Capacitance value measurement method for direct-current bus capacitor and electric energy conversion apparatus

Abstract

A capacitance value measurement method for a direct-current bus capacitor and an electric energy conversion apparatus. The method comprises: when a power supply is connected to a direct-current side of an electric energy conversion apparatus, acquiring the actual charging / discharging time of a direct-current bus capacitor of the electric energy conversion apparatus (101); when the actual charging / discharging time is the actual charging time, the voltage of the fully charged direct-current bus capacitor being smaller than the voltage of the power supply; comparing the actual charging / discharging time with a corresponding preset charging / discharging time to obtain a comparison result (102); and, according to the comparison result, determining whether the capacitance value of the direct current bus capacitor has been attenuated (103). The method does not need to specifically calculate capacitance values of direct-current bus capacitors so as to allow for a small amount of calculation, reducing pressure on corresponding processors and limitations on selecting the processors.

Description

DC bus capacitor capacitance detection method and electric energy conversion device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 18, 2023, with application number CN202311206614.0 and invention name “Capacitance detection method of DC bus capacitor and electric energy conversion device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of capacitance value detection, and in particular to a capacitance value detection method of a DC bus capacitor and an electric energy conversion device. Background Art

[0003] DC bus capacitors include large-capacity film capacitors and electrolytic capacitors. Because DC bus capacitors often operate in high-temperature and high-humidity environments, their capacitance is susceptible to degradation. This degradation can affect the normal operation of associated devices. Therefore, it's necessary to test the capacitance of DC bus capacitors to identify degraded DC bus capacitors.

[0004] Currently, voltage and current detection circuits are used to determine the DC bus capacitor voltage, current, and corresponding frequency. The DC bus capacitor's capacitance is then inferred based on the frequency. However, because the actual current waveform contains multiple frequency bands, this approach is computationally complex, placing increased pressure on the corresponding processor and limiting processor selection.

[0005] Summary of the Invention

[0006] In order to solve the problems in the prior art of complex calculation work, high pressure on the processor and limitations in processor selection, the present invention provides a capacitance detection method for a DC bus capacitor and an electric energy conversion device.

[0007] The technical solutions of the present invention are as follows:

[0008] The present invention provides a method for detecting the capacitance of a DC bus capacitor, comprising:

[0009] When a power supply is connected to the DC side of the electric energy conversion device, actual charging and discharging time of the DC bus capacitor of the electric energy conversion device is obtained; when the actual charging and discharging time is the actual charging time, the voltage of the DC bus capacitor when charging is completed is less than the voltage of the power supply;

[0010] Comparing the actual charge and discharge time with the corresponding preset charge and discharge time to obtain a comparison result;

[0011] According to the comparison result, it is determined whether the capacitance of the DC bus capacitor has attenuated.

[0012] Optionally, the comparison result is a ratio between the actual charge and discharge time and the preset charge and discharge time;

[0013] Judging whether the capacitance of the DC bus capacitor has attenuated according to the comparison result specifically includes:

[0014] Determining whether the ratio is less than a preset ratio threshold;

[0015] If the ratio is less than the preset ratio threshold, it is determined that the capacitance of the DC bus capacitor has decayed.

[0016] Optionally, obtaining the actual charging and discharging time of the DC bus capacitor of the electric energy conversion device specifically includes:

[0017] When the DC bus capacitor is in a charging state, obtaining an actual charging time of the DC bus capacitor; wherein the charging state is a charging state at the initial slow start within each preset cycle;

[0018] or,

[0019] When the DC bus capacitor is in a discharging state, an actual discharge duration of the DC bus capacitor is obtained.

[0020] Optionally, before comparing the actual charge and discharge time with the corresponding preset charge and discharge time, the method for detecting the capacitance of a DC bus capacitor of the present invention further includes:

[0021] Calculate the preset charge and discharge time.

[0022] Optionally, calculating the preset charge and discharge time specifically includes:

[0023] The preset charge and discharge duration is calculated according to the initial voltage and target voltage of the DC bus capacitor, the voltage of the power supply, the initial capacitance of the DC bus capacitor, and the resistance of the charge and discharge branch.

[0024] Optionally, when the actual charging and discharging time is the actual charging time of the DC bus capacitor in the charging state during the initial slow start within a preset period, the initial voltage is zero, and the resistance of the charging and discharging branch is the resistance of the slow start resistor between the power supply and the DC bus capacitor.

[0025] Optionally, the target voltage is equal to the difference between the voltage of the power supply and a preset voltage value.

[0026] Optionally, after determining whether the capacitance of the DC bus capacitor has attenuated based on the comparison result, the method for detecting the capacitance of the DC bus capacitor of the present invention further includes:

[0027] If the judgment result indicates that the capacitance of the DC bus capacitor has decayed, the device where the DC bus capacitor is located is controlled to shut down.

[0028] The present invention also provides an electric energy conversion device, comprising: a main circuit and a controller;

[0029] In the main circuit, a DC bus capacitor is connected between the positive and negative poles of the DC bus;

[0030] The controller is used to detect the capacitance of the DC bus capacitor using the method described above.

[0031] Optionally, the main circuit includes: a soft start unit and a power conversion circuit;

[0032] The DC side of the power conversion circuit is connected to the DC bus;

[0033] The slow-start unit is connected in parallel to the main contactor between the DC bus and the power supply.

[0034] Optionally, the slow-start unit includes: a slow-start contactor and a slow-start resistor;

[0035] The slow-start contactor and the slow-start resistor are connected in series.

[0036] The present invention adopts the above technical solution and has the following beneficial effects:

[0037] When the DC side of the power conversion device is connected to a power source, the actual charge and discharge duration of the DC bus capacitor of the power conversion device is obtained. The actual charge and discharge duration of the DC bus capacitor is then compared with the corresponding preset charge and discharge duration. Based on the comparison result, it is determined whether the capacitance of the DC bus capacitor has decayed. This method does not require specific calculation of the capacitance of the DC bus capacitor, and the computational complexity is relatively small, which allows the present invention to reduce the pressure on the corresponding processor and alleviate the limitations of processor selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0039] FIG1 is a schematic flow chart of a method for detecting the capacitance of a DC bus capacitor according to an embodiment of the present invention;

[0040] FIG2 is a schematic flow chart of another method for detecting the capacitance of a DC bus capacitor provided by an embodiment of the present invention;

[0041] FIG3 is a schematic structural diagram of an electric energy conversion device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] DC bus capacitors include large-capacity film capacitors and electrolytic capacitors. In power conversion devices using PWM (Pulse Width Modulation) control algorithms, DC bus capacitors are required to absorb ripple currents of the corresponding frequency. For example, in power conversion devices using SVPWM control algorithms, DC bus capacitors need to absorb ripple currents at three times the switching frequency, as well as switching frequency ripple.

[0044] However, because DC bus capacitors often operate in high-temperature and high-humidity environments, their capacitance is susceptible to degradation. When the DC bus capacitor's capacitance degrades, the ripple current increases. If the ripple current remains high for a long time, thermal runaway may occur in the power conversion device, affecting its normal operation. Therefore, it is necessary to monitor the DC bus capacitor's capacitance. If degradation is detected, the DC bus capacitor must be replaced or increased promptly.

[0045] Currently, voltage and current detection circuits are used to determine the DC bus capacitor voltage, current, and corresponding frequency. The DC bus capacitor's capacitance is then inferred based on the frequency. However, because the actual current waveform contains multiple frequency bands, this approach is computationally complex, placing increased pressure on the corresponding processor and limiting processor selection.

[0046] In order to reduce the amount of calculation in the capacitance detection process of the DC bus capacitor, thereby reducing the pressure on the corresponding processor and reducing the limitations on processor selection, the present invention provides a DC bus capacitor capacitance detection method and an electric energy conversion device.

[0047] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0048] FIG1 is a flow chart of a method for detecting the capacitance of a DC bus capacitor according to an embodiment of the present invention. As shown in FIG1 , the method for detecting the capacitance of a DC bus capacitor includes:

[0049] Step 101: When a power supply is connected to the DC side of the power conversion device, the actual charging and discharging time of the DC bus capacitor of the power conversion device is obtained; when the actual charging and discharging time is the actual charging time, the voltage of the DC bus capacitor when charging is completed is less than the voltage of the power supply.

[0050] In the embodiment of the present invention, the actual charge and discharge duration is the actual charge duration or the actual discharge duration. The actual charge duration of the DC bus capacitor may be the actual time it takes for the voltage of the DC bus capacitor to rise from any first voltage to any second voltage when the DC bus capacitor is in a charging state. The actual discharge duration of the DC bus capacitor may be the actual time it takes for the voltage of the DC bus capacitor to drop from any third voltage to any fourth voltage when the DC bus capacitor is in a discharging state.

[0051] In practical applications, during the charging process of the DC bus capacitor, when the voltage of the DC bus capacitor approaches the voltage of the power supply to which the DC bus capacitor is connected, the charging rate will slow down. Therefore, under the premise that the relevant contactor meets the closing current impact, the voltage of the DC bus capacitor when charging is completed is set to be lower than the voltage of the power supply. This is beneficial to shorten the charging time of the DC bus capacitor, so that the actual charging time of the DC bus capacitor can be quickly obtained, which is beneficial to improve the capacitance detection efficiency of the DC bus capacitor.

[0052] Step 102: Compare the actual charge and discharge time with the corresponding preset charge and discharge time to obtain a comparison result.

[0053] In an embodiment of the present invention, when the actual charging time of the DC bus capacitor is obtained in step 101, in step 102, the actual charging time of the DC bus capacitor is specifically compared with the corresponding theoretical charging time; and when the actual discharging time of the DC bus capacitor is obtained in step 101, in step 102, the actual discharging time of the DC bus capacitor is specifically compared with the corresponding theoretical discharge time.

[0054] The theoretical charging time corresponding to the actual charging time specifically refers to the time theoretically required for the voltage of the corresponding DC bus capacitor to rise from any of the first voltages to any of the second voltages when the capacitor is in a charging state at its initial capacitance. The theoretical discharge time corresponding to the actual discharging time specifically refers to the time theoretically required for the voltage of the corresponding DC bus capacitor to drop from any of the third voltages to any of the fourth voltages when the capacitor is in a discharging state at its initial capacitance.

[0055] Step 103: Determine whether the capacitance of the DC bus capacitor has attenuated based on the comparison result.

[0056] The embodiments of this specification utilize the aforementioned technical solution. When the DC side of an electric energy conversion device is connected to a power source, the actual charge and discharge duration of the DC bus capacitor of the electric energy conversion device is obtained. The actual charge and discharge duration of the DC bus capacitor is then compared with a corresponding preset charge and discharge duration, and based on the comparison result, whether the capacitance of the DC bus capacitor has decayed is determined. This method does not require specific calculations of the DC bus capacitor's capacitance, resulting in a relatively small computational effort. This reduces the burden on the corresponding processor and mitigates limitations on processor selection.

[0057] In the embodiment of the present invention, the comparison result may be a ratio between the actual charge and discharge time and the preset charge and discharge time.

[0058] Step 103: judging whether the capacitance of the DC bus capacitor has attenuated based on the comparison result, which may specifically include:

[0059] (1) Determine whether the ratio between the actual charge and discharge time and the preset charge and discharge time is less than a preset ratio threshold.

[0060] (2) If the ratio of the actual charge and discharge time to the preset charge and discharge time is less than the preset ratio threshold, it is determined that the capacitance of the DC bus capacitor has decayed.

[0061] In actual applications, the capacitance of a DC bus capacitor often fluctuates by a certain percentage, such as 10%. In embodiments of the present invention, a preset ratio threshold is determined based on the fluctuation ratio of the DC bus capacitor's capacitance. For example, the fluctuation ratio of the DC bus capacitor's capacitance can be directly determined as the preset ratio threshold, i.e., the preset ratio threshold can be 0.9. This helps improve the accuracy of the DC bus capacitor capacitance detection results.

[0062] In addition, the comparison result may also be the absolute value of the difference between the actual charge and discharge time and the preset charge and discharge time. In this case, step 103: judging whether the capacitance of the DC bus capacitor has decayed based on the comparison result may specifically include:

[0063] (1) Determine whether the absolute value of the difference between the actual charge and discharge time and the preset charge and discharge time is greater than a preset difference threshold.

[0064] (2) If the absolute value of the difference between the actual charge and discharge time and the preset charge and discharge time is greater than the preset difference threshold, it is determined that the capacitance of the DC bus capacitor has decayed.

[0065] The specific value of the preset difference threshold value can also be set according to the fluctuation of the capacitance of the DC bus capacitor; there is no specific limitation here, and it depends on the application environment.

[0066] In the embodiment of the present invention, step 101: obtaining the actual charging and discharging time of the DC bus capacitor of the electric energy conversion device may specifically include:

[0067] When the DC bus capacitor is in a charging state, obtain the actual charging time of the DC bus capacitor; or,

[0068] When the DC bus capacitor is in a discharging state, an actual discharging time of the DC bus capacitor is obtained.

[0069] In an embodiment of the present invention, the actual charging time of the DC bus capacitor can be compared with the corresponding theoretical charging time to determine whether the capacitance of the DC bus capacitor has decayed. In this case, step 101: obtaining the actual charging and discharging time of the DC bus capacitor of the electric energy conversion device can specifically include: obtaining the actual charging time of the DC bus capacitor when the DC bus capacitor is in a charging state.

[0070] Alternatively, the actual discharge time of the DC bus capacitor can be compared with the corresponding theoretical discharge time to determine whether the capacitance of the DC bus capacitor has decayed. In this case, step 101: obtaining the actual charge and discharge time of the DC bus capacitor of the electric energy conversion device can specifically include: obtaining the actual discharge time of the DC bus capacitor when the DC bus capacitor is in a discharging state.

[0071] In the embodiment of the present invention, obtaining the actual charging time of the DC bus capacitor may specifically include:

[0072] According to the start time and completion time of the DC bus capacitor slow start, the time between the two is determined as the actual charging time.

[0073] In an embodiment of the present invention, before determining the duration between the start time and the completion time of the slow start of the DC bus capacitor, the method of the embodiment of this specification may further include:

[0074] (1) When issuing a slow start instruction, record the current time as the start time.

[0075] (2) When the voltage of the DC bus capacitor reaches the target voltage, the current time is recorded as the completion time.

[0076] In the embodiment of the present invention, when the DC bus capacitor performs a slow start, the slow start is completed when the voltage thereof rises to a preset voltage, ie, a target voltage.

[0077] The target voltage can be equal to the difference between the voltage of the power supply connected to the DC bus capacitor and the preset voltage value. As can be seen from the foregoing, during the charging process of the DC bus capacitor, when the voltage of the DC bus capacitor approaches the voltage of the power supply connected to the DC bus capacitor, the charging rate will slow down. Therefore, under the premise that the relevant contactor meets the closing current impact, a larger preset voltage value should be set as much as possible to make the difference between the target voltage and the voltage of the power supply connected to the DC bus capacitor as large as possible. In a specific example, the preset voltage value is set to 30V.

[0078] Furthermore, in the above technical solution, since the difference between the target voltage and the voltage of the power supply connected to the DC bus capacitor is a known quantity, only one of the voltages can be detected and the other voltage can be calculated based on the difference; secondly, the two voltages can also be detected and the difference can be used to verify the voltage measurement results.

[0079] In the embodiment of the present invention, the charging state of the DC bus capacitor may refer to the charging state of the DC bus capacitor during each slow start, or may refer to the charging state of the DC bus capacitor during the initial slow start in each preset cycle.

[0080] In an embodiment of the present invention, when the electric energy conversion device is initially turned on, the voltage of the DC bus capacitor is generally 0. When the capacitance of the DC bus capacitor whose voltage is 0 at the initial slow start is detected, the actual time taken for the DC bus capacitor to complete the initial slow start can be compared with the theoretical time required to determine whether the capacitance of the DC bus capacitor has decayed. In this case, the charging state of the DC bus capacitor can be the charging state of the DC bus capacitor at the initial slow start. Based on this, since the voltage of the DC bus capacitor is a known quantity (0) at the initial slow start, this solution does not need to detect the initial voltage of the DC bus capacitor, which is conducive to improving the capacitance detection efficiency of the DC bus capacitor.

[0081] Secondly, in order to promptly detect the DC bus capacitor whose capacitance has decayed, the capacitance of the DC bus capacitor can be regularly tested. That is, the preset period can be set according to the actual situation. In a specific example, when the electric energy conversion device is initially turned on every day, the actual time spent using the DC bus capacitor to complete the initial slow start and the theoretical time required are used to perform a judgment process on whether the capacitance of the DC bus capacitor has decayed. In addition, the preset period can also be two days or a week, etc., and those skilled in the art can set the length of the preset period according to actual needs.

[0082] In the embodiment of the present invention, before comparing the actual charge and discharge duration with the corresponding preset charge and discharge duration, the method of the embodiment of this specification may further include:

[0083] Calculate the preset charge and discharge time.

[0084] In the embodiment of the present invention, calculating the preset charge and discharge time may specifically include:

[0085] The preset charge and discharge duration is calculated based on the initial voltage and target voltage of the DC bus capacitor, the voltage of the power supply to which the DC bus capacitor is connected, the initial capacitance of the DC bus capacitor, and the resistance of the charge and discharge branch.

[0086] In an embodiment of the present invention, when the actual charge and discharge duration is the actual charging duration of the DC bus capacitor during the initial slow-start charging state within a preset cycle, the initial voltage is zero, and the resistance of the charge and discharge branch is the resistance of the slow-start resistor between the power supply and the DC bus capacitor. Since the slow-start resistor operates a small number of times and has a high precision, the resistance of the slow-start resistor can be considered fixed.

[0087] In the embodiment of the present invention, the methods for calculating the theoretical charging time and the methods for calculating the theoretical discharging time are both prior arts, and are described below using the calculation of the theoretical charging time as an example.

[0088] In the embodiment of the present invention, when the DC bus capacitor is in a charging state, the voltage V of the DC bus capacitor at any time t is t is: V t =V O +(V bat -V0)(1-e -t / RC )......(1)

[0089] Among them, V O is the initial voltage of the DC bus capacitor; V bat is the voltage of the power supply connected to the DC bus capacitor; R is the resistance of the charging and discharging branch of the DC bus capacitor; C is the initial capacitance of the DC bus capacitor.

[0090] Among them, the theoretical charging time is V t The time it takes to reach the target voltage; when the power conversion device is a PCS (Power Conversion System, energy storage converter), V bat It is the voltage of the battery connected to the DC bus capacitor.

[0091] In V O When it is 0, the theoretical charging time t1 is: t1=RCln(V bat / V bat -V t )......(2)

[0092] Among them, V t Equal to the target voltage, continuing with the above example, V t =V bat-30.

[0093] In V O When it is not 0, those skilled in the art can also calculate the theoretical charging time t1 according to formula (1).

[0094] In the embodiment of the present invention, after step 103: determining whether the capacitance of the DC bus capacitor has attenuated based on the comparison result, the method of the embodiment of this specification may further include:

[0095] If the judgment result indicates that the capacitance of the DC bus capacitor has decayed, the device where the DC bus capacitor is located is controlled to shut down.

[0096] After the equipment where the DC bus capacitor is located is shut down, relevant personnel can replace the DC bus capacitor with attenuated capacitance.

[0097] The above technical solution is described below using the DC bus capacitor charging process as an example. In this embodiment, the actual time taken to complete the initial soft start using the DC bus capacitor and the theoretical time required are used to determine whether the capacitance of the DC bus capacitor has decayed.

[0098] It should be noted that the capacitance detection method during the discharge process of the DC bus capacitor is similar and will not be repeated here.

[0099] FIG2 is a flow chart of another method for detecting the capacitance of a DC bus capacitor provided by an embodiment of the present invention. This process is applied to an electric energy conversion device. As shown in FIG2 , this process includes:

[0100] Step 201 : When the DC bus capacitor performs a slow start, determine whether the slow start is an initial slow start; if the slow start is an initial slow start, execute step 202 ; otherwise, execute step 208 .

[0101] Step 202: Sample the voltage V of the power supply connected to the DC bus capacitor bat , and at the same time issue a slow start instruction and record the current time as time 0.

[0102] Step 203: Based on the voltage V of the power supply connected to the DC bus capacitor bat , calculate the actual time (i.e. theoretical charging time) t1 that the DC bus capacitor takes to complete the initial slow start.

[0103] Those skilled in the art will appreciate that step 203 may be performed at any time after step 202 and before step 206 and is performed only once.

[0104] Step 204: Determine the voltage V of the power supply connected to the DC bus capacitor bat , and the voltage V of the DC bus capacitor at the current moment tIs the difference between the two values ​​less than or equal to the preset voltage difference? If the voltage V bat The voltage V of the DC bus capacitor at the current moment t If the difference between them is less than or equal to the preset voltage difference, step 205 is executed; otherwise, step 202 is executed.

[0105] Continuing with the above example, the preset voltage difference may be 30.

[0106] Step 205: Record the current moment as the theoretical time length (actual charging time length) t2 required for the DC bus capacitor to complete the initial slow start.

[0107] Step 206: Determine whether the ratio between the actual charging time t2 and the theoretical charging time t1 is less than or equal to a preset ratio threshold; if the ratio between the actual charging time t2 and the theoretical charging time t1 is less than the preset ratio threshold, execute step 207; otherwise, execute step 209.

[0108] Step 207: Determine whether the capacitance of the DC bus capacitor has decayed, and control the power conversion device to shut down.

[0109] Step 208: The DC bus capacitor performs normal slow start.

[0110] Step 209: The electric energy conversion device operates normally.

[0111] Based on a general inventive concept, the present invention also provides an electric energy conversion device. FIG3 is a schematic structural diagram of an electric energy conversion device provided by an embodiment of the present invention. Referring to FIG3 , the electric energy conversion device includes: a main circuit 31 and a controller. The controller is not shown in FIG3 .

[0112] In the main circuit 31 , a DC bus capacitor 311 is connected between the positive and negative poles of the DC bus.

[0113] The controller is used to detect the capacitance of the DC bus capacitor 311 using the method described above.

[0114] In the embodiment of the present invention, the main circuit 31 includes a soft-start unit 312 and a power conversion circuit.

[0115] The power conversion circuit is arranged after the DC bus capacitor 311 , ie, on the right side of 311 as shown in FIG3 ; and the DC side of the power conversion circuit is connected to the DC bus.

[0116] The slow-start unit 312 is connected in parallel to the main contactor 313 between the DC bus and the power supply.

[0117] In the embodiment of the present invention, the power conversion circuit includes a DC / AC conversion circuit. When the DC / AC conversion circuit is a bidirectional DC / AC conversion circuit and the power source 32 is a storage battery (such as the RACK shown in the figure), the power conversion device is a PCS.

[0118] In the embodiment of the present invention, the slow-start unit 312 includes a slow-start contactor 3121 and a slow-start resistor 3122 .

[0119] The soft-start contactor 3121 and the soft-start resistor 3122 are connected in series.

[0120] For the sake of simplicity, the aforementioned method embodiments are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited to the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously.

[0121] Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0122] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similarities between the various embodiments can be referred to in conjunction with each other. For device embodiments, since they are generally similar to method embodiments, their description is relatively simple, and for relevant details, reference can be made to the description of the method embodiments.

[0123] The steps in the methods of the various embodiments of the present invention can be adjusted in sequence, combined, and deleted according to actual needs, and the technical features recorded in the various embodiments can be replaced or combined.

[0124] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0125] With respect to the above description of the disclosed embodiments, the features described in the various embodiments in this specification may be interchanged or combined to enable those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting the capacitance of a DC bus capacitor, characterized in that: include: When the DC side of the electric energy conversion device is connected to a power supply, obtaining the actual charging and discharging time of the DC bus capacitor of the electric energy conversion device; When the actual charge and discharge time is the actual charging time, the voltage of the DC bus capacitor after charging is completed is less than the voltage of the power supply; Comparing the actual charge and discharge time with the corresponding preset charge and discharge time to obtain a comparison result; According to the comparison result, it is determined whether the capacitance of the DC bus capacitor has decayed.

2. The method for detecting the capacitance of a DC bus capacitor according to claim 1, characterized in that: The comparison result is the ratio between the actual charge and discharge time and the preset charge and discharge time; Judging whether the capacitance of the DC bus capacitor has attenuated according to the comparison result specifically includes: Determining whether the ratio is less than a preset ratio threshold; If the ratio is less than the preset ratio threshold, it is determined that the capacitance of the DC bus capacitor has decayed.

3. The method for detecting the capacitance of a DC bus capacitor according to claim 1, characterized in that: The actual charging and discharging time of the DC bus capacitor of the electric energy conversion device is obtained, specifically including: When the DC bus capacitor is in a charging state, obtaining an actual charging time of the DC bus capacitor; wherein the charging state is a charging state at the initial slow start in each preset cycle; or, When the DC bus capacitor is in a discharging state, an actual discharging time of the DC bus capacitor is obtained.

4. The method for detecting the capacitance of a DC bus capacitor according to any one of claims 1 to 3, characterized in that: Before comparing the actual charge and discharge time with the corresponding preset charge and discharge time, the method further includes: The preset charge and discharge duration is calculated.

5. The method for detecting the capacitance of a DC bus capacitor according to claim 4, characterized in that: Calculating the preset charge and discharge time specifically includes: The preset charge and discharge duration is calculated according to the initial voltage and target voltage of the DC bus capacitor, the voltage of the power supply, and the initial capacitance and charge and discharge branch resistance of the DC bus capacitor.

6. The method for detecting the capacitance of a DC bus capacitor according to claim 5, characterized in that: When the actual charging and discharging time is the actual charging time of the DC bus capacitor in the charging state during the initial slow start within a preset period, the initial voltage is zero, and the resistance of the charging and discharging branch is the resistance of the slow start resistor between the power supply and the DC bus capacitor.

7. The method for detecting the capacitance of a DC bus capacitor according to claim 5, characterized in that: The target voltage is equal to the difference between the voltage of the power source and a preset voltage value.

8. The method for detecting the capacitance of a DC bus capacitor according to any one of claims 1 to 3, characterized in that: After determining whether the capacitance of the DC bus capacitor has decayed according to the comparison result, the method further includes: If the judgment result indicates that the capacitance of the DC bus capacitor has decayed, the device where the DC bus capacitor is located is controlled to shut down.

9. An electric energy conversion device, characterized in that: include: Main circuit and controller; In the main circuit, a DC bus capacitor is connected between the positive and negative poles of the DC bus; The controller is used to detect the capacitance of the DC bus capacitor using the method according to any one of claims 1 to 8.

10. The electric energy conversion device according to claim 9, characterized in that: The main circuit comprises: a slow-start unit and a power conversion circuit; The DC side of the power conversion circuit is connected to the DC bus; The slow-start unit is connected in parallel to the main contactor between the DC bus and the power supply.

11. The electric energy conversion device according to claim 10, characterized in that: The slow-start unit comprises: a slow-start contactor and a slow-start resistor; The slow-start contactor and the slow-start resistor are connected in series.

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