single-phase solar power system. In addition, the proposed technique's feasibility was demonstrated by reducing the distortion rate of the output current.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.1999-2001
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• 1997

The main two drawbacks of the Sin91e Stage PFC (SS-PFC) converters employing a DCM Boost PFC cell are relatively high voltage stress on the bulk capacitor and the input current harmonic distortion. The high voltage stress on bulk capacitor makes the SS-PFC converter impractical in a universal input application and the input current harmonic distortion lowers power factor. In this paper a selective variable frequency control that reduces the voltage stress on the bulk capacitor and the input current harmonic distortion is proposed. Computer simulation results of the proposed control method are presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.9
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• pp.1639-1645
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• 2011

A technique to allocate responsibilities among the interested parties in electric power system with harmonic voltage distortion at the point of common coupling (PCC) has been presented. The recursive least-squares technique has been used to estimate the parameters of the Thevenin equivalent load model. The validity of the technique has been verified using a simulation which considered the voltage waveform distortion at the PCC between the utility and two industrial consumers. With the estimated data from the measured voltage and current waveform at the PCC, the individual contributions to the distortion of voltage waveform at an interested harmonic frequency have been calculated and could provide a flexible solution to identify the source of harmonic pollution in distribution systems.