Conference Paper

Direct power control for Neutral-point-clamped three-level PWM rectifier

Coll. of Electr. & Electron. Eng., Huazhong Univ. of Sci. & Technol., Wuhan
DOI: 10.1109/ICIT.2008.4608487 Conference: Industrial Technology, 2008. ICIT 2008. IEEE International Conference on
Source: IEEE Xplore

ABSTRACT This paper proposes a direct power control (DPC) strategy employed for the neutral-point-clamped (NPC) three-level PWM rectifier. Mathematic model of NPC three-level rectifier is conducted firstly as a theoretical base. This topology generates a higher number of output voltage levels, increasing the flexibility for selecting an appropriate voltage vector. The direct instantaneous power control technique for the converter, which has been developed to control the instantaneous active and reactive power directly by selecting the optimum switching state of the converter, is discussed in detail in the paper. The neutral-point potential is controlled according to the direction of the mid-point current and a study of each switching vectorpsilas influence to active and reactive power. Theoretical analysis is presented and the performance of the proposed method is verified by simulation and experiment.

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    ABSTRACT: In this paper, a new switching table for direct power control (DPC) strategy is proposed for three-level NPC rectifier. The strategy is developed by analyzing active and reactive power and introducing convenient controllers to optimize the voltage selection which is the fundamental task in that control method. The dc-link voltages are maintained at the required level using hysteresis controller for the NP current exploiting the redundancy states of the rectifier. With a simple switching table, the excellent dynamic and transient performances are achieved under unity power factor operation. Simulation results verify the validity and feasibility of the proposed strategies.
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    ABSTRACT: This paper presents a mathematical model of three-level voltage PWM rectifier, and derives a power control model from the theory of instantaneous power. In the vector-space, the influences on instantaneous power exercised by all the switching vectors are studied and illustrated separately, then a direct power control (DPC) scheme for three-level PWM rectifier which uses multistage band hysteresis comparator is proposed, and a novel switching table is designed. Meanwhile, the neutral-point voltage unbalance is inhibited by selecting the redundancy switching states of small voltage vectors. Simulation and experimental results show that the proposed strategy can not only stabilize the DC bus voltage but also realize the unity power factor operation and the balance of neutral-point voltage. Moreover, the proposed method can improve the performance of the three-level rectifier.
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    ABSTRACT: Some of the main concerns in the use of power converters are their reliability and the ability to detect and maintain operation when in fault. Many techniques have been proposed to identify and respond to faults in Neutral-Point-Clamped converters. Most of these methods, however, require additional hardware and/or changes in the topology. In this paper, a NPC rectifier is investigated, including the impacts of each possible semiconductor fault in the operation. Methods for fault diagnosis and fault tolerant operation are presented. The presented diagnostic method does not require additional hardware and is not affected by the load. Open-circuit and short-circuit faults are detected in both IGBTs and diodes. Fault tolerant operation with different levels of action is presented. Experimental results are presented to demonstrate the effectiveness of the methods.
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