• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.111-112
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• 2013

The three-phase four-leg voltage source inverter (VSI) topology can be an interesting option for the three phase-four wire system. With an additional leg, this topology can handle the neutral current, hence the DC link capacitance can be reduced significantly. In this paper the three dimensional space vector modulation (3D SVM) in ${\alpha}{\beta}{\gamma}$ coordinates for the three-phase four-leg VSI is presented. By using the 3D SVM method, the DC link voltage can be reduced by 16% compared with the split DC link capacitor topology and the output distortion can also be reduced under the unbalanced load condition.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.291-292
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• 2014

The three-phase four-leg voltage source inverter (VSI) topology can be an interesting option for the three phase-four wire system. With an additional leg, this topology can achieve superior performance with unbalanced and/or nonlinear load. This paper proposes a new hybrid controller which combines PI controller and resonant controller in synchronous frame for three phase four leg inverter. The hybrid controller is simple in structure and easy to implement. The performance of proposed controller is verified by the experiments and compared with that of the conventional PI controller.

• Journal of Power Electronics
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• 제16권6호
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• pp.2231-2242
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• 2016

A simplified model predictive control method is presented in this paper. This method is based on a future reference voltage vector for a three-phase four-leg voltage source inverter (VSI). Compared with the three-leg VSIs, the four-leg VSI increases the possible switching states from 8 to 16 owing to a fourth leg. Among the possible states, this should be considered in the model predictive control method for selecting an optimal state. The increased number of candidate switching states and the corresponding voltage vectors increase the calculation burden. The proposed technique can preselect 5 among the 16 possible voltage vectors produced by the three-phase four-leg voltage source inverters, based on the position of the future reference voltage vector. The discrete-time model of the future reference voltage vector is built to predict the future movement of the load currents, and its position is used to choose five preselected vectors at every sampling period. As a result, the proposed method can reduce calculation load by decreasing the candidate voltage vectors used in the cost function for the four-leg VSIs, while exhibiting the same performance as the conventional method. The effectiveness of the proposed method is demonstrated with simulation and experiment results.

• 전력전자학회논문지
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• 제10권4호
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• pp.339-346
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• 2005

본 논문에서는 3-레그 2상 인버터의 새로운 PWM방식을 제안하였다. 기존의 3-레그 인버터의 PWM방식은 전형적인 SVPWM 방식을 적용하여 PWM 방식이 복잡하다. 3-레그 2상 인버터를 "중성점이 있는 4-레그 인버터"의 등가회로라고 할 때 3-레그 인버터에서 형성되는 6개의 섹터는 4개의 섹터로 축소되며, 각 영역에서는 SYPWM 방식 대신 단순화된 정현파형 PWM방식을 적용할 수 있다. 각 레그의 스위치마다 스위칭 시간을 계산하는 스위칭 패턴을 제시하였다. 제안된 ,3-레그 인버터의 PWM방식에 대한 타당성을 확인하기 위해 모의 실험과 실험이 실행되었다.

• Journal of Power Electronics
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• 제16권5호
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• pp.1928-1938
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• 2016

The three-phase four-wire shunt active power filter (APF) is an effective method to solve the harmonic problem in three-phase four-wire power systems. In addition, it has two possible topologies, a four-leg inverter and a three-leg inverter with a split-capacitor. There are some studies investigating DC-link voltage control in three-phase four-wire APFs. However, when compared to the four-leg inverter topology, maintaining the balance between the DC-link upper and lower capacitor voltages becomes a unique problem in the three-leg inverter with a split-capacitor topology, and previous studies seldom pay attention to this fact. In this paper, the influence of the balance between the two DC-link voltages on the compensation performance, and the influence of the voltage balance controller on the compensation performance, are analyzed. To achieve the balance between the two DC-link capacitor voltages, and to avoid the adverse effect the voltage balance controller has on the APF compensation performance, a new DC-link voltage balance control strategy for the three-phase four-wire split-capacitor APF is proposed. Representative simulation and experimental results are presented to verify the analysis and the proposed DC-link voltage balance control strategy.

• Journal of Power Electronics
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• 제17권1호
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• pp.181-189
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• 2017

The three-phase four-leg voltage-source inverter topology is an interesting option for the three-phase four-wire system. With an additional leg, this topology can achieve superior performance under unbalanced and nonlinear load conditions. However, because of the low bandwidth of conventional controllers in high-power inverter applications, the system cannot guarantee a balanced output voltage under the unbalanced load condition. Most of the methods proposed to solve this problem mainly use the multiple synchronous frame method, which requires several controllers and a large amount of computation because of frame transformation. This study proposes a simple hybrid controller that combines proportional-integral (PI) and resonant controllers in the synchronous frame synchronized with the positive-sequence component of the output voltage of the three-phase four-leg inverter. The design procedure for the controller and the theoretical analysis are presented. The performance of the proposed method is verified by the experimental results and compared with that of the conventional PI controller.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2004년도 춘계학술대회
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• pp.193-197
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• 2004

The four-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. In this paper a novel line interactive Uninterruptible Power Supply(UPS) using the two four-leg VSCs is proposed. One VSC is in parallel with the ac link reactor of the power source side, and the other is in series with the load. The parallel four-leg voltage source inverter controls the three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series four-leg voltage source inverter compensates the line voltage and allows it to be balanced and harmonic-free. Both of the parallel and series four-leg voltage source inverters always act as independently controllable voltage sources, so that the three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulations results.

• Journal of Power Electronics
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• 제14권5호
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• pp.1028-1037
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• 2014

To optimize controller design and improve static and dynamic performances of three-phase four-leg inverter systems, a compound control method that combines state feedback and quasi-sliding mode variable structure control is proposed. The linear coordinate change matrix and the state variable feedback equations are derived based on the mathematical model of three-phase four-leg inverters. Based on system relative degrees, sliding surfaces and quasi-sliding mode controllers are designed for converted linear systems. This control method exhibits the advantages of both state feedback and sliding mode control. The proposed controllers provide flexible dynamic control response and excellent stable control performance with chattering suppression. The feasibility of the proposed strategy is verified by conducting simulations and experiments.

• Journal of Power Electronics
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• 제10권1호
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• pp.91-96
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• 2010

In this paper, a simplified control algorithm for a three-phase, four-wire unified power quality conditioner (UPQC) is presented to compensate for supply voltage distortions/unbalance, supply current harmonics, the supply neutral current, the reactive power and the load unbalance as well as to maintain zero voltage regulation (ZVR) at the point of common coupling (PCC). The UPQC is realized by the integration of series and shunt active filters (AFs) sharing a common dc bus capacitor. The shunt AF is realized using a three-phase, four leg voltage source inverter (VSI) and the series AF is realized using a three-phase, three leg VSI. A dynamic model of the UPQC is developed in the MATLAB/SIMULINK environment and the simulation results demonstrating the power quality improvement in the system are presented for different supply and load conditions.

• 조명전기설비학회논문지
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• 제29권2호
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• pp.54-61
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• 2015

In 3-phase 4-wire inverter, the unbalanced loads cause to increase the neutral current which brings the voltage deviation between the split dc-link capacitors to be larger. In order to solve this problem, a neutral leg is provided additively to the ordinary inverter circuit and the associated control methods are devised. This paper proposes a new neutral-leg controller based on a PR controller and shows relatively good performance even under unbalanced linear loads and nonlinear loads. The proposed control strategy illustrates its effectiveness under the various operating conditions through simulation works.