A predictive control method for flyback converter based on continuous set model

Abstract

The application discloses a kind of prediction control method of flyback converter based on continuum model, characteristic is first to establish the state equation of flyback converter and deduce average value model, utilize the prediction model of output voltage and inductance current that forward Euler method is dispersed, then construct first cost function, make it minimum to obtain optimal control quantity;After predicting the inductance current of next time, and with the inductance current overcurrent threshold value set to compare whether overcurrent, when predicted value is less than inductance current overcurrent threshold value, directly optimal control quantity is transferred to PWM modulation module, when predicted current value is greater than inductance current overcurrent threshold value, construct second cost function and recalculate optimal control quantity, and PWM modulation module generates MOSFET drive signal according to optimal control quantity;Advantage is that control process has good steady state and dynamic performance, prevent transformer primary winding overcurrent.

Description

Technical Field

[0001] This invention relates to the field of control technology for DC-DC converters, and in particular to a predictive control method for a flyback converter based on a continuous set model. Background Technology

[0002] As the power supply equipment for all electronic products, the power supply must not only meet the performance requirements of the power supply products, but also have its own protection measures, such as overvoltage, overcurrent, and overheat protection. Once an electronic product malfunctions, it may cause further damage to the electronic product, or even cause electric shock and fire to the operator. Therefore, the overcurrent protection function of the switching power supply must be perfect.

[0003] Flyback converters, as a common power supply topology, have a simple circuit structure and advantages such as electrical isolation and easy switching transistor driving. They are widely used as power supplies for small and medium power electrical equipment and are generally controlled through a closed-loop controller. However, flyback converters exhibit nonlinearity due to the periodic switching modes of the switching transistors, and load uncertainties and line oscillations can seriously affect the stability of the closed-loop controller. When the converter is at different static operating points, a general linear model is insufficient to solve the problem of output voltage stability. Moreover, existing flyback converter control strategies do not consider the overcurrent situation in the transformer primary winding, which may lead to transformer oversaturation. This not only causes significant distortion of the output power but also causes the transformer's operating temperature to rise sharply, leading to overheating, damage, and ultimately, destruction of related equipment. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a predictive control method for a flyback converter based on a continuous set model with good steady-state and dynamic performance, while preventing overcurrent in the primary winding of the transformer.

[0005] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a predictive control method for a flyback converter based on a continuous set model, comprising the following steps:

[0006] Step 1): Establish the state equation of the flyback converter and derive the average value model of the flyback converter. Based on the average value model, use the forward Euler method to obtain the output voltage prediction model and the inductor current prediction model.

[0007] Step 2): Based on the preset control target for controlling the output voltage of the flyback converter to track the output voltage reference value, establish the first cost function corresponding to the condition that the output current is not overcurrent.

[0008] Step 3): Obtain the transformer DC side voltage, transformer magnetizing inductor current, flyback converter output voltage and flyback converter output current at the current prediction time. Obtain the first optimal duty cycle control quantity that minimizes the corresponding first cost function at the current prediction time. Substitute the first optimal duty cycle control quantity into the inductor current prediction model to obtain the inductor current prediction value at the next time step.

[0009] Step 4): Set the inductor current overcurrent threshold. Compare the predicted inductor current value with the inductor current overcurrent threshold. When the predicted inductor current value is less than the inductor current overcurrent threshold, use the first optimal duty cycle control value as the duty cycle control value of the PWM modulation module of the flyback converter at the next moment of the current prediction time. The PWM modulation module generates a corresponding drive signal to control the MOS transistor in the flyback converter according to the duty cycle control value of the next moment of the current prediction time, thereby realizing the predictive control of the flyback converter. When the predicted inductor current value is greater than the inductor current overcurrent threshold, proceed to step 5).

[0010] Step 5): Based on the control objective of overcurrent protection, establish a second cost function. Substitute the transformer DC side voltage, transformer magnetizing inductor current, flyback converter output voltage and flyback converter output current at the current prediction time into the second cost function, and obtain the second optimal duty cycle control quantity that minimizes the second cost function.

[0011] Step 6): The second optimal duty cycle control quantity is used as the duty cycle control quantity of the next time step of the current prediction time of the flyback converter's PWM modulation module. The PWM modulation module generates a corresponding drive signal based on the duty cycle control quantity of the next time step of the current prediction time to control the MOS transistor in the flyback converter to work, thereby realizing predictive control of the flyback converter.

[0012] In step 1), the state equation of the flyback converter when the MOS transistor is turned on is as follows:

[0013]

[0014] The state equation of the flyback converter when the MOSFET is turned off is as follows:

[0015]

[0016] Where L represents the transformer magnetizing inductance, Indicate i L The derivative of V with respect to time t dc R represents the DC side voltage of the transformer. L Indicates the internal resistance of the transformer, i LC represents the magnetizing inductance current of the transformer, and C represents the output capacitance of the flyback converter. V represents c The derivative of the transformer with respect to t, where n represents the transformer turns ratio, V c i represents the output voltage of the flyback converter. o This indicates the output current of the flyback converter;

[0017] After reorganization, the average value model of the flyback converter can be obtained as follows:

[0018] Where D represents the duty cycle, the average value model of the flyback converter is discretized using the forward Euler method, resulting in the output voltage prediction model as follows:

[0019] The inductor current prediction model is as follows: Among them, T s V represents the sampling period, k is any moment during the operation of the flyback converter, and V dc (k) represents the DC-side voltage of the transformer at time k, V c (k) represents the output voltage of the flyback converter at time k, i L (k) represents the inductor current of the flyback converter at time k, i o (k) represents the output current of the flyback converter at time k, V c (k+1) represents the predicted output voltage value at time k+1, i L (k+1) represents the predicted value of the inductor current at time k+1.

[0020] The first cost function g1 is:

[0021]

[0022] Among them, V cref (k+1) represents the preset output voltage reference value at time (k+1). By taking the partial derivative of D and setting the result to 0, the first cost function is minimized. The D obtained at this time is taken as the first optimal duty cycle control quantity D1.

[0023] The second cost function g2 is:

[0024] Among them, i Lref This represents the preset inductor current overcurrent threshold. By taking the partial derivative of D and setting the result to 0, the second cost function is minimized. The D obtained at this point is taken as the second optimal duty cycle control quantity D2.

[0025] Compared with existing technologies, the advantages of this invention are as follows: First, the state equation of the flyback converter is established and the average value model is derived. The output voltage and inductor current prediction models are obtained by discretizing using the forward Euler method. Then, a first cost function is constructed to control the output voltage to track the reference value, and its minimization yields the optimal control quantity. Next, based on the inductor current prediction model and the optimal control quantity, the inductor current at the next moment is predicted and compared with the set inductor current overcurrent threshold to determine whether overcurrent occurs. When the predicted value is less than the inductor current overcurrent threshold, the optimal control quantity is directly transmitted to the PWM modulation module. When the predicted current value is greater than the inductor current overcurrent threshold, a second cost function is constructed with the goal of preventing oversaturation to recalculate the optimal control quantity. Finally, the PWM modulation module generates a MOSFET drive signal based on the optimal control quantity. Through the above predictive control method, continuous set model predictive control of the flyback converter is realized. By tracking the output voltage without steady-state error, the goal of controlling the output voltage is achieved, exhibiting good steady-state and dynamic performance, while preventing overcurrent in the transformer primary winding and avoiding transformer oversaturation. Attached Figure Description

[0026] Figure 1 This is a topology diagram of the flyback converter in this invention;

[0027] Figure 2 This is a diagram of the overall control structure of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] A predictive control method for a flyback converter based on a continuous set model includes the following steps:

[0030] Step 1): Establish the state equation of the flyback converter and derive the average value model of the flyback converter. Based on the average value model, use the forward Euler method to obtain the output voltage prediction model and the inductor current prediction model.

[0031] Step 2): Based on the preset control target for controlling the output voltage of the flyback converter to track the output voltage reference value, establish the first cost function corresponding to the condition that the output current is not overcurrent.

[0032] Step 3): Obtain the transformer DC side voltage, transformer magnetizing inductor current, flyback converter output voltage and flyback converter output current at the current prediction time. Obtain the first optimal duty cycle control quantity that minimizes the corresponding first cost function at the current prediction time. Substitute the first optimal duty cycle control quantity into the inductor current prediction model to obtain the inductor current prediction value at the next time step.

[0033] Step 4): Set the inductor current overcurrent threshold. Compare the predicted inductor current value with the inductor current overcurrent threshold. When the predicted inductor current value is less than the inductor current overcurrent threshold, use the first optimal duty cycle control value as the duty cycle control value of the PWM modulation module of the flyback converter at the next moment of the current prediction time. The PWM modulation module generates a corresponding drive signal to control the MOS transistor in the flyback converter according to the duty cycle control value of the next moment of the current prediction time, thereby realizing the predictive control of the flyback converter. When the predicted inductor current value is greater than the inductor current overcurrent threshold, proceed to step 5).

[0034] Step 5): Based on the control objective of overcurrent protection, establish a second cost function. Substitute the transformer DC side voltage, transformer magnetizing inductor current, flyback converter output voltage and flyback converter output current at the current prediction time into the second cost function, and obtain the second optimal duty cycle control quantity that minimizes the second cost function.

[0035] Step 6): The second optimal duty cycle control quantity is used as the duty cycle control quantity of the next time step of the current prediction time of the flyback converter's PWM modulation module. The PWM modulation module generates a corresponding drive signal based on the duty cycle control quantity of the next time step of the current prediction time to control the MOS transistor in the flyback converter to work, thereby realizing predictive control of the flyback converter.

[0036] In step 1), the state equation of the flyback converter when the MOSFET is turned on is as follows:

[0037]

[0038] The state equation of the flyback converter when the MOSFET is turned off is as follows:

[0039]

[0040] Where L represents the transformer magnetizing inductance, Indicate i L The derivative of V with respect to time t dc R represents the DC side voltage of the transformer. L Indicates the internal resistance of the transformer, i L C represents the magnetizing inductance current of the transformer, and C represents the output capacitance of the flyback converter. V represents c The derivative of the transformer with respect to t, where n represents the transformer turns ratio, V c i represents the output voltage of the flyback converter. o This indicates the output current of the flyback converter;

[0041] After reorganization, the average value model of the flyback converter can be obtained as follows:

[0042] Where D represents the duty cycle, the average value model of the flyback converter is discretized using the forward Euler method, resulting in the output voltage prediction model as follows:

[0043] The inductor current prediction model is as follows: Among them, T s V represents the sampling period, k is any moment during the operation of the flyback converter, and V dc (k) represents the DC-side voltage of the transformer at time k, V c (k) represents the output voltage of the flyback converter at time k, i L (k) represents the inductor current of the flyback converter at time k, i o (k) represents the output current of the flyback converter at time k, V c (k+1) represents the predicted output voltage value at time k+1, i L (k+1) represents the predicted value of the inductor current at time k+1.

[0044] The first cost function g1 is:

[0045]

[0046] Among them, V cref (k+1) represents the preset output voltage reference value at time (k+1). By taking the partial derivative of D and setting the result to 0, the first cost function is minimized. The D obtained at this time is taken as the first optimal duty cycle control quantity D1.

[0047] The second cost function g2 is: Among them, i Lref This represents the preset inductor current overcurrent threshold. By taking the partial derivative of D and setting the result to 0, the second cost function is minimized. The D obtained at this point is taken as the second optimal duty cycle control quantity D2.

[0048] like Figure 1 As shown, the flyback converter in the above predictive control method is a conventional circuit, and its topology includes: DC power supply 1, input capacitor 2, transformer 3, NMOS transistor 4, diode 5, output capacitor 6, and load 7.

Claims

1. A predictive control method for a flyback converter based on a continuous set model, characterized in that... Includes the following steps: Step 1): Establish the state equation of the flyback converter and derive the average value model of the flyback converter. Based on the average value model, use the forward Euler method to obtain the output voltage prediction model and the inductor current prediction model. Step 2): Based on the preset control target for controlling the output voltage of the flyback converter to track the output voltage reference value, establish the first cost function corresponding to the condition that the output current is not overcurrent. Step 3): Obtain the transformer DC side voltage, transformer magnetizing inductor current, flyback converter output voltage and flyback converter output current at the current prediction time; obtain the first optimal duty cycle control quantity that minimizes the corresponding first cost function at the current prediction time; substitute the first optimal duty cycle control quantity into the inductor current prediction model to obtain the inductor current prediction value at the next time step at the current prediction time. Step 4): Set the inductor current overcurrent threshold. Compare the predicted inductor current value with the inductor current overcurrent threshold. When the predicted inductor current value is less than the inductor current overcurrent threshold, use the first optimal duty cycle control value as the duty cycle control value of the PWM modulation module of the flyback converter at the next predicted moment. The PWM modulation module generates a corresponding drive signal based on the duty cycle control value of the next predicted moment to control the MOSFET in the flyback converter, thereby realizing predictive control of the flyback converter. When the predicted inductor current value is greater than the inductor current overcurrent threshold, proceed to step 5). Step 5): Based on the control objective of overcurrent protection, establish a second cost function. Substitute the transformer DC side voltage, transformer magnetizing inductor current and flyback converter output voltage at the current prediction time into the second cost function, and obtain the second optimal duty cycle control quantity that minimizes the second cost function. Step 6): The second optimal duty cycle control quantity is used as the duty cycle control quantity of the next time step of the current prediction time of the flyback converter's PWM modulation module. The PWM modulation module generates a corresponding drive signal based on the duty cycle control quantity of the next time step of the current prediction time to control the MOS transistor in the flyback converter to work, thereby realizing predictive control of the flyback converter.

2. The predictive control method for a flyback converter based on a continuous set model according to claim 1, characterized in that... In step 1), the state equation of the flyback converter when the MOS transistor is turned on is as follows: ， The state equation of the flyback converter when the MOSFET is turned off is as follows: ， in, Indicates the magnetizing inductance of the transformer. express The derivative with respect to time t, Indicates the DC side voltage of the transformer. Indicates the internal resistance of the transformer. This represents the transformer magnetizing inductance current. This represents the output capacitance of the flyback converter. express The derivative with respect to t, Indicates the transformer turns ratio. This indicates the output voltage of the flyback converter. This indicates the output current of the flyback converter; After reorganization, the average value model of the flyback converter can be obtained as follows: ,in, Representing the duty cycle, the average value model of the flyback converter is discretized using the forward Euler method, resulting in the output voltage prediction model: , The inductor current prediction model is as follows: ,in, Indicates the sampling period. k For any given moment during the operation of the flyback converter, Indicates the first k The DC side voltage of the transformer at any given time Indicates the first k The output voltage of the flyback converter at a given time. Indicates the first k The transformer magnetizing inductance current at any given moment, Indicates the first k The output current of the flyback converter at any given time. Indicates the first k Predicted output voltage at time +1 Indicates the first k Predicted value of transformer magnetizing inductor current at time +1.

3. The predictive control method for a flyback converter based on a continuous set model according to claim 2, characterized in that... The first cost function for: , in, This represents the preset output voltage reference value at time k+1, obtained by... Find the partial derivative and set the result to 0 to minimize the first cost function. Take the resulting D as the first optimal duty cycle control value. , .

4. The predictive control method for a flyback converter based on a continuous set model according to claim 3, characterized in that... The second cost function for: ,in, This indicates the preset inductor current overcurrent threshold, which is determined by... Find the partial derivative and set the result to 0 to minimize the second cost function. Take the resulting D as the second optimal duty cycle control value. , .

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