A coating process for reducing winding insulation losses

Abstract

The present application relates to the technical field of high-efficiency motor manufacturing, and discloses a coating process for reducing winding insulation loss, which comprises the following steps: coating an insulation coating on the surface of a three-phase winding, generating Joule heat by applying alternating current, and generating induced eddy current heat by applying an alternating magnetic field with an induction heating coil, so as to build an inverted temperature field with an internal temperature higher than an external temperature to drive free solvent molecules to volatilize outward along the radial direction; collecting the online high-frequency complex impedance vector of the winding lead-out end, calculating the cross-linking state characteristic index after impedance variation correction, and tracking the first-order time derivative thereof; when the first-order time derivative meets the transition condition, the induced heating power is increased and the amplitude of the alternating current is reduced, so that the superficial layer of the insulation coating is heated to 140 DEG C to 160 DEG C for cross-linking and solidification; the present application adjusts the mass transfer driving force from the inside to the outside, eliminates the skin resistance, avoids internal pores, improves the uniformity of the edge and corner thickness, and stabilizes the local electric field concentration of the slot coil.

Description

Technical Field

[0001] This invention belongs to the field of high-efficiency motor manufacturing technology, and in particular relates to a coating process for reducing winding insulation loss. Background Technology

[0002] The insulation treatment of motor windings typically involves impregnation with polymer insulating varnish followed by overall baking with an external heat source. This forms a withstand-voltage coating on the surface of the stator windings and coils within the slots, capable of withstanding the electrical stress caused by high-frequency pulse voltages during frequency conversion drive. During the curing of the insulating medium, influenced by the spatial shape within the stator slots and the flow characteristics of the varnish, the varnish flows along the stator slot corners under surface tension and capillary action. This causes the varnish at the coil flanges and corners to run off to the surrounding areas, resulting in a thinner varnish film. Simultaneously, when using an external heat source for overall baking, heat is transferred from the outside in, causing the surface layer of the coating to effloresce first. Cross-linking reactions occur, forming a dense skin. Once the surface skin is formed, the channels for free solvent molecules inside the varnish film to evaporate outward are blocked. Under the action of evaporation pressure, the residual solvent inside either breaks through the skin layer and escapes or remains inside the varnish film, thus forming pores and causing interlayer stress concentration. Under the action of the high-frequency high-voltage pulse electric field output by the frequency converter, these pores are prone to continuous local ionization and discharge, which significantly increases the polarization loss of the winding insulation medium and generates local heat accumulation, leading to local dielectric breakdown and premature thermal aging and burnout of the insulation layer.

[0003] In existing technologies, extending the vacuum pumping time to forcibly expel gas can easily cause unstable flash evaporation of low-boiling-point solvents; increasing the external baking temperature will cause the coating surface to form a skin more quickly and lead to thermal embrittlement of the paint film; increasing the number of coating and dipping cycles can only increase the thickness of the paint film surface, but cannot change the way heat is transferred from the outside to the inside, nor can it change the mass transfer resistance of the coating surface. Therefore, it is difficult to eliminate the weak areas of the paint film formed by paint loss at the corners. Even if the dipping boundary is improved by optimizing the hardware structure such as tooling fixtures or roller shape, the overall physical adjustment is difficult to reach the surface unsteady mass transfer control. The process control methods for insulation treatment also have limitations. For example, Chinese invention patent application CN111793427A discloses an insulation treatment method for an electric motor, which uses stepped heating and fixed insulation to form a film. However, this open-loop temperature control scheduling implicitly relies on a static heat conduction model and fails to consider the unsteady heat transfer hysteresis and multiphase dynamic evolution caused by the complex spatial layout in the stator slots of high power density motors. Under actual complex working conditions, due to the lack of dynamic capture of the phase change nodes on the coating surface, the surface is prone to premature curing and skinning or resin overflow due to thermal resistance and conduction delay. It cannot fundamentally solve the contradiction between mechanical and dielectric defects such as internal pores and thinning at the edges and corners.

[0004] Therefore, the technical problem to be solved by this invention is how to change the traditional heat transfer method from the outside to the inside, and form a driving force to make the solvent in the coating migrate from the side close to the conductor to the outer surface without damaging the integrity of the surface coating, thereby eliminating the problems of pores inside the insulation layer and thinning of the coating at the edges and corners, and reducing the internal stress generated by the cross-linking shrinkage of the polymer insulating material. Summary of the Invention

[0005] The present invention aims to solve the problem of internal porosity and polarization loss caused by the external skinning that hinders solvent escape during the curing process of the insulating varnish film of motor windings.

[0006] In this technical solution, a coating process for reducing winding insulation loss includes the following steps:

[0007] Step S101: Apply an insulating coating to the surface of the three-phase winding of the high-efficiency motor, pass heating AC current to the three-phase winding to generate Joule heat, and at the same time apply an alternating magnetic field to the insulating coating through an external high-frequency induction heating coil to generate high-frequency induced eddy current heat, thereby constructing an inverted temperature field with an internal temperature higher than the external temperature, driving the free solvent molecules inside the insulating coating to evaporate radially outward from the inside out.

[0008] Step S102: Real-time acquisition of the online high-frequency complex impedance vector of the three-phase winding lead-out terminal under high-frequency excitation; the temperature compensation coefficient of the static lookup table type winding reference DC resistance is introduced by the control system to correct the impedance change caused by temperature rise; and the cross-linking state characteristic index is calculated in real time based on the resistance and reactance separated after correction of the online high-frequency complex impedance vector. The first time derivative of the cross-linking state characteristic index is continuously tracked with a fixed sampling period of 10ms.

[0009] Step S103: When the first time derivative of the crosslinking state characteristic index is greater than or equal to the critical volatile crosslinking transition threshold and the duration reaches 5s, it is determined that the free solvent molecules are completely exhausted. The output power of the external high-frequency induction heating coil is increased, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced, so that the shallow surface layer of the insulating coating is heated to 140°C to 160°C, and the shallow surface layer is crosslinked and cured.

[0010] Preferably, the coating process for reducing winding insulation loss further includes the following sequential steps: Step S104, continuously acquiring the online high-frequency complex impedance vector of the three-phase winding leads and calculating the impedance phase angle, and capturing the volume shrinkage stress generated by shallow cross-linking by monitoring the change of the time derivative of the impedance phase angle; Step S105, when the change rate of the time derivative of the impedance phase angle exceeds the reference change rate window, adding a DC bias component to the heating AC current to increase the internal temperature of the three-phase winding, using the thermal expansion of the metal conductor to offset the interlayer stress caused by cross-linking shrinkage, and superimposing an advance correction amount equivalent to the one-dimensional unsteady conduction delay time in the adjustment command.

[0011] Preferably, step S102 includes the following sub-steps as a refinement of step S102: Step S1021, constructing a standard mapping table containing multiple sets of temperature gradients and operating loads, using the initial measurement value of the online high-frequency complex impedance vector at the current temperature as the retrieval key value; Step S1022, matching and retrieving the corresponding static lookup table type winding reference DC resistance temperature compensation coefficient, multiplying the initial measurement value by the static lookup table type winding reference DC resistance temperature compensation coefficient to correct the material's inherent resistivity change caused by temperature rise, and outputting the stabilized corrected resistance and corrected reactance.

[0012] Preferably, in step S103, the critical volatile crosslinking transition threshold satisfies to .

[0013] Preferably, step S101 includes the following sub-steps as a refinement of step S101: Step S1011, adjusting the current density of the heating AC current supplied to the three-phase winding to 4A / mm² to 8A / mm², so that the core conductor of the three-phase winding is heated by Joule heating, forming a heat conduction path from the inside to the outside; Step S1012, adjusting the excitation frequency of the external high-frequency induction heating coil to 150kHz to 300kHz, using the electromagnetic skin effect to concentrate the induced heat on the shallow surface of the insulating coating, blocking the heat from penetrating to the core of the winding core.

[0014] Preferably, in step S103, the output power of the external high-frequency induction heating coil is increased to 115% to 130% of the initial power, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced to 40% to 60% of the initial amplitude.

[0015] Preferably, step S105 includes the following sub-steps as a refinement of step S105: Step S1051, obtain the core geometry of the three-phase winding and the thermal conductivity parameters of the insulating medium, and calculate the thermal conduction delay time of the insulating coating from the conductor core to the outer surface using a one-dimensional unsteady-state thermal conduction kinetic equation; Step S1052, inject an advance control phase equal to the thermal conduction delay time in the adjustment command, so that the change of current entering the three-phase winding occurs earlier than the stress fluctuation, thereby achieving a dynamic balance of stress inside the insulating coating.

[0016] Preferably, a coating process for reducing winding insulation loss further includes the following sequential steps: Step S106, placing the cured motor winding in a vacuum impregnation kettle with a pressure not exceeding 100 Pa, and applying an alternating electric field along the axial direction of the motor winding to generate a shear self-dilution effect inside the surface capillary channels; Step S107, maintaining the electric field strength of the alternating electric field at 50 V / mm to 120 V / mm, driving the impregnating resin to fill and penetrate into the pores inside the insulating coating.

[0017] Preferably, the insulating coating is any one of polyimide, polyamide-imide, and polyesterimide; the solid mass percentage content of the insulating coating is controlled to be 25% to 40%, and the thickness deviation of the insulating coating at the corner of the winding flange is not greater than 5 μm.

[0018] Compared with existing technologies, the coating process of the present invention for reducing winding insulation loss has the following advantages:

[0019] 1. In the coating process for reducing winding insulation loss, the Joule heat generated by the three-phase winding itself is combined with external high-frequency induction heating to make the internal temperature of the insulation coating higher than the external temperature. This allows free solvent molecules to diffuse from the inside to the outside and evaporate in time. This can prevent the surface of the insulation coating from curing and forming a skin too early, reduce the internal pores caused by residual solvent retention, and at the same time, the coating is less likely to become excessively thin due to flow at the winding flanges and corners, which is beneficial to improving the density and thickness uniformity of the insulation coating.

[0020] 2. By using online high-frequency complex impedance vector to determine the evaporation state of the solvent in the insulating coating and correcting the impedance deviation caused by temperature changes, the timing of the transition between the solvent evaporation stage and the cross-linking curing stage can be determined more accurately. Increasing the curing temperature of the shallow surface layer of the insulating coating after the solvent has fully evaporated is beneficial to making the surface curing process more stable, maintaining the uniformity of the paint film shape and thickness, and making the cross-linking process of the insulating medium continuous and stable.

[0021] 3. During the cross-linking curing process, the volume shrinkage of the insulating coating is judged based on the change in impedance phase angle. The thermal expansion of the winding conductor is used to counteract the interlayer stress caused by cross-linking shrinkage. At the same time, the influence of heat transfer delay on the adjustment effect is reduced by advance correction, so that the stress inside the insulating coating is kept relatively balanced, thereby reducing the risk of delamination and peeling of the insulating layer under thermal cycling conditions. Attached Figure Description

[0022] Figure 1 This is a flowchart of the insulation coating curing control process of the present invention;

[0023] Figure 2 This is a structural diagram of the motor winding insulation treatment device of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0025] A coating process for reducing winding insulation loss includes the following steps:

[0026] Step S101: Apply an insulating coating to the surface of the three-phase winding of the high-efficiency motor, pass heating AC current to the three-phase winding to generate Joule heat, and at the same time apply an alternating magnetic field to the insulating coating through an external high-frequency induction heating coil to generate high-frequency induced eddy current heat, thereby constructing an inverted temperature field with an internal temperature higher than the external temperature, driving the free solvent molecules inside the insulating coating to evaporate radially outward from the inside out.

[0027] Step S102: Real-time acquisition of the online high-frequency complex impedance vector of the three-phase winding lead-out terminal under high-frequency excitation; the control system introduces the static lookup table type winding reference DC resistance temperature compensation coefficient to correct the impedance temperature rise change caused by temperature rise; and calculates the cross-linking state characteristic index in real time based on the resistance and reactance separated after correction of the online high-frequency complex impedance vector; and continuously tracks the first time derivative of the cross-linking state characteristic index with a fixed sampling period of 10ms.

[0028] Step S103: When the first time derivative of the crosslinking state characteristic index is greater than or equal to the critical volatile crosslinking transition threshold and the duration reaches 5s, it is determined that the free solvent molecules are completely exhausted. The output power of the external high-frequency induction heating coil is increased, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced, so that the shallow surface layer of the insulating coating is heated to 140°C to 160°C, and the shallow surface layer is crosslinked and cured.

[0029] Preferably, a coating process for reducing winding insulation loss further includes the following sequential steps: Step S104, continuously acquiring the online high-frequency complex impedance vector of the three-phase winding leads and calculating the impedance phase angle, capturing the volume shrinkage stress generated by shallow cross-linking by monitoring the change in the time derivative of the impedance phase angle; Step S105, when the rate of change of the time derivative of the impedance phase angle exceeds the reference rate of change window, adding a DC bias component to the heating AC current to increase the internal temperature of the three-phase winding, using the thermal expansion of the metal conductor to offset the interlayer stress caused by cross-linking shrinkage, and superimposing an advance correction amount equivalent to the one-dimensional unsteady-state conduction delay time in the adjustment command.

[0030] Preferably, step S102 includes the following sub-steps as a refinement of step S102: Step S1021, constructing a standard mapping table containing multiple sets of temperature gradients and operating loads, using the initial measurement value of the online high-frequency complex impedance vector at the current temperature as the retrieval key value; Step S1022, matching and retrieving the corresponding static lookup table type winding reference DC resistance temperature compensation coefficient, multiplying the initial measurement value by the static lookup table type winding reference DC resistance temperature compensation coefficient to correct the material's inherent resistivity change caused by temperature rise, and outputting the stabilized corrected resistance and corrected reactance.

[0031] Preferably, in step S103, the critical volatile crosslinking transition threshold satisfies to .

[0032] Preferably, step S101 includes the following sub-steps as a refinement of step S101: Step S1011, adjusting the current density of the heating AC current supplied to the three-phase winding to 4A / mm² to 8A / mm², so that the core conductor of the three-phase winding is heated by Joule heating, forming a heat conduction path from the inside to the outside; Step S1012, adjusting the excitation frequency of the external high-frequency induction heating coil to 150kHz to 300kHz, using the electromagnetic skin effect to concentrate the induced heat on the shallow surface of the insulating coating, blocking the heat from penetrating to the core of the winding core.

[0033] Preferably, in step S103, the output power of the external high-frequency induction heating coil is increased to 115% to 130% of the initial power, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced to 40% to 60% of the initial amplitude.

[0034] Preferably, step S105 includes the following sub-steps as a refinement of step S105: Step S1051, obtain the core geometry of the three-phase winding and the thermal conductivity parameters of the insulating medium, and calculate the thermal conduction delay time of the insulating coating from the conductor core to the outer surface using a one-dimensional unsteady-state thermal conduction kinetic equation; Step S1052, inject an advance control phase equal to the thermal conduction delay time in the adjustment command, so that the change of current entering the three-phase winding occurs earlier than the stress fluctuation, thereby achieving a dynamic balance of stress inside the insulating coating.

[0035] Preferably, a coating process for reducing winding insulation loss further includes the following sequential steps: Step S106, placing the cured motor winding in a vacuum impregnation kettle with a pressure not exceeding 100 Pa, and applying an alternating electric field along the axial direction of the motor winding to generate a shear self-dilution effect inside the surface capillary channels; Step S107, maintaining the electric field strength of the alternating electric field at 50 V / mm to 120 V / mm, driving the impregnating resin to fill and penetrate into the pores inside the insulating coating.

[0036] Preferably, the insulating coating is any one of polyimide, polyamide-imide, and polyesterimide; the solid mass percentage content of the insulating coating is controlled to be 25% to 40%, and the thickness deviation of the insulating coating at the corner of the winding flange is not greater than 5 μm.

[0037] Example 1: In this example, the motor windings to be coated are fixed on a fixture. An insulating coating is applied to the surface of the three-phase windings of a high-power-density variable frequency drive motor. These three-phase windings experience dielectric polarization losses under high-frequency pulse voltages, and the insulating coating at the corners of the winding flanges is easily thinned due to coating flow. After coating is completed and excess coating is removed, the control system applies a heating AC current with a frequency of 10Hz to 30Hz to the leads of the three-phase windings, adjusting the current density to 4A / mm² to 8A / mm². Utilizing the characteristic of relatively uniform current distribution within the conductor cross-section under low-frequency conditions, the core conductor of the three-phase windings is heated through Joule heating, forming a heat conduction path from the inside out. Simultaneously, an external high-frequency induction heating coil is activated, adjusting the excitation frequency to 150kHz. From z to 300kHz, the distribution of the alternating magnetic field is constrained by the anisotropic magnetic permeability of the stator core. This alternating magnetic field acts on the insulating coating, generating high-frequency induced eddy current heat. Utilizing the electromagnetic skin effect, the induced heat is concentrated in the shallow layer of the insulating coating, preventing heat penetration into the stator core. The control system adjusts the power distribution ratio between the heating AC current and the external high-frequency induction heating coil, controlling the temperature of the three-phase winding core conductors at 90℃ to 110℃ and the temperature of the shallow layer of the insulating coating at 65℃ to 75℃. An inverted temperature field is formed between the three-phase winding core conductors and the shallow layer of the insulating coating, where the internal temperature is higher than the external temperature. This inverted temperature field monotonically decreases along the direction from the three-phase winding core conductors to the shallow layer of the insulating coating and satisfies the following relationship: ;in, For temperature gradient, For temperature, The spatial distance extending from the core conductor of the three-phase winding to the shallow surface layer of the insulating coating creates a mass transfer driving force that causes the free solvent molecules inside the insulating coating to diffuse radially outward and evaporate, reducing the blockage of solvent evaporation channels by premature cross-linking of the shallow surface layer of the insulating coating and reducing the formation of pores inside the insulating coating.

[0038] Before the process begins, the control system establishes a standard mapping table based on multiple temperature gradients and operating loads. Each entry records the correspondence between the initial measured value of the online high-frequency complex impedance vector and the temperature compensation coefficient of the static lookup table-type winding reference DC resistance. During the inverted temperature field, the control system applies a high-frequency excitation signal with a fixed frequency of 10kHz to the three-phase winding leads and acquires the initial measured value of the online high-frequency complex impedance vector at the current temperature in real time. First, the corresponding entries in the standard mapping table are filtered according to the current temperature gradient and operating load. Then, the initial measured value is used as the search key to match and retrieve the temperature compensation coefficient of the static lookup table-type winding reference DC resistance. The control system multiplies the resistance and reactance components separated from the initial measured value by this coefficient to correct the change in the inherent resistivity of the material caused by the temperature rise and the resulting change in the online high-frequency complex impedance vector, and outputs the corrected resistance. and corrected reactance The corrected online high-frequency complex impedance vector is denoted as... Online high-frequency complex impedance vector Satisfying the equation ;in, For online high-frequency complex impedance vectors, For the corrected resistance, For the corrected reactance, It is the imaginary unit.

[0039] The control system is based on the corrected resistance and corrected reactance Real-time calculation of crosslinking state characteristic index It satisfies the relation In this embodiment, Ω is used as the unit of measurement for resistance and reactance, and the same calibration caliber is used to calculate the crosslinking state characteristic index. This index is used to characterize the crosslinking state of the insulating coating and is not assigned any additional physical dimension. The control system tracks the crosslinking state with a fixed sampling period of 10ms. First time derivative ;in, The first time derivative of the crosslinking state characteristic index is the corrected resistance. and corrected reactance The crosslinking state characteristic index decreases as the crosslinking state of the insulating coating changes. The corresponding increase occurs when the control system detects... Meet the triggering conditions Furthermore, when the duration reaches 5 seconds, it is determined that the free solvent molecules inside the insulating coating are completely depleted and enter the polymer network cross-linking and curing stage; among which, The critical threshold for volatile crosslinking transition is defined as follows, and its value range is: to The control system then issues a power switching control command, increasing the output power of the external high-frequency induction heating coil to 115% to 130% of the initial power, and simultaneously reducing the amplitude of the heating AC current to 40% to 60% of the initial amplitude, so that the temperature of the shallow surface layer of the insulating coating rises to 140°C to 160°C, causing the polymer chain segments of the shallow surface layer of the insulating coating to crosslink and complete closed-loop curing.

[0040] During the polymer network crosslinking and curing stage, the control system continuously acquires online high-frequency complex impedance vectors and calculates impedance phase angles. Impedance phase angle Satisfying the equation ;in, The impedance phase angle is calculated in real time by the control system. First time derivative The rate of change of the first-order time derivative of the impedance phase angle is determined based on the difference between the first-order time derivatives in adjacent sampling periods and the sampling period; where, The unit is The reference rate of change window is calibrated using the rate of change data collected with the same calculation caliber, based on the stable heating stage before the cross-linking and shrinkage of the insulating coating. When the rate of change of the first time derivative of the impedance phase angle exceeds the reference rate of change window, the control system adjusts the switching duty cycle of the inverter bridge, increases the DC bias component in the heating AC current, and raises the temperature of the core conductor of the three-phase winding.

[0041] The control system simultaneously acquires the stator core geometry and thermal conductivity parameters of the insulating coating material corresponding to the three-phase windings. Using the outer surface of the core conductors of the three-phase windings and the shallow surface of the insulating coating as the two ends of the one-dimensional heat transfer path, the system calculates the attenuation of temperature change along this path and the time difference from the core conductors of the three-phase windings to the shallow surface of the insulating coating according to the one-dimensional unsteady-state heat conduction kinetic equation. This time difference is determined as the one-dimensional unsteady-state heat conduction delay time. An advance correction amount equal to the one-dimensional unsteady-state heat conduction delay time is injected into the adjustment command in advance. This causes the change in current flowing through the three-phase windings to occur earlier than the fluctuation of volume shrinkage stress; this advance correction amount is used to form an advance control phase in the adjustment command, and its value is controlled between 120ms and 180ms.

[0042] During the cross-linking and curing process, the polymer chain segments in the insulating coating undergo rearrangement, which alters the polarization characteristics of the surface dipoles in the insulating coating and causes overall volume shrinkage. This change in polarization characteristics affects the corrected reactance. With the corrected resistance The ratio changes and manifests as fluctuations in the impedance phase angle; the overall volume shrinkage generates volume shrinkage stress. Therefore, the rate of change of the first time derivative of the impedance phase angle is used to reflect the release and accumulation state of the volume shrinkage stress. After the control system raises the temperature of the core conductor of the three-phase winding, the metal conductor generates thermal expansion outward, which forms a force opposite to the cross-linking shrinkage of the insulating coating. This force counteracts the interlayer stress and shear stress caused by the cross-linking shrinkage at the contact interface, maintaining the interlayer adhesion state of the insulating coating and ensuring that the insulating coating maintains interlayer adhesion under thermal cycling conditions.

[0043] After the insulating coating has completed cross-linking and curing, the cured motor windings are placed in a vacuum impregnation kettle. Impregnation resin is injected into the kettle until the three-phase windings are submerged, and the pressure inside the kettle is controlled between 50 Pa and 100 Pa. The vacuum pump group drives the pressure inside the kettle to fluctuate sinusoidal negative pressure within this range with a period of 30 s to 60 s. An electric field generating device set at the axial end of the vacuum impregnation kettle applies an alternating electric field along the axial direction of the motor windings. The electric field strength is maintained between 50 V / mm and 120 V / mm, and the frequency is between 50 Hz and 200 Hz. At the pressure drop edge, the frequency of the axial alternating electric field is linearly increased to 400 Hz to 600 Hz, so that the impregnation resin in the surface capillary channels is subjected to electro-oscillatory shearing and the local apparent viscosity is reduced, resulting in a shear self-dilution effect. The polar bubbles at the dead corner of the coil slot flange burst and are discharged under the action of negative pressure expansion and electro-induced deformation, and the impregnation resin then fills and penetrates into the pores inside the insulating coating.

[0044] During the impregnation resin filling process, the control system adds a viscous damping bounce to the output head of the fluid injection pump. , To obtain the corrected pressure value for overcoming flow resistance, the control system measures the flow viscosity and capillary resistance of the impregnating resin within the stator slots, converts this to a pressure drop per unit flow rate according to the corresponding flow channel, and then multiplies it by the output flow rate of the fluid injection pump to obtain the corrected pressure value. When the impregnating resin experiences localized impregnation stagnation due to flow resistance, the control system increases the output head of the fluid injection pump, superimposing this corrected pressure value onto the base injection pressure to guide the impregnating resin into the deep pores of the stator coil slots and the insulating coating.

[0045] After the process is completed, the average thickness of the insulating coating at the corner of the coil flange of the stator winding is 24μm, the thickness deviation is no more than 5μm, the porosity inside the insulating coating is no more than 0.12%, the partial discharge initiation voltage is 1560V, and the dielectric loss factor is 0.005.

[0046] Example 2: This example uses a high power density stator manufacturing test platform to verify the coating process that reduces winding insulation loss. The test platform includes a vacuum impregnation kettle and an online high-frequency complex impedance vector acquisition circuit to simulate the electromagnetic and thermodynamic states of a high-efficiency motor under variable frequency drive conditions. The acquisition circuit reads the electrical response data of the three-phase winding leads under a high-frequency excitation signal, and superimposes Gaussian white noise with a signal-to-noise ratio of 20dB and power frequency electromagnetic harmonic interference with a frequency of 50Hz into the input data. Based on the fixed frequency of the high-frequency excitation signal, the rate of change of signal characteristics, and the processor's computational load, the sampling period is set to 10ms to reduce the influence of transient changes in polarization charge response under high-frequency pulses on the sampling results and to avoid sampling aliasing.

[0047] The experiment selected polyamide-imide with a solid content of 32% as the insulating coating material. During the injection process, the control system superimposed a viscous damping bounce on the output head of the fluid injection pump. The insulating coating material was allowed to penetrate the deep pores of the motor winding under the action of an axial alternating electric field. To compare the effects of vacuum degree, axial alternating electric field strength and the temperature of the core conductor of the three-phase winding on the film formation results, four sample groups and three control groups were set up in the experiment.

[0048] Sample group one uses the lower limit process settings: vacuum degree set to 50 Pa, axial alternating electric field strength set to 1500 V / m, electric field frequency set to 50 Hz, core conductor temperature of three-phase winding controlled at 90℃, and shallow surface temperature of insulating coating controlled at 65℃. Sample group two uses the median process settings: vacuum degree set to 100 Pa, axial alternating electric field strength set to 2500 V / m, electric field frequency set to 125 Hz, core conductor temperature of three-phase winding controlled at 100℃, and shallow surface temperature of insulating coating controlled at 65℃. The temperature was controlled at 70℃. Sample group three adopted the upper limit process setting, with the vacuum degree set at 150Pa, the axial alternating electric field strength set at 3500V / m, the electric field frequency set at 200Hz, the core conductor temperature of the three-phase winding controlled at 110℃, and the surface temperature of the insulating coating controlled at 75℃. Sample group four was subjected to pressure step fluctuations near the median process conditions. Its experimental record showed a vacuum degree of 80Pa, an axial alternating electric field strength of 2000V / m, and a core conductor temperature of 95℃.

[0049] Control group 1 was baked by an external heat source with a pressure of 101325 Pa, an axial alternating electric field strength of 0 V / m, and a temperature of 120 °C. Control group 2 had a vacuum of 100 Pa, an axial alternating electric field strength of 2500 V / m, and a core conductor temperature of 100 °C. The external high-frequency induction heating coil was not activated during the test. Control group 3 had a vacuum of 180 Pa, an axial alternating electric field strength of 2500 V / m, and a core conductor temperature of 125 °C. This was used to observe the film formation state after the process parameters deviated from the set range.

[0050] During the cross-linking and curing process of each group of insulating coatings, the acquisition circuit continuously reads the online high-frequency complex impedance vector. The control system suppresses Gaussian white noise and power frequency electromagnetic harmonic interference through differential amplifier circuits and low-pass filter circuits. It separates resistance and reactance from the corrected online high-frequency complex impedance vector and continuously calculates the cross-linking state characteristic index and its first-order time derivative. After each group has completed cross-linking and curing, the average thickness of the insulating coating at the corner of the winding flange, the porosity inside the insulating coating, the partial discharge initiation voltage, and the dielectric loss factor are measured respectively.

[0051] Under the lower limit process conditions of sample group one, the maximum measured value of the first time derivative of the crosslinking state characteristic index is The average thickness of the insulating coating at the corner of the winding flange is 22.3 μm, the porosity inside the insulating coating is 0.14%, the partial discharge initiation voltage is 1515 V, and the dielectric loss factor is 0.0056. The temperature difference between the core conductor temperature of the three-phase winding and the shallow surface temperature of the insulating coating is maintained. Free solvent molecules evaporate radially outward at the cross-linking front of the insulating coating, and a continuous insulating coating is retained at the corner.

[0052] Under the median process conditions of sample group two, the maximum measured value of the first time derivative of the crosslinking state characteristic index is The average thickness of the insulating coating at the corner of the winding flange is 24.2 μm, the internal porosity of the insulating coating is 0.11%, the partial discharge initiation voltage is 1570 V, and the dielectric loss factor is 0.0048. This group maintains an inverted temperature field during the solvent evaporation stage and switches the heating power after the free solvent molecules are exhausted, so that the shallow surface layer of the insulating coating enters the cross-linking and curing stage. The resulting insulating coating has a lower internal porosity and dielectric loss factor than the four sample groups.

[0053] Under the upper limit process conditions of sample group three, the maximum measured value of the first time derivative of the crosslinking state characteristic index is The average thickness of the insulating coating at the corner of the winding flange is 23.8 μm, the internal porosity of the insulating coating is 0.13%, the partial discharge initiation voltage is 1555 V, and the dielectric loss factor is 0.0051. As the temperature of the core conductor of the three-phase winding and the intensity of the axial alternating electric field increase, the evaporation rate of the free solvent molecules increases. However, the shallow layer of the insulating coating still completes cross-linking and curing after the solvent evaporates, and does not form a continuous internal pore channel.

[0054] Under the pressure step fluctuation conditions of sample group four, the maximum measured value of the first time derivative of the crosslinking state characteristic index is The average thickness of the insulating coating at the corner of the winding flange was 23.1 μm, the porosity of the insulating coating was 0.15%, the partial discharge initiation voltage was 1530 V, and the dielectric loss factor was 0.0054. Pressure changes caused fluctuations in the permeation state of the insulating coating material. The control system was still able to identify the changes in the crosslinking state from the online high-frequency complex impedance vector and switch the heating power according to the changes. The thickness deviation of the insulating coating at the corner of the winding flange of the four sample groups was kept within 5 μm, the partial discharge initiation voltage was between 1515 V and 1570 V, and the dielectric loss factor was between 0.0048 and 0.0056.

[0055] In control group one, the external heat source caused the shallow surface layer of the insulating coating to heat up before the interior, and the maximum measured value of the first time derivative of the crosslinking state characteristic index was [value missing]. After the shallow surface layer of the insulating coating is cross-linked in advance, the evaporation channels of free solvent molecules are blocked, the average thickness of the insulating coating at the corner of the winding flange is reduced to 11.5μm, the porosity inside the insulating coating increases to 1.84%, the partial discharge initiation voltage is 835V, and the dielectric loss factor is 0.0245.

[0056] In control group two, the external high-frequency induction heating coil was not activated, disrupting the power distribution between the heating AC current and the high-frequency induction heating. Consequently, the insulation coating could not maintain the inverted temperature field as set. The maximum measured value of the first-order time derivative of the crosslinking state characteristic index in this group was [value missing]. The insulating coating material at the corner of the winding flange flows to the adjacent area under capillary action, reducing the average thickness of the insulating coating to 12.1 μm, with an internal porosity of 1.42%, a partial discharge initiation voltage of 910 V, and a dielectric loss factor of 0.0195.

[0057] In control group three, the vacuum level was increased to 180 Pa, the core conductor temperature of the three-phase winding was increased to 125 °C, and the maximum measured value of the first-order time derivative of the crosslinking state characteristic index reached [value missing]. The low-boiling-point components in the insulating coating undergo flash evaporation before the free solvent molecules are expelled, and the polymer chain segments then cross-link, forming a gas phase to block the pores inside the insulating coating. The average thickness of the insulating coating at the corner of the winding flange is 18.4 μm, the internal porosity increases to 2.15%, the partial discharge initiation voltage drops to 780V, and the dielectric loss factor increases to 0.0312.

[0058] During the cross-linking and curing stage of the sample, the control system calculates the impedance phase angle based on the online high-frequency complex impedance vector. Continuously track its first time derivative The system obtains the rate of change of the first-order time derivative of the impedance phase angle based on the difference between the first-order time derivatives in adjacent sampling periods and the sampling period. When this rate of change exceeds the reference rate of change window, the control system adjusts the switching duty cycle of the inverter bridge, increases the DC bias component in the heating AC power, and superimposes a lead correction amount with a value ranging from 120ms to 180ms into the adjustment command. As the temperature rises, the core conductor of the three-phase winding undergoes thermal expansion, which, in turn, creates a force opposite to the cross-linking contraction of the insulating coating, thus reducing interlayer stress.

[0059] After the four sample groups completed film curing, the partial discharge initiation voltage of the coils in the stator winding slots was not lower than 1500V, the dielectric loss factor of the insulation coating was not higher than 0.006, and after the stator windings underwent 200 cycles of thermal shock, no interlayer peeling or local peeling of the insulation coating in the slots occurred, and the winding surface maintained a continuous and uniform insulation coating.

[0060] Example 3: The motor winding to be coated is fixed in a vacuum impregnation kettle to manufacture a high power density variable frequency drive motor stator winding that can withstand transient thermal stress. There is heat transfer hysteresis and local heating between the formed flat copper wire and the stator slot. The pressure inside the kettle is stabilized at 100 Pa. Polyamide-imide insulating coating material with a solid mass percentage content of 32% is injected into the kettle until the three-phase winding is submerged.

[0061] To address the impact of heat transfer hysteresis on interlayer stress regulation, the control system calculates the one-dimensional unsteady-state heat conduction delay time from the core conductor of the three-phase winding to the shallow surface of the insulation coating based on the stator core geometry and thermal conductivity parameters of the insulation coating material. An advance correction amount equal to this delay time is then added to the adjustment command beforehand. The lead correction amount is calibrated by comparing the delamination defect state of the insulating coating under different delay times: when When the thermal expansion lead of the core conductor of the three-phase winding is less than 120ms, the thermal expansion advance is insufficient; when When the time exceeds 180ms, excessive expansion occurs in the core conductor of the three-phase winding; when the parameter is set to 150ms, no stress cracks are observed on the surface of the insulation coating. Therefore, in this embodiment, 150ms is used as the timeframe. The specific value is used to form the advance control phase of the control command for adjusting the duty cycle of the inverter bridge switch.

[0062] The control system acquires online high-frequency complex impedance vector data at a fixed frequency of 10kHz through the three-phase winding leads. The corrected resistance is separated from the corrected online high-frequency complex impedance vector. and corrected reactance Based on this, the crosslinking state characteristic index is calculated. In an inverted temperature field where the core conductor temperature of the three-phase winding is 100℃ and the surface temperature of the insulation coating is 70℃, the first time derivative of the crosslinking state characteristic index is... The critical evaporation crosslinking threshold varies with the evaporation of free solvent molecules. By comparing the curing defect morphology on the surface of the insulating coating at different rates of change, the critical evaporation crosslinking threshold can be determined. Perform calibration when All 500 consecutive sampling points are greater than or equal to At that time, no delamination or blistering was observed on the surface of the insulating coating, based on which... Determined as the critical threshold for volatile crosslinking transition The determination boundary.

[0063] when When the threshold is reached and the duration reaches 5 seconds, the control system issues a power switching control command to increase the output power of the external high-frequency induction heating coil to 120% of the initial power, while reducing the amplitude of the heating AC current supplied to the three-phase winding to 50% of the initial amplitude, so that the temperature of the shallow surface layer of the insulation coating rises to 150°C within 10 seconds, causing the polymer chain segments of the shallow surface layer of the insulation coating to crosslink and complete closed-loop curing.

[0064] During high-temperature curing, spatial temperature gradient and advance correction amount The system jointly controls the heating timing of the core conductor of the three-phase winding, increases the DC bias component in the heating AC current, causes the metal conductor to thermally expand, counteracts the interlayer stress caused by the cross-linking shrinkage of the insulation coating, and maintains the balance of residual stress inside the insulation coating between the deep boundary of the stator core slot and the formed flat copper wire.

[0065] After curing, a partial cross-section of the stator winding core was performed. The cross-section showed that the insulating coating inside the slots was uniformly distributed, and the average thickness of the insulating coating at the corner of the coil flange was 24 μm with a thickness deviation of no more than 5 μm. The observation results of the impact section by scanning electron microscopy showed that no pores were observed inside the local insulating coating, the cross-section was a continuous single-phase state, and no gas channels caused by solvent residue were formed. The overall dielectric loss factor of the three-phase winding was 0.0048, the partial discharge initiation voltage was 1560V, and no local thermal breakdown occurred under high-frequency pulse voltage.

[0066] Example 4: This example combines Figures 1 to 2 This paper describes a coating process for reducing winding insulation loss, such as... Figure 1 As shown, an alternating magnetic field is applied to an external high-frequency induction heating coil to construct an inverted temperature field that drives molecules to volatilize outward. The inverted temperature field drives molecules to volatilize outward, causing the characteristic index to track the first-order time derivative. On the one hand, this performs cross-linking curing and increases the induction heating power; on the other hand, it is input to the control system to correct the impedance temperature rise change, and respectively acts on the external high-frequency induction heating coil to apply the alternating magnetic field and the cross-linking curing to increase the induction heating power.

[0067] like Figure 2As shown, the control system includes a storage register and an instruction register. The online high-frequency complex impedance vector acquisition circuit includes an acquisition probe, a differential amplifier circuit, and a low-pass filter circuit. The vacuum impregnation kettle includes an external high-frequency induction heating coil, an electric field generator, and a three-phase winding mounted on a tooling fixture. The system is also equipped with an inverter bridge, a fluid injection pump, and a vacuum pump group. The three-phase winding outputs a response signal to the acquisition probe, the acquisition probe inputs a signal to the control system, the control system feeds back a signal to the online high-frequency complex impedance vector acquisition circuit, the differential amplifier circuit and the low-pass filter circuit output a control signal to the external high-frequency induction heating coil, the control system simultaneously outputs a control signal to the external high-frequency induction heating coil, the control system outputs a control signal to the electric field generator, the control system outputs an adjustment signal to the inverter bridge, the instruction register outputs instruction signals to the fluid injection pump and the vacuum pump group respectively, the inverter bridge applies an electrical signal to the three-phase winding, and the fluid injection pump and the vacuum pump group are fluidly connected to the vacuum impregnation kettle.

[0068] Example 5: Before applying the coating process to reduce winding insulation loss to motor stator windings of different batches and stator core sizes, this example first calibrates the initial input parameters of the current batch. The control system collects the initial static DC resistance value of the three-phase winding at 20°C and performs batch calibration on a standard mapping table containing multiple temperature gradients and operating loads, based on the conductivity characteristic curve of the stator core material of the current batch. Subsequently, the initial measurement value of the online high-frequency complex impedance vector at the current temperature is collected. Using this initial measurement value as the retrieval key, the static lookup table type winding reference DC resistance temperature compensation coefficient is matched and retrieved from the standard mapping table and written into the storage register. During subsequent online monitoring, the control system uses this coefficient to perform temperature rise correction on the online high-frequency complex impedance vector and outputs the corrected resistance and reactance to reduce the influence of copper wire purity fluctuations on the crosslinking state characteristic index measurement value.

[0069] During the curing stage of the insulating coating, the control system calls the segmented step control program of the feedback adjustment operator to correct the control parameters based on the deviation of the rate of change of the first time derivative of the impedance phase angle from the reference rate of change window. The reference rate of change window is calibrated in the stable heating stage before the insulating coating has undergone cross-linking shrinkage: the first time derivative of the impedance phase angle of 100 sampling points is continuously collected, the change between adjacent sampling values ​​is calculated point by point, and the arithmetic mean of the obtained rate of change is used as the center of the window, and the fluctuation boundary is set to have an absolute value of no more than 0.005 rad / s.

[0070] When the rate of change of the first time derivative of the impedance phase angle is greater than the set boundary for 15 consecutive sampling points, the control system increases the switching duty cycle of the inverter bridge in a fixed step of 0.05, increases the DC bias component in the heating AC current supplied to the three-phase winding, and causes the metal conductor to expand due to heat. The control process continues until the rate of change returns to the reference rate of change window. At the same time, the control system writes the state that exceeds the window into the instruction register, triggers the state machine to switch, and adjusts the interlayer stress generated by crosslinking shrinkage accordingly, and controls the thickness deviation of the corner of the insulating coating to within 5μm.

[0071] Example 6: On a large-scale production line with multiple vacuum impregnation kettles operating in parallel, motor windings that have completed insulation coating curing but have not yet undergone vacuum impregnation are placed in each vacuum impregnation kettle. After long-term exposure to thermal cycling shocks, the acquisition probe of the online high-frequency complex impedance vector acquisition circuit will experience impedance zero-point drift. The difference in mutual inductance of electromagnetic shielding between each station will also introduce non-stationary parasitic harmonic interference. In order to calibrate the measurement zero point of each station, before injecting impregnation resin into the vacuum impregnation kettle, the control system applies a reference low-voltage excitation signal with a fixed frequency of 10kHz to the three-phase windings through the motor winding leads, and reads the initial residual values ​​of high-frequency resistance and high-frequency reactance in real time. The hardware differential amplifier circuit uses the two initial residual values ​​as the subtraction reference for background physical noise and latches them in the latch register to calibrate the measurement zero point of the online high-frequency complex impedance vector, correcting the deviation of the electrical polarization matrix caused by the aging of the acquisition probe and the change of spatial magnetic field coupling between parallel stations.

[0072] After the impregnation resin has submerged the three-phase winding, the control system continuously tracks the first time derivative of the cross-linking state characteristic index with a sampling period of 10ms. When the first time derivative is less than or equal to the preset lower limit threshold of flow hysteresis for 8 consecutive sampling points, it is determined that the impregnation resin in the dead corner of the slot is constrained by the viscous resistance caused by local temperature changes, resulting in stagnant penetration. The control system sends a frequency modulation command to the electric field generator to switch the frequency of the alternating electric field applied along the motor winding axis from the power frequency of 50Hz to a high-frequency sweep frequency state, and cyclically changes between 400Hz and 600Hz.

[0073] During the high-frequency sweep process, the electro-oscillatory stress generated by the axial alternating electric field shears the impregnating resin in the capillary channels of the surface layer, reducing the local apparent viscosity of the polar polymer chain segments and forming a shear self-dilution effect. The control system continuously monitors the first time derivative of the cross-linking state characteristic index until it exceeds the lower limit threshold of flow hysteresis and resumes a monotonically increasing trend, and then ends the high-frequency sweep adjustment. Through the transient frequency jump of the axial alternating electric field, the impregnating resin refills and permeates into the pores inside the insulating coating, reducing insufficient impregnation caused by the obstruction of material flow.

[0074] After curing, the average thickness of the insulating coating at the corner of the high-efficiency motor winding flange is 24μm, the porosity inside the insulating coating is less than 0.12%, and the partial discharge initiation voltage is 1560V.

[0075] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A coating process for reducing winding insulation loss, characterized in that, Includes the following steps: Step S101: Apply an insulating coating to the surface of the three-phase winding of the high-efficiency motor, pass heating AC current to the three-phase winding to generate Joule heat, and at the same time apply an alternating magnetic field to the insulating coating through an external high-frequency induction heating coil to generate high-frequency induced eddy current heat, thereby constructing an inverted temperature field with an internal temperature higher than the external temperature, driving the free solvent molecules inside the insulating coating to evaporate radially outward from the inside out. Step S102: Real-time acquisition of the online high-frequency complex impedance vector of the three-phase winding lead-out terminal under high-frequency excitation; the control system introduces the static lookup table type winding reference DC resistance temperature compensation coefficient to correct the impedance temperature rise change caused by temperature rise; and calculates the cross-linking state characteristic index in real time based on the resistance and reactance separated after correction of the online high-frequency complex impedance vector; and continuously tracks the first time derivative of the cross-linking state characteristic index with a fixed sampling period of 10ms. Step S103: When the first time derivative of the crosslinking state characteristic index is greater than or equal to the critical volatile crosslinking transition threshold and the duration reaches 5s, it is determined that the free solvent molecules are completely exhausted. The output power of the external high-frequency induction heating coil is increased, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced, so that the shallow surface layer of the insulating coating is heated to 140°C to 160°C, and the shallow surface layer is crosslinked and cured.

2. The coating process for reducing winding insulation loss according to claim 1, characterized in that, The coating process for reducing winding insulation loss also includes the following sequential steps: Step S104, continuously collect the online high-frequency complex impedance vector of the three-phase winding leads and calculate the impedance phase angle, and capture the volume shrinkage stress generated by shallow cross-linking by monitoring the change of the time derivative of the impedance phase angle; Step S105, when the change rate of the time derivative of the impedance phase angle exceeds the reference change rate window, add a DC bias component to the heating AC current to increase the internal temperature of the three-phase winding, use the thermal expansion of the metal conductor to offset the interlayer stress caused by cross-linking shrinkage, and superimpose an advance correction amount equivalent to the one-dimensional unsteady conduction delay time in the adjustment command.

3. The coating process for reducing winding insulation loss according to claim 1, characterized in that, Step S102 includes the following sub-steps as a refinement of step S102: Step S1021, construct a standard mapping table containing multiple sets of temperature gradients and operating loads, and use the initial measurement value of the online high-frequency complex impedance vector at the current temperature as the retrieval key value; Step S1022, match and retrieve the corresponding static lookup table type winding reference DC resistance temperature compensation coefficient, multiply the initial measurement value by the static lookup table type winding reference DC resistance temperature compensation coefficient to correct the material's inherent resistivity change caused by temperature rise, and output the stabilized corrected resistance and corrected reactance.

4. The coating process for reducing winding insulation loss according to claim 1, characterized in that, In step S103, the critical volatilization crosslinking transition threshold satisfies to .

5. The coating process for reducing winding insulation loss according to claim 1, characterized in that, Step S101 includes the following sub-steps as a refinement of step S101: Step S1011, adjust the current density of the heating AC current supplied to the three-phase winding to 4A / mm² to 8A / mm², so that the core conductor of the three-phase winding is heated by Joule heating, forming a heat conduction path from the inside to the outside; Step S1012, adjust the excitation frequency of the external high-frequency induction heating coil to 150kHz to 300kHz, and use the electromagnetic skin effect to concentrate the induced heat on the shallow surface of the insulating coating, blocking the heat from penetrating to the core of the winding iron core.

6. The coating process for reducing winding insulation loss according to claim 1, characterized in that, In step S103, the output power of the external high-frequency induction heating coil is increased to 115% to 130% of the initial power, and the amplitude of the heating AC current supplied to the three-phase winding is simultaneously reduced to 40% to 60% of the initial amplitude.

7. The coating process for reducing winding insulation loss according to claim 2, characterized in that, Step S105 includes the following sub-steps as a refinement of step S105: Step S1051, obtain the core geometry of the three-phase winding and the thermal conductivity parameters of the insulating medium, and calculate the thermal conduction delay time of the insulating coating from the conductor core to the outer surface using a one-dimensional unsteady-state thermal conduction kinetic equation; Step S1052, inject an advance control phase equal to the thermal conduction delay time in the adjustment command, so that the change of current entering the three-phase winding occurs earlier than the stress fluctuation, thereby achieving a dynamic balance of stress inside the insulating coating.

8. The coating process for reducing winding insulation loss according to claim 1, characterized in that, The coating process for reducing winding insulation loss also includes the following sequential steps: Step S106, placing the cured motor winding in a vacuum impregnation kettle with a pressure not exceeding 100 Pa, and applying an alternating electric field along the axial direction of the motor winding to generate a shear self-dilution effect inside the surface capillary channels; Step S107, maintaining the electric field strength of the alternating electric field at 50 V / mm to 120 V / mm, driving the impregnating resin to fill and penetrate into the pores inside the insulating coating.

9. The coating process for reducing winding insulation loss according to claim 1, characterized in that, The insulating coating is any one of polyimide, polyamide-imide, and polyesterimide; the solid mass percentage content of the insulating coating is controlled to be 25% to 40%, and the thickness deviation of the insulating coating at the corner of the winding flange is not greater than 5μm.

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