Water-cooled electromagnetic coil system and temperature control method

Abstract

The invention relates to the technical field of electromagnetic coils, and discloses a water-cooled electromagnetic coil system and a temperature control method. A cooling device; a water inlet of the spiral hollow pipe is connected with a water outlet of the water pump water tank, a water outlet of the spiral hollow pipe is connected with a water inlet of the water pump water tank, and the interior of the spiral hollow pipe is used for circulating cooling liquid; the wire is wound between the two spiral hollow pipes, and the wire and the spiral hollow pipes are connected in series to form an electromagnetic coil group; the control subsystem is used for adjusting the cooling liquid temperature and the cooling speed of the cooling liquid in the water pump water tank under the condition that the cooling liquid temperature in the water pump water tank is higher than the target cooling liquid temperature; and the controller is also used for adjusting the flow of the cooling liquid flowing through the spiral hollow pipe under the condition that the outlet cooling liquid temperature at the water outlet of the water pump water tank is higher than the target cooling liquid temperature. According to the invention, the temperature stability of the electromagnetic coil can be ensured while the required magnetic field intensity is met.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic coils, and in particular to a water-cooled electromagnetic coil system and a temperature control method. Background Art

[0002] Magnetic Particle Imaging (MPI) is a type of imaging based on the response of magnetic nanoparticles in an external magnetic field. In the MPI system, it is necessary to use an electromagnetic coil to pass current to achieve magnetic fields of different frequencies and intensities to achieve specific functions. Among them, the excitation coil is a key module. Generally, a sinusoidal current signal with a frequency of 25khz is used to generate a variable magnetic field of the mT level, which is used to excite magnetic nanoparticles (SuperparamagneticIronOxideNanoparticles, SPIONs) to produce a nonlinear magnetization response.

[0003] In order to achieve a stronger magnetic particle signal, the excitation coil needs to pass tens of amperes of current for a long time to stimulate the change of the magnetization vector of the superparamagnetic magnetic particles, and the large current brings about the heating problem of the resistive coil. In addition, the heat generated on the coil will gradually accumulate over time, causing the impedance of the coil to change, which in turn affects the phase and amplitude drift in the driving field and receiving circuit, affects the stability of the system background, and further affects the achievable signal-to-noise ratio and resolution. At the same time, the temperature rise of the coil will also increase the thermal noise of the system, increase the noise of the generated image, and seriously affect the quality of imaging; this part of the thermal noise is often not completely filtered out by signal processing methods such as filtering algorithms. Therefore, in order to ensure the stability of the MPI device signal and the imaging effect, it is necessary to solve the heat dissipation problem of the MPI excitation coil while ensuring the intensity of the excitation magnetic field.

[0004] At present, in response to the Joule heating problem of electromagnetic coils, some researchers have proposed a method to control the temperature of coils in magnetic nanoparticle imaging systems based on phase change thermal storage technology, that is, using PCM to make coil brackets to absorb the Joule heat of the coils; but the thermal conductivity of PCM is low, which makes them inefficient in absorbing or releasing heat, and is only suitable for low-power electromagnetic coils such as handheld devices; in addition, the heat absorption performance of PCM decreases rapidly after multiple phase change cycles. In addition, some researchers have proposed to improve the thermal stability of the system by actively heating the current-carrying elements in the coil and trimming the resonant circuit to the required frequency. However, when the scale of the MPI imaging system increases, a precise and complex control system is required to maintain the temperature of the capacitor bank, and it is also a great challenge to ensure that the heat energy is evenly distributed to all capacitors in practical applications. Although some domestic researchers use immersion cooling technology to place coils wound with litz copper wire or enameled wire in pressurized coolant (such as water or oil) to cool the coils, it can only cool the surface of the coil, and the cooling effect is difficult to control. In addition, in some related technologies, a hollow copper tube is used to wind the coil, and a coolant is circulated inside to reduce the temperature rise of the coil when it is subjected to a large current or a pulse current for a long time. However, in order to meet the magnetic field strength requirements of the MPI system, if only a coil wound by a copper tube is used, the number of turns of the coil needs to be increased, which will cause the coil volume to be too large. In addition, if a copper tube with a larger aperture cross-section is used to pass a larger current, although it can be achieved, doing so will increase the inductance of the coil. Larger inductance requires a higher voltage to generate the required driving magnetic field current, and it is unsafe to use high voltage near the test patient. In addition, the internal space of the MPI device is limited, and the output capacity of the power amplifier is also limited. These factors limit the increase in coil volume and the increase in current. Therefore, in order to achieve the required magnetic field strength under limited space and power conditions, a new MPI excitation coil structure and control method are urgently needed. Summary of the invention

[0005] In view of this, the present invention provides a water-cooled electromagnetic coil system and a temperature control method, so as to achieve the goal of maintaining the temperature of the electromagnetic coil while meeting the required magnetic field strength.

[0006] In a first aspect, the present invention provides a water-cooled electromagnetic coil system, the system comprising:

[0007] A water pump tank, the interior of which is used to contain coolant;

[0008] A cooling device for adjusting the temperature of the coolant in the water pump tank;

[0009] A spiral hollow tube, the water inlet of the spiral hollow tube is connected to the water outlet of the water pump tank, the water outlet of the spiral hollow tube is connected to the water inlet of the water pump tank, and the interior of the spiral hollow tube is used for circulating coolant;

[0010] The wire is wound between two spiral hollow tubes, and the wire and the spiral hollow tube are connected in series to form an electromagnetic coil group;

[0011] The control subsystem is used to adjust the coolant temperature and cooling speed of the coolant in the water pump tank when the coolant temperature in the water pump tank is higher than the target coolant temperature; and is also used to adjust the coolant flow rate flowing through the spiral hollow pipe when the outlet coolant temperature at the water outlet of the water pump tank is higher than the target coolant temperature.

[0012] In an optional embodiment, the control subsystem includes a temperature control device and a multi-stage cascade PID control device, and the temperature control device includes:

[0013] The temperature real-time detection module is respectively arranged at multiple preset positions of the water pump tank, the spiral hollow pipe and the wire, and is used to detect the temperature of the detection point at the corresponding position, and send the temperature of the detection point to the multi-stage cascade PID control module;

[0014] The cooling temperature control module is used to adjust the cooling device according to the temperature control signal sent by the multi-stage cascade PID control module to reduce the coolant temperature in the water pump water tank to the target coolant temperature.

[0015] In an optional embodiment, the temperature control module further includes:

[0016] The flow output control module is used to adjust the flow of the coolant flowing through the spiral hollow tube according to the flow control signal sent by the multi-stage cascade PID control module.

[0017] In an optional embodiment, the cooling device is a fan, and the temperature control module further includes:

[0018] The cooling speed control module is used to adjust the running speed of the fan according to the cooling speed control signal sent by the multi-stage cascade PID control module to adjust the cooling speed of the coolant in the water pump water tank.

[0019] In an optional embodiment, the control subsystem further includes:

[0020] The flow parameter simulation module is connected with the multi-stage cascade PID control module and is used to simulate the output flow corresponding to the coolant at different temperatures.

[0021] In an optional embodiment, both the inner surface and the outer surface of the spiral hollow tube are provided with an insulating layer.

[0022] In a second aspect, the present invention provides a temperature control method applicable to the water-cooled electromagnetic coil system described in any one of the above embodiments, the method comprising:

[0023] When the current coolant temperature of the coolant in the water pump water tank is higher than the target coolant temperature, adjusting the coolant temperature and cooling speed of the coolant in the water pump water tank;

[0024] When the outlet coolant temperature at the water outlet of the water pump tank is still higher than the target coolant temperature, the coolant flow rate flowing through the spiral hollow tube is adjusted.

[0025] In an optional embodiment, before adjusting the coolant temperature and cooling speed of the coolant in the water pump water tank, the method includes:

[0026] determining a temperature difference between a current coolant temperature and a target coolant temperature;

[0027] Establish a temperature expression function based on the temperature difference;

[0028] The temperature expression function is: V f =C×Δt″′ 2 -dΔt″′;

[0029] Where V f is the rotation speed of the cooling device, Δt″′ is the temperature difference, the value range of C is 0.5-1.5, and the value range of d is 0.8-1.2.

[0030] In an optional embodiment, before adjusting the flow rate of the coolant flowing through the spiral hollow tube, the method further includes:

[0031] Establishing a flow output expression function between coolants at different temperatures and corresponding output flows;

[0032] The flow output expression function is:

[0033] Wherein, V1 is the coolant flow rate corresponding to the outlet coolant temperature, V2 is the coolant flow rate corresponding to the target coolant temperature, h1 is the convective heat transfer coefficient corresponding to the outlet coolant temperature, and h2 is the convective heat transfer coefficient corresponding to the target coolant temperature.

[0034] In an optional embodiment, adjusting the coolant temperature of the coolant in the water pump water tank includes:

[0035] The coolant temperature is controlled based on the outermost loop PID control function, and the outermost loop PID control function is:

[0036]

[0037] Where k is the sampling number, i is the integration number, u(k) is the control value of the coolant temperature at the kth moment; k p1 , k i1 , k d1are the outermost loop coefficients, ΔT(k) is the temperature difference between the coolant temperature at the kth moment and the target coolant temperature; is the coolant temperature difference between the kth moment and the k-1th moment;

[0038] Adjusting the cooling rate of the coolant in the water pump tank includes:

[0039] The cooling speed is controlled based on the intermediate loop PID control function, and the intermediate loop PID control function is:

[0040]

[0041] Where u(k)′ is the control value of cooling rate at the kth moment, k p2 , k i2 , k d2 are the intermediate ring coefficients, Δt v (k) is the cooling rate at the kth moment, is the difference between the coolant temperature difference and the cooling rate difference, where the cooling rate difference is the cooling rate difference between the kth moment and the k-1th moment;

[0042] Regulating coolant flow through the spiral hollow tube includes:

[0043] Based on the innermost loop PID control function, the coolant flow is controlled, and the middle loop PID control function is:

[0044]

[0045] Where u(k)″ is the control amount of the coolant flow at the kth moment, k p3 , k i3 , k d3 is the innermost loop coefficient, ΔV(k) is the coolant flow rate at the kth moment, is the difference between the cooling speed difference and the coolant flow rate difference, wherein the coolant flow rate difference is the coolant flow rate difference between the kth moment and the k-1th moment.

[0046] The water-cooled electromagnetic coil system and temperature control method provided by the present invention can not only solve the problem of overheating of the MPI electromagnetic coil while meeting the required magnetic field strength, but also solve the problem of impedance drift, thermal noise and magnetic field instability in the working state of the MPI system caused by Joule heat of the electromagnetic coil of the magnetic nanoparticle system, which affect the imaging quality, and can also effectively reduce the thermal noise and system power consumption during the working process, thereby improving the imaging quality of the MPI. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 is a schematic structural diagram of a water-cooled electromagnetic coil according to an embodiment of the present invention;

[0049] Figure 2 is a schematic structural diagram of a two-layer electromagnetic coil according to an embodiment of the present invention;

[0050] Figure 3 is a cross-sectional schematic diagram of an electromagnetic coil assembly according to an embodiment of the present invention;

[0051] Figure 4 is a schematic flow chart of a water-cooled electromagnetic coil temperature control system according to an embodiment of the present invention;

[0052] Explanation of the reference numerals: 1-water pump and water tank, 2-spiral hollow pipe, 3-conducting wire, 4-first main road, 5-first pipeline connector, 6-first branch road, 7-second branch road, 8-second pipeline connector, 9-second main road. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0054] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0055] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0057] Generally speaking, immersion cooling of Leeds coils or liquid cooling of hollow copper tube coils is often limited by system space, power consumption and other issues, which will lead to significant Joule heat temperature rise and make it difficult to ensure the constant temperature of the electromagnetic coil. This will further lead to an increase in the system's thermal noise, increase the noise of the system-generated images, and affect the quality of magnetic particle imaging.

[0058] In this embodiment, a water-cooled electromagnetic coil system is provided, which can be used for magnetic particle imaging. Figure 1 It is a schematic structural diagram of a water-cooled electromagnetic coil system according to an embodiment of the present invention, including a water pump water tank 1, a cooling device (not shown in the figure), a spiral hollow tube 2, a wire 3, and a control subsystem (not shown in the figure), specifically as follows.

[0059] The water pump water tank 1 is used to contain cooling liquid inside the water pump water tank 1. The cooling liquid is insulating cooling liquid.

[0060] The cooling device is used to adjust the temperature of the coolant in the water pump tank 1. In this embodiment, the cooling device is a fan, which can be arranged on the top of the water pump tank 1 to cool the coolant.

[0061] The spiral hollow tube 2 has a water inlet connected to a water outlet of the water pump tank 1, and a water outlet of the spiral hollow tube 2 is connected to a water inlet of the water pump tank 1. The interior of the spiral hollow tube 2 is used for circulating cooling liquid. The spiral hollow tube 2 in this embodiment can be a hollow copper tube.

[0062] In terms of water connection, the multi-layer spiral hollow tube 2 can use a main line for water supply and a main line for water return. The water inlet and outlet of each layer of spiral hollow tube 2 are respectively used as branch loops, which are connected to the main line through pipe joints to complete inflow and outflow, and each branch loop constitutes a circulating water circuit of the coolant.

[0063] Specifically, refer to Figure 1As shown, the water pump tank 1 is connected to the first main road 4 for water supply, and the first branch pipeline of the multi-layer spiral hollow tube 2 is provided with coolant through the first pipeline connector 5. The coolant flows through the multiple spiral hollow tubes 2 layers of the overall water-cooled electromagnetic coil to dissipate heat, and then passes through the second branch loop, reaches the second main road 9 through the second pipeline connector 8, and returns to the water pump tank 1 to form a return water loop. In order to ensure the heat dissipation efficiency, each single-layer spiral hollow tube 2 is a separate cooling circulation loop when dissipating heat to the coil. The copper tube inside the spiral hollow tube 2 is used to circulate coolant, which can effectively reduce the Joule heat problem generated by the long-term operation of the electromagnetic coil.

[0064] The conductor 3 is wound between the two spiral hollow tubes 2, and the conductor 3 and the spiral hollow tube 2 are connected in series to form an electromagnetic coil group. The conductor 3 in this embodiment can be a Litz copper wire.

[0065] The MPI water-cooled electromagnetic coil provided in this embodiment adopts a multi-layer coil winding coupling structure, and two layers of spiral hollow tubes 2 and a layer of wire 3 form an electromagnetic coil. Figure 2 and Figure 3 As shown, the hollow tube is wound into a solenoid shape at a fixed pitch as the conductor of the coil of this layer and also as the support of the coil of the next layer. The wire 3 is wound on the outer surface of the spiral hollow tube 2 according to a certain size and number of turns, and then the spiral hollow tube coil is nested on the wire 3 coil to make them tightly connected, forming a coupled coil structure of "spiral hollow tube-wire-spiral hollow tube". In addition, according to the requirements of the magnetic field strength in actual applications, the number of coil layers can continue to be stacked, that is, the spiral hollow tube 2 and the wire 3 can continue to be stacked.

[0066] In terms of circuit connection, the outer surface of the spiral hollow tube 2 and the wire 3 are connected to a power source to generate an electromagnetic field. Specifically, the water inlet of the first layer of spiral hollow tube winding is used as a power source end of the electromagnetic coil, and the water outlet is used as the power source end of the coil of this layer, which is electrically connected to one end of the second wire coil winding, and the other end is electrically connected to the water inlet of the third layer of spiral hollow tube winding, and the water outlet is connected to the end of the next layer of coil or to the power source end. The electrical connection only needs to ensure that the current direction of each layer of coil winding is consistent and the magnetic field strength can be superimposed.

[0067] The MPI water-cooled electromagnetic coil structure provided in this embodiment adopts a multi-layer coil winding coupled heat dissipation structure, in which the cooling water circuits are connected in parallel and the circuits are connected in series. This structure can not only reduce the large inductance caused by the large size or large aperture cross-section of the simple copper tube winding coil, reduce the influence of the skin effect and proximity effect in high-frequency alternating current and the system power consumption, but also use the spiral hollow tube to circulate the cooling liquid to reduce the Joule heat of the cooling coil as a whole.

[0068] The control subsystem is used to adjust the coolant temperature and cooling speed of the coolant in the water pump tank 1 when the coolant temperature in the water pump tank 1 is higher than the target coolant temperature; and is also used to adjust the coolant flow rate flowing through the spiral hollow tube 2 when the outlet coolant temperature at the water outlet of the water pump tank 1 is higher than the target coolant temperature.

[0069] The present invention provides an MPI water-cooled electromagnetic coil structure with a spiral hollow tube and a wire coupled to dissipate heat, and proposes a set of real-time temperature monitoring and temperature control systems, i.e., a control subsystem, based on the structure. That is, a multi-stage cascade PID control algorithm is used to automatically adjust the coolant temperature, cooling speed, and flow output corresponding to different temperatures, thereby achieving precise temperature control of the time-varying electromagnetic coil and improving the magnetic field stability and imaging quality of the MPI system.

[0070] The MPI water-cooled electromagnetic coil system provided by the present invention can not only solve the problem of overheating of the MPI electromagnetic coil while meeting the required magnetic field strength, but also solve the problem of impedance drift, thermal noise and magnetic field instability caused by Joule heat of the electromagnetic coil of the magnetic nanoparticle system in the working state of the MPI system, which affects the imaging quality, and can also effectively reduce the thermal noise and system power consumption during the working process, thereby improving the imaging quality of the MPI.

[0071] In some optional embodiments, the control subsystem includes a temperature control device and a multi-stage cascade PID control device, and the temperature control device includes:

[0072] The temperature real-time detection module can use PT1000 temperature sensors, which are respectively set at multiple preset positions of the water pump tank 1, the spiral hollow tube 2 and the wire 3 to detect the temperature of the detection point at the corresponding position and send the detection point temperature to the multi-stage cascade PID control module. The output signal can communicate with the multi-stage cascade PID control module in the terminal through the temperature acquisition relay. The preset position can be the inlet, outlet, middle position, etc. of each layer of coil winding, water pump tank, etc.

[0073] The cooling temperature control module is used to adjust the cooling device according to the temperature control signal sent by the multi-stage cascade PID control module to reduce the coolant temperature in the water pump tank 1 to the target coolant temperature.

[0074] The coolant temperature control module in this embodiment mainly receives the temperature control signal, and then uses an additional cooling device to dissipate the heat of the coolant after the temperature is raised by the coil.

[0075] In some optional embodiments, the temperature control module further includes:

[0076] The flow output control module is used to adjust the flow of the coolant flowing through the spiral hollow tube 2 according to the flow control signal sent by the multi-stage cascade PID control module.

[0077] The flow output control module in this embodiment mainly adjusts the output flow according to the flow control signal output by the PID controller to ensure that the coil temperature is stable within a range.

[0078] In some optional embodiments, the cooling device is a fan, and the temperature control module further includes:

[0079] The cooling speed control module is used to adjust the running speed of the fan according to the cooling speed control signal sent by the multi-stage cascade PID control module, so as to adjust the cooling speed of the coolant in the water pump tank 1.

[0080] In some optional embodiments, the control subsystem further includes:

[0081] The flow parameter simulation module is connected with the multi-stage cascade PID control module and is used to simulate the output flow corresponding to the coolant at different temperatures.

[0082] The flow parameter simulation module establishes a numerical simulation model for coil heat dissipation based on the heat transfer equations of heat conduction and convection. It uses finite element multi-physics field calculations to obtain the flow output of coolant at different temperatures to ensure the constant temperature of the electromagnetic coil, and obtains the corresponding function relationship of the corresponding flow of coolant at different temperatures to keep the coil temperature constant for subsequent output control.

[0083] The multi-stage cascade PID control device in this embodiment includes three PID controllers. The first PID controller compares the difference between the temperature value detected by the temperature sensor and the target temperature value, outputs a temperature control signal and sends it to the coolant temperature control module; the second PID controller controls the cooling speed of the coolant; the third PID controller compares the flow rate corresponding to the current coolant temperature with the flow rate corresponding to the target temperature coolant through the flow parameter simulation result to keep the coil constant, outputs a flow control signal and sends it to the flow output control module.

[0084] In this embodiment, a control subsystem is provided for the water-cooled electromagnetic coil, which can realize real-time temperature monitoring of the electromagnetic coil and automatically adjust the output flow rate according to the temperature of the coolant, thereby realizing effective temperature control of the water-cooled electromagnetic coil of the MPI system working continuously, ensuring that the Joule heat temperature rise of the electromagnetic coil is always constant. It also effectively reduces the impedance drift caused by Joule heat, system power consumption and system thermal noise, improves imaging quality and resolution, and ensures the stability of the magnetic field.

[0085] Compared with traditional water-cooled electromagnetic coils, the water-cooled electromagnetic coil structure and temperature control system provided by the present invention effectively overcome the difficulty in precise temperature control, so that the Joule temperature rise of the coil is effectively controlled and the coil structure is compact, which to a certain extent avoids the problems of high current inductance and large space occupied by pure copper tube coils, and provides a reference for human-scale MPI equipment coils.

[0086] In some optional embodiments, both the inner surface and the outer surface of the spiral hollow tube 2 are provided with an insulation layer.

[0087] In order to improve the thermal conductivity between turns and layers, the excitation coil is wound using a "wet winding" process, that is, while winding the wire 3, thermal conductive silicone grease is applied to each layer of the wire. Before winding the wire 3, a 0.2 mm thick polytetrafluoroethylene insulation layer can be sprayed on the surface of the spiral hollow tube 2 to improve the compressive strength of the copper tube coil.

[0088] In this embodiment, a temperature control method is also provided, which can be performed by the water-cooled electromagnetic coil system in any of the above embodiments. The temperature control method includes:

[0089] When the current coolant temperature of the coolant in the water pump tank 1 is higher than the target coolant temperature, adjusting the coolant temperature and cooling speed of the coolant in the water pump tank 1;

[0090] When the outlet coolant temperature at the water outlet of the water pump tank 1 is still higher than the target coolant temperature, the coolant flow rate flowing through the spiral hollow tube 2 is adjusted.

[0091] The water-cooled electromagnetic coil system is described in detail above. In this embodiment, the coolant temperature in the water pump tank, the cooling speed, and the coolant flow rate flowing through the spiral hollow tube can be automatically adjusted, thereby effectively achieving precise control of the time-varying electromagnetic coil temperature, thereby effectively improving the magnetic field stability and imaging quality of the MPI system.

[0092] In addition, the outlet coolant temperature at the water pump tank outlet can also be calculated in the following way:

[0093] The heat conduction between the spiral hollow tube and the adjacent wire can be described by Fourier's law, which can be equivalent to the multi-layer cylindrical wall heat transfer model, that is:

[0094]

[0095] Where, T1 and T4 are the temperatures of the inner side of the first layer of spiral hollow tube coil and the outer side of the third layer of spiral hollow tube coil, δ1, δ2, δ3 are the thickness of the inner side coil of the first layer of spiral hollow tube, the wire coil and the thickness of the third layer of spiral hollow tube coil, k1, k2, k3 are the thermal conductivity of the three coils, A m1 , A m2 , A m3 is the average heat transfer area of ​​the three coils.

[0096] The expression of temperature change under convective heat transfer state is:

[0097]

[0098] Where Δt is the outlet coolant temperature at the water pump tank outlet, ρ is the density of the coolant, C p is the specific heat capacity of the coolant, h2 is the convection heat transfer coefficient, A is the surface area of ​​the copper tube, T c is the temperature of the coolant, T w is the temperature of the spiral hollow tube, and Q2 is the heat flux of the tube wall.

[0099] In some optional embodiments, before adjusting the coolant temperature and cooling speed of the coolant in the water pump water tank, the method includes:

[0100] The temperature difference between the current coolant temperature and the target coolant temperature is determined, ie, Δt″′=Δt′-Δt″.

[0101] A temperature expression function is established based on the temperature difference.

[0102] The temperature expression function is: V f =C×Δt″′ 2 -dΔt″′;

[0103] Where Δt′ is the current coolant temperature of the water pump tank, that is, the temperature of the coolant after convection heat transfer and the mixture in the water pump tank, and its value is given by the temperature sensor data, Δt″ is the target coolant temperature, V f is the rotation speed of the cooling device, Δt″′ is the temperature difference, the value range of C is 0.5-1.5, and the value range of d is 0.8-1.2.

[0104] In this embodiment, before adjusting the coolant temperature and cooling speed of the coolant in the water pump tank, the temperature difference between the current coolant temperature and the target coolant temperature is first determined, so as to provide a basis for adjusting the cooling device by analyzing the temperature difference in the subsequent PID control, thereby improving the adjustment accuracy of the system.

[0105] In some optional embodiments, before adjusting the flow rate of the coolant flowing through the spiral hollow tube, the method further includes:

[0106] Establish the flow output expression function between coolant of different temperatures and the corresponding output flow.

[0107] The flow output expression function is:

[0108] Wherein, V1 is the coolant flow rate corresponding to the outlet coolant temperature, V2 is the coolant flow rate corresponding to the target coolant temperature, h1 is the convective heat transfer coefficient corresponding to the outlet coolant temperature, and h2 is the convective heat transfer coefficient corresponding to the target coolant temperature.

[0109] The flow rate of the coolant will directly affect the cooling effect of the coolant. In this embodiment, before adjusting the flow rate of the coolant flowing through the spiral hollow tube, an expression for the relationship between different temperatures and the output flow rate is first established. This helps to accurately know the relationship between the coolant flow rate and flow rate at different temperatures, which is convenient for better control of the output flow rate in subsequent PID control.

[0110] Furthermore, the transfer function of the cooling process of the coolant is:

[0111] The transfer function of flow output corresponding to different temperatures is:

[0112] Wherein, s1 is the expression of the temperature difference Δt″′ after Laplace transformation; s2 is the expression of the flow output function after Laplace transformation.

[0113] The functional relationship after Laplace transformation is used as the input controller to achieve precise control of the output flow.

[0114] In some optional embodiments, adjusting the coolant temperature of the coolant in the water pump water tank includes:

[0115] The coolant temperature is controlled based on the outermost loop PID control function, and the outermost loop PID control function is:

[0116]

[0117] Where k is the sampling number, i is the integration number, u(k) is the control value of the coolant temperature at the kth moment; k p1 , k i1 , k d1 are the outermost loop coefficients, ΔT(k) is the difference between the coolant temperature at the kth moment and the target coolant temperature; is the coolant temperature difference between the kth moment and the k-1th moment;

[0118] Adjusting the cooling speed of the coolant in the water pump tank 1 includes:

[0119] The cooling speed is controlled based on the intermediate loop PID control function, and the intermediate loop PID control function is:

[0120]

[0121] Where u(k)′ is the control value of cooling rate at the kth moment, k p2 , k i2 , k d2 are the intermediate ring coefficients, Δt v (k) is the cooling rate at the kth moment, is the difference between the coolant temperature difference and the cooling rate difference, where the cooling rate difference is the cooling rate difference between the kth moment and the k-1th moment;

[0122] Regulating the coolant flow through the spiral hollow tube 2 includes:

[0123] Based on the innermost loop PID control function, the coolant flow is controlled, and the middle loop PID control function is:

[0124]

[0125] Where u(k)″ is the control amount of the coolant flow at the kth moment, k p3 , k i3 , k d3 is the innermost loop coefficient, ΔV(k) is the coolant flow rate at the kth moment, is the difference between the cooling speed difference and the coolant flow rate difference, wherein the coolant flow rate difference is the coolant flow rate difference between the kth moment and the k-1th moment.

[0126] In this three-level cascade PID control system, there is a coupling relationship between the loops. For example, changes in the coolant flow rate may affect the cooling speed, and then affect the cooling temperature. This coupling may cause the control performance of the system to deteriorate, so it needs to be decoupled.

[0127] First, determine the input-output relationship of the system. The input is: [ΔT(k),ΔT(k)-Δt v (k),Δt v (k)-ΔV(k)], the output is: [u(k),u(k)′,u(k)″].

[0128] The relationship between input and output is determined by the physical model of the system, namely:

[0129]

[0130] Construct the coupling matrix:

[0131]

[0132] The decoupling matrix is ​​D = A -1 , decoupling is completed after inverting the matrix A. Through the above decoupling steps, the cooling temperature, cooling speed and flow rate of the coolant can be effectively controlled by the control program.

[0133] Specifically, refer to Figure 4 As shown in the figure, firstly, the temperature control system temperature real-time detection module, cooling temperature control module, flow output control module, cooling speed control module, parameter simulation module and multi-stage cascade PID control module are established; the temperature sensor is used to monitor the temperature of each position of the electromagnetic coil and the cooling water tank in real time. Secondly, the temperature expression of the coolant cooling temperature control module and the functional relationship of the flow corresponding to the coolant at different temperatures are obtained respectively through the temperature sensor information and the flow parameter simulation results; then the temperature transfer function of the cooling process and the transfer function of the flow output corresponding to different temperatures are obtained through Laplace change; thirdly, the coolant cooling temperature difference, cooling speed and the flow output corresponding to the coolant at different temperatures are controlled by the multi-stage cascade PID controller; the outer loop algorithm of the multi-stage cascade PID controls the temperature difference of the coolant cooling, the middle loop algorithm controls the cooling speed of the coolant; the inner loop algorithm controls the flow output corresponding to the coolant at different temperatures. The multi-stage cascade PID control algorithm is used to automatically adjust the coolant temperature, cooling speed and the flow output corresponding to different temperatures, so as to realize the precise temperature control of the time-varying electromagnetic coil and improve the magnetic field stability and imaging quality of the MPI system.

[0134] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A water-cooled electromagnetic coil system, characterized in that: The system comprises: A water pump water tank (1), wherein the interior of the water pump water tank (1) is used to contain a coolant; A cooling device, used for adjusting the temperature of the coolant in the water pump water tank (1); A spiral hollow tube (2), wherein the water inlet of the spiral hollow tube (2) is connected to the water outlet of the water pump water tank (1), the water outlet of the spiral hollow tube (2) is connected to the water inlet of the water pump water tank (1), and the interior of the spiral hollow tube (2) is used for circulating cooling liquid; A conductor (3), the conductor (3) being wound between the two spiral hollow tubes (2), the conductor (3) and the spiral hollow tubes (2) being connected in series to form an electromagnetic coil group; The control subsystem is used to adjust the coolant temperature and cooling speed of the coolant in the water pump water tank (1) when the coolant temperature in the water pump water tank (1) is higher than the target coolant temperature; and is also used to adjust the coolant flow rate flowing through the spiral hollow tube (2) when the outlet coolant temperature at the water outlet of the water pump water tank (1) is higher than the target coolant temperature.

2. The system according to claim 1, characterized in that The control subsystem includes a temperature control device and a multi-stage cascade PID control device, and the temperature control device includes: A real-time temperature detection module, which is respectively arranged at a plurality of preset positions of the water pump tank (1), the spiral hollow tube (2) and the wire (3), and is used to detect the temperature of the detection point at the corresponding position, and send the temperature of the detection point to the multi-stage cascade PID control module; A cooling temperature control module is used to adjust the cooling device according to the temperature control signal sent by the multi-stage cascade PID control module to reduce the coolant temperature in the water pump water tank (1) to the target coolant temperature.

3. The system according to claim 2, characterized in that The temperature control module also includes: A flow output control module is used to adjust the flow of the coolant flowing through the spiral hollow tube (2) according to the flow control signal sent by the multi-stage cascade PID control module.

4. The system according to claim 2, characterized in that The cooling device is a fan, and the temperature control module further comprises: A cooling speed control module is used to adjust the running speed of the fan according to the cooling speed control signal sent by the multi-stage cascade PID control module, so as to adjust the cooling speed of the coolant in the water pump tank (1).

5. The system according to claim 2, characterized in that The control subsystem also includes: The flow parameter simulation module is connected to the cascade PID control module and is used to simulate the output flow corresponding to the coolant at different temperatures.

6. The system according to claim 1, characterized in that The inner surface and the outer surface of the spiral hollow tube (2) are both provided with an insulating layer.

7. A temperature control method, characterized in that: Applied to the water-cooled electromagnetic coil system according to any one of claims 1 to 6 above, the method comprises: When the current coolant temperature of the coolant in the water pump water tank (1) is higher than the target coolant temperature, adjusting the coolant temperature and cooling speed of the coolant in the water pump water tank (1); When the outlet coolant temperature at the water outlet of the water pump water tank (1) is still higher than the target coolant temperature, the coolant flow rate flowing through the spiral hollow tube (2) is adjusted.

8. The method according to claim 7, characterized in that Before adjusting the coolant temperature and cooling speed of the coolant in the water pump water tank (1), the method comprises: determining a temperature difference between the current coolant temperature and the target coolant temperature; Establishing a temperature expression function based on the temperature difference; The temperature expression function is: V f =C×Δt″′ 2 -dΔt″′; Where V f is the rotation speed of the cooling device, Δt″′ is the temperature difference, the value range of C is 0.5-1.5, and the value range of d is 0.8-1.

2.

9. The method according to claim 7, characterized in that: Before adjusting the flow rate of the coolant flowing through the spiral hollow tube (2), the method further comprises: Establishing a flow output expression function between coolants at different temperatures and corresponding output flows; The flow output expression function is: In the formula, V1 is the coolant flow rate corresponding to the outlet coolant temperature, V2 is the coolant flow rate corresponding to the target coolant temperature, h1 is the convective heat transfer coefficient corresponding to the outlet coolant temperature, and h2 is the convective heat transfer coefficient corresponding to the target coolant temperature.

10. The method according to claim 7, characterized in that The step of adjusting the coolant temperature of the coolant in the water pump water tank (1) comprises: The coolant temperature is controlled based on the outermost loop PID control function, and the outermost loop PID control function is: Where k is the sampling number, i is the integration number, u(k) is the control value of the coolant temperature at the kth moment; k p1 , k i1 , k d1 are the outermost loop coefficients, ΔT(k) is the difference between the coolant temperature at the kth moment and the target coolant temperature; is the coolant temperature difference between the kth moment and the k-1th moment; The step of adjusting the cooling speed of the coolant in the water pump water tank (1) comprises: The cooling speed is controlled based on the intermediate loop PID control function, and the intermediate loop PID control function is: Wherein, u(k)′ is the control amount of the cooling rate at the kth moment, k p2 , k i2 , k d2 are the intermediate ring coefficients, Δt v (k) is the cooling rate at the kth moment, is the difference between the coolant temperature difference and the cooling rate difference, wherein the cooling rate difference is the cooling rate difference between the kth moment and the k-1th moment; The step of regulating the flow rate of the coolant flowing through the spiral hollow tube (2) comprises: The coolant flow is controlled based on the innermost loop PID control function, and the middle loop PID control function is: Wherein, u(k)″ is the control amount of the coolant flow at the kth moment, k p3 , k i3 , k d3 is the innermost loop coefficient, ΔV(k) is the coolant flow rate at the kth moment, is the difference between the cooling speed difference and the coolant flow rate difference, wherein the coolant flow rate difference is the coolant flow rate difference between the kth moment and the k-1th moment.

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