Common-Mode Voltage Reduction of Three-Level Four-Leg PWM Converter

Abstract

This paper presents a carrier-based pulsewidth modulation (PWM) method that reduces the common-mode voltage (CMV) of a three-level four-leg converter. Based on an analysis of space vector PWM (SVPWM) and sinusoidal-PWM switching patterns, the fourth-leg pole voltage of a three-phase converter, known as the "f pole voltage," is manipulated to reduce the CMV. To synthesize the f pole voltage for the suppression of the CMV, positive and negative pole voltage references of the f leg are calculated. In addition, the offset voltage to prevent distortion of the a, b, and c phase voltages regarding the neutral point is deduced. The proposed PWM strategy can be easily implemented in the software of a DSP-based converter control. The three-level four-leg converter with the proposed PWM algorithm results in a remarkable reduction in the peak-to-peak value of the CMV. From the simulation and the experimental results, the peak-to-peak value of the CMV when using the proposed PWM method is 33% compared to that when using the SVPWM method, while the number of CMV transitions during the switching period in the proposed PWM method is only 25% of that when using the SVPWM method. Index Terms-Common-mode current (CMC), common-mode voltage (CMV), pulsewidth modulation (PWM), push-pull PWM (PPPWM), sinusoidal PWM (SPWM), space vector PWM (SVPWM), three-level four-leg converter. 0093-9994

A New Space-Vector-Modulation Algorithm for a Three-Level Four-Leg NPC Inverter

“…Three-level NPC inverters have well known advantages over the conventional two-level converter. For instance NPC converters can be connected to medium voltage systems without requiring a power transformer [4], they can operate with a relatively high effective switching frequency reducing the total harmonic distortion at the grid/load [5]. Moreover, for a similar application an NPC inverter requires a smaller power filter when compared with a conventional two-level VSI [5].…”

“…For instance NPC converters can be connected to medium voltage systems without requiring a power transformer [4], they can operate with a relatively high effective switching frequency reducing the total harmonic distortion at the grid/load [5]. Moreover, for a similar application an NPC inverter requires a smaller power filter when compared with a conventional two-level VSI [5]. In addition, lower dv/dt values, higher efficiency and less stress on the devices are also considered important advantages of the NPC converter over the conventional two-level topology [3], [5].…”

“…Moreover, for a similar application an NPC inverter requires a smaller power filter when compared with a conventional two-level VSI [5]. In addition, lower dv/dt values, higher efficiency and less stress on the devices are also considered important advantages of the NPC converter over the conventional two-level topology [3], [5]. There are several applications of the three-level VSI reported in the literature, for instance in Wind Energy Conversion Systems (WECSs) [4], [6], [7], where the nominal power of single WECs approaches 10MW.…”

“…4-leg multilevel converters, on the other hand, offer higher efficiency, lower switching losses, higher nominal voltage range and lower harmonic distortion. However, they have only been proposed recently as an interesting solution for 4-wire systems, for example in [5], [16], [17] where the application of three-level, 4-leg converters is discussed.…”

Investigation on Common-Mode Voltage Suppression in Smart Transformer-Fed Distributed Hybrid Grids

“…The neutral line can also be supplied by an additional leg [13], [22]. The goal of this paper is to analyze the CM of the three-and four-leg converters, constituting 3-phase 4-wire system.…”