Abstract
Pulse Width Modulation (PWM) strategies are crucial for controlling DC–AC power converters. In particular, transformerless inverters require specific PWM techniques to improve efficiency and to deal with leakage ground current issues. In this paper, three hybrid PWM methods are proposed for a DCM-232 three-phase topology. These methods are based on the concepts of carrier-based PWM and space vector modulation. Calculations of time intervals for active and null vectors are performed in a conventional way, and the resulting waveforms are compared with a carrier signal. The digital signals obtained are processed using Boolean functions, generating ten signals to control the DCM-232 three-phase inverter. The performance of the three proposed PWM methods is evaluated considering the reduction in leakage ground current and efficiency. The proposed modulation techniques have relevant performances complying with international standards, which make them suitable for transformerless three-phase photovoltaic (PV) inverter markets. To validate the proposed hybrid PWM strategies, numerical simulations and experimental tests were performed.
Highlights
Transformerless photovoltaic (PV) systems have increased their popularity due to their high performance in terms of efficiency, size, and price
The common-mode current (CMC) is the major issue in transformerless grid connected PV systems, as it can lead to additional power losses, protection tripping, important safety problems, and high total harmonic distortion (THD) of the current injected into the grid
It is important to highlight that the numerical results are obtained in an open loop configuration, since the main objective is to validate the proposed space vector based modulation (SVM) techniques operating with this topology
Summary
Transformerless photovoltaic (PV) systems have increased their popularity due to their high performance in terms of efficiency, size, and price. In [5,6,7], a family of topologies called Quasi Z-source inverters is presented, the main idea is to reduce the component rating, the source stress, and component count and to make some contributions to simplify the control strategies Another approach consists in the addition of active components in order to deal with the CMC, for instance, diodes, IGBTs, or MOSFETs as in [8], where additional diodes connected as a three-phase rectifier plus an IGBT are used to implement the null vectors in an SVM technique. This inverter is based on the 3P-FB topology at the AC output side, while on the DC input side, there are two DC sources that can be completely decoupled from the 3P-FB circuit by means of two semiconductors switched at the same time [16]. A comparative analysis between the proposed PWM techniques and some solutions available in the literature is performed
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