CN117184035A - Operating method, controller and computer program product for a hybrid powertrain system - Google Patents

Abstract

The present invention relates to a method of operating a hybrid system for a vehicle, the hybrid system comprising an engine and an electric motor, wherein a power battery is chargeable with power from the electric motor and/or the engine, the method of operation comprising: s100, comparing the speed of the vehicle with a speed threshold value to judge whether the vehicle runs in a high speed state or a low speed state; s101, comparing the SOC of the power battery with a first SOC threshold value in a low-speed state to select one of a pure electric mode and an engine participation mode as an operation mode of the hybrid system; s111, in a high vehicle speed state, the SOC is compared with a second SOC threshold value lower than the first SOC threshold value to select one of an electric-only mode and an engine participation mode as an operation mode. Corresponding controllers and computer program products are also presented. By the present invention, an alternative method for controlling mode switching of a hybrid powertrain is provided.

Description

Operating method, controller and computer program product for a hybrid powertrain system

Technical Field

The present invention relates to a method of operating a hybrid system for a vehicle, a controller for controlling a hybrid system of a vehicle and a computer program product.

Background

In recent years, in order to meet the demand for improving fuel economy and cope with the exhaust emission regulations continuously tightened in various countries, it has been increasingly desired to employ an environment-friendly power system. Hybrid power systems have been attracting attention as a realistic and viable solution to environmentally friendly power systems and have been applied to the fields of hybrid vehicles, ships, and the like.

A hybrid system is a power system that is powered via an engine that generates torque by combusting fuel and via an electric motor that generates torque by consuming electric energy of a power battery. The hybrid powertrain may operate in different modes of operation, such as electric-only mode, engine-driven mode, and hybrid mode, in which power is provided by the electric motor, the engine, or both, respectively.

To better exploit the advantages of both the engine and the motor, control strategies for hybrid systems are widely studied. The main objective of the control strategy of the hybrid powertrain is to improve fuel economy while meeting desired drivability. For example, the Equivalent Consumption Minimum Strategy (ECMS) is a real-time optimal control strategy based on calculating the fuel consumption of the engine and the equivalent fuel consumption of the electric drive section.

In ECMS, the hybrid system switches modes of operation with the goal of minimizing power consumption by the engine and motor for a given driver demand. However, such control strategies do not fully exploit the advantages of the hybrid system from a long term efficiency perspective. Also, during the mode switching, the driver tends to notice a change in the driving behavior characteristic of the vehicle. It is very difficult to calibrate the control strategy of the hybrid system to maintain consistent drivability in different modes of operation. This will present further challenges for calibration of the control strategy considering various driving modes driven by the electric only mode, such as electric creep, electric start, electric automatic stop, etc.

Disclosure of Invention

It is an object of the present invention to provide an alternative method for controlling mode switching of a hybrid powertrain system. In particular, a wider SOC operating range and/or better drivability consistency of the power cells of the hybrid system can be achieved.

According to one aspect of the present invention, there is provided a method of operating a hybrid system for a vehicle, the hybrid system comprising an engine for providing power by consuming fuel and an electric motor for providing power by consuming electric energy of a power battery, the power battery being chargeable with power from the electric motor and/or the engine, the hybrid system being configured to be selectively operable in an electric-only mode or an engine-engaged mode. The operation method comprises the following steps:

-S100: comparing the speed of the vehicle with a speed threshold to determine whether the vehicle is traveling in a high speed state or a low speed state;

-S101: comparing the SOC of the power battery with a first SOC threshold value to select one of an electric-only mode and an engine-engaged mode as an operation mode of the hybrid system in a case where the vehicle is running in a low-vehicle speed state; and

-S111: in the case where the vehicle is traveling in a high vehicle speed state, the SOC of the power battery is compared with a second SOC threshold value, which is lower than the first SOC threshold value, to select one of the electric-only mode and the engine-engaged mode as the operation mode of the hybrid system.

In one exemplary embodiment according to the present invention, the operation method further includes a step S102 that is performed in a case where the vehicle is traveling in a low vehicle speed state, wherein, in step S102, a driver required torque of the vehicle is compared with a motor maximum torque of the motor to select an operation mode of the hybrid system, wherein step S101 and step S102 are set to: in the case where the vehicle is running in a low vehicle speed state, the hybrid system is operated in the electric-only mode as long as the SOC of the power battery is not lower than the first SOC threshold value and the driver-required torque does not exceed the motor maximum torque.

In one exemplary embodiment according to the present invention, the operating method comprises a step S301, wherein in said step S301, in case the hybrid system is operated in an engine participation mode, a power split between the electric motor and the engine is determined from a reference SOC, wherein the first SOC threshold value is lower than the reference SOC.

According to another aspect of the invention, a controller for controlling a hybrid system of a vehicle is proposed, wherein the controller comprises a processor and a memory, wherein the memory stores computer program instructions which, when executed by the processor, are capable of executing the operating method according to the invention.

According to a further aspect of the invention, a computer program product is proposed, comprising computer program instructions, wherein the computer program instructions, when executed by one or more processors, are capable of executing the method of operation according to the invention.

In the operating method according to the invention, the operating mode of the hybrid system may be selected in accordance with the vehicle speed and the SOC of the power battery. Thus, the frequency of mode switching between the electric-only mode and the engine-engaged mode can be reduced. This is advantageous for drivability consistency, particularly in low vehicle speed conditions.

In existing control strategies for hybrid systems, such as switching of operation modes with the aim of minimizing power consumption by the engine and motor for a given driver demand, this will cause mode switching of the hybrid system and start and stop operations of the engine to occur frequently, especially in the case of vehicles driven by the hybrid system traveling at low vehicle speeds. During mode switching, the driver will notice a change in the driving behavior characteristics of the vehicle, especially at low vehicle speeds, as the differences between the different operating modes are easily distinguished, especially at low vehicle speeds. As previously described, it is very difficult to calibrate the control strategy of the hybrid powertrain to maintain consistent drivability in different modes of operation. Further, at low vehicle speeds, the start-up operation of the engine is easily noticeable to the driver. The starting operation of the engine can be activated via the starter or the clutch, wherein the starting operation via the clutch activation can result in better drivability, no jerk, and higher fuel efficiency, because the engine can be started by utilizing the kinetic energy of the wheel-side clutch through the pulsed contact of the wheel-side clutch with the engine-side clutch. However, when the vehicle is traveling at a low vehicle speed, the engine will be started more via the starter.

In addition, in existing control strategies for hybrid systems, mode switching of the hybrid system and torque distribution between the engine and the motor may be performed based on SOC (state of charge) balancing techniques, i.e., the SOC of the power battery will be kept near or within a narrow SOC reference range, such that the SOC of the power battery remains approximately the same at the beginning and end of one driving cycle. Due to such severe restrictions on the SOC of the power battery, the use of the power battery and the motor is also restricted. In addition, since the charging of the power battery is limited, the possibility of shifting the operating point of the engine to a more efficient operating point is also limited.

According to the present invention, different SOC thresholds are utilized to select the operating mode for the low and high vehicle speed states. Thus, the SOC operating range of the power battery can be widened. In particular, in a high vehicle speed state, the SOC of the power battery is allowed to reach a smaller lower limit value. Higher vehicle speeds mean greater potential for energy recovery that can be used in the future to charge the power cells. Therefore, even if the power battery is consumed to a relatively low SOC in a high vehicle speed state, it is ensured that the power battery can be charged again to a high SOC level later. Once the engine is started, it can also charge the power battery after providing power for driving the vehicle. The relatively low SOC of the power battery may force the engine to operate at a more efficient operating point.

Thus, according to the present invention, an alternative method of controlling mode switching of a hybrid powertrain is provided, wherein, among other things, a wider SOC operating range and/or better drivability consistency of the power battery is achieved.

Drawings

The principles, features and advantages of the present invention may be better understood by describing the present invention in more detail with reference to the drawings. The drawings include:

FIG. 1 illustrates a schematic diagram of a hybrid powertrain according to one embodiment of the present disclosure;

FIG. 2 schematically illustrates a flow chart of a method of operation according to one embodiment of the invention;

FIG. 3 schematically illustrates a flow chart of a method of operation according to another embodiment of the invention;

FIG. 4A schematically illustrates a BSFC (brake specific fuel consumption) map of an engine of a hybrid powertrain operating in a known manner; and

FIG. 4B schematically illustrates a BSFC map of an engine running a hybrid system in a method of operation according to one embodiment of the invention.

List of reference numerals

1. Vehicle with a vehicle body having a vehicle body support

10. Hybrid power system

11. Motor with a motor housing having a motor housing with a motor housing

12. Power battery

13. Engine with a motor

14. Transmission device

15. Clutch device

16. Speed reducing mechanism

17. Controller for controlling a power supply

20. Driving wheel

Detailed Description

In order to make the technical problems, technical solutions and advantageous technical effects to be solved by the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and a plurality of exemplary embodiments. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.

FIG. 1 illustrates a schematic diagram of a hybrid system 10 according to an exemplary embodiment of the invention. As shown in fig. 1, the hybrid system 10 is a drive system of the vehicle 1, for which purpose the hybrid system 10 is operatively connected to drive wheels 20 of the vehicle 1.

As can be seen from fig. 1, the hybrid system 10 includes at least an electric motor 11 for supplying power by consuming electric energy, a power battery 12 for supplying electric energy to the electric motor 11, and an engine 13 for supplying power by consuming fuel, wherein the power battery 12 can be charged with power from the electric motor 11 and/or the engine 13. For example, the power battery 12 may be configured as a secondary battery having an operating voltage of 48V. Optionally, the hybrid system 10 may also include a generator configured to provide electrical energy to the power cell 12 to recharge the power cell 12. The generator may be driven by the engine 13 or driven to recover kinetic energy during the coasting or regenerative braking phases of the vehicle 1. The electric motor 11 may also be configured as an electric motor that is also operable as a generator, which is capable of providing electric energy to the power battery 12 in order to charge the power battery 12. The engine 13 is a machine capable of converting energy into mechanical force or motion by consuming fuel, and is configured in particular as an internal combustion engine. The transmission 14 may be configured as a 5-speed AMT. The hybrid system 10 may further include a clutch 15 disposed between the engine 13 and the transmission 14 for connecting or disconnecting a power coupling from the engine 13 to the transmission 14, and a speed reduction mechanism 16 for the motor 11, and the motor 11 may be connected to an output of the transmission 14 through the speed reduction mechanism 16.

The hybrid powertrain 10 may be selectively operated in an electric-only mode or an engine-engaged mode. In the electric-only mode, the electric motor 11 is operated, and the engine 13 is turned off, whereby the hybrid system 10 is powered by the electric motor 11 alone. In the engine participation mode, the engine 13 is operating, and at least a portion of the power output by the hybrid system 10 is provided by the engine 13. In particular, in the engine-engaged mode, the electric motor 11 may be turned off, whereby the hybrid system 10 is powered only by the engine 13. Furthermore, the engine 13 may also drive an electric generator, which in turn provides electric energy to the power battery 12 in order to charge the power battery 12. In the engine participation mode, the electric motor 11 is also operable, whereby the hybrid powertrain 10 is powered by the engine 13 and the electric motor 11 together.

The operating mode of the hybrid powertrain 10 may be switched between electric-only and engine-engaged modes based on existing methods, such as ECMS-based or adaptive ECMS, to achieve minimal fuel consumption. Typically, a reference value of SOC is applied to balance the SOC, i.e., to control the SOC of the power battery 12 around the reference value. However, frequent mode switching, particularly at low vehicle speeds, is likely to occur in the existing methods, and drivability inconsistencies may result from frequent engine start/stop operations, engine start operations via starter activation, or loss of acceleration. The SOC of the power battery 12 is limited to a high, narrow range by the reference value of the SOC.

In one embodiment of the present invention, a method of operation for a hybrid powertrain 10 is presented. Fig. 2 shows a flow chart of the method of operation.

The operation method at least comprises the following steps:

-S100: comparing the vehicle speed of the vehicle 1 with a vehicle speed threshold value to determine whether the vehicle 1 is traveling in a high vehicle speed state or a low vehicle speed state;

-S101: in the case where the vehicle 1 is traveling in a low vehicle speed state, the SOC of the power battery 12 is compared with the first SOC threshold value to select one of the electric-only mode and the engine-engaged mode as the operation mode of the hybrid system 10; and

-S111: in the case where the vehicle 1 is traveling in the high vehicle speed state, the SOC of the power battery 12 is compared with a second SOC threshold value lower than the first SOC threshold value to select one of the electric-only mode and the engine-engaged mode as the operation mode of the hybrid system 10.

By the operating method, an alternative method of controlling mode switching of the hybrid powertrain 10 is provided, wherein, among other things, a wider SOC operating range and/or better drivability consistency of the power battery 12 may be achieved.

In the operation method, the operation mode is selected based on the vehicle speed and the SOC of the power battery 12. This reduces the frequency of mode switching between the electric-only mode and the engine-engaged mode. This is advantageous for drivability consistency, particularly in low vehicle speed conditions. For low and high vehicle speed conditions, different SOC thresholds are utilized to select the operating mode. This can widen the SOC operating range of the power battery 12. In particular, in the high vehicle speed state, the SOC of the power battery 12 is allowed to reach a smaller lower limit value. Higher vehicle speeds mean greater energy recovery potential that can be used in the future to charge the power cell 12. Therefore, even if the power battery 12 is consumed to a relatively low SOC in a high vehicle speed state, it is ensured that the power battery 12 can be charged to a high SOC level again later. Once the engine 13 is started, the engine 13 is able to charge the power battery 12 also after providing power for driving the vehicle 1. This facilitates operating the engine 14 at a more efficient operating point. Thus, the relatively low SOC of the power battery may force the engine 13 to operate at a more efficient operating point.

After step S101 or step S111, step S200 or S300 may be performed. In step S200, the hybrid system 10 is controlled to operate in the electric-only mode. In step S300, the hybrid system 10 is controlled to operate in the engine participation mode.

As shown in fig. 1, a controller 17 may be provided to perform the method of operation and control the operation of the hybrid system 10. The controller 17 may be communicatively coupled to and control the respective components (e.g., the sensors, the engine 13, the motor 11, etc.) and may receive operating conditions or sensed data of the respective components via communication lines to monitor and/or control the operation of the hybrid system 10. The controller 17 may include one or more processors, which may include: a microprocessor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or equivalent discrete or integrated logic circuit. The controller 17 may also include a memory, such as a non-transitory computer readable medium, storing computer program instructions that, when executed by the processor, cause the processor to perform a method of operation for the hybrid system 10. The memory may include various Random Access Memory (RAM), read Only Memory (ROM), or other memory.

Although the hybrid system 10 shown in fig. 1 is a parallel hybrid system 10, the present invention is also applicable to other types of hybrid systems 10, such as a series hybrid system 10 or a series-parallel hybrid system 10.

Fig. 3 shows a flow chart of a method of operation according to another embodiment of the invention.

As shown in fig. 3, in step S100, the vehicle speed v is compared with a vehicle speed threshold T _v In comparison, to determine whether the vehicle 1 is traveling in a high vehicle speed state or a low vehicle speed state. If the vehicle speed v is higher than the vehicle speed threshold T _v It is determined that the vehicle 1 is traveling in a high vehicle speed state. Otherwise, it is determined that the vehicle 1 is traveling in a low vehicle speed state.

After step S100, in the case where the vehicle 1 is traveling in a low vehicle speed state, step S101 is performed to match the SOC of the power battery 12 with the first SOC threshold value T _SOC1 Comparison. In step S101 shown in fig. 3, if the SOC of the power battery 12 is smaller than the first SOC threshold value T _SOC1 The engine participation mode is selected as the operation mode of the hybrid system 10, and step S300 is performed, otherwise step S102 is performed.

In step S102, the driver demand torque D of the vehicle 1 and the motor maximum torque M of the motor 11 are combined _T In comparison, one of the electric-only mode and the engine-engaged mode is selected as the operation mode of the hybrid system 10. Specifically, if the driver demand torque D of the vehicle 1 exceeds the motor maximum torque M _T Step S300 is performed, otherwise step S200 is performed. The driver demand torque D represents a torque demand that is set forth by the driver, for example, by operating an accelerator pedal of the vehicle 1. The driver demand torque D may be obtained based on accelerator pedal position, brake pedal travel, gear, engine speed, etc. Maximum motor torque M _T Is the maximum torque that the motor 11 can provide.

Step S101 and step S102 are set to: in the case where the vehicle 1 is traveling in a low vehicle speed state, as long as the SOC of the power battery 12 is not lower than the first SOC threshold value T _SOC1 And the driver demand torque D does not exceed the motor maximum torque M _T The hybrid powertrain 10 operates in an electric-only mode.

As described above, frequent mode switching is likely to occur in the known method, particularly at low vehicle speeds, and may be due to frequent engine start/stop operations, engine start operations via starter activation, or acceleration lossesThe drivability is inconsistent due to the misalignment. According to the embodiment of the invention, as long as the SOC of the power battery 12 is not lower than the first SOC threshold value T in the low vehicle speed state of the vehicle 1 by controlling the hybrid system 10 _SOC1 And the driver demand torque D does not exceed the motor maximum torque M _T The vehicle is operated in the electric-only mode, and frequent mode switching at low vehicle speeds can be avoided. This is advantageous for drivability consistency. Further, by performing the electric drive, the operating point of the engine 13, where the efficiency is low, can be avoided. It should be appreciated that in further embodiments, steps S100, S101 and S102 may be performed in a different order or simultaneously.

In one embodiment, the vehicle speed threshold T _v May be a fixed value. In another embodiment, the vehicle speed threshold T _v May vary as the SOC of the power cell 12 varies. In particular, the vehicle speed threshold T _v May be positively correlated to the SOC of the power cell 12. Therefore, if the power battery 12 has a relatively high SOC, the vehicle will be allowed to run in the electric-only mode at a relatively high vehicle speed. This is advantageous for further consuming the power of the power cell 12. In addition, in this case, the engine 13 will be started at a higher vehicle speed, which is advantageous in achieving better drivability and better fuel efficiency, because at higher vehicle speeds the engine 13 can be started by the clutch 16.

In one embodiment, a first SOC threshold T _SOC1 A fixed value may be set to provide uniformity in different driving modes, such as electric creep, electric start and electric drive. For example, a first SOC threshold T _SOC1 Can be set to 40%.

Fig. 4A shows a BSFC (brake specific fuel consumption) diagram of an engine of a hybrid system that switches between electric-only mode and engine-engaged mode based on a known ECMS. Fig. 4B shows a BSFC diagram of the engine 13 of the hybrid system 10 running in an operating method according to an embodiment of the invention in which the combination of steps S100, S101 and S102 described above is performed. In fig. 4A and 4B, the horizontal axis represents the engine speed ω in Revolutions Per Minute (RPM), and the vertical axis represents the engine torque T in newton meters (n·m).

In fig. 4A, there are more low efficiency operating points with low engine speed and high BSFC within the operating region of the engine. This represents a case where the vehicle is driven by the engine at a low vehicle speed. In contrast, as shown in fig. 4B, the low-efficiency operating point of the engine 13 with low engine speed and high BSFC is significantly reduced. In this case, the hybrid system 10 operating in the operating method according to the embodiment of the invention will operate in the electric-only mode. Accordingly, the SOC of the power battery 12 decreases for supplying electric power to the motor 11. Further, once the engine 13 is started thereafter, the power battery 12 will be charged. Thus, the engine 13 is not only powered to drive the drive wheels 20, but also to charge the power battery 12, which will force the engine 13 to operate at a more efficient operating point under greater load.

Returning now to fig. 3, the operating method may further include step S301 performed after step S300, wherein a power distribution between the motor 11 and the engine 13 is determined according to the reference SOC to balance the SOC, i.e., to control the SOC of the power battery 12 around the reference SOC. First SOC threshold T _SOC1 Below the reference SOC. It should be appreciated that the reference SOC may be a reference value or a reference range. For example, the reference SOC may be set to 60% or to a range of 50% to 70%. Preferably, the reference SOC may vary with the vehicle speed v. In particular, the reference SOC may be inversely related to the vehicle speed v.

In one embodiment according to the invention, the power distribution may be determined by an A-ECMS method, where the equivalent factor may vary with the SOC of the power cell 12 and the reference SOC.

In one embodiment according to the invention, the method of operation comprises a step S110 performed after step S100 and before step S111. After step S100, in the case where the vehicle 1 is traveling in a high vehicle speed state, step S110 is performed. In step S110, it is determined whether or not the acceleration a of the vehicle 1 is zero. If the acceleration a of the vehicle 1 is equal to zero, step S111 is performed; if not, an engine participation mode is selected as the operation mode of the hybrid system 10, and step S300 is performed.

When the vehicle 1 is at a speed greater than the vehicle speed threshold T _v The hybrid system 10 will operate in the engine participation mode in order to ensure that the hybrid system 10 provides sufficient power for the travel of the vehicle 1, with the vehicle speed v traveling and the acceleration a being non-zero.

When the vehicle 1 is at a speed greater than the vehicle speed threshold T _v If the vehicle speed v is constant for a certain period of time while the vehicle speed v is running, the engine 13 may be turned off and the driving wheels 20 will be driven by the motor 11. In this case, the motor 11 needs to provide less power to drive the drive wheels 20 by means of the inertia of the vehicle 1.

If the vehicle 1 is traveling at a high vehicle speed and zero acceleration, it is necessary to check the SOC of the power battery 12 and optionally the driver demand torque D of the vehicle 1 before selecting the electric-only mode as the operation mode of the hybrid system 10. For this, step S111 and step S112 are performed.

In step S111, if the SOC of the power battery 12 is smaller than the second SOC threshold value T _SOC2 The engine participation mode is selected as the operation mode of the hybrid system 10, otherwise step S112 will be executed. In step S112, the driver demand torque D of the vehicle 1 and the motor maximum torque M of the motor 11 are combined _T In comparison, one of the electric-only mode and the engine-engaged mode is selected as the operation mode of the hybrid system 10. If the driver demand torque D of the vehicle 1 exceeds the motor maximum torque M _T Step S300 is performed, and if not, step S200 is performed.

In one embodiment, a second SOC threshold T _SOC2 Is determined from the vehicle speed v. In other words, the second SOC threshold T _SOC2 May vary with the variation of the vehicle speed v. In particular, a second SOC threshold T _SOC2 May be inversely related to the vehicle speed v. If the vehicle 1 is traveling at a higher vehicle speed v, this means that a higher energy recovery potential can be provided that can be used to charge the power battery 12. Therefore, the second SOC threshold T can be lowered _SOC2 To allow further discharge of the power cell 12. For example, a second SOC threshold T _SOC2 May vary between 15% and 35%, even between 5% and 35%.

The invention also relates to a computer program product comprising computer program instructions, wherein the computer program instructions, when executed by one or more processors, are capable of performing the method of operation according to the invention. The computer program instructions may be stored in a computer readable storage medium, which may include, for example, high speed random access memory, but may also include non-volatile memory, such as a hard disk, memory, plug-in hard disk, smart Memory Card (SMC), secure Digital (SD) card, flash memory card, at least one disk storage device, or other volatile solid state storage device. The processor may be a central processing unit, but also other general purpose processors, digital signal processors, application specific integrated circuits, off-the-shelf programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. The above-described methods of operation, when executed by a processor, may be implemented by hardware, or by execution of corresponding software by hardware.

Although specific embodiments of the invention have been described in detail herein, they are presented for purposes of illustration only and are not to be construed as limiting the scope of the invention. In particular, the various features can be combined with one another where technically feasible according to the actual requirements. In particular, features from different embodiments may also be combined with one another. Various substitutions, alterations, and modifications can be made without departing from the spirit and scope of the invention.

Claims (10)

1. A method of operation for a hybrid system (10) of a vehicle (1), the hybrid system (10) comprising an engine (13) for providing power by consuming fuel and an electric motor (11) for providing power by consuming electric energy of a power battery (12), the power battery (12) being chargeable with power from the electric motor (11) and/or the engine (13), the hybrid system (10) being configured to be selectively operable in an electric-only mode or an engine-engaged mode,

wherein the operation method comprises the following steps:

-S100: comparing the vehicle speed of the vehicle (1) with a vehicle speed threshold value to determine whether the vehicle (1) is traveling in a high vehicle speed state or a low vehicle speed state;

-S101: comparing the SOC of the power battery (12) with a first SOC threshold value to select one of an electric-only mode and an engine participation mode as an operation mode of the hybrid system (10) in a case where the vehicle (1) is running in a low vehicle speed state; and

-S111: in a case where the vehicle (1) is traveling in a high vehicle speed state, the SOC of the power battery (12) is compared with a second SOC threshold value, which is lower than the first SOC threshold value, to select one of an electric-only mode and an engine participation mode as an operation mode of the hybrid system (10).

2. The operating method according to claim 1, wherein the operating method further includes a step S102 that is performed in a case where the vehicle (1) is traveling in a low vehicle speed state, wherein in step S102, a driver-required torque of the vehicle (1) is compared with a motor maximum torque of the motor (11) to select an operating mode of the hybrid system (10), wherein steps S101 and S102 are set to: in the case where the vehicle (1) is running in a low vehicle speed state, the hybrid system (10) is operated in the electric-only mode as long as the SOC of the power battery (12) is not lower than the first SOC threshold value and the driver demand torque does not exceed the motor maximum torque.

3. The operating method according to claim 1 or 2, wherein the operating method comprises a step S301, wherein in said step S301, in case the hybrid system (10) is operated in an engine participation mode, a power split between the electric motor (12) and the engine (13) is determined from a reference SOC, wherein the first SOC threshold value is lower than the reference SOC.

4. A method of operation according to any one of claims 1-3, wherein the vehicle speed threshold is positively correlated with the SOC of the power battery (12).

5. The operation method according to any one of claims 1-4, wherein the first SOC threshold value is set to a fixed value.

6. The operating method of any of claims 1-5, wherein the second SOC threshold value is inversely related to a vehicle speed.

7. The operating method according to any one of claims 1-6, wherein the operating method comprises a step S110 performed after step S100 and before step S111, wherein in the step S110 it is determined whether the acceleration of the vehicle (1) is zero, if yes, step S111 is performed, and if not, an engine participation mode is selected as the operating mode of the hybrid system (10).

8. The method of operation of any one of claims 1-7, wherein,

in step S111, if the SOC of the power battery (12) is less than the second SOC threshold value, an engine participation mode is selected as an operation mode of the hybrid system (10), otherwise step S112 will be performed;

in step S112, the driver-required torque of the vehicle (1) is compared with the motor maximum torque of the motor (13) to select one of the electric-only mode and the engine-engaged mode as the operation mode of the hybrid system (10).

9. A controller (17) for controlling a hybrid system (10) of a vehicle (1), wherein the controller (17) comprises a processor and a memory, wherein the memory stores computer program instructions that, when executed by the processor, are capable of performing the method of operation according to any one of claims 1-8.

10. A computer program product comprising computer program instructions, wherein the computer program instructions, when executed by one or more processors, are capable of performing the method of operation according to any one of claims 1-8.