Diagnostic Method for Busbar Capacitance of Elevator Drive System

Abstract

The present invention discloses a method for diagnosing bus capacitance in an elevator drive system. The elevator drive system is composed of a rectifier, a bus capacitor, and an inverter connected in sequence. The diagnostic method comprises: step S1, establishing an evaluation index, wherein the evaluation index is used to characterize the control performance of a rectifier controller, and the value of at least one control parameter of the rectifier controller is determined by the capacitance parameter value of the bus capacitor; step S2, establishing a mathematical model, wherein the mathematical model is used to describe the relationship between the evaluation index and a first change, wherein the first change is the change in the current value of the capacitance parameter value of the bus capacitor relative to a standard value; step S3, monitoring the evaluation index; step S4, determining the first change based on the evaluation index and the mathematical model; and step S5, determining whether the first change exceeds a set threshold, and when it is determined that the first change exceeds the set threshold, outputting information that the capacitance parameter value of the bus capacitor is abnormal. The present invention converts parameters used in the rectifier control process in the elevator drive system into evaluation indicators for monitoring, thereby achieving simple and accurate diagnosis of the capacitance value of the bus capacitor.

Description

Technical Field

[0001] The present invention relates to the technical field of elevators, and in particular to a method for diagnosing busbar capacitance of an elevator drive system. Background Art

[0002] Elevators, especially medium- and high-speed elevators, typically use an AC-DC-AC drive system, primarily consisting of a controlled rectifier, bus capacitors, and an inverter. Bus capacitors are typically electrolytic capacitors. Over time, their actual capacitance decreases due to factors such as age and ambient temperature. When this decreases to a certain level, it can severely impact elevator control performance, causing factors such as decreased DC bus voltage stability, reduced inverter output capacity, and increased motor torque fluctuations. Therefore, it's essential to monitor the DC capacitor's capacitance so that it can be replaced promptly when it drops below a certain level.

[0003] Document 1 (CN201410324056.2) proposes a method for detecting the busbar capacitance of an elevator inverter, including the following steps: controlling an elevator to ascend unloaded, with the number of floors reaching at least the minimum required to reach the elevator's rated speed; obtaining capacitance voltage data u1 and u2 of the inverter busbar capacitor at times t1 and t2 during the elevator's ascending motion; detecting car car travel distance data h1 and h2 at times t1 and t2 during the elevator's ascending motion; and calculating the capacitance C of the inverter busbar capacitor according to the following formula: C = [2*k*m*g*(h2-h1)*η-2*P*(t2-t1)] / (u22-u12), where C is the capacitance, k is the elevator balance coefficient, η is the elevator efficiency, P is the inverter standby power consumption, g is the acceleration of gravity, and m is the elevator's rated load. This solution enables low-cost and accurate detection and diagnosis of the elevator inverter busbar capacitance without adding any hardware. However, the capacitor capacity calculation of this solution utilizes the elevator balance coefficient, elevator efficiency, and inverter standby power consumption, all of which will change with the use time of the elevator, which seriously affects the accuracy of the calculation results of this solution.

[0004] Document 2 (CN202211484518.8) provides an elevator control device and an abnormality diagnosis method. This solution extracts information related to the amplitude of the power supply ripple noise from waveform data representing the time series changes in motor torque, thereby determining the abnormal state of the smoothing capacitor configured in the power supply driving the motor. However, in engineering practice, motor torque is not always available, and its time series waveform is affected not only by the ripple noise of the power supply but also by the motor load (such as when the motor is in a regenerative state). Therefore, it has the disadvantages of large computational complexity (waveform analysis - Fourier analysis) and low accuracy.

[0005] Therefore, how to achieve high-precision monitoring of busbar capacitance becomes a technical problem to be solved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to provide a technical solution that can perform high-precision monitoring of busbar capacitance.

[0007] To solve the above technical problems, the present invention provides a method for diagnosing bus capacitance of an elevator drive system. The elevator drive system is composed of a rectifier, a bus capacitance, and an inverter connected in sequence. The diagnostic method includes:

[0008] Step S1: establishing an evaluation index, wherein the evaluation index is used to characterize the control performance of the rectifier controller, and the value of at least one control parameter of the rectifier controller is determined by the capacitance parameter value of the bus capacitor;

[0009] Step S2: establishing a mathematical model, wherein the mathematical model is used to describe the relationship between the evaluation index and a first change, wherein the first change refers to a change in a current value of a capacitance parameter value of the busbar capacitor relative to a standard value;

[0010] Step S3, monitoring the evaluation index;

[0011] Step S4: determining the first change according to the evaluation index and the mathematical model;

[0012] Step S5: Determine whether the first change exceeds a set threshold, and when it is determined that the first change exceeds the set threshold, output information indicating that the capacitance parameter value of the bus capacitor is abnormal.

[0013] Preferably, the controller of the rectifier must meet the following conditions: Condition A: when the actual value of the capacitance parameter value of the bus capacitor is its standard value, the control performance of the controller is optimal; Condition B: when the actual value of the capacitance parameter value of the bus capacitor is not the standard value, the control performance of the controller is non-optimal; Condition C: the control performance of the controller changes with the actual value of the capacitance parameter value of the bus capacitor.

[0014] Preferably, the controller of the rectifier must also meet the following condition D: the control performance of the controller is a monotonic function with the first change as the independent variable.

[0015] Preferably, the evaluation index satisfies the following conditions: Condition 1, when the control performance of the controller is optimal, the value of the evaluation index is the maximum value; Condition 2, when the control performance of the controller is not optimal, the value of the evaluation index is not the maximum value; Condition 3, the evaluation index is a continuous function; Condition 4, the evaluation index is a monotonic function or a partially monotonic function.

[0016] Preferably, between step S4 and step S5, it also includes: step A1, judging whether the first change exceeds the attention threshold, the attention threshold is less than the set threshold, and when it is determined that the first change exceeds the attention threshold, predicting the remaining service life of the bus capacitor based on the evaluation index and / or its change trend.

[0017] Preferably, the controller of the rectifier is a robust controller with a robust parameter α, and the robustness parameter α is less than the attention threshold. The robustness parameter α indicates that under the control of the robust controller, the control performance of the robust controller will only be reduced when the deviation of the actual value of the parameter of its controlled object from the standard value exceeds α.

[0018] Preferably, after the elevator is in the uniform speed operation stage and the duration of the uniform speed operation stage exceeds a time threshold, the step S4 determines the first change according to the evaluation index and the mathematical model, and the step S5 is executed to determine whether the first change exceeds a set threshold, and the time threshold causes the control output of the rectifier or inverter to enter an interval with a change amplitude less than the amplitude threshold.

[0019] Preferably, when the controller of the rectifier includes a load-based feedforward control unit, at any time, step S4 can determine the first change based on the evaluation index and the mathematical model, and then step S5 is executed to determine whether the first change exceeds the set threshold.

[0020] Preferably, the evaluation index is the maximum value of the tracking error of the bus voltage within a certain period of time or the integral value of its absolute value.

[0021] The present invention also provides a method for diagnosing the bus capacitance of an elevator drive system, wherein the elevator drive system is composed of a rectifier, a bus capacitor and an inverter connected in sequence, and the controller of the rectifier has at least one specific control parameter, wherein the specific control parameter refers to a control parameter of the rectifier controller whose value is determined by the capacitance parameter value of the bus capacitor, and when the first value is equal to the second value, the control performance of the rectifier controller is optimal, the first value is the value of the capacitance parameter value of the bus capacitor used to calculate the specific control parameter, and the second value is the current value of the capacitance parameter value of the bus capacitor; by adjusting the specific control parameter, the control performance of the rectifier controller is always maintained in an optimal state; the diagnostic method monitors the specific control parameter, determines the current value of the capacitance parameter of the bus capacitor according to the specific control parameter, and when the difference between the current value of the capacitance parameter of the bus capacitor and its standard value exceeds a preset threshold, outputs information that the capacitance parameter value of the bus capacitor is abnormal.

[0022] Preferably, the controller of the rectifier adjusts the specific control parameter according to the following rule: step A1, changing the specific control parameter by a first change amount in the current direction based on the current value; step A2, controlling the rectifier using the changed specific control parameter; step A3, if the control performance improves, continuing to change the specific control parameter along the current adjustment direction until the control performance of the controller using the adjusted specific control parameter value is lower than that of the previous time, discarding the last change and retaining the previous specific control parameter value as the current value of the specific control parameter; if the control performance is reduced, changing the adjustment direction, and continuing to change the specific control parameter value along the changed adjustment direction until the control performance of the controller using the changed specific control parameter is lower than that of the previous time, discarding the last change and retaining the previous specific control parameter value as the current value of the specific control parameter; step A4, calculating the current value of the capacitance parameter of the bus capacitor using the current value of the specific control parameter based on the relationship between the specific control parameter and the capacitance parameter of the bus capacitor.

[0023] Preferably, the controller of the rectifier adjusts the specific control parameters according to the following rules: step B1, appropriately change the capacitance parameter value of the bus capacitor; step B2, update the specific control parameters using the changed capacitance parameter value; step B3, control the rectifier using the updated specific control parameters; step B4, if the control performance improves, continue to change the capacitance parameter value along the current adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor; if the control performance is reduced, change the adjustment direction and continue to change the capacitance parameter value along the changed adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor.

[0024] Compared with the prior art, the present invention converts parameters used in the rectifier control process in the elevator drive system into evaluation indicators for monitoring, thereby achieving simple and accurate diagnosis of the capacitance value of the bus capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0026] Figure 1 The figure is a structural diagram of an elevator drive system involved in the method for diagnosing bus capacitance of an elevator drive system according to the present invention. DETAILED DESCRIPTION

[0027] The following describes the implementation manner of the present invention through specific specific embodiments. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through different specific implementation manners, and the various details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without deviating from the overall design concept of the invention. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in a variety of different forms and should not be interpreted as being limited to the specific embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art.

[0028] Example 1

[0029] In this embodiment, Figure 1 As shown, elevator drive systems typically employ an AC-DC-AC structure, consisting of a rectifier (controllable using PWM), bus capacitors, and an inverter. The three-phase side of the rectifier is connected to the grid via an inductor, while the DC side is connected to the DC side of the inverter. Bus capacitors span the DC bus between the rectifier and inverter, while the three-phase side of the inverter is connected to the elevator's drive motor (traction motor). Since bus capacitors are typically electrolytic capacitors, their actual capacitance value slowly decreases after the elevator is put into operation, over time and due to factors such as ambient temperature. When the capacitance value decreases to a certain level, it can negatively impact elevator performance, such as decreased DC bus voltage stability, reduced inverter output capacity, and increased traction motor torque fluctuation. Therefore, it's important to monitor the DC capacitor's capacitance value so that it can be replaced promptly when it drops below a certain level.

[0030] The controlled object of the rectifier controller includes the bus capacitor, so the controller parameter setting of the rectifier controller uses the capacitance parameter value of the bus capacitor. When the capacitance parameter value of the bus capacitor is consistent with its actual value, the obtained controller parameter is the optimal parameter for the controlled object including the bus capacitor. Therefore, the rectifier controller using the optimal parameter controls the controlled object including the bus capacitor, and the control performance obtained is also optimal. If there is a deviation between the capacitance parameter value of the bus capacitor used in the controller parameter setting of the rectifier controller and its actual value, the control performance of the controller will inevitably be reduced compared to the control performance when the capacitance parameter value of the bus capacitor is consistent with its actual value. Therefore, the change in control performance can be used to monitor the capacitance parameter value of the bus capacitor.

[0031] Considering that the actual busbar capacitor capacitance parameter values ​​are the standard values ​​when the elevator is installed and put into use, the initial rectifier controller parameters are tuned using the standard values. These initial controller parameters are the optimal controller parameters for the controlled object at that time, and the control performance of the rectifier controller using the optimal controller parameters is also optimal. It can be expected that the control performance of the rectifier controller that deviates from the optimal controller parameters will inevitably be reduced compared to the control performance of the rectifier controller with the optimal parameters.

[0032] After the elevator is put into use, the actual value of the bus capacitor's capacitance parameter will gradually decrease due to factors such as the extension of usage time. This means that the controlled object containing the bus capacitor has changed compared to the initial use of the elevator. The controller parameters originally adjusted using the standard value of the bus capacitor's capacitance parameter value are no longer the optimal controller parameters for the controlled object at this time. Therefore, the control performance at this time will inevitably be reduced to a certain extent compared to the control performance at the initial use of the elevator. In this way, we can monitor the capacitance parameter value of the bus capacitor by monitoring the changes in the control performance of the rectifier controller.

[0033] The method for diagnosing the bus capacitance of the elevator drive system provided in this embodiment utilizes the above principle and includes the following steps:

[0034] Step S1: establishing an evaluation index, wherein the evaluation index is used to characterize the control performance of the rectifier controller, and the value of at least one control parameter of the rectifier controller is determined by the capacitance parameter value of the bus capacitor;

[0035] Step S2: establishing a mathematical model, wherein the mathematical model is used to describe the relationship between the evaluation index and a first change, wherein the first change refers to a change in a current value of a capacitance parameter value of the busbar capacitor relative to a standard value;

[0036] Step S3, monitoring the evaluation index;

[0037] Step S4: determining the first change according to the evaluation index and the mathematical model;

[0038] Step S5: Determine whether the first change exceeds a set threshold, and when it is determined that the first change exceeds the set threshold, output information indicating that the capacitance parameter value of the bus capacitor is abnormal.

[0039] In order to smoothly monitor the capacitance parameter value of the bus capacitor by monitoring the change of the control performance of the rectifier controller,

[0040] The rectifier controller must meet the following requirements:

[0041] Condition A: When the actual value of the capacitance parameter of the bus capacitor is its standard value, the control performance of the controller is optimal;

[0042] Condition B: When the actual value of the capacitance parameter value of the bus capacitor is not the standard value, the control performance of the controller is non-optimal;

[0043] Condition C: The control performance of the controller changes with the actual value of the capacitance parameter value of the bus capacitor.

[0044] Condition D: The control performance of the controller is a monotonic function with the first change as the independent variable.

[0045] In order to implement the monitoring of the control performance of the rectifier controller, it is necessary to pre-establish the evaluation index of the control performance and its calculation method. The basic quantity required for the calculation of the evaluation index needs to be detectable or obtainable from other systems. For example, the evaluation index is the maximum value of the tracking error of the bus voltage within a certain period of time or the integral value of its absolute value. The bus voltage tracking error can be directly obtained from the rectifier side control part in the elevator drive control system. This application does not limit the specific form of the evaluation index, as long as it can reflect the control performance of the controller and can be obtained. The conditions that the evaluation index needs to meet include:

[0046] Condition 1: When the controller's control performance is optimal, the evaluation index takes the maximum value;

[0047] Condition 2: When the control performance of the controller is not optimal, the value of the evaluation index is not the maximum value;

[0048] Condition 3: the evaluation index is a continuous function;

[0049] Condition 4: The evaluation index is a monotonic function or a partially monotonic function (some segments are constant or some segments are monotonic).

[0050] In theory, as long as the monitoring evaluation index shows a non-zero deviation (i.e., the two are not equal), it can be determined that the capacitance parameter value of the bus capacitor has changed relative to the initial value. However, from the perspective of engineering practice, only when the current value of the capacitance parameter value of the bus capacitor or its change (i.e., decrease) relative to the standard value meets certain conditions is it necessary to issue a warning or predict its remaining service life and then formulate a replacement plan. The condition here is the set threshold in step S5.

[0051] In order to use the control performance of the rectifier controller to determine the current value of the capacitance parameter value of the bus capacitor or the change in the control performance of the rectifier controller to determine the change in the current value of the capacitance parameter value of the bus capacitor relative to its standard value, it is necessary to pre-establish a corresponding relationship or model between the control performance (or its change) and the current value of the capacitance parameter value of the bus capacitor (or the change relative to its standard value). The corresponding relationship or model can be a table obtained by using experimental test data or a curve obtained by curve fitting using experimental test data, or a model established by using neural networks, machine learning, etc. for experimental test data; it can also be a formula established by using a mechanism modeling method, that is, using control theory to analyze the control structure and working principle of the rectifier controller, analyzing the sensitivity of the rectifier to the mathematical model of the controlled object, and using tools such as perturbation method to determine the influence and quantitative relationship between the control performance of the controller and the system parameter change in the controlled object. Since the relationship and model depend on the specific performance indicators and the specific structure of the controller, the tables and models corresponding to different controllers and / or different performance indicators are necessarily different, so the specific implementation of the relationship and model is not listed here.

[0052] Based on the above, the control performance evaluation index of the rectifier controller can be monitored. When the first change determined based on the evaluation index and the mathematical model exceeds a set threshold, an alarm is issued, indicating that the capacitance parameter value of the bus capacitor has dropped to a level that requires attention. The index threshold here is predetermined as needed. For example, a lower limit for control performance can be pre-set, that is, the control performance of the controller cannot fall below this lower limit. When it reaches or falls below this lower limit, the bus capacitor must be replaced immediately.

[0053] Preferably, a starting point of concern can be set. When the performance index gradually decreases from the initial optimal value to the starting point of concern, it indicates that the change in the capacitance parameter value of the bus capacitor relative to the standard value (usually a decrease relative to the standard value) has reached a certain level, and it is necessary to start paying appropriate attention to the capacitance parameter of the bus capacitor. Therefore, step A1 can be added between step S4 and step S5 to determine whether the first change exceeds the concern threshold, the concern threshold is less than the set threshold, and when it is determined that the first change exceeds the concern threshold, the remaining service life of the bus capacitor is predicted based on the evaluation index and / or its change trend, and a maintenance plan for the bus capacitor is formulated based on the life prediction results.

[0054] Another thing to note is that when the controller of the rectifier is a robust controller with a robust parameter α, and the robust parameter α is less than the attention threshold, the robust parameter α indicates that under the control of the robust controller, the control performance of the robust controller will only be reduced when the deviation of the actual value of the parameter of its controlled object from the standard value exceeds α.

[0055] Example 2

[0056] Considering that for the rectifier controller, the inverter and the subsequent traction machine and other loads are external interference to the bus voltage at both ends of the bus capacitor of the controlled rectifier (the rectifier controller is to control the bus voltage so that it follows the voltage command), this interference will inevitably affect the controller's control performance of the bus voltage, thereby affecting the corresponding evaluation indicators. In order to weaken or even eliminate the impact of external interference on the evaluation indicators, the following two methods can be adopted:

[0057] Method 1: Since the controller has a strong compensatory and inhibitory effect on constant interference, the constant interference will not affect the control performance of the controller. Therefore, it can be defined as follows: after the elevator is in a uniform speed operation stage and the duration of the uniform speed operation stage exceeds a time threshold, step S4 determines the first change according to the evaluation index and the mathematical model, and step S5 executes to determine whether the first change exceeds a set threshold, and the time threshold causes the control output of the rectifier or inverter to enter a change amplitude less than the amplitude threshold interval.

[0058] Method 2: Real-time calculation of the real-time power of the load formed by the combination of the inverter and traction machine on the rectifier. This real-time power is then introduced into the rectifier controller in a feedforward manner to eliminate the impact of load changes on the control performance of the rectifier controller. For example, the rectifier controller typically adopts a dual closed-loop structure of voltage and current. The voltage loop controls the bus voltage across the bus capacitor and outputs a current command (this command is actually the current required to make the bus voltage track its command value). The current loop controls the current in the rectifier (usually the d-axis current and q-axis current in the dq coordinate system) to make it track the current command. The real-time load power introduced as described above can be divided by the current value of the bus voltage and then added to the current value output by the voltage loop. The resulting sum is used as the current command value sent to the current loop. In Method 2, step S4 can determine the first change based on the evaluation index and the mathematical model at any time, and then step S5 is executed to determine whether the first change exceeds a set threshold.

[0059] Example 3

[0060] In this embodiment, the rectifier controller has a self-learning capability and a self-learning unit. The diagnosis method of the bus capacitance of the elevator drive system is specifically as follows:

[0061] The controller of the rectifier has at least one specific control parameter, where the specific control parameter is a control parameter of the rectifier controller whose value is determined by a capacitance parameter value of the bus capacitor, and the control performance of the rectifier controller is optimal when a first value is equal to a second value, the first value being a value of the capacitance parameter value of the bus capacitor used to calculate the specific control parameter, and the second value being a current value of the capacitance parameter value of the bus capacitor;

[0062] The specific control parameter is adjusted to maintain the control performance of the rectifier controller at an optimal state. The diagnostic method monitors the specific control parameter and determines the current value of the bus capacitor capacitance parameter based on the specific control parameter. When the difference between the current value of the bus capacitor capacitance parameter and its standard value exceeds a preset threshold, information indicating an abnormality in the bus capacitor capacitance parameter value is output. When the elevator is first put into use, the current value of the bus capacitor capacitance parameter is equal to its standard value, and the control performance is optimal.

[0063] There are two rules for the self-learning unit to adjust specific control parameters.

[0064] The first one is:

[0065] Step A1: changing the specific control parameter by a first change amount in the current direction based on the current value;

[0066] Step A2: controlling the rectifier using the changed specific control parameters;

[0067] Step A3: If the control performance improves, continue changing the specific control parameter along the current adjustment direction until the control performance of the controller using the adjusted specific control parameter value decreases compared to the previous value, discard the last change and retain the previous specific control parameter value as the current value of the specific control parameter; if the control performance decreases, change the adjustment direction and continue changing the specific control parameter value along the changed adjustment direction until the control performance of the controller using the changed specific control parameter decreases compared to the previous value, discard the last change and retain the previous specific control parameter value as the current value of the specific control parameter;

[0068] Step A4: Based on the relationship between the specific control parameter and the capacitance parameter of the bus capacitor, the current value of the capacitance parameter of the bus capacitor is calculated using the current value of the specific control parameter.

[0069] The second type is:

[0070] Step B1, appropriately changing the capacitance parameter value of the bus capacitor;

[0071] Step B2: Update the specific control parameter using the changed capacitance parameter value

[0072] Step B3, controlling the rectifier using the updated specific control parameters;

[0073] Step B4: If the control performance improves, continue to change the capacitance parameter value along the current adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor; if the control performance decreases, change the adjustment direction and continue to change the capacitance parameter value along the changed adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor.

[0074] Then, the current value of the capacitance parameter value of the bus capacitor is used to perform relevant judgments and warnings in the manner of Example 1.

[0075] The difference between this embodiment and embodiment 1 lies in the method for determining the current value of the capacitance parameter of the bus capacitor, and the rest is similar.

[0076] The present invention has been described in detail above by way of specific embodiments and examples, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may make many variations and improvements, which should also be considered within the scope of protection of the present invention.

Claims

1. A method for diagnosing busbar capacitance of an elevator drive system, wherein the elevator drive system is composed of a rectifier, a busbar capacitor, and an inverter connected in sequence, characterized in that: Step S1: establishing an evaluation index, wherein the evaluation index is used to characterize the control performance of the rectifier controller, and the value of at least one control parameter of the rectifier controller is determined by the capacitance parameter value of the bus capacitor; Step S2: establishing a mathematical model, wherein the mathematical model is used to describe the relationship between the evaluation index and a first change, wherein the first change refers to a change in a current value of a capacitance parameter value of the busbar capacitor relative to a standard value; Step S3, monitoring the evaluation index; Step S4: determining the first change according to the evaluation index and the mathematical model; Step S5: Determine whether the first change exceeds a set threshold, and when it is determined that the first change exceeds the set threshold, output information indicating that the capacitance parameter value of the bus capacitor is abnormal.

2. The method for diagnosing bus capacitance of an elevator drive system according to claim 1, characterized in that: The controller of the rectifier must meet the following requirements: Condition A: When the actual value of the capacitance parameter of the bus capacitor is its standard value, the control performance of the controller is optimal; Condition B: When the actual value of the capacitance parameter value of the bus capacitor is not the standard value, the control performance of the controller is non-optimal; Condition C: The control performance of the controller changes with the actual value of the capacitance parameter value of the bus capacitor.

3. The method for diagnosing bus capacitance of an elevator drive system according to claim 2, characterized in that: The controller of the rectifier must also meet the following requirements: Condition D: The control performance of the controller is a monotonic function with the first change as the independent variable.

4. The method for diagnosing bus capacitance of an elevator drive system according to claim 2 or 3, characterized in that: The evaluation indicators meet the following conditions: Condition 1: When the controller's control performance is optimal, the evaluation index takes the maximum value; Condition 2: When the control performance of the controller is not optimal, the value of the evaluation index is not the maximum value; Condition 3: the evaluation index is a continuous function; Condition 4: The evaluation index is a monotonic function or a partially monotonic function.

5. The method for diagnosing bus capacitance of an elevator drive system according to claim 1, characterized in that: Also included between step S4 and step S5: Step A1: Determine whether the first change exceeds a concern threshold, the concern threshold is less than the set threshold, and when it is determined that the first change exceeds the concern threshold, predict the remaining service life of the bus capacitor based on the evaluation index and / or its change trend.

6. The method for diagnosing bus capacitance of an elevator drive system according to claim 5, characterized in that: The controller of the rectifier is a robust controller with a robust parameter α, and the robustness parameter α is less than the attention threshold. The robustness parameter α indicates that under the control of the robust controller, the control performance of the robust controller will only be reduced when the deviation of the actual value of the parameter of its controlled object from the standard value exceeds α.

7. The method for diagnosing bus capacitance of an elevator drive system according to claim 1, characterized in that: After the elevator is in a uniform speed operation stage and the duration of the uniform speed operation stage exceeds a time threshold, the step S4 determines the first change based on the evaluation index and the mathematical model, and the step S5 is executed to determine whether the first change exceeds a set threshold. The time threshold causes the control output of the rectifier or inverter to enter an interval in which the change amplitude is less than the amplitude threshold.

8. The method for diagnosing bus capacitance of an elevator drive system according to claim 1, characterized in that: When the controller of the rectifier includes a load-based feedforward control unit, at any time, step S4 can determine the first change based on the evaluation index and the mathematical model, and then step S5 is executed to determine whether the first change exceeds a set threshold.

9. The method for diagnosing bus capacitance of an elevator drive system according to any one of claims 1 to 8, characterized in that: The evaluation index is the maximum value of the tracking error of the bus voltage within a certain period of time or the integral value of its absolute value.

10. A method for diagnosing busbar capacitance of an elevator drive system, wherein the elevator drive system is composed of a rectifier, a busbar capacitance, and an inverter connected in sequence, characterized in that: The controller of the rectifier has at least one specific control parameter, the specific control parameter being a control parameter of the rectifier controller whose value is determined by a capacitance parameter value of the bus capacitor, and the control performance of the rectifier controller is optimal when a first value is equal to a second value, the first value being a value of the capacitance parameter value of the bus capacitor used to calculate the specific control parameter, and the second value being a current value of the capacitance parameter value of the bus capacitor; By adjusting the specific control parameters, the control performance of the controller of the rectifier is always kept in an optimal state; The diagnostic method monitors the specific control parameter, determines the current value of the capacitance parameter of the bus capacitor based on the specific control parameter, and when the difference between the current value of the capacitance parameter of the bus capacitor and its standard value exceeds a preset threshold, outputs information that the capacitance parameter value of the bus capacitor is abnormal.

11. The method for diagnosing bus capacitance of an elevator drive system according to claim 10, characterized in that: The controller of the rectifier adjusts the specific control parameters according to the following rules: Step A1: changing the specific control parameter by a first change amount in the current direction based on the current value; Step A2: controlling the rectifier using the changed specific control parameters; Step A3: If the control performance improves, continue changing the specific control parameter along the current adjustment direction until the control performance of the controller using the adjusted specific control parameter value decreases compared to the previous value, discard the last change and retain the previous specific control parameter value as the current value of the specific control parameter; if the control performance decreases, change the adjustment direction and continue changing the specific control parameter value along the changed adjustment direction until the control performance of the controller using the changed specific control parameter decreases compared to the previous value, discard the last change and retain the previous specific control parameter value as the current value of the specific control parameter; Step A4: Based on the relationship between the specific control parameter and the capacitance parameter of the bus capacitor, the current value of the capacitance parameter of the bus capacitor is calculated using the current value of the specific control parameter.

12. The method for diagnosing bus capacitance of an elevator drive system according to claim 10, characterized in that: The controller of the rectifier adjusts the specific control parameters according to the following rules: Step B1, appropriately changing the capacitance parameter value of the bus capacitor; Step B2: updating the specific control parameter using the changed capacitance parameter value; Step B3: controlling the rectifier using the updated specific control parameters; Step B4: If the control performance improves, continue to change the capacitance parameter value along the current adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor; if the control performance decreases, change the adjustment direction and continue to change the capacitance parameter value along the changed adjustment direction until the control performance of the controller using the updated specific control parameters is lower than the previous one, discard the last change and retain the previous capacitance parameter value, and use it as the current value of the capacitance parameter value of the bus capacitor.

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