An open fault detection and analysis method for 7-level Cascaded H-Bridge Inverter based on BP Neural Network is proposed in this paper. A reconfiguration method is also discussed. The output voltage is used as a diagnostic signal to detect the fault types and locations. First, the output voltage is transformed by DFT to select the main harmonic information which is then used to train the neural network. After that, the classification task is performed by a BP neural network. If there is a fault, the reconfiguration system would reconstruct the inverter to make it continually work without affecting the inverter performance. The expected and simulation results are in good agreement with each other, which represents the proposed method can perform satisfactorily to detect the fault types and locations as well as conduct reconstruction. Keywords-Fault diagnosis Multilevel inverter Neural Network Power ElectronicsI.

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A novel transformerless three-phase unidirectional bridgeless flying capacitor (UBFC) rectifier for medium-voltage and high-voltage applications is presented by this paper. The rectifier consists of three single-phase rectifiers in wye connection, the DC outputs of the three single-phase rectifiers are connected in parallel to provide a high common DC-link bus which makes it convenient to connect with NPC or FC multilevel inverters. To avoid phase to phase current circulation, an additional inductor and diode are added to each single-phase rectifier. Compared with conventional bidirectional multilevel converters, only half IGBTs are employed with lower voltage stress, line-frequency transformers are no longer be required, which makes the proposed rectifier has a series of advantages such as reduced cost, simplified control complexity, increased reliability and improved overall efficiency. The basic operating principle of the proposed rectifier in continuous conduction mode is discussed, an improved carrier-based level-shifted PWM modulation method integrated with voltage balancing and the double closed-loop control strategy are proposed to achieve more voltage levels and keep the flying capacitors in balance. The feasibility of proposed rectifier is verified by the simulation as well as experimental results.

SummaryA novel transformerless three‐phase unidirectional bridgeless flying capacitor (UBFC) rectifier for medium‐voltage and high‐voltage applications is presented in this paper. The rectifier consists of three single‐phase rectifiers in wye connection; the DC outputs of the three single‐phase rectifiers are connected in parallel to provide a high common DC‐link bus, which makes it convenient to connect with neutral point clamped (NPC) or flying capacitor (FC) multilevel inverters. To avoid phase‐to‐phase current circulation, an additional inductor and diode are added to each single‐phase rectifier. Compared with conventional bidirectional multilevel converters, only half IGBTs are used, the voltage stress is lower, and the line‐frequency transformers are no longer required, which makes the proposed rectifier has a series of advantages such as reduced cost, simplified control complexity, increased reliability and improved overall efficiency. The basic operating principle of the proposed rectifier in continuous conduction mode is discussed; an improved carrier‐based level‐shifted pulse‐width modulation (PWM) method integrated with voltage balancing and the double closed‐loop control strategy are proposed to achieve more voltage levels and keep the flying capacitors in balance. The feasibility of the proposed rectifier is verified by the simulation and experimental results.

The paper presents a new STATCOM system based on H-bridge inverter. It can be used in mine power network. It has been commonly verified for the positive effects of SVG on the reactive power compensation and voltage fluctuation suppression. This paper focuses on a generalized structure of multilevel power converter where individual voltage sources are not necessarily the same. The cascade H-bridge consists of two cells, high-voltage cell and low-voltage cell. The high-voltage cell is responsible for voltage lifting, while the low-voltage cell is responsible for PWM modulation. If two cells are cascaded with DC voltages in a ratio of 2:1, the single-phase output voltage can reach 7 levels. Increasing voltage levels of output waveform can bring up AC current quality, optimize harmonic spectrum and enhance converter efficiency. The hybrid multilevel is characterized by per-phase series connection of a high-voltage H-bridge converter and a low-voltage H-bridge converter. Due to the different capacitor voltage, it is a key problem as to how to maintain the capacitor's voltage at a reference level. Independent DC source can effectively ensure the DC voltage. Through the reactive power compensation technology, the three-phase voltage and current can remain at the same phase.