Common Mode Leakage Current Research Articles

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.

A Multilevel Transformerless Inverter Employing Ground Connection Between PV Negative Terminal and Grid Neutral Point

For the safe operation of transformerless grid connected photovoltaic (PV) inverters, the issue of common mode (CM) leakage current needs to be addressed carefully. In this paper, a novel multilevel transformerless inverter topology is proposed, which completely eliminates CM leakage current by connecting grid neutral point directly to the PV negative terminal, thereby bypassing the PV stray capacitance. It provides a low-cost solution consisting of only four power switches, two capacitors, and a single filter inductor. As compared to half-bridge topologies, with this inverter a minimum of 27% and maximum of 100% more output voltage is obtained for the same dc-link voltage. The proposed inverter is analyzed in detail and its switching pattern to generate multilevel output while maintaining the capacitor voltage is discussed. Simulations and experiments results confirm the feasibility and good performance of the proposed inverter.

A Capacitance-Minimized, Doubly Grounded Transformer less Photovoltaic Inverter With Inherent Active-Power Decoupling

Two major challenges in the transformerless photovoltaic (PV) inverters are the presence of common-mode leakage currents, and as in most single-phase converters the need for reliable and compact double-line-frequency power decoupling. In the proposed doubly grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the capacitive-coupled common-mode ground currents. The decoupling capacitance requirement is minimized by a dynamically variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The topology uses only four switches and potentially enables a high power density solution. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100/75 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output with a wide range of power factor has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. Extensive experimental results from the prototype are presented to validate the concept, design, and superior performance of the proposed topology.

A Family of Neutral-Point-Clamped Circuits of Single-Phase PV Inverters: Generalized Principle and Implementation

The common-mode leakage current should be carefully considered when designing a transformer-less photovoltaic (PV) inverter since the leakage current can cause the output current distortion and increase the operational risk. The unipolar sinusoidal pulse width modulation of the traditional H-bridge inverter can produce the superior output performance but will cause a high-frequency fluctuated common-mode voltage and consequently the nonnegligible leakage current. To attenuate the fluctuation phenomena of common-mode voltage, few neutral-point-clamped (NPC) circuits have been designed to clamp the neutral-point voltage and maintain the common-mode voltage constant. This paper analyzes the equivalent common-mode circuit of single-phase inverters and proposes a generalized design principle of multiterminal NPC circuits, whose unidirectional and bidirectional variations are fully analyzed. Subsequently, two types of single-phase PV inverters with the NPC circuits are proposed. Also, the operational losses and component counts are compared between the proposed topologies and the traditional NPC inverters. The experimental results verified the theoretical findings.

Novel Hybrid Analytical/Numerical Conducted EMI Model of a Flyback Converter

A hybrid analytical/numerical conducted an electromagnetic interference (EMI) modeling approach, which adopts both numerical method and analytical method, is proposed in this paper. In this model, the noise source is calculated directly with the original data from oscilloscopes. The noise path at different operating status is extracted from the original converter topology and its analytical expression is then derived. Also, according to the EMI receiver detector mode, the algorithm of the EMI receiver is proposed in this paper. Peak (PK), average (AV), and quasipeak (QP) values of the EMI can then be calculated to analyze the impact of each relevant component. The analytical method is provided to carry out PK, AV, and QP simulations accurately and fast. The simulation and experimental results for common mode leakage currents validate this EMI model. Furthermore, two analysis examples are given to illustrate how this model is applied for engineers.

Analysis of the Modulation Strategy for the Minimization of the Leakage Current in the PV Grid-Connected Cascaded Multilevel Inverter

This paper presents a pulse width modulation (PWM) technique for the minimization of the leakage current in the grid-connected/stand-alone transformerless photovoltaic (PV)-cascaded multilevel inverter (CMLI). The proposed PWM technique is integrated with the MPPT algorithm and is applied to the five-level CMLI. Furthermore, using the proposed PWM technique the high-frequency voltage transitions in the terminal and common mode voltages are minimized. Thus, the proposed PWM technique minimizes the leakage current of the PV array and electromagnetic interference filter requirement in the system without addition of any extra switches. Furthermore, this paper also presents the analysis for the terminal voltage across the PV array and the common mode voltage of the inverter based on the switching function. Using the given analysis, the effect of the PWM technique can be analyzed, as it directly links the switching function with the common mode voltage and leakage current. Also, the proposed PWM technique requires reduced number of carrier waves compared to the conventional sinusoidal pulse width modulation technique for the given CMLI. Complete details of the working principle and analysis with the support of simulation and experimental results of the proposed PWM technique are presented in this paper.

Common mode behavior in grid connected DC and AC decoupled PV Inverter topologies

Abstract The transformer-less grid connected inverters are gaining more popularity due to their high efficiency, very low ground leakage current and economic feasibility especially in photovoltaic systems. The major issue which surfaces these systems is that of common mode leakage current which arises due to the absence of an electrical transformer connected between the inverter and the utility grid. Several topologies have evolved to reduce the impact of common mode leakage current and a majority of them have succeeded in eliminating the impacts and have well kept them within the limits of grid standards. This paper compares and analyses the impact of the common mode leakage current for four popular inverter configurations through simulation of the topologies such as H5, H6, HERIC and FBZVR inverters.

Improved single‐phase transformerless inverter with high power density and high efficiency for grid‐connected photovoltaic systems

This study proposes an improved single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems. The proposed inverter is comprised of the dual-paralleled-buck inverter and two auxiliary circuits for the zero-current switching turn-off of the diodes. The dual-paralleled-buck inverter and auxiliary circuits are joined by two coupled inductors. To achieve high power density, the proposed inverter operates at high switching frequency of 40 kHz. This leads to lower filter inductors and lower conduction losses of the filter inductors than conventional full-bridge inverters. Moreover, two auxiliary circuits reduce the switching losses caused by high switching frequency operation. Furthermore, the proposed inverter provides the low common-mode leakage current, which satisfies the criteria given by VDE-0126-1-1. Thus, the proposed inverter achieves the maximum efficiency of 99%. The operation principle of the proposed inverter is analysed and verified. Experimental results for a 1 kW prototype are obtained to show the performance of the proposed inverter.

Single-stage Three-phase Differential-mode Buck-Boost Inverters with Continuous Input Current for PV Applications

Differential-mode buck-boost inverters have merits such as reduced switch number, ability to provide voltages higher or lower than the input voltage magnitude, improved efficiency, reduced cost and size, and increased power density, especially in low-power applications. There are five buck-boost inverters that can provide flexible output voltage without the need of a large electrolytic input side capacitor, which degrades the reliability of inverters. The continuous input current of these inverters is appropriate for maximum power point tracking operation in photovoltaic and fuel cells applications. Three of the five inverters can be isolated with high-frequency-link transformers where the common-mode leakage current can be mitigated. However, the performance and control of such converters have not been discussed in detail. In this paper, the five possible single-stage three-phase differential-mode buck-boost inverters with continuous input current are investigated and compared in terms of total losses, maximum ripple current, total harmonic distortion, and device and passive element ratings. In addition, the possible methods are presented for eliminating the input third-order harmonic current, resulting from the stored energy in the passive elements, as well as the output second-order harmonic currents. The ability for isolating the input and output sides of the inverters with a small–high frequency transformers is discussed. A changeable-terminal 2.5-kW bidirectional inverter is used to validate the design flexibility of the inverter topologies, when digital signal processor-controlled.

A Novel Inverter Topology for Single-Phase Transformerless PV System

Transformerless photovoltaic (PV) power system is very promising due to its low cost, small size, and high efficiency. One of its most important issues is how to prevent the common mode leakage current. In order to solve the problem, a new inverter is proposed in this paper. The system common mode model is established, and the four operation modes of the inverter are analyzed. It reveals that the common mode voltage can be kept constant, and consequently the leakage current can be suppressed. Finally, the experimental tests are conducted. The experimental results verify the effectiveness of the proposed solution.

Semi‐Z‐source inverter topology for grid‐connected photovoltaic system

Transformer-less inverters are necessary parts for grid-connected renewable energy resources. Owing to its cost effectiveness, downsize and less weight, great attention has been paid to these inverters development. With these aforementioned advantages, these inverters have limitations like the flow of leakage current through photovoltaic arrays, high total harmonic distortion (THD) at inverter's output and DC current injection to the grid. This study presents coupled inductor-based single-phase transformer-less semi-Z-source inverter topology to lessen those limitations. Since the DC input and AC output voltage share a common ground, the presented inverter system is categorised under doubly grounded topologies. For the purpose of handling, the non-linearity of the voltage gain of semi-Z-source inverter, a non-linear sinusoidal pulse-width modulation technique has been employed. The prototype of the suggested inverter has been constructed. The performance and compatibility of modulation technique are verified under different loading conditions. The feasibility of the configuration is ensured based on the mitigated common-mode leakage current, the substantially lower THD as well as DC current injected to the grid. Moreover, the presence of coupled inductor significantly contributes in reducing input current ripple, installation area of the inverter and enhancing the efficiency. Finally, this topology exhibits appreciable performance to operate synchronously and transfer power to the grid.

Comparison of harmonic reduction of 2LLCL and 2LCL filters based on single phase inverter with H6 configuration

SUMMARY It is necessary for transformerless inverters to eliminate the common-mode leakage currents to enhance safety and current quality. The transformerless H6 inverter configuration is an adequate solution to photovoltaic low power modules as a result of its high efficiency, unipolar voltage across output filter, no need to input split capacitors and half input voltage compared with neutral point clamped inverters. In grids with a high grid impedance, there will be a rise in harmonic magnitude, so qualifying the standards for the harmonic limits may be problematic. In this paper, 2LLCL filter is offered to satisfy the current harmonic standards and decrease the filter weight and size. Experimental results of 300 W hardware prototype verify the proposed filter with H6 inverter configuration. Copyright © 2014 John Wiley & Sons, Ltd.

An improved transformerless grid connected photovoltaic inverter with reduced leakage current

Transformerless inverters are most preferred for grid connected photovoltaic (PV) generation system due to higher efficiency and lower cost. However, to meet the safety regulations, the leakage current which deteriorates the power quality and generates electro-magnetic interference in transformerless PV inverter, has to be addressed carefully. In order to eliminate the leakage current, an improved H5 topology is proposed in this paper. The operating principle, common mode (CM) characteristics, and the impact of junction capacitance of the switches on the CM voltage are investigated in details. The desired relationship among the junction capacitances is proposed to eliminate the CM leakage current. Three-level output voltage is achieved in the improved inverter employing unipolar sinusoidal pulse width modulation (SPWM). Furthermore, the European efficiency is improved by replacing the high frequency IGBT switches with MOSFETs. The proposed topology is compared with other transformerless topologies in terms of leakage current, different mode (DM) characteristics, and efficiency. The improved inverter topology is simulated in MATLAB/Simulink software to validate the accuracy of the theoretical explanations. Finally, a 1kW laboratory prototype has been built and tested. The experimental results show that the proposed inverter has a maximum efficiency of 98.0% and 97.45% European efficiency with 16kHz switching frequency.

Reduction of Output Common Mode Voltage Using a Novel SVM Implementation in Matrix Converters for Improved Motor Lifetime

This paper presents the study of an alternative space vector modulation (SVM) implementation for matrix converters (MCs), which reduces the output common mode (CM) voltage. The strategy is based on replacing the MC zero vectors with rotating ones. In doing this, the CM voltage (CMV) can be reduced, which, in turn, reduces the CM leakage current. By reducing the CM current, which flows inside the motor through the bearings and windings, the induction motor (IM) deterioration can be slowed down. This paper describes the SVM pattern and analyzes the CMV and the leakage current paths. Simulation and experimental results based on an MC-IM drive are provided to corroborate the presented approach.

Improved Transformerless Inverter With Common-Mode Leakage Current Elimination for a Photovoltaic Grid-Connected Power System

To eliminate the common-mode leakage current in the transformerless photovoltaic grid-connected system, an improved single-phase inverter topology is presented. The improved transformerless inverter can sustain the same low input voltage as the full-bridge inverter and guarantee to completely meet the condition of eliminating common-mode leakage current. Both the unipolar sinusoidal pulsewidth modulation (SPWM) as well as the double-frequency SPWM control strategy can be applied to implement the three-level output in the presented inverter. The high efficiency and convenient thermal design are achieved thanks to the decoupling of two additional switches connected to the dc side. Moreover, the higher frequency and lower current ripples are obtained by adopting the double-frequency SPWM, and thus the total harmonic distortion of the grid-connected current are reduced greatly. Furthermore, the influence of the phase shift between the output voltage and current, and the influence of the junction capacitances of the power switches are analyzed in detail. Finally, a 1-kW prototype has been simulated and tested to verify the theoretical analysis of this paper.

EMI modeling method of AC-AC power converters

This paper presents a new model for simulation of Electromagnetic Interference (EMI) in power converters. Despite the fact that a Matrix Converter (MC) has been selected, such methodology can be applied to other converter topologies. The EMI model relies on a combination of time and frequency domain techniques in order to not only reduce the computational complexity but also to avoid convergence problems. Common Mode (CM) leakage current, which lays basically in A band (10kHz to 150kHz), is simulated and such results are compared with those obtained from the MC prototype showing a good concordance in terms of peak value.

EMC Issues in High-Power Grid-Connected Photovoltaic Plants

This paper outlines the main electromagnetic compatibility issues frequently encountered in high-power grid-connected photovoltaic (PV) systems, and proposes several guidelines that allow to obtain an effective and highly efficient layout of the plant. At first, with reference to a 1-MWp PV plant of Sorgenia Solar, Italy, the paper focuses on the peculiar aspects concerning the radio-frequency behavior of a large-size PV plant: the great extent of the direct-current cabling, the capacitance toward earth of the PV source, the common-mode (CM) disturbance generated by inverters, the galvanic isolation ensured by dedicated low-voltage power transformers, and the presence of resonant circuits for CM leakage currents. The dominant electromagnetic phenomena and coupling mechanisms are pointed out by means of an equivalent circuit and through measurements. In the light of the matured experience, several guidelines are proposed and a new reliable layout is implemented on a second 1-MWp PV plant. New measurements confirm the validity of the proposed design strategy.