FR2974912A1 - METHOD AND DEVICE FOR CALIBRATING AMPEREMETERS OF A MULTI-MOTOR DRIVE SYSTEM - Google Patents

Abstract

Apparatus and method for calibrating phase current ammeters of a drive system having a plurality of electromotive units (2R, 2L), each having a polyphase motor (4R, 4L) fed by a common line (6). The ammeters (9) measure the current in a phase conductor (8) of the respective motor (4R, 4L), and balance the first and second drive units (2R, 2L) relative to one another using As a reference measuring installation, a motor current ammeter (10) is switched both in the current path of the first power unit (2R) and in the current path of the second power unit (2L).

Description

FIELD OF THE INVENTION The present invention relates to a method and a device for calibrating phase current ammeters of a drive system equipped with several electromotive drive units and in particular the control systems. drive wheel drive each driven by an individual drive unit. The invention also relates to the predefinition of a motor torque by adjusting the motor current and in particular means for balancing the motor units to provide the same motor currents. STATE OF THE ART Electric vehicles are equipped with drive systems in which each drive wheel is driven by a motor of its own. For stable and safe running, such drive systems require that the individual motors can be precisely controlled to provide a given torque. In particular, in the case of the driving wheel motors on the left and right sides of a vehicle, it is important to adjust the engine torque exactly because engines are not safe anymore. 20 tie. Electronically commutated electrical machines are controlled by a pilot circuit which converts the DC voltage into an AC voltage to create the rotating electric field of the electric machine. Torque control in such electrical machines is by field-oriented control which relies, among other things, on the measurement of the phase currents in the phase conductors and the overall current supplying the motor. The torque supplied by the motor is not only influenced by the motor power current, exactly predefined, but also by the type of construction and the individual tolerances of the motor. Intensity measurements (current measurement) of phase currents or motor currents are generally made using ammeters which are assigned tolerances related to their manufacture. To compensate for the tolerances of the ammeters, it is known to provide a calibration at the end of the manufacturing process of calibrating the various ammeters.

2 meters at the end of the manufacture of the power unit. Alternatively, extremely precise components can be used to measure the current, especially the measuring resistors, but their manufacture is expensive. The two means thus envisaged do not however make it possible to compensate for the tolerances of the ammeters related to the aging of the components. The phase currents and the motor current are generally adjusted by means of a current regulation which imposes a predefined setpoint current in the different phase conductors. If the current measurements (intensity measurements) are tainted with tolerances, the actual phase current may differ from the measured phase current and thus the current regulation sets a phase current different from the desired phase current and thus the supplied torque by the engine differs from the requested torque.

OBJECT OF THE INVENTION The object of the present invention is to develop means making it possible to guarantee that several motor units of an electric motor drive system provide the same motor torque or make it possible to avoid that, because of the tolerances of the different ammeters , deviations occur in the phase currents set between the different motors. SUMMARY OF THE INVENTION AND ADVANTAGES OF THE INVENTION To this end, the subject of the invention is a method for calibrating the ammeters of phase current of a drive system comprising a plurality of electromotive units, the motor units having each a polyphase motor supplied with electrical energy by a common supply line, - the phase current ammeters measuring the phase current in a phase conductor of the respective motor, - the phase current ammeters balancing a first and a second unit driving motor relative to each other using as a reference measuring installation an ammeter of motor current which can be switched in the current path of the first power unit and in the current path of the second power unit.

The subject of the invention is also a device for calibrating phase current ammeters of a drive system comprising a plurality of electromotive units; the motor units each having a polyphase motor powered by a common line; phase current ammeters measuring a phase current in a phase conductor of the respective motor, - the device calibrating the phase current ammeters of the first and second driving units with respect to each other using as reference a switchable motor current ammeter in the current path of the first drive unit and in the current path of the second drive unit. Finally, the subject of the invention is a computer program product with a program code which, executed by a data processing unit, applies the method as defined above. In other words, the subject of the invention is a method for calibrating the phase current ammeters of a driving system with a plurality of electromotive drive units each having a polyphase motor, this unit being powered by electrical energy through a common power line. The ammeters measure the phase current in the phase conductor of each of the motors. The phase current ammeters of a first and a second drive unit are balanced or calibrated against each other using a motor current ammeter which can switch at a time as a reference. in the current path of the first drive unit and that of the second drive unit. The basis of the method according to the invention applies to a motor drive system each equipped with a phase current ammeter and, with an ammeter of motor current, to measure the current in each of the units. drive (or motor units) and calibrate or balance all ampere-meters of phase current to measure the phase current of the different drive units, relative to each other. For this, the motor current ammeter measures the current in each

4 drives and serves as a reference ammeter to calibrate against each other, the ammeters of phase current associated with the various motors. The method developed above performs calibration or relative balancing of the phase current ammeters with respect to each other using the motor current ammeter. With the aid of this motor current ammeter, it is possible to calibrate the phase current ammeters with respect to each other so that the same phase currents in the phase conductors of the motors correspond to indications of identical currents. This ensures that a torque control based on a con-sign magnitude of the motor current for the drive unit thus sets identical torques. In order to achieve an absolute high accuracy of the current measurement, it is necessary to use only as the motor current ammeter measuring the total motor current in the various motors, a calibrated ammeter for accurately measuring the intensities. The process developed above makes it possible to use ammeters of less precision for phase current ammeters. According to one development, the method is characterized by the following steps: - calibrating the phase current ammeters of the first motive unit, by successively switching current paths not derived by the phase conductors of a motor of the first power unit, calibrating the phase current ammeters in the non-derived current paths by corrective terms to correct the phase current indication provided by the respective phase current ammeter, calibrate the motor current ammeter by giving it a corrective term to correct the indication of the motor current supplied by this ammeter, calibrate the phase current ammeters of the second motor unit, by successively switching the current paths not derived from the engine of the second power unit. According to a development, the motor current ammeter installed in the common power line is calibrated while a non-derivative current path is switched only by the phase conductors of the motor of the first power unit so that the current in the phase conductors corresponds to the current flowing in the motor current ammeter. According to another characteristic of the method, before calibrating the phase current ammeters, the correction terms associated with the phase current ammeters are determined so that the corrected phase current indications correspond to the indication. calibrated motor current. In particular, the phase current ammeters of the non-derivative current paths are calibrated by associating the correction terms so that the corrected phase current indications correspond. According to another development, the subject of the invention is a drive system with a plurality of electromotive drive units each having a polyphase motor, the unit being supplied with electrical energy by a common power supply line, and this system of electromotive drive. The drive is equipped with a phase current amperage calibration device as defined above, the phase current ammeters being installed in each phase lead of the respective motor. Drawings The present invention will hereinafter be described in more detail using a method and apparatus for calibrating phase current ammeters of a drive unit electromotor drive system. equipped with polyphase motors shown in the accompanying drawings in which:

FIG. 1 is a diagram of a drive system with two drive units supplied with electrical energy by a common power source; FIG. 2 is a flow chart explaining the application of the relative calibration method; ammeters fitted to the drive units. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 shows the diagram of a drive system 1 with two drive units 2R, 2L which supply electrical energy to a respective pilot circuit 3R, 3L and a motor 4R. 4L connected to its pilot circuit 3R, 3L. The 4R, 4L motors drive, for example, the drive wheel on the right side and the drive wheel on the left side (not shown) of a vehicle. The motor 4R, 4L is for example a polyphase motor with electronic commutation with several phase conductors connected by phase terminals. The motors 4R, 4L have a stator winding whose different phase conductors are for example connected in star or in triangle. Each pilot circuit 3R, 3L comprises several inverters such as those of an H bridge or a B6 bridge. The inverters each have a series connection formed of two separately controlled semiconductor switches 5; the number of in-pouring circuits of each pilot circuit 3R, 3L corresponds to the number of phase conductors of the motor 4R, 4L. Semiconductor switches 5 may be, for example, power semiconductors such as thyristors, IGBTs, IGCTs, power MOSFETs or such components. Each of the phase connections of the motors 4R, 4L of the power units 2R, 2L is connected by a phase conductor 8 to a node UR, VR, WR, UL, VL, WL of a series circuit of the pilot circuit 3R, 3L. . The nodes UR, VR, WR, UL, VL, WL are located between the two semiconductor switches 5 of the inverter circuit associated with the phase line. The series arrangements of the semiconductor switches 5 connect the high potential VH to the low potential VL supplied to the drive system 1 via feed lines 6.

The supply lines 6, that is to say those of the high potential VH and those of the low potential VL, are connected by an intermediate circuit capacitor 7 to smooth the current ripples in the supply lines 6, produced by the operation of the 4R, 4L motors. The phase conductors 8 connecting the nodes UR, VR, WR, UL, VL, WL of the series circuits of the pilot circuits 3R, 3L to the corresponding phase connection of the motor 4R, 4L, are equipped with current ammeters of phase 9 ( phase current measurement installation) for measuring the intensities IRU, IRV, IRW, ILU, ILV, ILW of the currents flowing in the phase conductor 8 and provide a phase current indication. A motor current ammeter 10 (current measurement installation in the motor), equips one of the supply lines 6 to detect the total motor current IG, supplying the motor units 2R, 2L and providing a corresponding indication of motor current. There is also provided a control unit 11 for controlling the different semiconductor switches 5. The control consists in that each pilot circuit 3R, 3L provides a rotating electric field for each of the electric machines of the associated motor 4R, 4L. In general, the control will be in each pilot circuit 3R, 3L by closing one of the semiconductor switches 5 connected to the high potential VH and one of the semiconductor switches of another serial assembly connected to the potential Low VL, while the other semiconductor switches 5, remain open. Thus, a phase current passes through one of the phase conductors 8 to the motor 4R, 4L and returns from the motor 4R, 4L by another phase conductor 8 thus constituting a defined current path. If such a drive system 1 is applied to a motor vehicle, it is often necessary for the motor units 2R, 2L to provide the same torque if the same torque is required. This is particularly the case if the motor units 2R, 2L drive a left-hand drive wheel and a right-hand drive wheel. For this, the 4R, 4L motors must be powered with pre-defined phase currents or the same motor current or motor currents.

8 defined to receive the same electrical energy or predefined electric energy. The setting or the predefining of the IRU, IRV, IRW, ILU, ILV, ILW phase currents or of the IGR, IGL motor currents is done by means of a regulation of current carried out by the control unit 11. Current regulation adjusts the phase current by appropriately adjusting the voltage applied by one of the driver circuits 3R, 3L (via the node UR, VR, WR, UL, VL, WL). The voltage is regulated by the pilot circuit 3R, 3L by controlling the semiconductor switches 5 by pulse width modulation to apply variable voltages to the nodes UR, VR, WR, UL, VL, WL of the pilot circuit 3R, 3L respective. However, such a current regulation requires the sending of a feedback message concerning the currents flowing in the phase conductors of the motors 2R, 2L. The control unit 11 has inputs for receiving indications relating to the phase currents and the motor current. The phase current ammeters 9 are connected for this purpose to the control unit 11 and provide such a feedback message, asserting that the phase current ammeters 9 are tainted with manufacturing tolerances and that it is possible to have measurement discrepancies. This means that there may be a difference between the measured intensity and the actual intensity. In order for the motor units 2R, 2L to provide the same torques, it is necessary to balance or calibrate the phase current ammeters 9, in particular the phase current ammeters 9 associated with the different motor units 2R, 2L. The control unit 11 also comprises memory elements for recording the correction terms associated with the different ammeters 9, 10 for the control unit 11 to correct the current indications supplied by the phase current ammeters (current sensors 9, 10, for example by adding corrective terms to the current indications. The method of calibration or relative balancing of phase current ammeters (current sensors) 9, 10, is represented by the flowchart of FIG. 2. According to this flow chart, in step S1, there is connected a semiconductor switch 5 of the first

9 motor unit 3R at high potential VH and another semiconductor switch 5 at low potential VL; the other semiconductor switches 5 remain open. This is done for example but not necessary during the shutdown of the first motor 4R. Thus, a current path is formed from the supply line 6 via the first phase conductor 8 of the first motor 4R to exit through the second phase conductor 8. The semiconductor switches 5 of the other power unit 2L stay open to turn off the power. The current path formed in the first drive unit 2R causes the same current to pass through the motor current ammeter 10 and two of the phase current ammeters 9. The current ammeters 9, 10 provide current indications. measured at the control unit 11; this compares the measured current indications in step S2 and establishes a correction term for each of the ammeters 9, 10. The correction terms are chosen so that, after correction of the current indications, the control unit 11 has the same current indications, corrected. One of the phase current ammeters 9 can be defined as a reference ammeter and thus receives a fixed correction term, for example 0 or some other value. Alternatively, the motor current ammeter 10 is taken as a reference and will be calibrated to an absolute intensity measurement by a separate calibration phase. The corrective terms of the phase current ammeters 9 for the powered phases of the motors 4R, 4L are then calibrated (balanced) on the motor current ammeter 10 and for this the corrective terms are fixed so that the indications are identical. The corrected current supplied by the control unit 11. In step S3, as described above, a current path is formed by the other phase conductors of one of the 4R, 4L motors to supply power. by current corresponding phase current ammeters 9, this current being that of the motor current ammeter 10. The fixing of the correction terms for phase current ammeters 9 which have not yet been calibrated, 35 c ' that is, to which no fix term has been assigned, is

i0 for the corrected phase current indications to correspond to the corrected motor current indications. The operation is repeated according to the request of step S4 until all phase current ammeters 9 of the first power unit 2 are assigned correction terms. When corrective terms are associated with all phase current ammeters 9 of the first power unit 2R, it is possible to calibrate (balance) the phase current sensors 9 of the second power unit 2L in a similar manner (step S5) ; this means that by appropriate switching of the semiconductor switches 5, a current path is formed through two phase current ammeters 9 of the phase conductors 8 and determining and assigning correction terms (step S6) for the corrected phase current indications correspond to the corrected current current indications of the balanced phase current ammeters 9. Also for the second motor unit 2L, current paths in the phases of the electric machines 4R, 4L are formed by the request of the step S7 until all the phase current ammeters are assigned correction terms. 9. This makes it possible to calibrate all phase current ammeters 9 with respect to each other so that, in response to a predefined motor torque, the phase current regulation by the control unit 11 makes it possible to set a phase current reference value (phase intensity) so that the two motor units 2R, 2L provide the desired torque, especially the same torque. To achieve the absolute high accuracy, it is sufficient to use only for the motor current ammeter 10, an ammeter having better accuracy or lower tolerances 30 whereas ammeters as current ammeters 9 phase can be used of lesser precision. The phase currents can be measured both during a calibration procedure at shutdown of the motor units 2R, 2L or during their operation, since during operation it must be ensured that the offset of the measurements current in

Phase 9 current ammeters and motor current ammeter 10 should be as small as possible to minimize the deviations produced by the chronological evolution of the currents. The measurement can be made during an initialization phase, during the charging of the intermediate circuit capacitor 7. For this, the supply voltage can be applied to the supply lines 6 by an intermediate resistor 12 which can be connected. . The motor units 2R, 2L can be connected by the intermediate resistor 12 to the supply voltage. The value of the intermediate resistor 12 and that of the phase lines correspond to the balancing current. The value of the intermediate resistance must be designed to minimize the residual error over the entire measurement range used. According to an alternative embodiment, it is possible to eliminate one of the phase current ammeters 9 of each drive unit 2R, 2L because for the phase connection not equipped with a phase current sensor 9, it will be possible to define the passage current from the current indications provided by the other current sensors 9, 10. This further reduces the cost of the system.

20 NOMENCLATURE 2R, 2L 3R, 3L 4R, 4L UR, VR, WR, UL, VL, WL IRU, IRV, IRW, ILU, ILV, ILW 5 6 7 8 9 10 11 12 drive unit pilot circuit motor node current semiconductor switch power supply line intermediate circuit phase conductor phase current ammeter motor current ammeter control unit intermediate resistance20

Claims (1)

CLAIMS1 °) Method for calibrating phase current ammeters of a drive system comprising a plurality of electromotive units (2R, 2L), - the driving units (2R, 2L) each having a polyphase motor (4R, 4L) powered in electrical energy by a common supply line (6), - the phase current ammeters (9) measuring the phase current in a phase conductor (8) of the respective motor (4R, 4L), - the ammeters of phase current (9) balancing first and second drive units (2R, 2L) relative to one another using a motor current ammeter (10) which can be switched the current path of the first power unit (2R) and in the current path of the second power unit (2L). Method according to claim 1, characterized by the following steps: - calibrating the phase current ammeters (9) of the first driving unit (2R), by successively switching current paths not derived by the conductors phase (8) of a motor (4R) of the first power unit (2R), * calibrating the phase current ammeters (9) in the non-derivative current paths by correction terms to correct the current indication provided by the respective phase current amper meter (9), - calibrating the motor current ammeter (10) with a corrective term for correcting the motor current indication supplied by that ammeter ( 10), - calibrating the phase current ammeters (9) of the second drive unit (2R), by successively switching current paths not derived from the motor (4L) of the second drive unit (2L), 14 * calibrating ammeters e phase current (9) in the non-derivative current paths, with corrective terms for correcting the phase current indication provided by the respective phase current amper meter (9) so that the indi - Corrected phase current cations, correspond to the corrected motor current indications. Method according to Claim 2, characterized in that the motor current ammeter (10) installed in the common supply line is calibrated while a non-derivative current path is switched only by the phase conductors (8) of the motor (4R) of the first drive unit (2R) so that the current in the phase conductors (8) corresponds to the current flowing in the motor current amperes (10) . 4) Method according to claim 2, characterized in that, before calibrating the phase current ammeters (9), the correction terms associated with the phase current ammeters (9) are determined so that the indications of phase current, corrected, correspond to the calibrated motor current indication. Method according to one of Claims 2 to 4, characterized in that the phase current ammeters (9) of the non-derived current paths are calibrated by associating the correction terms so that the phase current indications are present. corrected correspond. 6 °) Device for calibrating the phase current ammeters (9) of a drive system (1) comprising a plurality of electromotive units (2R, 2L), - the driving units (2R, 2L) each having a polyphase motor (4R, 4L) being supplied with electrical energy by a common line (6), - phase current ammeters (9) measuring a phase current in a phase conductor (8) of the motor (4R, 4L) ) respectively, - the device calibrating the phase current ammeters (9) of the first and second drive units (4R, 4L) relative to one another using a motor current ammeter as a reference ( 10) switchable in the current path of the first power unit (2R) and in the current path of the second power unit (2L). 7 °) Drive system (1) equipped with several electromotive units (2R, 2L) each having a polyphase motor (4R, 4L) supplied with electrical energy by a common supply line (6) and a dis-positive according to claim (6) for calibrating the phase current ammeters (9) for measuring the phase current in a phase conductor (8) of the respective motor (4R, 4L). 8) Computer program product comprising a program code which, executed by a data processing unit, applies the method of calibrating the phase current ammeters of a drive system comprising a plurality of electromotive units (2R, 2L ) according to any one of claims 1 to 5, - the motor units (2R, 2L) each having a polyphase motor (4R, 4L) supplied with electrical energy by a common supply line (6), - the ammeters of phase current (9) measuring the phase current in a phase conductor (8) of the respective motor (4R, 4L), - the phase current ammeters (9) balancing a first and a second drive unit (2R, 2L) ) relative to one another using as a reference measuring installation a motor current ammeter (10) which can be switched in the current path of the first power unit (2R) and in the neck path - the second mo unit trice (2L).