The uses of grid-connected photovoltaic (PV) inverters are increasing day by day due to the scarcity of fossil fuels such as coal and gas. On the other hand, due to their superior efficiency, lower cost, smaller size, and lighter weight when compared to inverters with transformers, transformerless inverters for low-voltage single-phase grid-tied photovoltaic (PV) systems have recently attracted more interest. However, there are some specific challenges, especially leakage current issues, which must be adequately addressed to ensure the safety standards of the grid codes. A variety of topologies has been presented in the literature to eliminate the leakage current using the decoupling or clamping technique. However, choosing an appropriate topology after comparison is challenging because each topology has a unique set of parameters. In this paper, the authors have selected a common set of parameters and simulated all the selected eighteen well-known topologies in MATLAB/Simulink to fairly analyze and compare their common mode characteristics and other output parameters. In addition, the power loss distribution of every switch of each of the eighteen topologies was calculated and presented to better understand the insight of the topologies.

Now-a-days, transformer-less inverters integrating renewable energy resources as solar photovoltaic systems are commonly employed in many grid-connected distributed energy systems in both industrial and residential settings. Transformer-less photovoltaic (TLPV) inverters have attracted increased attention due to their unique advantages, such as increased efficiency, low cost, and ease of installation. Converting fluctuating solar dc power to consistent ac power has been a difficulty in the recent decade to avoid security risks like ground fault currents and leakage currents. Leakage current minimization is one of the most crucial factors in the TLPV inverters. Different TLPV inverter topologies have been presented in the past, with leakage current being reduced by galvanic isolation on the dc or ac side of the inverter, common mode voltage (CMV) clamping, and modulation techniques. This paper proposed two novel single-phase grid-tied TLPV inverter topologies with control blocks, which can handle a wide variety of grid voltages. The proposed TLPV inverters offer very small leakage current, reduced total harmonic distortion (THD), and improved power quality. Based on the number of semiconductor devices, the proposed inverters are termed as H9 and H10 inverters. The switches are controlled using the unipolar sinusoidal pulse width modulation, which results in constant common mode voltage and reduction in leakage currents to 11.09 and 11.73 mA for the proposed H9 and H10 inverters, respectively. The proposed H9 and H10 inverters minimize the THDs to 1.62 and 2.09%, respectively. Besides, the proposed H9 and H10 inverters exhibit 98.19 and 98.12% European efficiency. The simulations are carried out on MATLAB/Simulink and the results are experimentally validated using downscale laboratory test platforms

This paper presents a new three-phase integrated module multilevel inverter (IMMLI) with reduced component count which is suitable for low, medium and high voltage renewable energy systems. The proposed inverter is a resultant structure of a number of integrated module and each module is configured with a number of series connected basic blocks. Each block consists of a dc voltage source, a blocking diode and a semiconductor switch. A computational combination and summation among the dc sources from different blocks results in a high number of levels within the output voltage. This task is performed by controlling the switches equipping appropriate switching algorithm. Thus, a high level of output is obtained employing reduced number of components. Since the topology owns two degree of modularity, the total stress voltage (TSV) of the system is low and distributed among the switches. Hence, the proposed topology allows to be implemented in high power systems with reduced amount of costs. The inverter also offers enhanced efficiency, as the number of simultaneously conducting switch is low. Additionally, in order to operate the presented inverter with optimum ac power quality, a multi-carrier based level shifted PWM scheme is addressed in this paper. This paper also shows how to prepare balanced dc sources that are required to implement the inverter using high-frequency magnetic-link. The operating principle of the IMMLI is explained with the help of a fifteen level (15-L) single phase unit and its performance is evaluated in MATLAB/Simulink considering different conditions. Experimental validation is also presented to support the simulation results and to evaluate its superiority over the existing.

Advancement in solid-state semiconductor technologies has led to the medium-voltage power converters, by obviating the need of step-up transformers in renewable power generation systems. To improve the injected power quality of medium-voltage grid-tied power converters i.e., the harmonic components (e.g. total harmonic distortions) of the output current is minimized by various types of pulse width modulation (PWM) switching schemes. In this paper, a composite harmonic injected pulse width modulation (CHIPWM) switching scheme is proposed based on the modular multilevel cascaded (MMC) converter. The main feature of this modulation scheme is that it can improve the frequency spectra while reducing the switching power losses. In order to validate the performance of the proposed switching scheme, a 55-level, 3-phase MMC inverter is made in the MATLAB/Simulink environment for an 11kV renewable energy based power system. The performance of the proposed switching scheme is compared with different existing switching schemes in terms of THDs and switching power loss. From the simulation and numerical results, it is obvious that the 55-level MMC inverter with the proposed modulation scheme improves the injected power quality and reduces the inverter power losses as compared to the existing modulation schemes, which are very essential for the integration of renewable energy sources (RESs) to the existing utility grid.

Among the renewable energy sources, photovoltaic (PV) solar power represents one of the most potential. The use of grid-integrated solar power is much more popular than off-grid systems. The total system cost and weight can be reduced by eliminating transformers for grid-tied applications. However, a leakage current with a high peak value flows across the system in the absence of galvanic isolation between an ac grid and PV. In addition, reactive power injection must be ensured in future grid-tied systems. In this paper, the authors have proposed a new hybrid topology using both decoupling and mid-point clamping techniques to reduce the root mean square (RMS) and peak value of leakage current. In addition, the proposed topology can provide both active and reactive power to the grid. The topology is simulated in the Matlab/Simulink environment for both the open loop and closed loop conditions and then validated through experiments. In the open loop conditions, leakage current issue has been addressed. In the closed loop conditions, active power (P) and reactive power (Q) are injected into the grid using model predictive control (MPC). Finally, a comparative analysis with other similar topologies has been performed.

One of the most promising renewable energy sources is photovoltaic (PV) solar power. Off-grid solar systems are far less common than grid-tied solar systems. Transformers are not used in transformerless grid-tied applications, which lowers the overall system cost and weight. When there is no galvanic separation between an AC grid and PV in a transformerless system, a leakage current with a high peak and root mean square (RMS) value flows throughout the system that disrupts safety matters. Furthermore, future grid-tied systems need to ensure reactive power injection to control voltage. In this paper, the authors have presented a new modulation method for HERIC active clamping topology to lower leakage current’s peak value and RMS value and introduce the reactive power injection capability to the grid. The open loop simulations and experiments have proven the leakage current suppression ability of the proposed modulation. The closed loop simulations and experiments have confirmed the reactive power injection capabilities of the grid by applying the proposed modulation with model predictive control (MPC). Finally, a comparison table related to similar topologies and modulations has been provided.