Control method of network-forming doubly-fed wind turbine generator
By replacing the traditional PI controller with a virtual oscillator in a grid-connected doubly-fed induction generator (DFIG) and utilizing its limiting loop oscillation characteristics and synchronization capability, the instability problem caused by grid phase jumps was solved, achieving better stability and dynamic response.
Patent Information
- Application Number
- CN202511336976.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-06-20
- Filing Date
- 2025-09-18
- Publication Date
- 2025-12-16
AI Technical Summary
Grid-connected doubly fed wind turbines are at risk of instability when the grid phase changes. Traditional PI current controller parameter tuning is difficult to balance steady-state accuracy and dynamic response, has limited robustness, and is difficult to effectively suppress instability.
A virtual oscillator is used as the inner loop current controller of the rotor-side converter. A voltage reference signal is generated by virtual capacitor voltage and virtual inductor current. The limiting loop oscillation characteristics and synchronization capability of the virtual oscillator are utilized to quickly respond to grid phase jumps and suppress the growth of current error.
It improves the system's stability and dynamic performance during grid phase transitions, enhances robustness, and effectively suppresses system oscillation and loss of synchronization risks.
Smart Images
Figure CN121150107A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a control method of a grid-connected doubly-fed wind turbine, belonging to the technical field of motor control. BACKGROUND
[0002] Doubly-fed induction generator (DFIG) has been widely used in renewable energy field such as wind power generation due to its small power converter capacity and the ability to realize variable speed constant frequency operation. Traditional DFIG control usually adopts vector control strategy based on stator flux linkage orientation or stator voltage orientation to control the grid-side converter and the rotor-side converter respectively, so as to realize decoupling control of active power and reactive power and stability of DC bus voltage.
[0003] With the increasing penetration of power electronic devices in power systems, the traditional mode of relying on synchronous generators to provide system inertia and damping is challenged. Grid-forming control technology emerges as the times require, and one of the widely used grid-forming control methods is virtual synchronous generator (VSG) control. It simulates the operating characteristics of synchronous generators (such as swing equation, speed regulation and voltage regulation characteristics), so that power electronic converters can provide inertia support, damping and primary frequency and voltage regulation capability for the grid, enhancing the stability of the grid. Applying VSG technology to DFIG systems is an important direction to improve the grid-friendliness of wind farms. However, the stability of grid-connected doubly-fed wind turbines is challenged during operation, especially when the grid is disturbed (such as voltage sag, phase jump, etc.). The outer ring of VSG control simulates the slow dynamic characteristics of synchronous generators, while the inner ring of the traditional rotor-side converter usually adopts a fast-responding proportional-integral (PI) current controller. This coupling of fast and slow dynamics, as well as the virtual inertia introduced by VSG control, can cause the current inner ring of the rotor-side converter to be difficult to quickly and accurately track the instructions when the grid phase jumps rapidly, resulting in a large current error or even overcurrent, and further causing system oscillation or loss of step, i.e. there is a risk of phase jump instability. The parameter setting of the traditional PI current controller is difficult to balance steady-state accuracy and dynamic response under wide range of operating conditions, and has limited robustness under strong disturbance, making it difficult to effectively suppress such instability phenomena. SUMMARY
[0004] In view of the problem that the existing control method of grid-connected doubly-fed wind turbines has instability risk when the grid phase jumps, the present application provides a control method of a grid-connected doubly-fed wind turbine.
[0005] The control method of a grid-connected doubly-fed wind turbine of the present application comprises controlling the rotor-side converter and the grid-side converter, wherein the control method of the rotor-side converter comprises:
[0006] According to the active power given value of the rotor-side converter and the reactive power given value , real-time collection and calculation of active power and reactive power , according to the control equation of the active and reactive power control of the VSG, the corresponding power angle and internal potential amplitude are calculated;
[0007] According to the power angle and internal potential amplitude, the d, q axis rotor voltage given value is obtained 、 , the 、 input voltage control link is generated d, q axis rotor current given value 、 ;
[0008] The 、 and rotor current actual value difference is converted to coordinate system respectively through coordinate transformation, and the gain generates voltage feedback signal 、 , the voltage feedback signal 、 as a virtual oscillator control input signal of inner loop, the virtual capacitor voltage and virtual inductance current are used as internal state variables in the virtual oscillator control inner loop, and the voltage reference signal in coordinate system 、 is generated based on the virtual capacitor voltage and virtual inductance current through voltage gain scaling;
[0009] According to the voltage reference signal 、 , after coordinate transformation, it is input to the pulse width modulation module to drive the rotor side converter. As a preferred, the method of generating the voltage reference signal in coordinate system 、 based on the virtual capacitor voltage and virtual inductance current through voltage gain scaling includes:
[0010] Nonlinear voltage source and nonlinear current source :
[0011]
[0012]
[0013] The virtual capacitor voltage is , the nominal oscillation amplitude is , the virtual inductance value is , the virtual capacitor value is , the virtual inductance current is gain scaling coefficient , is the convergence speed parameter;
[0014] , the differential equation is:
[0015]
[0016]
[0017] determining and after and obtaining:
[0018]
[0019] .
[0020] As a preference, the voltage feedback signal , are respectively:
[0021]
[0022]
[0023] wherein, is the current gain, , is the , actual value of the rotor current of the shaft, , is the , given value of the rotor current of the shaft.
[0024] As a preference, the virtual capacitance value satisfies:
[0025]
[0026] wherein, is the minimum rotor voltage, is the maximum allowed deviation, is the rated power, is the maximum power conversion time;
[0027] The virtual inductance value L is:
[0028]
[0029] wherein, is the nominal angular frequency of the power grid.
[0030] As a preference, the convergence speed parameter is:
[0031]
[0032] wherein, is the maximum voltage rise time.
[0033] As a preference, , , , The selection principle of is:
[0034] Cooperatively ensure that the virtual oscillator control inner loop can produce stable limit cycle oscillation at the desired frequency and amplitude, and meet the system dynamic response requirements including power conversion time and voltage rise time, while ensuring the stability of the entire control system.
[0035] As a preference, the method for calculating the corresponding power angle and internal voltage amplitude according to the control equation of the VSG active and reactive control sections includes:
[0036] The active section is based on the swing equation of the synchronous generator, and the VSG virtual synchronous angle is calculated :
[0037]
[0038]
[0039] wherein, is the virtual moment of inertia, represents the DFIG stator side output active power, represents the VSG active ring droop coefficient, represents the nominal angular frequency of the grid, is the virtual angular frequency, is the nominal angular frequency of the grid;
[0040] The power angle is obtained :
[0041]
[0042] The reactive section is based on the excitation control principle of the synchronous generator, and the internal voltage amplitude E is calculated:
[0043]
[0044] wherein, wherein, represents the reactive ring inertia coefficient, represents the given value of the grid-connected point voltage, represents the actual value of the grid-connected point voltage, This indicates the reactive power output on the stator side of the DFIG. This represents the reactive power loop droop coefficient.
[0045] The beneficial effects of this invention are as follows:
[0046] (1) Improve phase jump stability: Using a virtual oscillator as the inner loop current controller of the rotor-side converter, its inherent limiting loop oscillation characteristics and synchronization capability, compared with the traditional PI controller, can respond more quickly and limit the growth of current error when the grid phase jumps, effectively suppressing or avoiding system instability caused by current loop runaway.
[0047] (2) Enhanced robustness and dynamic performance: Virtual oscillator control is relatively less sensitive to changes in system parameters, and has better robustness and better dynamic response characteristics. Attached Figure Description
[0048] Figure 1 This is a schematic diagram of the overall structure of a grid-connected doubly-fed wind turbine.
[0049] Figure 2 This is a schematic diagram of the control principle of a DFIG grid-side converter based on vector control.
[0050] Figure 3 This is a schematic diagram of the rotor-side converter control principle based on the virtual oscillator control inner loop;
[0051] Figure 4 This is a schematic diagram of the control inner loop of a virtual oscillator.
[0052] Figure 5 The active power waveform of VSG-DFIG is obtained by using the current loop as the control inner loop when the grid voltage undergoes a phase jump.
[0053] Figure 6 The active power waveform of the VSG-DFIG in the inner loop of the virtual oscillator control system of this invention is used when the grid voltage undergoes a phase jump. Detailed Implementation
[0054] 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.
[0055] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.
[0056] The application will be further described below in conjunction with the accompanying drawings and specific embodiments, but not as a limitation of the application.
[0057] The embodiment proposes a control strategy of applying a virtual oscillator to a grid-connected double-fed wind turbine, which is a method of replacing a traditional PI controller current inner loop with a virtual oscillator as a rotor-side converter current control inner loop. The core idea is to replace the traditional PI controller current inner loop with the dynamic characteristics of the virtual oscillator, so as to obtain better stability and dynamic performance under grid phase jump and other disturbances.
[0058] The overall structure of the VSG-DFIG system in the embodiment is shown in Figure 1 The system mainly includes a double-fed induction generator (DFIG), a grid-side converter, a rotor-side converter, a DC bus capacitor, a connection transformer and a grid connection point. The grid-side converter adopts traditional vector control, which is responsible for maintaining the stability of the DC bus voltage and controlling the grid-side reactive power. The control method of the grid-connected double-fed wind turbine in the embodiment includes controlling the rotor-side converter and the grid-side converter. Since the capacity of the grid-side converter is small, the characteristics of the DFIG unit are mainly reflected through the rotor-side converter, so the core of the embodiment lies in the control strategy of the rotor-side converter.
[0059] The control principle diagram of the grid-side converter in the embodiment is shown in Figure 2 The grid-side converter adopts traditional vector control, which is usually implemented in a rotating d-q coordinate system synchronized with the grid voltage. The synchronization signal is provided by a phase-locked loop (PLL) for obtaining the phase and frequency information of the grid voltage. The control structure includes cascaded control links: the outer ring is a DC bus voltage control loop, which compares the measured DC voltage value with the given value through a PI controller, outputs the d-axis current given value, and controls the active power flowing through the grid-side converter, so as to stabilize the DC voltage. The inner ring is a grid-side current control loop, which includes two PI controllers, respectively responsible for quickly tracking the d-axis and q-axis current given values given by the outer ring, and outputs the d-axis and q-axis voltage reference signals. In order to improve the dynamic performance and realize d-q axis decoupling, the inner ring also includes a current cross-decoupling term. The final d-q axis voltage reference signals are converted to abc three-phase coordinate system through inverse Park transformation, which is used to generate the pulse width modulation (PWM) driving signal of the grid-side converter, and control the switching action of the grid-side converter.
[0060] The control method of the rotor-side converter in the embodiment is shown in Figure 3 The control method of the rotor-side converter in the embodiment is shown in Figure 3 The VSG control outer ring simulates the operating characteristics of a synchronous generator. The inputs are the active power given value Pref and the reactive power given value Qref, as well as the actual active power P and the reactive power Q obtained by real-time acquisition and calculation through the sensor.
[0061] The control method of the rotor-side converter of the embodiment includes:
[0062] Step 1, according to the active power given value P ref and the reactive power given value Q ref of the rotor-side converter, real-time collection and calculation of the active power and the reactive power , calculation of the corresponding power angle and the internal potential amplitude E according to the control equation of the active link and the reactive link of the VSG;
[0063] The active link is based on the swing equation of the synchronous generator, and the VSG virtual synchronous angle is calculated:
[0064]
[0065]
[0066] wherein, is the virtual moment of inertia, represents the active power output at the stator side of the DFIG, represents the droop coefficient of the active ring of the VSG, represents the nominal angular frequency of the power grid, and ω represents the virtual angular frequency, is the nominal angular frequency of the power grid.
[0067] On this basis, the VSG power angle is obtained:
[0068]
[0069] The reactive link is based on the excitation control principle of the synchronous generator, and the internal potential amplitude E is calculated:
[0070]
[0071] wherein, wherein, represents the inertia coefficient of the reactive ring, represents the given value of the grid-connected point voltage, represents the actual value of the grid-connected point voltage, represents the reactive power output at the stator side of the DFIG, represents the droop coefficient of the reactive ring.
[0072] Step 2, according to the power angle and the internal potential amplitude E, the given value of the d-axis rotor voltage and the q-axis rotor voltage , is obtained, , The input voltage control link generates d, q axis rotor current given values , ;
[0073] The calculated power angle δ and internal potential amplitude E constitute the internal state of the virtual synchronous generator. This state (usually represented as a phasor ) is converted into stator voltage given values in the d-q rotating coordinate system , . This step includes a voltage PI control link, the input of which is the difference between the stator voltage given values and actual values, and the output is the rotor current given values. The difference between the rotor current given values and actual values is converted into the α-β coordinate system and used as the input signal of the virtual oscillator control inner loop.
[0074] Step 3, the difference between , and the rotor current actual value is converted into the α-β coordinate system through coordinate transformation, and the voltage feedback signals u α , u β are generated through gain. The voltage feedback signals u α , u β are used as the input signals of the virtual oscillator control inner loop, the virtual capacitor voltage and the virtual inductor current are used as the internal state variables of the virtual oscillator control inner loop, and the voltage reference signals v α , v β in the α-β coordinate system are generated based on the virtual capacitor voltage and the virtual inductor current through voltage gain scaling; and the voltage reference signals v α , v β are input to the pulse width modulation module after coordinate transformation, so as to drive the rotor side converter.
[0075] The control principle diagram of the virtual oscillator control inner loop of the rotor side converter of the embodiment is shown in Figure 4 , and the control inner loop is responsible for accurately and quickly tracking the rotor current instruction given by the VSG outer loop.
[0076] Specifically, the virtual oscillator control inner loop receives the specified α, β axis rotor current error components; based on the rotor current error components, the voltage feedback signals u α , u β are generated through a processing link containing current gain. Specifically, the rotor current error signal is subjected to current gain to obtain the voltage feedback signals u α , u β :
[0077]
[0078]
[0079] in, For current gain, , These are the actual values of the rotor currents on the α and β axes. , The given values are the rotor currents for the α and β axes. The selection principle is to coordinate with the parameters of the virtual oscillator to achieve accurate current tracking and stable grid-connected operation. Voltage feedback signal u α u β The aim is to inject current error information into the oscillator dynamics, driving the oscillator output adjustment to reduce the error.
[0080] Then, run the virtual oscillator core module, which uses virtual capacitor voltage. and virtual inductor current As its internal state variable, its dynamic evolution is determined by the voltage feedback signal u. α , u β The system of differential equations describes this;
[0081] Depend on and and the nonlinear voltage source g determined by the design parameters L, C, ζ, k. v and nonlinear current source g i :
[0082]
[0083]
[0084] This is the virtual capacitor voltage. The nominal oscillation amplitude, This is a virtual inductance value. This is a virtual capacitance value. For virtual inductor current, , For convergence speed parameters;
[0085] Describe the state variable, virtual capacitor voltage v C and virtual inductor current i L The system of differential equations for dynamic evolution is as follows:
[0086]
[0087]
[0088] These equations model a resonant circuit, the non-linear voltage source and the non-linear current source ensure that the oscillator is able to generate a stable limit cycle oscillation, whose amplitude and frequency are determined by the design parameters L, C, ζ, k, the voltage feedback signal u α and u β directly act on these two differential equations, adjusting the behavior of the virtual oscillator.
[0089] The output variables of the virtual oscillator are the virtual capacitor voltage v C and the virtual inductor current i L The product of v
[0090]
[0091]
[0092] After αβ-abc transformation, the three-phase rotor voltage reference signal u rabc is obtained, which is sent to the PWM generator to generate the gate drive signal of the power electronic switch (such as IGBT) in the rotor-side converter, so as to control the rotor-side converter to output the expected voltage, and further adjust the rotor current to track the given value.
[0093] The selection principle of the oscillator design parameters in this embodiment is to: aim to ensure that the oscillator can generate a stable limit cycle oscillation at the expected frequency and amplitude, meet the system dynamic response requirements including power conversion time and voltage rise time, and ensure the stability of the entire control system.
[0094] The selection principle of the virtual capacitor value C and the virtual inductor value L is:
[0095] The selection of the virtual capacitor value C needs to meet the constraint conditions based on the minimum rotor voltage V min , the maximum allowable deviation e, the rated power S and the maximum power conversion time T trans , whose value range is defined by the following formula:
[0096]
[0097] The selection of the virtual inductor value L is combined with the selected virtual capacitor value C to match the natural resonant frequency of the virtual oscillator with the nominal angular frequency ω n of the power grid, whose value is defined by the following formula:
[0098]
[0099] In this embodiment, the selection principle of the convergence speed parameter ζ is to meet the constraint conditions based on the nominal oscillation amplitude A and the maximum voltage rise time t rminimum convergence speed requirement;
[0100] The implementation can be realized by a controller containing a microprocessor (such as a DSP or FPGA), a sensor (for measuring voltage, current), a memory (storing programs and data), and an interface circuit. The controller executes the calculation logic of the above-mentioned VSG outer loop and virtual oscillator control inner loop, and interacts with the hardware such as the converter and sensor of the DFIG system.
[0101] Figure 5 For the active power waveform of the VSG-DFIG unit using the current inner loop when the grid phase jumps, it can be seen that the system cannot well cope with the phase jump fault at this time, and the system is unstable.
[0102] Figure 6 For the active power waveform of the VSG-DFIG unit using the virtual oscillator as the inner loop current controller of the rotor-side converter when the grid phase jumps, it can be seen that the system can better re-synchronize with the grid when a fault occurs, and realize transient fault ride-through.
[0103] In summary, the virtual oscillator of the present embodiment is used as the inner loop current controller of the rotor-side converter of the VSG-DFIG, replacing the traditional PI controller, and its unique dynamic characteristics and synchronization capability are expected to improve the stability margin and dynamic performance of the system under grid phase jump and other disturbances.
[0104] Although the present application is described herein with reference to particular embodiments, it is to be understood that these examples are merely illustrative of principles and applications of the present application. It should therefore be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It should be understood that the features described in connection with the individual embodiments can be used in other described embodiments.
Claims
1. A control method for a grid-connected doubly-fed wind turbine, characterized in that, The method comprises controlling the rotor-side converter and the grid-side converter, wherein the control method of the rotor-side converter comprises: According to the active power given value of the rotor side converter And the reactive power given value , Real-time acquisition and calculation of active power And reactive power According to the control equation of the active and reactive power links of the VSG, the corresponding power angle and internal potential amplitude are calculated; The d, q axis rotor voltage given values are obtained according to the power angle and the internal potential amplitude 、 The d, q axis rotor current given values are generated by inputting the voltage control link 、 、 ; Will , The difference between the actual value of the rotor current and the actual value of the rotor current is transformed to the coordinate system. In the coordinate system, and after gaining, a voltage feedback signal is generated. , Voltage feedback signal , As the input signal for the inner loop of the virtual oscillator control, the inner loop uses virtual capacitor voltage and virtual inductor current as internal state variables, and generates the signal based on the virtual capacitor voltage and virtual inductor current through voltage gain scaling. Voltage reference signal in coordinate system , ; According to the voltage reference signal , After coordinate transformation, the input is sent to the pulse width modulation module to drive the rotor-side converter.
2. The control method of the grid integration doubly-fed wind power generator unit according to claim 1, characterized by, The generating of the virtual capacitor voltage and the virtual inductor current through the voltage gain scaling voltage reference signal in the coordinate system ,The method of includes: Nonlinear voltage source and nonlinear current source : virtual capacitor voltage, nominal oscillation amplitude, virtual inductance value, virtual capacitance value, virtual inductance current, gain scaling factor , convergence speed parameter; , The differential equation is: determining and after and resulting in 。 3. The control method of the grid integrated doubly-fed wind power unit according to claim 2, characterized by, voltage feedback signal , respectively: wherein is the current gain, , is , actual value of the rotor current of the shaft, , is , given value of the rotor current of the shaft.
4. The control method of the grid-connected doubly-fed wind power unit according to claim 2, characterized by, virtual capacitance value satisfies: wherein, is the minimum rotor voltage, is the maximum allowed deviation, is the rated power, is the maximum power conversion time; The virtual inductance value L is: wherein is the nominal angular frequency of the power grid.
5. The control method of the grid-connected doubly-fed wind power unit according to claim 2, characterized by, Convergence speed parameter is: wherein is the maximum voltage rise time.
6. The control method of network configured doubly-fed wind turbine of claim 2, characterized in that, , , , the selection principle of k is that: The virtual oscillator control inner loop can generate stable limit cycle oscillation at the desired frequency and amplitude, and meet the system dynamic response requirements including power conversion time and voltage rise time, while ensuring the stability of the entire control system.
7. The control method of network configured doubly-fed wind turbine of claim 2, characterized in that, The method for calculating the corresponding power angle and internal voltage amplitude according to the control equation of the active link and the reactive link under the VSG control comprises: The active part is based on the swing equation of the synchronous generator, and the virtual synchronous angle of the VSG is calculated : wherein, is a virtual moment of inertia, represents the DFIG stator side output active power, represents the VSG active power droop coefficient, represents the grid nominal angular frequency, is a virtual angular frequency, is the grid nominal angular frequency; obtaining the power angle : The reactive link calculates the internal voltage amplitude E based on the excitation control principle of the synchronous generator: wherein, wherein, represents a reactive loop inertia coefficient, represents a grid-connected point voltage given value, represents a grid-connected point voltage actual value, represents a DFIG stator-side output reactive power, represents a reactive loop droop coefficient.
8. A storage device readable by a computer, the storage device storing a computer program, characterized in that, The computer program is executed by the processor to realize the steps of the magnetic disk satellite moment attitude control method according to any one of claims 1 to 7.
9. A control device for a grid-forming doubly-fed wind turbine, comprising a storage device, a processor, and a computer program stored in the storage device and executable on the processor, characterized in that, The processor executes the computer program to realize the steps of the control method of the grid-connected double-fed wind turbine according to any one of claims 1 to 7.
10. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to realize the steps of the control method of the grid-connected double-fed wind turbine according to any one of claims 1 to 7.