Control method of network construction type doubly-fed asynchronous wind power generation system with power control capability

Abstract

The invention belongs to the technical field of power electronic converter control, and discloses a control method of a grid-forming type doubly-fed asynchronous wind power generation system with power control capability, which comprises a control process of a rotor-side converter and a control process of a grid-side converter, and is characterized in that the rotor-side converter forms a grid-forming type characteristic at a motor stator winding port, and the grid-side converter forms a grid-forming type characteristic at a motor stator winding port; the energy injected into the direct current bus capacitor is controlled; the grid-side converter maintains the input and output energy balance of the DC bus capacitor so as to control the voltage of the DC bus capacitor to be constant; the control process of the rotor side converter comprises a frequency support control loop, a power control loop, a voltage and current inner loop and pulse width modulation control, and the control process of the grid side converter comprises a direct current voltage control loop, a reactive power control loop, an alternating current control loop and pulse width modulation control. According to the invention, the capability of controlling the output power can be provided while the network construction type power dynamic index is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converter control, and relates to a control method for a grid-type double-fed asynchronous wind power generation system with power control capability. Background Art

[0002] As the proportion of renewable energy generation in the power system gradually increases, power electronic converter control technology based on renewable energy generation systems is becoming a key technology for the construction of new power systems. Wind power generation has the characteristics of centralized management, sustainability, and low operation and maintenance costs. Doubly-fed asynchronous wind turbines have lower costs due to the lack of permanent magnets and other characteristics, and have been widely used in wind farms.

[0003] The doubly-fed wind power generation system includes two power electronic converters, the rotor side converter (RSC) and the grid side converter (GSC). The AC port of the rotor side converter is connected to the rotor winding of the doubly-fed asynchronous motor, and the AC port of the grid side converter is connected to the stator winding and connected to the grid after passing through a transformer. The rotor side converter and the grid side converter are connected to the same DC bus capacitor through the DC port.

[0004] The control methods of power electronic converters can be divided into two categories: grid-following control and grid-forming control. Under grid-following control, the converter is synchronized with the grid voltage based on the information of the phase-locked loop, and presents a current source characteristic to the outside; under grid-forming control, the converter is synchronized with the grid voltage without relying on the phase-locked loop, and presents a voltage source characteristic to the outside.

[0005] The control method of power electronic converters in traditional wind power generation systems is grid-following control. Due to their external current source characteristics, a large number of connected new energy power electronic converters will reduce the strength of the power grid, which is reflected in the reduction of power system inertia, short-circuit capacity, and poor stability. Grid-following control converters can play a role in voltage support, thereby further improving the strength of the power grid after a large number of wind power generation systems are connected and improving the quality of power.

[0006] At present, there are still several shortcomings in the grid-controlled doubly-fed wind power generation system, which are mainly concentrated in the control coordination method between the rotor-side converter and the grid-side converter, as well as the dynamic characteristics of the grid-controlled power.

[0007] The DC capacitor voltage inertia synchronization grid control method adopted in the literature [S. Xu, H. Wang, Y. Cao, S. Igarashi, J. Li, and X. Cai, “InertiaResponse Control of Self-synchronous Voltage Source Doubly-fed Wind Turbinesin the Whole Wind Speed ​​Range”] forms voltage source characteristics in both the stator winding of the doubly-fed wind turbine generator and the AC port of the grid-side converter. However, since the line impedance between the stator winding of the doubly-fed wind turbine generator and the AC port of the grid-side converter is relatively small, this control method is prone to form power oscillation between the stator winding and the AC port of the grid-side converter. At the same time, the grid-side converter power synchronization method based on the DC bus capacitor voltage will cause the DC bus capacitor voltage to fluctuate, thereby affecting the excitation control effect of the rotor-side converter on the rotor winding of the doubly-fed wind turbine generator.

[0008] The virtual synchronous generator grid control method used in the literature [S. Wang, J. Hu, and X. Yuan, “Virtual Synchronous Control for Grid-Connected DFIG-Based Wind Turbines”] can simulate the power dynamic characteristics of synchronous generators in the power grid. However, the wind energy capture efficiency of a wind power generation system is related to its rotor rotation speed. This means that the power fluctuations generated when using the virtual synchronous generator grid control method will directly affect the rotor speed of the wind power generation system and affect the wind energy capture efficiency, which is not conducive to the full utilization of wind energy.

[0009] At the same time, wind power generation systems often specify upper and lower limits for output power and the frequency dead zone range of the frequency modulation function. Conventional grid-based control methods rely on the control structure switching mechanism to achieve the above functions, thereby introducing discontinuous nonlinear links in the control loop, which is not conducive to the smooth operation of the wind power generation system. Summary of the invention

[0010] The purpose of the present invention is to overcome the defects in the coordination between converters and the dynamic characteristics of grid-type control power in the above-mentioned prior art, and to provide a control method for a grid-type doubly-fed asynchronous wind power generation system with power control capability. The present invention can provide the ability of output power control while achieving the dynamic indicators of grid-type power.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions: A control method for a grid-type doubly-fed asynchronous wind power generation system with power control capability includes a control process of a rotor-side converter and a control process of a grid-side converter, wherein the rotor-side converter forms a grid-type characteristic at a motor stator winding port and controls the energy injected into a DC bus capacitor; the grid-side converter maintains an input and output energy balance of a DC bus capacitor, thereby controlling the DC bus capacitor voltage to be constant; The control process of the rotor-side converter includes: frequency support control loop, power control loop, voltage and current inner loop and pulse width modulation control, wherein the frequency support control loop constructs an output power instruction that meets the grid index according to the frequency change of the grid connection point; the power control loop controls the output power to follow the instruction signal by adjusting the converter reference phase instruction; the voltage and current inner loop adjusts the voltage modulation waveform according to the voltage phase instruction and the given amplitude instruction so that the stator voltage follows the voltage change; the modulation waveform output by the voltage and current inner loop is controlled by pulse width modulation to generate a drive signal for the rotor-side inverter; The control process of the grid-side converter includes: a DC voltage control loop, a reactive power control loop, an AC current control loop and a pulse width modulation control, wherein the DC voltage control loop maintains the DC bus capacitor voltage to follow a given command value by adjusting the AC current d-axis command; the reactive power control loop maintains the grid-side converter output reactive power to follow a given command value by adjusting the AC current q-axis command; the AC current control loop adjusts the voltage modulation waveform so that the output AC current follows the command value; the modulation waveform output by the AC current control loop is subjected to pulse width modulation control to generate a drive signal for the grid-side inverter.

[0012] Preferably, the input signal of the frequency support control loop is the AC voltage frequency at the grid connection point, and the mathematical expression of the frequency support control loop is as follows:

[0013] Among them, Δ P is the dynamic change of the output power command, K f is the primary frequency modulation coefficient, P set is the set output power of the current wind power generation system, f PCC is the AC voltage frequency at the grid connection point, Δ f PCC is the frequency change of AC voltage at the grid connection point, f N is the rated frequency of the grid voltage, T j is the inertia response time constant, T f is the filter time constant, s is the Laplace operator,f DB is the dead zone value for a given frequency.

[0014] Preferably, the input signal of the power control loop is the active power reference command and the reactive power reference command, and the output stator internal potential phase ref and stator voltage amplitude command U s , as follows:

[0015]

[0016] in: s is the Laplace operator, K d is the derivative controller coefficient, K p is the proportional controller coefficient, K i is the integral controller coefficient, K ii is the second-order integrator coefficient, P ref is the active power reference command, P is the actual output active power, U N is the rated stator voltage amplitude, K pQ is the proportional controller coefficient, K iQ is the integral controller coefficient, Q ref is the reactive power reference command, Q is the actual output reactive power.

[0017] Preferably, the voltage and current inner loop is implemented based on a proportional-integral controller and a coordinate rotation transformation.

[0018] Preferably, the voltage-current inner loop adjusts the voltage modulation waveform according to the voltage phase command and the given amplitude command so that the stator voltage follows the voltage change. The calculation method is as follows:

[0019] in, u rscd is the d-axis voltage modulation instruction of the rotor-side converter, u sq is the actual stator q-axis voltage, K rvp and K rvi are the proportional and integral coefficients of the voltage loop proportional-integral controller, sis the Laplace operator, i rd is the actual d-axis rotor current, K rcp and K rci are the proportional and integral coefficients of the current loop proportional-integral controller, ω is the angular frequency of the stator internal potential, L r is the filter inductance of the rotor-side converter, i rq is the actual q-axis rotor current, u rscq is the q-axis voltage modulation instruction of the rotor-side converter, U s is the stator voltage amplitude command, u sd is the actual stator d-axis voltage, i rq is the actual q-axis rotor current, i rq is the actual q-axis rotor current.

[0020] Preferably, the control of the grid-side converter includes a DC voltage control loop, a reactive power control loop and an AC current control loop, and the calculation method of the grid-side converter control is as follows:

[0021] in, u gscd is the d-axis voltage modulation instruction of the grid-side converter, u dc-ref is the DC bus capacitor voltage rating, u dc is the actual DC bus capacitor voltage, K gvp is the DC voltage controller proportional coefficient, s is the Laplace operator, K gvi is the integral coefficient of the DC voltage controller, i gd is the d-axis current output by the grid-side converter, K gcp is the AC current controller proportional coefficient, K gci is the integral coefficient of the AC current controller, u gd is the d-axis voltage reference of the grid-side converter, ω is the angular frequency of the stator internal potential, L g is the filter inductance of the grid-side converter, i gqis the q-axis current output by the grid-side converter, u gscq is the q-axis voltage modulation instruction of the grid-side converter, Q gref is the reactive power reference value of the grid-side converter, Q g is the actual output reactive power of the grid-side converter, K gqp is the reactive power controller proportional coefficient, K gqi is the integral coefficient of the reactive power controller, i gq is the q-axis current output by the grid-side converter, u gq is the q-axis voltage reference of the grid-side converter, i gd Output d-axis current for the grid-side converter.

[0022] Preferably, the frequency support control loop includes a frequency dead zone controller, an inertia response controller, a primary frequency modulation controller and a power limit controller; wherein the grid voltage and frequency information is first screened by the frequency dead zone controller, and the part exceeding the frequency dead zone range is sent to the inertia response controller and the primary frequency modulation controller, and the output power change required for the inertia support and the primary frequency modulation is calculated respectively, and after the upper and lower limits are adjusted by the power limit controller, an output power reference instruction is formed.

[0023] Preferably, the power control loop includes an active control loop and a reactive control loop, wherein the active control loop includes a proportional-integral-differential controller and a frequency integrator connected in parallel to generate a synchronous coordinate system reference phase; the reactive control loop adopts a proportional-integral controller to generate an AC voltage reference amplitude.

[0024] Preferably, the voltage and current inner loop includes a stator voltage control loop, a control coordinate system rotation and a rotor current control loop, wherein the stator voltage control loop uses a proportional-integral controller and the rotor current control loop uses a proportional-integral controller with a cross-decoupling term; wherein the control signal output by the stator voltage control loop is adjusted by the control coordinate system rotation and used as a reference instruction for the rotor current control loop.

[0025] Preferably, the AC current control loop is a proportional-integral controller with a cross-decoupling term and an AC voltage feed-forward term.

[0026] Compared with the prior art, the present invention has the following beneficial effects: The control method of the grid-type doubly-fed asynchronous wind power generation system with power control capability proposed in the present invention can improve the power output characteristics of the grid-type doubly-fed asynchronous wind power generation system, improve the wind energy utilization rate of the doubly-fed asynchronous wind power generation system, and realize the smooth switching of frequency dead zone and power limit in the frequency modulation process, which is specifically embodied in: 1. The whole machine realization idea of ​​grid-type control is adopted. The power control loop in the rotor-side converter control generates a voltage reference phase. θ ref , so that the converter can achieve synchronization with the power grid without relying on the phase-locked loop, has stronger adaptability to weak power grids, and has stronger grid frequency and voltage support capabilities during grid-connected operation. 2. Emphasize dual-port control coordination to achieve better grid-building characteristics. The rotor-side converter adopts a grid-building control method, and the grid-side converter adopts a grid-following control method. This avoids the power loop oscillation problem caused by the small AC line impedance when the grid-building control method of the converters on both sides is adopted, and realizes reasonable coordination of the converters on both sides. 3. The novel grid-building control architecture takes into account the flexibility of power control. The frequency support control loop and the power control loop are separated in the rotor-side converter control. The frequency support control loop simulates the dynamic characteristics of the grid. The independent power control loop, combined with the voltage and current inner loop control, can achieve fast and accurate tracking of the output power. Its advantage is that it can meet various power response modes such as frequency dead zone and power limiting without introducing control structure switching; at the same time, the power reference P ref As the wind speed and the rotor speed of the wind turbine change, the output power does not need to go through the dynamic adjustment process of the network, and can quickly track the power reference changes to improve the efficiency of wind energy capture. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a control block diagram of a grid-type double-fed asynchronous wind power generation system with power control capability of the present invention; Figure 2 This is a block diagram of the RSC frequency support control loop of the present invention; Figure 3 This is a block diagram of the RSC power control loop of the present invention; Figure 4 This is the RSC voltage and current inner loop control block diagram of the present invention; Figure 5 This is the GSC control block diagram of the present invention; Figure 6 The simulation result of the ramp change of the power grid frequency of 0.5 Hz / s in the embodiment of the present invention; Figure 7 This is the simulation result of a 0.2 Hz step deviation of the power grid frequency in an embodiment of the present invention; Figure 8 This is the simulation result of 0.2Hz step recovery of the power grid frequency in the embodiment of the present invention; Fig. 9It is the simulation result of the step in the dead zone of the power grid frequency and the set output power 0.5Pu step in the embodiment of the present invention. DETAILED DESCRIPTION

[0028] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0029] See also Figure 1 The present invention provides a control method for a grid-type doubly-fed asynchronous wind power generation system with power control capability, including a control method for a rotor-side converter and a control method for a grid-side converter of the grid-type doubly-fed wind power generation system. The rotor-side converter forms a grid-type characteristic at the motor stator winding port and controls the energy injected into the DC bus capacitor; the grid-side converter maintains the input and output energy balance of the DC bus capacitor, thereby controlling the DC bus capacitor voltage to be constant.

[0030] The control process of the rotor-side converter includes four parts: frequency support control loop, power control loop, voltage and current inner loop, and pulse width modulation control. The frequency support control loop includes a frequency dead zone controller, an inertia response controller, a primary frequency modulation controller, and a power limit controller. The grid voltage and frequency information is first screened by the frequency dead zone controller, and the part exceeding the frequency dead zone range is sent to the inertia response controller and the primary frequency modulation controller to calculate the output power change required for inertia support and primary frequency modulation, respectively. After the upper and lower limits are adjusted by the power limit controller, the output active power instruction of the wind power generation system is generated. P ref The power control loop includes an active control loop and a reactive control loop. The active control loop includes a proportional integral differential controller and a frequency integrator connected in parallel to generate a synchronous coordinate system reference phase θ ref ; The reactive control loop is a proportional-integral controller that generates an AC voltage reference amplitude U ref The voltage and current inner loop includes the stator voltage control loop, the control coordinate system rotation, and the rotor current control loop. The stator voltage control loop uses a proportional-integral controller, and the rotor current controller uses a proportional-integral controller with a cross-decoupling term. The control signal output by the stator voltage control loop is adjusted by the control coordinate system rotation and used as the reference instruction of the rotor current control loop. The modulated waveform output by the voltage and current inner loop is controlled by pulse width modulation to generate a drive signal for the rotor-side inverter.

[0031] The control process of the grid-side converter includes four parts: DC voltage control loop, reactive power control loop, AC current control loop and pulse width modulation control. The DC voltage control loop is a proportional-integral controller that generates a d-axis current reference command. i d-ref The reactive power control loop is a proportional-integral controller that generates the q-axis current reference command i q-ref The AC current control loop is a proportional-integral controller with a cross-decoupling term and an AC voltage feed-forward term. The modulation waveform output by the AC current control loop is controlled by pulse width modulation to generate a drive signal for the grid-side inverter.

[0032] For details, see Figure 1 , the control included in the present invention is mainly divided into two parts: rotor-side converter control and grid-side converter control, and also includes a control module for auxiliary coordinate transformation such as a phase-locked loop. In the rotor-side converter control, the frequency support control link constructs an output power instruction that meets the grid indicators according to the frequency change of the grid connection point; the power control loop controls the output power to follow the instruction signal by adjusting the converter reference phase instruction; the voltage and current inner loop adjusts the voltage modulation waveform according to the voltage phase instruction and the given amplitude instruction so that the stator voltage follows the voltage change. In the grid-side converter control, the DC voltage control loop maintains the DC bus capacitor voltage to follow the given instruction value by adjusting the AC current d-axis instruction; the reactive power control loop maintains the grid-side converter output reactive power to follow the given instruction value by adjusting the AC current q-axis instruction; the current inner loop adjusts the voltage modulation waveform so that the output AC current follows the instruction value.

[0033] like Figure 2 As shown, the input signal of the frequency support control loop is the AC voltage frequency at the grid connection point. f PCC . f DB is the dead zone value of a given frequency, f N is the rated frequency of the grid voltage. The filter adopts a first-order low-pass filter, and the filter time constant is T f The inertia response time constant is T j , the primary frequency modulation coefficient is K f , can be given according to the grid indicators. P is the dynamic change of the output power command, P set is the set output power of the current wind power generation system, P ref is the output power command value including the dynamic variation, sis the Laplace operator. The mathematical expression of the frequency support control loop is as follows:

[0034] The saturation limiter L1 is responsible for realizing the frequency dead zone of the inertia response, L2 is responsible for realizing the unidirectional response characteristics and adjustment limit of the inertia response, L3 is responsible for realizing the frequency dead zone and adjustment limit of the primary frequency modulation, and L4 is responsible for realizing the limit of the output power reference instruction.

[0035] like Figure 3 As shown, the input signal of the power control loop is the active power reference command P ref With reactive power reference command Q ref The active loop is implemented using a proportional-integral-derivative controller in parallel with a second-order integrator, where: P is the actual output active power, K p is the proportional controller coefficient, K i is the integral controller coefficient, K d is the derivative controller coefficient, K ii is the second-order integrator coefficient, is the rated grid angular frequency, is the angular frequency of the stator internal potential, ref is the potential phase in the stator, is the doubly-fed machine rotor electrical angle, is the potential phase in the rotor-side converter. The mathematical expression of the active loop is as follows:

[0036] The reactive loop is implemented using a proportional-integral controller, where: Q is the actual output reactive power, K pQ is the proportional controller coefficient, K iQ is the integral controller coefficient, U N is the rated stator voltage amplitude, U s is the stator voltage amplitude command. The mathematical expression of the reactive loop is as follows:

[0037] like Figure 4 As shown in the figure, the voltage and current inner loop of the rotor-side converter is realized based on the proportional-integral controller and the coordinate rotation transformation. u rscdis the d-axis voltage modulation instruction of the rotor-side converter, u rscq is the q-axis voltage modulation instruction of the rotor-side converter, u sd is the actual stator d-axis voltage, u sq is the actual stator q-axis voltage, i rd_ref is the d-axis rotor current reference command, i rq_ref is the q-axis rotor current reference instruction, i rd is the actual d-axis rotor current, i rq is the actual q-axis rotor current, u rd is the d-axis voltage reference of the rotor-side converter, u rq is the q-axis voltage reference of the rotor-side converter, L r is the filter inductance of the rotor-side converter. K rvp and K rvi are the proportional and integral coefficients of the voltage loop proportional-integral controller, K rcp and K rci They are the proportional and integral coefficients of the current loop proportional-integral controller respectively. The mathematical expression of the voltage and current inner loop is as follows:

[0038] like Figure 5 As shown, the control of the grid-side converter includes a DC voltage control loop, a reactive power control loop, and an AC current control loop. u gscd is the d-axis voltage modulation instruction of the grid-side converter, u gscq is the q-axis voltage modulation instruction of the grid-side converter, K gvp is the DC voltage controller proportional coefficient, K gvi is the integral coefficient of the DC voltage controller, K gcp is the AC current controller proportional coefficient, K gci is the integral coefficient of the AC current controller, K gqp is the reactive power controller proportional coefficient, K gqi is the integral coefficient of the reactive power controller, u dc-refis the DC bus capacitor voltage rating, u dc is the actual DC bus capacitor voltage, Q gref is the reactive power reference value of the grid-side converter, Q g is the actual output reactive power of the grid-side converter, i gd is the d-axis current output by the grid-side converter, i gq is the q-axis current output by the grid-side converter, u gd is the d-axis voltage reference of the grid-side converter, u gq is the grid-side converter q-axis voltage reference, and Lg is the grid-side converter filter inductance. The grid-side converter control mathematical expression is as follows:

[0039] The most important innovation of the wind power generation system control method proposed in the present invention lies in the design of the grid-type control link in the rotor-side converter. In traditional grid-type control, the relationship between power P and power angle θ is used to achieve synchronization between the wind turbine and the power grid; the difference in the effects of different grid-type control methods lies mainly in the different dynamic characteristics of the frequency support of the power grid, that is, when the power grid frequency changes, the dynamic characteristics of the output power of the wind turbine response are different. In the traditional grid-type control scheme, the two functions of "synchronization using the power-power angle relationship" and "constructing frequency support dynamic characteristics" are implemented in the same control loop, which makes the two affect each other and cannot achieve fast and accurate output power tracking; at the same time, the control structure switching introduced to achieve the dead zone of frequency support and the dead zone of dynamic adjustment will cause conflicts between multiple integrators in the control loop, requiring additional solutions.

[0040] The remaining parts, such as DC bus capacitor voltage control, reactive power-voltage amplitude control, current-type grid-following control scheme, etc., are not original designs of the present invention, but are only components that form a complete control scheme.

[0041] Example: The control parameters used in the simulation experiment are shown in Table 1: Table 1

[0042] The method proposed in this embodiment is different from the power grid frequency fluctuation process and the set output power P set Validity verification was carried out during the change process.

[0043] Figure 6-Figure 9The waveform diagram shows the changes in the grid frequency, the changes in the active power reference and actual output power, and the changes in the potential frequency within the grid control.

[0044] The result of the grid frequency changing with a ramp of 0.5 Hz / s is as follows: Figure 6 As shown. It can be seen that when the grid frequency exceeds the frequency dead zone range, the active power reference P ref It gradually increases until the set power upper limit is reached, and the actual output power always follows the power reference value.

[0045] The change process of the grid frequency deviating from the rated frequency by 0.2Hz step is as follows Figure 7 It can be seen that the active power can follow the reference value and exhibits an inertia response characteristic similar to that of the synchronous machine at the moment of frequency deviation step.

[0046] The grid frequency changes from a 0.2Hz step to the rated frequency as follows: Figure 8 It can be seen that the active power can follow the reference value and does not show the characteristics of inertia response during the frequency recovery step.

[0047] The process of the grid frequency changing within the dead zone and the set output power Pset undergoing a 0.5Pu step change is as follows: Fig. 9 It can be seen that when the grid frequency jumps in the dead zone, the output power still follows the power reference value; when the set output power Pset changes in a step, the output active power can quickly follow the power reference value and does not show the dynamic characteristics of inertia response.

[0048] It can be seen from the above scheme that in the present invention, for the doubly fed wind power generation system, a grid-type control method without a phase-locked loop is adopted in the rotor-side converter, and an inner loop with stator voltage control is introduced, which can realize the ability to independently build voltage at the stator port and improve the strength of the power grid; in the grid-side converter, the traditional grid-following control scheme is still adopted to realize fast and accurate control of the DC bus capacitor voltage, avoid conflicts with the rotor-side converter on control targets, and facilitate the existing wind farm to quickly complete the grid-type transformation of the generator; in the grid-type control link of the rotor-side converter, two relatively independent control parts such as the frequency support control loop and the power control loop are designed to separate the dynamic characteristics of the grid-type wind farm participating in frequency regulation from the power synchronization characteristics that depend on the power-phase angle relationship, so that the frequency dead zone, power limiting and other functions can be realized without relying on mode switching, and the wind turbine output power can be maintained to accurately follow the reference value.

[0049] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A control method for a grid-connected double-fed asynchronous wind power generation system with power control capability, characterized in that: The invention includes the control process of the rotor-side converter and the control process of the grid-side converter, wherein the rotor-side converter forms a grid-type characteristic at the motor stator winding port and controls the energy injected into the DC bus capacitor; the grid-side converter maintains the input and output energy balance of the DC bus capacitor, thereby controlling the DC bus capacitor voltage to be constant; The control process of the rotor-side converter includes: frequency support control loop, power control loop, voltage and current inner loop and pulse width modulation control, wherein the frequency support control loop constructs an output power instruction that meets the grid index according to the frequency change of the grid connection point; the power control loop controls the output power to follow the instruction signal by adjusting the converter reference phase instruction; the voltage and current inner loop adjusts the voltage modulation waveform according to the voltage phase instruction and the given amplitude instruction so that the stator voltage follows the voltage change; the modulation waveform output by the voltage and current inner loop is controlled by pulse width modulation to generate a drive signal for the rotor-side inverter; The control process of the grid-side converter includes: a DC voltage control loop, a reactive power control loop, an AC current control loop and a pulse width modulation control, wherein the DC voltage control loop maintains the DC bus capacitor voltage to follow a given command value by adjusting the AC current d-axis command; the reactive power control loop maintains the grid-side converter output reactive power to follow a given command value by adjusting the AC current q-axis command; the AC current control loop adjusts the voltage modulation waveform so that the output AC current follows the command value; the modulation waveform output by the AC current control loop is subjected to pulse width modulation control to generate a drive signal for the grid-side inverter.

2. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The input signal of the frequency support control loop is the AC voltage frequency at the grid connection point. The mathematical expression of the frequency support control loop is as follows: Among them, Δ P is the dynamic change of the output power command, K f is the primary frequency modulation coefficient, P set is the set output power of the current wind power generation system, f PCC is the AC voltage frequency at the grid connection point, Δ f PCC is the frequency change of AC voltage at the grid connection point, f N is the rated frequency of the grid voltage, T j is the inertia response time constant, T f is the filter time constant, s is the Laplace operator, f DB is the dead zone value for a given frequency.

3. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The input signals of the power control loop are the active power reference command and the reactive power reference command, and the output signals are the phase of the stator potential. ref and stator voltage amplitude command U s , as follows: in: s is the Laplace operator, K d is the derivative controller coefficient, K p is the proportional controller coefficient, K i is the integral controller coefficient, K ii is the second-order integrator coefficient, P ref is the active power reference command, P is the actual output active power, U N is the rated stator voltage amplitude, K pQ is the proportional controller coefficient, K iQ is the integral controller coefficient, Q ref is the reactive power reference command, Q is the actual output reactive power.

4. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The voltage and current inner loop is realized based on proportional-integral controller and coordinate rotation transformation.

5. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 4, characterized in that: The voltage and current inner loop adjusts the voltage modulation waveform according to the voltage phase command and the given amplitude command so that the stator voltage follows the voltage change. The calculation method is as follows: in, u rscd is the d-axis voltage modulation instruction of the rotor-side converter, u sq is the actual stator q-axis voltage, K rvp and K rvi are the proportional and integral coefficients of the voltage loop proportional-integral controller, s is the Laplace operator, i rd is the actual d-axis rotor current, K rcp and K rci are the proportional and integral coefficients of the current loop proportional-integral controller, ω is the angular frequency of the stator internal potential, L r is the filter inductance of the rotor-side converter, i rq is the actual q-axis rotor current, u rscq is the q-axis voltage modulation instruction of the rotor-side converter, U s is the stator voltage amplitude command, u sd is the actual stator d-axis voltage, i rq is the actual q-axis rotor current, i rq is the actual q-axis rotor current.

6. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The control of the grid-side converter includes a DC voltage control loop, a reactive power control loop, and an AC current control loop. The calculation method for the grid-side converter control is as follows: in, u gscd is the d-axis voltage modulation instruction of the grid-side converter, u dc-ref is the DC bus capacitor voltage rating, u dc is the actual DC bus capacitor voltage, K gvp is the DC voltage controller proportional coefficient, s is the Laplace operator, K gvi is the DC voltage controller integral coefficient, i gd is the d-axis current output by the grid-side converter, K gcp is the AC current controller proportional coefficient, K gci is the integral coefficient of the AC current controller, u gd is the d-axis voltage reference of the grid-side converter, ω is the angular frequency of the stator internal potential, L g is the filter inductance of the grid-side converter, i gq is the q-axis current output by the grid-side converter, u gscq is the q-axis voltage modulation instruction of the grid-side converter, Q gref is the reactive power reference value of the grid-side converter, Q g is the actual output reactive power of the grid-side converter, K gqp is the reactive power controller proportional coefficient, K gqi is the integral coefficient of the reactive power controller, i gq is the q-axis current output by the grid-side converter, u gq is the q-axis voltage reference of the grid-side converter, i gd Output d-axis current for the grid-side converter.

7. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The frequency support control loop includes a frequency dead zone controller, an inertia response controller, a primary frequency modulation controller and a power limit controller; wherein the grid voltage and frequency information is first screened by the frequency dead zone controller, and the part exceeding the frequency dead zone range is sent to the inertia response controller and the primary frequency modulation controller, and the output power variation required for the inertia support and the primary frequency modulation is calculated respectively, and after the upper and lower limits are adjusted by the power limit controller, an output power reference instruction is formed.

8. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The power control loop includes an active control loop and a reactive control loop, wherein the active control loop includes a proportional-integral-differential controller and a frequency integrator connected in parallel to generate a synchronous coordinate system reference phase; the reactive control loop uses a proportional-integral controller to generate an AC voltage reference amplitude.

9. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The voltage and current inner loop includes a stator voltage control loop, a control coordinate system rotation and a rotor current control loop. The stator voltage control loop uses a proportional-integral controller, and the rotor current control loop uses a proportional-integral controller with a cross-decoupling term. The control signal output by the stator voltage control loop is adjusted by the control coordinate system rotation and used as a reference instruction for the rotor current control loop.

10. The control method of a grid-connected double-fed asynchronous wind power generation system with power control capability according to claim 1, characterized in that: The AC current control loop is a proportional-integral controller with a cross-decoupling term and an AC voltage feed-forward term.

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