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Transition from a rectifying conditions to an inverting conditions

Figure 2.1

The direct-current machine is included in the load circuit. It operates either a motor is having an electromotive force Е_mot or a generator is having an opposite electromotive force E_gen.

External characteristics are same as with R - L -load for L _d =∞, i.e.

The addendum E_d0 cos(α) will increase if α decreases and U_dα may take up negative values.

When

when

δ - an angle of restoration of locking properties of a thyristor when the thyristor is across an inverse voltage;

β - a commutation delay angle the inverter, or an advance angle.

β = 180˚ - α

As U_dα and I_d are opposite direction, U_dα interferes flowing current I_d by inverter conditions.

Instantaneous power of a secondary winding is

.

During the most part of the period P ₂(υ) is negative;

The mean or active power for this reason also is negative.

The mean power across a circuit of a rectified current is also negative.

It means that in inverter conditions the power is delivered by the direct-current circuit to the ac-circuit. Thus a flux of active power changes direction at conversion from rectifier duty into an inverter duty. Thus there is not a rectifying, but it is inverting of a current. Energy is transferred by the direct-current circuit to the ac-circuit.

The inverter witch supplying the ac-circuit, names to as dependent inverter, because EMF of network enters into a contour of current commutation from the thyristor to the thyristor. The moment of switching on of a thyristor would depend from a commutation delay angle α (or β) which delays from the point of natural switching on thyristors which is determined by EMF of networks and a converter connection.

Figure 2.2

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