A sliding mode control method and system for Buck circuit

Abstract

The present invention discloses a sliding mode control method and system for a Buck circuit, which belongs to the technical field of Buck circuit control design, and includes: constructing a Buck circuit composed of a power supply, a fully controlled device MOSFET, a freewheeling diode, an LC filter network and a load; based on the Buck circuit, through sliding mode control, controlling the on-duty ratio D of the MOSFET device in each cycle to adjust the output voltage converged to the Buck circuit. The present invention performs sliding mode control on the Buck circuit, so that the controlled Buck circuit has the advantages of strong robustness, fast dynamic response, small overshoot, and strong adaptability, and enhances the anti-interference ability of the Buck circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of Buck circuit control design, and in particular to a sliding mode control method and system for a Buck circuit. Background Art

[0002] At present, in order to improve power efficiency, research on improving the conversion efficiency of switching power supplies has attracted much attention. There are two ways to improve the efficiency of the power supply: one is to change the topology of the power supply circuit, and the other is to add corresponding control to the circuit. In the control technology of switching power supplies, the commonly used control methods are current control, multi-loop control, charge control and single-cycle control, among which current control and multi-loop control have been more commonly used. Because electronic products are inevitably affected by frequent load switching and parameter drift during the actual charging process. For some electronic devices, such as medical equipment that detects weak human body current, the requirements for power supply are extremely high. To ensure that the output voltage of the power supply is accurate and stable, and returns to the balance point as soon as possible after disturbance, the output voltage control accuracy and anti-interference ability of the Buck circuit are high, and the ripple problem caused by high-frequency switch shutdown should be minimized as much as possible. Therefore, the research on the control of the Buck circuit and improving its anti-interference ability are crucial. Summary of the invention

[0003] In order to solve the above problems, an object of the present invention is to provide a sliding mode control technology for a Buck circuit to enhance the anti-interference capability of the Buck circuit.

[0004] In order to achieve the above technical objectives, the present application provides a sliding mode control method for a Buck circuit, comprising the following steps:

[0005] Construct a Buck circuit consisting of a power supply, a fully controlled MOSFET, a freewheeling diode, an LC filter network, and a load;

[0006] Based on the Buck circuit, the output voltage of the Buck circuit is adjusted by controlling the on-duty cycle D of the MOSFET device in each cycle through sliding mode control.

[0007] Preferably, in the process of constructing the Buck circuit, the output voltage ripple of the Buck circuit is less than 0.5%, and the inductor current ripple is less than 5%.

[0008] Preferably, in the process of obtaining the inductor current ripple, the inductor current ripple is expressed as:

[0009]

[0010] Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, VO is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON is the switch on time in one cycle.

[0011] Preferably, in the process of obtaining the output voltage ripple, the peak-to-peak value of the output voltage ripple is expressed as:

[0012]

[0013] In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the charge change in the filter capacitor in one cycle

[0014] Preferably, in the process of sliding mode control of the Buck circuit, by determining the sliding mode variable, the sliding mode surface and control rate in the sliding mode control are designed according to the approach motion phase attracted to the sliding mode surface and the sliding mode motion phase converging along the sliding mode surface, and sliding mode control of the Buck circuit is performed.

[0015] Preferably, in the process of determining the sliding mode variable, the sliding mode variable is expressed as:

[0016]

[0017] In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, u - (x) is the control function when the sliding mode variable is less than 0.

[0018] The present invention discloses a sliding mode control system for a Buck circuit, wherein the Buck circuit is composed of a power supply, a fully controlled device MOSFET, a freewheeling diode, an LC filter network and a load, including:

[0019] The sliding mode control module is used to adjust the output voltage of the Buck circuit by controlling the on-duty ratio D of the MOSFET device in each cycle through sliding mode control based on the Buck circuit.

[0020] Preferably, the output voltage ripple of the Buck circuit is less than 0.5%, and the inductor current ripple is less than 5%;

[0021] The inductor current ripple is expressed as:

[0022]

[0023] Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, V Ois the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON The switch conduction time in one cycle

[0024] The peak-to-peak value of the output voltage ripple is expressed as:

[0025]

[0026] In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the charge change in the filter capacitor in one cycle

[0027] Preferably, the sliding mode control module is also used to design the sliding mode surface and control rate in the sliding mode control by determining the sliding mode variable and performing sliding mode control on the Buck circuit according to the approach motion phase of being attracted to the sliding mode surface and the sliding motion phase of converging along the sliding mode surface.

[0028] Preferably, the sliding mode control module is also used to design a control rate sliding mode through a sliding mode variable, which is expressed as:

[0029]

[0030] In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, u - (x) is the control function when the sliding mode variable is less than 0.

[0031] The present invention discloses the following technical effects:

[0032] The present invention performs sliding mode control on the Buck circuit, so that the controlled Buck circuit has the advantages of strong robustness, fast dynamic response, small overshoot and strong adaptability, and enhances the anti-interference ability of the Buck circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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 will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 is the Buck circuit topology diagram of the present invention;

[0035] Figure 2 is a graph of capacitor current and inductor current according to the present invention;

[0036] Figure 3 It is a schematic diagram of the sliding mode control principle of the present invention;

[0037] Figure 4 is a schematic diagram of the effect of sliding mode control according to the present invention;

[0038] Figure 5 It is a schematic diagram of the method flow of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0040] like Figure 1-5 As shown, the present invention provides a sliding mode control method for a Buck circuit, comprising the following steps:

[0041] Construct a Buck circuit consisting of a power supply, a fully controlled MOSFET, a freewheeling diode, an LC filter network, and a load;

[0042] Based on the Buck circuit, the output voltage of the Buck circuit is adjusted by controlling the on-duty cycle D of the MOSFET device in each cycle through sliding mode control.

[0043] Further preferably, in the sliding mode control method provided by the present invention, during the process of constructing a Buck circuit, the output voltage ripple of the Buck circuit is less than 0.5%, and the inductor current ripple is less than 5%.

[0044] Further preferably, in the sliding mode control method provided by the present invention, in the process of obtaining the inductor current ripple, the inductor current ripple is expressed as:

[0045]

[0046] Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, V O is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, TON The switch conduction time in one cycle

[0047] Further preferably, in the sliding mode control method provided by the present invention, in the process of obtaining the output voltage ripple, the peak-to-peak value of the output voltage ripple is expressed as:

[0048]

[0049] In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the change in charge in the filter capacitor in one cycle.

[0050] Further preferably, the sliding mode control method provided by the present invention, in the process of performing sliding mode control on the Buck circuit, determines the sliding mode variable, designs the sliding mode surface and control rate in the sliding mode control according to the approach motion stage of being attracted to the sliding surface and the sliding motion stage of converging along the sliding surface, and performs sliding mode control on the Buck circuit.

[0051] Further preferably, in the sliding mode control method provided by the present invention, in the process of determining the sliding mode variable, the sliding mode variable is expressed as:

[0052]

[0053] In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, u - (x) is the control function when the sliding mode variable is less than 0.

[0054] The present invention discloses a sliding mode control system for a Buck circuit, wherein the Buck circuit is composed of a power supply, a fully controlled device MOSFET, a freewheeling diode, an LC filter network and a load, and includes:

[0055] The sliding mode control module is used to adjust the output voltage of the Buck circuit by controlling the on-duty ratio D of the MOSFET device in each cycle through sliding mode control based on the Buck circuit.

[0056] Further preferably, the output voltage ripple of the Buck circuit of the sliding mode control system disclosed in the present invention is less than 0.5%, and the inductor current ripple is less than 5%;

[0057] The inductor current ripple is expressed as:

[0058]

[0059] Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, VO is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON The switch conduction time in one cycle

[0060] The peak-to-peak value of the output voltage ripple is expressed as:

[0061]

[0062] In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the change in charge in the filter capacitor in one cycle.

[0063] Further preferably, the sliding mode control module of the sliding mode control system disclosed in the present invention is also used to design the sliding mode surface and control rate in the sliding mode control by determining the sliding mode variable, and perform sliding mode control on the Buck circuit according to the approach motion phase of being attracted to the sliding mode surface and the sliding motion phase of converging along the sliding mode surface.

[0064] Further preferably, the sliding mode control module of the sliding mode control system disclosed in the present invention is also used to design a control rate sliding mode through a sliding mode variable, which is expressed as:

[0065]

[0066] In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, y - (x) is the control function when the sliding mode variable is less than 0.

[0067] Embodiment: Buck circuit is a DC-DC step-down alternating circuit. Figure 1 The Buck circuit shown is usually composed of a power supply, a fully controlled device MOSFET, a freewheeling diode, an LC filter network and a load. The output voltage is adjusted by controlling the conduction duty cycle D of the MOSFET device in each cycle.

[0068] The on and off of the MOSFET switch correspond to two modes: when the MOSFET is on, the freewheeling diode is turned off due to the reverse voltage, and the power supply charges the LC through the switch tube. At this time, the inductor is in the energy storage stage. When the MOSFET is turned off, the input power supply cannot be connected to the output to form a loop. At this time, the inductor is in a discharge state, and the load circuit is powered through the freewheeling diode. It is precisely because the on-duty cycle is not 1 that the average voltage on the load side is always lower than the input voltage, thereby achieving voltage reduction.

[0069] The parameters designed by the present invention are input voltage of 60V, output voltage of 30V, maximum power of 1kW, output voltage ripple of less than 0.5%, and inductor current ripple of less than 5%.

[0070] From the maximum power and output voltage we can get:

[0071]

[0072] In the formula, R is the load, Uo is the output voltage, and P is the output power;

[0073] The inductor current is the sum of the capacitor current and the load current:

[0074] I L =I C +I R

[0075] In the formula, I L is the current through the energy storage and release filter inductor, I C is the current through the filter capacitor, I R is the load current;

[0076] The capacitor current ripple is approximately equal to the inductor current ripple ΔI, ΔI is equal to the inductor rise slope multiplied by the rise time, ΔI only rises when the switch is turned on. And when the switch is turned on, the inductor voltage is V IN -V O available:

[0077]

[0078] Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, V O is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON is the switch on time in one cycle;

[0079] So L is:

[0080]

[0081] For the peak-to-peak value of the output ripple voltage ΔV C , combined with the capacitance characteristic equation, the maximum value of the capacitance change is the area where the current is positive in one cycle:

[0082] In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S ΔIndicates the charge change in the filter capacitor in one cycle

[0083] So C is:

[0084] Where, ΔV C is the peak-to-peak value of the output ripple voltage;

[0085] According to the above formula, the relevant parameters can be calculated, as shown in Table 1:

[0086] Table 1. Circuit parameters of Buck at maximum power P = 1kW

[0087] Specific parameters Numeric Load resistance value R 0.9Ω Inductance value L (ignore equivalent resistance ESR) 4.5e-05H Capacitance value C (ignore equivalent resistance ESR, equivalent inductance ESL) 1.1213e-04F

[0088] For sliding mode control of Buck circuit:

[0089] Basic principles of sliding mode control:

[0090] Sliding mode control, also known as sliding mode variable structure control, is a nonlinear control for variable structure systems. The difference from conventional control systems lies in the discontinuity of control. Buck converter is a typical variable structure system. Sliding mode control with discontinuous control as its characteristic corresponds to the switch-on and switch-off modes. Therefore, sliding mode variable structure control is widely used in Buck converters.

[0091] For single input control systems:

[0092] Among them, t is the time variable, x is the system variable, and u is the control variable.

[0093] To design a sliding mode controller, we must first determine the sliding mode variable s(x), s(x)∈R, and seek the control law of the system:

[0094]

[0095] In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, y - (x) is the control function when the sliding mode variable is less than 0.

[0096] like Figure 3 As shown, is the dynamic nonlinear sliding surface; the sliding surface s = 0 divides the space into two parts. No matter which area the system state is located in, the system will move toward the sliding surface. According to the above analysis, for the sliding mode control system, the motion state can be divided into two parts: one is the approaching motion attracted to the sliding surface, and the other is the sliding motion stage that converges along the sliding surface. Therefore, the design of the sliding mode controller is the design of the sliding surface and the control rate.

[0097] For the application of sliding mode variable structure control in BUCK converter, based on BUCK topology circuit, under the condition of state space average and considering the uncertainty of load, the error state equation is:

[0098]

[0099] Where RLC is the load, energy storage and release filter inductor, and filter capacitor in the BUCK circuit; x1 is the error voltage of the filter capacitor; x2 is the derivative of x1; V on is the circuit power supply; d(t) is a constant varying from 0 to 1; V ref is the target voltage.

[0100] For convenience:

[0101]

[0102] Here, the second-order sliding mode control is selected in the Buck circuit, and the sliding mode surface is designed as:

[0103]

[0104] Among them, α>0, the derivative of the sliding surface equation can be obtained:

[0105]

[0106] Judging stability and accessibility:

[0107] When the system moving point performs sliding mode motion from the side where s>0, the following first condition needs to be met:

[0108] When the system moving point performs sliding mode motion from the side where s < 0, the following second condition needs to be met:

[0109] Combination and The points near the switching surface need to satisfy:

[0110] Stability is the property of the sliding surface to reach the equilibrium point, and accessibility is the property of reaching the sliding surface from the initial state. If α>0 (Hurwitz criterion), the sliding mode control must satisfy the following formula to be reachable and stable: They are the Hurwitz criterion and the Lyapunov criterion respectively. When both are satisfied, the system is stable and reachable.

[0111]

[0112] According to Lyapunov, if there exists V>0, it can make If it holds, the system is stable, and the Lyapunov function is:

[0113]

[0114] According to the above analysis, the sliding mode control function is designed:

[0115]

[0116] Among the switch items is a robust term used to overcome time-varying interference.

[0117] It can make V>0, and it can make It holds, so it satisfies the reachability and stability. According to the Hurwitz and Lyapunov criteria, the system is stable. Figure 4 As shown in the figure, through sliding mode control, the startup response time is reduced to 500μs, which is about 27% higher; in the average recovery time from the system being disturbed by load switching to the system being stable, the sliding mode control startup response time is reduced to 200μs, which is about 71% higher, and the disturbance amount is 0.7%.

[0118] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0119] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0120] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A sliding mode control method for a Buck circuit, characterized in that: The following steps are involved: Construct a Buck circuit consisting of a power supply, a fully controlled MOSFET, a freewheeling diode, an LC filter network, and a load; Based on the Buck circuit, the on-duty ratio D of the MOSFET device in each cycle is controlled by sliding mode control to adjust the output voltage that converges to the Buck circuit; In the process of constructing the Buck circuit, the output voltage ripple of the Buck circuit is set to be less than 0.5%, and the inductor current ripple is set to be less than 5%; In the process of obtaining the inductor current ripple, the inductor current ripple is expressed as: Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, V O is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON is the switch on time in one cycle; In the process of obtaining the output voltage ripple, the output voltage ripple is expressed as: In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the charge change in the filter capacitor in one cycle; In the process of sliding mode control of the Buck circuit, the sliding mode variable is determined, and the sliding mode surface and control rate in the sliding mode control are designed according to the approaching motion phase attracted to the sliding mode surface and the sliding mode motion phase converging along the sliding mode surface, so as to perform sliding mode control on the Buck circuit; In the process of determining the sliding mode variable S(x), the sliding mode control variable u(x) is expressed as: In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, u - (x) is the control function when the sliding mode variable is less than 0.

2. A sliding mode control system for a Buck circuit, characterized in that: The Buck circuit is composed of a power supply, a fully controlled device MOSFET, a freewheeling diode, an LC filter network and a load, including: A sliding mode control module, used to control the conduction duty cycle D of the MOSFET device in each cycle based on the Buck circuit through sliding mode control to adjust the output voltage of the Buck circuit; The output voltage ripple of the Buck circuit is less than 0.5%, and the inductor current ripple is less than 5%; The inductor current ripple is expressed as: Where D is the duty cycle of PWM, T S is the cycle time, V in is the input voltage, V O is the output voltage, L is the energy storage and release filter inductance, V L is the voltage at the end of the energy storage and release filter inductor, T ON The switch conduction time in one cycle The output voltage ripple is expressed as: In the formula, ΔI L is the peak-to-peak value of the energy storage and release filter inductance within one cycle, C is the filter capacitor, S Δ Indicates the charge change in the filter capacitor in one cycle; The sliding mode control module is further used to design the sliding mode surface and the control amount in the sliding mode control by determining the sliding mode variable according to the approaching motion phase attracted to the sliding mode surface and the sliding mode motion phase converging along the sliding mode surface, so as to perform sliding mode control on the Buck circuit; The sliding mode control module is also used to design a control rate sliding mode through a sliding mode variable, which is expressed as: In the formula, u(x) represents the control quantity, u + (x) is the control function when the sliding mode variable is greater than 0, u - (x) is the control function when the sliding mode variable is less than 0.

Images