Starting inhibit scheme for an hvdc converter

Claim 2

For automatically starting or restarting an HVDC electric power converter comprising a plurality of controllable electric valves connected in a bridge configuration between first and second sets oF power conductors, said first set of conductors being associated with a polyphase alternating voltage network and said second set being adapted to conduct direct current which periodically is commutated from one valve to another upon firing said valves in a predetermined normal sequence during each cycle of alternating voltage when the converter is running, said converter including means for cyclically firing said valves in said sequence and at a firing angle that can vary within a permissible range as a function of a variable control signal, the improvement comprising: a. blocking means effective when not disabled for causing the firing means to idle, in which state said cyclic valve firings are suspended; b. starting means operative in response to certain conditions for disabling said blocking means, whereupon said firing means is allowed to start or to restart the converter; and c. means coupled to said first and second sets of conductors and to said firing means for calculating the commutating ability of the converter and for inhibiting operation of said starting means if said commutating ability is insufficient to ensure successful commutation once the converter is running.

Claim 3

The improvement of claim 1 in which said certain conditions include the execution of a run order.

Claim 4

The improvement of claim 2 in which said blocking means is effective in response to the presence of a bypass order for causing the firing means to idle, and in which said certain conditions include the absence of said bypass order.

Claim 5

The improvement of claim 1 in which said means for calculating commutating ability is responsive to the relative magnitudes of a combination of parameters comprising said alternating voltage (e), said direct current (Id), and said firing angle ( Beta ).

Claim 6

The improvement of claim 4 in which said means for calculating commutating ability is constructed and arranged to inhibit operation of said starting means when the ratio of Id to E is greater than k(cos( Beta - gamma ) - cos Beta ), where k is a predetermined constant and gamma is the commutation angle.

Claim 7

The improvement of claim 1 in which said means for calculating commutating ability is constructed and arranged to inhibit operation of said starting means when either the commutating ability is insufficient or the magnitude of alternating voltage is under a predetermined mimimum limit.

Claim 8

The improvement of claim 1 in which said means for calculating commutating ability is constructed and arranged to inhibit operation of said starting means whenever the commutating ability is insufficient or the magnitude of direct current is over a predetermined maximum limit.

Claim 9

The improvement of claim 7 in which said means for calculating commutating ability is constructed and arranged additionally to inhibit operation of said starting means when the magnitude of alternating voltage is under a predetermined minimum limit.

Claim 10

The improvement of claim 1 in which said means for calculating commutating ability is constructed and arranged to inhibit operation of said starting means whenever the magnitude of direct current is over a maximum limit which is determined by an adjustable reference signal.

Claim 11

The improvement of claim 9 further comprising means coupled to said first set of conductors for adjusting said reference signal so as to raise said maximum limit in response to the alternating voltage increasing in magnitude faster than a predetermined rate of change.

Claim 12

The improvement of claim 9 further comprising means coupled to said first set of conductors for adjusting said reference signal so as to lower said maximum limit in response to the magnitude of alternating voltage decreasing below a predetermined level.

Claim 13

The improvement set forth in claim 1 for automatically starting or restarting a converter whose firing means comprises (i) a firing time computer for producing during each cycle of alternating voltage a family of periodic outPut signals whose timing, relative to recurrent reference points in said cycle, is determined by said control signal, and (ii) a valve firing system activated by the respective output signals of said family for firing said valves in said predetermined normal sequence, wherein said blocking means is connected between said firing time computer and said valve firing system and is effective when not disabled for preventing activation of said valve firing system by said output signals.

Claim 14

The improvement set forth in claim 12 in which said certain conditions include the coincidence of a run order and the leading edge of any one of said output signals.

Claim 15

The improvement of claim 12 in which said means for calculating commutating ability is constructed and arranged to inhibit operation of said starting means when either the magnitude of alternating voltage is under a predetermined minimum limit or the timing of said output pulses corresponds to a firing angle smaller than a predetermined magnitude.

Claim 16

The improvement of claim 12 further comprising means for supplying a first signal representative of said direct current and a second signal representative of said alternating voltage to said means for calculating commutating ability, and in which said firing time computer includes means for supplying to said calculating means a feedback signal representative of the predicted magnitude of the firing angle for each consecutive output signal that will in turn, when said blocking means is disabled, cause the next valve firing in said predetermined normal sequence, and in which said calculating means is responsive to the relative values of said first and second signals and of a third signal which approximates a cosine function of said feedback signal.

Claim 17

The improvement of claim 15 in which said calculating means is constructed and arranged to inhibit operation of said starting means whenever the commutating ability is insufficient or the value of said first signal exceeds a predetermined amount or the value of said second signal is less than another predetermined amount.

Claim 18

For automatically starting or restarting an HVDC electric power converter comprising a plurality of controllable electric valves connected in a bridge configuration between first and second sets of power conductors, said first set of conductors being associated with a polyphase alternating voltage network and said second set being adapted to conduct direct current which periodically is commutated from one valve to another upon firing said valves in a predetermined normal sequence during each cycle of alternating voltage when the converter is running, said converter including means for cyclically firing said valves in said sequence and at a firing angle ( Beta ) that can vary within a permissible range as a function of a variable control signal, the improvement comprising: a. blocking means effective when not disabled for causing the firing means to idle, in which state said cyclic valve firings are suspended; b. starting means operative in response to certain conditions for disabling said blocking means, whereupon said firing means is allowed to start or to restart the converter; c. means coupled to said second set of conductors for producing a first signal representative of the magnitude of said direct current; d. means coupled to said first set of conductors for producing a second signal representative of the magnitude of said alternating voltage; e. means associated with said firing means and operative when said firing means is idling and when Beta is at least as large as a predetermined threshold angle for producing a third signal which varies with the predicted magnitude of Beta for each consecutive valve firing in said predetermined normal sequence, the value of said third signal being zero whenever Beta is smaller than said threshold angle; and f. means supplied with said first, second, and third signals for inhibiting operation of said starting means whenEver i. the sum of said first signal and a predetermined bias signal is greater than the sum of said second and third signals, or ii. the value of said first signal exceeds a predetermined amount, or iii. the value of said second signal is less than another predetermined amount.

Claim 19

For automatically starting or restarting an HVDC electric power converter comprising a plurality of controllable electric valves connected in a bridge configuration between first and second sets of power conductors, said first set of conductors being associated with a polyphase alternating voltage network and said second set being adapted to conduct direct current which periodically is commutated from one valve to another upon firing said valves in a predetermined normal sequence during each cycle of alternating voltage when the converter is running, said converter including means for cyclically firing said valves in said sequence and at a firing angle ( Beta ) that can vary within a permissible range as a function of a variable control signal, the improvement comprising: a. blocking means effective when not disabled for causing the firing means to idle, in which state said cyclic valve firings are suspended; b. starting means operative in response to certain conditions for disabling said blocking means, whereupon said firing means is allowed to start or to restart the converter; c. means coupled to said second set of conductors for producing a first signal representative of the magnitude of said direct current; d. means coupled to said first set of conductors for producing a second signal representative of the magnitude of said alternating voltage; e. means associated with said firing means and operative when said firing means is idling and when Beta is at least as large as a predetermined threshold angle for producing a third signal which varies with the predicted magnitude of Beta for each consecutive valve firing in said predetermined normal sequence, the value of said third signal being zero whenever Beta is smaller than said threshold angle; and f. means supplied with said first, second, and third signals for inhibiting operation of said starting means whenEver i. the sum of said first signal and a predetermined bias signal is greater than the sum of said second and third signals, or ii. the value of said first signal exceeds a predetermined amount, or iii. the value of said second signal is less than another predetermined amount.

Claim 20

For automatically starting or restarting an HVDC electric power converter comprising a plurality of controllable electric valves connected in a bridge configuration between first and second sets of power conductors, said first set of conductors being associated with a polyphase alternating voltage network and said second set being adapted to conduct direct current which periodically is commutated from one valve to another upon firing said valves in a predetermined normal sequence during each cycle of alternating voltage when the converter is running, said converter including means for cyclically firing said valves in said sequence and at a firing angle that can vary within a permissible range as a function of a variable control signal, the improvement comprising: a. means effective when not disabled for blocking said cyclic valve firings; b. starting means operative in response to certain conditions for disabling said blocking means, whereupon the firing means is allowed to start or to restart the converter; and c. means coupled to said first and second sets of conductors for inhibiting operation of said starting means if the magnitude of alternating voltage is under a predetermined minimum limit or if the magnitude of direct current is over a predetermined maximum limit.

Claim 21

For automatically starting or restarting an HVDC electric power converter comprising a plurality of controllable electric valves connected in a bridge configuration between first and second sets of power conductors, said first set of conductors being associated with a polyphase alternating voltage network and said second set being adapted to conduct direct current which periodically is commutated from one valve to another upon firing said valves in a predetermined normal sequence during each cycle of alternating voltage when the converter is running, said converter including means for cyclically firing said valves in said sequence and at a firing angle that can vary within a permissible range as a function of a variable control signal, the improvement comprising: a. means effective when not disabled for blocking said cyclic valve firings; b. starting means operative in response to certain conditions for disabling said blocking means, whereupon the firing means is allowed to start or to restart the converter; and c. means coupled to said first and second sets of conductors for inhibiting operation of said starting means if the magnitude of alternating voltage is under a predetermined minimum limit or if the magnitude of direct current is over a predetermined maximum limit.

Claim 22

The improvement of claim 18 further comprising means associated with said firing means and operative when said cyclic valve firings are blocked for monitoring the predicted firing angle ( Beta ) for each consecutive valve firing in said predetermined normal sequence, wherein said inhibiting means is also connected to said firing angle monitoring means and is constructed and arranged to inhibit operation of said starting means if the magnitude of alternating voltage is under a predetermined mimimum limit of if the magnitude of direct current is over a predetermined maximum limit or if Beta is smaller than a predetermined magnitude.