Method and system for variable speed retrofit of an ac motor

Abstract

This invention proposes a method and system for speed-changing retrofitting of an AC motor, belonging to the field of motor speed-changing retrofitting technology. The method includes: setting up and connecting a converter between the AC motor and a transformer; establishing a correspondence table between winding parameters and voltage through digital simulation of the motor and the transformer respectively; obtaining the original stator winding operating voltage of the motor and the original motor-side port voltage of the transformer; and adjusting the stator winding parameters of the motor and the number of turns of the transformer's machine-side winding to adapt to the operating voltage range of the converter's machine-side and grid-side. This invention, by inserting a converter and using simulation modeling, optimizes and adjusts the parameters of the original stator winding of the motor and the original motor-side winding of the transformer, breaking the constraint of grid frequency on motor speed, achieving flexible speed adjustment according to operating conditions, while avoiding abnormal current density and magnetic flux imbalance, reducing various losses, and efficiently improving the overall energy efficiency of the system.

Description

Technical Field

[0001] This invention relates to the field of motor speed conversion technology, and more specifically, to a method and system for converting an AC motor to a variable speed. Background Technology

[0002] AC motors are widely used in numerous fields such as industrial production, pumping stations, and power generation, serving as core energy conversion equipment for various applications. With the deepening of global energy conservation and emission reduction efforts and the continuous improvement of energy efficiency requirements for industrial systems, traditional AC motors operating at fixed speeds can no longer meet the demands for high-efficiency operation under varying conditions. The industry urgently needs targeted technological upgrades to achieve flexible speed control and effective reduction of operating losses, while ensuring precise parameter matching between the upgraded equipment and the power grid and converter. This has become an important development direction in the current field of motor applications.

[0003] Traditional AC motors are directly connected to the power grid through transformers, and their speed is strictly constrained by the fixed frequency of the power grid. They cannot be flexibly adjusted according to changes in actual operating conditions such as load size and medium flow rate. This leads to frequent occurrences of decreased system efficiency and increased losses at non-optimal speeds, with a significant surge in eddy current losses in the motor core and copper losses in the windings. Furthermore, the lack of a scientific parameter matching system leads to additional switching losses in the converter due to voltage regulation. Abnormal voltage in the transformer causes the core magnetic flux density to be too high or too low, further aggravating the overall system losses and resulting in a long-term low energy efficiency level.

[0004] Therefore, it is necessary to design a method and system for the speed conversion of AC motors to solve the problems of existing technology where the motor speed is constrained by the power grid frequency and cannot be flexibly adjusted according to the operating conditions, resulting in significant losses under non-optimal operating conditions, and the lack of precise parameter matching methods, which leads to improper voltage matching between the motor, transformer and converter, resulting in excessive copper loss, iron loss and additional losses, making it difficult to achieve efficient system operation. Summary of the Invention

[0005] In view of this, the present invention proposes a method and system for the speed conversion of AC motors, aiming to solve the problems of existing technology where the motor speed is constrained by the power grid frequency and cannot be flexibly adjusted according to the operating conditions, resulting in significant losses under non-optimal operating conditions, and lack of precise parameter matching methods, leading to improper voltage matching between the motor, transformer and converter, causing excessive copper loss, iron loss and additional losses, making it difficult to achieve efficient system operation.

[0006] In one aspect, the present invention proposes a method for speed-changing modification of an AC motor, comprising: A converter is installed between the AC motor and the transformer, and the converter is connected to both the AC motor and the transformer. Based on the original AC motor parameters, a digital simulation motor with the same parameters as the original AC motor is established. By adjusting the simulation stator winding parameters of the digital simulation motor, the simulation stator winding operating voltage of the digital simulation motor is changed. The simulation stator winding parameters and the simulation stator winding operating voltage are recorded, and a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage is established. Using the first correspondence table, the original stator winding parameters of the AC motor before modification, the original stator winding operating voltage before modification, and the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are adjusted. When adjusting the original stator winding parameters, if the equivalent series turns of the branch of the stator winding are to be adjusted, the adjustment is made by using the product of the number of phases of the winding, the number of parallel branches, and the equivalent series turns of the branch as a coefficient. The number of parallel branches and the number of phases of the original stator winding are adjusted according to the adjusted equivalent series turns of the branch of the stator winding. Based on the original transformer parameters, a digital simulation transformer with the same parameters as the original transformer is established. By adjusting the number of turns of the simulated motor side winding of the digital simulation transformer, the voltage at the simulated motor side winding port of the digital simulation transformer is changed. The number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port are recorded, and a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port is established. Using the second correspondence table and the original number of turns of the motor-side winding before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the grid-side module of the converter, adjust the number of turns of the original transformer motor-side winding, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the grid-side module of the converter.

[0007] Furthermore, when connecting the converter to an AC motor and a transformer, the following is included: Connect the motor-side module to the stator winding of the AC motor; The grid-side module is connected to the motor-side winding of the transformer.

[0008] Furthermore, the original stator winding parameters and operating voltage of the AC motor before modification were obtained by using the original motor nameplate, original motor instruction manual, original motor technical contract, and on-site measurements.

[0009] Furthermore, when adjusting the original stator winding parameters based on the original stator winding operating voltage and the voltage range allowed for operation of the converter motor-side module, the following steps are included: When the original stator winding operating voltage is within the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are kept unchanged. When the original stator winding operating voltage is not within the voltage range allowed to operate by the converter motor side module, the simulated stator winding operating voltage that is not higher than the highest operating voltage of the converter motor side module and has the smallest difference from the highest operating voltage is found in the first correspondence table, and the original stator winding parameters are adjusted with reference to the simulated stator winding parameters corresponding to the simulated stator winding operating voltage.

[0010] Furthermore, when adjusting the equivalent series turns of the stator winding branch based on the adjusted stator winding turns, it includes: When the equivalent series turns of the stator winding branch after adjustment are greater than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is reduced based on the adjustment coefficient. When the equivalent series turns of the stator winding branch after adjustment are less than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is increased based on the adjustment coefficient.

[0011] Furthermore, when adjusting the equivalent number of series turns of the stator winding branches based on changes in the number of stator winding turns, the following is also included: The adjustment factor is the product of the number of phases of the winding, the number of parallel branches, and the equivalent number of series turns of the branches.

[0012] Furthermore, the original motor-side winding parameters and port voltages of the transformer before modification were obtained by utilizing the original transformer nameplate, original transformer instruction manual, original transformer technical contract, and on-site measurements.

[0013] Furthermore, when adjusting the number of turns of the transformer's original generator-side winding based on the voltage at the transformer's original generator-side winding port and the voltage range allowed for operation of the converter's grid-side module, the following steps are included: When the voltage at the original motor-side winding port of the transformer is within the voltage range allowed for operation of the grid-side module of the converter, the number of turns of the original motor-side winding of the transformer remains unchanged. When the voltage of the original motor side winding port of the transformer is not within the voltage range allowed to operate by the grid side module of the converter, the voltage of the simulated motor side winding port of the transformer that is not higher than the highest operating voltage of the grid side module of the converter and has the smallest difference from the highest operating voltage is found in the second correspondence table, and the number of turns of the original motor side winding of the transformer is adjusted with reference to the number of turns of the simulated motor side winding of the transformer corresponding to the voltage of the simulated motor side winding port of the transformer.

[0014] Furthermore, the operation of adjusting the original stator winding parameters of the AC motor includes: adjusting the number of phases, number of parallel branches, number of turns, pole pitch, pitch, number of unit motors (fractional slot windings) or number of coil groups (integer slot windings) of the stator winding of the AC motor by means of replacement, open circuit, short circuit, winding, series connection, parallel connection, etc. The operation of adjusting the number of turns of the original machine-side winding of the transformer includes: adjusting the number of turns of the original machine-side winding of the transformer by means of replacement, disconnection, short circuit, rewinding, series connection, parallel connection, etc.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for speed conversion of an AC motor of the present invention breaks the limitation that the speed of the motor is constrained by the grid frequency when the motor is directly connected to the grid through the transformer in the traditional way. This allows the motor to flexibly adjust its speed according to the operating conditions, thereby reducing inefficient losses at non-optimal speeds from the root. At the same time, the converter can independently control the voltage, current and frequency on the motor side. With the adjustment of stator winding parameters, it can avoid the surge in winding copper losses caused by abnormal current density, and ensure that the voltage on the motor side is adapted to the range of the converter on the machine side, reducing the additional voltage regulation losses of the converter. The transformer adjusts the number of turns to adapt the voltage at the motor side port to the range of the converter on the grid side, which can avoid the transformer core magnetic flux density being too high or too low caused by abnormal voltage. Ultimately, it significantly reduces the copper losses and iron losses of the motor, as well as the additional losses of the converter and transformer, and effectively improves the overall energy efficiency of the system.

[0016] On the other hand, the present invention proposes a speed-changing retrofit system for an AC motor, comprising: A connection module is used to install a converter between an AC motor and a transformer, and to connect the converter to the AC motor and the transformer; The first simulation module is used to establish a digital simulation motor consistent with the original AC motor parameters based on the original AC motor parameters, and to change the simulation stator winding operating voltage of the digital simulation motor by adjusting the simulation stator winding parameters of the digital simulation motor, record the simulation stator winding parameters and the simulation stator winding operating voltage, and establish a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage. The parameter adjustment module is used to adjust the original stator winding parameters using the first correspondence table, the original stator winding parameters before the AC motor modification, the original stator winding operating voltage before the modification, and the voltage range allowed to operate by the converter motor side module. The branch equivalent series turns adjustment module is used to adjust the original stator winding parameters. If the branch equivalent series turns of the stator winding are to be adjusted, the adjustment is performed by using the product of the number of phases, the number of parallel branches, and the branch equivalent series turns as a coefficient. The number of parallel branches and the number of phases of the original stator winding are adjusted according to the adjusted branch equivalent series turns of the stator winding. The second simulation module is used to establish a digital simulation transformer consistent with the original transformer parameters based on the original transformer parameters, and to change the voltage at the port of the simulated motor side winding of the digital simulation transformer by adjusting the number of turns of the simulated motor side winding. The module records the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding, and establishes a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding. The turns adjustment module is used to adjust the number of turns of the original transformer motor-side winding, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the converter grid-side module, using the second correspondence table, the original number of turns of the original motor-side winding before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the converter grid-side module.

[0017] It is understandable that the above-mentioned method and system for modifying the speed of an AC motor have the same beneficial effects, and will not be elaborated further here. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A flowchart of the AC motor speed-changing modification method provided in an embodiment of the present invention; Figure 2 This is a structural diagram of the AC motor application system before modification, provided in an embodiment of the present invention. Figure 3 This is a system structure diagram of the AC motor after speed change modification provided in an embodiment of the present invention; Figure 4 This is a diagram of the parallel branch structure of the stator winding before modification, provided in an embodiment of the present invention. Figure 5 This is a diagram of the parallel branch structure after the stator winding modification provided in an embodiment of the present invention; Figure 6 A diagram showing the number of turns of the transformer motor-side winding before modification, provided for an embodiment of the present invention; Figure 7 A diagram showing the number of turns of the modified transformer motor-side winding provided in an embodiment of the present invention; Figure 8 A functional block diagram of an AC motor speed-changing retrofit system provided in an embodiment of the present invention.

[0019] Among them, A-AC motor, A1-stator winding, A2-stator core, A3-rotor, B-converter, B1-motor side module, B2-grid side module, C-transformer, C1-motor side winding, C2-grid side winding. Detailed Implementation

[0020] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, without conflict, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] Reference Figure 1 As shown in some embodiments of this application, a method for speed modification of an AC motor includes: A converter is installed between the AC motor and the transformer, and the converter is connected to both the AC motor and the transformer. Based on the original AC motor parameters, a digital simulation motor with the same parameters as the original AC motor is established. By adjusting the simulation stator winding parameters of the digital simulation motor, the simulation stator winding operating voltage of the digital simulation motor is changed. The simulation stator winding parameters and the simulation stator winding operating voltage are recorded, and a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage is established. Using the first correspondence table, the original stator winding parameters of the AC motor before modification, the original stator winding operating voltage before modification, and the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are adjusted. When adjusting the original stator winding parameters, if the equivalent series turns of the branch of the stator winding are to be adjusted, the adjustment is made by using the product of the number of phases of the winding, the number of parallel branches, and the equivalent series turns of the branch as a coefficient. The number of parallel branches and the number of phases of the original stator winding are adjusted according to the adjusted equivalent series turns of the branch of the stator winding. Based on the original transformer parameters, a digital simulation transformer with the same parameters as the original transformer is established. By adjusting the number of turns of the simulated motor side winding of the digital simulation transformer, the voltage at the simulated motor side winding port of the digital simulation transformer is changed. The number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port are recorded, and a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port is established. Using the second correspondence table and the original number of turns of the motor-side winding before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the grid-side module of the converter, adjust the number of turns of the original transformer motor-side winding, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the grid-side module of the converter.

[0022] Specifically, the AC motors mentioned encompass all motor types based on AC winding theory, including synchronous generators, synchronous motors, synchronous generator-motors, asynchronous generators, asynchronous motors, asynchronous generator-motors, doubly-fed asynchronous generators, doubly-fed asynchronous motors, doubly-fed asynchronous generator-motors, permanent magnet synchronous motors, permanent magnet synchronous generators, and permanent magnet synchronous generator-motors. When simulating AC motors using digital simulation motors, the digital simulation motor must be completely identical to the actual AC motor in parameters such as stator core material, number of stator core slots, number of poles, and number of unit motors. Furthermore, the stator windings of the digital simulation motor... The rated voltage must match the rated voltage of the converter motor side module. When adjusting the original stator winding parameters of the AC motor, the adjustable parameters include the number of phases, number of parallel branches, number of turns, pole pitch, pitch, number of unit motors connected in series in the branches (fractional slot windings) or number of coil groups (integer slot windings). When simulating a transformer using a digital transformer simulation, the rated voltage, rated current, winding material, insulation class, and other parameters of the transformer grid side winding must be imported synchronously. When adjusting the number of turns of the simulator side winding, it is necessary to associate it with the number of turns of the grid side winding to ensure that the transformer turns ratio conforms to the basic design logic.

[0023] Understandably, by inserting a converter between the AC motor and the transformer, the limitation of traditional motor speed being constrained by the grid frequency is broken at the hardware level, making it possible for the motor to flexibly adjust its speed according to operating conditions, thereby reducing inefficient losses at non-optimal speeds from the root. At the same time, by establishing first and second correspondence tables for digitally simulated motors and digitally simulated transformers respectively, and combining the original stator winding working voltage of the motor and the original motor-side winding port voltage of the transformer, the blindness of subsequent parameter adjustments can be avoided. With the adjustment of stator winding parameters and transformer machine-side turns, it can be ensured that the motor stator voltage is adapted to the converter machine-side voltage range and the transformer motor-side voltage is adapted to the converter grid-side voltage range, reducing the additional voltage regulation losses of the converter, and providing data support for controlling the motor current density and transformer core magnetic flux density, ultimately helping to reduce motor copper losses, iron losses and additional losses of various components.

[0024] In some embodiments of this application, the original motor system is as follows: Figure 2 As shown, the modified variable speed motor system is as follows: Figure 3 As shown, when connecting the converter to an AC motor and a transformer, the following steps are included: Connect the motor-side module to the stator winding of the AC motor; The grid-side module is connected to the motor-side winding of the transformer.

[0025] Specifically, the converter includes a motor-side module and a grid-side module. The motor-side module must have voltage, current, and frequency regulation functions, while the grid-side module must have energy conversion functions adapted to the grid frequency. When connecting the converter's motor-side module to the AC motor stator winding, the stator winding terminals must be connected accordingly. Before wiring, the output phase of the motor-side module must be checked against the phase markings of the stator winding to ensure phase consistency. When connecting the converter's grid-side module to the transformer's motor-side winding, the lead wire markings of the transformer's motor-side winding must be confirmed first, and then connected one-to-one with the output terminals of the grid-side module to avoid phase mismatch. After connection, an insulation resistance meter must be used to test the insulation resistance values ​​between the converter and the motor, and between the converter and the transformer, to ensure that the insulation performance meets electrical safety standards. The test voltage level must be determined based on the rated voltage of the motor and the transformer.

[0026] Understandably, clearly defining the specific connection methods between the converter and the motor and transformer (the motor-side module connects to the motor stator winding, and the grid-side module connects to the transformer motor-side winding) is a key connection guarantee for the implementation of the core innovation. This connection method enables the converter's "dual-module independent control" function—the motor-side module can independently regulate the voltage, current, and frequency output to the motor, directly supporting flexible adjustment of the motor speed according to operating conditions and reducing inefficient losses at non-optimal speeds; the grid-side module focuses on adapting to the grid frequency, ensuring stable energy transmission between the converter and the transformer, avoiding frequency interference caused by improper connection methods, and thus reducing additional losses during energy conversion. At the same time, clear connection logic also avoids problems such as phase reversal and poor insulation, preventing equipment damage and additional losses caused by connection failures, and providing a safe and stable hardware foundation for subsequent parameter adjustments.

[0027] Reference Figure 4-5 As shown, in some embodiments of this application, the original parameters of the AC motor before modification, such as the original stator winding working voltage, number of parallel branches, number of unit motors, number of coil turns, number of poles, pole pitch, and pitch, are obtained by using the original motor nameplate, original motor instruction manual, original motor technical contract, and on-site measurement.

[0028] Specifically, when querying the original stator winding parameters in the first correspondence table, it is necessary to check them one by one in the following order: "Number of phases → Number of parallel branches → Number of unit motors connected in series in the branches (fractional slot windings) or Number of coil groups (integer slot windings) → Number of turns → Pole pitch → Pitch" to ensure that the queried parameters are completely consistent with the actual parameters of the original stator winding. When the original stator winding parameters are not found in the first correspondence table, the stator core parameters of the actual AC motor (including core length, core outer diameter, core inner diameter, and slot size) must first be imported into the digital simulation motor model. Then, the number of phases, number of parallel branches, number of unit motors connected in series in the branches (fractional slot windings) or Number of coil groups (integer slot windings), number of turns, pole pitch, and pitch of the simulated stator winding must be adjusted one by one to the original stator winding parameters. Then, the simulation program is started and run for a sufficient time to obtain a stable simulated stator winding operating voltage. Finally, the set of parameters and voltage data are entered into the first correspondence table to complete the update.

[0029] Understandably, the "query-complete-extract" steps ensure the accuracy of the obtained stator winding operating voltage, preventing subsequent parameter adjustments from being mishandled due to voltage data deviations. Inaccurate data can cause the motor-side voltage to deviate from the converter's range, leading to additional voltage regulation losses in the converter or abnormal motor winding current. When the original parameters are missing from the first correspondence table, updating the table data synchronously can improve the simulation database, providing accurate references for subsequent modifications to similar motors and reducing losses from repeated trial and error. At the same time, extracting voltage data based on a consistent simulation environment ensures that the data matches the actual operating conditions, laying the foundation for adapting the motor voltage to the converter's range and controlling the current density, indirectly reducing motor copper and iron losses.

[0030] Reference Figure 4-5 As shown in some embodiments of this application, Figure 4 The original stator winding shown contains two branches for a certain phase, with each branch connected in series with six unit motors. When adjusting the parameters of the original stator winding based on its operating voltage and the allowable operating voltage range of the converter motor-side module, the following steps are taken: When the original stator winding operating voltage is within the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are kept unchanged. When the original stator winding operating voltage is not within the voltage range allowed to operate by the converter motor side module, the simulated stator winding operating voltage that is not higher than the highest operating voltage of the converter motor side module and has the smallest difference from the highest operating voltage is found in the first correspondence table, and the original stator winding parameters are adjusted with reference to the simulated stator winding parameters corresponding to the simulated stator winding operating voltage.

[0031] Specifically, when determining whether the original stator winding operating voltage falls within the machine-side voltage range, the original stator winding operating voltage must be compared with the upper and lower limits of the machine-side voltage range. The deviation must be controlled within the set threshold range. If the deviation exceeds this range, it is determined that the voltage does not fall within the machine-side voltage range. When searching for the simulated stator winding operating voltage that is not higher than the highest operating voltage of the converter machine side and has the smallest difference from the highest operating voltage in the first correspondence table, all simulated stator winding operating voltage data in the table must be traversed, and the absolute difference between each voltage and the rated voltage of the machine side must be calculated. The simulated voltage with the smallest difference and the corresponding simulated stator winding parameters must be selected. When adjusting the original stator winding parameters with reference to these simulated parameters, the number of parallel branches, the number of unit motors connected in series in the branches (fractional slot windings), or the number of coil groups (integer slot windings) should be adjusted first. If the voltage still does not meet the requirements after adjustment, the pole pitch and pitch should be adjusted in sequence, and finally the number of phases and the number of turns should be adjusted. During the adjustment process, the actual voltage value should be recorded once after each parameter is adjusted until the voltage falls within the machine-side voltage range.

[0032] Specifically, the stator winding operating voltage is included within the converter's machine-side voltage range because the power devices (such as IGBTs) and insulation structures of the converter's motor-side module have clearly defined upper and lower limits for voltage tolerance. If the voltage exceeds this range, it may trigger the converter's overvoltage / undervoltage protection, causing the system to shut down. In severe cases, it may break down the insulation of the motor-side module or burn out the power devices. At the same time, voltage mismatch may also cause the motor stator winding current to increase abnormally (undervoltage) or decrease (overvoltage), resulting in a surge in winding copper losses and insufficient motor output.

[0033] Understandably, by determining whether the stator voltage is within the converter's machine-side voltage range, losses caused by overvoltage / undervoltage operation of the motor can be directly avoided—overvoltage may break down winding insulation and increase iron losses, while undervoltage may increase current and cause a surge in copper losses. When the voltage is mismatched, adjusting the parameters according to the principle of "minimum difference" based on simulation parameters can ensure that the motor stator winding parameters (such as the number of parallel branches, the number of unit motors or coil groups connected in series in the branches) are optimal. This avoids parameter redundancy losses caused by blind adjustments and allows the motor-side voltage to accurately match the converter's machine-side range, reducing switching losses caused by voltage compensation in the converter. At the same time, prioritizing the optimization of key parameters (the number of parallel branches, the number of unit motors or coil groups connected in series in the branches) during the adjustment process can quickly achieve motor-converter compatibility. Combined with the converter's frequency control function, the motor speed can be flexibly adjusted according to operating conditions, further reducing inefficient losses at non-optimal speeds.

[0034] Figure 5 The diagram shown is a schematic of a phase of the stator winding after adjustment in this embodiment. By changing the 6 unit motors connected in series in each branch of the original stator winding to parallel connection, the 2 branches are transformed into 12 branches.

[0035] In some embodiments of this application, adjusting the equivalent series turns of a stator winding branch based on the adjusted stator winding turns includes: When the equivalent series turns of the stator winding branch after adjustment are greater than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is reduced based on the adjustment coefficient. When the equivalent series turns of the stator winding branch after adjustment are less than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is increased based on the adjustment coefficient.

[0036] In some embodiments of this application, when adjusting the number of parallel branches of the stator winding based on the change in the equivalent number of series turns of the stator winding, the method further includes: The adjustment factor is the product of the number of phases of the winding, the number of parallel branches, and the equivalent number of series turns of the branches.

[0037] Specifically, before calculating the adjustment coefficient, the number of turns in the stator winding before adjustment needs to be obtained through actual measurement (this requires using the original design data or disassembling the motor stator winding to measure the number of turns; if the winding is multi-parallel, the equivalent series turns of each path must be measured first). Simultaneously, the diameter of the conductor before adjustment must be measured using a micrometer, and the cross-sectional area of ​​the conductor before adjustment must be calculated (if it is a multi-strand conductor, the diameter of a single strand must be measured first to calculate the cross-sectional area of ​​a single strand, then multiplied by the number of strands). The formula for calculating the adjustment coefficient is strictly based on the electromagnetic theory that "motor winding current is inversely proportional to the number of turns, and conductor cross-sectional area is directly proportional to current," and is only applicable to stator winding conductors of the same material, insulation class, and heat dissipation conditions. When calculating the cross-sectional area of ​​the conductor after adjustment, if the result is a non-standard conductor cross-sectional area specification, the closest standard specification conductor must be selected, with the deviation controlled within the threshold. Furthermore, digital simulation must be used to verify whether the current density corresponding to the standard specification conductor is within the design allowable range. After calculation, the adjusted cross-sectional area, number of turns, and other parameters must be marked on the conductor sample for verification during actual procurement and construction.

[0038] Understandably, providing a quantitative formula for adjusting the conductor cross-sectional area (adjustment coefficient, cross-sectional area calculation formula) is the technical support for ensuring stable current density in motor windings and accurately reducing copper losses. The adjustment coefficient is based on the electromagnetic theory that "current is inversely proportional to the number of turns, and cross-sectional area is directly proportional to current," ensuring that the coefficient calculation is scientific and avoiding deviations from adjustments based on experience. If the coefficient is inaccurate, it may lead to excessive or insufficient adjustment of the cross-sectional area, still causing copper loss problems. A clear cross-sectional area calculation formula allows the adjustment process to be quantified and controllable, ensuring that the adjusted cross-sectional area and the number of turns are perfectly matched, further stabilizing the current density and reducing copper loss fluctuations. At the same time, the application of the formula can avoid the excessive use or waste of conductor materials, reducing modification costs while ensuring that the adjusted conductor is compatible with the motor stator slot structure and does not affect the winding embedding process, indirectly reducing additional losses caused by process issues, and laying the foundation for long-term low-loss operation of the motor.

[0039] Reference Figure 6-7 As shown, in some embodiments of this application, the original motor-side winding parameters and port voltage of the transformer before modification are obtained by means of the original transformer nameplate, original transformer instruction manual, original transformer technical contract, on-site measurement, etc.

[0040] Specifically, when querying the original generator-side winding turns in the second correspondence table, it is necessary to first consult the transformer manufacturer's technical manual to obtain the original design turns of the generator-side winding, and then compare it with the simulated generator-side winding turns recorded in the table. If the manual data is missing, the transformer needs to be disassembled to measure the actual turns of the generator-side winding and the grid-side winding (the winding method needs to be recorded during measurement). When the original generator-side winding turns are not found in the second correspondence table, the core parameters (core material, core loss coefficient, core cross-sectional area) and grid-side winding parameters (turns, conductors) of the actual transformer need to be imported into the digital simulation transformer model. (Cross-sectional area, rated voltage), then adjust the number of turns of the simulator-side winding to the original number of turns of the simulator-side winding, set the simulated grid voltage to the rated value and the load rate to 100%, run the simulation program to obtain a stable simulated motor-side winding port voltage, and record the winding temperature and copper loss value during the simulation. Then enter these data into the second correspondence table to complete the update. When the original number of turns of the simulator-side winding exists in the second correspondence table, it is necessary to check whether the simulated grid-side voltage corresponding to that number of turns is consistent with the rated voltage of the actual grid. If they are inconsistent, voltage correction calculation is required, and then the corresponding original motor-side winding port voltage is obtained.

[0041] It is understandable that using the second correspondence table to obtain the original motor-side winding port voltage of the transformer is a prerequisite for accurately adjusting the number of transformer turns and reducing transformer iron losses. The "query-complete-extract" steps ensure the accuracy of the obtained original transformer port voltage, avoiding deviations in subsequent turns adjustment due to incorrect voltage data. Inaccurate data may cause the adjusted voltage to deviate from the operating range of the converter grid-side voltage, leading to abnormal transformer core magnetic flux density (too high increases iron losses, too low wastes resources). When the second correspondence table lacks original parameters, synchronously updating the table data can improve the transformer simulation database, providing accurate references for subsequent modifications of similar transformers and reducing trial-and-error losses. Simultaneously, combining voltage extraction with grid-side parameters ensures that the data conforms to the actual operating logic of the transformer, laying the foundation for subsequent turns adjustment and core magnetic flux density control, directly contributing to reducing transformer iron losses and enabling efficient energy transmission in conjunction with the converter.

[0042] Reference Figure 6-7 As shown, Figure 6This is a schematic diagram of the original generator-side winding of a transformer, which has 4 turns. In some embodiments of this application, adjusting the number of turns of the original generator-side winding of the transformer based on the port voltage of the original generator-side winding and the allowable operating voltage range of the converter grid-side module includes: When the voltage at the original motor-side winding port of the transformer is within the voltage range allowed for operation of the grid-side module of the converter, the number of turns of the original motor-side winding of the transformer remains unchanged. When the voltage of the original motor side winding port of the transformer is not within the voltage range allowed to operate by the grid side module of the converter, the voltage of the simulated motor side winding port of the transformer that is not higher than the highest operating voltage of the grid side module of the converter and has the smallest difference from the highest operating voltage is found in the second correspondence table, and the number of turns of the original motor side winding of the transformer is adjusted with reference to the number of turns of the simulated motor side winding of the transformer corresponding to the voltage of the simulated motor side winding port of the transformer.

[0043] Specifically, when determining whether the original motor-side winding port voltage falls within the grid-side voltage range, grid voltage fluctuations must be considered. Typically, the original motor-side winding port voltage is calculated based on the set threshold fluctuation range of the grid rated voltage. If all calculated values ​​fall within the grid-side voltage range, the original motor-side winding turns are retained. When the original motor-side winding port voltage does not fall within the grid-side voltage range, the simulated motor-side winding port voltage, which is not higher than the highest operating voltage of the converter grid-side module and has the smallest difference from the highest operating voltage, must also be considered... Considering the simulated grid voltage fluctuation range corresponding to the simulated voltage, ensure that the adjusted number of turns can still keep the motor-side port voltage within the allowable voltage range of the converter grid-side module when the grid voltage fluctuates; when adjusting the original number of turns of the generator-side winding with reference to the simulated number of turns of the generator-side winding, it is necessary to calculate the adjusted transformer ratio (ratio = number of turns of grid-side winding / adjusted number of turns of generator-side winding), and ensure that the ratio is consistent with the ratio of the rated voltage of the converter grid side and the rated voltage of the grid, and the deviation does not exceed the threshold range; after the adjustment is completed, the actual port voltage of the transformer generator-side winding needs to be measured through a no-load test to verify whether it is consistent with the design value. Figure 7 This is a schematic diagram of the adjusted transformer motor-side winding. The number of winding turns is adjusted to 2 turns by connecting the coils in parallel.

[0044] Specifically, ensuring that the voltage at the original motor-side winding port falls within the grid-side voltage range is crucial because the converter's grid-side module needs to achieve synchronous adaptation with the grid frequency and stable bidirectional energy transmission within the rated voltage range. If the voltage exceeds this range, the grid-side module will be unable to perform PWM modulation (pulse width modulation) normally, leading to energy transmission interruption. It may also damage the transformer's motor-side winding insulation due to excessively high voltage, or increase the transformer winding current due to excessively low voltage, resulting in increased copper losses and winding overheating. Ultimately, this ensures electrical parameter compatibility between the converter and the AC motor, and between the converter and the transformer, preventing equipment damage and system malfunctions.

[0045] Understandably, adjusting the number of turns based on the original transformer port voltage and the converter grid-side range is a core step in achieving normal system operation, optimal transformer parameters, and reduced iron losses. By determining whether the original voltage is within the grid-side range, losses caused by abnormal voltage can be directly avoided—overvoltage may damage winding insulation and increase iron losses due to excessive core magnetic flux density, while undervoltage may increase current and copper losses. When the voltage is mismatched, adjusting the number of turns according to the principle of "not higher and with the smallest difference" based on simulation ensures optimal transformer turn count. This avoids ratio imbalance caused by blind adjustment (leading to additional losses) and ensures that the motor-side port voltage accurately matches the converter grid-side range, reducing losses caused by voltage compensation in the converter. At the same time, adjusting the number of turns can directly control the core magnetic flux density within a reasonable range, avoiding a surge in iron losses due to excessively high magnetic flux density or material waste due to excessively low magnetic flux density. This perfectly meets the innovation point of "avoiding transformer core magnetic flux density problems caused by abnormal voltage," effectively reducing transformer iron losses.

[0046] In some embodiments of this application, the operation of adjusting the original stator winding parameters of the AC motor includes: adjusting the number of phases, number of parallel branches, number of turns, pole pitch, pitch, number of unit motors (fractional slot windings) or number of coil groups (integer slot windings) of the stator winding of the AC motor by means of replacement, open circuit, short circuit, winding, series connection, parallel connection, etc. The operation of adjusting the number of turns of the original machine-side winding of the transformer includes: adjusting the number of turns of the original machine-side winding of the transformer by means of replacement, disconnection, short circuit, rewinding, series connection, parallel connection, etc.

[0047] Specifically, when adjusting the original stator winding parameters using the replacement method, the original stator winding must first be removed (the winding sequence and wiring method must be recorded during removal), and then the winding must be rewound according to the adjusted parameters. During winding, it is essential to ensure uniform conductor tension to avoid conductor damage. When adjusting using the open-circuit method, the open-circuit operation must be performed at non-critical leads of the stator winding, and the open-circuit point must be wrapped with an insulating sleeve to prevent short circuits. When adjusting using the short-circuit method, the corresponding terminals of the winding must be short-circuited, and copper busbars must be used to connect the short-circuit points to ensure that the contact resistance is less than the value required by the technical specifications. When adjusting using the winding connection method, it is necessary to... When adding or removing part of the winding based on the existing winding, the winding joints need to be welded. The welding material must be matched with the conductor material (copper wire for copper conductors and aluminum wire for aluminum conductors). After welding, the welding slag must be removed and insulation treatment must be performed. When adjusting using series or parallel methods, it is necessary to ensure that the parameters of the series or parallel winding coils are consistent (including the number of turns, conductor cross-sectional area, and insulation class) to avoid circulating current. When adjusting the number of turns of the original machine-side winding of the transformer, the operation method is the same as that of the motor stator winding adjustment method. After adjustment, the transformer needs to be vacuum dried to remove moisture from the windings and ensure stable insulation performance.

[0048] Understandably, clearly defining the specific adjustment methods (replacement, circuit breaking, series connection, parallel connection, etc.) for the motor stator winding parameters and transformer turn count is a practical guarantee for ensuring the safe and reliable operation of the system, accurate parameter adjustment, and further reducing losses. Providing diverse adjustment methods allows for the selection of the optimal approach based on the actual structure of the motor and transformer (such as stator slot type and winding method). For example, adjusting the motor stator winding turn count can be done through series / parallel connection, while adjusting the transformer turn count can be done through replacement / short circuit. This avoids inaccurate parameter matching due to improper adjustment methods, thereby reducing losses. Furthermore, clearly defining the adjustment targets, including key parameters such as the number of phases, pole pitch, and pitch of the motor stator winding, can further optimize the motor's electromagnetic structure and reduce additional losses caused by parameter mismatch (such as leakage flux loss due to improper pole pitch). The adjustment method for the transformer turn count also ensures accurate turn count changes, enabling voltage adaptation in conjunction with the converter, ultimately helping to reduce motor copper losses, iron losses, and additional transformer losses, thus improving the overall system energy efficiency.

[0049] Reference Figure 8 As shown in some embodiments of this application, a speed-changing retrofit system for an AC motor includes: A connection module is used to install a converter between an AC motor and a transformer, and to connect the converter to the AC motor and the transformer; The first simulation module is used to establish a digital simulation motor consistent with the original AC motor parameters based on the original AC motor parameters, and to change the simulation stator winding operating voltage of the digital simulation motor by adjusting the simulation stator winding parameters of the digital simulation motor, record the simulation stator winding parameters and the simulation stator winding operating voltage, and establish a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage. The parameter adjustment module is used to adjust the original stator winding parameters using the first correspondence table, the original stator winding parameters before the AC motor modification, the original stator winding operating voltage before the modification, and the voltage range allowed to operate by the converter motor side module. The branch equivalent series turns adjustment module is used to adjust the original stator winding parameters. If the branch equivalent series turns of the stator winding are to be adjusted, the adjustment is performed by using the product of the number of phases, the number of parallel branches, and the branch equivalent series turns as a coefficient. The number of parallel branches and the number of phases of the original stator winding are adjusted according to the adjusted branch equivalent series turns of the stator winding. The second simulation module is used to establish a digital simulation transformer consistent with the original transformer parameters based on the original transformer parameters, and to change the voltage at the port of the simulated motor side winding of the digital simulation transformer by adjusting the number of turns of the simulated motor side winding. The module records the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding, and establishes a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding. The turns adjustment module is used to adjust the original motor-side winding turns of the transformer, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the converter grid-side module, using the second correspondence table, the original motor-side winding turns before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the converter grid-side module.

[0050] It is understandable that the above-mentioned method and system for modifying the speed of an AC motor have the same beneficial effects, and will not be elaborated further here.

[0051] It should be noted that: Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known structures and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0052] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of this application and form different embodiments.

[0053] The above description is merely a preferred embodiment 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 technical scope 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 speed conversion modification of an AC motor, characterized in that, include: A converter is installed between the AC motor and the transformer, and the converter is connected to both the AC motor and the transformer. Based on the original AC motor parameters, a digital simulation motor with the same parameters as the original AC motor is established. By adjusting the simulation stator winding parameters of the digital simulation motor, the simulation stator winding operating voltage of the digital simulation motor is changed. The simulation stator winding parameters and the simulation stator winding operating voltage are recorded, and a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage is established. Using the first correspondence table, the original stator winding parameters of the AC motor before modification, the original stator winding operating voltage before modification, and the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are adjusted. When adjusting the original stator winding parameters, if the equivalent series turns of the branch of the stator winding are to be adjusted, the adjustment is made by using the product of the number of phases of the winding, the number of parallel branches, and the equivalent series turns of the branch as a coefficient. The number of parallel branches and the number of phases of the original stator winding are adjusted according to the adjusted equivalent series turns of the branch of the stator winding. Based on the original transformer parameters, a digital simulation transformer with the same parameters as the original transformer is established. By adjusting the number of turns of the simulated motor side winding of the digital simulation transformer, the voltage at the simulated motor side winding port of the digital simulation transformer is changed. The number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port are recorded, and a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the simulated motor side winding port is established. Using the second correspondence table and the original number of turns of the motor-side winding before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the grid-side module of the converter, adjust the number of turns of the original transformer motor-side winding, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the grid-side module of the converter.

2. The method for speed conversion of an AC motor according to claim 1, characterized in that, When connecting a converter to an AC motor and a transformer, the following are included: Connect the motor-side module to the stator winding of the AC motor; The grid-side module is connected to the motor-side winding of the transformer.

3. The method for speed conversion modification of an AC motor according to claim 2, characterized in that, The original stator winding parameters and operating voltage of the AC motor before modification were obtained by using the original motor nameplate, original motor instruction manual, original motor technical contract, and on-site measurements.

4. The method for speed conversion of an AC motor according to claim 3, characterized in that, When adjusting the original stator winding parameters based on the original stator winding operating voltage and the voltage range allowed for operation of the converter motor-side module, the following steps are included: When the original stator winding operating voltage is within the voltage range allowed to operate by the converter motor side module, the original stator winding parameters are kept unchanged. When the original stator winding operating voltage is not within the voltage range allowed to operate by the converter motor side module, the simulated stator winding operating voltage that is not higher than the highest operating voltage of the converter motor side module and has the smallest difference from the highest operating voltage is found in the first correspondence table, and the original stator winding parameters are adjusted with reference to the simulated stator winding parameters corresponding to the simulated stator winding operating voltage.

5. The method for speed conversion modification of an AC motor according to claim 4, characterized in that, When adjusting the equivalent series turns of a stator winding branch based on the adjusted stator winding turns, the following applies: When the equivalent series turns of the stator winding branch after adjustment are greater than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is reduced based on the adjustment coefficient. When the equivalent series turns of the stator winding branch after adjustment are less than the equivalent series turns of the stator winding branch before adjustment, the number of parallel branches is increased based on the adjustment coefficient.

6. A method of variable speed retrofitting of an AC motor as defined in claim 5, wherein, When adjusting the equivalent series turns of a stator winding branch based on changes in the number of stator winding turns, the following is also included: The adjustment factor is the product of the number of phases of the winding, the number of parallel branches, and the equivalent number of series turns of the branches.

7. A method of variable speed retrofitting of an AC motor as defined in claim 6, wherein The original motor-side winding parameters and port voltages of the transformer before modification were obtained by using the original transformer nameplate, original transformer instruction manual, original transformer technical contract, and on-site measurements.

8. The method for speed conversion modification of an AC motor according to claim 7, characterized in that, When adjusting the number of turns of the transformer's original motor-side winding based on the voltage at the transformer's original motor-side winding port and the allowable operating voltage range of the converter's grid-side module, the following steps are included: When the voltage at the original motor-side winding port of the transformer is within the voltage range allowed for operation of the grid-side module of the converter, the number of turns of the original motor-side winding of the transformer remains unchanged. When the voltage of the original motor side winding port of the transformer is not within the voltage range allowed to operate by the grid side module of the converter, the voltage of the simulated motor side winding port of the transformer that is not higher than the highest operating voltage of the grid side module of the converter and has the smallest difference from the highest operating voltage is found in the second correspondence table, and the number of turns of the original motor side winding of the transformer is adjusted with reference to the number of turns of the simulated motor side winding of the transformer corresponding to the voltage of the simulated motor side winding port of the transformer.

9. The method for speed conversion modification of an AC motor according to claim 8, characterized in that, The operation of adjusting the original stator winding parameters of the AC motor includes: adjusting the number of phases, number of parallel branches, number of turns, pole pitch, pitch, number of unit motors or number of coil groups in series of branches of the AC motor stator winding by means of replacement, open circuit, short circuit, winding, series connection, parallel connection, etc. The operation of adjusting the number of turns of the original machine-side winding of the transformer includes: adjusting the number of turns of the original machine-side winding of the transformer by means of replacement, disconnection, short circuit, rewinding, series connection, parallel connection, etc.

10. A speed-changing retrofit system for an AC motor, characterized in that, A method for speed conversion modification of an AC motor according to any one of claims 1-9, comprising: A connection module is used to install a converter between an AC motor and a transformer, and to connect the converter to the AC motor and the transformer; The first simulation module is used to establish a digital simulation motor consistent with the original AC motor parameters based on the original AC motor parameters, and to change the simulation stator winding operating voltage of the digital simulation motor by adjusting the simulation stator winding parameters of the digital simulation motor, record the simulation stator winding parameters and the simulation stator winding operating voltage, and establish a first correspondence table between the simulation stator winding parameters and the simulation stator winding operating voltage. The parameter adjustment module is used to adjust the original stator winding parameters using the first correspondence table, the original stator winding parameters before the AC motor modification, the original stator winding operating voltage before the modification, and the voltage range allowed to operate by the converter motor side module. The branch equivalent series turns adjustment module is used to adjust the original stator winding parameters. If the branch equivalent series turns of the stator winding are adjusted, the number of parallel branches and the number of phases of the original stator winding are adjusted based on the adjusted branch equivalent series turns of the stator winding. The second simulation module is used to establish a digital simulation transformer consistent with the original transformer parameters based on the original transformer parameters, and to change the voltage at the port of the simulated motor side winding of the digital simulation transformer by adjusting the number of turns of the simulated motor side winding. The module records the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding, and establishes a second correspondence table between the number of turns of the simulated motor side winding and the voltage at the port of the simulated motor side winding. The turns adjustment module is used to adjust the number of turns of the original transformer motor-side winding, or replace the transformer with a transformer that matches the operating voltage, grid voltage, and capacity of the converter grid-side module, using the second correspondence table, the original number of turns of the original motor-side winding before the transformer modification, the original motor-side winding port voltage, and the voltage range allowed to operate by the converter grid-side module.

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