Circuit for sensing current in power trains for motor control

Details Circuit for sensing current in power trains for motor control Circuit for sensing current in power trains for motor control

1997-01-16

1999-11-09

Nappi, Robert E.

Electricity: motive power systems

Induction motor systems

Primary circuit control

H02P 534

Patent

active

059821361

ABSTRACT:
The invention relates to a circuit and method for sensing inverter current in a motor drive power train for purposes of detecting overload and fault conditions, based on the use of simple low cost ac current transformers and/or a low cost current-viewing resistor with non-critical inductance characteristics. The invention employs a current-viewing resistor in the negative dc bus of the inverter and a current transformer, connected in series with the current-viewing resistor, which is coupled to detect the current in the smoothing capacitor of the inverter circuit. If a motor braking circuit is included, the voltage developed across the braking resistor is summed with the inverter current signal to obtain a signal indicative of the total current in the inverter circuit. In accordance with another embodiment, a respective current transformer is coupled to each leg of the ac input line and a further current transformer is coupled to sense the filter capacitor current. The positive components of the three phase ac input line signal are added in an operational amplifier to the capacitor to obtain the total inverter current, which can then be compared to a reference signal.

REFERENCES:
patent: 4521840 (1985-06-01), Hoadley
patent: 4788485 (1988-11-01), Kawagishi et al.

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