An Improved Carrier-Based PWM Strategy with Reduced Common-Mode Voltage for a Three-Level NPC Inverter

Round 1

Reviewer 1 Report

The article is interesting and deals with an important issue. The authors referred to a wide range of literature and prepared a well-done Introduction, defining the analyzed problem.

However, the following Sections are very underdeveloped. It should be noted that the authors use far-reaching mental shortcuts. Sections 2 and 3.1 seem to have been rewrote from references. Not all letter designations of physical quantities are explained, there are also inconsistencies in the letter designation of the analyzed signals. All this requires refinement according to the detailed comments below.

It should also be noted that Section VI Conclusions need significant improvement and extension. The Conclusions should collect all the conclusions developed in the previous Sections.

1.     Figure 1a: In the whole work there is no description about how the S5a and S6a transistors are controlled by the signal.

2.     Table. 1: The Table 1 contains undefined letter designations of vectors.

3.     Text below the equation (3): Here, a topic is discussed that does not necessarily correspond to the title of section 2.2. The text about the virtual vector should be a separate subsection after defining the common mode voltage.

4.     Equation (8): There is no explanation of what d_max, d_mid and d_min are. In the line 128 letter x stand for name of phase, but in the equation (10) the letter x stand for max, mid and min.

5.     Equation (8), (9), (10):  It is not clear whether the x parameter means phase or max, min or mid.

6.     Equation (10): The notation of the equation (10)  is ambiguous. Which symbol should be substituted for x? Should all terms of the sum have the same symbol, or should they be different?

7.     Equation (13):  It is not clear when the max pattern applies as a modulating signal "p" in a given phase and when the mid pattern applies.

8.     Equation (13):  It is not clear when the min pattern applies as a modulating signal "n" in a given phase and when the mid pattern applies.

9.     Equation (14): The notation of equation (14) is ambiguous. A description is absolutely needed when the modulation waves are equal to d_max, d_min or d_mid.

10.                       Text below equation (15): There is: "...the reference voltage..." it should be "...reference voltage vector..."

11.                       Figure 9: There are no letter symbols on the coordinate axes.

12.                       Figure 15: and Figure 16: Figures should be placed in the text sequentially, according to numbering.

13.                       Line 219: No explanation of letter symbol.

14.                       Figure 18: Which waveform does the harmonic analysis apply to?

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors focus on an improved control strategy for a 3 phase three level NPC inverter. They introduce the basic concept and provide some background regarding the advantages and disadvantages of various control approaches. They propose also a hybrid control principle resulting in reduced (eliminated) neutral point voltage oscillations and reduced common-mode voltage. The data flow in the paper is adequate, there are however some points to be addressed for clarity.

List of some detailed observations:

L1: Affiliation section is missing data

L17: Reference order – reference numbering should follow the order of appearance.

L19: References needed.

L85: Figure 1b: Please define the symbols used (NPO, NPN, NOO….) or provide adequate information regarding the naming; define the ‘O’ state

L85-L86: text, graphics and tables are given on 3 pages – separated only by one index line?

Table 1: explain a term TL-ANPC, reduce the size of the table, define switching states ([P], [O], [N]…OU1, OU2, OL1, OL2

Table 2: medium not medium; define vectors and provide sufficient info on obtaining the current (i_a, i_b, i_c), what (where it is given) info supports this?

 

L174: Figure 8: what is given on vertical axes?

L179: Figure 9: X and y axis not defined

L185: Figure 10 and 11: Vertical axes gives what data?

L205: Eq (21): are C1 and C2 nominal capacitances? What if the real values differ from nominal?

L210: Figure 14: vertical axes?

L211: Figure 16: rearrange (reduce) the legend, use the same formatting for all items (2. Oscilloscope)

L219: Define F

Table 4: use italic notation for L and R, correct the mF and mH to mF and mH. And throughout the whole paper: use normal formatting for units and numbers, use italic for quantities

Figure 17, 18 and 19: is this data from the oscilloscope? Where are the GNDs of signals? The oscillograms are poorly visible (to small). What about simulation results?

Table 5: provide info on h₁, h₂, h₃ – what are they?  

L234: The conclusion section is rather short, would appreciate more comments.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors provided a revised version of the paper that focuses on an improved control strategy for a 3 phase three level NPC inverter. They addressed more or less the remarks from the first review. The paper in general has some grammatical issues.

List of some detailed observations:

L86: Figure 1 is now more clear, however, referring to L94: where can currents i_a, i_b and i_c be seen in the figure? There are only labels A, B, C. Where is “phase b” (and c…)? Please define correctly to correspond to Figure labelling.

L98: Table 2: column heading “medium” not “meduim”. In my opinion, a better explanation of definition of vectors is still missing and there is no sufficient info on obtaining the current (i_a, i_b, i_c), what (where it is given) info supports this? I.e.: V7 and V10 are correlated with i_b. Can you elaborate this principle to give a more clear picture?

L113: … are depicted…

L115: p-type and n-type… not defined

L125: … are shown? Instead of is  

L243: Figure 10 – use the same principle (font size!) as in Figure 8

L300: Please correct the labelling in Figures 17, 18 and 19: numbers and units are not to be written in italic

 

Author Response

Thank you so much for your feedback. All comments are incorporated in the revised version. Here is the point by point response:

1. phase a,b,c are replaced by A,B,C to have the same notation everywhere.
2. ia,ib,ic are now shown in Figure 1. 
3. fixed.
4. p-type and n-type are removed from the paper.
5. fixed.
6. fixed.
7. fixed.