CO-SIMULATION SYSTEM WITH DELAY COMPENSATION AND METHOD FOR CONTROL OF CO-SIMULATION SYSTEM

Abstract

A method of providing stable communication between subsystems in a co-simulation system, including providing a signal S.sub.1 describing an output angular velocity of a rotating body of the first physical system; filtering the signal S.sub.1 using a continuous moving average, CMA, filter; and forming a time discrete first output signal S.sub.1*. In a second subsystem the signal S.sub.1* is received and the angular velocity described by S.sub.1* is applied to the second physical system. A response signal S.sub.2* describes a torque generated by the second subsystem. The response signal S.sub.2* is received by the first subsystem where a time discrete feedback signal S.sub.F* is formed based on the difference between the response signal S.sub.2* and a time discrete damping signal S.sub.D*.

Claims

1. A method of providing stable communication between subsystems in a co-simulation system comprising a plurality of subsystems, each subsystem representing a physical system of a vehicle, the method comprising: in a first subsystem of the co-simulation system, simulating a first physical system, providing a first time continuous signal S.sub.1 describing a first output angular velocity of a rotating body of the first physical system; filtering the first time continuous signal S.sub.1 using a continuous moving average, CMA, filter and forming a time discrete first output signal S.sub.1*; in a second subsystem of the co-simulation system, simulating a second physical system, receiving the time discrete first output signal S.sub.1* from the first subsystem, applying the angular velocity described by the time discrete first output signal S.sub.1* to the second physical system, and providing a time discrete response signal S.sub.2* from the second subsystem describing a torque generated by the second subsystem; in the first subsystem, receiving the response signal S.sub.2* and forming a time discrete feedback signal S.sub.F* based on the difference between the response signal S.sub.2* and a time discrete damping signal S.sub.D*, wherein forming the damping signal S.sub.D* comprises applying an inertia to the rotating body of the first physical system, resulting in a time continuous damping signal S.sub.D representing a torque, followed by filtering the time continuous damping signal S.sub.D using a CMA-filter and applying a unit delay to form the time discrete damping signal S.sub.D*, thereby synchronizing S.sub.D* with S.sub.2*; and applying the time discrete feedback signal S.sub.F* as a torque to the rotating body.

2. The method according to claim 1, wherein the inertia is modeled by a spring-damper resonator system.

3. The method according to claim 2, wherein a natural frequency of the spring damper resonator system is higher than a Nyquist frequency for a sampling rate of the co-simulation system.

4. The method according to claim 1, wherein the continuous moving average, CMA, filter is an energy conserving filter.

5. The method according to claim 1, wherein the co-simulation system simulates an automotive transmission system.

6. The method according to claim 1, wherein the inertia is an estimated inertia based on a torque output from the second subsystem.

7. The method according to claim 1, further comprising, in the first subsystem: determining a time discrete acceleration signal A.sub.1* of the first time discrete output signal S.sub.1*; filtering the time discrete acceleration signal A.sub.1* with a time discrete moving average, DMA, filter; determining a torque of the second subsystem from the response signal S.sub.2*; and estimating the inertia based on the time discrete acceleration signal A.sub.1* and the torque from the time discrete response signal S.sub.2*.

8. The method according to claim 1, further comprising: determining a time discrete acceleration signal A.sub.1* of the first time discrete output signal S.sub.1*; filtering the time discrete acceleration signal A.sub.1* with a time discrete moving average, DMA, filter; determining a discrete time derivative of the acceleration signal A.sub.1*; determining a discrete time derivative of the response signal S.sub.2*; and estimating the inertia based on the discrete time derivative of the acceleration signal A.sub.1* and the discrete time derivative of the response signal S.sub.2*.

9. A co-simulation system comprising a plurality of subsystems, each subsystem representing a physical system of a vehicle, the co-simulation system comprising: a first subsystem of the co-simulation system, configured to simulate a first physical system, providing a first time continuous signal S.sub.1 describing a first output angular velocity of a rotating body of the first physical system; a continuous moving average, CMA, filter configured to filter the first time continuous signal S.sub.1 to form a time discrete first output signal S.sub.1*; a second subsystem of the co-simulation system, configured to simulate a second physical system, the second subsystem being configured to receive the time discrete first output signal S.sub.1* from the first subsystem, apply the angular velocity described by the time discrete first output signal S.sub.1* to the second physical system, and to provide a time discrete response signal S.sub.2* from the second subsystem describing a torque generated by the second subsystem; the first subsystem being further configured to: receive the response signal S.sub.2* and to form a time discrete feedback signal S.sub.F* based on the difference between the response signal S.sub.2* and a time discrete damping signal S.sub.D*, wherein the damping signal S.sub.D* is formed by applying an inertia to the rotating body of the first physical system, resulting in a time continuous damping signal S.sub.D representing a torque, followed by filtering the time continuous damping signal S.sub.D using a CMA-filter and applying a unit delay to form the time discrete damping signal S.sub.D*, thereby synchronizing S.sub.D* with S.sub.2*; and apply the time discrete feedback signal S.sub.F* as a torque to the rotating body.

10. The co-simulation system according to claim 9, wherein the first subsystem further comprises a spring-damper resonator system configured to model the inertia.

11. The co-simulation system according to claim 10, wherein the spring-damper resonator system is configured such that a natural frequency of the spring damper resonator system is higher than a Nyquist frequency for a sampling rate of the co-simulation system.

12. The co-simulation system according to claim 9, wherein the co-simulation system simulates an automotive transmission system.

13. The co-simulation system according to claim 9, wherein the inertia is an estimated inertia based on a torque output from the second subsystem.

14. The co-simulation system according to claim 9, wherein the first subsystem is further configured to: determine a time discrete acceleration signal A.sub.1* of the first time discrete output signal S.sub.1*; filter the time discrete acceleration signal A.sub.1* with a time discrete moving average, DMA, filter; determine a torque of the second subsystem from the response signal S.sub.2*; and estimate the inertia based on the time discrete acceleration signal A.sub.1* and the torque from the time discrete response signal S.sub.2*.

15. The co-simulation system according to claim 9, wherein the second subsystem is black box system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

[0027] FIG. 1 is a block diagram schematically illustrating a co-simulation system according to an embodiment of the invention;

[0028] FIG. 2 is a flow chart outlining the general steps of a method according to an embodiment of the invention;

[0029] FIG. 3 is a block diagram schematically illustrating features of a co-simulation system according to an embodiment of the invention;

[0030] FIG. 4 is a block diagram schematically illustrating a co-simulation system according to an embodiment of the invention;

[0031] FIGS. 5A-B are flow charts outlining steps of methods according to embodiments of the invention;

[0032] FIGS. 6A-B are diagrams schematically illustrating signals of a system according to an embodiment of the invention;

[0033] FIG. 7 is a diagram schematically illustrating signals of a system according to an embodiment of the invention; and

[0034] FIG. 8 is a diagram schematically illustrating signals of a system according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0035] In the present detailed description, various embodiments of the co-simulation system and the method for providing stable communication according to the present invention are mainly described with reference to a co-simulation system simulating an automotive transmission system operating in the angular mechanical energy domain.

[0036] FIG. 1 schematically illustrates a co-simulation system 100 according to an embodiment of the invention and FIG. 2 is a flow chart outlining the general steps of a method according to an embodiment of the invention.

[0037] In particular, FIG. 1 illustrates a first subsystem 102 of the co-simulation system 100, simulating a first physical system and a second subsystem 104 simulating a second physical system. In the present exemplifying description, the first subsystem 102 simulates an engine with a crank shaft having a rotating body 106 and the second subsystem 104 simulates a gearbox and possibly also the remaining components required to form a complete vehicle. It should however be understood that the described method comprising signal conditioning to reduce the risk of undesirable behavior at the interface between subsystems can be applied for a wide range of applications and energy domains.

[0038] The method comprises, in the first subsystem 102 of the co-simulation system 100, providing 200 a first time continuous signal S.sub.1 describing a first output angular velocity of the rotating body 106 of the first physical system. The signal S.sub.1 is acquired by determining the angular velocity of the rotating body 106. Next, the time continuous signal S.sub.1 is filtered 202 using an energy conserving continuous moving average, CMA, filter 108 and sampled to form a time discrete first output signal S.sub.1*. In the following description, any time discrete signal can be assumed to be extrapolated as a Zero-Order-Hold (ZOH) discrete signal when required. Moreover, signals notated with a star (*) superscript describe time discrete signals and signal notations with no superscript are time continuous signals. Moreover, the functionality of the CMA-filter 108 is described in detail in EP3136267. In short, the CMA-filter 108 acts as an energy conserving anti-aliasing filter.

[0039] In the next step, the second subsystem 104 of the co-simulation system 100, simulating a second physical system, receives the time discrete first output signal S.sub.1* from the first subsystem, where the angular velocity described by S.sub.1* is applied 204 to the second physical system 104. The second subsystem 104 can be assumed to comprise a rotating mass to which the angular velocity is applied.

[0040] Accordingly, the crank shaft angular velocity S.sub.1* is provided to the second subsystem 104 representing a gearbox. The gearbox will then provide 206 a time discrete response signal S.sub.2* representing a generated torque load which is subsequently provided to the first subsystem 102, i.e. the engine. The described example is typically numerically stable for low gears, but the described system will gradually deteriorate with increasing gears unless the described method including delay compensation is applied. It can be assumed that the second subsystem 104 comprises a filter corresponding to the above described CMA-filter 108 in order to provide a time discrete output signal S.sub.2* being compatible with the first subsystem 102. In applications where the second subsystem 104 is not equipped with an internal CMA-filter, such a filter can be inserted if intermediate solver steps of the second subsystem 104 are available where S.sub.2 is represented rather than S.sub.2*.

[0041] In the first subsystem 102, the response signal S.sub.2* is received and a time discrete feedback signal S.sub.F* is formed 216 based on the difference between the response signal S.sub.2* and a time discrete damping signal S.sub.D*. Forming the damping signal S.sub.D* comprises applying 210 an inertia, J, from an inertia block 110 to the rotating body 106 of the first physical system having the first output angular velocity, i.e. S.sub.1, resulting in a time continuous damping signal S.sub.D representing a torque. Next, the time continuous damping signal S.sub.D is filtered 212 using a CMA-filter 112 followed by applying a unit delay 114 to the filtered signal to form the time discrete damping signal S.sub.D*. The time delay is applied in order to synchronize S.sub.D* with S.sub.2*. Thereby, the feedback signal S.sub.F* can be formed as S.sub.F*=S.sub.2*S.sub.D*. In the final step, the time discrete feedback signal S.sub.F* is applied 218 as a torque to the rotating body 106.

[0042] FIG. 3 schematically illustrates an example embodiment where the inertia block 110 is modeled by a spring-damper resonator system 300 comprising a mass 302 (representing an inertia, J), a spring 304 and a damper 306. The parameters of the spring-damper resonator system 300 are selected such that a natural frequency of the spring damper resonator system 300 is higher than a Nyquist frequency for a sampling rate of the co-simulation system 100.

[0043] FIG. 4 schematically illustrates a co-simulation system 100 further comprising functionality for estimating the inertia based on the angular velocity S.sub.1* of the rotating mass and on the response signal S.sub.2* from the second subsystem. FIG. 4 will be discussed with reference to the flow chart of FIG. 5A outlining additional steps of a method according to an embodiment of the invention.

[0044] First, a time discrete acceleration signal A.sub.1* of the first time discrete output signal S.sub.1* is determined in 500 in an acceleration block 402. The time discrete acceleration signal A.sub.1* is filtered 502 using a time discrete moving average, DMA, filter 404, which is a time-discrete equivalent of the above described CMA-filter 108. An output torque of the second subsystem 104 is determined 504 from the response signal S.sub.2*. Finally, the inertia value is estimated 506 in an estimation block 406 based on the time discrete acceleration signal A.sub.1* and the torque from the time discrete response signal S.sub.2*. The inertia is then provided in the inertia block 110. A good estimation of the inertia is an inertia value that mitigates oscillatory instabilities and which does not impact the actual acceleration of the entire system significantly. E.g., while shifting through gears the aim is for the estimated inertia to follow the effective and sensed inertia. If the inertia does not follow the sensed inertia, the acceleration capacity at low gears would be impacted negatively. The motivation is thus to allow for the variable inertia to match the actual sensed load when the load has dynamically changing inertia with a significant spread.

[0045] The flow chart of FIG. 5B outlines the steps of a method of estimating the inertia according to an embodiment of the invention. The method comprises determining 500 a time discrete acceleration signal A.sub.1* of the first time discrete output signal S.sub.1*, filtering 502 the time discrete acceleration signal A.sub.1* with a time discrete moving average, DMA, filter, determining 508 a discrete time derivative of the acceleration signal A.sub.1*, determining 510 a discrete time derivative of the response signal S.sub.2*, and estimating 512 the inertia based on the discrete time derivative of the acceleration signal A.sub.1* and the discrete time derivative of the response signal S.sub.2*.

[0046] FIG. 6A is a diagram illustrating the time continuous angular velocity signal S.sub.1 at the rotating mass 106 and the resulting CMA-filtered time discrete angular velocity signal S.sub.1*. For comparison, FIG. 6B illustrates the same signals S.sub.1 and S.sub.1* in a co-simulation system without the delay compensation provided by the described method employing the feedback signal S.sub.F*. In FIG. 6B, the signals S.sub.1 and S.sub.1* exhibit an oscillatory an unstable behavior.

[0047] FIG. 7 is a diagram illustrating S.sub.2 representing a torque measured at a rotating mass (not shown) of the second subsystem 104. It can be seen that the torque comprises high spikes in amplitude. FIG. 7 further illustrates S.sub.2* representing the torque output from the second subsystem, which results from CMA-filtering of the signal S.sub.2. As is clear from FIG. 7, the CMA-filtered signal S.sub.2* has a very different behavior compared to S.sub.2 since the CMA-filter will average the spikes over two samples.

[0048] FIG. 8 is a diagram illustrating S.sub.2* together with the formed delay compensation signal S.sub.D* which has been delayed and thereby synchronized with S.sub.2*, and the resulting feedback signal S.sub.F* to be provided to the rotating mass 106.

[0049] Even though the invention 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 co-simulation 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 invention.

[0050] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, 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.