Impedance self-adaptive constant current control device and method

Abstract

The invention relates to an impedance adaptive constant current control device and method, and the device comprises an equivalent impedance calculation module which is used for calculating load equivalent impedance according to load output voltage and load output current; the PWM control module is used for generating a first chopper tube driving signal based on the current given value and the load output current, and the first chopper tube driving signal is a driving signal in a non-short-circuit state; the PFM control module is used for generating a second chopper tube driving signal based on the current given value and the load output current, and the second chopper tube driving signal is a driving signal in a short circuit state; and the output switching module is used for switching the control end of a chopper tube in the Buck converter to be connected with the output end of the PWM control module or the output end of the PFM control module according to the magnitude of the load equivalent impedance. According to the invention, even if the load is in a short circuit, the circuit can be regulated to realize constant current output.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an impedance adaptive constant current control device and method. Background Art

[0002] Buck converter is a typical DC-DC conversion circuit, with a DC power supply connected to its input side and a load connected to its output side. Through control, various control targets such as constant output voltage, constant current or constant power can be achieved. When the output side is short-circuited, the Buck converter is generally protected by detecting the current and blocking the wave to avoid damage to the Buck converter due to excessive current caused by load short circuit. In some working conditions, such as charging the supercapacitor when it is out of power (equivalent to a short circuit), the Buck converter needs to continue to operate and output a constant current when the output is short-circuited, rather than simply blocking the wave for protection.

[0003] The existing public patent document CN206402200U discloses a conversion circuit based on SG1525. The circuit is in PFM working mode under normal operation and is converted to PWM working mode under light load and no load, but it does not provide a processing method under short circuit. The existing public patent document CN214960216U drives high-power LED devices by simultaneously adjusting the duty cycle and switching frequency of the MOS tube in real time to output a constant current. It does not provide a solution to whether a constant current can be output when the load is short-circuited. The existing public patent document CN15664204A discloses a method for judging whether a resistor is short-circuited by comparing the output current with the actual current. This method turns off the output after a short circuit occurs, so it cannot output current after a short circuit. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an impedance adaptive constant current control device and method, so that the circuit can be regulated to achieve constant current output even when the load is short-circuited.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide an impedance adaptive constant current control device, comprising:

[0006] An equivalent impedance calculation module, used for calculating the load equivalent impedance according to the load output voltage and the load output current;

[0007] A PWM control module, used for generating a first chopper tube drive signal based on a current given value and a load output current, wherein the first chopper tube drive signal is a drive signal in a non-short-circuit state;

[0008] A PFM control module, used for generating a second chopper tube drive signal based on a current given value and a load output current, wherein the second chopper tube drive signal is a drive signal in a short-circuit state;

[0009] The output switching module is used to switch the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to be connected to the output end of the PFM control module according to the size of the load equivalent impedance.

[0010] The equivalent impedance calculation module adopts Z f =U f / I f Calculate the load equivalent impedance, where Z f is the load equivalent impedance, U f is the load output voltage, I f is the load output current.

[0011] The output switching module comprises:

[0012] A judging unit, used to judge whether the load equivalent impedance is greater than an impedance threshold;

[0013] The switching unit is used to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module when the load equivalent impedance is greater than the impedance threshold, and to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PFM control module when the load equivalent impedance is not greater than the impedance threshold.

[0014] The PWM control module comprises:

[0015] A first calculation unit, used for calculating the deviation between the current given value and the load output current;

[0016] A PWM regulator, used for adjusting the duty cycle of the signal according to the deviation;

[0017] The PWM modulator is used to generate a PWM drive signal as a first chopper tube drive signal according to the duty cycle of the signal.

[0018] The PFM control module includes:

[0019] A second calculation unit, used for calculating the deviation between the current given value and the load output current;

[0020] A PFM regulator, used for adjusting the pulse frequency according to the deviation;

[0021] The PFM modulator is used to generate a pulse drive signal as a second chopper tube drive signal according to the pulse frequency.

[0022] The technical solution adopted by the present invention to solve the technical problem is: to provide an impedance adaptive constant current control method, comprising the following steps:

[0023] Inputting the collected load output voltage and load output current into an equivalent impedance calculation module, and obtaining the load equivalent impedance through calculation by the equivalent impedance calculation module;

[0024] The load equivalent impedance is input into an output switching module, and the output switching module switches the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance;

[0025] Among them, the PWM control module generates a first chopper tube drive signal based on the current set value and the load output current, and the first chopper tube drive signal is a drive signal in a non-short-circuit state; the PFM control module generates a second chopper tube drive signal based on the current set value and the load output current, and the second chopper tube drive signal is a drive signal in a short-circuit state.

[0026] The output switching module switches the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance, specifically:

[0027] Determining whether the load equivalent impedance is greater than an impedance threshold;

[0028] If the load equivalent impedance is greater than the impedance threshold, controlling the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module;

[0029] If the load equivalent impedance is not greater than the impedance threshold, the control end of the chopper tube in the Buck converter is controlled to be connected to the output end of the PFM control module.

[0030] The equivalent impedance calculation module adopts Z f =U f / I f Calculate the load equivalent impedance, where Z f is the load equivalent impedance, U f is the load output voltage, I f is the load output current.

[0031] The PWM control module generates a first chopper tube drive signal based on a current given value and a load output current, specifically:

[0032] Calculating the deviation between the current given value and the load output current;

[0033] adjusting a duty cycle of a signal according to the deviation;

[0034] A PWM driving signal is generated according to the duty cycle of the signal as a first chopper tube driving signal.

[0035] The PFM control module generates a second chopper tube drive signal based on a current given value and a load output current, specifically:

[0036] Calculating the deviation between the current given value and the load output current;

[0037] adjusting the pulse frequency according to the deviation;

[0038] A pulse drive signal is generated according to the pulse frequency as a second chopper tube drive signal.

[0039] Beneficial Effects

[0040] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention determines whether the load is short-circuited by calculating the load equivalent impedance in real time, and switches the driving signal of the input chopper tube in real time based on the judgment criterion, thereby achieving the ability to control the circuit to achieve constant current output even under short-circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : is a structural principle diagram of an impedance adaptive constant current control device according to an embodiment of the present invention;

[0042] Figure 2 It is a timing diagram of control performed by the impedance adaptive constant current control device according to the embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0044] An embodiment of the present invention relates to an impedance adaptive constant current control device, which determines whether a load is short-circuited by calculating the load equivalent impedance in real time, thereby providing a real-time and reliable short-circuit criterion, and based on the criterion, it is possible to switch the drive signal of the input chopper tube in real time, that is, when the load is in a non-short-circuited state, a PWM working mode is adopted, and when the load is in a short-circuited state, a PFM working mode is adopted. This mode ensures that the circuit can be regulated to achieve constant current output even under a short circuit.

[0045] Figure 1The Buck converter shown includes a control circuit (i.e., the impedance adaptive constant current control device of this embodiment) and a power circuit. The power circuit includes a power supply, a chopper, a filter, and a load connected in sequence.

[0046] The control loop includes an equivalent impedance calculation module, a PWM control module, a PFM control module and an output switching module.

[0047] The equivalent impedance calculation module is used to calculate the load equivalent impedance according to the load output voltage and load output current. Therefore, it can calculate the load equivalent impedance according to the collected load output voltage U f and load output current I f , using Z f =U f / I f Calculate the load equivalent impedance Z f .

[0048] A PWM control module is used to generate a first chopper tube drive signal based on a current given value and a load output current, wherein the first chopper tube drive signal is a drive signal in a non-short circuit state. In this embodiment, the PWM control module includes: a first calculation unit, used to calculate the deviation between the current given value and the load output current; a PWM regulator, used to adjust the duty cycle of the signal according to the deviation; and a PWM modulator, used to generate a PWM drive signal as the first chopper tube drive signal according to the duty cycle of the signal.

[0049] Among them, the PWM regulator is mainly responsible for adjusting the duty cycle of the PWM signal according to the deviation between the current set value and the actual output current. It is usually part of a feedback control system, which can be implemented through different control algorithms, such as PID control algorithm. The PWM regulator can dynamically adjust the PWM signal to respond to load changes and system conditions, thereby achieving precise current control. The PWM modulator is responsible for generating a PWM waveform, i.e., a PWM drive signal, according to the duty cycle of the PWM signal output by the PWM regulator. It takes the duty cycle of the PWM signal as input and generates a corresponding PWM signal. The generated PWM signal can control the on and off of the chopper tube in the chopper.

[0050] The PFM control module is used to generate a second chopper tube drive signal based on a current given value and a load output current, wherein the second chopper tube drive signal is a drive signal in a short-circuit state. In this embodiment, the PFM control module includes: a second calculation unit, used to calculate the deviation between the current given value and the load output current; a PFM regulator, used to adjust the pulse frequency according to the deviation; and a PFM modulator, used to generate a pulse drive signal according to the pulse frequency as the second chopper tube drive signal.

[0051] Among them, the PFM regulator is mainly responsible for adjusting the pulse frequency according to the deviation between the current set value and the actual output current. In the PFM control method of this embodiment, the pulse width remains constant, and the frequency of the pulse is determined according to the deviation between the current set value and the actual output current. The PFM regulator controls and adjusts the circuit by adjusting the frequency of the pulse. The PFM modulator generates an actual pulse signal according to the pulse frequency output by the PFM regulator. In the PFM modulator, there is usually a timer or counter to generate a basic clock signal, and then adjusts the frequency of the clock signal according to the pulse frequency output by the regulator to generate a pulse signal.

[0052] The output switching module is used to switch the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance. In this embodiment, the output switching module includes: a judgment unit, which is used to judge whether the load equivalent impedance is greater than an impedance threshold; a switching unit, which is used to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module when the load equivalent impedance is greater than the impedance threshold (that is, it indicates that the load is not in a short-circuit state), and to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PFM control module when the load equivalent impedance is not greater than the impedance threshold (that is, it indicates that the load is in a short-circuit state).

[0053] The impedance adaptive constant current control device of this embodiment specifically includes the following steps when performing control:

[0054] Inputting the collected load output voltage and load output current into an equivalent impedance calculation module, and obtaining the load equivalent impedance through calculation by the equivalent impedance calculation module;

[0055] The load equivalent impedance is input into an output switching module, and the output switching module switches the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance.

[0056] The present invention is further illustrated by a specific embodiment below.

[0057] In this embodiment, the power circuit is composed of a power supply Us, a chopper, a filter and a load, specifically:

[0058] The positive electrode of the power supply Us is connected to the current input end of the chopper tube S, and the current output end of the chopper tube S is respectively connected to the first end of the flow tube D and the inductor L. The control end of the chopper tube S is connected to the driving signal output by the control loop.

[0059] The second end of the inductor L is connected to the first end of the capacitor C, and the second ends of the capacitor C and the freewheeling tube D are both connected to the negative electrode of the power supply. The capacitor C is connected in parallel with the load Zo. At the same time, the circuit measures the output current If and the output voltage Uf at the load Zo.

[0060] In this embodiment, the load Zo can be changed to simulate the load being in a short-circuit state and a non-short-circuit state. When a very small impedance value is set, the load is in a short-circuit state; when a larger impedance value is set, the load is in a non-short-circuit state.

[0061] The control loop includes a PWM control module, a PFM control module, an equivalent impedance calculation module and an output switching module.

[0062] The PWM control module forms a driving signal according to the current given value and the output current deviation through the PWM regulator and the PWM modulator. This module works when the load is not short-circuited.

[0063] The PFM control module forms a driving signal according to the current set value and the output current deviation through the PFM regulator and the PFM modulator. This module works when the load is short-circuited.

[0064] The equivalent impedance calculation module is based on the output value transmitted by the power circuit, according to Z f =U f / I f Output load equivalent impedance to the output switching module in real time.

[0065] When the load is disconnected, the output current I f The output is 0, and the equivalent load impedance Z f The calculation formula of Z f =U f / I f , when the denominator is 0, the equation will be meaningless. Therefore, in this embodiment, a supplementary condition is added: that is, when the output current I f Less than 1×10 -4 (unit: A), let its value be a constant, that is, let I f =1×10 -4 (Unit: A); In this way, even if the actual output current is 0, the calculation module can still continuously output the load equivalent impedance value, so that the control loop can normally output the driving signal of the chopper tube.

[0066] In addition, in this embodiment, the impedance threshold Z set You can set it in the following ways:

[0067] Let the DC power supply voltage be U1 and the carrier frequency be f a , that is, the carrier period is T1 = 1 / f a; The dead time of the chopper tube is set to T2, and the minimum duty cycle is D min =T2 / T1, so the minimum output voltage obtained by PWM control is U1×D min , if the constant current set under this control mode is I1, the calculated equivalent impedance threshold is

[0068]

[0069] like Figure 1 As shown, the input signals of the output switching module are PWM signal, load equivalent impedance Z from top to bottom. f , PFM signal. The output signal is connected to the control end of the chopper tube in the power circuit. Initially, the switch is placed at the PWM interface. f <Z set When the load is in a short-circuit state, the output signal switches to the PFM signal, and the chopper tube is driven by the PFM signal; otherwise, it is in a non-short-circuit state, the output signal is at the PWM interface, and the chopper tube is still driven by the PWM signal.

[0070] To avoid switching at the impedance threshold Z set In order to avoid frequent actions, this embodiment considers adding a hysteresis loop, that is, taking the error Z c , when the circuit is in PWM control mode, when Z f <Z set -Z c When the output signal is switched to the PFM control module, the chopper tube is connected to the PFM control signal; when the circuit is in the PFM control mode, when Z f >Z set +Z c , the output signal switches to the PWM signal, and the chopper tube is connected to the PWM control signal.

[0071] Figure 2 This is a timing diagram for controlling based on impedance criterion and given current value. The horizontal axis is time, and the curves in the figure are from bottom to top: the output equivalent impedance value Z f , threshold Z set , given current value I ref and load output current I f .

[0072] During the time period 0-t2, the equivalent impedance of the load calculated by the circuit is Z f1 Because Z f1 >Z set , the load is in a non-short-circuit state, so the driving signal of the chopper tube is a PWM signal. Among them, during the time 0-t1, the current given value is I ref1 , load output current I f1 Gradually increase from 0 and stabilize at Iref1 At time t1, the current setting value is reduced to I ref2 , the load output current responds immediately, gradually decreases and finally stabilizes, and there is I f2 =I ref2 .

[0073] At t2, the equivalent impedance drops to Z f2 , and Z f2 <Z set , the load is in short circuit state, at this time, the output signal of the output switching module is switched to the PFM signal, and the driving signal of the chopper tube is converted to PFM. After t2 time, there is always Z f2 <Z set , the circuit is always in PFM working state.

[0074] Among them, the current given value in the time period t2-t3 is still I ref2 , the current output value remains I f2 =I ref2 At t3, the current setpoint increases to I ref3 , the load output current increases immediately and finally stabilizes, and there is I f3 =I ref3 .

[0075] It is not difficult to find that this embodiment provides a real-time and reliable short-circuit criterion by calculating the load equivalent impedance in real time to determine whether it is short-circuited. Based on this criterion, the drive signal of the input chopper tube can be switched in real time, that is, when the load is in a non-short-circuited state, the circuit is in a PWM working mode; when the load is in a short-circuited state, the circuit is switched to a PFM working mode. This method ensures that even in a short-circuited state, the circuit can be regulated to achieve a constant current output.

Claims

1. An impedance adaptive constant current control device, characterized in that: include: An equivalent impedance calculation module, used for calculating the load equivalent impedance according to the load output voltage and the load output current; A PWM control module, used for generating a first chopper tube drive signal based on a current given value and a load output current, wherein the first chopper tube drive signal is a drive signal in a non-short-circuit state; A PFM control module, used for generating a second chopper tube drive signal based on a current given value and a load output current, wherein the second chopper tube drive signal is a drive signal in a short-circuit state; The output switching module is used to switch the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to be connected to the output end of the PFM control module according to the size of the load equivalent impedance.

2. The impedance adaptive constant current control device according to claim 1, characterized in that: The equivalent impedance calculation module adopts Z f =U f / I f Calculate the load equivalent impedance, where Z f is the load equivalent impedance, U f is the load output voltage, I f is the load output current.

3. The impedance adaptive constant current control device according to claim 1, characterized in that: The output switching module comprises: A judging unit, used to judge whether the load equivalent impedance is greater than an impedance threshold; The switching unit is used to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module when the load equivalent impedance is greater than the impedance threshold, and to control the control end of the chopper tube in the Buck converter to be connected to the output end of the PFM control module when the load equivalent impedance is not greater than the impedance threshold.

4. The impedance adaptive constant current control device according to claim 1, characterized in that: The PWM control module comprises: A first calculation unit, used for calculating the deviation between the current given value and the load output current; A PWM regulator, used for adjusting the duty cycle of the signal according to the deviation; The PWM modulator is used to generate a PWM drive signal as a first chopper tube drive signal according to the duty cycle of the signal.

5. The impedance adaptive constant current control device according to claim 1, characterized in that: The PFM control module includes: A second calculation unit, used for calculating the deviation between the current given value and the load output current; A PFM regulator, used for adjusting the pulse frequency according to the deviation; The PFM modulator is used to generate a pulse drive signal as a second chopper tube drive signal according to the pulse frequency.

6. An impedance adaptive constant current control method, characterized in that: The following steps are involved: Inputting the collected load output voltage and load output current into an equivalent impedance calculation module, and obtaining the load equivalent impedance through calculation by the equivalent impedance calculation module; The load equivalent impedance is input into an output switching module, and the output switching module switches the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance; Among them, the PWM control module generates a first chopper tube drive signal based on the current set value and the load output current, and the first chopper tube drive signal is a drive signal in a non-short-circuit state; the PFM control module generates a second chopper tube drive signal based on the current set value and the load output current, and the second chopper tube drive signal is a drive signal in a short-circuit state.

7. The impedance adaptive constant current control method according to claim 6, characterized in that: The output switching module switches the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module or to the output end of the PFM control module according to the size of the load equivalent impedance, specifically: Determining whether the load equivalent impedance is greater than an impedance threshold; If the load equivalent impedance is greater than the impedance threshold, controlling the control end of the chopper tube in the Buck converter to be connected to the output end of the PWM control module; If the load equivalent impedance is not greater than the impedance threshold, the control end of the chopper tube in the Buck converter is controlled to be connected to the output end of the PFM control module.

8. The impedance adaptive constant current control method according to claim 6, characterized in that: The equivalent impedance calculation module adopts Z f =U f / I f Calculate the load equivalent impedance, where Z f is the load equivalent impedance, U f is the load output voltage, I f is the load output current.

9. The impedance adaptive constant current control method according to claim 6, characterized in that: The PWM control module generates a first chopper tube drive signal based on a current given value and a load output current, specifically: Calculating the deviation between the current given value and the load output current; adjusting a duty cycle of a signal according to the deviation; A PWM driving signal is generated according to the duty cycle of the signal as the first chopper tube driving signal.

10. The impedance adaptive constant current control method according to claim 6, characterized in that: The PFM control module generates a second chopper tube drive signal based on a current given value and a load output current, specifically: Calculating the deviation between the current given value and the load output current; adjusting the pulse frequency according to the deviation; A pulse driving signal is generated according to the pulse frequency as a second chopper tube driving signal.

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