Sliding mode control method and system based on nonlinear disturbance observer for resonant converter

Abstract

The present invention belongs to the technical field of power electronic DC / DC converter control and discloses a nonlinear disturbance observer-based sliding mode control method and system for a resonant converter. The method comprises the following steps: obtaining the rectified current on the secondary side and the output capacitor voltage; using the sampled current and voltage values ​​and known circuit element parameters to establish a state space equation of an LLC resonant converter required for sliding mode control and disturbance observer design; designing a sliding mode surface of the sliding mode control based on sliding mode control theory for a system model, and designing a control law based on the sliding mode surface; and designing a nonlinear disturbance observer and a sliding mode control combination to optimize the control effect; performing an inverse transformation on the control law to obtain the actual value of the control variable switching frequency, using the value as input, and then obtaining a switching signal of a variable frequency via a voltage-controlled oscillator as a driving signal for a converter switch tube, and adjusting the output voltage of the converter by real-time control of the frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic DC / DC converter control, and in particular relates to a nonlinear disturbance observer-based sliding mode control method and system for an LLC resonant converter. Background Art

[0002] With the current trend toward high-voltage, high-power renewable energy generation and energy storage technologies, LLC resonant converters (LLC) have garnered significant attention from both industry and academia due to their high efficiency and power density. A key advantage of LLC is its ability to achieve soft switching across a wide operating range, helping to address the increased switching losses caused by high voltage stress on switching devices and improving converter efficiency. Therefore, LLC resonant converters hold great potential for application in microgrid DC bus converters and energy storage device port converters.

[0003] Numerous studies have been conducted on control strategies for LLC converters, primarily focusing on achieving wide-range voltage output and light-load operation. However, these loads are assumed to be purely resistive. In practical AC / DC microgrids, however, a large number of constant-power loads are connected to the DC bus of the AC / DC distribution system. These tightly regulated constant-power loads exhibit negative impedance characteristics, reducing system damping and potentially causing control system instability. PI control, due to its simple structure and ease of implementation, is currently the most common control method used in practical engineering. However, when parameter and load perturbations occur in the system, the LLC resonant cavity gain changes. Existing PI control methods do not account for the adverse effects of these load and parameter perturbations on the system, resulting in poor control performance.

[0004] The above analysis reveals the following problems and drawbacks of the existing technology: existing control strategies rarely consider the case where the LLC resonant converter's load is a constant-power load, and there is limited research on the LLC resonant converter's stability under large-signal disturbances such as load disturbances and parameter perturbations. The negative impedance characteristics of a constant-power load can weaken the system's stability, and internal and external interference during device operation can affect its performance. Furthermore, dynamic response capabilities are required to achieve complex operating instructions. Therefore, studying LLC resonant converter control strategies to improve the system's interference immunity and dynamic response capabilities has significant research significance and application value. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a sliding mode control method, system, medium and equipment based on a nonlinear disturbance observer, which solves the problem of the LLC converter outputting a stable voltage when encountering large signal disturbances such as load disturbances and input voltage fluctuations when carrying a constant power load (such as a motor drive, etc.).

[0006] Specifically, the object of the present invention is to improve the following aspects:

[0007] Existing LLC control methods are based on the LLC topology for resistive loads, with little attention paid to the case of constant-power loads. The complex impedance characteristics of constant-power loads can weaken system stability. With the increasing proportion of power electronic loads, the impact of these loads needs to be considered in control design.

[0008] The LLC control method proposed in the present invention is a sliding mode controller based on a disturbance observer, which can significantly improve the anti-interference ability of the system and effectively suppress the adverse effects of large signal disturbances such as load mutations and input voltage fluctuations on the system.

[0009] The present invention is achieved by comprising:

[0010] The first step is to obtain the rectified current on the secondary side and the output capacitor voltage;

[0011] The second step is to use the sampled current and voltage values ​​and the known circuit component parameters to establish the state space equations of the LLC resonant converter required for sliding mode control and disturbance observer design;

[0012] The third step is to design the sliding surface of the sliding mode control based on the sliding mode control theory for the system model, and then design the control law based on the sliding surface. Finally, a nonlinear disturbance observer is designed to be combined with the sliding mode control to optimize the control effect.

[0013] The fourth step is to perform an inverse transformation on the control law to obtain the actual value of the control quantity switching frequency, which is used as input. Then, a switching signal with a changing frequency is obtained through a voltage-controlled oscillator as the driving signal of the converter switch tube, and the output voltage of the converter is adjusted by real-time control of the frequency.

[0014] Further, the specific implementation method of the first step:

[0015] Use current sensors and voltage sensors to obtain the rectified current on the secondary side of the LLC resonant converter and the output capacitor voltage;

[0016] The acquired current and voltage signals are sampled to obtain discrete current and voltage values ​​for subsequent control system design.

[0017] Further, the specific implementation method of the second step:

[0018] Based on the discrete sampling values ​​of the secondary-side rectified current and the output capacitor voltage, combined with known circuit component parameters, the state space equation of the LLC resonant converter is established.

[0019] State-space equations typically include state variables such as current, voltage, and circuit element parameters.

[0020] Further, the specific implementation method of the third step:

[0021] Based on the state space equation of LLC resonant converter, sliding mode control theory is used to design the sliding mode surface and determine the target point of the control system;

[0022] Design the control law of sliding mode control so that the system state reaches the sliding surface quickly and stably and remains on the sliding surface;

[0023] A nonlinear disturbance observer is designed to estimate and offset the disturbance and uncertainty in the system based on the output feedback information of the system, thereby improving the robustness and control accuracy of the control system.

[0024] Further, the specific implementation method of the fourth step:

[0025] The designed control law is inversely transformed using the transfer function to obtain the actual control variable switching frequency value, which is passed as input to the voltage-controlled oscillator;

[0026] The voltage-controlled oscillator adjusts its output frequency according to the input frequency value, generating a switching signal with a variable frequency. This switching signal will drive the switching action of the converter switch tube, thereby adjusting the output voltage of the converter.

[0027] By real-time control of the frequency, the output voltage of the LLC resonant converter can be regulated and stabilized.

[0028] Furthermore, the nonlinear disturbance observer is integrated with the sliding mode control and applied to the control of the LLC resonant converter; by establishing a reduced-order model, designing a sliding mode controller and a nonlinear disturbance observer, the system can quickly and stably achieve the desired output voltage and current, and effectively offset the uncertainties and disturbances in the system; a variable frequency control method is adopted to adjust the output voltage according to the actual control variable switching frequency f, thereby improving the efficiency and performance of the converter.

[0029] Another object of the present invention is to provide a nonlinear disturbance observer-based sliding mode control system that implements the nonlinear disturbance observer-based sliding mode control method, the system comprising: a current sensor, a voltage sensor, a state variable calculation module, a reference value calculation module, a disturbance observer module, a sliding mode controller, a control law transformation module and a voltage-controlled oscillator module.

[0030] Furthermore, the current sensor is used to obtain the current after rectification on the secondary side;

[0031] The voltage sensor is used to obtain the output capacitor voltage;

[0032] The state variable calculation module calculates the real-time value of the state variable based on the established state space model of the LLC resonant converter;

[0033] The reference value calculation module calculates the reference value of the state variable in real time based on the output of other modules;

[0034] The disturbance observer module is designed based on a state space model and a nonlinear disturbance observer design method; it is used to calculate the change of the constant power load;

[0035] The sliding mode controller designs a sliding mode surface of the sliding mode control based on the linear system model obtained by the state variable calculation module and the sliding mode control theory; and designs a control law based on the sliding mode surface;

[0036] The inverse transformation module is used to transform the control law in the sliding mode control module and calculate the actual control quantity: the value of the switching frequency;

[0037] The voltage controlled oscillator obtains a converter driving signal with a variable frequency and a fixed duty cycle based on the switching frequency value obtained by the inverse conversion module, and adjusts the output voltage of the converter by real-time control of the switching frequency.

[0038] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0039] First, due to the presence of resonant elements, the mathematical model order is higher, making modeling the LLC resonant converter more difficult than traditional PWM converters. Therefore, control strategies based on precise small-signal mathematical models result in a more complex control structure. LLC resonant converters also suffer from operating point drift, and changes in load power will affect the LLC gain characteristic curve. These disturbances, to a certain extent, affect the performance of traditional control methods and may even affect system stability. The LLC control method proposed in this invention, based on a sliding-mode controller with a disturbance observer, can significantly improve the system's anti-interference capability and effectively suppress the adverse effects of large-signal disturbances such as sudden load changes and input voltage fluctuations. Compared with traditional PI control, it has advantages in the controllable maximum power variation range under constant-power loads, the response speed to disturbance signals, and the adjusted overshoot. While improving the system's anti-interference and dynamic response performance, this control method also reduces the use of peripheral hardware circuits (primarily sampling circuits) and minimizes the controller structure to facilitate subsequent analog or digital implementation.

[0040] Second, the present invention mainly fills the gap that little attention has been paid to constant power loads when studying LLC control methods at home and abroad. Since the negative impedance characteristics of constant power loads will weaken the stability of the system, and the operating point of the LLC converter will drift and change when the load changes. In response to these problems, the present invention designs a controller that can keep the output voltage stable when the LLC converter is subjected to large signal disturbances with a constant power load. The control method designed by the present invention broadens the use scenarios of LLC resonant converters, and can apply LLC resonant converters to systems with a large number of power electronic load devices such as microgrids, energy storage systems, and electric vehicles.

[0041] Third, each step of the nonlinear disturbance observer-based sliding mode control method has the following significant technical advancements:

[0042] The first step is to obtain the rectified current on the secondary side and the output capacitor voltage:

[0043] In this step, the important input parameters of the converter are obtained by obtaining the rectified secondary current and the output capacitor voltage. Accurately obtaining these parameters provides a critical data foundation for the subsequent sliding mode control and disturbance observer design.

[0044] In the second step, the sampled current and voltage values ​​and the known circuit component parameters are used to establish the state space equations of the LLC resonant converter required for sliding mode control and disturbance observer design:

[0045] By establishing the state space equation of the LLC resonant converter, information such as current, voltage and circuit element parameters are integrated into the system model, providing a basis for the subsequent sliding mode control and disturbance observer design.

[0046] The third step is to design a sliding surface based on sliding mode control theory. This surface is then used to design a control law. Finally, a nonlinear disturbance observer is designed to optimize the control effect in combination with sliding mode control. In this step, the sliding surface is designed using sliding mode control theory to achieve fast and robust control of the converter system. A nonlinear disturbance observer is then designed to estimate and offset system uncertainties and disturbances, thereby improving the robustness and stability of the control system.

[0047] The fourth step is to perform an inverse transformation on the control law to obtain the actual value of the control variable switching frequency. This value is used as input, and then a switching signal with a variable frequency is obtained through a voltage-controlled oscillator as the drive signal for the converter switch tube. The output voltage of the converter is adjusted by real-time control of the frequency:

[0048] This step applies the designed control law to actual control. By inversely transforming the control law, the actual switching frequency of the controlled variable is obtained. The switching signal of the frequency conversion is then generated through the voltage-controlled oscillator, thereby achieving real-time control and regulation of the converter's output voltage.

[0049] This sliding-mode control method based on a nonlinear disturbance observer combines sliding-mode control and disturbance observer techniques. By acquiring and integrating current, voltage, and circuit element parameters, and designing a nonlinear disturbance observer, it achieves efficient control and optimization of the LLC resonant converter. This method represents a significant technological advancement in improving control accuracy and robustness.

[0050] Fourth, this method is applicable to LLC resonant converters. The following is an interpretation of each technical feature based on the claims, and clarifies the significant technological advancement brought about by each claim:

[0051] 1. Claim 1:

[0052] Technical features: The four key steps of the nonlinear disturbance observer-based sliding mode control method applied to LLC resonant converter are clarified, covering the four core links of data acquisition, model establishment, control law design and practical application.

[0053] Significant technological advancement: Provides a complete workflow to ensure the integrity and feasibility of the method.

[0054] 2. Claim 2:

[0055] Technical features: It provides a specific implementation method for data acquisition, clarifies the use of current sensors and voltage sensors, and performs discrete sampling of signals.

[0056] Significant technological advancements ensure the accuracy and timeliness of data collection, providing a high-quality data source for subsequent steps.

[0057] 3. Claim 3:

[0058] Technical features: The design method of sliding mode control based on nonlinear disturbance observer for LLC resonant converter is clarified and designed in combination with state space equations.

[0059] Significant technological advancements: Improved system robustness, ensuring the control strategy can cope with uncertainties and disturbances, making the control effect more stable.

[0060] 5. Claim 5:

[0061] Technical features: Provides a specific implementation method for the practical application of control laws, including inverse transformation and driving converter switches.

[0062] Significant technological advancement: ensures the effective implementation of control strategies and ensures control quality.

[0063] 6. Claim 6:

[0064] Technical Features: This paper describes a complete implementation of a sliding mode control system based on a nonlinear disturbance observer for an LLC resonant converter.

[0065] Significant technological progress: It provides a specific implementation framework, which enables the entire control strategy to move from theory to practical application, greatly improving its practical application value.

[0066] These claims provide a sliding mode control method combined with a nonlinear disturbance observer for an LLC resonant converter, which not only ensures the accuracy and stability of control but also improves the robustness of the system, enabling it to maintain good control effects in the face of uncertainties and disturbances. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a control principle diagram of a sliding mode control method based on a nonlinear disturbance observer provided by an embodiment of the present invention;

[0068] Figure 2 This is a diagram showing the voltage control effect when the input voltage changes, provided by an embodiment of the present invention;

[0069] Figure 3 This is a diagram showing the voltage control effect when the voltage output reference value changes, provided by an embodiment of the present invention;

[0070] Figure 4 This is a comparison chart of the voltage control effects of the embodiment of the present invention and the traditional PI control method under the same load transformation. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0072] like Figure 1 As shown, the sliding mode control method based on disturbance observer provided by the embodiment of the present invention has the following steps:

[0073] S01, obtains the rectified current on the secondary side and the output capacitor voltage

[0074] S02, using the current and voltage values ​​sampled in step 1 and known circuit element parameters to establish the state space equation of the LLC resonant converter required for sliding mode control and disturbance observer design.

[0075] In step S03, based on the obtained system model, a disturbance observer is designed to estimate the disturbance. Based on sliding mode control theory, a sliding surface is designed for sliding mode control, and the control law is designed based on the sliding surface. Combining the nonlinear disturbance observer with sliding mode control optimizes the control effect.

[0076] S04, based on the control law, the control law of the LLC resonant converter with a constant power load is obtained, which is used as input, and then a switching signal with a variable frequency is obtained through a voltage-controlled oscillator as the driving signal of the converter switch tube, and the output voltage of the converter is adjusted by real-time control of the frequency.

[0077] The following are the specific implementation plans for each step:

[0078] The first step is to obtain the rectified current on the secondary side and the output capacitor voltage:

[0079] Use current sensors and voltage sensors to obtain the rectified current on the secondary side of the LLC resonant converter and the output capacitor voltage.

[0080] The acquired current and voltage signals are sampled to obtain discrete current and voltage values ​​for subsequent control system design.

[0081] The second step is to establish the state space equation of the LLC resonant converter required for sliding mode control and disturbance observer design:

[0082] Based on the discrete sampling values ​​of the rectified secondary-side current and the output capacitor voltage, combined with known circuit component parameters, the state-space equation of the LLC resonant converter is established.

[0083] State-space equations typically include state variables such as current, voltage, and circuit element parameters.

[0084] The third step is to design the sliding surface and control law of the sliding mode control, and design a nonlinear disturbance observer to combine with the sliding mode control to optimize the control effect:

[0085] Based on the state space equation of LLC resonant converter, sliding mode control theory is used to design the sliding mode surface and determine the target point of the control system.

[0086] The control law of sliding mode control is designed so that the system state reaches the sliding surface quickly and stably and remains on the sliding surface.

[0087] A nonlinear disturbance observer is designed to estimate and offset the disturbance and uncertainty in the system based on the output feedback information of the system, thereby improving the robustness and control accuracy of the control system.

[0088] The fourth step is to perform an inverse transformation on the control law to obtain the actual value of the control variable switching frequency. This value is used as input, and then a switching signal with a variable frequency is obtained through a voltage-controlled oscillator as the drive signal for the converter switch tube. The output voltage of the converter is adjusted by real-time control of the frequency:

[0089] The designed control law is inversely transformed to obtain the actual control variable switching frequency value, which will be passed to the voltage-controlled oscillator as input.

[0090] The voltage-controlled oscillator adjusts its output frequency according to the input frequency value to obtain a switching signal with a variable frequency. This switching signal will drive the switching action of the converter switch tube, thereby adjusting the output voltage of the converter.

[0091] By real-time control of the frequency, the output voltage of the LLC resonant converter can be regulated and stabilized.

[0092] In a specific embodiment, the present invention uses a reduced-order model derived from a full-order model and converts the reduced-order model into the form required for sliding mode control and disturbance observer design:

[0093]

[0094] Where C is the capacitance of the output capacitor, v o is the output voltage of the converter, i Br is the current rectified by the secondary side, P o is the output power, v n is the value of the resonant cavity output voltage equivalent to the secondary side, L s is the equivalent inductance, L s is equivalent to:

[0095] L s =π 2 / 8n 2 (1 / L r +1 / L m )

[0096] Among them, L r and L m are the inductance values ​​of the resonant inductance and the excitation inductance respectively.

[0097] The disturbance observer and sliding mode control are designed based on the following formalism:

[0098]

[0099] where x1 = v o , x2=i Br / C is the state variable, d1=P o / Cv o , is the disturbance amount, The system uncertainty is included. The disturbance mainly consists of the uncertainty of load power, output voltage and parameters.

[0100] In order to eliminate the impact of load power changes on the output voltage, disturbance information needs to be obtained. Designing a suitable disturbance observer not only helps to provide a fast dynamic response to external disturbances, but also reduces the number of sensors. The design of the disturbance observer is as follows:

[0101]

[0102] in and are the estimated values ​​of the disturbances d1 and d2, K di is the observer gain, β i is the internal state of the observer.

[0103] Furthermore, according to the sliding mode control theory, the sliding surface is set as:

[0104]

[0105] Among them, e x1 =x1-x 1ref , e x2 =x2-x 2ref is the state error, is the derivative of the state quantity x1 reference value with respect to time. Since the state quantity is the output voltage v o , so its reference value is the desired output voltage V ref . Considering that in steady state, the output current i o Equal to the average output current i of the rectifier Br , so the reference value x of the state variable x2 2ref Can be compared with the disturbance Therefore, the reference value of the state variable in the control design is:

[0106]

[0107] Taking the derivative of s, we get:

[0108]

[0109] According to the sliding mode control theory, in order to make s converge to zero, the designed control law k is:

[0110]

[0111] At this time, the derivative of s can be expressed as:

[0112]

[0113] When K s1 , K s2 When the appropriate value is taken, the sliding mode function s converges to 0. When s converges to zero, we can get

[0114]

[0115] When d1+x is satisfied 2ref = 0, e x1 The static error can converge to 0. ref is the reference value of the output voltage, is the observed value of the disturbance d1, obtained by the disturbance observer designed above. x1 When it converges to 0, the output voltage is equal to the reference value.

[0116] Furthermore, the actual control variable switching frequency f is obtained from the control rate k. Since LLC uses variable frequency control, the actual control signal is the normalized frequency f. The relationship between the control rate k and the normalized frequency can be obtained as follows:

[0117]

[0118] Substituting k obtained from the control system into this equation, the normalized frequency can be calculated. A voltage-controlled oscillator is then used to generate a PFM signal, which serves as the control signal for the switch.

[0119] Corresponding to the sliding mode control method of the DC buck converter with constant power load provided in the above embodiment, a specific embodiment of the present invention further provides a sliding mode control system of the LLC resonant converter with constant power load DC buck converter. The sliding mode control system includes: a current sensor, a voltage sensor, a state variable calculation module, a reference value calculation module, a disturbance observer module, a sliding mode controller, a control law conversion module and a voltage controlled oscillator module. Figure 1 Provide detailed explanation.

[0120] The control methods of this system include:

[0121] Step 1: Use the sampled current and voltage values ​​and known circuit component parameters to establish the state space equations of the LLC resonant converter required for sliding mode control and disturbance observer design.

[0122] Step 2: For the established LLC resonant converter model, considering parameter perturbations, a state-space equation is transformed into the form required for designing disturbance observer and sliding mode control.

[0123] Step 3: Based on the design method of nonlinear disturbance observer, a disturbance observer is designed for the state space equation obtained in step 2; a reference value of the state quantity is calculated based on the estimation of the disturbance observer for sliding mode control; according to the sliding mode control theory, a sliding surface of the sliding mode control is designed, and a control law is designed based on the sliding surface.

[0124] In step 4, the control law obtained in step 3 is inversely transformed to obtain the actual control law of the LLC resonant converter, which is used as input. A switching signal with a variable frequency is obtained through a voltage-controlled oscillator as the driving signal of the converter switch tube, and the output voltage of the converter is adjusted by real-time control of the frequency.

[0125] Step 1: In a specific embodiment, the present invention uses a reduced-order model derived from a full-order model and converts the reduced-order model into the form required for sliding mode control and disturbance observer design:

[0126]

[0127] Where C is the capacitance value of the output filter capacitor, v o is the output voltage of the converter, i Br is the current rectified by the secondary side, P o is the output power, v n is the value of the resonant cavity output voltage equivalent to the secondary side, L s is the equivalent inductance, L s is equivalent to:

[0128] L s =π 2 / 8n 2 (1 / L r +1 / L m )

[0129] Among them, L r and L m are the inductance values ​​of the resonant inductance and the excitation inductance respectively.

[0130] Step 2: The disturbance observer and sliding mode control are designed based on the following form:

[0131]

[0132] where x1 = v o , x2=i Br / C is the state variable, d1=P o / Cv o , is the disturbance amount, The system uncertainty is included. The disturbance mainly consists of the uncertainty of load power, output voltage and parameters.

[0133] Step 3:

[0134] In order to eliminate the impact of load power changes on the output voltage, disturbance information needs to be obtained. Designing a suitable disturbance observer not only helps to provide a fast dynamic response to external disturbances, but also reduces the number of sensors. The design of the disturbance observer is as follows:

[0135]

[0136] in and are the estimated values ​​of the disturbances d1 and d2, K di is the observer gain, β i is the internal state of the observer.

[0137] Furthermore, according to the sliding mode control theory, the sliding surface is set as:

[0138]

[0139] Among them, e x1 =x1-x 1ref , e x2 =x2-x 2ref is the state error, is the derivative of the state quantity x1 reference value with respect to time. Since the state quantity is the output voltage v o , so its reference value is the desired output voltage V ref . Considering that in steady state, the output current i o Equal to the average output current i of the rectifier Br , so the reference value x of the state variable x2 2ref Can be compared with the disturbance Therefore, the reference value of the state variable in the control design is:

[0140]

[0141] Taking the derivative of s, we get:

[0142]

[0143] According to the sliding mode control theory, in order to make s converge to zero, the designed control law k is:

[0144]

[0145] At this time, the derivative of s can be expressed as:

[0146]

[0147] When K s1 , Ks2 When the appropriate value is taken, the sliding mode function s converges to 0. When s converges to zero, we can get

[0148]

[0149] When d1+x is satisfied 2ref = 0, e x1 The static error can converge to 0. ref is the reference value of the output voltage, is the observed value of the disturbance d1, obtained by the disturbance observer designed above. x1 When it converges to 0, the output voltage is equal to the reference value.

[0150] Step 4:

[0151] Furthermore, the control rate k obtained in step 3 is converted into the actual control variable switching frequency f. Since LLC uses variable frequency control, the actual control signal is the normalized frequency f. The relationship between the control rate k and the normalized frequency can be obtained as follows:

[0152]

[0153] Substituting k obtained from the control system into this equation, the normalized frequency can be calculated. A voltage-controlled oscillator is then used to generate a PFM signal, which serves as the control signal for the switch.

[0154] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware portion can be implemented using dedicated logic; the software portion can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. Those skilled in the art will appreciate that the above-mentioned devices and methods can be implemented using computer-executable instructions and / or contained in processor control code, for example, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0155] Simulation conditions of the present invention:

[0156] The present invention is simulated by using MATLAB / Simulink software on a 12th Gen Intel(R) Core(TM) i5-12400F 2.50 GHz CPU, 16 GB RAM, and a WINDOWS 11 operating system.

[0157] The LLC control method proposed in the present invention is a sliding mode controller based on a disturbance observer, which can significantly improve the anti-interference ability of the system and effectively suppress the adverse effects of large signal disturbances such as load mutations and input voltage fluctuations on the system.

[0158] The proposed sliding mode control method based on disturbance observer was simulated in MATLAB / Simulink to verify its effectiveness. All simulations were performed under the condition of LLC resonant converter with constant power load.

[0159] First, verify the presence of a sudden change in input voltage. Figure 2 As shown, step changes are added to the input voltage at t = 0.1s (from 240V to 230V), t = 0.2s (from 230V to 250V), and t = 0.3s (from 250V to 240V), respectively, and the proposed controller still stabilizes the output voltage at its reference value.

[0160] Then the situation of sudden change of output voltage reference value was verified. Figure 3 As shown in the figure, the reference value changes from 27 V to 24 V, then gradually changes to 30 V, and finally drops to 24 V. After a small fluctuation, the output voltage quickly tracks the reference voltage.

[0161] Finally, the proposed control method is compared with the traditional PI controller. Figure 4 The output responses of the LLC resonant converters using the present invention and PI control are shown for the same CPL power variation. It can be seen that at 0.2s, when the constant power load power rises to 480W, the LLC converter controlled by PI loses output stability, while the controller designed by the present invention maintains output stability. Furthermore, compared to PI control, the system output response is faster when using the controller of the present invention.

[0162] Two specific embodiments and implementation schemes of the present invention are provided below:

[0163] Example 1: LLC resonant converter control for photovoltaic grid-connected systems

[0164] Background: Grid-connected photovoltaic systems need to convert direct current (DC) into alternating current (AC) for grid integration. Due to the instability of solar energy, the output power can be subject to significant fluctuations.

[0165] 1. Parameter acquisition module: Current and voltage sensors are installed at the output end of the photovoltaic grid-connected inverter to continuously monitor its output current and voltage.

[0166] 2. Equation transformation module: Based on the data obtained by the sensor and the known circuit parameters, the state space equation of the LLC resonant converter is established.

[0167] 3. Observer Design Module: Design a nonlinear disturbance observer to estimate and offset disturbances in the photovoltaic output. Use sliding mode control theory to design a sliding surface, and then design a control law based on this sliding surface.

[0168] 4. Voltage output module: According to the designed control law, the switching frequency is adjusted to regulate the output voltage of the grid-connected inverter to ensure that it is synchronized with the grid.

[0169] Example 2: LLC resonant converter control for drone battery charger

[0170] Background: Modern drone batteries require fast, stable, and safe charging methods. To meet these requirements, battery chargers need to be able to precisely control output voltage and current.

[0171] 1. Parameter acquisition module: At the output end of the charger, current and voltage sensors are installed to continuously monitor the charging current and voltage of the drone battery.

[0172] 2. Equation transformation module: Based on the data obtained by the sensor and the known circuit parameters, the state space equation of the LLC resonant converter is established.

[0173] 3. Observer Design Module: Because the battery's charging characteristics may change due to factors such as usage, environment, and lifespan, a nonlinear disturbance observer is designed to estimate these disturbances. Then, sliding mode control theory is used to design a sliding surface, and the control law is designed based on this sliding surface.

[0174] 4. Voltage output module: According to the designed control law, the switching frequency is adjusted to regulate the charging voltage and current of the drone battery to ensure that the battery is charged in the optimal state.

[0175] These two examples, starting from the two application scenarios of photovoltaic grid-connected and drone battery charger, respectively, demonstrate how to implement the LLC resonant converter control method based on nonlinear disturbance observer sliding mode control.

[0176] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A sliding mode control method based on nonlinear disturbance observer for LLC resonant converter, characterized in that: include: The first step is to obtain the rectified current on the secondary side and the output capacitor voltage; The second step is to use the sampled current and voltage values ​​and the known circuit component parameters to establish the state space equations of the LLC resonant converter required for sliding mode control and disturbance observer design; including: In step 1, the reduced-order model derived from the full-order model is used and converted into the form required for sliding mode control and disturbance observer design: Where C is the capacitance value of the output filter capacitor, v o is the output voltage of the converter, i Br is the current rectified by the secondary side, P o is the output power, v n is the value of the resonant cavity output voltage equivalent to the secondary side, L s is the equivalent inductance, L s is equivalent to: L s =π 2 / 8n 2 (1 / L r +1 / L m ), Among them, L r and L m are the inductance values ​​of resonant inductance and magnetizing inductance respectively; Step 2: The disturbance observer and sliding mode control are designed based on the following form: where x1 = v o , x2=i Br / C is the state variable, d1=P o / Cv o , is the disturbance amount, Contains the uncertainty of the system; the disturbance mainly consists of the uncertainty of load power, output voltage and parameters; Step 3, the design of the disturbance observer is as follows: in and are the estimated values ​​of the disturbances d1 and d2, K di is the observer gain, β i is the internal state of the observer; Set the sliding surface to: Among them, e x1 =x1-x 1ref , e x2 =x2-x 2ref is the state error, is the time derivative of the reference value of the state quantity x1; since the state quantity is the output voltage v o , which is the desired output voltage V ref ; Considering that in steady state, the output current i o Equal to the average output current i of the rectifier Br , so the reference value x of the state variable x2 2ref Can be compared with the disturbance Equal; in control design, the reference value of the state variable is: Taking the derivative of s, we get: In order to make s converge to zero, the designed control law k is: At this time, the derivative of s can be expressed as: When K s1 , K s2 When the appropriate value is taken, the sliding mode function s converges to 0; when s converges to zero, we can get When d1+x is satisfied 2ref = 0, e x1 The static error can converge to 0, where V ref is the reference value of the output voltage, is the observed value of the disturbance d1, obtained by the disturbance observer; when e x1 When it converges to 0, the output voltage is equal to the reference value; The third step is to design the sliding surface of the sliding mode control based on the sliding mode control theory for the system model, and then design the control law based on the sliding surface. Finally, a nonlinear disturbance observer is designed to be combined with the sliding mode control to optimize the control effect. The fourth step is to perform an inverse transformation on the control law to obtain the actual value of the control quantity switching frequency, which is used as input. Then, a switching signal with a changing frequency is obtained through a voltage-controlled oscillator as the driving signal of the converter switch tube, and the output voltage of the converter is adjusted by real-time control of the frequency.

2. The nonlinear disturbance observer-based sliding mode control method for LLC resonant converter according to claim 1, wherein: The specific implementation method of the first step: Use current sensors and voltage sensors to obtain the rectified current on the secondary side of the LLC resonant converter and the output capacitor voltage; The acquired current and voltage signals are sampled to obtain discrete current and voltage values ​​for subsequent control system design.

3. The nonlinear disturbance observer-based sliding mode control method for LLC resonant converter according to claim 1, wherein: The specific implementation method of the second step: Based on the discrete sampling values ​​of the secondary-side rectified current and the output capacitor voltage, combined with known circuit component parameters, the state space equation of the LLC resonant converter is established. State-space equations typically include state variables such as current, voltage, and circuit element parameters.

4. The nonlinear disturbance observer-based sliding mode control method for LLC resonant converter according to claim 1, wherein: The specific implementation method of the third step: Based on the state space equation of LLC resonant converter, sliding mode control theory is used to design the sliding mode surface and determine the target point of the control system; Design the control law of sliding mode control so that the system state reaches the sliding surface quickly and stably and remains on the sliding surface; A nonlinear disturbance observer is designed to estimate and offset the disturbance and uncertainty in the system based on the output feedback information of the system, thereby improving the robustness and control accuracy of the control system.

5. The nonlinear disturbance observer-based sliding mode control method for LLC resonant converter according to claim 1, wherein: Specific implementation method of the fourth step: The designed control law is inversely transformed to obtain the actual control variable switching frequency value, which will be passed to the voltage-controlled oscillator as input; The voltage-controlled oscillator adjusts its output frequency according to the input frequency value, generating a switching signal with a variable frequency. This switching signal will drive the switching action of the converter switch tube, thereby adjusting the output voltage of the converter. By real-time control of the frequency, the output voltage of the LLC resonant converter can be regulated and stabilized.

6. The nonlinear disturbance observer-based sliding mode control method for LLC resonant converter according to claim 1, wherein: The nonlinear disturbance observer is integrated with sliding mode control and applied to the LLC resonant converter control; By establishing a reduced-order model, designing a sliding mode controller and a nonlinear disturbance observer, the system can quickly and stably achieve the desired output voltage and current, and effectively offset uncertainties and disturbances in the system; by adopting a variable frequency control method, the output voltage is adjusted according to the actual control variable switching frequency f, thereby improving the efficiency and performance of the converter.

7. A nonlinear disturbance observer based sliding mode control system implementing the nonlinear disturbance observer based sliding mode control method for LLC resonant converter according to any one of claims 1 to 6, characterized in that: The nonlinear disturbance observer-based sliding mode control system includes: A parameter acquisition module is used to use the sampled current and voltage values ​​and known circuit component parameters to establish the state space equations of the LLC resonant converter required for sliding mode control and disturbance observer design; The equation transformation module is used to transform the state space equations into the form required for designing disturbance observer and sliding mode control while considering parameter perturbations for the established LLC resonant converter model; The observer design module is used to design a disturbance observer based on the obtained state-space equations based on the design method of nonlinear disturbance observers; the reference value of the state quantity is calculated based on the estimated quantity of the disturbance observer for sliding mode control; the sliding surface of the sliding mode control is designed according to the sliding mode control theory, and the control law is designed based on the sliding surface; The voltage output module is used to perform an inverse transformation on the obtained control law to obtain the actual control law of the LLC resonant converter, which is used as input. Then, a switching signal with a variable frequency is obtained through a voltage-controlled oscillator as the driving signal of the converter switch tube, and the output voltage of the converter is adjusted by real-time control of the frequency.

8. The nonlinear disturbance observer-based sliding mode control system for LLC resonant converter according to claim 7, characterized in that: Also includes: Current sensor, used to obtain the rectified current on the secondary side; A voltage sensor is used to obtain the output capacitor voltage; A state variable calculation module calculates the real-time value of the state variable based on the established state space model of the LLC resonant converter; The reference value calculation module calculates the reference value of the state variable in real time based on the output of other modules; The disturbance observer module is based on the state space model and the design method of nonlinear disturbance observer; it is used to calculate the changes of constant power load; Sliding mode controller, based on the linear system model obtained from the state variable calculation module and sliding mode control theory, designs the sliding surface of sliding mode control; and designs the control law based on the sliding surface; The inverse transformation module is used to transform the control law in the sliding mode control module and calculate the actual control quantity: the value of the switching frequency; The voltage-controlled oscillator obtains a converter drive signal with a variable frequency and a fixed duty cycle based on the switching frequency value obtained by the inverse transformation module, and adjusts the output voltage of the converter by real-time control of the switching frequency.

9. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the sliding mode control method based on a nonlinear disturbance observer according to any one of claims 1 to 5.

10. An information data processing terminal, characterized in that: The information data processing terminal is used to implement the nonlinear disturbance observer-based sliding mode control method described in any one of claims 1-5.

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