PWM Generator (2-Level)
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Pulse generation for a two-level converter with PWM control.
blockType: SubSystem
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Description
Block PWM Generator (2-Level) generates pulses for a pulse width modulation (PWM) converter using a two-level topology. The unit can control switching devices (FET, GTO or IGBT) of three different types of converters: single-phase half-bridge (1 arm), single-phase full-bridge (2 arms) or three-phase bridge (3 arms).
The reference signal (Uref), also called the modulating signal, is associated with a symmetrical triangular carrier. When the reference signal is larger than the carrier, the pulse for the upper switching device has a high level (1), and the pulse for the lower one has a low level (0).
To control a single-phase full-bridge device, you can select unipolar or bipolar PWM modulation. With unipolar modulation, each arm is independently controlled. The second reference signal is generated inside the converter by shifting the phase of the original reference signal by 180 degrees. When using bipolar modulation, the state of the lower switch of the second arm is the same as the state of the upper switch of the first arm, and the state of the upper switch of the second arm is the same as the state of the lower switch of the first arm. Unipolar modulation provides the best quality of the AC waveform, but bipolar modulation creates a very weakly varying common-mode voltage.
The figure shows three sampling methods for the reference signal Uref. The natural sampling method simulates the behavior of an analog implementation of a PWM oscillator. Using two uniform sampling methods, Uref can be sampled twice at both the minimum and peak of the carrier, or only once at the minimum of the carrier. The first method is called asymmetric sampling or the double-edge method. The second method is called symmetric sampling or the single edge method.
Ports
Entrance
# Uref is a reference signal for generating output pulses
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vector
Details
The reference signal used to generate the output pulses. Connect this port to a single-phase sinusoidal signal if the unit is used to control a single-phase half-bridge or full-bridge converter, or to a three-phase sinusoidal signal if the PWM generator unit controls a three-phase bridge converter. For linear operation of this block, the value of Uref must be in the range of −1 before +1.
Dependencies
To use this port, uncheck the box. Internal generation reference signal.
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| Support for complex numbers |
None |
# wt is an external reference signal used for carrier synchronization
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vector
Details
An external reference signal used for carrier synchronization.
Dependencies
To use this port, set the parameter Mode of operation: meaning Unsynchronized.
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| Support for complex numbers |
None |
Output
# P — pulse signals used to control self-switching devices
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vector
Details
The output contains two, four, or six pulse signals used to control self-switching devices (MOSFET, GTO, or IGBT) of a one-, two-, or three-band converter.
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| Support for complex numbers |
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# m — measuring output signal
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vector
Details
A measuring output that returns a carrier signal used to determine the output pulses and a sampled reference signal.
Dependencies
To use this port, check the box Show measurement port.
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| Support for complex numbers |
None |
Parameters
Main group
#
Generator type: —
number of pulses generated
Single-phase half-bridge (2 pulses) | Single-phase full-bridge (4 pulses) | Single-phase full-bridge - Bipolar modulation (4 pulses) | Three-phase bridge (6 pulses)
Details
Specify the number of pulses generated. The number of pulses generated by the unit is proportional to the number of controlled bridge arms.
Select a value Single-phase half-bridge (2 pulses) to control the self-switching devices of a single-phase half-bridge converter. Pulse 1 controls the upper device, and pulse 2 controls the lower one.
Select a value Single-phase full-bridge (4 pulses) to control the self-switching devices of a single-phase full-bridge converter. In this case, four pulses are generated. Pulses 1 and 3 control the upper devices of the first and second arms. Pulses 2 and 4 control the lower devices.
Select a value Single-phase full-bridge - Bipolar modulation (4 pulses) for controlling self-switching devices of a single-phase full-bridge converter. In this case, four pulses are generated. Pulses 1 and 3 control the upper devices of the first and second arms. Pulses 2 and 4 control the lower devices. Pulses 1 and 4 are identical. Pulses 2 and 3 are identical.
Select a value Three-phase bridge (6 pulses) for controlling self-switching devices of a three-phase bridge converter. Pulses 1, 3 and 5 control the upper devices of the first, second and third arms. Pulses 2, 4 and 6 control the lower devices.
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Yes |
Carrier
#
Mode of operation: —
carrier signal operation mode
Synchronized | Unsynchronized
Details
When selecting a value Unsynchronized The frequency of an unsynchronized carrier signal is determined by the parameter Frequency, Hz:.
When selecting a value Synchronized the carrier signal is synchronized with an external reference signal (input signal on port wt), and the frequency of the carrier signal is determined by the parameter Switching ratio (carrier frequency / output frequency):.
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Yes |
# Frequency, Hz: — frequency of the triangular carrier signal
Details
The frequency of the triangular carrier signal in Hz.
Dependencies
To use this parameter, set for the parameter Mode of operation: meaning Unsynchronized.
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| Evaluatable |
Yes |
# Initial phase, deg: — initial carrier phase
Details
The initial phase of the carrier in degrees. Meaning 90 degrees means that the initial position of the triangular carrier is set in the middle between the minimum and maximum values, and the slope is positive.
Dependencies
To use this parameter, set for the parameter Mode of operation: meaning Unsynchronized.
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| Evaluatable |
Yes |
# Switching ratio (carrier frequency / output frequency): — switching ratio
Details
Frequency ( ) of a triangular carrier signal is defined as the product of the switching coefficient and the frequency of the output voltage.
Dependencies
To use this parameter, set for the parameter Mode of operation: meaning Synchronized.
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| Evaluatable |
Yes |
# Minimum and maximum values: [Min, Max] — minimum and maximum values of the triangular carrier signal
Details
The minimum (trough) and maximum (peak) values of the triangular carrier signal.
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| Program usage name |
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| Evaluatable |
Yes |
Reference signal
#
Sampling technique: —
sampling method of the reference signal
Natural | Asymmetrical regular (double edge) | Symmetrical regular (single edge)
Details
Specify the sampling method of the reference signal: Natural, Asymmetrical regular (double edge) or Symmetrical regular (single edge).
When selecting uniform sampling methods, the parameter Sample time, s: must be an integer multiple of the sampling period. The sampling period is defined as for asymmetric sampling and how for symmetric discretization, where — carrier frequency.
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Yes |
# Internal generation reference signal — internal reference signal generation
Details
If this option is selected, the reference signal is generated by the block.
If this option is not selected, external reference signals are used to generate the pulses.
Dependencies
To use this parameter, set for the parameter Mode of operation: meaning Unsynchronized.
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| Evaluatable |
Yes |
# Modulation index: — The modulation index
Details
The modulation index is used to control the amplitude of the main component of the output voltage of the converter. The modulation index should be higher 0 and less than or equal to 1.
Dependencies
To use this option, check the box Internal generation reference signal.
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| Evaluatable |
Yes |
# Frequency, Hz: — frequency of the reference signal
Details
The frequency of the output voltage used to control the frequency of the main component of the output voltage of the converter.
Dependencies
To use this option, check the box Internal generation reference signal.
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| Evaluatable |
Yes |
# Phase, deg: — phase of the reference signal
Details
The phase of the fundamental harmonic of the output voltage of the converter.
Dependencies
To use this option, check the box Internal generation reference signal.
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| Evaluatable |
Yes |
Main
# Sample time, s: — sampling interval
Details
The block sampling interval in seconds. Set the value 0 to implement a continuous block. When choosing a uniform sampling method, the parameter Sample time, s: must be an integer multiple of the sampling period. The sampling period is defined as for asymmetric sampling and how for symmetric discretization, where — carrier frequency.
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| Evaluatable |
Yes |
# Show measurement port — enable the measurement output port
Details
Select this option to add the output port m to the block. The output returns a carrier signal used to determine the output pulses and sample the reference signal.
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| Program usage name |
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| Evaluatable |
Yes |