Space vector modulation theory

AN2154

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Space vector modulation theory

Figure 1 shows a three-phase inverter connected to a star connected motor.

Figure 1.

Motor connected to a three-phase inverter

switched on at one time. There are only eight possible switching states depending on the

transistors that are turned on:

Please note that in states 000 and 111 (null states), points A, B, and C are shortened to the

negative and positive DC bus links respectively through low side and high side transistors so

there are no line-to-line voltages applied to the motor. On the contrary, in the remaining six

states, a voltage is present across the motor phases, causing a current to flow through

statorical windings and flux to be produced by this current.

It is very useful to express the states reported in Table 1 as space vectors. The six active

vectors and the two null states can be plotted on the complex plane as shown in Figure 2:

Table 1.

Three-phase Inverter allowed states

State

Conducting transistor

000

T2, T4, T6

001

T2, T4, T5

010

T2, T3, T6

011

T2, T3, T5

100

T1, T4, T6

101

T1, T4, T5

110

T1, T3, T6

111

T1, T3, T5