Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1982-02-09
1984-05-01
Beha, Jr., William H.
Electric power conversion systems
Current conversion
Using semiconductor-type converter
363138, H02M 7537, H02M 7515
Patent
active
044465130
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a DC/AC converter consisting of controlled valves which are connected in a bridge and including recovery diodes also connected in a bridge, the device being of the type wherein the center points of the recovery diode bridge are connected to the corresponding center points of the valve bridge.
OBJECT OF THE INVENTION
The object of the invention is to improve the DC/AC converter of the above-said type.
In accordance with the invention, such a device is characterized in that it includes a switching aid and energy recovery circuit which is connected across the transistor or thyristor DC/AC converter.
THE PRIOR ART
Operation of power transistors with an inductive load, i.e. with the load type which is most frequently found in circuits where transistors play a switching role subjects same to stresses having adverse effects on the circuit efficiency and the transistor lifetime.
Specifically, the transistor is subjected to switching losses upon firing and blocking. Switching losses upon firing are associated with occurence of an overcurrent, while switching losses upon blocking are associated with simultaneous application of the overall voltage across the transistor while the load current is still flowing through the transistor.
It is known to reduce the firing overcurrent by inserting a switching aid inductor connected in series with the load into a circuit consisting of a diode in series with a resistor and connected in parallel with said inductor, whereby the diode is connected so as to be directly biased whenever the transistor is blocked. A drawback of such a circuit arrangement is that upon transistor blocking the energy stored in the switching aid inductor becomes dissipated in the resistor.
It is also known to reduce the blocking stress by arranging, in parallel with the transistor, a circuit consisting of a capacitor having a relatively low capacitance and an additional series-connected diode. An additional resistor is preferably connected in parallel either with said additional diode or with both diodes. Said additional diode is connected so as to be directly biased whenever the transistor becomes blocked. A drawback of such an arrangement is that upon transistor firing the energy stored in the capacitor becomes dissipated in said additional resistor.
Thus, known transistor switching aid circuits, although reducing transistor proper switching losses, undesirably generate losses through energy dissipation in the resistors included therein. These losses may become sufficiently high to destroy the transistor whenever the switching rate and/or the supply voltage exceed certain levels.
SUMMARY OF THE INVENTION
The present invention provides a DC/AC converter including a switching aid and energy recovery circuit wherein said dissipation losses are either reduced or removed.
The device in accordance with the invention includes first series circuit connected at each of the DC inputs of a thyristor valve bridge and consisting of a transistor and an inductor, the other terminal of said first series circuit being connected to the respective supply terminal; a second series circuit associated with each first series circuit and connected in parallel between the connecting point of the inductor and the transistor of each first series circuit and the respective supply terminal, said second series circuit comprising a series-connection of a storage capacitor and a diode the anode of which is connected to the connecting point of the inductor and the transistor and the cathode of which is connected to the storage capacitor and to the respective end of the diode-bridge; a low voltage-high voltage converter circuit the inputs of which are connected to the terminals of the storage capacitor and the outputs of which are connected to the terminals of the supply network; a switching aid capacitor which is associated with each first circuit and one terminal of which is connected to the connecting point of the transistor and the respective input of the thyristor bridg
REFERENCES:
patent: 3460021 (1969-08-01), Schlabach
patent: 3474322 (1969-10-01), King
patent: 4019117 (1977-04-01), Gehm et al.
patent: 4072882 (1978-02-01), Wiart
Beha Jr. William H.
Drucker William A.
La Telemecanique Electrique
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