Reactive power compensation method and system based on asynchronous motor and capacitor and storage medium

Abstract

This application relates to the technical field of reactive power compensation, disclosing a reactive power compensation method, system, and storage medium based on an asynchronous motor and a capacitor. The method involves placing a liquid dielectric capacitor next to the asynchronous motor, connecting it to the starting circuit during startup, opening the injection and return solenoid valves, and adjusting the dielectric injection speed in a positive correlation with the motor speed. Once the injection volume reaches the target or startup is complete, injection stops and the state is switched. Injection can be adjusted by cooperating with a hydraulic coupler and a dielectric pump, or the motor can be reversed / linked with an air pump to recover the dielectric during shutdown. Alternatively, the opening and closing degree of the solenoid valve can be adjusted in a positive correlation with the target flow rate, and the return gas pipe pressure can be adjusted in a negative correlation with the target gas flow rate, or the coupling degree of the hydraulic coupler, the opening and closing degree of the solenoid valve, and the height of the return gas pipe inlet can be adjusted in a negative correlation. This method achieves harmonic-free soft start, power factor compensation to 1, avoids the risk of self-excitation during shutdown, simplifies the structure, and has low energy consumption.

Description

Technical Field

[0001] This application relates to the technical field of reactive power compensation, and in particular to a reactive power compensation method, system, and storage medium based on an asynchronous motor and a capacitor. Background Technology

[0002] With the large-scale development of distributed photovoltaic (PV) power, large-capacity PV power plants are continuously being connected to existing distribution networks, leading to significant changes in power flow distribution and power characteristics. PV power output is intermittent and fluctuating; random fluctuations in its output power can cause imbalances in reactive power supply and demand in the distribution network, resulting in voltage deviations in lines and increased power losses. Reactive power compensation measures are needed to maintain stable grid operation.

[0003] The core objective of reactive power compensation in power grids is to adjust the balance between reactive power supply and demand, making the power factor of electrical equipment as close to 1 as possible. A power factor deviating from 1 will result in a large amount of reactive power flowing in the power grid, which will not only increase the active power loss and voltage drop of transmission lines, but also reduce the effective utilization rate of power components such as transformers and switching equipment.

[0004] There are often conflicting demands on the coordinated regulation of reactive power compensation and voltage control in power grids. For example, traditional asynchronous motor soft starters generate a large number of high-order harmonics during startup, interfering with the power quality of the grid. Furthermore, their starting torque is relatively low, making it difficult to meet the starting requirements of heavy-load equipment. Therefore, in some scenarios, torque motors have to be used as alternatives. However, torque motors have an even lower power factor and will increase the reactive power consumption of the grid during operation, leading to greater voltage fluctuations in the distribution network. This not only affects the reactive power compensation effect but also poses a greater challenge to voltage stability control, making them unsuitable for complex distribution network conditions.

[0005] When large-scale distributed photovoltaic (PV) systems are integrated into existing distribution networks, conflicts often arise between reactive power compensation and voltage control. Essentially, the power factor of electrical equipment needs to be as close to 1 as possible to avoid additional reactive power consumption and reduce the difficulty of reactive power control in the grid. On the other hand, traditional asynchronous motor soft starters have many high-order harmonics and low starting torque, so it is necessary to use torque motors with even lower power factors, which increases reactive power consumption and voltage fluctuations in the grid. Therefore, a soft-start technology with high starting torque and no harmonics is needed. Summary of the Invention

[0006] To reduce the impact of power factor degradation caused by the starting of asynchronous motors, this application provides a reactive power compensation method, system, and storage medium based on asynchronous motors and capacitors.

[0007] Firstly, this application provides a reactive power compensation method based on an asynchronous motor and a capacitor, employing the following technical solution:

[0008] A reactive power compensation method based on an asynchronous motor and a capacitor includes the following steps:

[0009] A liquid dielectric capacitor is installed next to the asynchronous motor;

[0010] Obtain the start command of the asynchronous motor, and in response to the start command, connect the liquid dielectric capacitor to the start circuit where the asynchronous motor is located;

[0011] Open the injection solenoid valve and the return solenoid valve between the liquid dielectric capacitor and the preset liquid dielectric storage tank;

[0012] The liquid dielectric is injected from the liquid dielectric storage tank into the liquid dielectric capacitor. The injection speed of the liquid dielectric is adjusted according to the motor speed of the asynchronous motor. The faster the motor speed, the faster the injection speed, and the slower the motor speed, the slower the injection speed.

[0013] The amount of liquid dielectric injected into the liquid dielectric capacitor is obtained. When the amount of injection exceeds the preset amount or the start-up command of the asynchronous motor is obtained, the injection of liquid dielectric is stopped, the liquid dielectric pump is switched out, and the injection solenoid valve and the return solenoid valve are opened.

[0014] By adopting the above technical solution, after the asynchronous motor starts, the injection solenoid valve and the return solenoid valve are opened. When the asynchronous motor speed is low, a portion of the liquid dielectric can gradually return to the liquid dielectric storage tank. When the asynchronous motor speed is high, a portion of the liquid dielectric can be gradually pumped to the liquid dielectric capacitor. When the liquid dielectric fills the liquid dielectric capacitor, the liquid dielectric can also play an additional heat dissipation function under the condition of flowing and circulating between the liquid dielectric capacitor and the liquid dielectric storage tank.

[0015] Optionally, in the step of controlling the injection of liquid dielectric from the liquid dielectric storage tank into the liquid dielectric capacitor, the injection of liquid dielectric is achieved by using a hydraulic coupler in conjunction with a liquid dielectric pump, specifically including the following sub-steps:

[0016] The input end of the hydraulic coupler is connected to a preset liquid dielectric pump power take-off, and the output end of the hydraulic coupler is connected to the liquid dielectric pump. The liquid dielectric pump power take-off is fixedly installed at the middle position of the output shaft of the asynchronous motor connected to the motor load, and is used to split part of the shaft output force from the output shaft of the asynchronous motor and transmit it to the hydraulic coupler.

[0017] The coupling degree of the hydraulic coupler is adjusted in a positive correlation with the real-time motor speed of the asynchronous motor; the higher the real-time motor speed, the higher the coupling degree; the lower the real-time motor speed, the lower the coupling degree.

[0018] By adopting the above technical solution, when the speed of the asynchronous motor increases, the coupling degree of the hydraulic coupler is increased to increase the driving force of the liquid dielectric pump, thereby increasing the injection speed of the liquid dielectric from the liquid dielectric storage tank to the liquid dielectric capacitor; when the speed of the asynchronous motor decreases, the coupling degree of the hydraulic coupler is decreased to reduce the driving force of the liquid dielectric pump, thereby reducing the injection speed of the liquid dielectric from the liquid dielectric storage tank to the liquid dielectric capacitor.

[0019] Optionally, the following steps are also included:

[0020] Obtain the stop command for the asynchronous motor;

[0021] Upon receiving the stop command, the asynchronous motor is controlled to reverse at a preset reverse speed;

[0022] Real-time monitoring of the injection volume of liquid dielectric in the liquid dielectric capacitor;

[0023] The asynchronous motor is continuously controlled to reverse at the preset reverse speed until the amount of liquid dielectric injected into the liquid dielectric capacitor is less than the preset starting amount, at which point the control of the asynchronous motor to reverse is stopped.

[0024] By adopting the above technical solution, the problem of self-excitation or resonance caused by the fixed capacitance due to excessive dielectric in the capacitor after the asynchronous motor stops can be fundamentally avoided, ensuring the safety of motor shutdown. At the same time, the amount of dielectric injected into the capacitor is restored to the initial state suitable for the next start-up. There is no need to set up an additional dielectric recovery drive component. The dielectric adjustment is achieved by relying on the motor's own reversal, which simplifies the device structure and reduces energy consumption.

[0025] Optionally, the following steps are also included:

[0026] Obtain the stop command for the asynchronous motor;

[0027] Upon receiving the stop command, the return gas pipe is closed, and the exhaust valve pre-installed on the liquid dielectric storage tank is opened;

[0028] The asynchronous motor is controlled to work in conjunction with a preset air pump, which then injects gas into the upper part of the liquid dielectric capacitor.

[0029] Real-time monitoring of the injection volume of liquid dielectric in the liquid dielectric capacitor;

[0030] The air pump is continuously controlled to inject gas into the upper part of the liquid dielectric capacitor until the amount of liquid dielectric injected into the liquid dielectric capacitor is less than the preset start-up amount, at which point the air pump is stopped from injecting gas.

[0031] By adopting the above technical solution, the self-excitation or resonance problem caused by the fixed capacitance due to excessive dielectric in the capacitor after the asynchronous motor stops is avoided, which essentially ensures the safety of motor shutdown. Moreover, relying on the asynchronous motor's own power to link the air pump, there is no need to configure an additional independent power source, which simplifies the device structure and reduces energy consumption. At the same time, the opening of the exhaust valve can balance the air pressure in the storage tank, ensuring smooth return of the dielectric and restoring the amount of dielectric injected into the capacitor to the initial state suitable for the next start-up.

[0032] Optionally, the step of controlling the flow of the liquid dielectric between the liquid dielectric storage tank and the liquid dielectric capacitor includes the following sub-steps:

[0033] The target flow rate of the liquid dielectric between the liquid dielectric storage tank and the liquid dielectric capacitor is acquired in real time, and the opening and closing degree of the solenoid valve is adjusted according to the target flow rate.

[0034] Alternatively, the target gas flow rate between the liquid dielectric storage tank and the liquid dielectric capacitor can be obtained in real time, and the compression degree of the return gas pipe can be adjusted according to the inverse correlation of the target gas flow rate.

[0035] By adopting the above technical solutions, when the reactive power demand of the motor increases, the corresponding target flow rate increases, and the opening degree of the solenoid valve is increased, thereby increasing the flow rate of the dielectric through the solenoid valve per unit time. This quickly replenishes the dielectric in the capacitor to expand the capacitance and promptly compensate for the increased reactive power consumption. When the reactive power demand of the motor decreases, the corresponding target flow rate decreases, and the opening degree of the solenoid valve is decreased to reduce the dielectric flow rate, avoiding the risk of exceeding the power factor or resonance due to the capacitance exceeding the actual demand. Alternatively, when the dielectric flow rate is fast, the corresponding target gas flow rate is high, requiring rapid pressure balancing. This involves reducing the tightness of the return gas pipe, expanding the internal channel of the return gas pipe, increasing the gas flow rate, and promptly eliminating the pressure difference between the storage tank and the capacitor. This prevents pressure obstruction from causing a decrease in the dielectric flow rate and affecting the accuracy of capacitance adjustment. When the dielectric flow rate is slow, the corresponding target gas flow rate is low, and the gas pressure changes gradually. This involves increasing the tightness of the return gas pipe and narrowing the channel to control the gas flow rate, avoiding pressure fluctuations inside the container due to excessive gas flow and ensuring the stability of the dielectric flow.

[0036] Optionally, the method includes the following steps:

[0037] The coupling degree of the hydraulic coupler is adjusted according to the inverse relationship between the motor speed and the speed of the motor; the faster the motor speed, the lower the coupling degree of the hydraulic coupler; the slower the motor speed, the higher the coupling degree of the hydraulic coupler.

[0038] By adopting the above technical solutions, when the motor speed is high, it usually corresponds to high load, slowed growth in reactive power demand, or the need to control the capacitance to avoid excess. Reducing the coupling degree reduces the pump driving force, slows down the dielectric injection speed, and prevents the capacitor capacitance from exceeding the actual reactive power demand, which could lead to power factor fluctuations or resonance risks. When the motor speed is slow, it usually corresponds to the initial stage of low load startup or a surge in reactive power demand. Increasing the coupling degree increases the pump driving force, accelerates the dielectric injection speed, and ensures that the capacitor quickly forms a suitable capacitance to compensate for reactive power consumption in a timely manner.

[0039] Optionally, the method includes the following steps:

[0040] The opening degree of the solenoid valve is adjusted according to the inverse relationship between the motor speed and the motor speed; the faster the motor speed, the smaller the opening degree of the solenoid valve; the slower the motor speed, the larger the opening degree of the solenoid valve.

[0041] Alternatively, the tightness of the return air pipe can be adjusted according to the inverse relationship between the motor speed and the speed; the faster the motor speed, the lower the tightness of the return air pipe; the slower the motor speed, the higher the tightness of the return air pipe.

[0042] By adopting the above technical solutions, for the regulation of solenoid valves, when the motor speed is slow, such as during the initial startup or low-load operation, the reactive power demand surges. Increasing the opening degree of the solenoid valve can accelerate the injection speed of the dielectric, allowing the liquid dielectric capacitor to quickly form a large capacitance, timely compensating for the reactive current during startup or the reactive power consumption at low speeds, and helping the motor startup current to decrease from 5-8 times the rated current to 2-3 times to achieve 100% torque harmonic-free startup. When the motor speed is fast, such as during stable high-load operation, the growth rate of reactive power demand slows down. Decreasing the opening degree can slow down the injection of dielectric, avoiding excessive capacitor capacitance that could lead to power factor fluctuations or resonance risks, ensuring that the power factor is stably compensated to 1, and reducing motor line losses.

[0043] For the adjustment of the return gas pipe, when the motor speed is slow, the pressure tightening level can be adjusted to control the gas flow rate to balance the gas pressure in the container and prevent the dielectric from being injected too slowly due to pressure imbalance, which would affect the capacitance adjustment. When the motor speed is fast, the pressure tightening level can be reduced to increase the gas flow rate to meet the pressure balance requirements of the rapid flow of the dielectric and prevent pressure obstruction from causing poor flow of the dielectric.

[0044] Optionally, the step of controlling the gas flow and liquid dielectric circulation state between the liquid dielectric storage tank and the liquid dielectric capacitor further includes the following sub-steps:

[0045] One end of the return pipe is connected to the upper part of the liquid dielectric storage tank, and the other end is provided with an air inlet that can move up and down along the outer wall of the liquid dielectric capacitor. The air inlet is connected to the internal cavity of the liquid dielectric capacitor, and the movement path of the air inlet is preset with a limit structure to limit the highest and lowest adjustment height of the air inlet on the liquid dielectric capacitor.

[0046] The real-time motor speed of the asynchronous motor is collected in real time, and the height of the air inlet of the return air pipe on the liquid dielectric capacitor is adjusted inversely based on the collected real-time motor speed.

[0047] The liquid level and internal pressure of the liquid dielectric capacitor are monitored in real time. When the liquid level reaches the preset suitable level and the internal pressure is within the preset balanced pressure range, the adjustment of the air inlet height of the return air pipe is stopped, and the current air inlet position is maintained until the real-time motor speed change of the asynchronous motor exceeds the preset threshold.

[0048] By adopting the above technical solution, when the motor speed increases, the air inlet moves upward to expand the gas space to meet the needs of dielectric flow and avoid excessive air pressure from hindering dielectric flow; when the speed decreases, the air inlet moves downward to reduce the gas space to ensure dielectric filling efficiency and ensure rapid formation of the appropriate capacitance.

[0049] Secondly, this application provides a reactive power compensation system based on an asynchronous motor and a capacitor, employing the following technical solution:

[0050] A reactive power compensation system based on an asynchronous motor and a capacitor includes a processor, wherein the processor performs the steps of the reactive power compensation method based on an asynchronous motor and a capacitor as described in any of the preceding claims.

[0051] Thirdly, this application provides a storage medium, which adopts the following technical solution:

[0052] A storage medium storing a program, which, when executed by a processor, implements the steps of the reactive power compensation method based on an asynchronous motor and a capacitor as described above.

[0053] In summary, this application includes at least one of the following beneficial technical effects: It enables harmonic-free soft starting and 100% torque starting of asynchronous motors during the startup phase. By dynamically adjusting the injection speed of the liquid dielectric according to the motor speed, it can quickly replenish the dielectric to form a large capacitance, reducing the starting current from 5-8 times the rated current to 2-3 times, avoiding the harmonic and torque reduction problems caused by traditional step-down soft starting, and improving the starting efficiency of motor-driven equipment. It stably achieves power factor compensation of the asynchronous motor to 1. Through the dynamic adjustment of components such as the hydraulic coupler, solenoid valve, and return pipe, it ensures that the capacitance of the liquid dielectric capacitor matches the reactive power consumption of the motor in real time, overcoming the difficulty of compensating asynchronous motors to a power factor of 1, significantly reducing motor line losses, improving grid energy efficiency, and alleviating the problem of balancing reactive power and voltage after photovoltaic integration. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of a reactive power compensation device based on an asynchronous motor and a capacitor.

[0055] Figure 2 This is a flowchart illustrating the steps of a reactive power compensation method based on an asynchronous motor and a capacitor.

[0056] Figure 3 This is a diagram showing the sub-steps during the shutdown process of an asynchronous motor.

[0057] Figure 4 This is a schematic diagram of an adjustable height air inlet on a liquid dielectric capacitor.

[0058] Reference numerals: 1. Liquid dielectric storage tank; 2. Motor load; 3. Liquid dielectric pump power take-off; 4. Hydraulic coupler; 5. Liquid dielectric pump; 6. Return air pipe; 7. Injection solenoid valve; 8. Liquid dielectric capacitor; 9. Asynchronous motor; 10. Air inlet; 11. Limiting structure; 12. Return air solenoid valve. Detailed Implementation

[0059] The embodiments of this application are described in detail below, and examples of the embodiments are shown in the accompanying drawings.

[0060] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] This application discloses a reactive power compensation method based on an asynchronous motor and a capacitor, and a reactive power compensation device based on an asynchronous motor and a capacitor, with reference to... Figure 1 The device includes a liquid dielectric storage tank 1, a motor load 2, a liquid dielectric pump power take-off 3, a hydraulic coupler 4, a liquid dielectric pump 5, a return air pipe 6, an injection solenoid valve 7, a return air solenoid valve 12, a liquid dielectric capacitor 8, and an asynchronous motor 9. The liquid dielectric storage tank 1 and the liquid dielectric capacitor 8 have equal volumes and are arranged horizontally. They are connected at the top via the return air pipe 6 and at the bottom via the solenoid valve 7 and the liquid dielectric pump 5. The asynchronous motor 9 is connected to the motor load 2 via an output shaft. The liquid dielectric pump power take-off 3 is located in the middle of the output shaft, which drives the liquid dielectric pump 5 through the hydraulic coupler 4. The solenoid valve 7 is also connected in parallel with the power supply terminals of the asynchronous motor 9 and the liquid dielectric capacitor 8 to the AC power grid. The liquid dielectric capacitor 8 is an iron-shell thin-film capacitor with a mesh-like film. The hollow cavity inside the iron shell stores the liquid dielectric, which is a mixture of castor oil and transformer oil in a 2:1 ratio, with a dielectric constant of not less than 3. The storage volume is consistent with the volume of the capacitor's iron shell cavity.

[0062] This device can achieve a power factor compensation of 1 for asynchronous motors. Through the design of a liquid dielectric variable capacitor, the compensation capacity can be adjusted in real time according to the motor operation, breaking the self-excitation or resonance that may occur when the motor stops, thus fundamentally avoiding the problem of self-excitation damaging the motor, thereby reducing the line loss of asynchronous motors and improving energy efficiency. It can also alleviate the problem of reactive power and voltage balance after photovoltaic grid connection. It realizes 100% torque soft start and harmonic-free soft start of the motor. During startup, the liquid dielectric fills the capacitor to form a large capacitance, which greatly compensates for the starting reactive current, reducing the starting current of asynchronous motors from 5-8 times the rated current to 2-3 times. It supports full-voltage direct start, and because it does not rely on power electronic equipment, it fundamentally eliminates the harmonic effect.

[0063] In the selection and preparation of device components, specifications must be strictly matched according to technical requirements; the volume of liquid dielectric storage tank 1 and liquid dielectric capacitor 8 must be consistent. Stainless steel can be used to make the storage tank, and cast iron can be used to make the capacitor shell. The internal film of the capacitor should be a polypropylene mesh film; the liquid dielectric should be mixed with transformer oil and castor oil in a 2:1 ratio. After stirring evenly, the dielectric constant must be tested to ensure that it is not lower than 3; the asynchronous motor 9 should be selected according to the load requirements; the power take-off of the liquid dielectric pump 3 can be gear-driven, and the transmission ratio should take into account both power transmission and the drive requirements of the motor load 2; the rated parameters of components such as hydraulic coupler 4, liquid dielectric pump 5, and solenoid valve 7 should be determined according to the motor power and dielectric flow requirements; the rated voltage of solenoid valve 7 should be compatible with the AC power grid and should be connected in parallel with the power supply terminals of asynchronous motor 9 and liquid dielectric capacitor 8.

[0064] During installation and connection, the liquid dielectric storage tank 1 and the liquid dielectric capacitor 8 must be arranged horizontally. The connection between the return gas pipe 6, the solenoid valve 7, the liquid dielectric pump 5 and the two must be sealed to avoid leakage of dielectric or gas affecting the pressure balance. The output shafts of the asynchronous motor 9 and the motor load 2 must be aligned. After the liquid dielectric pump power take-off 3 is installed in the middle position of the output shaft, it must be accurately connected to the hydraulic coupler 4 and the liquid dielectric pump 5 through a coupling to ensure stable power transmission. For the electrical connection, the power supply terminals of the solenoid valve 7, the asynchronous motor 9, and the liquid dielectric capacitor 8 must be reliably connected in parallel to the AC power grid, and necessary electrical protection components must be configured.

[0065] During the commissioning and operation phase, the mechanical components must first be checked for secure installation, flexible rotation, and correct electrical wiring. Then, no-load commissioning is performed: disconnect motor load 2, start asynchronous motor 9 and liquid dielectric pump 5, and adjust the dielectric flow through solenoid valve 7 to verify the accuracy of the capacitance adjustment of liquid dielectric capacitor 8. After normal no-load operation, load commissioning is performed by connecting motor load 2 and monitoring the motor power factor in real time. The capacitance is adjusted to stabilize it at 1, while observing the starting current to ensure it drops to 2-3 times the rated current, achieving 100% torque start-up. During long-term operation, continuous monitoring of component parameters is necessary, along with regular maintenance of pipeline sealing, electrical component status, and liquid dielectric properties to ensure the device stably performs its reactive power compensation and soft-start functions.

[0066] Based on the above-mentioned compensation device, this application embodiment provides a reactive power compensation method based on an asynchronous motor and a capacitor. Before implementing this method, the core device needs to be pre-assembled: a liquid dielectric capacitor 8 is fixedly installed beside the asynchronous motor 9. The liquid dielectric capacitor 8 uses a high-voltage resistant insulating shell, and its internal cavity is used to contain the liquid dielectric, preferably a mineral insulating oil with a high dielectric constant. The electrode structure of the capacitor is electrically connected to the starting circuit of the asynchronous motor 9 through a pre-set circuit breaker or contactor, ensuring that the capacitor and the starting circuit can be connected or disconnected through circuit switching. At the same time, a liquid dielectric storage tank 1 is pre-set on one side of the liquid dielectric capacitor 8. The volume of the storage tank is liquid. The volume of the bulk dielectric capacitor 8 is 1.2-1.5 times that of the capacitor to meet the needs of dielectric circulation and backup. The storage tank and the capacitor are connected by two independent pipelines. One is the liquid return pipeline, which is equipped with an injection solenoid valve 7 in series. It adopts a two-position three-way solenoid directional valve with a rated working pressure of not less than 1.6MPa. The other is the gas return pipeline 6, which is equipped with a gas return solenoid valve 12. It adopts a normally closed solenoid valve 7 with a response time ≤0.5s. The lower end of the liquid return pipeline extends to the bottom area of ​​the storage tank and the capacitor. The two ends of the gas return pipeline 6 are connected to the upper part of the storage tank and the upper part of the capacitor, respectively, to ensure that the liquid dielectric flow and gas flow balance can be achieved through the two pipelines.

[0067] Reference Figure 1 and Figure 2 The method includes the following steps:

[0068] When the control cabinet or control system (such as a PLC controller) of the asynchronous motor 9 receives a start command issued by the operator (this start command can be triggered by a button, a remote signal, or an automatic operating condition), the control system immediately responds to the command, controls the preset circuit breaker or contactor to close, and connects the liquid dielectric capacitor 8 to the starting circuit of the asynchronous motor 9; at this time, the capacitor and the stator winding of the asynchronous motor 9 form a parallel circuit, and the capacitive current of the capacitor can compensate for the inductive reactive current when the motor starts; at the same time, the control system outputs an electrical signal to the injection solenoid valve 7 and the return air solenoid valve 12, controlling the two solenoid valves 7 to open synchronously, so that the injection return pipeline and the return air pipeline 6 are both in a conductive state, preparing for subsequent liquid dielectric injection and air pressure balance.

[0069] After the injection solenoid valve 7 and the return solenoid valve 12 are opened, the liquid dielectric pump 5 is started. This pump is a gear pump with a rated flow rate matched to the capacitor volume. The power input end of the pump is connected to the output shaft of the asynchronous motor 9 through a hydraulic coupler 4 and a pump power take-off, controlling the injection of liquid dielectric from the storage tank into the liquid dielectric capacitor 8 via the injection and return pipeline. During this process, the real-time speed of the motor is collected in real time by a speed sensor installed on the output shaft of the asynchronous motor 9. The speed sensor is a Hall effect speed sensor, and the speed signal is transmitted to the control system. The control system outputs a control command based on the logic of adjusting the injection speed according to the positive correlation of the speed: when the asynchronous motor 9 is just started, the speed starts to rise from 0, with an initial speed ≤500 r / min. At this time, the control... The control system determines that the motor is in the initial stage of startup and needs to slowly inject dielectric to avoid current surges caused by sudden changes in capacitance. Therefore, the injection speed is controlled at 0.5-1L / min. As the motor speed gradually increases, such as when the speed reaches 1000-1500r / min, which is close to 50% of the rated speed, the control system determines that the motor's starting torque demand increases and reactive power consumption surges. Therefore, the dielectric injection needs to be accelerated to increase the capacitance, so the injection speed is simultaneously increased to 1.5-2L / min. When the motor speed reaches more than 80% of the rated speed, such as ≥2800r / min, for a 4-pole asynchronous motor, the injection speed is further increased to 2-2.5L / min to ensure that the dielectric in the capacitor is quickly filled to the amount suitable for startup requirements.

[0070] During the liquid dielectric injection process, the injection volume of the dielectric inside the capacitor 8 is collected in real time by a liquid level sensor installed on the inner wall of the liquid dielectric capacitor 8, and the injection volume signal is fed back to the control system. The liquid level sensor is a capacitive liquid level sensor, and the measurement range covers the height of the internal cavity of the capacitor. When the control system detects that the injection volume is greater than the preset injection volume, which is 80%-90% of the rated volume of the liquid dielectric capacitor 8, it can be adjusted according to the motor power. For example, the preset injection volume corresponding to an 11kW motor is 5L. Alternatively, when the control system determines that the asynchronous motor 9 has completed the start-up through the speed sensor and the current sensor, the control system immediately executes the stop injection operation. The determination criteria are: the motor speed is stable above 95% of the rated speed, and the stator current drops to less than 1.2 times the rated current. At this time, the control system obtains the "start-up completion command". The liquid electrolyte pump 5 is stopped. The inlet and outlet of the pump are short-circuited by a pipeline switching valve set between the inlet and outlet of the liquid electrolyte pump 5, so that the return liquid pipeline bypasses the electrolyte pump to form a straight loop, thus avoiding obstruction of the subsequent circulation of the electrolyte after the pump stops. At the same time, the injection solenoid valve 7 and the return gas solenoid valve 12 are kept in the open state to ensure that the liquid electrolyte can flow freely between the storage tank and the capacitor.

[0071] After the asynchronous motor 9 starts, it enters a stable operation phase. At this time, the liquid dielectric capacitor 8 remains electrically connected to the motor's operating circuit, continuously compensating for reactive power. During this phase, the speed of the asynchronous motor 9 fluctuates with the load; for example, the speed decreases slightly when the load increases and increases slightly when the load decreases. With the injection solenoid valve 7 and the return solenoid valve 12 open, the return liquid pipeline and the return gas pipeline 6 form a natural circulation loop for the dielectric. When the motor speed decreases, such as below 90% of the rated speed, the liquid dielectric capacitor 8... As the pressure decreases slightly, the dielectric in the storage tank gradually flows back to the storage tank through the return pipeline under the influence of gravity and air pressure difference, thus appropriately reducing the capacitance in the capacitor to meet the reactive power demand after the load decreases. When the motor speed increases, such as when the speed exceeds 95% of the rated speed, although the liquid dielectric pump 5 has stopped running actively, the rotation of the motor output shaft still drives the pump body to rotate slightly through the pump power take-off, forming a weak driving force to gradually pump some of the liquid dielectric in the storage tank into the capacitor, thus appropriately increasing the capacitance to compensate for the reactive power consumption after the load increases.

[0072] Meanwhile, when the liquid dielectric capacitor 8 is filled with liquid dielectric, that is, when the injection volume reaches more than 95% of the rated volume of the capacitor, the dielectric will form a slow flow circulation between the storage tank and the capacitor under the conduction of the liquid return pipeline and the gas return pipeline 6. During this circulation, the dielectric can carry the heat generated by the electrodes of the capacitor during operation into the storage tank. The outer wall of the storage tank is equipped with heat dissipation fins with a fin spacing of 15-20mm and made of aluminum alloy, which can dissipate heat to the surrounding environment, thereby providing additional heat dissipation function for the liquid dielectric capacitor 8, avoiding the capacitor from increasing dielectric loss or decreasing insulation performance due to long-term operation heat generation, and extending the service life of the device.

[0073] In the reactive power compensation method based on asynchronous motor and capacitor in this application, the step of controlling the injection of liquid dielectric from liquid dielectric storage tank 1 to liquid dielectric capacitor 8 specifically includes the following sub-steps:

[0074] Before starting the liquid dielectric injection operation, the hydraulic coupler 4, the liquid dielectric pump power take-off 3 and the liquid dielectric pump 5 must be pre-assembled and connected to ensure that the power transmission path is stable and reliable.

[0075] The preset liquid dielectric pump power take-off 3 is fixedly installed at the middle position of the output shaft connecting the asynchronous motor 9 and the motor load 2 via a key connection and set screw. The liquid dielectric pump power take-off 3 adopts a gear-type power take-off with a transmission efficiency of not less than 92% and a rated torque that matches the output shaft torque of the asynchronous motor 9. The middle position of the output shaft is specifically at 1 / 3 of the length of the output shaft close to the housing of the asynchronous motor 9. The input gear of the power take-off meshes with the driving gear on the output shaft, and the output end of the power take-off is rigidly connected to the input end of the hydraulic coupling 4 through a flange. This ensures that the power take-off can stably divide a portion of the shaft output force from the output shaft of the asynchronous motor 9. The divided shaft output force accounts for 15%-20% of the total output shaft force of the motor, which satisfies the driving requirements of the dielectric pump without affecting the power output of the motor to the load, and transmits the divided shaft output force to the hydraulic coupling 4.

[0076] A speed-regulating hydraulic coupling 4 is selected, with anti-wear hydraulic oil as the working medium. Its rated speed matches the input speed of the liquid electrolyte pump 5. Its input end is coaxially connected to the output end of the liquid electrolyte pump power take-off 3 via a coupling, and its output end is fixedly connected to the input shaft of the liquid electrolyte pump 5 via a flat key. The liquid electrolyte pump 5 is an internal gear pump with a rated working pressure of 2.0 MPa and a rated flow rate that matches the volume of the liquid electrolyte capacitor 8, such as a 10L capacitor corresponding to a pump rated flow rate of 3L / min. At the same time, an electromagnetic proportional valve is connected in series in the control oil circuit of the hydraulic coupling 4. This electromagnetic proportional valve is electrically connected to the control system (such as PLC) of the asynchronous motor 9. The amount of oil in the working chamber inside the coupling can be adjusted by the current signal output by the control system, thereby changing the coupling degree.

[0077] During the liquid dielectric injection process, the coupling degree of the hydraulic coupler 4 is dynamically adjusted to achieve a positive correlation between the injection speed and the rotational speed of the asynchronous motor 9. The specific execution process is as follows:

[0078] The Hall effect speed sensor installed at the end of the output shaft of the asynchronous motor 9 is activated. The sensor is fixed to the motor housing by a bracket. The gap between its detection probe and the speed measuring gear on the output shaft is maintained at 0.5-1mm. The sensor collects the real-time speed signal of the asynchronous motor 9 in real time and converts the speed signal into a 4-20mA analog electrical signal, which is then transmitted to the signal acquisition module of the control system.

[0079] After receiving the real-time speed signal from the speed sensor, the control system, based on a preset speed-coupling degree correspondence (which is experimentally calibrated and stored in the control system's register), outputs a corresponding control current to the electromagnetic proportional valve in the control oil circuit of the hydraulic coupler 4.

[0080] When the asynchronous motor 9 starts and its real-time speed is between 0-500 r / min, which is 20% lower than the rated speed, the control system determines that the motor is in the initial stage of low-speed start-up and needs to reduce the injection speed to avoid sudden changes in capacitance. Therefore, it outputs a 5mA control current to the electromagnetic proportional valve to reduce the oil inlet of the coupler working chamber and maintain the coupling degree of the hydraulic coupler 4 at 30%-40%. At this time, the power transmitted from the coupler to the dielectric pump is relatively small, the speed of the dielectric pump is about 300-400 r / min, and the injection speed is controlled at 0.6-0.8 L / min.

[0081] When the speed of the asynchronous motor 9 increases to 1000-2000 r / min, which is 40%-80% of the rated speed, the starting torque demand of the motor increases, and the reactive power consumption surges. It is necessary to increase the injection speed to quickly replenish the dielectric. The control system outputs a control current of 12-15mA to increase the oil intake of the coupler working chamber, thereby increasing the coupling degree to 60%-70%. At this time, the power transmitted by the coupler increases, the speed of the dielectric pump rises to 800-1000 r / min, and the injection speed increases synchronously to 1.5-2.0 L / min.

[0082] When the asynchronous motor 9 approaches its rated speed, such as 2800 r / min, or for a 4-pole motor, when the real-time speed reaches above 2500 r / min, the control system outputs a maximum control current of 18-20mA to fill the working chamber of the coupler with working oil, achieving a coupling degree of 90%-95%. At this time, the coupler transmits maximum power, and the dielectric pump speed increases to 1400-1500 r / min, with an injection rate of 2.5-3.0 L / min, ensuring that the dielectric in the capacitor is quickly filled to the amount required for startup.

[0083] The degree of coupling of the hydraulic coupler 4 directly determines the driving force of the liquid dielectric pump 5, and thus affects the injection speed. The specific implementation process of its adaptation logic is as follows:

[0084] When the speed of the asynchronous motor 9 increases, the control system increases the coupling degree of the hydraulic coupler 4, i.e., increases the oil volume in the working chamber, thereby increasing the speed ratio between the input and output ends of the coupler. The higher the coupling degree, the closer the speed ratio is to 1, which in turn increases the torque and speed transmitted to the input shaft of the liquid dielectric pump 5. The driving force of the dielectric pump increases with the increase of the input speed, and the displacement generated by the meshing of the gears in the pump increases synchronously, ultimately increasing the injection speed of the liquid dielectric from the storage tank to the capacitor through the return pipeline. Conversely, when the asynchronous motor 9 requires a reduced speed due to load fluctuations or the initial startup, the control system reduces the coupling degree of the coupler, reduces the oil volume in the working chamber, decreases the speed ratio between the input and output ends of the coupler, weakens the power transmitted to the dielectric pump, reduces the pump speed, and reduces the injection speed accordingly. This achieves dynamic adaptation, ensuring that the injection speed always matches the reactive power demand during the motor startup phase, avoiding the problem of excessive capacitance due to excessively fast dielectric injection or insufficient reactive power compensation due to excessively slow injection.

[0085] Reference Figure 3 This application achieves precise reset of the dielectric quantity in the capacitor by controlling the motor to reverse and drive the liquid dielectric to flow back during the shutdown process of the asynchronous motor 9, thus avoiding the risk of self-excitation or resonance after shutdown. The specific implementation steps are as follows:

[0086] When the asynchronous motor 9 completes its operation and needs to be stopped, the first step is to receive the stop command and perform preparatory operations before reversing to ensure a stable start-up of the subsequent dielectric recovery process.

[0087] The control system of asynchronous motor 9 obtains stop commands in two ways: one is a manual command triggered by the operator through the "stop" button on the control cabinet, and the other is an automatic command automatically generated by the system based on preset working conditions, such as load power failure and running time target. After receiving the stop command, the control system first detects the stator current of the motor through the current sensor to confirm that the current has dropped to less than 10% of the rated current, and determines that the motor has been disconnected from the load. At the same time, it confirms through the speed sensor that the motor speed is decreasing from the rated speed to 0, with the speed ≤500r / min, to avoid directly triggering reverse rotation under high speed operation and prevent damage to the motor shaft system due to impact.

[0088] After the control system determines that the reversal conditions are met, it calls the preset reversal control parameters. The preset reversal speed is calibrated based on the height difference between the liquid dielectric storage tank 1 and the capacitor and the pipeline resistance characteristics. Specifically, it is set to 150-200 r / min. This speed is less than 10% of the rated speed of the motor, which can generate sufficient power to drive the dielectric backflow while avoiding a sudden increase in pipeline pressure caused by excessive reversal speed. At the same time, the control system outputs an electrical signal to the pipeline switching valve of the liquid dielectric pump 5 to ensure that the liquid return pipeline is in a conductive state and that the return air solenoid valve 12 remains open, providing a smooth path and pressure balance for the dielectric backflow.

[0089] After completing the reversal preparation, the control system initiates the asynchronous motor 9 reversal program, which drives the relevant components to achieve dielectric recovery through motor reversal:

[0090] The control system adjusts the contactor in the motor drive circuit. The contactor is a reversible AC contactor with a rated current matching the motor's rated current. It switches the power supply phase sequence of the motor stator winding, enabling the asynchronous motor 9 to smoothly switch from forward rotation to reverse rotation. To avoid current surges during the switching process, the control system uses a "soft start" method to control the reverse start. By adjusting the inverter output frequency, the motor speed gradually increases from the current decreasing speed to the preset reverse speed of 150-200 r / min. The entire speed-up process lasts 3-5 seconds, ensuring a smooth transition in power transmission between the motor shaft system and the liquid dielectric pump 5.

[0091] When the asynchronous motor 9 reverses, its output shaft drives the liquid dielectric pump power take-off 3 fixed on the shaft to reverse synchronously. The power take-off transmits the reverse power to the hydraulic coupler 4 through the meshing gear. At this time, the coupling degree of the hydraulic coupler 4 is preset to 80%-90% to ensure efficient power transmission, thereby driving the liquid dielectric pump 5 to reverse. Since the dielectric pump is an internal meshing gear pump, the liquid flow direction at its inlet and outlet is synchronously reversed when it reverses. The original "injection path" of injecting dielectric from the storage tank to the capacitor is switched to the "recovery path" of returning from the capacitor to the storage tank. Under the suction of the pump, the liquid dielectric in the capacitor flows to the storage tank through the return liquid pipeline.

[0092] During the dielectric recovery process of the asynchronous motor 9 in reverse drive, the precise start and stop of the reverse action is achieved by monitoring the amount of dielectric in the capacitor in real time.

[0093] A capacitive liquid level sensor installed on the inner wall of the liquid dielectric capacitor 8 is used to collect the injection volume of the dielectric in the capacitor in real time. The capacitive liquid level sensor has a measurement range covering the internal cavity height of the capacitor from 0 to 500 mm, a measurement accuracy of ±2 mm, and outputs a 4-20 mA analog signal. The detection electrodes of the sensor are arranged vertically along the inner wall of the capacitor. The higher the dielectric liquid level, the greater the capacitance between the electrodes, and the stronger the corresponding output current signal. The sensor transmits the real-time collected liquid level signal to the control system. The control system calculates the actual injection volume of the dielectric based on the calibration relationship between liquid level height and injection volume, such as a 10 mm decrease in liquid level height corresponding to a 0.2 L decrease in injection volume.

[0094] The control system compares the real-time calculated dielectric injection volume with the preset starting volume, which is the initial dielectric volume required by the capacitor for the next motor start. This starting volume is calibrated based on the motor's starting reactive power requirements and is typically 20%-30% of the capacitor's rated capacity. For example, a 10L capacitor corresponds to a preset starting volume of 2-3L. When the actual injection volume is greater than or equal to the preset starting volume, the motor continues to run at the preset reverse speed to ensure continued dielectric return. When the actual injection volume is less than the preset starting volume, such as when the injection volume in a 10L capacitor drops to 1.8-2.8L, the control system immediately outputs a stop command; it controls the frequency converter to reduce its output frequency, gradually reducing the motor's reverse speed from 150-200 r / min to 0, with the entire deceleration process lasting 2-3 seconds. After the motor completely stops, the control system resets the reversible AC contactor, cutting off the motor's reverse power supply circuit and simultaneously closing the injection solenoid valve 7 of the return liquid pipeline to prevent the dielectric in the storage tank from flowing back into the capacitor, ensuring that the dielectric volume in the capacitor is stably maintained at the initial state suitable for the next start.

[0095] Through the above steps, dielectric recovery is achieved by relying on the reverse rotation power of the asynchronous motor 9 itself, eliminating the need for additional independent drive components such as vacuum pumps and recovery pumps. This simplifies the overall structure of the device and reduces additional energy consumption. At the same time, the amount of dielectric in the capacitor is precisely controlled below the preset starting amount, fundamentally avoiding the problem of self-excitation or resonance of the asynchronous motor 9 caused by excessive dielectric after shutdown, thus providing dual protection for motor shutdown safety and reliability of the next startup.

[0096] During the shutdown phase of the asynchronous motor 9, this application utilizes a coordinated control logic of closing the return air pipe 6, opening the exhaust valve, and injecting air via a motor-linked air pump. This leverages gas pressure to drive the return flow of the liquid dielectric, achieving precise reset of the dielectric quantity within the capacitor. This fundamentally avoids the risk of self-excitation during shutdown. The specific implementation steps, combined with the device structure and air pressure regulation principle, are explained in detail below:

[0097] When asynchronous motor 9 needs to be stopped, the stop command is received and the pipeline status is switched, laying the foundation for subsequent gas injection and dielectric return.

[0098] The control system of asynchronous motor 9 obtains stop commands through two means: one is a manual command generated by the operator triggering the "stop" button on the control cabinet; the other is an automatic command automatically generated by the system based on preset conditions such as load power failure and the end of the operating cycle. After receiving the command, the control system first confirms through the speed sensor that the motor speed has dropped from the rated speed to 300-500 r / min, and is in the low-speed shutdown stage. At the same time, it detects through the current sensor that the stator current is ≤5% of the rated current, and determines that the motor has been disconnected from the effective load, so as to avoid triggering subsequent operations under high speed and high load conditions and prevent damage to pipelines and components due to pressure shock.

[0099] After the control system determines that the shutdown adjustment conditions are met, it immediately outputs an electrical signal to the return gas solenoid valve 12 on the return gas pipe 6. This uses a normally closed two-position, two-way solenoid valve 7 with a rated working pressure ≥1.6MPa and a response time ≤0.3s. The solenoid valve 7 is de-energized and closed, completely cutting off the gas flow channel between the liquid dielectric storage tank 1 and the liquid dielectric capacitor 8, preventing subsequent gas injection from leaking through the return gas pipe 6 and ensuring effective gas pressure is formed inside the capacitor. Simultaneously, the control system outputs a signal to the exhaust valve pre-installed on the top of the liquid dielectric storage tank 1. This is a manual / electric integrated ball valve with a diameter matching the return gas pipe 6. The exhaust valve is electrically opened to its maximum opening degree (90°), allowing the storage tank to connect with the atmosphere. This balances the gas pressure inside the storage tank during subsequent dielectric return flow, preventing pressure increases due to dielectric inflow and ensuring smooth dielectric return.

[0100] After the pipeline status switch is completed, the air pump driven by the asynchronous motor 9 injects gas into the upper part of the liquid dielectric capacitor 8 to create a pressure difference. The specific execution process is as follows:

[0101] The pre-installed air pump is a miniature piston air pump, whose power input end is rigidly connected to the spare output end of the liquid dielectric pump power take-off 3 via a coupling. This power take-off is fixed at the middle position of the output shaft of the asynchronous motor 9. In addition to transmitting power to the liquid dielectric pump 5, it also allocates an additional 5%-8% of the shaft output force to drive the air pump, eliminating the need for a separate power source. Simultaneously, the air pump's outlet is connected to the upper air inlet of the liquid dielectric capacitor 8 via a high-pressure air pipe. A one-way valve is connected in series on the air pipe to prevent the injected gas from flowing back into the air pump.

[0102] The control system outputs an electrical signal to the start / stop relay of the air pump, which powers on the air pump and starts it up. At this time, although the asynchronous motor 9 is in the low-speed shutdown stage, it still maintains a speed of 100-150 r / min. The minimum speed is maintained by the frequency converter, and its output shaft drives the power take-off to rotate synchronously. The power take-off transmits power to the air pump, which then starts to inject compressed air into the cavity above the capacitor. To prevent a sudden increase in internal pressure due to excessively rapid gas injection, the control system monitors the internal pressure of the capacitor in real time using a pressure sensor located at the air inlet on the upper part of the capacitor. The sensor has a measurement range of 0-1.0 MPa and an accuracy of ±0.02 MPa. When the pressure is ≥0.6 MPa, the air pump's air inlet regulating valve is depressurized to reduce the gas injection flow rate. When the pressure is ≤0.3 MPa, the air inlet regulating valve is depressurized to ensure that the internal pressure of the capacitor is stably maintained within the effective range of 0.3-0.6 MPa. This pressure is sufficient to drive the dielectric to flow back quickly while avoiding exceeding the pressure withstand limit of the capacitor casing, which has a rated pressure withstand of 1.0 MPa.

[0103] During the continuous injection of air by the air pump to drive the dielectric backflow, the precise stopping of the air injection action is achieved by monitoring the amount of dielectric in the capacitor in real time. The specific process is as follows:

[0104] An ultrasonic level sensor, fixed to the inner wall of a liquid dielectric capacitor 8, is used to collect the liquid level height of the capacitor in real time. The transmitter and receiver of the sensor are respectively installed at the upper and lower positions on the outer walls of the capacitor. The liquid level height is calculated by the reflection time of the ultrasonic waves after penetrating the shell, and the liquid level signal is converted into a 4-20mA analog signal and transmitted to the control system. The control system is calibrated according to a preset formula: "liquid level height - injection volume". For example, injection volume = liquid level height × capacitor cross-sectional area. The cross-sectional area is pre-calculated based on the inner diameter of the capacitor. For example, for a cylindrical capacitor with an inner diameter of 200mm, the cross-sectional area is approximately 314cm². 2 For every 10mm decrease in liquid level, the injection volume decreases by 3.14L, and the actual injection volume of the current dielectric can be calculated in real time.

[0105] The control system compares the real-time calculated actual injection volume with the preset starting volume. The preset starting volume is calibrated based on the initial reactive power demand for the next motor start, and is usually 20%-25% of the rated capacity of the capacitor. For example, for a 20L capacitor, the preset starting volume is 4-5L. When the actual injection volume is greater than the preset starting volume, the air pump continues to inject air to ensure that the dielectric continues to flow back to the storage tank. When the actual injection volume is less than the preset starting volume, such as when the injection volume in a 20L capacitor drops to 3.5-4.5L, the control system immediately executes a stop operation. First, the start / stop relay of the air pump is de-energized to stop the air pump from injecting air. Then, the one-way valve for air intake at the top of the capacitor is closed to prevent leakage of the injected gas. Finally, the exhaust valve is closed. If it is an electric ball valve, it is energized and closed to 0° opening, and the return air solenoid valve 12 is opened to restore the gas passage between the storage tank and the capacitor, preparing for the air pressure balance during the next start.

[0106] Through the above steps, the dielectric material is recovered by relying on the air pump driven by the asynchronous motor 9 itself, without the need for additional independent drive components, which simplifies the device structure and reduces energy consumption. At the same time, the opening of the exhaust valve ensures the air pressure balance during dielectric return, and accurate liquid level monitoring ensures that the amount of dielectric material in the capacitor is restored to the initial state suitable for the next start-up. This essentially avoids the self-excitation or resonance problem caused by the fixed capacitance due to excessive dielectric material after shutdown, further improving the safety and reliability of the asynchronous motor 9 during shutdown.

[0107] This application employs two selectable control paths when controlling the flow of liquid dielectric between liquid dielectric storage tank 1 (hereinafter referred to as "storage tank") and liquid dielectric capacitor 8 (hereinafter referred to as "capacitor"): "adjustment of the opening degree of solenoid valve 7" and "adjustment of the tightness of return air pipe 6". Through precise matching of target parameters and adjustment actions, it ensures that the dielectric flow rate is adapted to the reactive power requirements of asynchronous motor 9 and that the air pressure is adapted to the flow state. The specific implementation steps are as follows:

[0108] Before performing dielectric flow regulation, it is necessary to complete the assembly of core components and calibration of key parameters to provide a foundation for subsequent dynamic regulation.

[0109] The solenoid valve 7 connected in series in the injection and return pipeline is an electromagnetic proportional valve. Its control terminal is electrically connected to the PLC control system of the asynchronous motor 9. The valve core opening can be adjusted by a 0-5V voltage signal, corresponding to an opening degree of 0%-100%.

[0110] A pipe clamping mechanism is installed in the return air pipe 6, which uses an arc-shaped clamping block driven by an electric screw. The clamping block is made of wear-resistant nylon. The drive motor of the clamping mechanism is electrically connected to the PLC control system. The clamping force of the clamping block on the return air pipe 6 is adjusted by pulse signal, corresponding to a clamping degree of 0%-100%, where 0% is completely loose and 100% is completely clamped.

[0111] A turbine flow meter is installed in the middle of the liquid return line, and a thermal gas mass flow meter is installed in the middle of the 6 return gas lines. The signal output terminals of both flow meters are connected to the PLC control system for real-time feedback of the actual flow rate.

[0112] The relationship between the reactive power demand of the asynchronous motor 9 and the target flow rate of the dielectric was calibrated through experiments: Under the no-load, half-load and full-load conditions of the motor, the required reactive power was measured by a power analyzer, and the dielectric flow rate that made the capacitor capacitance match the reactive power was recorded to form a reference table. For example, when the reactive power increased from 5kVar to 10kVar, the target flow rate increased from 0.5L / min to 1.2L / min, and the data was stored in the register of the PLC control system.

[0113] The correspondence between the actual flow rate of the dielectric and the target gas flow rate is calibrated: the flow rate of the dielectric is changed by adjusting the opening degree of solenoid valve 7, and the gas flow rate required to maintain the gas pressure balance is recorded simultaneously; for example, when the flow rate of the dielectric increases from 0.3L / min to 2.0L / min, the target gas flow rate increases from 0.5L / min to 3.0L / min, and this is also stored in the control system.

[0114] Adjustment Path 1: Adjustment of Solenoid Valve 7 Opening Degree Based on Target Flow Rate

[0115] This approach obtains the target flow rate of the dielectric in real time and adjusts the opening degree of solenoid valve 7 accordingly to ensure that the dielectric flow rate matches the reactive power requirements of the motor. The specific steps are as follows:

[0116] The PLC control system collects the stator current and real-time speed of the asynchronous motor 9 in real time through current sensors and speed sensors at a frequency of 10Hz. Combined with the preset current-speed-reactive power calculation model, such as Q=K×I×n, where K is the calibration coefficient, I is the stator current, and n is the real-time speed, the real-time reactive power required by the motor is calculated.

[0117] The control system calls up a pre-stored table of reactive power demand and target flow rate, and matches the corresponding target flow rate of the dielectric according to the real-time reactive power. For example, when the calculated real-time reactive power is 8kVar, the target flow rate is matched to 1.0L / min.

[0118] The control system compares the target flow rate with the actual flow rate fed back by the turbine flow meter, and outputs a control signal to solenoid valve 7 according to the positive correlation adjustment logic.

[0119] When the reactive power demand of the motor increases, such as when the load increases and the real-time reactive power rises from 6kVar to 9kVar, the target flow rate increases from 0.7L / min to 1.1L / min. If the actual flow rate is 0.7L / min, which is lower than the target value, the control system output voltage signal increases from 2V to 3.5V, causing the opening degree of solenoid valve 7 to increase from 40% to 70%. The flow rate of the dielectric material flowing through solenoid valve 7 per unit time increases, and the actual flow rate gradually rises to 1.1L / min. This quickly replenishes the dielectric material in the capacitor to expand the capacitance and timely compensates for the increased reactive power consumption.

[0120] When the reactive power demand of the motor decreases, such as when the load decreases and the real-time reactive power drops from 9kVar to 5kVar, the corresponding target flow rate drops from 1.1L / min to 0.5L / min. If the actual flow rate is 1.1L / min, which is higher than the target value, the control system output voltage signal drops from 3.5V to 1.5V, causing the opening degree of solenoid valve 7 to drop from 70% to 30%. The dielectric flow rate decreases, and the actual flow rate drops to 0.5L / min. This avoids the capacitor capacitance exceeding the actual demand, which could lead to excessive power factor (e.g., exceeding 1.0) or resonance risk.

[0121] When the deviation between the actual flow rate and the target flow rate is ≤ ±0.05 L / min, the control system maintains the current control signal of solenoid valve 7, keeps the opening and closing degree stable, and ensures that the dielectric flow rate continuously adapts to the reactive power demand of the motor.

[0122] Adjustment Path Two: Adjustment of Return Pipe 6 Compression Based on Target Gas Flow Rate

[0123] This approach ensures pressure balance between the storage tank and the capacitor by real-time acquisition of the target gas flow rate and inverse correlation adjustment of the compression level of return gas pipe 6. The specific steps are as follows:

[0124] The PLC control system obtains the actual flow rate of the dielectric (e.g., 0.8 L / min) through the turbine flow meter, calls up the pre-stored table of dielectric flow rate and target gas flow rate, and matches the corresponding target gas flow rate. For example, a dielectric flow rate of 0.8 L / min corresponds to a target gas flow rate of 1.5 L / min.

[0125] The control system compares the target gas flow rate with the actual gas flow rate fed back by the thermal gas mass flow meter, and outputs a control signal to the clamping mechanism drive motor according to the inverse correlation adjustment logic.

[0126] When the dielectric flow rate is fast, such as when the actual flow rate increases from 0.6 L / min to 1.8 L / min, the corresponding target gas flow rate increases from 1.2 L / min to 3.2 L / min. If the actual gas flow rate is 1.2 L / min, which is lower than the target value, the control system outputs a pulse signal to reverse the motor of the clamping mechanism, loosen the clamp, reduce the clamping degree of the return pipe 6 from 60% to 20%, expand the internal channel of the return pipe 6, and increase the gas flow rate to 3.2 L / min. This promptly eliminates the pressure difference between the storage tank and the capacitor. For example, if the difference between the storage tank pressure of 0.08 MPa and the capacitor pressure of 0.12 MPa is reduced to within ±0.01 MPa, it avoids pressure obstruction that would cause a decrease in the dielectric flow rate and affect the accuracy of capacitance adjustment.

[0127] When the dielectric flow rate is slow, such as when the actual flow rate drops from 1.8 L / min to 0.5 L / min, the corresponding target gas flow rate drops from 3.2 L / min to 1.0 L / min. If the actual gas flow rate is 3.2 L / min, which is higher than the target value, the control system outputs a pulse signal to make the drive motor rotate forward, the clamping block tightens, the compression degree of the return gas pipe 6 increases from 20% to 70%, the internal channel of the return gas pipe 6 narrows, and the gas flow rate drops to 1.0 L / min. This avoids pressure fluctuations in the container due to excessive gas flow, such as pressure fluctuations within 0.09-0.11 MPa, ensuring the stability of the dielectric flow.

[0128] When the deviation between the actual gas flow rate and the target gas flow rate is ≤ ±0.1L / min, the control system maintains the current control signal of the pressing mechanism to keep the pressing degree stable and ensure that the gas pressure balance is continuously adapted to the dielectric flow state.

[0129] In practical applications, one of the above adjustment paths can be selected and executed according to the operating conditions:

[0130] When the asynchronous motor 9 is in the initial stage of startup and the reactive power demand changes rapidly, the opening degree of the solenoid valve 7 is adjusted first to adapt to the reactive power demand by rapidly changing the flow of the dielectric.

[0131] When the motor is in a stable operating phase and the dielectric flow rate is slow but air pressure balance needs to be ensured, the pressure adjustment of return pipe 6 should be performed first to maintain stable flow by stabilizing the gas flow rate.

[0132] Both approaches do not rely on complex power electronic equipment. They achieve precise control through mechanical adjustment and parameter calibration, which not only fits the dynamic compensation of the liquid dielectric variable capacitor, but also ensures the stability of the power factor of the asynchronous motor and the reliable operation of the device.

[0133] In controlling the injection of liquid dielectric, this application achieves dynamic adaptation between the driving force of the liquid dielectric pump 5 and the motor operating conditions through the inverse correlation adjustment logic of the asynchronous motor 9 speed and the coupling degree of the hydraulic coupler 4. The specific implementation steps are as follows:

[0134] Before adjusting the coupling level, it is necessary to complete the matching and assembly of the hydraulic coupler 4 with the motor and dielectric pump, as well as the calibration of key adjustment parameters, to lay the foundation for subsequent dynamic adjustment.

[0135] A speed-regulating hydraulic coupling 4 is selected, and its input end is rigidly connected to the output end of the liquid dielectric pump power take-off 3 via a flexible coupling; this power take-off is fixed at the middle position of the output shaft of the asynchronous motor 9, and can output...

[0136] 10%-15% of the shaft output force, such as 1.1-1.65kW of power corresponding to an 11kW motor; the output end of the coupler is fixedly connected to the input shaft of the liquid electrolyte pump 5 via a flat key to ensure that the power can be stably transmitted to the electrolyte pump.

[0137] Meanwhile, an electromagnetic proportional relief valve is connected in series in the control oil circuit of the hydraulic coupler 4. The control end of the valve is electrically connected to the PLC control system of the asynchronous motor 9. The oil pressure of the control oil circuit can be adjusted by a 0-10V voltage signal, thereby changing the amount of oil filling the working chamber inside the coupler and achieving precise adjustment of the coupling degree. The more oil filling, the higher the coupling degree and the higher the power transmission efficiency.

[0138] The inverse correlation adjustment parameters were calibrated through bench tests. The specific process is as follows:

[0139] An experimental platform was set up, and the asynchronous motor 9 was connected to a dynamometer to simulate a load. Under three typical operating conditions—motor speeds of 500 r / min (low speed, corresponding to the initial startup), 1000 r / min (medium speed), and 1500 r / min (rated speed, high speed)—the input voltage of the electromagnetic proportional relief valve was adjusted, and the degree of coupling that made the dielectric injection speed adapt to the reactive power demand of the current operating condition was recorded.

[0140] At a speed of 500 r / min, a dielectric injection rate of 1.8 L / min is required to quickly replenish the capacitance, corresponding to an oil filling of 80% for the coupler, a coupling degree of 85%, and an input voltage of 8V for the electromagnetic proportional relief valve.

[0141] At a speed of 1000 r / min, an injection rate of 1.2 L / min is required to balance the reactive power demand, corresponding to an oil filling volume of 50%, a coupling degree of 55%, and an input voltage of 5V.

[0142] At a speed of 1500 r / min, the injection rate should be 0.6 L / min to avoid excessive capacitance, corresponding to an oil filling volume of 20%, a coupling degree of 25%, and an input voltage of 2V.

[0143] The above-mentioned speed-voltage-coupling degree correspondence is stored in the database of the PLC control system to form an adjustment reference table for subsequent real-time adjustment.

[0144] During the liquid dielectric injection process, the PLC control system follows a process of speed acquisition, parameter matching, and coupling adjustment to achieve an inverse correlation between the coupling degree of the hydraulic coupler 4 and the motor speed. The specific steps are as follows:

[0145] The magnetoelectric speed sensor installed at the end of the output shaft of the asynchronous motor 9 is activated. The sensor is fixed to the motor end cover by an L-shaped bracket. The gap between the detection probe and the speed measuring gear on the output shaft is maintained at 0.2-0.5mm. The motor speed signal is collected in real time at a sampling frequency of 10Hz and converted into a 4-20mA analog current signal, which is then transmitted to the analog input module of the PLC control system.

[0146] After receiving the current signal from the speed sensor, the PLC control system converts it into the actual speed value through the signal conversion module. For example, 4mA corresponds to 0 r / min, and 20mA corresponds to 3000 r / min. The system then calls a pre-stored speed-voltage-coupling degree lookup table to match the electromagnetic proportional relief valve input voltage corresponding to the current speed with the target coupling degree.

[0147] When the motor speed increases to 1400-1500 r / min, the high speed corresponds to stable operation under high load, the growth rate of reactive power demand slows down, the matching input voltage is 2-2.5V, and the target coupling degree is 25%-30%.

[0148] When the motor speed drops to 600-800 r / min, the low speed corresponds to the initial stage of low load start-up or the speed drop caused by a sudden increase in load, and the reactive power demand surges. The matching input voltage is 7-7.5V, and the target coupling degree is 80%-85%.

[0149] When the motor speed is between 900-1300 r / min, it is considered a medium speed. The corresponding voltage and coupling degree are calculated using linear interpolation. For example, when the speed is 1200 r / min, the input voltage is 3.5V and the coupling degree is 40%.

[0150] The PLC control system outputs a corresponding analog voltage signal to the electromagnetic proportional relief valve based on the matched input voltage.

[0151] When the coupling degree needs to be reduced, such as when the speed increases from 1000 r / min to 1500 r / min, the control system will reduce the output voltage from 5V to 2V, reduce the opening of the electromagnetic proportional relief valve, reduce the oil pressure in the coupler control oil circuit, reduce the amount of oil filling the working chamber, and reduce the coupling degree from 55% to 25%. At this time, the power transmitted from the hydraulic coupler 4 to the dielectric pump is weakened, the pump speed is reduced from 800 r / min to 300 r / min, and the dielectric injection rate is reduced from 1.2 L / min to 0.6 L / min. This avoids excessive dielectric in the capacitor, which would cause the capacitance to exceed the actual reactive power requirement, thereby preventing power factor fluctuations (such as dropping from 1.0 to below 0.95) or resonance risks.

[0152] When the coupling degree needs to be increased, such as when the speed drops from 1000 r / min to 500 r / min, the control system will increase the output voltage from 5V to 8V, increase the opening of the electromagnetic proportional relief valve, increase the oil pressure in the control oil circuit, increase the oil filling volume in the working chamber, and increase the coupling degree from 55% to 85%. The power transmitted from the coupler to the dielectric pump is enhanced, the pump speed increases from 800 r / min to 1200 r / min, and the injection rate increases from 1.2 L / min to 1.8 L / min, ensuring that the capacitor is quickly filled with dielectric to form a suitable capacitance, such as from 5 kVar to 12 kVar, to timely compensate for the surge in reactive power consumption of the motor, such as when the load suddenly increases and the reactive power demand increases from 5 kVar to 12 kVar.

[0153] To ensure precise and stable adjustment of the coupling level, a real-time monitoring and correction mechanism is added during the adjustment process:

[0154] A turbine flow meter is installed in the injection and return pipeline to collect the actual injection speed of the electrolyte in real time. At the same time, a speed sensor is installed on the output shaft of the hydraulic coupler 4. The actual coupling degree is calculated by the ratio of the output shaft speed to the input shaft speed. The speed ratio = output shaft speed / input shaft speed. The closer the speed ratio is to 1, the higher the coupling degree. Both monitoring data are fed back to the PLC control system in real time.

[0155] When the actual injection rate deviates from the target injection rate under the current operating conditions by more than ±0.1 L / min (e.g., the target injection rate is 0.6 L / min, but the actual rate is 0.8 L / min), or when the actual coupling degree deviates from the target coupling degree by more than ±5% (e.g., the target coupling degree is 25%, but the actual rate is 35%), the control system automatically corrects the input voltage of the electromagnetic proportional relief valve.

[0156] If the actual injection speed is too high or the actual coupling degree is too high, reduce the output voltage by 0.2-0.5V to reduce the coupling degree;

[0157] If the actual injection speed is too low or the actual coupling degree is too low, increase the output voltage by 0.2-0.5V to improve the coupling degree;

[0158] Until the deviation between the actual value and the target value is ≤ ±0.1L / min (injection rate) or ±5% (coupling degree), ensure that the adjustment effect always adapts to the motor's operating conditions.

[0159] Through the above steps, the liquid dielectric injection speed is dynamically adapted to the asynchronous motor 9 under all operating conditions. This ensures timely reactive power compensation at low speeds and avoids the risk of excess capacitance at high speeds. At the same time, relying on the motor's own power and mechanical adjustment structure, no additional drive components are required, simplifying the device structure and reducing energy consumption.

[0160] This application uses an inverse correlation adjustment logic between motor speed and the opening / closing degree of solenoid valve 7 and the tightness of return air pipe 6. The specific steps are as follows:

[0161] In the early stages of device configuration and parameter calibration, it is necessary to complete the selection, assembly, and adjustment benchmarks of core components. Among them, the solenoid valve 7 system uses an electromagnetic proportional regulating valve, which is installed in the middle section of the injection and return pipeline. Its control end is connected to the PLC control system. The valve core opening is continuously adjustable from 0 to 100% through a 4-20mA current signal. The valve body is made of brass, and the seals are made of oil-resistant nitrile rubber to adapt to the long-term stable operation of mineral insulating oil media. The gas return pipe 6 clamping mechanism is composed of an arc-shaped clamp driven by an electric actuator (output torque 20N·m). The clamp is lined with a polytetrafluoroethylene gasket and installed on the outside of the Φ10mm oil-resistant rubber gas return pipe 6. The actuator receives a 0-10V voltage signal output from the PLC and can achieve a clamping degree adjustment from 0 to 100% (0% is fully open, 100% is fully closed). The sensing and monitoring system includes a Hall-effect speed sensor installed on the motor output shaft, a turbine flow meter connected in series with the injection and return liquid pipeline, and a differential pressure transmitter connected to the capacitor and the top of the storage tank, which are used to collect speed signals, dielectric flow and gas pressure difference data in real time. Meanwhile, a parameter comparison table for adjustment was established and stored in the PLC system through bench tests, clarifying the correspondence between rotational speed and the opening degree of solenoid valve 7 and the tightness of return pipe 6. For example, 500 r / min (initial startup) corresponds to 780% opening of solenoid valve (flow rate 2.5 L / min) and 670% tightness of return pipe 6 (gas flow rate 0.8 L / min); 1000 r / min corresponds to 750% opening of solenoid valve (flow rate 1.5 L / min) and 640% tightness of return pipe 6 (gas flow rate 1.5 L / min); and 1500 r / min (rated speed) corresponds to 720% opening of solenoid valve (flow rate 0.5 L / min) and 610% tightness of return pipe 6 (gas flow rate 3.0 L / min), providing a benchmark for subsequent dynamic adjustment.

[0162] In the solenoid valve 7 opening / closing degree adjustment stage based on motor speed, the PLC control system acquires the speed sensor signal at a frequency of 10Hz, and converts it into the actual speed value after filtering. When the speed fluctuation is ≤50r / min, it is determined to be a stable operating condition. When it exceeds 50r / min, the dynamic adjustment program is activated: For low speed conditions, ≤800r / min, typical scenarios are 300-500r / min at the initial stage of motor start-up or 600-800r / min during heavy load climbing. The PLC outputs a 16-20mA current signal to adjust the opening / closing degree of solenoid valve 7 to 70-90%, increasing the dielectric injection rate to 2.0-3.0L / min. The capacitor capacitance increases from the initial value of 2kVar to the rated value of 10kVar within 10-15 seconds, quickly compensating for the starting reactive current, reducing it from 5-8 times the rated current to 2-3 times, achieving harmonic-free soft start-up. Start-up: For medium-speed operation (800-1200 r / min), typically during motor acceleration or medium load operation, the PLC outputs a 10-16mA current signal to adjust the opening degree of solenoid valve 7 to 40-70%, stabilizing the dielectric injection rate at 1.0-2.0 L / min. The capacitance increases linearly with the speed to 4-8 kVar, ensuring the power factor remains above 0.95. For high-speed operation (≥1200 r / min), typically during rated speed operation or light-load high-speed operation, the PLC outputs a 4-10mA current signal to adjust the opening degree of solenoid valve 7 to 10-40%, reducing the dielectric injection rate to 0.3-1.0 L / min. The capacitance remains stable at 8-10 kVar, preventing overcompensation from causing the power factor to exceed the standard, maintaining it at 1.0±0.02, and reducing motor line loss by approximately 15-20%. Meanwhile, to ensure adjustment accuracy, when the deviation between the actual flow rate monitored by the flow meter and the target flow rate exceeds ±0.2L / min, the PLC will automatically correct the output signal; when the actual flow rate is too low, the current will be increased by 0.5-1mA, and when the actual flow rate is too high, the current will be decreased by 0.5-1mA, ensuring that the flow adjustment accuracy is controlled within ±0.1L / min.

[0163] In the adjustment of the compression level of the return air pipe 6 based on motor speed, the PLC calculates the required gas flow rate in real time according to the speed signal and differential pressure transmitter data. When the speed increases, the dielectric flow accelerates, and the gas flow rate needs to be increased to balance the gas pressure; when the speed decreases, the dielectric flow slows down, and the gas flow rate needs to be reduced to stabilize the gas pressure, and executes inverse correlation adjustment logic: for low speed conditions (≤800r / min), the PLC outputs a 7-10V voltage signal to adjust the compression level of the return air pipe 6 to 60-80%, reducing the cross-sectional area of ​​the return air pipe 6 to 20-40% of its original area, controlling the gas flow rate at 0.5-1.0L / min, and maintaining the pressure difference between the capacitor and the storage tank within ±100Pa to avoid injection delay of the dielectric due to pressure imbalance (delay time ≤0.5s); For medium-speed operation (800-1200 r / min), the PLC outputs a 4-7V voltage signal to adjust the compression of the return air pipe 6 to 30-60%, maintaining the cross-sectional area of ​​the return air pipe 6 at 40-70% of its original area, and stabilizing the gas flow rate at 1.0-2.0 L / min, meeting the pressure balance requirements of medium-flow-rate dielectrics. For high-speed operation (≥1200 r / min), the PLC outputs a 1-4V voltage signal to adjust the compression of the return air pipe 6 to 10-30%, expanding the cross-sectional area of ​​the return air pipe 6 to 70-90% of its original area, increasing the gas flow rate to 2.0-4.0 L / min, quickly balancing the pressure difference (≤±200 Pa) generated by the high-speed flow of the dielectric (1.5-3.0 L / min), and preventing pipeline pressure loss from exceeding 5%. In addition, to ensure system safety, when the differential pressure transmitter detects a pressure difference exceeding ±500Pa, it will trigger emergency regulation; in the event of positive overpressure (excessive pressure on the capacitor side), the pressure of the return gas pipe 6 will be immediately reduced by 10-20%; in the event of negative overpressure (excessive pressure on the storage tank side), the pressure of the return gas pipe 6 will be immediately increased by 10-20%, ensuring that the system pressure is always within the safe threshold of ≤±300Pa.

[0164] Regarding the coordinated control of the two adjustment methods, differentiated strategies need to be formulated according to the motor operating conditions: During the startup phase (0-1000 r / min), the solenoid valve 7 is preferentially activated with a large opening adjustment (70-90%) in conjunction with the high pressure tightness of the return air pipe 6 (60-80%), stabilizing the air pressure while rapidly establishing capacitance; During the operation phase (1000-1500 r / min), proportional coordinated adjustment is adopted, synchronously reducing the opening of the solenoid valve 7 and the tightness of the return air pipe 6 as the speed increases, maintaining reactive power compensation accuracy; When an abnormal operating condition of sudden change in motor speed (≥300 r / min / s) is detected, a fast adjustment mode is triggered, shortening the adjustment response time of the solenoid valve 7 and the return air pipe 6 to within 0.3s, ensuring the dynamic following of the compensation system. Through the above adjustment mechanism, precise control of the liquid dielectric capacitor 8 under all operating conditions of the asynchronous motor 9 can be achieved, ensuring both rapid compensation capability during the startup phase and stability and safety during the operation phase, improving the overall energy efficiency of the motor system by 10-15%, while simplifying the complex control logic of traditional compensation devices.

[0165] Reference Figure 4 In controlling the gas flow and liquid dielectric circulation state between the liquid dielectric storage tank 1 and the liquid dielectric capacitor 8, this application achieves dynamic adaptation between the gas space and the dielectric circulation requirements through the movable air inlet 10 and the inverse correlation adjustment of the rotation speed. The specific steps are as follows:

[0166] The return gas pipe 6 is made of high-pressure resistant polytetrafluoroethylene pipe with an inner diameter of 12mm. One end of it is connected to the upper part of the storage tank through a flange interface with a sealing ring. The interface is located 80-100mm below the top of the storage tank to ensure that changes in the liquid level in the storage tank do not affect gas flow. The other end is connected to the component of the movable air inlet 10, which includes:

[0167] Air inlet 10: It adopts a copper cylindrical structure (outer diameter 10mm, length 30mm), and is equipped with a 40-mesh stainless steel filter screen at the end to prevent dielectric droplets from entering the pipeline and clogging the channel. Three air inlets with a diameter of 2mm are opened on the side wall to ensure smooth air entry.

[0168] The moving drive mechanism is as follows: A 500mm long dovetail groove guide rail is vertically fixed along the outer wall of the liquid dielectric capacitor 8. The guide rail is made of 6061 aluminum alloy with anodized surface treatment. The air inlet 10 mounting base is slidably connected to the guide rail. The mounting base is connected to the stepper motor through ball screw transmission. The stepper motor can drive the mounting base to move the air inlet 10 up and down along the guide rail.

[0169] Limiting structure 11: Mechanical limit switches are fixed at the upper and lower ends of the guide rail respectively. The highest limit switch is set 50mm below the top of the liquid dielectric capacitor 8 to limit the maximum adjustment height of the air inlet 10 and prevent it from exceeding the range of the liquid dielectric capacitor 8. The lowest limit switch is set 100mm above the bottom of the liquid dielectric capacitor 8 to limit the minimum adjustment height of the air inlet 10 and prevent the air inlet 10 from being immersed in the liquid dielectric. When the air inlet 10 moves to the limit position, the limit switch triggers a signal to the control system to forcibly stop the stepper motor.

[0170] Meanwhile, a capacitive liquid level sensor is installed on the inner wall of the capacitor to monitor the dielectric liquid level in real time; a diffused silicon pressure sensor is installed on the inner wall of the top of the capacitor to collect the internal pressure value in real time; and a rotary encoder is coaxially installed on the output shaft of the stepper motor to provide feedback on the current height position of the air inlet 10.

[0171] The relationship between the speed of asynchronous motor 9 and the target height of air inlet 10 was calibrated through bench testing. The specific process is as follows:

[0172] Simulating different motor speeds (500 r / min, 1000 r / min, and 1500 r / min), covering the start-up, acceleration, and rated operation phases, the height of the air inlet 10 was adjusted. The air inlet 10 height that stabilized the internal pressure of the capacitor within -50 to 50 Pa (balanced pressure range) and ensured that the dielectric flow rate matched the reactive power requirements was recorded.

[0173] At a speed of 500 r / min, during the initial startup, the dielectric needs to be injected quickly: the target height of the air inlet 10 is 150 mm, and it is far from the bottom of the capacitor. At this time, the gas space volume is about 0.6 L, which is suitable for an injection rate of 1.8-2.2 L / min.

[0174] At a rotational speed of 1000 r / min, during the acceleration phase, the dielectric flow rate is gradual: the target height of the air inlet 10 is 250 mm, the gas space volume is about 1.0 L, and it is suitable for a flow rate of 1.2-1.5 L / min.

[0175] Rotation speed 1500r / min, rated operation, dielectric needs to flow stably: air inlet 10 target height 350mm, gas space volume about 1.4L, adapted to a flow rate of 0.6-0.9L / min;

[0176] At the same time, the appropriate liquid level range is calibrated and determined according to the motor power. For example, an 11kW motor corresponds to a liquid level height of 200-300mm. The above parameters are stored in the database of the PLC control system to form an adjustment reference table.

[0177] During the operation of asynchronous motor 9, the control system follows the process of "speed acquisition - height adjustment - monitoring and correction" to achieve inverse correlation between the height of air inlet 10 and motor speed. The specific steps are as follows:

[0178] The Hall effect speed sensor installed at the output shaft end of the asynchronous motor 9 is activated. The sensor converts the collected speed signal into a 4-20mA analog signal and transmits it to the analog input module of the PLC control system. The control system performs digital filtering on the speed signal to remove high-frequency interference. When the speed change is ≤30r / min, it is determined to be a stable operating condition, and the current air inlet 10 height is maintained. When the speed change is ≥50r / min, it is determined to be an operating condition switch, and the air inlet 10 height adjustment program is triggered.

[0179] Based on the filtered real-time rotational speed, the control system retrieves the pre-stored rotational speed and target height reference table for air inlet 10, and outputs corresponding pulse signals to the stepper motor to drive air inlet 10 to move along the guide rail.

[0180] In low-speed operation, with a speed ≤800r / min, such as during initial startup or under heavy load at low speed: the motor's reactive power demand surges, requiring an accelerated dielectric injection speed (1.8-2.2L / min). The control system outputs a pulse signal to make the stepper motor rotate forward, driving the air inlet 10 to move down along the guide rail to a height of 150-200mm (distance from the bottom). The downward movement of the air inlet 10 reduces the gas space volume inside the capacitor (0.6-0.8L), which can avoid insufficient gas pressure caused by an excessively large gas space during rapid dielectric injection, ensuring that the dielectric is filled to the appropriate liquid level (200mm) within 10-15 seconds, quickly forming a capacitance of 5-8kVar to compensate for reactive power consumption in a timely manner.

[0181] Under medium speed conditions, 800-1200 r / min, such as during acceleration or under medium load: the motor speed gradually increases, the dielectric flow rate slows down (1.2-1.5 L / min), the control system outputs a pulse signal to make the stepper motor slowly reverse, driving the air inlet 10 to gradually move upward to a height of 200-300 mm; the gas space volume expands to 0.8-1.2 L, which can balance the air pressure fluctuation caused by the change in dielectric flow rate, and keep the air pressure inside the capacitor stable within the range of -30 to 30 Pa;

[0182] Under high-speed conditions, with a speed ≥1200r / min, such as rated operation or light-load high speed: the motor speed is stable, and the dielectric flow rate is low (0.6-0.9L / min). However, it is necessary to avoid excessive air pressure that may hinder the flow. The control system outputs a pulse signal to make the stepper motor continue to reverse, driving the air inlet 10 to move upward to a height of 300-400mm, close to the maximum limit. The gas space volume is expanded to 1.2-1.5L, providing sufficient buffer space for the dielectric flow, preventing the flow resistance from increasing due to air pressure exceeding 100Pa, and ensuring smooth dielectric flow.

[0183] During the height adjustment of the air inlet 10, the control system collects feedback signals from the liquid level sensor and the air pressure sensor in real time and executes the following correction logic:

[0184] When the liquid level in the capacitor is detected to reach the preset suitable liquid level range (e.g., 200-300mm) and the internal air pressure is within the preset balance air pressure range (-50 to 50Pa), the control system immediately stops outputting pulse signals to the stepper motor and locks the current position of the air inlet 10 through the electromagnetic brake to prevent height deviation due to vibration.

[0185] If the liquid level is within the acceptable range but the gas pressure exceeds the equilibrium range (e.g., gas pressure > 50 Pa), the control system outputs a fine-tuning pulse signal to drive the air inlet 10 upward by 5-10 mm to expand the gas space and reduce the gas pressure. If the gas pressure is < -50 Pa, the air inlet 10 is driven downward by 5-10 mm to reduce the gas space and increase the gas pressure until the gas pressure returns to the equilibrium range.

[0186] After the position of the air inlet 10 is locked, the control system continuously monitors the motor speed. When the speed change exceeds the preset threshold (±50r / min) again, the electromagnetic brake is unlocked and the above adjustment steps are repeated to achieve dynamic tracking of the height of the air inlet 10.

[0187] To ensure the safety and reliability of the air intake 10 height adjustment, multiple safety protection measures are implemented:

[0188] Over-limit protection: When the air inlet 10 moves to a distance of 50mm from the highest / lowest limit switch, the position signal fed back by the rotary encoder triggers an early warning, and the control system reduces the running speed of the stepper motor from 1000rpm to 300rpm; when the air inlet 10 touches the limit switch, the limit switch outputs an emergency stop signal, and the control system immediately cuts off the power supply to the stepper motor to prevent mechanical collision damage to the guide rail or the air inlet 10 assembly;

[0189] Abnormal air pressure handling: If the air pressure sensor detects that the air pressure inside the capacitor exceeds the safe range (±200Pa) and lasts for more than 3 seconds, the control system will automatically open the emergency exhaust valve on the top of the capacitor and drive the air inlet 10 to move to the middle position (250mm). After the air pressure drops to within ±50Pa, the emergency exhaust valve will be closed and normal adjustment will be restored.

[0190] Fault self-diagnosis: The control system performs an inlet 10 movement test every 30 minutes, controlling the inlet 10 to move up and down by 10mm. The actual position fed back by the rotary encoder is compared with the target position. If the deviation is >0.5mm, it is determined to be a stepper motor or ball screw fault, and an audible and visual alarm is immediately triggered. The control cabinet indicator light flashes and the buzzer sounds, and the fault code is recorded, such as "E01-Inlet 10 drive fault", to facilitate maintenance personnel to troubleshoot.

[0191] Through the above implementation steps, the height of the air inlet 10 of the return air pipe 6 is dynamically adapted to the speed of the asynchronous motor 9. This ensures the efficiency of dielectric filling by reducing the gas space at low speeds and avoids pressure obstruction by expanding the gas space at high speeds. Compared with the fixed air inlet 10 structure, the capacitance adjustment response speed is improved by 25-30%, and the gas pressure fluctuation amplitude is reduced by 40-50%. This further supports the liquid dielectric capacitor 8 to achieve accurate reactive power compensation of the asynchronous motor 9 under all operating conditions, ensuring the stability and energy efficiency of the system operation.

[0192] This application also discloses a reactive power compensation system based on an asynchronous motor and a capacitor, including a processor that executes the steps of the reactive power compensation method based on an asynchronous motor and a capacitor as described in any of the above embodiments.

[0193] This application also discloses a storage medium storing a program that, when executed by a processor, implements the steps of the reactive power compensation method based on asynchronous motors and capacitors described above.

[0194] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A reactive power compensation method based on an asynchronous motor and a capacitor, characterized in that, Includes the following steps: A liquid dielectric capacitor (8) is installed next to the asynchronous motor (9); Obtain the start command of the asynchronous motor (9), and in response to the start command, connect the liquid dielectric capacitor (8) to the start circuit where the asynchronous motor (9) is located; Open the injection solenoid valve (7) and the return solenoid valve (12) between the liquid dielectric capacitor (8) and the preset liquid dielectric storage tank (1); The liquid dielectric is injected from the liquid dielectric storage tank (1) into the liquid dielectric capacitor (8). The injection speed of the liquid dielectric is adjusted according to the motor speed of the asynchronous motor (9). The faster the motor speed, the faster the injection speed, and the slower the motor speed, the slower the injection speed. The amount of liquid dielectric injected into the liquid dielectric capacitor (8) is obtained. When the amount of injection is greater than the preset amount of injection or the start-up completion command of the asynchronous motor (9) is obtained, the injection of liquid dielectric is stopped, the liquid dielectric pump (5) is switched out, and the injection solenoid valve (7) and the return solenoid valve (12) are opened.

2. The reactive power compensation method based on asynchronous motor and capacitor according to claim 1, characterized in that, In the step of controlling the injection of liquid dielectric from the liquid dielectric storage tank (1) into the liquid dielectric capacitor (8), the injection of liquid dielectric is achieved by using a hydraulic coupler (4) in conjunction with a liquid dielectric pump (5), specifically including the following sub-steps: The input end of the hydraulic coupler (4) is connected to the preset liquid dielectric pump power take-off (3), and the output end of the hydraulic coupler (4) is connected to the liquid dielectric pump (5); the liquid dielectric pump power take-off (3) is fixedly installed at the middle position of the output shaft of the asynchronous motor (9) and the motor load (2), and is used to split part of the shaft output force from the output shaft of the asynchronous motor (9) and transmit it to the hydraulic coupler (4); The coupling degree of the hydraulic coupler (4) is adjusted according to the real-time motor speed of the asynchronous motor (9); the higher the real-time motor speed, the higher the coupling degree; the lower the real-time motor speed, the lower the coupling degree.

3. The reactive power compensation method based on asynchronous motors and capacitors according to claim 1, characterized in that, It also includes the following steps: Obtain the stop command of the asynchronous motor (9); Upon receiving the stop command, the asynchronous motor (9) is controlled to reverse at a preset reverse speed; The amount of liquid dielectric injected into the liquid dielectric capacitor (8) is monitored in real time. The asynchronous motor (9) is continuously controlled to reverse at the preset reverse speed until the amount of liquid dielectric injected into the liquid dielectric capacitor (8) is less than the preset starting amount, at which point the control of the asynchronous motor (9) to reverse is stopped.

4. The reactive power compensation method based on asynchronous motor and capacitor according to claim 1, characterized in that, It also includes the following steps: Obtain the stop command of the asynchronous motor (9); Upon receiving the stop command, the return gas pipe (6) is closed, and the exhaust valve preset on the liquid dielectric storage tank (1) is opened; The asynchronous motor (9) is controlled to work in conjunction with a preset air pump, so that the air pump injects gas into the upper part of the liquid dielectric capacitor (8); The amount of liquid dielectric injected into the liquid dielectric capacitor (8) is monitored in real time. The air pump is continuously controlled to inject gas into the upper part of the liquid dielectric capacitor (8) until the amount of liquid dielectric injected into the liquid dielectric capacitor (8) is less than the preset start amount, at which point the air pump is stopped from injecting gas.

5. The reactive power compensation method based on asynchronous motors and capacitors according to claim 1, characterized in that, The step of controlling the flow of the liquid dielectric between the liquid dielectric storage tank (1) and the liquid dielectric capacitor (8) includes the following sub-steps: The target flow rate of the liquid dielectric between the liquid dielectric storage tank (1) and the liquid dielectric capacitor (8) is obtained in real time, and the opening and closing degree of the solenoid valve (7) is adjusted according to the target flow rate. Alternatively, the target gas flow rate between the liquid dielectric storage tank (1) and the liquid dielectric capacitor (8) can be obtained in real time, and the compression degree of the return gas pipe (6) can be adjusted according to the inverse correlation of the target gas flow rate.

6. The reactive power compensation method based on asynchronous motor and capacitor according to claim 2, characterized in that, The method includes the following steps: The coupling degree of the hydraulic coupler (4) is adjusted according to the inverse correlation of the motor speed; the faster the motor speed, the lower the coupling degree of the hydraulic coupler (4); the slower the motor speed, the higher the coupling degree of the hydraulic coupler (4).

7. The reactive power compensation method based on asynchronous motor and capacitor according to claim 1, characterized in that, The method includes the following steps: The opening degree of the solenoid valve (7) is adjusted according to the inverse correlation of the motor speed; the faster the motor speed, the smaller the opening degree of the solenoid valve (7); the slower the motor speed, the larger the opening degree of the solenoid valve (7). Alternatively, the tightness of the return pipe (6) can be adjusted according to the inverse relationship of the motor speed; the faster the motor speed, the lower the tightness of the return pipe (6); the slower the motor speed, the higher the tightness of the return pipe (6).

8. The reactive power compensation method based on an asynchronous motor and a capacitor according to claim 1, characterized in that, The step of controlling the gas flow and liquid dielectric circulation state between the liquid dielectric storage tank (1) and the liquid dielectric capacitor (8) further includes the following sub-steps: One end of the return pipe (6) is connected to the upper part of the liquid dielectric storage tank (1), and the other end is provided with an air inlet (10) that can move up and down along the outer wall of the liquid dielectric capacitor (8). The air inlet (10) is connected to the internal cavity of the liquid dielectric capacitor (8), and the movement path of the air inlet (10) is preset with a limit structure (11) to limit the highest and lowest adjustment height of the air inlet (10) on the liquid dielectric capacitor (8). The real-time motor speed of the asynchronous motor (9) is collected in real time, and the height of the air inlet (10) of the return air pipe (6) on the liquid dielectric capacitor (8) is adjusted according to the collected real-time motor speed. The liquid level and internal pressure of the liquid dielectric capacitor (8) are monitored in real time. When the liquid level reaches the preset matching level and the internal pressure is within the preset balance pressure range, the height of the air inlet (10) of the return air pipe (6) is stopped, and the current position of the air inlet (10) is maintained until the real-time motor speed change of the asynchronous motor (9) exceeds the preset threshold.

9. A reactive power compensation system based on an asynchronous motor and a capacitor, characterized in that, Includes a processor, wherein the processor performs the steps of the reactive power compensation method based on an asynchronous motor and a capacitor as described in any one of claims 1-8.

10. A storage medium, characterized in that, The storage medium stores a program that, when executed by a processor, implements the steps of the reactive power compensation method based on an asynchronous motor and a capacitor as described in any one of claims 1-8.

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