The commutation voltage is provided by the grid

The load provides commutation voltage

Whenever the phase of the load current leads the load voltage, load commutation can be achieved.

Utilizing the self-shutoff capability of fully controlled devices for commutation

Set up an additional commutation circuit to apply reverse voltage or reverse current to the thyristor to be turned off.

0~t1: Midpoint—R—L—VD1—

t1~t2: —V1—L—R—midpoint

t2~t3:- —VD2—L—R—midpoint

t3~t4: Midpoint—R—L—V2— -

The output voltage is a rectangular wave; amplitude Um=Ud/2

There are four bridge arms in total, which can be regarded as a combination of two half-bridge circuits.

The two pairs of bridge arms conduct 180° alternately. The output voltage and current waveforms have the same shape as the half-bridge circuit but twice the amplitude.

Changing the effective value of the output AC voltage can only be achieved by changing the DC voltage U.

phase shift voltage regulation

Fundamental amplitude

Fundamental effective value

The output voltage is a rectangular wave; amplitude Um=Ud

Alternately drive two IGBTs, and add a rectangular wave alternating current to the load through transformer coupling. current voltage.

The function of the two diodes is also to provide feedback channels for reactive energy.

Comparison with full bridge circuit

The output voltage is a rectangular wave; amplitude Um=Ud

180° conductive mode; that is, each bridge arm conducts 180° The upper and lower arms of the same phase conduct electricity alternately, and the angle at which each phase begins to conduct electricity is 120 degrees different.

At any moment, there are three bridge arms conducting at the same time.

Each commutation is performed between the upper and lower arms of the same phase.

Valid values

Fundamental amplitude

Fundamental effective value

Valid values

Fundamental amplitude

Fundamental effective value

In the actual working process, the parameters of the induction coil change with time, and the operating frequency must be automatically adjusted to adapt to the changes in the load. This control method

Fixed operating frequency control method

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