A method, control system and device for flywheel starting of a frequency converter

Abstract

The application discloses a flywheel starting method, a control system and a device of a frequency converter, and belongs to the technical field of frequency drag. In the flywheel starting method, the frequency converter first applies excitation current to the synchronous motor and obtains three-phase voltage values at the output end of the frequency converter; then, the initial rotating speed value of the rotor is determined based on the three-phase voltage values, and the initial angle value of the rotor is determined according to the initial rotating speed value by using a corresponding angle detection strategy, so that the angle detection strategy can adapt to different rotating speed conditions, thereby the initial angle can be accurately obtained at various rotating speeds including a low rotating speed; finally, the frequency converter is controlled to start based on the obtained initial angle value. By using the corresponding angle detection strategy at different rotating speeds in the above manner, the accuracy of the initial angle of the rotor can be improved, and the reliability of the flywheel starting of the frequency converter is improved.

Description

Technical Field

[0001] This application relates to the field of variable frequency drive technology, specifically to a method, control system, and device for starting a vehicle using a variable frequency drive. Background Technology

[0002] In energy storage and industrial applications such as compressed air energy storage, pumped hydro storage, fans, and water pumps, synchronous motor rotors often reach a certain initial speed before the frequency converter starts, due to external airflow, fluid impact, or mechanical turning action, resulting in a non-zero speed rotational state. In this case, the frequency converter needs to have a flyback start function, meaning it must be able to quickly detect the rotor's current speed, position, and direction of rotation, smoothly track and synchronously connect to the motor, achieving a shock-free and smooth restart of the motor in a free-rotating state.

[0003] However, when the rotor speed is low, the initial rotor angle obtained by the frequency converter may be inaccurate, thus affecting the reliability of the frequency converter's overspeed start. Summary of the Invention

[0004] This application provides a method, control system, and apparatus for overspeed starting of a frequency converter, aiming to improve the accuracy of the rotor initial angle, thereby improving the reliability of overspeed starting of the frequency converter.

[0005] In a first aspect, this application provides a method for starting a motor by using a frequency converter, wherein the output terminal of the frequency converter is used for electrical connection with the motor terminal of a synchronous motor, and the method includes: Apply excitation current to the synchronous motor and obtain the three-phase voltage value at the output terminal of the frequency converter; Based on the three-phase voltage values, determine the initial rotor speed in the synchronous motor; Based on the initial rotational speed of the rotor, an angle detection strategy corresponding to the initial rotational speed is adopted to determine the initial angle value of the rotor. The frequency converter is started based on the initial angle value of the rotor.

[0006] In some implementations, the initial rotor speed in the synchronous motor is determined based on the three-phase voltage values, including: Based on the three-phase voltage values, determine the first and second voltage components in the stationary coordinate system; The initial rotational speed of the rotor in the synchronous motor is determined based on the first voltage component and the second voltage component.

[0007] In some implementations, determining the initial rotational speed of the rotor in the synchronous motor based on a first voltage component and a second voltage component includes: The first voltage component and the second voltage component are normalized to determine the first per-unit value and the second per-unit value. The Euclidean 2 norm of the first and second per-unit values ​​is determined as the composite per-unit value; Based on the per-unit synthesized value, the actual value of the excitation current of the synchronous motor, the no-load rated excitation current value of the synchronous motor, and the rated speed value of the rotor, the initial speed value of the rotor in the synchronous motor is determined.

[0008] In some implementations, based on the initial rotational speed of the rotor, an angle detection strategy corresponding to the initial rotational speed is used to determine the initial angle value of the rotor, including: Based on the initial speed value of the rotor, the speed range corresponding to the initial speed value is determined. The speed range includes a first speed range, a second speed range, and a third speed range. The upper limit of the speed in the first speed range is less than the lower limit of the speed in the second speed range, and the upper limit of the speed in the second speed range is less than the lower limit of the speed in the third speed range. Based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is adopted to determine the initial angle value of the rotor.

[0009] In some implementations, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is used to determine the initial angle value of the rotor, including: When the initial speed value corresponds to the first speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first and second voltage components and the first preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the arctangent value of the first and second voltage components.

[0010] In some implementations, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is used to determine the initial angle value of the rotor, including: When the initial speed value corresponds to the second speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first and second voltage components and the second preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first and second voltage components and the third preset angle compensation value.

[0011] In some implementations, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is used to determine the initial angle value of the rotor, including: When the initial speed value corresponds to the third speed range, the initial angle value of the rotor is determined based on the three-phase voltage value at the output terminal of the frequency converter.

[0012] In some implementations, applying an excitation current to the synchronous motor includes: Apply the excitation current of the synchronous motor to the no-load rated excitation current of the synchronous motor.

[0013] Secondly, this application also provides a fly-start control system for a frequency converter, applied to the fly-start method of the frequency converter as shown in the above example, the control system comprising: The first module is used to apply excitation current to the synchronous motor and obtain the three-phase voltage value at the output terminal of the frequency converter; The second module is used to determine the initial speed of the rotor in the synchronous motor based on the three-phase voltage values; The third module is used to determine the initial angle value of the rotor based on the initial rotational speed value and by adopting an angle detection strategy corresponding to the initial rotational speed value. The fourth module is used to control the inverter startup based on the initial angle value of the rotor.

[0014] Thirdly, this application also provides a fly-start device for a frequency converter, the fly-start device comprising: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the fly-start method of the frequency converter in any of the above examples.

[0015] This application provides a method for overspeed starting of a frequency converter. The output terminal of the frequency converter is used for electrical connection with the terminal of a synchronous motor. The frequency converter first applies excitation current to the synchronous motor and obtains three-phase voltage values ​​at its own output terminal. Then, based on the three-phase voltage values, it determines the initial rotor speed. Next, based on this initial speed value, it uses a corresponding angle detection strategy to determine the initial rotor angle value, enabling the angle detection strategy to adapt to different speed conditions, thus accurately obtaining the initial angle at various speeds, including lower speeds. Finally, the frequency converter is started based on the obtained initial angle value. By employing corresponding angle detection strategies at different speeds, this application improves the accuracy of the rotor's initial angle, thereby enhancing the reliability of the frequency converter's overspeed starting.

[0016] This application also provides a fly-start control system for a frequency converter, which is applied to the fly-start method of the frequency converter as shown in the example above. Therefore, the fly-start control system can have all the technical features and beneficial effects of the fly-start method, which will not be elaborated here.

[0017] This application also provides a fly-start device for a frequency converter, used to implement the fly-start method of the frequency converter in the above example. Therefore, the fly-start device can have all the technical features and beneficial effects of the fly-start method, which will not be repeated here. Attached Figure Description

[0018] Figure 1 A schematic diagram of a frequency converter system provided in an embodiment of this application; Figure 2 A flowchart illustrating a method for starting a frequency converter in accordance with an embodiment of this application; Figure 3 This is a schematic diagram of the overall process of a fly-start method for a frequency converter provided in an embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 100. Frequency converter; 200. Synchronous motor. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] References such as “one embodiment” or “some embodiments” as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the terms “comprising,” “including,” “having,” and variations thereof, as used in this specification, mean “including, but not limited to,” unless otherwise specifically emphasized.

[0023] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0024] Synchronous motors have excellent characteristics such as adjustable power factor, high operating efficiency, strong overload capacity, and stable dynamic response. They have significant advantages in industrial scenarios with large capacity, high reliability, and long-term continuous operation. They are widely used in key power equipment such as turbo compressors, gas pipeline booster units, large fans, and water pumps, and have become core drive devices in modern energy and chemical processes.

[0025] In energy storage and industrial applications such as compressed air energy storage, pumped hydro storage, fans, and water pumps, synchronous motor rotors often reach a certain initial speed before the frequency converter starts due to external airflow, fluid impact, or mechanical turning, resulting in a non-zero speed rotational state. To adapt to these special operating scenarios, the matching high-voltage frequency converter must be able to quickly detect the rotor's current speed, position, and direction of rotation without prior shutdown or mechanical braking, smoothly track and synchronously connect to the motor, achieving a shock-free and smooth restart of the motor in a free-rotating state. This avoids current surges, torque oscillations, and even equipment damage caused by speed mismatch, thereby ensuring continuous, safe, and stable system operation.

[0026] In other words, the frequency converter needs to have a fly start function, which means that the frequency converter needs to be able to quickly detect the current speed, position and direction of rotation of the rotor, smoothly track and synchronously connect to the motor, so as to achieve a shock-free and smooth restart of the motor in a free-rotating state.

[0027] However, at low rotor speeds, the initial rotor angle obtained by the frequency converter may be inaccurate, thus affecting the reliability of the frequency converter's overspeed start. Specifically, when the rotor is running at low speed, the motor back EMF amplitude is extremely low, the voltage signal-to-noise ratio is poor, and it is difficult to directly obtain an accurate initial rotor angle.

[0028] In view of this, this application provides a method, control system and apparatus for starting a frequency converter, which aims to solve at least one of the above-mentioned technical problems.

[0029] Please see Figure 1 , Figure 1 This is a schematic diagram of a frequency converter system provided in an embodiment of this application.

[0030] like Figure 1 As shown, the output terminal of the frequency converter 100 is used for electrical connection with the motor terminals of the synchronous motor 200. The input terminal of the frequency converter 100 is connected to a multi-winding transformer. The primary side of the multi-winding transformer is used to receive high-voltage grid power, and the secondary side includes multiple mutually isolated secondary windings, each of which supplies power to one power module unit in the frequency converter 100.

[0031] The frequency converter 100 may include multiple power module units. The multiple power module units are arranged in a three-phase configuration, and the output sides of the power module units in each phase are connected in series sequentially. One end of the series branch of the three-phase power module units is connected to each other to form a neutral point, and the other end is led out as the three-phase output terminal of the frequency converter 100.

[0032] like Figure 1 As shown in the figure, each link includes a power module unit. Links A1 to An are power module units on phase A, links B1 to Bn are power module units on phase B, and links C1 to Cn are power module units on phase C.

[0033] For example, such as Figure 1 As shown, the rectifier side of the power module unit can adopt a three-phase full-bridge rectifier circuit, and the inverter side can adopt a single-phase full-bridge inverter circuit. The output sides of multiple power module units are connected in series in sequence to form a cascaded H-bridge (CHB) type high-voltage frequency converter 100 topology.

[0034] The three-phase output terminals of the frequency converter 100 are electrically connected to the stator terminals of the synchronous motor 200 via an output switch. The stator terminals of the synchronous motor 200 refer to the three-phase lead-out terminals of the stator windings. The output switch is used to control the electrical connection between the three-phase output terminals of the frequency converter 100 and the stator windings of the synchronous motor 200. It should be noted that all conditions must be met before the frequency converter 100 is started. For example, before starting the frequency converter 100, the multi-winding transformer has been charged, the rectifier side has been unlocked, and all starting conditions are met. After the starting conditions are met, the output switch of the frequency converter 100 is closed, and simultaneously, an excitation current can be applied to the rotor windings of the synchronous motor 200. After the excitation current is suddenly applied, an induced electromotive force is generated in the stator windings of the synchronous motor 200.

[0035] The rotor winding of the synchronous motor 200 is electrically connected to an independent exciter. The independent exciter is used to apply excitation current to the rotor winding of the synchronous motor 200 based on control commands when the output switch of the frequency converter 100 is closed, so as to generate an induced electromotive force in the stator winding of the synchronous motor 200.

[0036] A voltage sampling device is installed at the three-phase output terminals of the frequency converter 100, located between the three-phase output terminals and the output switch. The voltage sampling device is used to collect the three-phase voltage on the output side of the frequency converter 100 after the output switch is closed. This three-phase voltage is the induced electromotive force generated by the stator windings of the synchronous motor 200. The voltage sampling device transmits this three-phase voltage value to the control unit of the frequency converter 100.

[0037] Please see Figure 2 , Figure 2This is a flowchart illustrating a method for starting a frequency converter in accordance with an embodiment of this application.

[0038] Based on the aforementioned hardware system, this application provides a method for starting a vehicle using a frequency converter 100. The output terminal of the frequency converter 100 is used for electrical connection with the motor terminal of the synchronous motor 200. The method includes steps S101 to S104. It should be noted that the method steps in this application embodiment can be controlled and executed by the control unit of the frequency converter 100, or by an additional control unit, depending on the specific implementation requirements. The following description assumes execution is controlled by the control unit of the frequency converter 100.

[0039] Step S101: Apply excitation current to synchronous motor 200 and obtain the three-phase voltage value at the output terminal of frequency converter 100.

[0040] It should be noted that the excitation current refers to the current supplied to the rotor windings of the synchronous motor 200 to establish the main magnetic field. The synchronous motor 200 typically uses an independent exciter to provide the excitation current, which is electrically connected to the rotor windings of the synchronous motor 200. In this embodiment, the control unit of the frequency converter 100 sends a command to the exciter, which outputs current to the rotor windings of the synchronous motor 200 according to the command, thereby establishing and stabilizing the main magnetic field within the air gap of the motor. The magnitude of the excitation current affects the strength of the air gap magnetic field and the amplitude of the terminal voltage.

[0041] Specifically, before the inverter 100 starts, the multi-winding transformer has been charged, the rectifier side of the inverter 100 has been unlocked, and all starting conditions are met. In this state, the control unit of the inverter 100 closes the output switch and simultaneously sends a command to the exciter. The exciter, according to this command, applies a rapidly changing excitation current to the rotor winding of the synchronous motor 200, relying on the change in magnetic flux in the motor's magnetic circuit to generate a transient terminal voltage. At the instant excitation is initiated and the magnetic field is established, the stator winding generates a corresponding induced electromotive force due to the rapid change in magnetic flux linkage; this electromotive force appears directly at the motor terminals. Subsequently, the control unit of the inverter 100 can acquire the three-phase voltages on the output side of the inverter 100 through voltage sampling devices (such as voltage Hall sensors and analog-to-digital converter chips) at the output of the inverter 100, obtaining the three-phase voltage values ​​Uma, Umb, and Umc. These three-phase voltages are the induced electromotive force generated by the stator winding of the synchronous motor 200.

[0042] It should be noted that the inverter 100 acquires the three-phase voltage values ​​after the synchronous motor 200 applies the excitation current. After the excitation current is applied, the rotor magnetic field gradually establishes up, the magnetic flux in the stator windings changes, and the terminal voltage establishes up and tends to stabilize. The voltage sampling device acquires the three-phase voltage values ​​for a period of time after the terminal voltage has established up and stabilized to avoid measurement inaccuracies caused by noise or sampling spikes. The voltage signal acquired at this time can accurately reflect the induced electromotive force generated by the rotor rotation, providing reliable input data for subsequent calculations of speed and angle.

[0043] In some embodiments, applying an excitation current to the synchronous motor 200 includes: applying the excitation current of the synchronous motor 200 to the no-load rated excitation current of the synchronous motor 200, so that the ratio of the terminal voltage to the speed matches the ratio of the rated terminal voltage to the rated speed under rated operating conditions, ensuring that the motor magnetic circuit operates at the rated design operating point, and avoiding over-excitation or under-excitation.

[0044] The no-load rated excitation current of the synchronous motor 200 refers to the excitation current required to be applied to the rotor winding when the synchronous motor 200 is running under no-load conditions (stator winding open circuit, no power output) and the terminal voltage reaches the rated value.

[0045] In other words, when applying excitation current to the synchronous motor 200, the excitation current can be applied up to the no-load rated excitation current. After the terminal voltage stabilizes near the terminal voltage corresponding to the no-load rated excitation current, the voltage sampling device at the output terminal of the frequency converter 100 collects the three-phase voltage values ​​on the output side of the frequency converter 100.

[0046] Step S102: Determine the initial rotational speed of the rotor in the synchronous motor 200 based on the three-phase voltage values.

[0047] Specifically, after the control unit of the inverter 100 obtains the three-phase voltage values ​​collected by the voltage sampling device, it can determine the initial speed value of the rotor in the synchronous motor 200 based on the three-phase voltage values ​​through preset processing and calculation, so as to provide a basis for subsequently determining the initial angle value of the rotor.

[0048] In some embodiments, determining the initial rotational speed of the rotor in the synchronous motor 200 based on the three-phase voltage values ​​includes: Step S201: Based on the three-phase voltage values, determine the first voltage component and the second voltage component in the stationary coordinate system.

[0049] Specifically, the control unit of the inverter 100 acquires the three-phase voltage values ​​Uma, Umb, and Umc collected by the voltage sampling device in step S101. Subsequently, the control unit performs coordinate transformation on the filtered three-phase voltage values, transforming them from a three-phase stationary coordinate system to a two-phase stationary coordinate system to obtain the first voltage component and the second voltage component.

[0050] For example, the coordinate transformation can be performed using the Clarke transformation, with the specific transformation relationship as follows: Um_alpha=2 / 3×Uma-1 / 3×(Umb+Umc); Um_beta = 1 / √3 × (Umb - Umc); Wherein, Um_alpha is the first voltage component and Um_beta is the second voltage component.

[0051] It should be noted that after the control unit of the inverter 100 obtains the three-phase voltage values ​​Uma, Umb, and Umc collected by the voltage sampling device in step S101, it needs to perform low-pass filtering on the three-phase voltage values ​​to filter out high-frequency noise components. Then, the control unit performs coordinate transformation on the filtered three-phase voltage values ​​to determine the first voltage component and the second voltage component in the stationary coordinate system.

[0052] Step S202: Determine the initial rotational speed of the rotor in the synchronous motor 200 based on the first voltage component and the second voltage component.

[0053] Specifically, after the control unit of the frequency converter 100 obtains the first voltage component and the second voltage component, it can determine the initial speed value of the rotor in the synchronous motor 200 through preset processing and calculation.

[0054] In some embodiments, determining the initial rotational speed of the rotor in the synchronous motor 200 based on a first voltage component and a second voltage component includes: Step S301: Standardize the first voltage component and the second voltage component to determine the first per-unit value and the second per-unit value.

[0055] Specifically, after obtaining the first voltage component Um_alpha and the second voltage component Um_beta, the control unit performs per-unit normalization. Per-unit normalization refers to dividing the actual value of a physical quantity by its reference value to obtain a dimensionless relative value.

[0056] For example, in this embodiment of the application, the reference value for per-unit processing is the rated value of the phase voltage at the motor terminals of the synchronous motor 200, that is, the effective value of the voltage of each phase of the motor stator winding under rated operating conditions. The specific calculation method for per-unit processing is as follows: Umpu_alpha=Um_alpha×k_umpu; Umpu_beta = Um_beta × k_umpu; Where k_umpu is the reciprocal of the rated value of the phase voltage at the generator terminal, Umpu_alpha is the first per-unit value, and Umpu_beta is the second per-unit value.

[0057] Step S302: Determine the Euclidean second norm of the first per-unit value and the second per-unit value as the per-unit composite value.

[0058] Specifically, the control unit calculates the Euclidean norm 2 (i.e., the arithmetic square root of the sum of squares) of the first per-unit value Umpu_alpha and the second per-unit value Umpu_beta to obtain the per-unit composite value. The specific calculation formula is as follows: Umpu_ab=sqrt(Umpu_alpha²+Umpu_beta²); Where Umpu_ab is the per-unit composite value.

[0059] Step S303: Based on the per-unit synthesized value, the actual value of the excitation current of the synchronous motor 200, the no-load rated excitation current value of the synchronous motor 200, and the rated speed value of the rotor, determine the initial speed value of the rotor in the synchronous motor 200.

[0060] Specifically, the control unit determines the initial rotor speed of the synchronous motor 200 based on the per-unit composite value, the actual excitation current value of the synchronous motor 200, the no-load rated excitation current value of the synchronous motor 200, and the rated speed value of the synchronous motor 200. The specific calculation formula is as follows: No = Umpu_ab × (If / If0) × Ne; Where No is the initial speed of the rotor, Umpu_ab is the per-unit composite value, If is the actual value of the excitation current, If0 is the no-load rated excitation current value, and Ne is the rated speed of the synchronous motor 200.

[0061] It should be noted that, according to the characteristics of the synchronous motor 200, the air gap flux is determined solely by the excitation current when the stator is open-circuited. With the excitation current remaining constant at the no-load rated excitation current value, the stator back electromotive force (terminal voltage) is proportional to the rotor speed. Therefore, the real-time rotor speed N can be calculated using the following expression: N=Ne Umpu_ab; In other words, the real-time speed N before the synchronous motor 200 starts, that is, before the inverter side is unlocked, is set as the initial rotor speed No. This initial speed is used to determine the angle detection strategy and control strategy subsequently adopted by the frequency converter 100, thereby providing a basis for the overspeed start of the frequency converter 100.

[0062] Step S103: Based on the initial rotational speed of the rotor, an angle detection strategy corresponding to the initial rotational speed is adopted to determine the initial angle value of the rotor.

[0063] It should be understood that in step S103, the angle detection strategy corresponding to the initial rotational speed value of the rotor is determined according to the initial rotational speed value of the rotor to determine the initial angle value of the rotor, so that the angle detection strategy matches the rotational speed working condition. An appropriate angle detection means can be adopted at different rotational speeds, so that the initial angle value of the rotor can be obtained relatively accurately under various rotational speed working conditions including a relatively low rotational speed, which provides a basis for improving the reliability of flying start.

[0064] It can be understood that after the initial rotational speed of the motor rotor is determined, the initial angle of the rotor also needs to be obtained accurately. The detection accuracy of this angle directly affects the reliability of the flying start and the magnitude of current shock during the start process. To this end, the present application proposes to adopt different strategies to obtain the initial angle of the rotor in different rotational speed intervals, so as to ensure the accuracy of angle information in the full rotational speed range, and reference may be made to the subsequent description for details.

[0065] In some embodiments, based on the initial rotational speed value of the rotor, adopting the angle detection strategy corresponding to the initial rotational speed value to determine the initial angle value of the rotor includes: In step S401, a rotational speed interval corresponding to the initial rotational speed value is determined based on the initial rotational speed value of the rotor. The rotational speed intervals include a first rotational speed interval, a second rotational speed interval and a third rotational speed interval, the upper rotational speed limit of the first rotational speed interval is less than the lower rotational speed limit of the second rotational speed interval, and the upper rotational speed limit of the second rotational speed interval is less than the lower rotational speed limit of the third rotational speed interval.

[0066] Specifically, the control unit of the frequency converter 100 determines the rotational speed interval in which the initial rotational speed value No is located according to the initial rotational speed value No determined in step S102. If 0≤No<N1, it is determined that the rotor is in the first rotational speed interval; if N1≤No<N2, it is determined that the rotor is in the second rotational speed interval; if N2≤No≤Ne, it is determined that the rotor is in the third rotational speed interval. N1 and N2 are preset rotational speed thresholds, Ne is the rated rotational speed value of the synchronous motor 200, and the specific values of N1 and N2 can be preset according to the parameters of the synchronous motor 200 and engineering experience.

[0067] For example, the first rotational speed interval may be a very low rotational speed interval, the second rotational speed interval may be a low rotational speed interval, and the third rotational speed interval may be a medium and high rotational speed interval. For example, the first rotational speed interval may be 0 pu to 0.001 pu, the second rotational speed interval may be 0.001 pu to 0.01 pu, and the third rotational speed interval may be 0.01 pu to 1 pu.

[0068] It should be noted that the above division of speed ranges is only an example, and the specific division of speed ranges can be set according to the actual implementation requirements. Furthermore, the first speed range, the second speed range, and the third speed range are continuous speed ranges, and the three ranges together cover the full speed range from zero speed to rated speed. This allows the angle detection strategy to be matched with different speed operating conditions, avoiding the impact on starting reliability due to the inapplicability of the angle detection strategy under certain speed operating conditions.

[0069] Step S402: Based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is adopted to determine the initial angle value of the rotor.

[0070] Specifically, the control unit determines the initial angle value of the synchronous motor 200 rotor by adopting an angle detection strategy corresponding to the speed range in which the initial speed value is located. The angle detection strategies corresponding to different speed ranges will be described later.

[0071] It is understood that, according to the speed range division method of this application embodiment, by dividing the initial speed value into multiple continuous ranges, the angle detection strategy can be matched and selected according to the actual speed conditions. Since the three ranges together cover the full speed range from zero speed to rated speed, regardless of the speed state of the synchronous motor 200 before the inverter 100 starts, it can fall into the corresponding speed range and adopt the appropriate angle detection strategy. This avoids the problem of inaccurate initial angle acquisition due to the inapplicability of the angle detection strategy under certain speed conditions, and helps to improve the reliability of the inverter 100's overspeed start-up across the entire speed range.

[0072] In some embodiments, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is adopted to determine the initial angle value of the rotor, including: when the speed range corresponding to the initial speed value is a first speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and a first preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the arctangent value of the first voltage component and the second voltage component.

[0073] Specifically, the control unit performs an arctangent operation on the first voltage component Um_alpha and the second voltage component Um_beta to obtain the arctangent value theta. When the initial speed value No is determined to be within the first speed range, i.e., when the synchronous motor 200 is in a very low speed rotation state, the control unit determines the initial angle value of the rotor according to the sign of the first voltage component Um_alpha: if Um_alpha < 0, then the initial angle value of the rotor theta_o = theta + theta_1; if Um_alpha ≥ 0, then the initial angle value of the rotor theta_o = theta. Here, theta_1 is a first preset angle compensation value, such as π, whose specific value can be preset according to the parameters of the synchronous motor 200 and engineering experience.

[0074] In some embodiments, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is adopted to determine the initial angle value of the rotor, including: when the speed range corresponding to the initial speed value is the second speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and the second preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and the third preset angle compensation value.

[0075] Specifically, the control unit performs an arctangent operation on the first voltage component Um_alpha and the second voltage component Um_beta to obtain the arctangent value theta. When the initial speed value No is determined to be within the second speed range, i.e., when the synchronous motor 200 is in a low-speed rotation state, the control unit determines the initial angle value of the rotor according to the sign of the first voltage component Um_alpha: if Um_alpha < 0, then the initial angle value of the rotor theta_o = theta + theta_2; if Um_alpha ≥ 0, then the initial angle value of the rotor theta_o = theta + theta_3. Here, theta_2 is the second preset angle compensation value, for example, 3π / 2; theta_3 is the third preset angle compensation value, for example, π / 2; the specific values ​​of theta_2 and theta_3 can be preset according to the parameters of the synchronous motor 200 and engineering experience.

[0076] In some embodiments, based on the speed range corresponding to the initial speed value, an angle detection strategy corresponding to the speed range is adopted to determine the initial angle value of the rotor, including: when the speed range corresponding to the initial speed value is the third speed range, the initial angle value of the rotor is determined based on the three-phase voltage value at the output terminal of the inverter 100.

[0077] Specifically, when the initial speed value No is determined to be in the third speed range, i.e., when the synchronous motor 200 is in a medium-to-high speed rotation state, the control unit uses a phase-locked loop (PLL) to track the phase of the three-phase voltage values ​​to obtain the initial angle value of the rotor. This is achieved by employing a specific sensorless orthogonal PLL algorithm to obtain the initial rotor angle. The specific working principle is as follows: the control unit transforms the collected three-phase voltage values ​​to obtain voltage components in a two-phase stationary coordinate system. These components are then input into the PLL. The PLL tracks the phase of the three-phase voltage values ​​through closed-loop regulation. After phase locking, it outputs the electrical angle of the synchronous motor 200 rotor, thus completing the real-time acquisition of the initial rotor angle.

[0078] It should be noted that all three angle detection strategies mentioned above are enabled while the control unit is determining the speed range. The determination result is used to determine which angle detection strategy's output to use as the rotor's initial angle value, rather than completing the speed range determination first and then activating the corresponding angle detection strategy. This parallel enabling method avoids the computational delay caused by strategy switching and improves the real-time performance of initial angle acquisition.

[0079] It should also be noted that the control unit calculates the arctangent value theta between Um_beta and Um_alpha, and latches the result of the arctangent calculation after a preset time following the application of the excitation current. Before latching, the control unit first compensates and corrects the result of the arctangent calculation according to the sign of the first voltage component Um_alpha, and uses the compensated and corrected value as the latching object. By compensating before latching, the timing deviation introduced by latching before compensation can be avoided, thus improving the accuracy of initial angle acquisition under extremely low speed conditions.

[0080] It is understood that in this embodiment of the application, the high-voltage frequency converter 100 obtains the rotor angle in a sensorless manner, that is, it does not rely on mechanical position sensors such as encoders or rotary transformers installed on the motor shaft to detect the rotor position, but calculates the rotor angle information through electrical signals collected by voltage sampling devices, thereby avoiding the problem that mechanical sensors are easily damaged or have limited installation under harsh conditions such as high voltage, high temperature, and vibration.

[0081] Step S104: Based on the initial angle value of the rotor, control the frequency converter 100 to start.

[0082] Specifically, the control unit of inverter 100 uses the initial angle value determined in step S103 as the initial phase of the output voltage of inverter 100. The control unit controls the inverter side of inverter 100 to unlock the output based on the initial phase, so that the initial phase of the three-phase voltage output by inverter 100 corresponds to the current actual position of the rotor of synchronous motor 200, thereby realizing the shockless start of synchronous motor 200 in rotation by inverter 100.

[0083] It should be noted that the starting method of the frequency converter 100 is related to the initial speed of the synchronous motor. The control modes of the frequency converter 100 include open-loop control mode and closed-loop control mode. Specifically, based on preset threshold speeds separating the open-loop and closed-loop control intervals, the corresponding control mode is automatically selected and entered. For example, when the initial speed is in the first or second speed range, the frequency converter 100 enters the open-loop control mode; when the initial speed is in the third speed range, the frequency converter 100 enters the closed-loop control mode. The open-loop control mode is suitable for lower speed conditions, in which the frequency converter can start and run without relying on real-time position feedback; the closed-loop control mode is suitable for medium-to-high speed conditions, in which the frequency converter continuously tracks the rotor position through a phase-locked loop to achieve precise synchronization.

[0084] In some examples, if the initial speed is in the first or second speed range (i.e., the motor is at a lower speed), the control unit starts the inverter 100 using open-loop control. In open-loop control, the control unit sets the initial phase of the inverter output voltage based on the detected initial angle value and gradually increases the frequency and amplitude of the output voltage according to a preset voltage-frequency curve, allowing the motor to smoothly accelerate from the initial speed. When the motor speed reaches the threshold corresponding to the closed-loop control range, the control unit automatically switches to closed-loop control. In closed-loop control, the control unit uses the angle information output by the phase-locked loop at the switching moment as the angle reference for closed-loop control, and the phase-locked loop continuously tracks the real-time position of the motor rotor. The control unit adjusts the inverter's output voltage based on the real-time angle information fed back by the phase-locked loop, achieving precise control of the motor speed and current through closed-loop regulation, and continuing to drive the motor to the target speed.

[0085] In other examples, if the initial speed is in the third speed range (i.e., the motor is already at a medium-high speed), the control unit directly starts the inverter 100 using closed-loop control. In closed-loop control, the control unit uses the detected initial angle value as the initial angle reference for closed-loop control. The phase-locked loop continuously tracks the real-time position of the motor rotor, achieving precise control of the motor speed and current through closed-loop adjustment, allowing the motor to smoothly run from the initial speed to the target speed. The target speed can be the rated speed, specifically set according to the requirements of the actual implementation plan.

[0086] Through the above method, this application can automatically select the corresponding control mode according to the initial speed of the synchronous motor 200, achieve reliable start-up through open-loop control at lower speeds, and achieve precise synchronization through closed-loop control at medium and high speeds, thereby balancing the reliability and control accuracy of the car start-up across the entire speed range.

[0087] Please see Figure 3 , Figure 3 This is a schematic diagram of the overall process of a fly-start method for a frequency converter provided in an embodiment of this application.

[0088] The overall control process of the overrun start method of inverter 100 includes the following steps: After the start-up process begins, the first step is to detect and process the sudden excitation current and the terminal voltage. This involves controlling the excitation system to apply excitation current to the rotor windings of the synchronous motor 200, and acquiring the induced electromotive force at the terminal through the voltage sampling device at the output of the frequency converter 100 to obtain the three-phase voltage values. For details, please refer to the description of step S101, which will not be repeated here.

[0089] Subsequently, the rotational speed is calculated based on the terminal voltage. This involves performing coordinate transformation and per-unit scaling on the collected three-phase voltage values, calculating the per-unit composite value, and then determining the initial rotor speed based on the per-unit composite value, the actual excitation current of the synchronous motor 200, the no-load rated excitation current of the synchronous motor 200, and the rated rotor speed. For details, please refer to the descriptions of steps S102, S201 to S202, and S301 to S303; they will not be repeated here.

[0090] After obtaining the initial rotor speed, the range of the speed is determined. If the initial speed is in the extremely low speed range, the initial rotor angle is obtained using initial angle compensation method one; if the initial speed is in the low speed range, the initial rotor angle is obtained using initial angle compensation methods two and three; if the initial speed is in the medium to high speed range, the output of the positionless phase-locked loop is used as the initial rotor angle. For details, please refer to steps S103, steps S401 to S402, and the description of the angle detection strategies corresponding to the three speed ranges mentioned above, which will not be repeated here.

[0091] After obtaining the initial rotor angle, it is further determined whether the current stage is FOC (Field-Oriented Control), i.e., the closed-loop control stage. If it has not yet entered the FOC stage, i.e., it is in the open-loop control stage, then the initial angle is used as the initial angle of the voltage output in open-loop mode; if it is already in the FOC stage, i.e., it is in the closed-loop control stage, then the initial angle is used as the initial angle of the voltage output under closed-loop vector control. Finally, based on the determined initial angle, the inverter side unlock output of the frequency converter 100 is controlled to complete the flyback start. For details, please refer to the description of step S104, which will not be repeated here.

[0092] It should be noted that the fly-start method provided in this application embodiment is applied to a hardware-in-the-loop real-time simulation system and engineering field tests. In the hardware-in-the-loop simulation environment, a real-time simulation platform including a multi-winding transformer, a power module unit, and a synchronous motor 200 model is built. In the engineering field test, this method is deployed in the actual high-voltage frequency converter 100 controller to drive a large-capacity synchronous motor 200 for a fly-start test. The test results show that during the process of the synchronous motor 200 rotor from a free-rotating state to a stable speed-up state to the rated speed state, the frequency converter 100 can accurately observe the rotor speed at the moment of startup, and no obvious current surge occurs during the startup connection process. This further demonstrates that the fly-start method of the frequency converter 100 provided in this application embodiment can accurately obtain the initial rotor angle in the full speed range, including low speed, to achieve shock-free and smooth fly-start of the synchronous motor 200.

[0093] In summary, the overspeed start method of the inverter 100 provided in this application embodiment applies an excitation current to the synchronous motor 200 and obtains the three-phase voltage value at the output terminal of the inverter 100. Based on the three-phase voltage value, the initial speed value of the rotor is determined. Then, according to the speed range in which the initial speed value is located (the three ranges together cover the full speed range from zero speed to rated speed), a corresponding angle detection strategy is adopted to determine the initial angle value of the rotor, and the inverter 100 is started based on the initial angle value. This method uses a partitioned matching approach to enable the angle detection strategy to adapt to different speed conditions, and can accurately obtain the initial rotor angle in the full speed range, including lower speeds, thereby suppressing the current surge at the moment of startup and improving the reliability of overspeed start.

[0094] This application embodiment also provides a flyback start control system for a frequency converter, applied to the flyback start method of the frequency converter 100 in the example above. The control system includes: The first module is used to apply excitation current to the synchronous motor 200 and obtain the three-phase voltage value at the output terminal of the frequency converter 100. The second module is used to determine the initial speed of the rotor in the synchronous motor 200 based on the three-phase voltage values. The third module is used to determine the initial angle value of the rotor based on the initial rotational speed value and by adopting an angle detection strategy corresponding to the initial rotational speed value. The fourth module is used to control the start of the frequency converter 100 based on the initial angle value of the rotor.

[0095] It should be noted that the control system corresponds one-to-one with steps S101 to S104 in the above method embodiment. The specific functions of each module can be found in the corresponding descriptions in the method embodiment, and will not be repeated here.

[0096] It is understood that the overspeed start control system of the inverter 100 provided in this application embodiment performs excitation application and voltage acquisition, initial speed determination, initial angle determination and start control through the first to fourth modules respectively. The functional division between each module corresponds one-to-one with each step of the above overspeed start method, so that the control system can match the corresponding angle detection strategy according to the speed condition of the synchronous motor 200, thereby accurately obtaining the rotor initial angle at various speeds, including lower speeds, and ensuring the reliability of overspeed start control.

[0097] This application also provides a fly-start device for a frequency converter 100, the fly-start device comprising: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the inverter 100 fly-start method of any of the above examples.

[0098] It is evident that the content of the above method embodiments is applicable to the present device embodiments. The specific functions implemented in the present device embodiments are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0099] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0100] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for starting a frequency converter by overspeed, characterized in that, The output terminal of the frequency converter (100) is used for electrical connection with the motor terminal of the synchronous motor (200), and the method includes: Apply excitation current to the synchronous motor (200) and obtain the three-phase voltage value at the output terminal of the frequency converter (100); Based on the three-phase voltage values, the initial rotational speed of the rotor in the synchronous motor (200) is determined; Based on the initial rotational speed of the rotor, an angle detection strategy corresponding to the initial rotational speed is used to determine the initial angle value of the rotor. Based on the initial angle value of the rotor, the frequency converter (100) is controlled to start.

2. The method for starting a frequency converter by overspeed according to claim 1, characterized in that, Determining the initial rotational speed of the rotor in the synchronous motor (200) based on the three-phase voltage values ​​includes: Based on the three-phase voltage values, determine the first voltage component and the second voltage component in the stationary coordinate system; Based on the first voltage component and the second voltage component, the initial speed value of the rotor in the synchronous motor (200) is determined.

3. The method for starting a frequency converter by overspeed according to claim 2, characterized in that, Determining the initial rotational speed of the rotor in the synchronous motor (200) based on the first voltage component and the second voltage component includes: The first voltage component and the second voltage component are normalized to determine the first per-unit value and the second per-unit value. The Euclidean 2 norm of the first per-unit value and the second per-unit value is determined as the composite per-unit value; Based on the per-unit composite value, the actual value of the excitation current of the synchronous motor (200), the no-load rated excitation current value of the synchronous motor (200), and the rated speed value of the rotor, the initial speed value of the rotor in the synchronous motor (200) is determined.

4. The method for starting a frequency converter by overspeed according to claim 2, characterized in that, The step of determining the initial angle value of the rotor based on the initial rotational speed value and using an angle detection strategy corresponding to the initial rotational speed value includes: Based on the initial rotational speed of the rotor, a rotational speed range corresponding to the initial rotational speed value is determined. The rotational speed range includes a first rotational speed range, a second rotational speed range, and a third rotational speed range. The upper limit of the rotational speed in the first rotational speed range is less than the lower limit of the rotational speed in the second rotational speed range, and the upper limit of the rotational speed in the second rotational speed range is less than the lower limit of the rotational speed in the third rotational speed range. Based on the speed range corresponding to the initial speed value, the initial angle value of the rotor is determined by adopting an angle detection strategy corresponding to the speed range.

5. The method for starting a frequency converter by overspeed according to claim 4, characterized in that, The step of determining the initial angle value of the rotor based on the speed range corresponding to the initial speed value, using an angle detection strategy corresponding to the speed range, includes: When the speed range corresponding to the initial speed value is the first speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and the first preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the arctangent value of the first voltage component and the second voltage component.

6. The method for starting a frequency converter by overspeed according to claim 4, characterized in that, The step of determining the initial angle value of the rotor based on the speed range corresponding to the initial speed value, using an angle detection strategy corresponding to the speed range, includes: When the speed range corresponding to the initial speed value is the second speed range, if the first voltage component is less than zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and the second preset angle compensation value; if the first voltage component is greater than or equal to zero, the initial angle value of the rotor is the sum of the arctangent values ​​of the first voltage component and the second voltage component and the third preset angle compensation value.

7. The method for starting a frequency converter by overspeed according to claim 4, characterized in that, The step of determining the initial angle value of the rotor based on the speed range corresponding to the initial speed value, using an angle detection strategy corresponding to the speed range, includes: When the speed range corresponding to the initial speed value is the third speed range, the initial angle value of the rotor is determined based on the three-phase voltage value at the output terminal of the frequency converter (100).

8. The method for starting a frequency converter by overspeed according to claim 1, characterized in that, Applying excitation current to the synchronous motor (200) includes: The excitation current of the synchronous motor (200) is applied to the no-load rated excitation current of the synchronous motor (200).

9. A fly-start control system for a frequency converter, applied to the fly-start method of the frequency converter (100) as described in any one of claims 1 to 8, characterized in that, include: The first module is used to apply excitation current to the synchronous motor (200) and obtain the three-phase voltage value at the output terminal of the frequency converter (100); The second module is used to determine the initial rotational speed of the rotor in the synchronous motor (200) based on the three-phase voltage values. The third module is used to determine the initial angle value of the rotor based on the initial rotational speed value of the rotor and by adopting an angle detection strategy corresponding to the initial rotational speed value. The fourth module is used to control the start of the frequency converter (100) based on the initial angle value of the rotor.

10. A flyover start device for a frequency converter, characterized in that, include: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the fly-start method of the inverter (100) according to any one of claims 1 to 8.

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