Patent ID: 11955900
Assignee: ABB SCHWEIZ AG
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H | IPC H

Claim 5:
6. A method for controlling a bi-directional switch for an inductive machine, wherein the bi-directional switch comprises a first power semiconductor transistor, wherein the first power semiconductor transistor includes a first source; a second power semiconductor transistor, wherein the second power semiconductor transistor includes a second source; the second source being directly connected to the first source; a firing angle reference generator, wherein the firing angle reference generator is configured to generate a linear ramp down from a fixed starting angle; and a soft-starter device including a control circuit, wherein the soft-starter device is for a three-phase load, the method comprising:
initializing the first power semiconductor transistor and the second power semiconductor transistor,
wherein the initializing comprises:
providing a first control signal,
wherein the first control signal sets the first power semiconductor transistor to an on state or an off state; and

providing a second control signal,
wherein the second control signal sets the second power semiconductor transistor to an on state or an off state;

detecting a falling edge of a turn-on pulse generated by comparing a measured phase angle to a reference firing angle for each half cycle of a supply voltage;
determining a number of return path devices in one or more phases, wherein the number of return path devices is based on a state of each return path device of the return path devices; and
comparing a measured phase current with a diode threshold current, wherein the comparing of the measured phase current with the diode threshold current comprises determining a slope of the measured phase current.