Abstract
Single-stage converters based on an impedance source (IS) network merged with a multilevel inverter remain a trending research topic, from both the topological and control perspectives, because of their potential in applications involving renewable energy. This paper presents a new, simplified space vector pulse-width modulation (SVPWM) for a three-phase three-level T-type quasi-impedance source inverter (3L-T-type qZSI). The benefits of the proposed modulation strategy include functionalities, such as boosting the input voltage and controlling the neutral-point (NP) voltage using the redundant small vectors, to mitigate the inner capacitors voltages imbalance. The proposed SVPWM guarantees a minimum common-mode voltage while preserving a very simple implementation, thus reducing the complex computations and cascaded proportional-integral (PI) control loops of the conventional SVPWM methods. The proposed algorithm can be applied to different multilevel inverter configurations combined with an IS network. A comprehensive simulation study and experimental results demonstrated the good performance of the proposed control method for dynamic response and imbalance conditions.
Highlights
T RANSFORMERLESS grid-connected inverters offer lower cost, smaller size and higher efficiency than inverters, including those with galvanic isolation
Many pulse-width modulation (PWM) methods have been developed for multilevel converters, most of them can be classified into two large families: (a) carrier-based PWM modulation and (b) spacevector modulation (SVM)
Output signal spectra contain harmonics related to the frequency modulation index, which must be filtered in power conversion applications [9]
Summary
T RANSFORMERLESS grid-connected inverters offer lower cost, smaller size and higher efficiency than inverters, including those with galvanic isolation. Particular issues related to this topology arise, such as balancing the neutral point voltage, reducing the common-mode voltage (CMV) and obtaining sinusoidal current shaping in the output of the converter, which have imposed challenging tasks on the design of modulation techniques for the qZS Ttype inverter. In [40], neutral point voltage control is addressed and in [41], the PWM algorithm considers a common-mode voltage reduction that is directly associated with leakage currents, being an important variable in transformerless inverters. Motivated by the aforementioned issues in existing SVPWM algorithms and based on preliminary work [42], this paper presents a simplified SVPWM algorithm incorporating NP voltage control and CMV reduction This algorithm uses specific small vectors in the modulation to reduce naturally CMV values and includes internal capacitors balancing.
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