AC / DC hybrid microgrid power router power regulation and control system

Abstract

The invention relates to the technical field of power system operation control, and discloses an AC / DC hybrid micro-grid power router power regulation and control system, which comprises a main circuit module, an acquisition module and a calculation control module. The calculation control module integrates a digital signal processing unit and a field programmable gate array unit. The digital signal processing unit calculates a DC bus transient energy elasticity index, a mechanical torque margin and an electromechanical resonance risk index, and synthesizes a positive sequence virtual impedance instruction and a negative sequence virtual impedance instruction. And the field programmable gate array unit executes high-frequency sampling and extracts frequency characteristics of the high-voltage alternating-current power transmission network, and generates a driving pulse signal according to the positive-sequence virtual impedance instruction and the negative-sequence virtual impedance instruction. And the driving pulse signal regulates and controls the port impedance characteristic of the main circuit module to the high-voltage alternating-current power transmission network. According to the invention, cooperation of power grid frequency support and equipment mechanical safety is realized.

Description

Technical Field

[0001] This invention relates to the field of power system operation and control technology, specifically to a power regulation system for an AC / DC hybrid microgrid power router. Background Technology

[0002] Hybrid AC / DC microgrids are crucial for accommodating distributed wind power clusters, and power routers play a vital role in energy exchange and voltage construction between the hybrid AC / DC microgrid and the high-voltage AC transmission network. In traditional control architectures, power routers employ vector control technology based on voltage source converters or virtual synchronous generator technology, simulating the external characteristics of rotating electrical machines to participate in frequency and voltage regulation of the high-voltage AC transmission network.

[0003] Existing power router control strategies primarily focus on optimizing the external characteristics of electrical ports, generally assuming that the DC-side energy source is an ideal constant-voltage source and that the prime mover system can respond to power commands without delay or limitation. However, in actual wind power generation scenarios, the mechanical transmission chain of a wind turbine unit is a flexible multi-mass system comprising gearboxes, hubs, and blades, possessing a specific torsional natural frequency. When frequency disturbances occur in the high-voltage AC transmission network, the power router rapidly adjusts its output electromagnetic power to provide inertial support. This rapidly changing electromagnetic power is converted into mechanical torque fluctuations acting on the wind turbine unit's shaft through the generator air gap.

[0004] Existing technologies neglect the dynamic coupling relationship between electrical control and mechanical systems. When the adjustment speed or cycle of the power router in response to changes in grid frequency is close to the natural frequency of the mechanical transmission chain of the wind turbine unit, electromechanical resonance is easily induced. This resonance not only causes continuous oscillations in the grid-connected power, weakening the grid support effect, but also causes fatigue damage or even breakage of the wind turbine unit's transmission shaft system. Furthermore, existing control strategies lack real-time assessment of the transient energy buffering capacity of the DC bus unit. If the power router blindly extracts or injects power to support the grid during sudden changes in grid frequency, the voltage across the DC capacitor components may momentarily exceed the safety boundary, triggering DC bus overvoltage protection or undervoltage shutdown, causing the AC / DC hybrid microgrid to disconnect from the high-voltage AC transmission network. Therefore, this invention proposes an AC / DC hybrid microgrid power router power regulation system to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a power regulation system for AC / DC hybrid microgrid power routers. This system solves the problems of existing power routers neglecting the dynamic coupling relationship between electrical control and the mechanical transmission chain of wind power generation units, as well as the transient energy buffer limit of DC bus units, which easily leads to electromechanical resonance causing mechanical damage and DC bus voltage exceeding limits causing grid disconnection.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a hybrid AC / DC microgrid power router power regulation system, applied to connect a wind power generation cluster to a high-voltage AC transmission network, comprising a main circuit module, a data acquisition module, and a computing and control module. The computing and control module includes a digital signal processing unit and a field-programmable gate array (FPGA) unit connected via a bus. The FPGA unit performs microsecond-level current inner-loop control and frequency tracking, while the digital signal processing unit performs millisecond-level power outer-loop control and multi-dimensional impedance reshaping strategy calculation.

[0007] Preferably, the digital signal processing unit calculates the transient energy elasticity index, mechanical torque margin, and electromechanical resonance risk index of the DC bus based on the data acquired by the acquisition module; and synthesizes positive-sequence virtual impedance commands and negative-sequence virtual impedance commands based on the transient energy elasticity index, mechanical torque margin, and electromechanical resonance risk index of the DC bus. The field-programmable gate array unit uses software phase-locked loop logic to extract the frequency characteristics of the high-voltage AC transmission network, and generates drive pulse signals based on the positive-sequence virtual impedance commands and the negative-sequence virtual impedance commands. The drive pulse signals act on the main circuit module to regulate the port impedance characteristics presented by the main circuit module to the high-voltage AC transmission network.

[0008] Preferably, regarding the acquisition of status data, the AC acquisition unit in the acquisition module is located at the grid-side common connection point to acquire three-phase voltage signals and three-phase current signals; the DC acquisition unit is located at both ends of the DC bus unit of the main circuit module to acquire real-time DC voltage signals at both ends of the DC capacitor element; and the mechanical acquisition unit is installed on the wind power generation unit drive chain to acquire the rotor mechanical angular velocity signal and pitch angle signal of the wind power generation unit.

[0009] Preferably, for the extraction of power grid frequency characteristics, the field-programmable gate array (FPGA) unit uses the symmetrical component method to decompose the three-phase voltage signal and the three-phase current signal into positive-sequence and negative-sequence components, and uses second-order generalized integrator phase-locked loop (PLL) technology to extract the estimated fundamental angular frequency of the power grid. The digital signal processing unit performs differential operations on the estimated fundamental angular frequency of the power grid and implements first-order inertial filtering to calculate the frequency change rate.

[0010] Preferably, for the calculation of the transient energy elasticity index of the DC bus, the digital signal processing unit determines the dynamic voltage boundary value according to the energy flow requirements of the main circuit module, calculates the absolute value of the difference between the square of the real-time DC bus voltage and the square of the dynamic voltage boundary value, and normalizes the absolute value of the difference.

[0011] Preferably, for calculating the mechanical torque margin, the digital signal processing unit internally stores an aerodynamic torque limit table for the wind power generation unit. The digital signal processing unit queries the aerodynamic torque limit table based on the rotor mechanical angular velocity signal and the propeller pitch angle signal to obtain the maximum permissible electromagnetic torque, and calculates the difference between the maximum permissible electromagnetic torque and the measured electromagnetic torque.

[0012] Preferably, for calculating the electromechanical resonance risk index, the digital signal processing unit internally stores a set of natural frequencies of the transmission chain of the wind power generation unit. The digital signal processing unit sets twice the estimated value of the fundamental angular frequency of the power grid as the pulsating source frequency, calculates the difference between the pulsating source frequency and each natural frequency in the set of natural frequencies of the transmission chain, and combines this with the voltage amplitude in the negative sequence component for calculation.

[0013] Preferably, during the synthesis of the virtual impedance command, the digital signal processing unit dynamically adjusts the virtual resistance parameter in the positive-sequence virtual impedance command based on the transient energy elasticity index of the DC bus and the mechanical torque margin. For the negative-sequence virtual impedance command, the digital signal processing unit adjusts the damping ratio parameter of the notch filter in real time based on the frequency change rate, wherein the frequency change rate is positively correlated with the damping ratio parameter; the digital signal processing unit determines the resonance suppression gain based on the electromechanical resonance risk index, and constructs the negative-sequence virtual impedance transfer function using the damping ratio parameter and the resonance suppression gain.

[0014] Preferably, to achieve discretized control, the digital signal processing unit uses the bilinear transform method to establish a mapping relationship from the continuous complex frequency domain to the discrete Z-domain, discretizing the negative-sequence virtual impedance transfer function into a difference equation. The digital signal processing unit uses the difference equation to calculate the resonance suppression voltage command, and superimposes the resonance suppression voltage command with the voltage drop generated by the basic negative-sequence resistance to generate the negative-sequence virtual impedance command.

[0015] Preferably, for the generation of the drive pulse signal, the field-programmable gate array (FPGA) calculates a voltage reference command based on the positive-sequence virtual impedance command and the negative-sequence virtual impedance command, combined with the grid-side point of common coupling voltage. The FPGA performs a dual-synchronous coordinate system inverse transformation on the voltage reference command using the real-time phase angle, synthesizing a total voltage reference command in a two-phase stationary coordinate system. After verifying the total voltage reference command against DC bus voltage constraints, the FPGA generates the drive pulse signal using a space vector pulse width modulation algorithm.

[0016] This invention provides a power regulation system for AC / DC hybrid microgrid power routers. It has the following advantages: 1. This invention calculates the transient energy elasticity index and mechanical torque margin of the DC bus in real time through a digital signal processing unit, and incorporates these indexes as constraints into the synthesis process of the positive-sequence virtual impedance command. When providing power support to the high-voltage AC transmission network, the AC / DC hybrid microgrid power router power control system can lock the voltage safety boundary of the DC capacitor element based on the transient energy elasticity index of the DC bus, and limit the electromagnetic torque mutation of the wind power generation unit based on the mechanical torque margin. This ensures that the system does not cause voltage collapse of the DC bus unit or mechanical damage to the wind power generation unit's transmission chain when responding to frequency changes in the high-voltage AC transmission network, achieving a balance between grid support performance and equipment physical safety.

[0017] 2. This invention utilizes a digital signal processing unit to calculate the electrical resonance risk index and constructs a negative-sequence virtual impedance transfer function based on the frequency change rate. When the frequency characteristics of the high-voltage AC transmission network change, causing the pulsating source frequency to approach the natural frequency set of the wind power generation unit's transmission chain, the AC / DC hybrid microgrid power router power control system can provide active damping by increasing the damping ratio parameter and resonance suppression gain. This suppresses the electromechanical resonance generated between the negative-sequence voltage component of the high-voltage AC transmission network and the mechanical transmission chain of the wind power generation unit, cutting off the coupling path of electrical disturbances from the grid to the mechanical system and improving the operational stability of the wind power cluster in complex grid environments.

[0018] 3. This invention employs a heterogeneous dual-closed-loop control architecture comprised of a digital signal processing unit (DSP) and a field-programmable gate array (FPGA). The FPGA handles microsecond-level high-frequency sampling control and frequency tracking, while the DSP performs millisecond-level complex impedance reshaping algorithm calculations. This hierarchical processing approach enables the AC / DC hybrid microgrid power router power regulation system to complete multi-dimensional state calculations, including the DC bus transient energy elasticity index and electromechanical resonance risk index, without reducing the current inner loop control bandwidth. This resolves the contradiction between the large computational load of complex control strategies and the high real-time requirements of power electronic equipment, ensuring both the system's rapid dynamic response and the accuracy of control commands. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system architecture of the present invention; Figure 2 This is a schematic diagram of the system flow of the present invention; Figure 3 This is a comparative schematic diagram of the DC bus voltage disturbance rejection performance of the present invention; Figure 4 This is a comparative schematic diagram of the mechanical torque pulsation suppression effect of the present invention; Figure 5This is a schematic diagram of the frequency domain characteristics of the negative-sequence virtual impedance of the present invention.

[0020] Among them, 100 is the main circuit module; 200 is the acquisition module; 210 is the AC acquisition unit; 220 is the DC acquisition unit; 230 is the mechanical acquisition unit; 300 is the computing and control module; 310 is the digital signal processing unit; 320 is the field programmable gate array unit; 400 is the high-voltage AC transmission network; and 500 is the wind power generation unit. Detailed Implementation

[0021] The technical solutions in 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.

[0022] Please see Figure 1 This invention provides an AC / DC hybrid microgrid power router power regulation system. This system is applied to connect a wind power generation cluster to a 750 kV or higher high-voltage AC transmission network 400. It is used to achieve AC / DC conversion of electrical energy, bidirectional regulation of power flow, and coordinated control for grid faults and mechanical stress. The system includes a main circuit module 100, a data acquisition module 200, and a calculation and control module 300. The main circuit module 100 serves as the physical carrier for power transmission; its high-voltage AC side is connected to the high-voltage AC transmission network 400, and its low-voltage AC side is connected to the wind power generation unit 500.

[0023] The main circuit module 100 adopts a modular multilevel converter topology or a cascaded H-bridge topology. Specifically, the main circuit module 100 includes a grid-side converter unit, a DC bus unit, and a generator-side converter unit. The grid-side converter unit is composed of multiple cascaded power semiconductor sub-modules, used to realize the power conversion between the high-voltage AC transmission network 400 and the DC bus unit. The DC bus unit has DC capacitors connected in parallel, which provide DC voltage support and act as a physical buffer for transient energy. The generator-side converter unit is connected between the DC bus unit and the wind power generation unit 500, used to regulate the AC power output of the wind power generation unit 500.

[0024] The acquisition module 200 is used to acquire the electrical and mechanical physical quantities of the system in real time. The acquisition module 200 includes an AC acquisition unit 210 located at the grid-side common connection point, a DC acquisition unit 220 located at both ends of the DC bus unit, and a mechanical acquisition unit 230 installed on the drive train of the wind power generation unit 500. The AC acquisition unit 210 is configured to acquire the three-phase voltage signal and three-phase current signal at the grid-side common connection point. The DC acquisition unit 220 is configured to acquire the real-time DC voltage signal across the DC capacitor element. The mechanical acquisition unit 230 is configured to acquire the rotor mechanical angular velocity signal and blade pitch angle signal of the wind power generation unit 500.

[0025] The computing control module 300 is connected to the acquisition module 200 and the main circuit module 100 via an optical fiber communication link or an industrial Ethernet bus. The computing control module 300 includes a digital signal processing unit 310 and a field-programmable gate array (FPGA) unit 320 in its hardware architecture.

[0026] The digital signal processing unit 310 is configured to execute complex floating-point operations and core control algorithms. Internally, the digital signal processing unit 310 stores preset system parameters, including at least a set of DC bus voltage safety thresholds, a set of natural frequencies of the transmission chain of the wind power generation unit 500, and an aerodynamic torque limit table for the wind power generation unit 500. The digital signal processing unit 310 is configured to calculate the DC bus transient energy elasticity index, mechanical torque margin, and electromechanical resonance risk index based on the signals input from the acquisition module 200, and accordingly synthesize positive-sequence virtual impedance commands and negative-sequence virtual impedance commands.

[0027] The field-programmable gate array (FPGA) unit 320 is connected to the digital signal processing unit 310 via a high-speed parallel bus. The FPGA unit 320 is configured to perform high-frequency sampling control and pulse-width modulation (PWM) signal generation. The FPGA unit 320 receives high-frequency analog signals from the AC acquisition unit 210 and performs analog-to-digital conversion. The FPGA unit 320 uses software phase-locked loop (PLL) logic to extract the fundamental frequency and frequency change rate of the high-voltage AC transmission network 400 in real time. Based on the voltage reference command output by the digital signal processing unit 310, the FPGA unit 320 generates drive pulse signals using a space vector pulse-width modulation (SVM) algorithm. These drive pulse signals act on the power semiconductor devices in the grid-side converter unit and the generator-side converter unit through the drive circuit, thereby changing the port impedance characteristics presented by the main circuit module 100 to the high-voltage AC transmission network 400.

[0028] The wind power generation unit 500 includes wind turbine blades, a gearbox drive train, and a generator. The set of natural frequencies of the drive train corresponds to the low-order torsional vibration mode frequencies of the gearbox drive train and the wind turbine blades in the wind power generation unit 500. The capacitance parameters of the DC capacitor element are pre-stored in the digital signal processing unit 310 and used to calculate the transient energy elasticity index of the DC bus.

[0029] In the AC / DC hybrid microgrid power router power regulation system, the digital signal processing unit 310 and the field-programmable gate array (FPGA) unit 320 work together to form a dual closed-loop control architecture. The FPGA unit 320 is responsible for microsecond-level current inner-loop control and frequency tracking, while the digital signal processing unit 310 is responsible for millisecond-level power outer-loop control and multi-dimensional impedance reshaping strategy calculation. This hardware architecture ensures that the system can maintain voltage stability of the DC bus unit and suppress mechanical resonance of the wind power generation unit 500 under conditions of voltage sag, frequency drift, or imbalance faults in the high-voltage AC transmission network 400.

[0030] See attached document Figure 2 The power regulation method for AC / DC hybrid microgrid power routers is mainly executed by the digital signal processing unit 310 in the computing control module 300 in conjunction with the field-programmable gate array unit 320. The core principle of this method is to transform traditional constant power control into state-constrained impedance control. By real-time sensing of the energy state of the DC capacitor and the mechanical stress state of the wind turbine shaft system, the equivalent resistance and inductance on the grid side of the power router are dynamically adjusted, making the power router behave as a nonlinear source with adaptive inertia and frequency-selective damping during grid faults, rather than a rigid power injection source. The AC / DC hybrid microgrid power router power regulation method specifically includes the following steps: The system acquires multi-dimensional state data and extracts grid frequency characteristics. The field-programmable gate array (FPGA) unit 320 obtains high-frequency sampling data through the AC acquisition unit 210 and the DC acquisition unit 220. For AC voltage and current signals, the FPGA unit 320 uses the symmetrical component method to decompose the AC voltage and current signals into positive-sequence and negative-sequence components in real time. For the frequency parameters of the high-voltage AC transmission network 400, the fundamental angular frequency estimate of the grid is extracted in real time using a second-order generalized integrator phase-locked loop (PLL) technique. Based on this, the digital signal processing unit 310 further calculates the frequency change rate. The frequency change rate physically characterizes the severity of grid frequency drift and is used to subsequently determine whether the notch filter needs to adjust its bandwidth to capture the escaping resonant frequency. The formula for calculating the frequency change rate is: ; in, Indicates the first The frequency change rate per control cycle, in radians per square second; This represents the estimated fundamental angular frequency of the power grid at the current moment; This represents the estimated fundamental angular frequency of the power grid at the previous moment; This indicates the sampling period of the control system, and its value typically ranges from 50 microseconds to 200 microseconds.

[0031] The transient energy elasticity index of the DC bus is calculated. This step physically treats the DC bus capacitor as a finite-capacity energy buffer and calculates the remaining power throughput potential of this buffer at the current moment through normalization. The digital signal processing unit 310 quantifies the energy throughput capacity of the DC bus unit without triggering hardware protection thresholds based on the current power flow demand. The transient energy elasticity index of the DC bus is calculated when the system needs to release energy to the high-voltage AC transmission network 400, or when the system needs to absorb energy from the high-voltage AC transmission network 400. Construct according to the following logic: ; in, This refers to the capacitance value of a DC capacitor. This refers to the real-time acquisition of DC bus voltage; These are dynamic voltage boundary values; when the system needs to support the grid voltage, The DC undervoltage protection threshold is selected when the system needs to suppress bus overvoltage. Select the DC overvoltage protection threshold; The rated power of the power router; This is a preset transient support time window parameter, which is set according to the grid low voltage ride-through standard and is typically set to 625 milliseconds to 3 seconds. The value is dimensionless. The larger the value, the greater the elasticity margin of the system in using DC capacitors to buffer power fluctuations.

[0032] The mechanical stress boundary mapping of the wind power generation unit 500 is constructed. This step aims to transform the torque limits in the mechanical field into real-time constraints in the electrical control field, preventing overload of the mechanical transmission chain due to electrical regulation overspeed. The digital signal processing unit 310 receives the rotor mechanical angular velocity and pitch angle signals uploaded by the mechanical acquisition unit 230, and determines the maximum permissible electromagnetic torque under the current operating condition by combining them with a preset aerodynamic torque limit table. The aerodynamic torque limit table is a data table pre-stored in the digital signal processing unit 310, which contains stress limit data of the wind turbine blades and transmission chain at different speeds and pitch angles. Based on the difference between the maximum permissible electromagnetic torque and the currently measured electromagnetic torque, a mechanical torque margin is generated. : ; in, To determine the rotor's mechanical angular velocity and propeller pitch angle The maximum permissible electromagnetic torque obtained from the table; This is the measured electromagnetic torque. A negative value indicates that the mechanical structure is at risk of overload.

[0033] To perform dynamic assessment of electromechanical resonance risk, the digital signal processing unit 310 performs risk matching at the frequency domain for the second harmonic power pulsation caused by an imbalance fault in the 400V AC transmission network. The system first calculates the pulsation source frequency, which is set to twice the estimated real-time grid fundamental angular frequency. Then, it iterates and compares this pulsation source frequency with the pre-stored set of natural frequencies of the wind turbine generator unit 500's transmission chain to calculate the resonance risk index. : ; in, This represents the total number of inherent frequencies that need to be considered. The frequency of the pulsation source calculated at the current moment; For the first The natural frequency of each transmission chain; This represents the amplitude of the negative sequence component of the grid voltage. The risk weighting coefficient is selected based on the stiffness of the wind turbine shaft system; To prevent small positive numbers with a denominator of zero, the value is usually taken to be between 0.01 and 0.1. This exponent will only increase when there is a negative sequence component in the grid voltage and the real-time pulsation source frequency approaches a certain natural frequency, thereby triggering subsequent impedance notch control.

[0034] Synthesize adaptive multidimensional virtual impedance commands. This step includes two parallel processes: positive-sequence virtual impedance synthesis and negative-sequence virtual impedance synthesis.

[0035] For positive-sequence virtual impedance, the system dynamically adjusts the virtual resistance parameters based on the transient energy elasticity index of the DC bus and the mechanical torque margin. The control logic is as follows: when energy is abundant and there is no mechanical risk, the resistance is reduced to exhibit stronger power supply characteristics; when energy is depleted or there is mechanical overload, the resistance is increased to exhibit load characteristics, thereby limiting power exchange.

[0036] For negative-sequence virtual impedance, the system constructs a notch filter model with adaptive bandwidth characteristics. The digital signal processing unit 310 adjusts the damping ratio parameter of the notch filter in real time according to the frequency change rate. : ; in, The base damping ratio, ranging from 0.01 to 0.1, is used to determine the notch depth when the frequency is stable. To adjust the gain, the sensitivity of the bandwidth expansion with frequency change rate is set. When the grid frequency drifts rapidly, the damping ratio increases, and the notch filter bandwidth widens to ensure coverage of the drifting resonant frequency point; This represents the absolute value of the rate of change of the power grid frequency. Based on this adaptive damping ratio, a negative-sequence virtual impedance is constructed. Transfer function model: ; in, For the Laplace operator, the physical meaning of this transfer function is: when the frequency of the negative sequence current in the power grid... Equal to the frequency of the pulsating source When the imaginary parts of the denominator in the transfer function cancel each other out, the negative-sequence virtual impedance... It exhibits purely resistive characteristics and its amplitude reaches its maximum value. This strongly suppresses the resonant current; when the negative sequence current frequency... Far from the frequency of the pulsation source At that time, the resonance suppression term decays to zero, and the negative-sequence virtual impedance... Restore to basic negative sequence resistance This ensures the system's control capability under normal unbalanced operating conditions. The digital signal processing unit 310 uses the bilinear transform method to process the negative-sequence virtual impedance. Discretize the data into a difference equation, and calculate the virtual impedance command value for the next control cycle based on the difference equation.

[0037] The field-programmable gate array (FPGA) unit 320 generates a modulation drive signal and calculates the voltage reference command for the grid-side converter unit based on the synthesized positive-sequence virtual impedance and negative-sequence virtual impedance. ; in, This refers to the voltage at the grid-side common coupling point; This is the positive-sequence virtual impedance; It is a positive sequence current; It is a negative-sequence virtual impedance; This is a negative sequence current. This voltage references the command. The input is fed into the space vector pulse width modulation module to generate drive pulse signals for turning on and off the power devices of the control grid-side converter unit, thereby realizing the dynamic reshaping of the power router port impedance at the physical level.

[0038] See attached document Figure 2The system's acquisition and processing of multidimensional state variables is primarily executed by the field-programmable gate array (FPGA) unit 320. The core logic of this process lies in using coordinate transformation technology to convert the physically coupled three-phase AC signals in the high-voltage AC transmission network 400 into mathematically orthogonally decoupled DC control signals, thereby achieving independent control of active power, reactive power, and unbalanced fault components. The acquisition and decoupling of electrical and mechanical state variables specifically includes the following steps: High-frequency synchronous sampling and analog-to-digital conversion are performed. A field-programmable gate array (FPGA) unit 320 controls a multi-channel analog-to-digital converter to discretize and read sensor signals at a preset sampling frequency. For electrical quantities at the grid-side common connection point, the instantaneous values ​​of three-phase AC voltage are acquired. , , and instantaneous value of three-phase alternating current , , Sampling frequency here The frequency range is set to 10 kHz to 20 kHz. This range is chosen to satisfy the Nyquist sampling theorem and ensure the analysis accuracy for harmonics up to the 50th order. For DC-side electrical quantities, the DC voltage signal across the DC capacitor is acquired. For DC voltage signals, a sliding window with a length of [missing information] is used. An average filter (with values ​​from 4 to 16) is used to process the signal to remove electromagnetic noise introduced by the high-frequency operation of the power switch. For the mechanical side signal, the rotor mechanical angular velocity of the wind turbine unit 500 is read. and propeller pitch angle All signals are timestamped using a unified clock source, eliminating phase delays caused by different sensor transmission paths.

[0039] To reduce the dimensionality of the control system and simplify the three-phase coupling relationship, the field-programmable gate array (FPGA) unit 320 uses the Clarke transformation matrix to map the AC electrical quantities in the three-phase stationary coordinate system to the two-phase stationary coordinate system by constructing electrical vectors in a two-phase stationary coordinate system. (Coordinate system). Taking grid-side AC voltage as an example, Axis voltage components and Axis voltage components The calculation is as follows: ; in, , , These are the instantaneous values ​​of the three-phase AC voltage collected at the current sampling time; These are the transformation coefficients under the constraint of constant amplitude. For the instantaneous value of three-phase AC current... , , Using the same transformation matrix, we obtain and This step reduces the three-dimensional variables to two-dimensional orthogonal variables, providing a mathematical foundation for subsequent vector decomposition.

[0040] To decouple the positive-sequence and negative-sequence components, under power grid imbalance fault conditions, the electrical vector simultaneously contains both positive-sequence and negative-sequence rotating components. The system utilizes an orthogonal signal generator based on a quarter-cycle delay (T / 4-Delay) for sequence component separation. Its physical principle is based on the property that the positive-sequence and negative-sequence vectors rotate in opposite directions in space (positive sequence counterclockwise, negative sequence clockwise), and algebraic cancellation is achieved by constructing orthogonal delayed signals. Definition for A signal lagging by 90 electrical degrees is defined as follows: for A signal lagging by 90 electrical degrees. The positive sequence voltage component is... Projection in coordinate system , and negative sequence voltage components in Projection in coordinate system , Calculate according to the following mathematical model: ; ; The hysteresis signal is obtained by reading historical data from the circular shift register. The register's backtracking depth... From real-time calculation formula round Confirmed, among which The fundamental frequency of the power grid is estimated in real time. This mechanism of dynamically adjusting the delay depth ensures that the system can still separate the positive and negative sequence components when the power grid frequency drifts, overcoming the defect of decoupling failure of the traditional fixed delay method when the frequency changes.

[0041] To extract the DC control quantity in the rotating coordinate system and achieve zero steady-state error tracking control, the system needs to convert the AC quantity into a DC quantity for PI regulation. The field-programmable gate array (FPGA) unit 320 will then convert the separated DC quantity into a DC quantity. Projecting coordinate system components onto a synchronously rotating coordinate system ( (Coordinate system). The phase angle of the grid voltage vector output by the phase-locked loop. Calculate the forward order using the Park transform shaft voltage Ascending order shaft voltage and negative order shaft voltage Negative sequence q-axis voltage The transformation formula for positive sequence voltage is as follows: ; in, This represents the rotation matrix of the Park transformation, used to implement rotational transformations of the coordinate system; and The trigonometric function values ​​calculated based on the phase angle are the core transformation coefficients of the matrix.

[0042] In the transformation formula for negative sequence voltage, the angle of the rotation transformation matrix is ​​taken as... .also, and It characterizes the amplitude and phase of the fundamental positive-sequence energy of the power grid; while the amplitude synthesized from the negative-sequence component... This serves as an indicator to quantify the current degree of power grid imbalance and is directly used to determine whether to activate resonance suppression control.

[0043] The standardization and synchronization of mechanical state quantities are performed by the field-programmable gate array unit 320, which reads the rotor mechanical angular velocity from the communication interface. Converted to standard International Units (rad / s) and aligned with electrical sampling data on the time axis. The system is based on the gearbox speed ratio of the wind turbine unit 500. The low-speed shaft speed is converted to the generator's high-speed shaft speed. The converted speed is then compared to the pitch angle. Together they serve as an index key, used to look up the aerodynamic torque limit table in the digital signal processing unit 310 to obtain the maximum permissible mechanical stress boundary under the current wind conditions.

[0044] See attached document Figure 2 The system utilizes a second-order generalized integrator to filter and orthogonalize the grid-side voltage signal, and achieves frequency locking of the 400 MHz high-voltage AC transmission network through a frequency adaptive feedback loop. The physical basis of this frequency extraction method lies in the fact that the second-order generalized integrator has an infinitely large open-loop gain at the resonant frequency, enabling it to track the fundamental component of the input signal without steady-state error, while exhibiting high attenuation characteristics for high-frequency harmonics and DC components, thus extracting a high-purity synchronization signal under grid voltage distortion conditions. The frequency extraction process based on the second-order generalized integrator phase-locked loop specifically includes the following steps: A frequency-adaptive second-order generalized integrator model is constructed, and the field-programmable gate array (FPGA) unit 320 directly reads the original data obtained in the step of constructing the electrical vector in the two-phase stationary coordinate system. Axis voltage components This signal is then input as the excitation signal to the second-order generalized integrator (SOGI) module. It should be noted that the electrical vector obtained in the step of constructing the two-phase stationary coordinate system... The signal is derived from real-time sampled data and contains high-order harmonics and noise. This step aims to utilize the bandpass filtering characteristics of SOGI to extract the pure fundamental component from the original signal. The second-order generalized integrator is configured as a closed-loop system, and its output contains two orthogonal signals: the filtered fundamental component and the... Axial components and orthogonal components with a 90-degree lag. The transfer function relationship is as follows: ; ; in, This is the damping coefficient of the second-order generalized integrator, with a value range of 1.0 to 1.414. This coefficient determines the quality factor of the filter. The smaller the value, the narrower the bandwidth, and the stronger the ability to suppress harmonics in the original signal output by the electrical vector step in the two-phase stationary coordinate system, but the slower the dynamic response. This is the real-time feedback estimate of the fundamental angular frequency of the power grid; This is the Laplace operator. Through the above processing, the system transforms the original coarse output signal into a pure orthogonal signal, solving the problem of noise sensitivity in traditional differential algorithms. In the digital implementation, the continuous transfer function is discretized using the bilinear transform method (Tustin transform).

[0045] Performing phase detection and loop filtering based on a synchronous rotating coordinate system, the field-programmable gate array (FPGA) unit 320 utilizes the output pure quadrature signal to... and A coordinate transformation is performed. The system utilizes the current grid voltage vector phase angle. Project the orthogonal signal from the stationary coordinate system onto the synchronously rotating coordinate system (Park transformation) and calculate... Shaft voltage error components : ; in, and The trigonometric function values ​​calculated based on the phase angle are the core transformation coefficients of the Park transformation matrix.

[0046] The physical meaning of this formula is to project the voltage vector output by the SOGI (second-order generalized integrator) onto the tangential component of the virtual rotation axis. If the phase-locked loop is fully locked, this error component should always be zero. Subsequently, The input is fed into a proportional-integral (PI) controller for regulation. The output of the PI controller is fed forward with respect to the grid's rated angular frequency. By superimposing the values, we obtain the current estimated fundamental angular frequency of the power grid. : ; in, This is the feedforward quantity for the rated angular frequency of the power grid; The sampling period for the control system; and To control the gain, it is based on the desired phase-locked loop bandwidth. Damping ratio According to the formula and Parameters are tuned to ensure rapid tracking capability during power grid frequency changes.

[0047] By implementing frequency feedback and phase integration output, the system will calculate the estimated fundamental angular frequency of the power grid. Real-time feedback is provided to the second-order generalized integrator module for dynamically updating the center frequency parameter in the transfer function. This feedback mechanism constitutes a frequency adaptive closed loop: when the grid frequency drifts, the phase detector and loop filter based on the synchronous rotating coordinate system detect the frequency change, and the step of constructing the frequency adaptive second-order generalized integrator model automatically adjusts the center frequency of the filter to align with the new grid frequency, thereby avoiding amplitude and phase measurement errors caused by frequency mismatch. Simultaneously, the fundamental angular frequency of the grid is estimated... Perform discrete-time integration to generate the real-time phase angle for coordinate transformation. : ; in, This indicates the real-time phase angle generated in the previous control cycle for coordinate transformation; This indicates the sampling period of the control system. This real-time phase angle... It serves as a unified phase reference for all coordinate transformation modules in the entire system.

[0048] See attached document Figure 2 After obtaining a high-precision estimate of the fundamental angular frequency of the power grid, the digital signal processing unit 310 calculates the rate of frequency change. The physical essence of this step is to perform differential processing on the time-varying frequency signal, aiming to mathematically quantify the acceleration of the power grid frequency deviating from its rated value, thereby providing a dynamic input variable characterizing the degree of power imbalance in the system for subsequent virtual inertia control. The real-time calculation process of the rate of frequency change specifically includes the following steps: The digital signal processing unit 310 performs discrete differential operations on the frequency signal and receives the estimated value of the power grid fundamental angular frequency. Since the digital control system is based on discrete-time sampling, the physical differentiation operation is implemented as a finite difference at the algorithm level. The digital signal processing unit 310 calculates the original value of the instantaneous frequency change rate. The calculation formula is as follows: ; in, For the current control cycle The estimated fundamental angular frequency of the power grid; For the previous control cycle The estimated fundamental angular frequency of the power grid; This represents the sampling period of the control system. It's important to note that direct differential operations have a high-pass characteristic, which amplifies quantization errors and high-frequency electromagnetic noise during the sampling process. If the unprocessed raw value of the instantaneous frequency change rate is... Using it directly for control can cause high-frequency fluctuations in the converter's output power, and may even lead to system instability.

[0049] First-order inertial filtering is implemented to suppress high-frequency noise introduced by differential operations while retaining low-frequency components that reflect the basic trend of the power grid frequency. The digital signal processing unit 310 processes the raw value of the instantaneous frequency change rate. Digital filtering is performed. The system uses the backward Euler method to transform the transfer function of a first-order low-pass filter in the continuous domain. Discretization was performed, and a time-domain difference equation was derived to control the rate of change of frequency. Measurement time constant This is a key parameter determining the performance of the frequency change rate detection, and its value range is set to 0.02 seconds to 0.1 seconds. This range is determined based on an engineering trade-off principle: if... If the cutoff frequency is less than 0.02 seconds, the filter's cutoff frequency is too high and cannot effectively filter out power frequency harmonic noise; if If the delay is greater than 0.1 seconds, the measurement delay will exceed 5 cycles, causing the virtual inertia support to lag behind the grid frequency drop, thus losing the optimal time for inertia support.

[0050] To avoid frequent triggering of inertial response under normal, minor random fluctuations in the power grid frequency (such as frequency jitter caused by load switch operation), the digital signal processing unit 310 determines the dead zone threshold for the frequency change rate. Set a start threshold. Only when the absolute value of the rate of change of frequency is... Exceeding the preset startup threshold At that time, the digital signal processing unit 310 determines that a frequency event requiring inertia support has occurred in the current power grid, and then... Output to subsequent control modules; otherwise, set the output value to zero. Startup threshold. The value ranges from 0.1 Hz / s to 0.5 Hz / s. This threshold is set with reference to the guidelines for power system safety and stability: 0.1 Hz / s is generally considered the critical point distinguishing normal frequency fluctuations from faulty frequency slippage; while 0.5 Hz / s corresponds to severe power deficit incidents. Using values ​​within this range ensures that the system neither malfunctions nor misses frequency faults.

[0051] See attached document Figure 2 The modeling process is executed by the digital signal processing unit 310, and its physical essence is to map the current remaining charge and discharge capacity of the DC capacitor into a normalized probability space. This establishes a dynamic gain adjustment variable tightly coupled to the system's physical boundaries to prevent DC bus voltage collapse caused by virtual inertia control providing frequency support. The modeling process for the DC bus transient energy elasticity index specifically includes the following steps: To establish the energy boundary for safe operation on the DC side, the digital signal processing unit 310 reads the DC bus hardware limit parameters pre-stored in the register. These DC bus hardware limit parameters include the DC bus capacitance value. DC bus rated operating voltage Maximum allowable voltage of DC bus and the minimum allowable voltage of the DC bus Maximum allowable voltage of DC bus The setting depends on the collector-emitter rated withstand voltage of the DC-side power semiconductor switching device (IGBT) and the breakdown voltage of the DC support capacitor, and is typically taken as 1.1 to 1.2 times the rated operating voltage of the DC bus. Minimum allowable voltage of the DC bus. The setting depends on the lower limit of the linear pulse width modulation (PWM) region of the grid-side converter. If the voltage is lower than this value, the converter will enter the over-modulation nonlinear region, resulting in output current distortion. Typically, this value is taken as 0.8 to 0.9 times the rated operating voltage of the DC bus. This is based on the physical formula of capacitor energy storage. The digital signal processing unit 310 logically defines the maximum energy storage boundary of the DC bus. Minimum energy storage boundary and rated energy storage status Although the physical model is based on energy, in engineering implementation, to reduce the computational burden on the digital signal processing unit 310, the energy state is directly represented using the squared voltage term, and the calculation formula is as follows: ; ; ; This processing method utilizes The monotonicity of the DC bus capacitor value is avoided in large-scale real-time calculations due to its monotonicity. Multiplication operation; where, This indicates a direct proportional relationship.

[0052] The digital signal processing unit 310 acquires real-time status data and determines energy flow demand based on the acquired and filtered real-time DC voltage signal. Calculate the equivalent energy state at the current moment. Meanwhile, the system determines the energy flow demand of the DC bus based on the current frequency change trend: when the grid frequency decreases, the DC bus needs to release energy (discharge); when the grid frequency increases, the DC bus needs to absorb energy (charge).

[0053] The normalized transient energy elasticity index is constructed, and the digital signal processing unit 310 constructs the transient energy elasticity index of the DC bus. This index is a piecewise defined nonlinear function designed to quantify the safe distance between the DC bus and the tripping of fault protection under the current voltage conditions; it is the transient energy elasticity index of the DC bus. The mathematical model is as follows: ; in, This is the saturation limiting function. If the calculated result is greater than 1, then it is set to 1; if the calculated result is less than 0, then it is set to 0. This is the maximum allowable voltage for the DC bus. This is the minimum allowable voltage for the DC bus. The control logic of this formula is as follows: When the DC bus voltage Equal to the rated voltage of the DC bus hour, A value of 1 indicates that the system has full regulatory flexibility. When the DC bus voltage... Approaching the maximum allowable voltage of the DC bus Or minimum allowable voltage of DC bus hour, A value approaching 0 indicates that energy reserves are depleted or saturated. (Through...) The computational control module 300 transforms complex voltage nonlinear constraints into dynamic gain coefficients, enabling adaptive adjustment of the control strength.

[0054] See attached document Figure 2 The wind turbine mechanical stress boundary mapping process is executed by the digital signal processing unit 310. Its technical principle lies in resolving the time scale difference between the large inertia (second-level response) of the mechanical transmission chain of the wind power generation unit 500 and the rapid electrical control (millisecond-level response) of the power router. By mapping the physical strength limit of mechanical components to the torque threshold in the electrical control algorithm in real time, the system ensures that the electromagnetic torque reaction force generated during rapid power regulation does not exceed the transient withstand capacity of the gearbox and drive shaft. The wind turbine mechanical stress boundary mapping process specifically includes the following steps: The synchronous acquisition and conversion of mechanical state quantities are performed. The digital signal processing unit 310 receives the rotor mechanical angular velocity uploaded by the mechanical acquisition unit 230 through the industrial fieldbus interface. and propeller pitch angle Because there is a fixed transmission ratio between the low-speed rotation of the wind turbine blades and the high-speed rotation of the generator, and the torque limit table is usually defined based on the generator speed, the digital signal processing unit 310 determines the transmission ratio based on the pre-stored gearbox speed ratio. The rotor mechanical angular velocity is converted to the generator side to calculate the equivalent generator angular velocity. : ; in, This represents the rotor mechanical angular velocity uploaded by the mechanical acquisition unit 230; Pre-stored gearbox speed ratio.

[0055] Meanwhile, the digital signal processing unit 310 reads the current measured electromagnetic torque of the grid-side converter unit. Measured electromagnetic torque From the machine-side converter shaft and The shaft current component is calculated through coordinate transformation and physically represents the braking torque exerted by the generator stator on the transmission chain.

[0056] Based on the limit torque retrieval from the aerodynamic limit table, the digital signal processing unit 310 calls the aerodynamic torque limit table pre-stored in non-volatile memory. The aerodynamic torque limit table is a two-dimensional data matrix. The row index of the matrix corresponds to the generator speed, and the column index corresponds to the pitch angle. The data stored in the matrix unit is the maximum steady-state mechanical torque that the transmission chain can withstand under the corresponding operating condition. The data in the aerodynamic torque limit table comes from the offline finite element analysis (FEA) and fatigue strength tests of the wind power generation unit 500, covering the gearbox tooth surface contact fatigue limit, main bearing load limit, and tower torsional vibration mode limits. Considering the real-time acquired equivalent generator angular velocity... and propeller pitch angle Typically located between discrete grid points defined in the aerodynamic torque limit table, the digital signal processing unit 310 uses a bilinear interpolation algorithm to calculate the current precise maximum permissible torque. That is, four adjacent grid points surrounding the current operating point are selected, and the smooth limit torque value is calculated by weighting the Euclidean distance between the current operating point and these four grid points, thereby avoiding the step of control command caused by table lookup quantization error.

[0057] The digital signal processing unit 310 calculates the real-time mechanical torque margin and then processes the calculated maximum allowable torque. Compared with the measured electromagnetic torque The absolute values ​​are used to perform difference calculations to calculate the mechanical torque margin. .

[0058] If mechanical torque margin A positive value indicates that there is still unused strength space in the transmission chain, allowing the power router to increase active power output; if the mechanical torque margin is... A value close to zero or negative indicates that the mechanical components are approaching their stress limit, and the power response on the electrical side must be limited.

[0059] To generate normalized mechanical stress constraint coefficients, and in order to transform the physical dimension of the mechanical torque margin into a dimensionless weighting factor suitable for the impedance control algorithm, the digital signal processing unit 310 generates the mechanical stress constraint coefficients. Mechanical stress constraint coefficient The calculation uses a normalization function with saturation characteristics: ; in, As a normalized baseline value, This is the saturation limiting function. If the calculated result is greater than 1, then it is set to 1; if the calculated result is less than 0, then it is set to 0.

[0060] Normalized baseline value Typically, this value is taken as 20% of the rated torque of the 500-ton wind turbine unit. This parameter determines the sensitivity of the control system to mechanical risks: when the margin is less than 20% of the rated torque, the constraint coefficient begins to decrease linearly, prompting the control algorithm to smoothly increase the virtual impedance, thereby limiting power flow; when the margin is exhausted, the constraint coefficient becomes 0, forcing the system to stop the inertial response, thereby achieving active protection of the mechanical transmission chain.

[0061] See attached document Figure 2 The dynamic assessment process for electromechanical resonance risk is executed by the digital signal processing unit 310. Its physical principle is based on the power oscillation theory under asymmetrical operating conditions: when an unbalanced fault occurs in the high-voltage AC transmission network 400, resulting in negative sequence voltage, the grid-side converter unit will generate a negative sequence current. The reverse rotating magnetic field generated by this negative sequence current cuts into the positive rotating main magnetic field of the generator rotor, generating electromagnetic torque pulsations in the generator air gap with a frequency twice the fundamental frequency of the grid. If this pulsation frequency falls within the natural frequency band of the mechanical transmission chain of the wind power generation unit 500, it will excite strong mechanical torsional vibration. The dynamic assessment process for electromechanical resonance risk specifically includes the following steps: The digital signal processing unit 310 determines the real-time frequency of the electromagnetic pulsation source and reads the estimated value of the fundamental angular frequency of the power grid output by the second-order generalized integrator phase-locked loop. Since the negative-order vector rotates in the opposite direction at twice the speed relative to the synchronous coordinate system rotating in the positive order, the digital signal processing unit 310 calculates the current pulsation source frequency. : Pulsation source frequency Physically, this corresponds to the frequency of alternating stress applied to a mechanical transmission chain.

[0062] The digital signal processing unit 310 obtains the negative sequence excitation intensity and the amplitude of the negative sequence component of the grid voltage calculated and output by the coordinate transformation module. Amplitude of the negative sequence component of grid voltage It is approximately proportional to the magnitude of the negative sequence current generated, and therefore is directly used as the excitation source intensity factor for quantifying the amplitude of electromagnetic torque ripple.

[0063] To calculate the multimodal resonance risk index, the digital signal processing unit 310 retrieves a pre-stored set of natural frequencies from the transmission chain of the wind turbine unit 500. This set of natural frequencies includes the natural frequency values ​​corresponding to the first-order flapping mode, the first-order oscillation mode of the wind turbine blades, and the torsional mode of the high-speed shaft of the gearbox. To assess whether the current operating conditions will trigger mechanical resonance, the digital signal processing unit 310 uses a spectral distance reciprocal weighted algorithm to calculate the resonance risk index. This algorithm simulates the amplitude-frequency response characteristics of a mechanical system: the closer the excitation frequency is to the natural frequency, the greater the response gain.

[0064] The digital signal processing unit 310 calculates the resonance risk index in real time. And compare it with the preset resonance start threshold. Comparison, resonant initiation threshold The threshold is set to 0.05 to 0.1 (per unit). The physical meaning of this threshold is: the system will only activate subsequent adaptive notch control when the grid imbalance reaches a certain level and the frequency is close to the resonance point, causing the estimated mechanical vibration amplitude to exceed 5% of the safety specification allowable value, so as to avoid unnecessarily sacrificing the negative sequence current control bandwidth of the system under non-resonant slight imbalance conditions.

[0065] See attached document Figure 2 The notch filter bandwidth adaptive adjustment logic is executed by the digital signal processing unit 310. Its technical principle lies in solving the failure problem of fixed-parameter filters under conditions of rapid grid frequency drift (high RoCoF). At the physical level, the filter's bandwidth determines the trade-off between its frequency capture range and steady-state phase lag: a wider bandwidth can cover rapidly shifting resonant frequencies, but introduces a larger phase lag, affecting fundamental frequency control; a narrower bandwidth has good frequency selectivity, but is prone to losing the target frequency when the frequency changes rapidly. Therefore, this embodiment adopts a dynamic damping adjustment mechanism based on the rate of frequency change to balance the above contradictions in real time. The notch filter bandwidth adaptive adjustment process specifically includes the following steps: The digital signal processing unit 310 calculates the adaptive damping ratio parameter and receives the real-time frequency change rate output by the frequency change rate calculation module. Real-time frequency change rate This characterizes the drift velocity of the fundamental frequency of the power grid per unit time. The digital signal processing unit 310 calculates the adaptive damping ratio based on a linear expansion model. The control logic of the linear expansion model is as follows: when the grid frequency fluctuates drastically, the damping ratio is increased to expand the effective stopband width of the filter, ensuring that the rapidly moving resonant frequency always falls within the high impedance region; when the grid frequency is stable, the damping ratio is decreased to narrow the stopband and reduce interference to signals in non-resonant frequency bands.

[0066] The digital signal processing unit 310 determines the resonance suppression gain based on the calculated resonance risk index. Determine the resonance suppression gain The switching state. The digital signal processing unit 310 employs hysteresis comparison logic to prevent the control state from repeatedly oscillating at the critical point: if resonance suppression gain Currently in a cut-out state, only when the resonance risk index... Greater than the activation threshold At that time, the resonance suppression gain will be reduced. Set to high impedance value If resonance suppresses gain Currently in an investment phase, only when the resonance risk index... Less than the closing threshold At that time, the resonance suppression gain will be reduced. Reset to zero. Enable threshold. The value range is 0.08 to 0.12 (per unit), and the threshold is turned off. The value ranges from 0.03 to 0.05 (per unit). High impedance value. The value ranges from 5 to 10 times the rated impedance of the power router. A high impedance value is connected in series at a specific frequency point. Physically, this is equivalent to constructing an open-circuit characteristic at that frequency point, thereby forcibly cutting off the specific frequency oscillating current generated by electromechanical coupling.

[0067] Constructing a negative-sequence virtual impedance transfer function, the digital signal processing unit 310 combines a basic negative-sequence resistor. Resonance suppression gain Adaptive damping ratio and the frequency of the pulsation source Constructing negative-order virtual impedance in the complex frequency domain Negative-sequence virtual impedance The mathematical construction of a bandpass filter based on a series resistor is adopted. Superimposing the bandpass characteristic in the impedance domain means forming a bandstop (notch) characteristic in the admittance domain (current domain).

[0068] See attached document Figure 2The discretization of the adaptive notch filter impedance model is executed by the digital signal processing unit 310. Its technical principle lies in solving the problem that dynamic impedance models defined in the continuous-time domain cannot be directly run in a discrete-time digital microprocessor. Since the center frequency and damping ratio of the notch filter change in real time with the power grid conditions, it belongs to a linear time-varying system (LTV). Therefore, a pre-calculated fixed coefficient table cannot be used. The coefficients of the difference equation must be solved in real time according to the current parameter values ​​in each control cycle to ensure that the digital filter can accurately reproduce the frequency domain characteristics of the analog prototype. The specific steps of the adaptive notch filter impedance model discretization implementation are as follows: A bilinear transform discretization mapping is established. The digital signal processing unit 310 employs the bilinear transform method to establish a mapping relationship from the continuous complex frequency domain to the discrete Z-domain. The technical basis for choosing the bilinear transform method is that it can map the entire left half of the stable region in the continuous complex frequency domain to the interior of the unit circle in the discrete Z-domain, thereby avoiding frequency aliasing and ensuring that the discretized digital filter is stable if and only if the analog filter is stable, without introducing non-physical divergent poles. The mapping relationship is defined as follows: ; in, The sampling period of the control system of the digital signal processing unit 310; The delay operator is a unit.

[0069] The digital signal processing unit 310 calculates the coefficients of the difference equation in real time based on the current resonance suppression gain. Adaptive damping ratio and pulse source frequency The coefficients of the second-order infinite impulse response filter are calculated. To reduce the number of floating-point division operations in the microprocessor, the digital signal processing unit 310 first calculates the common denominator term. . This is used to normalize the numerator and denominator coefficients. The calculation formula is as follows: ; in, Indicates the frequency of the pulsation source; Indicates resonance suppression gain; This represents the adaptive damping ratio.

[0070] Based on common denominator The digital signal processing unit 310 calculates the molecular coefficients respectively. , and denominator coefficient , The numerator and denominator coefficients determine the zero-pole distribution of the digital filter in the current control cycle. The calculation formula is as follows: ; ; ; ; ; Note that the numerator of the original continuous transfer function is The first-order term, after bilinear transformation expansion, is in the molecule coefficient of the term Mathematically, it is strictly zero. Utilizing this characteristic, the digital signal processing unit 310 can omit the corresponding multiplication terms in subsequent operations, thereby optimizing code execution efficiency.

[0071] The digital signal processing unit 310 executes the resonance suppression voltage command iteration and output synthesis. Using the coefficients of the difference equation derived by the bilinear transform method, it performs filtering operations on the real-time acquired negative-sequence current. To adapt to the dual-synchronous coordinate system control architecture, the difference equation iteration process is performed on the direct axis of the negative-sequence synchronous rotating coordinate system (…). (axis) and cross axis ( Execution is performed in parallel on the axis.

[0072] The digital signal processing unit 310 utilizes negative sequence direct-axis currents respectively. and negative sequence cross-axis current As input, calculate the direct-axis component of the resonant suppression voltage. and cross-axis components The direct-axis component of the resonant suppression voltage The iterative formula is as follows: ; in, , The numerator coefficient, , The coefficient is the denominator coefficient. Indicates the control cycle; and This indicates the previous control cycle. For the quadrature-axis component of the resonant suppression voltage... Using the same difference equation structure, only the input variable is replaced with negative-sequence quadrature-axis current. .

[0073] The digital signal processing unit 310 outputs the calculated resonance suppression voltage value. The voltage drop generated by the base negative sequence resistor is added together to generate the direct-axis component of the negative sequence voltage reference command that is ultimately sent to the space vector pulse width modulation module. and cross-axis components : ; ; in, It is the base negative sequence resistor.

[0074] By performing the above operations independently on the direct axis and the quadrature axis, the main circuit module 100 can accurately reshape the impedance characteristics for a specific frequency in a rotating coordinate system.

[0075] See attached document Figure 2 The virtual impedance synthesis and modulation process is executed by the digital signal processing unit 310. The technical principle of this process lies in mapping the positive-sequence DC control quantities and negative-sequence DC control quantities calculated separately in the control domain back to the two-phase stationary coordinate system in the physical domain, synthesizing a unique physical voltage vector, and converting this physical voltage vector into a time-series signal controlling the on / off state of the power semiconductor device. This mapping process ensures that the power router, while outputting fundamental power, can exhibit impedance characteristics at the physical port for a specific frequency. The virtual impedance synthesis and modulation process specifically includes the following steps: Performing a dual-synchronous coordinate system inverse transformation, the digital signal processing unit 310 obtains the positive-sequence voltage reference command output by the positive-sequence current control loop. and the negative sequence voltage reference command output by the resonance suppression module .because Defined in a synchronous coordinate system rotating positively at the fundamental angular frequency, and Defined in a synchronous coordinate system that rotates in the opposite direction to the fundamental angular frequency, the digital signal processing unit 310 must utilize the real-time phase angle provided by the phase-locked loop. For positive sequence voltage reference command and negative sequence voltage reference command The reverse Parker transform is performed separately and then vector superposition is performed. The digital signal processing unit 310 calculates the total voltage reference command in the two-phase stationary coordinate system. Axial components and Axial components The calculation formula is as follows: ; ; in, This is the direct-axis component of the positive-sequence voltage reference command; The quadrature-axis component of the positive-sequence voltage reference command; This is the direct-axis component of the negative-sequence voltage reference command; This is the quadrature-axis component of the negative-sequence voltage reference command. In the formula... and The term reflects the reverse rotation characteristic of the negative-sequence component relative to the positive-sequence component. The vector superposition operation reconstructs a comprehensive voltage vector in the stationary coordinate system, including information on imbalance suppression and electromechanical resonance damping.

[0076] The digital signal processing unit 310 reads the sampled value of the DC bus voltage to perform DC bus voltage constraint verification. To prevent the output voltage command from exceeding the inverter's physical output capacity (i.e., entering the overmodulation region) due to grid voltage drops or DC bus voltage fluctuations, the digital signal processing unit 310 must adjust the voltage vector amplitude. Linear modulation region verification is performed. The digital signal processing unit 310 defines the linear modulation threshold. : ; If the voltage vector magnitude Greater than the linear modulation threshold The digital signal processing unit 310 provides a total voltage reference command. Axial components and Axial components Perform proportional scaling correction: ; ; The physical meaning of proportional scaling correction is to prioritize keeping the phase direction of the synthesized voltage vector unchanged, that is, to maintain the stability direction of the control system, and to avoid the pulse width modulation module from entering the nonlinear saturation region by sacrificing the voltage amplitude, thereby preventing severe distortion of the current waveform.

[0077] The digital signal processing unit 310 generates a space vector pulse width modulation signal and uses the corrected total voltage reference command. Axial components and Axial components The space vector pulse width modulation (SVM) algorithm is executed. The digital signal processing unit 310 determines the six-sector region where the reference voltage vector resides and calculates the duration of action of the two adjacent basic voltage vectors and the zero vector based on the volt-second balance principle. The specific sector determination logic and time calculation formula for the SVM algorithm are well-known technologies in the field of power electronic control and will not be elaborated upon here. The digital signal processing unit 310 converts the calculated time series into six pulse width modulation comparison count values ​​for the three-phase full-bridge inverter.

[0078] The digital signal processing unit 310 inserts a dead time at the rising edge of the six pulse width modulation signals and drives the power devices. The dead time ranges from 2 microseconds to 5 microseconds. The physical purpose of setting the dead time is to prevent the upper and lower bridge arm power switches of the same phase bridge arm from conducting simultaneously due to their turn-off delay characteristics, which could cause a short circuit fault on the DC bus. The pulse width modulation signal after dead-time processing is sent to the gate drive circuit, which controls the turn-on and turn-off of the power semiconductor devices inside the power router, thereby synthesizing a physical voltage waveform with a specific fundamental voltage and impedance characteristics of a specific resonant frequency band at the AC output.

[0079] This embodiment applies to an AC / DC hybrid microgrid system. The AC / DC hybrid microgrid system connects a high-voltage AC grid to a DC bus via a power router, with the DC bus rated voltage set at 20kV. During system operation, it faces a complex environment of grid and mechanical coupling disturbances, specifically as follows: Grid-side disturbances: Frequency dip faults in high-voltage power grids during operation directly affect the voltage stability of DC buses.

[0080] Mechanical disturbances: The rotating mechanical loads (such as wind turbine generators) connected to the system have an inherent resonant frequency (about 100Hz), and this resonant frequency will drift with the operating conditions (drifting to 98Hz), which can easily cause mechanical torque pulsation and threaten the life of mechanical components such as gearboxes.

[0081] In response to the above scenario, this embodiment verifies the effectiveness of the present invention by comparing the experimental results of the traditional VSG control scheme with those of the present invention.

[0082] DC bus voltage disturbance rejection performance: Please refer to the appendix. Figure 3 This paper presents the response curve of the system DC bus voltage over time (0-1.5s) under high-voltage grid frequency sag conditions. The fault occurs in... It happens all the time.

[0083] Control group (traditional VSG control, dashed line in the figure): After the fault occurs, the DC bus voltage drops rapidly. Approximately... Around 100kV, the voltage curve dipped below the 18kV undervoltage protection threshold. Subsequently, the system triggered the undervoltage protection mechanism, causing it to disconnect from the grid, and the voltage could not be restored to the rated level.

[0084] Experimental group (the scheme of this invention, solid line in the figure): After the fault occurs, the transient energy elasticity index of the current bus inside the control system. Rapid intervention was implemented. Although the voltage curve showed a brief downward trend, it was effectively clamped within the safe range (the lowest point was above 18kV) and did not reach the undervoltage protection threshold, ensuring the system's continuous operation without disconnecting from the grid and verifying the invention's ability to support DC voltage.

[0085] Mechanical torque pulsation suppression effect: Please refer to the appendix. Figure 4 This demonstrates the system's performance. to Comparison of mechanical torque waveforms over a time period, with a torque reference value of 1.0 pu.

[0086] Control group (upper subplot, dashed line): The mechanical torque exhibits severe constant-amplitude oscillations. Data in the figure shows that its pulsation amplitude reaches 0.8 pu (peak value close to 1.4 pu), significantly exceeding the gearbox stress limit marked as 1.3 pu in the figure. This sustained high-amplitude pulsation will cause irreversible damage to the mechanical transmission chain.

[0087] Experimental group (lower subplot, solid line): In Subsequently, the control strategy of this invention takes effect, and the bandwidth of the notch filter is adaptively expanded. The oscillation amplitude of the torque waveform converges rapidly, and within about 0.2 seconds, the pulsation decays to below 0.1 pu and stabilizes at around 1.0 pu, eliminating the risk of mechanical resonance.

[0088] Adaptive reshaping of virtual impedance characteristics: Please refer to the appendix. Figure 5 This illustrates the frequency domain characteristics (94Hz-106Hz) of the negative-sequence virtual impedance amplitude of the system when the pulsating source frequency drifts. At this point, the actual pulsating source frequency has drifted from 100Hz to 98Hz (marked by the vertical dotted line in the figure).

[0089] Traditional solution (dashed line in the figure): Uses a fixed-parameter notch filter, whose impedance peak is fixed at the original resonance point of 100Hz. At the actual interference frequency of 98Hz (marked point data1 in the figure), its impedance amplitude drops significantly, entering a low-impedance state, which makes it impossible to suppress resonance at this frequency.

[0090] The present invention (solid line in the figure) works as follows: After the system detects the rate of frequency change, the impedance model is reshaped. As shown in the figure, the peak of the impedance curve automatically aligns with the drift frequency (98Hz), and the bandwidth widens. This ensures that, under frequency drift conditions, the controller can still provide a sufficiently large virtual impedance at 98Hz, thereby suppressing the resonant current.

Claims

1. A power regulation system for an AC / DC hybrid microgrid power router, characterized in that, It includes a main circuit module (100), an acquisition module (200), and a computing control module (300); The computing control module (300) includes a digital signal processing unit (310) and a field-programmable gate array unit (320). The digital signal processing unit (310) is used to calculate the transient energy elasticity index, mechanical torque margin and electromechanical resonance risk index of the DC bus based on the data collected by the acquisition module (200), and to synthesize positive sequence virtual impedance command and negative sequence virtual impedance command based on the transient energy elasticity index of the DC bus, the mechanical torque margin and the electromechanical resonance risk index. The field-programmable gate array (320) is used to perform high-frequency sampling control and extract the frequency characteristics of the high-voltage AC transmission network (400) using software phase-locked loop logic. It generates a driving pulse signal according to the positive-sequence virtual impedance command and the negative-sequence virtual impedance command. The driving pulse signal acts on the main circuit module (100) to regulate the port impedance characteristics presented by the main circuit module (100) to the high-voltage AC transmission network (400).

2. The AC / DC hybrid microgrid power router power regulation system according to claim 1, characterized in that, The acquisition module (200) includes: An AC acquisition unit (210) is located at the grid-side common connection point and is used to acquire three-phase voltage signals and three-phase current signals; A DC acquisition unit (220) is disposed at both ends of the DC bus unit of the main circuit module (100) and is used to acquire the real-time DC voltage signal at both ends of the DC capacitor element. The mechanical acquisition unit (230) is installed on the transmission chain of the wind power generation unit (500) and is used to acquire the rotor mechanical angular velocity signal and the pitch angle signal of the wind power generation unit (500).

3. The AC / DC hybrid microgrid power router power regulation system according to claim 2, characterized in that, The field-programmable gate array (320) is also used to decompose the three-phase voltage signal and the three-phase current signal acquired by the AC acquisition unit (210) into positive sequence components and negative sequence components using the symmetrical component method; The field-programmable gate array (320) uses second-order generalized integrator phase-locked loop technology to extract the estimated value of the fundamental angular frequency of the high-voltage AC transmission network (400); The digital signal processing unit (310) is also used to perform differential operation on the estimated fundamental angular frequency of the power grid and implement first-order inertial filtering to calculate the frequency change rate.

4. The AC / DC hybrid microgrid power router power regulation system according to claim 2, characterized in that, The digital signal processing unit (310) calculates the transient energy elasticity index of the DC bus, specifically including: The dynamic voltage boundary value is determined based on the energy flow requirements of the main circuit module (100); The absolute value of the difference between the square of the real-time DC bus voltage and the square of the dynamic voltage boundary value is calculated, and the absolute value of the difference is normalized to obtain the transient energy elasticity index of the DC bus, which is used to characterize the buffer power fluctuation elasticity margin of the DC capacitor element.

5. The AC / DC hybrid microgrid power router power regulation system according to claim 2, characterized in that, The digital signal processing unit (310) internally stores gearbox speed ratio parameters and aerodynamic torque limit table of wind power generation unit (500); The digital signal processing unit (310) calculates the mechanical torque margin specifically by: Using the gearbox speed ratio parameter, the rotor mechanical angular velocity signal is converted into generator speed; The maximum permissible electromagnetic torque is obtained by querying the aerodynamic torque limit table based on the generator speed and blade pitch angle signals. The mechanical torque margin is obtained by calculating the difference between the maximum permissible electromagnetic torque and the measured electromagnetic torque.

6. The AC / DC hybrid microgrid power router power regulation system according to claim 3, characterized in that, The digital signal processing unit (310) internally stores the set of inherent frequencies of the transmission chain of the wind power generation unit (500); The computer electrical resonance risk index of the digital signal processing unit (310) specifically includes: The frequency of the pulsating source is set to twice the estimated fundamental angular frequency of the power grid. The electromechanical resonance risk index is calculated by calculating the difference between the frequency of the pulsating source and each natural frequency in the set of natural frequencies of the transmission chain, and by combining the voltage amplitude in the negative sequence component.

7. The AC / DC hybrid microgrid power router power regulation system according to claim 3, characterized in that, The positive-sequence virtual impedance command synthesized based on the DC bus transient energy elasticity index, the mechanical torque margin, and the electromechanical resonance risk index specifically includes: The virtual resistance parameters are dynamically adjusted based on the transient energy elasticity index of the DC bus and the mechanical torque margin. The negative-sequence virtual impedance command synthesized based on the DC bus transient energy elasticity index, the mechanical torque margin, and the electromechanical resonance risk index specifically includes: The damping ratio parameter of the notch filter is adjusted in real time according to the frequency change rate; the larger the frequency change rate, the larger the damping ratio parameter. The resonance suppression gain is determined based on the electromechanical resonance risk index. A negative-sequence virtual impedance transfer function is constructed using the damping ratio parameter and the resonance suppression gain.

8. The AC / DC hybrid microgrid power router power regulation system according to claim 7, characterized in that, The digital signal processing unit (310) is also used to establish a mapping relationship from the continuous complex frequency domain to the discrete Z domain using the bilinear transform method, and to discretize the negative-order virtual impedance transfer function into a difference equation. The digital signal processing unit (310) uses the difference equation to calculate the resonance suppression voltage command and superimposes the resonance suppression voltage command with the voltage drop generated by the basic negative sequence resistor to generate the negative sequence virtual impedance command.

9. The AC / DC hybrid microgrid power router power regulation system according to claim 8, characterized in that, The generation of the driving pulse signal based on the positive-sequence virtual impedance command and the negative-sequence virtual impedance command specifically includes: Based on the positive-sequence virtual impedance command and the negative-sequence virtual impedance command, and in conjunction with the grid-side common coupling point voltage, calculate the voltage reference command; Using the real-time phase angle provided by the field programmable gate array unit (320), the voltage reference command is subjected to a dual synchronous coordinate system inverse transformation to synthesize the total voltage reference command in the two-phase stationary coordinate system; After verifying the DC bus voltage constraint of the total voltage reference command, the drive pulse signal is generated using a space vector pulse width modulation algorithm.

10. The AC / DC hybrid microgrid power router power regulation system according to claim 1, characterized in that, The digital signal processing unit (310) and the field-programmable gate array unit (320) form a dual closed-loop control architecture; The field-programmable gate array (320) is used to perform microsecond-level current inner loop control and frequency tracking; The digital signal processing unit (310) is used to perform millisecond-level power outer loop control and multidimensional impedance reshaping strategy calculation.

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