POWER DISSIPATING TORQUE CONTROLLER

Abstract

A method and a system are described for controlling power dissipation in an electric drive system for a hybrid electrical vehicle including determining the stator current of an electrical machine providing a maximum achievable power dissipation in the electrical drive system and determining a maximum available braking torque of an electrical machine.

Claims

1. A method for controlling power dissipation in an electric drive system for a hybrid electrical vehicle having a gear set or a gear box, an electrical machine connected to an axle of the gear set or gear box, a rechargeable battery operatively connected to the electrical machine, and a control unit configured to control the gear box and the electrical machine, the method comprising: determining a maximum available braking torque of the electrical machine for a given set of operating conditions based on a maximum power that the battery can receive and total normal power losses in the electric drive system; determining a stator current providing a maximum achievable power dissipation in the electrical drive system for a certain shaft torque value; receiving a requested braking torque for the electrical machine, lower than or equal to the maximum available braking torque, or receiving a requested power dissipation lower than or equal to a maximum achievable power dissipation in the electrical drive system; if the requested braking torque is equal to or lower than a torque required for providing a power corresponding to a sum of the maximum power that the battery can receive and the total normal power losses, providing the requested braking torque by providing power to the battery corresponding to a difference between the requested braking torque and the total normal power losses; if the requested braking torque exceeds the torque required for providing a power corresponding to the sum of the maximum power that the battery can receive and the total normal power losses, determining a stator current of the electrical machine that will dissipate an additional power needed while achieving a required braking torque; and if a power dissipation is requested, determining a stator current resulting in the requested power dissipation.

2. The method according to claim 1 wherein determining the stator current providing the maximum achievable power dissipation in the electrical drive system comprises determining electrical machine losses and inverter losses.

3. The method according to any claim 1 wherein determining a stator current vector of the electrical machine that will dissipate the additional power needed while achieving the required braking torque comprises modifying a maximum torque per ampere, MTPA, stator current along a constant torque line.

4. The method according to any claim 1 further comprising determining a plurality of maximum available braking torques of the electrical machine for a range of different operating conditions, and storing the plurality of available braking torques.

5. The method according to claim 1 wherein the operating conditions comprise stator winding temperature, DC voltage to the inverter, speed of the electrical machine and output torque from the electrical machine.

6. The method according to claim 1 wherein the total normal power losses in the electric drive system comprises losses from the electrical machine and from power consuming units of the vehicle.

7. The method according to claim 1 wherein the requested braking torque is utilized to perform gear synchronization.

8. The method according to claim 7 wherein the requested braking torque is a torque required to reduce the speed of the axle of the gear box in order to facilitate a shift to a higher gear.

9. The method according to claim 1 wherein the requested braking torque is utilized to increase a torque window for performing electrical braking of the vehicle.

10. The method according to claim 1 wherein the requested power dissipation is used to selectively control additional heating in the electrical machine and/or in the inverter.

11. A control system for controlling power dissipation in an electric drive system for a hybrid electrical vehicle having a gear set or a gear box, an electrical machine connected to an axle of the gear set or gear box, and a rechargeable battery operatively connected to the electrical machine via an inverter, the control system comprising: a control unit configured to control the gear box and the electrical machine, wherein the control unit is configured to determine a maximum available braking torque of the electrical machine for a given set of operating conditions based on a maximum power that the battery can receive and total normal power losses in the electric drive system; determine a stator current providing a maximum achievable power dissipation in the electrical drive system for a certain shaft torque value; receive a requested braking torque for the electrical machine, lower than or equal to a maximum available braking torque, or receive a requested power dissipation lower than or equal to the maximum achievable power dissipation; if a requested braking torque is equal to or lower than a torque required for providing a power corresponding to a sum of the maximum power that the battery can receive and the total normal power losses, provide the requested braking torque by providing power to the battery corresponding to a difference between the requested braking torque and the total normal power losses; if the required braking torque exceeds the torque required for providing a power corresponding to the sum of the maximum power that the battery can receive and the total normal power losses, determine a stator current of the electrical machine that will dissipate an additional power needed while still achieving a required braking torque; and if a power dissipation is requested, determine a stator current resulting in the requested power dissipation.

12. The control system according to claim 11 wherein the gear box is a dual clutch transmission gear box, wherein the electrical machine is operatively connected to an axle of one of the two clutches.

13. The control system according to claim 11 wherein the control unit is further configured to determine the stator current providing the maximum achievable power dissipation in the electrical drive system by determining electrical machine losses and inverter losses.

14. The control system according to claim 11 wherein the control unit is further configured to determine a stator current of the electrical machine that will dissipate the additional power needed while achieving the required braking torque by modifying a maximum torque per ampere, MTPA, stator current along a constant torque line.

15. The control system according to claim 11 wherein the control unit is further configured to determine a plurality of maximum available braking torques of the electrical machine for a range of different operating conditions, and to store the plurality of available braking torques.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present disclosure will now be described in more detail, with reference to the appended drawings showing an example embodiment of the disclosure, wherein:

[0034] FIG. 1 is a flow chart outlining the general steps of a method according to an embodiment of the disclosure;

[0035] FIG. 2 schematically illustrates an electric drive system for a hybrid electric vehicle according to an embodiment of the disclosure; and

[0036] FIG. 3 is a graph schematically illustrating stator current for an electrical machine according to embodiments of the disclosure.

DETAILED DESCRIPTION

[0037] As required, detailed embodiments are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary and that various and alternative forms may be employed. 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.

[0038] In the present detailed description, various embodiments of the method and system according to the present disclosure are mainly described with reference to an electric drive system for a hybrid vehicle comprising a dual clutch transmission. However, the general concept of the disclosure is equally applicable to hybrid drive systems utilizing other transmission configurations.

[0039] FIG. 1 is a flow chart outlining the general steps of a method according to an embodiment of the disclosure. The method of FIG. 1 will be discussed with further reference to FIG. 2 schematically illustrating an electric drive system for a hybrid electric vehicle.

[0040] FIG. 2 illustrates an electric drive system 200 comprising a gear set or a gear box 202. The gear box 202 is here illustrated as a dual-clutch transmission gear box 202, comprising a first and a second clutch, 204a, 204b connected to a respective first and second axle, 206a, 206b. An electrical machine 208 is operatively connected to the second axle 206b of the gear box 202, which in the present example can be considered to represent the even gears of the gear box 202. The gear box 202 is further arranged to receive power from an internal combustion engine (ICE) 210. A rechargeable battery 211 is operatively connected to the electrical machine 208 via an inverter and inverter controller unit 212.

[0041] The system further comprises a control unit 214 configured to control the gear box 202 and the electrical machine 208 and an engine control module (ECM) 216 controls the operation of the ICE 210. The various control units and modules are connected to a common communication interface, e.g. a CAN bus, for communicating with each other and with other modules in the vehicle in which the drive system is arranged. However, the skilled person realizes that the described functionality can be achieved in many different ways by using one or more dedicated or general purpose control units.

[0042] It should be noted that the control unit 214, the control module 216, as well as any logic, algorithm, system, device, unit, module, node or the like described herein may comprise and/or be implemented in or by one or more processing units, such as ASICs, or appropriately programmed microcontrollers or microprocessors (e.g., one or more processors including central processing units (CPUs)) and associated memory and/or storage, which may include operating system software, application software and/or any other suitable program, code or instructions executable by the processor(s) for controlling operation thereof, for providing and/or controlling interaction and/or cooperation between the various features and/or components described herein, and/or for performing the particular methods and/or algorithms represented by the various functions and/or operations described herein.

[0043] The method outlined in FIG. 1 comprises determining 102 a maximum available braking torque T.sub.Max of the electrical machine 208 for a given set of operating conditions based on a maximum power P.sub.B,Max 104 that the battery 210 can receive and the total normal power losses P.sub.Loss 106 in the electric drive system 200. Next, the stator current, I.sub.S,Max, providing the maximum achievable power dissipation P.sub.D,Max in the electrical drive system for a certain shaft torque value is determined 108.

[0044] The maximum available braking torque T.sub.Max is thus determined as the sum of the torque required to provide the maximum power to the battery, the normal power losses and the maximum achievable power dissipation, i.e. T.sub.Max˜(P.sub.B,Max+P.sub.Loss+P.sub.D,Max).

[0045] Next, the method comprises receiving 110 a requested braking torque T.sub.r for the electrical machine, lower than or equal to the maximum available braking torque T.sub.Max, or receiving 112 a requested power dissipation P.sub.D,r lower than or equal to the sum of the maximum achievable power dissipation in the electrical drive system, P.sub.D,EM, and the total normal power losses P.sub.Loss. Since the maximum available braking torque has been determined for a given set of operating conditions, this value can be communicated to other functionality of the vehicle such that the requested braking torque T.sub.r does not exceed the available torque T.sub.Max, for the given set of operating conditions. Furthermore, a requested power dissipation P.sub.D,r is limited by the maximum available power dissipation P.sub.D,Max=P.sub.D,EM+P.sub.Loss.

[0046] Moreover, the maximum available braking torque T.sub.Max may be determined for a wide range of operating conditions such that a torque map is created, for example in the form of a lookup table, thereby eliminating the need to recalculate the available torques, and also increasing the responsiveness and speed of the system since no online calculations need to be performed to determine the available torque values. The different operating conditions to take into consideration may for example comprise the stator winding temperature, the DC voltage to the inverter, the speed of the electrical machine and the output torque from the electrical machine. Furthermore, the maximum available braking torque T.sub.Max values for different operating conditions may be determined analytically or empirically.

[0047] Next, it is determined 114 if the requested braking torque T.sub.r is equal to or lower than the torque required for providing a power corresponding to the sum of the maximum power that the battery can receive P.sub.B,Max and the total power losses P.sub.Loss. If that is the case, the requested braking torque T.sub.r is provided by providing 116 power to the battery corresponding to the difference between the requested braking torque and the total normal power losses, i.e. P.sub.B=P(T.sub.r)−P.sub.Loss.

[0048] On the other hand, if it is determined 114 that the requested braking torque exceeds the torque required for providing a power corresponding to the sum of the maximum power that the battery can receive and the total normal power losses, a stator current I.sub.S of the electrical machine that will dissipate the additional power P.sub.IS needed while achieving the required braking torque is determined 118, i.e. P.sub.IS˜T.sub.r−(T(P.sub.B,Max)+T(P.sub.Loss)).

[0049] If there is a request is for dissipation of additional power, P.sub.D,r, the method comprises determining 120 a stator current I.sub.S corresponding to the difference between the requested power dissipation P.sub.D,r and the total normal power losses, P.sub.Loss.

[0050] The step of determining 108 the stator current, I.sub.S,max, providing the maximum achievable power dissipation P.sub.D,Max in the electrical drive system may comprise determining both the electrical machine losses in themselves as well as the inverter losses, since inverter losses are inherent in the electrical machine, and since the inverter losses also depend on the amplitude of the current provided to the electrical machine.

[0051] FIG. 3 is a diagram showing a vector representation of the stator current vector Is for the electrical machine 208. The stator current is represented by the d-and q-axis phase currents in a dq-reference frame, where the stator current is limited by a maximum current line to prevent damage to the electrical machine. In a normal operating mode where no additional power dissipation is required in the electrical machine, the stator current is determined as a maximum torque per ampere (MTPA) current, I.sub.S1, providing maximum efficiency. To increase the possible power dissipation in the electrical machine, the stator current is recalculated. The stator current I.sub.S2 is illustrated as being located along a constant torque line with respect to I.sub.S1, i.e. I.sub.S2 provides the same output torque but with a decreased efficiency.

[0052] For machine speed-and torque-levels covering the entire operating range, the d-axis and q-axis current resulting in the highest achievable stator current (MAPT—Maximum Ampere Per Torque) and resistive losses in the electric machine stator is calculated, where the considered resistive losses P.sub.cu are defined by

P.sub.cu=R.sub.S√{square root over (i.sub.d.sup.2+i.sub.q.sup.2)}

where R.sub.s is the stator winding resistance. The current i.sub.d is limited to ensure that permanent demagnetization does not occur.

[0053] The additional losses P.sub.add made possible by modifying the stator current I.sub.S1 can be approximately estimated by the increased resistive losses and determined as

P.sub.add=3/2R.sub.S(I.sub.S2.sup.2−I.sub.S1.sup.2).

[0054] In one embodiment of the disclosure, the requested braking torque is utilized to perform gear synchronization. In particular, the requested braking torque is a torque required to reduce the speed of the second axle 204b of the gear box 202 in order to facilitate a shift to a higher gear.

[0055] Even though the disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the method and system may be omitted, interchanged or arranged in various ways, the method and system yet being able to perform the functionality of the present disclosure.

[0056] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0057] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. 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 disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure.