Method for Predicting Capacitance Parameters Based on Online Monitoring Technology of Pulse Capacitors

Abstract

The present invention discloses a method for predicting capacitance parameters based on on-line monitoring technology of pulse capacitors, which is used in the technical field of pulse capacitors. By on-line monitoring the voltage and current waveforms during the discharge of pulse capacitors, a model is established to calculate the inverse peak coefficient k, and a function is established where the damping ratio ξ is a function of the inverse peak coefficient k, and the time T<subgt;m< / subgt> when the voltage of the capacitor discharge first crosses the zero point is a function of the damping ratio ξ. The time T<subgt;m< / subgt> when the voltage of the lossless capacitor discharge first crosses the zero point is deduced and compared with the measured time T<subgt;s< / subgt> when the voltage of the capacitor discharge first crosses the zero point to determine the remaining capacitance C of the capacitor at this time of discharge. The concept of the capacitor failure constant λ is proposed to predict the capacitance parameters and monitor the remaining capacitance in real time. It is used to solve the problem of whether the pulse capacitor fails after repeated discharges and form a reliable calculation scheme for the failure capacitance parameters.

Description

Technical Field

[0001] The present invention is applied to the technical field of pulse capacitors, and particularly relates to a method for predicting capacitance parameters based on online monitoring technology of pulse capacitors. Background Art

[0002] Pulse capacitors are the most widely used components in pulse power technology and an important part of pulse discharge equipment. They can store energy in the form of a relatively low voltage change rate and then quickly discharge to the load in an extremely short time. With the development and research of pulse capacitors in recent years, pulse power technology has also developed rapidly and has been widely applied in many fields, such as medical devices, food preservation, industrial wastewater treatment, shallow exploration, and military. In these engineering fields, pulse capacitors need to operate at a certain repetition frequency for long-term charge and discharge operations. At this time, large electrical stress damage and energy loss will accumulate inside the pulse capacitor, which will reduce the life of the pulse capacitor or even cause breakdown.

[0003] When the pulse capacitor is charging and discharging, its capacitance will gradually decrease. When it drops to a certain value, its performance will deteriorate sharply and the capacitance will also decrease rapidly, resulting in capacitor failure. Generally, when the capacitance loss exceeds 5% of the initial capacitance value, it is used as the failure standard. To ensure the normal operation of the pulse capacitor, it is necessary to be able to calculate the remaining capacitance of the pulse capacitor during charging and discharging. Therefore, it is of great significance to predict capacitance parameters by online monitoring technology of its discharge waveform. Summary of the Invention

[0004] A method for predicting capacitance parameters based on online monitoring technology of pulse capacitors, characterized in that: to solve the complexity of the existing capacitance life prediction methods, a method for predicting capacitance parameters based on online monitoring technology of pulse capacitors is proposed, and the time T when the voltage of the pulse capacitor first passes through zero is established m is a function of the damping ratio ξ, and the concept of capacitance failure constant λ is proposed to monitor the remaining capacitance in real time to solve the problem of whether the pulse capacitor fails after repeated discharges.

[0005] To achieve the above object, by performing a single discharge treatment on the pulse capacitor, monitoring the discharge voltage and current waveforms of the pulse capacitor, recording data, calculating the inverse peak coefficient k, and through formula derivation, it is obtained that the damping ratio ξ is a function of the inverse peak coefficient k, and the time T when the discharge voltage of the capacitor first passes through zero m is a function of the damping ratio ξ, and through mathematical analysis, the concept of capacitance failure constant λ is proposed. The remaining capacitance C of the pulse capacitor is proportional to the measured time T when the voltage first passes through zero s to form a reliable calculation scheme for failure capacitance parameters.

[0006] In order to achieve the above objectives, the present invention provides the following technical solutions:

[0007] A method for predicting capacitance parameters based on pulse capacitor online detection technology comprises the following steps:

[0008] Step 1: Select capacitor C0 according to the requirements, charge and discharge the capacitor once, measure the discharge waveform of the pulse capacitor, and record the waveform data;

[0009] Step 2: Build a model and determine the anti-peak coefficient k from the waveform data of step 1;

[0010] Step 3: Write the formula for the capacitor reverse peak voltage U c(min) , we get the expression of capacitance inverse peak coefficient k, which is a function of damping ratio ξ. We can reversely get the expression of damping ratio ξ with respect to capacitance inverse peak coefficient k. We can get the value of damping ratio ξ by the value of inverse peak coefficient k determined in step 2.

[0011] Step 4: Write the formula for the time T when the loop current reaches its peak max , maximum peak current I max , and the first zero-crossing time of the capacitor discharge voltage T m , combine the formula to get T m Regarding the function of the damping ratio ξ, the value of the damping ratio ξ obtained in step 3 is used to reversely calculate the first zero-crossing time T when the lossless capacitor discharges. m ;

[0012] Step 5: The first zero-crossing time T when the lossless capacitor is discharged m The first zero-crossing time T of the measured capacitor discharge s Compare and deduce the remaining capacitance C of the capacitor through the formula, and judge whether the capacitor has failed;

[0013] Step 6: Determine the capacitor failure constant λ and establish C and T s The functional relationship between the capacitor and the residual capacitance is monitored in real time during the discharge process, forming a reliable calculation scheme for the failure capacitor parameters.

[0014] Furthermore, in the step 1, the first zero-crossing time T of the capacitor discharge voltage is determined. s , the positive and negative peak currents of the first oscillation cycle of the discharge current;

[0015] Furthermore, in step 2: the reverse peak coefficient k is equal to the ratio of the reverse peak to the positive peak of the current when the capacitor is discharged in step 1;

[0016] Further, in step three:

[0017] Capacitor reverse peak voltage

[0018] Capacitor reverse peak coefficient

[0019] Then the damping ratio

[0020] Substitute the capacitor reverse peak coefficient k obtained in Step 2 to obtain the damping ratio ξ;

[0021] Among them, U c(min) is the capacitor reverse peak voltage, and U0 is the charging voltage of the capacitor;

[0022] Furthermore, in Step 4:

[0023] The time when the loop current reaches the peak value

[0024] Then the maximum peak current

[0025] The time when the capacitor discharges through zero for the first time

[0026] Multiply the expression of I max by the expression of T m to get:

[0027]

[0028] Transform the above formula to get:

[0029]

[0030] Since all other quantities are constants except ξ, substitute the damping ratio ξ obtained in Step 3 into the above formula to obtain the time T when the lossless capacitor discharges through zero for the first time m ;

[0031] Among them, I max can be measured in Step 1, and C0 is the initial capacitance of the capacitor;

[0032] Furthermore, in Step 5: By comparing T m with T s , if they are not equal, it means that the discharging capacitor has capacitance loss, and substitute T s into:

[0033]

[0034] to obtain the remaining capacitance C of the discharging capacitor at this time. Compare the capacitance value C at this time with the initial capacitance C0 of the capacitor. If then the capacitor fails at this time;

[0035] Furthermore, in Step 6: Analyze from the formula in Step 5:

[0036]

[0037] Since all other numbers are constants, it is found that C and T s are in a proportional relationship, and it can be obtained that After arrangement, we get Since C0 and T m are both known constants that can be obtained. Here, let Let λ be the capacitance failure constant, then:

[0038] C = λT s

[0039] The remaining capacitance during capacitor discharge can be calculated through this formula, forming a reliable calculation scheme for failure capacitor parameters.

[0040] The beneficial effects of the present invention are as follows:

[0041] (1) An underdamped attenuation oscillation model is established. By measuring the discharge voltage and current waveforms of the discharge capacitor, a method for predicting capacitor parameters based on the online monitoring technology of pulse capacitors is proposed. Compared with the traditional method, this method is simple to calculate and can reliably calculate capacitor failure parameters;

[0042] (2) Through formula derivation and analysis, it is established that the time T m when the discharge voltage waveform of the capacitor first crosses the zero point is a function of the loop damping ratio ξ of the circuit; and the time T m when the discharge voltage of the capacitor first crosses the zero point can be predicted by calculating the loop damping ratio ξ of the system. By comparing with the measured time T s when the discharge voltage first crosses the zero point, it is judged whether the capacitor fails;

[0043] (3) The concept of the capacitance failure constant λ is proposed. According to the capacitance failure constant λ, by measuring the time T s when the discharge voltage waveform of the discharge capacitor first crosses the zero point, the remaining capacitance C is detected in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to make the objectives, content, technical methods, and advantages of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings, where:

[0045] Figure 1 is the flowchart of the method for predicting capacitor parameters based on the online monitoring technology of pulse capacitors of the present invention;

[0046] Figure 2 is the equivalent circuit of the pulse capacitor discharge loop;

[0047] Figure 3 is the voltage waveform during the discharge process of the pulse capacitor;

[0048] Figure 4 is the current waveform during the discharge process of the pulsed capacitor; Detailed implementation manners

[0049] The following is an illustration with reference to the drawings. Through specific examples of pulsed capacitor discharge, the technical advantages of the present invention will be made clearer and more obvious. Researchers in this field can easily grasp the technical advantages of the present invention according to the specific content of the specification. It should be understood that the specific implementation manners given for the present invention are only to help those in this research field more easily master the technical content of the present invention, but are not limited to this specific implementation case. For those in this research field, they should be able to apply other specific implementations through this example. Moreover, the invention details described in this specification can be modified according to the actual situation without departing from the spirit of the invention. It should be noted that in the following specific implementation cases, the relevant invention technical features can be combined with each other under the condition that they do not conflict with each other.

[0050] The illustration of the drawings provided by the present invention is for better understanding and mastering the technical content of the present invention. It is a simulation schematic diagram and does not represent a physical diagram. Therefore, this cannot be a limitation of the present invention. In addition, for better understanding of the technical content of the present invention, the circuits and parameter selections in the following implementation manners are for better understanding of the present invention method and do not represent the actual circuits and parameters. The device and waveform size ratios in the drawings will be slightly enlarged or reduced and do not represent the sizes of actual cases. Researchers in this field can well understand the waveforms in the drawings and the following implementation manners.

[0051] As Figure 2 shown, it is the equivalent circuit of the pulsed capacitor discharge loop. In the discharge loop, a 50 μF capacitor is selected for the pulsed capacitor, and its charging voltage is 2000 V. The discharge process of the pulsed capacitor should be oscillatory decay, and the underdamped circuit conforms. According to the underdamped state conditions and discharge conditions, an equivalent resistance of 8 Ω and an equivalent inductance of 6 mH are selected for the discharge loop.

[0052] The method for predicting capacitance parameters using the above-mentioned pulsed capacitor on-line monitoring technology includes the following steps:

[0053] (1) Conduct a single charge and discharge during the capacitor discharge process, and the measured discharge waveform of the pulsed capacitor is as Figure 3 and Figure 4 shown;

[0054] (2) Measure the time T s = 1.09 ms when the capacitor discharge voltage first passes through zero, and calculate the reverse peak coefficient k = 0.3 based on the peak value;

[0055] (3) The reverse peak voltage of the capacitor

[0056] Then the reverse peak coefficient of the capacitor

[0057] The damping ratio

[0058] Substituting k = 0.3 into the above formula, we can obtain the damping ratio ξ = 0.36;

[0059] (4) Time when loop current reaches peak value

[0060] The maximum peak current

[0061] The first zero-crossing time of capacitor discharge

[0062] Will I max Expression and T m Multiplying the expressions, we get:

[0063]

[0064] Transform the above formula to get:

[0065]

[0066] Since all other variables except the damping ratio ξ are constant, the first zero crossing time T m It is a function of the circuit damping ratio ξ. Substituting the damping ratio ξ=0.36 and the initial capacitance C0=50uF into the above formula, we can obtain the theoretical first zero-crossing time T when the capacitor is discharged if the capacitor is intact at this time. m =1.17ms;

[0067] (5) Measure the time T when the capacitor discharge voltage first crosses zero s =1.09ms, and T m If there is a deviation, it means there is capacitance loss. max =111.6A, T s =1.09ms, U0=2000V, ξ=0.36, substituting into the above formula, we can get the residual capacitance C=46.5uF of the pulse capacitor. The initial value of the pulse capacitor is 50uF. When the capacitance loss exceeds 5%, it is considered as failure. This indicates that the pulse capacitor has failed at this time;

[0068] (6) And, analyze the formula:

[0069]

[0070] Since the other numbers are constants, we find that C and T s The proportional relationship is Arranged Since C0 and T m are both known constants that can be obtained. Here, let λ be called the capacitance failure constant, then:

[0071] C = λT s

[0072] Calculate the capacitance failure constant For this pulsed capacitor, C = 0.0427T s .

[0073] As long as the time T when the voltage of the pulsed capacitor first crosses zero at any discharge moment is measured s , the remaining capacitance of the pulsed capacitor can be calculated through this expression, and real-time monitoring can be carried out to determine whether the capacitor fails, forming a reliable calculation scheme for the parameters of the failed capacitor.

[0074] Finally, it should be added that the above-described implementation cases are only one of the preferred examples of the present invention and are not intended to limit the present invention. It is easy for researchers in the field to understand that any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting capacitance parameters based on on-line monitoring technology of pulse capacitors, characterized in that: This method establishes the time T when the voltage of the pulsed capacitor first crosses zero m which is a function of the damping ratio ξ, and proposes the concept of the capacitance failure constant λ to monitor the remaining capacitance in real time; The method includes the following steps: Step 1: Select a capacitor C0 according to requirements, perform a charge and discharge on the capacitor, actually measure the discharge waveform of the pulsed capacitor, and record the waveform data; Step 2: Establish a model and determine the inverse peak coefficient k from the waveform data in Step 1; Step 3: Write the formula for the capacitor reverse peak voltage U c(min) , obtain the expression of the capacitor reverse peak coefficient k, which is a function of the damping ratio ξ. By reverse deduction, obtain the expression of the damping ratio ξ with respect to the capacitor reverse peak coefficient k. Using the value of the reverse peak coefficient k determined in Step 2, calculate the value of the damping ratio ξ; Step 4: Write the formula for the time T when the loop current reaches its peak max , maximum peak current I max , and the first zero-crossing time of the capacitor discharge voltage T m , combine the formula to get T m Regarding the function of the damping ratio ξ, the value of the damping ratio ξ obtained in step 3 is used to reversely calculate the first zero-crossing time T when the lossless capacitor discharges. m ; Step Five: The first zero-crossing time T during the lossless capacitor discharge m is compared with the actually measured first zero-crossing time T during the capacitor discharge s and through formula derivation, the remaining capacitance C of the capacitor at this time is determined, and whether the capacitor fails is judged; Step 6: Determine the capacitance failure constant λ, establish the functional relationship between C and T s to form a reliable calculation scheme for the failure capacitance parameters by monitoring the remaining capacitance in real time during the capacitor discharge process; In the said Step 3: The expression for the capacitor reverse peak voltage is: where U0 is the charging voltage of the capacitor; The expression for the capacitance reverse peak coefficient is: The expression of the damping ratio ξ with respect to the anti-peak coefficient k is as follows: In the said Step 4: The first zero-crossing time T of the capacitor discharge voltage m The functional expression with respect to the damping ratio ξ is as follows: In the said Step 5: The required expression for calculating the remaining capacitance C of the capacitor at this time is: In the sixth step: based on the capacitance failure constant λ, establish the functional relationship between C and T s as C = λT s .

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