High-power-grid-adaptability doubly-fed generator converter circuit and control method

Abstract

The invention provides a doubly-fed generator converter circuit with strong power grid adaptability and a control method, and belongs to the technical field of doubly-fed wind generating set converter control, the doubly-fed generator converter circuit comprises a power grid access unit (1), a doubly-fed generator (2), a grid-connected converter, a rotor main converter (5), a rotor auxiliary converter (6), a stator auxiliary converter (7), an energy storage unit (8), a first capacitor (9) and a second capacitor (10); the doubly-fed generator (2) comprises a doubly-fed generator rotor (21) and a doubly-fed generator stator (22), the doubly-fed generator rotor (21) comprises three-phase windings, two end parts of each phase of winding are led out to form two groups of three-phase wiring terminals, the doubly-fed generator stator (22) comprises two sets of three-phase windings, and the two sets of windings are free of electrical connection and magnetic coupling. The double functions of energy storage unit access and doubly-fed generator transient control capability improvement are taken into consideration through the rotor auxiliary converter, unification of doubly-fed wind turbine generator power grid support and self power grid adaptability is realized, direct integration of the energy storage unit is realized without a DC / DC converter, and the energy storage efficiency is improved. The cost and the manufacturing complexity of the converter system are reduced, and the operation efficiency of the converter system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of current conversion control of a doubly-fed wind turbine generator set, and in particular relates to a current conversion circuit and a control method of a doubly-fed generator with strong grid adaptability. Background Art

[0002] Doubly-fed wind turbines have the characteristics of a wide speed regulation range, smooth active and reactive power regulation, strong flexibility and robustness; and have obvious advantages, such as high cost-effectiveness, high efficiency, low noise and high reliability, and the generator can operate in grid-connected or independent mode. It is one of the most widely used wind turbines. The development of doubly-fed wind power generation faces two challenges: on the one hand, the stability of the power grid urgently requires wind turbines to participate in frequency regulation to achieve active control of the power grid frequency; on the other hand, the change of the power grid voltage causes electromagnetic transients in the doubly-fed generator, which brings challenges to the effectiveness of the doubly-fed generator rotor-side converter control.

[0003] In order to improve the grid frequency support capability of wind turbines, overspeed load reduction control and pitch angle control are mainly used to reserve spare power capacity to cope with frequency reduction. However, this approach not only sacrifices the power generation during steady-state operation, but may also cause a secondary frequency drop when the speed is restored. Therefore, more and more attention is focused on equipping wind farms or wind turbines with energy storage units. Configuring an energy storage unit at the wind farm outlet bus can dynamically compensate for the inertia of the wind farm, but since the wind turbine itself does not participate in frequency regulation, the energy storage configuration cost is high. In contrast, equipping a single wind turbine with an energy storage unit helps to realize the comprehensive utilization of wind turbine inertia energy storage, thereby enhancing support for grid frequency and having strong economy and flexibility. For doubly fed wind turbines, the current common practice is to connect the energy storage unit to the DC bus of the doubly fed generator rotor back-to-back converter through a DC / DC converter.

[0004] Due to the special topological structure of the doubly-fed generator and the direct grid connection of the stator winding of the doubly-fed wind turbine, it is very sensitive to grid voltage fluctuations. Changes in the grid state will cause the electromagnetic transient process of the doubly-fed generator, endangering the safety of the rotor converter and the effectiveness of control. The fault mechanism of the doubly-fed generator is that the transient rotor electromotive force induced on the rotor due to the grid voltage drop exceeds the voltage control capability of the rotor converter. In fact, the grid adaptability problem of the doubly-fed wind turbine, that is, the operation control problem of the doubly-fed generator itself under grid faults or grid state changes, has been a hot topic in research in the past decade, and this problem has not been well solved so far. The crowbar solution widely used in engineering will, on the one hand, generate huge electromagnetic torque pulsations, endangering the health of the wind turbine shaft system; on the other hand, the wind turbine will lose controllability and absorb a large amount of reactive power from the grid, aggravating the deterioration of the grid voltage. Therefore, in view of the fault ride-through problem of the doubly-fed generator, the crowbar-free fault ride-through technology has attracted widespread attention at home and abroad. Scholars have proposed many hardware devices to replace the crowbar and achieved better fault ride-through effects.

[0005] The document “Control of a doubly fed induction generator in a wind turbine during grid fault ride-through” published in August 2006 (IEEE transactions on energy conversion, 2006, 21(3): 652-662) proposed a classic demagnetization control method, which injects the free component and negative sequence component of the stator flux into the current command, greatly reducing the rotor voltage demand, and accelerating the decay rate of the stator flux, effectively improving the fault ride-through performance. However, the demagnetization current of this method is very large, which is prone to overcurrent under severe faults and has defects such as weak reactive support and large electromagnetic torque pulsation. The document “Virtual Inductance Transient Self-Demagnetization Control of Doubly Fed Wind Turbines during Low Voltage Ride-through” (Yang Shuying et al., Automation of Electric Power Systems) published in February 2015 discloses that the demagnetization control of transient processes is realized by introducing a virtual inductance algorithm, which expands the adaptability range of doubly fed generators to voltage drops. However, in actual operation, not only a large current capacity is required, but also reactive power needs to be absorbed from the power grid, which is not conducive to the recovery of the power grid voltage. In order to improve the adaptability of the doubly fed generator set to changes in the power grid state, especially the operating capacity when the power grid fails, some scholars have introduced additional series converters to compensate for changes in the stator voltage of the doubly fed generator. The document "Enhanced control of DFIG wind turbine based on stator flux decay compensation" (IEEE Transactions on Energy Conversion, 2016, 31 (4): 1366-1376.) published in 2016 discloses that by connecting a dynamic voltage restorer (DVR) in series at the grid-connected end, the stator voltage drop and recovery method are changed, and an enhanced control strategy is proposed to approximate the flux decay to zero within a half-base frequency cycle, thereby significantly reducing the transient current pulse of the rotor during a power grid failure.The document "LVRT performance enhancement of DFIG-based wind farms by capacitive bridge-type fault current limiter" (IEEE Transactions on Sustainable Energy, 2017, 9(3): 1118-1125.) published in 2017 discloses the use of a fault current limiter (CBFCL), in which a DC reactor can limit the fault current increment without delay. This feature suppresses the instantaneous voltage drop, thereby limiting the transient overcurrent of the rotor and stator at the beginning and end of the fault period.

[0006] like Fig.11 The figure shows an existing system that integrates an energy storage unit in a doubly-fed wind power converter. The typical approach is to integrate the energy storage unit into its DC side through a DC / DC converter. For example, the document "Inertia and Primary Frequency Regulation Strategy of Doubly-Fed Wind Turbines Based on Supercapacitor Energy Storage Control" (Yan Xiangwu et al., Automation of Power Systems) published in July 2020 discloses connecting a supercapacitor to the DC bus of a back-to-back converter through a DC / DC converter, and realizing the passive exchange of energy between the energy storage unit and the grid through the DC voltage control of the grid-side converter. However, the converter circuit topology scheme of the integrated energy storage unit requires a high-power bidirectional DC / DC converter, which is difficult to manufacture and has low efficiency; its energy storage additional circuit does not provide benefits to the control of the doubly-fed generator itself; the voltage required for the control of the doubly-fed generator is only provided by one inverter of the RSC alone, which has low reliability and poor grid transient adaptability.

[0007] Through literature research, it is not difficult to find that the research on the grid support and grid adaptability of doubly-fed wind turbines tends to add converter hardware equipment, but the current publicly reported solutions do not yet have a circuit topology solution that takes into account both the adaptability of low voltage ride-through and the circuit topology of enhancing grid support capabilities through energy storage. The current research on the two aspects is relatively isolated and lacks a systematically considered optimized integrated topology. Therefore, in order to solve the problem of a unified converter topology solution for the integrated energy storage requirements of doubly-fed wind turbines and the grid adaptability control requirements of doubly-fed generators, it is an urgent task to provide a converter circuit topology solution that can take into account the direct integration of energy storage units and effectively improve the operating control performance of doubly-fed generators under grid faults. Summary of the invention

[0008] The technical problem to be solved by the present invention is how to design a doubly-fed generator converter circuit with strong grid adaptability, which can simultaneously take into account the adaptability of low voltage ride-through and enhance the grid support capability through energy storage.

[0009] The present invention solves the above technical problems through the following technical solutions: a double-fed generator conversion circuit with strong grid adaptability, comprising a grid access unit (1), a double-fed generator (2), a grid-connected converter, a rotor main converter (5), a rotor auxiliary converter (6), a stator auxiliary converter (7), an energy storage unit (8), a first capacitor (9), and a second capacitor (10); the double-fed generator (2) comprises a double-fed generator rotor (21) and a double-fed generator stator (22); the double-fed generator rotor (21) comprises a three-phase winding, and both ends of each phase winding are led out to form two groups of three-phase wiring terminals; the double-fed generator stator (22) comprises two sets of three-phase windings, the two sets of windings have no electrical connection and no magnetic coupling; the grid access unit (1) comprises three ports; the first port (12) of the grid access unit (1) is connected to the three-phase grid, and the second port (13) of the grid access unit (1) is connected to the double-fed generator The main winding of the stator (22) is connected, the third port (14) of the grid access unit (1) is connected to the AC side of the grid-connected converter, and the DC side of the grid-connected converter is connected to the DC side of the rotor main converter (5); the first capacitor (9) is connected in parallel between the DC side of the grid-connected converter and the DC side of the rotor main converter (5); the AC side of the rotor main converter (5) is connected to one group of three-phase terminals of the doubly fed generator rotor (21); the other group of three-phase terminals of the doubly fed generator rotor (21) is connected to the AC side of the rotor auxiliary converter (6); the three-phase terminals of the secondary winding of the doubly fed generator stator (22) are connected to the AC side of the stator auxiliary converter (7); the DC sides of the rotor auxiliary converter (6) and the stator auxiliary converter (7) are connected to the energy storage unit (8); and the second capacitor (10) is connected in parallel between the DC sides of the rotor auxiliary converter (6) and the stator auxiliary converter (7) and the energy storage unit (8).

[0010] As a further optimized technical solution, the doubly-fed generator converter circuit further includes a long-line filter (11), the AC side of the rotor main converter (5) is connected to one end of the long-line filter (11), and the other end of the long-line filter (11) is connected to one group of three-phase connection terminals of the doubly-fed generator rotor (21).

[0011] As a further optimized technical solution, the grid-connected converter comprises a grid-side power unit (3) and a grid-side filter unit (4); the first port (41) of the grid-side filter unit (4) is connected to the third port (14) of the grid access unit (1), and the second port (42) of the grid-side filter unit (4) is connected to the AC side of the grid-side power unit (3); and the DC side of the grid-side power unit (3) is connected to the DC side of the rotor main converter (5).

[0012] As a further optimized technical solution, the energy storage unit (8) adopts a battery or a supercapacitor or a combination of the two.

[0013] As a further optimized technical solution, the first capacitor (9) and the second capacitor (10) are electrolytic capacitors or film capacitors.

[0014] As a further optimized technical solution, a transformer is provided between each two ports of the three ports of the grid access unit (1), or no transformer is provided.

[0015] As a further optimized technical solution, the second port (13) and the third port (14) of the grid access unit (1) are both controlled on and off by relays.

[0016] As a further optimized technical solution, the grid-side filtering unit (4) adopts one of a three-phase LCL type, a three-phase LC type or a three-phase L type filter.

[0017] As a further optimized technical solution, the grid-side power unit (3), the rotor main converter (4), the rotor auxiliary converter (6) and the stator auxiliary converter (7) all adopt a three-phase bridge voltage source structure.

[0018] The present invention also provides a control method for a doubly-fed generator converter circuit with strong grid adaptability as described in any one of the above items, wherein the rotor main converter (5) controls the active power on the rotor side of the doubly-fed generator (2) during steady-state operation, and the rotor auxiliary converter (6) controls the reactive power on the rotor side of the doubly-fed generator (2). At the same time, the rotor auxiliary converter (6) also buffers the grid-connected power pulsation through the stator winding end of the doubly-fed generator (2) and the rotor main converter (5) and the grid-connected converter to smooth the grid-connected power. When an abnormality occurs in the grid or the grid state changes, the rotor main converter (5), the rotor auxiliary converter (6) and the stator auxiliary converter (7) cooperate to control the electromagnetic transient state of the doubly-fed generator (2). At the same time, the energy storage unit (8) provides active power control to the grid through the rotor auxiliary converter (6), the rotor main converter (5), the grid-connected converter and the grid access unit (1), and realizes active control of the grid frequency together with the inertial energy storage of the doubly-fed generator (2).

[0019] The advantages of the present invention are:

[0020] (1) The rotor-assisted converter (6) of the technical solution of the present invention simultaneously takes into account the dual functions of accessing the energy storage unit (8) and improving the transient control capability of the doubly-fed generator (2), thereby realizing the unification of the grid support of the doubly-fed wind turbine set and its own grid adaptability. Without the need for a DC / DC converter, the direct integration of the energy storage unit is realized, the converter system cost and manufacturing complexity are reduced, and the operating efficiency of the converter system is improved.

[0021] (2) The voltage required by the doubly-fed generator is provided by the rotor main converter (5) and the rotor auxiliary converter (6) together, which can increase the voltage supply capacity, thereby better controlling the rotor side current of the doubly-fed generator and better controlling the doubly-fed generator.

[0022] (3) The stator side of the doubly-fed generator has two sets of stator windings, of which the auxiliary winding is controlled by a stator auxiliary converter (7) and the DC side is powered by an energy storage unit (8). In the event of a fault, the auxiliary winding current is controlled to compensate for the main winding flux, thereby reducing the stator transient flux, thereby suppressing the rotor transient electromotive force and improving the transient control capability of the doubly-fed generator (2).

[0023] (4) By properly setting the switching timing of the rotor main converter (5) and the rotor auxiliary converter (6), the harmonics of the voltage applied to the rotor of the doubly-fed generator can be reduced, which is beneficial to improving the quality of the current waveform, thereby improving the quality of the grid-connected current and reducing the motor loss.

[0024] (5) The solution of the present invention has the capability of fault-tolerant operation in the event of an open-circuit fault in the switch tube. When an open-circuit fault occurs in an IGBT switch of a certain phase in the rotor main converter (5), the healthy IGBT switch tube of the phase can be kept in the on state. Through the cooperation of the rotor auxiliary converter (6), the reconstruction of the remaining state is achieved, thereby achieving fault operation of the converter and reducing the urgency of fault maintenance of the wind turbine set.

[0025] (6) The technical solution of the present invention can increase the size of the control voltage. By increasing the voltage parameters during motor design, the diameter of the motor lead cable can be reduced, thereby saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1a It is a schematic diagram of a topological structure of a doubly-fed generator driving a converter according to an embodiment of the present invention;

[0027] Figure 1b is a schematic diagram of another topological structure of a doubly-fed generator driving a converter according to an embodiment of the present invention;

[0028] Figure 2.1 , Figure 2.2 , Figure 2.3 and Figure 2.4 They are four possible structural schematic diagrams of the grid access unit 1 in FIG1 ;

[0029] Figure 3.1 , Figure 3.2 and Figure 3.3 They are schematic diagrams of three possible structures of the grid-side filtering unit 4 in FIG. 1 ;

[0030] Figure 4 It is a schematic diagram of the structure of the grid-side power unit 3 in FIG1 ;

[0031] Figure 5 It is a schematic structural diagram of the rotor main converter 5 in FIG1 ;

[0032] Figure 6 It is a schematic diagram of the structure of the rotor-side auxiliary converter 6 in FIG1 ;

[0033] Figure 7 1 is a schematic diagram of the structure of the stator side auxiliary converter 7

[0034] Figure 8 It is a schematic structural diagram of the long-line filter 11 in FIG1 ;

[0035] Fig. 9 It is a schematic diagram of power distribution relationship of the double-fed converter drive topology shown in FIG1 when the power grid is in a steady state;

[0036] Fig.10 It is a schematic diagram of the operating state of the double-fed converter drive topology shown in FIG1 when the power grid state changes;

[0037] Fig.11 It is a schematic diagram of a typical approach to integrating an energy storage unit into a doubly-fed wind turbine in the prior art. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0040] Embodiment 1

[0041] like Figure 1a As shown, a double-fed generator conversion circuit with strong grid adaptability includes a grid access unit 1, a double-fed generator 2, a grid-side power unit 3, a grid-side filter unit 4, a rotor main converter 5, a rotor auxiliary converter 6, a stator auxiliary converter 7, an energy storage unit 8, a first capacitor 9, and a second capacitor 10; the double-fed generator 2 includes a double-fed generator rotor 21 and a double-fed generator stator 22, and the double-fed generator rotor 21 includes a three-phase winding, and both ends of each phase winding are led out to form two groups of three-phase terminals: a r1 ,b r1 ,c r1 and a r2 ,b r2 ,c r2The doubly-fed generator stator 22 includes two sets of three-phase windings, which have no electrical connection or magnetic coupling and lead to a set of three-phase terminals: A s1 ,B s1 ,C s1 and A s2 ,B s2 ,C s2 The grid access unit 1 includes three ports, and the grid-side filter unit 4 includes two ports; the first port 12 of the grid access unit 1 is connected to the three-phase grid access points U, V, and W, and the second port 13 of the grid access unit 1 is connected to the main winding A of the stator 22 of the double-fed generator. s1 ,B s1 ,C s1 The third port 14 of the grid access unit 1 is connected to the first port 41 of the grid-side filter unit 4; the second port 42 of the grid-side filter unit 4 is connected to the AC port 31 of the AC side of the grid-side power unit 3, the DC port 32 of the DC side of the grid-side power unit 3 is connected to the DC port 52 of the DC side of the rotor main converter 5, the first capacitor 9 is connected in parallel between the DC side of the grid-side power unit 3 and the DC side of the rotor main converter 5, and the AC port 51 of the AC side of the rotor main converter 5 is connected to one group of three-phase connection terminals a of the doubly fed generator rotor 21. r1 ,b r1 ,c r1 Connect, another set of three-phase terminal a of the doubly-fed generator rotor 21 r2 ,b r2 ,c r2 Connected to the AC port 61 of the AC side of the rotor auxiliary converter 6, the auxiliary winding three-phase terminal A of the double-fed generator stator 22 s2 ,B s2 ,C s2 The AC port 71 on the AC side of the stator auxiliary converter 7 is connected, the DC ports 62 and 72 on the DC sides of the rotor auxiliary converter 6 and the stator auxiliary converter 7 are connected to the energy storage unit 8, and the second capacitor 10 is connected in parallel between the DC sides of the rotor auxiliary converter 6 and the stator auxiliary converter 7 and the energy storage unit 8.

[0042] like Figure 1b As shown, another double-fed generator converter circuit with strong grid adaptability is shown. Figure 1a Compared with the embodiment shown in the figure, the double-fed generator converter circuit with strong grid adaptability also includes a long-line filter 11, the AC side of the rotor main converter 5 is connected to one end of the long-line filter 11, and the other end of the long-line filter 11 is connected to one group of three-phase terminal a of the double-fed generator rotor 21. r1 ,b r1 ,c r1 connect.

[0043] The energy storage unit 8 is used as an energy storage system for the wind turbine generator set, and adopts batteries or super capacitors or a mixture of the two. If it is a mixture of the two, it includes a DC / DC converter for voltage matching between different energy storage elements.

[0044] The first capacitor 9 and the second capacitor 10 are used as DC absorption and buffer capacitors, and can be electrolytic capacitors or film capacitors.

[0045] Figure 2.1 , Figure 2.2 , Figure 2.3 and Figure 2.4 They are three structural schematic diagrams of the power grid access unit 1 provided in the embodiments of the present invention, Figure 2.1 , Figure 2.2 and Figure 2.3 The black dots on the circumference of the grid all represent the connection terminals of the corresponding transformer windings. The first port 12 of the grid access unit 1 is connected to the three-phase grid access points U, V, and W; the second port 13 of the grid access unit 1 and the third port 14 of the grid access unit 1 can be controlled by relays, and transformer windings may exist between the three ports of the grid access unit 1 for voltage matching.

[0046] like Figure 3.1-3.3 As shown in FIG. 1 , there are three possible structural schematic diagrams of the network-side filtering unit 4, wherein Figure 3.1 Shown is a three-phase LCL type filter, Figure 3.2 Shown is a three-phase LC type filter, Figure 3.3 The three-phase L-type filter is shown, and the grid-side filter unit 4 adopts one of the three-phase LCL type, three-phase LC type or three-phase L-type filter. The grid-side filter unit 4 is a filtering and buffering unit for the AC side of the grid-side power unit 3 to be connected to the grid, and plays a buffering role in filtering out the grid-connected current harmonics and the connection between the AC voltage source. Figure 3.1 Reactance 43 and reactance 44, Figure 3.2 The reactance in 46, Figure 3.3 The reactance 48 in the figure can be a three-phase independent magnetic core reactance or a three-phase common magnetic core structure reactance; Figure 3.1 The capacitor 45 and Figure 3.2 The middle capacitor 47 is composed of three groups of AC non-polarized capacitors, which can be connected in a star (Y) or triangle (△) structure.

[0047] The grid-side power unit 3, the rotor main converter 5, the rotor auxiliary converter 6 and the stator auxiliary converter 7 all adopt a three-phase bridge voltage source structure. Figure 4 , Figure 5 , Figure 6 and Figure 7 shown.

[0048] Figure 4T31, T32, T33, T34, T35, T36 represent power electronic devices IGBT, D31, D32, D33, D34, D35, D36 are power diodes, which can be independent diodes or IGBT device integrated diodes. Figure 4 The power electronic devices involved may be discrete devices or power electronic devices included in an all-in-one module. Figure 5 T51, T52, T53, T54, T55, T56 represent power electronic devices IGBT, D51, D52, D53, D54, D55, D56 are power diodes, which can be independent diodes or IGBT device integrated diodes. Figure 5 The power electronic devices designed in the invention can be discrete devices or power electronic devices included in an all-in-one module. Figure 6 T61, T62, T63, T64, T65, and T66 represent power electronic devices IGBT, and D61, D62, D63, D64, D65, and D66 are power diodes, which can be independent diodes or IGBT device integrated diodes. Figure 6 The power electronic devices designed in the invention can be discrete devices or power electronic devices included in an all-in-one module. Figure 7 T71, T72, T73, T74, T75, and T76 represent power electronic devices IGBT, and D71, D72, D73, D74, D75, and D76 are power diodes, which can be independent diodes or IGBT device integrated diodes. Figure 7 The power electronic devices designed in the system can be discrete devices or power electronic devices included in all-in-one modules.

[0049] like Figure 8 As shown, a long-line filter 11 structure is provided. The long-line filter 11 is connected in series on the AC side of the rotor main converter 5 to suppress the rotor end overvoltage caused by the reflection of the long-line transmission wave. At the same time, the long-line filter 11 can suppress the shaft voltage and shaft current.

[0050] The doubly-fed generator 2 is controlled by the rotor main converter 5 and the rotor auxiliary converter 6 through the rotor winding. Fig. 9 and Fig.10 As shown:

[0051] like Fig. 9As shown, when the power grid is stable, the rotor main converter 5 operates in the unity power factor state to control the active power of the rotor circuit of the doubly fed generator 2; the rotor auxiliary converter 6 controls the reactive power of the rotor circuit of the doubly fed generator 2. At the same time, the rotor auxiliary converter 6 suppresses and buffers the grid-connected power pulsation of the wind turbine through the doubly fed generator stator 22 and the doubly fed generator rotor 21, the rotor main converter 5 and the grid-side power unit 3. At this time, the corresponding power flow is Fig. 9 In this state, the energy storage unit 8 plays a role in buffering the grid-connected power pulsation. Fig.10 As shown, when the state of the power grid changes, according to the electromagnetic state of the doubly fed generator 2, the rotor main converter 5, the rotor auxiliary converter 6 and the stator auxiliary converter 7 are coordinated and controlled, with three purposes: the energy storage unit 8 provides necessary active power support to the power grid through the rotor auxiliary converter 6, the doubly fed generator rotor 21, the rotor main converter 5, the grid-side power unit 3, the grid-side filter unit 4, and the grid access unit 1; the rotor main converter 5 and the rotor auxiliary converter 6 control the electromagnetic transient state of the doubly fed generator 2 caused by the grid disturbance to the maximum extent, and realize the inertia simulation control of the doubly fed generator set according to the set strategy requirements; in the case of a fault, the stator auxiliary converter 7 is controlled to compensate for the main winding flux, so that the stator transient flux is reduced, thereby suppressing the rotor transient electromotive force and improving the transient control capability of the doubly fed generator 2. This control process is Fig.10 Since the voltage applied to the doubly-fed generator rotor 21 is the sum of the output voltages of the rotor main converter 5 and the rotor auxiliary converter 6, the converter topology has a stronger voltage output capability, thereby effectively controlling the electromagnetic transient state of the doubly-fed generator 2 and improving its own grid adaptability.

[0052] The present invention achieves the unification of the grid support of the doubly-fed wind turbine and its own grid adaptability by taking into account the dual functions of accessing the energy storage unit 8 and improving the transient control capability of the doubly-fed generator 2 through the rotor auxiliary converter 6, and realizes the direct integration of the energy storage unit 8 without the need for a DC / DC converter, thereby reducing the cost and manufacturing complexity of the converter system and improving the operating efficiency of the converter system; the voltage required by the doubly-fed generator 2 is jointly provided by the rotor main converter 5 and the rotor auxiliary converter 6, which can increase the voltage supply capacity, thereby better controlling the rotor side current of the doubly-fed generator 2 and better controlling the doubly-fed generator 2.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double-fed generator converter circuit with strong grid adaptability, characterized in that: The invention comprises a grid access unit (1), a doubly-fed generator (2), a grid-connected converter, a rotor main converter (5), a rotor auxiliary converter (6), a stator auxiliary converter (7), an energy storage unit (8), a first capacitor (9), and a second capacitor (10); the doubly-fed generator (2) comprises a doubly-fed generator rotor (21) and a doubly-fed generator stator (22); the doubly-fed generator rotor (21) comprises a three-phase winding, and both ends of each phase winding are led out to form two groups of three-phase terminals; the doubly-fed generator stator (22) comprises two sets of three-phase windings, and the two sets of windings have no electrical connection and no magnetic coupling; the grid access unit (1) comprises three ports; the first port (12) of the grid access unit (1) is connected to the three-phase grid, the second port (13) of the grid access unit (1) is connected to the main winding of the doubly-fed generator stator (22), and the grid access unit (1) The third port (14) is connected to the AC side of the grid-connected converter, and the DC side of the grid-connected converter is connected to the DC side of the rotor main converter (5); the first capacitor (9) is connected in parallel between the DC side of the grid-connected converter and the DC side of the rotor main converter (5); the AC side of the rotor main converter (5) is connected to one group of three-phase terminals of the doubly fed generator rotor (21); the other group of three-phase terminals of the doubly fed generator rotor (21) is connected to the AC side of the rotor auxiliary converter (6); the three-phase terminals of the secondary winding of the doubly fed generator stator (22) are connected to the AC side of the stator auxiliary converter (7); the DC sides of the rotor auxiliary converter (6) and the stator auxiliary converter (7) are connected to the energy storage unit (8); and the second capacitor (10) is connected in parallel between the DC sides of the rotor auxiliary converter (6) and the stator auxiliary converter (7) and the energy storage unit (8).

2. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The double-fed generator conversion circuit also includes a long-line filter (11), the AC side of the rotor main converter (5) is connected to one end of the long-line filter (11), and the other end of the long-line filter (11) is connected to one group of three-phase connection terminals of the double-fed generator rotor (21).

3. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The grid-connected converter comprises a grid-side power unit (3) and a grid-side filter unit (4); a first port (41) of the grid-side filter unit (4) is connected to a third port (14) of a grid access unit (1), and a second port (42) of the grid-side filter unit (4) is connected to an AC side of the grid-side power unit (3); and a DC side of the grid-side power unit (3) is connected to a DC side of a rotor main converter (5).

4. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The energy storage unit (8) is a battery or a super capacitor or a combination of the two.

5. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The first capacitor (9) and the second capacitor (10) are electrolytic capacitors or film capacitors.

6. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: A transformer is provided between each two ports of the three ports of the grid access unit (1), or no transformer is provided.

7. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The second port (13) and the third port (14) of the power grid access unit (1) are both controlled on and off by relays.

8. The double-fed generator converter circuit with strong grid adaptability according to claim 1, characterized in that: The grid-side filtering unit (4) adopts one of three-phase LCL type, three-phase LC type or three-phase L type filter.

9. The double-fed generator converter circuit with strong grid adaptability according to claim 3, characterized in that: The grid-side power unit (3), the rotor main converter (4), the rotor auxiliary converter (6) and the stator auxiliary converter (7) all adopt a three-phase bridge voltage source structure.

10. A control method for a doubly-fed generator converter circuit with strong grid adaptability according to any one of claims 1 to 9, characterized in that: The rotor main converter (5) controls the active power on the rotor side of the doubly fed generator (2) during steady-state operation, and the rotor auxiliary converter (6) controls the reactive power on the rotor side of the doubly fed generator (2). At the same time, the rotor auxiliary converter (6) also buffers the grid-connected power pulsation through the stator winding end of the doubly fed generator (2), the rotor main converter (5) and the grid-connected converter, so as to smooth the grid-connected power. When an abnormality occurs in the power grid or the state of the power grid changes, the rotor main converter (5), the rotor auxiliary converter (6) and the stator auxiliary converter (7) cooperate to control the electromagnetic transient state of the doubly fed generator (2), and at the same time, the energy storage unit (8) provides active power control to the power grid through the rotor auxiliary converter (6), the rotor main converter (5), the grid-connected converter and the power grid access unit (1), and together with the inertial energy storage of the doubly fed generator (2), active control of the power grid frequency is achieved.

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