Ground Leakage Current Research Articles

Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review

In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron- and copper-based transformers increase the weight/size and cost of the inverter while reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g., via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and $\text{A}S/N$ ZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the dc from the ac side and/or clamping the common mode (CM) voltage (CMV) during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck–boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next-generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analyzed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.

Reducing Common-Mode Voltage and Bearing Currents in Quasi-Resonant DC-Link Inverter

In this article, a concept of separation of an inverter-fed induction motor drive from its mains supply by two transistor switches inserted in the dc-link circuit is re-examined based on the proposed parallel quasi-resonant dc-link inverter (PQRDCLI). The objective of the article is to show an advantage of the proposed topology in limiting high-frequency common-mode voltage and bearing currents. In the laboratory setup, an induction machine was equipped with hybrid ceramic bearings and an insulated clutch to measure the shaft-to-frame bearing voltage and the shaft-grounding current. Experimental tests of the PQRDCLI confirm significant reduction of common-mode voltage and shaft-to-frame bearing voltage at dc-link zero voltage notches. By controlling the output voltage slopes, the shaft-grounding brush current and the ground leakage current are also reduced. The efficiency measurement and evaluation of the proposed topology, as compared with a two-level hard switched inverter, reveal comparable efficiency of around 95% and indicate loss distributions in both inverters.

Hardware analysis for upgrading the embedded component of Protegemed

The Protegemed platform is comprised of an embedded component and several other components designed to capture and analyze electrical currents of electromedical equipment in operating rooms and intensive care units. Differential currents in electromedical equipment have proven to be dangerous for patients. The Protegemed platform can help detect these currents and help research to develop better and safer equipment. In addition, the Protegemed platform can increase electrical safety in surgical procedures. Today, the Protegemed platform uses a 32-bit ARM Cortex M3 microprocessor (MBED with an LPC178 $\mu$C), but there are new features expected and the hardware is not enough, for example, to analyse the voltage and the ground leakage current. This article focused on researching, comparing options and selecting the best option to replace the current hardware of the embedded component. Initially, two groups of hardware options were selected, evaluating some models of each. The components surveyed were Single Board Computers and Mixed Signal Processors. In the second phase, the best option of each group was compared. The comparison takes into special consideration the performance of the system for digital analogue conversion. Research has shown that within Single Board Computing, Udoo Dual Lite is better than the other options analyzed and TM4C1294 is a better component among Mixed Signal Processor options. Between the Udoo Dual Lite and TM4C1294 options, the latter was the best choice to upgrade the embedded component of the Protegemed platform. The current firmware will be adapted for this hardware and the new features of the Protegemed platform can be implemented.

Parallel voltage sag compensator without an injection transformer

A parallel voltage sag compensator (PVSC) is a power electronics device to compensate the voltage sag and interruption. The conventional PVSC uses an energy storage device and a bidirectional inverter with an injection transformer. However, the injection transformer reduces the power efficiency with high power losses. This paper proposes a PVSC without the injection transformer. The proposed PVSC has a bidirectional DC–DC converter to transfer the electrical power between the energy storage device and the bidirectional inverter. It uses the common-mode filter capacitors for the AC-side filter in the bidirectional inverter. The ground leakage current can be effectively suppressed between the energy storage device and the AC voltage. The proposed system has high power efficiency and low ground leakage current. Experimental results are discussed to evaluate the performance of the proposed system.

A Simulation-Based Multifunctional Differential Mode and Common Mode Filter Design Method for Universal Converters

Existing filter design methods for grid-tied power converters either focus on grid current harmonic suppression or electromagnetic interference (EMI) noise attenuation. This article proposes a simulation-based, multifunctional filter design method, which can simultaneously handle multiple objectives, including minimizing grid current total harmonic distortion (THD), conductive EMI noise, ground leakage current, touch current, filter weight, and so on. By modeling equivalent filter circuit and simulating in the Powersim (PSIM) software, the approach avoids traditional complicated circuit analysis and mathematical computation. In addition, unlike most existing filter design approaches that only focus on one specific application or converter topology, this filter design method is a generalized approach and can also be used for universal converters that have variable applications. To demonstrate this feature, the filter design method is applied to a recently proposed series-capacitive-link universal converter. Experimental results verify the effectiveness of the proposed method.

Improved Transformerless Grid-Tied PV Inverter Effectively Operating at Twice the Switching Frequency With Constant CMV and Reactive Power Capability

In this article, an improved single-phase transformerless inverter is presented, which obviates the leakage current issue to a great extent. The proposed solution uses the dc-bypass (H6 type) topology with a diode clamp circuit, operated by a modified unipolar pulse-width modulation (PWM) scheme. An advantage of reduced switching losses comes with the use of the modified unipolar PWM, which produces effective double switching frequency at the inverter output. Due to the PWM strategy and diode clamp circuit, the common-mode voltage (CMV) of the inverter is constant throughout the operation. Consequently, the ground leakage current is negligible even in the presence of high parasitic capacitance of photovoltaic (PV) panels. Further, the other desirable features of the grid-tied inverters, such as reactive power injection for grid stability and low-voltage ride through (LVRT) are not compromised with the proposed scheme. A combination of high efficiency, constant CMV (and hence, negligible leakage current) and reactive power feeding capability with low component count stand the proposed system out among the existing transformerless grid-tied systems. The design and working principle of the proposed system are discussed and analyzed in detail. Simulation and experiment results are included to validate the proposed solution and its merits.

Mitigation of Leakage-Ground Currents in Transformerless Grid-Tied Inverters via Virtual-Ground Connection

This article studies the benefits of the virtual-ground (VG) connection for single-phase transformerless grid-tied inverters, which is used to mitigate the leakage-ground currents (LGCs) issue. This article also proposes common-mode and differential-mode models of single-phase inverters connected to the grid through an $LCL$ output filter, which are used as a theoretical support. It is shown that LGCs are simply common-mode currents (CMCs) circulating through the ground path, which represents a contribution in the development of an approach to find solutions in general scenarios. In most of the cases, these currents are produced by the existence of common-mode voltages (CMVs), which find a way through the ground path established after the stray capacitances in the terminals of, for instance, photovoltaic (PV) panels. To prove the advantages of the proposed interconnection and for analysis, the single-phase full-bridge version of a two-level conventional inverter, as well as a neutral-point-clamped (NPC) inverter, is considered for model derivation and experimental validation.

Design and Implementation of Transformer less Micro Inverter for PV-Grid Interface

The need for energy is increasing day-by-day, which is a large part of total global energy consumption. The crises of fossil fuels and nuclear power will run out someday in the future. Therefore, we aim to develop energy from Renewable Energy Sources (RES) especially from solar. The growth of solar energy has increase day by day to meet the demand in the future. In this paper, modeling and analyzing of a transformer-less grid-connected inverter is proposed for solar photovoltaic (PV)-grid interface system. The scope of the transformer-less inverter is used to minimize ground leakage current in the grid. The inverter is directly connected to unbiased grid line and PV array inverting terminal to compensate the ground leakage current. The transformer-less grid connected inverter is used to compensate reactive power, extraction of high energy from PV array, and low grid current distortion. The inverter is also used to improve tracking output current reference, grid synchronization, and to provide a safety margin of forced direct current into the grid. In the control circuit the Proportional Resonant (PR) controller is used. Atmega328 based reduced rated hardware is developed for verifying the system enhancements and the experimental results are used to prove the proposed methodology for control of transformer less grid interactive inverter which supports both active and reactive power to the loads.

CSI and CSI7 current source inverters for modular transformerless PV inverters

Current source inverter (CSI) is a class of power electronic converters that, thanks to the inherent boost capability and ease of control, is investigated for grid-tied photovoltaic power conversion applications. Traditional CSI and CSI7 topologies are here analyzed and compared with two kind of space vector modulation strategies mainly in terms of ground leakage current both in simulations and experiments. Furthermore, THD of the injected grid current and the computation of conduction and switching semiconductor power losses are also carried out in numerical simulations. The topology comparison is carried out with the use of a different number of PV modules, to analyze the robustness of the topologies to different size of the PV strings. Simulation and experimental results show that the CSI7 topology, with respect to conventional CSI, allows to strongly reduce ground leakage current, phase current THD and semicondutor power losses, at the price of an additional power device.

Photovoltaic AC Module Based on a Cuk Converter With a Switched-Inductor Structure

The development of a photovoltaic ac module composed of a high static gain nonisolated dc–dc converter with current source output characteristic followed by an unfolding low-frequency inverter is presented in this paper. The operation of the dc–dc converter with high static gain and with reduced switch voltage is obtained using the Cuk converter integrated with the switched-inductor technique. The nonisolated structure allows the elimination of the volume and losses of the power transformer and leakage inductance, and an output filter configuration is proposed to reduce the high-frequency ground leakage current. The grid-tied inverter operating in a discontinuous conduction mode (DCM) allows a sinusoidal output current with low harmonic distortion (THD = 3.72%) to be obtained without current control loop and without the use of a current sensor at the output. The maximum power point tracking operation is obtained without the use of the current sensor. The DCM operation increases the current stress, but the proposed converter presents two switches and two input inductors sharing the input current in these components. The theoretical analysis, design procedure, and experimental results are presented for a prototype with a dc input voltage Vi = 30 V, an ac output voltage Vo = 127 V, and output power Po = 180 W.

Effects of modulation techniques on leakage ground currents in a grid‐tied transformerless HB‐NPC inverter

In this paper, a comparative study of modulation techniques used in a transformerless H-bridge neutral point clamped (HB-NPC) multilevel inverters is presented. Transformerless inverters, usually found in photovoltaic (PV) applications, are more efficient and economically affordable than isolated systems. Nevertheless, they may cause leakage ground currents. The latter are produced by the stray capacitances formed between the PV panel frame and the ground path. There are different ways to overcome the leakage ground current issue in transformerless topologies, for instance using topologies that generate almost zero leakage currents, by using adequate modulation techniques, by inserting additional filters, and by using adequate control schemes, among others. The comparative study, considers five modulation strategies, namely, level-shifted pulse-width modulation (PWM), phase-shifted PWM, three-level PWM, two sectors hybrid PWM and six sectors hybrid PWM. As it will be demonstrated through the common-mode model analysis, the three last modulations strategies are aimed at alleviating the leakage ground current issue. In this study, the two sectors hybrid PWM and the six sectors hybrid PWM are proposed. These modulation techniques lead to obtaining five output voltage levels keeping the RMS value of the leakage currents bounded for the transformerless HB-NPC inverter.

Design and Analysis of the Performance of a Solar Driven Micro-Inverter Using Single Ended Primary Inductance Converter Topology

In typical solar power installations, multiple modules are connected to the grid through a single high-power inverter. However, an alternative approach is to connect each solar module directly to the grid through a micro-inverter. This approach makes the system robust to single module failures and results in better power tracking. PV based cower conditioning system need a high-efficiency dc–dc converter capable of regulation over a wide input voltage range for Maximum Power Point Tracking (MPPT) and a high-efficiency micro-inverter. To diminish the ground leakage currents, also to use a high-efficiency system, the proposed concept is required for this micro-inverter to provide galvanic isolation between the PV module and the inverter. This concept involves the design of a micro-inverter topology which includes design of Single Ended Primary Inductance Converter (SEPIC) dc/dc converter, isolated resonant inverter and a cyclo-converter. The SEPIC converter topology yields high efficiency through constant voltage MPPT algorithm. The Resonant inverter topology produces efficient output through low circulating currents, Zero Voltage Switching (ZVS), low-current switching of the primary side devices, and Zero Current Switching (ZCS) of the output diodes. This Resonant inverter topology is also able to provide voltage regulation through basic fixed-frequency Pulse Width Modulated (PWM) control. The features of proposed system can able to achieve w the simple addition of a secondary-side bidirectional ac switch to the isolated series resonant converter.

Internal Current Return Path for Ground Leakage Current Mitigation in Current Source Inverters

This paper analyzes in detail the effect of a simple solution for ground leakage current mitigation applicable to transformerless three-phase current source inverter (CSI). The circuit modification solution is assessed for both traditional CSI topology and for CSI with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the dc input inductance. In the present work, the solution is applied to grid-connected converters for string photovoltaic applications: scope of the circuit modification is to provide an internal return path from the wye connected capacitors of the output CL filter. This additional return path is able to significantly reduce the ground leakage current without adversely affecting THD. The performance of the proposed solution is assessed by the numerical simulations in case of a string of photovoltaic (PV) modules and the different behavior of CSI and CSI7 topologies is thoroughly investigated. Furthermore, the definition of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cm</sub> ZC is assessed by applying it to the common mode equivalent circuits for CSI7 with additional return path and their validation by means of a two-step simulation. The simulation results and experimental validation shows good agreement and confirm that the proposed solution is able to strongly reduce the ground leakage current.

Transformerless Line-Interactive UPS With Low Ground Leakage Current

This paper proposes a transformerless line-interactive uninterruptible power supply (UPS) with low ground leakage current. A high-efficiency bidirectional inverter is suggested, which performs the line-interactive UPS functions with low ground leakage current. It has a full-bridge inverter and a bidirectional switch, which operate with the unipolar pulsewidth modulation. Because the bidirectional switch operates at the line-frequency, switching losses can be lower than the previous transformerless inverters. As the inverter operates, the parasitic capacitance between the inverter and the ac voltage ground is clamped to zero voltage for a positive line cycle and to the ac voltage for a negative line cycle, respectively. Thus, the parasitic capacitance can be prevented from being charged or discharged, which ensures the absence of the ground leakage current. The operation modes of the proposed system are described. The control schemes are presented to design the proposed inverter for the line-interactive UPS. Experimental results for a 2.0 kW prototype are discussed to verify the performance of the proposed system.

Industrial Approach to Design a 2-kVa Inverter for Google Little Box Challenge

Uninterruptible power system, photovoltaics inverters, home appliances, motor drives, and automotive systems require highly efficient, reliable, and compact single-phase inverters. This paper presents different industrial design approach and experimental performance of high power density (100 W/in3) single-phase inverter with power output of 2 kVA that was presented for Google Little Box challenge. Multiple technical challenges were addressed, different methodologies described to achieve high power density and high efficiency reliable design. High power density was achieved by using the combination of optimized forced air cooled heatsinks, fully digital control, optimized component packaging, and by the introduction of a series active filter that enabled to reduce the size of dc bus capacitors. Low-loss high flux density magnetic materials such as Amoflux powder iron for power inductors and nanocrystalline magnetic materials for electromagnetic interference filter were also used. To minimize inverter switching losses, SiC devices operating at low switching frequency were adopted. Also, an innovative ground current control strategy is devised to minimize the ground leakage currents.

Analysis and Control of a Novel Transformer-Less Microinverter for PV-Grid Interface

In this paper, a novel single-phase, transformer-less microinverter configuration derived from the basic $ \ddot{\text C}$ uk topology is proposed for photovoltaic (PV)-grid interface applications. The topology has a direct connection between the grid neutral and the negative terminal of the PV array, which completely eliminates the ground leakage current. Further, the proposed topology has several appealing features such as high reliability due to the absence of shoot-through problems, symmetrical operation, low grid current distortion, capability of processing reactive power, low voltage ride through capability, and simple control for tracking the output current reference. Small-signal analysis has been employed to derive the topology's dynamic model using which a proportional resonant (PR) controller is designed and implemented. A step by step design procedure for obtaining the optimized proportional and integral gains of the PR controller, considering the effects of pulsewidth modulation transport and digital sampling delays, is presented. Theoretical claims and simulation results are corroborated by experimental studies carried out on a 200 W laboratory prototype controlled by using DSP TMS320F28335 controller.

A Single Phase Quasi H-Bridge Boost Inverter with Common Ground for Grid connected Applications

This paper presents a single-phase quasi H-bridge boost inverter with common ground for grid-connected applications. In this topology, the ground of ac grid and input dc voltage source is connected together directly. So, the ground leakage current is significantly limited. Furthermore, by combining a switched-capacitor boost converter with quasi H-bridge inverter, the RMS of output voltage can be greater than input dc voltage source. With the introduced simple PWM strategy, single phase quasi H-bridge boost inverter with common ground is applicable to photovoltaic applications where a low dc voltage source have to be inverted to a desired ac output voltage without transformer. The operating principles and circuit analysis for the single phase quasi H-bridge boost inverter with common ground are described. Simulation results by PSIM software are implemented to validate the performance of the introduced topology.

Single Phase Current Source Inverter With Multiloop Control for Transformerless Grid–PV Interface

In this paper, a modified single-phase current source inverter (CSI) with improved multiloop control is proposed for a transformerless grid-photovoltaic interface application. A split capacitor arrangement with the middle point connected to the grid neutral and a common mode choke are used to modify the conventional CSI structure to attenuate the ground leakage current. The proposed control method permits the use of reduced value of dc side inductor by maintaining the quality of the grid current as if a high value of input inductor is used. Furthermore, virtual resistance damping is incorporated in the control loop to reduce the effect of LC resonance without compromising the efficiency, thus proving the feasibility of using CSI for the grid interface. Rigorous study, analysis, and validation of the modified CSI structure with the proposed control technique are carried out with exhaustive simulations and experiments. The experimental results on a 250 W laboratory prototype using the controller TMS320F28335 prove the effectiveness of the proposed CSI structure and its control.

New Method for Common Mode Voltage Cancellation in Motor Drives: Concept, Realization, and Asymmetry Influence

This paper introduces a new concept of common mode voltage cancellation for pulse width modulated motor drives, aiming at solving issues such as ground leakage current, common mode electromagnetic interference, and bearing current. The balanced inverter topology and dual-winding stator configuration are proposed as a practical realization. Implementation considerations on the influence of circuit asymmetry are also investigated. Finally, a gallium nitride HEMT based induction motor drive prototype is built and tested to evaluate the performance of the cancellation concept in a practical situation.

High Performance Parallel Single-Phase Converter Reconfiguration for Enhanced Availability

Paralleling power converters is a common practice in industries to enhance total power rating, reliability, and availability of the system. In case of fault occurring in systems with parallel converters, the faulty power converter can be isolated and the system can still be operated at reduced power level. In this paper, a grid-connected power converter consisting of two parallel H-bridge converters with low ground leakage current is considered. Two contingency configurations, that are also of low ground leakage current, are proposed to enhance the availability of the system. This is done by reconfiguring the power circuit to a single H-bridge in the case of failure in one of the bridges. The power converter is experimentally tested with the proposed configurations for experimental validation. The results show that the second configuration has better performance in terms of power loss and current total harmonic distortion when operating at lower power level.