Patent Description:
A current measurement circuit that provides measurements of three individual phase currents using two current sensors is disclosed in the independent claim <NUM>. Additional embodiments are defined in the corresponding dependent claims <NUM>-<NUM>. 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 <NUM>:<NUM>:<NUM> with respect to the first conductor, the second conductor, and the third conductor, and the second current sensor comprises a turns ratio of <NUM>:<NUM> 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 <NUM>:<NUM>:<NUM> 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 <NUM>:<NUM> with respect to the second conductor and the third conductor.

In a further example, a method for measuring current is defined in the independent claim <NUM>. Additional embodiments are defined in the corresponding dependent claims <NUM>-<NUM>. In one example, the method 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 <NUM>:<NUM>:<NUM>.

In this description, the term "couple" or "couples" means either an indirect or direct wired or wireless connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections. Also, in this description, the recitation "based on" means "based at least in part on. " Therefore, if X is based on Y, then X may be a function of Y and any number of other factors.

Some inverters and other electric machine control systems include current measurement circuits that apply separate sensors to measure each of the phase currents driving the electric machine. In such systems, a current measurement circuit includes three current sensors, where each current sensor measures one phase current of a three-phase current produced by an inverter. However, to reduce cost some systems measure only two of the three phase currents and compute the third phase current based on the sum of currents in a balanced load (e.g., an electric motor) being equal to zero. In such systems, because no current sensor is provided to measure the third phase current, the power devices (e.g., insulated gate bipolar transistors or silicon carbide metal oxide semiconductor field effect transistors) connected to the third phase cannot be protected from ground faults (overcurrent conditions).

To provide ground fault and overcurrent protection to power devices, some systems that include only two current sensors apply discrete comparators to detect faults on the third phase. <FIG> shows block diagram for a system <NUM> that uses a comparator to identify overcurrent on a third phase. In the system <NUM>, a control circuit <NUM> generates pulse width modulation signals <NUM> that are provided to the driver circuit <NUM>. The driver circuit <NUM> generates gate drive signals <NUM> for driving the transistors <NUM>. The transistors <NUM> output three phase currents <NUM>, <NUM>, and <NUM> to drive the motor <NUM>.

A current sensor <NUM> measures the phase current <NUM>, and a current sensor <NUM> measures the phase current <NUM>. To reduce cost, no current sensor is provided to measure the phase current <NUM>. Instead, a comparator circuit <NUM> compares the voltage across a resistor <NUM> to a threshold to identify excessive current flow (an overcurrent condition). The comparator circuit <NUM> provides fault information to the control circuit <NUM>, but no measurements of the phase current <NUM> are provided to the control circuit <NUM>.

<FIG> shows a block diagram for an example current measurement circuit <NUM> that includes two current sensors to measure the current in three phases in accordance with this description. While the system <NUM> provided measurements of only two of the three phase currents using two current sensors, the current measurement circuit <NUM> uses two current sensors (e.g., no more than two current sensors) to provide measurements of three phase currents. The current measurement circuit <NUM> includes a current sensor <NUM>, a current sensor <NUM>, current computation circuitry <NUM>, a conductor <NUM>, a conductor <NUM>, and a conductor <NUM>. The conductor <NUM> conducts a first phase current generated by a three-phase current generation circuit <NUM> to the three-phase load <NUM>. The conductor <NUM> conducts a second phase current generated by a three-phase current generation circuit <NUM> to the three-phase load <NUM>. The conductor <NUM> conducts a third phase current generated by a three-phase current generation circuit <NUM> to the three-phase load <NUM>. In various implementations, the three-phase load <NUM> is an electric motor or any other electrical circuit/machine. In some implementations, the three-phase current generation circuit <NUM> includes the control circuit <NUM>, driver circuit <NUM>, and transistors <NUM> of the system <NUM>. In some implementations, the three-phase current generation circuit <NUM> is an electrical grid directly powering the three-phase load <NUM>.

The current sensor <NUM> is coupled to the conductor <NUM>, the conductor <NUM>, and the conductor <NUM>. The current sensor <NUM> senses a sum of the first, second, and third phase currents. Some implementations of the current sensor <NUM> include a magnetic core <NUM> and a sensor element <NUM> coupled to the magnetic core <NUM>. The sensor element <NUM> is a Hall sensor or a flux gate or any other current sensor in some implementations of the current sensor <NUM>. The conductor <NUM>, the conductor <NUM>, and the conductor <NUM> are wound about the magnetic core <NUM> in a <NUM>:<NUM>:<NUM> turns ratio. That is, there are two turns of the conductor <NUM> about the magnetic core <NUM> for each turn of the conductor <NUM> and the conductor <NUM> about the magnetic core <NUM>. The conductor <NUM> is wound about the magnetic core <NUM> in a direction opposite from the direction in which the conductor <NUM> and the conductor <NUM> are wound about the magnetic core <NUM>. Thus, in the current sensor <NUM>, current flow in the conductor <NUM> is in an opposite direction relative to the direction of current flow in the conductor <NUM> and the conductor <NUM>.

The sensor element <NUM> detects the magnetic flux produced in the magnetic core <NUM> or in the air gap by the first, second, and third phase currents. The current sensor <NUM> includes signal conditioning circuitry <NUM> coupled to the sensor element <NUM>. Some implementations of the signal conditioning circuitry <NUM> include an amplifier that drives output of the sensor element <NUM> to the current computation circuitry <NUM> as signal <NUM>. Some implementations of the signal conditioning circuitry <NUM> include an analog-to-digital converter to digitize output of the sensor element <NUM> and/or other digital circuit, such as a voltage-to-frequency converter, a voltage-to-pulse-width-modulation converter, encoder circuitry, transmitter/driver circuitry, etc.. Thus, in various implementations of the current sensor <NUM>, the signal <NUM> comprising the output of the sensor element <NUM> is provided to the current computation circuitry <NUM> as an analog signal or a digital signal. Given the described configuration of the current sensor <NUM>, the signal <NUM> may be expressed as: <MAT> where:.

The current sensor <NUM> is coupled to the conductor <NUM> and the conductor <NUM>. The current sensor <NUM> senses a sum of the second and third phase currents. Some implementations of the current sensor <NUM> include a magnetic core <NUM> and a sensor element <NUM> coupled to the magnetic core <NUM>. The sensor element <NUM> is a Hall sensor or a flux gate sensor in some implementations of the current sensor <NUM>. The conductor <NUM> and the conductor <NUM> are wound about the magnetic core <NUM> in a <NUM>:<NUM> turns ratio. That is, for each turn of the conductor <NUM> about the magnetic core <NUM> there is one turn of the conductor <NUM> about the magnetic core <NUM>. The conductor <NUM> is wound about the magnetic core <NUM> in a direction opposite from the direction in which the conductor <NUM> is wound about the magnetic core <NUM>. Thus, in the current sensor <NUM>, current flow in the conductor <NUM> is in an opposite direction relative to the direction of current flow in the conductor <NUM>.

The current sensor <NUM> includes signal conditioning circuitry <NUM> coupled to the sensor element <NUM>. Some implementations of the signal conditioning circuitry <NUM> include an amplifier that drives output of the sensor element <NUM> to the current computation circuitry <NUM> as the signal <NUM>. Some implementations of the signal conditioning circuitry <NUM> include an analog-to-digital converter to digitize output of the sensor element <NUM> and/or other digital circuit, such as a voltage-to-frequency converter, a voltage-to-pulse-width-modulation converter, encoder circuitry, transmitter/driver circuitry, etc. Thus, in various implementations of the current sensor <NUM> the signal <NUM> comprising the output of the sensor element <NUM> is provided to the current computation circuitry <NUM> as an analog signal or a digital signal. Given the described configuration of the current sensor <NUM>, the signal <NUM> may be expressed as: <MAT>.

The current sensor <NUM> and the current sensor <NUM> are configured to utilize a Clarke transformation to convert the three phase currents into two phases. The Clarke transformation matrix is expressed as: <MAT>.

The current computation circuitry <NUM> is coupled to the current sensor <NUM> and the current sensor <NUM>, and processes the signal <NUM> and the signal <NUM> to generate measurements of the first, second, and third phase currents respectively conducted by the conductor <NUM>, the conductor <NUM>, and the conductor <NUM>. Implementations of the current computation circuitry <NUM> apply an inverse Clarke transform to the signal <NUM> and the signal <NUM> to produce the measurements. The inverse Clarke transformation matrix applied by the current computation circuitry <NUM> is expressed as: <MAT>.

Various examples of the current computation circuitry <NUM> include hardware circuitry dedicated to implementing the inverse Clarke transform, or include a processor, such as a microcontroller or a digital signal processor that executes instructions stored in memory to implement the inverse Clarke transformation, or implement the inverse Clarke transform using a combination of hardware and software.

<FIG> shows an example summation of the phase currents in the current sensor <NUM> and the current sensor <NUM> in accordance with this description. The output of the current sensor <NUM> is a sum of the first phase current (IU) conducted by the conductor <NUM> scaled by <NUM>, the second phase current (IV) conducted by the conductor <NUM> scaled by -<NUM>, and the third phase current (IW) conducted by the conductor <NUM> scaled by -<NUM>. The output of the current sensor <NUM> is the sum of the second phase current (IV) and the negated third phase current (IW), where the sum is scaled by <NUM>.

<FIG> shows an example of detection of an overcurrent condition by the current measurement circuit current measurement circuit <NUM>. The three phase current values (IU, IV, and, IW) illustrated in <FIG>, are generated, as disclosed herein, by the current computation circuitry <NUM> based on the signal <NUM> and the signal <NUM> respectively provided by the current sensor <NUM> and the current sensor <NUM>. At about time <NUM> seconds, the current drawn from the conductor <NUM> (IU) increases to create an overcurrent condition. The increase in the first phase current (IU) is reflected in the increased amplitude of the first phase current (IU) values generated by the current computation circuitry <NUM>.

While <FIG> illustrates the current sensor <NUM> and the current sensor <NUM> as including a magnetic core about which the conductor <NUM>, the conductor <NUM>, and the conductor <NUM> are wound, some implementations of the current sensor <NUM> and the current sensor <NUM> do not include a magnetic core. In such implementations, the conductor <NUM>, the conductor <NUM>, and the conductor <NUM> are positioned relative to the sensor element such that current flowing in the conductors creates a magnetic field according to the desired direction and turns ratio for detection by the sensor element.

<FIG> shows the conductor <NUM>, the conductor <NUM>, and the conductor <NUM> disposed at equal distance from the sensor element <NUM>. In the conductors, a dot represent current flow in a first direction and an X represents current flow in the direction opposite that of the dot. With the conductor <NUM>, conductor <NUM>, and conductor <NUM> equidistant from the sensor element <NUM>, two turns of the conductor <NUM> are needed for each turn of the conductor <NUM> and the conductor <NUM> to provide the desired <NUM>:<NUM>:<NUM> ratio of the current signals for summation.

<FIG> shows the conductor <NUM> at difference distance from the sensor element <NUM> than the conductor <NUM> or the conductor <NUM>. The conductor <NUM> is disposed nearer the sensor element <NUM> than the conductor <NUM> or the conductor <NUM>. The conductor <NUM> and the conductor <NUM> are equidistant from the sensor element <NUM>. By disposing the conductor <NUM> nearer the sensor element <NUM> (than the conductors <NUM> or <NUM>), the magnetic field detected by the sensor element <NUM> due to current flow in the conductor <NUM> is relatively stronger than the magnetic field due to current flow in the conductor <NUM> of the conductor <NUM>. Thus, by positioning the conductor <NUM> closer to the sensor element <NUM> than the conductor <NUM> or conductor <NUM>, implementations of the current sensor <NUM> apply a turns ratio of <NUM>:<NUM>:<NUM> to provide the equivalent of the <NUM>:<NUM>:<NUM> signal ratio without using multiple turns of the conductor <NUM>.

<FIG> shows a flow diagram for a method <NUM> for current measurement that uses two current sensors to individually measure each phase current of a three-phase current in accordance with this description. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some implementations may perform only some of the actions shown. Operations of the method <NUM> are performed by an implementation of the current measurement circuit <NUM>.

In block <NUM>, the current sensor <NUM> measures a sum of the first phase current (IU), the second phase current (IV), and the third phase current (IW) respectively flowing in the conductor <NUM>, the conductor <NUM>, and the conductor <NUM>. The first phase current (IU), the second phase current (IV), and the third phase current (IW) are scaled for the sum in a ratio of <NUM>:<NUM>:<NUM>. The flow of the first phase current (IU) is in a first direction, and flow of the second phase current (IV), and the third phase current (IW) is in a direction opposite the first direction.

In block <NUM>, the current sensor <NUM> measures a sum of the second phase current (IV) and the third phase current (IW) respectively flowing in the conductor <NUM> and the conductor <NUM>. The second phase current (IV) and the third phase current (IW) are scaled for the sum in a ratio of <NUM>:<NUM>. The flow of the second phase current (IV) is in a first direction and the flow of the third phase current (IW) is in a direction opposite the first direction.

In block <NUM>, the current computation circuitry <NUM> applies an inverse Clarke transform to the signal <NUM> (the sum of currents measured by the current sensor <NUM>) and the signal <NUM> (the sum of currents measured by the current sensor <NUM>). The inverse Clarke transform produces as output individual measurements of the first phase current (IU), the second phase current (IV), and the third phase current (IW).

In block <NUM>, the individual measurements of the first phase current (IU), the second phase current (IV), and the third phase current (IW) generated in block <NUM> are applied to control the operation of an electric machine or other three-phase electrical load. For example, if one of the phase currents exceeds a threshold, then current provided to operation the electric machine may be reduced.

Claim 1:
A current measurement circuit, comprising:
a first current sensor (<NUM>) coupled to a first conductor (<NUM>), a second conductor (<NUM>), and a third conductor (<NUM>);
a second current sensor (<NUM>) coupled to the second conductor (<NUM>) and the third conductor (<NUM>), wherein the first conductor (<NUM>) conducts a first phase current, the second conductor (<NUM>) conducts a second phase current, and the third conductor (<NUM>) conducts a third phase current; and
current computation circuitry (<NUM>) coupled to the first current sensor (<NUM>) and the second current sensor (<NUM>), and configured to:
generate a measurement of the first phase current based an output of the first current sensor (<NUM>) and an output of the second current sensor (<NUM>);
generate a measurement of the second phase current based an output of the first current sensor (<NUM>) and an output of the second current sensor (<NUM>); and
generate a measurement of the third phase current based an output of the first current sensor (<NUM>) and an output of the second current sensor (<NUM>),
wherein the current computation circuitry (<NUM>) is configured to determine the first phase current, the second phase current, and the third phase current by applying an inverse Clarke transform to the output of the first current sensor (<NUM>) and the output of the second current sensor (<NUM>).