In grid-connected photovoltaic (PV) systems, a transformer is needed to achieve the galvanic isolation and voltage ratio transformations. Nevertheless, these traditional configurations of transformers increase the weight, size, and cost of the inverter while decreasing the efficiency and power density. The transformerless topologies have become a good solution. However, the problem is that commode-mode voltage and leakage current can occur via the stray capacitors between the PV array and the ground of the inverter. Various transformerless inverters have been introduced with different techniques, such as reducing the common-mode voltage or eliminating the leakage current. Furthermore, to introduce the development of transformerless PV inverters, especially in three-phase two-level inverter systems, this paper provides a comprehensive review of various common-mode voltage reduction three-phase two-level inverters.

This paper proposes a new isolated high step-down DC-DC converter based on the phase-shift full-bridge converter. The proposed converter has some properties very suitable for high step-down applications including a high step-down ratio, low transformer turns ratio, low voltage stress on power switches, wide soft-switching range, and no saturation problem. These attractive features are achieved by a simple pulse-width modulation control method and a unique split-capacitor structure on the input side. By split-capacitor structure, both switching voltage and stress voltage are decreased significantly. As a result, the required ZVS energy is reduced greatly, which means that an extended ZVS range can be obtained. This structure also leads to an inherent high step-down ratio, low transformer turns ratio, and de-saturation feature because the primary transformer voltage is decreased to a quarter of the input voltage and there are capacitors in series with the primary winding in power modes. In this paper, the operation principle is presented; the ZVS range and de-saturation feature are discussed in detail. In addition, a comprehensive comparison with some new isolated high step-down converters in the literature is also completed. Finally, a simulation verification using the LTSpice simulation program and an 800 W, 400 V input, and 48 V output prototype are developed and tested to verify the salient features of the proposed converter.

In this article, a novel single-stage transformerless buck–boost inverter is introduced. The proposed inverter can share a common ground between the DC input side and the grid; this leads to having a zero-leakage current. The proposed inverter also provides the buck and boost voltage capabilities. Additionally, the power switches are operated at high frequency in the half-cycle of the sinusoidal wave, so the efficiency of the proposed inverter can be improved. Operating analysis, design consideration, comparison, and simulation study are presented. Finally, a 500 W laboratory prototype is also built to confirm the correctness and feasibility of the proposed inverter.

Transformerless inverters (TIs) are widely employed in photovoltaic (PV) applications due to their cost-effectiveness, compact size, low weight, and high efficiency. However, the absence of electrical isolation can result in ground leakage current due to the parasitic behavior of PV systems, resulting in safety concerns and compromised power quality. Conventional five-level common-ground inverters can eliminate ground leakage current through the common-ground technique and achieve double voltage boosting capability. However, this topology necessitates a considerable amount of capacitance to efficiently minimize voltage ripple due to the extended discharge time during the negative half-cycle. Moreover, the high capacitance raises concerns regarding the potential for high current stress on switches during charging modes. In this article, a new single-stage common-ground boosting transformerless inverter is introduced. The proposed topology has fewer components, a lower number of conducting devices, and reduced capacitance requirements. The proposed topology can also be extended to three-phase applications using a single power source. The article includes explanations of the proposed topology, the control method, the component design process, and the power loss calculations. In addition, a comparison with similar topologies is conducted to highlight the advantages and disadvantages of the proposed topology. Simulation results are included to confirm the functionality and practicality of the proposed topology. Finally, experimental results for a 500-W prototype operating in a closed-loop system under different loads and load changes are presented. The converter demonstrates its capability in both buck and boost modes, achieving a high efficiency of over 95%.

This paper proposes an isolated DC–DC converter to cope with 800 V input voltage and 48 V output voltage conditions of the auxiliary power module in the next generation 800 V electric vehicles. On the primary side, a split-capacitor structure and a series capacitor are utilized while on the secondary side, a current doubler rectifier is designed, which repeats a part of the primary structure. Compared with existing isolated converters, the proposed converter has attractive characteristics: 1) a double step-down ratio; 2) the voltage stress on all primary switches and primary transformer are reduced to half of the input voltage; 3) the power switches have soft-switching capability by ZVS characteristic in the primary side, ZV-ZCS in secondary side; 4) the soft-switching range is wide, which maintained even at light-load conditions. 5) allow reuse conventional devices of 400 V system in the updated 800 V system. These characteristics are achieved with a simple control strategy by the pulse width modulation method for switches on the primary side and only repeating primary gating signals for switches on the secondary side. In this paper, the operation and performance of the proposed converter are presented. Besides, an experiment at 800 V input, 48 V–1.2 kW output is also completed to validate the operation and effectiveness of the proposed converter.

This paper proposes a single-phase, single-stage common-ground inverter with a non-electrolytic capacitor and buck-boost ability. The proposed single-stage inverter is employed by a boost stage DC-DC converter and bimodal circuit, which makes it satisfactory for PV systems with a wide input voltage range and lower switch voltage stress. The leakage current of the proposed single-stage inverter can effectively suppress because the parasitic capacitor between the PV panel and the ground is shortened. In addition, the proposed single-stage inverter does not include electrolytic capacitors, which reduces the equivalent series resistance of electrolytic capacitors and also the size of the inverter system. The topology, operating principle, and PWM control method of the proposed single-stage inverter are given. The design guidelines of components and comparative studies of the proposed single-stage inverter are provided. A 500 W laboratory prototype of the proposed single-stage inverter is built to verify the correctness of the simulation and theoretical analysis.