Portable transformer oil filter structure and oil pump flow velocity control method

Abstract

The invention discloses a portable transformer oil filter structure and an oil pump flow speed control method, the oil filter structure comprises an oil inlet, a ball valve, a coarse filter, an oil pump, a flow meter, a pressure gauge, a pressure release valve, a first isolation valve, a fine filter, a second isolation valve, a check valve, an oil outlet and a third isolation valve which are connected in sequence; the flow velocity control method comprises the following steps: connecting a power supply and connecting an oil filter with a pipeline according to a use scene; according to whether the filter element on-off isolating valve is used or not, the operation with the filter element or without the filter element is selected; an operation mode is selected, and the oil filter is started and operated; the method specifically comprises the steps that a system configures starting parameters according to a selected operation mode; the oil filter is started, and flow speed control is achieved through an MFAC controller; switching the operation mode of the oil filter; the method specifically comprises the steps that a system configures parameters according to a to-be-switched operation mode; and the oil filter stably operates at the new operation point, and the flow rate control is realized by the MFAC controller.

Description

Technical Field

[0001] The present application relates to the technical field of oil filter flow rate control, and in particular to a portable transformer oil filter structure and an oil pump flow rate control method. Background Art

[0002] When operating, power transformers are affected by factors such as equipment operating status, equipment sealing, and ambient temperature, and may face problems such as insulating oil aging and oil level fluctuations. To ensure the normal operation of the transformer and extend its service life, professional equipment such as oil filters are required to improve the quality of the insulating oil, and oil replenishment or oil draining operations should be performed in a timely manner according to actual conditions.

[0003] However, the existing oil filter lacks effective control over the flow rate of insulating oil. When the oil is replenished or filtered under power, the gas protection may malfunction due to the excessive oil flow rate, which may cause the three-phase transformer to trip, posing a great safety hazard. Even if the tripping pressure plate of the transformer protection is temporarily withdrawn when the oil filter is used, the gas relays of imported manufacturers such as MR and ABB have no reset function and still need to be manually reset when malfunctioning. This requirement cannot be achieved when the transformer is operating normally. Summary of the invention

[0004] The present application provides a portable transformer oil filter structure and an oil pump flow rate control method to solve the above-mentioned technical problems.

[0005] On the one hand, the present application provides a portable transformer oil filter structure, including an oil inlet, a ball valve, a coarse filter, an oil pump, a flow meter, a pressure gauge, a pressure relief valve, a first isolation valve, a fine filter, a second isolation valve, a check valve and an oil outlet and a third isolation valve connected in sequence; wherein, one end of the oil inlet is connected to a transformer or an oil tank, one end of the oil outlet is connected to a transformer, and the third isolation valve is connected between the pressure relief valve and the check valve.

[0006] The present application also provides an oil pump flow rate control method, which is applied to the aforementioned portable transformer oil filter structure, and the method includes: step S1: connecting the power supply and connecting the oil filter to the pipeline according to the usage scenario; the oil pump of the oil filter adopts a variable frequency squirrel cage asynchronous motor, including a grid-side converter, a DC link, a machine-side converter, and an asynchronous motor; step S2: depending on whether a filter element disconnect isolation valve is used, select operation with or without a filter element; step S3: selecting an operating mode and starting the oil filter; step S3 is specifically: the system configures startup parameters according to the selected operating mode; the oil filter is started, and flow rate control is achieved with an MFAC controller; step S4: switching the oil filter operating mode; step S4 is specifically: the system configures parameters according to the operating mode to be switched to; the oil filter runs smoothly at the new operating point, and flow rate control is achieved with an MFAC controller.

[0007] In one implementation of the present application, the switching process includes:

[0008] After the oil filter is turned on, the initial operation mode is selected, and then the startup parameters are configured according to the selection result of the initial operation mode to implement startup control;

[0009] If the mode needs to be switched during the operation of the oil filter, the system will configure the switching parameters after selecting the switching mode and perform switching control.

[0010] In one implementation of the present application, in the startup control, the absolute value of the initial slope of the inertia link is set to k m , the flow rate before control is v* K1 , switch to the desired operation control setting flow rate v* K2 , then the time constant is defined as follows:

[0011]

[0012] In one implementation of the present application, the grid-side converter adopts a dual closed-loop vector control method of DC voltage control and reactive power control.

[0013] In one implementation of the present application, the voltage equation of the magnetic field vector control of the asynchronous motor can be expressed as follows:

[0014]

[0015]

[0016]

[0017]

[0018] Among them, ψ sd and ψ sq are the stator flux of d-axis and q-axis respectively; ψ rd and ψ rq are the rotor flux of d-axis and q-axis respectively; i sd and i sq are the stator currents of the d-axis and q-axis respectively; i rd and i rq are the rotor currents of the d-axis and q-axis respectively; u sd and u sq are the stator voltages of the d-axis and q-axis respectively; u rd and u rq are the rotor voltages of the d-axis and q-axis respectively; R s and R r are the stator resistance and rotor resistance respectively; ω 1 is the stator rotation angular velocity, ωs is the slip angular velocity.

[0019] In one implementation of the present application, the motion equation of the asynchronous motor is as follows:

[0020]

[0021] Among them, T e is the electromagnetic torque of the motor, T L is the load torque, J is the moment of inertia, n p is the pole pair number, ω r is the rotor rotation angular velocity.

[0022] In one implementation of the present application, the method further includes:

[0023] Let L m is the excitation resistance of the asynchronous motor, and the asynchronous motor torque equation is solved based on the following formula:

[0024] T e =n p L m (i sq i rd -i sd i rq )=n p L m ψ rd i sq

[0025] The mathematical model of the asynchronous motor is organized as follows:

[0026]

[0027]

[0028]

[0029]

[0030] Among them, L r is the rotor inductance, L s is the stator inductance, s is the leakage coefficient:

[0031] In one implementation of the present application, the method also includes: based on the mathematical model of the asynchronous motor, two multi-input, multi-output model-free adaptive controllers are used to replace the traditional proportional differential controller, and the pseudo-Jacobian matrix constructed by the port parameters is estimated and used to construct a control link; the flow rate measurement signal of the flow meter is introduced for motor control, the flow rate of the insulating oil is adjusted, and the influence of noise and fluctuations in the intermediate links is avoided.

[0032] The present application provides a portable transformer oil filter structure and an oil pump flow rate control method, and proposes an oil filter oil pump motor control strategy involving flow rate control, which solves the problem that the existing oil filter cannot control the oil flow rate, which may cause the system to trip incorrectly; and develops oil filter operation modes under multiple scenarios, which is convenient for on-site maintenance personnel to adopt different oil filter operation modes according to work scenarios and needs, thereby ensuring the efficiency of on-site oil filtering work. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 A structural diagram of a portable transformer oil filter provided in an embodiment of the present application;

[0035] Figure 2 A flowchart of the oil filter startup control and switching control provided in the embodiment of the present application;

[0036] Figure 3 A block diagram of the oil filter startup control and switching control provided in the embodiment of the present application;

[0037] Figure 4 A structural diagram of an oil pump motor provided in an embodiment of the present application;

[0038] Figure 5 A control block diagram of the oil pump motor provided in an embodiment of the present application;

[0039] Figure 6 Equivalent framework diagram of the MFAC controller provided in the embodiment of the present application;

[0040] Figure 7 A control flow chart of the MFAC controller provided in an embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0042] The embodiment of the present application provides a portable transformer oil filter structure and an oil pump flow rate control method. The technical solution proposed in the embodiment of the present application is described in detail below with reference to the accompanying drawings.

[0043] Figure 1 A structure diagram of a portable transformer oil filter provided in an embodiment of the present application. The portable oil filter with controllable flow rate is composed of an oil inlet, a ball valve, a coarse filter, an oil pump, a flow meter, a pressure gauge, a pressure relief valve, an isolation valve 1, a fine filter, an isolation valve 2, an isolation valve 3, a check valve and an oil outlet. Figure 1 As shown. In order to achieve controllable flow rate, the flow rate signal of the flow meter is introduced into the control link of the oil pump motor; the pressure gauge introduces the pressure signal to the oil pump motor to participate in the power-off protection of the oil filter, ensuring that the motor automatically powers off when the pipeline pressure is too high, avoiding pipeline bursts caused by problems such as oil filter blockage and motor failure; the pressure relief valve automatically releases pressure when a certain pressure limit is met, forming a "double protection" with the power-off protection of the oil filter; the circuit composed of isolation valve 1, fine filter, isolation valve 2 and isolation valve 3 is parallel, and the oil filter equipment can be selected to run with or without a filter element. When the oil level is too high and the oil filter needs to be drained to lower the oil level, the operation without a filter element can be selected to reduce the consumption of the filter element.

[0044] The above is a control method provided in an embodiment of the present application. The embodiment of the present application also provides an oil pump flow rate control method, which mainly includes:

[0045] Step S1: Connect the power supply and connect the oil filter to the pipeline according to the usage scenario; the oil pump of the oil filter adopts a variable frequency squirrel cage asynchronous motor, including a grid-side converter, a DC link, a machine-side converter, and an asynchronous motor;

[0046] Step S2: Depending on whether the filter element is used to open the isolation valve, select operation with or without the filter element;

[0047] Step S3: Selecting an operation mode and starting the oil filter; Step S3 specifically includes: the system configures the start-up parameters according to the selected operation mode; the oil filter is started, and the flow rate is controlled by the MFAC controller;

[0048] Step S4: Switching the oil filter operation mode; Step S4 specifically includes: the system configures parameters according to the operation mode to be switched to; the oil filter operates smoothly at the new operation point, and the flow rate control is achieved by the MFAC controller.

[0049] In the embodiment of the present application, the oil filter operation mode described in step S3 and step S4, and its startup control strategy and operation mode switching control strategy are as follows:

[0050] (1) Slow mode: oil is injected at a constant speed of 0.6 m / s, which is used for oil replenishment without power outage during transformer operation;

[0051] (2) Adjustable mode: The oil filter mode in which the flow rate can be adjusted between the minimum and maximum values ​​is used in scenarios where the oil injection amount needs to be flexibly adjusted according to the actual oil level, taking into account both oil volume control and oil injection and discharge efficiency;

[0052] (3) Fast mode: Inject and release oil at the maximum power speed. It is used in the scene where fast injection and release of oil is required during the hanging casing and oil storage cabinet filling and deflation experiments. When the oil filter is in use, the operation and switching methods of various modes are as follows: Figure 2 shown.

[0053] Furthermore, after the oil filter is turned on, the initial operation mode is selected, and then the startup parameters are configured according to the selection result of the initial mode to start the machine, and then the machine runs in the selected mode. If the mode needs to be switched during the operation of the oil filter, the system will configure the switching parameters after selecting the switching mode and perform the switching control. The control block diagram of the startup control and the switching control is shown in the figure. Figure 3 As shown in the inertia link, v* is the set value of the oil filter mode operation control.

[0054] The control process of start-up control and switching control is the same, but the parameter setting values ​​are different. Let the absolute value of the initial slope of the inertia link be k m , the flow rate before control is v* K1 , switch to the desired operation control setting flow rate v* K2 . Then define the time constant:

[0055]

[0056] To reduce speed overshoot during startup control, set k m is 0.5, and k is set when switching control m Set it to 2 for faster response.

[0057] The motor control strategy of the oil filter pump described in step S3 and step S4 is:

[0058] The oil filter pump adopts a variable frequency squirrel cage asynchronous motor, which consists of four parts: grid-side converter, DC link, machine-side converter and asynchronous motor. Figure 4 shown.

[0059] The grid-side converter and the generator-side converter are controlled on and off by 6 fully controlled power electronic devices respectively, and the control method is double closed-loop vector control. Among them, the grid-side converter adopts the double closed-loop vector control method of DC voltage control and reactive power control which is more common in this field.

[0060] The dual closed-loop vector control method of the machine-side converter generally adopts rotor magnetic field orientation, which includes a speed outer loop, a flux outer loop and a current inner loop. The present invention uses flow velocity as the outer loop control target and adopts model-free adaptive control theory to realize inner and outer loop tracking control. The specific method is as follows.

[0061] For the asynchronous motor M of the oil pump, the voltage equation of its magnetic field fixed vector control can be expressed as follows:

[0062]

[0063]

[0064]

[0065]

[0066] In the formula, ψ sd and ψ sq are the stator flux of d-axis and q-axis respectively; ψ rd and ψ rq are the rotor flux of d-axis and q-axis respectively; i sd and i sq are the stator currents of the d-axis and q-axis respectively; i rd and i rq are the rotor currents of the d-axis and q-axis respectively; u sd and u sq are the stator voltages of the d-axis and q-axis respectively; u rd and u rq are the rotor voltages of the d-axis and q-axis respectively; R s and R r are the stator resistance and rotor resistance respectively; ω 1 is the stator rotation angular velocity, ω s is the slip angular velocity.

[0067] The motion equation of the asynchronous motor is as follows:

[0068]

[0069] Where, T e is the electromagnetic torque of the motor, T L is the load torque, J is the moment of inertia, n p is the pole pair number, ω r is the rotor rotation angular velocity.

[0070] Let L m is the excitation resistance of the asynchronous motor, then the torque equation of the asynchronous motor is as follows:

[0071] T e =n p Lm (i sq i rd -i sd i rq )=n p L m ψ rd i sq

[0072] Furthermore, the mathematical model of the asynchronous motor can be expressed as:

[0073]

[0074]

[0075]

[0076]

[0077] In the above formula, L r is the rotor inductance, L s is the stator inductance, s is the leakage coefficient:

[0078] The mathematical model of the asynchronous motor above constructs ψ rd with i sd ,ω r with i sq 、i sd with u sd 、i sq with u sq The conventional method is to use four proportional-differential controllers to construct a double closed-loop control. The present invention makes the following improvements:

[0079] (1) Two multi-input and multi-output model-free adaptive controllers are used to replace the traditional proportional-derivative controller. The pseudo-Jacobian matrix constructed by the port parameters is estimated and used to construct the control link to obtain better robustness and stability.

[0080] (2) Considering the proportional relationship between the rotational speed and the oil pump flow rate, the flow rate measurement signal of the flow meter is introduced for motor control, which can more directly adjust the flow rate of the insulating oil and avoid the influence of noise and fluctuations in the intermediate links.

[0081] The improved oil pump motor control block diagram is as follows: Figure 5 As shown, v is the insulating oil flow rate measured by the oil filter flow meter, ψ* rd 、v* g 、i* sd 、i* sq They are respectively rd 、v、i sd 、isq control objectives.

[0082] For the MFAC controller of the above model, the other control system connected to its input and output ports is a highly nonlinear system, that is, a two-input, two-output discrete-time nonlinear system. This nonlinear system can be expressed by compact dynamic linearization as follows:

[0083] y(k+1)=f(y(k),…,y(kn y ),u(k),…,u(kn u ))

[0084] Where f(·) represents the nonlinear system controlled by MFAC; u(k) and y(k) are both 2×1 column vectors, representing the output data and input data of MFAC at time k, and are also the input data and output data of the controlled nonlinear system; n y and n u represents the order of the controlled nonlinear system.

[0085] The equivalent framework of MFAC control for controlled nonlinear systems is as follows: Figure 6 shown.

[0086] The following assumptions are made for the controlled nonlinear system:

[0087] (1) Except for a limited number of time points, the partial derivative of the nonlinear system f(·) with respect to the input u(k) of the system is continuous.

[0088] (2) Except for a limited number of time points, the partial derivative of the output y(k) of the nonlinear system f(·) with respect to the input u(k) of the system is bounded, that is, the following formula:

[0089] ‖y(k+1)-y(k)‖≤c‖u(k)-u(k-1)‖

[0090] Among them, C is a bounded positive constant.

[0091] For the oil pump motor control system, except for the limited time points of sudden disconnection and short circuit, the above assumptions (1) and (2) are both valid.

[0092] Furthermore, the nonlinear system f(·) is expressed in the form of y(k) and u(k) and their partial derivatives through dynamic linearization, as follows:

[0093] Δy(k+1)=y(k)+Φ(k)Δu(k)

[0094] Among them, Δu(k)=u(k)-u(k-1) is the change of the system disturbance signal, and ||u(k)|| is a bounded quantity; the time-varying parameter Φ(k) is the pseudo-Jacobi matrix of f(·), and Φ(k) is bounded under the premise that f(·) satisfies Assumption 2, satisfying ||Φ(k)||≤C.

[0095] Consider the following criterion function:

[0096] J(u(k))=||y * (k+1)-y(k+1)|| 2 +λ||u(k)-u(k-1)|| 2

[0097] Where λ>0 is the weight factor used to penalize excessive changes in the control input, and y*(k+1) is the desired output signal.

[0098] According to the model-free adaptive control theory, combined with the dynamic linearization data model, the control algorithm obtained by the criterion function can be expressed as follows:

[0099]

[0100] Among them, 0<ρ<1 is the weight factor, which can make the control algorithm more general.

[0101] Due to the time-varying nature of the Φ(k) parameter, it still needs to be obtained through parameter estimation. The parameter estimation criterion function is defined as follows: Among them, μ>0 is the weight factor used to penalize excessive changes in control input; is an estimate of the pseudo-Jacobian matrix Φ(k).

[0102] According to the model-free adaptive control theory, combined with the dynamic linearization data model, the pseudo-Jacobi matrix estimation algorithm obtained by the criterion function can be expressed as follows:

[0103]

[0104] Among them, 0<h≤2 is the step size factor. Therefore, the control process of MFAC in discrete space is as follows Figure 7 As mentioned above, due to Figure 7 Two MFAC controllers are used in the oil pump motor control block diagram shown, so their control links are constructed separately according to the above-mentioned model-free adaptive control principle.

[0105] Each embodiment in this application is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0106] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0107] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A portable transformer oil filter structure, characterized in that: It includes an oil inlet, a ball valve, a coarse filter, an oil pump, a flow meter, a pressure gauge, a pressure relief valve, a first isolation valve, a fine filter, a second isolation valve, a check valve, an oil outlet and a third isolation valve connected in sequence; wherein one end of the oil inlet is connected to a transformer or an oil tank, one end of the oil outlet is connected to a transformer, and the third isolation valve is connected between the pressure relief valve and the check valve.

2. A method for controlling oil pump flow rate, applied to a portable transformer oil filter structure as claimed in claim 1, characterized in that: The method comprises: Step S1: Connect the power supply and connect the oil filter to the pipeline according to the usage scenario; the oil pump of the oil filter adopts a variable frequency squirrel cage asynchronous motor, including a grid-side converter, a DC link, a machine-side converter, and an asynchronous motor; Step S2: Depending on whether the filter element is used to open the isolation valve, select operation with or without the filter element; Step S3: Selecting an operation mode and starting the oil filter; Step S3 specifically includes: the system configures the start-up parameters according to the selected operation mode; the oil filter is started, and the flow rate is controlled by the MFAC controller; Step S4: Switching the oil filter operation mode; Step S4 specifically includes: the system configures parameters according to the operation mode to be switched to; the oil filter operates smoothly at the new operation point, and the flow rate control is achieved by the MFAC controller.

3. The oil pump flow rate control method according to claim 2, characterized in that: The switching process includes: After the oil filter is turned on, the initial operation mode is selected, and then the startup parameters are configured according to the selection result of the initial operation mode to implement startup control; If the mode needs to be switched during the operation of the oil filter, the system will configure the switching parameters after selecting the switching mode and perform switching control.

4. The oil pump flow rate control method according to claim 1, characterized in that: The MFAC controller is a two-input, two-output discrete-time nonlinear system, which can be expressed as follows through compact dynamic linearization: y(k+1)=f(y(k),…,y(k-n y ),u(k),…,u(k-n u )) Where f(·) represents the nonlinear system controlled by MFAC; u(k) and y(k) are both 2×1 column vectors, representing the output data and input data of MFAC at time k, and are also the input data and output data of the controlled nonlinear system; n y and n u represents the order of the controlled nonlinear system.

5. The oil pump flow rate control method according to claim 3, characterized in that: In the startup control, let the absolute value of the initial slope of the inertia link be k m , the flow rate before control is v* K1 , switch to the desired operation control setting flow rate v* K2 , then the time constant is defined as follows:

6. The oil pump flow rate control method according to claim 2, characterized in that: The grid-side converter adopts a double closed-loop vector control method of DC voltage control and reactive power control.

7. The oil pump flow rate control method according to claim 2, characterized in that: The voltage equation of the magnetic field vector control of the asynchronous motor can be expressed as follows: Among them, ψ sd and ψ sq are the stator flux of d-axis and q-axis respectively; ψ rd and ψ rq are the rotor flux of d-axis and q-axis respectively; i sd and i sq are the stator currents of the d-axis and q-axis respectively; i rd and i rq are the rotor currents of the d-axis and q-axis respectively; u sd and u sq are the stator voltages of the d-axis and q-axis respectively; u rd and u rq are the rotor voltages of the d-axis and q-axis respectively; R s and R r are the stator resistance and rotor resistance respectively; ω1 is the stator rotation angular velocity, ω s is the slip angular velocity.

8. The oil pump flow rate control method according to claim 2, characterized in that: The motion equation of the asynchronous motor is as follows: Among them, T e is the electromagnetic torque of the motor, T L is the load torque, J is the moment of inertia, n p is the pole pair number, ω r is the rotor rotation angular velocity.

9. The oil pump flow rate control method according to claim 2, characterized in that: The method further comprises: Based on the mathematical model of the asynchronous motor, two multi-input and multi-output model-free adaptive controllers are used to replace the traditional proportional-derivative controller, and the pseudo-Jacobian matrix constructed by the port parameters is estimated and used to construct the control link; The flow rate measurement signal from the flow meter is introduced to control the motor and adjust the flow rate of the insulating oil to avoid the influence of noise and fluctuations in the intermediate links.

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