Piston displacement detection method for free piston Stirling power generation system

Abstract

The invention discloses a piston displacement detection method for a free piston Stirling power generation system, and the method comprises the steps: 1, constructing a second-order sliding-mode observer based on the power generation principle of a linear motor, and carrying out the observation of a counter electromotive force signal of the power generation system; 2, a third-order generalized integrator with a frequency-locked loop is adopted to suppress a direct-current component, filtering integration is carried out on the back electromotive force signal, and the filtered back electromotive force signal and an orthogonal signal of the filtered back electromotive force signal are output; 3, according to the relation between the piston displacement amplitude and the back electromotive force amplitude and the relation between the piston speed phase and the back electromotive force, the real-time displacement amplitude and speed phase information of the piston are calculated from the filtered back electromotive force signal and the orthogonal signal of the back electromotive force signal through a phase-locked loop; and 4, inputting the real-time displacement amplitude and the speed phase information of the piston into a control system of the power generation system to realize control operation of the power generation system. By means of the method, the real-time displacement amplitude and speed phase information of the piston can be accurately calculated, and efficient and stable control over the system is achieved.

Description

Technical Field

[0001] This invention relates to the field of space power and thermoelectric conversion technology, and in particular to a method for detecting piston displacement in a free piston Stirling power generation system. Background Technology

[0002] With the deepening of space exploration missions, efficient and stable space power systems have become a core requirement. Power generation schemes using nuclear reactors as heat sources and free-piston Stirling generator systems as thermoelectric conversion mechanisms are considered ideal solutions for future space power applications due to their high energy conversion efficiency and reliability. This power generation system mainly consists of a free-piston Stirling engine and a linear motor. Its power generation principle is as follows: the engine converts the heat from the nuclear reactor into mechanical energy, driving the linear generator's mover to generate an induced electromotive force, thereby converting mechanical energy into electrical energy. During system operation, to ensure stable startup and power generation, and to prevent safety accidents due to overstroke, it is necessary to monitor the displacement information of the power generation system in real time to ensure stable displacement movement.

[0003] Traditional methods rely on deploying hardware displacement sensors for detection. However, the compact internal structure and extreme high-temperature, high-pressure operating environment of free-piston Stirling generator systems make sensor deployment difficult and prevent long-term, stable, and accurate detection. Therefore, a reliable sensorless detection solution is needed. For single-phase Stirling linear generator systems, based on their power generation principle, the back-EMF integration method can typically be used for sensorless displacement detection. However, the back-EMF integration method is an open-loop detection method. During system operation, motor parameters are easily affected by temperature fluctuations, and the DC components in the voltage and current detection signals accumulate during integration, leading to integrator output saturation. Ultimately, this results in distorted piston displacement detection results, failing to meet the system's precise control requirements.

[0004] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0005] The purpose of this invention is to construct a second-order sliding mode observer to observe the back EMF signal in real time, and to use a third-order generalized integrator with a frequency-locked loop to completely suppress the DC component and filter and integrate the back EMF signal to accurately calculate the real-time displacement amplitude and velocity phase information of the piston, thereby achieving efficient and stable control of the system.

[0006] To achieve the above objectives, the present invention provides a piston displacement detection method for a free piston Stirling power generation system, comprising at least the following steps: Step 1: Based on the linear motor power generation principle, construct a second-order sliding mode observer to observe the back EMF signal of the power generation system; Step 2: A third-order generalized integrator with a frequency-locked loop is used to suppress the DC component and filter and integrate the back EMF signal to output the filtered back EMF signal and the back EMF quadrature signal. Step 3: Based on the proportional relationship between the piston displacement amplitude and the back EMF amplitude, and the in-phase relationship between the piston velocity phase and the back EMF phase, the real-time displacement amplitude and velocity phase information of the piston are calculated from the filtered back EMF signal and the back EMF quadrature signal using a phase-locked loop. Step 4: Input the real-time displacement amplitude and velocity phase information of the piston into the control system of the power generation system to realize the control operation of the power generation system.

[0007] Optionally, in step 1, constructing the second-order sliding mode observer includes: 1) Establish the current error state equation with current as the state variable; 2) Design a sliding mode control law based on the superhelical algorithm and the sliding mode surface at the integral end, wherein the sliding mode control law is the observed value of the back EMF signal.

[0008] Optionally, the sliding mode control law is designed using the following formula: in, e smo Here, R is the observed value of the back EMF signal, and R is the stator resistance of the linear motor. Where L is the integral gain, and L is the stator inductance of the linear motor. For current error, s is the sliding surface at the integration end, k1 and k2 are the sliding mode gain coefficients, and sign() is the switching function.

[0009] Optionally, in step 3, the state equation of the third-order generalized integrator with a frequency-locked loop is: in, , , These represent three state variables. , , These represent the first derivatives of the three state variables. k Represents the sliding mode gain coefficient. k dc The sliding mode gain coefficient representing DC bias. e smo The observed value representing the back electromotive force signal. , These represent the filtered back EMF signal and the back EMF quadrature signal, respectively. , These represent the detection frequency and the reference frequency, respectively. , Representing the first derivatives of the detection frequency and the reference frequency, respectively, and y represents the output matrix. γ This represents the gain of the frequency-locked loop.

[0010] Optionally, the transfer function of the third-order generalized integrator for the DC component is zero, so as to completely suppress the DC component in the input signal.

[0011] Optionally, in step 3, the proportional relationship between the piston displacement amplitude and the back electromotive force amplitude satisfies: in, x m This represents the piston displacement amplitude. E m The magnitude of the back electromotive force. K e This is the thrust coefficient of the linear motor. This refers to the operating frequency.

[0012] Optionally, in step 3, the piston velocity phase is the same as the back electromotive force phase.

[0013] Optionally, after step 1 and before step 2, the method further includes: verifying the stability of the second-order sliding mode observer based on the Lyapunov function; if the Lyapunov function is satisfied, the second-order sliding mode observer is stable; if the Lyapunov function is not satisfied, the second-order sliding mode observer is unstable.

[0014] Optionally, in step 2, the third-order generalized integrator with a frequency-locked loop can adaptively track the fluctuations in the operating frequency of the power generation system.

[0015] Optionally, in step 4, the control system performs amplitude limiting protection control on the stroke of the power generation system based on the real-time displacement amplitude of the piston; and adjusts the power or frequency of the power generation system based on the speed phase information of the piston.

[0016] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: 1) This invention uses a second-order sliding mode observer to accurately observe the back EMF signal online, and combined with subsequent signal processing, it realizes reliable calculation of piston displacement and velocity phase, providing key and accurate state feedback for closed-loop control of the power generation system.

[0017] 2) Furthermore, a second-order sliding mode observer is designed using an integral end sliding surface based on the superspiral algorithm. Compared with the first-order sliding mode observer, it significantly suppresses high-frequency chattering in the back EMF signal, improves the observation accuracy from the signal source, and lays a solid foundation for subsequent high-precision displacement calculation.

[0018] 3) Furthermore, a third-order generalized integrator with a frequency-locked loop is innovatively introduced to process the observed signal. This not only generates high-quality orthogonal signals to support accurate phase-locking, but its unique transfer function can completely suppress the DC component in the input signal, fundamentally eliminating detection errors caused by sensor zero-point drift. At the same time, the frequency-locked loop mechanism improves the adaptive capability of the power generation system to operating frequency fluctuations, significantly enhancing the accuracy and robustness of the entire detection method. Attached Figure Description

[0019] Figure 1 This is a flowchart of the piston displacement detection method for the free piston Stirling power generation system of the present invention.

[0020] Figure 2 This is a schematic diagram of the second-order sliding mode observer structure of the present invention.

[0021] Figure 3 This is a schematic diagram of the third-order generalized integrator with a frequency-locked loop according to the present invention.

[0022] Figure 4 This is a comparison chart of the true value and the detected value of the back electromotive force according to the present invention.

[0023] Figure 5 This is a piston displacement amplitude detection diagram of the present invention.

[0024] Figure 6 This is a comparison diagram of the true value and the detected value of the velocity phase according to the present invention. Detailed Implementation

[0025] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the piston displacement detection method for a free piston Stirling power generation system proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0026] In existing technologies, displacement detection is typically achieved by deploying displacement sensors. However, the compact internal structure of free piston Stirling generator systems and their extreme high-temperature and high-pressure operating environment make sensor deployment difficult and prevent long-term stable and accurate detection. When using sensorless open-loop detection methods for displacement detection, the motor parameters are easily affected by temperature and drift during system operation. At the same time, the DC components contained in the voltage and current detection signals accumulate continuously during integration, causing the integrator output to saturate, ultimately resulting in a large deviation in the piston displacement detection results.

[0027] To address the aforementioned problems, this invention proposes a sensorless displacement detection method based on a second-order sliding mode observer. By constructing a second-order sliding mode observer to monitor the back EMF signal in real time, and utilizing a third-order generalized integrator with a frequency-locked loop to completely suppress the DC component and filter and integrate the back EMF signal, the real-time displacement amplitude and velocity phase information of the piston can be accurately calculated, thereby achieving efficient and stable control of the system. A detailed description follows.

[0028] like Figure 1 As shown, the present invention provides a piston displacement detection method for a free piston Stirling power generation system, comprising at least the following steps: Step 1: Based on the linear motor generation principle, a second-order sliding mode observer is constructed to observe the back EMF signal of the power generation system. The structure of the second-order sliding mode observer is as follows: Figure 2 As shown.

[0029] When the free piston Stirling generator system is generating electricity, taking the direction of the generated current as positive, the voltage equation for the linear motor in the generating state is: Where u is the terminal voltage of the linear motor, i is the current, R and L are the stator resistance and stator inductance of the linear motor, respectively, and e is the back EMF of the motor armature in the generator system.

[0030] Choosing current i as the state variable, the current state equation can be obtained as follows: The current error state equation based on the sliding mode observer is: in, e smo The observed value of the back electromotive force signal. This is for current error.

[0031] The basic form of the superspiral sliding mode algorithm is: in, Represents state variables. Represents the sliding mode gain coefficient. The variable represents the sliding mode variable, and sign() represents the switching function. This represents the system disturbance term.

[0032] Combining integral and end-effector sliding surfaces, an integral end-effector sliding surface is designed, and the integral end-effector sliding surface is selected as follows: in, represents the integral gain, and r represents the power exponent order.

[0033] Based on the sliding surface at the end of the integral, we can obtain: When the state variable approximates the sliding surface, the first derivative... =0, the current error will converge to 0, and the observed back EMF will be equal to the true back EMF value, that is... Setting ds / dt=0, we can obtain the equivalent control law. u eq for: Combining the superhelical algorithm and the integral end sliding surface, the sliding mode control law can be obtained. The sliding mode control law is the observed value of the back EMF signal. The sliding mode control law is designed using the following formula: in, e smo Here, R is the observed value of the back EMF signal, and R is the stator resistance of the linear motor. Where L is the integral gain, and L is the stator inductance of the linear motor. For current error,s is the sliding surface at the integration end, k1 and k2 are sliding gain coefficients greater than zero, and sign() is the switching function.

[0034] The process, which takes place between step 1 and step 2, also includes: verifying the stability of the second-order sliding mode observer based on the Lyapunov function.

[0035] The selected Lyapunov function is: Taking its derivative, we get: Since both k1 and k2 are greater than 0, when s > 0, <0; when s<0 >0. According to the Lyapunov stability theorem, if the system satisfies the Lyapunov function, the second-order sliding mode observer is stable; if it does not satisfy the Lyapunov function, the second-order sliding mode observer is unstable.

[0036] Step 2: A third-order generalized integrator with a frequency-locked loop is used to suppress the DC component and filter and integrate the back EMF signal, outputting a filtered back EMF signal and a back EMF quadrature signal. The structure of the third-order generalized integrator with a frequency-locked loop is as follows: Figure 3 As shown.

[0037] The state equation of a third-order generalized integrator with a frequency-locked loop is: in, , , These represent three state variables. , , These represent the first derivatives of the three state variables. k Represents the sliding mode gain coefficient. k dc The sliding mode gain coefficient representing DC bias. e smo The observed value representing the back electromotive force signal. , These represent the filtered back EMF signal and the back EMF quadrature signal, respectively. , These represent the detection frequency and the reference frequency, respectively. , Representing the first derivatives of the detection frequency and the reference frequency, respectively, and y represents the output matrix. γ This represents the gain of the frequency-locked loop.

[0038] Filtered back EMF signal ( ), back potential orthogonal signal ( ) and DC bias signal ( The transfer functions of ) can be expressed as follows: Therefore, high-frequency chattering caused by the switching function in the sliding mode observer can be filtered out, and DC components caused by current and voltage detection errors can be completely suppressed. At the same time, the third-order generalized integrator with frequency-locked loop can adaptively track the fluctuations of the power generation system's operating frequency.

[0039] Step 3: Based on the proportional relationship between the piston displacement amplitude and the back EMF amplitude, and the in-phase relationship between the piston velocity phase and the back EMF phase, the real-time displacement amplitude and velocity phase information of the piston are calculated from the filtered back EMF signal and its orthogonal signals using a phase-locked loop.

[0040] During the operation of the Stirling generator system, the proportional relationship between the piston displacement amplitude and the back electromotive force amplitude satisfies: in, x m This represents the piston displacement amplitude. E m The magnitude of the back electromotive force. K e This is the thrust coefficient of the linear motor. This refers to the operating frequency.

[0041] The piston velocity phase and the back EMF phase satisfy the following relationship: the piston velocity phase and the back EMF phase are the same. Step 4: Input the real-time displacement amplitude and velocity phase information of the piston into the control system of the power generation system to realize the control operation of the power generation system.

[0042] The control system limits the stroke of the power generation system based on the real-time displacement amplitude of the piston; and adjusts the power or frequency of the power generation system based on the speed and phase information of the piston.

[0043] In this embodiment, a free piston Stirling power generation system heated by a heat source is used as an example. The piston displacement is detected using the above method. The linear motor stator inductance is 0.0538H, the linear motor stator resistance is 2Ω, the linear motor thrust coefficient is 92, and the power generation system operates at a frequency of 80Hz. During the operation of the power generation system, the results of the actual back EMF and the detected back EMF are as follows: Figure 4 As shown, from Figure 4As can be seen, the difference between the true and detected back EMF values ​​is extremely small, indicating that this method achieves accurate and reliable detection of back EMF. The detection results of the real-time displacement amplitude and velocity phase of the piston, obtained after phase-locked loop and proportional calculation, are shown below. Figure 5 and Figure 6 As shown in the figure, the displacement amplitude of the piston fluctuates relatively little (e.g. Figure 5 As shown), the difference between the true value and the detected value of the velocity phase is extremely small (e.g. Figure 6 As shown in the figure, this method achieves accurate detection of the real-time displacement amplitude and velocity phase of the piston, with strong detection accuracy, and can be used for real-time operation control of power generation systems.

[0044] In summary, this invention constructs a second-order sliding mode observer to observe the back EMF signal in real time, and uses a third-order generalized integrator with a frequency-locked loop to completely suppress the DC component and filter and integrate the back EMF signal to accurately calculate the real-time displacement amplitude and velocity phase information of the piston, thereby achieving efficient and stable control of the system.

[0045] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0046] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for detecting piston displacement in a free-piston Stirling generator system, characterized in that, Include at least the following steps: Step 1: Based on the linear motor power generation principle, construct a second-order sliding mode observer to observe the back EMF signal of the power generation system; Step 2: A third-order generalized integrator with a frequency-locked loop is used to suppress the DC component and filter and integrate the back EMF signal to output the filtered back EMF signal and the back EMF quadrature signal. Step 3: Based on the proportional relationship between the piston displacement amplitude and the back EMF amplitude, and the in-phase relationship between the piston velocity phase and the back EMF phase, the real-time displacement amplitude and velocity phase information of the piston are calculated from the filtered back EMF signal and the back EMF quadrature signal using a phase-locked loop. Step 4: Input the real-time displacement amplitude and velocity phase information of the piston into the control system of the power generation system to realize the control operation of the power generation system.

2. The method as described in claim 1, characterized in that, In step 1, constructing the second-order sliding mode observer includes: 1) Establish the current error state equation with current as the state variable; 2) Design a sliding mode control law based on the superhelical algorithm and the sliding mode surface at the integral end, wherein the sliding mode control law is the observed value of the back EMF signal.

3. The method as described in claim 2, characterized in that, The sliding mode control law is designed using the following formula: in, e smo Here, R is the observed value of the back EMF signal, and R is the stator resistance of the linear motor. Where L is the integral gain, and L is the stator inductance of the linear motor. For current error, s is the sliding surface at the integration end, k1 and k2 are the sliding mode gain coefficients, and sign() is the switching function.

4. The method as described in claim 1, characterized in that, In step 3, the state equation of the third-order generalized integrator with a frequency-locked loop is: in, , , These represent three state variables. , , These represent the first derivatives of the three state variables. k Represents the sliding mode gain coefficient. k dc The sliding mode gain coefficient representing DC bias. e smo The observed value representing the back electromotive force signal. , These represent the filtered back EMF signal and the back EMF quadrature signal, respectively. , These represent the detection frequency and the reference frequency, respectively. , Representing the first derivatives of the detection frequency and the reference frequency, respectively, and y represents the output matrix. γ This represents the gain of the frequency-locked loop.

5. The method as described in claim 4, characterized in that, The third-order generalized integrator has a transfer function of zero for the DC component, so as to completely suppress the DC component in the input signal.

6. The method as described in claim 1, characterized in that, In step 3, the proportional relationship between the piston displacement amplitude and the back electromotive force amplitude satisfies: in, x m This represents the piston displacement amplitude. E m The magnitude of the back electromotive force. K e This is the thrust coefficient of the linear motor. This refers to the operating frequency.

7. The method as described in claim 1, characterized in that, In step 3, the piston velocity phase is the same as the back electromotive force phase.

8. The method as described in claim 1, characterized in that, The process after step 1 and before step 2 also includes: verifying the stability of the second-order sliding mode observer based on the Lyapunov function; if the Lyapunov function is satisfied, the second-order sliding mode observer is stable; if the Lyapunov function is not satisfied, the second-order sliding mode observer is unstable.

9. The method as described in claim 1, characterized in that, In step 2, the third-order generalized integrator with frequency-locked loop can adaptively track the fluctuations in the operating frequency of the power generation system.

10. The method as described in claim 1, characterized in that, In step 4, the control system performs amplitude limiting protection control on the stroke of the power generation system based on the real-time displacement amplitude of the piston; and adjusts the power or frequency of the power generation system based on the speed phase information of the piston.

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