GB2513866A

GB2513866A - Current transducer

Info

Publication number: GB2513866A
Application number: GB201308179A
Authority: GB
Inventors: Ken Thompson
Original assignee: Sevcon Ltd
Current assignee: Sevcon Ltd
Priority date: 2013-05-07
Filing date: 2013-05-07
Publication date: 2014-11-12
Also published as: GB201308179D0

Abstract

A current transducer 8 comprising hall effect sensors 28a-e configured to sense a combined magnetic field arising from currents flowing in conductors 22a-d. The magnetic field arising from each conductor is sensed by hall effect sensors nearest each conductor. In operation, when currents flow in the conductors the hall effect sensors at either end of the hall effect sensor array sense a field based on the nearest conductor, those in the middle of the array sense a combined magnetic field arising from the two nearest conductors, each sensor outputs a voltage signal to a current determiner 12. The magnetic fields from current carrying conductors combine constructively or destructively in dependence on the phase offset between the consecutive currents. The current determiner can therefore derive the current flowing in any of the conductors based on the current flowing in one of the conductors and the combined signals from the rest. The current transducer can further comprise a memory configured to store known current data in relation to at least one of the currents. The current transducer can be used to determine currents flowing in a two, three or four phase electric motor, or a multi phase electric motor.

Description

Current Transducer The present disclosure relates to measuring electric current, and more particularly to methods and apparatus for measuring each of a plurality of currents associated with an inverter for a multiphase electric motor.

There is a drive in the motor vehicle industry towards miniaturisation of motor vehicle components to meet environmental, performance, and aesthetic demands by saving space.

An AC induction motor for a motor vehicle requires an inverter for converting a DC battery current into a multiphase AC power supply. It is important to monitor the phases of the multiphase current to enable control of motor performance because, for example, unbalanced phases have negative performance implications.

To measure each phase component of a multiphase current carried in a plurality of current-carrying conductors, it has been proposed to provide each current-carrying conductor with a magnetic field sensor to provide a voltage based on the sensed field, from which the current in the conductor may be determined. A problem is that hall effect sensors are liable to sense stray and unwanted magnetic fields, and this limits how closely spaced they may be if sensor readings are to be reliable. Embodiments of the disclosure may reduce the size of a current monitoring apparatus without unduly compromising the reliability of current measurements.

Accordingly the present disclosure addresses the problem of measuring each of a plurality of currents within a confined area. For example, the disclosure provides a current transducer having a hall effect sensor is configured to sense a combined magnetic field arising from a first current and a second current and a current determiner coupled to receive a first signal from the first hall effect sensor based on the combined magnetic field, and to determine the first current based on the first signal and a second signal based on the second current.

Aspects and examples of the invention are set out in the claims and aim to provide an improved current measuring apparatus.

In a first aspect, there is provided a current transducer comprising: a hall effect sensor configured to sense a combined magnetic field arising from a first current and a second current; and a current determiner coupled to receive a first signal from the first hall effect sensor based on the combined magnetic field, and to determine the first current based on the first signal and a second signal based on the second current. By utilising a sensor signal based on a combined magnetic field arising from a first current and a second current, conductors carrying the first and second currents respectively may both be placed in close proximity to the same hall effect sensor without compromising the utility of the hall effect sensor signal.

This provides a space saving advantage.

In an embodiment, there is provided a current transducer comprising a second hall effect sensor configured to provide the second signal based on sensing a magnetic field produced by the second current.

In an embodiment, there is provided a current transducer, wherein the current determiner is configured additively combine the first signal and the second sensor signal to determine the first current.

In an embodiment, there is provided a current transducer, wherein the current determiner is configured to obtain a phase difference between the first current and the second current and determine the amplitude of the first current based on the first sensor signal, the second sensor signal and the phase difference.

In an embodiment, there is provided a current transducer, wherein obtaining the phase difference comprises determining the phase difference based on the first sensor signal and the second sensor signal.

In an embodiment, there is provided a current transducer, wherein obtaining the phase difference comprises receiving a signal based on a selected phase difference value. This allows known phase difference data to be used in place of sensor data, which may enable the provision of fewer sensors than would otherwise be required.

In an embodiment, there is provided a current transducer, wherein the sensors are spaced apart so that a conductor carrying the second current can pass through a space between the first sensor and the second sensor.

In an embodiment, there is provided a current transducer comprising a body arranged to carry the magnetic field arising from the second current to enable it to be sensed by the first sensor and the second sensor.

In an embodiment, there is provided a current transducer, comprising a body arranged to carry the magnetic field arising from the first current to enable it to be sensed by the first sensor, optionally wherein the sensors are arranged on a substrate, and the body comprises a first body on one side of the substrate and a second body on the other side of the substrate.

In an embodiment, there is provided a current transducer comprising a plurality of magnetic field sensors of which at least one is configured to sense a combined magnetic field based on the magnetic fields of two of a plurality of currents, and the current transducer is configured to enable one of said currents to be determined from the combined magnetic field. This allows a single magnetic field sensoi to be placed in close proximity to two current canying conductors.

In a second aspect, there is provided a method of determining a phase component of a multiphase current, the method comprising: obtaining, from a first hall effect sensor, a first signal based on a combined magnetic field arising from a fiist phase component current of the multiphase current and a second cuiient; obtaining a second signal based on the second current; and determining the first phase component current based on the first signal and the second signal.

In an embodiment, there is provided a method, wherein obtaining the second signal comprises obtaining a signal based on the second current from a second hall effect sensor.

In an embodiment, there is provided a method! comprising additively combining the first signal and the second signal to determine the fiist phase component current.

In an embodiment, there is provided a method in which the second curient is a DC current.

In an embodiment, there is provided a method in which the second current is a second phase component current of the multiphase current.

In an embodiment, there is provided a method, comprising obtaining a phase difference between the first phase component current and the second phase component current to determine the first phase component current based on the first signal, the second signal and the phase difference.

In an embodiment, there is piovided a method, wherein obtaining the phase difference complises determining the phase difference based on the first signal and the second signal.

In an embodiment, there is piovided a method, wherein obtaining the phase difference complises leceiving a first signal based on a selected phase difference value.

In an embodiment, there is provided a current transducer configured to operate according to a method described herein.

In a third aspect, there is provided an inverter for converting a DC current input to a three-phase AC output input for an electric motor, the inverter comprising: DC couplings to receive to a DC battery current input; AC coupling to provide a three-phase AC current output; and a current transducer as described herein to monitor the each of the phase component currents through the AC couplings and at least one of the currents through the DC coupling.

Examples of the disclosure enable the measurement of each of a plurality of currents, and in particular a plurality of currents associated with an inverter for an electric motor, using a plurality of hall effect sensors arranged to couple to magnetic fields arising from the plurality of currents, such that the each of the currents may be measured using a current measuring apparatus which is more spatially compact than known current measurement apparatus.

The disclosure provides a current transducer having a body arranged to couple to magnetic fields of each of a plurality of currents, and a plurality of hall effect sensors coupled together by the body such that a magnetic field strength sensed by at least one of the hall effect sensors is based on the respective magnetic fields of two of said current-carrying conductors. The sensing of two magnetic fields per hall effect sensor is technically significant because it permits a more compact arrangement of measurement apparatus for a given number of currents than in known apparatus.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure la schematically illustrates a current transducer arranged to determine a plurality of currents associated with an inverter for a battery-powered electric motor; Figure ibis a schematic isometric view of the current transducer of Figure la; and Figure 2 is a schematic exploded cross section along the line A-A of the current transducer of Figure lb. To place the disclosure in context, Figure la shows a system i. comprising a battery 2, an inverter 4 and a multiphase motor 6, in which a current transducer 8 is arranged to monitor and determine currents associated with the inverter 4. The system 1 could be, for example, a drive system for a motor vehicle engine.

The inverter 4 is arranged to receive a DC from the battery 2, to convert the DC current to a multiphase current useable by the multiphase motor 6, and to output the multiphase current to the multiphase motor 6. Conductor 22b couples the DC current battery to the inverter 4, and conductors 22a, 22c and 22d couple the multiphase output of the inverter 4 to the multiphase motor 6. A current transducer 8 (indicated by the phantom line), comprises hall effect sensors 28, first and second bodies 24, 26 (see Figure ib) and a current determiner 12. The first and second bodies 24, 26 have a magnetic permeability greater than unity and are arranged to carry the magnetic fields arising from the currents in the conductors 22 to allow the fields to be sensed by the hail effect sensors 28. The hall effect sensors 28 are arranged to sense magnetic fields arising from the input and output currents of the inverter 6 and to provide indications of the sensed magnetic fields to the current determiner 12. The current determiner 12 is configured to determine one or more of the inverter currents based on the indications of the sensed magnetic fields. The inverter 4 and the conductors 22 and the current transducer 8 are provided on a printed circuit board (pcb) 30.

The multiphase motor 6 is a three-phase electric motor and each of the three conductors 22b, 22c and 22d carrying the output of the inverter carries a phase component of the three-phase cuirent.

The hall effect sensors 28 are each configured to sense a magnetic field and to output a voltage based on the strength of the sensed magnetic field. The first and second bodies 24, 26 which carry the magnetic fields to allow them to be sensed by the hall effect sensors 28 are described in relation to Figure lb and Figure 2.

The current determiner 12 is configured to additively combine the voltage signals from the hall effect sensors 28 to determine the currents carried in the conductors 22. In the present example, the current determiner 12 is provided by laminations on the substrate but it will be appreciated that the current determiner could equally be embodied in other forms of hardware, software or firmware or any combination thereot.

In operation, the battery supplies a DC current, via conductor 22a, to the inverter 4. The inverter 4 converts the DC current to a multiphase current and provides the multiphase current, via conductors 22b, 22c and 22d, to the multiphase motor 6 to cause the motor 6 to run. Each of the hall effect sensors 28 senses a magnetic field based on the current in nearest conductor or conductors 22 and outputs a voltage signal based on the sensed field to the current determiner 12. The current determiner 12 additively combines the voltage signals to determine one or more of the currents.

Figure lb shows a portion of the pcb 30 carrying the conductors 22, the inverter 4 and the current transducer 8.

The conductors 22 are spaced apart on the pcb 30 to form a regular linear conductor array.

Conductor 22a at a first end of the conductor array carries a DC input current to the inverter.

Conductors 22b, 22c and 22d each carry a phase component of the multiphase current from the inverter 4.

The hall effect sensors 28 are spaced apart on the pcb 30 to form a regular linear sensor array. The sensor array is coaxial with the conductor array such that each conductor 22 passes through a space between two consecutive hall effect sensors 28. Thus, hall effect sensors 28 at the ends of the sensor array are each adjacent a single conductor, i.e. they each have a single nearest conductor, and intermediate hall effect sensors 28 are each adjacent two conductors, that is they each have two nearest conductors 22. For example, the single nearest conductor 22 to end sensor 28a is conductor 22a and the nearest conductors 22 to hall effect sensor 28b are conductors 22a and 22b. Having regular linear arrays with regular spacings between adjacent hall effect sensors 28 and conductors 22 avoids or reduces a need for a calibration procedure when interpreting the signals 60 received trom the hall effect sensors 28.

The first body 24 is seated on the hall effect sensors 28 on a first side of the pcb 30 and the second body 26 is arranged in alignment with the first body 24 on a second side of the pcb 30. The first body 24 has gaps which are arranged to bridge respective conductors 22 so that each conductor 22 is received through a gap, one conductor 22 per gap. In bridging the gap, the first body 24 bridges the gaps to couple together the hall effect sensors 28.

Figure 2, which illustrates a schematic cross section through the line A-A in Figure ib, shows how the first and second bodies 24, 26 in use carry complete circuits of magnetic flux from the magnetic fields of each current-carrying conductor 22 to be coupled to the hall effect sensors 28 nearest each conductor 22. In this way, the magnetic field arising from each conductor 22 is sensed by the two hall effect sensors 28 nearest the conductor 22. So, for example, flux circuit 40a representing the magnetic field arising from the current in conductor 22a is sensed by hall effect sensors 28a and 28b.

In operation, when currents flow in the conductors, the hall effect sensors 28 at either end of the sensor array 28a, 28e sense a field based on the nearest conductor and outputs a voltage signal to the current determiner 12 based on the strength of the sensed field. Each of the intermediate hall effect sensors, 28b, 28c, 28d senses a combined magnetic field arising from the two conductors 22 nearest the hail effect sensor 28 and outputs a voltage signal to the current determiner 12 based on the strength of the sensed combined field. For example, sensor 28b senses a combined magnetic field based on the currents in the conductors 22a and 22b and outputs a voltage signal 60b based on the combined field.

Sensing a combined field arising from a first current and a second current comprises sensing a magnetic field predominantly based on a first magnetic field arising from the first current and a second magnetic field arising from the second current. The arrangement of the conductois 22, the hall effect sensors 28 and the body 24, 26 is such that the effect on a magnetic field sensed by a given hall effect sensor 28 from other magnetic fields, for example magnetic fields of current-carrying conductors not adjacent, or nearest, to the given hall effect sensor 28, are small or negligible compared to the effect of the magnetic field arising from the nearest current (for an end-of-array sensor 28) or nearest currents (for an intermediate sensor 28).

The magnetic fields arising from consecutive current-carrying conductors 22 combine constructively or destructively in dependence on the phase offset between the consecutive currents. Sensing a combined magnetic field arising from a first current and a second current therefore comprises sensing a magnetic field based on the sum or the difference of a first magnetic field arising from the first current and a second magnetic field arising from the second current. Sensing a magnetic field includes sensing the amplitude of the magnetic field. Sensing the combined magnetic field may include sensing the phase offset. Alternatively the phase offset may be known.

In the illustrated example, the first hall effect sensor 28a outputs a first signal 60a based on the current in the first conductor 22a. The second hall effect sensor 28b provides a second voltage signal 60b based on the combined magnetic fields of first current-carrying conductor 22a and the second current-carrying conductor 22b. The third hall effect sensor 28c provides a third voltage signal 60c based on the combined magnetic fields of the second current-carrying conductor 22b and the third current-carrying conductor 22c, and so on.

The current determiner 12 is configured to derive the current in the first conductor 22a based on the first voltage signal 60a. The current determiner is configured to additively combine the first and second signals 60a, 60b and, based on the combined signal and the determined first current, to determine the second current. Based on combining the second and third signals having determined the second current, the current transducer 12 determines the third current, and so on. In this way, the determination of one current in the array enables a next current in the array to be determined. Thus, by knowing a current in one of the conductors, a current in any of the other conductors may be determined.

Determining a current comprises determining an amplitude of the current. Additionally or alternatively, determine a current comprises determining a phase of the current. Determining a phase of the current in one conductor may comprises determining a phase difference with respect to the current in a consecutive conductor. Optionally, determining a current comprises determining a full waveform for the current.

In an embodiment of the invention, the current transducer 8 further comprises a memory coupled to the current transducer 12, in which the programmable memory is configured to store known current data in relation to at least one of the currents. For example, when the DC current is known, the memory could be programmed to hold current data in ielation to the conductor 22a which carries the DC current. The current determiner 12 is configured to use the known current data in place of one of the hall effect sensor signals to determine the current in a next conductor 22 of the conductor array. It will be appreciated that when at least one of the currents in the array is known, one less hall effect sensor 28 need be provided.

The data related to the current could comprise the current amplitude and/or phase and may comprise a full waveform of the current. The data could relate to the DC current and/or one or more of the multiphase component currents.

While the exemplary embodiment described a three-phase electric motor, it will be appreciated that a current transducer according to embodiments of the invention may be provided to monitor and/or determine currents associated with a two-phase, four-phase or any other multiphase electric motor 4. One or two components of a DC current could also be monitored, but it will be appreciated that the DC current need not be monitored.

It will moreover be appreciated that while the exemplary current transducer is described as a current transducer for measuring a plurality of currents associated with an inverter for an electric motor, current transducers according to the invention may be used to monitor and/or determine a plurality of currents in any suitable application.

Preferably the pcb is non-conductive to reduce its interaction with the magnetic fields arising fiom the current cairying conductois 22. Although a printed cilcuit board is desciibed, it will be appreciated that any appropriate substrate could be provided.

While the embodiment of Figure 2 shows Hall Effect sensois 28, in the context of the present disclosure, those skilled in the art will appreciate that the sensors could comprise any magnetic field sensor havin9 circuitry configured to output a voltage based on a sensed

magnetic field.

In the illustrated example, five hall effect sensors 28 are provided for the four conductors 22.

In general, for an array of n conductors 22, n+1 hall effect sensois 28 may be provided.

While the hall effect sensors 28 are described as forming a regular linear array on one side of a substrate 30, it will be appreciated that the sensors 28 could be provided on different sides of the substrate 30 and/or at irregular inteivals along the substrate. Each sensor could indeed be provided on its own substrate, with the lespective substrates coupled togethei by one of both of the bodies 24, 26. The array could be non-linear, including circular or arcuate.

Preferably, in the case that the sensors 28 and conductors 22 do not form a regular array, the current determiner 12 would be configuied to perform a suitable calibration procedure to account for the effect of spatial asymmetries on the sensor signals 60.While in the disclosed embodiment at least one hall effect sensor 28 is arranged to sense a combined magnetic based on a magnetic field arising from a first current and a magnetic field arising from a second current, it will be appreciated that in other examples, at least one hall effect sensor may be arranged to sense a combined magnetic field based arising from three currents, and that the sensed field may be used to determine one of the currents when the other two are known or determined.

The bodies 24, 26 could instead provide a single body, or could comprise a plurality of separate body portions arranged to carry magnetic fields arising from each of the current carlying conductors to enable the fields to be sensed by the hall effect sensors 28 as described in relation to Figure 2. The bodies, 24, 26 could comprise a ferrous or ferrite material or any material a magnetic permeability greater than 1. The first and second bodies 24, 26 could comprise different materials with different magnetic permeabilities, in which case pieferably the cuiient deteiminer 12 would be configured to perfoim a suitable calibration procedure to account tor the effect of spatial asymmetries on the sensor signals 60.

While the bodies 24, 26 are described as carrying the magnetic field from each current carrying conductor to allow the field to be sensed by hall effect sensors between which the conductor passes, it will be appreciated that carrying may comprise any or all of guiding, focusing and directing. It will be appreciated that the magnetic field of each current carrying conductor is carried so as to be sensed primary only by whichever two hall effect sensors 28 the current passes between, and substantially not sensed by any of the other hall effect sensors 28.

In examples, the current determiner 12 comprises memory for storing data related to known currents and/or memory for storing data related to determined currents. The memory may be volatile or non-volatile. In an example, volatile memory is provided for storing determined currents based on sensor data so that data related to a given measurement may be replaced by data related to a new measurement, and non-volatile memory is provided for storing known current data so that it may be kept for comparison with updated sensor data. The current determiner 12 may comprise a processor implemented in hardware, software, firmware or any combination thereof.

In examples, the current transducer 8 forms part of a motor controller to control operation of the electric motor 6, wherein determined currents may be used to monitor and/or control operational parameters of the motor 6. A user interface could be provided to receive input data related to known currents and/or operational parameters of the inverter 4 and/or multiphase motor 6.. The user interface could comprise a display for displaying determined current data.

Claims

CLAIMS1. A current transducer comprising: a hall effect sensor configured to sense a combined magnetic field arising from a first current and a second current; and a current determiner coupled to receive a first signal from the first hall effect sensor based on the combined magnetic field, and to determine the first current based on the first signal and a second signal based on the second current.
2. The current transducer of claim 1, comprising a second hall effect sensor configured to provide the second signal based on sensing a magnetic field produced by the second current.
3. The current transducer of claim 1 or 2, wherein the current determiner is configured additively combine the first signal and the second sensor signal to determine the first current.
4. The current transducer of claim 1 or 2, wherein the current determiner is configured to: obtain a phase difference between the first current and the second current; and determine the amplitude of the first current based on the first sensor signal, the second sensor signal and the phase difference.
5. The current transducer of claim 4, wherein obtaining the phase difference comprises determining the phase difference based on the first sensor signal and the second sensor signal.
6. The current transducer of claim 4, wherein obtaining the phase difference comprises receiving a signal based on a selected phase difference value.
7. The current transducer of any of claims 2 to 6, wherein the sensors are spaced apart so that a conductor carrying the second current can pass through a space between the first sensor and the second sensor.
8. The current transducer of claim 7, comprising a body arranged to carry the magnetic field arising from the second current to enable it to be sensed by the first sensor and the second sensor.
9. The current transducer of claim 7 or 8, comprising a body arranged to carry the magnetic field arising from the first current to enable it to be sensed by the first sensor.
10. The current transducer of claim 8 or 9, wherein the sensors are arranged on a substrate, and the body comprises a first body on one side of the substrate and a second body on the other side of the substrate.
11. A method of determining a phase component of a multiphase current, the method comprising obtaining, from a first hall effect sensor, a first signal based on a combined magnetic field arising from a first phase component current of the multiphase current and a second current; obtaining a second signal based on the second current; and determining the first phase component current based on the first signal and the second signal.
12. The method of claim 11, wherein obtaining the second signal comprises obtaining a signal based on the second current from a second hall effect sensor.
13. The method of claim 11 or 12, comprising additively combining the first signal and the second signal to determine the first phase component current.
14. The method of any of claims 11 to 13, in which the second current is a DC current.
15. The method of any of claims 11 to 13, in which the second current is a second phase component current of the multiphase current.
16. The method of claim 15, comprising obtaining a phase difference between the first phase component current and the second phase component current to determine the first phase component current based on the first signal, the second signal and the phase difference.
17. The method of claim 16, wherein obtaining the phase difference comprises determining the phase difference based on the first signal and the second signal.
18. The method of claim 16, wherein obtaining the phase difference comprises receiving a first signal based on a selected phase difference value.
19. A current transducer configured to operate according to the method of any of claims 11 to 18.
20. An inverter for converting a DC current input to a three-phase AC output input for an electric motor, the inverter comprising: DC couplings to receive to a DC battery current input; AC coupling to provide a three-phase AC current output; and the current transducer of any of claims 11 to 19 to monitor the each of the phase component currents through the AC couplings and at least one of the currents through the DC coupling.
21. A motor vehicle comprising the inverter of claim 20.
22. A current transducer substantially as described herein with reference to the accompanying figures.
23. A computer-readable medium carrying computer-readable instructions for executing the method of any of claims 11 to 19.
24. A method of measuring each of a plurality of currents substantially as described herein with reference to the accompanying figures.