Common Mode Leakage Research Articles

Doubly grounded buck‐boost PV grid‐connected inverter without shoot‐through problem

AbstractTransformerless grid‐connected inverters (GCIs) are universally utilized in the PV system. However, they have the shoot‐through issue and common mode leakage current (CMLC). To address the above‐mentioned issues, a transformerless common‐ground GCI without shoot‐through issue is proposed. The proposed topology has one common ground between the PV array and the grid that eliminates the CMLC. The topology is the combination of two buck‐boost converters, so it has the boost capability. Each buck‐boost converter operates in half‐line period, so the proposed inverter is a single‐stage system. Only two switches operate in high frequency in positive half‐line period and only one switch operates in high frequency in negative half‐line period. Therefore, efficiency of the system can be improved. There is no current flowing through the body diode of the MOSFET. Additionally, the presented inverter has no shoot‐through problem. The operating principle is elaborated. At last, simulation and experimental results of a 250 W proposed inverter validate the theoretical analysis. The maximum efficiency of the system is 96.2%.

Novel Cascaded PV System with Common Mode Leakage Current Suppression

Novel Cascaded PV System with Common Mode Leakage Current Suppression

Leakage current suppression methods for single-phase photovoltaic inverters

Given the swift expansion of the worlds population and economy, the decline in environmental quality caused by global warming, frequent climate disasters, ecosystem damage, sea level rise and other problems makes the world energy structure is changing, which means many countries start to develop their new energy industry and technology in order to meet their growing demand for energy. Therefore, promoting the energy transformation and innovation has become a new focus, and photovoltaic (PV) power generation as a green energy source is the focus of attention. PV inverters are essential components of photovoltaic array systems since they are the principal equipment capable of converting the fluctuating DC voltage produced by solar panels into mains frequency alternating current. However, the leakage current problem appeared during its operation has become one of the most important focuses of electrical engineers in recent years. This paper takes three aspects which is topology, filter and modulation mode to discuss how to suppress common mode leakage current in inverters. This paper reviews the existing research results and looks forward to their future development trends, which provides a reference for the following research.

Topology derivation and control method of high‐reliability buck‐boost double‐grounded transformerless three‐phase inverters

SummaryAs the traditional transformerless three‐phase (TTP) inverters have the shoot‐through and common mode leakage current (CMLC) problems, as well as not being able to realize the buck‐boost conversion, topology derivation and control method of high‐reliability buck‐boost double‐grounded TTP inverters are proposed. These topologies consist of two‐port or three‐port converters with boost capability and three dual‐buck inverters. The two‐port or three‐port converters with boost capability provide the positive and negative bus voltages for the three dual‐buck inverters, realizing the boost conversion. The dual‐buck inverters address the shoot‐through problem. The double‐grounded structure is used to solve the CMLC problem. Dead time between switches is not needed, which reduces the complexity of the control system. Detailed topology derivation of the dual‐buck double grounded TTP inverters with boost capability is given. The operating principle, parameters design of the filters, and stability analysis of this inverter are analyzed in detail. Loss analysis of the inverter is given. The simulation and experimental results of a 750‐W TTP inverter are used to verify the theoretical analysis.

Improved Common-Mode Leakage Current Measurement Method for Insulation Condition Monitoring in Distribution Grids

Common-mode (CM) leakage current is an essential insulation indicator for condition monitoring in distribution grids. However, online measurement of CM leakage current is a difficult task in the industry due to the disturbances of far larger load currents. To address this challenge, a novel CM leakage current measurement method based on multi-layer magnetic shield has been proposed in this paper. The analytical solution for the magnetic field around the shield is firstly derived and validated by finite element analysis. Comprehensive comparison with previous single-layer shield design is then conducted for a typical industrial case, proving that an improvement of about 46 dB can be achieved for CM leakage current measurement by the novel design. A sensor prototype has also been developed with optimized parameters and validated by experiments. The effectiveness of the proposed method is proved, with minor CM leakage current accurately extracted from load currents which are 3000 times larger.

Three‐phase common‐ground‐type photovoltaic inverter without shoot‐through problem

SummarySince there are common mode leakage current (CMLC) and shoot‐through problems in the conventional three‐phase transformerless photovoltaic (PV) inverters, the three‐phase common‐ground‐type transformerless dual‐buck inverters (DBIs) are derived. By shorting the neutral point of the three‐phase load and the negative terminal of the PV panel, the CMLC is eliminated. The DBIs has no shoot‐through problem and there is no current flowing through the body diode of the SiC metal oxide semiconductor field‐effect transistor (MOSFET). The three‐phase DBI combined with a buck‐boost converter is taken as an example to illustrate the operating principle of the derived inverters. The control strategy of the inverter is given. A prototype is built to validate the proposed inverter. Finally, comparison among the proposed inverter and other three‐phase inverters is given.

Nonisolated Three-Phase Current DC-Link Buck–Boost EV Charger With Virtual Output Midpoint Grounding and Ground Current Control

Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Three-phase double-grounded buck-boost PV inverter without shoot-through problem

The conventional transformerless photovoltaic(PV) inverter has the common mode leakage current and shoot-through problems. In addition, the output voltage of the PV module is low under the shading condition, resulting in the inverter not working properly. A three-phase double-grounded buck-boost PV inverter without shoot-through problem is proposed. The front-end converter of this inverter is composed of two boost converters, which can realize boost conversion. The rear-end inverter consists of three dual-buck half-bridge inverters, which solves the shoot-through problem. In this topology, the load ground is connected to the negative ground of the PV module, eliminating the common mode leakage current. The operating principle and mode analysis are described in detail. Finally, a simulation circuit is built to verify the theoretical analysis.

Topology review of doubly grounded transformer‐less single‐phase inverters

AbstractPhotovoltaic (PV) transformer‐less single‐phase inverters are widely used in the solar generation systems because of low cost, high power density, and high efficiency. However, there is a common mode leakage current in the transformer‐less inverters, which may endanger personal safety. In order to reduce the common mode leakage current, extra semiconductors should be added into the PV inverters to decouple the dc side from the ac side. However, the common mode leakage current is affected by the environmental condition and parameters of power devices. Since grounds of the PV array and the output terminal of the inverter are shorted, the common mode leakage current in the doubly grounded inverters can be eliminated thoroughly. Topologies of the doubly grounded inverters are reviewed in this paper, which can be divided into two categories, that is, hybrid topologies and topologies using energy storage elements. Derivation of the reviewed topologies is given. Different topologies of doubly grounded transformer‐less single‐phase inverters are compared.

A Novel Online Monitoring Scheme for Underground Power Cable Insulation Based on Common-Mode Leakage Current Measurement

Insulation aging of underground power cables may lead to severe fault and system outages. Condition monitoring of cable insulation is essential to maintain power system reliability. However, most existing insulation monitoring methods can only work in offline mode and cannot describe cable aging severity quantitatively. In this article, a novel online monitoring scheme for underground power cable insulation based on common-mode (CM) leakage current measurement is proposed. An online neutral-point voltage injection approach is proposed, and CM leakage current distribution model for both the cables with and without metal sheath under the injected voltage is derived. The insulation capacitance can therefore be monitored online without disturbance to the system operation. Simulations and experiments are conducted to prove the effectiveness of the proposed method. With the aid of a designed CM leakage current sensor, CM leakage current smaller than 5 mA can be detected and the accurate evaluation of aging severity is achieved. The key feature of the proposed method lies in its nonintrusiveness and online fashion: the normal operation of the system will not be interrupted, and accurate quantitative monitoring of cable insulation can be achieved online.

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 hybrid technique for transformer-less grid-tie Hybrid Renewable Energy Source with reduction of common mode leakage current

A hybrid method for transformer-less grid-tie hybrid Renewable Energy Source (HRES), such as photovoltaic (PV) and wind energy system (WES) with minimization of common mode leakage current is proposed in this manuscript. The proposed system is the combined execution of Vascular Invasive Tumor Growth (VSTG) Optimization Algorithm and extreme gradient boosting (XGBOOST) named VSTG-XGBOOST control topology. The main intention of transformerless grid-connected HRES system is “to lessen the leakage current, maximum power point (MPP) extraction and maximal power point tracking (MPPT), the active and reactive power controller, and having the unity power factor. To attain the above-mentioned aims, the following actions have been performed in this proposed work. Two turn-off snapper circuits are inserted parallel to the switches to share the input DC voltage among snubber capacitors. By then, VSTG is used to estimate the optimal gain parameters under various source currents as normal value is used to generate the optimal control signal database offline. Based on the attained dataset, the XGBOOST forecasts the optimal control signals of the grid-connected HRES inverter in the online way. This control technique allows two sources to supply the load separately depending on the availability of the energy sources and keeps common DC voltage constant.

Analysis of a Single-Phase Transformerless Bidirectional PFC

This paper presents a single-phase transformerless bidirectional power factor corrector (PFC). A capacitor is inserted into a conventional full-bridge PFC by connecting the ac line terminal and a terminal of DC voltage. The functions of this inserted capacitor have two roles: to bypass the common-mode leakage current from the stray capacitor; to form an LCL filter to reduce the inductor current ripple. A hybrid modulation method is employed in this PFC. The unipolar switching scheme is applied to modulate the PFC, which can achieve high efficiency. Meanwhile, an additional modulation is inserted into the blank time of low-frequency switches to decrease the changing speed of the voltage on the inserted capacitor, and to decrease the spike on the inductor current and leakage current. The performance of the PFC is experimentally verified using a 5 kW prototype.

A novel design and control method for improved LCL filter three-level inverter to suppress common mode resonant current and leakage current

The method of connecting the common point of the LCL filter capacitor of the three-level grid-connected inverter to the midpoint of the DC side can effectively suppress the leakage current between the DC side photovoltaic panel and the power grid. However, the improved MLCL inverter is easy to generate common mode resonance, which results in excessively increasing the midline current and affecting the efficiency and stability of the system. Aiming at the common mode resonance problem of MLCL three-level inverter, this paper expounds the generation of common mode resonance current and large neutral current by establishing the mathematical model of the improved MLCL filter. After analyzing the restraining effect and limitation of traditional passive damping control scheme on common mode resonance, a novel filtering structure is proposed in this paper, which is combined with PI+ PR double closed-loop control scheme to solve the above problems. Simulation results verify the validity of the analysis on common mode resonance and neutral current, and the effectiveness of the scheme in suppressing common mode resonance current, midline current and leakage current is also confirmed.

Multioutput Hybrid Solar Inverter With No Right Half-Plane Zero and Reduced Common-Mode Leakage Current

In this article, a multioutput-based transformerless hybrid solar inverter (TLHSI) with no right half-plane zero (RHPZ) and reduced common-mode leakage/ground current is presented for photovoltaic (PV) based microgrid applications. In the proposed multioutput TLHSI, two magnetically coupled inductor coils are placed between the input and dc output sides along with a dc-link capacitor to continuously provide the stored energy to the dc load so that the RHPZ is eliminated and, thus, makes it a minimum phase system. Furthermore, a hybrid unipolar sinusoidal pulsewidth modulation technique is established to nullify the high-frequency components of common-mode voltage across the PV to ground stray capacitor. Also, it normalizes both dc and ac loads at the same instant from a single dc input during each operating state of the proposed TLHSI. The shoot-through issue is resolved in the proposed TLHSI, which increases the system reliability. Furthermore, as the deadtime is not required in between the switching pulses, the quality of the inverter output voltage improves. The performance analysis of the proposed TLHSI is compared with the existing topologies. To validate the performance of TLHSI, a scaled down 340 W laboratory prototype is developed.

Overview of Recent Advanced Topologies for Transformerless Dual-Grounded Inverters

Transformerless inverters, most of which are H-bridge inverters, have been widely used and studied in grid-connected power systems in the last decades. However, the H-bridge inverter is affected by the low- and high-frequency common-mode voltage between the input and output terminals, resulting in a large common-mode leakage current. An alternative solution is to connect the ground of the input terminal to the output load or grid, that is, the dual-grounded inverter. In this case, the low- and high-frequency common-mode voltages can be mitigated or eliminated. As a matter of fact, scholars have made several research results on dual-grounded inverters. However, as of now, there is still no literature that comprehensively and systematically summarizes these research results. To fill this gap, this article classifies different types of dual-grounded inverters from the perspective of topology for the first time, and compares and summarizes their advantages and disadvantages. More than 60 works of literature have been reviewed to identify the practical implementation challenges and research opportunities in the application of dual-grounded inverters.

Single phase transformerless inverter for grid connected photovoltaic system with reduced leakage current

Introduction. Transformerless inverters are of vital importance in the field of grid connected solar photovoltaic systems offering higher efficiency than the conventional one. i.e., using transformer. General grid connected inverters are constituting of transformers requires more area besides the loss in them. Problem. Eliminating transformers can cause leakage current due to the variation of common mode voltage which in turn due to parasitic capacitance effect. Research literature in transformerless inverters has addressed the problems of common mode leakage current issues by offering the study of different inverter topologies like H4, H5, H6 and HERIC etc. utilizing variety of modulation strategies like unipolar, bipolar pulse width modulations. Goal. The paper significantly presents a new transformerless inverter topology, analyzes common mode voltage and leakage current behavior of the system. The simulation is carried out for comparing the leakage current profiles with other transformerless inverter topologies in literature. Novelty. This paper gives an impression of the efficient transformerless inverter for grid connected photovoltaic system. Results. The various inverter topologies full bridge with different pulse width modulation techniques are analyzed and to determine the common mode voltages and leakage currents.

A Novel Single-Stage Common-Ground Zeta-Based Inverter With Nonelectrolytic Capacitor

Aiming at the key problems of the existing nonisolated photovoltaic (PV) inverter, such as the common mode (CM) leakage current, the voltage up and down ability, and the service life restricted by the electrolytic capacitor, a novel single-stage common-ground zeta-based inverter with nonelectrolytic capacitor is proposed in this article. The proposed inverter is based on zeta dc converter and has the inherent voltage conversion characteristics of zeta converter, which makes it more suitable for PV system with wide input voltage fluctuation range. In addition, common-ground structure is adopted in this inverter, which can shorten the parasitic capacitor of the PV array to the ground. Therefore, it can effectively suppress the CM leakage current, reduce the shutdown frequency of the PV system, and improve the utilization rate of solar energy. Moreover, the proposed inverter does not contain electrolytic capacitors, which avoids the problem of high maintenance cost due to the short service life and high equivalent series resistance of electrolytic capacitors. First, the topology of the proposed inverter is given, and the modulation and operating principle are analyzed. Second, the passive components are analyzed. Finally, a 1 kW prototype is built for experimental verification. The experimental results verify the correctness of the theoretical analysis and simulation.

A Common-Mode Voltage Suppression Strategy Based on Double Zero-Sequence Injection PWM for Two-Level Six-Phase VSIs

A common-mode voltage (CMV) suppression strategy, namely double zero-sequence injection common-mode voltage (DZICMV), is proposed in this paper for an asymmetrical six-phase induction motor fed by two-level dual three-phase voltage source inverters (VSIs). In this strategy, the sinusoidal waveforms injected by double zero-sequence signals are employed as modulation signals, and two opposite triangular waveforms are used as carriers. The fundamental period is divided into 24 sectors. In each sector, the carrier used by the medium amplitude phase is distinct from the carriers used by the other two phases in each set of three-phase windings. Using this method, the zero vectors (000) and (111) in each set of three-phase windings can be eliminated, and the peak values of sub-CMV and total CMV can be reduced from ±Udc/2 to ±Udc/6. The experiment results show that the root mean square (RMS) value of common-mode leakage current in DZICMV can be reduced by 51.83% compared with the double zero-sequence injection PWM (DZIPWM) strategy. It is also found in the other four existing benchmark CMV suppression strategies that the peak values of sub-CMV therein are nearly all ±Udc/2, and only in the low linear modulation region could one of these strategies suppress sub-CMV peak values to ±Udc/6. However, the proposed DZICMV can suppress the sub-CMV peak values to ±Udc/6 in the whole linear modulation range. Moreover, the maximum linear modulation index of the DZICMV is 1.15, which is larger than that of the four benchmark strategies, whose maximum modulation index is 1.