Current limiter for a load commutated inverter

Claim 3

A method as defined by claim 1 wherein said synchronous motor comprises a polyphase synchronous motor.

Claim 4

The method as defined by claim 1 wherein the motor current comprises the stator current of said motor.

Claim 5

The method as defined by claim 3 wherein said step of controlling motor current comprises controlling the current in said DC link circuit.

Claim 6

The method as defined by claim 4 wherein said step of controlling the DC link circuit comprises controlling said AC to DC converter by said torque reference signal.

Claim 9

The method as defined by claim 6 wherein the peak value of the stator current is obtained by (i) detecting the motor terminal voltage, (ii) integrating the motor terminal voltage, and (iii) detecting the peak value of the integral of the motor terminal voltage.

Claim 10

The method as defined by claim 7 and wherein said motor comprises a polyphase synchronous motor.

Claim 11

The method as defined by claim 8 wherein said AC source comprises a polyphase AC source.

Claim 12

Apparatus for controlling the torque of a synchronous motor driven by a DC to AC converter coupled to an AC to DC converter via a DC link circuit comprising: (a) means for generating a torque reference signal in response to a desired motor speed; (b) means for controlling motor current in response to said torque reference signal by the operation of said DC to AC converter and said AC to DC converter in response to said torque reference signal; (c) means for determining magnitude of the motor stator current; and (d) means for limiting the torque reference signal in response to a predetermined magnitude of the motor stator current.

Claim 13

Apparatus for controlling the torque of a synchronous motor driven by a DC to AC converter coupled to an AC to DC converter via a DC link circuit comprising: (a) means for generating a torque reference signal in response to a desired motor speed; (b) means for controlling motor current in response to said torque reference signal by the operation of said DC to AC converter and said AC to DC converter in response to said torque reference signal; (c) means for determining magnitude of the motor stator current; and (d) means for limiting the torque reference signal in response to a predetermined magnitude of the motor stator current.

Claim 14

Apparatus for controlling an AC synchronous motor drive system supplying powerof a variable current magnitude and frequency to a synchronous motor providing a predetermined rotational motor speed and output torque in response to a desired motor speed, comprising: (a) means for providing a controlled variable DC current source for providing a DC output which varies in magnitude and response to a first control signal applied thereto; (b) means for providing a controlled variable AC current source for providing an AC current which varies in frequency to said motor in response to a second control signal applied thereto; (c) DC link circuit means connecting said DC current source to said AC current source; (d) means generating a torque reference signal in response to a commanded motor speed; (e) means generating said first and second control signals in response to the torque reference signal whereby said controlled variable DC current source primarily controls the current supplied to said motor through a DC current supplied to said variable AC current source via said DC link circuit; (f) means generating a signal which is a function of the stator current of said synchronous motor; (g) means for determining the peak value of said stator current signal and providing a peak value signal; and (h) means for limiting torque reference signal in response to said peak value signal whereby the torque reference signal is limited to providing the value of the output torque corresponding to the region of peak output torque obtainable for the motor's operating parameters.

Claim 15

Apparatus for controlling an AC synchronous motor drive system supplying powerof a variable current magnitude and frequency to a synchronous motor providing a predetermined rotational motor speed and output torque in response to a desired motor speed, comprising: (a) means for providing a controlled variable DC current source for providing a DC output which varies in magnitude and response to a first control signal applied thereto; (b) means for providing a controlled variable AC current source for providing an AC current which varies in frequency to said motor in response to a second control signal applied thereto; (c) DC link circuit means connecting said DC current source to said AC current source; (d) means generating a torque reference signal in response to a commanded motor speed; (e) means generating said first and second control signals in response to the torque reference signal whereby said controlled variable DC current source primarily controls the current supplied to said motor through a DC current supplied to said variable AC current source via said DC link circuit; (f) means generating a signal which is a function of the stator current of said synchronous motor; (g) means for determining the peak value of said stator current signal and providing a peak value signal; and (h) means for limiting torque reference signal in response to said peak value signal whereby the torque reference signal is limited to providing the value of the output torque corresponding to the region of peak output torque obtainable for the motor's operating parameters.

Claim 16

The apparatus as defined by claim 11 wherein said variable DC current source comprises an AC to DC thyristor converter.

Claim 17

The apparatus as defined by claim 11 wherein said variable AC current source comprises a DC to AC converter.

Claim 18

The apparatus as defined by claim 13 wherein said DC to AC converter comprises a load commutated inverter.

Claim 19

The apparatus as defined by claim 11 wherein said variable DC current source includes an AC to DC thyristor converter coupled to a polyphase AC source.

Claim 20

The apparatus as defined by claim 15 and wherein said variable AC current source includes a DC to AC thyristor converter coupled to a polyphase synchronous motor.

Claim 21

The apparatus as defined by claim 16 and wherein said polyphase source comprises a three phase source and said polyphase synchronous motor comprises a three phase motor.

Claim 22

The apparatus as defined by claim 16 wherein said variable DC current source and said variable AC current source additionally include respective first and second means for controlling the thyristor firing of said AC to DC converter and said DC to AC converter.

Claim 23

The apparatus as defined by claim 18 and wherein said first control signal comprises a current reference signal and said second control signal comprises an angle reference signal.

Claim 24

The apparatus as defined by claim 19 wherein said current reference signal controls angle of thyristor firing of said AC to DC thyristor converter and wherein said angle reference signal controls the angle of thyristor firing of said DC to AC thyristor converter.

Claim 25

The apparatus as defined by claim 11 wherein said means (f) for generating a signal which is a function of the stator current of said motor comprises means for detecting a pseudo flux waveform voltage of said motor, and wherein said means (g) for determining the peak value of said stator current comprises determining the peak value of said flux waveform voltage.

Claim 26

The apparatus as defined by claim 11 wherein said means (f) for generating a signal which is a function of the motor stator current comprises (i) means for sensing the motor terminal voltage and (ii) means for integrating the motor terminal voltage, and wherein said means (g) for determining the peak value of said stator current comprises means for determining the peak value of the integral of the motor terminal voltage.