This paper presents a transformerless single-phase inverter topology based on a modified H-bridge based multilevel converter. The topology comprises two legs, namely, a usual twolevel leg, and a T-type leg. The latter is based on a usual two-level leg, which has been modified to gain access the mid-point of the split DC-link by means of a bidirectional switch. The topology is referred as asymmetrical T-type five-level (5L-T-AHB) inverter. An ad-hoc modulation strategy based on sinusoidal pulse width modulation (PWM) is also presented to control the 5L-T-AHB inverter, where the two-level leg is commuted at fundamental frequency. Numerical and experimental results show that the proposed 5L-T-AHB inverter achieves high efficiency, exhibits reduced leakage currents, and complies with the transformerless norms and regulations, which makes it suitable for the transformerless PV inverters market¹.

This paper presents the modeling and control processes of the single-phase cascade H-bridge multilevel converter used as a shunt active filter. Based on the obtained model, a controller is proposed to compensate for harmonic distortion and reactive power caused by a nonlinear load. These issues are solved by guaranteeing tracking of the line current toward an appropriately defined current reference. In the proposed approach, the current reference has been selected to be a signal proportional to either the line voltage or to its fundamental component; however, the proposed method can also be extended to other reference definitions. The proposed controller also includes voltage loops to guarantee regulation and balance of the involved capacitor voltages toward constant references. Experimental results on a 2-kVA prototype are presented to assess the performance of the proposed controller.

Transformerless photovoltaic systems are one of the best options to connect a photovoltaic system to the electrical grid given their high efficiency, low cost, small size and low weight regarding their counterparts based on a transformer. In this paper a multilevel single-phase inverter is aimed to link a photovoltaic generator with the electrical grid with reduced common mode current. A sinusoidal based modulation strategy is also presented which focus not only in the reduction of the common mode current but also in the reduction of the switching and conduction losses. Five voltage levels are obtained at the inverter output, therefore, a good behavior is achieved regarding harmonic distortion. Numerical results show that the proposed inverter and modulation strategy give a reduced common mode current and low harmonic distortion which is suitable for transformerless photovoltaic systems.

This paper presents a model-based controller for the direct control of real and reactive powers in a three-phase three-wire rectifier. As the unbalanced operation is considered, it is convenient to express the grid voltage in terms of both positive and negative sequences, in order to obtain a more complete description of the system. In particular, the positive sequence of the grid voltage is used as the transformation basis to reconstruct the average, i.e., a particular subset, of the conventional power definition. Based on this transformation, the regulation of the average of both real and reactive powers is possible without deformation of the grid current. The proposed controller also incorporates an adaptation mechanism to cope with parameter uncertainties. For comparison purposes, a conventional controller based on the complete definition of the instantaneous powers is also presented. Experimental results are provided to assess the performance of the proposed positive-sequence-based solution and compared with those obtained using a conventional controller.

In this paper, a comparative study of modulation techniques used in a transformerless H‐bridge neutral point clamped (HB‐NPC) multilevel inverters is presented. Transformerless inverters, usually found in photovoltaic (PV) applications, are more efficient and economically affordable than isolated systems. Nevertheless, they may cause leakage ground currents. The latter are produced by the stray capacitances formed between the PV panel frame and the ground path. There are different ways to overcome the leakage ground current issue in transformerless topologies, for instance using topologies that generate almost zero leakage currents, by using adequate modulation techniques, by inserting additional filters, and by using adequate control schemes, among others. The comparative study, considers five modulation strategies, namely, level‐shifted pulse‐width modulation (PWM), phase‐shifted PWM, three‐level PWM, two sectors hybrid PWM and six sectors hybrid PWM. As it will be demonstrated through the common‐mode model analysis, the three last modulations strategies are aimed at alleviating the leakage ground current issue. In this study, the two sectors hybrid PWM and the six sectors hybrid PWM are proposed. These modulation techniques lead to obtaining five output voltage levels keeping the RMS value of the leakage currents bounded for the transformerless HB‐NPC inverter.