Cycloconverter and method for its operation

• US 4,086,621 A
• Filed: 09/08/1976
• Issued: 04/25/1978
• Est. Priority Date: 09/18/1975
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Vukasovic, Lovro
• Primary Examiner(s): Shoop, William M.
• Application Number:
  US05/721,490
• Time in Patent Office: 594 Days
• Field of Search: 321/4, 321/14, 321/45 C, 321/45 S, 219/10.77, 363/37, 363/49, 363/136
• US Class Current: 363/37
• CPC Class Codes: H02M 7/5155 wherein each commutation element has its own extinguishing means

Abstract

A method of operating a cycloconverter which is adapted for use with a load in the form of a parallel resonant circuit and for use with an intermediate d-c link supplied by an a-c voltage source and including a smoothing choke and a controlled rectifier, the cycloconverter including an inverter circuit comprising a bridge circuit having output terminals adapted to be connected to the load and input terminals adapted to be connected to the d-c link, in which starting of the cycloconverter is realized by firing the thyristors of an auxiliary commutating device for a time interval sufficient to charge commutation capacitors to a predetermined voltage and the thyristors of the inverter then fired for a time interval sufficient to result in a current of predetermined magnitude, the latter being held constant by controlling the rectifier in the d-c link, and, thereupon, prior to each zero crossing of the resonant circuit voltage, first firing the thyristors of the auxiliary device followed, after a predetermined time interval, by the firing of the thyristors of the inverter and continuing this until the resonant circuit voltage reaches a value sufficient for direct commutation.

Claims

1. A method of operating a cycloconverter, the cycloconverter being adapted for use with a load comprising a parallel resonant circuit and for use with an intermediate DC link supplied by an AC voltage source and including a smoothing choke and a controlled rectifier, the cycloconverter including:

2. an inverter circuit comprising a bridge circuit having output terminals adapted to be connected to said load and input terminals adapted to be connected to said DC link, said bridge circuit including:

first and second bridge branches having a first common terminal therebetween;

each of said first and second bridge branches including a controllable thyristor;

third and fourth bridge branches having a second common terminal therebetween, each said third and fourth bridge branches including a controllable thyristor;

an auxiliary commutating device including;

first and second converter branches having a third common terminal therebetween and connected in parallel with said first and second bridge branches, each said converter branches including a controllable thyristor poled in the same direction as the thyristors of said bridge branches;

third and fourth converter branches having a fourth common terminal therebetween and connected in parallel with said third and fourth bridge branches, each said third and fourth converter, branches including a thyristor poled in the direction of the thyristors of said bridge branches;

and first and second commutation capacitors;

said first commutation capacitor being connected to said first and third common main terminals and said second commutation capacitor being connected to said second and fourth common main terminals;

the method including a start-up phase comprising;

firing thyristors of diagonal converter branches and maintaining the fired converter thyristors in conduction until the voltage on each commutating capacitor reaches a predetermined magnitude;

thereafter, firing thyristors of diagonal bridge branches of the inverter and maintaining the fired inverter thyristors in conduction until a constant current of predetermined magnitude flows;

controlling the rectifier so as to maintain the constant current constant throughout the succeeding steps;

firing thyristors of the converter branches which are next in succession to be brought into conduction;

after a predetermined time interval determined by the voltage of predetermined magnitude and said constant current, firing the thyristors of the bridge branches next in succession to be brought into conduction;

and repeating the immediately preceding two steps in succession prior to each said resonantcircuit voltage makes a zero crossing until said resonant circuit voltage reaches a predetermined magnitude.