• Journal of Power Electronics
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• v.16 no.5
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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 Electrical Engineering and Technology
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• v.13 no.3
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• pp.1131-1137
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• 2018

In this paper, the authors suggest a new control algorithm for a three-phase four-wire photovoltaic (PV) inverter with imbalance load compensation function using conventional proportional-integral (PI) controllers. The maximum power of PV panel is calculated by the MPPT control loop. The reference varying signals of current controllers are transformed to two different rotating frames where they become constant signals. Then simple PI controllers are applied to achieve zero steady-state error of the controllers. The proposed control algorithm are modeled and simulated with imbalance load configuration to verify its performance. The simulation results show that the maximum PV power is transferred to the grid and the imbalance power is compensated successfully by the proposed control algorithm. The inverter has a fast response (~4 cycles) during the transient period. The proposed control algorithm can be effectively utilized to the three-phase four-wire inverter with imbalance load compensation function.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1315-1324
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• 2018

A novel three-phase four-wire inverter topology is presented in this paper. This topology is equipped with a special capacitor balance grid without magnetic saturation. In response to unbalanced load and unequal split DC-link capacitors problems, a qusi-full-bridge DC/DC topology is applied in the balance grid. By using a high-frequency transformer, the energy transfer within the two split dc-link capacitors is realized. The novel topology makes the voltage across two split dc-link capacitors balanced so that the neutral point voltage ripple is inhibited. Under the condition of a stable neutral point voltage, the three-phase four-wire inverter can be equivalent to three independent single phase inverters. As a result, the three-phase inverter can produce symmetrical voltage waves with an unbalanced load. To avoid forward transformer magnetic saturation, the voltages of the primary and secondary windings are controlled to reverse once during each switching period. Furthermore, an improved mode chosen operating principle for this novel topology is designed and analyzed in detail. The simulated results verified the feasibility of this topology and an experimental inverter has been built to test the power quality produced by this topology. Finally, simulation results verify that the novel topology can effectively improve the inhibition of an inverter with a three-phase unbalanced load while decreasing the value of the split capacitor.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.4
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• pp.333-341
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• 2013

In this paper, a feedback linearization control is proposed to regulate the output voltages of a three-phase four-wire inverter under the unbalanced and nonlinear load conditions. First, the nonlinear model of system including the output LC filters is derived in the d-q-0 synchronous reference frame. Then, the system is linearized by the multi-input multi-output feedback linearization. The tracking controllers for d-q-0-components of three-phase line-to-neutral load voltages are designed by linear control theory. The experimental results have shown that the proposed control method gives the good performance in response to the load conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.2
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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.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.4
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• pp.359-365
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• 2002

Three-phase four-wire electrical distribution systems have been widely employed in manufacturing plants, commercial and residential buildings. Due to the nonlinear loads, the neutral conductor carries excessive harmonic currents resulting in wiring failure of the neutral conductor, overloading of the distribution transformer and a voltage drop between the neutral and the ground. This paper proposes a reduced rating active power filter to suppress neutral current harmonics in three-phase four-wire electrical distribution systems. The proposed system is simple in control and the VA rating of the inverter could be significantly reduced since only the fundamental current due to unbalanced loading flows through the inverter switch. The experimental results on a prototype validate the proposed control approach.

• Proceedings of the KIPE Conference
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• 2013.11a
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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.

• Proceedings of the KIPE Conference
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• 2014.07a
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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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• v.17 no.1
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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.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.2
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• pp.176-183
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• 2014

Three-phase four-wire distribution systems are used for both three-phase three-wire loads and single-phase two-wire consumer appliances in South Korea, Myanmar and other countries. Unbalanced load conditions frequently occur in these distribution systems. These unbalanced load conditions cause unbalanced voltages for three-phase and single-phase loads, and increase the loss in the distribution transformer. In this paper, we propose constant DC capacitor voltage control based strategy for the active load balancer (ALB) in the three-phase four-wire distribution systems. Constant DC capacitor voltage control is always used in active power line conditioners. The proposed control strategy does not require any computation blocks of the active and reactive currents on the distribution systems. Balanced source-side currents with a unity power factor are obtained without any calculation block of the unbalanced active and reactive components on the load side. The basic principle of the constant DC capacitor voltage control based strategy for the ALB is discussed in detail and then confirmed by both digital computer simulations using PSIM software and prototype experimental model. Simulation and experimental results demonstrate that the proposed control strategy for the ALB can balance the source currents with a unity power factor in the three-phase four-wire distribution systems.