BACKGROUND

Efficient operation of electric machines, such as electric motors, powered by three phase inverters often requires control of the individual phase currents generated by the inverters. Measurement of the individual phase currents is an initial step in controlling the phase currents, and in protecting electronic power switches and electrical loads from damage caused by over current.

SUMMARY

A current measurement circuit that provides measurements of three individual phase currents using two current sensors is disclosed herein. In one example, a current measurement circuit includes a first current sensor, a second current sensor, and current computation circuitry. The first current sensor is coupled to a first conductor, a second conductor, and a third conductor. The second current sensor is coupled to the second conductor and the third conductor. The first conductor conducts a first phase current, the second conductor conducts a second phase current, and the third conductor conducts a third phase current. The current computation circuitry is coupled to the first current sensor and the second current sensor, and configured to: provide a measurement of the first phase current based an output of the first current sensor and an output of the second current sensor, provide a measurement of the second phase current based an output of the first current sensor and an output of the second current sensor, and provide a measurement of the third phase current based an output of the first current sensor and an output of the second current sensor. In some implementations of the current measurement circuit, the first current sensor comprises a turns ratio of 2:1:1 with respect to the first conductor, the second conductor, and the third conductor, and the second current sensor comprises a turns ratio of 1:1 with respect to the second conductor and the third conductor.

In another example, a current measurement circuit includes a first conductor, a second conductor, a third conductor, a first current sensor, a second current sensor, and current computation circuitry. The first conductor is configured to conduct a first phase current of a three-phase current. The second conductor is configured to conduct a second phase current of the three-phase current. The third conductor is configured to conduct a third phase current of the three-phase current. The first current sensor is coupled to the first conductor, the second conductor, and the third conductor. The second current sensor is coupled to the second conductor and the third conductor. The current computation circuitry is coupled to the first current sensor and the second current sensor, and is configured to determine the first phase current, the second phase current, and the third phase current by applying an inverse Clarke transform to an output of the first current sensor and an output of the second current sensor. In some implementations of the current measurement circuit, the first current sensor is configured to provide a turns ratio of 2:1:1 with respect to the first conductor, the second conductor, and the third conductor, and the second current sensor is configured to provide a turns ratio of 1:1 with respect to the second conductor and the third conductor.

In a further example, a method for measuring current includes measuring a sum of a first phase current, a second phase current, and a third phase current of a three-phase current in a first current sensor, and measuring a sum of the second phase current, and the third phase current of the three-phase current in a second current sensor. The method also includes determining the first phase current, the second phase current, and the third phase current by applying an inverse Clarke transform to the sum of the currents measured by the first current sensor and the sum of the currents measured by the second current sensor. Some implementations of the method also include measuring, in the first current sensor, the first phase current, the second phase current, and the third phase current respectively in a ratio of 2:1:1.

