A Research on Cascaded H-Bridge Module Level Photovoltaic Inverter Based on a Switching Modulation Strategy

Abstract

The stable operating region of a photovoltaic (PV) cascaded H-bridge (CHB) grid-tied module level inverter is extended by adopting the hybrid modulation strategy. However, the traditional single hybrid modulation method is unable to regulate the DC-side voltage of each module precisely, which may aggravate the fluctuation of modules’ DC-side voltages or even cause the deviation of modules’ DC-side voltages under some fault conditions and, thus, degrade the energy harvesting of PV panels. To tackle this problem, a switching modulation strategy for PV CHB inverter is proposed in this paper. When the CHB inverter is operating in normal mode, the hybrid modulation strategy containing the zero state is adopted to suppress DC-side voltage fluctuation, thereby, improving the output power of PV modules. When the CHB inverter is operating in fault mode owing to failing solar panels, the hybrid modulation strategy without the zero state is utilized to make the DC-side voltages reach the references and, thus, maintain a higher energy yield under fault conditions. Experimental results achieved by a laboratory prototype of a single-phase eleven-level CHB inverter demonstrate both the feasibility and effectiveness of the proposed method.

Modulation for Cascaded Multilevel Converters in PV Applications With High Input Power Imbalance

“…In other word, the modulation index of a higher loading cell is increasing, which causes the over-modulation under the heavy mismatched condition. This impacts the power quality and may affect the closed-loop control to become unstable [10], [14], [15].…”

Discontinuous Space Vector PWM Strategy for Three-Phase Three-Level Electric Vehicle Traction Inverter Fed Two-Phase Load

“…There are three main types of topology for three-level inverters: cascade H-bridge (CHB) [5], flying capacitor (FC) [6], and neutral-point-clamped (NPC) [7]. Among them, NPC three-level inverters play a dominant role in industrial applications.…”

PV Module-Level CHB Inverter with Integrated Battery Energy Storage System

“…As a consequence, the PV CHB inverter should allow uneven operation of PVCs, by considering that the H-Bridge cells are series-connected, so sharing the same output current, while the power delivered by each cell is different (directly related to the amplitude of its voltage modulation index) [5][6][7]10,11]. The main drawback of PV CHB topology is the possibility to operate the system under deep mismatch conditions when overmodulation occurs [10,18,19] theoretically up to square-wave operation, which represents the maximum allowable power capacity of a cell. In such a case, the modulation strategy should be able to ensure CHB inverter operation also in overmodulation region, but conventional modulation techniques (also in their properly modified versions) cannot exploit an extended modulation index range [10,11], while hybrid modulation method [10,15,16] can reach overmodulation with no detrimental effect on the harmonic content of the output current (i.e., grid current) and ensuring optimal performance in terms of MPPT efficiency (also if the operating voltage of PVG will keep away from its MPP).…”

“…As previously discussed, the double-stage configuration of the single power cell can solve the issues related to the MPPT performance, while also assuring a total dc-link voltage higher than the grid peak voltage with a reduced number of cells, but the main drawback of system operation under deep mismatch conditions, when overmodulation occurs, is unfortunately still present. In fact, it can be partially solved only by means of suitable modulation strategy [10,15,16,18,19], which allows system operation in the overmodulation region, otherwise, the high-power cells, which reach the overmodulation region, generate more harmonics at their output terminals. As a consequence, due to the series connection of CHB cells at the ac side, the total ac voltage (or rather its fundamental component) results to be highly distorted, thus affecting the current injected to the grid [11].…”