Online capacitance value detection circuit and method for energy storage capacitor

Abstract

The invention relates to the technical field of electronics, in particular to an on-line capacitance detection circuit and method for an energy storage capacitor. An undervoltage detection circuit is connected with a charging circuit, the charging circuit is connected with a discharging circuit, the discharging circuit is connected with a voltage following circuit, and the voltage following circuit is connected with a two-pole same-proportion voltage division circuit and a pulse output circuit; the pulse output circuit is connected with the sampling protection circuit, and the pulse output circuit is connected with the two-pole same-proportion voltage division circuit; the two-pole same-proportion voltage division circuit is connected with the sampling protection circuit; the under-voltage detection circuit is connected with the discharge circuit and the pulse generation circuit, and the pulse generation circuit is connected with the sampling hold circuit. The method has the advantages that detection is automatically started when the power module is powered down or overhauled, detection is directly completed through a hardware detection circuit, online detection is achieved, and shutdown or manual intervention is not needed; an analog circuit (a pulse output circuit, a two-pole same-proportion voltage division circuit, a sampling hold circuit and the like) is adopted to realize detection.

Description

Technical Field

[0001] This invention relates to the field of electronic technology, and in particular to an online capacitance detection circuit and method for energy storage capacitors. Background Technology

[0002] Energy storage capacitors play a crucial role in modern power electronic equipment. Their primary function is to store electrical energy and release it rapidly when needed to meet the instantaneous power demands of the equipment. For example, in a bypass trigger board, the energy storage capacitor provides sufficient energy to trigger the thyristor, ensuring that the bypass switch can close quickly and reliably.

[0003] Although energy storage capacitors play a crucial role in power electronic systems, their lifespan is typically shorter than that of other semiconductor devices, such as thyristors and freewheeling diodes. The capacitance of energy storage capacitors gradually decreases over time, affecting their energy storage capacity and energy release efficiency. When the capacitance drops to a certain level, it may cause bypass switches to fail to close properly, thus impacting the normal operation of the entire power system. Therefore, monitoring the capacitance of energy storage capacitors is essential.

[0004] However, during normal operation of the bypass trigger board, the voltage of the energy storage capacitor is stable, making capacitance measurement difficult. Current measurement methods typically require the bypass trigger board to be powered down during power module maintenance, and the results are then reported to the controller. This method is not only time-consuming and labor-intensive, but also fails to monitor the capacitor's health status in real time, making it difficult to meet the high reliability and efficiency requirements of modern power electronic systems. Summary of the Invention

[0005] The purpose of this invention is to provide an online capacitance detection circuit and method for energy storage capacitors. By using a detection circuit for the capacitance of energy storage capacitor C1, the signal width output by the detection circuit is directly proportional to the capacitance value of energy storage capacitor C1, thereby realizing the detection of the capacitance value of energy storage capacitor C1. This solves the problems of traditional capacitor detection methods being unable to be performed online and relying on software.

[0006] To achieve the above objectives, the present invention provides the following technical solution: An online capacitance detection circuit for energy storage capacitors includes a charging circuit, a discharging circuit, a voltage follower circuit, an undervoltage detection circuit, a pulse generation circuit, a two-stage proportional voltage divider circuit, a sample and hold circuit, and a pulse output circuit. The input terminal of the undervoltage detection circuit is connected to the input terminal of the charging circuit, the output terminal of the charging circuit is connected to the input terminal of the discharging circuit, the second output terminal of the discharging circuit is connected to the input terminal of the voltage follower circuit, the output terminal of the voltage follower circuit is connected to the first input terminal of the two-stage proportional voltage divider circuit and the first input terminal of the pulse output circuit, the output terminal of the pulse output circuit is connected to the sample protection circuit, and the second input terminal of the pulse output circuit is connected to the second output terminal of the two-stage proportional voltage divider circuit. Both input terminals one and two of the two-pole proportional voltage divider circuit are connected to the sampling protection circuit, and output terminal one of the two-pole proportional voltage divider circuit is connected to the sampling protection circuit. The output of the undervoltage detection circuit is connected to the output of the discharge circuit and the input of the pulse generation circuit, respectively. The output of the pulse generation circuit is connected to the sample and hold circuit.

[0007] The two-stage proportional voltage divider circuit includes voltage divider circuit one and voltage divider circuit two. The input terminal of voltage divider circuit one is connected to the output terminal of the voltage follower circuit, the input terminal one of the pulse output circuit, and the sampling protection circuit, respectively. The output terminal of voltage divider circuit one is connected to the sampling protection circuit. The input terminal of voltage divider circuit two is connected to the sampling protection circuit, and the output terminal of voltage divider circuit two is connected to the input terminal two of the pulse output circuit.

[0008] Voltage divider circuit one includes resistors R7 and R8, and operational amplifier chip IC4. Resistors R7 and R8 are connected in series, and the connection point between resistors R7 and R8 is connected to the non-inverting input terminal of operational amplifier chip IC4. The other end of resistor R7 is connected to the input terminal of voltage divider circuit one. The input terminal of voltage divider circuit one is also connected to a sample-and-hold circuit. The other end of resistor R8 is grounded. The output terminal of operational amplifier chip IC4 is connected to the output terminal of voltage divider circuit one. Voltage divider circuit two includes resistors R9 and R10, and operational amplifier chip IC5. Resistors R9 and R10 are connected in series, and the connection point between resistors R9 and R10 is connected to the output terminal of voltage divider circuit two. The non-inverting input terminal of operational amplifier chip IC5 is connected to the input terminal of voltage divider circuit two. The other end of resistor R9 is connected to the output terminal of operational amplifier chip IC5, and the other end of resistor R10 is grounded.

[0009] The pulse output circuit includes resistor R11, capacitor C4, XOR gate chip IC7, and comparator chip IC6. Resistor R11 and capacitor C4 are connected in series. The negative input terminal of comparator chip IC6 is connected to input terminal one of the pulse output circuit, and the positive input terminal of comparator chip IC6 is connected to input terminal two of the pulse output circuit. The output terminal of comparator chip IC6 is connected to the first input terminal of XOR gate chip IC7. The connection point of resistor R11 and capacitor C4 is connected to the second input terminal of XOR gate chip IC7. The other end of resistor R11 is connected to the first input terminal of XOR gate chip IC7, and the other end of capacitor C4 is grounded. The output terminal of XOR gate chip IC7 is connected to the output terminal of the pulse output circuit.

[0010] The sample-and-hold circuit includes a comparator chip IC8, a sample-and-hold capacitor C3, and an opto-isolator switch Q2. One output terminal of the opto-isolator switch Q2 is connected to the output terminal of the first voltage divider circuit. The other output terminal of the opto-isolator switch Q2 is connected to the negative input terminal of the comparator chip IC8, one end of the sample-and-hold capacitor C3, and the input terminal of the second voltage divider circuit. The cathode of the light-emitting diode of the opto-isolator switch Q2 and the other end of the sample-and-hold capacitor C3 are grounded. The anode of the LED in opto-isolating switch Q2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the output terminal of the pulse generation circuit; the anode of the LED in opto-isolating switch Q2 is connected to the cathode of diode D3, and the anode of diode D3 is connected to the output terminal of the pulse output circuit. The positive input terminal of comparator IC8 is connected to the input terminal of voltage divider circuit one; the output terminal of comparator IC8 is used to connect to a counter or MCU chip.

[0011] The voltage follower circuit includes an operational amplifier chip IC1. The non-inverting input terminal of the operational amplifier chip IC1 is connected to the input terminal of the voltage follower circuit, and the output terminal of the operational amplifier chip IC1 is connected to the output terminal of the voltage follower circuit. The discharge circuit includes an opto-isolating switch Q1, resistors R2 and R3. Resistors R2 and R3 are connected in series. The other end of resistor R2 is connected to one output terminal of opto-isolating switch Q1. The other output terminal of opto-isolating switch Q1 is connected to the input terminal of the discharge circuit. The cathode of the light-emitting diode of opto-isolating switch Q1 and the other end of resistor R3 are grounded. The anode of the light-emitting diode of opto-isolating switch Q1 is connected to one output terminal of the discharge circuit. The connection point between resistors R2 and R3 is connected to the other output terminal of the discharge circuit. The charging circuit includes a voltage source DC1, a reverse polarity protection diode D1, a charging resistor R1, and an energy storage capacitor C1 connected in series. One end of the energy storage capacitor C1 is connected to the output terminal of the charging circuit, and the other end of the voltage source DC1 and the other end of the energy storage capacitor C1 are grounded. The connection between the anode of the reverse polarity protection diode D1 and the voltage source DC1 is connected to the input terminal of the charging circuit.

[0012] The undervoltage detection circuit includes sampling resistor R4, sampling resistor R5, and comparator chip IC2. Sampling resistors R4 and R5 are connected in series. The connection point between sampling resistors R4 and R5 is connected to the inverting input terminal of comparator chip IC2. The non-inverting input terminal of comparator chip IC2 is connected to the reference voltage source vref. The other end of sampling resistor R4 is connected to the input terminal of the undervoltage detection circuit. The other end of sampling resistor R5 is grounded. The output terminal of comparator chip IC2 is connected to the output terminal of the undervoltage detection circuit. The pulse generation circuit includes a resistor R6, a filter capacitor C2, and an XOR gate chip IC3. The resistor R6 and the filter capacitor C2 are connected in series. The other end of the resistor R6 is connected to the input terminal of the pulse generation circuit. The other end of the resistor R6 is also connected to the first input terminal of the XOR gate chip IC3. The connection point of the resistor R6 and the filter capacitor C2 is connected to the second input terminal of the XOR gate chip IC3. The filter capacitor C2 is grounded. The output terminal of the XOR gate chip IC3 is connected to the output terminal of the pulse generation circuit.

[0013] A method for online capacitance detection of an energy storage capacitor, wherein the energy storage capacitor C1 is the object of detection, and a voltage source DC1 participates in the online capacitance detection of the energy storage capacitor C1, serving as the start-up input signal for the detection circuit, specifically including: The undervoltage state of voltage source DC1 is detected by an undervoltage detection circuit; When an undervoltage condition is detected, the control discharge circuit discharges the energy storage capacitor C1. The voltage signal of the energy storage capacitor C1 is output through the voltage follower circuit; The voltage ratio of the energy storage capacitor C1 is output by voltage divider circuit 1 and voltage divider circuit 2 respectively. Under the control of the narrow pulse output by the pulse generation circuit, the sample and hold circuit stores the output voltage ratio of the operational amplifier chip IC1; The sample-and-hold circuit compares the output voltage of the operational amplifier chip IC1 with the voltage of the sample-and-hold capacitor C3, and outputs a square wave signal. The period of the square wave signal reflects the capacitance value of the energy storage capacitor C1. The capacitance value of the energy storage capacitor C1 is cyclically detected through a pulse output circuit.

[0014] The undervoltage detection circuit detects the undervoltage state of voltage source DC1. When the voltage division value of sampling resistor R4 and sampling resistor R5 is lower than that of reference voltage source Vref, the comparator chip IC2 outputs a high level. The pulse generation circuit outputs a narrow pulse through the filter resistor R6, the filter capacitor C2 and the XOR gate chip IC3. The pulse is briefly turned on by the opto-isolation switch Q2, so that the sampling and holding capacitor C3 stores the proportional value of the output voltage of the operational amplifier chip IC1 at this time.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Automatically starts detection when the power module is powered off or under maintenance, requiring no additional operation and not affecting the normal operation of the equipment. The detection is completed directly through the hardware detection circuit, avoiding the cumbersome process of traditional offline detection. There is no need to remove capacitors, realizing true online detection without shutdown or manual intervention; it does not rely on software algorithms, but uses analog circuits (pulse output circuit, two-pole proportional voltage divider circuit, sample and hold circuit, etc.) to realize detection, avoiding the delay or misjudgment caused by software calculation; 2. A two-stage proportional voltage divider circuit is adopted, such as cascading a 0.9-fold voltage divider (0.9 × 0.9 = 0.81), to accurately capture the exponential decay trend of the energy storage capacitor voltage and ensure that the detection logic is consistent with the physical characteristics of the capacitor; the reference voltage is updated in real time through opto-isolation switches and sampling holding capacitors to avoid errors caused by traditional fixed thresholds. 3. The output signal of the detection circuit directly reflects the capacitance value of the energy storage capacitor. The square wave period is proportional to the capacitance value. The signal width of the output of the comparison chip IC8 directly corresponds to the capacitance value of the energy storage capacitor C1. External circuits (such as counters or PLCs) can easily read the signal without complicated conversion. It supports cyclic detection and triggers sampling multiple times during the continuous discharge of the capacitor, improving data reliability. 4. The detection circuit has a simple structure and uses common components such as operational amplifiers, comparators, resistors, and capacitors, without the need for high-precision ADCs or dedicated chips; it adopts a modular design: it can be directly embedded into existing bypass trigger boards and other equipment without significant modifications to the original circuit. 5. It can provide early warning of capacitor aging, detect abnormalities when the capacitance of energy storage capacitor C1 drops to the critical point, avoid failure of bypass trigger board and other equipment due to the failure of energy storage capacitor C1, reduce unexpected downtime, and realize predictive maintenance through periodic automatic detection by pulse output circuit, thereby reducing the risk of sudden failure. Attached Figure Description

[0016] Figure 1 This is a circuit diagram for online capacitance detection of energy storage capacitors. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0018] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods. Example 1

[0019] See Figure 1 An online capacitance detection circuit for energy storage capacitors includes a charging circuit, a discharging circuit, a voltage follower circuit, an undervoltage detection circuit, a pulse generation circuit, a two-stage proportional voltage divider circuit, a sample-and-hold circuit, and a pulse output circuit. The input terminal of the undervoltage detection circuit is connected to the input terminal of the charging circuit. The output terminal of the charging circuit is connected to the input terminal of the discharging circuit. The second output terminal of the discharging circuit is connected to the input terminal of the voltage follower circuit. The output terminal of the voltage follower circuit is connected to both the first input terminal of the two-stage proportional voltage divider circuit and the first input terminal of the pulse output circuit. The output terminal of the pulse output circuit is connected to a sample protection circuit. The second input terminal of the pulse output circuit is connected to the second output terminal of the two-stage proportional voltage divider circuit. Both the first and second input terminals of the two-stage proportional voltage divider circuit are connected to the sample protection circuit. The first output terminal of the two-stage proportional voltage divider circuit is connected to the sample protection circuit. The output terminal of the undervoltage detection circuit is connected to both the first output terminal of the discharging circuit and the input terminal of the pulse generation circuit. The output terminal of the pulse generation circuit is connected to the sample-and-hold circuit.

[0020] The charging circuit includes a voltage source DC1, a reverse polarity protection diode D1, a charging resistor R1, and an energy storage capacitor C1 connected in series. One end of the energy storage capacitor C1 is connected to the output terminal of the charging circuit, and the other end of the voltage source DC1 and the other end of the energy storage capacitor C1 are grounded. The connection point between the anode of the reverse polarity protection diode D1 and the voltage source DC1 is connected to the input terminal of the charging circuit. The discharging circuit includes an opto-isolating switch Q1, resistors R2 and R3, connected in series. The other end of resistor R2 is connected to one output terminal of opto-isolating switch Q1, and the other output terminal of opto-isolating switch Q1 is connected to the input terminal of the discharging circuit. The cathode of the LED in opto-isolating switch Q1 and the other end of resistor R3 are grounded. The anode of the LED in opto-isolating switch Q1 is connected to one output terminal of the discharging circuit, and the connection point between resistors R2 and R3 is connected to the other output terminal of the discharging circuit. The voltage follower circuit includes an operational amplifier chip IC1. The non-inverting input terminal of operational amplifier chip IC1 is connected to the input terminal of the voltage follower circuit, and the output terminal of operational amplifier chip IC1 is connected to the output terminal of the voltage follower circuit. The two-stage proportional voltage divider circuit includes voltage divider circuit one and voltage divider circuit two. The input terminal of voltage divider circuit one is connected to the output terminal of the voltage follower circuit, the input terminal one of the pulse output circuit, and the sampling protection circuit, respectively. The output terminal of voltage divider circuit one is connected to the sampling protection circuit. The input terminal of voltage divider circuit two is connected to the sampling protection circuit, and the output terminal of voltage divider circuit two is connected to the input terminal two of the pulse output circuit. Voltage divider circuit one includes resistors R7 and R8, and operational amplifier chip IC4. Resistors R7 and R8 are connected in series, and the connection point between resistors R7 and R8 is connected to the non-inverting input terminal of operational amplifier chip IC4. The other end of resistor R7 is connected to the input terminal of voltage divider circuit one, which is also connected to the sample-and-hold circuit. The other end of resistor R8 is grounded. The output terminal of operational amplifier chip IC4 is connected to the output terminal of voltage divider circuit one. Voltage divider circuit two includes resistors R9 and R10, and operational amplifier chip IC5. Resistors R9 and R10 are connected in series. The connection point between resistors R9 and R10 is connected to the output terminal of voltage divider circuit two. The non-inverting input terminal of operational amplifier chip IC5 is connected to the input terminal of voltage divider circuit two. The other end of resistor R9 is connected to the output terminal of operational amplifier chip IC5, and the other end of resistor R10 is grounded.The sample-and-hold circuit includes a comparator chip IC8, a sample-and-hold capacitor C3, and an opto-isolator switch Q2. One output terminal of the opto-isolator switch Q2 is connected to the output terminal of voltage divider circuit one. Another output terminal of the opto-isolator switch Q2 is connected to the negative input terminal of comparator chip IC8, one end of sample-and-hold capacitor C3, and the input terminal of voltage divider circuit two. The cathode of the LED in opto-isolator switch Q2 and the other end of sample-and-hold capacitor C3 are grounded. The anode of the LED in opto-isolator switch Q2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the output terminal of pulse generation circuit. The anode of the LED in opto-isolator switch Q2 is connected to the cathode of diode D3, and the anode of diode D3 is connected to the output terminal of pulse output circuit. The positive input terminal of comparator chip IC8 is connected to the input terminal of voltage divider circuit one. The output terminal of comparator chip IC8 is used to connect to a counter or MCU chip.

[0021] The undervoltage detection circuit includes sampling resistors R4 and R5, and comparator chip IC2. Sampling resistors R4 and R5 are connected in series. The connection point between sampling resistors R4 and R5 is connected to the inverting input of comparator chip IC2. The non-inverting input of comparator chip IC2 is connected to the reference voltage source vref. The other end of sampling resistor R4 is connected to the input of the undervoltage detection circuit, and the other end of sampling resistor R5 is grounded. The output of comparator chip IC2 is connected to the output of the undervoltage detection circuit. The pulse generation circuit includes resistor R6, filter capacitor C2, and XOR gate chip IC3. The XOR gate chip IC3 is model SN74LV1T86. Resistor R6 and filter capacitor C2 are connected in series. The other end of resistor R6 is connected to the input of the pulse generation circuit and also to the first input of XOR gate chip IC3. The connection point between resistor R6 and filter capacitor C2 is connected to the second input of XOR gate chip IC3. Filter capacitor C2 is grounded. The output of XOR gate chip IC3 is connected to the output of the pulse generation circuit. The pulse output circuit includes resistor R11, capacitor C4, XOR gate chip IC7, and comparator chip IC6. The comparator chip IC6 is either LM211 or LM2903. Resistor R11 and capacitor C4 are connected in series. The negative input terminal of comparator chip IC6 is connected to input terminal one of the pulse output circuit, and the positive input terminal of comparator chip IC6 is connected to input terminal two of the pulse output circuit. The output terminal of comparator chip IC6 is connected to the first input terminal of XOR gate chip IC7. The connection point of resistor R11 and capacitor C4 is connected to the second input terminal of XOR gate chip IC7. The other end of resistor R11 is connected to the first input terminal of XOR gate chip IC7, and the other end of capacitor C4 is grounded. The output terminal of XOR gate chip IC7 is connected to the output terminal of the pulse output circuit.

[0022] A method for online capacitance detection of energy storage capacitors, the details of which are as follows: The energy storage capacitor C1 is the object of detection in this invention. The voltage source DC1 also participates in the online capacitance detection of the energy storage capacitor, serving as the start-up input signal for the detection circuit. The power module is in a half-bridge or full-bridge topology, and the bypass switch is connected to the output port of the power module. When the power module fails and bypass is required, the energy storage capacitor C1 is a key component to ensure that the bypass trigger circuit effectively triggers the bypass switch to close.

[0023] During the power module power-down process, when the voltage division value of sampling resistors R4 and R5 is lower than the reference voltage source Vref, the comparator chip IC2 outputs a high level.

[0024] Working principle of photoelectric switch Q1: The primary side of photoelectric switch Q1 is a light-emitting diode (LED), and the secondary side is a MOSFET. When the LED emits light with an external power supply, the MOSFET on the secondary side conducts; when the LED does not emit light, the MOSFET on the secondary side is turned off. Comparator chip IC2 outputs a high level, controlling photoelectric switch Q1 to conduct. This causes the discharge circuit composed of resistors R2 and R3 connected in series to be connected in parallel across the energy storage capacitor C1, discharging the energy storage capacitor C1. The voltage divider circuit controlled by the photoelectric switch sends the sampled voltage to operational amplifier chip IC1. Operational amplifier chip IC1 forms a voltage follower circuit, outputting a signal that can provide feedback on the voltage of energy storage capacitor C1.

[0025] Voltage divider circuit one consists of resistors R7 and R8, and operational amplifier chip IC4. The output of voltage divider circuit one is 0.9 times the output voltage of operational amplifier chip IC1. Note: This example uses 0.9 times.

[0026] Voltage divider circuit two consists of resistors R9 and R10, and operational amplifier chip IC5. The output of voltage divider circuit two is 0.9 times the voltage of the sample-and-hold capacitor. Note: This example uses 0.9 times, which is consistent with the 0.9 times voltage of the voltage divider circuit consisting of resistors R7 and R8, and operational amplifier chip IC4.

[0027] The voltage signal output by the comparison chip IC2 is processed by a pulse generation circuit consisting of a filter resistor R6, a filter capacitor C2, and an XOR gate chip IC3. The output is a narrow pulse, which controls the primary diode of the opto-isolation switch Q2 to light up for a short time. This controls the secondary MOS to turn on, so that the sample-and-hold capacitor C3 stores 0.9 times the current output voltage of the operational amplifier chip IC1.

[0028] The non-inverting input of comparator IC8 is connected to the output of operational amplifier IC1, and the non-inverting input of comparator IC8 is connected to sample-and-hold capacitor C3.

[0029] The period of the output signal of the comparison chip IC8 can reflect the capacitance value of the energy storage capacitor C1. The principle is explained below: 1) After the XOR gate chip IC3 outputs a narrow pulse to turn on the photoelectric switch Q2, the sample holding capacitor C3 holds 0.9 times the initial voltage, and the comparator chip IC8 outputs high at this time; when the energy storage capacitor C1 starts to discharge to below 0.9 times the initial voltage, the comparator chip IC8 outputs low.

[0030] 2) When the voltage of the energy storage capacitor C1 drops to 0.81 times the initial voltage (i.e., 0.9 times the voltage divided by resistors R7 and R8, multiplied by 0.9 times the voltage divided by resistors R9 and R10), the output of comparator chip IC6 goes low. At this time, the circuit consisting of resistor R11, capacitor C4, and XOR gate chip IC7 outputs a narrow pulse, controlling the opto-isolation switch Q2 to turn on briefly. This causes the sampling and holding capacitor C3 to store the voltage value of 0.9 times the output voltage of operational amplifier chip IC1 at this time. The output of comparator chip IC8 then goes high again. As the voltage of the energy storage capacitor C1 continues to drop, the detection circuit continues to operate in a loop.

[0031] By comparing the width of the square wave high signal and the width of the square wave low signal output by chip IC8, which coincide with the time when the voltage of energy storage capacitor C1 drops by 10%, data proportional to the capacitance value of energy storage capacitor C1 can be obtained by detecting the period of the waveform of the output signal of IC8 through external circuit.

[0032] Design principle of diodes D2 and D3: The high level output of XOR gate chip IC3 and XOR gate chip IC7 can control the secondary side of the photoelectric switch to conduct. Similarly, when XOR gate chip IC3 outputs a high level and XOR gate chip IC7 outputs a low level, the secondary side of the photoelectric switch can also be controlled to conduct.

[0033] This invention automatically initiates detection when the power module is powered off or under maintenance, requiring no additional operation and not affecting normal equipment operation. Detection is completed directly through hardware detection circuitry, avoiding the cumbersome process of traditional offline detection. It eliminates the need to disassemble capacitors, achieving true online detection without downtime or manual intervention. It does not rely on software algorithms, employing analog circuitry (pulse output circuit, two-stage proportional voltage divider circuit, sample-and-hold circuit, etc.) for detection, avoiding delays or misjudgments caused by software calculations. The use of a two-stage proportional voltage divider circuit, such as through cascading a 0.9 voltage divider (0.9 × 0.9 = 0.81), accurately captures the exponential decay trend of the energy storage capacitor voltage, ensuring consistency between the detection logic and the capacitor's physical characteristics. The reference voltage is updated in real time through an opto-isolated switch and a sample-and-hold capacitor, avoiding errors caused by traditional fixed thresholds. The output signal of the detection circuit directly reflects the capacitance value of the energy storage capacitor. The square wave period is proportional to the capacitance value. The signal width of the comparator chip IC8 directly corresponds to the capacitance value of the energy storage capacitor C1. External circuits (such as counters or PLCs) can easily read the signal without complex conversions. It supports cyclic detection, triggering sampling multiple times during the continuous discharge of the capacitor to improve data reliability. The detection circuit has a simple structure, using common components such as operational amplifiers, comparators, resistors, and capacitors, eliminating the need for high-precision ADCs or dedicated chips. It adopts a modular design, directly embedding into existing bypass trigger boards and other equipment without significant modifications to the original circuitry. It can provide early warning of capacitor aging, detecting anomalies when the capacitance value of the energy storage capacitor C1 drops to a critical point, preventing failure of bypass trigger boards and other equipment due to C1 failure, reducing unexpected downtime. Regular automatic detection via pulse output circuit enables predictive maintenance, reducing the risk of sudden failures.

Claims

1. An online capacitance detection circuit for energy storage capacitors, characterized in that, It includes a charging circuit, a discharging circuit, a voltage follower circuit, an undervoltage detection circuit, a pulse generation circuit, a two-stage proportional voltage divider circuit, a sample and hold circuit, and a pulse output circuit. The input terminal of the undervoltage detection circuit is connected to the input terminal of the charging circuit. The output terminal of the charging circuit is connected to the input terminal of the discharging circuit. The second output terminal of the discharging circuit is connected to the input terminal of the voltage follower circuit. The output terminal of the voltage follower circuit is connected to the first input terminal of the two-stage proportional voltage divider circuit and the first input terminal of the pulse output circuit. The output terminal of the pulse output circuit is connected to the sample protection circuit. The second input terminal of the pulse output circuit is connected to the second output terminal of the two-stage proportional voltage divider circuit. Both input terminals one and two of the two-pole proportional voltage divider circuit are connected to the sampling protection circuit, and output terminal one of the two-pole proportional voltage divider circuit is connected to the sampling protection circuit. The output of the undervoltage detection circuit is connected to the output of the discharge circuit and the input of the pulse generation circuit, respectively. The output of the pulse generation circuit is connected to the sample and hold circuit.

2. The online capacitance detection circuit for energy storage capacitors according to claim 1, characterized in that, The aforementioned two-stage proportional voltage divider circuit includes a voltage divider circuit one and a voltage divider circuit two. The input terminal of voltage divider circuit one is connected to the output terminal of the voltage follower circuit, the input terminal one of the pulse output circuit, and the sampling protection circuit, respectively. The output terminal of voltage divider circuit one is connected to the sampling protection circuit. The input terminal of voltage divider circuit two is connected to the sampling protection circuit, and the output terminal of voltage divider circuit two is connected to the input terminal two of the pulse output circuit.

3. The online capacitance detection circuit for an energy storage capacitor according to claim 2, characterized in that, The voltage divider circuit includes resistors R7 and R8, and operational amplifier chip IC4. Resistors R7 and R8 are connected in series, and the connection point between resistors R7 and R8 is connected to the non-inverting input terminal of operational amplifier chip IC4. The other end of resistor R7 is connected to the input terminal of voltage divider circuit one. The input terminal of voltage divider circuit one is also connected to a sample-and-hold circuit. The other end of resistor R8 is grounded, and the output terminal of operational amplifier chip IC4 is connected to the output terminal of voltage divider circuit one. The voltage divider circuit two includes resistors R9 and R10, and operational amplifier chip IC5. Resistors R9 and R10 are connected in series. The connection point between resistors R9 and R10 is connected to the output terminal of the voltage divider circuit two. The non-inverting input terminal of operational amplifier chip IC5 is connected to the input terminal of the voltage divider circuit two. The other end of resistor R9 is connected to the output terminal of operational amplifier chip IC5, and the other end of resistor R10 is grounded.

4. The online capacitance detection circuit for an energy storage capacitor according to claim 1, characterized in that, The pulse output circuit includes a resistor R11, a capacitor C4, an XOR gate chip IC7, and a comparator chip IC6. The resistor R11 and capacitor C4 are connected in series. The negative input terminal of the comparator chip IC6 is connected to input terminal one of the pulse output circuit, and the positive input terminal of the comparator chip IC6 is connected to input terminal two of the pulse output circuit. The output terminal of the comparator chip IC6 is connected to the first input terminal of the XOR gate chip IC7. The connection point of the resistor R11 and capacitor C4 is connected to the second input terminal of the XOR gate chip IC7. The other end of the resistor R11 is connected to the first input terminal of the XOR gate chip IC7, and the other end of the capacitor C4 is grounded. The output terminal of the XOR gate chip IC7 is connected to the output terminal of the pulse output circuit.

5. The online capacitance detection circuit for an energy storage capacitor according to claim 1, characterized in that, The sample-and-hold circuit includes a comparator chip IC8, a sample-and-hold capacitor C3, and an opto-isolator switch Q2. One output terminal of the opto-isolator switch Q2 is connected to the output terminal of the first voltage divider circuit. The other output terminal of the opto-isolator switch Q2 is connected to the negative input terminal of the comparator chip IC8, one end of the sample-and-hold capacitor C3, and the input terminal of the second voltage divider circuit. The cathode of the light-emitting diode of the opto-isolator switch Q2 and the other end of the sample-and-hold capacitor C3 are grounded. The anode of the LED in opto-isolating switch Q2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the output terminal of the pulse generation circuit; the anode of the LED in opto-isolating switch Q2 is connected to the cathode of diode D3, and the anode of diode D3 is connected to the output terminal of the pulse output circuit. The positive input terminal of comparator IC8 is connected to the input terminal of voltage divider circuit one; the output terminal of comparator IC8 is used to connect to a counter or MCU chip.

6. The online capacitance detection circuit for an energy storage capacitor according to claim 1, characterized in that, The voltage follower circuit includes an operational amplifier chip IC1, the non-inverting input terminal of the operational amplifier chip IC1 is connected to the input terminal of the voltage follower circuit, and the output terminal of the operational amplifier chip IC1 is connected to the output terminal of the voltage follower circuit. The discharge circuit includes an opto-isolating switch Q1, resistors R2 and R3. Resistors R2 and R3 are connected in series. The other end of resistor R2 is connected to one output terminal of opto-isolating switch Q1. The other output terminal of opto-isolating switch Q1 is connected to the input terminal of the discharge circuit. The cathode of the light-emitting diode of opto-isolating switch Q1 and the other end of resistor R3 are grounded. The anode of the light-emitting diode of opto-isolating switch Q1 is connected to one output terminal of the discharge circuit. The connection point between resistors R2 and R3 is connected to the other output terminal of the discharge circuit. The charging circuit includes a voltage source DC1, a reverse polarity protection diode D1, a charging resistor R1, and an energy storage capacitor C1 connected in series. One end of the energy storage capacitor C1 is connected to the output terminal of the charging circuit, and the other end of the voltage source DC1 and the other end of the energy storage capacitor C1 are grounded. The connection between the anode of the reverse polarity protection diode D1 and the voltage source DC1 is connected to the input terminal of the charging circuit.

7. The online capacitance detection circuit for an energy storage capacitor according to claim 1, characterized in that, The undervoltage detection circuit includes sampling resistor R4, sampling resistor R5, and comparator chip IC2. Sampling resistors R4 and R5 are connected in series. The connection point between sampling resistors R4 and R5 is connected to the inverting input terminal of comparator chip IC2. The non-inverting input terminal of comparator chip IC2 is connected to the reference voltage source vref. The other end of sampling resistor R4 is connected to the input terminal of the undervoltage detection circuit. The other end of sampling resistor R5 is grounded. The output terminal of comparator chip IC2 is connected to the output terminal of the undervoltage detection circuit. The pulse generation circuit includes a resistor R6, a filter capacitor C2, and an XOR gate chip IC3. The resistor R6 and the filter capacitor C2 are connected in series. The other end of the resistor R6 is connected to the input terminal of the pulse generation circuit. The other end of the resistor R6 is also connected to the first input terminal of the XOR gate chip IC3. The connection point of the resistor R6 and the filter capacitor C2 is connected to the second input terminal of the XOR gate chip IC3. The filter capacitor C2 is grounded. The output terminal of the XOR gate chip IC3 is connected to the output terminal of the pulse generation circuit.

8. A method for online capacitance detection of an energy storage capacitor for implementing the circuit described in any one of claims 1-7, characterized in that, The energy storage capacitor C1 is the object of detection. Voltage source DC1 participates in the online capacitance detection of energy storage capacitor C1, serving as the start-up input signal for the detection circuit, specifically including: The undervoltage state of voltage source DC1 is detected by an undervoltage detection circuit; When an undervoltage condition is detected, the control discharge circuit discharges the energy storage capacitor C1. The voltage signal of the energy storage capacitor C1 is output through the voltage follower circuit; The voltage ratio of the energy storage capacitor C1 is output by voltage divider circuit 1 and voltage divider circuit 2 respectively. Under the control of the narrow pulse output by the pulse generation circuit, the sample and hold circuit stores the output voltage ratio of the operational amplifier chip IC1; The sample-and-hold circuit compares the output voltage of the operational amplifier chip IC1 with the voltage of the sample-and-hold capacitor C3, and outputs a square wave signal. The period of the square wave signal reflects the capacitance value of the energy storage capacitor C1. The capacitance value of the energy storage capacitor C1 is cyclically detected through a pulse output circuit.

9. The method for online capacitance detection of an energy storage capacitor according to claim 8, characterized in that, The undervoltage detection circuit detects the undervoltage state of voltage source DC1 by means of the comparator chip IC2 outputting a high level when the voltage division value of sampling resistor R4 and sampling resistor R5 is lower than that of reference voltage source Vref.

10. The method for online capacitance detection of an energy storage capacitor according to claim 8, characterized in that, The pulse generation circuit outputs a narrow pulse through the filter resistor R6, the filter capacitor C2 and the XOR gate chip IC3. The pulse is briefly turned on by the opto-isolation switch Q2, so that the sampling and holding capacitor C3 stores the proportional value of the output voltage of the operational amplifier chip IC1 at this time.

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