A Second-Order Sliding Mode Control Method Based on a High-Power Buck Converter

Abstract

This invention provides a second-order sliding mode control method based on a high-power Buck converter, belonging to the field of power electronic converter technology. The invention constructs a Buck-type DC-DC converter model; constructs a second-order sliding mode controller to control the Buck-type DC-DC converter model; the construction of the second-order sliding mode controller includes: constructing the sliding surface of the second-order sliding mode controller based on the state variable relationships of the Buck-type DC-DC converter model; and designing the parameter recognition rate of the second-order sliding mode controller. This solves the problems of untimely dynamic response and insufficient output voltage accuracy in high-power Buck converters.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and in particular to a second-order sliding mode control method based on a high-power Buck converter. Background Technology

[0002] As society enters a high-speed, intelligent, and information-driven era, people's demand for energy is increasing daily. To alleviate the increasingly serious energy crisis, people have begun to develop and utilize green energy sources such as solar, tidal, and wind power, and to process renewable energy through power electronic conversion technology, thus promoting the development of new energy technologies. Among these, high-power DC-DC converters are often used in the power electronic conversion of new energy technologies. Therefore, to promote the application of green energy, it is necessary to further improve the performance of DC-DC converters. DC-DC converters are nonlinear systems, and in green energy power generation scenarios, the load or parameters are prone to large changes. Furthermore, as the load increases, the control circuit of high-power converters needs to handle large current and high voltage signals, requiring high-capacity, high-voltage, and low-on-resistance power switching elements, such as insulated-gate bipolar transistors (IGBTs) or wide-bandgap power devices such as silicon carbide (SiC) and gallium nitride (GaN). These devices require dedicated drive circuits to ensure reliable switching operation. The drive circuit must be able to provide sufficient drive current and appropriate drive voltage waveforms to meet the requirements of rapid switching of high-power devices. Therefore, the control of power transistors is particularly important.

[0003] However, current technologies primarily utilize PI controllers for control, a classic linear system control method. Therefore, using a linear control method to control a nonlinear system is unsuitable. While it can bring the system to stability within a finite time, its dynamic and steady-state performance still has room for improvement to address the system's speed issue. Consequently, existing technologies propose using nonlinear control methods to mitigate this problem, such as sliding mode control. However, because its control signal directly includes switching terms, the control effect depends on the selection of the sliding surface, leading to high-frequency chattering.

[0004] Therefore, a control method for high-power DC-DC converters that can provide fast dynamic response and improve system stability is needed. Summary of the Invention

[0005] In view of this, the present invention provides a second-order sliding mode control method based on a high-power Buck converter to solve the problems of untimely dynamic response and insufficient output voltage accuracy of the high-power Buck converter.

[0006] Therefore, the present invention provides the following technical solution:

[0007] A second-order sliding mode control method based on a high-power Buck converter includes:

[0008] A second-order sliding mode controller is used to control a Buck-type DC-DC converter;

[0009] The sliding surface of the second-order sliding mode controller is:

[0010]

[0011] The system output target voltage value is V. e The error in the system output voltage is e(t), e(t) = V0 - V e =x1-V e k and δ are any constants greater than 0, used to adjust the robustness of the system.

[0012] Furthermore, the topology of the Buck-type DC-DC converter includes:

[0013] The components include a DC power supply (DC), two MOSFETs, an energy storage inductor (L), a filter capacitor (C), and a load resistor (R).

[0014] Furthermore, the second-order sliding mode control method based on a high-power Buck converter also includes:

[0015] Construct a Buck-type DC-DC converter model;

[0016] Based on the state variable relationship of the Buck-type DC-DC converter model, the parameter recognition rate of the second-order sliding mode controller is designed.

[0017] Furthermore, the construction of the Buck-type DC-DC converter model includes:

[0018] Construct a state-space averaged model of the system over a switching cycle T:

[0019]

[0020] in, This indicates the duty cycle of the power switch drive signal; the system output voltage is V0.

[0021] Furthermore, the state variable relationships of the Buck-type DC-DC converter model are as follows:

[0022]

[0023] Wherein, the system output voltage V0 is the state variable x1; the first derivative of V0 is the state variable x2; d(t) is the system uncertainty disturbance term, d(t) = 0.1sin t; u(t) is the state switching control function of the power switch, which is obtained by converting the state variables through the duty cycle D. When u(t) = 1, the power transistor is turned on, and when u(t) = 0, the power transistor is turned off.

[0024] Furthermore, the parameter recognition rate of the second-order sliding mode controller includes:

[0025]

[0026] Where δ represents the parameters of the second-order sliding mode controller.

[0027] Advantages and positive effects of the present invention:

[0028] 1) This invention controls the MOSFET switches in the converter through a sliding mode controller, reduces steady-state error by adding an integral term in the sliding surface, and reduces jitter by increasing the order of the sliding surface, thereby improving the dynamic response speed of the system. At the same time, the output voltage is more stable and the load regulation is optimized.

[0029] 2) By designing the parameter recognition rate, this invention can accurately identify sliding mode control parameters, improve the accuracy of output voltage, and demonstrate stronger practicality. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is the Buck converter topology in an embodiment of the present invention;

[0032] Figure 2 This is a simulation model of a second-order sliding mode controller in an embodiment of the present invention;

[0033] Figure 3 This is the evolution curve of the sliding surface over time in an embodiment of the present invention;

[0034] Figure 4 This is the evolution curve of the first-order sliding surface over time in an embodiment of the present invention;

[0035] Figure 5 As described in the embodiments of the present invention Evolution curve over time;

[0036] Figure 6 This is the voltage output response curve when δ changes in an embodiment of the present invention;

[0037] Figure 7 This is the voltage output response curve when k changes in an embodiment of the present invention;

[0038] Figure 8The voltage output response curve of the Buck-type DC-DC converter in this embodiment of the invention;

[0039] Figure 9 The inductor current output response curve is shown in an embodiment of the present invention.

[0040] Figure 10 This is the output voltage response curve when the load changes in an embodiment of the present invention. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0043] This invention provides a second-order sliding mode control method based on a high-power Buck converter, which improves the dynamic response speed of the system, makes the system output voltage more stable, and optimizes the load regulation rate.

[0044] This invention controls the MOSFET switching in a DC-DC converter using a second-order sliding mode controller. Considering the uncertainties in system parameters and system robustness, an integral term is added to the sliding surface to reduce steady-state error, and the order of the sliding surface is increased to reduce jitter. Based on the designed parameter recognition rate, the design parameters can be accurately identified, improving the accuracy of the output voltage and thus quickly obtaining a stable and high-precision output voltage.

[0045] S1. Construct a mathematical model for a Buck-type DC-DC converter;

[0046] Combination Figure 1The basic topology of the Buck-type DC-DC converter shown further illustrates the digital model of the converter of this invention:

[0047] A traditional Buck converter consists of a power MOSFET and a freewheeling diode. Since the converter has a relatively high power rating, this embodiment uses a MOSFET instead of a freewheeling diode. This avoids the diode's reverse recovery problem and reduces the power transistor's losses.

[0048] In this embodiment, the Buck converter includes: a DC power supply DC, two power MOSFETs, an energy storage inductor L, a filter capacitor C, and a load resistor R.

[0049] When power switch Q1 is turned on, its circuit is equivalent to a short circuit, while power switch Q2 is turned off, equivalent to an open circuit. The input voltage is directly connected to inductor L, causing the inductor current to gradually increase, and due to the self-inductance effect, electrical energy is converted into magnetic energy and stored. After the total current flows through inductor L, it flows to capacitor C to charge it, and to the load R. At this time, the system output voltage is V0, and the formula for calculating V0 is:

[0050]

[0051] Where, Δt on ΔI represents the on-time of power switch Q1. L1 Indicates that in Δt on The change in inductor current over a period of time.

[0052] When power switch Q1 is off, its circuit is equivalent to an open circuit; when power switch Q2 is on, it is equivalent to a short circuit. The current in the circuit still flows clockwise through inductor L and gradually decreases. Due to self-induction, an induced electromotive force (EMF) is generated across inductor L, with the left side negative and the right side positive, to resist the decreasing current trend. The formula for calculating the circuit output voltage V0 at this time is:

[0053]

[0054] Where, Δt off ΔI represents the cutoff time of power switch Q1. L2 Indicates that in Δt off The change in inductor current over a period of time.

[0055] Based on the on / off state of the power transistor, within one switching cycle T, the weighted average of the system's state-space differential equations is calculated to obtain a state-space average model of the system:

[0056]

[0057] in, This indicates the duty cycle of the power switch drive signal.

[0058] S2. Design a second-order sliding mode control method to control the MOSFET switching of a Buck-type DC-DC converter;

[0059] S21. Construct the relational expressions for the state variables of the model;

[0060] The switching of a DC-DC converter requires a trigger signal to turn on. In existing technologies, DC-DC converters control the switching of the power transistors by outputting a PWM waveform from a microcontroller; that is, the microcontroller outputs a PWM waveform, which is then driven by a driver circuit to turn the power transistors on and off. In this embodiment, to ensure a constant and stable output voltage, a second-order sliding mode control method is used to generate the PWM waveform output by the microcontroller. By changing the control parameters, the duty cycle of the PWM waveform is changed, thereby obtaining a high-precision output voltage.

[0061] Based on the current variation through inductor L in a Buck-type DC-DC converter, the circuit's operating modes can be divided into three types: Continuous Conduction Mode (CCM), Boundary Conduction Mode (BCM), and Discontinuous Conduction Mode (DCM). In Continuous Conduction Mode, the ratio of the power transistor's on / off time directly affects the output voltage, resulting in better output stability and lower ripple.

[0062] Therefore, in this embodiment, preferably, the control of the Buck-type DC-DC converter operating under CCM is achieved by combining the PWM modulation principle.

[0063] Therefore, based on the state-space average model of the system in equation (3), the relationship between the state variables is constructed as follows:

[0064]

[0065] Wherein, let the output voltage V0 of the system be the state variable x1; the first derivative of V0 be the state variable x2; d(t) is the system's uncertain disturbance term, in this embodiment, d(t) = 0.1sin t; u(t) is the power switch state switching control function, which is obtained by converting the state variables through the duty cycle D. When u(t) = 1, the power transistor is turned on, and when u(t) = 0, the power transistor is turned off.

[0066] Because the switching control law u(t) and the duty cycle D of the drive signal are equivalent, u(t) is the discrete expression of the system control law in the microscopic view, and in the macroscopic view it is represented by the duty cycle D of the control signal. Their mathematical relationship is that D is the average value of u(t) over one switching cycle. In this embodiment, the result obtained by the algorithm ultimately needs to be realized through the duty cycle D of the actual circuit's control signal PWM waveform.

[0067] By designing a sliding mode variable structure controller, the system state can be reached and maintained on this sliding mode surface in a short time. Once the system enters the sliding motion stage, it has strong robustness to disturbances and uncertainties.

[0068] S22. Construct the sliding surface;

[0069] Based on the target output voltage value of the DC-DC converter, which is V e The error of the system output voltage is e(t). The system output error e(t) is obtained as follows:

[0070] e(t) = V0 - V e =x1-V e (5)

[0071] Differentiate the system output error e(t):

[0072]

[0073] Based on the working principle and mathematical model of the Buck-type DC-DC converter, and considering the uncertainty of system parameters and system robustness, an integral term is added to the sliding surface to reduce steady-state error, and the jitter is reduced by increasing the order of the sliding surface. In this embodiment, the sliding surface is constructed as follows:

[0074]

[0075] The derivative is:

[0076] Where k and δ are any constants greater than 0, used to adjust the robustness of the system.

[0077] S23. The system control law and control parameter recognition rate are constructed based on the sliding surface;

[0078] A Buck-type DC-DC converter can stabilize its output voltage for a short time, which requires meeting the controller output u(t) and control parameters. The relationship, namely the system control law and the recognition rate of control parameters:

[0079]

[0080] S24. Using the Lyapunov second method stability criterion, verify the recognition rate of the sliding surface, system control law, and control parameters.

[0081] Constructing Lyapunov functions:

[0082]

[0083] Differentiate equation (12) with respect to time, and substitute equations (4) and (7) into the equation:

[0084]

[0085]

[0086] According to Lyapunov's second stability criterion, if V(t) is positive definite, and If the time is negative definite or semi-negative definite, then the system is asymptotically stable over a wide range. Therefore, in order to ensure... make

[0087]

[0088] Solving equation (14) yields the parameters. The identification law is shown in equation (10), that is, the parameter identification law is proved. Substituting the controller output equations (10) and (11) into equation (13):

[0089]

[0090] According to the inequality theorem:

[0091]

[0092] Where, if ω≥|s(t)|, then there must exist According to Lyapunov's second method stability criterion With a negative or semi-negative constant voltage, the system is asymptotically stable, meaning that the Buck-type DC-DC converter can stabilize the output voltage for a short time.

[0093] The effectiveness of the method of the present invention is verified by specific embodiments below:

[0094] Based on the design of the second-order sliding mode controller and the theoretical verification of its stability using the above method, the control law and control parameter recognition rate of the second-order sliding mode controller for the Buck DC-DC converter are obtained, namely equations (10) and (11). A simulation model of the second-order sliding mode controller is then established, as follows: Figure 2 As shown, the second-order sliding mode controller method was verified using Matlab / Smulink.

[0095] In this embodiment, the input voltage of the Buck-type DC-DC converter is 800V; the expected output voltage is 360V and the output power is 3.6KW; the load resistance is 36Ω and the simulation time is 0.7s.

[0096] Simulation results are as follows Figure 3-10 As shown. Figure 3 Figure 4 These are the evolution curves of the sliding surface and the first-order sliding surface over time, respectively. From Figure 3 Figure 4 It can be seen that the system maintains a stable position on the sliding surface for about 0.07s, and the control action is continuous and stable with very little jitter.

[0097] Figure 5 It is a parameter variable The evolution curve of the recognition law over time. (From...) Figure 5 It can be known After a brief adjustment, the design parameters can be quickly and accurately identified. The value is 0.01.

[0098] from Figure 6 It can be seen that when δ is 0.01, the system output voltage value is closest to the target voltage value; when δ is 200, the system output voltage value drops to 340.5V. It is evident that the design parameter δ affects the accuracy of the system output voltage. By controlling the design parameter identification, the control accuracy of the system output can be improved.

[0099] Figure 7 The voltage output response curve is given when parameter k varies. Figure 7 It can be seen that when k = 0.1, the system response time is significantly faster than when k = 10. However, the output curve fluctuation is larger when k = 10, indicating that the system stability is not as good as when k = 10. Considering both system speed and stability, k = 10 and δ = 0.01 are chosen. The system output voltage and inductor current response curves at this time are as follows: Figure 8 Figure 9 As shown. Figure 8 and Figure 9 As can be seen, the system rise time is 0.046s, and the system enters a steady state at 0.073s. Therefore, using a second-order sliding mode controller to control the switching of the power transistor has a very good response speed. Figure 8 The output voltage is 360.1V, the maximum overshoot voltage is 20.4V, the maximum overshoot is 5.67%, and the steady-state error is 0.03%. Figure 9 The output inductor current is 10.01A, while the target current is 10A, with a steady-state error of 0.1%. Figure 8 Figure 9As can be seen from this, using a second-order sliding mode controller to control a Buck-type DC-DC converter can effectively suppress system overshoot and improve system stability and control accuracy. Figure 10 It can be seen that when the load disconnects the 10Ω resistor at 0.4s, the output voltage drops from 360.1V to 341.2V when a second-order sliding mode controller is used. It recovers after 0.028s and re-enters a stable state.

[0100] The sliding mode controller designed in this embodiment has better anti-interference capability and stronger regulation performance in response to load changes, and its load regulation rate is superior. Therefore, this control method can improve the stability of the output voltage of the Buck DC-DC converter.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A second-order sliding mode control method based on a high-power Buck converter, characterized in that, include: A second-order sliding mode controller is used to control a Buck-type DC-DC converter; Constructing a Buck-type DC-DC converter model: Built in a switching cycle Internally, the state-space average model of the system: in, , representing the duty cycle of the power switch drive signal; the system output voltage is ; The sliding surface of the second-order sliding mode controller is: The system output target voltage value is The error of the system output voltage is , ; , It is any constant greater than 0, used to adjust the system's robustness; Based on the state variable relationships of the Buck-type DC-DC converter model, the parameter recognition rate of a second-order sliding mode controller is designed; the state variable relationships of the Buck-type DC-DC converter model are as follows: Among them, the system's output voltage State variables ; The first derivative of the state variable ; For the system's uncertain disturbance term, ; It is the state switching control function of the power switch, which is determined by the duty cycle. D Obtained by performing state variable transformations, when When the power transistor is turned on, The power transistor is turned off. The parameter recognition rate of the second-order sliding mode controller: in, These are the parameters for a second-order sliding mode controller.

2. The second-order sliding mode control method based on a high-power Buck converter according to claim 1, characterized in that, The topology of the Buck-type DC-DC converter includes: The components include a DC power supply (DC), two MOSFETs, an energy storage inductor (L), a filter capacitor (C), and a load resistor (R).

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