Abstract
When single-phase three-level neutral-point-clamped (NPC) converters operate, there are two main control objectives that need to be met for correct operation. First, the ac source current must be controlled to be sinusoidal. Second, the dc capacitor voltages must be balanced. In original model predictive control (MPC) methods for NPC converters, an optimization process involving an empirical weighting factor design is required to meet both of these objectives simultaneously. This study proposes an MPC approach developed for single-phase three-level NPC converters to meet these objectives using a single reference voltage consisting of a difference-mode term and a common-mode term in each phase. The difference-mode term and the common-mode term are responsible for sinusoidal ac source current synthesis and dc capacitor voltage balancing, respectively. Then, a single cost function compares the adjusted reference voltage with possible voltage candidates to select an optimal switching state, resulting in the smallest cost function value. Different from the conventional MPC method, the proposed approach avoids the selection of weighting factors and the attendance of various control objectives. Thanks to the deterministic approach, the proposed MPC method is straightforward to implement and maintain fast transient performance while guaranteeing the control objectives. Finally, the effectiveness and feasibility of the proposed approach for single-phase three-level NPC are verified through comprehensive experimental results.
Highlights
Single-phase three-level neutral point clamped (NPC) converters have been addressed for various applications, especially in the interface of renewable energy sources and storage system because of its reduced total harmonic distortion (THD), lower device power losses, and lower electromagnetic interference (EMI) compared with two-level converters [1,2,3,4,5,6,7,8]
This paper proposes an model predictive control (MPC) method for NPC converters to accomplish multiple objectives using single reference voltages without using a weighting factor in a cost function
The difference-mode term and the common-mode term are responsible for sinusoidal source current synthesis and capacitor voltage balancing, respectively
Summary
Single-phase three-level neutral point clamped (NPC) converters have been addressed for various applications, especially in the interface of renewable energy sources and storage system because of its reduced total harmonic distortion (THD), lower device power losses, and lower electromagnetic interference (EMI) compared with two-level converters [1,2,3,4,5,6,7,8]. The corresponding weighting factor can be removed because the cost function only consists of the current control terms In this algorithm, the capacitor voltage adjustment is obtained by selecting an appropriate small vector and a corresponding switching state to reduce the neutral point (NP) voltage unbalance in advance. The capacitor voltage adjustment is obtained by selecting an appropriate small vector and a corresponding switching state to reduce the neutral point (NP) voltage unbalance in advance This method can successfully eliminate the weighting factor, the capacitor voltage balance can be limited in operating regions with high reference voltage magnitude, which does not employ the small vectors. Based on the deterministic approach and previous work [31,32,33], this paper presents an MPC control scheme using a novel cost function design using only one reference voltage to achieve the multiple control objectives for single-phase three-level NPC converters. 3 ofare confirmed by the presented experimental results using a prototype test
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