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Voltage source inverter (VSI)

Next the switching states of the voltage source inverter will be discussed. To do this,

is simplified to a half-bridge. Also, the DC-bus capacitor is divided into two

equal capacitances C

1

and C

2

. Now if IGBT T

1

is turned on and IGBT T

2

is off, current

flows through T

1

(with a load connected) and the voltage U

UN

(output phase to centre N

of the capacitors) takes the value

DC

U

2

1

. If thenT

1

is turned off, the current commutates

to the diode D

2

(assuming an inductive load) and U

UN

settles to

DC

U

2

1

−

relative to the

centreN. The output voltage can therefore only be switched between two voltage levels

DC

U

2

1

±

. The VSI in this topology is therefore also known as two-level voltage

converter.

Switching states of theVSI

Two-level VSI are the most widely used converter topology. Applications range from

household applications (e.g. washing machine inverters) to general purpose drives

(GPD) to high-power applications in the range of megawatts (e.g. converters in wind

power applications).

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