Method, device, equipment, medium and program product for monitoring series capacitors on a DC link

Abstract

The present invention discloses a method, device, equipment, medium and program product for monitoring a series capacitor in a DC link. The method includes: controlling the state of a power switch to control the charging and discharging states of an electrolytic capacitor, and collecting capacitance voltage data during the charging and discharging processes of the electrolytic capacitor. The charging and discharging states include the charging state and the discharging state of the electrolytic capacitor. Performing linear analysis based on the capacitance voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharging time, and monitoring the electrolytic capacitor in the DC link of the power converter according to the linear relationship; Since the present invention performs linear analysis on the capacitance value and discharging time of the electrolytic capacitor and monitors the capacitor on the DC link based on the linear relationship, the monitoring complexity is effectively reduced. Without complex sampling and calculation, accurate monitoring of the capacitor state is achieved, the monitoring cost is effectively reduced, and the capacitance monitoring efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of power technologies, and particularly to a method, device, equipment, medium and program product for monitoring series capacitors on a DC link. Background Art

[0002] Capacitors are one of the most vulnerable components in power converters. Compared with other types of capacitors, aluminum electrolytic capacitors have a shorter service life. Due to their low rated voltage, they are usually connected in series, especially in high-voltage DC links. To meet the requirement of total capacitance, more capacitors are needed, resulting in poor reliability.

[0003] Currently, the main capacitance state monitoring schemes can be divided into three categories, including offline, quasi-online and real-time online schemes. The above three schemes all have problems and defects. The offline scheme requires stopping the operation of the converter, which requires a large amount of manual intervention and cannot be completed automatically; the quasi-online scheme cannot achieve continuous estimation during normal operation; the real-time online scheme needs to process a large amount of ripple data, which requires some complex algorithms, resulting in a significant increase in monitoring cost and complexity. And due to the large amount of data processing, there are calculation errors in the real-time online scheme. Therefore, at present, capacitors cannot be effectively monitored, and there are problems of low efficiency, high cost and large monitoring errors. Summary of the Invention

[0004] The main object of the present invention is to provide a method, device, equipment, medium and program product for monitoring series capacitors on a DC link, aiming to solve the technical problems that the prior art cannot effectively monitor capacitors, with low efficiency, high cost and large monitoring errors.

[0005] To achieve the above object, the present invention provides a method for monitoring series capacitors on a DC link, which is applied to a power converter. The power converter includes a power switch, a balancing resistor and an electrolytic capacitor, and the balancing resistor is connected in parallel with the electrolytic capacitor. The method includes the following steps:

[0006] Control the state of the power switch to control the charging and discharging state of the electrolytic capacitor, and collect the capacitance voltage data during the charging and discharging process of the electrolytic capacitor. The charging and discharging state includes the charging state and the discharging state of the electrolytic capacitor;

[0007] Perform linear analysis based on the capacitance voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharging time;

[0008] Monitor the electrolytic capacitor in the DC link of the power converter according to the linear relationship.

[0009] Optionally, the electrolytic capacitor includes a first capacitor and a second capacitor; the capacitor voltage data includes first capacitor voltage data, second capacitor voltage data, and third capacitor voltage data; controlling the state of the power switch to control the charge and discharge state of the electrolytic capacitor and collecting the capacitor voltage data during the charge and discharge process of the electrolytic capacitor includes:

[0010] When the power switch is in the off state, collect the first capacitor voltage data of the first capacitor and the second capacitor;

[0011] Control the power switch to turn on and collect the second capacitor voltage data when the first capacitor is in the charging state and the second capacitor is in the discharging state;

[0012] Control the power switch to turn off and collect the third capacitor voltage data when the first capacitor is in the discharging state and the second capacitor is in the charging state.

[0013] Optionally, the first capacitor voltage data includes:

[0014] ;

[0015] Wherein, and are the capacitor voltage values of the first capacitor and the second capacitor, is the instantaneous DC link voltage value, is the DC link steady-state voltage value, is the instantaneous DC link ripple voltage value, and the DC link is the DC bus between the machine-side power module and the grid-side power module in the power converter;

[0016] The second capacitor voltage data includes:

[0017] ;

[0018] Wherein, is the capacitor voltage value of the first capacitor in the charging state, is the capacitor voltage value of the second capacitor in the discharging state, is the instantaneous DC link voltage value, is the DC link steady-state voltage value, is the instantaneous DC link ripple voltage value, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, is the time constant, is the voltage division coefficient after the power switch is turned on, is the auxiliary discharge resistor connected in series with the power switch, is a balancing resistor;

[0019] The third capacitor voltage data includes:

[0020] ;

[0021] Among them, is the voltage difference between the first capacitor and the second capacitor, is the capacitance voltage value of the first capacitor in the discharge state, is the capacitance voltage value of the second capacitor in the charging state.

[0022] Optionally, the linear analysis based on the capacitance voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time includes:

[0023] Determine the voltage difference information between the first capacitor and the second capacitor based on the capacitance voltage data;

[0024] Obtain the discharge time of the electrolytic capacitor during the charge and discharge process;

[0025] Based on the voltage difference information and the discharge time, perform a linear analysis to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0026] Optionally, the linear analysis based on the voltage difference information and the discharge time to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time includes:

[0027] Determine the total capacitance formula of the first capacitor and the second capacitor based on the voltage difference information and the discharge time:

[0028] ;

[0029] Among them, is the total capacitance value of the first capacitor and the second capacitor, is the voltage difference between the first capacitor and the second capacitor, is the DC link steady-state voltage value, is the voltage division coefficient after the power switch is turned on, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is a balancing resistor;

[0030] Based on the total capacitance formula, perform a linear analysis to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time:

[0031] ;

[0032] Wherein, is the total capacitance value of the first capacitor and the second capacitor, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor, is the voltage division coefficient after the power switch is turned on, is the instantaneous DC link voltage value.

[0033] Optionally, the linear analysis based on the capacitor voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time includes:

[0034] Obtaining the measured capacitance values of the electrolytic capacitor collected under multiple temperature conditions;

[0035] Performing linear analysis based on the capacitor voltage data to obtain an initial relationship between the capacitance value of the electrolytic capacitor and the discharge time;

[0036] Correcting the initial relationship according to the measured capacitance values to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0037] In addition, to achieve the above object, the present invention also provides a monitoring device for series capacitors on a DC link, and the monitoring device for series capacitors on a DC link includes:

[0038] A control module, configured to control the state of the power switch to control the charging and discharging states of the electrolytic capacitor, and collect the capacitor voltage data during the charging and discharging processes of the electrolytic capacitor, where the charging and discharging states include the charging state and the discharging state of the electrolytic capacitor;

[0039] An analysis module, configured to perform linear analysis based on the capacitor voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time;

[0040] A monitoring module, configured to monitor the electrolytic capacitor in the DC link of the power converter according to the linear relationship.

[0041] In addition, to achieve the above object, the present application also provides a monitoring device for series capacitors on a DC link, and the device includes: a memory, a processor, and a computer program stored on the memory and executable on the processor, where the computer program is configured to implement the steps of the monitoring method for series capacitors on a DC link as described above.

[0042] In addition, to achieve the above object, the present application also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the method for monitoring series capacitors on a DC link as described above are implemented.

[0043] In addition, to achieve the above object, the present application also provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, the steps of the method for monitoring series capacitors on a DC link as described above are implemented.

[0044] The present invention is applied to a power converter, which includes a power switch, a balancing resistor, and an electrolytic capacitor. The balancing resistor is connected in parallel with the electrolytic capacitor. The present invention controls the state of the power switch to control the charging and discharging state of the electrolytic capacitor, and collects the capacitor voltage data during the charging and discharging process of the electrolytic capacitor. The charging and discharging state includes the charging state and the discharging state of the electrolytic capacitor; based on the capacitor voltage data, a linear analysis is performed to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharging time; according to the linear relationship, the electrolytic capacitor on the DC link in the power converter is monitored; since the present invention performs a linear analysis on the capacitance value and the discharging time of the electrolytic capacitor and monitors the capacitor on the DC link based on the linear relationship, the monitoring complexity is effectively reduced. Without complex sampling and calculation, the accurate monitoring of the capacitor state is realized, the monitoring cost is effectively reduced, and the capacitor monitoring efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0046] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0047] Figure 1 It is a schematic structural diagram of a device for monitoring series capacitors on a DC link in a hardware operating environment related to the embodiment solution of the present invention;

[0048] Figure 2 It is a schematic flowchart of the first embodiment of the method for monitoring series capacitors on a DC link according to the present invention;

[0049] Figure 3This is the circuit structure diagram of a power converter in an embodiment of the method for monitoring series capacitors on the DC link of the present invention;

[0050] Figure 4 This is a schematic diagram of the voltage curve of an electrolytic capacitor during the process of controlling a power switch to adjust its switching state in an embodiment of the method for monitoring series capacitors on the DC link of the present invention;

[0051] Figure 5 This is an equivalent schematic diagram of multiple capacitors connected in series on the DC link in an embodiment of the method for monitoring series capacitors on the DC link of the present invention;

[0052] Figure 6 This is the structural block diagram of the first embodiment of the device for monitoring series capacitors on the DC link of the present invention.

[0053] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiment

[0054] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0055] Refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of the device for monitoring series capacitors on the DC link in the hardware operating environment related to the embodiment solution of the present invention.

[0056] As Figure 1 shown, the device for monitoring series capacitors on the DC link may include: a processor 1001, such as a Central Processing Unit (CPU), a communication bus 1002, a user interface 1003, a network interface 1004, and a memory 1005. Among them, the communication bus 1002 is used to realize the connection and communication between these components. The user interface 1003 may include a display screen (Display) and an input unit such as a keyboard (Keyboard). Optionally, the user interface 1003 may further include a standard wired interface and a wireless interface. The network interface 1004 may optionally include a standard wired interface and a wireless interface (such as a Wireless-Fidelity (WI-FI) interface). The memory 1005 may be a high-speed Random Access Memory (RAM) or a stable Non-Volatile Memory (NVM), such as a disk memory. Optionally, the memory 1005 may also be a storage device independent of the aforementioned processor 1001.

[0057] Those skilled in the art can understand that Figure 1The structure shown does not constitute a limitation on the series capacitor monitoring device on the DC link, and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0058] As Figure 1 shown, the memory 1005, as a computer-readable storage medium, may include an operating system, a network communication module, a user interface module, and a series capacitor monitoring program on the DC link.

[0059] In Figure 1 the series capacitor monitoring device on the DC link shown, the network interface 1004 is mainly used for data communication with a network server; the user interface 1003 is mainly used for data interaction with a user; the processor 1001 and the memory 1005 in the series capacitor monitoring device of the present invention can be provided in the series capacitor monitoring device on the DC link. The series capacitor monitoring device on the DC link calls the series capacitor monitoring program stored in the memory 1005 through the processor 1001 and executes the series capacitor monitoring method provided by the embodiments of the present invention.

[0060] The embodiments of the present invention provide a series capacitor monitoring method on a DC link. Referring to Figure 2 , Figure 2 is a schematic flowchart of the first embodiment of the series capacitor monitoring method of the present invention on the DC link.

[0061] In this embodiment, it is applied to a power converter, which includes a power switch, a balancing resistor, and an electrolytic capacitor. The balancing resistor is connected in parallel with the electrolytic capacitor. The series capacitor monitoring method on the DC link includes the following steps:

[0062] Step S10: Control the state of the power switch to control the charging and discharging state of the electrolytic capacitor, and collect the capacitance voltage data during the charging and discharging process of the electrolytic capacitor.

[0063] It should be noted that the execution subject of this embodiment can be a computing service device with data processing, network communication, and program running functions, such as a control device of a power converter, a microcontroller, etc., or a terminal electronic device capable of implementing the above functions. Hereinafter, a series capacitor monitoring device on the DC link (abbreviated as a monitoring device) will be used as an example to describe this embodiment and the following embodiments.

[0064] It should be noted that the above charging and discharging state includes the charging state and the discharging state of the electrolytic capacitor.

[0065] It can be understood that this embodiment is applied to a power converter (such as a wind power converter, etc.). The power converter includes a power switch, a balancing resistor, and an electrolytic capacitor. The balancing resistor is connected in parallel with the electrolytic capacitor.

[0066] In some embodiments, referring to Figure 3 , Figure 3 is a circuit structure diagram of a power converter. The power converter includes a machine-side power module, a grid-side power module, and a DC bus connecting the machine-side power module and the grid-side power module. The DC bus is a DC link. The DC link includes an auxiliary discharge network and a grid-side capacitor. The auxiliary discharge network includes a power switch and an auxiliary discharge resistor. The grid-side capacitor includes an electrolytic capacitor and a balancing resistor. Among them, C1 and C2 are electrolytic capacitors, R b1 and R b2 are balancing resistors, S is a power switch, and Ra is an auxiliary discharge resistor.

[0067] In some embodiments, in a wind power back-to-back power converter, usually two electrolytic capacitors are connected in series to share the DC voltage. To ensure voltage sharing, referring to Figure 3 , equal balancing resistors R b1 and R b2 can be connected in parallel with each electrolytic capacitor.

[0068] It should be understood that the monitoring device can control the power switch to open and close to charge and discharge the electrolytic capacitor, and estimate the capacitance of the electrolytic capacitor by measuring the voltage response of the electrolytic capacitor and the instantaneous DC connection voltage.

[0069] Furthermore, in order to accurately collect capacitance voltage data to accurately analyze the linear relationship, the electrolytic capacitor includes a first capacitor and a second capacitor; the capacitance voltage data includes first capacitance voltage data, second capacitance voltage data, and third capacitance voltage data;

[0070] The above step S10 may include:

[0071] Step S101: When the power switch is in the off state, collect the first capacitance voltage data of the first capacitor and the second capacitor;

[0072] Step S102: Control the power switch to turn on and collect the second capacitance voltage data when the first capacitor is in the charging state and the second capacitor is in the discharging state;

[0073] Step S103: Control the power switch to turn off and collect the third capacitance voltage data when the first capacitor is in the discharging state and the second capacitor is in the charging state.

[0074] It can be understood that the monitoring device controls the power switch and may include three stages. The first stage includes: the power switch is in the off state. At this time, due to the existence of the balancing resistor, the voltage values between the electrolytic capacitors are the same. The first capacitor voltage data is collected in this stage;

[0075] The second stage includes: controlling the power switch to turn on. At this time, due to the different analysis coefficients of the electrolytic capacitors, the first capacitor starts to charge and the second capacitor starts to discharge. The electrolytic capacitors on the DC link and the auxiliary discharge network (including the power switch and the auxiliary discharge resistor) form a first-order RC circuit. The second capacitor voltage data is collected in this stage;

[0076] The third stage includes: controlling the power switch to turn off. The first capacitor starts to discharge and the second capacitor starts to charge. The third capacitor voltage data is collected in this stage.

[0077] It should be noted that the first capacitor voltage data includes:

[0078] ;

[0079] Among them, and are the capacitance voltage values of the first capacitor and the second capacitor, is the instantaneous DC link voltage value, is the steady-state DC link voltage value, is the instantaneous DC link ripple voltage value. The DC link is the DC bus between the machine-side power module and the grid-side power module in the power converter;

[0080] The second capacitor voltage data includes:

[0081] ;

[0082] Among them, is the capacitance voltage value of the first capacitor in the charging state, is the capacitance voltage value of the second capacitor in the discharging state, is the instantaneous DC link voltage value, is the steady-state DC link voltage value, is the instantaneous DC link ripple voltage value, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, is the time constant, is the voltage division coefficient after the power switch is turned on, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor;

[0083] The third capacitor voltage data includes:

[0084] ;

[0085] Wherein, is the voltage difference between the first capacitor and the second capacitor, is the capacitor voltage value of the first capacitor in the discharge state, is the capacitor voltage value of the second capacitor in the charging state.

[0086] In some embodiments, the monitoring device can control three stages of the power switch based on a time interval. For example, referring to Figure 4 , Figure 4 is a schematic diagram of the voltage curve of the electrolytic capacitor during the process of controlling the power switch to adjust the switch state. t0 - t1 is the first stage, the power switch is off, and the voltages of the first capacitor and the second capacitor are the same; t1 - t2 is the second stage, at this time the power switch is on, and the second capacitor starts to discharge due to different voltage division coefficients. At the same time, the first capacitor starts to charge, and the electrolytic capacitor and the auxiliary discharge network are connected in series to form a first-order RC circuit; t2 - t3 is the third stage. During the period from t2 to t3, the voltage value returns to the initial voltage. At this time, the power switch is off, the second capacitor starts to charge, and the first capacitor starts to discharge. The time interval of t2 - t3 should be long enough to make the voltages of the first capacitor and the second capacitor return to the initial voltage value (i.e., the voltage value in the first stage). Since the life of the electrolytic capacitor lasts for thousands of hours and the capacitance changes slowly, the power loss during the charge and discharge process and the voltage stress on C1 are reduced. The measurement process only lasts for a few seconds every few hours.

[0087] In some embodiments, t0 depends on the moment when the capacitance monitoring program starts, t1 depends on the local controller sampling and calculating the to reach a preset value, such as 50V, and t2 only represents the moment when the converter returns to the initial state and does not involve control.

[0088] It should be noted that the method of monitoring the electrolytic capacitor of the DC link based on the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time of the present invention can be applied to different average DC link voltages. The value of the auxiliary discharge resistor affects the final voltage, and its resistance should be designed according to the charge and discharge time. In practical applications, electrolytic capacitors of the same type and batch number should have similar initial capacitances. At the same time, they have the same working conditions throughout their life cycles. Therefore, the first capacitor and the second capacitor should have similar degradation degrees and capacitances. The total capacitance can also be estimated by measuring u C2 (t) at a fixed discharge time. But in this way, C1 + C2 becomes u C2(t) exponential function, resulting in a higher computational burden on the controller. Since this method measures capacitance only through the charge and discharge characteristics of the capacitor, it is applicable not only to electrolytic capacitors but also to metallized polypropylene film capacitors.

[0089] In some embodiments, multiple capacitors connected in series may be included on the DC link of the power converter. Refer to Figure 5 , Figure 5 which is an equivalent schematic diagram of n capacitors connected in series on the DC link, where C 1 ...C n are electrolytic capacitors, S is the power switch, and R b1 ...R bn are balancing resistors. Assuming that the capacitance of all electrolytic capacitors is equal to C, similar to two series capacitors, the analysis process includes three stages:

[0090] The first stage: The power switch S is turned off. Due to the presence of the balancing resistor, the voltage values between C 1 ...C n are the same. At this time, the voltage value of C n can be expressed as:

[0091] ;

[0092] where is the voltage value of C n , is the instantaneous DC link voltage value.

[0093] The second stage: The power switch S is turned on. C n starts to discharge due to different voltage division coefficients, and at the same time, C 1 -C n-1 starts to charge. The charging and discharging processes can be expressed as: ;

[0094] where is the capacitance voltage value of the first capacitor in the charging state, is the capacitance voltage value of the second capacitor in the discharging state, is the instantaneous DC link voltage value, is the steady-state voltage value of the DC link, is the instantaneous DC link ripple voltage value, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, is the time constant, is the voltage division coefficient after the power switch is turned on, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor;

[0095] The third stage: The power switch S is turned off, and the voltage values of all electrolytic capacitors gradually return to the steady-state value. The capacitance value C can be calculated based on the following formula:

[0096] ;

[0097] where C is the total capacitance value of the first capacitor and the second capacitor, is the voltage difference between the first capacitor and the second capacitor, is the steady-state voltage value of the DC link, is the voltage division coefficient after the power switch is turned on, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor.

[0098] Step S20: Perform a linear analysis based on the capacitor voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0099] It should be noted that the capacitor voltage data may include the voltage values, charging times, discharge times, voltage division coefficients, instantaneous DC link voltage values, steady-state DC link voltage values, and instantaneous DC link ripple voltage values of each electrolytic capacitor in different stages. The monitoring device can collect and measure the capacitor voltage data through a voltage sensor.

[0100] It can be understood that the monitoring device can construct an expression formula of the electrolytic capacitor based on the capacitor voltage data, analyze the linear relationship between the capacitance value and the discharge time based on the expression formula, and construct a linear formula between the capacitance value and the discharge time based on the analysis results.

[0101] Furthermore, in order to accurately analyze the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time, the above step S20 may include:

[0102] Step S201: Determine the voltage difference information between the first capacitor and the second capacitor based on the capacitor voltage data;

[0103] Step S202: Obtain the discharge time of the electrolytic capacitor during the charge and discharge process;

[0104] Step S203: Perform a linear analysis based on the voltage difference information and the discharge time to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0105] It should be noted that since the first capacitor and the second capacitor have similar initial capacitances and, at the same time, they have the same operating conditions throughout their life cycles, the first capacitor and the second capacitor should have similar degradation degrees and capacitances. Therefore, in this embodiment, the capacitance can be measured through the charge and discharge characteristics of the capacitor, and thus it is applicable not only to electrolytic capacitors but also to metallized polypropylene film capacitors.

[0106] Furthermore, in order to effectively reduce the computational burden, ensure the reduction of the monitoring cost while improving the monitoring accuracy, step S203 described above may include:

[0107] Step S2031: Determine the total capacitance formula of the first capacitor and the second capacitor based on the voltage difference information and the discharge time.

[0108] It should be noted that the above total capacitance formula may include:

[0109] ;

[0110] Wherein, is the total capacitance value of the first capacitor and the second capacitor, is the voltage difference between the first capacitor and the second capacitor, is the DC link steady-state voltage value, is the voltage division coefficient after the power switch is turned on, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor;

[0111] Step S2032: Perform linear analysis based on the total capacitance formula to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0112] It should be noted that the above linear relationship can be a linear formula between the capacitance value and the discharge time, and may include:

[0113] ;

[0114] Wherein, is the total capacitance value of the first capacitor and the second capacitor, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor, is the voltage division coefficient after the power switch is turned on, is the instantaneous DC link voltage value.

[0115] Further, to decouple the influence of temperature on the capacitor, step S20 described above may include:

[0116] Step S21: Obtain the measured capacitance values of the electrolytic capacitor collected under multiple temperature conditions;

[0117] Step S22: Perform linear analysis based on the capacitance voltage data to obtain the initial relationship between the capacitance value of the electrolytic capacitor and the discharge time;

[0118] Step S23: Correct the initial relationship according to the measured capacitance values to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0119] It should be noted that to decouple the influence of temperature on the capacitance value of the electrolytic capacitor, the monitoring device can place the electrolytic capacitor in a thermal chamber at different temperatures for measurement and analysis. Record the capacitance results estimated by the proposed solution and the capacitance results measured by the LCR meter. For example, when the capacitor is placed under different temperature conditions, the power switch can be controlled respectively to control the charging and discharging of the electrolytic capacitor, and the capacitance voltage data can be collected, so as to obtain the capacitance voltage data under different temperature conditions.

[0120] In some embodiments, to improve the accuracy of state monitoring, a temperature sensor can be used. The capacitances measured by the LCR meter at different temperatures are pre-stored in the microcontroller unit (MCU). A look-up table can be used for temperature correction during the estimation process.

[0121] Step S30: Monitor the electrolytic capacitor in the DC link of the power converter according to the linear relationship.

[0122] In some embodiments, during the steady-state operation of the power converter, in response to a detection instruction, the monitoring device samples and monitors the DC bus voltage U DC and the voltages U C1 and U C2 of the electrolytic capacitors C1 and C2 connected in series on the DC link. The auxiliary discharge switch S is turned on, and C2 starts to discharge due to different voltage division coefficients. At the same time, C1 starts to charge. The DC link capacitor C2 in series with the auxiliary discharge network forms a first-order RC circuit. The voltage values of C1 and C2 changing with time during the charge and discharge process are sampled. The auxiliary discharge switch S is turned off, C2 starts to charge, C1 starts to discharge, and the voltage values of C1 and C2 changing with time during the recovery process are sampled, that is, the capacitance voltage data is obtained. The capacitance value of the electrolytic capacitor is calculated based on the following calculation model: ;

[0123] Wherein, is the total capacitance of the electrolytic capacitor, is the discharge time, is an auxiliary discharge resistor connected in series with the power switch, is the balancing resistor, is the instantaneous DC link voltage value, is the voltage difference between each electrolytic capacitor, is the voltage division coefficient after the power switch is turned on.

[0124] Based on the calculation model, the capacitance value is calculated. Based on the capacitance value of the electrolytic capacitor, the health state of the electrolytic capacitor is determined. When the capacitance value decreases by more than a preset threshold, it is determined that the capacitor has failed, thereby realizing the state monitoring of the capacitor.

[0125] In this embodiment, the state of the power switch is controlled to control the charge and discharge state of the electrolytic capacitor, and the capacitance voltage data during the charge and discharge process of the electrolytic capacitor is collected. The charge and discharge state includes the charge state and the discharge state of the electrolytic capacitor; based on the capacitance voltage data, linear analysis is performed to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor; according to the linear relationship, the electrolytic capacitor in the DC link of the power converter is monitored; since in this embodiment, linear analysis is performed on the capacitance value and the discharge time of the electrolytic capacitor, and the capacitor on the DC link is monitored based on the linear relationship, the monitoring complexity is effectively reduced. Without complex sampling and calculation, the accurate monitoring of the capacitor state is realized, the monitoring cost is effectively reduced, and the capacitance monitoring efficiency is improved.

[0126] In addition, an embodiment of the present invention also proposes a computer-readable storage medium, on which a monitoring program for series capacitors on the DC link is stored. When the monitoring program for series capacitors on the DC link is executed by a processor, the steps of the method for monitoring series capacitors on the DC link as described above are realized.

[0127] The computer-readable storage medium provided by the present application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or components, or any combination of the above. More specific examples of the computer-readable storage medium may include, but are not limited to: electrical connections with one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or flash memory, optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, device, or component. The program code contained on the computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (radio frequency), etc., or any suitable combination of the above.

[0128] The above computer-readable storage medium may be included in the series-connected capacitor monitoring device on the DC link; or it may exist separately and not be assembled into the series-connected capacitor monitoring device on the DC link.

[0129] In addition, an embodiment of the present invention also provides a computer program product, including a series-connected capacitor monitoring program on the DC link. When the series-connected capacitor monitoring program on the DC link is executed by a processor, the steps of the series-connected capacitor monitoring method described above are implemented.

[0130] The specific implementation manner of the computer program product of the present invention is basically the same as that of each embodiment of the above series-connected capacitor monitoring method on the DC link, and will not be described in detail here.

[0131] Refer to Figure 6 , Figure 6 which is the structural block diagram of the first embodiment of the series-connected capacitor monitoring device on the DC link of the present invention.

[0132] As Figure 6 shown, the series-connected capacitor monitoring device proposed by the embodiment of the present invention includes:

[0133] A control module 10, configured to control the state of the power switch to control the charge and discharge state of the electrolytic capacitor, and collect the capacitance voltage data during the charge and discharge process of the electrolytic capacitor. The charge and discharge state includes the charge state and the discharge state of the electrolytic capacitor;

[0134] An analysis module 20, configured to perform a linear analysis based on the capacitor voltage data to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time;

[0135] A monitoring module 30, configured to monitor the electrolytic capacitor in the DC link of the power converter according to the linear relationship.

[0136] Further, the electrolytic capacitor includes a first capacitor and a second capacitor; the capacitor voltage data includes first capacitor voltage data, second capacitor voltage data, and third capacitor voltage data; the control module 10 is further configured to, when the power switch is in the off state, collect the first capacitor voltage data of the first capacitor and the second capacitor, control the power switch to turn on, and collect the second capacitor voltage data when the first capacitor is in the charging state and the second capacitor is in the discharging state; control the power switch to turn off, and collect the third capacitor voltage data when the first capacitor is in the discharging state and the second capacitor is in the charging state.

[0137] Further, the first capacitor voltage data includes:

[0138] ;

[0139] Wherein, and are the capacitor voltage values of the first capacitor and the second capacitor, is the instantaneous DC link voltage value, is the steady-state DC link voltage value, is the instantaneous DC link ripple voltage value, and the DC link is the DC bus between the machine-side power module and the grid-side power module in the power converter;

[0140] The second capacitor voltage data includes:

[0141] ;

[0142] Wherein, is the capacitor voltage value of the first capacitor in the charging state, is the capacitor voltage value of the second capacitor in the discharging state, is the instantaneous DC link voltage value, is the steady-state DC link voltage value, is the instantaneous DC link ripple voltage value, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, is the time constant, is the voltage division coefficient after the power switch is turned on, The auxiliary discharge resistor is connected in series with the power switch, which is the balancing resistor;

[0143] The third capacitor voltage data includes:

[0144] ;

[0145] Among them, is the voltage difference between the first capacitor and the second capacitor, is the capacitance voltage value of the first capacitor in the discharge state, is the capacitance voltage value of the second capacitor in the charging state.

[0146] Furthermore, the analysis module 20 is further configured to determine the voltage difference information between the first capacitor and the second capacitor based on the capacitance voltage data; obtain the discharge time of the electrolytic capacitor during the charge and discharge process; perform a linear analysis based on the voltage difference information and the discharge time to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

[0147] Furthermore, the analysis module 20 is further configured to determine the total capacitance formula of the first capacitor and the second capacitor based on the voltage difference information and the discharge time: ;

[0148] Among them, is the total capacitance value of the first capacitor and the second capacitor, is the voltage difference between the first capacitor and the second capacitor, is the DC link steady-state voltage value, is the voltage division coefficient after the power switch is turned on, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor;

[0149] Perform a linear analysis based on the total capacitance formula to determine the linear relationship between the capacitance value of the electrolytic capacitor and the discharge time: ;

[0150] Among them, is the total capacitance value of the first capacitor and the second capacitor, is the discharge time, is the auxiliary discharge resistor connected in series with the power switch, is the balancing resistor, is the voltage division coefficient after the power switch is turned on, is the instantaneous DC link voltage value.

[0151] Further, the analysis module 20 is further configured to obtain the measured capacitance values of the electrolytic capacitor collected under multiple temperature conditions; perform linear analysis based on the capacitance-voltage data to obtain an initial relationship between the capacitance value and the discharge time of the electrolytic capacitor; and correct the initial relationship according to the measured capacitance values to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor.

[0152] In this embodiment, the charging and discharging states of the electrolytic capacitor are controlled by controlling the state of the power switch, and the capacitance-voltage data during the charging and discharging processes of the electrolytic capacitor are collected. The charging and discharging states include the charging state and the discharging state of the electrolytic capacitor. Linear analysis is performed based on the capacitance-voltage data to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor. The electrolytic capacitor in the DC link of the power converter is monitored according to the linear relationship. Since the capacitance value and the discharge time of the electrolytic capacitor are linearly analyzed in this embodiment, and the capacitor on the DC link is monitored based on the linear relationship, the monitoring complexity is effectively reduced. Without complex sampling and calculation, the accurate monitoring of the capacitor state is realized, the monitoring cost is effectively reduced, and the capacitance monitoring efficiency is improved.

[0153] The series capacitor monitoring device on the DC link provided in this application adopts the series capacitor monitoring method on the DC link in the above embodiment, and can solve the technical problem of monitoring the series capacitor on the DC link. Compared with the prior art, the beneficial effects of the series capacitor monitoring device on the DC link provided in this application are the same as those of the series capacitor monitoring method on the DC link provided in the above embodiment, and the other technical features in the series capacitor monitoring device on the DC link are the same as the features disclosed in the method of the above embodiment, which will not be elaborated here.

[0154] It should be understood that the above is only an example for illustration and does not constitute any limitation to the technical solution of the present invention. In specific applications, those skilled in the art can set according to needs, and the present invention does not limit this.

[0155] It should be noted that the above-described work process is only illustrative and does not limit the protection scope of the present invention. In actual applications, those skilled in the art can select some or all of them according to actual needs to achieve the purpose of the solution of this embodiment, and no limitation is made here.

[0156] In addition, for the technical details not described in detail in this embodiment, reference can be made to the series capacitor monitoring method on the DC link provided in any embodiment of the present invention, which will not be elaborated here.

[0157] It should be noted that in this article, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such a process, method, article or system. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or system including that element.

[0158] The serial numbers of the embodiments of the present invention above are only for description and do not represent the superiority or inferiority of the embodiments.

[0159] Through the description of the above embodiments, those skilled in the art can clearly understand that the above embodiment methods can be implemented by means of software plus a necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, in essence, or the part that makes a contribution to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as a read-only memory / random access memory, magnetic disk, optical disk), and includes several instructions to enable a terminal device (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in various embodiments of the present invention.

[0160] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the accompanying drawings, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for monitoring capacitors in series on a DC link, characterized in that: The method is applied to a power converter, the power converter includes a machine-side power module, a grid-side power module, and a DC bus connected between the machine-side power module and the grid-side power module, the DC bus is a DC link, the DC link includes an auxiliary discharge network and a grid-side capacitor, the auxiliary discharge network includes a power switch and an auxiliary discharge resistor, the grid-side capacitor includes an electrolytic capacitor and a balancing resistor, the balancing resistor is connected in parallel with the electrolytic capacitor, the electrolytic capacitor includes a first capacitor and a second capacitor, the first capacitor is connected in series with the second capacitor, and the method includes: Controlling the state of the power switch to control the charge and discharge state of the electrolytic capacitor, and collecting capacitance voltage data during the charge and discharge process of the electrolytic capacitor, wherein the charge and discharge state includes the charge state and the discharge state of the electrolytic capacitor; Performing a linear analysis based on the capacitance-voltage data to determine a linear relationship between the capacitance value and the discharge time of the electrolytic capacitor; monitoring an electrolytic capacitor of a DC link in the power converter according to the linear relationship; The capacitor voltage data includes first capacitor voltage data, second capacitor voltage data and third capacitor voltage data; the state control of the power switch to control the charge and discharge state of the electrolytic capacitor and collect the capacitor voltage data during the charge and discharge process of the electrolytic capacitor includes: When the power switch is in an off state, collecting first capacitance voltage data of the first capacitor and the second capacitor; Controlling the power switch to turn on, and collecting second capacitor voltage data when the first capacitor is in a charging state and the second capacitor is in a discharging state; The power switch is controlled to be turned off, and third capacitor voltage data is collected when the first capacitor is in a discharging state and the second capacitor is in a charging state.

2. The method for monitoring capacitors in series on a DC link according to claim 1, characterized in that: The first capacitor voltage data includes: ； in, and is the capacitance voltage value of the first capacitor and the second capacitor, is the instantaneous DC link voltage value, is the DC link steady-state voltage value, is the instantaneous DC link ripple voltage value, the DC link being a DC bus between the machine-side power module and the grid-side power module in the power converter; The second capacitor voltage data includes: ； in, is the capacitance voltage value of the first capacitor in the charging state, is the capacitance voltage value of the second capacitor in the discharge state, is the instantaneous DC link voltage value, is the DC link steady-state voltage value, is the instantaneous DC link ripple voltage value, is the capacitance value of the first capacitor, is the capacitance value of the second capacitor, is the time constant, is the voltage division coefficient after the power switch is turned on, Auxiliary discharge resistor connected in series with the power switch, is the balancing resistance; The third capacitor voltage data includes: ； in, is the voltage difference between the first capacitor and the second capacitor, is the capacitance voltage value of the first capacitor in the discharge state, is the capacitance voltage value of the second capacitor in a charging state.

3. The method for monitoring capacitors in series on a DC link according to any one of claims 1 or 2, characterized in that: The performing linear analysis based on the capacitance voltage data to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor includes: determining voltage difference information between the first capacitor and the second capacitor based on the capacitor voltage data; Obtaining the discharge time of the electrolytic capacitor during the charging and discharging process; A linear analysis is performed based on the voltage difference information and the discharge time to determine a linear relationship between the capacitance value of the electrolytic capacitor and the discharge time.

4. The method for monitoring capacitors in series on a DC link according to claim 3, characterized in that: The performing a linear analysis based on the voltage difference information and the discharge time to determine a linear relationship between the capacitance value of the electrolytic capacitor and the discharge time includes: The total capacitance formula of the first capacitor and the second capacitor is determined based on the voltage difference information and the discharge time: ； in, is the total capacitance of the first capacitor and the second capacitor, is the voltage difference between the first capacitor and the second capacitor, is the DC link steady-state voltage value, is the voltage division coefficient after the power switch is turned on, is the discharge time, Auxiliary discharge resistor connected in series with the power switch, is the balancing resistance; Based on the total capacitance formula, a linear analysis is performed to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor: ； in, is the total capacitance of the first capacitor and the second capacitor, is the discharge time, Auxiliary discharge resistor connected in series with the power switch, is the balancing resistance, is the voltage division coefficient after the power switch is turned on, is the instantaneous DC link voltage value.

5. The method for monitoring capacitors in series on a DC link according to any one of claims 1 or 2, characterized in that: The performing linear analysis based on the capacitance voltage data to determine the linear relationship between the capacitance value and the discharge time of the electrolytic capacitor includes: Obtaining test capacitance values ​​of the electrolytic capacitor collected under multiple temperature conditions; Performing linear analysis based on the capacitance-voltage data to obtain an initial relationship between the capacitance value and the discharge time of the electrolytic capacitor; The initial relationship is corrected according to the test capacitance value to determine a linear relationship between the capacitance value and the discharge time of the electrolytic capacitor.

6. A monitoring device for series capacitors on a DC link, characterized in that: The device for monitoring capacitors in series on a DC link is applied to a power converter, wherein the power converter comprises a machine-side power module, a grid-side power module, and a DC bus connected between the machine-side power module and the grid-side power module, wherein the DC bus is a DC link, wherein the DC link comprises an auxiliary discharge network and a grid-side capacitor, wherein the auxiliary discharge network comprises a power switch and an auxiliary discharge resistor, wherein the grid-side capacitor comprises an electrolytic capacitor and a balancing resistor, wherein the balancing resistor is connected in parallel with the electrolytic capacitor, wherein the electrolytic capacitor comprises a first capacitor and a second capacitor, wherein the first capacitor is connected in series with the second capacitor; The DC link series capacitor monitoring device comprises: A control module, used to control the state of the power switch to control the charge and discharge state of the electrolytic capacitor, and collect capacitor voltage data during the charge and discharge process of the electrolytic capacitor, wherein the charge and discharge state includes the charge state and discharge state of the electrolytic capacitor; An analysis module, configured to perform a linear analysis based on the capacitance voltage data to determine a linear relationship between the capacitance value and the discharge time of the electrolytic capacitor; A monitoring module, configured to monitor an electrolytic capacitor of a DC link in a power converter according to the linear relationship; The capacitor voltage data includes first capacitor voltage data, second capacitor voltage data and third capacitor voltage data; the control module is further used to collect first capacitor voltage data of the first capacitor and the second capacitor when the power switch is in an off state; control the power switch to turn on, and collect second capacitor voltage data when the first capacitor is in a charging state and the second capacitor is in a discharging state; control the power switch to turn off, and collect third capacitor voltage data when the first capacitor is in a discharging state and the second capacitor is in a charging state.

7. A monitoring device for series capacitors on a DC link, characterized in that: The DC link series capacitor monitoring device includes: a memory, a processor, and a DC link series capacitor monitoring program stored in the memory and executable on the processor, wherein the DC link series capacitor monitoring program is configured to implement a DC link series capacitor monitoring method as described in any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a monitoring program for capacitors in series on a DC link, and when the monitoring program for capacitors in series on a DC link is executed by a processor, the method for monitoring capacitors in series on a DC link according to any one of claims 1 to 5 is implemented.

9. A computer program product, characterized in that The computer program product comprises a monitoring program for series capacitors on a DC link, and when the monitoring program for series capacitors on a DC link is executed by a processor, the steps of the method for monitoring series capacitors on a DC link according to any one of claims 1 to 5 are implemented.

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