Guard system for inverter apparatus

Claim 2

A guard system for an inverter comprising: an inverter for converting DC power to AC power to be supplied to a load, said inverter comprising semiconductor switching devices; first guard means for simultaneously cutting off said switching devices; second guard means for simultaneously turning on said switching devices; and means for preventing the operation of said first guard means during the operation of said second guard means.

Claim 3

A guard system for an inverter according to claim 1, wherein said first guard means responds to a predetermined value of a current flowing through said load.

Claim 4

A guard system for an inverter according to claim 2, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 5

A guard system for an inverter according to claim 2, wherein said second guard means responds to operation of means detecting a short circuit of an arm caused by simultaneous conduction of two sets of switching devices connected in series in said inverter.

Claim 6

A guard system for an inverter according to claim 4, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 7

A guard system for an inverter according to claim 4, wherein said arm short circuit detecting means responds to a drop in voltage across said two switching devices connected in series.

Claim 8

A guard system for an inverter according to claim 6, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 9

A guard system for an inverter-according to claim 1, wherein said first guard means responds to a current flowing through said load which exceeds a first predetermined value and does not exceed a second predetermined value in magnitude.

Claim 10

A guard system for an inverter according to claim 8, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 11

A guard system for an inverter according to claim 1, wherein said first guard means responds to a current flowing through said load which exceeds a first predetermined value and does not exceed a second predetermined value, and wherein said first predetermined value is a maximum value under normal conditions and said second predetermined value is a current value which can be interrupted by said switching devices.

Claim 12

A guard system for an inverter according to claim 10, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 13

A guard system for an inverter according to claim 1, wherein said second guard means responds to operation of means detecting a short circuit of an arm caused by simultaneous conduction of two sets of switching devices connected in series in said inverter.

Claim 14

A guard system for an inverter according to claim 12, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 15

A guard system for an inverter according to claim 12, wherein said arm short circuit detecting means responds to a drop in voltage across said two switching devices connected in series.

Claim 16

A guard system for an inverter according to claim 14, wherein said semiconductor swiching devices comprise gate turn-off thyristors.

Claim 17

A guard system for an inverter according to claim 1, wherein said semiconductor switching devices comprise gate turn-off thyristors.

Claim 18

A guard system for an inverter according to claim 1, wherein said preventing means comprises two NAND gates connected in series as a first stage and a second stage in an ON-OFF signal transmission path and wherein the NAND gate of the first stage is supplied with a simultaneous gate off signal and the NAND gate of the second stage is supplied with a simultaneous gate on signal.

Claim 19

A guard system for an inverter comprising: a three-phase inverter supplied with DC power from an aerial conductor through a switch and a high-speed breaker, said three-phase inverter including six GTOs connected as three series connected pairs, each pair comprising an arm of a three phase bridge configuration; a three-phase induction motor supplied with power by said three-phase inverter, said induction motor being connected to center taps of said three series connected pairs of said GTOs; an electric car driven by said induction motor; pulse width modulator means; gate drive circuits for turning on and turning off said GTOs on the basis of an ON-OFF signal sent out from said modulator means; first guard means for simultaneously turning off said GTOs, in response to a current of said induction motor larger than the maximum current at normal conditions and not larger than the interruptible current of the GTOs; second guard means for simultaneously turning on all of said GTOs, in response to simultaneous conduction of one series connected pair of said GTOs; and means for preventing the operation of said first guard means, in response to the operation of said second guard means.

Claim 20

A guard system for an inverter comprising: a three-phase inverter supplied with DC power from an aerial conductor through a switch and a high-speed breaker, said three-phase inverter including six GTOs connected as three series connected pairs, each pair comprising an arm of a three phase bridge configuration; a three-phase induction motor supplied with power by said three-phase inverter, said induction motor being connected to center taps of said three series connected pairs of said GTOs; an electric car driven by said induction motor; pulse width modulator means; gate drive circuits for turning on and turning off said GTOs on the basis of an ON-OFF signal sent out from said modulator means; first guard means for simultaneously turning off said GTOs, in response to a current of said induction motor larger than the maximum current at normal conditions and not larger than the interruptible current of the GTOs; second guard means for simultaneously turning on all of said GTOs, in response to simultaneous conduction of one series connected pair of said GTOs; and means for preventing the operation of said first guard means, in response to the operation of said second guard means.