Failure diagnosis method for inverter circuit

Abstract

A failure diagnosis method for an inverter circuit, which easily performs failure diagnosis of an FET of the inverter circuit without delay includes the steps: comparing a motor terminal voltage corresponding to each phase of the inverter circuit including semiconductor switching devices (FETs) to drive a motor, with a threshold voltage by comparators as voltage comparison circuitry. At this time,the threshold voltage is changed according to a high-side FET and a low-side FET on which failure diagnosis is to be performed. Subsequently, by a digital output from the comparator, whether there isa short circuit of each FET of the motor terminal voltage is determined.

Description

technical field [0001] The present invention relates to a fault diagnosis method of an inverter circuit constituting, for example, a motor control unit of an electric power steering apparatus. Background technique [0002] An electric power steering apparatus including an electric motor that generates assist torque for a driver's steering operation of a vehicle such as an automobile, a control device for the electric motor, and the like operates at all times. Therefore, when a component constituting the motor drive unit fails while driving, it is necessary to perform control such as suspending the assist operation of the steering wheel and to identify the failed component. [0003] Conventionally, as a FET failure diagnosis method for an inverter circuit of an electric power steering system, it is known to monitor the terminal voltage between the high-side FET and the low-side FET constituting the inverter circuit using the A / D conversion function of the CPU. Methods. In t...

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Problems solved by technology

[0010] In the above-mentioned Patent Document 1, since not only the motor terminal voltage detecting means but also an overcurrent detector for judging the short-circuit fault of the FET of the motor drive circuit is provided, the structure for fault judgment becomes complicated.

In addition, there is also a problem that the comparison between the value based on the terminal voltage and the predetermined threshold value is repeated for a predetermined number of times, and if the number of times the value based on the terminal voltage exceeds the threshold value is less than or equal to the predetermined value, it is determined that there is a fault in the motor drive circuit. Therefore, it not only makes the judgment time longer, but also can only determine whether the fault is the motor or the motor drive circuit, and cannot independently determine the fault of the FET that constitutes the motor drive circuit.

[0011] In the abnormality determination of Patent Document 2, in addition to the normal FET control circuit, a drive pulse generation circuit for abnormality determination is provided separately, and in addition to adopting a configuration for operating the drive pulse generation circuit at the time of diagnosis, Control to initialize the charge of the capacitor is required, thus complicating the structure for abnormal judgment

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