CN111355372A - A Linear and Nonlinear Hybrid Control Method for Buck Converters - Google Patents

Abstract

The invention discloses a linear and nonlinear hybrid control method of Buck converter. The control method combines the advantages of steady-state performance of PI control and the advantages of dynamic performance of sliding mode control. Sampling, calculate the average inductor current value in DCM mode and CCM mode with a unified formula, and compare the average inductor current value and the average value of the inductor current in critical mode to determine the working mode of the Buck converter. When the DCM/CCM mode switches, Buck The double closed-loop control voltage outer loop of the converter is immediately switched from PI control to sliding mode control, and after detecting that the output voltage returns to steady state under sliding mode control, it immediately switches back to PI control, and adopts a switching structure with output pre-compensation To achieve smooth switching between the two control methods.

Description

A Linear and Nonlinear Hybrid Control Method for Buck Converters

technical field

The invention relates to a linear and nonlinear hybrid control method of a Buck converter, belonging to the field of switching power supplies.

Background technique

Buck converter is a kind of power electronic device that can realize the DC step-down function. It has the advantages of simple structure and high power density. At present, it has been widely used in aerospace, DC motor drive, electric vehicle charging and renewable energy and other industrial fields. Under the traditional PI double closed-loop control, when the Buck converter is disturbed by the load of the inductor current continuous mode and the inductor current discontinuous mode switching, the dynamic performance is poor, which will seriously affect the working quality of the load, and may even cause the load to fail to work normally. . Therefore, improving the output anti-disturbance performance has become an urgent problem to be solved.

In view of the problem that the Buck converter has poor anti-load disturbance performance under traditional PI control, many discussions have been carried out at home and abroad. Among them, sliding mode control has the advantages of simple form, excellent dynamic performance and strong robustness to system uncertain disturbances. , many achievements have been made in the field of high-performance control of Buck converters. "Design of Buck Converter with Controlled Sliding Mode Control" (see "Chinese Journal of Electrical Engineering", 2010) A traditional single-loop linear sliding mode controller is designed based on the output voltage error and its first derivative, and the voltage robustness is better than the traditional PI The control has been improved to a certain extent, but it introduces voltage differential and adopts hysteresis variable frequency control, which is more sensitive to system noise, and its output voltage dynamic response is much worse than double closed-loop control. "Robust Discrete Integral Sliding Mode Control of Buck Converters" (see "Journal of Electrotechnical Technology", 2019) proposes a robust discrete integral sliding mode (DISM) voltage control strategy, which is based on retaining the traditional double closed-loop control current inner loop On the other hand, the discrete voltage model with centralized disturbance is reconstructed, and the global robust DISM voltage controller is designed to improve the dynamic quality and disturbance immunity of the output voltage, but the high-frequency chattering of the sliding mode control will seriously affect the stability of the output voltage. state performance.

SUMMARY OF THE INVENTION

Aiming at the problem of poor dynamic characteristics of the Buck converter under the traditional PI double closed-loop control, when the Buck converter is subjected to the load disturbance of the inductor current continuous mode and the inductor current discontinuous mode switching, the invention proposes a linear and nonlinear Buck converter. Hybrid control method.

In order to realize the above method, the present invention adopts the control system shown in FIG. 1 to realize, the system includes five parts: Buck converter, signal sampling module, average inductor current correction module, mode monitoring module, and control algorithm module.

The power supply voltage signal u _i , the output voltage signal u _o , and the inductor current signal i _L of the Buck converter are sent to the signal sampling module, and the power supply voltage sampling signal u _in is obtained by sampling at the midpoint of the rising edge or falling edge of the inductor current, and the output The voltage sampling signal u _on , the inductor current sampling signal i _Ln , wherein the sampling period is T, and the sampling time is nT.

The power supply voltage sampling signal u _in , the output voltage sampling signal u _on , the inductor current sampling signal i _Ln and the duty cycle D output by the control algorithm module output by the signal sampling module are used as the input of the average inductor current correction module, and the output average inductance is calculated by calculating Current signal I _Ln .

The power supply voltage sampling signal u _in , the output voltage sampling signal u _on and the average inductor current signal I _Ln output by the average inductor current correction module output by the signal sampling module are given to the mode monitoring module for judging the operating mode of the Buck converter. Buck converter operation modes include Inductor Current Discontinuous Mode (DCM) and Inductor Current Continuous Mode (CCM). The mode monitoring module outputs different modes a according to different operation modes, and is used as the input of the control algorithm module for control method switching. .

The output voltage reference value u _ref , the average inductor current signal I _Ln , the mode a and the output voltage sampling signal u _on are used as the input of the control algorithm module, and the duty cycle D and PWM are output, wherein the duty cycle D is used as the average inductor current correction module The input is used for the calculation of the average inductor current signal I _Ln ; PWM is used as the input of the Buck converter to control the on-off of the power switch S.

The control algorithm module includes three parts: the outer loop hybrid control module, the inner loop PI control module, and the PWM generation module; wherein, the output voltage reference value u _ref , the output voltage sampling signal u _on and the mode a are used as the input of the outer loop hybrid control module, And select sliding mode control (SMC) or PI control through switching conditions, and output the inductor current reference value i _Lref ; the inductor current reference value i _Lref and the average inductor current signal I _Ln are given to the inner loop PI control module, and the output modulation is adjusted by PI. The modulated wave signal is given to the PWM generation module, and the duty cycle D and PWM are output through the PWM generation module, wherein the duty cycle D is used as the input of the average inductor current correction module for the calculation of the average inductor current signal I _Ln ; PWM As the input of the Buck converter, it is used to control the on-off of the power switch tube S.

The average inductor current correction module calculates the average inductor current signal I _Ln through the power supply voltage sampling signal u _in , the output voltage sampling signal u _on , the inductor current sampling signal i _Ln and the duty cycle D output by the control algorithm module. The formula is:

The mode monitoring module judges the mode by comparing the average inductor current signal I _Ln with the average value of the inductor current in the critical mode. The judgment conditions are:

When it is judged that the Buck converter is running in the DCM mode, the mode monitoring module outputs the signal mode a=0; when it is judged that the Buck converter is running in the CCM mode, the mode monitoring module outputs the signal mode a=1.

The control method switching condition of the outer loop hybrid control module is: when the mode a changes from 1 to 0, or from 0 to 1, that is, when the Buck converter switches from CCM mode to DCM mode, or from DCM mode to CCM mode, the external The loop hybrid control module switches from PI control to SMC control immediately, and then runs under SMC control. When it is judged that the output voltage sampling signal u _on returns to a steady state, the outer loop hybrid control module immediately switches from SMC control to PI control.

The outer-loop hybrid control module adopts a switching structure with output pre-compensation, through which the smooth switching between PI control and SMC control can be achieved; assuming that the outer-loop hybrid control module outputs the inductor current reference value i _Lref under PI control, at this time The PI control output is used as the reference value, the SMC control output is used as the feedback value, and the error between the two is used as the SMC control input, so that the SMC control output is consistent with the PI control output at all times, and the SMC control output is pre-compensated. Therefore, when the PI control is switched to the SMC control, the smooth switching of the two control methods can be realized. Assuming that the outer loop hybrid control module outputs the reference value of the inductor current i _Lref under the SMC control, the SMC control output is used as the reference value, and the The output of the PI control is used as the feedback value, and the error of the two is used as the input of the PI control, so that the output of the PI control is consistent with the output of the SMC control at all times, and the output of the PI control is pre-compensated, so that the SMC control is switched to the PI control. The smooth switching between the two control methods is realized.

Compared with the existing Buck converter control method, the present invention has the advantages that: the control method combines the advantages of the steady-state performance of the PI control and the dynamic performance of the sliding mode control, and can achieve smooth switching between the control methods; The sampling is performed at the midpoint of the rising edge or falling edge of the inductor current, and the average inductor current value in the DCM mode and the CCM mode is corrected by a unified formula, which solves the problem that the average inductor current value in the DCM mode is difficult to sample.

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments:

Description of drawings

FIG. 1 is a system structure diagram of the Buck converter linear and nonlinear hybrid control method according to the present invention.

Detailed ways

The present invention provides a linear and nonlinear hybrid control method for a Buck converter, which will be further described in detail with reference to the accompanying drawings.

In order to realize the control method, the present invention adopts the system shown in FIG. 1 to realize, the system mainly includes five parts: Buck converter, signal sampling module, average inductor current correction module, mode monitoring module and control algorithm module.

The power supply voltage signal u _i , the output voltage signal u _o , and the inductor current signal i _L of the Buck converter are sent to the signal sampling module, and the power supply voltage sampling signal u _in is obtained by sampling at the midpoint of the rising edge or falling edge of the inductor current, and the output The sampling period of the voltage sampling signal u _on and the inductor current sampling signal i _Ln is T, and the sampling time is nT.

The sampled power supply voltage sampling signal u _in , output voltage sampling signal u _on , inductor current sampling signal i _Ln and the duty cycle D output by the control algorithm module are given to the average inductor current correction module, and the average inductor current signal is calculated through these signals _ILn .

The power supply voltage sampling signal u _in , the output voltage sampling signal u _on , and the average inductor current signal I _Ln are used as the input of the mode monitoring module, and the Buck transformation is determined by comparing the average inductor current signal I _Ln and the average value of the critical mode inductor current. Inverter operation mode, in which Buck converter operation mode includes inductor current discontinuous mode (DCM) and inductor current continuous mode (CCM), and the mode monitoring module can output different mode a signals according to different operation modes, and give it to the control algorithm Module, used to control the switching of methods.

The output voltage reference value u _ref , the average inductor current signal I _Ln , the mode a and the output voltage sampling signal u _on are used as the input of the control algorithm module, and the control algorithm module switches the control method according to these signals and outputs the duty cycle D and PWM, The duty ratio D is used as the input of the average inductor current correction module to calculate the average inductor current signal I _Ln ; the PWM is used as the input of the Buck converter to control the on-off of the power switch S.

The control algorithm module includes three parts: the outer loop hybrid control module, the inner loop PI control module, and the PWM generation module; wherein, the output voltage reference value u _ref , the output voltage sampling signal u _on and the mode a are used as the input of the outer loop hybrid control module, And select sliding mode control (SMC) or PI control through switching conditions, and output the inductor current reference value i _Lref , where the difference between the voltage reference value u _ref and the output voltage sampling signal u _on is used as the two kinds of control in the outer loop hybrid control module The input of the method; the difference between the inductor current reference value i _Lref and the average inductor current signal I _Ln is given to the inner loop PI control module, and the modulated wave signal is output through the inner loop PI control module; the modulated wave signal is given to the PWM generation module, through the PWM The generation module outputs duty cycle D and PWM, wherein the duty cycle D is used as the input of the average inductor current correction module for the calculation of the average inductor current signal I _Ln ; PWM is used as the input of the Buck converter to control the power switch tube S on and off.

The average inductor current correction module calculates the average inductor current signal I _Ln through the power supply voltage sampling signal u _in , the output voltage sampling signal u _on , the inductor current sampling signal i _Ln and the duty cycle D output by the control algorithm module. The formula is:

The mode monitoring module judges the mode by comparing the average inductor current signal I _Ln with the average value of the inductor current in the critical mode. The judgment conditions are:

When it is judged that the Buck converter is running in the DCM mode, the mode monitoring module outputs the signal mode a=0; when it is judged that the Buck converter is running in the CCM mode, the mode monitoring module outputs the signal mode a=1.

The control method switching condition of the outer loop hybrid control module is: when the mode a changes from 1 to 0, or from 0 to 1, that is, when the Buck converter switches from CCM mode to DCM mode, or from DCM mode to CCM mode, the external The loop hybrid control module switches from PI control to SMC control immediately, and then runs under SMC control. When it is judged that the output voltage sampling signal u _on returns to steady state, the outer loop hybrid control module immediately switches from SMC control to PI control.

As shown in Figure 1, the outer loop hybrid control module adopts a switching structure of output pre-compensation, through which the smooth switching between PI control and SMC control can be realized; when the outer loop hybrid control module selects the PI control output inductor current reference value When i _Lref , the logic control switches K ₅ , K ₆ and K ₂ are closed, K ₁ , K ₃ and K ₄ are open, the PI control output is used as the reference value, the SMC control output is used as the feedback value, and the two The error amount of the SMC is used as the input of the SMC control to ensure that the SMC control output follows the PI control output, so that the SMC control output is consistent with the PI control output at all times, and the sliding mode control output is pre-compensated, so as to realize when the PI control is switched to the SMC control. Smooth switching of the control method _; similarly, when the control method is SMC control, the logic control switches _K1 , K3 and _K4 are closed, and _K5 , _K6 and _K2 are disconnected. The method of pre-compensation ensures that the PI control output is consistent with the SMC control output at all times, so that the control method can be smoothly switched when the SMC control is switched to the PI control.

The linear and nonlinear hybrid control method of the Buck converter, by sampling at the midpoint of the rising edge or falling edge of the inductor current, corrects the average inductor current value in DCM mode and CCM mode with a unified formula, and compares the average inductor current value with the critical value. The working mode of the Buck converter is determined by the average value of the mode inductor current. When the DCM/CCM mode switch occurs, the double closed-loop control voltage outer loop of the Buck converter is immediately switched from the PI control to the SMC control, and the output voltage is detected under the SMC control. After the steady state is restored, it switches back to PI control immediately, in which a switching structure with output pre-compensation is used to achieve smooth switching between the two control methods.

Claims (3)

1. A Buck converter linear and nonlinear hybrid control method is characterized by comprising the following steps: the control system of the method comprises: the device comprises a Buck converter (1), a signal sampling module (2), an average inductive current correction module (3), a mode monitoring module (4) and a control algorithm module (5);

supply voltage signal u of Buck converter (1)_iOutput voltage signal u_oInductor current signal i_LTo a signal sampling module (2) and by samplingSample output power supply voltage sampling signal u_inAnd output voltage sampling signal u_onInductor current sampling signal i_Ln；

The power supply voltage sampling signal u output by the signal sampling module (2)_inAnd output voltage sampling signal u_onInductor current sampling signal i_LnThe duty ratio D output by the control algorithm module (5) is used as the input of the average inductive current correction module (3), and an average inductive current signal I is output through calculation_Ln；

The power supply voltage sampling signal u output by the signal sampling module (2)_inAnd output voltage sampling signal u_onAnd an average inductive current signal I output by the average inductive current correction module (3)_LnThe mode monitoring module is used as the input of the mode monitoring module (4) and is used for judging the operation mode of the Buck converter (1); the operation modes of the Buck converter (1) comprise an inductive current discontinuous mode (DCM) and an inductive Current Continuous Mode (CCM);

the output signal of the mode monitoring module (4) is a mode a, and is used as the input of the control algorithm module (5) for controlling the switching of the method;

reference value u of output voltage_refAnd an output voltage sampling signal u output by the signal sampling module (2)_onAverage inductive current signal I output by average inductive current correction module (3)_LnThe mode a output by the mode monitoring module (4) is used as the input of the control algorithm module (5);

the output signal of the control algorithm module (5) comprises a duty ratio D and PWM, wherein the duty ratio D is used as the input of the average inductive current correction module (3); PWM is used as the input of the Buck converter (1) and is used for controlling the on-off of a power switch tube S;

the control algorithm module (5) comprises: the device comprises an outer ring hybrid control module (5-1), an inner ring PI control module (5-2) and a PWM generation module (5-3); reference value u of output voltage_refAnd output voltage sampling signal u_onAnd the mode a is used as the input of an outer ring hybrid control module (5-1), Sliding Mode Control (SMC) or PI control is selected according to the switching condition, and an inductance current reference value i is output_Lref(ii) a Reference value of inductor current i_LrefAnd average inductor current signalNumber I_LnThe input of the inner loop PI control module (5-2) is used for outputting a modulation wave signal through PI regulation; the modulation wave signal is sent to a PWM (pulse-width modulation) generation module (5-3) and a duty ratio D and PWM are output, wherein the duty ratio D is used as the input of an average inductive current correction module (3), and the PWM is used as the input of a Buck converter (1) and is used for controlling the on-off of a power switch tube S;

the average inductive current signal I of the output signal of the average inductive current correction module (3)_LnThe calculation formula is as follows:

the mode judgment condition of the mode monitoring module (4) is as follows:

in the formula, T represents a switching period, and L represents inductance;

when the mode monitoring module (4) judges that the Buck converter (1) operates in the DCM, the output signal mode a is 0; when the mode monitoring module (4) judges that the Buck converter (1) operates in the CCM mode, the output signal mode a is 1;

the outer ring hybrid control module (5-1) controls the switching conditions of the method to be as follows: when the mode a changes from 1 to 0 or from 0 to 1, the outer-loop hybrid control module (5-1) immediately switches from PI control to SMC control, and outputs the voltage sampling signal u under SMC control_onWhen the steady state is recovered, the outer loop hybrid control module (5-1) immediately switches from SMC control to PI control.

2. The Buck converter linear and nonlinear hybrid control method according to claim 1, wherein: the power supply voltage sampling signal u output by the signal sampling module (2)_inAnd output voltage sampling signal u_onInductor current sampling signal i_LnThe sampling is obtained by sampling at the middle point of the rising edge or the falling edge of the inductor current, the sampling period is T, and the sampling time is nT.

3. The Buck converter linear and nonlinear hybrid control method according to claim 1, wherein: an output pre-compensation switching structure is adopted in the outer ring hybrid control module (5-1); an outer ring hybrid control module (5-1) is assumed to output an inductive current reference value i under PI control_LrefAt the moment, the PI control output quantity is used as a reference value, the output quantity of SMC control is used as a feedback value, and the error quantity of the PI control output quantity and the output quantity of SMC control is used as the input of SMC control, so that the SMC control output quantity and the PI control output quantity are kept consistent at the moment, the SMC control output quantity is pre-compensated, and the stable switching of two control methods is realized when the PI control is switched to the SMC control; the outer ring hybrid control module (5-1) is assumed to output an inductive current reference value i under the control of SMC_LrefAt the moment, the PI control output quantity is pre-compensated through the switching structure, so that the smooth switching of the two control methods is realized when the SMC control is switched to the PI control.

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