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EP-3581432-B1 - ELECTRIC POWER SYSTEM OF AN ELECTRIC DRIVE VEHICLE AND RELATIVE CONTROL METHOD

EP3581432B1EP 3581432 B1EP3581432 B1EP 3581432B1EP-3581432-B1

Inventors

  • PEZZATI, Andrea

Dates

Publication Date
20260506
Application Date
20190611

Claims (9)

  1. An electric power system (18) of a vehicle (1) with an electric drive obtained by means of at least one electric machine (8); the electric power system (18) comprises: a storage system (14) comprising a first pack (15) of chemical batteries and a second pack (16) of chemical batteries, which are electrically separated from one another; a first electronic DC-AC power converter (19), which has a direct current side connected to the first pack (15) of chemical batteries and an alternating current side connected to terminals of the electric machine (8); a second electronic DC-AC power converter (20), which has a direct current side connected to the second pack (15) of chemical batteries and an alternating current side connected to the terminals of the electric machine (8), in addition and in parallel to the first electronic power converter (19), so that the electric machine (8) can be controlled by the first electronic power converter (19) or by the second electronic power converter (20); and a control unit (21), which establishes which one of the two electronic power converters (19, 20) has to control the electric machine (8) and, therefore, establishes when to switch the electronic power converter (19, 20) controlling the electric machine (8); the electric power system (14) is characterized in that: the first pack (15) of chemical batteries has a greater specific storable electric energy and a smaller specific deliverable electric power compared to the second pack (16) of chemical batteries; the direct current side of each electronic power converter (19, 20) is connected only to the corresponding pack (15, 16) of chemical batteries and, hence, is completely isolated from the other electronic power converter (19, 20) and from the other pack (15, 16) of chemical batteries; the three-phase alternating current side of each electronic power converter (19, 20) is connected to the same electric machine (8) as the three-phase alternating current side of the other electronic power converter (19, 20), namely, the two electronic power converters (19, 20) are connected in parallel to the terminals of the same electric machine (8); the electric machine (8) is always controlled by one single electronic power converter (19, 20) at a time, namely, in any situation, one single electronic power converter (19, 20) at a time applies an alternating voltage to terminals of the electric machine (8) and, therefore, supplies/absorbs an alternating current flowing through the terminals of the electric machine (8); the control unit (21) estimates an electric power to be supplied/absorbed to/by the electric machine (8) and establishes which one of the two electronic power converters (19, 20) has to control the electric machine (8) based on the electric power to be supplied/absorbed to/by the electric machine (8); when the electric power to be supplied/absorbed to/by the electric machine (8) exceeds a threshold value, the electric machine (8) is controlled by the second electronic power converter (20); when the electric power to be supplied/absorbed to/by the electric machine (8) is below a threshold value, the electric machine (8) is controlled by the first electronic power converter (19); and the control unit (21) changes the threshold value based on an actual temperature of the electronic power converters (19, 20) so that an electronic power converter (19, 20) close to overheating is used less), based on an actual temperature of the packs (15, 16) of chemical batteries so that a pack (15, 16) of chemical batteries close to overheating is used less, and based on the state of charge of the packs (15, 16) of chemical batteries so that a more exhausted pack (15, 16) of chemical batteries is used less.
  2. An electric power system (18) according to claim 1, wherein the control unit (21) applies a hysteresis to the threshold value, so as to avoid an excessive switching frequency when the electric power to be supplied/absorbed to/by the electric machine (8) straddles the threshold value.
  3. An electric power system (18) according to claim 1 or 2, wherein the threshold value is differentiated between the case of electric power supplied to the electric machine (8) and the case of electric power absorbed by the electric machine (8).
  4. An electric power system (18) according to claim 1, 2 or 3, wherein the control unit (21) receives a rotation speed objective for the electric machine (8) and a supplied/absorbed torque objective for the electric machine (8) and determines the electric power to supplied/absorbed to/by the electric machine (8) based on the rotation speed objective for the electric machine (8) and based on the supplied/absorbed torque objective for the electric machine (8) .
  5. An electric power system (18) according to one of the claims from 1 to 4, wherein the control unit (21) switches the electronic power converter (19, 20) controlling the electric machine (8) by exclusively acting upon the electronics of the electronic power converters (19, 20), namely by turning off the electronic power converter (19, 20) currently working and by turning on the other electronic power converter (20, 19).
  6. An electric power system (18) according to one of the claims from 1 to 5, wherein, when the electric machine (8) does not necessarily have to be controlled, the control unit (21) can control the two electronic power converters (19, 20) so as to transfer electric energy between the two packs (15, 16) of chemical batteries.
  7. An electric power system (18) according to one of the claims from 1 to 6 and comprising: a first switch (25), which is interposed between the first pack (15) of batteries and the first electronic power converter (19); and a second switch (26), which is interposed between the second pack (16) of batteries and the second electronic power converter (20).
  8. An electric power system (18) according to one of the claims from 1 to 7 and comprising: a third switch (25), which is interposed between the first electronic power converter (19) and the electric machine (8); and a fourth switch (26), which is interposed between the second electronic power converter (20) and the electric machine (8).
  9. A method to control an electric power system (18) of a vehicle (1) with an electric drive obtained by means of at least one electric machine (8); the electric power system (18) comprises: a storage system (14) comprising a first pack (15) of chemical batteries and a second pack (16) of chemical batteries, which are electrically separated from one another; a first electronic DC-AC power converter (19), which has a direct current side connected to the first pack (15) of chemical batteries and an alternating current side connected to terminals of the electric machine (8); a second electronic DC-AC power converter (20), which has a direct current side connected to the second pack (15) of chemical batteries and an alternating current side connected to the terminals of the electric machine (8), in addition and in parallel to the first electronic power converter (19), so that the electric machine (8) can be controlled by the first electronic power converter (19) or by the second electronic power converter (20); and a control unit (21), which establishes which one of the two electronic power converters (19, 20) has to control the electric machine (8) and, therefore, establishes when to switch the electronic power converter (19, 20) controlling the electric machine (8); the control method is characterized in that it comprises the steps of: always controlling the electric machine (8) with one single electronic power converter (19, 20) at a time, namely, in any situation, one single electronic power converter (19, 20) at a time applies an alternating voltage to terminals of the electric machine (8) and, therefore, supplies/absorbs an alternating current flowing through the terminals of the electric machine (8). estimating an electric power to be supplied/absorbed to/by the electric machine (8); establishing which one of the two electronic power converters (19, 20) has to control the electric machine (8) based on the electric power to be supplied/absorbed to/by the electric machine (8); controlling the electric machine (8) with the second electronic power converter (20) when the electric power to be supplied/absorbed to/by the electric machine (8) exceeds a threshold value; and controlling the electric machine (8) with the first electronic power converter (19) when the electric power to be supplied/absorbed to/by the electric machine (8) is below a threshold value; wherein the first pack (15) of chemical batteries has a greater specific storable electric energy and a smaller specific deliverable electric power compared to the second pack (16) of chemical batteries; wherein the direct current side of each electronic power converter (19, 20) is connected only to the corresponding pack (15, 16) of chemical batteries and, hence, is completely isolated from the other electronic power converter (19, 20) and from the other pack (15, 16) of chemical batteries; wherein the three-phase alternating current side of each electronic power converter (19, 20) is connected to the same electric machine (8) as the three-phase alternating current side of the other electronic power converter (19, 20), namely, the two electronic power converters (19, 20) are connected in parallel to the terminals of the same electric machine (8); and wherein the threshold value is changed based on an actual temperature of the electronic power converters (19, 20) so that an electronic power converter (19, 20) close to overheating is used less), based on an actual temperature of the packs (15, 16) of chemical batteries so that a pack (15, 16) of chemical batteries close to overheating is used less, and based on the state of charge of the packs (15, 16) of chemical batteries so that a more exhausted pack (15, 16) of chemical batteries is used less.

Description

TECHNICAL FIELD The invention relates to an electric power system of an electric drive vehicle and to a corresponding control method. The invention finds advantageous application in a road vehicle with hybrid drive, to which explicit reference will be made in the description below without because of this loosing in generality. PRIOR ART A hybrid vehicle comprises an internal combustion heat engine, which transmits a torque to the drive wheels by means of a drivetrain provided with a transmission, and at least one electric machine, which is electrically connected to a power storage system and is mechanically connected to the drive wheels. The electric power system of a hybrid vehicle comprises a storage system provided with a pack of chemical batteries and a two-way electronic DC-AC power converter, which, on the direct current side, is connected to the storage device and, on the alternating current side is connected to the electric machine and fulfils the function of controlling the electric machine. The chemical batteries used in current road vehicles with hybrid drive can have a large specific storable electric energy (i.e. per unit of mass and/or volume) and a small specific deliverable electric power (i.e. per unit of mass and/or volume) and, hence, be suited to fulfil the needs of a long stretch of road covered at a moderate speed (and, especially, with limited acceleration/decelerations). Alternatively, the chemical batteries used in current road vehicles with hybrid drive can have a small specific storable electric energy (i.e. per unit of mass and/or volume) and a large specific deliverable electric power (i.e. per unit of mass and/or volume) and, hence, be suited to fulfil the needs of a short stretch of road covered at a significant speed (and, especially, with high acceleration/decelerations). In order to try and obtain an acceptable compromise between the range needs (which require chemical batteries with a large specific electric energy) and the performance needs (which require chemical batteries with a large specific electric power), manufacturers have tried to produce compromise chemical batteries with intermediate features between the two extremes; however, these compromise chemical batteries turn out to be a "downward" compromise, namely, before a significant reduction of the specific electric energy, they do not feature an equally significant increase in the specific electric power and vice versa. In order to try and obtain an acceptable compromise between the range needs (which require chemical batteries with a large specific electric energy) and the performance needs (which require chemical batteries with a large specific electric power), manufacturers have also suggested to insert, in the storage system, both chemical batteries with a large specific electric energy and chemical batteries with a large specific electric power. However, the overall results (in terms of range and performances) and, in particular, the operating life of the chemical batteries turn out to be hardly satisfactory, as the "final result" is in some way smaller than the sum of the single parts. Italian patent application BO2012A000315 discloses an electric power system of a vehicle with an electric drive obtained by means of at least one first electric machine. The electric power system has: a storage system comprising at least two packs of chemical batteries, which are electrically separate from one another; an electronic DC-AC power converter, which exchanges electric energy with the storage system and controls the first electric machine; and a pair of electronic DC-DC power converters, each increasing the voltage and having a low-voltage side, which is electrically connected only to a corresponding pack of chemical batteries, and a high-voltage side, which is connected to the electronic DC-AC power converter in parallel to the high-voltage side of the other electronic DC-DC power converter. However, the electric power system described in patent application BO2012A000315 is relatively expensive, heavy and large-sized, since, in order to control one single electric machine, it requires the presence of three electronic power converters (two electronic DC-DC power converters and one electronic DC-AC power converter). Patent US8102142B2 describes an electric power system of an electric drive vehicle comprising: a storage system comprising a first pack of chemical batteries and a second pack of chemical batteries, which are electrically separate from one another; a first electronic DC-AC power converter, which has a direct current side connected to the first pack of chemical batteries and an alternating current side connected to the electric machine; and a second electronic DC-AC power converter, which has a direct current side connected to the second pack of chemical batteries and an alternating current side connected to the electric machine, in addition to the first electronic power converter, so that the electric m