A constant voltage and constant current mode switching control method and system for a DC power supply

Abstract

The present invention provides a constant voltage and constant current mode switching control method and system for a direct current power supply. In the constant current mode, a voltage loop controller is reset at each control moment through a voltage controller reset logic unit. After the reset, the voltage loop controller counter is cleared, and a recursive calculation is performed again according to an externally set initial value of the voltage loop controller. The constant current and constant voltage modes can be automatically switched smoothly as expected, and the problems of voltage overshoot, oscillation, etc. that are usually caused by limiting the larger value of the voltage controller output value and the current loop controller output value are solved.

Description

Technical Field

[0001] The invention relates to the field of direct current power supply control, and in particular to a control method suitable for smooth and automatic switching between a constant voltage mode and a constant current mode in a direct current power supply. Background Art

[0002] In the field of DC power supply control, constant current output and constant voltage output are two commonly used output modes. In the process of starting up an ideal DC power supply, it is usually in constant current mode first. When the output voltage reaches the set voltage, it switches to constant voltage mode smoothly and without overshoot. In the process of sudden increase or decrease of the load, the power supply can achieve smooth switching between constant current output mode and constant voltage output mode without overshoot or oscillation. The commonly used switching logic between constant current mode and constant voltage mode is to compare the output values ​​of the voltage loop controller and the current loop controller, take the minimum value as the modulation wave and modulate it with the triangular carrier, and limit the larger value of the voltage controller output value and the current loop controller output value. This switching logic usually brings problems such as voltage overshoot and oscillation.

[0003] Taking the common buck type DC converter as an example, the Buck circuit is as follows Figure 1 As shown in the figure, it consists of a DC bus E, a fully controlled MOSFET, a diode D, an energy storage inductor L, an energy storage capacitor C and a load R. In the control of a DC power supply, a common constant current and constant voltage control block diagram is shown in the figure below. Figure 2 As shown. When this method is used, since both the voltage controller and the current loop controller are common PI controllers, the conventional way of setting the controller output threshold is likely to cause output voltage oscillations during the startup process and the constant current and constant voltage switching process. The specific reason is: if the output of the voltage controller is less than the output of the current controller, the power supply is in a constant voltage output state, and the current feedback value is less than the current set value, that is, the error input signal of the current loop controller is positive for a considerable period of time. Due to the existence of the integral effect of the current loop controller, the current loop controller will quickly reach its limiting threshold. At this time, if the load is increased, the current feedback value is greater than the current set value, that is, the error input signal of the current loop controller begins to become negative. At this moment, the output of the current loop controller begins to decrease based on the positive threshold, and the output of the voltage controller remains basically unchanged until the output of the current loop controller is less than the output of the voltage controller, and then it will enter the constant current mode. During the period from when the load suddenly increases to when it enters the constant current mode, the output current is much greater than the set current, so that the constant current mode cannot work according to the expected state, such as Figure 3 shown. Summary of the invention

[0004] The object of the present invention is to provide a constant voltage and constant current mode switching control method and system for a DC power supply, which can automatically switch the constant current and constant voltage mode smoothly as expected when the load value changes.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A constant voltage and constant current mode switching control method for a direct current power supply. In the constant current mode, a voltage loop controller is reset at each control moment through a voltage controller reset logic unit, the voltage loop controller counter is cleared after reset, and recursive calculation is performed again according to an externally set initial value of the voltage loop controller; in the constant voltage mode, a current loop controller is reset through a current controller reset logic unit, the current loop controller counter is cleared after reset, and recursive calculation is performed again according to an externally set initial value of the current loop controller.

[0007] Preferably, the voltage loop controller and the current loop controller are both PI controllers, and the calculation formula of the PI controller in a non-reset state is:

[0008] u(k)=u(k-1)+K·e(k)-K·A·e(k-1)

[0009] The calculation formula in the reset state is:

[0010] u(k)=u(k-1)+K·e(k)

[0011] If the PI controller is always in the reset state, the calculation formula is expressed as:

[0012] u(0)=u(0)+K·e(0)

[0013] Among them, u(k) is the output signal of the controller at the current kth moment, u(k-1) is the output signal of the controller at the k-1th moment, e(k) is the difference between the given signal at the current moment and the feedback signal at the current moment, e(k-1) is the difference between the given signal and the feedback signal at the previous moment, K is the proportional factor of the controller, which is a fixed value, and A is the zero point of the controller, which is a fixed value.

[0014] Preferably, the PI controller resets when the reset interface is at a high level, and the control logic of the voltage controller reset logic unit is:

[0015] At the current kth moment, the voltage controller output value u of the pre-saved k-1th moment is sc (k-1) and the output value of the current loop controller I sc (k-1) for comparison, if u sc (k-1)≥I sc (k-1), then usc_reset Output high level and maintain a sampling cycle, and at the same time the output value C of the loop comparison logic at the previous moment sc (k-1) is used as the initial value of the voltage loop controller;

[0016] The control logic of the current controller reset logic unit is:

[0017] At the current kth moment, the voltage controller output value u of the pre-saved k-1th moment is sc (k-1) and the output value of the current loop controller I sc (k-1) for comparison, if I sc (k-1)≥u sc (k-1), then I sc_reset Output high level and maintain a sampling cycle, and at the same time the output value C of the loop comparison logic at the previous moment sc (k-1) is used as the initial value of the current loop controller.

[0018] Preferably, the switching mode between the constant voltage mode and the constant current mode when the load increases is:

[0019] The output of the voltage controller is less than the output of the current controller. The power supply is in constant voltage mode. The current loop controller is always in reset state. The output value of the current loop controller at the kth moment is C sc (k-1)+K·[I sr (k)-I sb (k)], the output of the voltage controller is C sc (k), current given I sr (k) is greater than the current feedback I sb (k), then C sc (k-1)+K·[I sr (k)-I sb (k)]>C sc (k-1), it is considered that C sc (k)≈C sc (k-1), therefore, C sc (k-1)+K·[I sr (k)-I sb (k)]>C sc (k), the output value of the current loop controller is K larger than the output value of the voltage controller. sr (k)-I sb (k)];

[0020] If the load is increased, the current feedback I sb (k) value starts to increase, the output C of the current loop controller sc (k-1)+K·[I sr (k)-Isb (k)] starts to decrease and soon reaches C sc (k) is equal, and then the power supply enters constant current operation, and the voltage loop is reset repeatedly in each control cycle, and its output value becomes C sc (k-1)+K·[U sr (k)-U sb (k)], which is greater than the output value C of the current loop sc (k), when the load suddenly decreases, the voltage feedback U sb (k) increases, and when the output value of the voltage loop becomes equal to the output value of the current loop, the power supply enters the constant voltage working mode.

[0021] A constant voltage and constant current mode switching control system for a DC power supply, used to implement the above method, comprising: a voltage loop controller, a voltage controller reset logic unit, a current loop controller, a current controller reset logic unit, and a loop comparison logic unit, wherein the voltage loop controller is controlled by the voltage controller reset logic unit, the current loop controller is controlled by the current controller reset logic unit, the two inputs of the loop comparison logic unit are respectively connected to the outputs of the voltage loop controller and the current loop controller, and the output of the loop comparison logic unit is the modulation wave C at the current moment. sc (k).

[0022] Preferably, the voltage loop controller includes an external initial value given u sc (0) and reset interface u sc_reset The current loop controller includes an external initial value given i sc (0) and reset interface I sc_reset , the voltage loop controller and the current loop controller are both PI controllers, and the modulation wave C at the current moment sc (k) is the minimum value between the two inputs.

[0023] The advantages of the present invention are that: when the present invention is in a constant voltage output state, the current loop controller is always in a reset state, and the output value of the current loop controller is BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the Buck circuit diagram;

[0025] Figure 2 This is a common DC power supply constant current and constant voltage control block diagram;

[0026] Figure 3 This is the output curve under traditional switching logic;

[0027] Figure 4 Schematic diagram of a constant current and constant voltage switching method in an embodiment of the present invention;

[0028] Figure 5 This is a constant current and constant voltage control block diagram in an embodiment of the present invention;

[0029] Figure 6 This is an output curve under the switching logic of an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] A constant voltage and constant current mode switching control system for a DC power supply, please refer to Figure 4 , including: a voltage loop controller, a voltage controller reset logic unit, a current loop controller, a current controller reset logic unit, and a loop comparison logic unit. The voltage loop controller is controlled by the voltage controller reset logic unit, and the current loop controller is controlled by the current controller reset logic unit. The two inputs of the loop comparison logic unit are respectively connected to the outputs of the voltage loop controller and the current loop controller. The output of the loop comparison logic unit is the modulation wave C at the current moment. sc (k).

[0032] The voltage loop controller includes an external initial value given u sc (0) and reset interface u sc_reset The current loop controller includes an external initial value given i sc (0) and reset interface I sc_reset , the voltage loop controller and the current loop controller are both PI controllers, and they are reset when the reset interface is high. After the reset, the counter inside the controller is cleared, and the recursive calculation is performed again according to the initial value set externally. The modulation wave C at the current moment sc (k) is the minimum value between the two inputs. This system replaces the existing power supply constant current and constant voltage switching control in the entire switching block diagram. Please refer to Figure 2 and Figure 5 .

[0033] The calculation formula of the PI controller in the non-reset state is:

[0034] u(k)=u(k-1)+K·e(k)-K·A·e(k-1)

[0035] The calculation formula in the reset state is:

[0036] u(k)=u(k-1)+K·e(k)

[0037] If the PI controller is always in the reset state, the calculation formula is expressed as:

[0038] u(0)=u(0)+K·e(0)

[0039] Among them, u(k) is the output signal of the controller at the current kth moment, u(k-1) is the output signal of the controller at the k-1th moment, e(k) is the difference between the given signal at the current moment and the feedback signal at the current moment, e(k-1) is the difference between the given signal and the feedback signal at the previous moment, K is the proportional factor of the controller, which is determined by the controlled object and is a fixed value, and A is the zero point of the controller, which is determined by the controlled object and is a fixed value.

[0040] The control logic of the voltage controller reset logic unit is:

[0041] At the current kth moment, the voltage controller output value u of the pre-saved k-1th moment is sc (k-1) and the output value of the current loop controller I sc (k-1) for comparison, if u sc (k-1)≥I sc (k-1), then u sc_reset Output high level and maintain a sampling cycle, and at the same time the output value C of the loop comparison logic at the previous moment sc (k-1) is used as the initial value of the voltage loop controller.

[0042] The control logic of the current controller reset logic unit is:

[0043] At the current kth moment, the voltage controller output value u of the pre-saved k-1th moment is sc (k-1) and the output value of the current loop controller I sc (k-1) for comparison, if I sc (k-1)≥u sc (k-1), then I sc_reset Output high level and maintain a sampling cycle, and at the same time the output value C of the loop comparison logic at the previous moment sc (k-1) is used as the initial value of the current loop controller.

[0044] The loop comparison logic is used to compare the output u of the voltage loop controller at the current moment. sc (k) and the output of the current controller I sc (k) Compare and select the smallest one between the two as the modulation wave C at the current moment sc (k) Output.

[0045] If the output of the voltage controller is less than the output of the current controller, the power supply is in constant voltage mode, and the current loop controller is always in reset state. The output value of the current loop controller at the kth moment is:

[0046] C sc (k-1)+K·[I sr (k)-Isb (k)]

[0047] The output of the voltage controller is C sc (k), current given I sr (k) is greater than the current feedback I sb (k), then:

[0048] C sc (k-1)+K·[I sr (k)-I sb (k)]>C sc (k-1)

[0049] Since the time interval between each control is very small, it is assumed that the output value of the controller is approximately equal in the two cycles before and after, that is, C sc (k)≈C sc (k-1), so:

[0050] C sc (k-1)+K·[I sr (k)-I sb (k)]>C sc (k)

[0051] The output value of the current loop controller is K larger than the output value of the voltage controller. sr (k)-I sb (k)].

[0052] If the load is increased, the current feedback I sb (k) value starts to increase, the output C of the current loop controller sc (k-1)+K·[I sr (k)-I sb (k)] starts to decrease and soon becomes equal to Csc(k). After that, the power supply enters constant current operation, and the voltage loop is reset repeatedly in each control cycle, and its output value becomes:

[0053] C sc (k-1)+K·[U sr (k)-U sb (k)]

[0054] The output value is greater than the output value C of the current loop sc (k), when the load suddenly decreases, the voltage feedback U sb (k) increases, and the output value of the voltage loop becomes equal to the output value of the current loop, and the power supply enters the constant voltage working mode. Please refer to Figure 6 .

[0055] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A constant voltage and constant current mode switching control method for a DC power supply, characterized in that: In the constant current mode, the voltage loop controller is reset at each control moment through the voltage controller reset logic unit, the voltage loop controller counter is cleared after the reset, and the recursive calculation is performed again according to the externally set initial value of the voltage loop controller; in the constant voltage mode, the current loop controller is reset through the current controller reset logic unit, the current loop controller counter is cleared after the reset, and the recursive calculation is performed again according to the externally set initial value of the current loop controller; The voltage loop controller and the current loop controller are both PI controllers. The calculation formula of the PI controller in a non-reset state is: The calculation formula in the reset state is: If the PI controller is always in the reset state, the calculation formula is expressed as: in, is the controller output signal at the current k-th moment, For the The output signal of the timing controller, is the difference between the given signal at the current moment and the feedback signal at the current moment, is the difference between the given signal and the feedback signal at the previous moment, K is the proportional factor of the controller, which is a fixed value, and A is the zero point of the controller, which is a fixed value; The PI controller resets when the reset interface is at a high level. The control logic of the voltage controller reset logic unit is: At the current kth moment, the voltage controller output value of the pre-saved k-1th moment is and the output value of the current loop controller For comparison, if , then Output high level and maintain a sampling cycle, and at the same time the output value of the loop comparison logic at the previous moment As the initial value of the voltage loop controller; The control logic of the current controller reset logic unit is: At the current kth moment, the voltage controller output value of the pre-saved k-1th moment is and the output value of the current loop controller For comparison, if , then Output high level and maintain a sampling cycle, and at the same time the output value of the loop comparison logic at the previous moment As the initial value of the current loop controller; The switching mode between constant voltage mode and constant current mode when the load increases is: The output of the voltage controller is less than the output of the current controller. The power supply is in constant voltage mode. The current loop controller is always in reset state. The output value of the current loop controller at the kth moment is , the output of the voltage controller is , current given Greater than current feedback ,but ,think ,therefore, , the output value of the current loop controller is larger than the output value of the voltage controller ; If the load is increased, the current feedback The value starts to increase, and the output of the current loop controller Begins to decrease and soon After that, the power supply enters constant current operation, and the voltage loop is reset repeatedly in each control cycle, and its output value becomes , greater than the output value of the current loop , when the load suddenly decreases, the voltage feedback Increases, and when the output value of the voltage loop is equal to the output value of the current loop, the power supply enters the constant voltage working mode.

2. A constant voltage and constant current mode switching control system for a DC power supply, used to implement the constant voltage and constant current mode switching control method for a DC power supply as claimed in claim 1, characterized in that: include: A voltage loop controller, a voltage controller reset logic unit, a current loop controller, a current controller reset logic unit, and a loop comparison logic unit. The voltage loop controller is controlled by the voltage controller reset logic unit, and the current loop controller is controlled by the current controller reset logic unit. The two inputs of the loop comparison logic unit are respectively connected to the outputs of the voltage loop controller and the current loop controller. The output of the loop comparison logic unit is the modulation wave at the current moment. .

3. The constant voltage and constant current mode switching control system for a DC power supply according to claim 2, characterized in that: The voltage loop controller includes an external initial value setting and reset interface , the current loop controller includes an external initial value setting and reset interface , the voltage loop controller and the current loop controller are both PI controllers, and the modulation wave at the current moment is the minimum value between the two inputs.

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