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Abstract Among different types of transformerless photovoltaic inverters, multi‐level inverters based on switched‐capacitors (SC) are the burning topic of recent decades due to their potential advantages, such as, single source requirement, voltage boosting capability, and high power density. However, for a seven level output voltage, a conventional SC based inverter architecture uses more than two units of SC, a large amount of power switches, which then lead to capacitor voltage balancing problems. This paper presents a seven‐level switched‐capacitor transformerless inverter (SCTI), which is structured with only two SC units, ten power switches, and a single DC source. The proposed SCTI ensures voltage boosting capability, self‐voltage balancing, and low power semiconductor losses. Apart from these, a modified sinusoidal pulse width modulation (MSPWM) is also proposed in this work, which guarantees better thermal performance and low inverter output voltage THD for the proposed SCTI. The proposed SCTI along with the MSPWM is simulated in MATLAB/Simulink and PLECS computer simulation environments. A reduced scale laboratory prototype is also built and tested to ensure the feasibility of the proposed SCTI.

Among different types of transformerless photovoltaic inverters, multi‐level inverters based on switched‐capacitors (SC) are the burning topic of recent decades due to their potential advantages, such as, single source requirement, voltage boosting capability, and high power density. However, for a seven level output voltage, a conventional SC based inverter architecture uses more than two units of SC, a large amount of power switches, which then lead to capacitor voltage balancing problems. This paper presents a seven‐level switched‐capacitor transformerless inverter (SCTI), which is structured with only two SC units, ten power switches, and a single DC source. The proposed SCTI ensures voltage boosting capability, self‐voltage balancing, and low power semiconductor losses. Apart from these, a modified sinusoidal pulse width modulation (MSPWM) is also proposed in this work, which guarantees better thermal performance and low inverter output voltage THD for the proposed SCTI. The proposed SCTI along with the MSPWM is simulated in MATLAB/Simulink and PLECS computer simulation environments. A reduced scale laboratory prototype is also built and tested to ensure the feasibility of the proposed SCTI. [ABSTRACT FROM AUTHOR]

This article presents a new nine-level common ground (CG) type transformerless inverter (TL) structure with an integrated boost (IB) cell. The proposed structure eliminates the leakage current due to the CG structure between the input source and the grid neutral. The proposed topology is derived by combining a DC-DC boost converter and switched capacitor (SC) cell, capable of generating the nine-level output voltage over a wide range of input voltage variations. By maintaining the duty cycle of the IB converter switch at 50%, the proposed topology generates the output voltage with a boosting factor of 4. Besides, soft charging of the involved SCs and reduced inrush current is also achieved through the inductor, which ensures the permissible current stresses of the power switches. Furthermore, the voltage across the SCs is self-balanced, eliminating the need for complex independent control techniques. A 725-W laboratory prototype is built to test the performance of the proposed topology under various operating conditions, such as input and load variations. The measured efficiency of 96.9% at 725 W is obtained and is comparable with the simulation efficiency. Finally, the merits of the proposed topology are highlighted using a detailed comparison with the other recent nine-level inverter topologies. [ABSTRACT FROM AUTHOR]

This paper proposes a new generalised boost integrated multilevel inverter (MLI) with reduced components. The proposed MLI is developed by using a modified boost integrated switched capacitor unit, which provides four-level output from each cell. The operation of the proposed MLI for symmetrical 17-level operation with sinusoidal pulse width modulation & nearest level control and asymmetrical 31-level operation with NLC is explained and validated experimentally. The experimental results of static and dynamic load conditions are analysed and discussed in detail. In addition, the proposed topology is compared with recent boost MLI topologies in terms of component count, device stress, efficiency, capacitor size and cost. From the comparative study, it is evident that the proposed MLI provides features such as reduced component count, capacitors size, overall cost and improved voltage gain. [ABSTRACT FROM AUTHOR]

Step‐up multilevel inverters with common‐ground feature are attractive for transformerless photovoltaic systems. However, their performance deteriorates at step‐down voltage range. Considering a five‐level inverter with double voltage gain, the number of output voltage levels decreases from 5 to 3 for a modulation index smaller than 0.5, declining the quality of the output currents. This paper proposes a new dual‐mode five‐level common‐grounded inverter with a reduced number of switches. The proposed topology has the ability to operate as step‐up or step‐down making it well suited for application with wide input voltage range. The proposed inverter consists of five unidirectional switches, one bidirectional switch, two diodes, and two capacitors. In addition, the description of the topology, the design guidelines, and a comparison among the main topologies are given in detail. Experimental results are obtained to attest the practicability of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes a transformerless common ground based single phase single‐stage switched boost inverter for solar photovoltaic (PV) applications. In the proposed inverter, the input DC source and output AC load share a common ground. As a result, the high‐frequency common mode voltage across the parasitic capacitance is eliminated, resulting in negligible leakage current (iLK) and the associated power loss, and harmonics in the inverter. Moreover, the higher voltage gain of the inverter facilitates the inverter to operate with high modulation index and lower shoot through (ST) duty ratio. Hence, the DC link voltage requirement across the inverter leg is reduced. Consequently, the voltage stress across the switches is minimized. Here, a modified PWM control technique is adopted, where the dual active states of the proposed inverter reduce the inductor current ripple and make it suitable for solar PV applications. The voltage boosting capability of the proposed inverter is extendable with the help of an additional number of intermediate impedance sub‐networks. The detailed steady‐state analysis of the proposed inverter is verified with the help of MATLAB simulation. To verify the simulation results, a 200 W, 120 V, and 50 Hz experimental prototype is developed. The prototype is tested for unity and lagging power factor load conditions with a wide range of input DC voltages, and all the major results are included in the paper. The power and thermal loss analysis is carried out using PLECS software, and the results show that the inverter has a maximum efficiency of 97.48%. From the experimental results, it can be inferred that the proposed inverter has a higher modulation index, lesser inductor current ripple, and zero leakage current as compared to the contemporary inverters. [ABSTRACT FROM AUTHOR]

As is well known in practice, conventional transformerless inverters may suffer the risk of high-frequency leakage currents between the photovoltaic (PV) array or battery energy storage systems (BESS) and the ground due to the stray capacitances. This operational condition can generate several electrical problems. Recently, we proposed in [1] a new method for designing transformerless topologies of single-phase voltage source inverters (VSI) with common ground derived from four classical DC-DC converters. As a sequence of that previous work, a novel control technique based on a feedback linearization approach is proposed to control that class of transformerless VSI with common ground in this paper. Unlike the classical local linearization techniques commonly used in the technical literature, this approach allows to obtain large-signal linear equations, by means of the feedback linearization of the non-linear terms. Real-time simulation results using Hardware-in-the-Loop allow validation of the proposed discrete control technique applied to this class of VSI topologies.

Transformerless inverters (TLIs) are extensively used in the photovoltaic (PV) grid‐connected system. TLI with a common ground structure exhibits multiple excellent features that improve the efficiency of the inverter, eliminating leakage current and boosting the voltage. The use of TLI eliminates the electrical isolation required between PV and the grid, resulting in a leakage current (LC) issue. The LC affects the power quality of the inverter and creates a safety‐related issue. This paper presents a new TLI topology based on the common ground (CG) structure. This topology uses eight switches and two self‐balanced switched capacitors. Phase disposition pulse width modulation (PD‐PWM) control scheme is used to create a five‐level output voltage. Further, adequate analysis for component selection and loss analysis is carried out to evaluate the efficiency. Its CG configuration certifies that there is minimal LC and common mode voltage (CMV). It also supports the active and reactive power of the grid. Its dual gain makes it suitable for photovoltaic (PV) applications. This topology is simulated for leading, lagging, unity power factor (UPF), and changes in input voltage and load conditions. Later, a corresponding experimental test is carried out on a laboratory prototype (1 kW). An equitable comparison is carried out for the component, stresses, and features like CG, and LC, along with efficiency. [ABSTRACT FROM AUTHOR]

Introduction. In recent years the usage of electricity has increased tremendously as the electrical needs and loads got increased. Hence the researchers focused on the electricity generation from renewable sources in order to promote sustainable green environment. Owing to the lesser cost and more reliable high efficiency system with reduced use of equipments became prominent for the grid connected photovoltaic single phase systems. The novelty of this proposed converters are to reduce total power loss and to analyze the performance of the converter under various modulation index and to have lesser harmonics using sinusoidal pulse width modulation technique for both T-type and F-type inverter. Interest of the work is to merge two DC-DC converters which have same output voltage in order to have transformer less utilization of power. This has given pathway to develop a new DC-DC converter network by merging the common input nodes of CUK and SEPIC converter. Purpose. This similar structure of both converters made it easy to combine the input stages of and to get bipolar output. Methods. Here we can get bipolar output without the utilization of transformer which minimizes the overall size of the proposed system. In this paper, a combined CUK-SEPIC based grid connected transformerless inverter for photovoltaic application is suggested. Results. The suggested converter is simulated using MATLAB and the results were discussed. Further the circuit is extended with a 1 kW F-type inverter to demonstrate grid connection of the converter. Practical value. This converter can be implemented for photovoltaic applications for obtaining the bipolar DC output from the DC source.

Summary: Transformerless inverters (TLI) are widely accepted in photovoltaic (PV) systems. With the application of TLI, the bulky transformer from the conventional system can be removed, enhancing the PV system's compactness, cost, and efficiency. The direct connection of PV to the grid through the TLI causes common mode voltage (CMV). The variation of CMV causes the leakage current (LC) in the TLI topology. This paper suggests a new topology of five‐level TLI for the PV system. The problem of LC is mitigated by providing common ground (CG) for both PV and the grid neutral. This topology uses only five switches, a diode, two DC link capacitors, and a switched capacitor (SC) to produce the five‐level output voltage. Only two switches are conducted for positive and negative voltage level generation. The charging current of the SC is limited by using the front‐end inductor. A level‐shifted pulse width modulation (LS‐PWM) is adopted for generating the gate pulses. A detailed mathematical approach has been suggested for the component selection and the losses associated with it through theoretical calculation and simulation. Further, an explicit comparative study is performed with existing similar kinds of topologies to claim the merits of the proposed topology. This topology is validated using both MATLAB/Simulink and the laboratory prototype model for a 1 kW system. It is observed that the voltage stress and current stress across the component are very less. Overall, the component count is reduced and helps to get an enhanced efficiency of 96.7%. [ABSTRACT FROM AUTHOR]

The objective of reducing the size and cost of the grid-connected photovoltaic system has led to advancements in the field of transformerless grid-connected inverters and gained high popularity in recent years. However, in such systems, the major limitation lies in realizing maximum power from individual modules. In this regard, this paper proposes a modular transformerless grid-connected photovoltaic multilevel inverter that realizes the individual maximum power point (MPP) of each module under different operating scenarios. The presented configuration is simple and modular, providing flexibility to increase the number of inputs with less component count. A single-phase synchronous reference frame PI (SRF-PI) controller has been designed and realized for the proposed system. The systematic procedure for designing the controller has been detailed. The converter and controller allow the system to realize individual MPP of the modules and simultaneously achieve the load demand maintaining the desired grid voltage. This has been verified under different operating scenarios in the MATLAB/Simulink environment. The same has been validated on a 300W laboratory prototype under source and load intermittencies. The proposed configuration has been compared with the similar works reported in the literature and it has been observed that it employs only 18 components. Also, the efficiency of the converter has been observed in the range of 89-95%. Further, the common-mode voltage and the leakage current have been measured to verify their suitability for grid-connected systems as per German VDE 0126-1-1 standards.

Transformerless grid-connected inverters have attained a lot of research interest in renewable energy interface applications, due to certain promising properties like greater efficiency, light weight, affordable price, and tolerable power density. Among various types of transformerless grid-tied photovoltaic (PV) inverters, multilevel inverters (MLIs) are mostly popular due to their ability to transmit reactive power, small filter size for reducing total harmonic distortion (THD) and their common-ground (CG) configuration to mitigate the detrimental leakage current due to the parasitic capacitances of the PV array. Again, among different types of MLIs for PV systems, switched-capacitor (SC) based multilevel inverter topologies are the burning topic in current decades due to their single source requirements for producing multilevel output voltage. However, for mostly used single-phase five-level inverters, most of the existing SC based topology requires at least two SCs for power conversion. In this paper, a five-level transformerless inverter based on a single SC is proposed, requiring only seven switches, no diode, a single capacitor, and one dc voltage source. The proposed transformerless MLI also has auto-boosting capability. Notably, the number of power switches operating at high frequency is limited to three, which lowers down the switching losses of the inverter. Rather than a new single SC based five-level transformerless inverter topology, a control scheme is also presented to inject a precisely regulated current into the grid that can govern both the active and reactive power support modes. In-depth comparisons between the proposed and cutting-edge MLIs are also provided. All these claims are validated through MATLAB/Simulink and PLECS computer simulation environments. A laboratory-scaled prototype is also built and tested to support the simulated claims further and validate the effectiveness and feasibility of the proposed five-level transformerless inverter topology.

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.

This article proposes a single-stage, seven-level (7L), switched-capacitor-based grid-connected inverter architecture with a common ground feature. This topology has the ability to boost the output voltage up to three times the input voltage. The proposed topology can diminish the leakage current in grid-connected photovoltaic (GC-PV) applications, and its capacitor voltages are self-balanced without any additional control strategies. The different operating modes are described in detail with their related mathematical expressions. The design of passive components and a detailed power loss analysis are presented. The merits of the proposed structure are demonstrated using a detailed comparative assessment. The grid-connected operation of the proposed inverter structure is simulated in the MATLAB/Simulink environment, and the results are presented. The laboratory prototype of 935 W is built and analyzed to validate the performance of the proposed structure. [ABSTRACT FROM AUTHOR]

Utility grid-tied photovoltaic (PV) installations are becoming a typical component of the current electrical energy grid. The adoption of transformerless inverters has recently changed the topology of these systems. Despite being small, inexpensive, and effective, transformerless inverters have a recurring leakage current issue. Numerous studies are being conducted to improve its performance and bring the leakage current down to acceptable levels. The studies propose three tracks for addressing the leakage current problem of transformerless PV systems: the control technique, the inverter modulation, and the inverter topology. This study applies the model-free predictive control (MFPC) technique to a grid-connected NPC 3-φ transformerless converter powered by a PV panel. An LCL filter connects the transformerless inverter to the grid. The system model considers the grid filter components and the internal impedance of the utility grid. The proposed system's discrete model is established before describing the MFPC controller's algorithm. The suggested system is simulated in MATLAB using the MFPC and a standard PI current controller with SVPWM modulation. According to the simulation's findings, the MFPC controller performs best regarding current spectrum, THD, and earth leakage current. Additionally, MFPC-based systems are more efficient than those that use PI controllers. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the topologies of single-phase transformerless inverters with different levels using a proportional-integral-resonant (PIR) AC controller, and the multi-level cascade inverter topology with sinusoidal pulse with modulation (SPWM) control in an open and closed loop. To ensure that these photovoltaic inverters can inject a defined amount of reactive power into the grid according to international regulations. Therefore, precise monitoring of the mains voltage vector by a phase-locked loop (PLL) system is applied to ensure the proper functioning of this system. For inverter topologies with less than three levels, the simulation results show that the highly efficient and reliable inverter concept (HERIC) topology performance is better than that of H5 and H6. On the other hand, the performance of the topology H6 ameliorate is superior to those of H4, H5, and HERIC in currents of leakage. On the other hand, for the control of cascaded multi-level closed-loop inverters, we notice that there is an improvement in the spectra and the elimination of all frequency harmonics, close to that of the fundamental, and a reduction in the rate of harmonic current distortion. [ABSTRACT FROM AUTHOR]

Introduction. In recent years the usage of electricity has increased tremendously as the electrical needs and loads got increased. Hence the researchers focused on the electricity generation from renewable sources in order to promote sustainable green environment. Owing to the lesser cost and more reliable high efficiency system with reduced use of equipments became prominent for the grid connected photovoltaic single phase systems. The novelty of this proposed converters are to reduce total power loss and to analyze the performance of the converter under various modulation index and to have lesser harmonics using sinusoidal pulse width modulation technique for both T-type and F-type inverter. Interest of the work is to merge two DC-DC converters which have same output voltage in order to have transformer less utilization of power. This has given pathway to develop a new DC-DC converter network by merging the common input nodes of CUK and SEPIC converter. Purpose. This similar structure of both converters made it easy to combine the input stages of and to get bipolar output. Methods. Here we can get bipolar output without the utilization of transformer which minimizes the overall size of the proposed system. In this paper, a combined CUK-SEPIC based grid connected transformerless inverter for photovoltaic application is suggested. Results. The suggested converter is simulated using MATLAB and the results were discussed. Further the circuit is extended with a 1 kW F-type inverter to demonstrate grid connection of the converter. Practical value. This converter can be implemented for photovoltaic applications for obtaining the bipolar DC output from the DC source. [ABSTRACT FROM AUTHOR]

Distributed generations, using solar photovoltaic (PV) generation systems, are generally connected to ungrounded distribution systems to ensure operational continuity and avoid electro-chemical corrosions. The ungrounded power distribution system possesses an advantage of continuous operation regardless of primary fault occurrence due to a small fault current. Conversely, a subsequent secondary fault can induce a large fault current representing that of other electrical grounding types, resulting in inevitable power shutdowns. As preventative methods, both insulation status monitoring and primary failure detection have become of high importance. This paper presents a method enabling the cooperative use of IMD (Insulation Monitoring Device) and GPT (Ground Potential Transformer) in an ungrounded distribution system connected with a transformerless inverter. Moreover, factors leading to errors during IMD insulation monitoring, CLR (Current Limit Resistor) burnout of a GPT, and malfunctions of related protection devices are presented. Furthermore, a method for selecting the inductor and capacitor in consideration of the operating characteristics of IMD and GPT is discussed. The proposed cooperative operation method enables the accurate measurement of insulation resistance using IMD, while concurrently reducing the constitutively induced zero-sequence voltage in the CLR of a GPT to prevent CLR burnouts and malfunctions of connected protection devices. Hence, the method is anticipated to contribute to the stable operation of alternating current (AC) and Direct Current (DC) combined systems connected with transformerless inverters. [ABSTRACT FROM AUTHOR]

In this article, a new inverter unit is proposed. It is a compact switched-capacitor-based inverter, which is combined of four switches, two diodes, and four capacitors. Since this inverter unit is a mid-point-clamped inverter, it can mitigate the capacitive leakage current in many applications. One of the main applications of the proposed inverter is in grid-tied photovoltaic systems, where the common-mode current brings many challenges. Other than the mentioned feature, the proposed inverter includes the following advantages: 1) spontaneous balancing of the voltage across the capacitors without needing any control system or auxiliary circuits; 2) capability of full reactive power transfer; 3) low voltage stress on the capacitors compared to common three-level inverter topologies (NPC, T-type-NPC, FC, etc.); and 4) symmetric switching sequence, which causes a continuous input current. The feasibility and versatility of the proposed inverter unit is validated by experimental tests, which are conducted by using a lab-scale prototype. [ABSTRACT FROM AUTHOR]

Transformerless inverters are prominently used in the single-phase grid-connected system due to their reduced size, weight, and high efficiency. Common-mode leakage current is the main issue of transformerless inverters, which has to be mitigated. An AC-decoupled high gain inverter is proposed in the inverter capable of attaining the gain more than ten times. Hence, even if the PV voltage is less, the inverter can continue to supply the grid. Unlike the two-stage inverters, the proposed inverter doesn’t require the DC-link capacitor, and it’s charging diode between the boosting and inverter stages. The AC-decoupling method used in the inverter helps to reduce the leakage current within the German standard limit VDE0126-1-1. A detailed steady-state analysis of the inverter is presented. The proposed inverter is simulated in the MATLAB Simulink platform to validate its working principle. The comparative loss and thermal analysis of the semiconductor switches made of three different materials (Gallium Nitride, Silicon Carbide, and Silicon) are made in the PLECS platform. The comparative analysis proves that the proposed inverter with Gallium Nitride made switches offers higher efficiency and reliability.

This paper proposes a pseudo-DC link type DC-decoupled transformerless inverter. The variation of common mode voltage is the primary reason for the flow of common-mode leakage current in the transformerless inverter. The proposed topology uses the DC-decoupling method to mitigate the common-mode leakage current. In contrast to two-stage inverters, the proposed topology’s pseudo-DC link structure avoids the necessity for a DC-link capacitor and associated charging diode between the boosting and inverter stages. The proposed inverter’s excellent boosting ability allows it to work with a wide input voltage range. The modulation strategy used here avoids the need for dead time and the problem of shoot-through. The MATLAB simulation model directly confirms the feasibility and efficacy of the proposed topology and its modulation strategy. The loss calculation and thermal analysis of the inverter made of three different materials are compared in PLECS platform. The thermal analysis helps to decide the heat sink size and thermal protection of switches.

A new common ground transformerless inverter topology based on the switched-capacitor concept has been introduced in the proposed article. In the proposed design, ten switches, two capacitors, and a single DC source are used to enhance the output voltage to double that of the supply voltage by using a single DC source. The technique of common ground connection, in which the negative terminal of the photovoltaic modules is directly connected to the neutral point of the utility grid, is used to prevent leakage current. Furthermore, the topology description, the operating principle of the various states, and the computation of capacitance are all thoroughly investigated. To ensure that the proposed topology executes smoothly at all times, a level shift pulse width modulation technique is adopted. As an additional benefit of the suggested topology, detailed comparison evaluations are offered to highlight the advantages of the proposed topology. The proposed work has been carried out to establish the practicality of the proposed topology by modeling and conducting experimental tests on a five-level structure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article presents a method for generating a family of transformerless inverters with common ground, for the connection of photovoltaic or battery energy storage systems with the electrical grid. Using the proposed method, four common-ground buck type inverter topologies are derived from bidirectional dc–dc converters based on buck–boost, SEPIC, zeta and boost–buck converters, which have in common the static gain given by ${D \mathord{/ {\vphantom {D {(1 - D)}}} } {(1 - D)}}$. The operation of each generated topology is explained and confirmed by computer simulation results. A comparative analysis between the four generated topologies and other transformerless common-ground inverters are included, considering the number of components, voltage ratings, output power, switching frequency, reported efficiency at rated power, and the requirement for filter insertion. Experimental results obtained in the laboratory, with tests performed on a nonoptimized experimental prototype are presented, for the topology based on the bidirectional zeta converter. [ABSTRACT FROM AUTHOR]

Since three‐phase transformerless (TPT) PV inverters have large common mode leakage current (CMLC), a TPT PV inverter without CMLC is proposed. The proposed inverter is derived from three single‐phase half‐bridge inverters and a boost converter. Grounds of the PV array and three‐phase loads are connected directly, so no CMLC exists in the TPT solar inverter. Operating principle, stability analysis, and loss calculation and example of the proposed three‐phase inverter are illustrated in detail. The pulse‐width modulation (PWM) and sinusoidal PWM control methods are used in the boost converter and three‐phase inverter, respectively. The proposed inverter is a stable system. Finally, simulation and experimental results of a 900‐W TPT PV inverter confirm the theoretical analysis. The CMLC in the proposed inverter is only about 0.8 mA, which is mainly caused by the ground line inductance and oscilloscope probe noise. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Since three‐phase transformerless (TPT) PV inverters have large common mode leakage current (CMLC), a TPT PV inverter without CMLC is proposed. The proposed inverter is derived from three single‐phase half‐bridge inverters and a boost converter. Grounds of the PV array and three‐phase loads are connected directly, so no CMLC exists in the TPT solar inverter. Operating principle, stability analysis, and loss calculation and example of the proposed three‐phase inverter are illustrated in detail. The pulse‐width modulation (PWM) and sinusoidal PWM control methods are used in the boost converter and three‐phase inverter, respectively. The proposed inverter is a stable system. Finally, simulation and experimental results of a 900‐W TPT PV inverter confirm the theoretical analysis. The CMLC in the proposed inverter is only about 0.8 mA, which is mainly caused by the ground line inductance and oscilloscope probe noise.

The 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. [ABSTRACT FROM AUTHOR]

There is increasing utilization of photovoltaic (PV) grid-connected systems in modern power networks. Currently, PV grid-connected systems utilize transformerless inverters that have the advantages of being low cost, low weight, a small size, and highly efficient. Unfortunately, these inverters have an earth leakage current problem due to the absence of galvanic isolation. This phenomenon represents safety and electrical problems for those systems. Recently, the H8 transformerless inverter was introduced to eliminate the earth leakage current. The present study proposes improving the performance of an H8 transformerless inverter using model predictive control (MPC). The inverter was supplied by PV energy and attached to the grid through an LCL filter. During system modeling, the grid weakness was identified. The discrete model of the overall system, including the PV panel, the boost converter, the H8 transformerless inverter, and the controllers, was derived. Then, the introduced H8 transformerless inverter system was simulated and analyzed by the Matlab/Simulink program. The proposed system response using MPC was tested under step disturbances in the PV insolation level. Moreover, the effect of the weak and strong grid operations was considered. The simulation results indicate that the MPC controller has better performance and high-quality injected power. Despite the excellent performance of the strong grid, the nearly weak grid performance is acceptable. Moreover, the Hardware-in-the-Loop (HIL) of the proposed system was implemented using the DSP target LaunchPadXLTMS320F28379D kit to validate the simulation results. Finally, the system performance under the parameter variations showed good robustness. [ABSTRACT FROM AUTHOR]

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This article proposes a single-stage, seven-level (7L), switched-capacitor-based grid-connected inverter architecture with a common ground feature. This topology has the ability to boost the output voltage up to three times the input voltage. The proposed topology can diminish the leakage current in grid-connected photovoltaic (GC-PV) applications, and its capacitor voltages are self-balanced without any additional control strategies. The different operating modes are described in detail with their related mathematical expressions. The design of passive components and a detailed power loss analysis are presented. The merits of the proposed structure are demonstrated using a detailed comparative assessment. The grid-connected operation of the proposed inverter structure is simulated in the MATLAB/Simulink environment, and the results are presented. The laboratory prototype of 935 W is built and analyzed to validate the performance of the proposed structure.

Utility grid-tied photovoltaic (PV) installations are becoming a typical component of the current electrical energy grid. The adoption of transformerless inverters has recently changed the topology of these systems. Despite being small, inexpensive, and effective, transformerless inverters have a recurring leakage current issue. Numerous studies are being conducted to improve its performance and bring the leakage current down to acceptable levels. The studies propose three tracks for addressing the leakage current problem of transformerless PV systems: the control technique, the inverter modulation, and the inverter topology. This study applies the model-free predictive control (MFPC) technique to a grid-connected NPC 3-φ transformerless converter powered by a PV panel. An LCL filter connects the transformerless inverter to the grid. The system model considers the grid filter components and the internal impedance of the utility grid. The proposed system’s discrete model is established before describing the MFPC controller’s algorithm. The suggested system is simulated in MATLAB using the MFPC and a standard PI current controller with SVPWM modulation. According to the simulation’s findings, the MFPC controller performs best regarding current spectrum, THD, and earth leakage current. Additionally, MFPC-based systems are more efficient than those that use PI controllers.

Presence of a transformer in a grid connected photovoltaic system provides galvanic isolation between the photovoltaic panels and the grid. However, it increases the overall cost, makes the circuit bulky and reduces the efficiency of the system. Hence, transformerless inverters have gained significant importance owing to its low cost, light weight and increased efficiency. However, due to the absence of the transformer, there is no galvanic isolation between photovoltaic panels and the grid and there is always a threat of flow of leakage current. In this research paper, an elaborate analysis of H4, H5 and H6 transformerless inverter is carried out. DC side decoupled circuits are studied to eliminate the leakage current. Their performances are compared based on the simulations carried out in MATLAB/SIMULINK software. A novel H6 inverter is proposed by introducing an additional switch in H5 topology. A direct current path is provided in H5 topology during one of the active modes, so that current flows through few switches thereby reducing the conduction losses. Common mode voltage remains constant in the proposed H6 inverter and hence the leakage current is eliminated. The proposed H6 inverter can thus be a promising topology to eliminate leakage current and reduce conduction loss in the transformerless grid connected photovoltaic system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Due to the advancements of power electronic devices and photovoltaic (PV) power systems, there has been an increasing interest in transformerless grid-connected PV inverters, which offer lower cost, smaller volume, and higher efficiency than the one with the transformer. However, transformerless inverters with conventional topologies suffer from leakage current problem, which needs to be handled carefully. To overcome the conduction loss and leakage current problem associated with conventional transformerless inverters, a new transformerless H6 (six-switch-based) inverter topology is proposed in this article that can maintain constant common-mode (CM) voltage. At the same time, reduce or eliminate the leakage current problem. The proposed inverter topology is simulated using MATLAB/Simulink software to validate the proposed system's accuracy. The proposed topology's effectiveness is verified through the comparative results of CM voltage, CM leakage current, and conduction loss of the proposed topology with the conventional H6-I, H6-II, and H5 topologies. Finally, to validate the proposed topology, a laboratory prototype is also built and tested. The experimental results validate the theoretical analysis and simulation results. [ABSTRACT FROM AUTHOR]

The development of the world demands on the progress of electricity operation and quality enhancement. Microgrid (MG) is a solution that manages the additional need of electricity. The MG generates electricity mostly from renewable energy sources, e.g. solar, wind and hydro. Most renewable energy sources require energy storage system as they are highly unpredictable in nature. An inverter is needed to convert that stored DC power to AC. The presence of a capacitor within the grid provides a galvanic connection that varies the common mode (CM) voltage of the inverter. Thus, the leakage current as well as the total harmonic distortion (THD) of the grid voltage and current increases. The increase of the leakage current hampers the safe operation of the MG. Now-a-days transformerless inverter is gaining more attention because of high efficiency, low cost, less weight and the capability of eliminating the high frequency component from the inverter CM voltage. In addition, a controller inclusion with a transformerless inverter can maintain a near-seamless performance. This paper proposes a blended technique of an improved H5 topology with an Integral Linear Quadratic Gaussian (ILQG) controller for grid-connected MG operations, that reduces the inverter leakage current by keeping the CM voltage constant. Thus it has the capability to reduce the THD of voltage and current. A comparative analysis has been carried out between this technique and existing topologies with different modulation techniques that helps to find out the most optimum inverter package to eliminate the leakage current and reduce the THD of grid voltage and grid current to almost zero.

Transformerless grid-connected inverters offer greater efficiencies when transferring power from renewable energy sources to the electrical grid. If the grid-inverter connection is done with an LCL filter, high attenuation of switching harmonics is achieved while preserving a small-size output filter. However, damping must be included in the controller to assure closed-loop stability. This paper proposes a reference computation methodology for the inverter-side current feedback in a photovoltaic (PV) generation system connected to the grid through an LCL filter. Theoretical analysis of the closed-loop system stability and of the steady-state performance are presented as well as experimental validation of the closed-loop performance. The feedback controller includes active damping and relies on a resonant control structure which improves the ability of dealing with grid harmonic distortion. The controller uses a reduced set of measurements, which requires the inverter-side current and grid voltage only, and assures a power factor close to unity.

Distributed generations, using solar photovoltaic (PV) generation systems, are generally connected to ungrounded distribution systems to ensure operational continuity and avoid electro-chemical corrosions. The ungrounded power distribution system possesses an advantage of continuous operation regardless of primary fault occurrence due to a small fault current. Conversely, a subsequent secondary fault can induce a large fault current representing that of other electrical grounding types, resulting in inevitable power shutdowns. As preventative methods, both insulation status monitoring and primary failure detection have become of high importance. This paper presents a method enabling the cooperative use of IMD (Insulation Monitoring Device) and GPT (Ground Potential Transformer) in an ungrounded distribution system connected with a transformerless inverter. Moreover, factors leading to errors during IMD insulation monitoring, CLR (Current Limit Resistor) burnout of a GPT, and malfunctions of related protection devices are presented. Furthermore, a method for selecting the inductor and capacitor in consideration of the operating characteristics of IMD and GPT is discussed. The proposed cooperative operation method enables the accurate measurement of insulation resistance using IMD, while concurrently reducing the constitutively induced zero-sequence voltage in the CLR of a GPT to prevent CLR burnouts and malfunctions of connected protection devices. Hence, the method is anticipated to contribute to the stable operation of alternating current (AC) and Direct Current (DC) combined systems connected with transformerless inverters.

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. [ABSTRACT FROM AUTHOR]

Summary: In this article, a three‐phase transformerless inverter (TLI) for a solar photovoltaic (PV) system connected to a high‐power grid are proposed, which has advantages of better performance and lower cost. The primary concern about the TLI is fluctuations in the common‐mode voltage, which impacts switching frequency leakage current and grid interface system. An improved H7 common‐mode voltage (CMV) clamped TLI with discontinuous pulse width modulation (DPWM) is designed using a conventional neural network (CNN)‐based deep learning approach. In this, a completely minimized leakage current is obtained to avoid CMV transients. The proposed PV‐connected improved H7‐TLI provides low‐loss DC‐side decoupling, which further reduces leakage current and isolation of the PV system during off‐grid. In addition, the effects of several factors on CNN deep learning performance are explored, including training data size, image resolution, and network configuration. The proposed technique has the potential to be used in a test instrument for intelligent signal analysis or used in an artificial intelligence system. Switching loss is analyzed using proposed and existing H7 inverters under different load conditions. To verify the theoretical explanation, existing H7 inverters is analyzed by MATLAB/Simulink, and the outcomes are tested experimentally. The total harmonic distortion (THD) analysis of proposed and existing topology is analyzed and compared. The THD values of the existing and proposed topology are 3.74% and 3.23%, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a transformerless common-ground single-phase inverter for battery energy storage system (BESS) applications. With regard to conventional converters operating as a voltage source inverter (VSI), the proposed converter offers the advantage of a common connection between the battery bank negative terminal and the ground. Hence, the common-mode voltage becomes continuous while common-mode currents flowing through parasitic capacitances located between the battery bank and the grounded metallic frame are eliminated, allowing operation without a transformer. This new topology has only two power semiconductors, two inductors and one capacitor, without the need for a filter on the AC grid side. The converter operation is described and the relevant equations for sizing are presented along with the main characteristics. A 1 kW non-optimized prototype was dimensioned, built and tested to validate in practice the theoretical analysis, and a maximum efficiency of 95.25% was obtained. Due to the simplicity, low number of active components, no clamping circuit requirement and the common-ground, this topology is a very interesting option for the above-mentioned application.

Harnessing the energy from renewable sources has gained more significance as the conventional sources will not be lasting for upcoming decades. Besides these alternative energy sources are free, the advanced energy conversion mechanisms raising their demand. Out of all the renewable resources photo voltaic (PV) energy conversion is widely used due to its less maintenance, descent efficiency of conversion. Grid connected PV systems became more popular in the recent years with the advent of sophisticated inverter topologies and conversion techniques. In grid connected PV systems transformer can be eliminated by which space, size of the system can be reduced, and efficiency of the system can be improved. However, by removing transformer, isolation of PV panels and grid is not achieved. If isolation is not achieved, the effect of virtual stary capacitance between PV panels and ground will cause leakage currents due to variation in common mode voltage. A single phase full-bridge/H-bridge inverter is used and is connected to grid through a LCL filter. Bipolar pulse width modulation is used to eliminate or to suppress leakage current. This paper includes implementation of transformerless inverter for grid connected PV systems using MATLAB/Simulink. It also gives the analysis of various parameters like inverter, grid voltages, currents, and common mode leakage current at various solar irradiance levels. [ABSTRACT FROM AUTHOR]