Documentation

Space Vector Modulator

Implement space vector modulator for PWM VSI AC motor drive

Library

Electric Drives/Fundamental Drive Blocks

Description

The Space Vector Modulator block generates pulses for either a detailed or average-value three-phase inverter following the space vector pulse-width modulation strategy.

The Space Vector Modulator block consists of seven main blocks.

  • The three-phase generator produces three sine waves with variable frequency and amplitude. The three signals are out of phase with each other by 120 degrees. The inverter-requested frequency and voltage are two of the block inputs.

  • The low-pass bus filter removes fast transients from the DC bus voltage measurement. This filtered voltage computes the voltage vector applied to the motor.

  • The alpha-beta transformation converts variables from the three-phase system to the two-phase αβ system.

  • The αβ vector sector finds the sector of the αβ plane in which the voltage vector lies. The αβ plane is divided into six different sectors spaced by 60 degrees.

  • The ramp generator produces a unitary ramp at the PWM switching frequency. This ramp is a time base for the switching sequence.

  • The switching time calculator calculates the timing of the voltage vector applied to the motor. The block input is the sector in which the voltage vector lies.

  • The gates logic receives the timing sequence from the switching-time calculator and the ramp from the ramp generator. This block compares the ramp and the gate timing signals to activate the inverter switches as needed.

When using an average-value inverter, the gates logic block is disabled and the inverter leg PWM duty cycles are issued by the switching time calculator. In this mode, the Space Vector Modulator block outputs the duty cycles of the various pulses but not the pulses themselves. These duty cycle signals are expected by the average-value Three-Phase Inverter block when used in space vector modulation mode.

Parameters

Model detail level

Specify the model detail level to use:

  • Detailed (default)

  • Average

Low-pass filter cutoff frequency (Hz)

The cutoff frequency, in hertz, of the first-order filter applied to the DC bus voltage measurement. The default value is 50.

Carrier frequency (Hz)

The inverter switching frequency, in hertz. The default value is 4500.

Modulator sample time (s)

The Space Vector Modulator sampling time, in seconds. The sampling time must be a multiple of the simulation time step. The default value is 20e-6.

Network sample time (s)

The simulation time step, in seconds. The default value is 2e-6.

Inputs and Outputs

Freq*

The output frequency set point of the inverter.

Volts*

The maximum AC output voltage set point of the inverter.

dir

Motor speed sign (-1 for negative speed, 1 for positive, or 0).

Vdc Bus

DC Bus voltage.

Gates

The switching signals for the three-phase inverter. This output is visible only when the Model detail level parameter is set to Detailed.

Duty

A vector containing the duty cycles of the three inverter arms. This output is visible only when the Model detail level parameter is set to Average.

Examples

The Space Vector Modulator block is used in the AC2 block of the Electric Drives library.

References

[1] Bose, B. K. Modern Power Electronics and AC Drives. Upper Saddle River, NJ: Prentice-Hall, 2002.

Introduced in R2015b

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