A New PWM Strategy for Grid-Connected Half-Bridge Active NPC Converters With Losses Distribution Balancing Mechanism

Abstract

Abstract-Photovoltaic systems technological development is driven by the request for higher efficiency and safety. These concerns influence also the choice of the power converter stage. Several topologies have been proposed and many of them are available commercially. Among them, the neutral point clamped (NPC) and derived topologies offers high efficiency, low leakage current, and low EMI. However, one main disadvantage of the NPC inverter is given by an unequal distribution of the losses in the semiconductor devices, which leads to an unequal distribution of temperature that can affect lifetime. By using the active NPC (ANPC) topology, where the clamping diodes are replaced by bidirectional switches, the power losses distribution problem is alleviated. The modulation strategy is a key issue for losses distribution in this topology. In this paper, two known strategies are discussed and a new PWM strategy, namely the adjustable losses distribution is proposed for better losses distribution in the ANPC topology. Simulations and experimental results help in evaluating the modulation strategies.

Analysis of the Robustness of Transformerless PV Inverter Topologies to the Choice of Power Devices

“…This means that by optimizing the switching frequency the losses are reduced and the overall efficiency increases. It has been reported in [37] that the outer switches (here #2 and #4) are stressed more due to the switching losses than the inner switches which operate at grid frequency and that the uneven losses distribution increases with increasing switching frequency. Thus, the optimization of the switching frequency of the HB-NPC topology at fixed LCL parameters, which allows the reduction of the switching frequency in comparison to the other topologies, would lead to lower switching losses of the outer switches and, thus, to an increasing efficiency.…”

“…The reduction of the leakage current in a H7 3φ inverter is also the target in [8]. Moreover, the PV inverter lifetime can be increased by means of a better balance of the power losses in TL topologies [9] and reducing the leakage current without increasing the number of power devices [10]. In [11] a novel 2-D analytical model for the parasitic capacitance of PV systems is presented, allowing for a more precise evaluation of leakage current during the design stage.…”

A Highly Efficient Single-Phase Three-Level Neutral Point Clamped (NPC) Converter Based on Predictive Control with Reduced Number of Commutations

“…Consideration of all possible switching states in the conventional method can choose a switching state involved in many commutations as an optimal switching state for the next step, which can lead to an increased number of switchings and corresponding switching losses [14][15][16][17][18]. In addition, the conventional MPC method changes the optimal switching state by evaluating the capacitor voltage balance term using the redundant switching states to equal the two capacitor voltages [19,20] owing to a slight voltage difference even when the converter does not require a change in the voltage level. Thus, this operation can increase the number of switchings and switching losses as well [21,22].…”

Three-Level Neutral Point Clamped Inverter Fed By A Photovoltaic System Under Partial Shading

“…One problem with the tree-level Neutral-Point-Clamped (NPC) topology is the natural unbalance of their dc-link capacitor voltages [7], [8]. As a consequence, when the PV Manuscript received 19/03/2016; first revision 07/05/2016; accepted for publication 04/07/2016, by recommendation of Editor Marcelo Cabral Cavalcanti. output voltage is stable, the use of the NPC inverter is attractive [9], [10]. However, when there is partial shading the capacitor voltage balance is not anymore guaranteed and provokes loss of quality in the output signals [1].…”