Second-order sliding mode control method based on high-power Buck converter

Abstract

The invention provides a second-order sliding mode control method based on a high-power Buck converter, and belongs to the technical field of power electronic converters. The method comprises the following steps: constructing a Buck type DC-DC converter model; a second-order sliding mode controller is constructed, and a Buck type DC-DC converter model is controlled; the construction of the second-order sliding mode controller comprises the following steps: constructing a sliding mode surface of the second-order sliding mode controller based on a state variable relationship of a Buck type DC-DC converter model; and designing a parameter identification rate of the second-order sliding mode controller. The problems that a high-power Buck converter is not timely in dynamic response and low in output voltage precision are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a second-order sliding mode control method based on a high-power Buck converter. Background Art

[0002] As society enters the era of high-speed, intelligent information technology, people's demand for energy is growing. In order to alleviate the increasingly serious energy crisis, people have begun to develop and utilize green energy such as solar energy, tidal energy and wind energy, and process renewable energy through power electronic conversion technology to promote the development of new energy technology. Among them, high-power DC-DC converters are often used in power electronic conversion of new energy technology. Therefore, in order 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. In the green energy power generation scenario, the load or parameters are prone to large changes. As the load increases, the control circuit of the high-power converter needs to process large current and high-voltage signals, and requires high-capacity, high-voltage, and low-on-resistance power switching elements, such as insulated gate bipolar transistors or wide bandgap power devices such as silicon carbide and gallium nitride. These devices require special 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 fast switching of high-power devices. Therefore, the control of power tubes is particularly important.

[0003] However, in the prior art, control is basically performed through a PI controller, which is a classic linear system control method. Therefore, it is not appropriate to use a linear control method to control a nonlinear system. Although the system can be stabilized within a limited time, its dynamic performance and steady-state performance still have room for improvement to solve the rapidity problem of the system. Therefore, the prior art proposes that this problem can be improved through nonlinear control methods, such as sliding mode control, but because the control signal directly includes switching items, the control effect depends on the selection of the sliding mode surface, and the system will therefore produce high-frequency jitter.

[0004] Therefore, a high-power DC-DC converter control method is needed that can quickly respond to dynamic conditions and improve system stability. 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] To this end, the present invention provides the following technical solutions:

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

[0008] Use a second-order sliding mode controller to control the Buck type DC-DC converter;

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

[0010]

[0011] Among them, the system output target voltage value is V e ; The error of 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 system robustness.

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

[0013] DC power supply DC, two power tubes MOSFET, energy storage inductor L, filter capacitor C and load resistor R.

[0014] Furthermore, the second-order sliding mode control method based on the 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 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 the state space average model of the system within a switching cycle T:

[0019]

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

[0021] Furthermore, the state variable relationship of the Buck type DC-DC converter model is:

[0022]

[0023] Among them, the output voltage V0 of the system is the state variable x1; the first-order derivative of V0 is the state variable x2; d(t) is the system uncertain 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 variable through the duty cycle D. When u(t) = 1, the power tube is turned on, and when u(t) = 0, the power tube is turned off.

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

[0025]

[0026] Where δ is the parameter of the second-order sliding mode controller.

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

[0028] 1) The present invention controls the MOSFET switch in the converter through a sliding mode controller, adds an integral term in the sliding mode surface to reduce the steady-state error, and reduces the jitter by increasing the order of the sliding surface, thereby improving the dynamic response speed of the system, while the output voltage is more stable and the load regulation rate is optimized;

[0029] 2) The present invention can accurately identify sliding mode control parameters by designing parameter recognition rate, improve the accuracy of output voltage, and show stronger practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 The Buck converter topology structure in the embodiment of the present invention;

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

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

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

[0035] Figure 5 In the embodiment of the present invention Evolution curve over time;

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

[0037] Figure 7 is a 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 the embodiment of the present invention;

[0039] Fig. 9 is an inductor current output response curve in an embodiment of the present invention;

[0040] Fig.10 1 is an output voltage response curve when the load changes in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] The present 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] The present invention controls the MOSFET switch in the DC-DC converter through a second-order sliding mode controller. Considering the uncertainty of system parameters and system robustness, an integral term is added to the sliding mode surface to reduce the steady-state error, and the jitter is reduced by increasing the order of the sliding surface; based on the designed parameter recognition rate, the design parameters can be accurately identified, the accuracy of the output voltage can be improved, and a stable and high-precision output voltage can be quickly obtained.

[0045] S1. Construct the mathematical model of Buck type DC-DC converter;

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

[0047] The traditional Buck converter consists of a power MOS tube and a freewheeling diode. Since the converter power is relatively large, a MOSFET is used in this embodiment to replace the freewheeling diode, which can avoid the diode reverse recovery problem and reduce the loss of the power tube.

[0048] The Buck converter in this embodiment includes: a direct current power supply DC, two power tubes MOSFET, an energy storage inductor L, a filter capacitor C, and a load resistor R.

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

[0050]

[0051] Among them, Δt on Indicates the conduction time of the power switch tube Q1, ΔI L1 Indicates that at Δt on The change in inductor current over time.

[0052] When the power switch tube Q1 is turned off, the circuit it is in is equivalent to an open circuit; the power switch tube Q2 is turned on, which is equivalent to a short circuit. The current in the circuit still passes through the inductor L in a clockwise manner and gradually decreases. Due to the self-inductance phenomenon, an induced electromotive force with a negative left and a positive right is generated at both ends of the inductor L to hinder the trend of current reduction. At this time, the calculation formula of the circuit output voltage V0 is:

[0053]

[0054] Among them, Δt off Indicates the cut-off time of the power switch tube Q1, ΔI L2 Indicated at Δt off The change in inductor current over time.

[0055] According to the on-off status of the power tube, within a switching cycle T, the weighted average of the state space differential equation of the system is calculated to obtain a state space average model of the system:

[0056]

[0057] in, Indicates the duty cycle of the power switch tube drive signal.

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

[0059] S21, construct the relational expression of the state variables of the model;

[0060] The conduction of the switch tube of the DC-DC converter requires a trigger signal. In the prior art, the DC-DC converter outputs a PWM waveform through a single-chip microcomputer to control the on and off of the power tube, that is, the single-chip microcomputer outputs a PWM waveform, and then drives the on and off of the power tube through a driving circuit. In this embodiment, in order to ensure that the output voltage is constant and stable, a second-order sliding mode control method is used to generate the PWM waveform output by the single-chip microcomputer. By changing the control parameters, the duty cycle of the PWM waveform is changed, thereby obtaining a high-precision output voltage.

[0061] According to the change of current passing through the inductor L in the Buck DC-DC converter, the circuit operation mode can be divided into three types, namely, continuous conduction mode (CCM), boundary conduction mode (BCM), and discontinuous conduction mode (DCM). Among them, in the continuous conduction mode, the on-off time ratio of the power tube will directly affect the output voltage, and the output stability is also good, and the ripple is also small.

[0062] Therefore, in this embodiment, as a preferred embodiment, the PWM modulation principle is combined to realize the control of the Buck type DC-DC converter working in CCM.

[0063] Therefore, according to the state space average model of the system in formula (3), the relationship between the state variables is constructed:

[0064]

[0065] In which, the output voltage V0 of the system is assumed to be the state variable x1; the first-order derivative of V0 is assumed to be the state variable x2; d(t) is the system uncertain disturbance term, and in this embodiment, d(t)=0.1sin t; u(t) is the state switching control function of the power switch, which is obtained by converting the state variable through the duty cycle D. When u(t)=1, the power tube is turned on, and when u(t)=0, the power tube is turned off.

[0066] Because the switch 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 is reflected as the duty cycle D of the control signal in the macroscopic view. Their mathematical relationship is reflected in that D is the average value of u(t) in a switching cycle. In this embodiment, the result obtained by the algorithm ultimately needs to be realized by the duty cycle D of the control signal PWM waveform of the actual circuit.

[0067] Based on the sliding mode variable structure controller, a sliding surface is designed to make the system state reach and remain on this sliding surface in a short time. Once the system enters the sliding mode motion stage, it has strong robustness to the interference and uncertainty of the system.

[0068] S22, constructing a sliding surface;

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

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

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

[0072]

[0073] According to the working principle and mathematical model of the Buck DC-DC converter, considering the uncertainty of system parameters and system robustness, an integral term is added to the sliding surface to reduce the 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] Among them, k and δ are any constants greater than 0, which are used to adjust the system robustness.

[0077] S23, constructing system control law and control parameter recognition rate based on sliding surface;

[0078] Buck DC-DC converter can stabilize the output voltage in a short time, which needs to meet the controller output u(t) and control parameters Relationship, that is, system control law and control parameter recognition rate:

[0079]

[0080] S24, using Lyapunov's second method stability criterion, verify the sliding surface and system control law and control parameter identification rate;

[0081] Construct the Lyapunov function:

[0082]

[0083] Derivative (12) with respect to time and substitute (4) and (7) into:

[0084]

[0085]

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

[0087]

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

[0089]

[0090] According to the inequality theorem:

[0091]

[0092] Among them, if ω ≥ |s(t)|, then there must be According to the stability criterion of Lyapunov's second method The system is asymptotically stable when it is negative or semi-negative, that is, the Buck type DC-DC converter can stabilize the output voltage in a short time.

[0093] The following is a specific example to verify the effect of the method of the present invention:

[0094] Based on the design of the second-order sliding mode controller in the above method and the theoretical verification of its stability, the control law and control parameter recognition rate of the second-order sliding mode controller of the Buck DC-DC converter are obtained, that is, equations (10) and (11), and the simulation model of the second-order sliding mode controller is established, as shown in Figure 2 As shown in the figure, Matlab / Smulink is used to verify the control method of the second-order sliding mode controller.

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

[0096] The simulation results are as follows Figure 3-10 shown. Figure 3 Figure 4 They are the time evolution curves of sliding surface and first-order sliding surface respectively. Figure 3 Figure 4 It can be seen that the system maintains smoothly on the sliding surface at around 0.07s, the control action is continuous and stable, and the jitter is very small.

[0097] Figure 5 Is a parameter variable The recognition law evolves over time. Figure 5 Knowable After a short adjustment, the design parameters can be identified quickly and accurately. The value of 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 can be seen 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 This is the voltage output response curve when the parameter k changes. Figure 7 It can be seen that when k is 0.1, the system response time is significantly faster than when k = 10, but the output curve fluctuation is greater than when k = 10, which shows that the system stability is not as good as k = 10. Considering the system's rapidity and stability, k = 10, δ = 0.01, the system output voltage and inductor current response curves are as follows Figure 8 Fig. 9 As shown. Figure 8 and Fig. 9 It can be seen that the system rise time is 0.046s, and the system enters a stable state at 0.073s. Therefore, the second-order sliding mode controller is used to control the switch of the power tube, which has a 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%; Fig. 9 The output inductor current is 10.01A, while the target current is 10A, and the steady-state error is 0.1%. Figure 8 Fig. 9It can be seen that the use of a second-order sliding mode controller to control the Buck DC-DC converter can effectively suppress the system overshoot phenomenon and improve the system stability and control accuracy. Fig.10 It can be seen that when the load cuts off the 10Ω resistance at 0.4s and the second-order sliding mode controller is used, the output voltage drops from 360.1V to 341.2V, recovers after 0.028s, and re-enters a stable state.

[0100] The sliding mode controller designed in this embodiment has better anti-interference ability and stronger regulation performance for load changes, and has better load regulation performance. Therefore, this control method can improve the stability of the output voltage of the Buck type 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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: Use a second-order sliding mode controller to control the Buck type DC-DC converter; The sliding surface of the second-order sliding mode controller is: Among them, the system output target voltage value is V e ; The error of the system output voltage is e(t), e(t) = V0-V e =x1-V e ; k and δ are any constants greater than 0, which are used to adjust the robustness of the system.

2. According to claim 1, a second-order sliding mode control method based on a high-power Buck converter is characterized in that: The topological structure of the Buck type DC-DC converter includes: DC power supply DC, two power tubes MOSFET, energy storage inductor L, filter capacitor C and load resistor R.

3. According to claim 1, a second-order sliding mode control method based on a high-power Buck converter is characterized in that: The second-order sliding mode control method based on high-power Buck converter also includes: Construct a Buck type DC-DC converter model; Based on the state variable relationship of the Buck DC-DC converter model, the parameter recognition rate of the second-order sliding mode controller is designed.

4. According to claim 1, a second-order sliding mode control method based on a high-power Buck converter is characterized in that: The Buck type DC-DC converter model is constructed, comprising: Construct the state space average model of the system within a switching cycle T: in, Indicates the duty cycle of the power switch tube drive signal; the system output voltage is V0.

5. According to claim 1, a second-order sliding mode control method based on a high-power Buck converter is characterized in that: The state variable relationship of the Buck type DC-DC converter model is: Among them, the output voltage V0 of the system is the state variable x1; the first-order derivative of V0 is the state variable x2; d(t) is the system uncertain disturbance term, d(t) = 0.1sint; u(t) is the state switching control function of the power switch, which is obtained by converting the state variable through the duty cycle D. When u(t) = 1, the power tube is turned on, and when u(t) = 0, the power tube is turned off.

6. According to claim 1, a second-order sliding mode control method based on a high-power Buck converter is characterized in that: The second-order sliding mode controller parameter recognition rate includes: Where δ is the parameter of the second-order sliding mode controller.

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