A high-voltage variable-frequency low-voltage ride-through control method and system

Abstract

The application discloses a high-voltage frequency converter low-voltage ride-through control method and system, relates to the technical field of frequency converter ride-through control, and comprises the following steps: constructing a motor-grid joint model; detecting the grid voltage connected with the frequency converter in real time; converting motor rotary kinetic energy into electric energy to be fed back to a DC bus through dynamic flux modulation and virtual braking torque synthesis; when detecting that the grid voltage is restored, tracing the motor rotor position and speed in real time, outputting matched voltage at the voltage restoration moment, and completing impact-free reclosing. The application solves the technical problems that the prior art cannot effectively inhibit asymmetric voltage disturbance of a power grid, redundant kinetic energy is difficult to reasonably dissipate and stabilize voltage during motor drop, and reclosing after the power grid is restored is prone to impact and operation stability is poor, achieves asymmetric disturbance inhibition and motor kinetic energy feedback voltage stabilization when the power grid voltage drops, and improves the technical effects of high-voltage frequency converter low-voltage ride-through capability and power grid grid-connected operation stability.

Description

Technical Field

[0001] This invention relates to the field of inverter ride-through control technology, specifically to a low-voltage ride-through control method and system for high-voltage inverters. Background Technology

[0002] High-voltage frequency converters are widely used in large industrial motor drive scenarios. In actual power grid operation, voltage drops and three-phase voltage asymmetry disturbances often occur due to factors such as line faults, load fluctuations, and lightning interference. Most existing conventional low-voltage ride-through control schemes only provide single compensation control for symmetrical voltage drops, which makes it difficult to accurately identify and suppress the adverse effects of negative sequence voltage. They cannot effectively utilize the redundant kinetic energy of the motor rotation to achieve DC bus voltage stabilization, and are prone to bus voltage fluctuations and equipment instability. At the same time, after the grid voltage recovers, traditional control methods cannot accurately match the real-time rotor position and speed of the motor. The reclosing process is prone to generating large inrush currents and torque oscillations, which in turn leads to increased wear and tear on the frequency converter and motor equipment and reduced operational reliability. This makes it difficult to meet the actual needs of high-voltage frequency converters for long-term stable operation under complex power grid conditions.

[0003] Existing technologies cannot effectively suppress asymmetrical voltage disturbances in the power grid, and redundant kinetic energy during motor drops is difficult to dissipate and stabilize, resulting in technical problems such as easy impact during reclosing after the power grid is restored and poor operational stability. Summary of the Invention

[0004] This application provides a low-voltage ride-through control method and system for high-voltage frequency converters, which addresses the technical problems of existing technologies being unable to effectively suppress asymmetrical voltage disturbances in the power grid, and the difficulty in reasonably dissipating and stabilizing redundant kinetic energy during motor voltage drops, resulting in easy impacts and poor operational stability when reclosing after the power grid is restored.

[0005] In view of the above problems, this application provides a low voltage ride-through control method and system for high voltage frequency converters.

[0006] A first aspect of this application provides a low-voltage ride-through control method for a high-voltage frequency converter, the method comprising: A motor-grid joint model is constructed for the frequency converter. This model runs continuously during frequency converter operation and uses a state estimator to calibrate motor parameters in real time. It monitors the grid voltage connected to the frequency converter in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence and negative-sequence voltage components, generating a disturbance intensity index characterizing the degree of asymmetry. Based on the motor-grid joint model, using the negative-sequence voltage component and the disturbance intensity index, a virtual braking torque is synthesized through dynamic flux linkage modulation, converting the motor's rotational kinetic energy into electrical energy fed back to the DC bus. When grid voltage recovery is detected, based on the motor rotor position and speed tracked in real time by the motor-grid joint model, a matching voltage is output at the instant of voltage recovery, completing a shockless reclosing.

[0007] A second aspect of this application provides a low-voltage ride-through control system for a high-voltage frequency converter, the system comprising: The system includes a joint model construction module for building a motor-grid joint model for the frequency converter. This model runs continuously during frequency converter operation and uses a state estimator to calibrate motor parameters in real time. A disturbance intensity index generation module is used to detect the grid voltage connected to the frequency converter in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence and negative-sequence voltage components, and a disturbance intensity index characterizing the degree of asymmetry is generated. A motor rotational kinetic energy conversion module is used, based on the motor-grid joint model, to synthesize a virtual braking torque through dynamic flux linkage modulation using the negative-sequence voltage component and the disturbance intensity index, converting the motor's rotational kinetic energy into electrical energy to be fed back to the DC bus. A shockless reclosing completion module is used to output a matching voltage at the instant the grid voltage recovers, based on the motor rotor position and speed tracked in real time by the motor-grid joint model, to complete shockless reclosing when the grid voltage is detected to recover.

[0008] One or more technical solutions provided in this application have at least the following technical effects or advantages: A motor-grid joint model is constructed for the frequency converter. The grid voltage connected to the frequency converter is monitored in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence and negative-sequence voltage components, and a disturbance intensity index characterizing the degree of asymmetry is generated. Using the negative-sequence voltage component and the disturbance intensity index, a virtual braking torque is synthesized through dynamic flux linkage modulation, converting the motor's rotational kinetic energy into electrical energy fed back to the DC bus. When the grid voltage recovers, based on the motor rotor position and speed tracked in real time by the motor-grid joint model, a matching voltage is output at the instant of voltage recovery, completing impact-free reclosing. This achieves the technical effects of suppressing asymmetric disturbances during grid voltage drops and stabilizing the motor's kinetic energy feedback, improving the low-voltage ride-through capability of the high-voltage frequency converter and the stability of grid-connected operation. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 A schematic flowchart of a low-voltage ride-through control method for a high-voltage frequency converter is provided in an embodiment of this application. Figure 2 This is a schematic diagram of a low-voltage ride-through control system for a high-voltage frequency converter, provided as an embodiment of this application.

[0011] Figure labeling: Joint model construction module 10, disturbance intensity index generation module 20, motor rotation kinetic energy conversion module 30, and impact-free reclosing completion module 40. Detailed Implementation

[0012] This application provides a low-voltage ride-through control method and system for high-voltage frequency converters, which addresses the technical problems of existing technologies being unable to effectively suppress asymmetrical voltage disturbances in the power grid, and the difficulty in reasonably dissipating and stabilizing redundant kinetic energy during motor voltage drops, resulting in easy impacts and poor operational stability when reclosing after the power grid is restored.

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0014] Example 1, as Figure 1As shown, this application provides a low-voltage ride-through control method for a high-voltage frequency converter, the method comprising: Step S100: Construct a motor-grid joint model for the frequency converter. The motor-grid joint model runs continuously during the operation of the frequency converter and uses a state estimator to calibrate the motor parameters in real time.

[0015] Specifically, for high-voltage frequency converters and their driven physical motors, a motor-grid joint model is established, incorporating the motor's electrical characteristics, operating characteristics, and grid-side electrical constraints. This model is constructed in the form of a digital twin, equating the frequency converter, motor body, and grid interface to a unified mathematical simulation model. Throughout the normal operation of the frequency converter, the motor-grid joint model maintains real-time online continuous computation, synchronously following the operating state of the physical system. Through a built-in state estimator, it collects feedback quantities such as grid-side voltage and motor-side current in real time, dynamically identifying and calibrating key parameters such as motor stator resistance, rotor resistance, stator inductance, and rotor inductance. This continuously corrects the model parameters and state output, ensuring that the electrical parameters and operating state of the motor-grid joint model remain consistent with the physical motor in real time. This provides an accurate and reliable model foundation for subsequent voltage drop detection, kinetic energy feedback, and impact-free reclosing.

[0016] Step S200: Real-time detection of the grid voltage connected to the frequency converter. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence voltage component and the negative-sequence voltage component, and a disturbance intensity index characterizing the degree of asymmetry is generated.

[0017] Specifically, the instantaneous three-phase grid voltage values ​​on the incoming side of the high-voltage inverter are collected in real time at a set sampling frequency. The collected values ​​are continuously compared with the rated voltage. When the voltage amplitude of any phase drops below a preset threshold, a voltage sag is determined. Within a predetermined sampling window after the sag is determined, an orthogonal signal generator based on dual generalized integrators is used in combination with the symmetrical component method to perform sequence component decoupling operation on the voltage signal, separating the positive sequence voltage component representing the symmetrical component of the grid and the negative sequence voltage component representing the asymmetrical component of the grid, and outputting amplitude and phase information simultaneously. Based on the imbalance ratio of the negative sequence voltage amplitude to the positive sequence voltage amplitude, combined with the sag depth weighting coefficient dynamically determined by the ratio of the current positive sequence voltage amplitude to the rated voltage, a disturbance intensity index is generated to quantify the severity of grid voltage asymmetry disturbances.

[0018] Step S300: Based on the motor-grid joint model, using the negative sequence voltage component and the disturbance intensity index, a virtual braking torque is synthesized through dynamic flux linkage modulation, and the motor rotational kinetic energy is converted into electrical energy and fed back to the DC bus.

[0019] Specifically, based on a motor-grid joint model that is calibrated in real time and synchronized with the physical motor, the current real-time speed of the motor is read, and the negative sequence voltage component and disturbance intensity index are used as feedforward inputs. Combined with the speed correction coefficient, the target value of braking torque is calculated. The amplitude and phase of the stator flux linkage of the motor are dynamically adjusted by dynamic flux linkage modulation, and a virtual braking torque opposite to the rotor rotation direction is synthesized in the air gap of the motor. This braking torque is used to convert the rotational kinetic energy stored in the motor rotor into electromagnetic energy, which is fed back to the DC bus of the inverter through the inverter to maintain the stability of the DC bus voltage and avoid overvoltage or undervoltage of the bus.

[0020] Step S400: When the grid voltage is detected to be restored, based on the motor rotor position and speed tracked in real time by the motor-grid joint model, a matching voltage is output at the instant the voltage is restored to complete the impact-free reclosing.

[0021] Specifically, the grid voltage on the input side of the frequency converter is continuously monitored. When the voltage amplitude rises to a preset proportion of the rated voltage and remains stable for a predetermined time, the grid voltage is determined to have recovered. Based on the instantaneous values ​​of the motor rotor position and motor speed obtained in real time by the motor-grid joint model during the voltage drop, the target voltage amplitude, target frequency, and target phase that perfectly match the current operating conditions of the motor are calculated. At the instant the grid voltage recovers, the frequency converter is controlled to directly output the matching voltage, achieving shockless reclosing without current surges or torque mutations.

[0022] In one possible implementation, step S200 further includes: Step S210: Collect the instantaneous three-phase voltage values ​​on the input side of the frequency converter at a set frequency.

[0023] Step S220: Continuously compare the instantaneous values ​​of the three-phase voltages with the rated voltages. When the voltage amplitude of any phase drops below a preset threshold, a voltage drop event is determined to have occurred.

[0024] Step S230: Within the predetermined sampling window after the drop is determined, the three-phase voltage signal is subjected to sequence component decoupling operation, and the positive sequence voltage amplitude, negative sequence voltage amplitude and phase information are output synchronously to obtain the positive sequence voltage component and the negative sequence voltage component.

[0025] Step S240: Calculate and output the disturbance intensity index based on the relative ratio between the negative sequence voltage amplitude and the positive sequence voltage amplitude.

[0026] Specifically, the instantaneous values ​​of the three-phase voltage on the input side of the frequency converter are collected in real time according to a pre-set fixed sampling frequency. The set frequency is the voltage signal sampling rate preset by the system. The input side of the frequency converter refers to the input port directly connected to the power grid by the high-voltage frequency converter. The instantaneous values ​​of the three-phase voltage are the real-time voltage amplitudes of the three phases A, B, and C of the power grid at the current sampling time, so as to ensure the real-time performance and integrity of the voltage signal acquisition.

[0027] The instantaneous values ​​of the three-phase voltages are collected and continuously compared with the rated voltage preset by the system in real time. The rated voltage is the standard grid voltage amplitude when the frequency converter and motor are working normally. When the voltage amplitude of any one of the three phases A, B, and C drops below a preset threshold, it is immediately determined that a voltage drop event has occurred in the grid. The preset threshold is a critical value used to identify abnormal voltage drops.

[0028] Within a predetermined sampling window after a voltage drop is detected, preferably 1 to 2 milliseconds, to ensure decoupling accuracy while meeting transient response speed requirements, the collected three-phase voltage signals are processed using an orthogonal signal generator based on dual generalized integrators combined with the symmetrical component method to perform sequence component decoupling calculations. The positive sequence voltage amplitude, negative sequence voltage amplitude, and corresponding phase information are separated and output synchronously in real time. The positive sequence voltage component is the fundamental component representing the symmetrical operation of the power grid, and the negative sequence voltage component is the disturbance component representing the asymmetrical fault of the power grid. Finally, the complete positive sequence voltage component and negative sequence voltage component are obtained.

[0029] The disturbance intensity index is calculated and output based on the relative ratio between the negative-sequence voltage amplitude and the positive-sequence voltage amplitude. Specifically, the negative-sequence voltage amplitude is divided by the positive-sequence voltage amplitude to obtain the imbalance ratio, which characterizes the degree of three-phase imbalance in the power grid. This imbalance ratio is then multiplied by the voltage drop depth weighting coefficient to obtain the disturbance intensity index used to quantify the severity of voltage disturbances in the power grid. The voltage drop depth weighting coefficient is dynamically determined based on the ratio of the current positive-sequence voltage amplitude to the rated voltage. It can adaptively adjust the weights according to the voltage drop depth, so that the disturbance intensity index can more accurately reflect the actual degree of asymmetrical disturbances in the power grid.

[0030] In one possible implementation, step S230 further includes: Step S231: The three-phase voltage signal is filtered and the orthogonal components are extracted using an orthogonal signal generator based on a dual generalized integrator.

[0031] Step S232: Perform instantaneous symmetric component decomposition on the extracted orthogonal components using the symmetric component method, and output the positive sequence voltage amplitude, the negative sequence voltage amplitude, and the phase information.

[0032] Specifically, an orthogonal signal generator based on dual generalized integrators is used to process the acquired three-phase voltage signals. The dual generalized integrators are the core computing units that can suppress harmonics, filter high-frequency noise, and achieve orthogonal phase output. The orthogonal signal generator is used to generate two orthogonal signals with a 90-degree phase difference. The device is used to filter the three-phase voltage signals to eliminate interference and harmonic components in the signals, and simultaneously extracts orthogonal components to obtain pure, orthogonal voltage signals, providing a stable and reliable input basis for subsequent symmetrical component decomposition.

[0033] The symmetrical component method, commonly used in power systems, is employed to perform instantaneous symmetrical component decomposition on the extracted orthogonal components. This decouples the three-phase unbalanced voltage into symmetrical positive-sequence components and unbalanced negative-sequence components. The positive-sequence voltage amplitude, negative-sequence voltage amplitude, and corresponding phase information are calculated and output in real time. The symmetrical component method is a standard decoupling algorithm used to analyze unbalanced faults in three-phase systems. Instantaneous symmetrical component decomposition refers to the real-time calculation of sequence components at each sampling moment. The positive-sequence voltage amplitude is the amplitude of the symmetrical fundamental component of the power grid, the negative-sequence voltage amplitude is the amplitude of the unbalanced disturbance component of the power grid, and the phase information is the real-time phase angle corresponding to each sequence component.

[0034] In one possible implementation, step S240 further includes: Step S241: Divide the negative sequence voltage amplitude by the positive sequence voltage amplitude to obtain the unbalance ratio.

[0035] Step S242: Multiply the imbalance ratio by the drop depth weighting coefficient to obtain the disturbance intensity index.

[0036] The drop depth weighting coefficient is dynamically determined based on the ratio of the current positive sequence voltage amplitude to the rated voltage.

[0037] Specifically, the negative sequence voltage amplitude obtained by instantaneous symmetrical component decomposition is used as the numerator, and the positive sequence voltage amplitude calculated in the same period is used as the denominator. The quotient of the two is obtained by division, and this quotient is the unbalance ratio used to intuitively characterize the degree of three-phase voltage asymmetry in the power grid.

[0038] The system reads the positive sequence voltage amplitude and the system rated voltage in real time, and dynamically calculates the voltage drop depth weighting coefficient by calculating the ratio between the two. The larger the voltage drop amplitude, the higher the corresponding weighting coefficient value, thus completing the dynamic weight allocation of the voltage drop depth dimension. Then, the output imbalance ratio is retrieved, and a fixed-point multiplication operation is performed on this ratio and the real-time updated voltage drop depth weighting coefficient. Through the weighted coupling operation method, the voltage imbalance characteristics and voltage drop characteristics are integrated, and finally, the disturbance intensity index that quantifies the severity of the grid voltage asymmetry fault is accurately calculated and output.

[0039] The voltage drop weighting coefficient is calculated in real time using a fixed operational logic. The core operational parameters are the current positive-sequence voltage amplitude and the system rated voltage, obtained through real-time analysis. First, the real-time ratio of the current positive-sequence voltage amplitude to the rated voltage is calculated. Then, the difference between the rated voltage and the positive-sequence voltage amplitude is divided by the rated voltage to linearly solve for the voltage drop weighting coefficient. The greater the voltage drop depth, the lower the current positive-sequence voltage amplitude, and the higher the calculated voltage drop weighting coefficient becomes. This allows for precise differentiation of different voltage drop levels, objectively quantifying the comprehensive harm of asymmetrical voltage drops to the stable operation, insulation life, and torque output of asynchronous or synchronous motors, and enabling the weighting coefficient to dynamically and adaptively update in accordance with the real-time operating conditions of the grid voltage.

[0040] In one possible implementation, step S300 further includes: Step S310: Read the current motor speed from the motor-grid joint model.

[0041] Step S320: Using the negative sequence voltage component and disturbance intensity index as feedforward inputs, and combining them with the motor speed, calculate the required target value of braking torque.

[0042] Step S330: Based on the target braking torque value, dynamically adjust the amplitude and phase of the motor stator flux linkage to generate a braking torque component in the motor air gap that is opposite to the direction of rotation. The braking torque component converts the kinetic energy of the motor rotor into electromagnetic energy, which is fed back to the DC bus via the inverter.

[0043] Specifically, the system retrieves real-time operating data from the pre-built motor-grid joint model and reads the real-time speed parameters of the motor under its current operating conditions through the model's built-in data acquisition interface. This provides continuous and accurate real-time values ​​of the motor speed, offering basic operating parameter support for subsequent closed-loop calculation and dynamic control of braking torque.

[0044] The negative-sequence voltage component obtained from real-time analysis and the disturbance intensity index, which quantifies the severity of power grid faults, are used together as control feedforward inputs. Simultaneously, the real-time acquired motor speed is introduced to participate in the calculation, thereby accurately calculating the target braking torque value that matches the operating conditions. During the calculation, the disturbance intensity index is uniformly used as the basic gain coefficient for braking torque calculation. The reference amplitude of braking torque is determined based on the real-time amplitude of the negative-sequence voltage component. Then, the basic gain coefficient and the reference amplitude of braking torque are multiplied to obtain the initial braking torque value. Further, relying on a pre-calibrated parameter lookup table, the corresponding speed correction coefficient is retrieved in real-time according to the current motor speed. The initial braking torque is multiplied again with the speed correction coefficient to complete the dynamic limiting and adaptive correction of the torque value. Finally, a stable braking torque target value that adapts to the real-time operating state of the motor is output.

[0045] Using the calculated target braking torque value as the core control benchmark, a stator flux linkage oriented control method is adopted to dynamically adjust the stator flux linkage of the motor. The stator flux linkage refers to the sum of magnetic flux corresponding to the magnetic field generated by the current flowing through the stator windings of the motor, which is the basis for the electromagnetic torque generated by the motor. The air gap of the motor refers to the gap between the stator and rotor of the motor, which is the key area for magnetic field interaction. The braking torque component refers to the reverse electromagnetic torque used to impede the rotation of the motor rotor and consume the rotor's kinetic energy. Specifically, based on the target braking torque value, the amplitude of the stator flux linkage, i.e., the magnitude and phase of the magnetic flux, i.e., the spatial direction of the magnetic field, is adjusted in real time to form a braking torque component in the air gap opposite to the rotor's rotation direction. This braking torque component continuously acts on the motor rotor, forcing the rotor to decelerate and converting the rotor's mechanical kinetic energy into electromagnetic energy. Subsequently, through an inverter, power electronic devices convert alternating current into direct current, rectifying this electromagnetic energy, and finally feeding the converted electrical energy back to the DC bus for energy storage and to provide a stable DC power supply for motor operation, thus achieving the synchronous completion of the braking process and energy recovery.

[0046] In one possible implementation, step S320 further includes: Step S321: Use the disturbance intensity index as the basic gain coefficient of the braking torque.

[0047] Step S322: Determine the reference amplitude of the braking torque based on the amplitude of the negative sequence voltage component.

[0048] Step S323: Multiply the basic gain coefficient by the reference amplitude to obtain the initial braking torque.

[0049] Step S324: Obtain the speed correction coefficient from the table based on the motor speed, multiply the initial braking torque by the speed correction coefficient, and obtain the target braking torque value after speed limiting.

[0050] Specifically, the disturbance intensity index calculated in real time is set as the basic gain coefficient of the braking torque calculation stage. This coefficient can objectively reflect the overall severity of the grid voltage asymmetry drop and can be dynamically updated in real time according to the changes in the strength of the grid disturbance conditions, thereby providing a global weight constraint for the overall output intensity of the braking torque.

[0051] The real-time acquired three-phase power grid voltage signal is processed by sequence component decomposition to separate and extract the negative sequence voltage component, which represents the three-phase voltage imbalance. The negative sequence voltage component is the voltage component with the opposite phase sequence to the positive sequence voltage during normal motor operation. Then, through effective value calculation and peak value solving algorithms, the real-time amplitude of the negative sequence voltage component is accurately calculated. This amplitude is used to intuitively reflect the strength level of the power grid asymmetric disturbance. Relying on the linear fitting function or segmented calibration data table pre-stored in the equipment, the real-time amplitude of the negative sequence voltage component is used as an independent input variable. According to the one-to-one quantitative mapping rule, the initial basic torque value is calculated. This initial basic torque value is the reference amplitude of the braking torque. The reference amplitude of the braking torque is the original braking torque reference value before gain weighting and speed correction. This completes the quantitative determination of the reference amplitude based on the degree of negative sequence voltage distortion.

[0052] Two types of operational parameters are retrieved: the base gain coefficient and the reference amplitude of the braking torque. The base gain coefficient is a global weight adjustment parameter set based on the disturbance intensity index, used to characterize the overall disturbance hazard level of the power grid. The reference amplitude of the braking torque is the original braking torque reference value obtained by quantitative matching based on the amplitude of the negative sequence voltage component. Through the floating-point multiplication unit inside the controller, the base gain coefficient and the reference amplitude of the braking torque are multiplied in real time, and the global gain ratio of the reference amplitude is adjusted to correct the output intensity of the base braking torque. Finally, an initial braking torque that has not been corrected by the speed parameter and can reflect the overall level of the current asymmetric disturbance of the power grid is generated.

[0053] The system collects the motor speed during real-time operation, where motor speed refers to the actual rotational speed of the motor rotor per unit time, serving as the retrieval basis for parameter lookup. The controller has a pre-calibrated and fixed speed correction coefficient lookup table model. This model features zoned adjustment logic, setting the speed correction coefficient to less than 1 in the low-speed operating range, gradually decreasing as the motor speed decreases. This is used to gradually reduce the braking torque in the low-speed range, effectively preventing excessive braking force from causing the motor to stop prematurely at low speeds. Simultaneously, the speed correction coefficient is kept constant at 1 in the high-speed operating range to ensure maximum braking capacity at high speeds. The system recovers the inertial kinetic energy stored in the motor rotor; it uses the real-time motor speed as an index to query and match the corresponding speed correction coefficient, which is a proportional correction parameter used to adapt to different speed ranges and adjust the output of braking torque; it retrieves the calculated initial braking torque, which is an intermediate torque value obtained after matching the negative sequence voltage reference amplitude and weighting by the disturbance intensity index gain; it multiplies the initial braking torque with the speed correction coefficient obtained by the table through the control calculation unit; it uses the characteristics of the partition coefficient to complete the dynamic limiting and adaptive correction of the braking torque; and finally calculates the target braking torque value that takes into account both low-speed operation stability and high-speed energy recovery efficiency.

[0054] In one possible implementation, step S400 further includes: Step S410: Continuously monitor the three-phase voltage on the incoming line side. When the voltage amplitude recovers to the preset proportion of the rated voltage and remains stable for a predetermined time, it is determined that the grid voltage has recovered.

[0055] Step S420: Read the instantaneous values ​​of the motor rotor position angle and speed continuously tracked during the voltage drop from the motor-grid joint model.

[0056] Step S430: Calculate the target amplitude, target frequency, and target phase of the inverter output voltage based on the rotor position angle and the instantaneous speed value.

[0057] Step S440: At the moment of reclosing, control the frequency converter to directly output a voltage that is consistent with the target amplitude, the target frequency and the target phase.

[0058] Specifically, the control system continuously collects and monitors the three-phase voltage signal on the power supply input side in real time. The three-phase voltage on the input side is the three-phase AC input voltage from the power grid to the electrical equipment. The rated voltage is the standard rated input voltage designed for normal and stable operation of the equipment. The controller calculates the actual operating amplitude of the three-phase voltage in real time and compares the real-time voltage amplitude with the rated voltage. There are preset voltage ratio thresholds and stabilization time thresholds for determining power grid recovery. When the actual amplitude of the three-phase voltage is detected to rise to the preset ratio value corresponding to the rated voltage, and the voltage amplitude is maintained in a stable state for a predetermined time without fluctuations or drops, the system completes the voltage recovery condition judgment, reliably determines that the power grid voltage fault condition has been resolved, and the power grid power supply status has returned to normal.

[0059] The motor-grid joint model is an integrated simulation and monitoring model that couples the motor's operating characteristics with the grid's power supply status in real time. It can continuously collect and store key operating status quantities of the motor throughout the entire period from the occurrence to the end of a grid voltage drop fault. The motor rotor position angle is used to characterize the spatial relative angle between the motor rotor magnetic field and the stator winding magnetic field. It is a core parameter of variable frequency synchronous control. The instantaneous speed value is the real-time rotational speed data of the motor rotor at any moment. After the grid voltage fault is cleared, the control unit immediately retrieves the data from the internal buffer area of ​​the motor-grid joint model and accurately reads the motor rotor position angle and instantaneous speed values ​​that have been continuously tracked, recorded and saved in real time throughout the entire voltage drop process, thus completely preserving the motor's true operating status during the fault stage.

[0060] Based on the rotor position angle and the instantaneous speed value, the target amplitude, target frequency, and target phase of the inverter output voltage are calculated. Specifically, the instantaneous speed value is directly set as the target frequency of the inverter output voltage. The target phase of the output voltage is obtained by superimposing a preset compensation angle on the rotor position angle. The preset compensation angle is used to compensate for the phase lag caused by the operation delay of the control component and the switching delay of the power device. Then, based on the inverter's preset voltage-frequency ratio characteristic curve, the determined target frequency is used as a lookup condition, and the corresponding target voltage amplitude is obtained by matching through a lookup table. The accurate calculation of the target frequency, target phase, and target amplitude of the output voltage is completed in sequence, providing accurate control parameters for the synchronous regulated output of the inverter at the reclosing time.

[0061] At the instant the power grid completes voltage restoration and performs reclosing, the controller immediately locks the target voltage amplitude, target frequency, and target phase calculated in the previous steps. It synchronously sends these three sets of parameters to the inverter's space vector modulation control unit, updates the inverter's internal voltage modulation command in real time, and quickly drives the inverter's internal power switching devices to operate according to the preset modulation logic. It strictly controls the effective value of the output voltage according to the predetermined target amplitude, maintains the alternating cycle of the output voltage based on the target frequency, and calibrates the initial angle of the output voltage waveform based on the target phase. This allows the inverter to directly output a three-phase AC voltage that is completely consistent with all target parameters at the moment of reclosing. This achieves instantaneous and precise synchronization between the inverter's output voltage, the motor rotor operating status, and the restored grid voltage, effectively suppressing the inrush current and electromagnetic torque fluctuations at the moment of closing, and ensuring the smooth and shock-free grid-connected operation of the motor.

[0062] In one possible implementation, step S430 further includes: Step S431: Use the instantaneous value of the rotational speed as the target frequency of the output voltage, and use the rotor position angle superimposed with a preset compensation angle as the target phase of the output voltage, wherein the preset compensation angle is used to compensate for the phase lag caused by the delay of the control component and the switching delay of the power device.

[0063] Step S432: Based on the inverter's voltage-to-frequency ratio characteristic curve, obtain the target voltage amplitude from the target frequency by looking up the table.

[0064] Specifically, the instantaneous value of the motor speed obtained in real time is directly taken and set as the target frequency of the inverter output voltage, so that the output voltage frequency keeps synchronized with the real-time speed of the motor; the rotor position angle obtained in real time is retrieved and a pre-calibrated and determined preset compensation angle is superimposed on this angle to obtain the target phase of the inverter output voltage; using this preset compensation angle, the phase shift caused by the signal response lag of the control component and the switching action lag of the power device is compensated in advance, and the phase lag caused by the delay factor is offset to ensure that the output voltage phase is accurately matched with the actual operating state of the motor.

[0065] The voltage-frequency ratio characteristic curve is a pre-calibrated curve based on motor operating parameters and stored in the control logic. This curve standardizes the matching relationship between different operating frequencies and reasonable output voltage amplitudes. Using the determined target frequency as the reference, the voltage-frequency ratio characteristic curve is compared and searched one by one to obtain a unique corresponding voltage value. This voltage value is the target voltage amplitude of the inverter output voltage. By combining the target frequency with a lookup table to determine the target voltage amplitude, it can coordinate with the target frequency and target phase determined above, so that the subsequent output voltage of the inverter can achieve full synchronization matching with the power supply voltage after the grid is restored in three dimensions: amplitude, frequency, and phase. This eliminates the operational shock caused by differences in electrical parameters and ensures the smooth grid-connected operation of the motor.

[0066] In one possible implementation, step S100 further includes: The motor-grid joint model is a digital twin model that continuously and automatically corrects the motor's resistance and inductance parameters based on real-time voltage and current feedback.

[0067] Specifically, the motor-grid joint model adopts a digital twin model architecture, which is a digital mirror model that can synchronously map the operating status of physical equipment. The model collects grid-side voltage signals and motor operating current signals in real time as feedback data. Based on the real-time collected voltage and current operating feedback information, it continuously and dynamically corrects and automatically calibrates the resistance and inductance parameters of the motor body. The motor resistance and inductance are susceptible to parameter drift due to changes in winding temperature and long-term aging of electrical components. Through a real-time parameter adaptive correction mechanism, the parameter drift caused by factors such as temperature fluctuations and component aging can be effectively offset, ensuring that the key electrical parameters of the motor inside the model are always consistent with the actual operating conditions of the physical motor, thereby improving the accuracy of status monitoring and computational control.

[0068] Example 2, based on the same inventive concept as the low-voltage ride-through control method for a high-voltage frequency converter in the foregoing examples, such as... Figure 2 As shown, this application provides a low-voltage ride-through control system for a high-voltage frequency converter. The system and method embodiments in this application are based on the same inventive concept. The system includes: The joint model building module 10 is used to build a motor-grid joint model for the frequency converter. The motor-grid joint model runs continuously when the frequency converter is running and uses a state estimator to calibrate the motor parameters in real time.

[0069] The disturbance intensity index generation module 20 is used to detect the grid voltage connected to the frequency converter in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive sequence voltage component and the negative sequence voltage component, and a disturbance intensity index characterizing the degree of asymmetry is generated.

[0070] The motor rotational kinetic energy conversion module 30 is used to convert the motor rotational kinetic energy into electrical energy and feed it back to the DC bus by using the negative sequence voltage component and the disturbance intensity index to synthesize virtual braking torque through dynamic flux modulation based on the motor-grid joint model.

[0071] The shockless reclosing completion module 40 is used to output a matching voltage at the instant the voltage is restored, based on the motor rotor position and speed tracked in real time by the motor-grid joint model when the grid voltage is detected to be restored, so as to complete the shockless reclosing.

[0072] Furthermore, the system is also used to implement the following functions: The instantaneous values ​​of the three-phase voltage on the input side of the frequency converter are collected at a set frequency; the instantaneous values ​​of the three-phase voltage are continuously compared with the rated voltage, and a voltage drop event is determined when the voltage amplitude of any phase drops below a preset threshold; within the predetermined sampling window after the drop is determined, the sequence component decoupling operation is performed on the three-phase voltage signal, and the positive sequence voltage amplitude, negative sequence voltage amplitude and phase information are output synchronously to obtain the positive sequence voltage component and the negative sequence voltage component; the disturbance intensity index is calculated and output according to the relative ratio between the negative sequence voltage amplitude and the positive sequence voltage amplitude.

[0073] Furthermore, the system is also used to implement the following functions: The three-phase voltage signal is filtered and its orthogonal components are extracted using an orthogonal signal generator based on a dual generalized integrator. The extracted orthogonal components are then decomposed into instantaneous symmetrical components using the symmetrical component method, and the positive-sequence voltage amplitude, the negative-sequence voltage amplitude, and the phase information are output.

[0074] Furthermore, the system is also used to implement the following functions: Divide the negative sequence voltage amplitude by the positive sequence voltage amplitude to obtain the imbalance ratio; multiply the imbalance ratio by the drop depth weighting coefficient to obtain the disturbance intensity index; wherein the drop depth weighting coefficient is dynamically determined based on the ratio of the current positive sequence voltage amplitude to the rated voltage.

[0075] Furthermore, the system is also used to implement the following functions: The current motor speed is read from the motor-grid joint model; the negative sequence voltage component and disturbance intensity index are used as feedforward inputs, and the required braking torque target value is calculated in combination with the motor speed; according to the braking torque target value, the amplitude and phase of the motor stator flux linkage are dynamically adjusted to generate a braking torque component in the motor air gap that is opposite to the direction of rotation. The braking torque component converts the motor rotor kinetic energy into electromagnetic energy, which is fed back to the DC bus via the inverter.

[0076] Furthermore, the system is also used to implement the following functions: The disturbance intensity index is used as the basic gain coefficient of the braking torque; the reference amplitude of the braking torque is determined according to the amplitude of the negative sequence voltage component; the basic gain coefficient is multiplied by the reference amplitude to obtain the initial braking torque; the speed correction coefficient is obtained by looking up the table according to the motor speed; the initial braking torque is multiplied by the speed correction coefficient to obtain the target value of the braking torque after speed limiting.

[0077] Furthermore, the system is also used to implement the following functions: The incoming three-phase voltage is continuously monitored. When the voltage amplitude recovers to a preset proportion of the rated voltage and remains stable for a predetermined time, the grid voltage is determined to have recovered. The instantaneous values ​​of the motor rotor position angle and speed during the voltage drop period are continuously tracked from the motor-grid joint model. Based on the rotor position angle and the instantaneous speed, the target amplitude, target frequency, and target phase of the inverter output voltage are calculated. At the moment of reclosing, the inverter is controlled to directly output a voltage consistent with the target amplitude, target frequency, and target phase.

[0078] Furthermore, the system is also used to implement the following functions: The instantaneous rotational speed is used as the target frequency of the output voltage, and the rotor position angle is superimposed with a preset compensation angle as the target phase of the output voltage. The preset compensation angle is used to compensate for the phase lag caused by the delay of the control component and the switching delay of the power device. The target voltage amplitude is obtained by looking up the table from the target frequency according to the inverter voltage-frequency ratio characteristic curve.

[0079] Furthermore, the system is also used to implement the following functions: The motor-grid joint model is a digital twin model that continuously and automatically corrects the motor's resistance and inductance parameters based on real-time voltage and current feedback.

[0080] It should be noted that the order of the embodiments described above is for descriptive purposes only and does not represent the superiority or inferiority of the embodiments. Specific embodiments of this specification have been described above. Furthermore, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0081] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0082] This specification and accompanying drawings are merely illustrative examples of this application and are intended to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Therefore, if such modifications and variations fall within the scope of this application and its equivalents, this application intends to include such modifications and variations.

Claims

1. A low-voltage ride-through control method for a high-voltage frequency converter, characterized in that, include: A motor-grid joint model is constructed for the frequency converter. The motor-grid joint model runs continuously during the operation of the frequency converter and uses a state estimator to calibrate the motor parameters in real time. The motor-grid joint model is constructed in the form of a digital twin, which equates the frequency converter, the motor body, and the grid interface to a unified mathematical simulation model. The voltage of the grid connected to the frequency converter is detected in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence voltage component and the negative-sequence voltage component, and a disturbance intensity index characterizing the degree of asymmetry is generated. Based on the motor-grid joint model, the negative sequence voltage component and the disturbance intensity index are used to synthesize virtual braking torque through dynamic flux modulation, and the motor rotational kinetic energy is converted into electromagnetic energy and fed back to the DC bus. When the grid voltage is detected to be restored, the motor rotor position and speed are tracked in real time based on the motor-grid joint model, and a matching voltage is output at the moment of voltage restoration to complete the impact-free reclosing; Specifically, based on the aforementioned motor-grid joint model, using the negative sequence voltage component and the disturbance intensity index, a virtual braking torque is synthesized through dynamic flux linkage modulation to convert the motor's rotational kinetic energy into electrical energy fed back to the DC bus, including: Read the current motor speed from the motor-grid joint model; The negative sequence voltage component and disturbance intensity index are used as feedforward inputs, and the required target value of braking torque is calculated in combination with the motor speed. Based on the target braking torque value, the amplitude and phase of the motor stator flux linkage are dynamically adjusted to generate a virtual braking torque in the motor air gap that is opposite to the direction of rotation. The virtual braking torque converts the motor rotor kinetic energy into electromagnetic energy, which is then fed back to the DC bus via the inverter.

2. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 1, characterized in that, The system monitors the grid voltage connected to the frequency converter in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence and negative-sequence voltage components, and a disturbance intensity index characterizing the degree of asymmetry is generated, including: The instantaneous values ​​of the three-phase voltage on the input side of the frequency converter are collected at a set frequency; The instantaneous values ​​of the three-phase voltages are continuously compared with the rated voltage. When the voltage amplitude of any phase drops below a preset threshold, a voltage drop event is determined to have occurred. Within the predetermined sampling window after the drop is determined, the three-phase voltage signal is subjected to sequence component decoupling operation, and the positive sequence voltage amplitude, negative sequence voltage amplitude and phase information are output synchronously to obtain the positive sequence voltage component and the negative sequence voltage component. The disturbance intensity index is calculated and output based on the relative ratio between the negative sequence voltage amplitude and the positive sequence voltage amplitude.

3. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 2, characterized in that, The three-phase voltage signal undergoes sequence component decoupling operation, synchronously outputting the positive-sequence voltage amplitude, negative-sequence voltage amplitude, and phase information, including: The three-phase voltage signal is filtered and its orthogonal components are extracted using an orthogonal signal generator based on a dual generalized integrator. The extracted orthogonal components are decomposed into instantaneous symmetric components using the symmetric component method, and the positive sequence voltage amplitude, the negative sequence voltage amplitude, and the phase information are output.

4. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 2, characterized in that, Based on the relative proportion between the negative-sequence voltage amplitude and the positive-sequence voltage amplitude, the disturbance intensity index is calculated and output, including: Divide the negative sequence voltage amplitude by the positive sequence voltage amplitude to obtain the unbalance ratio; Multiplying the imbalance ratio by the drop depth weighting coefficient yields the disturbance intensity index; The drop depth weighting coefficient is dynamically determined based on the ratio of the current positive sequence voltage amplitude to the rated voltage.

5. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 1, characterized in that, Using the negative sequence voltage component and disturbance intensity index as feedforward inputs, and combining them with the motor speed, the required target braking torque value is calculated, including: The disturbance intensity index is used as the basic gain coefficient for braking torque; The reference amplitude of the braking torque is determined based on the amplitude of the negative sequence voltage component; Multiplying the basic gain coefficient by the reference amplitude yields the initial braking torque; The speed correction coefficient is obtained by looking up the motor speed in a table. The initial braking torque is then multiplied by the speed correction coefficient to obtain the target braking torque value after speed limiting.

6. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 1, characterized in that, When grid voltage recovery is detected, based on the motor rotor position and speed tracked in real time by the motor-grid joint model, a matching voltage is output at the instant of voltage recovery to complete shockless reclosing, including: The three-phase voltage on the incoming line side is continuously monitored. When the voltage amplitude recovers to the preset proportion of the rated voltage and remains stable for a predetermined time, it is determined that the grid voltage has recovered. The instantaneous values ​​of the motor rotor position angle and rotational speed, continuously tracked during the voltage drop, are read from the motor-grid joint model. Based on the rotor position angle and the instantaneous speed value, calculate the target amplitude, target frequency, and target phase of the inverter output voltage; At the moment of reclosing, the control inverter directly outputs a voltage that is consistent with the target amplitude, the target frequency and the target phase.

7. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 6, characterized in that, Based on the rotor position angle and the instantaneous speed value, calculate the target amplitude, target frequency, and target phase of the inverter output voltage, including: The instantaneous rotational speed is used as the target frequency of the output voltage, and the rotor position angle is superimposed with a preset compensation angle as the target phase of the output voltage. The preset compensation angle is used to compensate for the phase lag caused by the delay of the control component and the switching delay of the power device. The target voltage amplitude is obtained by looking up a table from the target frequency based on the inverter's voltage-to-frequency ratio characteristic curve.

8. The low-voltage ride-through control method for a high-voltage frequency converter as described in claim 1, characterized in that, The motor-grid joint model is a digital twin model that continuously and automatically corrects the motor's resistance and inductance parameters based on real-time voltage and current feedback.

9. A low-voltage ride-through control system for a high-voltage frequency converter, characterized in that, The system is used to implement the low-voltage ride-through control method for a high-voltage frequency converter according to any one of claims 1-8, and the system includes: The joint model building module is used to build a motor-grid joint model for the frequency converter. The motor-grid joint model runs continuously during the operation of the frequency converter and uses a state estimator to calibrate the motor parameters in real time. The motor-grid joint model is built in the form of a digital twin, which equates the frequency converter, motor body, and grid interface to a unified mathematical simulation model. The disturbance intensity index generation module is used to detect the grid voltage connected to the frequency converter in real time. When a voltage drop is detected, the voltage signal is deconstructed within a predetermined sampling window to separate the positive-sequence voltage component and the negative-sequence voltage component, and a disturbance intensity index characterizing the degree of asymmetry is generated. The motor rotational kinetic energy conversion module is used to convert the motor rotational kinetic energy into electromagnetic energy and feed it back to the DC bus based on the motor-grid joint model, using the negative sequence voltage component and the disturbance intensity index, and synthesizing virtual braking torque through dynamic flux linkage modulation. The impact-free reclosing completion module is used to output a matching voltage at the instant the voltage is restored, based on the motor rotor position and speed tracked in real time by the motor-grid joint model when the grid voltage is detected to be restored, so as to complete the impact-free reclosing.

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