基于平移调制波的三电平有源中点钳位逆变器容错下中点电位平衡策略

doi:10.19595/j.cnki.1000-6753.tces.250377

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Abstract The three-level active neutral-point-clamped (ANPC) inverter is widely used in high-power applications due to its superior output characteristics and balanced power loss distribution. However, under open-circuit faults, the redundancy of small vectors is disrupted, rendering traditional neutral-point (NP) voltage balancing methods ineffective. The divergence of the capacitive voltage on the DC side can lead to problems such as increased voltage stress and reduced output quality. Addressing NP imbalance without compromising system stability or efficiency remains a critical challenge for ANPC inverters in fault-tolerant operation.
First, this paper analyzes the operational principles of a three-level ANPC inverter under open-circuit faults. When a phase leg is clamped to the NP, the redundancy of small vectors is disrupted, and traditional voltage balancing methods relying on redundant vector adjustments become ineffective. The study identifies that the distortion of current paths and output voltage anomalies exacerbate NP voltage imbalance, leading to increased capacitor stress and degraded system performance. By clamping the faulty phase to the NP and reconfiguring the modulation strategy, the topology retains partial functionality but requires a novel approach to address persistent NP imbalance. Second, this paper derives a fault-tolerant modulation wave by injecting a zero-sequence component into the original three-phase modulation signals. This approach eliminates sector judgments and trigonometric calculations inherent in conventional space vector pulse-width modulation (SVPWM). The unified modulation wave formula for clamped phases simplifies the process of modulation. For instance, in a phase-a fault, the zero-sequence component is defined as m₀=-m_a, and the adjusted modulation waves for healthy phases are expressed as $m_{\mathrm{b}}^{\prime}=m_{\mathrm{b}}-m_{\mathrm{a}}$ and $m_{\mathrm{c}}^{\prime}=m_{\mathrm{c}}-m_{\mathrm{a}}$. This modification ensures equivalent SVPWM outputs while maintaining linear modulation capabilities. Then, a voltage balance based on translation modulation (VBBTM) strategy is proposed under fault-tolerant control. By analyzing the correspondence between the dwell time of small vectors and the NP current, specific small vectors required for balancing the NP voltage are selected. Combined with the charge balance method, the translation direction of modulation waves is dynamically adjusted to calculate the translation amount of modulation waves quantitatively. Limiting the translated modulation waves based on sector position effects is then applied, ultimately achieving adaptive NP voltage balancing under varying bus voltage conditions.
Finally, simulations in Matlab/Simulink and experimental tests on a three-level ANPC platform validate the effectiveness of the VBBTM strategy under diverse fault scenarios, including single/multiple switch faults in a single-phase leg and varying modulation ratios. Results show that the NP voltage rapidly converges after applying the VBBTM strategy, with stable three-phase currents and minimal impacts on system performance. Specifically, current unbalance remains below 7.7% (at m=0.5), voltage vector trajectory deviation is within ±3%, and common mode voltage and differential mode voltage exhibit no significant distortion. Comparative analysis highlights the advantages of the VBBTM strategy in low computational complexity, no switching losses, and adaptability to dynamic modulation ratios. The strategy demonstrates robustness under varying load conditions and bus voltage fluctuations, achieving adaptive NP voltage balancing. The study confirms the practicality of VBBTM for high-power ANPC inverters, ensuring reliable fault-tolerant operation with only minor degradation in output quality.

Key words： Active neutral-point-clamped inverter open-circuit fault fault-tolerant control translational modulation wave neutral-point voltage balance

Received: 10 March 2025

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	Zhao Xianglin
	Li Weichao
	Zhou Liang

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Zhao Xianglin,Li Weichao,Zhou Liang. Neutral-Point Voltage Balancing Strategy under Fault-Tolerant Operation of Three-Level Active Neutral-Point-Clamped Inverter Based on Translational Modulation Wave[J]. Transactions of China Electrotechnical Society, 2026, 41(4): 1352-1368.

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