A control method, device and medium of a virtual synchronous generator

Abstract

The present application belongs to the technical field of virtual synchronous generators, and particularly relates to a control method and device of a virtual synchronous generator and a medium, which calculates a maximum power reference value according to a fan rotating speed. The direct current voltage is stabilized through a generator-side converter. Through a grid-side converter, the power reference value is tracked based on a virtual synchronous generator model and the synchronous machine characteristics are simulated to realize the active and reactive power control of the grid. Through control cooperation, wind energy capture is realized. When the grid frequency or voltage is abnormal, the output power is adjusted to provide support and normal operation is restored after the fault. The method enables the wind turbine generator to have the inertia and damping characteristics of the synchronous generator, can support the grid frequency and voltage, improves the stability of the power system under new energy access, ensures smooth recovery after the fault, and improves the wind energy utilization rate and power supply reliability.

Description

Technical Field

[0001] This invention belongs to the field of virtual synchronous generator technology, and specifically relates to a control method, device and medium for a virtual synchronous generator. Background Technology

[0002] In wind power generation, the control method limits the task of the generator-side converter to regulating the wind turbine speed to capture maximum wind energy, while the task of the grid-side converter is limited to regulating the DC link voltage. Under this division of labor, the DC link capacitor becomes the only buffer for power imbalance between the two sides. When disturbances occur on the grid side, the generator side cannot detect changes in grid demand in time, and the difference between the generated power and the transmitted power accumulates entirely on the DC bus, resulting in severe voltage fluctuations.

[0003] Offshore wind farms transmit power to the onshore power grid via high-voltage AC transmission lines, with transmission distances often reaching tens of kilometers. Wind power systems are connected to the grid via full-power converters. Since these converters have no rotating mass, when the grid frequency shifts, the system cannot, like a synchronous generator, naturally release or absorb electromagnetic power through rotor kinetic energy, resulting in inherently insufficient frequency support capabilities.

[0004] Furthermore, in a topology where a permanent magnet synchronous generator (PMSG) is paired with a back-to-back converter, if a virtual synchronous generator control is introduced on the grid side while the generator side maintains its original speed loop, and the control objectives on both sides are independent, when the grid side generates additional active power simulating synchronous machine characteristics, the generator side may fail to reduce the power injected into the DC link in a timely manner, causing the DC voltage to spike. Conversely, when the grid side reduces active power, the generator side may fail to compensate in a timely manner, causing the DC voltage to drop. This asynchrony between the two sides significantly increases the risk of instability in the DC link during fault periods. Summary of the Invention

[0005] The first aspect of this invention is a control method for a virtual synchronous generator, in which the DC voltage is independently regulated by the generator side and is not affected by grid frequency fluctuations and voltage drops. The two converters have clear division of labor and are coupled by electromagnetic torque, so that the rotor speed automatically adapts to wind speed changes and the blade tip speed ratio is always locked at the optimal value.

[0006] The methods include: S1: Close the circuit breaker to connect the wind power generation system to the AC power grid via transformer and transmission line; S2: Obtain the rotor speed of the wind turbine, determine the maximum captureable mechanical power based on the rotor speed and the preset optimal power coefficient, and generate a reference value of active power to be transmitted to the AC grid; S3: Using the actual value of the DC link voltage as feedback, adjust the torque current of the permanent magnet synchronous generator to stabilize the DC link voltage at the preset reference value; S4: Based on the active power reference value generated in step S2 and the preset reactive power reference value, generate a power control command; control the grid-side converter to output active power to the AC grid and adjust the reactive power according to the power control command, wherein the output of active power is adjusted with the change of grid frequency; S5: Based on the control of DC link voltage in step S3 and the tracking control of active power reference value in step S4, the electromagnetic torque of permanent magnet synchronous generator is adjusted in a coordinated manner so that the rotor speed of wind turbine changes with wind speed, the tip speed ratio is maintained at the optimal value, and maximum power point tracking is achieved. S6: Monitor the operating status parameters of the AC power grid. When the operating status parameters deviate from the corresponding preset threshold, adjust the active or reactive power output of the grid-side converter according to the power control command generated in step S4. When the operating status parameters return to the preset threshold range, return to the maximum power point tracking state.

[0007] The second aspect of this invention is a monitoring device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the control method for the virtual synchronous generator.

[0008] The third aspect of the present invention is a storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the control method for the virtual synchronous generator.

[0009] As can be seen from the above technical solutions, the present invention has the following advantages: This invention transfers the stabilization of the DC link voltage to the generator-side converter, eliminating the direct impact of offshore AC grid disturbances on the DC link voltage. The grid-side converter independently regulates active and reactive power. The active power reference value is calculated in real-time based on the rotor speed using a cubic function, while the reactive power reference value is set according to grid dispatch requirements. The grid-side converter employs a synchronous converter control structure, with the active power output responding to grid frequency deviations and the reactive power output responding to voltage reference values, giving the wind power system the external characteristics of a synchronous generator. The generator-side converter uses a dual-loop structure with an outer DC voltage loop and an inner torque current loop. The magnetic field current is always set to zero. The outer loop voltage deviation is processed by the regulator to output a torque current reference value. The inner loop quickly tracks this reference value and changes the electromagnetic torque, thereby regulating the active power injected into the DC link by the permanent magnet synchronous generator and maintaining the DC link voltage at the set reference value.

[0010] The electromagnetic torque variation of this invention eliminates the axial balance between the mechanical torque and electromagnetic torque of the wind turbine, allowing the rotor speed to change freely with wind speed, and the tip speed ratio to automatically tend towards the optimal value, achieving maximum power point tracking. When the grid frequency deviates from the nominal value or the grid voltage is lower than the threshold, the grid-side converter adjusts the active or reactive power output, while the generator-side converter independently maintains the DC link voltage. Both sides operate in closed loops, without relying on high-speed communication across controllers.

[0011] The wind power system of this invention exhibits power-frequency characteristics and voltage regulation characteristics similar to those of a synchronous generator after grid connection. It automatically increases active power generation when the grid frequency drops and automatically increases reactive power generation when the grid voltage drops, providing active support for the offshore AC grid. The DC link voltage is locked in a closed loop by the generator-side converter under all operating conditions, and grid-side power regulation does not cause DC bus voltage collapse or spikes. There is no control mode switching between normal power generation and fault ride-through; power commands change continuously, rotor speed transitions are smooth, the mechanical drivetrain of the wind turbine experiences minimal impact, and the system quickly returns to optimal wind energy capture state after fault clearance. Attached Figure Description

[0012] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 The flowchart shows the control method for a virtual synchronous generator. Figure 2 A schematic diagram of the power coefficient at different pitch angles; Figure 3 This is a schematic diagram of maximum power point tracking at different wind speeds when β=0; Figure 4 This is a schematic diagram of the monitoring equipment. Detailed Implementation

[0014] The control method for the virtual synchronous generator involved in this application will be described in detail below. Specific details such as particular system structures and technologies are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application can also be implemented in other embodiments without these specific details.

[0015] The terms "one embodiment" or "some embodiments" used in this application mean that one or more embodiments of this application include the specific features, structures, or characteristics described in that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this application do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0016] 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.

[0017] Please see Figure 1 The diagram shows a flowchart of a control method for a virtual synchronous generator in a specific embodiment. The method includes: S1. Set the active power reference value, reactive power reference value, and DC link voltage reference value of the wind power generation system, which includes a wind turbine, permanent magnet synchronous generator, back-to-back converter, transformer, transmission line, and connecting circuit breaker, to the initial values; close the connecting circuit breaker to connect the wind power generation system to the AC power grid via the transformer and transmission line.

[0018] In some embodiments, the initial parameters of the entire offshore wind power system, including a wind turbine, a permanent magnet synchronous generator, a back-to-back converter, a two-stage transformer, a high-voltage transmission line, and a connecting circuit breaker, are configured. The active power reference value and the reactive power reference value are both set to zero, the DC link voltage reference value is fixed at 5.5kV, and the swept area of ​​the wind turbine is A=πR², where R is the rotor radius of the wind turbine.

[0019] After the parameters are configured, the circuit breaker is closed. The electrical energy output by the wind power system is first stepped up by the generator transformer, then raised to the grid voltage level by the main transformer, and finally connected to the onshore AC grid via a 50km high-voltage AC transmission line. The grid connection process is executed step by step according to the preset sequence.

[0020] S2. Obtain the rotor speed of the wind turbine, determine the maximum captureable mechanical power based on the rotor speed and the preset optimal power coefficient, and generate a reference value of active power to be transmitted to the AC grid.

[0021] In some embodiments, the rotor speed of the wind turbine is acquired in real time. ,according to Establish the rotor speed, wind speed, and tip speed ratio, and maintain the tip speed ratio λ at the optimal level. opt According to Cp=f(λ,β), the power coefficient is optimized to the preset optimal power coefficient C when the pitch angle β=0. popt .

[0022] according to Determine the mechanical power captured by the wind turbine, where A = πR², and ρ is the air density; Substitution The original expression for maximum power is obtained.

[0023] The expression, after simplification, is as follows: It means that K opt The factors are air density ρ, rotor radius R, and optimal power coefficient C. popt and the optimal tip speed ratio λ opt The adjustment was achieved.

[0024] according to Calculate the maximum captureable mechanical power .according to The active power is corrected for losses to generate a reference value Pref for active power to be transmitted to the AC power grid.

[0025] S3. Using the actual value of the DC link voltage as feedback, adjust the torque current of the permanent magnet synchronous generator to stabilize the DC link voltage at the preset reference value.

[0026] In some embodiments, the actual value of the DC link voltage is used as feedback by controlling the generator-side converter of the back-to-back converter. The relationship between the charging and discharging of the DC link capacitor, i.e., the proportional relationship between the DC link voltage change rate and the difference between the generator-side input current and the grid-side output current, determines the direction of DC link voltage regulation.

[0027] For the DC link capacitor C DC The total current. C DC This is the capacitance value of the DC link capacitor, used to store electrical energy and stabilize the DC bus voltage. DC link voltage E DC The rate of change over time reflects how fast the capacitor charges and discharges. The current flowing out of the DC link capacitor flows to the grid-side converter and is injected into the AC grid.

[0028] Furthermore, the actual value of the DC link voltage is compared with the preset reference value EDC. refThe voltage deviation is obtained by subtraction, and the voltage deviation is used by the voltage regulator to output the torque current reference value. , the reference value of magnetic field current Set to zero. Detect the three-phase stator current of the permanent magnet synchronous generator, and obtain the actual d-axis current value i through coordinate transformation. sd and the actual value of the q-axis current i sq .

[0029] based on with i sd The d-axis current deviation is obtained by subtraction. with i sq The q-axis current deviation is obtained by subtraction, and the initial voltage value is output through the current regulator.

[0030] according to and Cross-coupling compensation is performed to obtain the d-axis voltage command value v. sd and q-axis voltage command value v sq By v sd and v sq A three-phase voltage modulation signal is generated through coordinate transformation, which controls the switching of power switching devices to form a three-phase AC voltage at the stator terminals of the permanent magnet synchronous generator, thereby changing the q-axis component i in the stator current. sq .according to Change electromagnetic torque T e In the formula, p is the pole logarithm, Ψ f The rotor flux stabilizes the DC link voltage at a preset reference value.

[0031] Where Rs is the phase resistance of the generator stator winding. ω e L is the rotational angular velocity of the generator rotor. sq This represents the flux linkage variation characteristic along the q-axis. sd This represents the flux linkage variation characteristics along the d-axis.

[0032] This reflects the induced voltage generated by the q-axis current in the rotating magnetic field. It reflects the induced voltage generated by the d-axis current in the rotating magnetic field.

[0033] S4. Based on the active power reference value generated in step S2 and the preset reactive power reference value, generate a power control command; control the grid-side converter to output active power to the AC grid and adjust the reactive power according to the power control command, wherein the output of active power is adjusted with the change of grid frequency.

[0034] S5. Based on the control of the DC link voltage in step S3 and the tracking control of the active power reference value in step S4, the electromagnetic torque of the permanent magnet synchronous generator is adjusted in a coordinated manner so that the rotor speed of the wind turbine follows the wind speed change, so as to maintain the blade tip speed ratio at the optimal value and achieve maximum power point tracking.

[0035] In some embodiments, according to Changing the electromagnetic torque Te, the difference between the electromagnetic torque Te and the mechanical torque of the wind turbine changes the rotor angular acceleration on the drive shaft, thus changing the rotor speed ω. m Increase or decrease. Rotor speed ω m After the change, according to By changing the tip speed ratio λ, the tip speed ratio is gradually approached from the preset optimal tip speed ratio λ. opt At the optimal tip speed ratio λ opt Below, based on To achieve the optimal power coefficient Cpopt when the pitch angle β=0. Based on In the formula, A=πR², ρ is the air density, so that the mechanical power captured by the wind turbine reaches the maximum value at this wind speed, thus achieving maximum power point tracking.

[0036] S6. Monitor the operating status parameters of the AC power grid. When the operating status parameters deviate from the corresponding preset threshold, adjust the active or reactive power output of the grid-side converter according to the power control command generated in step S4. When the operating status parameters return to the preset threshold range, restore to the maximum power point tracking state.

[0037] In some embodiments, S6 specifically includes: when the grid frequency is detected to deviate from the nominal value, adjusting the active power output of the grid-side converter according to the power control command generated in step S4 to respond to the deviation of the grid frequency; and restoring to the maximum power point tracking state after the frequency disturbance ends.

[0038] In one embodiment of the present invention, a possible implementation will be described below in a non-limiting manner.

[0039] S611: Detect the AC grid frequency, compare the measured grid frequency value with the nominal frequency value to obtain the frequency deviation, and determine the active power compensation increment command value based on the active power and frequency correspondence in the synchronous converter control structure.

[0040] S612: The active power compensation increment command value is superimposed with the active power reference value generated in step S4 to obtain the total active power command value. Based on the total active power command value, the grid-side converter is controlled to increase the active power output to the AC grid.

[0041] In some embodiments, when the grid frequency decreases, the grid-side converter adds an extra active power compensation to the original maximum power point tracking control, increasing the active power injection into the grid. The generator-side converter uses the actual DC link voltage as feedback to independently adjust the torque current of the permanent magnet synchronous generator, compensating for DC link voltage fluctuations caused by power changes in the grid-side converter and maintaining a constant DC link voltage. The back-to-back converters have clearly defined roles: the grid side responds to grid frequency changes, while the generator side maintains a stable DC link voltage.

[0042] S613: Detect that the grid frequency has recovered to the allowable range of the nominal frequency value, cancel the active power compensation increment command value, so that the grid-side converter can resume operation according to the power control command in step S4, and re-execute maximum power point tracking.

[0043] In some embodiments, the grid-side converter continuously monitors the grid frequency measurement of the AC grid. When the measurement value returns to the allowable fluctuation range of the nominal frequency value, the active power compensation increment command value generated in step S611 is set to zero. The total active power command value of the grid-side converter is restored to the active power reference value generated in step S4, and the grid-side converter adjusts the active power output to the AC grid according to the restored power control command. Under the regulation of torque current by the generator-side converter, the rotor speed of the wind turbine gradually recovers to the optimal speed value corresponding to the current wind speed, the tip speed ratio of the system returns to the optimal value, and maximum power point tracking is re-executed.

[0044] In some embodiments, S6 further includes: when the AC grid voltage is detected to be lower than a preset voltage threshold, adjusting the reactive power output of the grid-side converter according to the power control command generated in step S4 to respond to the deviation of the AC grid voltage; maintaining the DC link voltage stability through step S3 to ensure that the wind power generation system operates uninterruptedly during and after the fault is cleared, thereby achieving fault handling.

[0045] In one embodiment of the present invention, a possible implementation will be described below in a non-limiting manner.

[0046] S621: The grid-side converter collects the instantaneous voltage values ​​of each phase of the AC grid at preset time intervals, calculates the grid voltage amplitude from the instantaneous voltage values, compares the grid voltage amplitude with a preset voltage threshold to obtain the voltage drop depth value, and determines the reactive power compensation increment command value from the voltage drop depth value based on the correspondence between the reactive power output and the grid voltage amplitude in the synchronous converter control structure. The reactive power compensation increment command value is obtained by multiplying the virtual rotor excitation current regulation and the virtual mutual inductance constant in the synchronous converter control structure.

[0047] S622: The determined reactive power compensation increment command value is superimposed with the reactive power reference value generated in step S4 to obtain the total reactive power command value. The grid-side converter controls the on / off duty cycle of the power switching devices according to the total reactive power command value to increase the reactive power output to the AC grid. During the process of the grid-side converter increasing the reactive power output, the generator-side converter uses the actual value of the DC link voltage as feedback to adjust the torque current of the permanent magnet synchronous generator, stabilize the DC link voltage at the preset reference value, and keep the power coefficient of the wind turbine at the optimal value.

[0048] In some embodiments, the grid-side converter adds additional reactive power compensation to the existing maximum power point tracking control, injecting reactive power into the grid. The generator-side converter uses the actual DC link voltage as feedback to independently adjust the torque current of the permanent magnet synchronous generator, compensating for DC link voltage fluctuations caused by power changes in the grid-side converter, thus maintaining a constant DC link voltage. The back-to-back converters have clearly defined roles: the grid side responds to changes in AC grid voltage, while the generator side maintains a stable DC link voltage. The power factor is maintained at its optimal value, ensuring that the wind turbine continues to capture maximum wind energy during voltage dips.

[0049] S623: The grid-side converter continuously monitors the grid voltage amplitude of the AC grid. When the grid voltage amplitude rises above the preset voltage threshold, the reactive power compensation increment command value in step S621 is set to zero, and the total reactive power command value of the grid-side converter is restored to the reactive power reference value generated in step S4. The grid-side converter adjusts the reactive power output to the AC grid according to the restored power control command. The generator-side converter continues to maintain the DC link voltage stability through torque current regulation. The rotor speed of the wind turbine is maintained at the optimal speed value corresponding to the current wind speed under the action of electromagnetic torque regulation, and the tip speed ratio is maintained at the optimal value.

[0050] In some embodiments, after the AC grid voltage is restored, the synchronous converter control structure exits the voltage support state. The reactive power output of the grid-side converter returns to the normal tracking reference value, and the electromagnetic torque of the permanent magnet synchronous generator is re-matched with the mechanical torque of the wind turbine. The generator-side converter maintains a stable DC link voltage, and the rotor speed is maintained at the speed value corresponding to the optimal tip speed ratio under torque current regulation. The system smoothly transitions from the voltage support state back to the maximum power point tracking state.

[0051] In one embodiment of the present invention, based on step S3, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0052] S31: Collect the actual value of the DC link voltage, subtract the DC link voltage reference value from the actual value to obtain the voltage control deviation value, input the voltage control deviation value into the PI controller to obtain the intermediate control quantity, and obtain the torque current reference value according to the calculation relationship of the torque current reference value based on the intermediate control quantity, the rotor flux linkage and the number of pole pairs of the permanent magnet synchronous generator, and set the magnetic field current reference value to zero.

[0053] In some embodiments, in the field-oriented control mode, the field current is kept zero, the armature reaction flux is perpendicular to the rotor flux, the armature reaction is minimized, and all stator current is used to generate electromagnetic torque. The electromagnetic torque is proportional to the torque current, with the relationship Te equal to 3 times the number of pole pairs, the torque current, and the rotor flux. The generator-side converter obtains active power from the DC link, and the active power is equal to the product of the DC link voltage and current. By adjusting the torque current, the electromagnetic torque is changed, thereby changing the active power delivered by the permanent magnet synchronous generator to the DC link, so that the actual DC link voltage tracks the reference value. Here, the PI controller generates an intermediate control quantity based on the voltage control deviation value, and this intermediate control quantity, after proportional-integral calculation, determines the magnitude and direction of the torque current reference value.

[0054] S32: Detect the three-phase current on the stator side of the permanent magnet synchronous generator. After coordinate transformation, obtain the actual values ​​of the d-axis current and q-axis current. Subtract the actual d-axis current from the reference value of the magnetic field current to obtain the d-axis current deviation value. Subtract the actual q-axis current from the reference value of the torque current to obtain the q-axis current deviation value. Input the d-axis current deviation value and q-axis current deviation value into the current regulator. The current regulator outputs the preliminary voltage value. Combine the preliminary voltage value with the stator resistance, rotor electric angular velocity, d-axis synchronous inductance, q-axis synchronous inductance, and rotor flux linkage. Perform cross-coupling term compensation according to the steady-state voltage equation of the permanent magnet synchronous generator to obtain the d-axis voltage command value and q-axis voltage command value.

[0055] It should be noted that in a permanent magnet synchronous generator (PMSG) in a rotating coordinate system, the d-axis and q-axis voltages and currents are cross-coupled. The d-axis voltage is affected by the q-axis current, and the q-axis voltage is affected by both the d-axis current and the rotor flux linkage. After the current regulator outputs the initial voltage value, compensation is required according to the inductance voltage drop and back electromotive force terms in the steady-state voltage equation to eliminate the coupling between the d-axis and q-axis. The decoupled d-axis and q-axis voltage command values ​​correspond to the voltage components that need to be applied to the stator windings in the d-axis and q-axis directions, respectively, ensuring that the actual d-axis current tracks zero and the actual q-axis current tracks the torque current reference value. The magnetic field current remains zero, ensuring that all current is used to generate electromagnetic torque, achieving maximum torque control per ampere.

[0056] S33: Based on the rotor's electrical angular velocity, the d-axis voltage command value and the q-axis voltage command value are transformed to generate a three-phase voltage modulation signal in a three-phase stationary coordinate system. The three-phase voltage modulation signal is sent to the pulse width modulation unit of the generator-side converter. The pulse width modulation unit outputs the drive pulses of each bridge arm power switching device to control the on-off sequence of the power switching devices. The power switching devices alternately turn on and off according to the drive pulses, forming a three-phase AC voltage on the three-phase terminals of the permanent magnet synchronous generator stator winding. The three-phase AC voltage changes the magnitude and phase of the current in the stator winding, so that the actual value of the q-axis current tracks the torque current reference value, thereby changing the active power output of the permanent magnet synchronous generator to the DC link of the back-to-back converter, and maintaining the actual value of the DC link voltage at the preset reference value.

[0057] It should be noted that the generator-side converter is a voltage source converter, and the on / off state of the power switching devices determines the amplitude and frequency of the output voltage. After pulse width modulation, the three-phase voltage modulation signal forms an equivalent sinusoidal voltage at the stator winding terminals under the switching action of the power switching devices. This voltage establishes a current in the stator winding, where the q-axis current component directly determines the magnitude of the electromagnetic torque. Changes in electromagnetic torque alter the rate at which the mechanical energy of the permanent magnet synchronous generator is converted into electrical energy, thereby changing the direction of active power flow in the DC link. When the actual value of the DC link voltage is lower than the reference value, the torque current reference value increases, the q-axis current increases, the electromagnetic torque increases, the generator inputs more active power into the DC link, and the DC link voltage rises; conversely, the DC link voltage falls.

[0058] In one embodiment of the present invention, based on step S4, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0059] S41. Based on the active power reference value P generated in step S2 ref Based on the rotor speed of the wind turbine, a reference value Tm for simulating the mechanical torque of the synchronous generator is calculated using a virtual synchronous generator model. ref .

[0060] S42. The mechanical torque reference value Tm obtained in step S41 is... ref The preset reactive power reference value Q ref The actual active power P and actual reactive power Q output by the grid-side converter are input into a mathematical model simulating the electromechanical transient process of a synchronous generator. By calculating the second-order differential equation simulating rotor motion, the phase angle δ and amplitude E of the output voltage of the grid-side converter are output as power control commands.

[0061] It should be noted that the active power reference value P refBased on step S2 and maximum power point tracking, P represents the average active power expected to be delivered to the grid. In the analogy of a virtual synchronous generator, the electrical power output needs to be driven by a virtual mechanical input power. Here, P... ref Converted into virtual mechanical power Pm ref P ref It can be set to be slightly less than the maximum mechanical power.

[0062] Rotor speed ω of a wind turbine tur This is known and can be obtained from the generator speed. Therefore, the reference value Tm for the mechanical torque input to the synchronous generator prime mover is used to simulate the synchronous generator. ref It is possible Tm ref =Pm ref / ω tur Calculated. Tm ref It will be used as input to the virtual synchronous generator model to simulate the driving torque of the prime mover on the virtual rotor.

[0063] In step S42, the second-order differential equation for simulating the rotor motion of the synchronous generator is: J*d(Δω) / dt=Tm-Te-D*Δω.

[0064] Where J is the virtual moment of inertia constant, D is the virtual damping coefficient, and D simulates the effect of the damping winding to suppress speed oscillation. Δω is the deviation between the virtual rotor angular velocity and the grid synchronous angular velocity, Tm is the input mechanical torque, and Te is the electromagnetic torque, which is related to the actual active power P output by the converter and the virtual rotor angular velocity, and can be expressed as Te≈P / ω, where ω is the virtual rotor angular velocity.

[0065] The second-order differential equation is expressed in Tm. ref Using the actual measured value P as input, the angular velocity ω of the virtual rotor and the power angle δ relative to the grid voltage are calculated through integration and other operations, where δ = ∫(ω - ω) grid The power angle δ depends on the phase of the fundamental frequency of the converter output voltage.

[0066] To control reactive power, the excitation regulation characteristics of a synchronous generator are simulated. This is achieved by setting a preset reactive power reference value Q. refThe actual reactive power Q output by the converter is compared to the voltage output of the generator, generating a command to adjust the converter output voltage amplitude E. This adjustment process simulates the characteristics of a synchronous generator adjusting its terminal voltage and reactive power by changing the excitation current through a voltage regulator. Finally, the phase angle δ and voltage amplitude E output in step S42 constitute the reference command for the grid-side converter output voltage, i.e., the power control command. The power control command is sent to the converter's pulse width modulation stage to generate a switching signal, causing the converter to output a three-phase voltage with the required phase and amplitude, thereby controlling the active power P and reactive power Q injected into the grid.

[0067] Furthermore, when the power grid frequency changes, i.e., ω grid When the frequency changes, the equation calculates the change in δ, and then adjusts the active power output by changing the phase of the output voltage, thus achieving an active response to the frequency.

[0068] In one embodiment of the present invention, based on step S5, a possible embodiment will be given below, and its specific implementation will be described in a non-limiting manner.

[0069] S51: Detect the actual value of active power output from the grid-side converter to the AC grid, subtract the actual value of active power from the active power reference value generated in step S2 to obtain the power deviation value; add the power deviation value to the voltage deviation value obtained by subtracting the actual value of DC link voltage and the preset reference value in step S3 to obtain the composite deviation value; input the composite deviation value to the voltage regulator of the outer loop of the generator-side converter, and the voltage regulator outputs the torque current reference value, while the magnetic field current reference value remains at zero.

[0070] It should be noted that the outer loop of the generator-side converter uses the DC link voltage as the controlled variable, and the input of the outer loop regulator includes voltage deviation and grid-side power deviation. The grid-side power deviation is obtained by comparing the actual active power output of the grid-side converter with the active power reference value generated in step S2. The active power reference value is obtained by... Sure.

[0071] When wind speed changes, the mechanical power of the wind turbine changes. To track the maximum power point, the grid-side converter needs to adjust its active power output, causing a change in the power deviation. The combined deviation value, obtained by adding the power deviation value to the voltage deviation value, is sent to the voltage regulator, allowing the torque current reference value to begin adjusting before the DC link voltage deviates significantly. This adjustment of the torque current reference value alters the electromagnetic torque of the permanent magnet synchronous generator, thereby changing the active power input to the DC link and maintaining the DC link voltage at a preset reference value. The magnetic field current reference value remains zero, with all stator current used to generate electromagnetic torque.

[0072] S52: The generator-side converter compares the torque current reference value output in step S51 with the actual q-axis current value detected by the inner loop to obtain the q-axis current deviation value. The q-axis current deviation value is output by the current regulator to change the on / off state of the power switching device and adjust the q-axis component of the stator current of the permanent magnet synchronous generator.

[0073] The change in the q-axis component is based on The electromagnetic torque is changed. The difference between the electromagnetic torque and the mechanical torque of the wind turbine changes the rotor angular acceleration via the drive shaft, causing the rotor angular velocity to increase or decrease accordingly. After the rotor angular velocity changes, it is followed... The tip speed ratio changes accordingly, gradually approaching the preset optimal tip speed ratio λ. opt .

[0074] It should be noted that the wind energy captured by the wind turbine is converted into mechanical torque, which is balanced with the electromagnetic torque of the permanent magnet synchronous generator on the drive shaft. When the wind speed changes, the mechanical torque of the wind turbine changes, disrupting the original torque balance. After adjusting the torque current reference value in step S51, the inner loop of the generator-side converter rapidly changes the q-axis current, based on... This causes a change in the electromagnetic torque. The difference between the electromagnetic torque and the mechanical torque generates rotor angular acceleration, which in turn changes the rotor angular velocity. After the rotor angular velocity changes, according to... The tip speed ratio changes accordingly. During the process of the electromagnetic torque and mechanical torque re-balancing, the rotor angular velocity tends towards the wind speed at which the tip speed ratio equals the optimal tip speed ratio λ. opt The rotational speed value, because the active power reference value in step S2 is determined by... Sure.

[0075] Furthermore, as a refinement of the specific implementation of the above embodiments, the following is a specific example of the method, which includes: S101, The active power reference value P of a wind power generation system having a wind turbine, permanent magnet synchronous generator, back-to-back converter, transformer, transmission line and circuit breaker. ref Reactive power reference value Q ref and DC link voltage reference value EDC ref Set to the initial value; the swept area of ​​the wind turbine A = πR²; close the circuit breaker to connect the wind power generation system to the AC power grid via the transformer and transmission line.

[0076] S102. Real-time acquisition of the rotor speed ω of the wind turbine. m ;based on Establish the relationship between rotor speed, wind speed, and tip speed ratio, and maintain the tip speed ratio λ at the optimal level. opt .like Figure 2 and Figure 3 As shown, according to When the pitch angle β=0, the power coefficient reaches the preset optimal power coefficient Cp. opt ;according to Determine the mechanical power captured by the wind turbine, where A = πR²; based on The original expression for maximum power shown is simplified by... It means that K opt The factors are air density ρ, rotor radius R, and optimal power coefficient Cp. opt and the optimal tip speed ratio λ opt The adjustment was achieved.

[0077] according to Calculate the maximum captureable mechanical power Pm max ;according to Loss corrections are applied to the active power to generate a reference value P for the active power transmitted to the AC power grid. ref .

[0078] S103, By controlling the generator-side converter of the back-to-back converter, feedback is given based on the actual value of the DC link voltage; according to The DC link capacitor charging and discharging relationship, i.e., the proportional relationship between the DC link voltage change rate and the difference between the generator-side input current and the grid-side output current, determines the direction of DC link voltage adjustment. The actual DC link voltage value is compared with the preset reference value EDC. ref The voltage deviation is obtained by subtraction. This voltage deviation is then used by the voltage regulator to output the torque current reference value isqref, and the magnetic field current reference value isd is used to further subtract the voltage deviation. ref Set to zero. Detect the three-phase stator current of the permanent magnet synchronous generator, and obtain the actual d-axis current value i through coordinate transformation. sd and the actual value of the q-axis current i sq ; by i sdref with i sd The d-axis current deviation is obtained by subtraction, from i sqref with i sq The q-axis current deviation is obtained by subtraction, and the initial voltage value is output through the current regulator. According to... and Cross-coupling compensation is performed to obtain the d-axis voltage command value v. sd and q-axis voltage command value v sq ; by v sd and v sq A three-phase voltage modulation signal is generated through coordinate transformation, which controls the switching of power switching devices to form a three-phase AC voltage at the stator terminals of the permanent magnet synchronous generator, thereby changing the q-axis component i in the stator current. sq ;according to The electromagnetic torque Te is changed, where p is the number of pole pairs, Ψ fFor rotor flux linkage, stabilize the DC link voltage at a preset reference value EDC. ref .

[0079] S104. By controlling the grid-side converter of the back-to-back converter, based on the active power reference value P generated in step S2. ref and the preset reactive power reference value Q ref Generate power control commands; P ref According to step S2 as well as Determine; control the grid-side converter to output active power to the AC grid and regulate reactive power, with the output of active power adjusted in response to changes in grid frequency.

[0080] S105. Based on the control of the DC link voltage in step S3 and the control of the active power reference value P in step S4. ref The tracking control coordinates and adjusts the electromagnetic torque of the permanent magnet synchronous generator; according to... Changing the electromagnetic torque Te, the difference between the electromagnetic torque Te and the mechanical torque of the wind turbine changes the rotor angular acceleration on the drive shaft, thus changing the rotor speed ω. m Increase or decrease; rotor speed ω m After the change, the tip speed ratio λ is gradually adjusted to approach the preset optimal tip speed ratio λ. opt At the optimal tip speed ratio λ opt And when the pitch angle β=0, the power coefficient Cp reaches the optimal power coefficient Cp. opt ;Depend on This allows the mechanical power captured by the wind turbine to reach its maximum value at that wind speed, thus achieving maximum power point tracking.

[0081] S106. Monitor the operating status parameters of the AC power grid. When the operating status parameters deviate from the corresponding preset threshold, adjust the active or reactive power output of the grid-side converter according to the power control command generated in step S4. During the adjustment of active or reactive power by the grid-side converter, step S3 continuously uses the actual value of the DC link voltage as feedback. The electromagnetic torque Te is adjusted by the voltage deviation through the output torque current reference value of the voltage regulator to maintain the stability of the DC link voltage. When the operating status parameters return to the preset threshold range, the system returns to the maximum power point tracking state.

[0082] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0083] The following are embodiments of the control system for a virtual synchronous generator provided in this disclosure. This system and the control methods for virtual synchronous generators in the above embodiments belong to the same inventive concept. For details not described in detail in the embodiments of the control system for the virtual synchronous generator, please refer to the embodiments of the control methods for the virtual synchronous generator described above.

[0084] The system includes: interconnected wind power generation systems and monitoring equipment; A wind power generation system includes: a wind turbine, a permanent magnet synchronous generator, a back-to-back converter, a transformer, transmission lines, and connecting circuit breakers; The monitoring equipment is used to close the circuit breaker and connect the wind power generation system to the AC power grid via transformers and transmission lines; The rotor speed of the wind turbine is obtained, and the maximum captureable mechanical power is determined based on the rotor speed and the preset optimal power coefficient. A reference value of active power to be transmitted to the AC grid is generated. The actual value of the DC link voltage is used as feedback to adjust the torque current of the permanent magnet synchronous generator and stabilize the DC link voltage at a preset reference value. Based on the generated active power reference value and the preset reactive power reference value, a power control command is generated; according to the power control command, the grid-side converter is controlled to output active power to the AC grid and adjust reactive power, wherein the output of active power is adjusted with the change of grid frequency; The control of DC link voltage and the tracking control of active power reference value are coordinated to adjust the electromagnetic torque of permanent magnet synchronous generator, so that the rotor speed of wind turbine changes with wind speed, maintain the tip speed ratio at the optimal value, and achieve maximum power point tracking. The system monitors the operating status parameters of the AC power grid. When the operating status parameters deviate from the corresponding preset threshold, it adjusts the active or reactive power output of the grid-side converter according to the generated power control command. When the operating status parameters return to the preset threshold range, it returns to the maximum power point tracking state.

[0085] like Figure 4 As shown, this application also provides a monitoring device, including a display module 103, a memory 102, a processor 101, a communication module 104, and a computer program stored in the memory and executable on the processor 101. When the processor 101 executes the program, it implements the steps of a control method for a virtual synchronous generator.

[0086] In embodiments of the present invention, the monitoring device includes, but is not limited to, laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The monitoring device may also represent various forms of mobile devices, such as personal digital assistants, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the embodiments described and / or claimed herein.

[0087] In this embodiment, processor 101 may be implemented using at least one of an application-specific integrated circuit, a programmable logic device, a field-programmable gate array, a processor, a controller, a microcontroller, a microprocessor, or an electronic unit designed to perform the functions described herein. In some cases, such an implementation may be implemented within a controller. For software implementation, implementations such as processes or functions may be implemented with separate software modules that allow the performance of at least one function or operation. Software code may be implemented by a software application (or program) written in any suitable programming language, and the software code may be stored in memory and executed by the controller.

[0088] The display module 103 is used to display information input by the user or information provided to the user. The display module 103 may include a display panel, which may be configured in the form of a liquid crystal display, an organic light-emitting diode, or the like.

[0089] The memory 102 can be used to store software programs and various data. The memory 102 may include high-speed random access memory, and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0090] The communication module 104 transmits radio signals to and / or receives radio signals from at least one of a base station, an external terminal, and a server. Such radio signals may include voice call signals, video call signals, or various types of data sent and / or received according to text and / or multimedia messages.

[0091] The present invention also provides a storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the control method for the virtual synchronous generator.

[0092] The storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example,, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0093] The storage medium stores a program product capable of implementing the methods described above in this specification. In some possible implementations, various aspects of this disclosure may also be implemented as a program product comprising program code that, when run on a terminal device, causes the terminal device to perform the steps described in the "Exemplary Methods" section of this specification according to various exemplary embodiments of this disclosure.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a virtual synchronous generator, characterized in that, The methods include: S1: Close the circuit breaker to connect the wind power generation system to the AC power grid via transformer and transmission line; S2: Obtain the rotor speed of the wind turbine, determine the maximum captureable mechanical power based on the rotor speed and the preset optimal power coefficient, and generate a reference value of active power to be transmitted to the AC grid; S3: Using the actual value of the DC link voltage as feedback, adjust the torque current of the permanent magnet synchronous generator to stabilize the DC link voltage at the preset reference value; S4: Based on the active power reference value generated in step S2 and the preset reactive power reference value, generate a power control command; control the grid-side converter to output active power to the AC grid and adjust the reactive power according to the power control command, wherein the output of active power is adjusted with the change of grid frequency; S5: Based on the control of DC link voltage in step S3 and the tracking control of active power reference value in step S4, the electromagnetic torque of permanent magnet synchronous generator is adjusted in a coordinated manner so that the rotor speed of wind turbine changes with wind speed, the tip speed ratio is maintained at the optimal value, and maximum power point tracking is achieved. S6: Monitor the operating status parameters of the AC power grid. When the operating status parameters deviate from the corresponding preset threshold, adjust the active or reactive power output of the grid-side converter according to the power control command generated in step S4. Once the operating status parameters return to the preset threshold range, the system will revert to maximum power point tracking.

2. The control method for a virtual synchronous generator according to claim 1, characterized in that, S6 specifically includes: When the grid frequency is detected to deviate from the nominal value, the active power output of the grid-side converter is adjusted according to the power control command generated in step S4 to respond to the grid frequency deviation; and after the frequency disturbance ends, it is restored to the maximum power point tracking state. When the AC grid voltage is detected to be lower than the preset voltage threshold, the reactive power output of the grid-side converter is adjusted according to the power control command generated in step S4 to respond to the deviation of the AC grid voltage; the DC link voltage is maintained stable through step S3 to ensure that the wind power generation system operates continuously during and after the fault is cleared, thereby realizing fault handling.

3. The control method for a virtual synchronous generator according to claim 2, characterized in that, The step of adjusting the active power output of the grid-side converter according to the power control command generated in step S4 specifically includes the following methods: The frequency of the AC power grid is detected, and the frequency deviation is obtained by comparing the measured value of the power grid frequency with the nominal frequency value. Based on the correspondence between active power and frequency in the control structure of the synchronous converter, the active power compensation increment command value is determined. The active power compensation increment command value is superimposed with the active power reference value generated in step S4 to obtain the total active power command value. Based on the total active power command value, the grid-side converter is controlled to increase the active power output to the AC grid. Once the grid frequency is detected to have returned to the allowable range of the nominal frequency value, the active power compensation increment command value is cancelled, so that the grid-side converter resumes operation according to the power control command in step S4, and maximum power point tracking is re-executed.

4. The control method for a virtual synchronous generator according to claim 2, characterized in that, When the AC grid voltage is detected to be lower than a preset voltage threshold, the reactive power output of the grid-side converter is adjusted according to the power control command generated in step S4. This adjustment specifically includes the following methods: The grid-side converter collects the instantaneous voltage values ​​of each phase of the AC grid at preset time intervals, compares the grid voltage amplitude with the preset voltage threshold to obtain the voltage drop depth value, and determines the reactive power compensation increment command value based on the correspondence between the reactive power output and the grid voltage amplitude in the synchronous converter control structure. The determined reactive power compensation increment command value is superimposed with the reactive power reference value generated in step S4 to obtain the total reactive power command value. The grid-side converter controls the on / off duty cycle of the power switching devices according to the total reactive power command value to increase the reactive power output to the AC grid. During the process of the grid-side converter increasing the reactive power output, the generator-side converter uses the actual value of the DC link voltage as feedback to adjust the torque current of the permanent magnet synchronous generator, stabilize the DC link voltage at the preset reference value, and keep the power coefficient of the wind turbine at the optimal value.

5. The control method for a virtual synchronous generator according to claim 4, characterized in that, The grid-side converter continuously monitors the grid voltage amplitude of the AC grid. When the grid voltage amplitude rises above the preset voltage threshold, the reactive power compensation increment command value is set to zero, and the total reactive power command value of the grid-side converter is restored to the reactive power reference value generated in step S4. The grid-side converter adjusts the reactive power output to the AC grid according to the restored power control command. The generator-side converter continues to maintain the DC link voltage stability through torque current regulation. Under the action of electromagnetic torque regulation, the rotor speed of the wind turbine is maintained at the optimal speed value corresponding to the current wind speed, and the tip speed ratio is maintained at the optimal value.

6. The control method for a virtual synchronous generator according to claim 1, characterized in that, S3 specifically includes the following steps: S31: Collect the actual value of DC link voltage, subtract the reference value of DC link voltage from the actual value to obtain the voltage control deviation value, input the voltage control deviation value into the PI controller to obtain the intermediate control quantity, and obtain the torque current reference value according to the calculation relationship of the torque current reference value based on the intermediate control quantity, the rotor flux linkage and the number of pole pairs of the permanent magnet synchronous generator, and set the magnetic field current reference value to zero. S32: Detect the three-phase current on the stator side of the permanent magnet synchronous generator, obtain the actual values ​​of the d-axis current and q-axis current through coordinate transformation, obtain the d-axis current deviation value by subtracting the actual value of the d-axis current from the reference value of the magnetic field current, and obtain the q-axis current deviation value by subtracting the actual value of the q-axis current from the reference value of the torque current. Input the d-axis current deviation value and q-axis current deviation value into the current regulator respectively. The current regulator outputs the preliminary voltage value. Combine the preliminary voltage value with the stator resistance, rotor electric angular velocity, d-axis synchronous inductance, q-axis synchronous inductance and rotor flux linkage, and perform cross-coupling term compensation according to the steady-state voltage equation of the permanent magnet synchronous generator to obtain the d-axis voltage command value and q-axis voltage command value. S33: Based on the rotor's electrical angular velocity, the d-axis voltage command value and the q-axis voltage command value are transformed to generate a three-phase voltage modulation signal in a three-phase stationary coordinate system. The three-phase voltage modulation signal is sent to the pulse width modulation unit of the generator-side converter. The pulse width modulation unit outputs the drive pulses of each bridge arm power switching device to control the on-off sequence of the power switching devices. The power switching devices alternately turn on and off according to the drive pulses, forming a three-phase AC voltage on the three-phase terminals of the permanent magnet synchronous generator stator winding. The three-phase AC voltage changes the magnitude and phase of the current in the stator winding, so that the actual value of the q-axis current tracks the torque current reference value, thereby changing the active power output of the permanent magnet synchronous generator to the DC link of the back-to-back converter, and maintaining the actual value of the DC link voltage at the preset reference value.

7. The control method for a virtual synchronous generator according to claim 1, characterized in that, S4 specifically includes the following steps: S41. Based on the active power reference value P generated in step S2 ref Based on the rotor speed of the wind turbine, a reference value Tm for simulating the mechanical torque of the synchronous generator is calculated using a virtual synchronous generator model. ref ; S42. The mechanical torque reference value Tm obtained in step S41 is... ref The preset reactive power reference value Q ref The actual active power P and actual reactive power Q output by the grid-side converter are input into a mathematical model simulating the electromechanical transient process of a synchronous generator. By calculating the second-order differential equation simulating rotor motion, the phase angle δ and amplitude E of the output voltage of the grid-side converter are output as power control commands.

8. The control method for a virtual synchronous generator according to claim 1, characterized in that, S5 specifically includes the following steps: S51: Detect the actual value of active power output from the grid-side converter to the AC grid, subtract the actual value of active power from the active power reference value generated in step S2 to obtain the power deviation value; add the power deviation value to the voltage deviation value obtained by subtracting the actual value of DC link voltage and the preset reference value in step S3 to obtain the composite deviation value; input the composite deviation value to the voltage regulator of the outer loop of the generator-side converter, and the voltage regulator outputs the torque current reference value, while the magnetic field current reference value remains at zero; S52: The generator-side converter compares the torque current reference value output in step S51 with the actual value of the q-axis current detected by the inner loop to obtain the q-axis current deviation value. The q-axis current deviation value is output by the current regulator to change the on / off state of the power switching device and adjust the q-axis component of the stator current of the permanent magnet synchronous generator. The change in the q-axis component is based on The electromagnetic torque is changed; the difference between the electromagnetic torque and the mechanical torque of the wind turbine changes the rotor angular acceleration via the drive shaft, causing the rotor angular velocity to increase or decrease accordingly; after the rotor angular velocity changes, it is followed... The tip speed ratio changes accordingly, gradually approaching the preset optimal tip speed ratio λ. opt .

9. A monitoring device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the control method for the virtual synchronous generator as described in any one of claims 1 to 8.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for the virtual synchronous generator as described in any one of claims 1 to 8.

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