A high dynamic response low-ripple DC-DC converter control system

Abstract

The application discloses a high-dynamic-response low-ripple DC-DC converter control system, which comprises a DC-DC converter main topology circuit and a control circuit, the control circuit and the DC-DC converter main topology circuit form a closed loop, the control circuit comprises a voltage sampling module, an error calculation module, a PID operation unit, a sign function generation unit, a control parameter generation unit and a PWM driving module; the PID operation module generates a PID control quantity according to the error according to a PID calculation method; the sign function generation unit determines the output of itself according to the error, thereby controlling the sign of a correction coefficient, and generating a correction term; the control parameter generation unit adds the PID control quantity and the correction term, generates a control parameter of a next period, and transmits the control parameter to the PWM driving module. The application does not need mode switching logic, has a simple structure, fast dynamic response, controllable steady-state ripple, and is suitable for various DC converters.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control technology, specifically relating to a low-ripple DC-DC converter control system with high dynamic response. Background Technology

[0002] Constant voltage control is a core requirement of power supply systems. Traditional proportional-integral-derivative (PID) control is widely used due to its simple structure and ease of eliminating static errors. However, while pursuing fast dynamic response, traditional PID control often struggles to minimize steady-state output ripple. On the other hand, although pure on-off control (hysteresis control) produces a controllable triangular ripple in steady state, its dynamic response speed is limited by the hysteresis width and the switching frequency is not fixed.

[0003] In existing technologies, some have proposed a parallel structure of PID control and hysteresis loop, but such methods usually require additional design of hysteresis comparators and mode switching logic, resulting in complex control and difficult parameter tuning. Therefore, there is an urgent need for a simple constant voltage control method that can retain the speed of PID control during dynamic processes, generate regular and controllable triangular ripples in steady state, and eliminate the need for complex mode switching. Summary of the Invention

[0004] The purpose of this invention is to provide a low-ripple DC-DC converter control system with high dynamic response, which enables the power supply to have dynamic performance almost identical to that of a traditional PID controller when the load or input voltage changes abruptly, and automatically enters a self-sustaining limit loop state during steady-state operation, generating a correction amount through the error of the previous cycle, thereby reducing the output voltage ripple of the system.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high dynamic response, low ripple DC-DC converter control system includes a DC-DC converter main topology circuit and a control circuit. The control circuit forms a closed loop with the DC-DC converter main topology circuit. The control circuit includes a voltage sampling module, an error calculation module, a PID operation unit, a sign function generation unit, a control parameter generation unit, and a PWM drive module.

[0007] The voltage sampling module samples the output voltage based on the output voltage information of the DC-DC converter and transmits it to the error calculation module;

[0008] The error calculation module performs a subtraction operation between the sampled output voltage and the expected output voltage to obtain the error of the output voltage and transmits it to the PID calculation module and the sign function generation unit.

[0009] The PID calculation module generates PID control quantities based on the error according to the PID calculation method.

[0010] The sign function generation unit determines its own output based on the error, thereby controlling the sign of the correction coefficient and generating the correction term;

[0011] The control parameter generation unit adds the PID control quantity to the correction term to generate the control parameters for the next cycle, and then transmits them to the PWM drive module.

[0012] The PWM drive module determines the switching control signal in the main topology circuit of the DC-DC converter based on the control parameters and primary side information.

[0013] Furthermore, the voltage sampling module samples the output voltage using an ADC, dual-line sampling, or single-line sampling method.

[0014] Furthermore, the PID control quantity generated by the PID calculation module is: ,in This is the proportionality coefficient. The integral coefficient is... Differential coefficients This is the error.

[0015] Furthermore, the symbol function generation unit generates a generation correction term. , The preset correction factor. For the symbolic function, it is:

[0016]

[0017] for The singularity is that the correction term is the correction term from the previous time step. .

[0018] Furthermore, the correction coefficient The value is taken as 1% to 10% of the amplitude of the output control quantity of the PID calculation module.

[0019] Furthermore, the control parameter generation unit consists of an adder that adds the PID control quantity to the correction term.

[0020] Furthermore, the control parameters for generating the next cycle specifically include:

[0021] Generate total control quantity: ;

[0022] By limiting the total control quantity, the final control parameters are obtained: , The minimum and maximum values ​​are set.

[0023] Furthermore, , The value range is 0.05-0.5.

[0024] Compared with the prior art, the beneficial effects of this invention are as follows: Based on traditional proportional-integral-derivative (PID) control, this invention adds a fixed-amplitude sign function term, the sign of which is determined by the sign of the output voltage error; during dynamic processes, the PID term dominates, and the system response speed is the same as that of traditional PID; in steady state, by designing the proportional coefficient... Integral coefficient and differential coefficients The value of the variable makes the change in the PID term negligible compared to the magnitude of the correction term; in steady state, a limit loop control dominated by the correction term is formed, and the output voltage exhibits a controllable triangular ripple. When the load changes, the output voltage change causes the error to increase, and the PID term quickly takes over, thus changing the duty cycle to make the output voltage quickly approach the desired value, and the system automatically enters a new limit loop. This invention does not require mode switching logic, has a simple structure, fast dynamic response, controllable steady-state ripple, and is suitable for various DC-DC converters. Attached Figure Description

[0025] Figure 1 This is a block diagram illustrating the principle of the control method of the present invention.

[0026] Figure 2 This is a block diagram of the overall system structure. Figure 3 Implement a flowchart for the digital controller. Detailed Implementation

[0027] This embodiment uses a flyback converter as an example, and its structural block diagram is as follows: Figure 2 The diagram illustrates the application of the method of this invention in isolated DC-DC power supplies. Flyback converters are commonly used in low-to-medium power applications, such as auxiliary power supplies, chargers, and LED drivers. Their outputs are electrically isolated from their inputs, and they have high requirements for output ripple. The method of this invention can ensure dynamic performance while producing a controllable triangular wave ripple in the steady-state output voltage, facilitating subsequent filter design.

[0028] Main circuit parameters: Input voltage (Typical industrial bus or battery voltage), output reference voltage Output power (load resistance) Transformer primary inductance Secondary inductor (turns ratio) Switching frequency (Fixed-frequency PWM control). Output capacitor. (Consider ESR).

[0029] This embodiment provides a high dynamic response, low ripple constant voltage power supply control system, including a DC-DC converter main topology circuit and a control circuit, such as... Figure 1 and Figure 2 As shown, the control circuit includes a voltage sampling module, an error calculation module, a PID operation unit, a sign function generation unit, a control parameter generation unit, and a PWM drive module; wherein:

[0030] The voltage sampling module samples the output voltage based on the output voltage information. The data is then transmitted to the error calculation module; the voltage sampling module can perform sampling via an ADC, or via traditional dual-line or single-line sampling methods.

[0031] The error calculation module calculates the difference between the actual output voltage and the expected output voltage based on the output voltage sampled. The subtraction operation is performed to obtain the error in the output voltage, which is then transmitted to the PID calculation module and the sign function generation unit; the error signal is calculated as follows:

[0032]

[0033] The PID calculation module generates a PID control quantity based on the calculated error using the traditional PID calculation method, and dynamically adjusts the power supply system; the PID control quantity is:

[0034]

[0035] in This is the proportionality coefficient. The integral coefficient is... These are the differential coefficients. By rationally designing the proportional coefficients... Integral coefficient and differential coefficients The value of is such that the change in the PID term in steady state is negligible compared to the magnitude of the correction term.

[0036] The sign function generation unit determines its own output based on the error, thereby controlling the sign of the correction coefficient and generating the correction term;

[0037]

[0038] In the formula The preset correction factor is used. Generally, the amplitude of the PID control input is taken as 1% to 10%, and the sign function is defined as follows:

[0039]

[0040] for The singular case is defined as 0. In this case, the control quantity of the system in the next cycle is the same as the PID control quantity in the next cycle, that is, the final generated control quantity does not contain the correction term.

[0041] The control parameter generation unit consists of an adder that adds the PID control quantity and the correction term to synthesize the final control quantity. This generates the control parameters for the next cycle and transmits them to the PWM drive module. This control quantity is used to adjust the duty cycle / drive signal of the power switch, thereby controlling the output voltage.

[0042] The PWM drive module determines the switching control signal in the main topology circuit based on the control parameters and primary side information, forming a closed loop with the main topology circuit.

[0043] When the system starts working, the PID control quantity takes the lead to ensure that the system enters a steady-state working state; after entering the steady-state working state, the correction term takes the lead, thereby reducing the system output voltage ripple.

[0044] This embodiment employs a primary-side feedback method to reduce costs: the output voltage is sampled using an auxiliary winding (isolated and without optocoupler), divided, and then fed into an ADC. The control circuit executes the control algorithm of this invention based on an FPGA, outputting a PWM signal to drive the primary-side MOSFET. The control quantity is the duty cycle of the MOSFET. , range 0~ (This example takes) (To prevent transformer magnetic saturation).

[0045] Controller parameter tuning: Since the small-signal model of the flyback converter contains right-half-plane zeros (in continuous conduction mode, CCM), the PID parameters need to be tuned using a typical method to ensure stability: select 1 / 5 of the switching frequency as the crossover frequency. The phase margin is 45°. The calculated proportional gain is: Integral coefficient (Corresponding to the continuous field) , = .

[0046] Discretization (sampling frequency) , ):

[0047]

[0048] Correction coefficient (Normalized duty cycle change, corresponding to actual duty cycle change ±0.05). The duty cycle of the switching transistor is limited. (Leave a margin).

[0049] Combination Figure 3 The implementation method of the digital controller based on the high dynamic response low ripple DC-DC converter control system includes:

[0050] Step 1: System initialization, configure ADC (sampling auxiliary winding voltage), PWM timer (complementary output optional), and set control cycle. (The switching period does not necessarily have to be the same as the PWM period; for simplicity, it is set to twice the switching period here).

[0051] Step 2: Enter timer interrupt and sample output voltage. (Converted back to the true value of the secondary side using a proportional conversion), calculation error:

[0052]

[0053] Step 3: Update the digital integrator:

[0054]

[0055] To prevent integral saturation, an integral limit is set as follows: (Corresponding duty cycle adjustment range).

[0056] Step 4: Calculate the differential term

[0057]

[0058] in , This is the filtering time constant.

[0059] Step 5: Calculate the PID output:

[0060]

[0061] Step 6: Generate a correction signal based on the error sign:

[0062]

[0063] Step 7: Generate the total control quantity:

[0064]

[0065] Step 8: Limiting comparison generates the final control value. This control quantity Used to adjust the duty cycle / drive signal of the power switching transistor, thereby controlling the output voltage.

[0066]

[0067] in (To prevent insufficient output voltage due to an excessively low duty cycle) .

[0068] Step 9: Based on the final control quantity Update the PWM compare register, output the drive signal, and return from the interrupt.

[0069] Dynamic process (large error stage): When the output voltage deviates significantly from the reference value, Larger, PID term is much larger The influence of the correction signal is negligible, and the dynamic response speed of the system is almost the same as that of a traditional PID controller.

[0070] Steady-state process (small error stage): When the output voltage approaches the reference value, the proportional part of the PID term approaches 0, the integral term converges to a certain constant value, but the correction term... It continues to act, forcing the controller output to... The system switches periodically between these values. This switching causes the output voltage to oscillate around the reference value with a constant amplitude, forming a symmetrical triangular wave, indicating that the system has entered a limit cycle operating state. In this state, the average value of the output voltage is strictly equal to... (The integrator guarantees zero steady-state error), ripple peak-to-peak value Mainly depends on and power supply main circuit parameters.

[0071] Correction coefficient The steady-state ripple magnitude is determined by the input voltage, typically taken as 1% to 10% of the PID controller's output limit. Increasing this value... It can improve robustness to parameter perturbations, but it will increase ripple.

[0072] PID coefficients : Tune according to the traditional PID method to meet dynamic response indicators (such as crossover frequency and phase margin). It should not be too large, otherwise it will suppress the limit cycle and cause the system to enter a static error state; It should be small enough to avoid the limiting cycle frequency being too high; It should not be too large either.

[0073] To reduce output voltage ripple, you can reduce (For example, set to 0.025), but the dynamic recovery time may increase slightly.

[0074] To improve dynamic response, increase At the same time, appropriately increase This accelerates the integral action. The control method is equally effective in discontinuous conduction mode (DCM), and the small-signal model is simpler, allowing for more flexible PID parameter design. In this embodiment, if the system enters DCM under light load, no parameter adjustments are required, and the control algorithm will still function normally (only the limiting cycle frequency may change).

[0075] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high dynamic response low ripple DC-DC converter control system, comprising a DC-DC converter main topology circuit and a control circuit, the control circuit and the DC-DC converter main topology circuit form a closed loop, characterized in that, The control circuit includes a voltage sampling module, an error calculation module, a PID operation unit, a sign function generation unit, a control parameter generation unit, and a PWM drive module; wherein: The voltage sampling module samples the output voltage based on the output voltage information of the DC-DC converter and transmits it to the error calculation module; The error calculation module performs a subtraction operation between the sampled output voltage and the expected output voltage to obtain the error of the output voltage and transmits it to the PID calculation module and the sign function generation unit. The PID calculation module generates PID control quantities based on the error according to the PID calculation method. The sign function generation unit determines its own output based on the error, thereby controlling the sign of the correction coefficient and generating the correction term; The control parameter generation unit adds the PID control quantity to the correction term to generate the control parameters for the next cycle, and then transmits them to the PWM drive module. The PWM drive module determines the switching control signal in the main topology circuit of the DC-DC converter based on the control parameters and primary side information.

2. The low-ripple DC-DC converter control system of claim 1, wherein, The voltage sampling module samples the output voltage using an ADC, dual-line sampling, or single-line sampling method.

3. The low-ripple DC-DC converter control system according to claim 1, characterized in that, The PID operation module generates a PID control quantity: wherein is a proportional coefficient, is an integral coefficient, is a differential coefficient is an error.

4. The low-ripple DC-DC converter control system according to claim 1, characterized in that, The symbol function generation unit generates a generation correction term. , The preset correction factor. For the symbolic function, it is: for The singularity is that the correction term is the correction term from the previous time step. .

5. The system according to claim 4, characterized in that, Correction coefficient The value is taken as 1% to 10% of the amplitude of the output control quantity of the PID calculation module.

6. The low-ripple DC-DC converter control system according to claim 1, characterized in that, The control parameter generation unit consists of an adder that adds the PID control quantity to the correction term.

7. The low-ripple DC-DC converter control system according to claim 1, characterized in that, The control parameters for generating the next cycle specifically include: Generate total control quantity: ; By limiting the total control quantity, the final control parameters are obtained: , The minimum and maximum values ​​are set.

8. The low-ripple DC-DC converter control system according to claim 7, characterized in that, , The value range is 0.05-0.5.

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