A Fault Diagnosis Method for Single-ended Forward Converter Based on Output Voltage Differential Value

Abstract

The present invention discloses a single-ended forward converter fault diagnosis method based on output voltage differential value. The method is based on the single-ended forward converter, including a switch device and a magnetic reset circuit on the primary side and an output rectifier diode D1, a freewheeling diode D2, an inductor and a capacitor on the secondary side. The method includes the following steps: obtaining the relationship between the output voltage and the duty cycle according to a small signal model corresponding to the single-ended forward converter, and calculating the differential value of the output voltage; judging the open-short circuit fault of the switch device and / or the open-short circuit fault of the capacitor according to the differential value; and also calculating the second-order differential value of the output voltage, and judging the open-short circuit fault of the freewheeling diode according to the second-order differential value.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a single-ended forward converter fault diagnosis method based on an output voltage differential value. Background Art

[0002] At present, DC / DC converters are widely used in various DC power conversion occasions, promoting the development of DC. In modular DC-DC converters, in order to ensure that each series module has an independent ground, most of them choose isolated topology. Among them, the single-ended forward converter has the advantages of small size, low loss, and high efficiency, and is more suitable for some special scenarios, such as the multi-bus level power supply system of all-electric unmanned aircraft. However, this kind of occasion has extremely high requirements for the reliability of system power supply, so it is particularly important to improve the reliability of the single-ended forward converter.

[0003] Regardless of the application and power level, the primary-side semiconductor power switch and output capacitor are listed as the main fault sources of the converter. At the same time, the normal operation of the freewheeling diode during the off cycle also greatly affects the operating state of the single-ended forward converter. The above three types of components cause the vast majority of the total faults faced by this type of converter. In order to improve the robustness and availability of the converter, it is necessary to analyze the fault characteristics and mechanisms of the switch device, capacitor, and freewheeling diode, and propose corresponding accurate fault diagnosis strategies on this basis. There are six types of fault types for the three types of components, open and short circuit, and there are situations where the fault characteristics are not obvious. If there is a lack of various fault protection designs, the module may face the situation of running with faults, causing the fault to spread and eventually paralyze the entire system; at the same time, there are situations where the fault characteristics are similar. If there is a lack of fault characteristic differentiation design, it is difficult to quickly and accurately determine the fault location and fault type during fault maintenance, which will consume more manpower and material resources during maintenance and a long maintenance cycle.

[0004] In the prior art, there is a DC / DC converter fault diagnosis method that starts from the diode voltage and combines the drive signal to design a set of diagnostic processes, which are implemented through hardware circuits. The fault identification of the switch tube and the diode can be completed, and it is suitable for non-isolated DC-DC topologies. However, the circuit structure to implement the above method is relatively complex, the execution is relatively cumbersome, and the debugging workload is huge. Other technicians have also conducted detailed research on the fault diagnosis of IPOP type Boost converters, using input current The slope of is used as the diagnosis basis, considering the interleaved parallel connection and the different duty cycles. The slope characteristics of the boost converter are analyzed, and the differences between normal working conditions and any switch tube open circuit fault are analyzed to achieve fault diagnosis. However, the diagnostic algorithm is too complicated, and the method is only implemented on the dSPACE platform, which is still far from practical application. Some researchers have proposed sampling the inductor current of the boost converter once every half switching cycle, and comparing the three adjacent sampling values. The size relationship of the three values ​​under normal, open and short circuit conditions has different characteristics, and fault diagnosis can be achieved based on this. However, this method uses the inductor current as the diagnostic quantity, but the instantaneous value sampling of the inductor current is easily disturbed by the load, and the sampling error will lead to the problem of misjudgment of faults. , which requires high sampling accuracy; there is also a method in the prior art for a phase-shifted full-bridge converter, which proposes to monitor the DC side current through a pulse transformer and observe the ratio of the peak value and the integral value of the DC side current as a basis for diagnosis. However, the diagnosis time is long and a large amount of fault data needs to be accumulated. In actual applications, changes in operating conditions and other parameters will cause the method to fail. Another method is for a three-level Boost converter, which selects two output capacitor voltages for maximum power point tracking as diagnostic signals. The difference between the two can reflect the open circuit fault of the two switching tubes, but due to the slow change of the capacitor voltage, the diagnostic speed is not ideal. Summary of the invention

[0005] In view of this, the present invention provides a single-ended forward converter fault diagnosis method based on output voltage differential value, so as to at least solve the problem of low availability and robustness of converter fault diagnosis methods in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A single-ended forward converter fault diagnosis method based on output voltage differential value, based on a single-ended forward converter, including a primary side switch device, a magnetic reset circuit and a secondary side output rectifier diode D 1 , freewheeling diode D 2 , inductors and capacitors, comprising the following steps:

[0008] The relationship between the output voltage and the duty cycle is obtained according to the small signal model corresponding to the single-ended forward converter, and the differential value of the output voltage is calculated;

[0009] The open-short circuit fault of the switch device and / or the open-short circuit fault of the capacitor is determined according to the differential value, wherein:

[0010] The open-short circuit fault diagnosis method of the switching device includes:

[0011] The digital signal PWME corresponding to the differential value is compared with the PWM signal. When the PWME signal and the PWM signal change asynchronously, it is judged as a switch device failure, and the output Error_M signal is 1:

[0012] The PWME signal is inverted and used as the input of the D flip-flop. Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, an open circuit fault occurs in the switch device.

[0013] The PWME signal is used as the input of the D flip-flop, and Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, a short circuit fault occurs in the switch device;

[0014] The open-short circuit fault diagnosis methods of capacitors include:

[0015] If a positive peak appears in the output voltage differential waveform, the capacitor is open circuit fault;

[0016] If a negative spike appears in the output voltage differential waveform, the capacitor is short-circuited.

[0017] Preferably, the differential value is converted into a corresponding digital signal PWME through a voltage comparator, and 1 is output when the differential value is greater than a preset voltage threshold Vth, and 0 is output when the differential value is less than Vth.

[0018] Preferably, in order to eliminate the transmission delay between the PWME signal and the PWM signal, after comparing the PWME signal with the PWM signal, the comparison result signal Error_MB is input into a delay elimination circuit for delay elimination, and an Error_M signal is output;

[0019] The delay elimination circuit includes an operational amplifier and a voltage comparator, the output end of the operational amplifier is connected to the inverting input end of the voltage comparator, the positive and negative input ends of the operational amplifier and the positive input end of the voltage comparator are respectively connected to a voltage source, a capacitor is arranged between the inverting input end and the output end of the operational amplifier, a resistor is arranged between the inverting input end of the operational amplifier and its voltage source, and the output end of the voltage comparator outputs an Error_M signal.

[0020] Preferably, the open-short circuit fault diagnosis of the capacitor is performed by a voltage comparator and an RS latch, wherein:

[0021] For open circuit fault of capacitor:

[0022] The differential value is input into the positive input terminal of the voltage comparator, and compared with the preset positive upper threshold value Vth_H input through the inverting input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is greater than the preset positive upper threshold value Vth_H, the capacitor is open circuit fault;

[0023] For capacitor short circuit fault:

[0024] The differential value is input into the inverting input terminal of the voltage comparator and compared with the preset negative lower limit threshold Vth_L input through the positive input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is less than the preset negative lower limit threshold Vth_L, the capacitor is short-circuited.

[0025] A single-ended forward converter fault diagnosis method based on output voltage differential value, based on a single-ended forward converter, including a primary side switch device, a magnetic reset circuit and a secondary side output rectifier diode D 1 , freewheeling diode D 2 , inductors and capacitors, comprising the following steps:

[0026] The relationship between the output voltage and the duty cycle is obtained according to the small signal model corresponding to the single-ended forward converter, and the second-order differential value of the output voltage is calculated. The open-short circuit fault of the freewheeling diode is judged by the second-order differential value. The specific contents include:

[0027] If the duration of the second-order differential value being negative during the shutdown period is less than the negative duration threshold corresponding to the normal state, the freewheeling diode is open-circuit fault;

[0028] If the second-order differential value is always negative during the on and off cycles, the freewheeling diode is short-circuited.

[0029] Preferably, the freewheeling diode open circuit fault diagnosis is performed by a voltage comparator, a counter and an RS latch, wherein:

[0030] Input the second-order differential value to the positive input terminal of the first voltage comparator and the inverting input terminal of the second voltage comparator respectively, and compare them with the reference voltage Vth_0 of the inverting input terminal of the corresponding voltage comparator respectively, and input the comparison results of the first voltage comparator and the second voltage comparator to the first counter and the second counter respectively, wherein the first counter and the second counter are both used to obtain the duration of the second-order differential value being in a negative value;

[0031] The counting result is input into the first holder and the second holder respectively, and the first holder and the second holder are used to hold the maximum value of the counting result in the switching cycle. The outputs of the first holder and the second holder are respectively input into the positive input terminals of the third voltage comparator and the fourth voltage comparator. The negative time upper and lower limit thresholds Vth_1 and Vth_2 of the second-order differential value in the cycle under normal conditions are respectively input into the negative input terminals of the third voltage comparator and the fourth voltage comparator. In the third voltage comparator and the fourth voltage comparator, when the positive input terminal value is greater than the negative input terminal value, 1 is output, otherwise 0 is output, and the corresponding output results are input into the selection switch;

[0032] When the output of the fourth voltage comparator is not 0, the output of the third voltage comparator is input to the third counter, and when it is 0, the constant value 1 is input to the third counter as the output;

[0033] The third counter is used to obtain the 0-level duration in the input value, and input the counting result to the positive input terminal of the fifth voltage comparator. The comparison result after comparison with Vth_3 input at the inverting input terminal of the fifth voltage comparator is input to the RS latch, wherein Vth_3 is the critical threshold of the 0-level duration when the freewheeling diode open circuit fault occurs. If it is greater than Vth_3, it is judged that the freewheeling diode is open circuit fault.

[0034] Preferably, the freewheeling diode short-circuit fault diagnosis is performed by a freewheeling diode short-circuit fault diagnosis circuit, wherein:

[0035] The second-order differential value is input into the positive input terminal of the first voltage comparator, and compared with the reference voltage Vth_0 input through the inverting input terminal of the first voltage comparator. The output result of the first voltage comparator is input into the counter. The counter is used to obtain the duration of the second-order differential value being negative. The counter inputs the counting result into the positive input terminal of the second voltage comparator, and compares it with Vth_1 input through the inverting input terminal of the second voltage comparator. Vth_1 is the negative duration threshold of the second-order differential value in the normal state within the cycle, and the comparison result is input into the RS latch.

[0036] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a single-ended forward converter fault diagnosis method based on output voltage differential value, which has the following beneficial effects:

[0037] 1. The present invention proposes a simple and accurate method for diagnosing multiple fault types of a single-ended forward converter. The fault diagnosis strategy uses the differential value and the secondary differential value of the output voltage to quickly identify and locate the position of the faulty device, which can improve the reliable operation capability and certain robustness of the single-ended forward converter.

[0038] 2. Compared with the existing single-ended forward converter fault diagnosis method, the method of the present invention has higher fault diagnosis accuracy and the technical capability to diagnose switching device faults within one switching cycle at the fastest; at the same time, the method only uses the control quantity collected in the closed-loop control - the output voltage, and does not need to add additional sensors or detection circuits to collect additional fault characteristic values, which greatly reduces the system cost and volume.

[0039] 3. The present invention can identify six fault types using only a single fault characteristic value, which is more efficient and more practical than existing fault diagnosis methods.

[0040] 4. The present invention designs a detection circuit for fault diagnosis, which has simple control and topology, and is easy to install and configure on existing equipment, with low hardware cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 A typical single-ended forward converter topology structure disclosed in an embodiment of the present invention;

[0043] Figure 2 A small signal model of a single-ended forward converter disclosed in an embodiment of the present invention;

[0044] Figure 3 A delay elimination circuit disclosed in an embodiment of the present invention;

[0045] Figure 4 A switch device open circuit and short circuit fault diagnosis circuit disclosed in an embodiment of the present invention;

[0046] Figure 5 A capacitor open circuit and short circuit fault diagnosis circuit disclosed in an embodiment of the present invention;

[0047] Figure 6 A freewheeling diode open circuit fault diagnosis circuit disclosed in an embodiment of the present invention;

[0048] Figure 7 The invention discloses a freewheeling diode short-circuit fault diagnosis circuit. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The present invention provides a single-ended forward converter fault diagnosis method based on output voltage differential value, based on the single-ended forward converter, such as Figure 1 As shown, it includes the switch device on the primary side, the magnetic reset circuit and the output rectifier diode D on the secondary side. 1 , freewheeling diode D 2 , inductors and capacitors, comprising the following steps:

[0051] The relationship between the output voltage and the duty cycle is obtained according to the small signal model corresponding to the single-ended forward converter, and the differential value of the output voltage is calculated;

[0052] The open-short circuit fault of the switch device and / or the open-short circuit fault of the capacitor is determined according to the differential value, wherein:

[0053] The open-short circuit fault diagnosis method of the switching device includes:

[0054] The digital signal PWME corresponding to the differential value is compared with the PWM signal. When the PWME signal and the PWM signal change asynchronously, it is judged as a switch device failure, and the output Error_M signal is 1:

[0055] The PWME signal is inverted and used as the input of the D flip-flop. Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, an open circuit fault occurs in the switch device.

[0056] The PWME signal is used as the input of the D flip-flop, and Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, a short circuit fault occurs in the switch device;

[0057] The open-short circuit fault diagnosis methods of capacitors include:

[0058] If a positive peak appears in the output voltage differential waveform, the capacitor is open circuit fault;

[0059] If a negative spike appears in the output voltage differential waveform, the capacitor is short-circuited.

[0060] It should be noted that:

[0061] The small signal model of a single-ended forward converter is as follows: Figure 2 As shown. Where D is the duty cycle of the module in steady state; is the disturbance of the module duty cycle; is the input voltage of the module in steady state; is the input voltage disturbance of the module; is the output inductor current of each module in steady state; is the output inductor current disturbance of the module; is the original secondary turns ratio; is the output inductor current disturbance of the module. ,and The disturbance is relatively small, so the relationship between the output voltage and the duty cycle can be obtained by simplifying the small signal model:

[0062] (1)

[0063] Through the inverse Laplace transform, we can get:

[0064] (2)

[0065] It can be seen that the differential of the output voltage reflects the change of the duty cycle, and then after being processed by the comparator, the 0 and 1 levels can be obtained, which is the PWME signal. During normal operation, it changes synchronously with the PWM signal, and when a fault occurs, it presents different states according to different fault types. At the same time, the second-order differential of the output voltage can reflect the severity of the fluctuation of the output voltage, and can also be used to determine the fault type.

[0066] Analysis of the principles of open and short circuit failures of switching devices:

[0067] The PWME signal is XORed with the PWM signal, and the output signal is set to Error_M. Under normal working conditions, the PWME signal and the PWM signal are basically synchronized, so they always maintain a 0 level.

[0068] (1) Open circuit fault:

[0069] When the switch is open, the output voltage gradually decreases to 0, then , at this time, the PWME signal is 0; while the PWM signal duty cycle gradually increases, and finally always remains at 1. At this time, the PWM signal and the PWME signal are no longer synchronized, and the Error_M signal jumps from 0 to 1, and is input to the D flip-flop as a clock pulse for rising edge triggering, while PWME is used as the input of the D flip-flop through the inverter. If the output of the D flip-flop is 1, it means that the switch device has an open circuit fault.

[0070] (2) Short circuit fault:

[0071] When the switch tube is short-circuited, the output voltage gradually increases to , then , at this time, the PWME signal is 1; and the PWM signal duty cycle gradually decreases, and finally remains at 0. At this time, the PWM signal and the PWME signal are no longer synchronized, and the Error_M signal jumps from 0 to 1, and is input as a clock pulse to the D flip-flop for rising edge triggering, and PWME is used as the input of the D flip-flop. If the output of the D flip-flop is 1, it means that a short circuit fault occurs in the switching device.

[0072] Analysis of the principle of capacitor open and short circuit failure:

[0073] Whether the switch is on or off, the inductor current remains in the same direction, while the capacitor current changes with The on-time is positive and the off-time is negative.

[0074] Capacitor open and short circuit fault diagnosis circuit Figure 5 shown.

[0075] (1) Open circuit fault:

[0076] If an open circuit fault occurs in the capacitor during the conduction cycle, the inductor current cannot change suddenly, and the capacitor current suddenly disappears, so the load current increases and the output voltage increases instantaneously. A positive spike appears; if an open circuit fault occurs in the capacitor during the shutdown cycle, the inductor current cannot change suddenly, and the capacitor current suddenly disappears, so the load current decreases and the output voltage decreases instantaneously. When a negative spike appears and the conduction cycle is entered again, the output voltage will oscillate greatly due to the lack of the capacitor's voltage stabilization function. Since it is still in the same cycle, the rapidity of fault diagnosis is still maintained, so the same positive spike recognition circuit can be used to obtain the fault signal.

[0077] (2) Short circuit fault:

[0078] Since the capacitor is short-circuited, the output voltage becomes 0 instantly. When a very large negative spike appears, a negative spike recognition circuit can be used to obtain a fault signal. By setting a negative lower limit threshold, misdiagnosis of the capacitor open circuit fault in the above-mentioned off cycle can be avoided.

[0079] In order to further implement the above technical solution, the differential value is converted into a corresponding digital signal PWME through a voltage comparator, and 1 is output when the differential value is greater than a preset voltage threshold Vth, and 0 is output when the differential value is less than Vth.

[0080] In order to further implement the above technical solution, in order to eliminate the transmission delay between the PWME signal and the PWM signal, after comparing the PWME signal with the PWM signal, the comparison result signal Error_MB is input into the delay elimination circuit for delay elimination, and the Error_M signal is output;

[0081] The delay elimination circuit includes an operational amplifier and a voltage comparator, the output end of the operational amplifier is connected to the inverting input end of the voltage comparator, the positive and negative input ends of the operational amplifier and the positive input end of the voltage comparator are respectively connected to a voltage source, a capacitor is arranged between the inverting input end and the output end of the operational amplifier, a resistor is arranged between the inverting input end of the operational amplifier and its voltage source, and the output end of the voltage comparator outputs an Error_M signal.

[0082] It should be noted that:

[0083] Due to the transmission delay between the PWME signal and the PWM signal, the Error_M signal will have an erroneous transition. Figure 3 The circuit shown in the figure is eliminated. The switch device open and short circuit fault diagnosis circuit with delay elimination circuit is shown in the figure. Figure 4shown.

[0084] In order to further implement the above technical solution, the open-short circuit fault diagnosis of the capacitor is performed through a voltage comparator and an RS latch, wherein:

[0085] For open circuit fault of capacitor:

[0086] The differential value is input into the positive input terminal of the voltage comparator, and compared with the preset positive upper threshold value Vth_H input through the inverting input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is greater than the preset positive upper threshold value Vth_H, the capacitor is open circuit fault;

[0087] For capacitor short circuit fault:

[0088] The differential value is input into the inverting input terminal of the voltage comparator and compared with the preset negative lower limit threshold Vth_L input through the positive input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is less than the preset negative lower limit threshold Vth_L, the capacitor is short-circuited.

[0089] A single-ended forward converter fault diagnosis method based on output voltage differential value, based on a single-ended forward converter, including a primary side switch device, a magnetic reset circuit and a secondary side output rectifier diode D 1 , freewheeling diode D 2 , inductors and capacitors, comprising the following steps:

[0090] The relationship between the output voltage and the duty cycle is obtained according to the small signal model corresponding to the single-ended forward converter, and the second-order differential value of the output voltage is calculated. The open-short circuit fault of the freewheeling diode is judged by the second-order differential value. The specific contents include:

[0091] If the duration of the second-order differential value being negative during the shutdown period is less than the negative duration threshold corresponding to the normal state, the freewheeling diode is open-circuit fault;

[0092] If the second-order differential value is always negative during the on and off cycles, the freewheeling diode is short-circuited.

[0093] It should be noted that:

[0094] Analysis of the open and short circuit fault principles of the freewheeling diode:

[0095] When the freewheeling diode is open or short-circuited, its fault characteristics are similar to those of the switch tube being open, so it does not cause misdiagnosis. Processing cannot meet the rapidity of fault detection, and In normal operation, it also changes periodically in synchronization with the PWM signal, and the fault characteristics are obvious, so the second-order differential value of the output voltage is used. A counter circuit can be designed to When it is a negative value, it counts, and Cleared to zero when positive.

[0096] (1) Open circuit fault:

[0097] When the freewheeling diode is open, it means that there is no freewheeling circuit during the off cycle. At this time, the inductor discharge speed during the off cycle is faster than the normal freewheeling state and will drop to 0. According to the formula, at this time The rate of change of is greater than that of the normal continuous flow state, that is When the inductor discharges completely, that is, the inductor current is 0, the output voltage is maintained by the capacitor. Negative values ​​become smaller, and becomes positive, then within the entire cycle The time in negative value becomes shorter. Therefore, the counter value is less than the counting threshold value in normal operation during the fault. At this time, the maximum value of the counter in each cycle is maintained by the keeper, and the output is 1 after comparison by the comparator, indicating that the freewheeling diode is open circuit fault. Diagnostic circuit is as follows Figure 6 shown.

[0098] (2) Short circuit fault:

[0099] When the freewheeling diode is short-circuited, the circuit is always in the freewheeling state, the inductor continues to discharge, and the output voltage enters the oscillation state. Continuously decreasing, is always negative, and a fault characteristic different from other fault states appears. If it is always negative, the count value during the fault is greater than the count threshold during normal operation. At this time, the comparator output is 1, indicating that the freewheeling diode is short-circuited. Figure 7 shown.

[0100] In order to further implement the above technical solution, the freewheeling diode open circuit fault diagnosis is performed through a voltage comparator, a counter and an RS latch, wherein:

[0101] Input the second-order differential value to the positive input terminal of the first voltage comparator and the inverting input terminal of the second voltage comparator respectively, and compare them with the reference voltage Vth_0 of the inverting input terminal of the corresponding voltage comparator respectively, and input the comparison results of the first voltage comparator and the second voltage comparator to the first counter and the second counter respectively, wherein the first counter and the second counter are both used to obtain the duration of the second-order differential value being in a negative value;

[0102] The counting result is input into the first holder and the second holder respectively, and the first holder and the second holder are used to hold the maximum value of the counting result in the switching cycle. The outputs of the first holder and the second holder are respectively input into the positive input terminals of the third voltage comparator and the fourth voltage comparator. The negative time upper and lower limit thresholds Vth_1 and Vth_2 of the second-order differential value in the cycle under normal conditions are respectively input into the negative input terminals of the third voltage comparator and the fourth voltage comparator. In the third voltage comparator and the fourth voltage comparator, when the positive input terminal value is greater than the negative input terminal value, 1 is output, otherwise 0 is output, and the corresponding output results are input into the selection switch;

[0103] When the output of the fourth voltage comparator is not 0, the output of the third voltage comparator is input to the third counter, and when it is 0, the constant value 1 is input to the third counter as the output;

[0104] The third counter is used to obtain the 0-level duration in the input value, and input the counting result to the positive input terminal of the fifth voltage comparator. The comparison result after comparison with Vth_3 input at the inverting input terminal of the fifth voltage comparator is input to the RS latch, wherein Vth_3 is the critical threshold of the 0-level duration when the freewheeling diode open circuit fault occurs. If it is greater than Vth_3, it is judged that the freewheeling diode is open circuit fault.

[0105] In order to further implement the above technical solution, a freewheeling diode short-circuit fault diagnosis circuit is used to diagnose the freewheeling diode short-circuit fault, wherein:

[0106] The second-order differential value is input into the positive input terminal of the first voltage comparator, and compared with the reference voltage Vth_0 input through the inverting input terminal of the first voltage comparator. The output result of the first voltage comparator is input into the counter. The counter is used to obtain the duration of the second-order differential value being negative. The counter inputs the counting result into the positive input terminal of the second voltage comparator, and compares it with Vth_1 input through the inverting input terminal of the second voltage comparator. Vth_1 is the negative duration threshold of the second-order differential value in the normal state within the cycle, and the comparison result is input into the RS latch.

[0107] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A single-ended forward converter fault diagnosis method based on output voltage differential value, based on a single-ended forward converter, including a primary switch device, a magnetic reset circuit and a secondary output rectifier diode D1, a freewheeling diode D2, an inductor and a capacitor, characterized in that: The following steps are involved: The relationship between the output voltage and the duty cycle of the PWM signal is obtained according to the small signal model corresponding to the single-ended forward converter, and the differential value of the output voltage is calculated; The open-short circuit fault of the switch device and / or the open-short circuit fault of the capacitor is determined according to the differential value, wherein: The open-short circuit fault diagnosis method of the switching device includes: The digital signal PWME corresponding to the differential value is compared with the PWM signal. When the PWME signal and the PWM signal change asynchronously, it is judged as a switch device failure, and the output Error_M signal is 1: The PWME signal is inverted and used as the input of the D flip-flop. Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, an open circuit fault occurs in the switch device. The PWME signal is used as the input of the D flip-flop, and Error_M is used as the clock pulse input to the D flip-flop for rising edge triggering. If the output of the D flip-flop is 1, a short circuit fault occurs in the switch device; The open-short circuit fault diagnosis methods of capacitors include: If a positive peak appears in the output voltage differential waveform, the capacitor is open circuit fault; If a negative spike appears in the output voltage differential waveform, the capacitor is short-circuited.

2. The single-ended forward converter fault diagnosis method based on output voltage differential value according to claim 1, characterized in that: The differential value is converted into a corresponding digital signal PWME through a voltage comparator. When the differential value is greater than a preset voltage threshold Vth, 1 is output, and when it is less than Vth, 0 is output.

3. The single-ended forward converter fault diagnosis method based on output voltage differential value according to claim 1, characterized in that: In order to eliminate the transmission delay between the PWME signal and the PWM signal, after comparing the PWME signal with the PWM signal, the comparison result signal Error_MB is input into the delay elimination circuit for delay elimination, and the Error_M signal is output; The delay elimination circuit includes an operational amplifier and a voltage comparator, the output end of the operational amplifier is connected to the inverting input end of the voltage comparator, the positive and negative input ends of the operational amplifier and the positive input end of the voltage comparator are respectively connected to a voltage source, a capacitor is arranged between the inverting input end and the output end of the operational amplifier, a resistor is arranged between the inverting input end of the operational amplifier and its voltage source, and the output end of the voltage comparator outputs an Error_M signal.

4. The single-ended forward converter fault diagnosis method based on output voltage differential value according to claim 1, characterized in that: The open-short circuit fault diagnosis of the capacitor is performed through the voltage comparator and RS latch, where: For open circuit fault of capacitor: The differential value is input into the positive input terminal of the voltage comparator, and compared with the preset positive upper threshold value Vth_H input through the inverting input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is greater than the preset positive upper threshold value Vth_H, the capacitor is open circuit fault; For capacitor short circuit fault: The differential value is input into the inverting input terminal of the voltage comparator and compared with the preset negative lower limit threshold Vth_L input through the positive input terminal of the voltage comparator, and the output result of the voltage comparator is input into the set terminal of the RS latch; when the differential value is less than the preset negative lower limit threshold Vth_L, the capacitor is short-circuited.

5. A single-ended forward converter fault diagnosis method based on output voltage differential value, based on a single-ended forward converter, including a primary switch device, a magnetic reset circuit and a secondary output rectifier diode D1, a freewheeling diode D2, an inductor and a capacitor, characterized in that: The following steps are involved: According to the small signal model corresponding to the single-ended forward converter, the relationship between the output voltage and the duty cycle of the PWM signal is obtained, and the second-order differential value of the output voltage is calculated. The open-short circuit fault of the freewheeling diode is judged by the second-order differential value. The specific contents include: If the duration of the second-order differential value being negative during the shutdown period is less than the negative duration threshold corresponding to the normal state, the freewheeling diode is open-circuit fault; If the second-order differential value is always negative during the on and off cycles, the freewheeling diode is short-circuited.

6. The single-ended forward converter fault diagnosis method based on output voltage differential value according to claim 5, characterized in that: The freewheeling diode open circuit fault diagnosis is performed through a voltage comparator, a counter, and an RS latch, where: Input the second-order differential value to the positive input terminal of the first voltage comparator and the inverting input terminal of the second voltage comparator respectively, and compare them with the reference voltage Vth_0 of the inverting input terminal of the corresponding voltage comparator respectively, and input the comparison results of the first voltage comparator and the second voltage comparator to the first counter and the second counter respectively, wherein the first counter and the second counter are both used to obtain the duration of the second-order differential value being in a negative value; The counting result is input into the first holder and the second holder respectively, and the first holder and the second holder are used to hold the maximum value of the counting result in the switching cycle. The outputs of the first holder and the second holder are respectively input into the positive input terminals of the third voltage comparator and the fourth voltage comparator. The negative time upper and lower limit thresholds Vth_1 and Vth_2 of the second-order differential value in the cycle under normal conditions are respectively input into the negative input terminals of the third voltage comparator and the fourth voltage comparator. In the third voltage comparator and the fourth voltage comparator, when the positive input terminal value is greater than the negative input terminal value, 1 is output, otherwise 0 is output, and the corresponding output results are input into the selection switch; When the output of the fourth voltage comparator is not 0, the output of the third voltage comparator is input to the third counter, and when it is 0, the constant value 1 is input to the third counter as the output; The third counter is used to obtain the 0-level duration in the input value, and input the counting result to the positive input terminal of the fifth voltage comparator. The comparison result after comparison with Vth_3 input at the inverting input terminal of the fifth voltage comparator is input to the RS latch, wherein Vth_3 is the critical threshold of the 0-level duration when the freewheeling diode open circuit fault occurs. If it is greater than Vth_3, it is judged that the freewheeling diode is open circuit fault.

7. The single-ended forward converter fault diagnosis method based on output voltage differential value according to claim 5, characterized in that: The freewheeling diode short circuit fault diagnosis is performed through a voltage comparator, a counter and an RS latch, where: The second-order differential value is input into the positive input terminal of the first voltage comparator, and compared with the reference voltage Vth_0 input through the inverting input terminal of the first voltage comparator. The output result of the first voltage comparator is input into the counter. The counter is used to obtain the duration of the second-order differential value being negative. The counter inputs the counting result into the positive input terminal of the second voltage comparator, and compares it with Vth_1 input through the inverting input terminal of the second voltage comparator. If it is greater than Vth_1, it is judged that the freewheeling diode is short-circuited. Vth_1 is the negative duration threshold of the second-order differential value in the cycle under normal conditions, and the comparison result is input into the RS latch.

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