Engine idle speed stability control method based on generator torque ripple compensation

Abstract

According to the engine idle speed stability control method based on generator torque ripple compensation, engine idle speed fluctuation can be restrained, the stability of engine idle speed control is improved, and therefore the system performance and the fuel economy are improved. Comprising the following steps: step 1, sampling a target rotating speed in an idling stage, entering a digital controller, and converting the target rotating speed into a digital quantity; the idling speed reference value and the idling speed sampling value are subtracted through a digital controller to obtain a speed difference, and the speed difference enters an engine idling speed controller to obtain a corresponding throttling instruction; secondly, an electronic throttle valve control loop changes the opening degree of a throttle valve or the air inlet amount of a bypass air channel according to the throttling instruction, the throttling angle is adjusted, and therefore the amount of air entering an engine is controlled; and thirdly, according to the throttling angle and an engine model, the output torque of the adjusted engine is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of engine idle speed control, and particularly to an engine idle speed stability control method based on generator torque fluctuation compensation. Background Art

[0002] An engine-generator set is a device that converts the mechanical energy of an engine into electrical energy and is widely used in multiple fields such as industry, commerce, household, and portable power sources. In the automotive field, a range extender composed of an engine, a generator, and a controller is a device that, when the on-vehicle rechargeable energy storage system cannot meet the vehicle's cruising range requirements, drives the generator through the engine to provide additional electrical energy for the vehicle's power system, thereby increasing the driving range. The range-extended power system combines the advantages of a pure electric system and a traditional fuel power system, can provide a flexible energy solution while having a long endurance, and is expected to play an important role in future new energy power systems.

[0003] The core of idle speed control is to keep the engine running at the lowest stable speed. An excessively high idle speed will increase fuel consumption, and an excessively low idle speed will cause the engine idle speed to be unstable. The main power source of the range extender is the engine. In one working cycle of the engine, the intermittent torque generated by the sequential ignition of each cylinder and the inertial torque generated by the reciprocating motion of the piston make the torque output by the engine have a periodic fluctuation characteristic. Therefore, the speed also has a periodic fluctuation characteristic. Engine idle torque compensation refers to compensating for the speed fluctuation caused by changes in external load or internal working conditions through various control strategies during engine idle operation to maintain the stability of the engine speed. Idle torque compensation is of great significance for improving the stability of the engine, reducing emissions, and improving fuel economy.

[0004] In the prior art, after an outer rotor generator replaces the traditional flywheel, the stability of the range-extended engine during low-speed operation deteriorates, and it is necessary to increase the idle speed to reduce speed fluctuations, but this will increase energy loss. Moreover, due to the inherent delay and slow response of the engine torque, traditional idle speed control methods may limit the performance of the system. Designing a safe and reliable engine idle speed control method and system based on the engine-generator set, improving the stability of the engine idle speed, reducing energy loss, and enhancing the overall performance are particularly important; in addition, with the increasing demand for electricity and the need for energy conservation and emission reduction, the design requirement for lightweight of the unit is also more urgent.

[0005] Patent CN 101982332 B proposes a starting generator hybrid system equipped with a flywheel. In this system, the flywheel is arranged between the engine and the generator, and the starting generator is connected to the flywheel through a planetary gear system. During the starting process, the flywheel plays a role in torque compensation to make the idle speed more stable. However, after the outer rotor generator in this type of generator set replaces the traditional flywheel and is connected to the engine, the stability of the engine during low-speed operation deteriorates, and the original idle speed cannot be maintained. It is necessary to increase the idle speed to reduce the speed fluctuation, but this will increase the energy loss. Moreover, due to the inherent delay and slow response of the engine torque, the traditional idle speed control method may limit the performance of the system. If an additional flywheel is used to provide torque compensation to make the idle speed more stable, it will greatly increase the volume and weight of the unit, which does not meet the requirements of lightweight design. Summary of the Invention

[0006] The present invention proposes an engine idle speed stability control method based on generator torque fluctuation compensation, which can suppress the fluctuation of the engine idle speed, improve the stability of the engine idle speed control, and thus improve the system performance and fuel economy.

[0007] The present invention is realized through the following technical solutions.

[0008] An engine idle speed stability control method based on generator torque fluctuation compensation, characterized by including the following steps:

[0009] Step 1: Sample the target speed in the idle speed stage and input it into the digital controller, and convert it into a digital quantity; through the digital controller, subtract the idle speed reference value ω * from the idle speed sampled value ω to obtain the speed difference Δω, and input it into the engine idle speed controller to obtain the corresponding throttle command θ R ;

[0010] Step 2: According to the throttle command θ R of the electronic throttle control loop, change the opening of the throttle valve or the intake air volume of the bypass air passage, adjust the throttle angle θ, so as to control the air volume entering the engine;

[0011] Step 3: According to the throttle angle θ and the engine model, obtain the output torque T en of the adjusted engine;

[0012] Step 4: By extracting the speed difference shunt part, introduce a quasi-proportional resonance algorithm with a resonance frequency at the harmonic frequency with the largest harmonic content in the speed difference, and amplify the gain of the speed difference Δω to obtain the compensation torque command of the generator

[0013] Step 5: The generator torque controller receives the compensation torque command Perform real-time regulation on the generator torque, so as to output the generator compensation torque used to compensate for the periodic torque fluctuation of the engine;

[0014] Step Six: Subtract the output torque T en of the generator and the generator compensation torque to obtain the adjusted engine speed ω according to the engine inertia principle;

[0015] Step Seven: In the next control cycle, repeat Steps One to Six to achieve closed-loop control of the engine idle speed.

[0016] Advantages of the present invention:

[0017] 1. Since the traditional PI controller can only perform error-free control on DC signals, when there are AC components, the PI controller cannot generate effective commands to compensate for them. The resonant controller can achieve zero steady-state error control for sinusoidal signals at the resonant frequency point. According to this characteristic, on the basis of the engine idle speed closed-loop control system, the present invention adopts the method of adding a quasi-resonant controller to suppress the rotational speed harmonics with large harmonic content by compensating the torque fluctuation of the engine at idle speed through the generator, effectively reducing the rotational speed fluctuation caused by engine torque pulsation and improving the smoothness of idle operation;

[0018] 2. The present invention helps to reduce unnecessary fuel consumption and emissions. By maintaining a stable idle speed, the fuel consumption of the engine at idle can be reduced, and at the same time, the emission pollutants can be reduced;

[0019] 3. The present invention uses generator torque compensation to assist in controlling the engine idle speed, reducing the risk of engine stalling;

[0020] 4. The present invention does not require additional devices, which helps to achieve lightweight design of the engine-generator set. Description of the Drawings

[0021] Figure 1 is a schematic diagram of the common structure of the engine-generator set system implemented by the present invention;

[0022] Figure 2 is a schematic diagram of the flow of the engine idle speed stability control method based on generator torque fluctuation compensation of the present invention. Detailed Embodiments

[0023] The following will describe in detail the exemplary embodiments of the present invention with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the drawings are only exemplary, intended to explain the principles and spirit of the present invention, and not to limit the scope of the present invention.

[0024] As Figure 1As shown in the figure, the engine - generator set system to which the present invention is applied includes an engine, a generator, a three - phase full - bridge controllable rectifier, and a load; the engine and the generator operate with a coaxial shaft, the output terminal of the generator is connected to the three - phase full - bridge controllable rectifier, and the rectifier uses the PWM controllable rectification method to rectify the alternating current generated by the generator into direct current with an adjustable voltage value within a certain range to supply the load.

[0025] Based on the above system, as Figure 2 shown in the figure, the engine idle - speed stability control method based on generator torque ripple compensation of the present invention specifically includes the following steps:

[0026] Step 1: Sample the target speed in the idle - speed stage and input it into the digital controller, and convert it into a digital quantity; through the digital controller, subtract the idle - speed sampling value ω of the idle - speed from the idle - speed reference value ω to obtain the speed difference Δω, and then input it into the engine idle - speed controller to obtain the corresponding throttle command θ * ; R ;

[0027] Step 2: The electronic throttle control loop changes the opening of the throttle valve or the intake air volume of the bypass air passage according to the throttle command θ R , adjusts the throttle angle θ, and thus controls the air volume entering the engine;

[0028] Step 3: According to the throttle angle θ and the engine model, obtain the output torque T of the adjusted engine en ;

[0029] Step 4: By extracting the speed - difference shunt part, introduce a quasi - proportional - resonant algorithm with a resonant frequency at the harmonic frequency where the harmonic content of the speed difference is the largest, and amplify the gain of the speed difference Δω to obtain the compensation torque command of the generator

[0030] In this embodiment, the quasi - proportional - resonant transfer function of the quasi - proportional - resonant algorithm is:

[0031]

[0032] where ω c is the cut - off frequency, ω o is the resonant frequency, k p and k r are the proportional gain and the resonant gain respectively; in specific implementation, the resonant frequency ω o is the harmonic frequency where the harmonic content of the speed difference is the largest, the cut - off frequency ω c is set to 1% of the harmonic frequency where the harmonic content of the speed difference is the largest; s is a complex intermediate variable used to analyze and describe the behavior of a linear time - invariant system in the frequency domain, and the frequency - domain transfer function is converted into a discrete - domain transfer function by using the bilinear transformation, which is specifically expressed as:

[0033]

[0034] Among them, T represents the sampling period of the digital signal processor, which is equal to the switching period; Z represents a discrete quantity;

[0035] Therefore, the discrete expression of the quasi-proportional resonant function is:

[0036]

[0037] Convert the quasi-proportional resonant algorithm into C language that can be recognized by the digital controller according to Equation (3);

[0038] Step Five: The generator torque controller receives the compensation torque command and adjusts the generator torque in real time, thereby outputting the generator compensation torque to compensate for the periodic torque fluctuations of the engine;

[0039] Step Six: Subtract the output torque T en of the generator from the generator compensation torque and obtain the adjusted engine speed ω according to the engine inertia principle;

[0040] Step Seven: In the next control cycle, repeat Steps One to Six to achieve closed-loop control of the engine idle speed.

[0041] To sum up, the above is only the preferred embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0042] For those skilled in the art, it is obvious that the embodiments of the present invention are not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the embodiments of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the embodiments of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to cover all changes falling within the meaning and scope of the equivalent elements of the claims in the embodiments of the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights. In addition, it is obvious that the word "including" does not exclude other units or steps, and the singular does not exclude the plural. The multiple units, modules or devices stated in the system, device or terminal claims can also be implemented by the same unit, module or device through software or hardware. First, second, etc. are used to represent names and do not represent any specific order.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the embodiments of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An engine idle stability control method based on generator torque fluctuation compensation, characterized in that, It includes the following steps: Step 1. Sample the target speed in the idle stage and input it into the digital controller, and convert it into a digital quantity; use the digital controller to subtract the idle speed reference value ω * from the idle speed sampled value ω to obtain the speed difference Δω, and input it into the engine idle speed controller to obtain the corresponding throttle command θ R ; Step 2: The electronic throttle control circuit changes the opening degree of the throttle valve or the intake air volume of the bypass air passage according to the throttle command θ R , adjusts the throttle angle θ, and thus controls the air volume entering the engine; Step 3: Obtain the output torque T of the adjusted engine according to the throttling angle θ and the engine model en ; Step 4: By extracting the rotational speed difference shunt part, introduce a quasi-proportional resonance algorithm with a resonance frequency at the harmonic frequency where the harmonic content of the rotational speed difference is the largest, and amplify the gain of the rotational speed difference Δω to obtain the compensation torque command of the generator 2. The engine idle stability control method based on generator torque fluctuation compensation according to claim 1, characterized in that After step four, it further includes: Step 5: The generator torque controller receives the compensation torque command and adjusts the generator torque in real time, thereby outputting the generator compensation torque to compensate for the periodic torque fluctuations of the engine.

3. The engine idle stability control method based on generator torque fluctuation compensation according to claim 2, wherein, After step five, it further includes: Step 6. Subtract the output torque T of the generator en from the compensation torque of the generator to obtain the adjusted engine speed ω according to the engine inertia principle.

4. The engine idle stability control method based on generator torque fluctuation compensation according to claim 3, characterized in that After step six, it further includes: Step seven, in the next control cycle, repeat steps one to six to achieve closed-loop control of the engine idle speed.

5. A method for controlling the engine idle stability based on generator torque fluctuation compensation according to claim 1 or 2 or 3 or 4, characterized in that, The quasi-proportional-resonant transfer function of the quasi-proportional-resonant algorithm is: where ω c is the cut-off frequency, ω o is the resonant frequency, k p and k r are the proportional gain and the resonant gain respectively; in specific implementation, the resonant frequency ω o is the harmonic frequency with the largest harmonic content of the rotational speed difference, and the cut-off frequency ω c is set to 1% of the harmonic frequency with the largest harmonic content of the rotational speed difference; s is a complex intermediate variable used to analyze and describe the behavior of a linear time-invariant system in the frequency domain. The bilinear transformation is used to convert the frequency-domain transfer function into a discrete-domain transfer function, which is specifically expressed as: Where, T represents the sampling period of the digital signal processor, which is equal to the switching period; Z represents the discrete quantity; Therefore, the discrete expression of the quasi-proportional-resonant function is: According to Equation (3), convert the quasi-proportional-resonant algorithm into C language that can be recognized by the digital controller.

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