Abstract
A fault-tolerant control technique is discussed for the Neutral-Point-Clamped (NPC) three-level inverter, which ensures that the NPC inverter operates normally even under device failures. A two-level leg is added to the NPC inverter; when the device open circuit fault occurs, the load of this faulty phase is connected to the neutral point of this two-level leg through the bidirectional thyristors. An improved Space Vector Pulse Width Modulation (SVPWM) strategy called “addition and subtraction substitution SVPWM” is proposed to effectively suppress fluctuation in capacitor neutral-point voltages by readjusting the sequence and action time of voltage vectors. The fault-tolerant topology in this paper has the advantages of fewer switching devices and lower circuit costs. Experimental results show that the proposed fault-tolerant system can operate in balance of capacitor neutral-point voltages at full output power and the reliability of the inverter is greatly enhanced.
Highlights
Compared with the conventional two-level inverters, multilevel inverters have the advantages of lower voltage stress, better waveform spectrum, less voltage change rate, and waveform distortion [1,2,3]
In order to ensure the NPC inverter can output the full-rated power under device failures, a two-level leg serves as the additional leg for the faulty phase in this paper
In order to enable the NPC inverter to operate at full output power under the device failures, a two-level leg is taken as the additional leg of the faulty phase in this paper, which is controlled with the two switching states P and N
Summary
Compared with the conventional two-level inverters, multilevel inverters have the advantages of lower voltage stress, better waveform spectrum, less voltage change rate, and waveform distortion [1,2,3]. The inverter can operate in balance of capacitor neutral-point voltages with symmetrical three-phase output after the proposed fault-tolerant control method is applied. A software redundancy faulttolerant control algorithm of the NPC inverter has been proposed in [21] This method is implemented by using the redundant voltage vectors, with some limitations that apply only to open circuit fault and short circuit fault of outer switches. In order to ensure the NPC inverter can output the full-rated power under device failures, a two-level leg serves as the additional leg for the faulty phase in this paper. When the open circuit fault occurs in the NPC inverter, the faulty leg is connected to the additional leg through the bidirectional thyristors Both the switching states P and N, generated by modifying the SVPWM algorithm, are employed to control the additional leg. In order to accurately suppress the fluctuation of the capacitor neutral-point voltages, an improved SVPWM strategy called “addition and subtraction substitution SVPWM” is proposed to readjust the sequence and action time of voltage vectors in SVPWM algorithm
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