An alternating current excitation system self-starting control method and system

Abstract

The application discloses an alternating current excitation system self-starting control method and system, and the method comprises the following steps: acquiring a rotor current rotating frequency and an actual rotor rotating frequency, and generating a slip frequency; comparing the slip frequency with a preset dynamic threshold value, and dynamically adjusting a rotating speed given value; inquiring a preset multi-stage segmented current control curve according to the actual rotor rotating frequency, and outputting a d-axis current given value; generating a q-axis current given value based on PI adjustment of the slip frequency, and applying a corresponding preset current threshold value limit according to a frequency band where the actual rotor rotating frequency is located; adopting a non-coupling parameter setting algorithm to independently configure parameters of a magnetic flux current control loop and a torque current control loop; and generating an optimal starting parameter combination under the condition of meeting a stable starting constraint condition in a unit starting process. The application realizes stable self-starting of the alternating current excitation system by dynamically adjusting the rotating speed given value and segmentally controlling the current, and improves the reliability and efficiency of the starting process.

Description

Technical Field

[0001] This invention relates to the field of power system control, specifically to a self-starting control method for an AC excitation system. Background Technology

[0002] An AC excitation system is a device that provides AC excitation power to the rotor of synchronous motors or doubly-fed induction motors. Its core is the injection of adjustable AC current in frequency, amplitude, and phase into the rotor windings via a power electronic converter (such as a fully controlled converter based on IGBTs), enabling flexible control of motor speed, reactive power, and energy flow. Utilizing algorithms such as vector control and direct torque control, this system endows the motor with wide-range variable speed operation, four-quadrant energy conversion (electrical energy can flow in and out of the rotor bidirectionally), and dynamic reactive power compensation capabilities. It is widely used in wind power generation (such as doubly-fed wind turbines achieving variable-speed constant-frequency power generation through rotor excitation), variable-speed pumped storage, and flywheel energy storage. Especially in renewable energy grid integration, it can optimize power quality and improve grid stability by adjusting the rotor current. It boasts advantages such as no mechanical contact loss, high control precision, and adaptability to the volatility of renewable energy, making it one of the key technologies for modern smart grids and high-efficiency drive systems.

[0003] Existing self-starting control methods for AC excitation systems still have some technical problems: First, during self-starting, excessive slip can easily lead to flux breakage, affecting system stability; second, under the field weakening control principle, if the magnetic field decays too early, the motor torque will be insufficient in the early stage, making it unable to start effectively; while if the decay is too late, it will be difficult to accelerate in the later stage, affecting starting efficiency; third, under the constant power control strategy, there is a coupling relationship between torque current and magnetic flux current, making parameter matching difficult and easily causing oscillation shutdown, affecting system reliability.

[0004] Furthermore, existing control parameters are typically fixed, lacking the ability to dynamically adjust based on actual operating conditions, and thus failing to adapt to startup requirements under different load conditions. Simultaneously, existing control methods often employ uniform parameter configurations for controlling the d-axis and q-axis currents, failing to fully consider the different characteristics of the two control loops, resulting in insufficient control accuracy.

[0005] Therefore, there is an urgent need for an AC excitation system self-starting control method that can decouple current, simplify parameter tuning, and optimize control curves to improve the system's startup performance and operational stability. Summary of the Invention

[0006] To overcome the technical problems of excessive slip leading to flux breakage, improper attenuation timing under the field weakening control principle resulting in insufficient torque or difficulty in speed-up, and current coupling causing oscillation shutdown during the self-starting process of AC exciter, this invention provides a self-starting control method and system for AC excitation system.

[0007] To solve the above problems, the present invention is implemented according to the following technical solution:

[0008] In a first aspect, the present invention provides a self-starting control method for an AC excitation system, comprising the following steps: acquiring the rotor current rotational frequency and the actual rotor rotational frequency, and generating a slip frequency through a slip calculation module; comparing the slip frequency with a preset dynamic threshold, and dynamically adjusting the speed setpoint based on the comparison result; querying a preset multi-level segmented current control curve based on the actual rotor rotational frequency, and outputting the d-axis current setpoint and a set of change slope parameters; generating a q-axis current setpoint based on the slip frequency using PI regulation, and applying a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotational frequency; employing a non-coupled parameter tuning algorithm to independently configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint; and generating an optimal combination of starting parameters during unit startup, under the condition of satisfying the unit's stable startup constraints.

[0009] In conjunction with the first aspect, the present invention provides a first specific implementation of the first aspect. Specifically, comparing the slip frequency with a preset dynamic threshold and dynamically adjusting the speed setpoint based on the comparison result specifically includes: maintaining the current speed setpoint when the slip frequency is not less than the preset dynamic threshold; incrementally adjusting the speed setpoint when the slip frequency is less than the preset dynamic threshold and the slip frequency is greater than 0; and forcing the speed setpoint to track the actual rotor rotation frequency when the slip frequency is less than 0, thus forming a closed-loop frequency correction mechanism.

[0010] In conjunction with the first aspect, the present invention provides a second specific implementation of the first aspect, specifically, the calculation formula for incrementally adjusting the given rotational speed is: N' reset =N reset +T S ·K reset ; where N reset Given the rotational speed, N' reset T is the adjusted speed setpoint. S K represents the system interrupt frequency. reset For a given speed increase coefficient.

[0011] In conjunction with the first aspect, the present invention provides a third specific implementation of the first aspect. Specifically, the preset multi-level segmented current control curve is as follows: different d-axis current setting values ​​are sequentially set in multiple consecutive speed ranges; the multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range; wherein an initial d-axis current setting value is set in the first speed range, a first d-axis current setting value is set in the second speed range, a second d-axis current setting value is set in the third speed range, and a third d-axis current setting value is set in the fourth speed range; the initial d-axis current setting value is dynamically corrected according to the inertia characteristics of the mechanical system.

[0012] In conjunction with the first aspect, the present invention provides a fourth specific implementation of the first aspect. Specifically, the step of generating a q-axis current setpoint based on slip frequency using PI regulation, and applying a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency, specifically includes: generating a q-axis current setpoint based on slip frequency using PI regulation; and applying a preset maximum current threshold limit to the q-axis current setpoint according to different speed frequency bands of the actual rotor rotation frequency of the motor; wherein the different speed frequency bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

[0013] In conjunction with the first aspect, the present invention provides a fifth specific implementation of the first aspect, wherein, under the field weakening control state, the initial d-axis current setting value, the first d-axis current setting value, the second d-axis current setting value, and the third d-axis current setting value decrease sequentially.

[0014] Secondly, the present invention also provides an AC excitation system self-starting control system, comprising: a signal acquisition module for acquiring the rotor current rotation frequency and the actual rotor rotation frequency; a slip calculation module connected to the signal acquisition module for calculating the slip frequency; a dynamic adjustment module connected to the slip calculation module for comparing the slip frequency with a preset dynamic threshold and dynamically adjusting the speed setpoint based on the comparison result; a segmented control module for querying a preset multi-level segmented current control curve based on the actual rotor rotation frequency and outputting the d-axis current setpoint and a set of change slope parameters; a q-axis limiting module for generating the q-axis current setpoint through PI regulation based on the slip frequency and applying a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency; a decoupling tuning module for independently configuring the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint using a non-coupled parameter tuning algorithm; and an optimization engine module for generating the optimal combination of starting parameters under the condition of meeting the unit's stable start-up constraints during unit startup.

[0015] In conjunction with the second aspect, the present invention provides a first specific implementation of the second aspect. Specifically, the dynamic adjustment module dynamically adjusts the speed setpoint based on the comparison result between the slip signal and a preset dynamic threshold. Specifically, this includes: maintaining the current speed setpoint when the slip frequency is not less than the preset dynamic threshold; incrementally adjusting the speed setpoint when the slip frequency is less than the preset dynamic threshold and the slip frequency is greater than 0; and forcing the speed setpoint to track the actual rotor speed signal when the slip frequency is less than 0, thus forming a closed-loop frequency correction mechanism.

[0016] In conjunction with the second aspect, the present invention provides a second specific implementation of the second aspect. Specifically, the segmented control module executes a preset multi-level segmented current control curve, specifically by sequentially setting different d-axis current setting values ​​within multiple consecutive speed ranges; the multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range; wherein, an initial d-axis current setting value is set within the first speed range, a first d-axis current setting value is set within the second speed range, a second d-axis current setting value is set within the third speed range, and a third d-axis current setting value is set within the fourth speed range; the initial d-axis current setting value is dynamically corrected based on the inertia characteristics of the mechanical system; under field weakening control, the initial d-axis current setting value, the first d-axis current setting value, the second d-axis current setting value, and the third d-axis current setting value decrease sequentially.

[0017] In conjunction with the second aspect, the present invention provides a third specific implementation of the second aspect. Specifically, the q-axis limiting module performs PI regulation based on the slip frequency to generate a q-axis current setpoint, and applies a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. Specifically, this includes: generating a q-axis current setpoint based on the slip frequency; and applying a preset maximum current threshold limit to the q-axis current setpoint according to different speed frequency bands of the actual rotor rotation frequency of the motor; wherein the different speed frequency bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: Improved system stability is achieved through optimized speed-given control strategy; segmented control of flux current and torque current based on frequency optimizes the current control curve, resulting in different current change slopes at different stages to match actual motor characteristics; decoupling of torque current and flux current simplifies parameter configuration; faster tuning of starting parameters while ensuring stable unit startup optimizes startup speed; and avoids the problem of flux linkage breakage caused by excessive q-axis current during the field weakening stage. Compared with existing technologies, this invention effectively solves the technical difficulties in the self-starting process of traditional AC exciters through segmented current control curves and decoupled parameter tuning algorithms, achieving more stable and efficient self-starting control. Attached Figure Description

[0019] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0020] Figure 1 This is a flowchart of an AC excitation system self-starting control method according to the present invention. Detailed Implementation

[0021] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0022] like Figure 1 As shown, this invention provides a self-starting control method and system for an AC excitation system.

[0023] Example 1

[0024] A self-starting control method for an AC excitation system includes the following steps:

[0025] S100: Obtain the rotor current rotational frequency and the actual rotor rotational frequency, and generate the slip frequency through the slip calculation module;

[0026] S200: Compares the slip frequency with a preset dynamic threshold and dynamically adjusts the speed setpoint based on the comparison result;

[0027] S300: Based on the actual rotor rotation frequency, query the preset multi-level segmented current control curve and output the d-axis current setpoint and change slope parameter set;

[0028] S400: Generates q-axis current setpoint by PI regulation based on slip frequency, and applies corresponding preset current threshold limit to q-axis current setpoint according to the frequency band of the actual rotor rotation frequency.

[0029] S500: Employs a non-coupled parameter tuning algorithm to independently configure the parameters of the flux current control loop based on the d-axis current reference value and the torque current control loop based on the q-axis current reference value.

[0030] S600: During the unit startup process, under the condition of meeting the unit stable startup constraints, generate the optimal combination of startup parameters.

[0031] In a preferred embodiment, the rotor current rotational frequency and the actual rotor rotational frequency are obtained, and the slip frequency is generated by the slip calculation module. The slip frequency calculation formula is ΔNr = Nr ram -Nr; where ΔNr is the angular frequency, Nr ram Where is the rotor current rotational frequency, and Nr is the actual rotor rotational frequency.

[0032] Specifically, in an AC excitation system, a current sensor collects the three-phase rotor current. The three-phase current undergoes Clark transform, Park transform, and their inverse transform to obtain the rotor current rotational frequency. The actual rotor rotational frequency is directly measured by a speed sensor (such as a photoelectric encoder or rotary transformer). The photoelectric encoder outputs a pulse signal corresponding to the actual rotor speed, and the actual rotor rotational frequency is calculated by counting the number of pulses per unit time. The slip calculation module receives these two frequency signals and calculates the slip frequency, which is the difference between the rotor current rotational frequency and the actual rotor rotational frequency.

[0033] Specifically, the given values ​​of the three-phase AC excitation current are obtained from the motor control system, and are denoted as i a i b i c The given value of the AC excitation current in the three-phase stationary coordinate system (abc) is transformed to the two-phase stationary coordinate system (αβ). The transformation formula is: The current reference value in the two-phase stationary coordinate system (αβ) is transformed to the two-phase rotating coordinate system (dq). The transformation formula is as follows: Where θ is the rotor position angle, which can be obtained through a position sensor or a sensorless estimation method. After the above transformation, the obtained ip_ref That is, the d-axis current setpoint, i q_ref This is the given value for the q-axis current.

[0034] In a preferred embodiment, the slip frequency is compared with a preset dynamic threshold, and the speed setpoint is dynamically adjusted according to the comparison result. When the slip frequency is not less than the preset dynamic threshold, the system maintains the current speed setpoint unchanged. When the slip frequency is less than the preset dynamic threshold but greater than 0, the system performs incremental adjustment on the speed setpoint. When the slip frequency is less than 0, the system forces the speed setpoint to track the actual rotor rotation frequency, forming a closed-loop frequency correction mechanism.

[0035] Specifically, a dynamic threshold Nr is set based on the motor's operating conditions, load characteristics, and control requirements. deltaSet Its value range is [0, 10] Hz (the specific unit can be determined according to the actual motor parameters and frequency conversion). In the initial stage, the dynamic threshold is preset to 1 Hz as a benchmark for judging whether the slip is reasonable. During motor operation, the calculated slip is compared with the preset dynamic threshold Nr in real time. deltaSet The comparison is performed, and different speed setpoint adjustment states are triggered based on the comparison results.

[0036] State 1: ΔNr≥Nr deltaSet This indicates that the motor rotor currently has a large slip, possibly under light or underload conditions, and its speed is too high. At this time, the speed setpoint N is executed. reset Maintain the current operation and wait for the rotor frequency to increase due to load changes or motor self-adjustment, thereby reducing slip. During the maintenance period, continuously monitor the slip frequency. Once the slip frequency decreases and falls below the threshold, consider switching to other states to adjust the speed setpoint.

[0037] State 2: 0 < ΔNr <Nr deltaSet This indicates that the motor is operating relatively normally, but there is still room to increase its speed to better adapt to potential load demands or improve operating efficiency. At this point, according to formula N′... reset =N reset +T S ·K reset The speed setpoint is adjusted incrementally, where N reset Given the rotational speed, N' reset T is the adjusted speed setpoint. S K represents the system interrupt frequency. reset Let T be the given speed increase coefficient. S K represents the system interrupt frequency, i.e., the periodic interval at which the system updates the speed setpoint. resetThe speed increase coefficient can be preset and adjusted according to the motor's dynamic response characteristics and control requirements. In this way, the speed setpoint increases steadily, gradually increasing the motor speed to optimize the motor's operating performance.

[0038] State 3: When ΔNr < 0, it means that the actual rotor rotation frequency is higher than the rotor current rotation frequency. This situation may occur under special operating conditions such as when the motor is in braking mode or the load suddenly decreases. In this case, in order to quickly adapt to this change and avoid unstable operation of the motor, the speed setpoint N is directly set to... reset The speed is set to the actual rotor rotation frequency collected in this cycle. This immediately matches the motor speed setting with the actual speed, ensuring the stability and safety of motor operation.

[0039] In a preferred embodiment, the system queries a preset multi-level segmented current control curve based on the actual rotor rotation frequency and outputs the corresponding d-axis current setpoint and slope parameter set. Specifically, the preset multi-level segmented current control curve involves sequentially setting different d-axis current setpoints within multiple consecutive speed ranges; these multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range; wherein an initial d-axis current setpoint is set within the first speed range, a first d-axis current setpoint is set within the second speed range, a second d-axis current setpoint is set within the third speed range, and a third d-axis current setpoint is set within the fourth speed range; the initial d-axis current setpoint is dynamically corrected based on the mechanical system's inertia characteristics.

[0040] Specifically, the segmented control is as follows: In the first speed range (0–30Hz), the system sets an initial d-axis current setting. In the second speed range (30–40Hz), the system sets a first d-axis current setting. In the third speed range (40–45Hz), the system sets a second d-axis current setting. In the fourth speed range (45–50Hz), the system sets a third d-axis current setting. The initial d-axis current setting is dynamically corrected by an adaptive adjustment module based on the mechanical system's inertia characteristics to match the d-axis current rise rate with the load's mechanical characteristics. The initial, first, second, and third d-axis current settings decrease sequentially to achieve field weakening control.

[0041] Based on the actual rotor rotation frequency (Nr), the corresponding frequency value is calculated (f = Nr / 60, unit: Hz). The 50Hz frequency is divided into four frequency ranges: 0–30Hz, 30–40Hz, 40–45Hz, and 45–50Hz, corresponding to the initial d-axis current setting value Ird_set30, the first d-axis current setting value Ird_set40, the second d-axis current setting value Ird_set45, and the third d-axis current setting value Ird_set50, respectively. The value range of each d-axis setting value is 0 to the rated excitation current value (the rated excitation current value depends on the specific parameters and rated operating conditions of the motor). In the initial stage, each setting value can be set to a small initial value, and then adjusted according to the tuning requirements.

[0042] Set the initial d-axis current setting value Ird_set30. Start with a small initial value for Ird_set30, and gradually increase the setting value in increments of a certain amount each time. After each adjustment, start the motor and observe its initial acceleration, starting stability, and system current. Determine the initial acceleration and starting stability by measuring the time it takes for the motor speed to rise and the speed fluctuations during startup. Record the time required for the motor to accelerate from a standstill to a certain speed; a shorter time indicates a faster initial acceleration. Simultaneously observe the smoothness of the speed curve during startup; small speed fluctuations without significant oscillations indicate good starting stability. Monitor the motor's current and speed signals in real time. If significant periodic fluctuations occur in the current or speed during startup, and the amplitude continuously increases, it indicates system oscillation. Once oscillation occurs, stop increasing Ird_set30 and appropriately decrease its setting value. Set up a current monitoring device to monitor the motor's phase current or total current in real time. If the current exceeds the motor's rated current or the maximum current allowed by the control system, it is considered an overcurrent in the system. At this point, the increase of Ird_set30 should be stopped, and the setting should be reverted to the non-overcurrent setting. After a gradual adjustment process, when Ird_set30 is increased to a certain value, it can meet the requirements of a high initial rise rate and good startup stability, without causing system oscillation or overcurrent. The corresponding Ird_set30 value at this point is the final determined d-axis current setpoint for this frequency range.

[0043] Field weakening control is used to maintain a constant or near-rated air gap flux in motors when operating at higher frequencies (close to or above the rated frequency) by appropriately reducing the excitation current (i.e., d-axis current). This prevents problems such as increased iron losses, reduced efficiency, and deteriorated motor performance caused by magnetic circuit oversaturation. Therefore, as the frequency increases, the d-axis setting values ​​at each stage need to be gradually reduced according to a certain pattern. Based on the established Ird_set30, and following the general principles of field weakening control, the initial values ​​of the first d-axis current setting Ird_set40, the second d-axis current setting Ird_set45, and the third d-axis current setting Ird_set50 are set. After each adjustment of the setting values, a motor self-start test is performed, recording the start-up time from a standstill to the rated speed corresponding to 50Hz, as well as the changes in current and speed during the start-up process. The focus is on observing whether the motor can start smoothly and reach the rated speed, and whether there are any abnormal phenomena such as oscillation or overcurrent during the start-up process. With the goal of reducing self-starting time, the settings at each level were repeatedly adjusted and optimized while ensuring that the system did not oscillate, did not experience overcurrent, and could self-start to the rated 50Hz. If the self-starting time was found to be too long under the current settings, but without violating the limiting conditions, the values ​​of Ird_set40, Ird_set45, and Ird_set50 could be appropriately increased to accelerate the initial acceleration process of the motor; conversely, if oscillation or overcurrent occurred, the corresponding settings needed to be decreased. Through multiple tests and adjustments, a set of four-level d-axis current settings was finally determined that could achieve rapid self-starting while satisfying system stability and safety. The determined values ​​of Ird_set30, Ird_set40, Ird_set45, and Ird_set50 were plotted on a d-axis current versus frequency coordinate graph according to the corresponding frequency range, forming a segmented d-axis current control curve. Simultaneously, a corresponding slope parameter is determined for each setpoint. This slope parameter can be set according to the motor's dynamic response requirements and system stability requirements. A gentler slope can be set in the lower frequency range to ensure smooth startup; in the higher frequency range, the slope can be appropriately increased to accelerate current adjustment, enabling the motor to quickly adapt to high-frequency operating conditions. During motor operation, the actual rotor rotation frequency (Nr) is acquired in real time and converted to the corresponding frequency value (f = Nr / 60). Based on this frequency value, the corresponding d-axis current setpoint and slope parameter set are queried from the preset multi-level segmented current control curve. When f = 35Hz, the corresponding d-axis current setpoint is found to be Ird_set40, and the slope parameter is the pre-set k40_slope; when f = 48Hz, the corresponding d-axis current setpoint is found to be Ird_set50, and the slope parameter is k50_slope.The retrieved d-axis current setpoint and slope parameter set are output to the motor control system for real-time control and adjustment of the d-axis current, so as to achieve the optimal operating performance of the motor at different speeds.

[0044] In a preferred embodiment, the q-axis current setpoint is generated based on the slip frequency using PI control, and a corresponding preset current threshold limit is applied to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. Specifically, the q-axis current setpoint is generated based on the slip frequency using PI control; a preset maximum current threshold limit is applied to the q-axis current setpoint according to different speed bands of the actual rotor rotation frequency; wherein the different speed bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

[0045] Specifically, based on the actual rotor rotation frequency of the motor, a preset maximum current threshold is applied to the q-axis current setpoint: a first maximum current threshold is applied within the speed range of 0–40 Hz; a second maximum current threshold is applied within the speed range of 40–45 Hz; and a third maximum current threshold is applied within the speed range of 45–50 Hz. These three maximum current thresholds are theoretically in an increasing relationship to ensure that the q-axis current can increase when the d-axis current decreases, allowing for continued speed increase in an approximately constant power mode. In particular, if the actual motor startup process causes unit oscillation due to an excessively large calculated q-axis current, the above increasing relationship may not be followed. When the actual speed is within a certain frequency band, the system limits the q-axis current setpoint to not exceed the maximum current threshold corresponding to that frequency band.

[0046] Perform a PI calculation on the slip frequency ΔNr to obtain the q-axis current setpoint i. q_ref The formula for calculating PI is: i q_ref =K p_q· ΔNr+K i_q ·∫ΔNr·dt, where K p_q For proportional gain, K i_q This is the integral gain. The PI parameter K is tuned. p_q and K i_q The goal is to reduce the motor's self-starting time while ensuring the system does not oscillate or experience overcurrent. Appropriately increasing K... p_q This can accelerate system response, allowing the rotational speed to track the given value more quickly, thereby shortening the self-starting time; increasing K i This helps eliminate steady-state speed error and further improves starting accuracy. If K p_q If K is too large, the system is prone to oscillation; therefore, K needs to be reduced. p_q If the integral effect is too strong (K) i_q (If the value is too large), it can also cause oscillations, requiring adjustment of K. i_qKeep it at a suitable level. Monitor the motor current in real time; if overcurrent tendency is observed, appropriately reduce K. p_q and K i_q This limits the growth rate of the given value of the q-axis current.

[0047] Based on the actual rotor rotation frequency Nr, the corresponding frequency value f = Nr / 60 is calculated, and the 0-50Hz range is divided into three frequency intervals: 0-40Hz corresponds to the first maximum current threshold I. rq_max40 40-45Hz corresponds to the second maximum current threshold I rq_max45 The third maximum current threshold I corresponds to 45-50Hz. rq_max50 The threshold range for each level is 0 to the rated excitation current value. During motor operation, the actual rotor rotation frequency Nr is acquired in real time, converted to a frequency value f, and its corresponding frequency range is determined. This information is then used to set the q-axis current value i. q_ref Apply appropriate threshold restrictions:

[0048] If f∈[0Hz,40Hz], then i q_limited =min(i q_ref I rq_max40 );

[0049] If f∈(40Hz,45Hz], then i q_limited =min(i q_ref I rq_max45 );

[0050] If f∈(45Hz,50Hz], then i q_limited =min(i q_ref I rq_max50 );

[0051] Within the 0–40Hz range, the system steadily increases the rotor frequency at a relatively rapid pace. This is achieved by setting a relatively high IF. rq_max40 The threshold value allows for a larger q-axis current setpoint, enabling the motor to output greater torque, accelerating the rotor acceleration process, and shortening the start-up time. Within the 40–50 Hz range (field weakening stage), as the frequency increases, it enters the field weakening stage. If the magnetic flux is stable, the threshold value (I)... rq_max45 and I rq_max50 The threshold can be increased incrementally, allowing the motor to continue operating at approximately constant power. If flux linkage breaks due to a decrease in d-axis current and an increase in q-axis current, the threshold (I) can be gradually decreased. rq_max45 and I rq_max50 The motor continues to accelerate at a lower power. This ensures system stability while reasonably limiting the q-axis current, guaranteeing flux stability and allowing the motor to run smoothly up to its rated 50Hz. The q-axis current setpoint i after threshold limiting is then... q_limitedThe output is sent to the motor control system, where it works in conjunction with the d-axis current setpoint to control motor operation. During actual motor operation, the PI parameters and three-level threshold are further optimized based on start-up time and stability performance: if the start-up time is too long, K can be appropriately increased. p_q and K i_q Simultaneously check for overcurrent or oscillation. If magnetic flux instability occurs during the weak magnetic phase, appropriately reduce I. rq_max45 and I rq_max50 .

[0052] In a preferred embodiment, the system employs a decoupled parameter tuning algorithm to independently configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint. The decoupled parameter tuning algorithm, based on the motor mathematical model, decouples the d-axis and q-axis control loops, allowing the two loops to be adjusted independently.

[0053] The purpose of the uncoupled parameter tuning algorithm is to decouple the d-axis and q-axis current control loops, enabling independent parameter configuration and optimization for both loops. Its core idea is based on the mathematical model of the motor, and through reasonable control law design, to eliminate the mutual coupling influence between the d and q axes, thereby achieving precise and independent control of the magnetic flux current (d-axis current) and torque current (q-axis current). The d-axis current control model is established. Based on the motor's voltage equations, in the d-q rotating coordinate system, the d-axis voltage equation is: u d =R s ·i d +L d ·(d(i d ) / dt)-ω e ·L q ·i q +dΨ / dt; where u d R is the d-axis voltage. s L is the stator resistance. d For the d-axis inductance, i d Let ω be the d-axis current. e L is the electric angular velocity of the motor. q For q-axis inductance, i q Let ρ be the q-axis current and Ψ be the magnetic flux linkage. In steady state, neglecting the rate of change of magnetic flux linkage dψ / dt, the simplified equation is: u d ≈R s ·i d +L d ·(d(i d ) / dt)-ω e ·L q ·i q .

[0054] A PI controller is used to regulate the d-axis current, and the controller output is the d-axis voltage setpoint u.d_ref The expression for the PI controller is: u d_ref =K p_d ·(i rd_ref -i rd )+K i_d ·∫(i rd_ref -i rd )dt; where i rd_ref i is the given value for the d-axis current. rd K represents the actual d-axis current feedback value. p_d K is the proportional gain of the d-axis current loop. i_d This is the d-axis current loop proportional gain.

[0055] Establish the q-axis current control model. Based on the motor's voltage equation, in the dq rotating coordinate system, the q-axis voltage equation is: u q =R s ·i q +L q ·(d(i q ) / dt)-ω e ·L d ·i d +dΨ / dt; where u q Let i be the q-axis voltage. q Let be the q-axis current; the other parameters have the same meaning as in the d-axis voltage equation. In steady-state conditions, the simplified equation is: u q ≈R s ·i q +L q ·(d(i q ) / dt)-ω e ·L d ·i d Similarly, a PI controller is used to regulate the q-axis current, and the controller output is the q-axis voltage setpoint u. q_ref The expression for the PI controller is: u q_ref =K p_q ·(i rq_ref -i rq )+K i_q ·∫(i rq_ref -i rq )dt; where i rq_ref Given the q-axis current, i rq K represents the actual q-axis current feedback value. p_q K is the proportional gain of the q-axis current loop. i_q This is the proportional gain of the q-axis current loop.

[0056] To eliminate the mutual coupling effect between the d and q axes, a decoupling control law is designed. Based on the motor's voltage equation, the decoupling control law can be expressed as: u d_ref =Kp_d ·(i rd_ref -i rd )+K i_d ·∫(i rd_ref -i rd )dt+ω e ·L q ·i q ;u q_ref =K p_q ·(i rq_ref -i rq )+K i_q ·∫(i rq_ref -i rq )dt+ω e ·L d ·i d The first two terms are the outputs of the dq-axis current loop PI controller, and the last two terms are decoupling compensation terms used to eliminate the coupling effect between the dq axes.

[0057] By acquiring the electric angular velocity ω of the motor in real time e Actual d-axis current feedback value i rd and the actual q-axis current feedback value i rq Calculate the d-axis and q-axis voltage setpoints u based on the decoupling control law. d_ref and u q_ref The calculated u d_ref and u q_ref The voltage setpoint u is transformed into a two-phase stationary coordinate system by the inverse Park transform. α_ref and u β_ref Finally, a three-phase PWM signal is generated using SVPWM (Space Vector Pulse Width Modulation) or other PWM techniques to control the switching action of the inverter, thereby achieving precise control of the motor.

[0058] In a preferred embodiment, during unit startup, the system generates an optimal combination of startup parameters while meeting the constraints of stable unit startup. The system dynamically adjusts startup parameters, including the d-axis current rise rate, q-axis current limit, and speed setpoint growth coefficient, based on unit characteristics and load conditions to achieve optimal startup performance.

[0059] Specifically, the system monitors key parameters during startup, such as rotor current, stator current, slip frequency, and rate of change of speed, to determine whether the startup state is stable. If an unstable state is detected, the system automatically adjusts the startup parameters to ensure stable unit startup. The optimal startup parameter combination is generated based on a multi-objective optimization algorithm, comprehensively considering factors such as startup time, peak startup current, and energy consumption. The system predicts the optimal parameter combination based on historical startup data and the current unit status, and makes fine adjustments based on the actual response during startup.

[0060] Example 2

[0061] An AC excitation system self-starting control system, comprising:

[0062] The signal acquisition module is used to obtain the rotor current rotation frequency and the actual rotor rotation frequency;

[0063] A slip calculation module, connected to the signal acquisition module, is used to calculate the slip frequency;

[0064] A dynamic adjustment module, which is connected to a slip calculation module, is used to compare the slip frequency with a preset dynamic threshold and dynamically adjust the speed setpoint based on the comparison result.

[0065] The segmented control module is used to query the preset multi-level segmented current control curve based on the actual rotor rotation frequency, and output the d-axis current setpoint and the set of change slope parameters.

[0066] The q-axis limiting module is used to generate a q-axis current setpoint based on the slip frequency using PI regulation, and to apply a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency.

[0067] The decoupling tuning module is used to configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint independently using a non-coupled parameter tuning algorithm.

[0068] The optimization engine module is used to generate the optimal combination of startup parameters during the unit startup process, under the condition of meeting the unit's stable startup constraints.

[0069] In a preferred embodiment, the signal acquisition module includes a current sensor and a speed sensor. The current sensor acquires the three-phase current signal of the rotor, and after passing through a signal conditioning circuit and an analog-to-digital converter, outputs a digitized current signal. The speed sensor acquires the actual rotational speed signal of the rotor, and similarly outputs it after signal conditioning and digitization. The signal acquisition module also includes a filtering unit to filter out noise and interference in the signal, improving signal quality.

[0070] In a preferred embodiment, the slip calculation module receives the rotor current rotational frequency and the actual rotor rotational frequency signal from the signal acquisition module, and calculates the difference between the two, i.e., the slip frequency. The slip calculation module includes a frequency extraction unit and a difference calculation unit. The frequency extraction unit extracts the rotational frequency from the rotor current signal, and the difference calculation unit calculates the slip frequency.

[0071] In a preferred embodiment, the dynamic adjustment module dynamically adjusts the speed setpoint based on a comparison between the slip signal and a preset dynamic threshold. The dynamic adjustment module includes a comparison unit and an adjustment unit. The comparison unit compares the slip frequency with the preset dynamic threshold, and the adjustment unit adjusts the speed setpoint based on the comparison result.

[0072] In a preferred embodiment, when the slip frequency is not less than a preset dynamic threshold, the dynamic adjustment module maintains the current speed setpoint; when the slip frequency is less than the preset dynamic threshold but greater than 0, the dynamic adjustment module performs incremental adjustment on the speed setpoint; when the slip frequency is less than 0, the dynamic adjustment module forces the speed setpoint to track the actual rotor speed signal, forming a closed-loop frequency correction mechanism.

[0073] In a preferred embodiment, the segmented control module queries a preset multi-level segmented current control curve based on the actual rotor rotation frequency, and outputs the d-axis current setpoint and a set of change slope parameters. The segmented control module includes a frequency detection unit, a lookup table unit, and an output unit. The frequency detection unit detects the actual rotor rotation frequency, the lookup table unit queries the corresponding d-axis current setpoint based on the frequency, and the output unit generates the d-axis current setpoint and change slope parameters.

[0074] In a preferred embodiment, the segmented control module executes a preset multi-level segmented current control curve, specifically by sequentially setting different d-axis current setting values ​​within multiple consecutive speed ranges; the multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range; wherein, an initial d-axis current setting value is set within the first speed range, a first d-axis current setting value is set within the second speed range, a second d-axis current setting value is set within the third speed range, and a third d-axis current setting value is set within the fourth speed range; the initial d-axis current setting value is dynamically corrected based on the inertia characteristics of the mechanical system; under field weakening control, the initial d-axis current setting value, the first d-axis current setting value, the second d-axis current setting value, and the third d-axis current setting value decrease sequentially.

[0075] Specifically, an initial d-axis current setting is set within a first speed range of 0–30 Hz; a second d-axis current setting is set within a second speed range of 30–40 Hz; a second d-axis current setting is set within a third speed range of 40–45 Hz; and a third d-axis current setting is set within a fourth speed range of 45–50 Hz. The initial d-axis current setting is dynamically corrected by an adaptive adjustment module based on the inertia characteristics of the mechanical system to match the d-axis current rise rate with the load's mechanical characteristics. The initial d-axis current setting is adjusted according to the inertia characteristics to match the d-axis current rise rate with the load's mechanical characteristics. For systems with high inertia, the inertia adaptive unit increases the initial d-axis current setting; for systems with low inertia, it decreases the initial d-axis current setting. Under field weakening control, the initial d-axis current setting, the first d-axis current setting, the second d-axis current setting, and the third d-axis current setting decrease sequentially.

[0076] In a preferred embodiment, the q-axis limiting module generates a q-axis current setpoint based on the slip frequency using PI control, and applies a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. The q-axis limiting module includes a PI control unit, a frequency band determination unit, and a limiting unit. The PI control unit generates an initial q-axis current setpoint based on the slip frequency, the frequency band determination unit determines the frequency band of the current rotation speed, and the limiting unit applies a corresponding current threshold limit based on the frequency band.

[0077] In a preferred embodiment, the q-axis limiting module performs PI regulation based on the slip frequency to generate a q-axis current setpoint, and applies a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. Specifically, this includes: generating a q-axis current setpoint based on the slip frequency; and applying a preset maximum current threshold limit to the q-axis current setpoint according to different speed frequency bands of the actual rotor rotation frequency of the motor; wherein the different speed frequency bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

[0078] Specifically, a PI control is performed based on the slip frequency to generate a q-axis current setpoint; according to the actual rotor rotation frequency of the motor, a preset maximum current threshold is applied to the q-axis current setpoint. A first maximum current threshold is applied within the speed range of 0 to 40 Hz; a second maximum current threshold is applied within the speed range of 40 to 45 Hz; and a third maximum current threshold is applied within the speed range of 45 to 50 Hz. When the actual speed is in a certain frequency band, the q-axis current setpoint is limited to not exceeding the maximum current threshold corresponding to that frequency band.

[0079] In a preferred embodiment, the decoupling tuning module is used to independently configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint using an uncoupled parameter tuning algorithm. The decoupling tuning module includes a model calculation unit, a parameter optimization unit, and a controller configuration unit. The model calculation unit establishes a mathematical model based on the motor parameters, the parameter optimization unit calculates the optimal control parameters, and the controller configuration unit applies the parameters to the control loop.

[0080] In a preferred embodiment, the optimization engine module generates an optimal combination of startup parameters during unit startup, provided that the unit's stable startup constraints are met. The optimization engine module includes a status monitoring unit, a parameter prediction unit, and a parameter adjustment unit. The status monitoring unit monitors key parameters during startup, the parameter prediction unit predicts the optimal parameter combination, and the parameter adjustment unit adjusts the parameters based on the actual response.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An AC excitation system self-starting control method, characterized by, Includes the following steps: The rotor current rotational frequency and the actual rotor rotational frequency are obtained, and the slip frequency is generated through the slip calculation module. The slip frequency is compared with a preset dynamic threshold, and the speed setpoint is dynamically adjusted according to the comparison result. The step of comparing the slip frequency with a preset dynamic threshold and dynamically adjusting the speed setpoint based on the comparison result specifically includes: When the slip frequency is not less than the preset dynamic threshold, the current speed setpoint is maintained. When the slip frequency is less than a preset dynamic threshold and the slip frequency is greater than 0, the speed setpoint is adjusted incrementally. When the slip frequency is less than 0, the speed setpoint is forced to track the actual rotor rotation frequency, forming a closed-loop frequency correction mechanism. Based on the actual rotor rotation frequency, query the preset multi-level segmented current control curve and output the d-axis current setpoint and change slope parameter. The preset multi-level segmented current control curve is specifically as follows: Different d-axis current settings are sequentially set within multiple consecutive speed ranges; The multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range that increase sequentially. Specifically, an initial d-axis current setting value is set in the first speed range, a first d-axis current setting value is set in the second speed range, a second d-axis current setting value is set in the third speed range, and a third d-axis current setting value is set in the fourth speed range. The initial d-axis current setting value is dynamically corrected based on the inertia characteristics of the mechanical system; In the field weakening control state, the initial d-axis current setting value, the first d-axis current setting value, the second d-axis current setting value, and the third d-axis current setting value decrease sequentially. The q-axis current setpoint is generated by PI regulation based on the slip frequency, and a corresponding preset current threshold limit is applied to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. An uncoupled parameter tuning algorithm is used to independently configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint. During the unit startup process, the optimal combination of startup parameters is generated under the condition of meeting the unit's stable startup constraints.

2. The method of claim 1, wherein the method further comprises: The calculation formula for incrementally adjusting the given speed value is as follows: ； wherein is the rotational speed setpoint, is the adjusted rotational speed setpoint, is the system interruption frequency, is the rotational speed growth coefficient.

3. The self-starting control method for an AC excitation system according to claim 1, characterized in that, The step of generating a q-axis current setpoint based on slip frequency using PI regulation, and applying a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency, specifically includes: The q-axis current setpoint is generated by PI regulation based on the slip frequency. Based on the different speed bands where the actual rotor rotation frequency of the motor is located, a preset maximum current threshold limit is applied to the given value of the q-axis current. The different rotational speed frequency bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

4. A self-starting control system for an AC excitation system, characterized in that, include: The signal acquisition module is used to obtain the rotor current rotation frequency and the actual rotor rotation frequency; A slip calculation module, connected to the signal acquisition module, is used to calculate the slip frequency; A dynamic adjustment module, which is connected to a slip calculation module, is used to compare the slip frequency with a preset dynamic threshold and dynamically adjust the speed setpoint based on the comparison result. The dynamic adjustment module dynamically adjusts the speed setpoint based on the comparison result between the slip frequency and the preset dynamic threshold, specifically including: When the slip frequency is not less than the preset dynamic threshold, the current speed setpoint is maintained. When the slip frequency is less than a preset dynamic threshold and the slip frequency is greater than 0, the speed setpoint is adjusted incrementally. When the slip frequency is less than 0, the speed setpoint is forced to track the actual rotor speed signal, forming a closed-loop frequency correction mechanism. The segmented control module is used to query the preset multi-level segmented current control curve based on the actual rotor rotation frequency, and output the d-axis current setpoint and the change slope parameter. The segmented control module executes a preset multi-level segmented current control curve, specifically: Different d-axis current settings are sequentially set within multiple consecutive speed ranges; The multiple consecutive speed ranges include a first speed range, a second speed range, a third speed range, and a fourth speed range that increase sequentially. Specifically, an initial d-axis current setting value is set in the first speed range, a first d-axis current setting value is set in the second speed range, a second d-axis current setting value is set in the third speed range, and a third d-axis current setting value is set in the fourth speed range. The initial d-axis current setting value is dynamically corrected based on the inertia characteristics of the mechanical system; In the field weakening control state, the initial d-axis current setting value, the first d-axis current setting value, the second d-axis current setting value, and the third d-axis current setting value decrease sequentially. The q-axis limiting module is used to generate a q-axis current setpoint based on the slip frequency using PI regulation, and to apply a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. The decoupling tuning module is used to configure the parameters of the flux current control loop based on the d-axis current setpoint and the torque current control loop based on the q-axis current setpoint independently using a non-coupled parameter tuning algorithm. The optimization engine module is used to generate the optimal combination of startup parameters during the unit startup process, under the condition of meeting the unit's stable startup constraints.

5. The self-starting control system for an AC excitation system according to claim 4, characterized in that, The q-axis limiting module performs PI regulation based on the slip frequency to generate a q-axis current setpoint. It then applies a corresponding preset current threshold limit to the q-axis current setpoint according to the frequency band of the actual rotor rotation frequency. Specifically, this includes: The q-axis current setpoint is generated by PI regulation based on the slip frequency. Based on the different speed bands where the actual rotor rotation frequency of the motor is located, a preset maximum current threshold limit is applied to the given value of the q-axis current. The different rotational speed frequency bands include at least three consecutive frequency bands, and different maximum current threshold limits are applied to each of the at least three consecutive frequency bands.

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