A test system and control method for electromagnetic unloading of thrust bearing of pumped storage generator

Abstract

A kind of test system and control method for pumped storage generator thrust bearing electromagnetic unloading belong to pumped storage generator thrust bearing test technical field, the present application is to solve the problems existing in prior art, such as slow dynamic response, waveform tracking distortion, poor multi-channel synchronism, large current ripple and imperfect protection etc.The test system includes four independent constant-current source channels, a main control unit, an HMI human-machine interface and a common protection unit, each constant-current source channel is composed of a main loop and a DSP closed-loop control loop, and a three-phase rectifier, a bus voltage stabilizer and a step-down DC / DC converter are used to supply power to the excitation coil.The control method is based on model predictive control algorithm, the current trajectory is predicted by discrete model, the multi-objective cost function is constructed to solve the optimal control quantity, and the multi-channel phase cumulative error compensation is completed by synchronizing clock to ensure the phase synchronization of four output currents.

Description

Technical Field

[0001] This invention relates to the field of thrust bearing testing technology for pumped storage generator sets, specifically to a testing system and control method for electromagnetic load reduction of thrust bearings in pumped storage generators. Background Technology

[0002] Electromagnetic unloading of the thrust bearing in pumped-storage generator sets utilizes electromagnetic force to axially unload or suspend the turbine generator rotor above the mechanical thrust bearing, achieving thrust unloading or contactless support of the mechanical bearing. This offers significant advantages such as no wear, no lubrication required, high speed, and low vibration. The levitation force is precisely controlled by the excitation current in the excitation coil; the stability, dynamic response capability, and waveform tracking accuracy of the current directly determine the bearing's load-bearing capacity and the rotor's operational stability.

[0003] To ensure the effectiveness of electromagnetic load shedding control, the electromagnetic load shedding test of the thrust bearing of the pumped storage generator unit needs to simulate various excitation current modes under actual operating conditions, including:

[0004] DC current during steady-state levitation: requires low ripple and high stability;

[0005] Triangular wave current during dynamic adjustment: used to test the bearing's response to step or linear changes;

[0006] Sinusoidal current during disturbance suppression: simulating rotor eccentricity or unbalanced force;

[0007] Multi-excitation coil coordinated excitation: Multiple bearing excitation coils need to work simultaneously, and may require a specific phase relationship.

[0008] However, existing constant current source systems have the following problems:

[0009] Slow dynamic response, specifically manifested in: traditional linear constant current sources have low efficiency and high heat dissipation; switching constant current sources exhibit significant phase lag (>5ms) when tracking sine waves above 100Hz.

[0010] The waveform distortion is severe, specifically manifested as: sharp peaks, saturation, or flat-top distortions are prone to occur when tracking triangular waves, affecting the linearity of bearing force;

[0011] The noise and ripple are large, specifically manifested as: insufficient coupling between the main circuit and the control board, and difficulty in filtering out high-frequency ripple (>10kHz) caused by PWM modulation.

[0012] The lack of multi-channel coordination is specifically manifested in the fact that most constant current sources are single-channel designs, which cannot meet the requirements of multiple excitation coils working simultaneously or phase difference control in the test bench.

[0013] The protection function is inadequate, specifically: it lacks multiple protections such as overcurrent, overvoltage, overheat, and short circuit, which can easily damage IGBTs and loads.

[0014] Therefore, there is an urgent need for a dedicated multi-channel constant current source system suitable for electromagnetic load reduction tests of thrust bearings in pumped storage generator sets, featuring high precision, fast response, low ripple, strong waveform tracking capability, multi-channel coordination, and comprehensive protection. Summary of the Invention

[0015] To address the problems of slow dynamic response, waveform tracking distortion, poor multi-channel synchronization, large current ripple, and imperfect protection in existing technologies, this invention provides a test system for electromagnetic load shearing of the thrust bearing of a pumped-storage generator.

[0016] In a first aspect, the present invention provides a testing system for electromagnetic load reduction of the thrust bearing of a pumped-storage generator, comprising:

[0017] Four independent constant current source channels, each constant current source channel outputs one-to-one drive of a single excitation coil corresponding to the suspension thrust bearing;

[0018] The main control unit is used to send the current setpoint value at the current moment to each constant current source channel;

[0019] The HMI (Human-Machine Interface) is used to receive setting instructions from the user and transmit the setting instructions to the main control unit.

[0020] The single-channel constant current source includes a main circuit and a closed-loop control circuit;

[0021] The main circuit includes a three-phase rectifier bridge, a DC bus capacitor, and a step-down DC / DC converter. The three-phase AC input is rectified by the three-phase rectifier bridge, then stabilized by the DC bus capacitor, and then the output voltage is adjusted by the step-down DC / DC converter to power one excitation coil of the suspended thrust bearing.

[0022] The control loop includes a DSP controller, a PWM generation unit, a signal shaping and isolation drive unit, and a sampling unit;

[0023] The sampling unit acquires the actual output current and voltage signals of the constant current source channel and sends the sampled signals to the DSP controller;

[0024] The DSP controller receives the current setpoint from the main control unit and the feedback signal output by the sampling unit. It has an embedded model predictive control algorithm to generate a PWM drive signal based on the current setpoint and the feedback signal. The PWM drive signal drives the buck DC / DC converter through the signal shaping and isolation drive unit to achieve high-precision closed-loop constant current control of the single-channel output current.

[0025] Preferably, the main control unit is further configured to send a synchronization clock signal to the four constant current source channels;

[0026] The DSP controller of each constant current source channel is also configured to: perform cumulative error compensation on the phase of the output current of this channel according to the synchronization clock signal, so as to achieve phase synchronization between the output currents of the four constant current source channels.

[0027] Preferably, it further includes:

[0028] A common protection unit is connected to the four constant current source channels and the main control unit respectively. It is used to detect overcurrent, overvoltage, overheating or short circuit faults in the system, and outputs a total blocking signal to each constant current source channel when the fault is detected.

[0029] Secondly, the present invention provides a test system control method for electromagnetic load reduction of the thrust bearing of a pumped-storage generator, the method comprising the following steps:

[0030] Current setting step: The main control unit sends the current setting value at the current moment to each constant current source channel according to the user command received by the HMI human-machine interface;

[0031] Current tracking control steps: Each constant current source channel independently acquires the output current feedback signal of its own channel, and generates a drive signal based on the deviation between the current setpoint and the output current feedback signal, using a predictive control algorithm. The drive signal controls the switching state of the power converter inside the channel, so that the output current of the channel tracks the current setpoint.

[0032] Multi-channel synchronization steps: The output current of each constant current source channel is kept in phase synchronization.

[0033] Preferably, the multi-channel synchronization step includes:

[0034] The main control unit sends a synchronization clock signal to each constant current source channel;

[0035] Each of the constant current source channels receives the synchronous clock signal and performs cumulative error compensation on the phase of the output current of this channel.

[0036] Preferably, the cumulative error compensation includes:

[0037] Detect the deviation between the actual arrival time and the theoretical arrival time of the synchronization clock signal;

[0038] When the deviation exceeds a preset threshold, the phase compensation amount is calculated based on the deviation;

[0039] The phase compensation amount is accumulated into the phase control command of this channel.

[0040] Preferably, the predictive control algorithm includes:

[0041] Establish a discrete-time prediction model for the controlled object;

[0042] Within each control cycle, find the optimal control quantity that minimizes the cost function;

[0043] The cost function includes a tracking error term and a weighted sum of at least one of the following constraint terms: voltage constraint term, switching smoothing constraint term, and ripple suppression term.

[0044] Preferably, it further includes:

[0045] Weight adjustment steps: Based on the real-time operating status of the system, dynamically adjust the correction coefficients of the weights of each constraint term in the cost function;

[0046] The real-time operating status includes at least one of the following: tracking error status, observer convergence status, and load status.

[0047] Preferably, the weight adjustment step specifically includes:

[0048] Based on the magnitude of the tracking error, the tracking error status is divided into multiple levels;

[0049] Based on the magnitude of the observer's convergence error, the observer's convergence state is divided into multiple levels;

[0050] Based on the magnitude of the output current, the load status is divided into multiple levels;

[0051] Based on the aforementioned state levels, the basic weights and correction coefficients of each constraint term are determined, and the final weights of each constraint term in the cost function are calculated by multiplying the basic weights and correction coefficients.

[0052] Preferably, it further includes:

[0053] Common protection steps: The common protection unit detects overcurrent, overvoltage, overheating or short circuit faults in the system, and outputs a total blocking signal to each constant current source channel when the fault is detected.

[0054] The beneficial effects of this invention are:

[0055] 1. This invention adopts an adaptive current prediction control algorithm based on model prediction, which solves the problems of slow response and large distortion of existing constant current sources in dynamic current tracking such as triangular waves and sine waves, and realizes high-precision, low-delay and strong robust current output.

[0056] 2. This invention introduces a multi-objective adaptive weight adjustment mechanism, which defines a system state space with three dimensions: tracking error state, observer convergence state, and load state. The weight coefficients in the cost function are dynamically adjusted through a multi-level weight adjustment rule table, so that the system can automatically balance between dynamic and steady state, taking into account both fast response and low ripple.

[0057] 3. This invention adopts a multi-channel synchronous control method based on phase accumulation error compensation. It solves the phase accumulation error caused by crystal oscillator temperature drift after long-term operation through a dynamic phase holding mechanism. The synchronous clock pulse deviation is detected every 1 second and phase compensation is triggered when |Δt|>1μs. The compensation amount is accumulated on the phase control command. The phase accuracy can be dynamically maintained without restarting, which meets the stringent requirements of the hydro-generator vertical electromagnetic suspension bearing test bench for the coordinated excitation of multiple excitation coils. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the overall structure of a test system for electromagnetic load reduction of the thrust bearing of a pumped-storage generator, as described in this invention.

[0059] Figure 2 This is a schematic diagram of the main circuit and control circuit topology of the single-channel constant current source channel described in this invention;

[0060] Figure 3 This is a flowchart of the predictive control algorithm described in this invention;

[0061] Figure 4 This is the waveform diagram of the triangular wave current tracking test described in this invention;

[0062] Figure 5 This is the waveform diagram of the sinusoidal current tracking test described in this invention. Detailed Implementation

[0063] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0064] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0065] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0066] In the electromagnetic load reduction test of the thrust bearing of a pumped storage generator unit, the thrust bearing adopts an electromagnetic suspension bearing. The electromagnetic suspension bearing has four excitation coils: an outer ring excitation coil, an inner ring excitation coil, an outer ring compensation coil, and an inner ring compensation coil. A constant current source provides excitation current to the four coils, generating a supporting electromagnetic force through current control to achieve rotor suspension support. The test needs to simulate various excitation current forms under actual operating conditions, including DC current during steady-state suspension, triangular wave current during dynamic adjustment, sinusoidal current during disturbance suppression, and coordinated excitation of multiple excitation coils. Existing constant current source systems have the following technical defects:

[0067] Regarding the issue of slow dynamic response, traditional linear constant current sources are inefficient and generate significant heat; switching constant current sources exhibit significant phase lag when tracking sinusoidal waves above 100Hz. The root cause lies in the fact that traditional control algorithms are driven by error feedback, only compensating after current deviations occur, and cannot predict load changes. When the current setpoint changes rapidly, the controller cannot respond in time, resulting in significant phase lag and waveform distortion.

[0068] Regarding the issue of severe waveform distortion, triangular wave tracking is prone to spikes, saturation, or flat-top distortion, affecting the linearity of bearing force. The root cause lies in the lack of predictability of current change rate by traditional PWM modulation strategies. The triangular wave exhibits the largest current change rate at its peak and trough, requiring a high voltage margin to maintain this rate. Traditional controllers reduce the control input when the current approaches a given value, resulting in insufficient voltage margin and the current failing to change according to the given slope, thus producing spikes or flat-top distortion.

[0069] Regarding the issues of high noise and ripple, insufficient coupling between the main circuit and the control board makes it difficult to filter out high-frequency ripple caused by PWM modulation. The root cause lies in the fact that traditional control algorithms treat tracking accuracy and ripple suppression as independent problems, lacking a unified multi-objective optimization mechanism. Improving tracking accuracy requires fast response and high gain, but high gain amplifies noise and ripple; reducing ripple requires filtering and low gain, but low gain reduces response speed. Traditional algorithms cannot achieve a balance between these two conflicting objectives.

[0070] Regarding the lack of multi-channel coordination, most constant current sources are single-channel designs, which cannot meet the requirements of simultaneous operation of multiple excitation coils or phase difference control in test benches. The root cause lies in the lack of a unified synchronous clock reference and phase closed-loop calibration mechanism. Traditional systems can only set the phase at startup. During operation, inconsistent temperature drift of crystal oscillators in each channel leads to a gradual increase in phase accumulation error. After long-term operation, the phase relationship deviates significantly from the set value, failing to meet the requirements of complex operating conditions such as rotating magnetic field simulation.

[0071] Regarding the issue of inadequate protection functions, the lack of multiple protections against overcurrent, overvoltage, overheating, and short circuits can easily damage power devices and loads. The root cause lies in the lack of a hardware-level protection unit independent of the controller. Traditional systems rely on software protection within the DSP controller, and the process of detecting faults, responding to interrupts, and executing protection takes milliseconds. However, the withstand time of power devices under short-circuit conditions is only about 10 microseconds, making it impossible for software protection to act in a timely manner.

[0072] To address the aforementioned technical problems, this invention provides a testing system and control method for electromagnetic load reduction of the thrust bearing of a pumped-storage generator. The following detailed description of this embodiment is provided in conjunction with the accompanying drawings.

[0073] Combination Figure 1 As shown, the test system for electromagnetic load shearing of the thrust bearing of a pumped-storage generator according to the present invention includes:

[0074] Four independent constant current source channels, each constant current source channel outputs one-to-one drive of a single excitation coil corresponding to the suspension thrust bearing;

[0075] The main control unit is used to send the current setpoint value at the current moment to each constant current source channel;

[0076] The HMI (Human-Machine Interface) is used to receive setting instructions from the user and transmit the setting instructions to the main control unit.

[0077] The single-channel constant current source includes a main circuit and a closed-loop control circuit;

[0078] The main circuit includes a three-phase rectifier bridge, a DC bus capacitor, and a step-down DC / DC converter. The three-phase AC input is rectified by the three-phase rectifier bridge, then stabilized by the DC bus capacitor, and then the output voltage is adjusted by the step-down DC / DC converter to power one excitation coil of the suspended thrust bearing.

[0079] The control loop includes a DSP controller, a PWM generation unit, a signal shaping and isolation drive unit, and a sampling unit;

[0080] The sampling unit acquires the actual output current and voltage signals of the constant current source channel and sends the sampled signals to the DSP controller;

[0081] The DSP controller receives the current setpoint from the main control unit and the feedback signal output by the sampling unit. It has an embedded model predictive control algorithm to generate a PWM drive signal based on the current setpoint and the feedback signal. The PWM drive signal drives the buck DC / DC converter through the signal shaping and isolation drive unit to achieve high-precision closed-loop constant current control of the single-channel output current.

[0082] Specifically, the test system of this embodiment addresses the problems of weak multi-channel coordination, low single-channel control accuracy, and incomplete protection functions in existing technologies from the system architecture level. Its design principle is as follows: it employs four completely independent constant current source channels, each channel independently controlling one excitation coil. The main control unit uniformly allocates current setpoints, the HMI (Human-Machine Interface) allows users to set external commands, and a common protection unit implements system-level fault protection. The advantages of this architecture are: each channel is synchronously controlled by the main control unit, and the output current of each channel is finely adjusted to control the loading force of the four excitation coils of the levitation thrust bearing; the main control unit only issues setpoints and does not participate in low-level control, reducing system coupling and communication latency; the HMI is separated from the main control unit, facilitating remote operation and monitoring, and adapting to the actual need for separation between the test bench and the control room; the common protection unit is independent of each channel controller, achieving rapid hardware-level protection and solving the problem of insufficient response time in software protection.

[0083] A preferred embodiment includes: four independent constant current source channels (#1, #2, #3, #4), each channel's output driving a single excitation coil corresponding to the levitation thrust bearing; a main control unit, used to send the current setpoint to each constant current source channel; an HMI (Human-Machine Interface), used to receive user-issued setting commands and transmit them to the main control unit via a communication bus; a common protection unit, connected to the four constant current source channels and the main control unit, used to detect overcurrent, overvoltage, overheating, or short-circuit faults, and outputting a total blocking signal to each constant current source channel upon fault detection, with a response time <1μs; and a synchronous clock bus for multi-channel phase synchronization, with an accuracy of ±0.1μs. This system architecture forms a high-precision constant current source system with four independently controllable, collaborative, and multi-protection channels.

[0084] Furthermore, as shown in the appendix Figure 2 As shown, this embodiment further defines the internal structure of the single-channel constant current source to solve the problem of high-precision control of single-channel current. Its design principle is as follows: a two-stage power architecture of three-phase rectification plus buck converter is adopted, combined with a DSP controller to achieve digital closed-loop control. The three-phase rectifier bridge converts the AC input into a DC bus voltage. The bus capacitor smooths and filters the rectified voltage. The buck DC / DC converter adjusts the output voltage according to the PWM signal generated by the DSP controller, thereby controlling the output current. The sampling unit collects the output current and voltage in real time and feeds them back to the DSP controller, forming a closed-loop control circuit. The signal shaping and isolation drive unit shapes and isolates the PWM signal to ensure reliable drive of the power switching transistors. The advantages of this two-stage architecture are: the front-stage rectification provides a stable DC bus voltage for the subsequent stage, isolating the impact of grid fluctuations on the output; the subsequent buck converter has a simple topology, high efficiency, and fast dynamic response, suitable for a wide range of outputs; the DSP controller has strong processing capabilities and can run complex predictive control algorithms.

[0085] Furthermore, the main control unit is also used to send a synchronization clock signal to the four constant current source channels; the DSP controller of each constant current source channel is also configured to: perform cumulative error compensation on the phase of the output current of the channel according to the synchronization clock signal, so as to realize phase synchronization between the output currents of the four constant current source channels.

[0086] Specifically, the multi-channel synchronization control mechanism is explained. (See attached document.) Figure 1 As shown, this embodiment addresses the issue of phase asynchrony during multi-channel collaborative operation by introducing a synchronous clock signal and an accumulated error compensation mechanism into the testing system. The design principle is as follows: the main control unit simultaneously sends synchronous clock signals to the four constant current source channels via a synchronous clock bus. The DSP controller of each channel compensates for the accumulated error in the output current phase based on this synchronous clock signal. The main sources of phase error are the temperature drift of the crystal oscillators in each channel and the accumulated deviation generated over long-term operation. Traditional systems can only set the phase at startup and cannot dynamically adjust it during operation; after prolonged operation, the accumulated phase error increases linearly with running time. This embodiment periodically detects the arrival time of the synchronous clock pulse, calculates the deviation between the actual and theoretical values, and triggers phase compensation when the deviation exceeds a preset threshold. The compensation amount is accumulated in the phase control command, forming a closed-loop calibration, which dynamically maintains phase accuracy without requiring a restart.

[0087] In this embodiment, the main control unit is also used to send synchronization clock signals to the four constant current source channels. The DSP controller of each constant current source channel is further configured to perform cumulative error compensation on the phase of the output current based on the synchronization clock signal, thereby achieving phase synchronization between the four output currents. This synchronization mechanism is suitable for simulating various complex operating conditions such as rotor eccentricity, rotating magnetic fields, and dynamic imbalance. Through the above synchronization mechanism, the phase relationship of the four excitation currents can be precisely controlled.

[0088] Furthermore, it also includes a common protection unit, which is connected to the four constant current source channels and the main control unit respectively, for detecting overcurrent, overvoltage, overheating or short circuit faults in the system, and outputting a total blocking signal to each constant current source channel when the fault is detected.

[0089] Specifically, the common protection unit is described below. This implementation addresses the problems of inadequate constant current source protection functions and susceptibility to damage to power devices and loads by incorporating a common protection unit into the test system. Its design principle is as follows: power devices withstand short-circuit conditions for approximately 10μs, while traditional software protection requires milliseconds, making timely action impossible. The common protection unit uses hardware comparators and logic gates to implement fault detection and blocking signal output, with a response time of less than 1μs, enabling protection action to be completed before the power device experiences overcurrent surges. The protection unit is independent of each channel's DSP controller, ensuring reliable operation even if the controller malfunctions due to interference. The advantages of this centralized protection architecture are: simultaneous blocking of multiple channels from a single detection point prevents fault propagation; protection thresholds can be set in hardware, unaffected by software malfunctions; and the fault status can be queried through the main control unit after protection action, facilitating fault diagnosis.

[0090] In this embodiment, the common protection unit is connected to the four constant current source channels and the main control unit respectively, and is used to detect overcurrent, overvoltage, overheating or short circuit faults, and outputs a total blocking signal to each constant current source channel when a fault is detected. Through the above protection mechanism, a system-level rapid fault response is achieved, significantly improving the reliability and safety of the test system.

[0091] This invention also provides a test system control method for electromagnetic load shearing of the thrust bearing of a pumped-storage generator, the method comprising the following steps:

[0092] Current setting step: The main control unit sends the current setting value at the current moment to each constant current source channel according to the user command received by the HMI human-machine interface;

[0093] Specifically, in the current setting step, the main control unit sends the current setpoint value for the current moment to each constant current source channel based on the user command received from the HMI (Human Machine Interface). This step achieves unified allocation of current commands across multiple channels. The principle is that the user sets the waveform type, amplitude, frequency, and phase of each channel through the HMI, and the main control unit converts these settings into the current setpoint value for each channel at the current moment and sends it down via the communication bus. The advantages of this approach are: command sending is decoupled from the underlying control; the user only needs to make settings on the HMI without needing to concern themselves with the underlying implementation details; and the communication bus ensures the real-time nature of command sending.

[0094] Current tracking control steps: Each constant current source channel independently acquires the output current feedback signal of its own channel, and generates a drive signal based on the deviation between the current setpoint and the output current feedback signal, using a predictive control algorithm. The drive signal controls the switching state of the power converter inside the channel, so that the output current of the channel tracks the current setpoint.

[0095] Specifically, in the current tracking control step, each constant current source channel independently acquires its own output current feedback signal. Based on the deviation between the current setpoint and the feedback signal, a drive signal is generated using a predictive control algorithm to control the switching state of the power converter within that channel, ensuring that the output current tracks the current setpoint. This step achieves high-precision tracking of a single current channel, with the core being the model predictive control algorithm.

[0096] Multi-channel synchronization steps: The output current of each constant current source channel is kept in phase synchronization.

[0097] Specifically, in the multi-channel synchronization step, the output currents of each constant current source channel maintain phase synchronization. This step achieves phase consistency during multi-channel collaborative operation. The principle is that each channel uses the synchronization clock signal issued by the main control unit as a reference and dynamically adjusts the phase of its output current through an accumulated error compensation mechanism to ensure that the phase difference between the currents meets the test requirements. Through the above method, a complete control link is formed from user commands to multi-channel synchronized current output.

[0098] The control method provided in this embodiment includes three core components: a current setting step, a current tracking control step, and a multi-channel synchronization step. Its design principle is as follows: First, the user sets the waveform type, amplitude, frequency, and phase of each channel via the HMI. The main control unit converts these settings into the current setpoint value for each channel at the current moment and sends it through the communication bus, achieving unified allocation of current commands across multiple channels. Then, each channel independently acquires its output current feedback signal and generates a drive signal based on a predictive control algorithm to control the switching state of the power converter, enabling the output current to track the setpoint value and achieving high-precision control of the single-channel current. Finally, each channel uses the synchronization clock signal sent by the main control unit as a reference and dynamically adjusts the phase of its output current through an accumulated error compensation mechanism to ensure that the phase difference between the currents meets the experimental requirements. The advantages of this three-layer architecture are: command issuance is decoupled from the underlying control; the user only needs to make settings on the HMI without needing to concern themselves with the underlying implementation details; each channel independently completes current closed-loop control without interference, and a single-channel failure does not affect other channels; the synchronization clock signal is uniformly managed, ensuring the coordinated accuracy of multiple channels.

[0099] Furthermore, the multi-channel synchronization step includes:

[0100] The main control unit sends a synchronization clock signal to each constant current source channel;

[0101] Each of the constant current source channels receives the synchronous clock signal and performs cumulative error compensation on the phase of the output current of this channel.

[0102] Furthermore, the cumulative error compensation includes:

[0103] Detect the deviation between the actual arrival time and the theoretical arrival time of the synchronization clock signal;

[0104] When the deviation exceeds a preset threshold, the phase compensation amount is calculated based on the deviation;

[0105] The phase compensation amount is accumulated into the phase control command of this channel.

[0106] Specifically, the implementation details of the multi-channel synchronization steps and cumulative error compensation are explained below. This implementation method addresses the phase accumulation error problem caused by crystal oscillator temperature drift after long-term operation by designing a dynamic phase-holding mechanism. Its design principle is as follows: Let the theoretical arrival time be... The actual arrival time is ,deviation Cumulative model of phase error ,in, For clock frequency, if no compensation is performed, the phase compensation amount is... It continues to increase with runtime. When Phase compensation is triggered at time, and the formula for calculating the phase compensation amount is as follows: .Will Phase correction can be achieved by accumulating the phase information into the current phase control command. Traditional multi-channel constant current source systems can only set the phase at startup and cannot dynamically adjust it during operation, and they lack a phase closed-loop calibration mechanism. After long-term operation, inconsistent temperature drift of the crystal oscillators in each channel leads to cumulative phase errors, which seriously affects the coordinated excitation effect of multiple excitation coils. The dynamic phase holding mechanism of this embodiment can dynamically maintain phase accuracy without restarting through periodic detection and closed-loop compensation.

[0107] In a preferred embodiment, in conjunction with the appendix Figure 1 The system detects the arrival time of the synchronization clock pulse every second and calculates the deviation between the actual and theoretical values. ,like This triggers phase compensation. The detected clock drift is converted into a phase compensation amount: The compensation amount is then added to the phase control command. Through the above compensation algorithm, a dynamically maintained precise phase relationship is achieved, meeting the stringent requirements of the hydro-generator vertical electromagnetic suspension bearing test bench for coordinated excitation of multiple excitation coils.

[0108] Furthermore, the predictive control algorithm includes:

[0109] Establish a discrete-time prediction model for the controlled object;

[0110] Within each control cycle, find the optimal control quantity that minimizes the cost function;

[0111] The cost function includes a tracking error term and a weighted sum of at least one of the following constraint terms: voltage constraint term, switching smoothing constraint term, and ripple suppression term.

[0112] Specifically, the details of the predictive control algorithm are explained below. This implementation proposes a model-predictive current control algorithm to address the problems of slow dynamic response, severe waveform distortion, and large noise and ripple in existing constant current sources. Its design principles are explained from four aspects: controlled object characteristics, predictive model, rolling optimization, and feedback correction.

[0113] First, a mathematical model of the controlled object is established. The excitation coil of the electromagnetic levitation bearing is equivalent to an RL series circuit, and its discretization equation is:

[0114]

[0115] Where: Current state coefficient Voltage input coefficient , The equivalent resistance of the coil, This is the equivalent inductance of the coil;

[0116] The sampling period of the DSP controller system;

[0117] For the first The constant current source output voltage at any given time;

[0118] This is the system disturbance term.

[0119] For the first The constant current source output current at any given time; this current is also the current flowing through the coil.

[0120] This model describes the quantitative relationship between the current voltage and the current at the next moment. Unlike traditional PID control, this model enables the DSP controller to predict the future current value corresponding to different voltage commands, thereby achieving anticipatory compensation.

[0121] Secondly, rolling optimization is performed using model predictive control. Ignoring disturbance terms, the predictive model is:

[0122]

[0123] In the formula, For the first The predicted current value at time [time] For the first The constant current source output current at any time For the first The constant current source output voltage at any given time.

[0124] Within each control cycle, the optimal voltage sequence that minimizes the cost function is searched. The cost function is designed as a multi-objective weighted form:

[0125]

[0126] in To track error terms and ensure that the output current accurately tracks the given value; , To predict the length of the time domain, the controller predicts the system state (such as current) forward by the number of steps. For predicting the step index in the time domain; The current setpoint issued by the main control unit; In the first The first step in time planning The current given value at time t, In the first The first time predicted Output current at any given moment;

[0127] This is a voltage constraint term that limits the output voltage amplitude to protect power devices. , In the first The solution is obtained at time 1. The optimal control voltage at any given time; this control voltage is applied to the buck DC / DC converter, and the converter output follows this voltage, that is, the sampled value is consistent with the control voltage value. To control the length of the time domain, the controller takes the number of steps to solve for the optimal control quantity (such as voltage).

[0128] A switching smoothing constraint term is used to suppress sudden changes in PWM duty cycle in order to reduce switching losses and high-frequency ripple. , In the first The solution is obtained at time 1. The optimal control voltage at any given time.

[0129] As a ripple suppression term, it directly constrains the rate of change of current to reduce output ripple;

[0130] , In the first The first time predicted Output current at any given time.

[0131] To track error weights, For voltage limiting weight, Switching frequency smoothing weights, Ripple suppression weights.

[0132] Within each control cycle, the optimal voltage sequence is solved by searching, ensuring system stability even in the event of model mismatch. This predictive control algorithm achieves high-precision, fast-response, and low-ripple current tracking.

[0133] This multi-objective cost function solves the problem that traditional algorithms cannot achieve a balance between tracking accuracy and ripple suppression.

[0134] The advantages of predictive control algorithms are: they predict in advance rather than compensate afterward, resulting in faster response speeds and solving the phase lag problem in high-frequency sine wave tracking; they can simultaneously optimize multiple objectives, solving the problems of peak distortion in triangular wave tracking and the difficulty in filtering out high-frequency ripple in PWM; and they have strong robustness to load parameter changes, solving the problem of control performance degradation caused by time-varying parameters.

[0135] Furthermore, it also includes:

[0136] Weight adjustment steps: Based on the real-time operating status of the system, dynamically adjust the correction coefficients of the weights of each constraint term in the cost function;

[0137] The real-time operating status includes at least one of the following: tracking error status, observer convergence status, and load status.

[0138] Furthermore, the weight adjustment step specifically includes:

[0139] Based on the magnitude of the tracking error, the tracking error status is divided into multiple levels;

[0140] Based on the magnitude of the observer's convergence error, the observer's convergence state is divided into multiple levels;

[0141] Based on the magnitude of the output current, the load status is divided into multiple levels;

[0142] Based on the aforementioned state levels, the basic weights and correction coefficients of each constraint term are determined, and the final weights of each constraint term in the cost function are calculated by multiplying the basic weights and correction coefficients.

[0143] Specifically, the multi-objective adaptive weight adjustment mechanism is explained below. This implementation addresses the problem that fixed weights cannot adapt to changes in operating conditions by designing an adaptive weight adjustment method based on state recognition. The design principle is as follows: the values ​​of the weight coefficients in the cost function determine the behavioral preferences of the control system under different operating conditions. Under large dynamic errors, high gain is needed to quickly reduce deviations, so the tracking error weight should be increased; under steady-state conditions, low gain is beneficial for suppressing noise and ripple, so the ripple suppression weight should be increased; under heavy loads, the voltage output approaches saturation, so the voltage constraint weight should be increased to prevent overshoot; when the observer has not converged, the model prediction accuracy decreases, so the tracking error weight should be increased to ensure robustness. Fixed-weight cost functions cannot adapt to these changes in operating conditions. This implementation achieves adaptive optimization of the control system under different operating conditions by dynamically adjusting the weight coefficients in real-time by identifying the system state.

[0144] This implementation first defines the system's operating state space, comprising three dimensions: tracking error state, observer convergence state, and load state. The tracking error state is divided based on the root mean square error and maximum error of the current tracking; the observer convergence state is divided based on the observer convergence error; and the load state is divided based on the output current. Based on the above state identification results, a multi-level weight adjustment rule table is designed. Through multi-level division and rule table lookup, the complex weight adjustment problem is transformed into a table lookup and selection problem, reducing the online computational burden on the DSP controller.

[0145] The specific weight adjustment steps include: classifying the tracking error state into multiple levels based on the magnitude of the tracking error; classifying the observer convergence state into multiple levels based on the magnitude of the observer convergence error; classifying the load state into multiple levels based on the magnitude of the output current amplitude; and determining the basic weights and correction coefficients based on the above state levels, and calculating the final weights of each constraint term in the cost function.

[0146] In a preferred embodiment, in conjunction with the appendix Figure 3 The system states are divided as follows:

[0147] Tracking error status based on the root mean square error of current tracking and maximum error Divide, among which, , The specific design is shown in Table 1:

[0148] Table 1

[0149]

[0150] The observer convergence state is based on the observer convergence error. Division, The specific design is shown in Table 2:

[0151] Table 2

[0152]

[0153] Load status based on output current The division is specifically designed as shown in Table 3:

[0154] Table 3

[0155]

[0156] Based on the aforementioned state levels, the basic weights and correction coefficients for each constraint term are determined. The final weights are obtained by multiplying the basic weights by the corresponding correction coefficients. Through this weight adjustment mechanism, the weight coefficients are adapted to tracking error, observer convergence state, and load state, enabling the control system to automatically balance dynamic response and steady-state ripple, thus balancing fast response and low ripple.

[0157] Specifically, the basic weight configuration is given first, see Table 4:

[0158] Table 4

[0159]

[0160] Then, the observer state correction coefficients are given. See Table 5:

[0161] Table 5

[0162]

[0163] Next, the load condition correction coefficient is given. See Table 6:

[0164] Table 6

[0165]

[0166] Based on the above rules, the final weight is calculated using the following formula:

[0167]

[0168]

[0169]

[0170]

[0171] For the final tracking error weights, For the final voltage limiting weight, Smoothing weights for the final switching frequency, This is the final ripple suppression weight. The adaptive weights enable the system to automatically balance between dynamic and steady-state states, taking into account both fast response and low ripple.

[0172] Furthermore, it also includes:

[0173] Common protection steps: The common protection unit detects overcurrent, overvoltage, overheating or short circuit faults in the system, and outputs a total blocking signal to each constant current source channel when the fault is detected.

[0174] Specifically, the common protection steps are described below. This implementation also includes common protection steps, which are executed corresponding to the common protection unit in the test system. Its design principle is as follows: the common protection unit monitors key parameters such as bus voltage, output current, and power device temperature in real time. When any parameter exceeds a preset threshold, the protection unit immediately outputs a blocking signal to the PWM signal generation unit of all channels through hardware logic, forcibly shutting down all power switches. The response path of this hardware-level protection is: analog comparator detection → logic gate combination → PWM blocking, with a total delay of less than 1 microsecond. In contrast, the response path of traditional software protection is: ADC sampling → interrupt triggering → ISR execution → PWM update, with a total delay of approximately 1 millisecond. Hardware-level protection can complete the protection action within the power device's tolerance time.

[0175] In this embodiment, the common protection step detects overcurrent, overvoltage, overheating, or short-circuit faults and outputs a total blocking signal to each constant current source channel when a fault is detected. Through the above common protection step, a system-level fast fault response is achieved, effectively protecting power devices and load coils.

[0176] The technical effects of the present invention will be illustrated below through specific embodiments and experimental verification.

[0177] Example 1: System Parameter Configuration

[0178] In this embodiment, the specific parameters of the test system are configured as follows: four constant current source channels, each with an output range of 0–100A, capable of independent or coordinated operation. The three-phase AC input is 380V / 50Hz industrial power. The three-phase rectifier bridge uses a 35A / 1600V specification. The DC bus capacitors are 2200μF / 800V electrolytic capacitors connected in parallel. The step-down DC / DC converter has a switching frequency of 20kHz and uses IGBTs as power switching devices. The output uses a smoothing reactor with an inductance of 5mH. The sampling unit includes current sampling, voltage sampling, and temperature sampling. The DSP controller uses a TMS320F28335 with a main frequency of 150MHz. The communication bus is RS485 with a baud rate of 115200bps. The synchronous clock bus uses a differential signal with an accuracy of ±0.1μs.

[0179] Example 2: Triangular Wave Current Tracking Test

[0180] Test conditions: Output current range 0–100A, triangular wave frequency 100Hz, load inductance variation range ±30%, load resistance variation range ±20%.

[0181] As attached Figure 4 The figure shown is a waveform diagram of the triangular wave current tracking test in this embodiment. The upper waveform in the figure is the current command signal, and the lower waveform is the actual output current tracking waveform. (See attached diagram.) Figure 4 As can be seen, the model predictive control algorithm of this invention produces a smooth triangular wave current tracking waveform with no spikes, saturation, or flat-top distortion at the peak and valley transition points, and the actual output current highly coincides with the given signal. Measurements show a tracking error of less than ±0.5% and a response time of less than 0.5ms. In contrast, under the same conditions, traditional PID control exhibits obvious spikes at the peak of the triangular wave and flat-top distortion at the valley, resulting in a larger tracking error and a longer response time. The advantage of this invention lies in its predictive control algorithm's ability to anticipate current change trends and provide sufficient voltage margin at rapid current transition points, fundamentally avoiding spikes and distortions.

[0182] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A test system for electromagnetic load shearing of thrust bearings in pumped-storage generators, characterized in that, include: Four independent constant current source channels, each constant current source channel outputs one-to-one drive of a single excitation coil corresponding to the suspension thrust bearing; The main control unit is used to send the current setpoint value at the current moment to each constant current source channel; The HMI (Human-Machine Interface) is used to receive setting instructions from the user and transmit the setting instructions to the main control unit. The single-channel constant current source includes a main circuit and a closed-loop control circuit; The main circuit includes a three-phase rectifier bridge, a DC bus capacitor, and a step-down DC / DC converter. The three-phase AC input is rectified by the three-phase rectifier bridge, then stabilized by the DC bus capacitor, and then the output voltage is adjusted by the step-down DC / DC converter to power one excitation coil of the suspended thrust bearing. The control loop includes a DSP controller, a PWM generation unit, a signal shaping and isolation drive unit, and a sampling unit; The sampling unit acquires the actual output current and voltage signals of the constant current source channel and sends the sampled signals to the DSP controller; The DSP controller receives the current setpoint from the main control unit and the feedback signal output by the sampling unit. It has an embedded model predictive control algorithm to generate a PWM drive signal based on the current setpoint and the feedback signal. The PWM drive signal drives the buck DC / DC converter through the signal shaping and isolation drive unit to achieve high-precision closed-loop constant current control of the single-channel output current.

2. The test system for electromagnetic load shearing of the thrust bearing of a pumped-storage generator according to claim 1, characterized in that, The main control unit is also used to send synchronous clock signals to the four constant current source channels; The DSP controller of each constant current source channel is also configured to: perform cumulative error compensation on the phase of the output current of this channel according to the synchronization clock signal, so as to achieve phase synchronization between the output currents of the four constant current source channels.

3. The test system for electromagnetic load shearing of the thrust bearing of a pumped-storage generator according to claim 1, characterized in that, Also includes: A common protection unit is connected to the four constant current source channels and the main control unit respectively. It is used to detect overcurrent, overvoltage, overheating or short circuit faults in the system, and outputs a total blocking signal to each constant current source channel when the fault is detected.

4. A control method for a test system of electromagnetic load shearing of thrust bearings in pumped-storage generators, wherein the method is applied to the test system described in any one of claims 1 to 3, characterized in that, The method includes the following steps: Current setting step: The main control unit sends the current setting value at the current moment to each constant current source channel according to the user command received by the HMI human-machine interface; Current tracking control steps: Each constant current source channel independently acquires the output current feedback signal of its own channel, and generates a drive signal based on the deviation between the current setpoint and the output current feedback signal, using a predictive control algorithm. The drive signal controls the switching state of the power converter inside the channel, so that the output current of the channel tracks the current setpoint. Multi-channel synchronization steps: The output current of each constant current source channel is kept in phase synchronization.

5. The test system control method for electromagnetic load shearing of thrust bearing in pumped-storage generators according to claim 4, characterized in that, The multi-channel synchronization steps include: The main control unit sends a synchronization clock signal to each constant current source channel; Each of the constant current source channels receives the synchronous clock signal and performs cumulative error compensation on the phase of the output current of this channel.

6. The control method for a test system of electromagnetic load shearing for the thrust bearing of a pumped-storage generator according to claim 5, characterized in that, The cumulative error compensation includes: Detect the deviation between the actual arrival time and the theoretical arrival time of the synchronization clock signal; When the deviation exceeds a preset threshold, the phase compensation amount is calculated based on the deviation; The phase compensation amount is accumulated into the phase control command of this channel.

7. The test system control method for electromagnetic load shearing of thrust bearing in pumped-storage generators according to claim 4, characterized in that, The predictive control algorithm includes: Establish a discrete-time prediction model for the controlled object; Within each control cycle, find the optimal control quantity that minimizes the cost function; The cost function includes a tracking error term and a weighted sum of at least one of the following constraint terms: voltage constraint term, switching smoothing constraint term, and ripple suppression term.

8. The test system control method for electromagnetic load shearing of thrust bearing in pumped-storage generators according to claim 7, characterized in that, Also includes: Weight adjustment steps: Based on the real-time operating status of the system, dynamically adjust the correction coefficients of the weights of each constraint term in the cost function; The real-time operating status includes at least one of the following: tracking error status, observer convergence status, and load status.

9. The test system control method for electromagnetic load shearing of thrust bearing in pumped-storage generators according to claim 8, characterized in that, The weight adjustment steps specifically include: Based on the magnitude of the tracking error, the tracking error status is divided into multiple levels; Based on the magnitude of the observer's convergence error, the observer's convergence state is divided into multiple levels; Based on the magnitude of the output current, the load status is divided into multiple levels; Based on the aforementioned state levels, the basic weights and correction coefficients of each constraint term are determined, and the final weights of each constraint term in the cost function are calculated by multiplying the basic weights and correction coefficients.

10. The test system control method for electromagnetic load shearing of the thrust bearing of a pumped-storage generator according to claim 4, characterized in that, Also includes: Common protection steps: The common protection unit detects overcurrent, overvoltage, overheating or short circuit faults in the system, and outputs a total blocking signal to each constant current source channel when the fault is detected.

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