A brushless double-fed motor speed control system

Abstract

The present invention relates to the technical field of speed regulation systems, and discloses a brushless doubly-fed motor speed regulation system, including: a brushless doubly-fed motor, whose power winding is connected to a power grid, and the power grid provides a first set ratio of power to the power winding; a speed controller, which is used to control the power grid to provide a second set ratio of power to the control winding of the brushless doubly-fed motor according to the speed required by the operating conditions; a speed increaser, which is connected to the output end of the brushless doubly-fed motor, and the speed increaser operates at a set speed increase ratio; when the connection between the speed controller and the control winding is cut off, the speed output by the speed increaser is within the set speed regulation range. In normal operation, the speed of the load is adjusted by the speed controller; in abnormal operation, the adverse effects caused by power failure, power shaking or speed controller failure are reduced by designing the set speed increase ratio and controlling the abnormal operation, so that the load can work without stopping; the risk of shutdown and production suspension due to electrical equipment failure is eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of speed regulation systems, and more specifically, to a brushless double-fed motor speed regulation system. Background Art

[0002] At present, the following two solutions are generally used to convert steam turbine-driven high-speed compressors to motor-driven ones: the first solution is to use a high-speed, high-voltage, and high-power motor directly connected to the compressor under the drive of a high-voltage inverter; the second solution is to use a high-power motor driven by a high-voltage inverter and connected to the compressor through a speed increaser.

[0003] However, the first solution mentioned above has extremely high requirements for motors. The current motor technology level has not yet developed to meet the requirements of high speed, high voltage and high power. The relatively mature high-speed motor products in China with a speed higher than 10,000 rpm have a power lower than 500KW, and the power of current high-speed motors abroad is also lower than 1,000KW. Therefore, the solution of directly using high-speed motors to directly drive compressors is not yet mature. In the second solution mentioned above, the motor and the speed increaser are both mature products on the market, and the combined solution is also mature and feasible. However, it adopts a combination of high-voltage inverter, high-voltage motor and speed increaser. Due to the large size and high failure rate of the high-voltage inverter, there will be a risk of shutdown once power failure, power shaking or inverter failure occurs.

[0004] Therefore, it is necessary to propose a brushless doubly-fed motor speed control system to at least partially solve the problems existing in the prior art. Summary of the invention

[0005] A series of simplified concepts are introduced in the Summary of the Invention, which will be further described in detail in the Detailed Description of the Invention. The Summary of the Invention does not mean to attempt to define the key features and essential technical features of the claimed technical solution, nor does it mean to attempt to determine the scope of protection of the claimed technical solution.

[0006] In order to at least partially solve the above problems, the present invention provides a brushless doubly-fed motor speed control system, comprising:

[0007] A brushless double-fed motor, wherein a power winding is connected to a power grid, and the power grid provides a first set ratio of power to the power winding;

[0008] A speed controller, used for controlling the power grid to provide a second set ratio of power to the control winding of the brushless double-fed motor according to the speed required by the operating conditions;

[0009] A speed increaser connected to the output end of the brushless double-fed motor, the speed increaser operates at a set speed increase ratio;

[0010] When the connection between the speed controller and the control winding is cut off, the speed output by the speed increaser is within the set speed regulation range.

[0011] Preferably, the set speed increasing ratio of the speed increaser is set according to the set speed regulating range and the first set proportion of power provided by the power grid to the power winding, so that the set speed increasing ratio meets the design conditions.

[0012] Preferably, the design condition is that when the connection between the speed controller and the control winding is cut off, the product of the rated speed corresponding to the brushless double-fed motor running at a first set power ratio and the set speed increase ratio is within the set speed regulation range.

[0013] Preferably, the first set ratio is seventy percent.

[0014] Preferably, the speed controller is connected to the control winding via a switching switch; when an abnormal operation situation occurs that requires cutting off the connection between the speed controller and the control winding, the switching switch is used to cut off the connection.

[0015] Preferably, the switch includes: a first group of contactors connected to the speed controller, a second group of contactors connected to the wires, and a third group of contactors connected to the resistors.

[0016] Preferably, during normal operation, the switch is controlled to be in the first working state, so that the control winding of the brushless double-fed motor is connected to the power grid through the speed controller;

[0017] During abnormal operation, the switching switch is controlled to the second working state, so that the control winding of the brushless double-fed motor is disconnected from the speed controller, and the control winding is connected to the resistor. The switching switch needs to maintain the second working state for a set time; after the set time is reached, the switching switch is controlled to the third working state to short-circuit the control winding of the brushless double-fed motor.

[0018] Preferably, the first working state is that the first group of contactors are closed, and the second group of contactors and the third group of contactors are both disconnected;

[0019] The second working state is that the third group of contactors is closed, and the first group of contactors and the second group of contactors are both disconnected;

[0020] The third working state is that the second group of contactors are closed, and the first group of contactors and the third group of contactors are both opened.

[0021] Preferably, the set time is 3 seconds to 5 seconds.

[0022] Preferably, the prediction and determination of the set time includes:

[0023] Obtaining a first current difference value of the control winding in a current switching process, a second current difference value in a previous switching process, and a predicted set time change amount between the current switching process and the previous switching process;

[0024] Predicting a set time difference between a current switching process and a previous switching process according to the first current difference, the second current difference and the predicted set time variation;

[0025] The set time in the current switching process is determined according to the predicted set time difference.

[0026] Preferably, predicting the set time difference between the current switching process and the previous switching process according to the first current difference, the second current difference and the predicted set time change includes:

[0027] If the second current difference is positive, the set time difference between the current switching process and the previous switching process is the predicted set time change between the current switching process and the previous switching process;

[0028] If the second current difference is not positive, the set time difference between the current switching process and the previous switching process is 0.

[0029] Preferably, determining the set time in the current switching process according to the predicted set time difference includes:

[0030] If the predicted setting time difference is the predicted setting time change between the current switching process and the previous switching process, then the setting time in the current switching process is: the sum of the setting time of the previous switching process and the predicted setting time change between the current switching process and the previous switching process;

[0031] If the predicted set time difference is 0, determining whether the first current difference is positive;

[0032] If the first current difference is not positive, determining that the set time in the current switching process is: the same as the set time in the previous switching process;

[0033] If the first current difference is positive, the setting time in the current switching process is determined to be: the reference setting time.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The brushless doubly-fed motor speed control system described in the present invention can adjust the rotational speed of the load through the speed controller during normal operation; in the event of abnormal operation, the adverse effects caused by power failure, power shaking or speed controller failure can be reduced by designing a set speed increase ratio and controlling the abnormal operation, and the load can continue to work without stopping, thereby eliminating the risk of shutdown due to electrical equipment failure; in addition, the first set proportion of power of the power winding is directly provided by the power grid, so the pollution caused by harmonics to the power grid is relatively small, the system efficiency is higher than that of ordinary motors, and the self-consumption of the entire speed control system is reduced by more than 70% compared with the traditional full-power inverter, achieving a good energy-saving effect.

[0036] The brushless doubly-fed motor speed control system described in the present invention, other advantages, objectives and features of the present invention will be partially reflected through the following description, and will also be partially understood by technicians in this field through research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 It is a block diagram of the brushless double-fed motor speed control system of the present invention;

[0039] Figure 2 It is a circuit diagram of connecting the control winding of the brushless double-fed motor and the switching switch in the brushless double-fed motor speed control system of the present invention;

[0040] Figure 3 It is a circuit diagram of the brushless double-fed motor speed control system of the present invention when the switch is in the first working state;

[0041] Figure 4 It is a circuit diagram of the brushless double-fed motor speed control system of the present invention when the switch is in the second working state;

[0042] Figure 5 It is a circuit diagram of the brushless double-fed motor speed control system of the present invention when the switching switch is in the third working state. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments so that those skilled in the art can implement the invention with reference to the description.

[0044] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0045] like Figure 1 As shown, the present invention provides a brushless double-fed motor speed control system, comprising:

[0046] A brushless double-fed motor, wherein a power winding is connected to a power grid, and the power grid provides a first set ratio of power to the power winding;

[0047] A speed controller, used for controlling the power grid to provide a second set ratio of power to the control winding of the brushless double-fed motor according to the speed required by the operating conditions;

[0048] A speed increaser connected to the output end of the brushless double-fed motor, wherein the speed increaser operates at a set speed increase ratio (1:N);

[0049] When the connection between the speed controller and the control winding is cut off, the speed output by the speed increaser is within the set speed regulation range.

[0050] It also includes: a detection module for detecting abnormal operating conditions. If the detection module detects abnormal operating conditions, it is necessary to cut off the connection between the speed controller and the control winding; wherein the abnormal operating conditions refer to power failure, power shaking or speed controller failure.

[0051] In normal operation, the power grid directly provides the power winding with a first set ratio of power, and the power winding operates at the corresponding rated speed. At the same time, according to the difference between the speed required by the brushless double-fed motor under the load operating condition and the rated speed of the power winding, the speed of the control winding after adjustment is obtained, and the power of the control winding at the second set ratio can be adjusted accordingly through the speed controller to achieve speed regulation according to the load operating condition.

[0052] In addition, the brushless doubly-fed motor has the characteristic of bidirectional speed regulation, and can operate at a speed higher or lower than the rated speed (such as the rated speed of the power winding is 750r / min). According to the operating needs of the on-site working conditions (such as the temporary required speed regulation range of 600r / min-700r / min), when the motor speed is adjusted to 600r / min through the control winding of the brushless doubly-fed motor, the speed after the speed increaser outputs the set speed increase ratio (1:1.13) is 678r / min. Various speeds are calculated in the above manner to meet the needs of various operating conditions;

[0053] When abnormal operation occurs, it is necessary to cut off the connection between the speed controller and the control winding, and the control winding will not be involved in the work. The brushless doubly fed motor only works at the rated speed through the power winding. At this time, the speed output by the speed increaser is within the set speed regulation range.

[0054] The following is an example: the speed increase ratio of the speed increaser can be set according to the actual operating conditions;

[0055] Example 1: If the power of a steam turbine is 1000KW, the rated speed is 10515r / min, and the set speed range is 7886r / min-11040r / min;

[0056] If a brushless doubly-fed motor is used to replace the steam turbine to achieve speed regulation, the speed increase ratio will be set to 1:10.6. During normal operation, the rated speed of the power winding is 750r / min, and the output speed after passing through the speed increaser is 7950r / min. The speed required for the operating condition is: the sum of the power winding's 7950r / min (after speed increase by the speed increaser) and the control winding's speed (speed regulated by the speed controller and after speed increase by the speed increaser); in the event of abnormal operation, that is, power failure, power shaking or speed controller failure, the control winding does not participate in the speed output, and the speed output by the brushless doubly-fed motor is the rated speed of the power winding. The speed after output through the speed increaser is 7950r / min, which is within the set speed regulation range of 7886r / min-11040r / min.

[0057] Example 2: When there is a need for non-stop operation in power plants, steel mills, tap water, water conservancy and hydropower, etc., the speed increase ratio of the speed increaser used in conjunction with the brushless double-fed motor can be set within the range of 1:0.5 to 1:100. For example, the power of a boiler fan or water pump motor is 1000KW, the rated speed is 1000r / min, and the set speed regulation range is 750r / min-1000r / min; if a brushless double-fed motor is used to replace an ordinary motor to achieve speed regulation, the set speed increase ratio can be designed to be 1:1.1 (such as the design safe operating speed is: 825r / min), then the brushless double-fed motor The rated speed is 750r / min, and the output speed after passing through the speed increaser is 825r / min; when the working conditions require a certain speed, the motor will be adjusted to the required speed through the control winding of the brushless doubly fed motor. In the event of abnormal operation, that is, power failure, power shaking or speed controller failure, the control winding will not output power, and the output speed of the brushless doubly fed motor is the rated speed of the power winding (that is, 750r / min). The speed after output through the speed increaser is 825r / min, and it operates within the set speed regulation range of 750r / min-1000r / min (other set speed increase ratios are designed in the same way).

[0058] Example 3: The power of a boiler fan or water pump motor is 1000kW, the rated speed is 1500r / min, and the set speed range is 1000r / min-1500r / min. If a brushless double-fed motor is used to replace the ordinary motor to achieve speed regulation, the set speed ratio can be designed to be 1:1.5 (such as the design safety working speed is: 1125 / min); then the rated speed of the brushless double-fed motor is 750r / min, and the output speed after passing through the speed increaser is 1125r / min; when the working The motor speed is adjusted to the required speed through the control winding of the brushless doubly fed motor according to the required speed under certain conditions. In case of abnormal operation, that is, power failure, power shaking or speed controller failure, the control winding does not output power. The speed output by the brushless doubly fed motor is the rated speed of the power winding (750r / min), and the speed after output through the speed increaser is 1125r / min, running within the set speed regulation range of 1000r / min-1500r / min (other set speed increase ratios are designed in the same way).

[0059] The above technical scheme can adjust the speed of the load through the speed controller during normal operation; in the event of abnormal operation, the adverse effects caused by power failure, power shaking or speed controller failure can be reduced by designing the set speed increase ratio and controlling the abnormal operation, and the load can continue to work without stopping, eliminating the risk of shutdown due to electrical equipment failure; in addition, the first set proportion of power of the power winding is directly provided by the power grid, so the pollution caused by harmonics to the power grid is relatively small, the system efficiency is higher than that of ordinary motors, and the self-consumption of the entire speed control system is reduced by more than 70% compared with the traditional full-power inverter, achieving a good energy-saving effect.

[0060] In one embodiment, the set speed increase ratio of the speed increaser is set according to the set speed regulation range and the first set proportion of power provided by the power grid to the power winding, so that the set speed increase ratio meets the design conditions.

[0061] Furthermore, the design condition is that when the connection between the speed controller and the control winding is cut off, the product of the rated speed corresponding to the brushless double-fed motor running at a first set power ratio and the set speed increase ratio is within the set speed regulation range.

[0062] Furthermore, the first setting ratio is seventy percent; of course, it can also be set according to actual working conditions and is not limited here.

[0063] The set speed regulation range is known. For example, the set speed regulation range of the steam turbine is 7886r / min-11040r / min. After the steam turbine is converted to electric drive, the speed output by the speed increaser should be within the set speed regulation range of 7886r / min-11040r / min. When an abnormal operation occurs, the brushless doubly fed motor operates with the first set proportion of power provided by the power grid as the power winding, and its output speed is the rated speed of the power winding. Therefore, it is necessary to ensure that under the above circumstances, the speed output by the brushless doubly fed motor driving the speed increaser is within the set speed regulation range, so as to design the set speed increase ratio to ensure the normal operation of the load.

[0064] Furthermore, the difference between the product of the rated speed and the set speed increase ratio and the minimum speed of the set speed regulation range is within the set difference range.

[0065] The product of the rated speed and the set speed increase ratio is close to the minimum speed of the set speed regulation range. Therefore, when an abnormal operation occurs, the output speed can be close to the minimum speed of the set speed regulation range to ensure the normal operation of the load.

[0066] like Figure 2 As shown, in one embodiment, the speed controller is connected to the control winding via a switching switch; when an abnormal operating condition occurs that requires cutting off the connection between the speed controller and the control winding, the connection is cut off via the switching switch.

[0067] When the detection module detects an abnormal operation, the control switch is controlled to cut off the connection between the speed controller and the control winding, so that the power grid no longer supplies power to the control winding, and the brushless double-fed motor outputs the rated speed only through the power winding.

[0068] like Figure 2 As shown, further, the switching switch includes: a first group of contactors KM1 connected to the speed controller, a second group of contactors KM2 connected to the wire, and a third group of contactors KM3 connected to the resistor R.

[0069] The speed controller is connected to the power grid, and the power grid provides voltage to the control winding. The voltage provided to the control winding can be changed according to the output power of the brushless double-fed motor, that is, the voltage provided to the control winding can be designed to be a variety of voltages, including low voltages of 380V, 690V, 1140V, and 3000V, and high voltages of 6kV and 10kV;

[0070] The power grid directly provides high voltage to the power winding, including 6kV and 10KV;

[0071] Specific as Figure 2As shown, the control winding voltage is 380V, the power winding voltage is 10KV, and other voltage designs are not shown in the figure;

[0072] The control winding is provided with three lead wires, and the number of contactors in the first group of contactors KM1, the second group of contactors KM2 and the third group of contactors KM3 can be set to three, and each lead wire is respectively connected to one contactor in the first group of contactors KM1, one contactor in the second group of contactors KM2 and one contactor in the third group of contactors KM3; the number of resistors is also three, and the number of wires is also three;

[0073] The other end of each contactor in the first group of contactors KM1 is connected to the speed controller; the other end of each contactor in the second group of contactors KM2 is respectively connected to one end of each wire, and the other ends of the three wires are connected to each other; the other end of each contactor in the third group of contactors KM3 is respectively connected to one end of each resistor, and the other ends of the three resistors are connected to each other.

[0074] Furthermore, during normal operation, the switch is controlled to be in a first working state, so that the control winding of the brushless double-fed motor is connected to the power grid through the speed controller;

[0075] Wherein, the first working state is, Figure 3 As shown, the first contactor group KM1 is closed, and the second contactor group KM2 and the third contactor group KM3 are both disconnected;

[0076] It should be noted that, at startup, the third group of contactors KM3 can be controlled to close first, and the first group of contactors KM1 and the second group of contactors KM2 can be disconnected, so that the resistor is connected to the control winding of the brushless doubly-fed motor. When the output speed of the brushless doubly-fed motor reaches or approaches the rated speed of the power winding, the third group of contactors KM3 is controlled to disconnect, the first group of contactors KM1 is closed, and the second group of contactors KM2 remains disconnected, so as to prevent current shock.

[0077] During abnormal operation, the switch is controlled to the second working state, so that the control winding of the brushless double-fed motor is disconnected from the speed controller, and the control winding is connected to the resistor. The switch needs to maintain the second working state for a set time; after the set time is reached, the switch is controlled to the third working state, so that the control winding of the brushless double-fed motor is short-circuited;

[0078] Wherein, the second working state is as follows: Figure 4 As shown, the third contactor group KM3 is closed, and the first contactor group KM1 and the second contactor group KM2 are both disconnected;

[0079] The third working state is as follows: Figure 5As shown, the second group of contactors KM2 is closed, and the first group of contactors KM1 and the third group of contactors KM3 are both open.

[0080] When the detection module detects an abnormal operation, it is necessary to cut off the control winding and the speed controller by switching the switch to maintain the normal operation of the brushless double-fed motor;

[0081] Specifically, first, the third group of contactors KM3 is controlled to be closed, and the first group of contactors KM1 and the second group of contactors KM2 are disconnected, then the resistor will be connected to the control winding, and a part of the current can be absorbed by the resistor, reducing the current impact caused by directly short-circuiting the control winding. However, the resistor will heat up when it is connected to the control winding for a long time. In order to reduce the current impact and avoid the resistor from heating up for a long time, the switching switch is maintained in the second working state for only a set time. After the set time is reached, the switching switch is controlled to be in the third working state, that is, the second group of contactors KM2 is controlled to be closed, and the first group of contactors KM1 and the third group of contactors KM3 are disconnected, then the control winding is short-circuited, and at this time, the brushless doubly-fed motor operates at the first set ratio of power, that is, the brushless doubly-fed motor outputs the rated speed only through the operation of the power winding;

[0082] Therefore, through the above scheme, when power failure, power shaking or speed controller failure occurs, the speed controller and the control winding can be cut off, so that the control winding does not participate in the output of the brushless doubly-fed motor speed, thereby achieving continuous operation of the load without stopping, eliminating the risk of shutdown due to electrical equipment failure; and can ensure the stability of the switching process in the event of abnormal operation, reducing the adverse effects of current shocks.

[0083] Further, the set time is a fixed value or an adjustable value;

[0084] When the set time is a fixed value, it is 3 seconds to 5 seconds.

[0085] When the set time is an adjustable value, the set time of the current switching process can be predicted and determined;

[0086] The prediction and determination of the set time includes:

[0087] Obtaining a first current difference value of the control winding in a current switching process, a second current difference value in a previous switching process, and a predicted set time change amount between the current switching process and the previous switching process;

[0088] The predicted change in set time between the current switching process and the previous switching process can be predicted by a trained neural network model, the input of the neural network model is the first current difference and the second current difference, and the output is the change in set time between the current switching process and the previous switching process;

[0089] Predicting a set time difference between a current switching process and a previous switching process according to the first current difference, the second current difference and the predicted set time variation;

[0090] Determine the setting time in the current switching process according to the predicted setting time difference;

[0091] Since the setting time of the previous switching process is known, the setting time of the current switching process can be obtained according to the setting time of the previous switching process and the predicted setting time difference. In the current switching process, the switch maintains the second working state within the above-determined setting time;

[0092] Among them, the first current difference is the difference between the first current and the reference current in the current switching process; the second current difference is the difference between the second current and the reference current in the previous switching process; the reference current corresponds to a reference setting time, the reference current is the average current when the control winding is working, and the reference setting time is the initial setting time set when the abnormal operation occurs for the first time; the conditions that the reference setting time needs to meet are: within the reference setting time, the reference current generates heat on the resistor and consumes part of the current, which can ensure the stability of the switching process and reduce the impact of the current on the power grid.

[0093] It should be noted that the switching process is a process in which the switching switch is controlled to cut off the control winding and the speed controller when an abnormal operation is detected by the detection module.

[0094] Further, predicting a set time difference between a current switching process and a previous switching process according to the first current difference, the second current difference and the predicted set time variation includes:

[0095] If the second current difference is positive, the set time difference between the current switching process and the previous switching process is the predicted set time change between the current switching process and the previous switching process;

[0096] If the second current difference is not positive, the set time difference between the current switching process and the previous switching process is 0.

[0097] Further, determining the setting time in the current switching process according to the predicted setting time difference includes:

[0098] If the predicted setting time difference is the predicted setting time change between the current switching process and the previous switching process, then the setting time in the current switching process is: the sum of the setting time of the previous switching process and the predicted setting time change between the current switching process and the previous switching process;

[0099] If the predicted set time difference is 0, determining whether the first current difference is positive;

[0100] If the first current difference is not positive, determining that the set time in the current switching process is: the same as the set time in the previous switching process;

[0101] If the first current difference is positive, the setting time in the current switching process is determined to be: the reference setting time.

[0102] Specifically, when the second current difference is positive, there are two cases for the first current difference. The first case is that the first current difference is also positive, and the second case is that the first current difference is not positive. In both cases, the second current is greater than the reference current. Then, the reference setting time cannot guarantee the stability of the switching, that is, there is a risk of current shock. Therefore, the setting time in the current switching process is determined as: the sum of the setting time of the previous switching process and the predicted setting time change between the current switching process and the previous switching process;

[0103] When the second current difference is negative, there are two cases for the first current difference. The first case is that the first current difference is positive, and the second case is that the first current difference is not positive. This indicates that the second current is smaller than the reference current in both cases. Therefore, the reference setting time can ensure the stability of the switching and prevent the risk of current shock. Therefore, the setting time in the current switching process is determined to be: the same as the setting time of the previous switching process (when the first current difference is not positive), or the reference setting time (when the first current difference is positive).

[0104] By predicting and determining the set time in the current switching process as mentioned above, the time for connecting the resistor to the control winding can be guaranteed, thereby avoiding the risk of current impacting the power grid. In addition, by correlating the prediction of the set time with the current on the control winding, it can be ensured that the resistor consumes a certain amount of current in the form of heat, thereby ensuring the current consumption. This can avoid current impacting the power grid through more precise control, thereby further improving the stability of the switching process.

[0105] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes, and can be fully applicable to various fields suitable for the present invention, including but not limited to power plants, steel plants, tap water, water conservancy and hydropower, etc. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A brushless double-fed motor speed control system, characterized in that: include: A brushless double-fed motor, wherein a power winding is connected to a power grid, and the power grid provides a first set ratio of power to the power winding; A speed controller, used for controlling the power grid to provide a second set ratio of power to the control winding of the brushless double-fed motor according to the speed required by the operating conditions; A speed increaser connected to the output end of the brushless double-fed motor, the speed increaser operates at a set speed increase ratio; When the connection between the speed controller and the control winding is cut off, the speed output by the speed increaser is within the set speed range; The speed controller is connected to the control winding via a switching switch; when an abnormal operation situation occurs that requires disconnection of the speed controller and the control winding, the connection is disconnected via the switching switch; In normal operation, the switch is controlled to be in the first working state, so that the control winding of the brushless double-fed motor is connected to the power grid through the speed controller; During abnormal operation, the switch is controlled to be in the second working state, so that the control winding of the brushless double-fed motor is disconnected from the speed controller, and the control winding is connected to the resistor. The switch needs to be maintained in the second working state for a set time; After the set time is reached, the switch is controlled to be in the third working state, so that the control winding of the brushless double-fed motor is short-circuited; The prediction and determination of the set time includes: Obtaining a first current difference value of the control winding in a current switching process, a second current difference value in a previous switching process, and a predicted set time change amount between the current switching process and the previous switching process; Predicting a set time difference between a current switching process and a previous switching process according to the first current difference, the second current difference and the predicted set time variation; The set time in the current switching process is determined according to the predicted set time difference.

2. The brushless doubly-fed motor speed control system according to claim 1, characterized in that: The set speed increasing ratio of the speed increaser is set according to the set speed regulating range and the first set proportion of power provided by the power grid to the power winding, so that the set speed increasing ratio meets the design conditions.

3. The brushless doubly-fed motor speed control system according to claim 2, characterized in that: The design condition is that when the connection between the speed controller and the control winding is cut off, the product of the rated speed corresponding to the brushless double-fed motor running at a first set power ratio and the set speed increase ratio is within the set speed regulation range.

4. The brushless doubly-fed motor speed control system according to claim 1, characterized in that: The first set ratio is seventy percent.

5. The brushless doubly-fed motor speed control system according to claim 1, characterized in that: The switch comprises: a first group of contactors connected to the speed controller, a second group of contactors connected to the wires, and a third group of contactors connected to the resistors.

6. The brushless doubly-fed motor speed control system according to claim 5, characterized in that: The first working state is that the first group of contactors is closed, and the second group of contactors and the third group of contactors are both disconnected; the second working state is that the third group of contactors is closed, and the first group of contactors and the second group of contactors are both disconnected; The third working state is that the second group of contactors are closed, and the first group of contactors and the third group of contactors are both opened.

7. The brushless doubly-fed motor speed control system according to claim 1, characterized in that: The set time is 3 seconds to 5 seconds.

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