Over-current protection method and system for isolated DC / DC converter

Abstract

The invention relates to an overcurrent protection method and system for an isolated DC / DC converter, and belongs to the technical field of overcurrent protection of DC / DC converters. The method comprises the steps that S1, when it is detected that the output current of the isolated DC / DC converter is overcurrent, a control signal used for driving the converter to operate is blocked so as to control the converter to stop operating, after a set time, the control signal is unlocked so as to control the converter to continue operating, and whether the output current of the converter is overcurrent or not continues to be detected; s2, the step S1 is repeated, and when it is detected that the output current of the converter is over-current continuously for set times, the converter is controlled to stop running; the set times are greater than or equal to 2. Under the condition that the safety of the converter is ensured as much as possible, the influence on power transmission to a post-stage power supply area is reduced, so that the overall power supply reliability of a power distribution end is greatly improved, a power supply system is more stable, and meanwhile, self-recovery of power supply in a non-fault area is facilitated.

Description

Technical Field

[0001] The invention relates to an overcurrent protection method and system for an isolated DC / DC converter, belonging to the technical field of overcurrent protection of DC / DC converters. Background Art

[0002] In DC microgrid system engineering, isolated DC / DC converters are usually used at the distribution end to output stable DC voltage as a power supply to supply power to subsequent DC loads. However, DC loads in daily application scenarios have unstable characteristics and may experience short-term short circuits.

[0003] In the prior art, when a short circuit fault occurs in a certain link in the subsequent power supply area, the isolated DC / DC converter will detect that the output current is overcurrent, and the overcurrent protection mechanism of the DC / DC converter will be triggered at this time, causing the DC / DC converter to shut down immediately and report the fault, thereby protecting the safety of the DC / DC converter. However, when the DC / DC converter shuts down, both the fault area and the non-fault area of ​​the entire subsequent power supply area will lose power, resulting in a reduction in the overall power supply reliability of the distribution end, and it is difficult for the power supply of the non-fault area to recover by itself. Summary of the invention

[0004] The purpose of the present invention is to provide an overcurrent protection method and system for an isolated DC / DC converter, so as to solve the problem that when a short circuit fault occurs in a subsequent power supply area, the existing overcurrent protection method of the isolated DC / DC converter will cause the overall power supply of the distribution end to be interrupted, thereby reducing the power supply reliability and making it difficult for the power supply in the non-fault area to recover automatically.

[0005] In order to solve the above technical problems, the present invention provides an overcurrent protection method for an isolated DC / DC converter, comprising the following steps:

[0006] S1: When an overcurrent is detected in the output current of the isolated DC / DC converter, a control signal for driving the converter to operate is blocked to control the converter to suspend operation. After a set time, the control signal is unlocked to control the converter to continue to operate, and the output current of the converter is continuously detected to determine whether an overcurrent occurs.

[0007] S2: Repeat S1, and when the output current of the converter is detected to be overcurrent for a set number of consecutive times, control the converter to stop running; the set number of times is greater than or equal to 2.

[0008] Furthermore, when an overcurrent is detected in the output current of the isolated DC / DC converter, the method for blocking the control signal used to drive the converter to operate includes: when an overcurrent is detected in the output current of the converter, an overcurrent signal generated according to the sampling output result of the sampling circuit is sent to the control end of the converter, and after receiving the overcurrent signal, the control end latches the overcurrent signal to continuously trigger the blocking signal during the latching of the overcurrent signal, and the blocking signal is used to block the control signal used to drive the converter to operate during the triggered period.

[0009] Furthermore, the setting time has a value range of 5ms to 10ms.

[0010] Furthermore, the set number of times is greater than or equal to 7.

[0011] Furthermore, the method of unlocking the control signal includes: generating an unlocking signal, wherein the unlocking signal clears the overcurrent signal to stop triggering the blocking signal.

[0012] Furthermore, during the process of performing step S1, the operation instruction corresponding to the converter is maintained valid; the method of controlling the converter to stop operating includes: controlling the operation instruction corresponding to the converter to be invalid.

[0013] Beneficial effect: The present invention provides a new overcurrent protection method for an isolated DC / DC converter. When an overcurrent is detected in the output current of the isolated DC / DC converter, the method blocks the control signal used to drive the converter to operate so as to control the converter to suspend operation. After a set time, the control signal is unlocked to control the converter to continue to operate. The method detects whether the output current of the isolated DC / DC converter is overcurrent again to detect whether the fault of the subsequent stage exists. If an overcurrent is still detected, the fault still exists at this time, and the process of blocking the control signal for driving the converter to operate is repeated. After a set time, the control signal is unlocked. When the output current of the above-mentioned converter is detected to be overcurrent for a set number of consecutive times, it indicates that a serious short-circuit fault occurs in the subsequent stage, and the fault is difficult to be removed, so the converter is controlled to stop operating. The set number is greater than or equal to 2. This is equivalent to not directly performing the fault removal when an overcurrent is detected. The DC / DC converter does not perform a shutdown operation due to a fault, but suspends the output of the DC / DC converter to try to wait for the short-circuit fault causing the overcurrent to disappear or be removed. After a period of time, the output of the DC / DC converter is restored to transmit power to the subsequent power supply area. At the same time, it is determined whether the short-circuit fault still exists. If it still exists, the above-mentioned suspension and recovery process is repeated to operate in an interval output method; if the short-circuit fault does not exist during the interval output process, the DC / DC converter switches to normal operation to ensure the self-recovery of power supply in the non-fault area. If the current still does not return to normal after several consecutive interval outputs, it means that the short-circuit fault in the subsequent stage is relatively serious and cannot be processed in a short time. Only in this case is the converter truly controlled to shut down, thereby ensuring the safety of the converter itself as much as possible and reducing the impact on power transmission to the subsequent power supply area, thereby greatly improving the reliability of the overall power supply at the distribution end, making the power supply system more stable, and at the same time facilitating the self-recovery of power supply in the non-fault area.

[0014] The present invention also provides an overcurrent protection system for an isolated DC / DC converter, comprising a processor, wherein the processor is used to execute computer program instructions to implement the steps of the overcurrent protection method for the isolated DC / DC converter.

[0015] The overcurrent protection system of the isolated DC / DC converter can achieve the same beneficial effects as the overcurrent protection method of the isolated DC / DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a main circuit topology diagram of an isolated DC / DC converter in an embodiment of an overcurrent protection method for an isolated DC / DC converter of the present invention;

[0017] Figure 2 1 is a control principle diagram of overcurrent protection of an isolated DC / DC converter in an embodiment of an overcurrent protection method for an isolated DC / DC converter of the present invention;

[0018] Figure 3 is a flow chart of an overcurrent protection method for an isolated DC / DC converter in an embodiment of the overcurrent protection method for an isolated DC / DC converter of the present invention;

[0019] Figure 4a It is an example diagram of a PWM output timing waveform under the control of the overcurrent protection method for the isolated DC / DC converter in the embodiment of the overcurrent protection method for the isolated DC / DC converter of the present invention when an overcurrent occurs in the output current of the isolated DC / DC converter;

[0020] Figure 4b It is an example diagram of a PWM output timing waveform under the control of the overcurrent protection method for the isolated DC / DC converter in the embodiment of the overcurrent protection method for the isolated DC / DC converter of the present invention when the output current of the isolated DC / DC converter has multiple consecutive overcurrents;

[0021] Figure 5 It is a test waveform diagram of the PWM output of the driving circuit when the output current of the simulated converter is overcurrent in the embodiment of the overcurrent protection method of the isolated DC / DC converter of the present invention;

[0022] Figure 6 It is a test waveform diagram of the PWM pulse signal output by the drive circuit and the output current and voltage of the isolated DC / DC converter in the embodiment of the overcurrent protection method of the isolated DC / DC converter of the present invention. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0024] Overcurrent protection method embodiment of isolated DC / DC converter

[0025] This embodiment provides a technical solution for an overcurrent protection method of an isolated DC / DC converter, the method comprising the following steps:

[0026] S1: When an overcurrent is detected in the output current of the isolated DC / DC converter, the control signal used to drive the converter to operate is blocked to control the converter to suspend operation. After a set time, the control signal is unlocked to control the converter to continue to operate and continue to detect whether the output current of the converter is overcurrent;

[0027] S2: Repeat S1. When the output current of the converter is detected to be overcurrent for a set number of consecutive times, the converter is controlled to stop running; the set number of times is greater than or equal to 2.

[0028] The method is equivalent to not directly performing a fault shutdown operation when an overcurrent is detected, but suspending the output of the DC / DC converter to try to wait for the short-circuit fault causing the overcurrent to disappear or be removed, and then restoring the output of the DC / DC converter after a period of time to transmit power to the subsequent power supply area, and at the same time judging whether the short-circuit fault still exists, if it still exists, repeating the above-mentioned pause and recovery process, and operating in an interval output method; if the short-circuit fault does not exist during the interval output process, the DC / DC converter switches to normal operation to ensure the self-recovery of power supply in the non-fault area, if the current still does not return to normal after several consecutive interval outputs, it means that the short-circuit fault in the subsequent stage is relatively serious and cannot be processed in a short time. Only in this case is the converter truly controlled to shut down, thereby minimizing the impact on power transmission to the subsequent power supply area while ensuring the safety of the converter itself as much as possible, thereby greatly improving the reliability of the overall power supply at the distribution end, making the power supply system more stable, and at the same time facilitating the self-recovery of power supply in the non-fault area.

[0029] The main circuit topology of the isolated DC / DC converter used in this embodiment is shown in FIG. Figure 1 As shown, the front stage of the converter adopts a symmetrical full-bridge LLC resonant converter, which can ensure the consistency of bidirectional operation. During bidirectional operation, it has the same excellent soft switching characteristics as the LLC resonant converter. Secondly, compared with the asymmetric design, it reduces the design difficulty of the resonant converter; the back stage of the converter adopts a three-phase interleaved parallel Buck-Boost topology structure, which can widen the range of the converter output voltage and reduce the ripple of the converter output current.

[0030] The control principle diagram of the overcurrent protection of the isolated DC / DC converter is as follows Figure 2 As shown, the sampling circuit, control circuit and drive circuit of the converter jointly control the main circuit of the isolated DC / DC converter, wherein the sampling circuit is used to complete the sampling, processing and transmission of the output voltage and current signals of the converter, wherein the output voltage sampling collects the voltage signal of the output port of the converter through the resistor voltage divider circuit, then amplifies the signal through the signal amplification circuit, and then filters the signal through the filter circuit, and finally outputs the signal to the control circuit; the current sampling uses the Hall current sensor to collect the current of the main circuit, and then the sensor will output a corresponding voltage signal, and this voltage signal is output to the control circuit after voltage following and filtering.

[0031] In this embodiment, the control signal for driving the converter to operate is a PWM pulse signal output by the drive circuit to the BUCK-BOOST circuit side of the converter, and the locking signal (PWM_Lock) is a locking pulse signal (PWM_Lock) for locking the control signal for driving the converter to operate during the triggered period, that is, for locking the PWM pulse signal output to the BUCK-BOOST circuit side of the converter during the triggered period.

[0032] The control circuit (also called the control end) is used to control the interval output of the PWM pulse signal sent to the drive circuit after receiving the overcurrent signal (I_Over) generated according to the sampling output result of the sampling circuit, and stop sending the PWM pulse signal to the drive circuit after receiving the overcurrent signal for a set number of consecutive times; the drive circuit is used to receive the PWM pulse signal from the control circuit, convert the level of the PWM pulse signal and output it to the converter BUCK-BOOST circuit side (i.e., the switch tube of the converter power main circuit), so as to drive the converter to operate. It can be seen that in this embodiment, the locking signal (PWM_Lock) blocks the control signal used to drive the converter to operate during the triggering period by indirectly controlling the blocking of the PWM pulse signal sent to the drive circuit. In other embodiments, the locking signal (PWM_Lock) can also directly block the PWM pulse signal output by the drive circuit to the converter BUCK-BOOST circuit side during the triggering period.

[0033] The flowchart of the overcurrent protection method of the isolated DC / DC converter is as follows Figure 3 As shown below, combined Figure 3 The method is described in detail:

[0034] S1: When an overcurrent is detected in the output current of the isolated DC / DC converter, the control signal used to drive the converter to operate is blocked to control the converter to suspend operation. After a set time, the control signal is unlocked to control the converter to continue operating, and continue to detect whether the output current of the converter is overcurrent; in this embodiment, the set time ranges from 5ms to 10ms.

[0035] Among them, the DC / DC converter on the DC distribution side generally operates in a voltage source mode, and the overcurrent protection method of the isolated DC / DC converter is also applicable in other operating modes; when an output current of the operating isolated DC / DC converter is detected to be overcurrent, the method of blocking the control signal used to drive the converter to operate includes: when an overcurrent is detected in the output current of the converter, an overcurrent signal generated according to the current sampling output result of the sampling circuit is sent to the control end of the converter (in this embodiment, the control end is also called a control circuit), and after receiving the overcurrent signal, the control end latches the overcurrent signal to continuously trigger the blocking signal during the latching of the overcurrent signal, and the blocking signal is used to block the control signal used to drive the converter to operate during the triggered period.

[0036] The method of unlocking the control signal used to drive the converter to operate includes: generating an unlock signal (PWM_Unlock), which is used to clear the overcurrent signal to stop triggering the blocking signal used to block the control signal used to drive the converter to operate during the triggered period, that is, stop blocking the PWM pulse signal output to the converter BUCK-BOOST circuit side.

[0037] Wherein, during the process of performing step S1, the operation instruction (Run) corresponding to the converter is maintained valid; the manner of controlling the converter to stop running includes: controlling the operation instruction (Run) corresponding to the converter to be invalid.

[0038] S2: Repeat S1. When the output current of the converter is detected to be overcurrent for a set number of consecutive times, the converter is controlled to stop running. The set number of times is greater than or equal to 2. In this embodiment, the set number of times is greater than or equal to 7. Specifically, the set number of times is 7.

[0039] When an overcurrent occurs in the output current of the isolated DC / DC converter, an example of the PWM output timing waveform under the control of the overcurrent protection method of the isolated DC / DC converter is shown in the figure below: Figure 4aAs shown, when the current sampling circuit detects that the output current of the isolated DC / DC converter is overcurrent, the overcurrent signal (I_Over) generated according to the sampling output result of the sampling circuit is sent to the control circuit. After receiving the overcurrent signal (I_Over), the control circuit first latches the overcurrent signal and sends a blocking signal (PWM_Lock) to the converter to block the PWM pulse signal output to the converter BUCK-BOOST circuit side. After a set time, an unlocking signal (PWM_Unlock) is sent to the converter. The unlocking signal is used to clear the overcurrent signal (I_Over) to stop triggering the blocking signal (PWM_Lock), that is, to stop blocking the PWM pulse signal output to the converter BUCK-BOOST circuit side. At this time, the control circuit continues to output PWM pulses to the converter BUCK-BOOST circuit side. Figure 2 It is found that after the PWM pulse continues to be output, no overcurrent signal (I_Over) appears again, which means that the short-circuit fault of the rear stage of the converter disappears or the fault area is cut off, and the converter continues to operate normally in the voltage source mode to supply power to the rear-stage power supply area normally; in the above process, the corresponding operation instruction (Run) of the converter is maintained valid all the time (in this embodiment, the corresponding operation instruction of the converter is maintained valid all the time by controlling the signal corresponding to Run to continuously output a high level).

[0040] When the output current of the isolated DC / DC converter is overcurrent multiple times continuously, the PWM output timing waveform under the control of the overcurrent protection method of the isolated DC / DC converter is shown in the figure below: Figure 4b As shown in the figure, after the PWM pulse signal for driving the converter to operate is output to the converter BUCK-BOOST circuit side for the first time, the control circuit receives the overcurrent signal (I_Over) generated according to the sampling result of the sampling circuit, and then continues to repeatedly output the above PWM pulse signal (i.e., first latching the overcurrent signal and sending a blocking signal (PWM_Lock) to the converter to block the PWM pulse signal output to the converter BUCK-BOOST circuit side, and after a set time, sending an unlocking signal (PWM_Unlock) to the converter for clearing the overcurrent signal (I_Over) to stop triggering the blocking signal (PWM_Lock); Figure 4bIn the case where the above-mentioned set number of times is 7, after the above-mentioned interval output PWM pulse signal process is repeated for 6 times (that is, after the overcurrent signal is received for 6 times in a row), when the control circuit receives the overcurrent signal (I_Over) again during the next interval output, the control circuit stops outputting the above-mentioned PWM pulse signal to the BUCK-BOOST circuit side of the converter, controls the converter to stop running, and the corresponding running instruction (Run) of the control converter is invalid at this time (in this embodiment, the corresponding running instruction of the control converter is invalidated by controlling the signal corresponding to Run to start to continuously output a low level), and the control circuit reports fault information at the same time, indicating that the subsequent fault is difficult to remove at this time.

[0041] The test waveform of the PWM output of the drive circuit when the output current of the simulated converter is overcurrent is as follows: Figure 5 As shown in the figure, in the actual test phase, a signal generator is used to send an overcurrent signal to the sampling circuit to simulate the overcurrent of the converter output current, and then the output of the drive circuit on the converter BUCK-BOOST circuit side is observed through an oscilloscope. Before the overcurrent signal is triggered, the PWM pulse signal output by the drive circuit for driving the converter operation is normally and continuously output ( Figure 5 After the overcurrent signal is triggered, the PWM pulse signal starts to be output at intervals. When the PWM pulse signal is output at intervals for 6 times continuously and overcurrent occurs again (the set number of times is 7), the isolated DC / DC converter stops and the PWM pulse signal is completely blocked.

[0042] In the actual test stage, a switch is connected to the output side of the converter to test the overcurrent protection method of the isolated DC / DC converter of this embodiment. When the switch is closed, a short circuit overcurrent occurs on the output side of the converter. When the switch is opened, the short circuit overcurrent is cut off. The closing and opening of the switch is controlled to simulate the short circuit fault occurring in the rear stage of the converter during the actual power supply process. The waveforms of the PWM pulse signal output by the drive circuit and the output current and voltage of the isolated DC / DC converter are shown in FIG. Figure 6 As shown, Figure 6 Medium dark blue wave index Figure 1 The Vds waveform of the middle and upper tube (Q9), the sky blue waveform indicates Figure 1 The waveform of Vgs of the middle upper tube (Q9). Before the first switch is closed, the PWM pulse signal output by the drive circuit to drive the converter to operate is normally and continuously output. The converter output voltage and current (output voltage corresponds to Figure 6 The purple waveform in the figure shows the output current corresponding to Figure 6The green waveform in the figure is normal. When the switch is closed, the converter output will have an instantaneous overcurrent. The PWM pulse signal will be output after a period of time. During this period, the output current can be controlled to be maintained within the limit to cooperate with the action of the subsequent protection device. The subsequent protection device can automatically cut off the fault through the software and hardware protection mechanism after the fault overcurrent. This protection device belongs to the prior art and will not be described in detail here. When the switch is disconnected, the converter output current will have an instantaneous overcurrent again (the instantaneous overcurrent occurs at this time because the transient state of using the switch to cut off the short-circuit fault will cause a spike in the output current, and this spike will trigger the overcurrent fault). Then the PWM pulse signal is output again after a period of time, and the overcurrent fault is triggered by the PWM pulse signal. Figure 6 It was found that the output voltage and current of the subsequent converter returned to normal, and the converter continued to operate normally. Therefore, after actual testing, the overcurrent protection method can transmit power to the converter's subsequent stage under the premise of ensuring the safety of the converter when the converter output current is overcurrent. Only when the converter safety is seriously affected by overcurrent (that is, the converter output current is detected to be overcurrent after multiple consecutive interval outputs), the converter is controlled to shut down, so that the power supply is interrupted to protect the safety of the converter itself.

[0043] Embodiment of overcurrent protection system for isolated DC / DC converter

[0044] This embodiment provides a technical solution for an overcurrent protection system for an isolated DC / DC converter. The system includes a processor, which is used to execute computer program instructions to implement the steps of an overcurrent protection method for an isolated DC / DC converter.

[0045] Since the specific implementation process and principle of the overcurrent protection system of the isolated DC / DC converter of this embodiment have been described in detail in the embodiment of the overcurrent protection method of the isolated DC / DC converter, they will not be repeated here.

Claims

1. An overcurrent protection method for an isolated DC / DC converter, characterized in that: The steps include: S1: When an overcurrent is detected in the output current of the isolated DC / DC converter, a control signal for driving the converter to operate is blocked to control the converter to suspend operation. After a set time, the control signal is unlocked to control the converter to continue to operate, and the output current of the converter is continuously detected to determine whether an overcurrent occurs. S2: Repeat S1, and when the output current of the converter is detected to be overcurrent for a set number of consecutive times, control the converter to stop running; the set number of times is greater than or equal to 2.

2. The overcurrent protection method for an isolated DC / DC converter according to claim 1, characterized in that: When an overcurrent is detected in the output current of the isolated DC / DC converter, the method of blocking the control signal used to drive the converter to operate includes: when an overcurrent is detected in the output current of the converter, an overcurrent signal generated according to the sampling output result of the sampling circuit is sent to the control end of the converter, so that the control end latches the overcurrent signal after receiving the overcurrent signal to continuously trigger the blocking signal during the latching of the overcurrent signal, and the blocking signal is used to block the control signal used to drive the converter to operate during the triggered period.

3. The overcurrent protection method for an isolated DC / DC converter according to claim 1 or 2, characterized in that: The setting time has a value range of 5ms to 10ms.

4. The overcurrent protection method for an isolated DC / DC converter according to claim 1 or 2, characterized in that: The set number of times is greater than or equal to 7.

5. The overcurrent protection method for an isolated DC / DC converter according to claim 2, characterized in that: The method of unlocking the control signal includes: generating an unlock signal, wherein the unlock signal is used to clear the overcurrent signal to stop triggering the blocking signal.

6. The overcurrent protection method for an isolated DC / DC converter according to claim 1 or 2, characterized in that: During step S1, the operation instruction corresponding to the converter is maintained valid; The method of controlling the converter to stop running includes: controlling the running instruction corresponding to the converter to be invalid.

7. An overcurrent protection system for an isolated DC / DC converter, comprising a processor, characterized in that: The processor is used to execute computer program instructions to implement the steps of the overcurrent protection method for an isolated DC / DC converter according to any one of claims 1 to 6.

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