PWM Generator (3-Level)

Generate pulses for PWM-controlled three-level converter

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Libraries:
Simscape / Electrical / Specialized Power Systems / Power Electronics / Power Electronics Control

Description

The PWM Generator (3-Level) block generates pulses for carrier-based pulse-width modulation (PWM) converters using three-level topology. The block can control switching devices (FETs, GTOs, or IGBTs) of three different converter types: single-phase half-bridge (one arm), single-phase full-bridge (two arms), or three-phase bridge (three arms).

The reference signal (Uref input), also called the modulating signal, is naturally sampled and compared with two symmetrical level-shifted triangle carriers.

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

The converter arm 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 smaller than the negative carrier, the state of the arm is −1.

Otherwise, the state is 0. Based on the current state of the arm, the appropriate pulses are generated.

State	Q1	Q2	Q3	Q4
1	1	1	0	0
0	0	1	1	0
−1	0	0	1	1

One reference signal is required to generate the four pulses of an arm. For a single-phase full-bridge converter, a second reference signal is required to generate the four pulses of the second arm. This signal is internally generated by phase-shifting the original reference signal by 180 degrees. For a three-phase bridge, three reference signals are required to generate the 12 pulses.

The reference signal also can be internally generated by the PWM generator. In this case, specify a modulation index, voltage output frequency, and phase.

Examples

The power_PWMGenerator3Level model uses a simple circuit to show how the PWM Generator (3-Level) operates. Run the simulation and use the FFT Analysis tool of the Powergui block to see the harmonics and the THD value of the voltages produced by the three-phase three-level converter.

The model sample time is parameterized by the Ts variable set to a default value of 2e-6. Set Ts to 0 in the command window and change the Simulation type parameter of the Powergui block to Continuous to simulate the model in continuous mode.

Characteristics

Sample Time	Specified in the Sample Time parameter Continuous if Sample Time = 0
Scalar Expansion	No
Dimensionalized	No

Ports

Input

Uref — Reference signal used to generate output pulses

Vectorized reference signal used to generate the output pulses. Connect this input to a single-phase sinusoidal signal when the block is used to control a single-phase half- or full-bridge converter, or to a three-phase sinusoidal signal when the PWM Generator block is controlling a three-phase bridge converter. For linear operation of this block, the magnitude of Uref must be between −1 and +1.

Dependencies

To enable this port when Mode of operation is Synchronized, clear the Internal generation of modulating signal (s) parameter.

wt — External reference signal used to synchronize carrier

External reference signal used to synchronize the carrier.

Dependencies

To enable this port, set Mode of operation to Synchronized.

Output

m — Measurement output

The output contains the 4, 8, or 12 pulses used to fire the self-commutated devices (MOSFETs, GTOs, or IGBTs) of a one-, two- or three-arm three-level converter.

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Generator type — Number of pulses to generate

Single-phase half-bridge (4 pulses) (default) | Single-phase full-bridge (8 pulses) | Three-phase bridge (12 pulses)

Specify the number of pulses to generate. The number of pulses generated by the block is proportional to the number of bridge arms to fire.

Select Single-phase half-bridge (4 pulses) to fire the self-commutated devices of a single-phase half-bridge converter. Pulses (1, 2) fire the upper devices and pulses (3, 4) fire the lower devices.

Select Single-phase full-bridge (8 pulses) to fire the self-commutated devices of a single-phase full-bridge converter. Eight pulses are then generated. Pulses (1, 2) and (5, 6) fire the upper devices of the first and second arms. Pulses (3, 4) and (7, 8) fire the lower devices of the first and second arms.

Select Three-phase bridge (12 pulses) (default) to fire the self-commutated devices of a three-phase bridge converter. Pulses (1, 2), (5, 6), and (9, 10) fire the upper devices of the first, second, and third arms. Pulses (3, 4), (7, 8), and (11, 12) fire the lower devices of the three arms.

Mode of operation — Mode of operation of carrier signal

Unsynchronized (default) | Synchronized

When set to Unsynchronized, the frequency of the unsynchronized carrier signal is determined by the Carrier frequency (Hz) parameter.

When set to Synchronized, the carrier signal is synchronized to an external reference signal (input wt) and the carrier frequency is determined by the Switching ratio (carrier frequency/output frequency) parameter.

Carrier frequency (Hz) — Frequency of triangular carrier signal

27*60 (default)

Frequency, in hertz, of the triangular carrier signal.

Dependencies

To enable this parameter, set Mode of operation to Unsynchronized.

Switching ratio (carrier frequency/output frequency) — Frequency of triangular carrier signal

27 (default)

Frequency (F_c) of the triangular carrier signal.

$$F_c=SwitchingRatio\times OutputVoltageFrequency$$

Dependencies

To enable this parameter, set Mode of operation to Synchronized.

Internal generation of reference signal(s) — Internal generation of reference signal

off (default) | on

When selected, the reference signal is generated by the block.

When not selected, external reference signals are used for pulse generation.

This parameter is available only if the Mode of operation parameter is set to Unsynchronized.

Dependencies

To enable this parameter, set Mode of operation to Unsynchronized.

Modulation index — Modulation index

0.8 (default)

Modulation index to control the amplitude of the fundamental component of the output voltage of the converter. The modulation index must be greater than 0 and lower than or equal to 1.

Dependencies

To enable this parameter, set Mode of operation to Unsynchronized and select Internal generation of reference signal.

Output voltage frequency (Hz) — Frequency of reference signal

60 (default)

Output voltage frequency used to control the frequency of the fundamental component of the output voltage of the converter.

Dependencies

To enable this parameter, set Mode of operation to Unsynchronized and select Internal generation of reference signal.

Output voltage phase (degrees) — Phase of reference signal

0 (default)

Phase of the fundamental component of the output voltage of the converter.

Dependencies

To enable this parameter, set Mode of operation to Unsynchronized and select Internal generation of reference signal.

Sample time — Sample time

0 (default)

Sample time of the block, in seconds. Set to 0 to implement a continuous block.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2013a