Drive system for a hybrid or electric vehicle

Abstract

A drive system for a hybrid or electric vehicle comprises an electric energy source (2), an electric machine (3), a switching device (6) connected to the electric machine (3) and selectively switchable between a first configuration having a first electrical configuration of phases and a second configuration having a second electrical configuration of phases, a regulating device (4) connected to the electric machine (3) and configured to vary its operating parameters, and a control unit (5). In the first electrical configuration of phases, the electric machine (3) comprises a first number of conductors in series per phase, to be able to provide a first drive torque (T1) and having a first breakaway speed (ω cp1 ) and a first preset no-load operating speed (ω NL1 ); and in the second electrical configuration of phases, the electric machine (3) comprises a second number of conductors in series per phase, to be able to provide a second drive torque (T2) lower than the first drive torque (T1) and having a second breakaway speed (ω cp1 ) higher than the first breakaway speed (ω cp2 ). The ratio between the first no-load operating speed (ω NL1 ) and the second breakaway speed (ω cp2 ) is between 0.7 and 1.3.

Description

Technical Field

[0001] This invention relates to a drive system and control method for hybrid or electric vehicles.

[0002] Therefore, the present invention is particularly applicable to the field of vehicles, and more precisely, to the design and manufacture of electric or electric / heat-absorbing hybrid propulsion vehicles. Background Technology

[0003] In this field, there has long been a desire to expand the effective range of electric motors so that they can be used even in the absence of mechanical transmissions, or in any case, in the presence of simple mechanical transmissions.

[0004] To date, several methods are known that are suitable for traction applications and that use appropriate segments of the stator winding in different sections, which can be selectively combined with each other, to change the “configuration” of the motor, thereby enabling it to be adapted to operating conditions and to expand its operating range.

[0005] Eckart Nipp explored such a solution in his 1999 doctoral dissertation, perhaps the first of its kind, which described a reconfigurable motor capable of achieving good performance under a wide range of operating conditions.

[0006] This solution is only described on paper or in test benches and has limited application in the market, mainly due to the difficulty of its implementation / construction.

[0007] Nipp actually proposed reconfiguring the system to be coupled to the motor, designed so that the configuration changes once the speed reaches the inflection point speed value under the maximum load of the existing (or starting) configuration. Here, the expression "inflection point speed" is understood to be the maximum speed at which the machine can follow the characteristic curve under the maximum constant torque in the starting configuration.

[0008] In other words, the inflection point speed (or base speed) is the speed at which the machine's characteristic torque-speed curve changes from a constant torque state to a decreasing torque state.

[0009] Therefore, according to the prior art, given a starting configuration that can define the aforementioned characteristic curve, the control unit of the reconfiguration system based on Nippon theory drives the machine such that when the inflection point speed is reached (during acceleration), the stator winding is reconfigured from a starting configuration that typically has higher torque and lower speed to a finished configuration that typically has lower torque and higher speed (with the same power supply conditions: current and voltage).

[0010] The downside is that while the solution is particularly reasonable from a safety point of view, enabling the avoidance of uncontrolled generator operation (UGO), it has significant limitations from a transmission smoothness point of view, as the driver experiences a significant torque / power gap during acceleration.

[0011] Therefore, the object of the present invention is to provide a drive system for hybrid or electric vehicles that overcomes the disadvantages of the prior art described above. Summary of the Invention

[0012] Specifically, the object of the present invention is to provide a drive system for hybrid or electric vehicles that is particularly high-performance and very safe.

[0013] More specifically, the object of the present invention is to provide a drive system for hybrid or electric vehicles that is optimized for vehicle applications and is able to ensure the continuity of power transmission and limit any torque defects as much as possible.

[0014] The objective is achieved by a drive system for hybrid or electric vehicles, which has one or more of the following features.

[0015] Specifically, the objective is achieved by a drive system comprising an electrical energy source, a motor, a regulating device (e.g., an inverter) connected to the motor, and a control unit.

[0016] The regulating device is preferably an inverter and is configured to change the operating parameters of the motor.

[0017] The motor is preferably synchronous (magnetic or reluctance) and is equipped with a rotor that rotates about its own axis of rotation and a stator comprising multiple phases extending between their respective terminals. The motor is also reconfigurable.

[0018] Therefore, the drive system (or motor) includes a switching device that can selectively switch between a first configuration and a second configuration, in which the stator phase has a first electrical configuration and in the second configuration, the stator phase has a second electrical configuration.

[0019] The control unit is connected to the switching device and the regulating device and is configured to drive the switching device and the regulating device according to the operating conditions of the vehicle.

[0020] Advantageously, in this way, the configuration of the motor can be changed, and thus its "effective range" can be altered, by issuing a simple and unique command from the control unit.

[0021] It should be noted that, preferably, the term “electrical configuration” is used to define the wiring diagram for connecting conductor bundles in series, i.e., the wiring diagram of each phase, when the connection type between the connector bundles changes, the characteristic curve of the motor changes, for example by increasing or decreasing the base speed at the expense of or with the advantage of maximum drive torque (with the same voltage or current supply).

[0022] In this respect, in the first electrical configuration of the stator, the motor includes a first number of conductors connected in series according to phase to provide a first drive torque and have a first inflection point speed (or a first base speed) and a preset first no-load operating speed.

[0023] Furthermore, preferably, in the second electrical configuration of the stator, the motor includes a second number of conductors connected in series according to phase, so as to provide a second drive torque lower than the first drive torque, and has a second inflection point speed (or second base speed) higher than the first inflection point speed.

[0024] According to one aspect of the invention, the ratio between the first no-load operating speed and the second inflection point speed is between 0.7 and 1.3.

[0025] According to another aspect of the invention, the control unit is configured to:

[0026] - When the rotor speed is higher than the first inflection point speed, the driving adjustment device is activated to control the motor to be in the flux reduction mode;

[0027] - To enable the switching device to switch from the first configuration to the second configuration, so as to achieve a switching speed that is higher than the first inflection point speed and lower than the first no-load operating speed.

[0028] It should be noted that the term "magnetic flux reduction" is used in this paper to define a type of motor drive in which, in order to increase the rotor speed beyond the inflection point speed value, and because the voltage (limit value) cannot be increased, the amplitude of the voltage limit circumferences is reduced, and therefore the maximum torque relative to the current used (in plane Id, Iq) is shifted to a value that produces a magnetic flux component opposite to the magnetic flux component produced by the permanent magnet.

[0029] In this way, the configuration of the drive system is conducive to optimizing power delivery during acceleration, minimizing the "torque deficit" between the first and second configurations, i.e. avoiding sudden transitions from one configuration to another, and avoiding the establishment of uncontrolled generator operation that disrupts vehicle operation.

[0030] Preferably, the first and second configurations of the motor have a first characteristic curve and a second characteristic curve extending on the torque-speed plane, that is, they operate according to the first characteristic curve and the second characteristic curve.

[0031] The first characteristic curve preferably intersects the second characteristic curve at the intersection velocity.

[0032] It should be noted that, in this respect, the characteristic curve can be defined solely by the characteristics of the motor, or by the maximum mechanical power required by the application (or rated mechanical power) of the motor.

[0033] The control unit is preferably configured to cause the motor to switch from a first configuration to a second configuration, in order to achieve a switching speed:

[0034] -If the first no-load operating speed is greater than the intersection speed, the switching speed is included between the intersection speed and the first no-load operating speed;

[0035] - If the first no-load operating speed is lower than the intersection speed, then the switching speed is lower than the first no-load operating speed.

[0036] In this way, the flux reduction of the initial (first) configuration can be fully utilized to ensure the continuity of torque / power transmission where possible.

[0037] Similarly, this ensures that the machine does not exceed the safety limits of the first configuration (first no-load operating speed), thereby preventing dangerous situations from occurring in the motor structure or drive.

[0038] To ensure maximum transmission continuity and thus maximum driving comfort, if the second inflection point speed is lower than the first no-load operating speed, the switching speed is between the intersection speed and the second inflection point speed; more preferably, it corresponds to the intersection speed to avoid any torque defects (unless a transient defect exists).

[0039] Furthermore, preferably, in order to maximize the performance of the drive system, the applicant has found that some of the motor's construction parameters must fall within predetermined intervals obtained through experiments and analysis.

[0040] Therefore, preferably, the first no-load operating speed is at least 1.5 times the first inflection point speed.

[0041] Preferably, the ratio between the first number and the second number of conductors connected in phase series is between 1 and 5, and more preferably between 1.5 and 3.5.

[0042] Preferably, the physical anisotropy of the motor is between 1 and 11, and more preferably between 3 and 7.

[0043] Advantageously, these parameters enable the machine to operate within its optimal operating range, allowing for the reconfiguration of the stator windings in the same safe and efficient manner. Attached Figure Description

[0044] Other features and associated technical advantages will be more clearly illustrated by the illustrative but non-limiting description of a preferred, and therefore non-exclusive, embodiment of a drive system for a hybrid or electric vehicle shown in the accompanying drawings, wherein:

[0045] - Figure 1 The drive system according to the present invention is illustrated schematically;

[0046] - Figure 2 It shows Figure 1 The characteristic curves of the system under operating conditions. Detailed Implementation

[0047] Referring to the accompanying drawings, reference numeral 1 indicates a drive system for a hybrid or electric vehicle according to the present invention.

[0048] Therefore, drive system 1 is a set of components that are cascaded together to generate the power / torque to be supplied to the vehicle wheels.

[0049] System 1 can be entirely electric or a hybrid of electric and endothermic.

[0050] In any case, the present invention relates to an “electrical branch” of a drive system 1, wherein the drive system 1 includes an electrical energy source 2, a motor 3, an adjustment device 4 (e.g., an inverter) connected to the motor 3, and a control unit 5.

[0051] The electrical energy source 2, not shown in detail here, is preferably defined by a battery pack. Alternatively, in any case, another source may be used, such as a fuel cell, generator, solid-state battery, or other equivalent (or better) technology.

[0052] The motor 3 is preferably a synchronous type (magnet or reluctance) and is equipped with a rotor 3a that rotates about its own axis of rotation and a stator 3b containing multiple phases extending between their respective terminals.

[0053] Therefore, each phase is defined by a pre-fixed number of conductor bundles that are conveniently connected in series with each other.

[0054] The phase can be of various types, but is preferably defined by strip conductors conveniently arranged in a cavity formed in the stator 3b housing and electrically connected to each other at at least one free end.

[0055] Therefore, motor 3 is of the multiphase type, which includes the number of phases from two phases to an additional number depending on the type or application.

[0056] In a preferred embodiment, motor 3 is defined as a three-phase synchronous motor in any case.

[0057] In a preferred embodiment, the physical anisotropy of the motor is between 1 and 11, more preferably between 3 and 7.

[0058] The regulating device 4 is preferably an inverter (or similar device) and is configured to change the operating parameters of the motor.

[0059] According to one aspect of the invention, phases (or phase portions) can be connected together in a suitable manner to change the operating configuration of the motor 3.

[0060] In other words, motor 3 is preferably a reconfigurable type.

[0061] Therefore, in this respect, there should be a switching device 6 connected to the motor 3 (in particular, connected to the stator 3b), which is capable of selectively switching between a first configuration and a second configuration, in which the stator phase has a first electrical configuration and in which the stator phase has a second electrical configuration.

[0062] Advantageously, in this way, the configuration of motor 3 can be changed by a simple and unique command provided by control unit 5, and thus its "effective range" can be altered.

[0063] It should be noted that, preferably, the term "electrical configuration" is used to define the wiring diagram for connecting conductor bundles in series, i.e., the wiring diagram of each phase, and the characteristic curve of the motor changes when the connection type between the conductor bundles is changed, for example by increasing or decreasing the base speed at the expense of or with the advantage of drive torque.

[0064] The applicant recently developed its own switching device, which is protected by Italian patent applications 102019000004667 and 102019000011655.

[0065] However, other switching devices, including mechanical and other types, such as semiconductors or relays, can be used in the drive system 1 according to the invention.

[0066] For the purposes of this invention, it is sufficient for the stator 3b of the motor 3 to have multiple reconfigurable phases, wherein any switching device 6 capable of changing its electrical configuration is connected to multiple reconfigurable phases.

[0067] Therefore, the control unit 5 is connected to the switching device 6 and the regulating device 4, and is configured to drive the switching device 6 and the regulating device 4 according to the operating conditions of the vehicle.

[0068] Therefore, the motor 3 can be selectively configured in at least one first electrical configuration and one second electrical configuration, the at least one first electrical configuration and one second electrical configuration being defined by the first configuration and the second configuration of the switching device 6, respectively.

[0069] Preferably, there may be more configurations, the purpose of which is always to increase the rotational speed or decrease the torque supply during transitions between two configurations. In a preferred embodiment, in addition to the first two configurations, the motor 3 is configured to be arranged in a third configuration.

[0070] Preferably, but not exclusively, the first and second (and any third) electrical configurations are selected from the following list:

[0071] - Triangle series configuration,

[0072] - Triangle parallel configuration,

[0073] - Star-connected series configuration

[0074] - Star-shaped parallel configuration.

[0075] In the first electrical configuration of stator 3b, the motor includes a first number of conductors connected in series according to phase to provide a first (maximum) drive torque T1 and has a first inflection point speed ω. cp1 And the pre-set first no-load running speed.

[0076] As stated above, the term "inflection point speed" in this article should be understood as the maximum speed at which a machine, in its respective configuration, can follow its own constant torque characteristic curve.

[0077] In other words, the inflection point speed (or base speed) is the speed at which the machine's characteristic torque-speed curve changes from a constant torque state to a decreasing torque state (under constant mechanical power).

[0078] In this respect, in this first configuration, the motor has a first characteristic curve extending on the torque-speed plane, for speeds below or equal to the first inflection point ω. cp1 The speed value has a constant torque equal to the first driving torque T1, and for speeds above the first inflection point ω cp1 The speed has a constant power equal to the first maximum transmittable power P1.

[0079] In other words, the first characteristic curve has a first part and a second part, the first part having a constant torque and the second part having a constant power.

[0080] Similarly, in the second electrical configuration of stator 3b, motor 3 includes a second number of conductors connected in series according to phase, to provide a second (maximum) drive torque T2 lower than the first drive torque T1, and having a speed ω higher than the first inflection point.cp1 The second inflection point velocity ω cp2 (and the second no-load operating speed, not shown).

[0081] Therefore, in the second configuration, the motor 3 has a second characteristic curve extending on the torque-speed plane, having a constant torque equal to the second drive torque T2 for speed values ​​below or equal to the second inflection point speed, and a constant power equal to the second maximum transmittable power P2 for speeds above the second inflection point speed.

[0082] In other words, the second characteristic curve has a first part and a second part, with the first part having a constant torque and the second part having a constant power.

[0083] It should be noted that, preferably, the ratio between the first and second number of conductors in phase series is between 1 and 5, and more preferably between 1.5 and 3.5.

[0084] Furthermore, preferably, the first characteristic curve and the second characteristic curve intersect at a velocity ω. cross intersect.

[0085] It should be noted that, in this respect, the characteristic curve can be defined solely by the characteristics of the motor, or in part by the maximum mechanical power required by the application (or rated mechanical power) of the motor.

[0086] In other words, if the maximum power curve is below the first inflection point speed ω cp1 Or the second inflection point velocity ω cp2 If the speed (i.e., in the constant torque segment) "intersects" with the first characteristic curve or the second characteristic curve, then the constant power segment of the curve can correspond to the same maximum power curve.

[0087] Advantageously, this helps to achieve control strategies designed to provide a continuous supply of torque.

[0088] Therefore, referring to the preferred embodiment, the third electrical configuration of the phase includes a third number of conductors connected in series according to the phase, to provide a third drive torque lower than the second drive torque T2, and having a speed higher than the second inflection point ω. cp2 The third inflection point velocity.

[0089] Similarly, in the third configuration, the motor 3 has a corresponding third characteristic curve extending on the torque-speed plane, having a constant torque equal to the third drive torque for speeds below the third inflection point speed, and a constant power equal to the third maximum transmittable power for speeds above the third inflection point speed.

[0090] Preferably, the second characteristic curve and the third characteristic curve also intersect at an intersection velocity (not shown).

[0091] According to another aspect of the invention, the control unit 5 is configured to:

[0092] -When the rotational speed of rotor 3a is higher than the first inflection point speed ω cp1 At this time, drive adjustment device 4 to control the motor to be in magnetic flux reduction mode;

[0093] - To enable the switching device to switch from the first configuration to the second configuration, thereby achieving a switching speed ω. switch The velocity ω is higher than the first inflection point. cp1 And lower than the first no-load operating speed ω NL1 .

[0094] It should be noted that the term "magnetic flux reduction" in this article should be understood as defining a control method for exhausting a magnetic field that can increase the operating speed of a motor at the expense of mechanical torque.

[0095] In other words, in order to increase the rotor speed to a value exceeding the inflection point speed, since the voltage (limit value) cannot be increased, the amplitude around the voltage limit decreases, and therefore the maximum torque relative to the current used (in plane Id, Iq) moves to a value that produces a flux component opposite to the flux component produced by the permanent magnet.

[0096] In this way, the drive in the first configuration can be fully utilized, and the speed and torque during switching can be made to values ​​compatible with the second configuration, avoiding torque defects, while at the same time avoiding risks to the safety of motor 3 or the vehicle.

[0097] In this regard, it should be noted that the first no-load operating speed ω NL1 The preferred value is equal to the velocity ω at the first inflection point. cp1 At least 1.5 times, more preferably at least equal to the velocity ω at the first inflection point. cp1 2 times.

[0098] Advantageously, this allows for sufficient "room" to safely utilize the reduced magnetic flux of the first configuration.

[0099] In addition, the first no-load operating speed ω NL1 With the second inflection point velocity ω cp2 The ratio between them is preferably between 0.7 and 1.3.

[0100] Advantageously, the motor design allows for a second inflection point speed ω cp2 Approaching the first no-load operating speed ω NL1 This fact ensures maximum utilization of the first configuration, and thus ensures the continuity of maximum torque supply.

[0101] It should be noted that the interval 0.7-1.3 is considered optimal because it takes into account the ratio ω. NL1 / ω cp2 The changes experienced as a function of magnet temperature mean that the motor operates optimally even without considering this parameter.

[0102] In all cases, it should be noted that, preferably, for magnet temperatures that allow full speed to be achieved (e.g., greater than 120°C), the second inflection point velocity ω cp2 Lower than the first no-load operating speed ω NL1 (i.e. ω) NL1 / ω cp2 (The range is between 1 and 1.3).

[0103] In this regard, preferably, the switching speed ω switch for:

[0104] -If the first no-load running speed ω NL1 Greater than the intersection velocity ω cross Then the switching speed ω switch Including the intersection velocity ω cross and the first no-load running speed ω NL1 between;

[0105] -If the first no-load running speed ω NL1 Below the intersection velocity ω cross Then the switching speed ω switch Lower than the first no-load operating speed ω NL1 .

[0106] It should be noted that when the velocity ω at the second inflection point... cp2 and intersection velocity ω cross Lower than the first no-load operating speed ω NL1 At that time, the switching speed ω switch Between the intersection velocity ω cross and the second inflection point velocity ω cp2 between.

[0107] More preferably, the switching speed ω switch Velocity ω at the second inflection point cp2 Nearby, to avoid torque defects, it is preferable to correspond to the intersection speed ω cross .

[0108] It should be noted that, in the preferred high-performance embodiment, the intersection velocity ω cross Second inflection point velocity ω cp2 The ratio between 0.7 and 1 is to maximize the continuity of power / torque supply and make the driver's driving experience comfortable.

[0109] More preferably, the second inflection point velocity (ω) cp2 The following relationship (which should be considered as a single quantity based on voltage, i.e., per unit system):

[0110]

[0111] in:

[0112] -ξ represents the anisotropy of the machine.

[0113] -L d It is the direct reluctance on the d-axis;

[0114] -n t It is the ratio between the first number and the second number of conductors connected in series for each phase;

[0115] -γ is the current angle along the maximum torque curve per ampere;

[0116] -λ m It is magnetic flux;

[0117] -i s It is the peak current of the line.

[0118] Advantageously, this relationship allows the second inflection point velocity ω to be... cp2 With "conversion ratio" n t (i.e., the ratio between the first and second quantities of conductors in phase series) and associated with machine parameters such as inductance, anisotropy and magnetic flux, thereby optimizing machine characteristics for variable configuration applications.

[0119] In this regard, the following should be noted:

[0120] - The magnetic flux λ is usually determined based on the number of coils. m To design a synchronous magnet machine;

[0121] -First no-load operating speed ω NL1 The following relationship exists between magnetic flux (i.e., magnetic quantity) and magnetic flux:

[0122]

[0123] Substituting this into a voltage-based single system (per unit), the result is:

[0124]

[0125] Therefore, this relationship shows the correlation between the first no-load operating speed and the second inflection point speed, allowing the physical characteristics of the machine to be optimized for the desired application.

[0126] However, due to the drive system according to the present invention, a reconfigurable motor 3 control method can be implemented, wherein, after the initial "magnetic flux weakening drive" section, a switching speed ω is achieved between the intersection speed and the no-load running speed of the characteristic curves of the two configurations involved and the starting speed. switch Switching between various configurations, wherein, preferably, due to the design of motor 3, the intersection speed falls near the inflection point speed of the configuration to be achieved and is lower than the no-load operating speed.

[0127] This invention achieves its intended purpose and thus yields significant advantages.

[0128] In fact, due to this structure of the motor, the safety issues identified in the prior art can be overcome and the potential of the electric motor can be fully developed, making its performance closer to that of an automatic transmission drive system with continuous speed variation (i.e., no torque defects).

Claims

1. A drive system for a hybrid or electric vehicle, comprising: - an electric energy source (2); - an electric machine (3) equipped with a rotor (3a) having magnets and rotating around its own axis of rotation and a stator (3b) containing a plurality of phases extending between respective terminals; - a switching device (6) connected to the electric machine (3) and selectively switchable between a first configuration, in which the plurality of phases has a first electrical configuration, and a second configuration, in which the plurality of phases has a second electrical configuration; - a regulation device (4) connected to the electric machine (3) and configured to vary an operating parameter of the electric machine; - a control unit (5) connected to the switching device (6) and to the regulation device (4) and configured to drive the switching device (6) and the regulation device (4) as a function of an operating state of the vehicle; wherein, in said first electric configuration of said stator (3b), said electric motor (3) comprises a first number of conductors in series by phase, so as to be able to provide a first driving torque (T1) and to have a first inflection speed (ω cp1 ) and a first preset no-load running speed (ω NL1 ); wherein, in said second electric configuration of said stator (3b), said electric motor (3) comprises a second number of conductors in series by phase, so as to be able to provide a second drive torque (T2) lower than said first drive torque (T1) and having a second inflection point speed (ω cp2 ) higher than said first inflection point speed (ω cp1 ). wherein the ratio between the first no-load operating speed (ω NL1 ) and the second inflection speed (ω cp2 ) is between 0.7 and 1.3; wherein the control unit (5) is configured to drive the adjustment device (4) to control the electric machine (3) in flux-weakening mode when the rotational speed of the rotor (3a) is higher than the first inflection speed (ω cp1 ) and the current of the electric machine (3) is lower than the first inflection current (I cp1 ). wherein the control unit (5) is configured to cause the switching device (6) to switch from the first configuration to the second configuration to reach a switching speed (ω switch ) higher than the first inflection point speed (ω cp1 ) and lower than the first no-load operating speed (ω NL1 ), wherein: - said first configuration of said electric machine (3) has a first characteristic curve extending on a torque-speed plane, having, on said first characteristic curve, a constant torque equal to said first drive torque (T1) for speed values lower than or equal to said first inflection speed (ω cp1 ), a constant power equal to a first maximum deliverable power (P1) for speeds higher than said first inflection speed (ω cp1 ); - said second configuration of said electric machine has a second characteristic curve extending on a torque-speed plane, having, on said second characteristic curve, a constant torque equal to said second drive torque (T2) for speed values lower than or equal to said second inflection speed (ω cp2 ), a constant power equal to a second maximum deliverable power (P2) for speeds higher than said second inflection speed (ω cp2 ), wherein said first characteristic curve and said second characteristic curve intersect at an intersection speed (ω cross ); and wherein: - the ratio between said intersection speed (ω cross ) and said second inflection speed (ω cp2 ) is between 0.7 and 1 ; - said first no-load operating speed (ω NL1 ) is equal to at least 1.5 times said first inflection point speed (ω cp1 ); - the ratio between the first number and the second number of conductors in series per phase is comprised between 1 and 5, wherein the electric machine has a physical anisotropy of the machine comprised between 1 and 11, wherein the value of the second inflection point speed (ω cp2 ) is generated by the following relationship: wherein: - ξ is the anisotropy of the machine; - L d is the direct magnetic reluctance on the d-axis; - n t is the ratio between said first number and said second number of conductors in series for each phase; - γ is the current angle along the maximum torque per amp curve; - λ m is the magnetic flux; i s is the peak current of the line.

2. The drive system of claim 1, wherein, if the first no-load operating speed (ω NL1 ) is greater than the intersection speed (ω cross ), then the switching speed (ω switch ) is comprised between the intersection speed (ω cross ) and the first no-load operating speed (ω NL1 ).

3. The drive system of claim 1, wherein, if the second inflection point speed (ω cp2 ) is lower than the first no-load operation speed (ω NL1 ), the switching speed (ω switch ) is comprised between the intersection speed (ω cross ) and the second inflection point speed (ω cp2 ).

4. The drive system of claim 3, wherein, if the intersection speed (ω cross ) is lower than the first no-load operating speed (ω NL1 ), the switching speed (ω switch ) corresponds to the intersection speed (ω cross ) to avoid torque defects.

5. The drive system of claim 1, wherein, For magnet temperatures above 120°C, the second inflection point speed (ω cp2 ) is lower than the first no-load operating speed (ω NL1 ).

6. The drive system according to claim 1, wherein: - said switching device (6) is selectively switchable to a third configuration in which said plurality of phases has a third electrical configuration comprising a third number of conductors in series by phase, to be able to provide a third drive torque lower than said second drive torque (T2) and having a third inflection point speed higher than said second inflection point speed (ω cp2 ); - the second configuration comprises a second no-load operating speed, wherein the ratio between the second no-load operating speed and the third inflection point speed is comprised between 0.7 and 1.3; said control unit (5) is configured to move said switching device (6) from said second configuration to said third configuration when a second switching speed higher than said second inflection point speed (ω cp2 ) and lower than said second no-load operation speed is reached.

7. The drive system of claim 1, wherein, the first, second and third electrical configurations are selected from the following list: - a delta series configuration, - a delta parallel configuration, - a star series configuration, - a star parallel configuration.

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