Method for evaluating service life of flywheel energy storage motor under insulation square wave voltage and environmental stress

Abstract

The invention discloses a service life evaluation method for a flywheel energy storage motor under insulation square wave voltage and environmental stress. The service life evaluation method comprises the following steps: constructing an accelerated aging experiment platform comprising temperature control, air pressure control, a high-frequency and high-voltage square wave source, partial discharge detection and a breakdown protection circuit; multiple groups of accelerated aging tests are carried out on the motor insulation sample through a control variable method, and service life models under the square wave frequency, the rise time, the environment temperature and the air pressure single stress are obtained respectively; taking each single-stress life model as a life item, combining with a coupling life correction item, and establishing a multi-stress life evaluation model in a reciprocal form of the sum of reciprocals of the life items; and calculating a coupling life correction term and averaging by inversely solving an equivalent value of the single-stress life model under a multi-stress reference condition to complete model parameter calibration. The service life prediction precision and reliability are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of motor insulation life assessment technology, and particularly relates to a method for assessing the life of a flywheel energy storage motor under square wave voltage and environmental stress. Background Technology

[0002] Flywheel energy storage is an electromechanical energy conversion and storage device. The system mainly includes a rotor, bearings, a high-speed motor, and a power conversion system. Its working principle is as follows: the power electronic conversion device receives electrical energy from the outside to drive the motor to rotate, which in turn drives the flywheel to rotate. The flywheel stores kinetic energy (mechanical energy). When an external load requires energy, the flywheel drives a generator to rotate, converting the kinetic energy into electrical energy. This electrical energy is then converted by the power electronic conversion device into electrical energy of various frequencies and voltage levels required by the load to meet different needs. As a physical energy storage method, it overcomes the limitations of chemical energy storage and has attracted much attention due to its advantages such as being environmentally friendly, having high energy density, high instantaneous power, and long service life. It has been widely used in important technological fields such as aerospace, new energy vehicles, and power grid peak shaving and frequency regulation.

[0003] The electric field experienced by the flywheel energy storage motor is the square wave voltage stress driven by the inverter. As the switching speed and frequency of the devices increase, overvoltage and uneven voltage distribution between windings are prone to occur at the motor terminals. Simultaneously, the flywheel energy storage motor operates in harsh environments (high / low temperature and low pressure) (e.g., high-speed rotation of the flywheel in the system, typically operating in a low-vacuum environment to reduce wind friction losses), which leads to an increase in the mean free path of electrons, promoting electron avalanche development. Therefore, the operating environment of the flywheel energy storage motor is more prone to partial discharge than that under power frequency voltage and normal temperature and pressure, threatening the reliability of the motor insulation. Prolonged aging may lead to insulation breakdown, damaging power equipment and even causing large-scale power outages.

[0004] The inverse power law of lifetime (IPL) is a classic empirical model in reliability engineering used to describe the nonlinear relationship between electrical stress (voltage, current, power) and insulation lifetime. Its core idea is that lifetime decreases inversely with electrical stress as a function of power. The inverse power law of motor insulation lifetime and voltage is as follows:

[0005]

[0006] Where L is the insulation life (in hours) at voltage V; L0 is the life at reference voltage V0; and n is the voltage stress exponent (dimensionless, calibrated by material testing, typically n≈2-12). Based on the inverse power law, accelerated aging tests can be performed to accelerate the aging of motor insulation at 2.5 times the partial discharge initiation voltage. The insulation life will be significantly shortened under these conditions. The obtained life, calculated using the inverse power law, can then be used to determine the expected life of the insulation at different voltage levels. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress, which significantly improves the accuracy and reliability of lifespan prediction.

[0008] To achieve the above objectives, the present invention provides a method for assessing the insulation square wave voltage and environmental stress of a flywheel energy storage motor, comprising:

[0009] An accelerated aging test platform was constructed, which includes temperature control, air pressure control, high-frequency high-voltage square wave source, partial discharge detection and breakdown protection circuits.

[0010] Multiple accelerated aging tests were conducted on motor insulation samples using the controlled variable method to obtain life models under square wave frequency, rise time, ambient temperature, and single air pressure stress.

[0011] Each single-stress life model is used as a life term, and combined with the coupled life correction term, a multi-stress life assessment model is established by taking the reciprocal form of the sum of the reciprocals of each life term.

[0012] By inversely solving the equivalent value of the single-stress lifetime model under multi-stress reference conditions, calculating the coupled lifetime correction term and taking the average, the model parameter calibration is completed.

[0013] Optional accelerated aging testing platforms include:

[0014] Temperature and pressure controllable cavity, adjustable temperature range 20-200℃ and pressure range 20-100kPa;

[0015] High-frequency high-voltage square wave source, outputting a square wave with a peak-to-peak value of 15kV, a rise time of 40ns, and a frequency of 10kHz;

[0016] A partial discharge detection antenna is fixed 5cm outside the cavity to collect ultra-high frequency signals;

[0017] When the protection circuit breaks down, the current is monitored by a Hall sensor, and the optocoupler relay cuts off the high-voltage circuit when the threshold current is reached.

[0018] Optionally, the process of obtaining the single-stress life model includes:

[0019] A square wave with 2.5 times the partial discharge initiation voltage was applied to the sample;

[0020] With other stresses fixed at reference conditions, adjust the square wave frequency, rise time, temperature, or air pressure individually.

[0021] Record the breakdown time of the sample as the lifetime value, and conduct 5 tests for each set of conditions and take the average value.

[0022] Optionally, the single-stress lifetime model for square wave frequency is in the form of a power function, and the lifetime is related to the frequency by a negative power.

[0023] Optionally, the single-stress lifetime model for the rise time of the square wave is in the form of a negative exponential function, and the lifetime decreases as the rise time decreases.

[0024] Optionally, the ambient temperature single-stress life model is in the form of the Arrhenius equation, and the life decreases exponentially with increasing temperature.

[0025] Optionally, the environmental pressure single-stress life model is a linear function, and the life is positively correlated with the air pressure.

[0026] Optionally, the calculation process for the coupling lifetime correction term includes:

[0027] The baseline conditions were set as follows: 250 ns rise time, 5 kHz frequency, 140 °C temperature, and 100 kPa air pressure.

[0028] Substitute the single-stress model into the right side of the multi-stress model equation, and substitute the life value under the corresponding reference conditions into the left side.

[0029] The coupling lifetime correction term is solved by reverse calculation, and the arithmetic mean of the four sets of calculation results is taken.

[0030] Technical effects of the invention:

[0031] 1. Comprehensive coverage of multiple stresses: For the first time, it integrates square wave electrical stress (frequency, rise time) and environmental stress (temperature, air pressure) to solve the blind spot in life prediction under the special working conditions of flywheel energy storage and break through the limitations of traditional single voltage model.

[0032] 2. Precise quantification of coupling effects: The coupling correction term characterizes the synergistic effect of multiple stresses (such as low pressure promoting discharge and high temperature superimposed thermal aging), which significantly improves the accuracy and reliability of lifetime prediction.

[0033] 3. Enhanced engineering applicability: The standardized experimental platform (including vacuum oven, square wave source and protection circuit) ensures experimental safety, and the average value of multiple repeated tests effectively controls prediction error.

[0034] 4. Breakthrough technological innovation: The first multi-stress life assessment model was established, providing an assessment standard that is closer to the actual operating environment for the insulation design of flywheel energy storage motors. Attached Figure Description

[0035] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0036] Figure 1 This is a schematic diagram of the structure of the accelerated aging test platform for the phase insulation of the flywheel energy storage motor according to an embodiment of the present invention;

[0037] Figure 2 This is a circuit diagram for motor insulation aging protection according to an embodiment of the present invention;

[0038] Figure 3 This is a physical diagram of the motor insulation aging protection circuit according to an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the model fitting results of square wave frequency and lifetime in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the model fitting results for the rise time and lifetime of a square wave according to an embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the model fitting results for environmental temperature and lifespan in an embodiment of the present invention;

[0042] Figure 7 This is a schematic diagram of the model fitting results of environmental air pressure and lifespan in an embodiment of the present invention. Detailed Implementation

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0045] This embodiment provides a method for assessing the insulation square wave voltage and environmental stress of a flywheel energy storage motor, including:

[0046] To address the lack of a multi-stress life model in current flywheel energy storage technologies, accelerated aging experiments were conducted to analyze the impact of different stresses on the insulation life of flywheel energy storage motors. A life assessment model for the phase-to-phase insulation of the motors under the influence of high-voltage, high-frequency square waves and various environmental stress factors was proposed.

[0047] High-frequency high-voltage square wave frequency:

[0048] The relationship between frequency and aging lifetime was fitted using an inverse power-law model:

[0049] L=αf -β ;

[0050] Where L is the aging life (min), f is the frequency of the square wave voltage (Hz), α is dimensionless (min / Hz), and β is dimensionless.

[0051] Using a power function to fit the relationship between frequency and aging lifetime:

[0052]

[0053] Where t r Let θ be the rise time (ns) of the square wave voltage, and k be the dimensionless value in ns. The dimensionless range is min.

[0054] According to the Arrhenius Law, the relationship between reaction rate and temperature is obtained:

[0055]

[0056] Where k is the reaction rate, A is the pre-exponential factor (constant), and R is the gas constant, which is 8.314 (J·mol⁻¹). -1 ·K -1 (), where T is the thermodynamic temperature. The relationship between aging life and temperature is fitted by the reciprocal of the reaction rate, i.e.:

[0057]

[0058] Where T is the thermodynamic ambient temperature (K), a is dimensionless (min), and b is dimensionless (K).

[0059] Fitting a linear function relationship between air pressure and lifespan:

[0060] L = cP + d;

[0061] P is the air pressure (kPa), c is in the dimension of min / kPa, and d is in the dimension of min.

[0062] The phase insulation life of flywheel energy storage motors is affected by the frequency of high-frequency high-voltage square waves, the rise time of high-frequency high-voltage square waves, ambient temperature, and ambient air pressure. As the square wave frequency increases, the rise time decreases, the temperature increases, and the air pressure decreases, the life decreases accordingly.

[0063] During the aging process of motor insulation, stress factors such as electric field, temperature, and air pressure accelerate aging by affecting the energy state and physicochemical reactions within the insulation material. Different stress factors interact and undergo energy conversion. Starting from the aging mechanism of insulation materials, this study comprehensively considers the individual effects and coupling effects of electrical stress and environmental stress on insulation life. During motor operation, the superposition of Joule heating induced by the electric field and partial discharge, along with ambient temperature, accelerates thermal aging of the insulation; low air pressure promotes electron avalanche development and enhances partial discharge activity. A multi-factor model based on mechanism coupling is established, organically integrating single-factor models by adding correction terms reflecting the coupling effect. The innovation lies in the correction terms based on the aging mechanism, making the model more realistic and accurately predicting insulation life under varying operating conditions.

[0064]

[0065] Where L represents the insulation life after comprehensive multi-stress, and L represents the life under individual consideration of square wave frequency rise time, ambient temperature, and air pressure, respectively. coup This is the lifetime correction term. It is obtained by solving the following formula:

[0066]

[0067] Accelerated aging tests were conducted on the insulation samples of the motor. The experimental platform was as follows: Figure 1 As shown, a flat wire sample is used as an example (flat wire).

[0068] The system consists of a high-voltage square wave power supply, protective resistors, a vacuum oven, protection circuitry, and a detection antenna. The square wave source has adjustable parameters, with a maximum peak-to-peak voltage of 15kV, an open-circuit voltage rise time of 40ns, and a maximum voltage repetition frequency of 10kHz. A dual-ridged horn antenna, used to detect partial discharge signals, is placed in a fixed position outside the cavity, approximately 5cm from the cavity surface, to avoid affecting the signal strength due to position changes. The temperature of the vacuum oven is controllable within the range of 20℃-200℃, and the air pressure is controllable within the range of 20kPa-100kPa. A 10kV withstand voltage probe is used to measure the square wave voltage, which is then connected to an oscilloscope.

[0069] In accelerated aging tests of motor insulation, a protection circuit is required to limit the large current during insulation breakdown and prevent short-circuit damage to the equipment. In this protection circuit, a Hall effect sensor monitors the current throughout the circuit, converting it into a voltage signal via the Hall effect. After processing by a data acquisition card, once the current value reaches a threshold, the program controls an optocoupler relay to disconnect the high-voltage circuit. The schematic diagram and physical prototype of the motor insulation aging protection circuit are shown below. Figure 2 and Figure 3 As shown.

[0070] Step 1: Prepare flat wire sample

[0071] Twist both ends of the flat wire so that the ends open outwards like ram's horns, while ensuring that the parallel sections of the sample are parallel and not bent. Use insulating material to evenly fix the two flat wires, controlling the air gap of different samples to be consistent and reduce the dispersion of experimental results. Grind away the polyimide insulating layer at both ends of the ram's horn pair to expose the metal part, and connect it to a high-voltage high-frequency square wave power supply and ground respectively during the experiment.

[0072] Step 2: Accelerated aging test

[0073] The samples were placed individually in an oven, and a square wave voltage of 2.5 times the partial discharge initiation voltage was applied to the flat wire samples under different rise times, frequencies, temperatures, and air pressures. When studying the effect of a single stress, other conditions related to the model should remain constant. The square wave frequency can be changed by adjusting the square wave source trigger circuit or related settings, the square wave rise time can be changed by adjusting the protection resistor and load characteristics, and the air pressure and temperature around the sample can be changed by heating and evacuating the cavity. The environmental stress and voltage stress of the sample were kept constant until the sample insulation failed and aging breakdown caused the protection circuit to activate. The time taken for the sample to break down under specific conditions was recorded, which is the sample life. Five sets of aging experiments were performed under each condition, and the average value was taken to reduce the dispersion of the results.

[0074] Step 3: Single Stress Model Calculation

[0075] The model described in this invention was applied to the accelerated aging experiment results, using L=αf respectively. -β , The relationship between the fitted lifetime L = cP + d and the square wave frequency, rise time, temperature, and air pressure is obtained, and α, β, a, b, c, d, k, and θ are calculated. Equal fitting coefficients.

[0076] Step 4: Calculation of Multi-Stress Synthetic Model

[0077] To obtain a complete life assessment model for the phase-to-phase insulation of the motor under the influence of high-voltage high-frequency square waves and various environmental stress factors, it is necessary to calculate the life correction term L. coup The obtained single-factor model is used as the current multi-factor lifetime model and substituted into the left and right sides of the multi-factor model formula, respectively. The remaining factors are substituted into the insulation lifetime under the baseline conditions of the selected area during the experiment: (taking P as an example)

[0078]

[0079] L obtained by solving different factors couptr L coupf L coupT L coupP The final L can be obtained by taking the average value. coup Therefore, Lcouptr L coupf L coupT L coupP The smaller the variance, the smaller the dispersion, and the better the final model can reflect the actual lifespan of the sample.

[0080] Example

[0081] A square wave voltage of 2.5 times the partial discharge initiation voltage was applied to flat wire samples under different rise times (250 ns, 350 ns, 500 ns, and 1000 ns), frequencies (1 kHz, 2 kHz, 4 kHz, and 5 kHz), temperatures (20℃, 60℃, 100℃, 140℃, and 180℃), and pressures (20 kPa, 40 kPa, 60 kPa, 80 kPa, and 100 kPa). Five sets of aging experiments were conducted under each condition, and the average value was taken. When studying the effect of a single stress, other conditions related to the model were kept constant: 250 ns, 5000 Hz, 140℃, and 100 kPa.

[0082] The fitting results of the experimental sample aging life with square wave frequency, square wave rise time, temperature, and air pressure are as follows: Figure 4 , 5 As shown in Figures 6 and 7, we obtain:

[0083] L = 58752.87f -0.879 (min);

[0084]

[0085] L = 0.58p + 6.17 (min);

[0086] Based on the single-stress model above, the single-factor lifetime corresponding to the baseline condition is calculated as: L 250ns =22.97mn, L 5000Hz =32.93min, L 140℃ =35.61min, L 100kPa =64.17min;

[0087] That is, the life assessment model for the phase-to-phase insulation of the motor under the influence of high voltage, high frequency square wave and various environmental stress factors is as follows:

[0088]

[0089] Substituting the fitting results of the sample aging lifetime with square wave frequency, square wave rise time, temperature, and air pressure into the left side of the equation, and then substituting the single-factor lifetime under the reference conditions, we obtain L. coupf =-11.47, L couptr =-13.51, L coupP=-9.81, L coupT = -11.17, take the average to get L coup = -11.49. Therefore, we have:

[0090]

[0091] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress, characterized in that, include: An accelerated aging test platform was constructed, which includes temperature control, air pressure control, high-frequency high-voltage square wave source, partial discharge detection and breakdown protection circuits. Multiple accelerated aging tests were conducted on motor insulation samples using the controlled variable method to obtain life models under square wave frequency, rise time, ambient temperature, and single air pressure stress. Each single-stress life model is used as a life term, and combined with the coupled life correction term, a multi-stress life assessment model is established by taking the reciprocal form of the sum of the reciprocals of each life term. By inversely solving the equivalent value of the single-stress lifetime model under multi-stress reference conditions, calculating the coupled lifetime correction term and taking the average, the model parameter calibration is completed.

2. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The accelerated aging testing platform includes: Temperature and pressure controllable cavity, adjustable temperature range 20-200℃ and pressure range 20-100kPa; High-frequency high-voltage square wave source, outputting a square wave with a peak-to-peak value of 15kV, a rise time of 40ns, and a frequency of 10kHz; A partial discharge detection antenna is fixed 5cm outside the cavity to collect ultra-high frequency signals; When the protection circuit breaks down, the current is monitored by a Hall sensor, and the optocoupler relay cuts off the high-voltage circuit when the threshold current is reached.

3. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The process of obtaining the single stress life model includes: A square wave with 2.5 times the partial discharge initiation voltage was applied to the sample; With other stresses fixed at reference conditions, adjust the square wave frequency, rise time, temperature, or air pressure individually. Record the breakdown time of the sample as the lifetime value, and conduct 5 tests for each set of conditions and take the average value.

4. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The single-stress lifetime model for square wave frequency is a power function, and the lifetime is related to the frequency by a negative power.

5. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The single-stress lifetime model for square wave rise time is a negative exponential function, and the lifetime decreases as the rise time decreases.

6. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The ambient temperature single-stress life model is in the form of the Arrhenius equation, and the life decreases exponentially with increasing temperature.

7. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The environmental pressure single-stress life model is a linear function, and the life is positively correlated with the air pressure.

8. The method for assessing the lifespan of a flywheel energy storage motor under insulation square wave voltage and environmental stress as described in claim 1, characterized in that, The calculation process for the coupling lifetime correction term includes: The baseline conditions were set as follows: 250 ns rise time, 5 kHz frequency, 140 °C temperature, and 100 kPa air pressure. Substitute the single-stress model into the right side of the multi-stress model equation, and substitute the life value under the corresponding reference conditions into the left side. The coupling lifetime correction term is solved by reverse calculation, and the arithmetic mean of the four sets of calculation results is taken.

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