Abstract
The Neutral Point Clamped (NPC) Multi-Level Inverters (MLI) have been ruling the power electronics industries for the past two decades. The Multi-Carrier Pulse Width Modulation (MCPWM) is common PWM techniques which are widely used in NPC-MLI applications. However, MCPWM is not having a good impact on the balancing of DC-link voltages, Common Mode Voltage (CMV) and limiting the Total Harmonics Distortion (THD). The Selective Harmonic Elimination (SHE) technique is introduced for reducing the THD, however all the switching angles should be maintained less than π/2 to keep the eliminated harmonics at constant level which narrows down the modulation index range. Hence, in recent days Space Vector Modulation (SVM) technique is widely used in NPC-MLI, which gives better DC-link voltage balancing, self-neutral point balancing, near-zero CMV reduction, better-quality harmonics profile and switching loss minimization. Hence, it is a preferred solution for the majority of electrical conversion applications such as electric traction, high power industrial drives, renewable power generation, and grid-connected inverters, etc. The paper gives a comprehensive review of the SVM for NPC-MLI. First, this paper deliberates the state of art for two-level SVM and extends it to three-level (3L) SVM. Also compares the 3L SVM performance with other MCPWM techniques. Followed by the various modified MLI SVM techniques in terms of their implementations, DC-link capacitor balancing, and reduction of CMV. Further, the review of MLI SVM is widened to open-end winding Inverters and multiphase MLIs. The final part of this paper discussed the future trends and research directions on MLI SVM techniques and its applications.
Highlights
The two-level (2L) VSI has been ruling the industrial world before the development of Multi-Level Inverters (MLI)
Though many PWM and Space Vector Modulation (SVM) techniques are available for the 3-phase inverters to reduce the DC-link voltage, switching loss, Common Mode Voltage (CMV) etc., The development of Open-End Winding (OEW) inverter gives the solution for the above-mentioned limitations
While in Phase Opposition and Disposition (POD) PWM technique [59], the carrier signals are placed in different positions and the phase angles are shifted by 180◦ for the signals placed below zero reference when compared to the signals placed above zero reference as shown in Fig.5 (b)
Summary
The two-level (2L) VSI has been ruling the industrial world before the development of MLI. Though many PWM and SVM techniques are available for the 3-phase inverters to reduce the DC-link voltage, switching loss, CMV etc., The development of Open-End Winding (OEW) inverter gives the solution for the above-mentioned limitations. The Space Vector Modulation technique for 2L and 3L three-phase Inverter has been discussed in the chapter III. While in POD PWM technique [59], the carrier signals are placed in different positions and the phase angles are shifted by 180◦ for the signals placed below zero reference when compared to the signals placed above zero reference as shown in Fig. (b). SPACE VECTOR MODULATION The SVM technique is a digital modulating technique which generates PWM based on the vector representation These digital signals are given directly to switches which are controlled as per vector representation. The SVM can be represented in g-h coordinate system and K-L coordinate system
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