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 Еmot or a generator is having an opposite electromotive force Egen.
External characteristics are same as with R - L -load for L d =∞, i.e.
The addendum Ed0 cos(α) will increase if α decreases and Udα 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 Udα and Id are opposite direction, Udα interferes flowing current Id 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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