Leakage Current Elimination Research Articles

A Five-Level Transformer-Less Grid-Tied Inverter Structure With Capacitive Voltage Divider Concept With Leakage Current Elimination

This paper presents a novel single-phase inverter with six switches and five levels that shares a common ground and does not require a transformer. The proposed inverter is intended for use in photovoltaic systems that are connected to the grid. The proposed inverter is derived from the concept of a capacitive voltage divider (CVD) circuit, so that, the leakage current will be eliminated. The CVD circuit produces three levels of output voltages in the proposed inverter. The proposed novel inverter has several significant advantages, such as the elimination of leakage current without the need for additional components, the ability to transfer reactive power fully, and the use of fewer components compared to current five-level transformer-less inverters. Additionally, the voltage stress is evenly distributed across power switches, resulting in higher efficiency. Furthermore, the inverter is designed to automatically balance voltage in capacitors without requiring an additional control system. The proposed inverter achieves these advantages using a suitable switching scheme. The paper also includes an explanation of the proposed circuit, the process for designing minimum capacitors, theoretical loss calculation, and a comparison of features with similar topologies todemonstrate the efficiency of the proposedinverter. Inaddition, a 1 kVA experimental prototype is constructed to showcase the effectiveness of the proposed inverter.

A new transformer‐less common grounded five‐level grid‐tied inverter with leakage current elimination and voltage boosting capability for photovoltaic applications

AbstractDue to serious Concerns such as air pollution, global warming, and fossil fuels shortcoming, renewable energy sources such as photovoltaic applications are dramatically being integrated into the power generation systems all of the world. Here, a new switched‐capacitor‐based transformer‐less grid‐tied inverter has been proposed. By applying the series–parallel switching technique of the utilized switched‐capacitor module, the voltage boosting capability has been obtained. By implementing common ground technique, high overall efficiency and leakage current elimination capability have been obtained. Since the proposed inverter provides a multi‐level output voltage, the total harmonic distortion of the injected grid current is reduced. The introduced control strategy has been implemented to control both active and reactive powers and generate the switches pulses. Therefore, a high quality and adjusted current is injected to the grid. This inverter requires a single renewable energy source as input DC source. Here, the comprehensive description of the proposed inverter and its performance with design considerations have been presented. The proposed structure has been compared with several similar structures and the obtained results have been investigated. To evaluate the performance of the proposed inverter, a 620 W laboratory prototype is assembled and experimental results are analyzed.

Integrated Transformerless EV Charger With Symmetrical Modulation

This article introduces a modulation technique that nearly eliminates the common-mode (CM) leakage currents in the transformerless (nonisolated) dual-inverter single-phase charger. This improvement allows for the safe use and commercialization of the transformerless charger, making superior charger efficiency, power density, and cost possible. The CM model of the system is derived to guide the choice of the modulation scheme. Simulations are conducted to validate the CM performance predictions derived analytically. Finally, an experimental 6.6-kW charger prototype is presented to verify the CM leakage current elimination. The experimental results show not only that the proposed modulation meets the required standards regarding CM currents, but also that it does so by a wide margin, and it even outperforms the isolated system used for comparison.

A New Transformer-Less Single-Phase Photovoltaic Inverter to Improve the Performance of Grid-Connected Solar Photovoltaic Systems

Photovoltaic (PV) energy systems have found diverse applications in fulfilling the increasing energy demand worldwide. Transformer-less PV inverters convert the DC energy from PV systems to AC energy and deliver it to the grid through a non-isolated connection. This paper proposes a new transformer-less grid-connected PV inverter. A closed-loop control scheme is presented for the proposed transformer-less inverter to connect it with the power grid. The proposed transformer-less inverter reduces extra leakage current and holds the common-mode voltage at a constant point. To eliminate extra leakage current, as well as achieve constant common-mode voltage, a midpoint clamping method is utilized to operate the inverter. The proposed transformer-less inverter is formed of seven insulated gate bipolar transistors (IGBTs) employing a unipolar sinusoidal pulse width modulation (SPWM) technique for switching purposes. An LCL filter is employed to reshape the two-level inverter output voltage and current to obtain closer sinusoidal waveforms. The output voltage and current total harmonic distortion (THD) of the proposed transformer-less inverter were found to be 1.25% and 0.94%, respectively, in the grid-connected mode. The leakage current elimination mechanism with the proposed transformer-less inverter is deeply analyzed in this paper. The performances of the proposed transformer-less inverter were evaluated with MATLAB/Simulink simulation and validated in a laboratory scale experiment.

Analysis of a Photovoltaic System Based on a Highly Efficient Single-Phase Transformerless Inverter

The essential requirement for a cleaner environment, along with rising consumption, puts a strain on the distribution system and power plants, reducing electricity availability, quality, and security. Grid-connected photovoltaic systems are one of the solutions for overcoming this. The examination and verification of transformerless topologies and control techniques was a significant goal of this study. The transformerless concept is advantageous for its high efficiency; the transformerless converter has added advantages of reduced price, complexity, weight, and size. This study presents a novel high-efficiency transformerless architecture that does not create common-mode currents and does not inject DC current into the grid. A single-phase transformerless inverter circuit with two step-down converters was constructed in this study. Low-frequency switches determine the polarity of the grid connection. In order to control the gate pulses of switching devices, which each regulate a half-wave of the output current, a PIC 16F877 was employed. Because there were fewer semiconductors and they were simpler to operate, it was possible to achieve a high degree of efficiency and reliability. A prototype model with input 12 V, 2 A was fabricated, test results were obtained with reduced common-mode current and DC current, and high efficiency was obtained with reduced switching losses. Further investigation for the improvement of efficiency with the elimination of ground current and leakage current has been analysed through simulation.

Enhanced Power Quality PV Inverter With Leakage Current Suppression for Three-Phase SECS

This article presents an enhanced power quality solar photovoltaic (PV) inverter enabling common-mode leakage current elimination. A three-phase transformerless solar energy conversion system is considered here, which, along with peak active-power production from PV array, ensures different power quality improvement capabilities such as grid current harmonics mitigation, grid currents balancing while also offering the grid reactive power support. Unlike conventional power quality inverters, this strategy is robust with respect to abnormalities in grid voltages at far radial ends, and does not compromise with the leakage currents caused by parasitic capacitance of PV array with ground. Common practice in the PV inverter power quality control is to neglect the PV leakage currents; however, they considerably affect the system performance by deteriorating the power quality and causing the safety issues of operating personnel. The standards VDE-00126 and NB/T-32004, therefore, compel the transformerless PV systems to operate with leakage current under 300 mA range. Various simulation and test results show the satisfactory performance of the presented strategy, even under various grid-side abnormalities. The comparative analysis with the state-of-the-art techniques shows the effectiveness of the strategy. Under all test conditions, the harmonics in grid currents are observed within limits as per the IEEE-519 and IEC-61727 standards, whereas the PV leakage currents are maintained well within the range recommended by VDE-00126 standard.

High Efficiency Transformerless Photovoltaic DC/AC Converter with Common Mode Leakage Current Elimination: Analysis and Implementation

Photovoltaic (PV) electricity is widely used because of its positive environmental impact. To properly feed this energy into the grid, an electronic power converter, known as a PV inverter, is needed, which may or may not use a transformer. This article details the analysis and design of a transformerless photovoltaic inverter topology for grid-connected applications. This converter offers high efficiency, a low number of elements, and negligible leakage current, which makes it a good alternative for this application. The converter has been validated through an experimental prototype and compared with other topologies with similar characteristics.

A simplified implementation of NLSPWM control strategy for SqZS inverter via model‐driven processor programming method

AbstractThe transformerless single‐phase semi‐quasi‐Z‐source inverter (SqZSI) has a nonlinear gain curve and requires nonlinear sinusoidal pulse width modulation (NLSPWM) to achieve sinusoidal voltage at the output AC terminal. Although the SqZSI provides some advantages, for example, leakage current elimination, doubly grounded, low volume, and low cost, it needs nonlinear modulation control. The NLSPWM is relatively complex among single‐phase modulation methods and it is considered a disadvantage for this topology, so this paper presents a model‐driven processor programming method that facilitates the implementation of NLSPWM. The developed programming method utilizes a Blockset environment in MATLAB/Simulink to implement NLSPWM, and then the obtained model is compiled and directly uploaded to the ARM Cortex‐M4‐based STM32F4 processor. In this approach, there is no need for coding in C programming language, and only the Simulink mathematical blocks are used so it simplifies the implementation process. The same Simulink model used to model the inverter control is slightly edited for implementation, which accelerates the debugging cycle. Experimental results of 100 W SqZSI confirm the desired and accurate performance of this low‐cost method. The qualitative comparison of the processor programming methods and the performance comparison of the developed SqZSI based on this approach verify the simplicity of implementation.

A Common Ground Four Quadrant Buck Converter for DC-AC Conversion

With the increasing stand-alone and grid integrated low power renewable energy generation, the use of non-isolated DC-AC converters has increased multifold. However, the non-isolated power conversion with conventional DC-AC converters can cause high leakage currents due to parasitic capacitances. To resolve this problem, research on common ground converter topologies is gaining significance. This paper presents a novel single-phase DC-AC converter with common ground for the input and output terminals. There are only minor modifications required in comparison to the topology of the commonly used conventional H-bridge inverter for DC-AC conversion. In addition, the basic components and their counts remain the same. The gain ratio of the proposed inverter is such that it reduces the effect of switching delays. The availability of common ground for DC input and AC output sides provides the advantage of zero common-mode voltage and avoids leakage currents due to parasitic capacitances. The voltage gain ratio of the proposed converter is superior compared to the H-bridge inverter. Further, the switch stresses, switch utilization ratio and ratings of the constituent components have been derived for an accurate design of the converter. The proposed converter is observed to be more preferable when compared with other converters and modulation techniques for leakage current elimination based on the number of components and complexity of the circuit and control. The simulation and experimental results for different loads and load changes are presented to verify the theoretical claims. It is capable of supporting real and reactive power while operating competently under sudden changes in load. Therefore, the proposed common ground DC-AC converter can replace the H-bridge by modifying its circuit or replacing it with readily available half-bridge modules to obtain zero common-mode voltage and leakage currents. Hence, it is particularly attractive for low-power renewable generation and energy storage system applications.

Highly Efficient Transformerless Inverter with Flying-Capacitor Buck–Boost for Single-Phase Grid-Connected PV Systems

Grid-connected inverters (GCI) are commonly used in PV system applications to generate a regulated AC current to feed into the grid. Transformerless inverters are the most advanced inverters that are used in industry, which provide efficiency with smaller size and lower cost. This paper proposes a grid-connected single-phase transformerless inverter with the technology of common ground and the virtual DC bus concept. In this topology, the grid neutral is connected directly to the PV ground, which generates a constant common mode voltage (CMV), thus leading to the elimination of the leakage current caused by the PV array’s parasitic capacitance. The proposed inverter has a buck–boost circuit with a flying capacitor to generate the DC bus for a negative power cycle, four switches, and two diodes. A unipolar sinusoidal pulse width modulation (SPWM) technique is used which reduces the output filter requirements. In addition, only one switch carries the load current during the active states of both the negative and positive power cycle, thus minimizing the conduction losses. One more advantage presented in the proposed inverter is its ability to charge the flying capacitor during all operation states due to the existence of the buck–boost circuit. Design and theoretical calculations were conducted in this paper to optimize the losses. Moreover, the PSIM simulation was used to validate the proposed topology inverter, verify the performance by showing leakage current elimination, and achieve unipolar voltage in the output bus. The simulation results show a peak efficiency of 98.57% for a 2 kW inverter, which agrees with the theoretical calculations.

A Five-Level Transformer-Less Inverter With Self-Voltage Balancing and Boosting Ability

Transformer-less inverters (TIs) are widely used in photovoltaic (PV) applications owing to their low cost and high efficiency. However, the combined effect of high-frequency common mode voltage and PV parasitic capacitance burdens the TIs with undesired ground leakage current. In this article, a switched capacitor (SC)-based five-level TI is proposed. The negative dc rail of the proposed TI is directly connected to the grid neutral, thereby completely eliminating the leakage current. Besides, it has the inherent capability of boosting the output voltage without using any magnetic component or additional circuitry. For several instances in every fundamental cycle, the SCs are paralleled with the input voltage source and hence are self-balanced. The proposed topology does not have any limitation on modulation index since the SC voltages are self-balanced and hence less complex or no dedicated control scheme is required. Further, a quantitative comparative study is presented, highlighting the benefits of the proposed TI regarding boosted voltage, elimination of leakage current, and reduced component count. Finally, in order to verify the performance of the proposed TI, detailed simulations followed by experiments on a laboratory prototype developed by using DS1202/1302 dSPACE controller are carried out and the results presented for both steady-state and dynamic conditions verify the feasibility of the proposed TI.

A Single-Phase Five-Level Transformer-Less PV Inverter for Leakage Current Reduction

Multilevel inverters are becoming more and more popular in photovoltaic applications because of lower total harmonic distortion, lower switching stress and lower electromagnetic interference. In this article, a single-phase five-level transformer-less PV inverter is proposed for the purpose of leakage current reduction. The inverter is based on a flying capacitor (FC) configuration, the voltages of FCs are balanced at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> /4 through the coordination of the two half-bridge at the switching frequency, helps to reduce investment cost in passive elements. Two bidirectional circuits are added to guarantee a constant common-mode (CM) voltage. The leakage current elimination mechanism is analyzed in detail with operational states and CM equivalent model. The losses are analyzed, the control strategy and the FCs are detailed designed. A comparison is also made in terms of the number of elements, voltage stress and CM voltage. Experiment results under grid-connected condition show that the proposed topology achieves both excellent differential-mode and CM performance.

Multilevel common‐ground inverter with voltage boosting for PV applications

Nowadays, transformer-less Photovoltaic-based grid-connected inverters are more popular in renewable energy application due to their reduced size, cost, and high efficiency. However, the absence of galvanic isolation leads to the flow of leakage current in such system hindering personal safety, and deteriorating power quality. Therefore, this paper presents a five-level transformer-less inverter topology for PV applications with less component count and reduced complexity. The proposed inverter topology completely eliminates the common mode leakage current. Besides, the proposed topology has an inherent capability to boost the voltage without using any magnetic component or boosting circuit, and is based on the principle of switched/auxiliary capacitor. The proposed topology do not have any limitation of modulation index since the auxiliary capacitors are naturally balanced, hence less complex or no dedicated control scheme is required for balancing/regulating the auxiliary capacitor voltages. In order to verify the performance of the proposed inverter topology, a laboratory prototype is developed which confirms the operation, and feasibility of the proposed inverter. Results depicting the output voltage, load current, and voltage across the auxiliary capacitor are presented for various operating conditions. Further, simulation results depicting the leakage current in the proposed, H5, and H6 topologies are included. Finally, a quantitative comparison study is done, highlighting the benefits of the proposed inverter topology regarding boosted voltage, elimination of leakage current, and reduced component count.

Low Voltage Ride-Through Capability of a Novel Grid Connected Inverter Suitable for Transformer-Less Solar PV–Grid Interface

In order to face the challenges due to the large-scale integration of photovoltaic (PV) inverters on the distribution side, the grid-connected PV inverters are expected to provide certain ancillary services. These ancillary services include reactive power support, low voltage ride through (LVRT), and harmonic compensation, just to name a few. In this article, the LVRT capability of a $\ddot{\text{C}}$ uk-derived novel inverter, 6sw- $\ddot{\text{C}}$ uk derived transformer-less inverter (6sw-CDTI), suitable for transformer-less grid–PV interface, is explored. The transformer-less inverter, 6sw-CDTI, considered in this work can provide the desired ancillary services more efficiently and at a lesser cost as compared to the conventional inverters. Reactive power support to the grid can be provided without distorting the injected current by 6sw-CDTI with no dc injection due to symmetrical operation in both half cycles. Besides this, the leakage current elimination is not affected because the topological structure is not altered. Experimental results obtained from a 200-W laboratory prototype illustrate how additional control features can be integrated in the inverter control scheme for LVRT. Single-phase instantaneous p-q theory is used for inverter control, and a feed-forward component is added in the control scheme for improved dynamic response.

Integrated step‐up non‐isolated inverter with leakage current elimination for grid‐tied photovoltaic system

This study presents a non-isolated step-up inverter without leakage current for low-voltage renewable energy generation such as photovoltaic (PV) cells grid connection. From the structure of the proposed inverter, the negative terminal of the PV array is directly linked with the grid neutral, so the common mode voltage of the parasitic capacitance can be kept constant and the leakage current will not be generated in theory. Moreover, this transformerless inverter can produce an AC output voltage higher than the input DC voltage, which will reduce the sizes of the generation system. A switching modulation strategy carrier-based is analysed in detail when the input inductor current is operated in discontinuous conduction mode. The operation modes of the proposed inverter are also discussed, respectively, in positive and negative half line cycles. Finally, a digital experimental prototype is tested in the laboratory, and the experimental results are consistent with the theoretical analysis.

An Improved Proposed Single Phase Transformerless Inverter with Leakage Current Elimination and Reactive Power Capability for PV Systems Application

Single-phase transformerless inverters are broadly studied in literature for residential-scale PV applications due to their great advantages in reducing system weight, cost and elevating system efficiency. The design of transformerless inverters is based on the galvanic isolation method to eliminate the generation of leakage current. Unfortunately, the use of the galvanic isolation method alone cannot achieve constant common mode voltage (CMV). Therefore, a complete elimination of leakage current cannot be achieved. In addition, modulation techniques of single-phase transformerless inverters are designed for the application of the unity power factor. Indeed, next-generation PV systems are required to support reactive power to enable connectivity to the utility grid. In this paper, a proposed single-phase transformerless inverter is modified with the clamping method to achieve constant CMV during all inverter operating modes. Furthermore, the modulation technique is modified by creating a new current path in the negative power region. As a result, a bidirectional current path is created in the negative power region to achieve reactive power generation. The simulation results show that the CMV is completely clamped at half the DC link voltage and the leakage current is almost completely eliminated. Furthermore, a reactive power generation is achieved with the modified modulation techniques. Additionally, the total harmonic distortion (THD) of the grid current with the conventional and a modified modulation technique is analyzed. The efficiency of the system is enhanced by using wide-bandgap (WBG) switching devices such as SiC MOSFET. It is observed that the efficiency of the system decreased with reactive power generation due to the bidirectional current path, which leads to increasing conduction losses.

Model predictive control methods of leakage current elimination for a three‐level T‐type transformerless PV inverter

This study presents finite control set model predictive control (FCS-MPC) methods to eliminate leakage current for a three-level T-type transformerless photovoltaic (PV) inverter without any modification on topology or any hardware changes. The proposed FCS-MPC methods are capable of eliminating the leakage current in the transformerless PV system by applying the defined candidate voltage vector (VV) combinations with only six medium and one zero VVs (6MV1Z) or three large and three small VVs, which generate constant common-mode voltage to perform the optimisation in every control period. With fewer VVs used for the optimisation, the computational burden can be significantly reduced. Furthermore, comparative analysis is performed to show that among these proposed methods, the 6MV1Z method can achieve satisfactory performances in both grid current tracking and neutral point potentials balance control even with less number of candidate VVs, which exhibits the FCS-MPC as an alternative control strategy to be used in the grid-connected transformerless PV system. Finally, experiments are performed to validate the analysis and the effectiveness of the proposed methods.

Analytical study and simulation of a transformer-less photovoltaic grid-connected inverter with a delta-type tri-direction clamping cell for leakage current elimination

PurposeThis paper aims to propose a new transformer-less inverter structure to reduce the common-mode leakage current in grid-connected photovoltaic (PV) systems.Design/methodology/approachThe proposed circuit structure is the same as the conventional full-bridge inverter with three additional power switches in a triangular structure. These three power switches are between the bridge and the output filter, and they mitigate the common-mode leakage current flowing toward the PV panels’ capacitors. The common-mode leakage current mitigation is done through the three-direction clamping cell (TDCC) concept. By clamping the common-mode voltage to the middle voltage of the DC-link capacitors, the leakage current and the total harmonic distortion (THD) of the injected current to the grid is effectively reduced. Therefore, the efficiency is improved.FindingsThe switching modes and the control method are introduced. A comparison is carried out between the proposed structure and other solutions in the literature. The proposed topology and its respective control method are simulated by PSCAD/EMTDC software. The simulation results validate the advantages of the presented structure such as clamping the common-mode voltage and reducing leakage current and THD of injected current to the grid.Originality/valuePresenting a single phase-improved inverter structure with low-leakage current for grid-connected PV power systems represents a significant original contribution to this work. The proposed structure can inject a sinusoidal current with low THD to the AC grid, and the power factor is unity on the AC side. In the half positive cycle, one of the switches in the TDCC is turned off under zero current. Besides, one of the other switches in TDCC is turned on with zero voltage and, therefore, its turn-on switching losses are zero. The efficiency of the proposed topology is high because of the reduction of leakage current and power losses. Accordingly, the presented topology can be a good solution to the leakage current elimination.

Dual‐buck full‐bridge grid‐connected inverter with common‐mode leakage current elimination

The dual-buck full-bridge grid-connected inverter (DFGI) is well known as its no shoot-through problem, high efficiency and high reliability, but the common-mode leakage current exists in the positive half cycle. To solve the problems of common-mode leakage current of the conventional DFGI, a new DFGI topology is proposed. The corresponding modulation strategy is presented. Meanwhile, on the basis of the theoretical analysis, it can eliminate the common-mode leakage current of conventional DFGI. The experimental results prove the validity of the theoretical analysis.

Improved Transformerless Inverter with Common-mode Leakage Current Elimination for a Photovoltaic Energy Conversion System

Improved Transformerless Inverter with Common-mode Leakage Current Elimination for a Photovoltaic Energy Conversion System