• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.120-126
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• 2021

DC-link capacitors are one of the main components in two-level three-phase voltage source inverters (VSIs); they provide the pulsating input current and stabilize the vacillating DC-link voltage. Ideally, the larger the capacitance of DC-link capacitors, the better the DC-link voltage stabilizes. However, high capacitance increases the cost and decreases the power density of VSI systems. Therefore, the capacitance should be chosen carefully on the basis of the DC-link voltage ripple requirement. However, the DC-link voltage ripple is dependent on the pulse-width modulation (PWM) strategy. This study especially presents a DC-link voltage ripple analysis when the minimum loss discontinuous PWM strategy is applied. Furthermore, an equation for the selection of the minimum capacitance of DC-link capacitors is proposed. Experimental results with R-L loads are also provided to verify the effectiveness of the presented analysis.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1351-1365
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• 2019

This paper proposes two modified Z-source inverter topologies, namely an embedded L-Z-source inverter (EL-ZSI) and a coupled inductor L-Z source inverter (CL-ZSI). The proposed topologies offer a high voltage gain with a reduced passive component count and reduction in source current ripple when compared to conventional ZSI topologies. Additionally, they prevent overshoot in the dc-link voltage by suppressing heavy inrush currents. This feature reduces the transition time to reach the peak value of the dc-link voltage, and reduces the risk of component failure and overrating due to the inrush current. EL-ZSI and CL-ZSI possess all of the inherent advantages of the conventional L-ZSI topology while eliminating its drawbacks. To verify the effectiveness of the proposed topologies, MATLAB/Simulink models and scaled down laboratory prototypes were constructed. Experiments were performed at a low shoot through duty ratio of 0.1 and a modulation index as high as 0.9 to obtain a peak dc-link voltage of 53 V. This paper demonstrates the superiority of the proposed topologies over conventional ZSI topologies through a detailed comparative analysis. Moreover, experimental results verify that the proposed topologies would be advantageous for renewable energy source applications since they provide voltage gain enhancement, inrush current, dc-link voltage overshoot suppression and a reduction of the peak to peak source current ripple.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.974-976
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• 2001

This paper presents a method to reduce commutation torque ripples occurred during commutation in brushless do motor drives using a single DC-link current sensor. In brushless dc motor drives with a single dc current sensor instead of 3-phase line current sensors, it is noted that dc-link current sensor cannot give any information corresponding to the motor currents during line current commutation intervals. A new technique to resolve such a problem is dealt with based on a deadbeat current control in which motor armature voltage command is computed from a dc-link current reference, an actual current and counter emf voltage. The simulation results show that the proposed method reduces the torque ripple significantly.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.2
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• pp.94-100
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• 2018

Generally, in a single-phase energy storage system (ESS) for households, AC ripple component with twice the fundamental frequency exists inevitably in the DC link voltage of single-phase PCS. In the grid-connected mode of a single-phase inverter, the AC ripple component in the DC link voltage causes low-order harmonics on grid-side current that deteriorates power quality on an AC grid. In this work, a control system adopting a feedforward controller is established to eliminate the AC ripple interference on the DC link side. Optimal battery nominal voltage design method is also proposed by considering the voltage loss and AC ripple voltage on DC link side in a single-phase ESS. Finally, the control system and battery nominal voltage design method are verified through simulations and experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.73-78
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• 2020

In this study, a novel reactive power control scheme is proposed to supply stable reactive power to the distribution line by compensating a ripple voltage of DC link. In a single-phase system, a magnitude of second harmonic is inevitably generated in the DC link voltage, and this phenomenon is further increased when the capacity of DC link capacitor decreases. Reactive power control was performed by controlling the d-axis current in the virtual synchronous reference frame, and the voltage control for maintaining the DC link voltage was implemented through the q-axis current control. The proposed method for compensating the ripple voltage was classified into three parts, which consist of the extraction unit of DC link voltage, high pass filter (HPF), and time delay unit. HPF removes an offset component of DC link voltage extracted from integral, and a time delay unit compensates the phase leading effect due to the HPF. The compensated DC voltage is used as feedback component of voltage control loop to supply stable reactive power. The performance of the proposed algorithm was verified through simulation and experiments. At DC link capacitance of 375 uF, the magnitude of ripple voltage decreased to 8 Vpp from 74 Vpp in the voltage control loop, and the total harmonic distortion of the current was improved.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1062-1069
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• 2013

This paper proposes a simple current compensation method to improve the control performance of B4 inverters. Four-switch inverters so called B4 inverters employ only four switches. They have a split dc-link and one phase of three-phase motors is connected to the center-tap of split dc-link capacitors in B4 inverters. The voltage ripples in the center tap of the dc-link generate unbalanced three-phase voltages causing current ripples. To solve this problem, this paper presents a simple compensation method that adjusts switching times considering dc-link voltage ripples. The validity of the proposed method is verified by simulations and experiments carried out with a 1 HP induction machine.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.47-53
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• 2006

In this paper, a simple scheme compensating for the effect of dc-link ripple voltages on output voltage of two-leg and three-phase PWM inverters is proposed, where single-phase half-bridge PWM convertor and two-leg inverter are used. The voltage at neutral point of the dc-link is controlled so that the upper-half of do-link voltage is equal to the lower-half voltage in average concept. However, the effect of the do-link ripple voltage results in the inverter output voltage and current distortion. This effect can be eliminated by introducing a compensation voltage in switching time calculation. Also, the inverter dead time should be compensated for sinusoidal output waveform. The proposed scheme has been verified by experimental results which were obtained from the V/F constant operation of the induction motor fed by two-leg inverter.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1851-1860
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• 2016

The traction motors in electric multiple unit (EMU) trains are powered by AC-DC-AC converters, and the DC link voltage is generated by single phase PWM converters, with a fluctuation component under twice the frequency of the input catenary AC grid, which causes fluctuations in the motor torque and current. Traditionally, heavy and low-efficiency hardware LC resonant filters parallel in the DC side are adopted to reduce the ripple effect. In this paper, an analytical model of the ripple phenomenon is derived and analyzed in the frequency domain, and a ripple control scheme compensating the slip frequency of rotor vector control systems without a hardware filter is applied to reduce the torque and current ripple amplitude. Then a relatively simple discretization method is chosen to discretize the algorithm with a high discrete accuracy. Simulation and experimental results validate the proposed ripple control strategy.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.110-116
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• 2013

This paper proposes a current ripple reduction method to improve the control performance of B4 type inverter that is studied for cost-effective drive systems. B4 inverters employ only four switches and they have a center-tapped connection between the split dc-link capacitors and one phase of a three-phase motor or load. In the B4 topology, unbalanced three-phase voltages will be generated due to the dc-link voltage ripple. To solve this problem, this paper presents a voltage distortion compensation method that adjusts the voltage reference with the consideration of dc-link voltage ripple. The validity of the proposed method is verified by simulation and excremental results with an induction machine.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.5
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• pp.377-387
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• 2012

A single-phase grid-connected PV system is known as suitable for housing of less than 3 kW. The DC link voltage in a single-phase PV system has necessarily twice component of fundamental wave. It makes high THD in the grid current. According to the problem, power quality is lower. Many engineers have studied about this problem. The most simple method is to use low pass filter on DC link voltage control. However it is affected by DC link voltage control bandwidth. If cutoff frequency is reduced to increase the performance of low pass filter, it also lowers DC link voltage control bandwidth. Second method is using band stop filter, it works good on steady state but not good on transient state. This paper proposes the new method for removing ripple voltage to get an exact current reference. It improves the responses on steady state and transient state. The performance was verified through computer simulation using MATLAB and actual experiments.