Starting system for chopper controlled motor-commutated thyristor inverter

• US 4,488,101 A
• Filed: 12/23/1982
• Issued: 12/11/1984
• Est. Priority Date: 12/23/1982
• Status: Expired due to Fees

• Current Assignee: BorgWarner Incorporated
• Original Assignee: BorgWarner Incorporated
• Inventors: Studtmann, George H.
• Primary Examiner(s): Goldberg, E. A.
• Assistant Examiner(s): EVANS, ARTHUR G
• Application Number:
  US06/452,557
• Time in Patent Office: 719 Days
• Field of Search: 318/769, 318/798, 318/799, 318/800, 318/801, 318/802, 318/803, 318/805-811, 318/778-782, 318/139, 363/34, 363/37, 363/135-138
• US Class Current: 318/800
• CPC Class Codes: H02M 5/45 using semiconductor devices only
• CPC Class Codes: H02M 7/5152 with separate extinguishing means
• CPC Class Codes: H02P 1/52 by progressive increase of frequency of supply to motor
• CPC Class Codes: H02P 25/03 with brushless excitation

Abstract

If the thyristor switching devices of a chopper controlled inverter are normally motor-commutated during running operation, a starting system is needed to initially rotate the motor fast enough to develop a sufficient back EMF in the motor for motor commutation to occur. This is achieved by regulating the operation of the chopper to produce bus current pulses and by gating the thyristors on in predetermined sets and in a prescribed sequence to current pulse energize the motor to effect step-by-step rotation. After a set of conducting thryistors have supplied a bus current pulse to the motor, the reactive energy that builds up and becomes locked or stored in the inductances, through which the motor current flows, must be dissipated in order to commutate the conducting thyristors off and reduce the motor current to zero before the next set of thyristors are turned on. The required energy dissipation is accomplished by a circuit path which is effective during the intervals between the bus current pulses from the chopper. A d-c voltage source, in the circuit path causes the reactive energy to be rapidly absorbed, to permit faster turn on of the next set of thyristors and consequently faster starting. Once the motor has reached a speed sufficiently high to permit motor commutation to occur, and SCR is gated on to by-pass the d-c voltage source and provide a low loss free-wheeling path for reactive energy during running operation of the system.

Claims

1. A starting system for a chopper controlled motor-commutated thyristor inverter comprising:

means for regulating the chopper and for turning on the thyristor switching devices in the inverter in predetermined sets and in a prescribed sequence to current pulse energize the motor to effect step-by-step rotation thereof;

and means, including a d-c voltage source, for rapidly absorbing the reactive energy locked in the motor inductance to minimize the decay time of the motor current to zero at the termination of each energizing pulse to permit faster turn on of the next set of thyristor switching devices.

2. A starting system for an inverter-motor system wherein a synchronous motor is driven, during running operation, by the output a-c voltage developed by a thyristor inverter, having a series of motor-commutated thyristors that are gated on in predetermined sets and in a prescribed sequence, from an applied adjustable d-c bus voltage received over a d-c bus and through a series-connected delay inductance from the output of a controlled chopper, said starting system comprising:

means for controlling the chopper to apply bus current pulses to the inverter and for gating on a new set of thyristors during each bus current pulse to supply time-separated energizing current pulses to the synchronous motor to effect step-by-step rotation thereof;

a circuit path for dissipating the reactive energy that builds up and becomes locked in the delay and motor inductances, at the conclusion of each bus current pulse during which pulse a set of thyristors are gated into conduction, to commutate the conducting thyristors off and reduce the motor current to zero before the next set of thyristors are gated on;

and a d-c voltage source, included in said circuit path, for expediting the absorption of the reactive energy to decrease the decay time of the motor current to zero in order to facilitate faster operation of the thyristors.

3. A starting system according to claim 2 wherein said d-c voltage source includes a resistor across which a d-c voltage is developed during commutation.

4. A starting system according to claim 2 wherein said d-c voltage souce includes a resistor and a capacitor connected in parallel.

5. A starting system according to claim 2 wherein said d-c voltage source is effectively coupled in series with the delay and motor inductances when the conducting thyristors are being commutated off during the starting mode, and wherein the stored reactive energy produces, across the delay and motor inductances, voltages of a polarity opposed to that of said d-c voltage source.

6. A starting system according to claim 2 wherein the chopper includes a chopper switch, in series with the d-c bus, which is alternated between on and off conditions at a relatively high frequency during running operation, and wherein a thyristor, which is gated into conduction during running operation, shunts and bypasses said d-c voltage source and functions as a free-wheeling diode to provide a current path for the reactive energy in the delay and motor inductances each time the chopper switch is turned off.

7. A starting system according to claim 2 wherein said circuit path includes a network, comprising said d-c voltage source and a series-connected isolating diode, which network is shunt-connected across the d-c bus such that the delay inductance, the motor inductance and the network are all connected in series and conduct the decaying motor current when the conducting thyristors are commutated off, during which commutation time there is no d-c bus voltage produced by the chopper, said diode being polarized to block the flow of current through the network when the chopper is operated and d-c bus voltage is developed for application to the d-c bus.

8. A starting system according to claim 7 wherein the chopper includes a chopper switch, in series with the d-c bus, which is alternated between on and off conditions at a relatively high frequency to produce each bus current pulse during the starting operating mode, and wherein an inductor is included in series with said isolating diode in said network to limit the time rate of application of current through the chopper switch and to limit the reverse recovery current through said isolating diode when the chopper switch is first turned on, after the thyristors have been commutated off, to initiate the development of another bus current pulse during starting.

9. A starting system according to claim 8 wherein and SCR, which is gated into conduction during the running operating mode, is connected to said network, at a circuit junction between said isolating diode and said inductor, in order to by-pass said d-c voltage source and provide a free-wheeling diode for translating the reactive energy, stored in the delay and motor inductances, each time the chopper switch is turned off, said inductor serving to limit the amount of reverse recovery current through said SCR each time the chopper switch is turned on.

10. A starting system according to claim 8 wherein an SCR, which is gated into conduction during the running operating mode, is connected to said network, at a circuit junction between said isolating diode and said d-c voltage source, in order to bypass said d-c voltage source and provide a free-wheeling diode for translating the reactive energy, stored in the delay and motor inductances, each time the chopper switch is turned off, said inductor serving to limit the amount of reverse recovery current through said SCR each time the chopper switch is turned on.