Totem pole PFC circuit control method based on sliding mode control

Abstract

The invention relates to the technical field of power factor correction, and discloses a totem pole PFC circuit control method based on sliding mode control. The method comprises the following steps: firstly, modeling a totem-pole bridgeless PFC circuit system and establishing a state-space equation; then, designing a sliding mode surface, defining an error between a reference current and an actual current, designing u to control s, and then introducing a switching item by using a saturation function to compensate disturbance; and finally, carrying out Lyapunov stability analysis on the sliding mode, and proving that the system has global stability under the control of the sliding mode.

Description

Technical Field

[0001] The present invention relates to the technical field of power factor correction, and in particular to a totem pole PFC circuit control method based on sliding film control. Background Art

[0002] The totem pole power factor correction (PFC) circuit is a bridgeless PFC topology that has received widespread attention in single-phase AC input applications. Traditional PFC control methods mostly use average current mode control and peak current mode control. Average current mode control uses an inner and outer double-loop control structure to enable the current control loop to track the desired average current value. The advantages are low current harmonic content and high power factor. However, since it adjusts the average current, the response speed is slow and it is prone to lag when the load changes dynamically. In contrast, peak current mode control directly adjusts the peak value of the instantaneous current, has a faster response speed, and can better cope with rapidly changing load requirements. However, peak current mode control is easily affected by switching noise, the current waveform is relatively unstable, and the robustness to changes in system parameters is poor.

[0003] In addition, as the power supply system's requirements for efficiency and power density continue to increase, the limitations of traditional PFC control methods under high-frequency switching and high power density conditions are gradually becoming apparent. In this case, it is difficult to achieve ideal dynamic response and steady-state accuracy by relying solely on these two types of control, especially in terms of the accuracy, dynamics, and anti-interference capability of the current loop control. Therefore, studying a more efficient and robust control method has become an important direction for improving the performance of the totem pole PFC circuit. Summary of the invention

[0004] In view of the above problems, the present invention proposes a totem pole PFC circuit control method based on sliding mode control. By introducing a sliding mode control strategy in a traditional totem pole PFC circuit, accurate control of the input current is achieved to improve the dynamic response, steady-state accuracy and anti-disturbance performance of the system. Specifically, the present invention designs a sliding surface to describe the dynamic error state of the system, and adopts a switching control law based on the sliding surface. The sliding surface defines the error between the reference current and the actual current, so that the system can converge along the sliding surface to ensure that the inductor current closely tracks the reference current. The switching control law compensates for the disturbance by introducing a switching term according to the deviation between the system state and the sliding surface, thereby improving the robustness of the system and its adaptability to load changes. In order to reduce the common jitter phenomenon in traditional sliding mode control, the present invention further designs a smoothing method to optimize the stability of the control output. The sliding mode control method of the present invention is suitable for different load conditions and input voltage fluctuations, has excellent dynamic performance and steady-state accuracy, and can simplify the control structure and reduce the need for complex compensation circuits.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A totem pole PFC circuit control method based on sliding film control comprises the following steps:

[0007] Step 1: Model the totem pole bridgeless PFC circuit system and establish the state space equation. The process is as follows:

[0008] The current i flowing through the inductor L is the object of control, the goal is to make the inductor current i L The reference current i tracks the sinusoidal waveform of the input voltage ref ; According to the working principle of the circuit, the inductor current equation and the output voltage equation are obtained, and then the state space equation is established with the inductor current and output voltage as state variables.

[0009] Step 2: Define the sliding surface and adopt the sliding film control strategy. The process is as follows:

[0010] In order to achieve the inductor current i L For the target reference current i ref The goal of sliding mode control is to keep the system moving on the sliding surface, that is, to keep s = 0 by designing the control input u. When s = 0, it means that the inductor current i L Full Tracking ref , which is exactly the goal of the PFC circuit. By maintaining the motion on the sliding surface, we can effectively suppress the system error and achieve precise control of the target current.

[0011] Step 3: Stability analysis, the process is as follows:

[0012] The stability of sliding mode control is usually analyzed by Lyapunov stability condition, which is to ensure To make the system state tend to be stable along the sliding surface. Substituting the expression into the sliding mode condition, the stability condition can be met by properly selecting the values ​​of K and ε, thereby ensuring the robustness of the sliding mode control.

[0013] Furthermore, in step 1, the process of establishing the inductor current equation and the output voltage equation, and the state space equation with the inductor current and the output voltage as state variables is as follows:

[0014] 1.1) According to the inductor voltage relationship, the inductor current equation is obtained:

[0015]

[0016] Where u = 1-D, D is the duty cycle;

[0017] 1.2) The filter capacitor C and the load resistor R jointly determine the change of the output voltage. The output voltage equation is as follows:

[0018]

[0019] 1.3) The state space equation established with inductor current and output voltage as state variables is as follows:

[0020]

[0021] Furthermore, in step 2, the synovial control strategy is adopted as follows:

[0022] 2.1) Define the sliding surface s as the current tracking error, that is

[0023] s=e=i ref -i L ;

[0024] 2.2) The goal of sliding mode control is to make s = 0, which requires differentiating s so that To ensure that s is close to 0. Differentiating s gives:

[0025]

[0026] let The equivalent control u can be obtained eq：

[0027]

[0028] 2.3) In order to ensure that the system state quickly reaches and remains on the sliding surface, a switching control term is usually added. The control law can be written as:

[0029] u=u eq +u n ,

[0030] Where u n is a switching control term, and the sign function sgn(s) is often used. However, in order to reduce the common chattering phenomenon in traditional sliding film control, the present invention uses a saturation function instead of a sign function. This method smoothes the output and reduces chattering by limiting the switching frequency near the sliding surface. Therefore, the switching control term u n for:

[0031]

[0032] Where K is the control gain coefficient, which determines the strength of the sliding mode control. ε is the boundary layer thickness that controls the smoothness near the sliding surface. Increasing ε will reduce chattering, but may lead to an increase in tracking error. The saturation function is defined as:

[0033]

[0034] The final control input u can be expressed as the sum of the equivalent control term and the switching control term, that is:

[0035]

[0036] Furthermore, in step 3, the stability analysis process is as follows:

[0037] 3.1) Construct the Lyapunov function V(s), which is defined as half of the square of the sliding surface, that is:

[0038]

[0039] Derivative of V(s):

[0040]

[0041] 3.2) Substitute the final control input u into We can get:

[0042]

[0043] After finishing, we can get:

[0044]

[0045] 3.3) Substituting the derivative of the Lyapunov function V(s), we get:

[0046]

[0047] When |s|>ε, therefore have:

[0048]

[0049] When |s|<ε, So we have:

[0050]

[0051] Because the derivative of V(s) is less than 0 for s≠0, the system is asymptotically stable near the sliding film surface, that is, the sliding film control can make s tend to 0, so that i L Gradually tending towards ref .

[0052] The design idea of ​​the present invention is as follows: First, the totem pole bridgeless PFC circuit system is modeled and the state space equation is established. Then, a sliding surface is designed to define the error between the reference current and the actual current, and u is designed to control s. Then, a switching term is introduced using a saturation function to compensate for the disturbance. Finally, a Lyapunov stability analysis is performed on it, proving that the system has global stability under sliding film control.

[0053] The beneficial effects of the present invention are: 1) Sliding mode control can effectively deal with uncertainties and disturbances in the system and make current tracking stable; 2) Saturation function is used for smooth switching to reduce high-frequency jitter and extend the life of power devices; 3) The inductor current accurately tracks the reference current to achieve high power factor and low harmonic distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is the totem pole bridgeless PFC circuit topology diagram. In the figure, V in is the input AC voltage, L is the inductor, S1 to S4 are 4 switches, C is the capacitor, and R is the load resistance;

[0055] Figure 2 It is the design diagram of the synovial control algorithm;

[0056] Figure 3 Yes V out =360V, input voltage and input current waveform of average current mode control;

[0057] Figure 4 Yes V out =360V, output voltage waveform of average current mode control;

[0058] Figure 5 Yes V out =360V, the input voltage and input current waveform diagram of the present invention;

[0059] Figure 6 Yes V out =360V, the output voltage waveform of the present invention;

[0060] Figure 7 Yes V out =380V, average current mode control input voltage and input current waveform;

[0061] Figure 8 Yes V out =380V, output voltage waveform of average current mode control;

[0062] Fig. 9 Yes V out =380V, the input voltage and input current waveform diagram of the present invention;

[0063] Fig.10 Yes V out =380V, the output voltage waveform of the present invention;

[0064] Fig.11 Yes V out =400V, average current mode control input voltage and input current waveform;

[0065] Fig.12 Yes V out =400V, output voltage waveform of average current mode control;

[0066] Fig.13 Yes V out =400V, the input voltage and input current waveforms of the present invention;

[0067] Fig.14 Yes V out =400V, the output voltage waveform of the present invention. DETAILED DESCRIPTION

[0068] The present invention is further described below.

[0069] A totem pole PFC circuit control method based on sliding film control comprises the following steps:

[0070] Step 1: Model the totem pole bridgeless PFC circuit system and establish the state space equation. The process is as follows:

[0071] In this embodiment, refer to Figure 1 , the input AC voltage of the totem pole bridgeless PFC is V in =v in *sin(wt), output voltage is V out , the inductance is L, the inductor current is i L , the capacitance is C, the resistance is R, and the duty cycle is D.

[0072] 1.1) According to the inductor voltage relationship, the inductor current equation is obtained:

[0073]

[0074] Where u = 1-D, D is the duty cycle;

[0075] 1.2) The filter capacitor C and the load resistor R jointly determine the change of the output voltage. The output voltage equation is as follows:

[0076]

[0077] 1.3) The state space equation established with inductor current and output voltage as state variables is as follows:

[0078]

[0079] Step 2: Define the sliding surface and adopt the sliding film control strategy. The process is as follows:

[0080] 2.1) Define the sliding surface s as the current tracking error, that is

[0081] s=e=i ref -i L ;

[0082] 2.2) Differentiate s to obtain:

[0083]

[0084] let The equivalent control u can be obtained eq：

[0085]

[0086] 2.3) The control law can be written as:

[0087] u=u eq +u n ,

[0088] Where u n is a switching control term. The present invention uses a saturation function to replace the sign function, so the switching control term u n for:

[0089]

[0090] Where K is the control gain coefficient, which determines the strength of the sliding mode control. ε is the boundary layer thickness that controls the smoothness near the sliding surface. Increasing ε will reduce chattering, but may lead to an increase in tracking error. The saturation function is defined as:

[0091]

[0092] In this embodiment, refer to Figure 2 , the final control input u can be expressed as the sum of the equivalent control term and the switching control term, that is:

[0093]

[0094] Finally, u is used as the input signal of the switching tube PWM.

[0095] Step 3: Stability analysis, the process is as follows:

[0096] 3.1) Construct the Lyapunov function V(s), which is defined as half of the square of the sliding surface, that is:

[0097]

[0098] Derivative of V(s):

[0099]

[0100] 3.2) Substitute the final control input u into have to:

[0101]

[0102] Arranged:

[0103]

[0104] 3.3) Substituting the derivative of the Lyapunov function V(s), we get:

[0105]

[0106] When |s|>ε, therefore have:

[0107]

[0108] When |s|>ε, Therefore, we have:

[0109]

[0110] Because the derivative of V(s) is less than 0 for s≠0, the system is asymptotically stable near the sliding film surface, that is, the sliding film control can make s tend to 0, so that i L Gradually tending towards ref . Specific embodiment:

[0112] based on Figure 1 As shown in the circuit topology diagram, the parameters are set as follows: input voltage 220V, frequency 50Hz, boost inductor 390μH, capacitor 2486μF, load resistance 64Ω, switch tube switching frequency 80kHz. Figures 3 to 14 , the output voltages were set to 360V, 380V and 400V respectively, the waveforms of input voltage and input current were measured, and the performance was compared and analyzed with that of the traditional average current control strategy.

[0113] 1) Input voltage and current waveform analysis:

[0114] The input voltage and input current waveforms under different output voltage conditions were recorded in the experiment. The results show that:

[0115] Under the sliding mode control method of the present invention, the input current waveform is closer to a sine wave, the harmonic content is significantly reduced, and the power factor is higher. Compared with the traditional average current control method, the response speed of the sliding mode control under dynamic conditions is significantly improved, and the input current can track the changes in the input voltage more quickly, reducing dynamic errors.

[0116] 2) Output voltage stability analysis:

[0117] Under the output conditions of 360V, 380V and 400V, the sliding mode control method of the present invention can keep the output voltage stable with a fluctuation range of about 1%. In contrast, the traditional average current control method has a large fluctuation in output voltage and a long recovery time when the load changes suddenly, while the sliding mode control method can respond quickly and recover to the set value.

[0118] 3) Experimental conclusion

[0119] Experimental results show that the sliding mode control totem pole PFC circuit proposed in the present invention has the following advantages: better input current waveform, lower harmonic content, and higher power factor; faster dynamic response speed, and stronger ability to adapt to load mutations and input voltage fluctuations; and significantly improved steady-state accuracy and dynamic stability of the output voltage.

[0120] The contents described in the embodiments of this specification are merely enumerations of implementation forms of the inventive concept and are for illustrative purposes only. The protection scope of the present invention should not be considered to be limited to the specific forms described in this embodiment, and the protection scope of the present invention also extends to equivalent technical means that can be thought of by ordinary technicians in this field based on the inventive concept.

Claims

1. A totem pole PFC circuit control method based on sliding film control, characterized in that: The following steps are involved: Step 1: Model the totem pole bridgeless PFC circuit system and establish the state space equation. The process is as follows: The current i flowing through the inductor L As the object of control, the goal is to make the inductor current i L The reference current i tracks the sinusoidal waveform of the input voltage ref ; According to the working principle of the circuit, the inductor current equation and the output voltage equation are obtained, and then the state space equation is established with the inductor current and the output voltage as state variables; Step 2: Define the sliding surface and adopt the sliding film control strategy. The process is as follows: Define a sliding surface s. The goal of sliding mode control is to make the system move on the sliding surface, that is, to keep s = 0 by designing the control input u; to achieve the inductor current i L Full Tracking ref Targets; Step 3: Stability analysis, the process is as follows: Through Lyapunov stability conditions, we can ensure To make the system state tend to be stable along the sliding surface; The expression is substituted into the sliding mode condition, and the stability condition is met by selecting the values ​​of the control gain coefficient K and the smoothness ε to ensure the robustness of the sliding mode control.

2. The totem pole PFC circuit control method based on sliding film control according to claim 1, characterized in that: In step 1, the process of establishing the inductor current equation and the output voltage equation, and the state space equation with the inductor current and the output voltage as state variables is as follows: 1.1) According to the inductor voltage relationship, the inductor current equation is obtained: Where u = 1-D, D is the duty cycle; V in is the input voltage, V out is the output voltage, L is the inductance; 1.2) The filter capacitor C and the load resistor R jointly determine the change of the output voltage. The output voltage equation is as follows: 1.3) The state space equation established with inductor current and output voltage as state variables is as follows:

3. The totem pole PFC circuit control method based on sliding film control according to claim 1, characterized in that: In step 2, the synovial control strategy is adopted as follows: 2.1) Define the sliding surface s as the current tracking error, that is s=e=i ref -i L ; 2.2) The goal of sliding mode control is to make s = 0 and differentiate s so that To ensure that s is close to 0; Differentiating s gives: let Find the equivalent control u eq： 2.3) To ensure that the system state quickly reaches and remains on the sliding surface, a switching control term is added; the control law is written as: in=in eq +in n , Where u n is a switching control term. The saturation function is used instead of the sign function. Then the switching control term u n for: Where K is the control gain coefficient, ε is the smoothness near the sliding surface controlled by the boundary layer thickness; The saturation function is defined as: The final control input u is expressed as the sum of the equivalent control term and the switching control term, that is:

4. The totem pole PFC circuit control method based on sliding film control according to claim 1, characterized in that: In step 3, the stability analysis process is as follows: 3.1) Construct the Lyapunov function V(s), which is defined as half of the square of the sliding surface, that is: Derivative of V(s): 3.2) Substitute the final control input u into have to: Arranged: 3.3) Substituting the derivative of the Lyapunov function V(s), we get: When |s|>ε, therefore have: When |s|<ε, So we have: Because the derivative of V(s) is less than 0 for s≠0, the system is asymptotically stable near the sliding film surface, that is, the sliding film control can make s tend to 0, so that i L Gradually tending towards ref .

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