Indian Institute of Science
Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter.
Degree: PhD, Faculty of Engineering, 2018, Indian Institute of Science
Neutral-point-clamped (NPC) three-level inverter is capable of handling higher dc bus voltage and producing output waveform of better quality than a conventional two-level inverter. The main objective of the present work is to analyze the existing PWM schemes for two-level and three-level inverters in terms of line current ripple, and to design new PWM techniques for the NPC inverter to reduce line current distortion.
Various discontinuous PWM or bus-clamping PWM (BCPWM) methods for a two-level voltage source inverter are analyzed in terms of rms line current ripple, which is evaluated by integrating the error voltage (i.e. error between the applied and reference voltages). The BCPWM schemes can be broadly classified into continual-clamp PWM (CCPWM) and split-clamp PWM (SCPWM). It is shown that split-clamp PWM scheme leads to lower harmonic distortion than CCPWM scheme. Further, advanced bus-clamping PWM (ABCPWM) methods for a two-level inverter are also studied. These methods clamp each phase to the positive and negative DC terminals over certain intervals as in BCPWM schemes, and also switch each phase at double the nominal frequency in certain other intervals unlike in BCPWM. Analytical closed-form expressions are derived for the total rms harmonic distortion due to SCPWM, CCPWM and ABCPWM schemes.
Existing sinusoidal and bus-clamping PWM schemes for three-level NPC inverters are also analyzed in the space vector domain. These methods are compared in terms of line current ripple analytically as well as experimentally. As earlier, closed-form expressions are derived for the harmonic distortion factors corresponding to centered space vector PWM (CSVPWM) and the various BCPWM methods.
A three-level inverter can be viewed as an equivalent two-level inverter in each sixth of the fundamental cycle or hextant. This is widely used to simplify the control of an NPC inverter. Further, this approach makes it simple to extend the BCPWM and ABCPWM methods for two-level inverters to three-level inverters. Furthermore, the method of analysis of line current ripple for the two-level inverter can also be easily extended to the three-level case.
The pivot vector, which is half the length of the longest voltage vectors produced by the NPC inverter, acts as an equivalent null vector for the conceptual two-level inverter. Each pivot vector can be produced by two inverter states termed as “pivot states”. Typically, in continuous modulation methods for NPC inverter such as sinusoidal PWM and centered space vector PWM, the switching sequence (i.e. the sequence in which the voltage vectors are applied) begins and ends with the same pivot vector in each subcycle, which is equivalent to a half-carrier cycle. To be more precise, the switching sequence starts with one pivot state and ends with the other in each subcycle.
However, in case of BCPWM schemes, only one pivot state is used in a subcycle. The choice of pivot state results in a variety of BCPWM schemes for an NPC inverter. Different BCPWM schemes are evaluated in terms of rms…
Advisors/Committee Members: Narayanan, G (advisor).
Subjects/Keywords: Pulse Width Modulation; Neutral Point Clamped Inverters; Multilevel Converters; Voltage Source Inverters; Inverters - Modulation; Sinusoidal Pulse Width Modulation; Bus-Clamping Pulse Width Modulation; Hybrid Pulse Width Modulation; Sinusoidal PWM Schemes; Neutral-point-clamped Inverter; Bus-clamping PWM (BCPWM); Electronic Engineering
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APA (6th Edition):
Das, S. (2018). Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/3169
Chicago Manual of Style (16th Edition):
Das, Soumitra. “Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed September 22, 2020.
MLA Handbook (7th Edition):
Das, Soumitra. “Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter.” 2018. Web. 22 Sep 2020.
Das S. Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2020 Sep 22].
Available from: http://etd.iisc.ac.in/handle/2005/3169.
Council of Science Editors:
Das S. Study on Pulsewidth Modulation Techniques for a Neutral-Point-Clamped Voltage Source Inverter. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/3169