Transformerless PV Inverter Research Articles

Common Mode and Terminal Voltages With Effect of Device Junction Capacitance in Five-Level Transformerless PV Inverter

Common Mode and Terminal Voltages With Effect of Device Junction Capacitance in Five-Level Transformerless PV Inverter

Performance analysis of a new single-phase transformerless PV inverter structure based on a buck-boost converter

A single-phase inverter based on a buck-boost converter is increasingly used in modern power electronics, particularly in solar photovoltaic systems. Unlike traditional inverters that utilize transformers to electrically isolate the solar system from the power grid, this transformerless design enhances efficiency, reduces weight, and lowers costs. However, the absence of a transformer introduces challenges related to Electromagnetic Compatibility (EMC) and the potential for increased leakage currents, which must be carefully managed to ensure system safety and performance. In this paper, the performances of a new configuration of a single-phase transformerless PV inverter based on a dc-dc buck-boost converter is proposed and analyzed. Since it is the only switch (mosfet) in the DC-DC converter that operates at high frequency, and it is controlled by pulse width modulation (PWM) to adjust the output voltage. This allows for flexible voltage conversion, enabling the inverter to either step up (boost) or step down (buck) the input voltage as needed. Therefore, switching losses can be significantly reduced to improve efficiency and reduce electromagnetic interference of the single-phase inverter structure. In order to demonstrate the EMC performances and evaluate the leakage current of the proposed structure, an EMC model is developed under the Simscape-MATLAB/Simulink environment, this model offers an EMC analysis including the prediction of leakage current over a frequency range from 100 Hz to 2 MHz. The results clearly showed that the level of the Total harmonic distortion (THD), as well as the levels of leakage current, are below the requested EMC standards.

Three-Phase Transformerless PV Inverter With Reconfigurable LCL Filter and Reactive Power Capability

Three-Phase Transformerless PV Inverter With Reconfigurable <i>LCL</i> Filter and Reactive Power Capability

Innovative approaches for minimizing leakage current in three-phase transformerless PV inverters

Innovative approaches for minimizing leakage current in three-phase transformerless PV inverters

Analysis and Improved Behavior of a Single-Phase Transformerless PV Inverter

Transformerless inverters have an important role in the electrical energy market. The high-efficiency and reliable inverter concept is one of the most widely used inverters in single-phase photovoltaic systems because of its high efficiency, low cost, and reduced leakage ground current. However, the leakage ground current behavior depends on the power and weather conditions, which can increase the parasitic capacitance value, thus producing an increase in the leakage ground current magnitude. In this paper, it is proposed to add a passive inductive–capacitive output filter to the inverter structure in order to reduce the dependency of the leakage ground current on the system power and weather conditions. The inductive–capacitive output filter is designed in such a way that it can provide a low impedance path for the leakage ground current, different from the ground path. The proposed system was evaluated both through simulations and experimentally in a 1 kW laboratory prototype.

A Novel Single Phase Three Level Triple Boost CG Switched-Capacitor Based Grid-Connected Transformerless PV Inverter

A new three-level inverter based on the switched capacitor (SC) with a common grounding (CG) configuration has been introduced in this article, which is capable of boosting the input voltage up to three times. Therefore, this inverter is configured without any boost dc/dc converter stage for low voltage PV application. To step up the input PV voltage and facilitate three level in output voltage, two SC cells are connected in parallel. This inverter's common grounding configuration helps in bypassing the stray capacitance, which eliminates the leakage current and consequently reduces electro-magnetic interference (EMI) considerably. Hence, for electro-magnetic compatibility (EMC), this inverter does not require any EMI filter. Additionally, this inverter handles reactive power during the grid's lagging/leading power factor (pf) condition. A proportional resonant (PR) current controller is designed to regulate active and reactive grid power. The proposed modulation strategy helps in balancing capacitor voltages at their base values with allowable ripple. The inverter circuit details, control technique, PWM scheme, thermal modeling, and loss analysis with component design guidelines are described in detail. Experimental results are presented to validate the effectiveness and feasibility of this proposed inverter.

Five-Level Transformerless Common Ground Type Inverter with Reduced Device Count

In recent days, the transformerless grid-connected PV inverter is paid more attention due to its compactness and high efficiency with low cost. This paper presents a new five-level transformerless switched capacitor type inverter with a reduced number of power components. The proposed topology has a lower number of power components with a common ground connection between the negative terminal of the input side and load that eliminates the leakage current. The switched capacitors do not require any sensors for their balancing. The different modes of operation and control of the PWM technique are discussed. The proposed topology is compared with recent transformerless inverters, and the advantages of the proposed topology are highlighted. The simulation and experimental results are presented. The prototype hardware setup is built for 1.2 kW and has the simulated maximum efficiency of 96.4%. The performance of the proposed topology is measured by applying various load and modulation index variations.

Review of Existing Transformer-Less PV Inverter Topologies and Design a Modified Topology to Reduce Leakage Current

"ENGINEER", established in 1973 by The Institution of Engineers, is a Journal for dissemination of Engineering knowledge, published quarterly.If you are interested in contributing an Original Technical Paper based on research by the author(s) (intended for Section I) or an Original Article of Professional or Technical interest related to Engineering. (Section II) to this journal please go through the publication checklist which can be downloaded from here.Cover DescriptionCover images show views of the Giant tank and the Tekkama anicut.

Three‐phase transformerless photovoltaic inverter without common mode leakage current

AbstractSince 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.

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

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

Four-Switch Single-Phase Common-Ground PV Inverter With Active Power Decoupling

This letter presents a transformerless single-phase PV inverter, which combines with common-ground and active power decoupling techniques. The leakage current is eliminated and bulky electrolytic capacitors are removed, thus improving the system safety and reliability. In addition, it needs only four switches and can be implemented conveniently by a commercial H-bridge module. The validity of the inverter is verified with a 2-kW prototype.

A Transformerless 1-, 5-Level Half-Bridge PV Inverter Configuration Based on Switched-Capacitor Technique

Leakage current is a serious problem in the transformerless solar PV inverter configurations. The flow of leakage current is mainly due to the high-frequency oscillations in the voltage across PV parasitic capacitance (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CPV</sub> ). Half-bridge (HB) and common ground type inverter topologies are highly suitable for eliminating these oscillations as these configurations allow direct electrical connection between the source and the load/grid ground. However, they suffer from either poor dc-bus utilization or asymmetric operation leading to dc-offset in the output voltage. In this article, a novel 1-φ, 5-level inverter is proposed, which employs a HB structure to eliminate voltage oscillations from v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CPV</sub> without compromising with the dc-bus utilization or symmetric operation. This is achieved by integrating a switched capacitor network with the HB structure. All the necessary analysis and design procedures are included to support the various claims. The claims are further validated using MATLAB simulations and experiments on a laboratory prototype. The proposed topology is compared with the various existing topologies of similar nature (like 5-level output voltage, common ground or HB type configuration and 1-φ) to prove its superiority.

Transformerless Grid-Connected PV Inverter Without Common Mode Leakage Current and Shoot-Through Problems

As there is shoot-through problem and common mode leakage current in conventional transformerless grid-connected PV inverters, a transformerless grid-connected PV inverter without common mode leakage current and shoot-through problems is proposed. The proposed inverter consists of a buck-boost converter and a dual-buck half-bridge inverter, so there is no shoot-through problem in the proposed inverter. As grounds of the input source and the grid are shorted, there is no common mode leakage current. No current flows through the body diodes of switches, so efficiency of the system is improved. Operating principle of the proposed inverter is elaborated in detail. Experimental results of a 350 W proposed inverter validate the theoretical analysis.

A Coupled Inductor-Based Buck–Boost Type Grid Connected Transformerless PV Inverter Having the Ability to Control Two Subarrays Simultaneously

A coupled inductor-based buck-boost type single phase transformerless grid connected photo voltaic inverter which has the ability to extract maximum power simultaneously from two serially connected subarrays is proposed in this article. The series connection of the two subarrays, and the buck-boost nature of the inverter result in reduction of the number of modules which are connected in series in a subarray. Further, independent operation of the two subarrays enhances the overall power extracted from the subarrays while they are experiencing significant mismatch in their operating conditions. The deployment of the coupled inductors has reduced the component count and overall size, weight, and volume of the proposed inverter. On the other hand it helps to achieve moderately high overall operating efficiency at higher power level as compared to the single inductor-based buck-boost schemes. A new inductor current control technique which is independent of the mode of operation (CCM or DCM) is adopted to control the grid current. The topological structure of the inverter, and its control technique restrict the overall leakage current related to the subarrays within the permissible limit. A 1-kW experimental setup has been fabricated and thorough experimental analysis are performed to confirm the viability of the proposed inverter.

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.

Investigation of the Effects of DC Current Injected by Transformer-Less PV Inverters on Distribution Transformers

Rooftop transformer-less photovoltaic inverters (TLPVIs) have the potential to inject a very small dc current into the distribution network. The dc current quantity can be very high in a residential power distribution system where several TLPVIs are installed. Distribution transformers (DTs) supplying power to the customers in the networks can be adversely saturated with this high dc current accumulated from the small dc current injected by individual TLPVI. In this paper, a systematic investigation is carried out on the dc current injection potential of commercially available TLPVIs. Furthermore, the influence of this aggregated dc current on the DTs are analyzed through modelling, simulation, and laboratory testing. A three-phase three-leg transformer is used to analyze the effects of the high dc injection from the TLPVIs. A finite element analysis is carried out in COMSOL Multiphysics environment to explore the dc current injection effect. The results show that the injected dc current from TLPVIs highly affect the DTs and a solution is needed to overcome this challenge before the problem spreads widely and causes a barrier to the growth of the integration of renewable resources to the power grids.

Mitigation of DC Current Injection in Transformer-Less Grid-Connected Inverters Using a Voltage Filtering DC Extraction Approach

Transformer-less grid-connected PV inverters are an attractive technology choice due to their high-efficiency performance and relatively small volume. However, in the absence of galvanic isolation, dc current can potentially flow into the grid and adversely affect the grid performance. In addition, as the sinusoidal ac output is significantly larger than the dc injection component, accurate dc current sensing at the inverter output remains a technical challenge. As a result, this paper proposes a two-stage dc voltage detection technique that employs an isolated RC attenuation circuit and a software dc-component filtering algorithm. The principle of the proposed technique can be applied in many switch-mode power converter topologies. The simple and cost-effective combination facilitates dc component extraction within the accuracy of 1 mV; moreover, this can be further used as digital dc feedback for active current control purposes. Experimental results from a laboratory prototype demonstrate the high performance of the proposed dc extraction and suppression approach.

Control of Single Phase Grid Connected Transformerless PV Inverter System

Control of Single Phase Grid Connected Transformerless PV Inverter System

Control of Single Phase Grid Connected Transformerless PV Inverter System

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Quasi-resonant DC-Link transformer-less structures for grid-connected PV systems

This paper presents the quasi-resonant DC-Link transformer-less structures whereby the efficiency of the grid-connected PV systems could be improved. Transformer-less PV inverters as a critical part in power conditioning units are more advantageous to the user. However leakage current that is resulted from omitting bulky transformers can compromise their higher efficiency. So the low leakage current and high efficiency are two crucial points in transformer-less PV systems. By incorporating Quasi-resonant DC-Link as a method of soft switching into the H6 structures two new DC-decoupled soft-switched transformer-less PV inverters are proposed by which the switching losses of power devices as well as high di/dt, dv/dt and EMI could be avoided. A new auxiliary circuit is extracted from available structures. Proposed auxiliary circuit features lower voltage stress and saves one gate drive circuitry as well. Using only two auxiliary switches, ZVS turn on/off for high frequency DC bus switches and ZVS turn on/off of the antiparallel diodes of all grid frequency main switches are realized. Soft switching condition for auxiliary switches and their antiparallel diodes are also provided. Finally a 20 kHz 1-kW universal prototype is built and Operation characteristics, soft switching conditions and efficiency improvement of proposed QRDCL transformer-less PV inverters are verified.