Leakage Current Reduction of Three-Phase <i>Z</i>-Source Three-Level Four-Leg Inverter for Transformerless PV System

Guo, Xiaoqiang; Yang, Yong; Wang, Baocheng; Blaabjerg, Frede

doi:10.1109/tpel.2018.2873223

Cited by 52 publications

(32 citation statements)

References 47 publications

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“…Compared with the two-level converter, the three-level converter operates only half of the switches in one cycle, which can effectively reduce the voltage stress of the switch [8,9]. The main functions of the high-frequency transformer are (1) to achieve electrical isolation of the DC bus and energy storage components, to reduce electromagnetic interference (EMI); (2) to adjust the voltage conversion level;…”

Section: Isolated Three-level Biditioanl Dc/dc Converter (Tl-bdc)mentioning

confidence: 99%

“…To avoid the risk caused by long-distance communication control, each unit is divided into three control layers according to the normalized voltage of DC bus and coordinated control of various units [7]. Compared with the two-level converter, the three-level converter has only half of the switches to change state peer cycle, and the voltage stress on the switch is only half of the bus voltage [8,9].…”

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confidence: 99%

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Bidirectional DC/DC and SOC Drooping Control for DC Microgrid Application

Zhang

Guo

2020

Electronics

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In DC microgrids, distributed energy storage plays a key role in stabilizing the DC bus voltage. The bidirectional DC/DC converter in the distributed energy storage system should be designed according to the voltage level and electromagnetic isolation requirements, and multiple energy storage units should be coordinated for load current distribution according to the state of charge (SOC). This paper proposes a SOC power index droop control strategy by communication lines to coordinate the fast and high-precision distribution of load current among multiple energy storage units, and the SOC between energy storage units quickly converges to a consistent state. Considering that communication lines are susceptible to interference, this paper further proposes an improved SOC power index droop control to overcome the effects of communication line failures. Considering the high cost of the energy storage unit, it should be connected to the DC microgrid in layers to achieve a reasonable allocation of resources in practical applications. In order to provide high-quality power to a large power grid, the quantification standards of the DC bus fluctuation range and the working range of each converter are further discussed to maximize the stability of the DC bus voltage and grid-connected power fluctuation.Keywords: bidirectional DC/DC converter; DC microgrid; distributed energy storage; SOC (state of charge) droop control IntroductionDistributed energy storage is the key issue to solve the issue of grid-connected renewable energy generation. For example, it can improve the ability of the grid to accept wind and photovoltaic (PV) power [1-3]. A typical DC microgrid structure is mainly composed of a distributed generation unit, an energy storage unit, a load cell, and a grid-connected converter [4][5][6], as shown in Figure 1. DC microgrid research focuses on stabilizing the DC bus voltage to ensure the power balance of the system. To stabilize bus voltage fluctuations and solve energy supply volatility issues, adding energy storage devices can improve the device's voltage sag and the inrush issues caused by load-switching, changes in natural conditions, and instantaneous faults in DC microgrid systems; this improves the reliability and scheduling flexibility of the distributed generation grid connection. Using low bandwidth communication control reduces the long-distance stability and DC microgrid distribution of the system due to network delay packet loss and other issues. To avoid the risk caused by long-distance communication control, each unit is divided into three control layers according to the normalized voltage of DC bus and coordinated control of various units [7]. Compared with the two-level converter, the three-level converter has only half of the switches to change state peer cycle, and the voltage stress on the switch is only half of the bus voltage [8,9].

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Section: Isolated Three-level Biditioanl Dc/dc Converter (Tl-bdc)mentioning

confidence: 99%

mentioning

confidence: 99%

Bidirectional DC/DC and SOC Drooping Control for DC Microgrid Application

Zhang

Guo

2020

Electronics

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“…The grid-connected PV inverters should be used in accordance with the grid standards and the applicable laws so as to comply with system protection and operation criteria. [10][11][12][13][14][15][16][17] Electrical factors such as leakage current protection, network frequency monitoring, active and reactive power control, and power quality are among these factors. [18][19][20][21] To this end, the most stringent and accurate standards are announced for PV systems to ensure the safety and reliability requirements of the system.…”

Section: Introductionmentioning

confidence: 99%

An FPGA‐based switching photovoltaic‐connected inverter topology for leakage current suppression in grid‐connected utilizations

Ghaderi

2020

Circuit Theory & Apps

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This study presents a symmetrical photovoltaic (PV)-connected inverter topology for eliminating the common-state leakage current in grid-connected inverters. A new inverter topology is introduced that minimizes the leakage current, increases efficiency, and is economically viable because it consists of six power switches and two power diodes that, compared with similar ones, consist of the same element numbers. In this inverter, power losses are lower than popular topologies such as H5, H6, and HERIC, and the voltage stresses of the switches are reduced. These features are due to the unique composition of the inverter branches and the location of the switches and diodes and the formation of a suitable freewheeling path for the current. The freewheeling path separates the alternating current (AC) side from the direct current side in the converter and cuts off the PV array leakage current to the AC grid. This will improve network reliability indices and maintain conservation standards. Finally, the content of this method is validated by comparing the proposed inverter with the existing conventional topologies. A prototype has been implemented for the performance analysis of the proposed inverter and results presented.

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“…By using ST mode which is achieved by switching all switches in the inverter leg, this topology can solve the ST problem, which causes the short-circuit phenomenon in conventional inverters, without incorporating the dead-time in the control signals of switches before feeding to switches, so the output distortion can be avoided. Due to the benefits of ZS topology, it is widely applied to photovoltaic (PV) systems [5], uninterruptable power supply (UPS) systems [6], and motor drives, etc. In [7][8][9][10][11][12] the authors explored the combination between the ZS network and the conventional 3L-T 2 I as well as 3L-NPCI topologies.…”

Section: Introductionmentioning

confidence: 99%

A Three-Level DC-Link Quasi-Switch Boost T-Type Inverter with Voltage Stress Reduction

Tran

et al. 2020

Energies

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In recent years, the three-level T-Type inverter has been considered the best choice for many low and medium power applications. Nevertheless, this topology is known as a buck converter. Therefore, in this paper, a new topology incorporating the dc-link type quasi-switched boost network with the traditional three-level T-type inverter is proposed to overcome the limit of traditional three-level T-Type inverter. The space vector pulse width modulation scheme is considered to control this topology, which provides some benefits such as enhancing modulation index and reducing the magnitude of common-mode voltage. For this scheme, the zero, medium, and large vectors are utilized to generate the output voltage. The shoot-through state which is adopted by turning on all power switches of inverter leg is inserted into zero vector to boost the dc-link voltage. As a result, there is no distortion at the output waveform. The control signal of intermediate network power switches is also detailed to improve the boost factor and voltage gain. As a result, the voltage stress on power devices like capacitors, diodes, and switches is decreased significantly. To demonstrate the outstanding of proposed structure and its control strategy, some comparisons between the proposed method and other ones are performed. Simulation and experimental prototype results are conducted to verify the accuracy of the theory and effectiveness of the inverter.

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Leakage Current Reduction of Three-Phase Z-Source Three-Level Four-Leg Inverter for Transformerless PV System

Cited by 52 publications

References 47 publications

Bidirectional DC/DC and SOC Drooping Control for DC Microgrid Application

Bidirectional DC/DC and SOC Drooping Control for DC Microgrid Application

An FPGA‐based switching photovoltaic‐connected inverter topology for leakage current suppression in grid‐connected utilizations

A Three-Level DC-Link Quasi-Switch Boost T-Type Inverter with Voltage Stress Reduction

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