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Generate pulses for SVPWM-controlled two-level converter

Simscape / Electrical / Specialized Power Systems / Control & Measurements / Pulse & Signal Generators

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks / Power Electronics / Pulse & Signal Generators

The SVPWM Generator (2-Level) block generates pulses for three-phase two-level DC/AC converters using the space-vector pulse width modulation (SVPWM) technique.

The converter switches are represented by the following equivalent circuit:

As shown in the following figure, the objective of the SVPWM
technique is to approximate the reference voltage vector (U_{ref})
instantaneously by combining the switching states corresponding to
the basic space vectors.

More precisely, for every PWM period, the reference vector U_{ref} is
averaged by using its two adjacent space vectors (U_{3} and
U_{4} in the figure) for a certain duration of
time and a null vector (U_{7} or U_{8})
for the rest of the period.

Vector | Q1 | Q3 | Q5 |
---|---|---|---|

U_{1} | 1 | 0 | 0 |

U_{2} | 1 | 1 | 0 |

U_{3} | 0 | 1 | 0 |

U_{4} | 0 | 1 | 1 |

U_{5} | 0 | 0 | 1 |

U_{6} | 1 | 0 | 1 |

U_{7} | 0 | 0 | 0 |

U_{8} | 1 | 1 | 1 |

The block implements two symmetrical switching patterns[1]:

Pattern #1: With this pattern, known as Software-Determined, each PWM channel switches twice per every PWM period.

Pattern #2: With this pattern, known as Hardware-Determined, one PWM channel remains constant for the entire PWM period. Consequently, the number of switching times for this pattern is less than pattern #1. As a result, switching losses are reduced with Pattern #2.

**Data type of input reference vector (Uref)**Specify the type of reference vector.

When set to

`Magnitude-Angle (rad)`

(default), the U_{ref}vector is specified by the following inputs:|

*U*|`Magnitude of Uref (value between 0 and 1)`

When set to

`alpha-beta components`

, the U_{ref}vector is specified by the Uα and Uβ inputs.When set to

`Internally generated`

, the U_{ref}is no longer an input to the block. It is internally generated in order to control the converter output voltage as specified in the output voltage parameter.**Switching pattern**When set to

`Pattern #1`

(default), every device of the converter switches twice per every PWM period.When set to

`Pattern #2`

, the status of one of the three arms stays constant (no switching) for the entire PWM period.**PWM frequency (Hz)**Specify the PWM frequency that determines the PWM period.

$$PWMperiod=1/PWMFrequency$$

Default is

`2000`

.**Output voltage: [ Mag (0<m<1), Phase (degrees), Freq (Hz)]**Specify the magnitude, phase, and frequency of the output voltage of the two level converter controlled by the block. Default is

`[0.8 -30 50]`

. The magnitude of the fundamental component of the converter line-to-line output voltage is defined as$${V}_{LLrms}=m\times \frac{{V}_{dc}}{\sqrt{2}}$$

This parameter is visible only when the

**Data type of input reference vector Uref**parameter is set to`Internally generated`

.**Sample time**Specify the sample time of the block, in seconds. Set to 0 to implement a continuous block. Default is

`0`

.

`Uref`

When the

**Data type of input reference vector Uref**parameter is set to`Magnitude-Angle (rad)`

, the two block inputs are the magnitude and the phase, in radians, of the rotating reference vector U_{ref}.When the

**Data type of input reference vector Uref**parameter is set to`alpha-beta components`

, the two block inputs are the alpha-beta components of U_{ref}.The output contains the six pulse signals to fire the self-commutated devices (Q1 to Q6) of a converter device.

Sample Time | Specified in the Sample Time parameterContinuous if Sample Time = 0 |

Scalar Expansion | No |

Dimensionalized | No |

The `power_SVPWMGenerator2Level`

model
uses two simple circuits to show how the SVPWM Generator (2-Level)
works and to compare the two switching pattern options. Run the simulation
and open the FFT Analysis tool of the Powergui block to see the harmonics
and the THD value of the voltages produced by the two converters.

The model sample time is parameterized by the Ts variable set
to a default value of 2e-6 s. 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.

[1] Yu, Z., *Application Report SPRA524, Space-Vector
PWM with TMS320C24x Using H/W & S/W Determined Switching Patterns*,
Texas Instruments, 1999.