Phase-locked loop-free Boost PFC converter fixed time switching control method and system

Abstract

The invention discloses a fixed time switching control method and system for a Boost PFC converter without a phase-locked loop, and belongs to the technical field of power electronic control. The invention provides a composite control architecture based on a switching linear system in order to solve the problems that in traditional PFC control, dynamic response of a phase-locked loop is slow, convergence time of an observer is greatly influenced by an initial value, and load sudden change robustness is poor. The method comprises the following steps: firstly, establishing a Boost PFC switching linear model containing a parallel load disturbance component; estimating load step disturbance in real time by using an extended state observer; a non-linear fixed time observer is introduced to quickly decouple the amplitude and phase of the input voltage within a preset time irrelevant to an initial value, and a traditional phase-locked loop is replaced; and finally, designing a switching control law based on Lyapunov stability. Through collaborative design of the observer and the controller, rapid locking of power grid voltage fluctuation and zero static error compensation of load abrupt change are realized, and the dynamic quality and the power factor of the converter are remarkably improved.

Description

Technical Field

[0001] This invention relates to high-performance control technology for power electronic converters, specifically to a fixed-time switching control method for Boost power factor correction (PFC) converters, which features fast disturbance rejection and no phase-locked loop characteristics. Background Technology

[0002] With the increasing complexity of power grid environments, Boost PFC converters, as front-end rectifier devices, face more stringent control requirements. Existing control technologies mainly suffer from the following three core bottlenecks: 1. Reliance on Phase-Locked Loop (PLL): Traditional control requires obtaining the grid phase through a PLL. However, a PLL is essentially a closed-loop feedback system with inherent dynamic lag, and it is prone to introducing current distortion due to phase detection errors when the grid voltage is distorted or unbalanced.

[0003] 2. Uncertainty in observer convergence speed: Existing state observers are mostly based on asymptotic convergence (such as the Luenberger observer) or finite-time convergence. Although finite-time observers can theoretically converge in a finite time, their convergence time is heavily dependent on the magnitude of the initial error. During system startup or when encountering large power grid fluctuations, the convergence time may be too long, leading to control failure.

[0004] 3. Slow recovery from load surges: Traditional dual-loop control relies mainly on the PI regulation of the voltage loop to respond to load surges, which often results in a large drop or overshoot in the output voltage at the moment of load change.

[0005] Therefore, developing a control method whose convergence time is independent of the initial value, requires no PLL, and can actively compensate for load disturbances is the key to breaking through the performance bottleneck of existing PFC. Summary of the Invention

[0006] The purpose of this invention is to provide a Boost PFC converter switching control method and system based on a fixed-time observer, which solves the problems of slow observer convergence speed and weak anti-disturbance capability in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The proposed fixed-time switching control method for a phase-locked loop-free Boost PFC converter includes the following steps: Step S1: Construct a switching linear system model of the Boost PFC converter; define state variables and establish an extended state-space equation that includes load disturbance components for load changes; Step S2: Design a load switching disturbance observer, use the Lyapunov function to ensure the convergence of the observation error, and observe the step disturbance of the load current in real time. Step S3: Design a fixed-time observer for the input voltage amplitude and phase; based on the sinusoidal characteristics of the input voltage, construct the observer using the sign function and nonlinear gain term to ensure that the estimation error of the voltage amplitude and phase converges to zero within a fixed time. Step S4: Design the switching controller; set the current reference value according to the desired power factor correction target, and combine the observations from steps S2 and S3 to construct a switching law based on Lyapunov stability to control the on and off of the Boost PFC converter switching transistors.

[0008] In step S1, the switching linear system model satisfies: inductor current i L Output voltage V o and the rectifier side input voltage V in Define the state vector The derivative of the state vector when the switch is turned on is , The derivative of the state vector when the switch is turned off is

[0009] Where A1 and A2 are composed of L, C, and R L The system matrix is ​​determined by the load equivalent parameters, and the system output matrix is... System disturbance observation matrix , It is a system load disturbance observation.

[0010] In step S2, the method for constructing the load switching disturbance observer is as follows: Assume the load disturbance changes in a step manner, i.e., the disturbance derivative is zero. State variables Measurable, therefore the load switching disturbance observer is as follows:

[0011] In the formula: To switch the gain of the disturbance observer for the load, in the disturbance term The following is an example:

[0012] In step S3, the method for constructing the fixed-time voltage amplitude and phase observer is as follows: The input voltage is a sinusoidal signal with a frequency of Given that the input voltage frequency is the same as the power grid frequency, in order to ensure the control effect, it is necessary to observe the amplitude and phase of the input voltage, and the model is as follows:

[0013] In the formula: It is the symbol for the input voltage signal function. yes The derivative of It is the amplitude of the input voltage.

[0014] The designed fixed-time observer is shown below:

[0015] In the formula: Gain The symbolic function is defined as follows: .

[0016] The following observations can be obtained:

[0017] In the formula:

[0018] In step S4, the design method for the switching controller includes the following steps: Based on the requirements of the PFC converter, the inductor current reference value With input voltage V in In phase:

[0019] Define the reference point based on the model construction as follows:

[0020] Error variables For system state and inductor current reference trajectory Difference:

[0021] Choose a Lyapunov function V that includes the error variable:

[0022] In the formula: P is a positive definite matrix, Q is the system matrix of the Boost PFC converter.

[0023] Finally, design the switching law:

[0024] in: Then the system state x converges to the reference trajectory. .

[0025] The Boost PFC converter control system of the method is characterized by comprising: a signal acquisition module for acquiring inductor current. i L Output voltage V o and input voltage signal V in The observer module, which incorporates the load switching disturbance observer and fixed-time input voltage observer algorithms, is used to output disturbance estimates and voltage parameters; the controller module receives the acquired signals and observations, executes the switching control law, and outputs PWM drive signals; and the drive circuit is used to drive the power switching transistors in the Boost circuit.

[0026] Compared with the prior art, the present invention has the following outstanding substantive features and significant progress: First, the voltage observer designed using fixed-time stability theory possesses a deterministic convergence speed. Regardless of the initial error, it can converge to the true value within a preset global time bound independent of the initial value, providing a strict time window guarantee for the reliable operation of the system. Second, by directly decoupling the voltage amplitude and phase through this observer, a phase-locked loop-free architecture is constructed, completely eliminating the traditional PLL module. This fundamentally eliminates the phase lag and harmonic sensitivity problems caused by PLLs, simplifying the control system software structure, saving computational resources, and significantly improving the input current quality (THD) of the PFC. Secondly, it achieves active disturbance rejection control by establishing a dynamic equation for load disturbance in the switching linear model and directly incorporating the observed disturbance value into the switching control law, forming an "active defense" mechanism. When the load changes abruptly, the duty cycle can be quickly adjusted without waiting for the output voltage to drop, significantly reducing the voltage fluctuation amplitude. Finally, unlike PWM control based on the average model, this invention directly controls the switching system based on the hybrid logic dynamic characteristics of the converter, which is more in line with the discrete switching nature of power electronic devices, avoids the loss of model accuracy in the averaging process, and ensures high control accuracy and strong robustness.

[0027] The beneficial effects of this invention are as follows: By observing the amplitude and phase of the input voltage at fixed times, this invention achieves rapid and deterministic acquisition of grid synchronization information, thereby avoiding the trade-offs between steady-state accuracy and dynamic response, and the resulting phase delay, inherent in traditional PLL phase-locked loops. Simultaneously, by equating load mutations to parallel disturbances and performing rapid observation, it can significantly suppress input current distortion and output voltage drops caused by load step jumps, improving the dynamic quality of the system under strong disturbance conditions. At the control level, this invention directly designs control laws based on a switching system framework, providing stability guarantees without the need for averaging duty cycle modeling, enhancing the rigor of control design and its fit to switching behavior. This control and observation structure can be implemented on common DSPs / MCUs, with the overall computational load mainly derived from observer recursive updates and two-mode criterion calculations, facilitating engineering deployment and widespread application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following is a brief introduction to the drawings used in the prior art and embodiments. The following drawings are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a block diagram of the overall control system for the Boost PFC converter proposed in this invention; Figure 2 This is a flowchart of the switching linear system control decision-making process for the Boost PFC converter proposed in this invention. Figure 3 The voltage and corrected current waveforms are the results of the system simulation experiment of this invention. Figure 4 The voltage and corrected current waveforms are from the system response simulation experiment under a step load change of this invention. Figure 5 This is a voltage-corrected current waveform from a simulation experiment of the system response under varying input voltage according to the present invention. Detailed Implementation To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0031] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. Furthermore, in the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if there is transmission of electrical signals or data between the connected objects.

[0032] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0033] In one embodiment provided by the present invention, such as Figure 1 and Figure 2 As shown, a switching control method and system construction approach for a Boost PFC converter based on a fixed-time observer are presented. The following describes an implementable flow using a single-phase Boost PFC as an example. The converter consists of a rectifier bridge, a Boost inductor L, a power switch Q, a diode D, an output capacitor C, and a load R. The controller samples i... L V o V in The sampling frequency can be set from 20 kHz to 100 kHz.

[0034] The proposed fixed-time switching control method for a phase-locked loop-free Boost PFC converter includes the following steps: Step S1: Construct a switching linear system model of the Boost PFC converter; define state variables and establish an extended state-space equation that includes load disturbance components for load changes; Step S2: Design a load switching disturbance observer, use the Lyapunov function to ensure the convergence of the observation error, and observe the step disturbance of the load current in real time. Step S3: Design a fixed-time observer for the input voltage amplitude and phase; based on the sinusoidal characteristics of the input voltage, construct the observer using the sign function and nonlinear gain term to ensure that the estimation error of the voltage amplitude and phase converges to zero within a fixed time. Step S4: Design the switching controller; set the current reference value according to the desired power factor correction target, and combine the observations from steps S2 and S3 to construct a switching law based on Lyapunov stability to control the on and off of the Boost PFC converter switching transistors.

[0035] In step S1, the switching linear system model satisfies: inductor current i L Output voltage V o and the rectifier side input voltage V in Define the state vector The derivative of the state vector when the switch is turned on is , The derivative of the state vector when the switch is turned off is

[0036] Where A1 and A2 are composed of L, C, and R L The system matrix is ​​determined by the load equivalent parameters, and the system output matrix is... System disturbance observation matrix , It is a system load disturbance observation.

[0037] In step S2, the method for constructing the load switching disturbance observer is as follows: Assume the load disturbance changes in a step manner, i.e., the disturbance derivative is zero. State variables Measurable, therefore the load switching disturbance observer is as follows:

[0038] In the formula: To switch the gain of the disturbance observer for the load, in the disturbance term The following is an example:

[0039] Stability proof: Let observation error ,So Choose the Lyapunov function ,So

[0040] In the formula It is a positive definite matrix. In order to ensure the stability of the observer ,So:

[0041] because It is known that ,in .

[0042] In step S3, the method for constructing the fixed-time voltage amplitude and phase observer is as follows: The input voltage is a sinusoidal signal with a frequency of Given that the input voltage frequency is the same as the power grid frequency, in order to ensure the control effect, it is necessary to observe the amplitude and phase of the input voltage, and the model is as follows:

[0043] In the formula: It is the symbol for the input voltage signal function. yes The derivative of It is the amplitude of the input voltage.

[0044] The designed fixed-time observer is shown below:

[0045] In the formula: Gain The symbolic function is defined as follows: .

[0046] The following observations can be obtained:

[0047] In the formula:

[0048] To prove the stability of the observer: First, let the observation error be: , The error equation can be obtained as follows:

[0049] Then take the combination error: In the formula: We can obtain:

[0050] The Lyapunov function is constructed as follows:

[0051] In the formula: Differentiating the above equation yields:

[0052] Record deviation , According to the generalized Young's inequality, Lemma 1: For any , so that:

[0053] And there are , .

[0054] Lemma 2: For any , ,have

[0055] Lemma 3: Let It is a non-negative, continuously differentiable function that satisfies the differential inequality.

[0056] in:

[0057] Then the system equilibrium point It is stable within a fixed time, and the convergence time has a global upper bound.

[0058] And this upper bound is the same as the initial value. Irrelevant.

[0059] By the lemma we can obtain , ,So It can be simplified to:

[0060] In the formula: ,set up According to Lemma 3, we can obtain: Therefore, the observer designed in this invention can stabilize at a fixed time. In step S4, the design method for the switching controller includes the following steps: Based on the requirements of the PFC converter, the inductor current reference value With input voltage V in In phase:

[0061] Define the reference point based on the model construction as follows:

[0062] Error variables For system state and inductor current reference trajectory Difference:

[0063] Choose a Lyapunov function V that includes the error variable:

[0064] In the formula: P is a positive definite matrix, Q is the system matrix of the Boost PFC converter.

[0065] Finally, design the switching law:

[0066] in: Then the system state x converges to the reference trajectory. .

[0067] The stability of the controller is proven as follows: Define the error variable. ,in: It is the inductor current error. It's the output voltage error. Therefore:

[0068] Choosing Lyapunov functions We can obtain:

[0069]

[0070] in: ,

[0071] So, system state Converging to the reference trajectory Q.E.D.

[0072] The control method and system proposed in this invention were simulated and verified in Matlab. The output voltage was set to 400V, the input voltage to 220V AC at 50Hz, the sampling frequency to 50kHz, and the load to 1kW. The following experimental results were obtained: Figure 3 , Figure 4 , Figure 5 As shown, during normal operation, the output voltage of this invention can reach the set value, and the corrected current THD value is 0.2%, and the PF value is 0.99. Figure 3 As shown; when the load changes abruptly, switching from full load to half load in 0.25s, the corrected current THD value is 4%, and the PF value is 0.99. Figure 4 As shown, when a voltage surge occurs, the input voltage is adjusted to 1.2 times the current value within 0.25 seconds. The output voltage and the corrected input current remain distorted, and the corrected current THD value is still 0.2%, with a power factor (PF) value of 0.99. This surpasses industry standards and verifies the switching control method and system proposed in this invention.

[0073] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A fixed-time switching control method for a Boost PFC converter without a phase-locked loop, characterized in that, Includes the following steps: Step S1: Construct a switching linear system model of the Boost PFC converter; define state variables and establish an extended state-space equation that includes load disturbance components for load changes; Step S2: Design a load switching disturbance observer, use the Lyapunov function to ensure the convergence of the observation error, and observe the step disturbance of the load current in real time. Step S3: Design a fixed-time observer for the input voltage amplitude and phase; Based on the sinusoidal characteristics of the input voltage, an observer is constructed using a sign function and a nonlinear gain term to ensure that the estimation errors of voltage amplitude and phase converge to zero within a fixed time. Step S4: Design a nonlinear switching controller; set the current reference value according to the desired power factor correction target, and combine the observations from steps S2 and S3 to construct a switching law based on Lyapunov stability to control the on and off of the Boost PFC converter switching transistors.

2. The method according to claim 1, characterized in that, In step S1, the state variable x of the switched linear system model is defined as The inductor current i L Output voltage V o and the rectifier side input voltage V in The derivative of the state vector when the switch is turned on is... ， The derivative of the state vector when the switch is turned off is in, A 1. A 2 is the reason L , C , R L The system matrix is ​​determined by the load equivalent parameters, and the system output matrix is... System disturbance observation matrix , It is a system load disturbance observation.

3. The method according to claim 1, characterized in that, In step S2, the method for constructing the load switching disturbance observer is as follows: S1. Assume that the load disturbance changes in a step manner, that is, the disturbance derivative is zero; S2. Construct the observer state equation and use the error feedback between the system measurement and the observation to correct the disturbance estimate; S3. The stability of the observer is proved by selecting a quadratic Lyapunov function, and the observer gain matrix is ​​determined by solving the linear matrix inequality.

4. The method according to claim 1, characterized in that, In step S4, the design method for the switching controller includes the following steps: S1. Define the inductor current reference value. With input voltage V in In phase; S2. Define error variables For system state and inductor current reference trajectory difference; S3. Select the Lyapunov function V that includes the error variable; S4, Design Switching Law The derivative of the Lyapunov function is such that This ensures that the system state is tracked by the reference trajectory.

5. A fixed-time switching control system for a Boost PFC converter without a phase-locked loop, characterized in that, include: The signal acquisition module is used to acquire inductor current. i L Output voltage V o and input voltage signal V in The observer module, which integrates the load switching disturbance observer and the fixed-time input voltage observer, as well as the switching control algorithm, is used to output disturbance estimates and voltage parameters; the controller module receives the acquired signals and observed values, executes the switching control law, and outputs PWM drive signals. The driving circuit is used to drive the power switching transistors in the Boost circuit.

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