Direct current bus capacitor monitoring method and device
By assigning a total weighting coefficient to each capacitance value in the DC bus capacitance monitoring method, and combining the capacitance values of multiple preset periods with the total weighting coefficient to calculate the capacitance monitoring value, the performance degradation problem caused by capacitor aging is solved, and the monitoring accuracy and adaptability are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DELTA ELECTRONICS INC(CN)
- Filing Date
- 2024-11-29
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, capacitor aging leads to performance degradation, affecting the operating characteristics of power electronic devices, and hardware monitoring methods increase costs and limit the usage environment.
By assigning a total weight coefficient to each capacitance value in the DC bus capacitance monitoring method, and combining the capacitance values of multiple preset periods with the total weight coefficient to calculate the capacitance monitoring value, the calculation accuracy and adaptability are improved.
This improves the accuracy of capacitance monitoring value calculation, avoids the problem that a single preset cycle cannot reflect the current environment, and enhances the adaptability and accuracy of capacitance monitoring.
Smart Images
Figure CN122109930A_ABST
Abstract
Description
Technical Field
[0001] This case relates to a method and device for monitoring DC bus capacitance, and more particularly to a method and device for monitoring DC bus capacitance of a converter. Background Technology
[0002] Due to aging, capacitor performance degrades rapidly and significantly. Symptoms of capacitor performance degradation include a decrease in equivalent capacitance, an increase in equivalent series resistance (ESR), and an increase in leakage current. Capacitor performance degradation affects the operating characteristics of power electronic equipment, potentially leading to shutdowns or malfunctions.
[0003] As the requirements for the reliability of electronic devices become increasingly stringent, existing technologies have incorporated capacitor condition monitoring. By estimating the equivalent parameters of capacitors in real time, the aging state of capacitors can be monitored, thereby promptly identifying capacitor performance degradation and preventing electronic device failures.
[0004] Existing capacitance monitoring methods are divided into hardware-based and software-based methods. If hardware-based capacitance monitoring is used, additional hardware equipment is required, thus increasing costs and limiting the application environment.
[0005] Therefore, developing a DC bus capacitance monitoring method and device that can improve upon the shortcomings of the existing technology is an urgent need at present. Summary of the Invention
[0006] The purpose of this invention is to provide a method and apparatus for monitoring DC bus capacitance. In this method and apparatus, each capacitance value is assigned a corresponding total weighting coefficient, thereby improving the calculation accuracy of the capacitance monitoring value. Furthermore, since the capacitance monitoring value is calculated based on capacitance values obtained over multiple preset periods and the total weighting coefficient, it avoids the situation where capacitance monitoring values calculated using a single preset period cannot reflect the current monitoring environment, thus improving adaptability.
[0007] According to one aspect of the concept, this invention provides a method for monitoring DC bus capacitance. The DC bus capacitor is electrically connected to the output terminal of a converter, and the input terminal of the converter is electrically connected to an AC bus. The DC bus capacitance monitoring method includes the following steps: (a) sampling the input voltage and input current at the input terminal and the output voltage at the output terminal of the converter within a preset period, and obtaining the input power using the input voltage and input current; (b) filtering the input power and output voltage to obtain the AC component of the input power and the AC component of the output voltage; (c) obtaining the DC component of the output voltage, and calculating the capacitance value based on the DC component of the output voltage, the AC component of the input power, and the AC component of the output voltage; (d) obtaining a total weighting coefficient corresponding to the capacitance value based on at least one of the AC component of the input power, the AC component of the output voltage, and the operating temperature of the DC bus capacitor, wherein the total weighting coefficient is the product of multiple weighting coefficients; and (e) outputting the capacitance monitoring value of the DC bus capacitor based on the multiple capacitance values calculated and obtained within multiple preset periods and the multiple total weighting coefficients corresponding to the multiple capacitance values.
[0008] According to another aspect of this invention, a DC bus capacitance monitoring device is provided, comprising a converter and a controller. The input and output terminals of the converter are electrically connected to the AC bus and the DC bus capacitance, respectively. The controller is used to execute the DC bus capacitance monitoring method. Attached Figure Description
[0009] Figure 1 This is a schematic diagram of the circuit structure of the DC bus capacitance monitoring device according to a preferred embodiment of this invention.
[0010] Figure 2 This is a flowchart of a preferred embodiment of the DC bus capacitance monitoring method in this case.
[0011] Figure 3 for Figure 2 The detailed flowchart of step S3.
[0012] Figure 4 for Figure 1 The waveform diagram of the AC component of the output voltage and the AC component of the input power acquired by the controller within a preset cycle.
[0013] Figure 5 for Figure 1 A waveform diagram of the AC component of the output voltage acquired by the controller within a preset cycle.
[0014] The reference numerals in the attached figures are explained as follows:
[0015] 1: DC bus capacitance monitoring device
[0016] 2: Converter
[0017] 20: Input end
[0018] 21: Output terminal
[0019] 3: Controller
[0020] 4: AC power supply
[0021] 5: DC bus capacitor
[0022] 6: System
[0023] t0, t1, t2, t3, t4: Time points
[0024] T: Preset period
[0025] U dcMax The maximum value of the AC component of the output voltage.
[0026] U dcmi The minimum value of the AC component of the output voltage.
[0027] φ: Phase difference
[0028] S1, S2, S3, S4, S5, S31, S32, S33, S34: Steps Detailed Implementation
[0029] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention can have various variations in different implementations, all of which do not depart from the scope of this invention, and the descriptions and illustrations therein are for illustrative purposes only and are not intended to limit this invention.
[0030] Figure 1 This is a schematic diagram of the circuit structure of the DC bus capacitance monitoring device 1 according to a preferred embodiment of this invention. Figure 2 This is a flowchart illustrating the DC bus capacitance monitoring method of a preferred embodiment of this invention. Please also refer to... Figure 1 and Figure 2 The DC bus capacitor monitoring device 1 in this case includes a converter 2 and a controller 3. The input terminal 20 and output terminal 21 of the converter 2 are electrically connected to the AC bus and the DC bus capacitor 5, respectively. The controller 3 is configured to execute... Figure 2 The method for monitoring DC bus capacitance is shown. In some embodiments, converter 2 is an AC / DC converter. In some embodiments, the AC bus is electrically connected to AC power supply 4. In some embodiments, converter 2 is electrically connected to system 6 to supply the DC voltage output by converter 2 to system 6.
[0031] Please refer to the following: Figure 2The capacitance monitoring method of this case includes steps S1, S2, S3, S4, and S5. In step S1, the input voltage and input current at the input terminal and the output voltage at the output terminal are sampled within a preset period, and the input power is obtained using the input voltage and input current. The preset period can be set according to actual needs. In some embodiments, the preset period is half of the fundamental period of the input voltage.
[0032] In step S2, the input power and output voltage are filtered to obtain the AC components of the input power and the output voltage. In some embodiments, the frequency range of the AC component of the input power and the frequency range of the AC component of the output voltage are both twice the fundamental frequency range of the input voltage, for example, by using a bandpass filter.
[0033] In step S3, the capacitance value of the DC bus capacitor 5 is calculated based on the DC component of the output voltage, the AC component of the input power, and the AC component of the output voltage.
[0034] In step S4, the total weighting coefficient for the corresponding capacitor value is obtained based on at least one of the AC component of the input power and the AC component of the output voltage. In some embodiments, the total weighting coefficient is the product of multiple weighting coefficients.
[0035] In step S5, the capacitance monitoring value of the DC bus capacitor 5 is output based on multiple capacitance values calculated over multiple preset periods and multiple total weighting coefficients corresponding to the multiple capacitance values. In some embodiments, the multiple capacitance values calculated over multiple preset periods are capacitance values that have been corrected for the effects of environmental factors.
[0036] In the DC bus capacitance monitoring method and apparatus of this invention, each capacitance value is assigned a corresponding total weighting coefficient, thereby improving the calculation accuracy of the capacitance monitoring value. Furthermore, since the capacitance monitoring value is calculated based on the capacitance values obtained from multiple preset periods and the total weighting coefficient, it avoids the situation where the capacitance monitoring value calculated using a single preset period cannot reflect the current monitoring environment, thus improving adaptability.
[0037] The following describes the calculation method for the DC bus capacitor 5 in step S3 of this case. Step S3 in the capacitance monitoring method of this case also includes steps S31, S32, S33, and S34. Please refer to... Figure 3 In step S31, for any preset period, the amplitude of the AC component of the input power within the preset period is obtained. In step S32, the amplitude of the AC component of the output voltage within the preset period is obtained. In step S33, the amplitude of the DC component of the output voltage within the preset period is obtained. In step S34, the capacitance value is calculated based on the amplitudes of the AC component of the input power, the AC component of the output voltage, the DC component of the output voltage, and the preset period.
[0038] The calculation of the capacitance value in step S34 above satisfies the following equation (1).
[0039]
[0040] Where C is the capacitance value, u dc,dc P is the amplitude of the DC component of the output voltage within a preset period. in,ac The amplitude of the AC component of the input power within a preset period, u dc,ac f is the amplitude of the AC component of the output voltage within a preset period. ω The frequency corresponding to the preset period.
[0041] The total weight coefficient mentioned in step S4 of this case can be a single weight coefficient or a product of multiple weight coefficients. The weight coefficients may include, for example, a first weight coefficient, a second weight coefficient, a third weight coefficient, and a fourth weight coefficient, but are not limited to this. The specific methods for obtaining the first weight coefficient, the second weight coefficient, the third weight coefficient, and the fourth weight coefficient are explained below.
[0042] The first weighting coefficient comprises a plurality of first sub-weighting coefficients, and each first sub-weighting coefficient is associated with a corresponding sine parameter, wherein the sine parameter characterizes at least one of the sinusoidal properties of the AC component waveform of the input power and the sinusoidal properties of the AC component waveform of the output voltage. In some embodiments, the first weighting coefficient is the product of the plurality of first sub-weighting coefficients.
[0043] Specifically, the range of the sine parameter determines the magnitude of the first sub-weight coefficient, which is between 0 and 1. When the sine parameter falls within the first sine range, the first sub-weight coefficient is 1; when the sine parameter exceeds the first sine range but falls within the second sine range, the first sub-weight coefficient is between 0 and 1; and when the sine parameter exceeds the second sine range, the first sub-weight coefficient is 0. The first and second sine ranges in this design can be set according to actual needs without restriction.
[0044] In some embodiments, the AC component of the input power or the AC component of the output voltage has multiple sampling points within a preset period. The aforementioned sinusoidal parameter is the absolute value of the quotient of the maximum or minimum value of the AC component of the input power or the AC component of the output voltage within the current preset period and the sum of all positive sampling points within the current preset period; or, the absolute value of the quotient of the maximum or minimum value of the AC component of the input power or the AC component of the output voltage within the current preset period and the sum of all negative sampling points within the current preset period. In other embodiments, the aforementioned sinusoidal parameter is the sum of the maximum and minimum values of the AC component of the input power or the AC component of the output voltage among all sampling points within the preset period. In still other embodiments, the aforementioned sinusoidal parameter is the sum of the AC component of the input power or the AC component of the output voltage among all sampling points within the preset period.
[0045] The second weighting coefficient is related to the phase difference between the waveforms of the AC component of the input power and the AC component of the output voltage. Specifically, the range of this phase difference determines the magnitude of the second weighting coefficient, which is between 0 and 1. (See also...) Figure 4 , Figure 4 for Figure 1 The waveform diagram shows the AC component of the output voltage and the AC component of the input power acquired by controller 3 within a preset cycle. Figure 4 It is known that there is a phase difference φ between the AC component of the input power and the AC component of the output voltage. When the phase difference φ falls within the first phase range, the second weighting coefficient is 1; when the phase difference φ exceeds the first phase range but falls within the second phase range, the second weighting coefficient is between 0 and 1; and when the phase difference φ exceeds the second phase range, the second weighting coefficient is 0. The first and second phase ranges in this invention can be set according to actual needs without limitation. In some embodiments, the first phase range can be set to approximately 270 degrees. Therefore, when the phase difference between the AC component of the input power and the AC component of the output voltage is approximately 270 degrees (i.e., the AC component of the output voltage leads the AC component of the input power by approximately 90 degrees), the second weighting coefficient is 1. In some embodiments, Figure 4 The AC components of the output voltage and the AC components of the input power shown are obtained by sampling the output voltage of converter 2 within a preset period T and calculating the input power from the input voltage and input current and then filtering. Therefore, the phase difference between the AC components of the input power and the AC components of the output voltage can be determined based on the number of sampling points between the zero crossings of the AC components of the input power and the AC components of the output voltage.
[0046] The third weighting coefficient is related to the input power of the AC bus electrically connected to the converter input terminal. Under the same operating environment, such as the same temperature, the accuracy of capacitor value monitoring is positively correlated with the input power. Specifically, the third weighting coefficient is positively correlated with the input power of the AC bus electrically connected to the converter input terminal 20, and the third weighting coefficient is between 0 and 1. The larger the input power, the closer the third weighting coefficient is to 1; conversely, the smaller the input power, the closer the third weighting coefficient is to 0. In some embodiments, the rated power of converter 2 is used as a reference. When the input power is equal to the rated power of converter 2, the third weighting coefficient is 1. The closer the input power is to the rated power of converter 2, the closer the third weighting coefficient is to 1; conversely, the further the input power is from the rated power of converter 2, the closer the third weighting coefficient is to zero. In some embodiments, the magnitude of the input power can be determined based on the amplitude of the AC component of the input power or the AC component of the output voltage waveform. The larger the amplitude, the larger the input power.
[0047] The fourth weighting coefficient is related to the operating temperature of the DC bus capacitor 5. Under the same operating environment, such as when the input power is the same, the accuracy of capacitor value detection is related to temperature. Specifically, the range of the operating temperature of the DC bus capacitor 5 determines the magnitude of the fourth weighting coefficient, which is between 0 and 1. When the operating temperature of the DC bus capacitor 5 falls within the first temperature range, the fourth weighting coefficient is 1; and when the operating temperature of the DC bus capacitor 5 exceeds the first temperature range, the fourth weighting coefficient is between 0 and 1. The closer the operating temperature of the DC bus capacitor 5 is to the first temperature range, the closer the fourth weighting coefficient is to 1. Conversely, the further the operating temperature of the DC bus capacitor 5 is from the first temperature range, the closer the fourth weighting coefficient is to 0. In some embodiments, the first temperature range is 20℃-22℃. Therefore, when the operating temperature of the DC bus capacitor 5 falls within 20℃-22℃, the fourth weighting coefficient is 1.
[0048] Figure 5 for Figure 1 The following is a schematic diagram of the AC component waveform of the output voltage acquired by controller 3 within a preset period T. Figure 5 The AC component of the output voltage shown is used as an example to illustrate how to obtain its sinusoidal parameter using the sinusoidality of the waveform of the AC component of the output voltage, and then use the sinusoidal parameter to obtain the first sub-weighting coefficient. Figure 5 The AC component of the output voltage shown is obtained by sampling the output voltage of converter 2 within a preset period T and then filtering it, where the sampling frequency is f0 (Hz) and the frequency of the preset period T is f1 (Hz). Therefore, within one preset period T, the AC component of the output voltage has F sampling points, where F is f0 / f1. Figure 5In the embodiment shown, the duration from time t0 to t4 is a preset period T, and the durations from time t0 to t1, from time t1 to t2, from time t2 to t3, and from time t3 to t4 are all a quarter of a preset period T.
[0049] like Figure 5 As shown, the maximum value of the AC component of the output voltage at all sampling points within a preset period T is U. dcMax The minimum value of the AC component of the output voltage at all sampling points within a preset period T is U. dcmin The sum of all sampling points of the AC component of the output voltage between time t0 and t1 is U. dcSum0 The sum of all sampling points of the AC component of the output voltage between time t1 and t2 is U. dcSum1 The sum of all sampling points of the AC component of the output voltage between time t2 and t3 is U. dcSum2 The sum of all sampling points of the AC component of the output voltage between time t3 and t4 is U. dcSum3 The sum of all sampling points of the AC component of the output voltage from time t0 to t4 is U. dcSum , among which, U dcSum =U dcSum0 +U dcSum1 +U dcSum2 +U dcSum3 .
[0050] In some embodiments, the sinusoidal parameter is the sum of the maximum and minimum values of the AC component of the output voltage across all sampling points within a preset period T. Specifically, in this embodiment, the sinusoidal parameter is U. dcMax +U dcmin . When U dcMax +U dcmin When it falls within the range of the first sine wave, the first sub-weight coefficient is 1. Ideally, U dcMax +U dcmin The value is 0, but in practice, a certain margin needs to be considered. In this embodiment, a second sine range is also provided, which is larger than the first sine range. When U... dcMax +U dcmin When the value falls within the range of the first sine wave but not within the range of the second sine wave, the first sub-weight coefficient is between 0 and 1, where U dcMax +U dcmin The closer U is to the range of the first sine wave, the closer the first sub-weight coefficient is to 1. dcMax +U dcmin The closer to the boundary of the second sine range, the closer the first sub-weight coefficient is to 0. When U dcMax +U dcmin When the range exceeds the second sine range, the first sub-weight coefficient is 0.
[0051] In some embodiments, the sinusoidal parameter is the sum of all sampling points of the AC component of the output voltage within a preset period T. Specifically, the sum of all sampling points of the AC component of the output voltage within time t0 to t4 is U. dcSum In this embodiment, the sine parameter is U. dcSum Ideally, U dcSum It is 0, but in practice, a certain margin needs to be considered. When U dcSum When U falls within the first sine range, the first sub-weight coefficient is 1. In this embodiment, a second sine range is also provided, which is larger than the first sine range. dcSum When the value exceeds the first sine range but falls within the second sine range, the first sub-weight coefficient is between 0 and 1, where U dcSum The closer U is to the range of the first sine wave, the closer the first sub-weight coefficient is to 1. dcSum The closer to the boundary of the second sine range, the closer the first sub-weight coefficient is to 0. When U dcSum When the range exceeds the second sine range, the first sub-weight coefficient is 0.
[0052] In some embodiments, the sinusoidal parameter is the quotient of the absolute value of the maximum or minimum value of the AC component of the output voltage and the sum of all positive sampling points within half a period of a preset period, or the quotient of the absolute value of the maximum or minimum value of the AC component of the output voltage and the sum of all negative sampling points within half a period of a preset period. Specifically, the maximum value of the AC component of the output voltage from time t0 to t4 is U. dcMax The sum of all positive sampling points within half a period of the preset period is (U dcSum0 +U dcSum3 Therefore, in this embodiment, the sine parameter is U. dcMax / (U dcSum0 +U dcSum3 Ideally, U dcMax / (U dcSum0 +U dcSum3 The value is π×f1 / f0, but a certain margin needs to be considered in practice. When U dcMax / (U dcSum0 +U dcSum3 When U falls within the first sine range, the first sub-weight coefficient is 1. In this embodiment, a second sine range is also provided, which is larger than the first sine range. dcMax / (U dcSum0 +U dcSum3 When the value exceeds the first sine range but falls within the second sine range, the first sub-weight coefficient is between 0 and 1, where U dcMax / (U dcSum0 +U dcSum3 The closer U is to the range of the first sine wave, the closer the first sub-weight coefficient is to 1. dcMax / (UdcSum0 +U dcSum3 The closer U is to the boundary of the second sine range, the closer the first sub-weight coefficient is to 0. dcMax / (U dcSum0 +U dcSum3 When the value exceeds the range of the first sine wave, the first sub-weight coefficient is 0.
[0053] In some embodiments, the sine parameter is related to the cumulative number of sampling points at a preset period. For example, at time t1, if the cumulative number of sampling points is... Then the first sub-weight coefficient is 1. If the cumulative number of sampling points is... The first sub-weight coefficient is between 0 and 1. If the cumulative number of sampling points is not... or The first sub-weight coefficient is then 0. The first sub-weight coefficient can be obtained in a similar way at times t1, t2, t3 and t4, so it will not be elaborated here.
[0054] In the capacitance monitoring method of this case, the ultimate goal is to confirm the health status of the capacitor. Since the capacitance value calculated in each preset period is under different environmental conditions, and different environmental conditions will have a certain impact on the calculated capacitance value, it is necessary to unify the calculated capacitance value to the same reference environment for comparison. That is, the capacitance value calculated in each preset period is corrected, including temperature correction and power correction. Only after correction can the health status of the capacitor be accurately reflected.
[0055] In some embodiments, the capacitance monitoring method of this invention further includes: acquiring a first relationship curve between the capacitance value of the DC bus capacitor and temperature (it should be understood that this can be obtained in advance by measurement or according to parameters from the capacitor manufacturer); setting a reference temperature, i.e., correcting the capacitance value calculated in each preset period to the reference temperature; acquiring the operating temperature of the DC bus capacitor in each preset period, and acquiring a temperature correction coefficient for the current period based on the operating temperature, the reference temperature, and the first relationship curve; multiplying the capacitance value calculated in each preset period by the corresponding temperature correction coefficient to obtain the temperature-corrected capacitance value, wherein the temperature correction coefficient is the ratio of the capacitance value corresponding to the reference temperature (e.g., room temperature 20°C) in the first relationship curve to the capacitance value corresponding to the operating temperature in the first relationship curve. After correcting the capacitance values calculated in all preset periods to the reference temperature, the obtained capacitance monitoring values can reflect the health status of the capacitor and are more meaningful for reference.
[0056] In some embodiments, the capacitance monitoring method of this invention further includes: obtaining a second relationship curve between the capacitance value of the DC bus capacitor and the input power at the input terminal (it should be understood that this can be obtained in advance through measurement); setting a reference power, i.e., correcting the capacitance value calculated in each preset period to the reference power; obtaining the input power in each preset period, and deriving the corresponding power correction coefficient in this preset period based on the input power, the reference power, and the second relationship curve; multiplying the capacitance value calculated in each preset period by the corresponding power correction coefficient to obtain the power-corrected capacitance value, wherein the power correction coefficient is the ratio of the capacitance value corresponding to the reference power in the relationship curve to the capacitance value corresponding to the actual input power. After correcting the capacitance values calculated in all preset periods to the reference power, the obtained capacitance value can reflect the health of the capacitor and is more meaningful for reference. It should be understood that in some embodiments, temperature correction and power correction can be performed simultaneously. The corrected capacitance value is then calculated with the total weighting coefficient to obtain the final capacitance monitoring value.
[0057] The following example illustrates how the capacitance monitoring value is obtained in step S5 of this case. At the end of each preset cycle, the DC bus capacitance monitoring method of this case outputs the corresponding capacitance monitoring value. The calculation formula for the capacitance monitoring value Cout(n) output at the end of the nth preset cycle is explained below.
[0058] When n equals 1, the capacitance monitoring value at the end of the first preset cycle is Cout(1), and it satisfies the following equation (2).
[0059]
[0060] Wherein, C(1) is the capacitance value calculated in the first preset cycle, and more specifically, it is the capacitance value obtained after temperature correction and power correction of the capacitance value calculated in the first preset cycle; K(1) is the total weighting coefficient corresponding to the capacitance value in the first preset cycle; and C(0) is the factory value of the DC bus capacitor 5. In some embodiments, the total weighting coefficient is the product of the first weighting coefficient, the second weighting coefficient, the third weighting coefficient, and the fourth weighting coefficient.
[0061] When n equals 2, the capacitance monitoring value at the end of the second preset cycle is Cout(2), and it satisfies the following equation (3).
[0062]
[0063] Wherein, C(2) is the capacitance value calculated in the second preset period, and further, it is the capacitance value obtained after temperature correction and power correction of the capacitance value calculated in the second preset period, and K(2) is the total weighting coefficient corresponding to the capacitance value in the second preset period.
[0064] When n is greater than or equal to 3, it means that the capacitance monitoring value at the end of the nth preset period is Cout(n), and it satisfies the following equation (4).
[0065]
[0066] Wherein, Cout(n-1) is the capacitance monitoring value of the (n-1)th preset period, K(n-1) is the total weight coefficient corresponding to the capacitance value of the (n-1)th preset period, C(n) is the capacitance value of the nth preset period, K(n) is the total weight coefficient corresponding to the capacitance value of the nth preset period, and K(n-2) is the total weight coefficient corresponding to the capacitance value of the (n-2)th preset period.
[0067] In summary, this invention provides a DC bus capacitance monitoring method and apparatus that assigns a corresponding total weighting coefficient to each capacitance value, thereby improving the calculation accuracy of the capacitance monitoring value. Furthermore, since the capacitance monitoring value is calculated based on capacitance values obtained over multiple preset periods and the total weighting coefficient, it avoids the situation where capacitance monitoring values calculated using a single preset period cannot reflect the current monitoring environment, thus improving adaptability.
[0068] It should be noted that the above are merely preferred embodiments for illustrating this case, and this case is not limited to the described embodiments. The scope of this case is determined by the claims. Furthermore, this case can be modified in various ways by those skilled in the art, but all such modifications will not depart from the protection sought by the claims.
Claims
1. A method for monitoring DC bus capacitance, wherein, The DC bus capacitor is electrically connected to an output terminal of a converter, and an input terminal of the converter is electrically connected to an AC bus. The DC bus capacitance monitoring method includes: (a) Sample an input voltage and an input current at the input terminal and an output voltage at the output terminal within a preset period, and obtain an input power using the input voltage and the input current; (b) Filter the input power and the output voltage to obtain an AC component of the input power and an AC component of the output voltage; (c) Obtain the DC component of the output voltage and calculate a capacitor value based on the DC component of the output voltage, the AC component of the input power, and the AC component of the output voltage. (d) Based on at least one of the AC component of the input power, the AC component of the output voltage, and the operating temperature of the DC bus capacitor, obtain a total weighting coefficient corresponding to the capacitor value, wherein the total weighting coefficient is the product of multiple weighting coefficients; and (e) Output a capacitance monitoring value of the DC bus capacitor based on a plurality of capacitance values obtained by calculation over a plurality of preset periods and a plurality of total weighting coefficients corresponding to the plurality of capacitance values.
2. The DC bus capacitance monitoring method as described in claim 1, wherein, The frequency range of the AC component of the input power and the frequency range of the AC component of the output voltage are both twice the fundamental frequency range of the input voltage.
3. The DC bus capacitance monitoring method as described in claim 1, wherein, The preset period is half the fundamental period of the input voltage.
4. The DC bus capacitance monitoring method as described in claim 1, wherein, The plurality of weighting coefficients includes a first weighting coefficient, which contains a plurality of first sub-weighting coefficients, and each of the first sub-weighting coefficients is associated with a sinusoidal parameter, wherein the sinusoidal parameter represents at least one of a waveform of the AC component of the input power and a waveform of the AC component of the output voltage, wherein the AC component of the output voltage has a plurality of sampling points in the preset period.
5. The DC bus capacitance monitoring method as described in claim 4, wherein, When the sine parameter falls within a first sine range, the first sub-weight coefficient is 1; when the sine parameter exceeds the first sine range and falls within a second sine range, the first sub-weight coefficient is between 0 and 1; and when the sine parameter exceeds the second sine range, the first sub-weight coefficient is 0.
6. The DC bus capacitance monitoring method as described in claim 4, wherein, At least one of the sinusoidal parameters is the absolute value of the quotient of the maximum or minimum value of the AC component of the input power or the AC component of the output voltage within a preset period and the sum of all positive sampling points within the preset period, or the absolute value of the quotient of the maximum or minimum value of the AC component of the input power or the AC component of the output voltage within a preset period and the sum of all negative sampling points within the preset period.
7. The DC bus capacitance monitoring method as described in claim 4, wherein, At least one of the sinusoidal parameters is the sum of a maximum value and a minimum value of the AC component of the input power or the AC component of the output voltage at all of the plurality of sampling points within the preset period.
8. The DC bus capacitance monitoring method as described in claim 4, wherein, At least one of the sinusoidal parameters is the sum of the AC component of the input power or the AC component of the output voltage within the preset period of all the plurality of sampling points.
9. The DC bus capacitance monitoring method as described in claim 1, wherein, The plurality of weighting coefficients includes a second weighting coefficient that is related to a phase difference between a waveform of the AC component of the input power and a waveform of the AC component of the output voltage.
10. The DC bus capacitance monitoring method as described in claim 9, wherein, When the phase difference falls within a first phase range, the second weighting coefficient is 1; when the phase difference exceeds the first phase range but falls within a second phase range, the second weighting coefficient is between 0 and 1; and when the phase difference exceeds the second phase range, the second weighting coefficient is 0.
11. The DC bus capacitance monitoring method as described in claim 1, wherein, The plurality of weighting coefficients includes a third weighting coefficient, which is positively correlated with the magnitude of the input power and is between 0 and 1.
12. The DC bus capacitance monitoring method as described in claim 1, wherein, The plurality of weighting coefficients includes a fourth weighting coefficient, which is used to obtain an operating temperature of the DC bus capacitor. The fourth weighting coefficient is related to the operating temperature of the DC bus capacitor. When the operating temperature of the DC bus capacitor falls within a first temperature range, the fourth weighting coefficient is 1; and when the operating temperature of the DC bus capacitor exceeds the first temperature range, the fourth weighting coefficient is between 0 and 1. The closer the operating temperature of the DC bus capacitor is to the first temperature range, the closer the fourth weighting coefficient is to 1.
13. The DC bus capacitance monitoring method as described in claim 1, wherein, Step (c) also includes the following steps: (c1) For any given preset period, obtain a value of the AC component of the input power; (c2) Obtain the amplitude of the AC component of the output voltage within the preset period; (c3) Obtain the amplitude of the DC component of the output voltage within the preset period; as well as (c4) Calculate the capacitance value based on the amplitude of the AC component of the input power, the amplitude of the AC component of the output voltage, the amplitude of the DC component of the output voltage, and the preset period.
14. The DC bus capacitance monitoring method as described in claim 13, wherein, The capacitance value satisfies the following formula: C is the capacitance value, u dc,dc P is the amplitude of the DC component of the output voltage within the preset period. in,ac The amplitude of the AC component of the input power within the preset period, u dc,ac f is the amplitude of the AC component of the output voltage within the preset period. ω This is the frequency corresponding to the preset period.
15. The DC bus capacitance monitoring method as described in claim 1, further comprising: Obtain the first curve showing the relationship between the capacitance value of the DC bus capacitor and temperature; Set a reference temperature; Within each of these preset cycles: Obtain the operating temperature of the DC bus capacitor; A temperature correction coefficient is obtained based on the operating temperature, the reference temperature, and the first relationship curve. Multiplying the calculated capacitance value by the temperature correction factor yields a temperature-corrected capacitance value.
16. The DC bus capacitance monitoring method as described in claim 1, further comprising: Obtain the second relationship curve between the capacitance value of the DC bus capacitor and the input power; Set a reference power; Within each of these preset cycles: A power correction coefficient is obtained based on the input power, the reference power, and the second relationship curve; Multiplying the calculated capacitance value by the power correction factor yields a power-corrected capacitance value.
17. A DC bus capacitance monitoring device, comprising: A converter, wherein an input terminal and an output terminal of the converter are electrically connected to an AC bus and a DC bus capacitor, respectively; A controller for performing the DC bus capacitance monitoring method as described in any one of claims 1 to 16.