A power switching control method for a BUCK converter

Abstract

The present invention discloses a buck converter power switching control method, comprising the following steps: Step 1: establishing a buck converter power switching model; Step 2: designing buck converter switching rules. This method can directly express the active power state of the buck converter system and accurately describe its operating process. The designed switching controller directly selects the buck converter switching state by determining the error state between the system power and the expected value. This method has the advantages of simple implementation, rapid response, no control parameters, no need for complex vector pulse width modulation (PWM) processes, and good control effects. It is easily applicable to new energy power generation systems such as photovoltaic and wind power systems that require system input power control or maximum power point tracking control.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a BUCK converter power switching control method. Background Art

[0002] Buck converters, due to their simple circuit structure, easy control, and ability to convert DC power, are widely used in various energy conversion and control fields, including renewable energy generation, electric vehicles, and motor speed regulation. They are particularly common in renewable energy generation systems such as photovoltaic and wind power, where they utilize buck converters to regulate the output power of photovoltaic cells or wind turbines and track maximum power points.

[0003] However, due to the presence of switching devices, the buck converter is a typical nonlinear system. Under fixed switching conditions, the system state varies continuously, while the switching devices exhibit discrete variations. Therefore, accurate buck converter modeling is extremely difficult. Traditional buck converter models built using approximation and linearization methods are inaccurate and struggle to reflect the actual operation of the buck converter. Furthermore, the state parameters of commonly used buck converter models are typically the inductor current and output DC voltage. In applications such as photovoltaic cell maximum power point tracking control, current buck converter state models based on inductor current and output DC voltage cannot directly describe the buck converter's power state. Furthermore, traditional duty-cycle-based buck converter control requires a complex pulse vector modulation (PWM) process, resulting in poor control performance when exposed to large signal interference. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the proposed method establishes a buck converter power switching model to directly express the buck converter's active power state and accurately describe its operating process. Simultaneously, switching rules are designed to directly regulate the switch state to control the buck converter's power. This method addresses technical issues such as the inability of conventional buck converter models to accurately describe the converter's operating process, the complex pulse vector modulation (PWM) process required for duty-cycle-based converter control, and poor control effectiveness in the presence of large signal interference.

[0005] To achieve the above object, the present invention provides the following technical solution: a BUCK converter power switching control method, comprising the following steps:

[0006] Step 1: Establish a power switching model for the BUCK converter;

[0007] For the BUCK converter, its power switching model is established as shown in formula (1):

[0008]

[0009] In formula (1), P is the active power value of the BUCK converter; Represents the derivative of active power P over time; U s The DC voltage input to the BUCK converter; U o is the output DC voltage of the BUCK converter; s is the switching state of the BUCK converter, s=1 indicates that the power switch device in the BUCK converter is on, s=0 indicates that the power switch device in the BUCK converter is off; L is the inductance value.

[0010] Step 2: Design the Buck converter switching rules

[0011] The switching rule of the buck converter is designed to implement the input power control of the buck converter using the switching rule defined by the following theorem. The specific theorem is:

[0012]

Theorem

[0013]

[0014] or

[0015]

[0016] Proof: Define the active power P of the BUCK converter and the expected power value P of the BUCK converter r Lyapunov function composed of time errors As shown in the following formula:

[0017]

[0018] In formula (4), is the error between the active power and the expected power of the BUCK converter. Taking the derivative of (4) we can get:

[0019]

[0020] From the theory of switched systems, namely the Lyapunov stability theorem, we know that for the Lyapunov function in formula (4) If we can ensure that (5) The BUCK converter switches stably under different switching states s and the power error is an asymptotically stable equilibrium point.

[0021] a) When the actual system power P of the BUCK converter is greater than the expected value P r When PP r ≥0, from the above analysis we can see that we need to ensure that

[0022] From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s Therefore, if and only if the BUCK converter switching state s=0 The derivative of the Lyapunov function in formula (5) is semi-negative definite, which meets the Lyapunov stability requirement.

[0023] b) When the actual system power P of the BUCK converter is less than or equal to the expected value P r When PP r ≤0, from the above analysis we can see that we need to ensure that

[0024] From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s Therefore, if and only if the BUCK converter switching state s=1 The derivative of the Lyapunov function in formula (5) is negative definite, which meets the Lyapunov stability requirement.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a BUCK converter power switching control method, which has the following beneficial effects: in step 1, the power switching model realizes a direct description of the active power state of the BUCK converter and the modeling process does not require operations such as approximation, linearization, and averaging, and can accurately reflect the converter working process; in step 2, the current converter power value P and the expected value P are calculated. r By determining the error between the input and output voltages and directly generating the buck converter switching state s by determining the error sign, the buck converter power control is achieved. This approach has the advantages of no control parameters, good control effect, simple implementation, fast system response, and no need for complex vector pulse width modulation (PWM) processes. It is suitable for use in renewable energy power generation systems such as photovoltaic and wind power generation that require system input power control or maximum power point tracking control. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 BUCK converter circuit topology diagram of the present invention;

[0028] Figure 2 This is a simulation waveform diagram of the active power of the BUCK converter of the present invention tracking its expected value change;

[0029] Figure 3 This is a simulation waveform diagram of the active power of the BUCK converter under the condition of transient change of the power expectation value of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions of the present invention in the embodiments of the present invention in conjunction with the drawings of the present invention in the embodiments of the present invention. Obviously, the embodiments described 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 making creative efforts are within the scope of protection of the present invention.

[0031] Example 1

[0032] The present invention provides a BUCK converter power switching control method, comprising the following steps:

[0033] Step 1: Establish a power switching model for the BUCK converter;

[0034] Buck converter topology Figure 1 As shown, where U s is the input DC voltage of the BUCK converter; L is the inductor; s is the switching state of the power switch device, s = 1 means the power switch device in the BUCK converter is on, s = 0 means the power switch device in the BUCK converter is off; D is the diode; C is the output filter capacitor, R is the load; U o is the output DC voltage.

[0035] for Figure 1 The power switching model of the BUCK converter shown in the figure is as follows:

[0036]

[0037] In formula (1), P is the active power value of the BUCK converter; It represents the derivative of power P with time.

[0038] As can be seen from formula (1), the BUCK converter can be regarded as different subsystems in different switching states s. By directly controlling the BUCK converter switching state s, the BUCK converter can be switched between different subsystems to achieve the purpose of regulating the active power P of the BUCK converter.

[0039] Step 2: Design the buck converter switching rules:

[0040] Switching system control is achieved by controlling the orderly switching between different subsystems through switching rules. To ensure the stability of the buck converter during switching between different subsystems and to achieve the goal of tracking the system input power state to the expected value through switching between subsystems, it is necessary to conduct a stability analysis of the switching process and design switching rules based on the conclusions of the stability analysis.

[0041] Therefore, the following theorem is proposed:

[0042]

Theorem

[0043]

[0044] or

[0045]

[0046]

Proof

[0047]

[0048] In formula (4), is the error between the active power and the expected power of the BUCK converter. Derivative (4) yields:

[0049]

[0050] According to the switching system theory, namely the Lyapunov stability theorem, for the Lyapunov function in formula (4) If we can ensure that The BUCK converter switches stably under different switching states s and the power error is an asymptotically stable equilibrium point.

[0051] a) When the actual system power P of the BUCK converter is greater than the expected value P r When PP r ≥0, from the above analysis we can see that we need to ensure that

[0052] From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s Therefore, if and only if the BUCK converter switching state s=0 The derivative of the Lyapunov function in formula (5) is semi-negative definite, which meets the Lyapunov stability requirement.

[0053] b) When the actual system power P of the BUCK converter is less than or equal to the expected value P r When PP r ≤0, from the above analysis we can see that we need to ensure that

[0054] From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s Therefore, if and only if the BUCK converter switching state s=1 The derivative of the Lyapunov function in formula (5) is negative definite, which meets the Lyapunov stability requirement.

[0055] In summary, for the BUCK converter power switching model in formula (1), the following switching rules can be used to achieve tracking control of its active power relative to the expected value:

[0056]

[0057] or

[0058]

[0059] Simulation and experimental verification:

[0060] According to the above BUCK converter power switching control method, a Matlab / Simulink simulation model is built to realize simulation verification. The simulation parameters are as follows: BUCK converter input voltage U s =100V, inductor L = 400μH, output filter capacitor C = 400μF, load resistance R = 12.5 ohms, expected active power P r =150 watts.

[0061] Figure 2 This is the simulation waveform of the BUCK converter active power tracking its expected value change. Figure 2 In the figure, the dotted line is the expected value of active power P of the BUCK converter. r The solid line is the simulation waveform of the active power P of the BUCK converter. Figure 2 It can be seen that the active power of the BUCK converter quickly reaches the expected value, has a fast response speed, no steady-state error, and no need to adjust the control parameters, reflecting a good control effect.

[0062] Figure 3 The following is the simulation waveform of the active power of the BUCK converter under the condition of transient change of the power expectation value: Figure 3 In the figure, the dotted line is the expected value of active power P of the BUCK converter. r The solid line is the simulation waveform of the active power P of the BUCK converter. Figure 3 It can be seen that at 0.2 seconds, the expected value of the converter active power P r When the power is changed from 150 watts to 250 watts, the active power value of the BUCK converter quickly reaches the new expected value. The system responds quickly, there is no steady-state error, the simulation waveform has no overshoot, and there is no need to adjust the control parameters, which reflects a good control effect.

[0063] The present invention can directly express the active power state of the buck converter system and accurately describe the working process. The designed switching controller directly selects the buck converter switching state control method by determining the error state between the system power and the expected value. It has the advantages of simple implementation, rapid response, no control parameters, no need for complex vector pulse width modulation (PWM) process, and good control effect. It is easy to apply to new energy power generation systems such as photovoltaic and wind energy that require system input power control or maximum power point tracking control.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A BUCK converter power switching control method, characterized in that: The following steps are involved: Step 1: Establish a power switching model for the BUCK converter; Step 2: Design the switching rules of the BUCK converter; In step 1, a power switching model of the BUCK converter is established as shown in formula (1): In formula (1), P is the active power value of the BUCK converter; Represents the derivative of active power P over time; U s The DC voltage input to the BUCK converter; U o is the output DC voltage of the BUCK converter; s is the switching function of the BUCK converter, s=1 indicates that the power switch device in the BUCK converter is turned on, and s=0 indicates that the power switch device in the BUCK converter is turned off; L is the inductance value; In step 2, the buck converter switching rule is designed to implement input power control for the buck converter using the switching rule defined by the following theorem: Theorem: For the BUCK converter power switching model of formula (1), if the switching rule of formula (2) is adopted, the active power P of the system will achieve its expected value P in a finite time. r The asymptotically stable tracking control of , that is, the system satisfies Lyapunov asymptotic stability, and the switching rule is defined as: or Proof: Define the active power P of the BUCK converter and the expected power value P of the BUCK converter r Lyapunov function composed of time errors As shown in the following formula: In formula (4), is the error between the active power and the desired power of the BUCK converter; taking the derivative of (4), we can get: From the theory of switched systems, namely the Lyapunov stability theorem, we know that for the Lyapunov function in formula (4) If we can ensure that (5) The BUCK converter switches stably under different switching states s and the power error is an asymptotically stable equilibrium point; a) When the actual system power P of the BUCK converter is greater than the expected value P r When PP r ≥0, from the above analysis we can see that we need to ensure that From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s ; Therefore, if and only if the BUCK converter switching state s=0 (5) The derivative of the Lyapunov function is semi-negative definite, which meets the Lyapunov stability requirements; b) When the actual system power P of the BUCK converter is less than or equal to the expected value P r When PP r ≤0, from the above analysis we can see that we need to ensure that From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s ; Therefore, if and only if the BUCK converter switching state s=1 The derivative of the Lyapunov function in formula (5) is negative definite, which meets the Lyapunov stability requirement.

2. A BUCK converter power switching control method according to claim 1, characterized in that: The theorem of step 2 is proved based on the Lyapunov function and its derivative expressions of formula (4) and formula (5) and the switching rules are designed according to the following two conditions: a) When the actual system power P of the BUCK converter is greater than the expected value P r When PP r ≥0, from the above analysis we can see that we need to ensure that From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s ; Therefore, if and only if the BUCK converter switching state s=0 (5) The derivative of the Lyapunov function is semi-negative definite, which meets the Lyapunov stability requirements; b) When the actual system power P of the BUCK converter is less than or equal to the expected value P r When PP r ≤0, from the above analysis we can see that we need to ensure that From the working principle of BUCK converter, we know that it is a step-down converter circuit, which outputs DC voltage U o Always less than the input DC voltage U s , that is U o ≤U s ; Therefore, if and only if the BUCK converter switching state s=1 The derivative of the Lyapunov function in formula (5) is negative definite, which meets the Lyapunov stability requirement.

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