Multilevel waveform design tool – user guide

1. General information

The Multilevel waveform design tool was developed in C language, using Builder 1.0 (for Windows) visual programming environment. All sources are available from the author ( sdaher@secrel. com. br / daher@re. e-technik. uni-kassel. de ). Main features are:

– Construction of multilevel waveforms up to 35 levels per quarter cycle, with the possibility to include user-defined hold-on-at-zero time;

– Determination of waveforms with reduced THD contents through fine adjustment of the switching angels ("improved" waveforms);

– Inclusion of configurable smoothness in waveforms with non-zero hold-on-at-zero time;

– Calculus of THD and Modulation index for all generated waveforms;

– Generation of look-up tables in C-code format for direct implementation in a microcontroller;

– Generation of waveforms text file (length: 1000 points);

– Generation of text file containing analysis data and switching angels.

2. Description of input parameters

Parameter

Description

p:

Number of levels per quarter cycle (also the number of switching angels);

INI:

First harmonic included in THD calculus;

SEL:

Last harmonic used in the calculus of the THDsel output;

X:

Last harmonic used in the calculus of the THDx output;

FREQ:

Waveform frequency;

Aref:

Defines the reference sinus

(used only by the "NATURAL" command).

Tz:

Defines the user hold-on-at-zero time (in us).

Mi:

Desired value of modulation index (if equal to 0, then it is not considered).

Wmin:

minimum width of any step;

Max Hsel:

Used by the command "MIN(X)", to define a constraint for the maximum allowed THDsel (THDsel <= Max Hsel)

Max Hx:

Used by the command "MIN(SEL)", to define a constraint for the maximum allowed THDx (THDx <= Max Hx)

INT:

Defines the control interval (in us).

Step_INI:

Height of the initial step ( used by the "SMOOTH" command )

Step_ADD:

Height of the additional steps (used by the "SMOOTH" command)

RAMP:

Force the commands "MIN(x)" and "MIN(sel)" to search waveforms where step widths increase gradually. RAMP is marked as default.

3. Description of commands

Parameter

Description

NATURAL

Generates a waveform based on the straightforward* method described in section 4.5.1. Used parameters: p, Mi, Aref and Tz.

*In case of Mi Ф 0, the last switching angle is adjusted to produce the specified Mi.

SMOOTH

Introduces smoothness in a waveform generated previously. Used parameters: Step INI, Step ADD and INT.

MIN(X)

Fine adjustment of the current waveform: search of an improved waveform with minimum value of THDx (subjected to the MAX_Hsel constraint). Used parameters: Tz, Mi, Wmin, RAMP, MAX Hsel and INT.

MIN(SEL)

Fine adjustment of the current waveform: search of an improved waveform with minimum value of THDsel (subjected to the MAX_Hx constraint). Used parameters: Tz, Mi, Wmin, RAMP, MAX Hx and INT.

C CODE

Generates an output text file containing the equivalent C source code for the current waveform.

MANUAL

Generates a waveform based on arbitrary values of switching angels (specified on the right side of the window: T1 – T35). Used parameter: p.

STOP

Used to stop the current search ("MIN" functions) when convergence is reached (when there is no more changes in the values of THDx or THDsel shown above the STOP button).

SAVE DATA

Save data for the current waveform.

THD WAVE

Makes the analysis of the current waveform in the screen (analysis of the graphical data points).

FILE MENU

Used to load and display waveform data in. CSV format (direct from Tektronic oscilloscope – spreadsheet format) or in. MAT format (ASCII text file, one row).

3. Example of use

Find all waveform data for p = 16, with Tz = 700us and 64 points per cycle.

– Set INT = 75 and use other parameters as defaults

– Press NATURAL

– Press MIN(X)

– Press STOP (when convergence applies)

– Press SMOOTH

– Press SAVE DATA

– Press AVRCODE

– Press SAVE DATA

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