Abstract:
An electric vehicle battery arrangement includes a current sensor. The current sensor has a core and a magnetic field detector. An N-turn coil is wrapped around the core. A controller is configured to adjust an output of the detector indicative of current according to a comparison between a magnetic field caused by a given current in the coil as detected by the detector and a magnetic field expected to be caused by the given current in the coil.

Description:
TECHNICAL FIELD 
     The present invention relates to improving accuracy of a current sensor configured to sense current flowing between an electric vehicle battery and either a load or a source. 
     BACKGROUND 
     Battery electric vehicles (BEVs) may be caused to move by operation of an electric motor. Plug-in hybrid electric vehicles (PHEVs) and hybrid electric vehicles (HEVs) may be caused to move by operation of an electric motor and/or an internal combustion engine. The motor, in either case, may receive electrical power from an on-board battery. Here, the motor is a load to the battery as current flows from the battery to the motor, for example, via an inverter. For BEVs and PHEVs, the battery may be chargeable with electrical power from a utility grid via a charger. Here, the charger is a source to the battery as current flows from the charger to the battery. 
     The battery electronics may include a current sensor configured to measure the current flow. Amp hour integration accuracy is a primary metric for battery recharging and it is costly to get relatively excellent accuracy. An in-vehicle calibration with a precise current allows for a relatively much less expensive current sensor. 
     SUMMARY 
     An electric vehicle battery arrangement (or system) includes a current sensor having a core and a magnetic field detector, an N-turn coil wrapped around the core, and a controller. The controller is configured to adjust an output of the detector indicative of current according to a comparison between a magnetic field caused by a given current in the coil as detected by the detector and a magnetic field expected to be caused by the given current in the coil. 
     The arrangement may further include a conductor extending through a central opening of the core. In this case, the output of the detector is indicative of current on the conductor. 
     The conductor may extend between a battery and a switch. In this case, the switch is opened while the given current is in the coil, and the switch is closed and current is absent from the coil while current is on the conductor. 
     The coil may be wrapped around a leg of the core. 
     N may be greater than one. In this case, the magnetic field expected to be caused by the current in the coil is proportional to the product of the current in the coil and N. Also, in this case, the current in the coil causes N times greater magnetic field than that caused by the current with the coil being a one-turn coil such that the magnetic field expected to be caused by the current in the coil is N times greater than the magnetic field expected to be caused by the current in the coil with the coil being a one-turn coil. 
     A method includes providing a current sensor having a core and a magnetic field detector and a N-turn coil wrapped around the core. The method further includes adjusting an output of the detector indicative of current according to a comparison between a magnetic field caused by a given current in the coil as detected by the detector and a magnetic field expected to be caused by the given current in the coil. 
     An electric vehicle includes a battery, a switch, a current sensor having a core and a magnetic field detector, a conduction line extending between the battery and the switch and extending through a central opening of the core, an N-turn coil wrapped around the core, and a controller. The controller is configured to adjust an output of the detector indicative of current on the conduction line according to a comparison between a magnetic field caused by a given current in the coil as detected by the detector and a magnetic field expected to be caused by the given current in the coil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of a plug-in hybrid electric vehicle (PHEV); 
         FIG. 2  illustrates a block diagram of the battery electronics of an electric vehicle such as the PHEV; 
         FIG. 3  illustrates a block diagram of the battery electronics including a current sensor arrangement in accordance with an embodiment of the present invention; and 
         FIG. 4  illustrates a block diagram of the battery electronics including a current sensor arrangement in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring now to  FIG. 1 , a block diagram of a plug-in hybrid electric vehicle (PHEV)  10  is shown. PHEV  10  includes a high-voltage, direct current (DC) traction battery  12 , an electric motor  14 , an engine  16 , a transmission  18 , and wheels  20 . Motor  14 , engine  16 , and wheels  20  are mechanically connected with transmission  18  such that motor  14  and/or engine  16  may drive wheels  20  and such that wheels  20  may drive motor  14 . As such, battery  12  may provide energy to or receive energy from motor  14  via an inverter (not shown). Battery  14  may receive energy from a utility grid or other off-board energy source (not shown) via a (alternating current (AC)/DC)) charger  22 . 
     Referring now to  FIG. 2 , a block diagram of battery electronics  30  of an electric vehicle such as PHEV  10  is shown. Battery electronics  30  includes battery  12  and a current sensor  32 . Current sensor  32  is connected between battery  12  and load/source  34  when load/source  34  is connected to battery  12 . As such, current sensor  32  is configured to measure the current flowing from battery  12  to load/source  34  when load/source  34  is a load such as motor  14 . Likewise, current sensor  32  is configured to measure the current flowing to battery  12  from load/source  34  when load/source  34  is a source such as charger  22 . 
     Battery electronics  30  further includes a battery energy control module (BECM)  36 . BECM  36  is configured to power current sensor  32  to enable its operation. BECM  36  is further configured to read an output generated by current sensor  32  which is indicative of the current flowing between battery  12  and load/source  34 . 
     Referring now to  FIG. 3 , a block diagram of battery electronics  40  including a current sensor arrangement  42  in accordance with an embodiment of the present invention is shown. Battery electronics  40  further includes battery  12 , main contactors (MC+, MC−) (e.g., switches)  44   a ,  44   b , a conductor line  46   a  connected between battery  12  and MC+ contactor  44   a , and a conductor line  46   b  connected between battery  12  and MC− contactor  44   b . Battery  12  is connected to load/source  34  when MC+, MC− contactors  44   a ,  44   b  are closed. In this case, current may flow from/to battery  12  to/from load/source  34 . 
     Current sensor arrangement  42  includes a current sensor  48 . Current sensor  48  is configured to measure the current flow between battery  12  and load/source  34  when battery  12  and load/source  34  are connected. 
     Current sensor  48  includes a ferrite core  50  and a Hall-effect IC  52 . Current sensor  48  is positioned between battery  12  and MC+ contactor  44   a  with conductor line  46   a  extending through the center opening of core  50  of current sensor  48 . As such, core  50  of current sensor  48  extends around conductor line  46   a . Conductor line  46   a  thereby passes the battery (or source) current through the center of core  50  of current sensor  48  when battery  12  is connected to load/source  34 . That is, the same current flowing through battery  12 , MC+, MC− contactors  44   a ,  44   b , and load/source  34  also flows through the center of core  50  of current sensor  48 . This current creates a magnetic field in core  50  of current sensor  48  which is measured by Hall IC  52  of current sensor  48 . As such, in this case, the output of Hall IC  52  of current sensor  48  is indicative of the current flowing between battery  12  and load/source  34 . 
     Current sensor arrangement  42  further includes a BECM  54 . BECM  54  powers Hall IC  52  of current sensor  48  and reads the output value of Hall IC  52 . The output value of Hall IC  52  represents the magnetic field applied to Hall IC  52 , which is linearly proportional to the current through conductor line  46   a  that passes from battery  12  to MC+ contactor  44   a.    
     Again, the aggregate of ferrite core  50  and Hall IC  52  is current sensor  48  of current sensor arrangement  42 . The current of current sensor  48  is that which passes through the center of core  50  of current sensor  48 , namely the current between battery  12  and load/source  34  via closed MC+, MC− contactors  44   a ,  44   b.    
     A single point calibration can be performed on current sensor  48  to remove the zero offset. The zero offset is the same as the voltage output of Hall IC  52  at a time when the current through MC+ contactor  44   a  is zero (i.e., when MC+ contactor  44   a  is open). For instance, BECM  54  may measure the output voltage of Hall IC  52  of current sensor  48  when the vehicle is just starting up and MC+ contactor  44   a  is still open such that the current of current sensor  48  (and the MC+ current) is known to be zero. The output voltage of Hall IC  52  of current sensor  48  at this moment is referred to as the “zero offset.” Ever after, an opposite sign but same magnitude correction can be applied to current sensor  48  in order to “zero” current sensor  48 . 
     Current sensor arrangement  42  further includes a sensor coil interface  56  (e.g., a power supply). Sensor coil interface  56  may be a part of BECM  54  as shown in  FIG. 3 . Sensor coil interface  56  is configured to generate a relatively precise input current. In this regard, the magnitude of the input current is relatively low such that it is relatively easy for sensor coil interface  56  to generate the input current precisely. For instance, the input current is a direct current of 1.0 amps. 
     Current sensor arrangement  42  further includes an N-turn coil  58 . N-turn coil  58  is wrapped around a leg of core  50  of current sensor  48 . Sensor coil interface  56  forms a closed circuit with N-turn coil  58  and feeds the 1.0 amp input current into one of the two sides of N-turn coil  58 . Both sides of N-turn coil  58  are connected to sensor coil interface  56  as shown in  FIG. 3 . 
     The amount of N turns of N-turn coil  58  generates the amount of magnetic field applied to Hall IC  52  of current sensor  48  due to the 1.0 amp input current flowing through N-turn coil  58 . For instance, when N is 100 the magnetic field applied to Hall IC  52  is 100 times the magnetic field which would have been applied to Hall IC  52  with N being one. That is, when N is 100, Hall IC  52  reads 100 times the current in N-turn coil  58 . Therefore, for the 1.0 amp input current in N-turn coil  58 , Hall IC  52  reads a value on the order of 100 amps (although only 1.0 amps is actually flowing through N-turn coil  58 ). 
     Accordingly, with addition of sensor coil interface  56  and N-turn coil  58 , a second calibration can be added to current sensor  48 . In particular, at the time when the vehicle is being started and MC+ contactor  44   a  is open and current flow from/to battery  12  is zero, a two-step calibration can be performed. The first step, involving zero offsetting, includes BECM  54  measuring the output of Hall IC  52  while MC+ contactor  44   a  is open and sensor coil interface  56  is shut off (e.g., while sensor coil interface  56  is disconnected from N-turn coil  58 ). This is the zero-offset value for Hall IC  52  as there is zero magnetic field (no current). 
     The second step includes supplying a precise input current such as the 1.0 amp input current from sensor coil interface  56  to N-turn coil  58  while MC+ contactor  44   a  is still open. With the 1.0 amp input current flowing in N-turn coil  58 , and with the current flow from/to battery  12  being zero, BECM  54  measures the output of Hall IC  52 . The actual output of Hall IC  52  will be on the order of the ideal output of 100 amps (i.e., the ideal output is 1.0 amps*100 turns). The actual output of Hall IC  52  is zero-offset corrected from the first step. The correction factor to correct from the zero-offset corrected actual output to the ideal output of 100 A is called the “gain correction.” BECM  54  calculates the gain correction (gain correction=absolute magnitude of (ideal output/absolute magnitude of (actual output−zero offset)). BECM  54  stores the gain correction and the zero offset. BECM  54  uses the gain correction and the zero offset in correcting subsequent outputs of Hall IC  52  generated in response to current sensor  48  measuring current flow to/from battery  12  through conductor line  46   a.    
     As described, current sensor  48  can have a second calibration (also known as a gain calibration) which can be as accurate as accurate as the current can be measured through N-turn coil  58 . For example, the input current from sensor coil interface  56  may have a tolerance of 0.1% and therefore current sensor  48  can be just as accurate. This is an excellent accuracy for a current sensor at 100 amps. By changing the amount of N turns of N-turn coil  58  or by changing the amount of input current from sensor coil interface  56  to N-turn coil  58 , the equivalent of any current value can be obtained for current sensor  48 . For example, it may be desirable to gain-calibrate a PHEV current sensor at its maximum current such as 250 amps. 
     It is noted that in the embodiment of battery electronics  40  shown in  FIG. 3 , current sensor  48  is positioned between battery  12  and MC+ contactor  44   a  as current sensor  48  is on the left hand-side of MC+ contactor  44   a . In a variation, current sensor  48  is positioned between MC+ contactor  44   a  and load/source  34  such that current sensor  48  is on the right-hand side of MC+ contactor  44   a . In this event, sensor coil interface  56  is configured to provide the precise input current to N-turn coil  58  when MC+ contactor  44   a  is open in the manner described above. Alternatively, load/source  34  is configured to provide (or draw) the precise input current to N-turn coil  58  when MC+ contactor  44   a  is open in order to perform the second calibration step. The conductor line from load/source  34  which passes through core  50  of current sensor  48  has zero current as load/source  34  is disconnected from this conductor line during the second calibration step. The first calibration step may be performed in similar manner as described above. 
     Referring now to  FIG. 4 , with continual reference to  FIG. 3 , a block diagram of battery electronics  60  including a current sensor arrangement  62  in accordance with another embodiment of the present invention is shown. Battery electronics  60  is similar to battery electronics  40  and like components include like reference numbers. 
     Current sensor arrangement  62  includes current sensor  48 , BECM  54 , and N-turn coil  58  like current sensor arrangement  42  of battery electronics  40 . Current sensor arrangement  62  is different in that current sensor arrangement  62  includes a sensor coil interface  64  variation instead of sensor coil interface  56 . 
     Sensor coil interface  64  may be part of BECM  54  as shown in  FIG. 4 . Sensor coil interface  64  includes a microprocessor  66 . Processor  66  includes a first A/D 1  input  68   a  and a second A/D 2  input  68   b . Sensor coil interface  64  includes a precision voltage reference supply  69  (e.g., 5.0 volts), which is measured by second A/D 2  input  68   b . This relatively precise 5.0 DC voltage is fed into one of the two sides of N-turn coil  58 . The two sides of N-turn coil  58  are connected to A/D 1  input  68   a  and A/D 2  input  68   b , respectively. The side of N-turn coil  58  connected to first A/D 1  input  68   a  is also connected to a sense resistor  70  of sensor coil interface  64 , as shown in  FIG. 4 . Sense resistor  70  sets the coil current in conjunction with voltage reference supply  69  and the resistance of N-turn coil  58 . Sense resistor  70  is a precision resistor with, for instance, a 0.1% tolerance. 
     As described, BECM  54  includes processor  66  which contains first A/D 1  input  68   a  and second A/D 2  input  68   b . Second A/D 2  input  68   b  reads the value of voltage reference supply  69 . First A/D 1  input  68   a  reads voltage V sns , which is across sense resistor  70 . Since sense resistor  70  is a precise and known value of ohmic resistance, then Ohm&#39;s Law (R*I=V) can be applied to calculate the exact current flowing through N-turn coil  58 . For instance, with the proper ohmic value for sense resistor  70 , the coil current is 1.0 amps. The precise value of this coil current can be measured by first A/D 1  input  68   a.    
     Again, at the time when the vehicle is being started and MC+ contactor  44   a  is open and the battery current is zero, the two-step calibration can be performed. The first step is to measure the output of Hall IC  52  with MC+ contactor  44   a  open and voltage reference supply  69  turned off (i.e., set to zero volts). This is the zero-offset value for Hall IC  52  as there will be zero magnetic field (no current through conductor line  46   a  passing through core  50  of current sensor  48 ). 
     With MC+ contactor  52  still open, the second step commences by applying the 5.0 volts to the output of voltage reference supply  69 . This causes an input current on the order of 1.0 amps to flow in N-turn coil  58 . The exact supply voltage is read by second A/D 2  input  68   b  and the exact coil current is measured by first A/D 1  input  68   a . With this current flowing in N-turn coil  58 , BECM  54  measures the output of Hall IC  52 . The actual output of Hall IC  52  will be on the order of the ideal output of 100 A (1.0 A*100 turns). The output of Hall IC  52  is zero-offset corrected from the first step. The correction factor to correct from the actual output to the ideal output of 100 A is the gain correction. 
     As indicated above, current sensor  48  now has a second calibration (i.e., the gain calibration) which can be as accurate as accurate as the current can be measured through N-turn coil  58 , which is about 0.1% with sense resistor  70  having 0.1% tolerance. This is an excellent accuracy for a current sensor at 100 A. Again, by simply changing the amount N turns of N-turn coil  58 , or by changing the amount of current by changing voltage reference supply  69 , or by changing the resistance of sense resistor  70 , the equivalent of any current value desired for the current sensor can be obtained. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the present invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the present invention.