31-05-2012, 05:30 PM
SPACE VECTOR MODULATION
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INTRODUCTION
Space Vector Modulation became a standard for the
switching power converters and important research effort has
been dedicated to this topic. Tens of papers, research reports
and patents were developed in the last ten years and the
theory of Space Vector Modulation is already wellestablished.
Diverse implementation methods were tried and
some dedicated hardware pieces were developed based on
this principle. The initial use of Space Vector Modulation at
three-phase voltage-source inverters has been expanded by
application to novel three-phase topologies as AC/DC
Voltage Source Converter, AC/DC or DC/AC Current Source
Converters, Resonant Three-Phase Converters, B4-inverter,
Multilevel Converters, AC/AC Matrix Converters, and so on).
This tutorial presents the base theory of SVM when applied to
a 3-phase voltage source inverter.
VECTORIAL PWM
A. Theory
The three-phase inverter presented in Fig.2 is herein
considered. Generally, the tip of the voltage Space Vector
should follow a circular locus. This cannot be achieved by a
switching power converter that is leading to discrete positions
of the voltage Space Vector. Each desired position on the
circular locus can be achieved by an average relationship
IECON'01: The 27th Annual Conference of the IEEE Industrial Electronics Society between two neighboring active vectors. Zero state vectors
are used to fill-up the gap to a constant sampling interval.
Definition of the switching reference function
Directly using the time allocated to states given for (ta, tb) is
sometimes not convenient for digital implementation. The
definition of the switching sequence would result to be
implemented in software only. It is more advantageous to
define a function called “Switching reference function” with
the same meaning as the reference used in sine-triangle
comparison based PWM methods. It represents the duty ratio
of each inverter leg or the conduction time normalized to the
sampling period for a given switch and it is a mathematical
function with variation between 0 and 1, centered around 0.5.
Conclusion
The theory of the Space Vector Modulation for a 3-phase
inverter is presented by this tutorial. This theory has been
further extended to other 3-phase converter systems and
nowadays became a standard for industry.