A downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning
By constructing a comprehensive evaluation model and an IF control strategy with self-tuning optimal power angle in a downhole SPMSM, the problems of motor underdamping and high temperature rise in traditional methods are solved, and motor operation with low temperature rise and high robustness is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA UNIV OF PETROLEUM (EAST CHINA)
- Filing Date
- 2026-04-27
- Publication Date
- 2026-06-30
AI Technical Summary
Traditional IF control methods in downhole SPMSMs result in underdamped systems due to conservative current settings, which can easily lead to low-frequency oscillations in rotational speed and severe temperature rise in stator windings, posing a risk of thermal failure.
By constructing a stiffness-heat dissipation comprehensive evaluation model, determining the optimal power angle and performing closed-loop tuning, the stator current is adaptively adjusted to achieve high anti-disturbance stiffness and low heat loss, and an IF control strategy with optimal power angle self-tuning is adopted.
It effectively suppressed redundant heat loss of stator windings, reduced the risk of thermal failure of downhole motors, eliminated low-frequency oscillation of speed, and ensured the safe operation of the system.
Smart Images
Figure CN122316151A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of permanent magnet synchronous motor control technology, specifically to a downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning. Background Technology
[0002] As directional drilling advances into complex formations, surface-mounted permanent magnet synchronous motors (SPMSMs) have become core components of downhole equipment. Due to the extreme high temperatures downhole can easily damage traditional mechanical position sensors, sensorless control has become an inevitable choice for downhole motor drive systems. However, during low-speed operation, traditional fundamental wave observers fail due to weak back electromotive force, and high-frequency injection methods are limited by the lack of salient pole effect in the motor. Therefore, IF control methods are often introduced to achieve startup. However, to prevent startup synchronization issues, existing methods often set a constant amplitude and overly conservative given current. This strategy has two drawbacks: first, the system is severely underdamped, making it highly susceptible to low-frequency speed oscillations when encountering external disturbances; second, it generates a large amount of redundant stator heat loss, leading to severe winding temperature rise. Under the harsh heat dissipation conditions downhole, this can easily cause serious thermal failure accidents such as winding thermal breakdown or permanent magnet demagnetization, endangering the safe operation of the equipment. Summary of the Invention
[0003] To address the aforementioned shortcomings, this invention provides a downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning, the overall structure of which is shown in the diagram below. Figure 1 As shown. This strategy uses torque overload margin as a constraint and completes the closed-loop tuning of the optimal power angle through adaptive adjustment of stator current. While maintaining the high disturbance rejection stiffness of the system, it overcomes the problem of severe temperature rise of stator winding caused by conservative current setting in traditional IF control, and effectively reduces the risk of thermal runaway of motor under extreme downhole conditions.
[0004] The specific solution adopted in this invention includes the following steps:
[0005] Step 1: Construct a comprehensive evaluation model for stiffness and heat dissipation and determine the optimal target work angle. The specific implementation process is as follows:
[0006] Step 1.1: Based on the steady-state operation mechanism of the surface-mounted permanent magnet synchronous motor, considering the low speed of the motor during the low-speed IF control stage, and given that the core loss and mechanical loss, which are positively correlated with the speed, have minimal impact at this stage, the total system heat dissipation under low-speed conditions is approximated as pure stator copper loss. Based on this, and combined with Ohm's thermal law, the steady-state electromagnetic stiffness of the system is established. With winding steady-state temperature rise Regarding the physical angle of work The parse relations are expressed as follows:
[0007] (1)
[0008] (2)
[0009] Physical work angle;
[0010] External load torque;
[0011] System overall heat consumption constant;
[0012] Stator phase resistance;
[0013] : Steady-state thermal resistance of the motor;
[0014] Torque constant.
[0015] Step 1.2, introduce the thermal penalty coefficient. Construct a comprehensive performance evaluation index function to measure disturbance rejection capability and temperature rise cost. :
[0016] (3)
[0017] This index is used to characterize the effective disturbance rejection stiffness gain that a system can obtain under different degrees of thermal penalty.
[0018] Step 1.3, using the extreme value stationary point analysis method, for the... Find information about the angle of attack. By finding the maximum value of the target angle, the optimal target power angle that balances high disturbance rejection stiffness and low heat loss is derived. The analytical calculation formula is as follows:
[0019] (4)
[0020] Step 1.4: To ensure the system has sufficient disturbance rejection capability under extreme operating conditions, the system's torque overload margin is defined as the ratio of the maximum electromagnetic torque under the current given current to the current steady-state load. Its mathematical expression is:
[0021] (5)
[0022] Torque overload margin coefficient;
[0023] The maximum torque that the current can provide;
[0024] To ensure the system has an 80% torque overload margin (i.e. ), combined with the constraint of extreme points Established through analytical solution The effective interval is:
[0025] (6)
[0026] Step 2: System initialization and control parameter preset. The specific implementation process is as follows:
[0027] Step 2.1: Determine the thermal penalty coefficient based on the system torque overload margin requirement. The value of is taken, and the corresponding optimal target power angle is calculated. .
[0028] Step 2.2, preset target speed And the critical convergence speed at which the sensorless observer can converge effectively. At the same time, a preset starting current is set. This current is a conservative current setting value that is sufficient to enable the motor to overcome static friction torque and start reliably.
[0029] Step 3: Determine operating conditions and obtain actual power angle. The specific implementation process is as follows:
[0030] Step 3.1: The controller determines in real time whether the target rotational speed is within the low-speed blind zone where the observer cannot converge; if it is within the blind zone, the IF synchronous drive loop is activated. First, the system generates a continuously changing virtual synchronous rotation angle based on a preset acceleration speed trajectory. Its mathematical expression is:
[0031] (7)
[0032] Step 3.2, combined Figure 2 The coordinate system is defined as shown, and the controller is in the coordinate system defined by... Virtual coordinate system based on On-axis output start-up setting current Under this mechanism, the synthesized current vector Always position On the axis, and with angular velocity Rotation. Due to the rotor's inertia, the actual rotor position... Often lags behind the set position The actual d-axis and the virtual d-axis The complementary angle between axes is defined as the physical work angle. ( During steady-state operation, the stator magnetic field leads the rotor magnetic field. By generating synchronous electromagnetic torque to drive the rotor, the rotor is forced to rotate in accordance with the stator current vector, thereby achieving a passive "forced start".
[0033] Step 3.3: After the motor is driven to the critical convergence speed and enters steady-state operation, in order to eliminate electromagnetic transient disturbances during acceleration, timing constraints are introduced, and the transient elimination time constraint is set as follows: ( This refers to the holding time after the motor reaches its critical speed. (This refers to the system's preset transient elimination time threshold). After satisfying this timing constraint and confirming that the stator current has entered the steady-state output range with no steady-state error, the controller acquires the internally generated virtual synchronous rotation angle. Compared with the actual rotor position angle extracted by the observer The difference between the two is used to obtain the actual observed power angle at the initial stage. .
[0034] Step 4: Optimal current adaptive tuning. The specific implementation process is as follows:
[0035] Step 4.1: Based on the dynamic characteristics of the motor running at low speed with an approximately constant external load, the torque balance equation between the current detection condition and the target optimal condition is established using the principle of torque conservation.
[0036] (8)
[0037] Step 4.2, the controller combines the results determined in step 2.1. Compared with what was observed in step 3.3 The optimal stator current is calculated based on the torque balance equation. :
[0038] (9)
[0039] Step 5: Execute optimal power angle closed-loop control. The specific implementation process is as follows:
[0040] Step 5.1, calculate the... Update the current setpoint to the virtual q-axis in the IF control system, and simultaneously update the system's set speed command to the target speed. .
[0041] Step 5.2, the system is described in Driven by this, the actual physical power angle is forced to spontaneously and smoothly converge to the optimal target power angle, thereby minimizing the temperature rise of the stator winding while maintaining the preset anti-disturbance stiffness, and achieving low-temperature operation of the motor.
[0042] Compared with existing technologies, this invention has the following advantages: It breaks through the limitations of traditional IF control, which relies excessively on constant and conservative current settings. By constructing a comprehensive evaluation model of disturbance rejection stiffness and steady-state heat dissipation, it guides the stator current to adaptively adjust, thereby achieving closed-loop tuning of the optimal power angle. This allows the motor to converge and continuously operate at the target optimal power angle, balancing high robustness and low heat loss. On the one hand, under the constraint of ensuring sufficient torque overload margin, the steady-state operating current is adaptively lowered to the optimal level, significantly suppressing redundant heat loss in the stator windings and effectively reducing the risk of motor thermal failure under extreme high-temperature conditions downhole. On the other hand, through self-tuning of the optimal power angle, this invention rationally optimizes the system's damping characteristics, effectively eliminating the low-frequency speed oscillation phenomenon that is easily caused by external disturbances or state switching. Attached Figure Description
[0043] Figure 1 To improve the overall block diagram of IF control;
[0044] Figure 2 This is a schematic diagram illustrating the coordinate system definition and vector relationships under IF control.
[0045] Figure 3 This is a diagram showing the influence of the thermal penalty coefficient on motor control performance, provided in an embodiment of the present invention.
[0046] Figure 4 This is a flowchart of the low-speed blind zone optimal given current self-tuning process provided in an embodiment of the present invention;
[0047] Figure 5 This is a bar chart comparing the steady-state temperature rise of the winding at different rotational speeds, provided in an embodiment of the present invention.
[0048] Figure 6 A comparison diagram of the fitting between the winding theory and the actual steady-state temperature rise provided in the embodiments of the present invention;
[0049] Figure 7 This is a comparison chart of measured steady-state speed and current control performance of the motor provided in an embodiment of the present invention. Detailed Implementation
[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0051] This embodiment uses a surface-mount permanent magnet synchronous motor (SPMSM) as the controlled object and provides a drive control implementation scheme to effectively reduce motor heat generation under extreme high-temperature conditions. The execution of this scheme includes preliminary theoretical parameter analysis and preparation, as well as subsequent online closed-loop execution relying on the microcontroller's underlying driver program. The specific engineering implementation steps are as follows:
[0052] Step 1: Core preset parameter parsing (offline preparation).
[0053] First, based on the torque overload margin control requirements of directional drilling operations, combined with Figure 3 The graph showing the influence of the thermal penalty coefficient on motor control performance is within the effective engineering adjustment range. Internally established heat penalty coefficient (In this embodiment, 0.7 is used), and the selected Substitute into the optimal power angle mapping model In the process, the optimal power angle of the target is calculated offline. (Approximately 39.2° in this embodiment). Secondly, a starting current sufficient to overcome the static friction of the motor is preset. Finally, the target steady-state speed of the preset system is determined. (In this implementation, two speed points are set at 50 rpm and 500 rpm) and the critical convergence speed for effective convergence of the observer. (In this implementation, it is set to 500 rpm).
[0054] Step 2: Low-speed blind zone condition determination and IF drag control execution.
[0055] like Figure 4 As shown, after receiving the start command, the controller first determines whether the current target speed is in the low-speed blind zone where the observer cannot effectively converge. If it is in this blind zone, the controller activates the improved IF control loop. The system generates a virtual synchronous rotation angle based on the integral of the target speed command. It also directly outputs the pre-configured start-up current on the virtual q-axis. The controller accelerates the motor to a critical steady-state speed that allows the observer to converge. .
[0056] Step 3: Observer convergence state assessment and steady-state work angle extraction.
[0057] Once the motor accelerates to the preset critical speed, the controller monitors the convergence status of the rotor position observer in real time. When the system detects that the motor start-up time exceeds a preset time threshold... After confirming that the stator current has fully entered the steady-state output range with no steady-state error, the controller resolves the actual observed power angle under the current steady state within a single sampling period. .
[0058] Step 4: Optimal setting current online calculation and optimal power angle closed-loop control execution.
[0059] Using the information obtained in step 3 Based on the dynamic characteristics of the motor during low-speed driving, where the external load torque is approximately constant, the controller calculates the target optimal given current using real-time algebraic solutions. After the calculation is completed, the system triggers the current and speed switching logic: on the one hand, the given current of the virtual q-axis is adjusted from the initial set value to the optimal given current along the planned trajectory; on the other hand, the speed given command is simultaneously adjusted from the critical convergence speed. Transition to the target speed according to the planned trajectory. .
[0060] At this point, the system officially entered the closed-loop collaborative operation phase. While maintaining the preset anti-disturbance stiffness constraint, it greatly reduced the heat loss of the stator winding and achieved safe operation at low temperatures in the harsh underground environment.
[0061] To verify the effectiveness of the above scheme in actual engineering, the following experimental results are illustrated with reference to the attached diagram:
[0062] like Figure 5 As shown, under the same stator drive current setting, the steady-state temperature rise data of the winding at two different low-speed points of the system are basically the same. This phenomenon indicates that during the low-speed operation of the motor, the influence of core loss and mechanical loss on the total heat generation of the system is negligible, thus verifying that the physical premise of equating the total heat loss with stator copper loss when deriving the heat loss evaluation model in this invention is reasonable.
[0063] like Figure 6 As shown, the measured steady-state temperature rise data scatter plots agree well with the theoretical curve constructed based on this invention. The results intuitively reflect the nonlinear mapping relationship between stator current and winding steady-state temperature rise, further confirming the accuracy of the stiffness-heat dissipation evaluation model and providing reliable data support for the self-tuning calculation of the optimal power angle.
[0064] like Figure 7 As shown, when using the traditional strategy of constant conservative current (solid line), significant low-frequency oscillations occur in both the actual speed and the feedback current due to system damping mismatch. However, after adopting the adaptive tuning strategy proposed in this invention (dashed line), speed fluctuations and current ripples are significantly suppressed. Simultaneously, under the same operating conditions, the motor temperature rise is significantly reduced. Comparative data demonstrate that this invention, while ensuring system disturbance rejection robustness, significantly reduces motor stator losses and possesses significant thermal protection value in extreme downhole high-temperature environments.
[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.
Claims
1. A downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning, characterized in that, Includes the following steps: Step 1: Construct a stiffness-heat dissipation comprehensive evaluation model, and under the condition of satisfying the preset torque overload margin constraint, analyze the optimal target power angle of the system. Step 2: Perform system initialization and control parameter preset, establish the thermal penalty coefficient and calculate the optimal target power angle, and preset the starting current, target steady-state speed and critical convergence speed for effective convergence of the sensorless observer. Step 3: When the target speed is determined to be in the low-speed blind zone where the observer cannot converge, the IF synchronous drive circuit is activated to drive the motor to the critical convergence speed with the starting set current, and after the preset transient elimination time constraint condition is met, the actual observed power angle under the current steady state is obtained. Step 4: Based on the principle of torque conservation where the external load is approximately constant during the low-speed operation of the motor, and combining the actual observed power angle with the optimal target power angle, calculate the optimal given current required to maintain the target optimal operating condition using online real-time algebraic solution. Step 5: Smoothly switch the current command of the virtual q-axis in the IF control system from the starting set current to the optimal command current, and simultaneously smoothly transition the system speed command to the target steady-state speed, thereby guiding the motor physical power angle to spontaneously converge to the optimal target power angle to achieve low-temperature steady-state operation.
2. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning as described in claim 1, characterized in that, The process of constructing the stiffness-heat dissipation comprehensive evaluation model and analyzing the optimal target power angle in step 1 specifically includes: Considering that the core loss and mechanical loss of the motor are relatively small during the low-speed IF control stage, the total heat loss of the system under low-speed conditions is approximately equivalent to the pure stator copper loss. Based on the thermal Ohm's law, analytical relationships between the steady-state electromagnetic stiffness of the system and the steady-state temperature rise of the winding with respect to the physical power angle are established respectively. (1) (2) Physical work angle; External load torque; System overall heat consumption constant; Stator phase resistance; : Steady-state thermal resistance of the motor; Torque constant; Electromagnetic stiffness; Steady-state temperature rise of windings. A thermal penalty coefficient is introduced to construct a comprehensive performance evaluation index function to measure the system's disturbance rejection capability and temperature rise cost. This function is used to characterize the effective disturbance rejection stiffness gain that the system can obtain under different degrees of thermal penalty. (3) : A comprehensive performance evaluation index function that measures the immunity to disturbances and the cost of temperature rise; : Thermal penalty coefficient. By using the extreme stationary point analysis method, the maximum value of the comprehensive performance evaluation index function with respect to the physical power angle is obtained, and the analytical calculation formula of the optimal target power angle is derived.
3. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning according to claim 2, characterized in that, The analytical formula for calculating the optimal target power angle is: (4) Optimal target angle of attack.
4. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning according to claim 1, characterized in that, The torque overload margin is defined as the ratio of the maximum electromagnetic torque under the current given current to the current steady-state load, and its mathematical expression is: (5) Torque overload margin coefficient; The maximum torque that the current can provide; Current steady-state load; Torque constant; : The current given. In step 1, the effective engineering adjustment range of the thermal penalty coefficient is determined by presetting the torque overload margin requirement threshold and combining it with the extreme point existence constraint of the comprehensive performance evaluation index function.
5. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning according to claim 1, characterized in that, The process of obtaining the actual observed power angle under the current steady state in step 3 specifically includes: Once the system meets the timing constraints and confirms that the stator current has entered the steady-state output range with no static error, the controller synchronously acquires the virtual synchronous rotation angle generated by internal integration and the real rotor position angle extracted by the observer within a single sampling period; calculates the difference between the virtual synchronous rotation angle and the real rotor position angle, and accurately extracts the actual observed power angle in the start-up phase.
6. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning according to claim 1, characterized in that, The formula for calculating the optimal given current using online algebraic solution in step 4 is as follows: (6) The actual observed power angle obtained in step 3.
7. The downhole SPMSM temperature rise suppression IF control strategy based on optimal power angle self-tuning according to claim 1, characterized in that, The smooth switching mechanism between current and speed in step 5 is as follows: The current command for the controller driving the virtual q-axis is smoothly adjusted from the initial set current along a preset decay trajectory to the optimal given current; at the same time, the speed command for the cooperative drive system is continuously and smoothly transitioned from the current critical convergence speed to the target steady-state speed.