The PWM generator generates pulses for carrier-based pulse width modulation (PWM) converters using three-level topology.

Note: This component should be used with the 3-Level Converter (Switching Devices).

Mask and Parameters

Parameter Name	Description	Unit	Variable = {Possible Values}
Description	Use this field to add all kinds of information about the component		Description = {'string'}
PWM carrier frequency	Frequency of the triangular carrier signal	Hz	FrequencyCarrier = { [0, 1e12] }
PWM carrier initial phase	Initial phase of the carrier. A value of 90° means that the triangle carrier initial position is set to midpoint between its minimum and maximum value and the slope is positive.	°	InitialPhase = { [0, 360] }

Inputs, Outputs and Signals Available for Monitoring

Inputs

Name	Description
Vref	Vectorized reference voltage signal containing the phase-ground voltages from the AC side (Va, Vb, Vc).

Outputs

Name	Description
P	Vectorized signal containing twelve firing pulses to control the converter.

Sensors

Name	Description	Unit
Va	Reference voltage signal for voltage from phase A on the AC side.	V
Vb	Reference voltage signal for voltage from phase B on the AC side.
Vc	Reference voltage signal for voltage from phase C on the AC side.
P1	Signal containing a firing pulse to control Q1 (phase A upper arm of the converter).
P2	Signal containing a firing pulse to control Q2 (phase A upper arm of the converter).
P3	Signal containing a firing pulse to control Q3 (phase A lower arm of the converter).
P4	Signal containing a firing pulse to control Q4 (phase A lower arm of the converter).
P5	Signal containing a firing pulse to control Q5 (phase B upper arm of the converter).
P6	Signal containing a firing pulse to control Q6 (phase B upper arm of the converter).
P7	Signal containing a firing pulse to control Q7 (phase B lower arm of the converter).
P8	Signal containing a firing pulse to control Q8 (phase B lower arm of the converter).
P9	Signal containing a firing pulse to control Q9 (phase C upper arm of the converter).
P10	Signal containing a firing pulse to control Q10 (phase C upper arm of the converter).
P11	Signal containing a firing pulse to control Q11 (phase C lower arm of the converter).
P12	Signal containing a firing pulse to control Q12 (phase C lower arm of the converter).

Additional Information

The reference signal (Vref input), also known as the modulation signal, is naturally sampled and compared with two symmetrical level-shifted triangle carries. The converter arm (1 arm per phase for a three-level converter), can have three states: +1 , 0 or 1. When the reference signal is greater than the positive carrier, the state of the arm is +1; when the reference signal is less than the negative carrier, the state of the arm is equal to -1 . For all other cases, the state is 0. Based on the current state of the arm, the pulses are generated properly.

The carrier frequency (fc) is defined by the frequency of the converter output voltage and by the converter switching ratio, from the following equation:

A reference signal is necessary to generate the four pulses of an arm; for a three-level converter, three reference signals are necessary to generate the 12 pulses.

To control the 3-Level Converter (Switching Devices), the pulse generator generates the pulses (1, 2), (5, 6) and (9, 10) for the upper switching components of the first, second and third arms, while pulses (3, 4), (7, 8) and (11, 12) are generated for the lower switching components of the first, second and third arms.

The figure below describes a technique used to sample the reference signal Vref. The natural sampling technique models the behavior of an analog implementation of a PWM generator .

The figure below shows how the pulses are generated for a single-phase, half-bridge three-level converter.

Internal Circuit

Limitations

This component should be used with the 3-Level Converter (Switching Devices).

References

MathWorks, PWM Generator (3-Level) Mathworks.com. https://www.mathworks.com/help/physmod/sps/powersys/ref/pwmgenerator3level.html.

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