Novel Single-Phase Grid-Tied NPC Five-Level Converter with an Inherent DC-Link Voltage Balancing Strategy for Power Quality Improvement

Abstract

This paper presents a novel single-phase grid-tied neutral-point-clamped (NPC) five-level converter (SPFLC). Unlike the literature on five-level NPC topologies, the proposed one is capable of inherently balancing the voltage of the DC-link split capacitors. For this purpose, a simple Multicarrier Phase Disposition (MPD) Pulse Width Modulation (PWM) technique is used, thus avoiding both complex modifications to the Space Vector Modulation (SVM) and offset voltage injections into the carrier based (CB) PWM, as commonly done in most conventional balancing algorithms. Bearing in mind that the proposed balancing strategy only requires measuring the capacitors’ voltages and the sign of the converter output current, it has a very low complexity. The developed strategy is not only straightforwardly implemented but is also very effective for obtaining symmetrical and undistorted voltage levels from the proposed multilevel converter, as well as for significantly improving the power quality of the SPFLC output voltage and, in turn, of the grid current. The simulation results obtained with MATLAB-SimPowerSystems as well as the experimental results obtained with the prototype built in the laboratory validate the topology of the proposed NPC five-level converter and the voltage balancing strategy, by showing a good performance under step-changes and exhaustive operating test conditions.

Performance Evaluation of an Active Neutral-Point-Clamped Multilevel Converter for Active Filtering in G2V-V2G and V2H Applications

“…In the V2H mode, 𝑉 5𝐿𝐶 is simply obtained from a virtual PLL that outputs a 60Hz sine wave with the same peak voltage of the grid operating in normal conditions. The classical multicarrier phase-disposition (PD) PWM has been used for generating the ten switching signals 𝑆 1−10 [4], [14]. A detailed scheme of the PD-PWM block included on the right-hand side of Figure 4 is shown in Figure 6.…”

“…Later, the output from the 𝐻 𝐶 𝑖 (𝑠) compensator becomes the voltage reference 𝑉 5𝐿𝐶 of the converter. This voltage is assumed to be ideally synthetized with the ANPC 5LC by means of the multicarrier PD-PWM [4], [14]. Note that the resulting state 𝑆𝑆 𝑘 is sent to the voltage balancing block that finally outputs the switching signals 𝑆 1−10 of the converter.…”

“…In applications where these converters are further series-connected with an EV battery charger, the power transfer between the battery, the grid and the load can be controlled, thus giving rise to three possible operation modes, i.e., grid-to-vehicle (G2V), vehicle-to-grid (V2G) and vehicle-to-home (V2H) [12], [13]. The disregard of the splitcapacitors voltage imbalance in the NPC/ANPC topologies results in a distorted output voltage from the converter [14]. However, under the G2V/V2G modes, this distortion is not of fairly importance since its detrimental effect on the grid current quality is in turn compensated by the active filtering algorithm.…”

A Multilevel Inverter Topology Using Diode Half-Bridge Circuit with Reduced Power Component

“…The modular multilevel converter (MMC) [34][35][36][37] is quite famous for high voltage applications. However, this NPC MLI and MMC circuit needs separate control techniques to balance the capacitors, and also the number of device counts is high [36,38]. It was observed that the presented topology required a low number of IGBTs.…”

Symmetrical Cascaded Switched-Capacitor Multilevel Inverter Based on Hybrid Pulse Width Modulation

“…One dc voltage source is equipped in the diodeclamped and capacitor-clamped multilevel inverter, which utilizes diodes or capacitors to divide the dc source voltage into multiple voltage levels. A large number of power switches, complex switching strategies and capacitor voltage balancing control are required for the clamped-type multilevel inverter [3][4][5]. On the other side, the cascaded H-bridge multilevel inverter has less switch voltage stress, and it is easy to realize the modular design.…”