A rectifier unit for 3-phase a.c. to d.c. conversion is of the type having a transformer with a star-connected and a delta-connected secondary the outputs of which are rectified and combined to give 12-pulse operation. To reduce the danger of current imbalance between the two secondaries, a compensating transformer unit is interposed between the secondaries and the rectifiers which modifies the signals such that any difference in the current drawn from one secondary compared with the other tends to equalize the current drawn from the secondaries. The compensating transformer unit can take the form of 3 individual transformer units but is preferably a single transformer with 3 limbs, each of which carries a main winding connected to one secondary and two opposed subsidiary windings which receive the phases from the other secondary which are closest to and on either side of the phase of the associated main winding.
In a transformer-rectifier converter system, at least one inductance is inserted in the commutation path of two adjacent diode or thyristor devices in a cluster of three devices related to a common DC polarity pole, the reactance due to such inductance being sufficient to lengthen the commutation overlap thereby to minimize AC line harmonics. The invention is applicable to AC/DC as well as to DC/AC conversion.
Dc aerospace power supplies include neutral point controllers to interconnect primary or secondary windings of the supplies into wye connected primary or secondary circuits. In power supplies having neutral point controllers in the primary circuits, the power supplies may alternately or in addition have first and second compound wye connected secondary circuits having a separate or common neutral point.
At least two three-phase transformer arrangements include a plurality of primary windings connected in a wye configuration and at least two converter arrangements, each converter arrangement comprising a plurality of secondary windings connected in a double-wye configuration. A separate rectifier is connected in series with each secondary winding of each converter arrangement.
A three-phase transformer having a delta-connected primary and two identical secondary windings per phase connected in hexagon, has symmetrical taps on each secondary winding connected to rectifying devices for generating DC energy from a first group of six symmetrical AC voltages at 60.degree. with respect to the virtual neutral for one polarity and from a second group of six symmetrical AC voltages at 60.degree. with respect to the virtual neutral for the other polarity, the first and second groups being at 30.degree. phase shift to one another.
This invention is designed to prevent the large charging current from flowing to the capacitor at the start of the elevator for preventing damage of the elements of the rectifier device. Thus the present device provides a control device for an a.c. elevator which includes: a commercial a.c. source, a capacitor for smoothing the output voltage of the commercial a.c. source, an inverter for converting the smoothed output voltage of the capacitor into an a.c. power of the variable frequency, an a.c. motor for driving the elevator car by the a.c. power supplied from said inverter, and a rectifier for rectifying the voltage of the commercial a.c. source and charging said capacitor by the thus rectified voltage at least when the car is stopped.
