Single-phase induction motor drive system and motor drive method
By controlling the frequency and voltage of power commands through the processor and utilizing frequency variation curves and current thresholds, the problem of starting single-phase induction motors has been solved, achieving stable and rapid motor starting and acceleration, and improving the success rate and efficiency of starting.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DELTA ELECTRONICS INC(CN)
- Filing Date
- 2025-06-19
- Publication Date
- 2026-06-12
AI Technical Summary
When a single-phase induction motor starts, it cannot directly generate a rotating magnetic field because single-phase AC power cannot be used. It needs to be started through an auxiliary circuit. However, when the frequency is too low, the auxiliary winding cannot provide enough starting torque, which leads to starting failure and difficulty in stable operation.
By controlling the frequency and voltage of the power command through the processor, and using the frequency change curve and current threshold, the frequency and voltage of the power command are gradually adjusted to ensure that the rotor accelerates stably from zero speed to the target frequency, thus avoiding startup failure caused by too low a frequency.
It achieves stable and rapid start-up of single-phase induction motors, avoids start-up failures, improves the start-up success rate, and reaches the target frequency within a preset time, possessing stable and efficient drive characteristics.
Smart Images
Figure CN122203918A_ABST
Abstract
Description
Technical Field
[0001] This application relates to a single-phase induction motor, and more particularly to a single-phase induction motor drive system and a motor drive method. Background Technology
[0002] Single-phase induction motors are a widely used type of AC motor, commonly used in household appliances, fans, water pumps, and other equipment. Because the single-phase AC power used in a single-phase induction motor cannot directly generate a rotating magnetic field, it requires auxiliary circuitry (such as capacitors) to start and stabilize its operation. Summary of the Invention
[0003] This application relates to a single-phase induction motor drive system, comprising a single-phase induction motor and a processor. The single-phase induction motor includes a stator and a rotor. The processor is coupled to the stator and is used to provide power commands to the stator. The processor is used to acquire a frequency variation curve, which indicates multiple set frequencies corresponding to different times, including a target frequency corresponding to stable operation of the single-phase induction motor. The processor is used to determine the following conditions to provide the power command: setting the current frequency of the power command to an initial frequency to drive the rotor via the power command, wherein the initial frequency is lower than the target frequency; when one of the multiple set frequencies corresponding to the current time is greater than the initial frequency, controlling the current frequency of the power command according to the frequency variation curve; when one of the multiple set frequencies corresponding to the current time is less than or equal to the initial frequency, maintaining the current frequency of the power command at the initial frequency, and determining whether the output current of the stator is higher than or equal to a current threshold; when the output current of the stator is higher than or equal to the current threshold, fixing the current voltage of the power command; and when the output current of the stator is lower than the current threshold, increasing the current voltage of the power command.
[0004] This application also relates to a motor driving method, comprising: obtaining a frequency change curve corresponding to a single-phase induction motor via a processor, wherein the frequency change curve indicates multiple set frequencies corresponding to different times, and includes a target frequency corresponding to the stable operation of the single-phase induction motor; providing a power command to the single-phase induction motor via the processor, causing the stator of the single-phase induction motor to drive the rotor to rotate, wherein the initial frequency of the power command is less than the target frequency; when one of the multiple set frequencies corresponding to the current time is greater than the initial frequency, controlling the current frequency of the power command via the processor according to the frequency change curve; when one of the multiple set frequencies corresponding to the current time is less than or equal to the initial frequency, maintaining the current frequency of the power command at the initial frequency via the processor, and determining whether the output current of the stator is higher than or equal to a current threshold; when the output current of the stator is higher than or equal to the current threshold, fixing the current voltage of the power command via the processor; and when the output current of the stator is lower than the current threshold, increasing the current voltage of the power command via the processor.
[0005] Accordingly, by setting the initial frequency of the power command and judging the result of comparing the current frequency of the power command with the target frequency, the frequency and voltage of the power command can be controlled in different ways, which can stably and efficiently drive the single-phase induction motor and successfully drive the rotor to rotate from zero speed. Attached Figure Description
[0006] Figure 1 This is a schematic diagram of a single-phase induction motor according to a partial embodiment of the present application.
[0007] Figure 2 This is a schematic diagram of the stator of a single-phase induction motor according to a partial embodiment of the present application.
[0008] Figure 3 This is a flowchart of a motor driving method according to a portion of the embodiments of this application.
[0009] Figure 4A This is a schematic diagram illustrating the frequency variation of a single-phase induction motor according to a partial embodiment of the present application.
[0010] Figure 4B This is a schematic diagram illustrating the voltage variation of a single-phase induction motor according to a partial embodiment of the present application.
[0011] Figure 4C This is a schematic diagram illustrating the current variation of a single-phase induction motor according to a partial embodiment of the present application.
[0012] Explanation of reference numerals in the attached figures
[0013] 100: Single-phase induction motor drive system
[0014] 110: Single-phase induction motor,
[0015] 111: Stator
[0016] 112: Rotor,
[0017] 120: Processor
[0018] 411: Frequency variation curve
[0019] 412: Actual rotor frequency curve
[0020] 421: Voltage variation curve
[0021] 422: Actual voltage curve
[0022] 423: Initial boost curve,
[0023] 431: Output current,
[0024] 432: Envelope,
[0025] C21: Auxiliary capacitor
[0026] fstart: Initial frequency
[0027] frun: target frequency
[0028] Iref: Current threshold
[0029] L21: Main winding
[0030] L22: Auxiliary winding
[0031] S301-S307: Steps,
[0032] Vref: Target voltage
[0033] V21: Power command Detailed Implementation
[0034] Several embodiments of the present invention will be disclosed below with reference to the accompanying drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details should not be used to limit the invention. That is, in some embodiments of the present invention, these practical details are not essential. Furthermore, for the sake of simplicity, some well-known and conventional structures and components will be illustrated in the drawings in a simple schematic manner.
[0035] In this document, when a component is referred to as a “connection” or “coupled,” it may mean an “electrical connection” or “electrical coupling.” “Connection” or “coupled” can also be used to indicate the operation or interaction between two or more components. Furthermore, although terms such as “first,” “second,” etc., are used herein to describe different components, these terms are only used to distinguish components or operations described using the same technical terms. Unless the context clearly indicates otherwise, these terms do not specifically refer to or imply any order or sequence, and are not intended to limit the invention.
[0036] This application relates to a single-phase induction motor drive system and driving method. Please refer to [link / reference]. Figure 1 As shown, a single-phase induction motor drive system 100 includes a single-phase induction motor 110 and a processor 120. The single-phase induction motor 110 includes a stator 111 and a rotor 112. The processor 120 is coupled to the stator 111 of the single-phase induction motor 110 and is used to supply power and output power commands to drive the single-phase induction motor 110. In subsequent embodiments, the single-phase AC power or control commands provided by the processor 120 to the single-phase induction motor 110 will be referred to as "power commands" for simplicity.
[0037] Since single-phase alternating current cannot directly generate a magnetic field in the direction of rotation, when the single-phase induction motor 110 starts, it needs to be operated stably through an auxiliary circuit. Figure 2 The diagram shows a stator 111 of a single-phase induction motor 110 according to a partial embodiment of the present application. In this embodiment, the stator 111 includes a main winding L21, an auxiliary winding L22, and an auxiliary capacitor C21. The auxiliary winding L22 and the auxiliary capacitor C21 are the main components of the auxiliary circuit that assists in starting the single-phase induction motor 110, enabling the magnetic field generated by the main winding L21 and the auxiliary winding L22 to drive the rotor 112 to rotate.
[0038] Continuing from the above, according to the power command V21 provided by the processor 120, the auxiliary capacitor C21 changes its current phase, causing the current phase of the auxiliary winding L22 to be out of sync with the current phase of the main winding L21, thereby generating an effect similar to a rotating magnetic field to drive the rotor 112 to rotate. When the rotation frequency of the rotor 112 reaches the default frequency (hereinafter referred to as the "target frequency"), it indicates that the single-phase induction motor 110 is in a stable operating state. In some embodiments, the target frequency can be set according to the rated frequency of the single-phase induction motor, for example, 50% of the rated frequency.
[0039] However, please see Figure 2 As shown, during the process of the processor 120 starting the single-phase induction motor 110, the frequency of the power command V21 gradually increases from zero to the target frequency. When the frequency of the power command V21 is too low, the auxiliary capacitor C21 is like an open circuit. Furthermore, because the impedance of the main winding L21 is extremely low, the current will not flow through the auxiliary winding L22, making it impossible for the auxiliary winding L22 to provide sufficient starting torque. This makes it difficult for the single-phase induction motor 110 to start and achieve stable operation.
[0040] This application modifies the control method of the processor 120 for power commands to enable the single-phase induction motor 110 to achieve stable operation. Specifically, the processor 120 stores (or calculates to obtain) a frequency variation curve, which defines the correspondence between "time" and "frequency of the power command". That is, the frequency variation curve indicates the reference frequency (hereinafter referred to as the set frequency) of the power command at multiple different times starting from zero speed, and also includes the target frequency (e.g., 30Hz) when the rotor 112 is operating stably. The table below is a schematic diagram of the frequency variation curve:
[0041] Startup time (seconds) Set frequency (Hz) 0 0 1 5 2 10 3 15 4 20 5 25 6 30
[0042] The "frequency variation curve" serves as a reference for the processor 120 when controlling power commands. However, during startup, the processor 120 does not consistently control the frequency of power commands based on the frequency variation curve. When initially providing a power command to the stator 111, the processor 120 sets the initial frequency of the power command to a specific frequency value, such as 12Hz, which is lower than the target frequency. Since the frequency of the power command changes over time, for ease of subsequent explanation, the real-time frequency of the power command corresponding to the current time will be referred to as the "current frequency."
[0043] Following the above, after the power command is provided (i.e., the single-phase induction motor 110 is started), the processor 120 times the elapsed time to compare and determine the relative magnitude of the "initial frequency" and the "set frequency corresponding to the time in the frequency change curve". If the current frequency corresponding to the current time is less than or equal to the initial frequency, the processor 120 will maintain the current frequency of the power command at the initial frequency. Conversely, if the current frequency corresponding to the current time is greater than the initial frequency, the processor 120 will control the current frequency of the power command according to the frequency change curve. It should be noted that, ignoring other factors such as friction, the current frequency of the motor will be consistent with the set frequency in the table.
[0044] For example, referring to the aforementioned table illustrating the frequency variation curve, if the initial frequency is 12Hz, then within 2 seconds after the processor 120 starts the single-phase induction motor 110 (i.e., after the power command is first provided), because the initial frequency is lower than the set frequency, the processor 120 will maintain the current frequency of the power command at the initial frequency and continue to drive the motor. After 3 seconds of startup, because the set frequency (15Hz) corresponding to the time (3 seconds) of the frequency variation curve is higher than the initial frequency, the processor 120 will switch to controlling the power command according to the frequency variation curve, i.e., controlling it at 15Hz in the 3rd second, controlling it at 20Hz in the 4th second, and so on.
[0045] In some embodiments, when the current frequency corresponding to the current time is less than or equal to the initial frequency, the processor 120 will increase the current voltage of the power command as much as possible to maximize the output current of the stator 111, thereby obtaining higher torque and improving the success rate of motor operation. The processor 120 will also continuously monitor the output current of the stator 111. When the output current is higher than or equal to a preset current threshold, the processor will limit and fix the output voltage to protect the motor until the current frequency corresponding to the current time in the frequency change curve is greater than the initial frequency. The "current threshold" can be set based on the rated current of the single-phase induction motor 110, for example, 250% of the rated current.
[0046] Accordingly, by setting the initial frequency of the power command and controlling the frequency of the power command using a frequency change curve at specific times, the problem of insufficient starting torque in the auxiliary winding L22 due to an excessively low power command frequency during start-up from zero speed can be avoided. Furthermore, the processor 120 also detects the output current of the stator 111 and increases the voltage as quickly as possible within the current threshold range to increase torque, enabling the single-phase induction motor 110 to start faster and achieve stable operation.
[0047] For ease of explanation, here we will use Figure 3 The following flowchart illustrates the motor drive method. First, when the processor 120 is ready to start the single-phase induction motor 110, the processor 120 will first obtain the aforementioned frequency change curve. The frequency change curve can be pre-stored in the processor 120, or calculated and generated by the processor 120 according to set parameters, or the processor 120 can communicate with a server to obtain the frequency change curve. Other control steps will be described later.
[0048] Please refer to this as well. Figure 4A This is a schematic diagram of the frequency change of a single-phase induction motor according to a portion of the embodiments of this application, wherein 411 represents the frequency change curve, fstart represents the initial frequency (e.g., 12Hz), and frun represents the target frequency (e.g., 30Hz). 412 represents... Figure 3 The method shown includes actual rotor frequency curves corresponding to the rotor frequency at different times. In one embodiment, processor 120 generates a frequency change curve 411 based on a target frequency and a default target time. The "target time" is the default start-up time, for example, 5 seconds or a time between 6 and 10 seconds. Processor 120 can calculate a default slope based on the target time, calculate the acceleration trend of the rotor 112's operating frequency from zero to the target frequency frun over time, and then plan the frequency change curve. In other words, the frequency change curve is calculated by processor 120 controlling the trend of the rotor 112's operating frequency rising from zero to the target frequency frun based on the slope.
[0049] Furthermore, in this embodiment, the processor 120 also generates a voltage change curve corresponding to the frequency change curve 411. The "voltage change curve" is used to indicate multiple set voltages at different times. See also... Figure 4B The diagram shown illustrates the voltage variation of a single-phase induction motor according to a partial embodiment of this application. Item 421 represents the voltage variation curve, showing the trend of voltage increase from zero to the target voltage Vref during the target time. Item 422 represents... Figure 3 In the method shown, the power command corresponds to the actual voltage curve at different times.
[0050] Please see Figure 3 and Figures 4A to 4C In step S301, the processor 120 provides a power command to the stator 111 of the single-phase induction motor 110 based on the initial frequency fstart, so that the stator 111 drives the rotor 112. The initial frequency fstart is less than the target frequency frun when the rotor 112 rotates stably. In some embodiments, the initial frequency fstart is between 5% and 99% of the target frequency frun. In one embodiment, the initial frequency fstart is between 15% and 75% of the target frequency frun. In another embodiment, the initial frequency fstart is between 40% and 60% of the target frequency frun.
[0051] In step S302, the processor 120 determines whether the set frequency corresponding to the current time in the frequency change curve 411 is greater than the initial frequency fstart. In other words, the processor 120 finds the set frequency corresponding to the current time on the frequency change curve 411 based on the current timing and compares it with the initial frequency fstart. It should be noted that, ignoring other factors such as friction, the rotor's current frequency will be consistent with the set frequency.
[0052] If the set frequency corresponding to the current time is less than or equal to the initial frequency fstart, in step S303, the processor 120 maintains the current frequency of the power command at the initial frequency fstart and continues to operate. See also... Figure 4A As shown, before the startup time of 2.5 seconds, the set frequency of the frequency change curve 411 is less than or equal to the initial frequency fstart. Therefore, the frequency of the power command will remain at the initial frequency fstart.
[0053] Next, in step S304, the processor 120 will further determine whether the output current of the stator 111 is higher than or equal to the current threshold. (See also...) Figure 4CThe diagram illustrates the current variation of a single-phase induction motor 110 according to a partial embodiment of this application. The symbol Iref represents the current threshold, 431 represents the output current of the stator 111 at the current time, and 432 represents the envelope of the output current 431, indicating the trend of the peak value of the output current 431, which is calculated based on the sine wave of the output current of the stator 111. In some embodiments, the processor 120 compares the peak value of the output current 431 with the current threshold Iref to determine whether the output current 431 is higher than or equal to the current threshold Iref. In other embodiments, the processor 120 may calculate the envelope 432 of the output current 431 (or record multiple peak values of the output current 431 at different times), and then compare the envelope 432 with the current threshold Iref to determine whether the output current 431 is higher than or equal to the current threshold Iref.
[0054] If the output current 431 is lower than the current threshold, then in step S305, the processor 120 will increase the current voltage of the power command according to the boost curve 423 of the front section of the actual voltage curve 422. Specifically, as Figure 4B As shown, processor 120 will change at a first rate of change (e.g.: Figure 4B In the process, the slope of the boost curve 423 preceding the actual voltage curve 422 increases the current voltage of the power supply command, and this first rate of change is greater than the second rate of change of the voltage change curve 421 (i.e., the slope of the voltage change curve 421).
[0055] In step S306, if the output current is higher than or equal to the current threshold, the processor 120 will no longer stop increasing the current voltage of the power command, but will decrease the current voltage of the power command at a default slope to suppress the output current below the current threshold. Then, the current voltage of the power command is fixed / maintained until the corresponding set frequency of the frequency change curve 411 is greater than the initial frequency fstart. In one embodiment, as... Figure 4B and Figure 4C As shown, the processor 120 will first reduce the current voltage of the power command at a preset slope in order to reduce the output current 431.
[0056] Once the output current drops below the current threshold, and the set frequency corresponding to the current time on the frequency change curve 411 is lower than the initial frequency fstart, the processor 120 will maintain the current voltage of the power supply command to ensure that the output current 431 remains below the current threshold Iref.
[0057] If the set frequency corresponding to the current time on the frequency change curve 411 is greater than the initial frequency fstart, in step S307, the processor 120 will no longer maintain the current voltage of the power command, nor will it maintain the current frequency conforming to the initial frequency fstart. Instead, it will control the current frequency of the power command according to the frequency change curve 411. Figure 4A As shown, after 2.5 seconds of startup, since the current frequency of the frequency change curve 411 is greater than the initial frequency fstart, the processor 120 will continue to increase the current frequency of the power command according to the frequency change curve 411 until the current frequency of the power command is equal to the target frequency frun.
[0058] Similarly, during the process of increasing the current frequency of the power command, the processor 120 will also control / increase the current voltage of the power command according to the voltage change curve 421 until the current voltage of the power command is equal to the target voltage Vref.
[0059] The motor driving method used in this application starts a single-phase induction motor 110 by controlling the frequency and voltage of the power command. In some embodiments, the voltage of the power command can affect the output current of the stator 111, and when the output current approaches the current threshold, the frequency of the rotor 112 will naturally approach the frequency of the power command. Therefore, the processor 120 can start the single-phase induction motor 110 without detecting the rotor frequency.
[0060] Overall, the single-phase induction motor drive system of this application can stably and quickly drive the rotor of the single-phase induction motor 110 from zero speed and accelerate it to the target frequency, avoiding the need for additional restart mechanisms due to startup failure. Furthermore, the motor drive method used in this application does not place excessive load on the processor 120 and can drive the rotor 112 to the target frequency within a preset time (e.g., the aforementioned target time), combining stability and efficiency.
[0061] The components, method steps, or technical features in the foregoing embodiments can be combined with each other, and are not limited to the order of textual description or the order of presentation of drawings in this application.
[0062] Although the contents of this application have been disclosed above with reference to embodiments, they are not intended to limit the contents of this application. Any person skilled in the art may make various modifications and refinements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the appended claims.
Claims
1. A single-phase induction motor drive system, characterized in that, Include: A single-phase induction motor, comprising a stator and a rotor; and A processor, coupled to the stator, is configured to provide a power command to the stator, wherein the processor is configured to obtain a frequency variation curve, the frequency variation curve being configured to indicate multiple set frequencies corresponding to different times, and including a target frequency corresponding to the stable operation of the single-phase induction motor. The processor is used to determine the following conditions in order to provide the power command: The power command is set to a current frequency with an initial frequency so that the stator drives the rotor by the power command, wherein the initial frequency is less than the target frequency; If one of the multiple set frequencies corresponding to the current time is greater than the initial frequency, the current frequency of the power command is controlled according to the frequency change curve. If one of the multiple set frequencies corresponding to the current time is less than or equal to the initial frequency, the current frequency of the power command is maintained at the initial frequency, and it is determined whether an output current of the stator is higher than or equal to a current threshold. When the output current of the stator is higher than or equal to the current threshold, a current voltage of the power supply command is fixed; as well as When the output current of the stator is lower than the current threshold, the current voltage of the power supply command is increased.
2. The single-phase induction motor drive system according to claim 1, characterized in that, The processor obtains the frequency variation curve based on the target frequency and a target time.
3. The single-phase induction motor drive system according to claim 2, characterized in that, The frequency change curve is obtained by controlling the rotor's operating frequency from zero to the target frequency based on a changing slope, using the processor.
4. The single-phase induction motor drive system according to claim 1, characterized in that, The processor also generates a voltage change curve corresponding to the frequency change curve. When the processor controls the current frequency of the power command based on the frequency change curve, the processor also controls the current voltage of the power command based on the voltage change curve.
5. The single-phase induction motor drive system according to claim 4, characterized in that, When the output current of the stator is lower than the current threshold, the processor increases the current voltage of the power command according to a first rate of change, the slope of the voltage change curve corresponds to a second rate of change, and the first rate of change is greater than the second rate of change.
6. The single-phase induction motor drive system according to claim 4, characterized in that, When the output current of the stator is higher than or equal to the current threshold, the processor fixes the current voltage of the power command until one of the multiple set frequencies corresponding to the current time is greater than the initial frequency, and then the processor controls the current voltage of the power command according to the voltage change curve.
7. The single-phase induction motor drive system according to claim 1, characterized in that, When the output current of the stator is higher than or equal to the current threshold, the processor reduces the current voltage of the power command at a preset slope, and the processor maintains the current voltage of the power command after the output current is lower than the current threshold.
8. The single-phase induction motor drive system according to claim 1, characterized in that, The processor compares a peak value of the output current with the current threshold to determine whether the output current is higher than or equal to the current threshold.
9. The single-phase induction motor drive system according to claim 8, characterized in that, The processor is used to calculate an envelope of the output current to determine whether the output current is higher than or equal to the current threshold, wherein the envelope represents the trend of the peak value.
10. The single-phase induction motor drive system according to claim 1, characterized in that, The initial frequency is between 15% and 75% of the target frequency.
11. A motor driving method, characterized in that, Include: A processor obtains a frequency variation curve corresponding to a single-phase induction motor, wherein the frequency variation curve is used to indicate multiple set frequencies corresponding to different times, and includes a target frequency corresponding to the stable operation of the single-phase induction motor. The processor provides a power command to the single-phase induction motor, causing the stator of the single-phase induction motor to drive a rotor to rotate, wherein the initial frequency of the power command is less than the target frequency. When one of the multiple set frequencies corresponding to the current time is greater than the initial frequency, the processor controls a current frequency of the power command based on the frequency change curve. When one of the multiple set frequencies corresponding to the current time is less than or equal to the initial frequency, the processor maintains the current frequency of the power command at the initial frequency and determines whether an output current of the stator is higher than or equal to a current threshold. When the output current of the stator is higher than or equal to the current threshold, the processor fixes a current voltage of the power supply command. as well as When the output current of the stator is lower than the current threshold, the processor increases the current voltage of the power supply command.
12. The motor driving method according to claim 11, characterized in that, Also includes: The processor obtains the frequency variation curve based on the target frequency and a target time.
13. The motor driving method according to claim 12, characterized in that, The frequency change curve is obtained by controlling the rotor's operating frequency from zero to the target frequency based on a changing slope, using the processor.
14. The motor driving method according to claim 11, characterized in that, The step of controlling the current frequency of the power command based on the frequency change curve includes: The current voltage of the power supply command is controlled based on a voltage change curve, wherein the voltage change curve corresponds to the frequency change curve.
15. The motor driving method according to claim 14, characterized in that, The steps to increase the current voltage of the power command include: The current voltage of the power supply command is increased according to a first rate of change, wherein a slope of the voltage change curve corresponds to a second rate of change, and the first rate of change is greater than the second rate of change.
16. The motor driving method according to claim 11, characterized in that, The step of fixing the current voltage of the power supply command includes: The current voltage of the power command is fixed until one of the plurality of set frequencies corresponding to the current time is greater than the initial frequency.
17. The motor driving method according to claim 11, characterized in that, The step of fixing the current voltage of the power supply command includes: The current voltage of the power supply command is reduced by a preset slope; and Once the output current falls below the current threshold, the current voltage of the power supply command is maintained.
18. The motor driving method according to claim 11, characterized in that, The steps for determining whether the output current of the stator is higher than or equal to the current threshold include: A peak value of the output current is compared with the current threshold to determine whether the output current is higher than or equal to the current threshold.
19. The motor driving method according to claim 18, characterized in that, The steps for determining whether the output current of the stator is higher than or equal to the current threshold include: Calculate an envelope of the output current to determine whether the output current is higher than or equal to the current threshold, where the envelope represents the trend of the peak value.
20. The motor driving method according to claim 11, characterized in that, The initial frequency is between 15% and 75% of the target frequency.