Method for controlling a rectifier circuit with controlled rectifiers and associated quenching devices

Claim 2

In a method for controlling a rectifier circuit for an A.C. supply voltage and a corresponding A.C. supply current having a controlled rectifier and quenching means for the controlled rectifier, the quenching means being connected in parallel with the controlled rectifier and having a quenching thyristor and a quenching capacitor, the method including firing the controlled rectifier at an adjustably selected firing electrical angle Alpha and the improvement comprising the steps of: establishing a quenching period between the electrical angle after which the A.C. supply current has reached its maximum value and prior to the electrical angle at which the A.C. supply voltage subsequently crosses through zero, said step of establishing a quenching period including the steps of producing a delta voltage signal in synchronism with a halfperiod of the A.C. supply voltage, producing a selectively variable first D.C. voltage signal, and comparing the delta voltage signal with the first D.C. voltage signal to determine the electrical angle of intersection of the delta voltage signal and the first D.C. voltage, said angle of intersection determining the beginning of the quenching period; quenching the controlled rectifier at a quenching electrical angle Beta lying within said quenching period, and whose value is adjusted in dependence on a momentary value of the A.C. supply current, so that upon quenching of the controlled rectifier the resulting increase in voltage in the rectifier circuit is below the peak value of the A.C. supply voltage, said step of quenching at the adjustable angle Beta including the steps of producing a selectively variable second D.C. voltage, comparing a voltage signal representative of the halfperiod of the A.C. supply current with the second D.C. voltage signal, and controlling the quenching means for the controlled rectifier, by firing the quenching thyristor, to quench the controlled rectifier at the electrical angle following the beginning of the quenching period when the voltage signal representative of the A.C. supply current falls below the second D.C. voltage signal.

Claim 3

A method as defined in claim 1 wherein said step of comparing the first D.C. voltage signal and the delta voltage signal includes producing a quenching voltage signal for the duration of said quenching period; and wherein said step of quenching further includes: generating a gating signal when, as a result of said step of comparing, the voltage signal representative of the A.C. supply current falls below the second D.C. voltage signal, and utilizing the gating signal to gate the quenching voltage to the quenching means in order to initiate the quenching of the controlled rectifier.

Claim 4

In a circuit arrangement for controlling a rectifier circuit for an A.C. supply voltage, and corresponding A.C. supply current, having a controlled rectifier, firing means for firing the controlled rectifier at an adjustably selected firing electrical angle Alpha and quenching means for quenching the controlled rectifier at a quenching electrical angle Beta , the quenching means including a circuit connected In parallel with the controlled rectifier and including a quenching capacitor and a controlled quenching thyristor connected in series and means including a charging diode connected to the series connection of the quenching capacitor and control quenching thyristor for charging the quenching capacitor, the improvement comprising: a pulse means for producing a pulse signal output during an adjustable period between the electrical angle at which the A.C. supply current has reached its maximum value and the angle at which the A.C. supply voltage subsequently crosses through zero thereby defining a quenching period, said pulse means including a delta voltage generating means for producing a delta voltage signal, timing means responsive to the A.C. supply voltage for synchronizing the intitation of the delta voltage means with a half-period of the A.C. supply voltage, a first D.C. voltage generating means for generating a selectively variable first D.C. voltage signal, a first comparing means for comparing the delta voltage signal with the first D.C. voltage signal and for producing a pulse at the electrical angle of intersection between the delta voltage signal and the first D.C. Voltage signal thereby establishing the beginning of the quenching period; control means, connected to said pulse means, for producing a gating signal during the quenching period, and at a quenching electrical angle Beta which is adjustable in dependence on a momentary value of the A.C. supply current, for gating the pulse signal output of said pulse means, said control means including angle selecting means for adjustably selecting the quenching angle Beta within the quenching period so that upon quenching said controlled rectifier the resulting increase in voltage is below the peak value of the A.C. supply voltage, said angle selecting means including a second D.C. voltage generating means for producing a selectively variable second D.C. voltage signal, a means for producing a voltage signal representative of a half-period of the A.C. supply current, a second comparing means for comparing the voltage signal representative of the A.C. supply current with the second D.C. voltage signal and producing the gating signal for gating said pulse means at an electrical angle following the beginning of the quenching region when the voltage signal representative of the A.C. supply current falls below the second D.C. voltage signal; and connecting means for connecting the gated pulse signal output of said pulse means to said control quenching thyristor for initiating the quenching of said controlled rectifier.

Claim 5

In a circuit arrangement for controlling a rectifier circuit for an A.C. supply voltage, and corresponding A.C. supply current, having a controlled rectifier, firing means for firing the controlled rectifier at an adjustably selected firing electrical angle Alpha and quenching means for quenching the controlled rectifier at a quenching electrical angle Beta , the quenching means including a circuit connected In parallel with the controlled rectifier and including a quenching capacitor and a controlled quenching thyristor connected in series and means including a charging diode connected to the series connection of the quenching capacitor and control quenching thyristor for charging the quenching capacitor, the improvement comprising: a pulse means for producing a pulse signal output during an adjustable period between the electrical angle at which the A.C. supply current has reached its maximum value and the angle at which the A.C. supply voltage subsequently crosses through zero thereby defining a quenching period, said pulse means including a delta voltage generating means for producing a delta voltage signal, timing means responsive to the A.C. supply voltage for synchronizing the intitation of the delta voltage means with a half-period of the A.C. supply voltage, a first D.C. voltage generating means for generating a selectively variable first D.C. voltage signal, a first comparing means for comparing the delta voltage signal with the first D.C. voltage signal and for producing a pulse at the electrical angle of intersection between the delta voltage signal and the first D.C. Voltage signal thereby establishing the beginning of the quenching period; control means, connected to said pulse means, for producing a gating signal during the quenching period, and at a quenching electrical angle Beta which is adjustable in dependence on a momentary value of the A.C. supply current, for gating the pulse signal output of said pulse means, said control means including angle selecting means for adjustably selecting the quenching angle Beta within the quenching period so that upon quenching said controlled rectifier the resulting increase in voltage is below the peak value of the A.C. supply voltage, said angle selecting means including a second D.C. voltage generating means for producing a selectively variable second D.C. voltage signal, a means for producing a voltage signal representative of a half-period of the A.C. supply current, a second comparing means for comparing the voltage signal representative of the A.C. supply current with the second D.C. voltage signal and producing the gating signal for gating said pulse means at an electrical angle following the beginning of the quenching region when the voltage signal representative of the A.C. supply current falls below the second D.C. voltage signal; and connecting means for connecting the gated pulse signal output of said pulse means to said control quenching thyristor for initiating the quenching of said controlled rectifier.

Claim 6

A circuit arrangement as defined in claim 3 wherein said means for producing a voltage signal representative of the A.C. supply current includes a rated value separating filter connected to the incoming signal via a current converter.

Claim 7

A circuit arrangement as defined in claim 4 wherein: said rectifier circuit is a full wave rectifier having first and second branches having therein first and second controlled rectifiers respectively, each of said controlled rectifiers having a said quenching means associated therewith, said pulse means produces a pulse signal output during each half-period of the A.C. voltage; said delta voltage generating means includes a first and second delta voltage generators, said timing means is connected to both said first and second delta voltage generators for initiating said delta voltage generators during alternating half-periods of the A.C. voltage; said first comparing means includes a first and second comparators associated with said first and second delta voltage generators respectively for establishing the beginning of the quenching period for said first and second controlled rectifiers respectively, said means for producing a voltage signal representative of the A.C. supply current produces a voltage representative of each half-period of the A.C. supply current; and said second comparing means including first and second gating comparators each producing gating signals during alternating half-periods of the A.C. supply current, the outputs of said first and second gating comparators being connected to said first and second comparators respectively.