Three-phase current measurement

Abstract

A current measurement circuit includes first, second and third conductors, a first current sensor, a second current sensor and a current calculation circuit system. 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, second and third conductors. The second current sensor is coupled to the second conductor and the third conductor. The current calculation circuit system is coupled to the first current sensor and the second current sensor and is configured to determine the first current, the second current and the third current by applying an inverse Clarke transform to an output of the first current sensor and an output of the second current sensor.

Description

Background Art

[0001] Efficient operation of an electric machine (e.g., an electric motor) powered by a three-phase inverter generally requires control of the individual phase currents produced by the inverter. Measurement of the individual phase currents is an initial step in controlling the phase currents and protecting electronic power switches and electrical loads from damage caused by overcurrent. Summary of the invention

[0002] A current measurement circuit that uses two current sensors to provide measurements of three individual phase currents is disclosed herein. In one example, a current measurement circuit includes a first current sensor, a second current sensor, and a current calculation circuit system. 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 calculation circuit system is coupled to the first current sensor and the second current sensor and is configured to: provide a measurement of the first phase current based on an output of the first current sensor and an output of the second current sensor; provide a measurement of the second phase current based on 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 on 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 includes 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 includes a turns ratio of 1:1 with respect to the second conductor and the third conductor.

[0003] 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 a current calculation circuit system. The first conductor is configured to conduct a first phase current in a three-phase current. The second conductor is configured to conduct a second phase current in the three-phase current. The third conductor is configured to conduct a third phase current in 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 calculation circuit system 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 the output of the first current sensor and the 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.

[0004] In a further example, a method for measuring current includes measuring the sum of a first phase current, a second phase current, and a third phase current of three phase currents in a first current sensor, and measuring the sum of the second phase current and the third phase current of the three phase currents 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 the first phase current, the second phase current, and the third phase current in the first current sensor, respectively, at a ratio of 2:1:1. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] For a detailed description of various embodiments, reference will now be made to the accompanying drawings, in which:

[0006] Figure 1 A block diagram showing a current measurement circuit using a comparator to identify overcurrent on the third phase;

[0007] Figure 2 A block diagram showing an example current measurement circuit including two current sensors to individually measure each of three phase currents according to the present description;

[0008] Figure 3 Demonstrate the Figure 2 Example summation of phase currents in two current sensors;

[0009] Figure 4 An example of detecting an overcurrent condition in a current measurement circuit including two current sensors according to the present description is shown;

[0010] Figure 5 and 6 showing an example arrangement of conductors relative to sensor elements in a current sensor according to the present description; and

[0011] Figure 7 A flow chart of a method for current measurement using two current sensors to individually measure each of three-phase currents according to the present description is shown. DETAILED DESCRIPTION

[0012] In this description, the term "couple" or "couples" means an indirect or direct wired or wireless connection. Thus, if a first device is coupled to a second device, the connection may be through a direct connection or through an indirect connection via other devices and connections. Also, in this description, the statement "based on" means "based at least in part on." Thus, if X is based on Y, X may be a function of Y and any number of other factors.

[0013] Some inverters and other motor control systems include current measurement circuits that apply separate sensors to measure each of the phase currents driving the motor. In such systems, the current measurement circuit includes three current sensors, each of which measures one of the three phase currents generated by the inverter. However, to reduce costs, some systems measure only two of the three phase currents and calculate the third phase current based on the sum of the currents in the balanced load (e.g., electric motor) being equal to zero. In such systems, because no current sensor is provided to measure the third phase current, the power device (e.g., insulated gate bipolar transistor or silicon carbide metal oxide semiconductor field effect transistor) connected to the third phase cannot be protected from a ground fault (overcurrent condition).

[0014] To provide ground fault and overcurrent protection to power devices, some systems including only two current sensors apply discrete comparators to detect faults on the third phase. Figure 1 A block diagram of a system 100 using a comparator to identify overcurrent on the third phase is shown. In the system 100, a control circuit 102 generates a pulse width modulated signal 104 that is provided to a driver circuit 106. The driver circuit 106 generates a gate drive signal 108 for driving a transistor 110. The transistor 110 outputs three-phase currents 112, 114, 116 to drive a motor 118.

[0015] Current sensor 120 measures phase current 112, and current sensor 122 measures phase current 116. To reduce cost, current sensors are not provided to measure phase current 114. Instead, comparator circuit 126 compares the voltage across resistor 124 to a threshold value to identify excessive current flow (overcurrent condition). Comparator circuit 126 provides fault information to control circuit 102, but does not provide a measurement of phase current 114 to control circuit 102.

[0016] Figure 2 A block diagram of an example current measurement circuit 200 including two current sensors to measure current in three phases according to the present description is shown. While system 100 uses two current sensors to provide measurement of only two of the three-phase currents, current measurement circuit 200 uses two current sensors (e.g., no more than two current sensors) to provide measurement of the three-phase currents. Current measurement circuit 200 includes current sensor 204, current sensor 206, current calculation circuit system 208, conductor 212, conductor 214, and conductor 216. Conductor 212 conducts a first phase current generated by three-phase current generation circuit 202 to three-phase load 210. Conductor 214 conducts a second phase current generated by three-phase current generation circuit 202 to three-phase load 210. Conductor 216 conducts a third phase current generated by three-phase current generation circuit 202 to three-phase load 210. In various implementations, three-phase load 210 is an electric motor or any other circuit / motor. In some implementations, the three-phase current generating circuit 202 includes the control circuit 102 of the system 100, the driver circuit 106, and the transistor 110. In some implementations, the three-phase current generating circuit 202 is a power grid that directly powers the three-phase load 210.

[0017] The current sensor 204 is coupled to the conductor 212, the conductor 214, and the conductor 216. The current sensor 204 senses the sum of the first, second, and third phase currents. Some implementations of the current sensor 204 include a magnetic core 218 and a sensor element 220 coupled to the magnetic core 218. In some implementations of the current sensor 204, the sensor element 220 is a Hall sensor or a flux gate or any other current sensor. The conductor 212, the conductor 214, and the conductor 216 are wound around the magnetic core 218 with a 2:1:1 turns ratio. That is, for each turn of the conductor 214 and the conductor 216 around the magnetic core 218, there are two turns of the conductor 212 around the magnetic core 218. The conductor 212 is wound around the magnetic core 218 in a direction opposite to the direction in which the conductor 214 and the conductor 216 are wound around the magnetic core 218. Therefore, in the current sensor 204, the current flow in the conductor 212 is in the opposite direction relative to the current flow direction in the conductor 214 and the conductor 216.

[0018] The sensor element 220 detects the magnetic flux generated by the first, second, and third phase currents in the magnetic core 218 or in the air gap. The current sensor 204 includes a signal conditioning circuit system 222 coupled to the sensor element 220. Some implementations of the signal conditioning circuit system 222 include an amplifier that drives the output of the sensor element 220 as a signal 230 to the current calculation circuit system 208. Some implementations of the signal conditioning circuit system 222 include an analog-to-digital converter to digitize the output of the sensor element 220 and / or other digital circuits, such as a voltage-to-frequency converter, a voltage pulse width modulation converter, an encoder circuit system, a transmitter / driver circuit system, etc. Therefore, in various implementations of the current sensor 204, the signal 230 including the output of the sensor element 220 is provided to the current calculation circuit system 208 as an analog signal or a digital signal. Given the described configuration of the current sensor 204, the signal 230 can be expressed as:

[0019] V α =F{0.666I U -0.333I V -0.333I W}

[0020] in:

[0021] I U is the first phase current (the current in conductor 212);

[0022] I V is the second phase current (the current in conductor 214); and

[0023] I W is the third phase current (the current in conductor 216).

[0024] The current sensor 206 is coupled to the conductor 214 and the conductor 216. The current sensor 206 senses the sum of the second and third phase currents. Some implementations of the current sensor 206 include a magnetic core 224 and a sensor element 226 coupled to the magnetic core 224. In some implementations of the current sensor 206, the sensor element 226 is a Hall sensor or a fluxgate sensor. The conductor 214 and the conductor 216 are wound around the magnetic core 218 with a 1:1 turns ratio. That is, for each turn of the conductor 214 around the magnetic core 224, there is one turn of the conductor 216 around the magnetic core 224. The conductor 214 is wound around the magnetic core 224 in a direction opposite to the direction in which the conductor 216 is wound around the magnetic core 224. Therefore, in the current sensor 206, the current flow in the conductor 214 is in the opposite direction relative to the current flow direction in the conductor 216.

[0025] The current sensor 206 includes a signal conditioning circuit system 228 coupled to the sensor element 226. Some implementations of the signal conditioning circuit system 228 include an amplifier that drives the output of the sensor element 226 as a signal 232 to the current calculation circuit system 208. Some implementations of the signal conditioning circuit system 228 include an analog-to-digital converter to digitize the output of the sensor element 226 and / or other digital circuits (e.g., a voltage-to-frequency converter, a voltage pulse width modulation converter, an encoder circuit system, a transmitter / driver circuit system, etc.). Therefore, in various implementations of the current sensor 206, the signal 232 including the output of the sensor element 226 is provided to the current calculation circuit system 208 as an analog signal or a digital signal. Given the described configuration of the current sensor 206, the signal 232 can be expressed as:

[0026] V β =F{0.57737(I V -I W )}

[0027] The current sensor 204 and the current sensor 206 are configured to utilize Clarke transformation to convert the three-phase current into two phases. The Clarke transformation matrix is ​​expressed as:

[0028]

[0029] Current calculation circuitry 208 is coupled to current sensor 204 and current sensor 206 and processes signal 230 and signal 232 to produce measurements of the first, second, and third phase currents conducted by conductor 212, conductor 214, and conductor 216, respectively. An implementation of current calculation circuitry 208 applies an inverse Clarke transform to signal 230 and signal 232 to produce the measurements. The inverse Clarke transform matrix applied by current calculation circuitry 208 is expressed as:

[0030]

[0031] Various examples of current calculation circuitry 208 include hardware circuitry dedicated to implementing the inverse Clarke transform, or include a processor such as a microcontroller or digital signal processor that executes instructions stored in a memory to implement the inverse Clarke transform, or uses a combination of hardware and software to implement the inverse Clarke transform.

[0032] Figure 3 An example summation of the phase currents in current sensor 204 and current sensor 206 according to the present description is shown. The output of current sensor 204 is the first phase current (I U ) is scaled by 0.6666, and the second phase current (I V) is scaled by -0.3333 and the third phase current (I W ) is the sum of the scaled values ​​of -0.3333. The output of the current sensor 206 is the second phase current (I V ) and negative third phase current (I W ), where the sum is scaled by 0.57737.

[0033] Figure 4 An example of detection of an over-current condition of current measurement circuit 200 is shown. As disclosed herein, current calculation circuitry 208 generates a current signal based on signals 230 and 232 provided by current sensor 204 and current sensor 206, respectively. Figure 4 The three-phase current values ​​(I U ,I V and I W At about 0.175 seconds, the current drawn from conductor 212 (I U ) increases to produce an overcurrent condition. The first phase current (I U ) is reflected in the first phase current (I U ) value increases.

[0034] Although Figure 2 Current sensor 204 and current sensor 206 are illustrated as including a magnetic core around which conductors 212, 214, and 216 are wound, but some implementations of current sensor 204 and current sensor 206 do not include a magnetic core. In such implementations, conductors 212, 214, and 216 are positioned relative to the sensor element so that current flowing in the conductors generates a magnetic field according to a desired direction and turns ratio for detection by the sensor element.

[0035] Figure 5 Conductor 212, conductor 214, and conductor 216 are shown disposed at equal distances from sensor element 220. In the conductors, dots represent current flow in a first direction and Xs represent current flow in a direction opposite to the direction of the dots. With conductor 212, conductor 214, and conductor 216 equidistant from sensor element 220, two turns of conductor 212 are required for each turn of conductor 214 and conductor 216 to provide the desired 2:1:1 ratio of the current signals for summing.

[0036] Figure 6The conductor 212 is shown at a different distance from the sensor element 220 than the conductor 214 or the conductor 216. The conductor 212 is disposed closer to the sensor element 220 than the conductor 214 or the conductor 216. The conductor 214 and the conductor 216 are equidistant from the sensor element 220. By disposing the conductor 212 closer to the sensor element 220 (compared to the conductor 214 or the conductor 216), the magnetic field detected by the sensor element 220 due to the current flowing in the conductor 212 is relatively stronger than the magnetic field caused by the current flowing in the conductor 212 or the conductor 216. Therefore, by positioning the conductor 212 closer to the sensor element 220 than the conductor 214 or the conductor 216, the implementation of the current sensor 204 applies a turns ratio of 1:1:1 to provide the equivalent of a 2:1:1 signal ratio without using multiple turns of the conductor 212.

[0037] Figure 7 A flow chart of a method 700 for current measurement using two current sensors to individually measure each of three phase currents in accordance with the present description is shown. Although depicted sequentially for convenience, at least some of the actions shown may be performed in a different order and / or in parallel. Additionally, some implementations may perform only some of the actions shown. The operations of method 700 are performed by an implementation of current measurement circuit 200.

[0038] In block 702, current sensor 204 measures a first phase current (I ) flowing in conductor 212, conductor 214, and conductor 216, respectively. U ), the second phase current (I V ) and the third phase current (I W ). The first phase current (I U ), the second phase current (I V ) and the third phase current (I W ) is scaled by a ratio of 2:1:1 for summing. The first phase current (I U ) flows in the first direction, and the second phase current (I V ) and the third phase current (I W ) is in a direction opposite to the first direction.

[0039] In block 704, current sensor 206 measures the second phase current (I V ) and the third phase current (I W ). The second phase current (I V ) and the third phase current (I W ) is scaled 1:1 for summing. The second phase current (I V ) flows in the first direction and the third phase current (I W) is in a direction opposite to the first direction.

[0040] In block 706, current calculation circuitry 208 applies an inverse Clarke transform to signal 230 (the sum of the currents measured by current sensor 204) and signal 232 (the sum of the currents measured by current sensor 206). The inverse Clarke transform produces a first phase current (I U ), the second phase current (I V ) and the third phase current (I W ) as output.

[0041] In block 708, the first phase current (I U ), the second phase current (I V ) and the third phase current (I W ) to control the operation of a motor or other three-phase electrical load. For example, if one of the phase currents exceeds a threshold, the current provided to the operation of the motor may be reduced.

[0042] Modifications in the described embodiments are possible, and other embodiments are possible within the scope of the claims.

Claims

1. A current measuring circuit, include: a first current sensor coupled to the first conductor, the second conductor, and the third conductor; a second current sensor coupled to the second conductor and the third conductor, wherein 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; and a current calculation circuit system coupled to the first current sensor and the second current sensor and configured to: generating a measurement of the first phase current based on an output of the first current sensor and an output of the second current sensor; generating a measurement of the second phase current based on an output of the first current sensor and an output of the second current sensor; and generating a measurement of the third phase current based on an output of the first current sensor and an output of the second current sensor; Wherein the current calculation circuitry 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 and the output of the second current sensor. 2 . The current measurement circuit of claim 1 , wherein with respect to the first current sensor, current flows in the first conductor in a direction opposite to current flows in the second conductor and the third conductor. 3 . The current measurement circuit of claim 1 , wherein with respect to the second current sensor, current flows in the second conductor in an opposite direction relative to current flows in the third conductor. 4 . The current measurement circuit of claim 1 , wherein 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. 5 . The current measurement circuit of claim 4 , wherein the first conductor, the second conductor, and the third conductor are disposed at the same distance from a sensor element of the first current sensor. 6 . The current measurement circuit of claim 1 , wherein the second current sensor comprises a 1:1 turns ratio with respect to the second conductor and the third conductor.

7. The current measurement circuit of claim 1, comprising no more than two current sensors to measure currents in the first conductor, the second conductor, and the third conductor.

8. The current measuring circuit according to claim 1, in: The first current sensor includes a turns ratio of 1:1:1 with respect to the first conductor, the second conductor, and the third conductor; and The first current sensor includes a sensor element disposed at a first distance from the first conductor and at a second distance from the second conductor and the third conductor; The first distance is smaller than the second distance.

9. A current measuring circuit, include: a first conductor configured to conduct a first phase current among three-phase currents; a second conductor configured to conduct a second phase current of the three-phase current; a third conductor configured to conduct a third phase current of the three-phase current; a first current sensor coupled to the first conductor, the second conductor, and the third conductor; a second current sensor coupled to the second conductor and the third conductor, wherein the second current sensor is a Hall sensor or a fluxgate sensor; and A current calculation circuit system 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 the output of the first current sensor and the output of the second current sensor.

10. The current measurement circuit of claim 9, wherein the first current sensor is configured to provide a current flow in the first conductor that is opposite in direction relative to a current flow in the second conductor and the third conductor.

11. The current measurement circuit of claim 9, wherein the second current sensor is configured to provide a current flow in the second conductor that is opposite in direction relative to a current flow in the third conductor.

12. The current measurement circuit of claim 9, wherein 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.

13. The current measurement circuit of claim 12, wherein the first current sensor is configured to dispose the first conductor, the second conductor, and the third conductor at the same distance from a sensor element.

14. The current measurement circuit of claim 9, wherein the second current sensor is configured to provide a 1:1 turns ratio with respect to the second conductor and the third conductor.

15. The current measuring circuit according to claim 9, in: The first current sensor is configured to provide a turns ratio of 1:1:1 with respect to the first conductor, the second conductor, and the third conductor; A sensor element of the first current sensor is disposed at a first distance from the first conductor and at a second distance from the second conductor and the third conductor; and The first distance is smaller than the second distance.

16. A method for measuring electric current, wherein include: Measuring the sum of the first phase current, the second phase current and the third phase current of the three-phase current in the first current sensor; measuring the sum of the second phase current and the third phase current of the three-phase current in a second current sensor; and The first, second, and third phase currents are determined by current calculation circuitry 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. 17 . The method of claim 16 , further comprising measuring, in the first current sensor, the first phase current in a direction opposite to directions of the second phase current and the third phase current. 18 . The method of claim 16 , further comprising measuring the second phase current in the second current sensor in a direction opposite to a direction of the third phase current. 19 . The method of claim 16 , further comprising measuring the first phase current, the second phase current, and the third phase current in the first current sensor at a ratio of 2:1:1, respectively.

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