Direct current networking wind power generator system and control method thereof

Abstract

The application discloses a direct-current networking wind generator system and a control method thereof, adopts decentralized and decentralized power generation control, and comprises a wind generator set, a generator controller, an energy storage battery system and a PCS converter; the wind generator set adopts a doubly salient direct-current excitation generator assembly; the generator controller can convert three-phase alternating current output by the doubly salient direct-current excitation generator assembly into high-voltage direct-current shaft voltage through a full-bridge diode rectification filter circuit, and an additional machine end inverter is not needed; each generator controller is connected with one wind generator set, and a plurality of generator controllers are connected in parallel through a direct-current bus. The direct-current voltage output by the doubly salient direct-current excitation generator assembly can automatically follow the common direct-current bus voltage and keep dynamic stability, and will not fluctuate with the dynamic change of the wind turbine speed; the current backflow phenomenon and the crosstalk problem can be effectively avoided, and the wind turbine industry multi-machine direct-current networking demand is perfectly met.

Description

Technical Field

[0001] This invention relates to the field of new energy wind power generation technology, and in particular to a DC grid-connected wind turbine generator system and its control method. Background Technology

[0002] Currently, all permanent magnet wind turbines of various specifications worldwide, regardless of power output, follow the same power conversion and grid connection process. First, the three-phase AC power generated by the generator is directly converted into DC power by a full-bridge inverter composed of six IGBTs. Then, it is immediately converted back into AC power by the grid-side converter PCS, ultimately enabling grid connection and power supply.

[0003] The aforementioned permanent magnet wind turbines suffer from two major technical defects that hinder the realization of multi-generator DC grid connections. First, the permanent magnet wind turbines incorporate rare-earth magnets, creating a constant magnetic field. The DC voltage output through the turbine-side inverter varies significantly with the generator speed (affected by wind speed). At higher wind speeds, the generator speed increases, and the generated voltage increases accordingly; at lower wind speeds, the generator speed decreases, and the generated voltage decreases accordingly. Because of the differences in the DC voltage output of each permanent magnet wind turbine, their turbine-side inverters cannot be directly connected in parallel. Otherwise, a phenomenon known as "current backflow" would occur, where a higher-voltage turbine charges a lower-voltage turbine, severely impacting system operational safety. Second, under different wind speed conditions, the DC power output of each permanent magnet wind turbine fluctuates significantly and is extremely unstable. Directly inputting this highly volatile DC power into the grid-side PCS converter, and then converting it into AC power for grid connection, would impact the AC grid. This unstable power is referred to in the industry as "garbage electricity," affecting the quality of power supply.

[0004] Based on this, the wind turbine industry generally has a clear technical requirement: to connect the fluctuating DC power and DC voltage output from multiple wind turbines into a DC grid, and then combine them into a common DC bus to form an average and stable DC power. This smoothed DC power is then inverted and connected to the grid through a single grid-side converter (PCS), which avoids current backflow and reduces the impact on the power grid.

[0005] From a circuit principle perspective, one existing solution involves adding a mature DC / DC converter to the DC output terminal of the inverter at each wind turbine. This DC / DC converter provides isolation and voltage regulation, ensuring that even when the DC voltage output from the turbine inverter fluctuates within a certain range, the DC voltage output from the DC / DC converter remains constant and consistent. This allows the DC outputs of multiple wind turbines' DC / DC converters to be combined via a common DC bus, and the smoothed DC power to be fed into a grid-side converter (PCS) for grid connection. However, this solution suffers from significant commercial application bottlenecks. Each wind turbine requires a full-power DC / DC converter, leading to a substantial increase in system cost. Furthermore, the associated cooling system is overly complex, hindering large-scale commercial application.

[0006] The invention patent CN103023067B discloses a direct-drive wind power generation system based on a common DC bus. It adds a power direction control switch module between the generator-side inverter and the common DC bus. This module includes a high-power feed diode, a bypass switch, and a special power direction control circuit, which is equivalent to a simplified DC / DC converter circuit. Theoretically, this can reduce system costs, but it still does not completely solve the core problems of cost and structural complexity. Summary of the Invention

[0007] The purpose of this invention is to provide a DC grid-connected wind turbine generator system and its control method to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a DC grid-connected wind turbine generator system, which adopts a distributed, decentralized power generation control, including multiple wind turbine generator sets, multiple generator controllers, an energy storage battery system, and a PCS converter;

[0009] The wind turbine generator set adopts a double salient pole DC excitation generator assembly to convert wind power into three-phase AC power;

[0010] The generator controller is used to control the wind turbine generator set to generate DC power, and converts the three-phase AC power output from the doubly salient pole DC excitation generator assembly into high-voltage DC shaftless voltage through a full-bridge diode rectifier and filter circuit. The output terminal of the generator controller is connected to a DC bus, and the DC voltage at the output terminal of the generator controller can actively follow the voltage change of the DC bus. Each generator controller is connected to one wind turbine generator set, and multiple generator controllers are connected in parallel through the DC bus without crosstalk.

[0011] The PCS converter is used to convert the DC power generated by the wind turbine generator into AC power through the DC bus and then input it at a single point to supply power to the load or to the grid.

[0012] Further optimization involves the energy storage battery system comprising one or more energy storage battery modules, with multiple energy storage battery modules directly connected in parallel via the DC bus.

[0013] In a further optimization, the energy storage battery system is directly connected to the DC bus to provide a basic dynamic operating voltage for the DC bus. The energy storage battery system can store the DC power converted by the generator controller and can release the stored DC power to the DC bus.

[0014] Further optimization includes a double salient pole DC excitation generator assembly and wind turbine blades for driving the double salient pole DC excitation generator assembly to rotate. The wind turbine generator set includes, but is not limited to, a three-bladed horizontal axis conventional wind turbine, a three-bladed horizontal axis wind-concentrating shroud wind turbine, an H-type vertical axis wind turbine, and other irregularly shaped vertical axis wind turbines.

[0015] Further optimization is made to include, but is not limited to, 400Vdc, 600Vdc, 800Vdc and 1200Vdc for the rated voltage of the DC bus.

[0016] The present invention also provides a control method for a DC grid-connected wind turbine system, which, based on the above-described DC grid-connected wind turbine system, includes the following steps:

[0017] Step 1, Start-up and wake-up judgment: The generator controller monitors the rotational speed of the doubly salient pole DC excitation generator assembly of the wind turbine generator set in real time. When the rotational speed of the doubly salient pole DC excitation generator assembly reaches the start-up speed, the generator controller is woken up and enters the power generation control process; when the rotational speed of the doubly salient pole DC excitation generator assembly is insufficient, the generator controller remains in a powered sleep state, maintaining zero DC excitation current, so that the doubly salient pole DC excitation generator assembly can rotate freely.

[0018] Step 2, Bus voltage detection and branching: When the generator controller is awakened, it reads the voltage of the DC bus and compares it with the starting voltage of the doubly salient pole DC excitation generator assembly. Based on the comparison result, different control branches are executed.

[0019] Step 3, High Voltage Branch Control: When the DC output voltage Vbus of the generator controller is detected to be higher than the starting voltage of the doubly salient pole DC excitation generator assembly, the generator controller sets Vbus as the next voltage follow-up control target and follows the control target to enter the power follow-up generation control strategy to generate electricity.

[0020] Step 4, Power Follow-up Generation Control: During the power follow-up generation control process, if the DC output voltage Vbus of the generator controller is detected to exceed the maximum allowable voltage, the generator controller sets the DC excitation current of the doubly salient pole DC excitation generator assembly to 0, stops power generation, and allows the wind turbine generator set to enter a free-rotation state; if Vbus does not exceed the maximum allowable voltage, the generator controller calculates the target generation current It based on the target terminal voltage and enters the wind turbine maximum power follow-up generation mode under constant voltage target.

[0021] Step 5, Speed ​​Monitoring and Braking Control: During maximum power following generation, if the speed of the doubly salient pole DC excitation generator assembly does not exceed the braking speed, the generator controller enters closed-loop control to continuously maintain the maximum power following generation mode; if the speed of the doubly salient pole DC excitation generator assembly exceeds the braking speed, the generator controller enters braking control mode to rapidly reduce the speed of the wind turbine generator set.

[0022] Step 6, Low-voltage branch pre-charge control: When the DC output voltage Vbus of the generator controller is detected to be lower than the starting voltage of the salient-pole DC excitation generator, the generator controller enters the residual magnetization generation mode of the double salient-pole DC excitation generator assembly with the pre-charge voltage as the target, pre-charges the filter capacitor until Vbus is higher than the pre-charge voltage, and then re-enters the maximum power follower mode under constant voltage generation state.

[0023] Further optimization is achieved by refining the control logic for the wind turbine maximum power following the power generation mode under the constant pressure target in step 4 as follows:

[0024] (1) When the actual generated voltage is higher than the target voltage, the generator controller reduces the DC excitation current to reduce the generated current of the doubly salient pole DC excitation generator assembly;

[0025] (2) When the actual generated voltage is lower than the target voltage, the generator controller increases the DC excitation current to increase the generated current of the doubly salient pole DC excitation generator assembly.

[0026] Further optimization is achieved by including the following braking control modes in step 5:

[0027] 1) The generator controller rapidly increases the power generation to the peak power, causing the power generation current of the doubly salient pole DC excitation generator assembly to increase sharply to the peak current. The generator controller then enters closed-loop control, causing the wind turbine generator speed to decrease rapidly.

[0028] 2) The generator controller issues a braking command to activate the electromagnetic braking device and lock the wind turbine generator set;

[0029] 3) The generator controller enters a energized sleep state and waits for the speed of the doubly salient pole DC excitation generator assembly to recover to the starting conditions before waking up again.

[0030] In a further optimization, in step 6, when the DC output voltage Vbus of the generator controller is detected to be lower than the starting voltage of the doubly salient pole DC excitation generator assembly, it is determined that the energy storage battery system on the DC bus is missing or disconnected, and the other wind turbine generators on the DC bus are not in DC power generation state.

[0031] In a further optimization, in step 6, the generator controller performs constant voltage pre-charge closed-loop control in residual magnetism power generation mode until the DC output voltage Vbus of the generator controller is higher than the pre-charge voltage.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This DC grid-connected wind turbine system consists of a wind turbine generator set with a doubly salient pole DC excitation generator assembly and a matching generator controller. Multiple generator assemblies are connected in parallel via a DC bus. The generator controller controls the magnitude of the DC excitation current, dynamically adjusting the magnetic field strength of the generator, and thus enabling closed-loop regulation of the DC generation voltage at different generator speeds. The three-phase AC output from the doubly salient pole DC excitation generator assembly can be directly converted into high-voltage DC shaftless voltage through a simple full-bridge diode rectifier and filter circuit, eliminating the need for an additional turbine-side inverter. By controlling the excitation current in a closed loop, the DC voltage output from the doubly salient pole DC excitation generator assembly automatically follows the common DC bus voltage, maintaining dynamic stability and preventing fluctuations with changes in wind turbine speed. Simultaneously, the full-bridge diode rectifier circuit has unidirectional conduction characteristics, allowing the outputs of multiple generator controllers to be directly connected in parallel via the DC bus, effectively avoiding current backflow and crosstalk problems. This perfectly aligns with the multi-unit DC grid-connected requirements of the wind turbine industry and the industry's development direction of grid-connected wind turbine units. Furthermore, its simple structure and controllable cost make it suitable for commercial applications.

[0034] The control method of smoothing the power supply curve through DC grid-connected current collection enables the DC grid-connected wind turbine system to adopt decentralized power generation control. Each wind turbine can autonomously control its power generation voltage and DC power generation current. Any one or more wind turbines can be dynamically connected to or disconnected from the DC bus without affecting the stable operation of the DC grid-connected wind turbine system. This effectively solves the problem of drastic fluctuations in the power generation of a single wind turbine when it is independently connected to the grid with changes in wind speed. At the same time, it solves the problems of random dynamic parallel connection and use of multiple wind turbine power generation systems under decentralized control of DC grid connection.

[0035] This DC grid-connected wind turbine system and its control method can effectively smooth the power and voltage fluctuations of multiple wind turbines caused by wind speed changes. After averaging, it outputs high-quality and stable green electricity to directly supply user loads or power the grid. It can improve the power generation of wind turbines at low wind speeds and features high integration, simple maintenance and high reliability. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the DC grid-connected wind turbine generator system disclosed in this invention;

[0037] Figure 2 This is a schematic diagram of the equivalent structure of the decentralized multi-wind turbine control system used in the DC grid-connected wind turbine power generation system disclosed in this invention.

[0038] Figure 3 This is a simplified flowchart illustrating the control method for DC grid-connected doubly salient pole wind turbine generators disclosed in this invention.

[0039] Figure reference numerals: 1-Double salient pole DC excitation generator assembly, 2-Generator controller, 3-Wind turbine blade, 4-PCS converter, 5-DC bus, 6-Energy storage battery system. Detailed Implementation

[0040] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0041] like Figure 1 and Figure 2 As shown, this application discloses a DC grid-connected wind turbine generator system. The DC grid-connected wind turbine generator system adopts a distributed, decentralized power generation control, including multiple wind turbine generator sets, multiple generator controllers 2, an energy storage battery system 6, and a PCS converter 4.

[0042] The wind turbine generator set adopts a doubly salient pole DC excitation generator assembly 1, which is used to convert wind power into three-phase AC power;

[0043] Generator controller 2 is used to control the wind turbine generator set to generate DC power, and converts the three-phase AC power output from the doubly salient pole DC excitation generator assembly 1 into high-voltage DC shaftless voltage through a full-bridge diode rectifier and filter circuit. The output terminal of generator controller 2 is connected to DC bus 5. The DC voltage at the output terminal of generator controller can actively follow the voltage change of DC bus 5. Each generator controller 2 is connected to a wind turbine generator set. Multiple generator controllers 2 are connected in parallel through DC bus 5 without crosstalk.

[0044] PCS converter 4 is used to convert the DC power generated by the wind turbine generator set into AC power through the DC bus 5 and then input it at a single point to supply power to the load or the grid.

[0045] In this application, the DC grid-connected wind turbine system employs distributed, decentralized power generation control. Each wind turbine autonomously controls its generation voltage and DC current, ensuring the reliability and stability of the system's operation. It allows any one or more wind turbines to dynamically connect to or disconnect from the DC bus without affecting the system's stable operation. The system includes wind turbines, generator controllers 2, PCS converters 4, DC bus 5, and an energy storage battery system 6. Each wind turbine and its corresponding generator controller 2 are integrated to form an independent generator assembly. This assembly directly generates DC current following the voltage of the DC bus 5. Multiple generator assemblies are combined via the DC bus 5 formed after DC grid connection, and the averaged DC power provides a smooth DC power supply curve for the PCS converter 4, improving the stability of the system after grid connection.

[0046] The wind turbine generator set employing the doubly salient pole DC excitation generator assembly 1 can convert wind energy into mechanical kinetic energy. Then, relying on changes in magnetic reluctance and electromagnetic induction, the mechanical kinetic energy is converted into electrical energy. Through the conduction of the three-phase armature windings of the stator, the combined effect of alternating magnetic flux and magnetic field cutting, along with the distribution of the three-phase armature windings, generates a three-phase alternating electromotive force, ultimately outputting three-phase alternating current. Furthermore, the adjustable excitation current characteristic of the doubly salient pole DC excitation generator assembly 1 provides the hardware foundation for the core strategies of voltage following, power following, and braking control in this application, adapting to the dynamic control requirements of DC grid-connected wind power generation systems.

[0047] The generator controller 2, with its built-in full-bridge diode rectifier and filter circuit, is the core control and power conversion unit of the wind turbine generator set. It enables full-process control of the wind turbine generator set's power generation, ensuring that the wind turbine generator set completes DC power generation according to a preset strategy. Simultaneously, it rectifies and filters the three-phase AC power output from the doubly salient pole DC excitation generator assembly 1. The generator controller 2 dynamically adjusts the generator's magnetic field strength by controlling the magnitude of the DC excitation current, achieving closed-loop control of the DC power generation current at different speeds. It can convert the three-phase AC power output from the doubly salient pole DC excitation generator assembly 1 into high-voltage DC shaftless voltage through the full-bridge diode rectifier and filter circuit, eliminating the need for an inverter. The output of the generator controller 2 is directly connected to the DC bus 5, and the DC voltage at the generator controller 2's output has an active following characteristic, dynamically and adaptively adjusting to follow the voltage of the DC bus 5. This ensures that the output voltage of the generator controller 2 matches and is linked to the voltage of the DC bus 5, and does not change with the wind turbine generator set's speed. Furthermore, utilizing the unidirectional conduction characteristic of the full-bridge diode rectifier circuit allows the output terminals of multiple generator controllers 2 to be connected in parallel via the DC bus 5. This effectively blocks reverse current and voltage interference between the output terminals of each generator controller 2, ensuring that the DC output terminals of multiple generator controllers 2 can be directly connected in parallel via the DC bus 5. Each generator controller 2 independently completes power rectification and output control, with no electrical crosstalk between them, guaranteeing the operational independence and system stability when multiple generator assemblies are connected in DC. That is, when one generator assembly is not generating power, the DC power generated by other generator assemblies connected to the same DC bus 5 will not flow back into the non-generating generator assembly.

[0048] PCS converter 4 serves as the core unit for AC-DC conversion in this DC grid-connected wind power generation system. Its input terminal is connected to DC bus 5, receiving DC power generated by multiple wind turbine generators and integrated through DC bus 5, achieving single-point input. PCS converter 4 completes the DC-to-AC conversion through an inverter topology. The converted AC power can be flexibly output according to actual needs to provide AC power to the load, and can be directly connected to the grid to achieve power supply, completing the power form conversion and external power supply of the entire wind power generation system.

[0049] The energy storage battery system 6 can be directly connected to the DC bus 5 to provide the DC bus 5 with a basic dynamic working voltage. It can directly store the DC peak power generated by the DC grid wind turbine system under strong winds, and release the stored energy to the DC bus 5 when the wind speed is low or there is no wind, thus achieving a smooth power supply curve.

[0050] For example, multiple wind turbine generators, due to their distance from each other, generally experience significant differences in wind speed. Some have very low wind speeds and low power generation, while others have very high wind speeds and high power generation, with the power generation varying drastically with changes in wind speed. Since each generator controller 2 controls its actual generated voltage to a target voltage consistent with the DC bus 5, the generated current at different power levels can directly converge onto the DC bus 5 without crosstalk issues. Finally, the DC bus 5 receives the average total DC generated current, which is input to the grid-side PCS converter 4 for inverter output of stable and smooth AC power.

[0051] If all wind turbines experience strong winds and high speeds simultaneously under extreme weather conditions, the peak DC power generated will exceed the rated input power range of the grid-side PCS converter 4 after flowing into DC bus 5. In this case, the energy storage battery 6 will store the excess power, ensuring that the grid-side PCS converter 4 can stably and continuously output a smooth AC rated power. If all wind turbines experience weak winds and low speeds simultaneously, the very small DC power generated will be far lower than the rated power output requirement of the grid-side PCS converter 4 after flowing into DC bus 5. In this case, the energy storage battery 6 will release the stored energy to compensate for the insufficient DC power generated by the wind turbines, ensuring that the grid-side PCS converter 4 can stably and continuously output a rated AC power, achieving a peak shaving and valley filling buffering effect.

[0052] like Figure 1 As shown, in one embodiment of this application, the energy storage battery system 6 includes one or more energy storage battery modules. The multiple energy storage battery modules are directly connected in parallel through the DC bus 5, defining the dynamic operating voltage of the DC bus 5. The peak DC power generated by the wind turbine generator under strong winds is directly stored, and the stored energy is released to the DC bus 5 when the wind speed is low or there is no wind, supplementing the power supply of the DC bus 5. This effectively smooths the fluctuation of the bus power supply caused by changes in wind conditions, realizes the smooth and stable power supply curve of the DC bus, and ensures the continuous and stable input of the downstream PCS converter 4.

[0053] Furthermore, the energy storage battery system 6 is directly connected to the DC bus 5, serving as the voltage support unit for the DC bus 5. It provides the DC bus 5 with a basic dynamic operating voltage, ensuring that the bus voltage remains within a preset range during system operation. The energy storage battery system 6 can store the DC power converted by the generator controller 2, realizing the recovery and storage of surplus wind power; and it can release the stored DC power to the DC bus 5, working with the generator assembly to achieve a balance between the supply and demand of power on the bus, supporting the stable operation of this DC grid-connected wind turbine generator system.

[0054] In another embodiment of this application, the wind turbine generator set includes a doubly salient pole DC excitation generator assembly 1 and a wind turbine blade 3 for driving the doubly salient pole DC excitation generator assembly 1 to rotate. The wind turbine generator set includes, but is not limited to, a conventional three-blade horizontal axis wind turbine generator, a three-blade horizontal axis wind-concentrating shroud wind turbine generator, an H-type vertical axis wind turbine generator, and other irregularly shaped wind turbine generators with other structural forms.

[0055] Among them, the wind turbine blades 3, as wind energy capture components, convert wind energy into mechanical rotational power through wind capture rotation, and directly drive the rotor of the double salient pole DC excitation generator assembly 1 to rotate, providing the mechanical power basis for power generation. The structural form of the wind turbine generator set is not limited, including but not limited to traditional three-bladed horizontal axis wind turbine generators, three-bladed horizontal axis wind-concentrating shroud wind turbine generators, H-type vertical axis wind turbine generators, and other irregularly shaped wind turbine generators. All types of wind turbine generator sets can be adapted to the control strategy and grid requirements of this DC grid wind power generation system, and have good system adaptability and structural scalability.

[0056] In another embodiment of this application, the rated voltage of the DC bus 5 includes, but is not limited to, 400Vdc, 600Vdc, 800Vdc and 1200Vdc. It can be adapted and selected according to the configuration quantity of wind turbine generators, power generation, capacity of energy storage battery system 6 and inverter requirements of PCS converter 4, to meet the voltage matching requirements of DC grid wind power generation systems of different scales, realize flexible selection of system installed capacity, power supply scenario and equipment adaptability, and ensure voltage matching and efficient power transmission between system units.

[0057] like Figure 2 As shown, in another embodiment of this application, based on the structure of the aforementioned DC grid-connected wind turbine system, DC distributed resistors R1, R2, ..., Rn (n = 1, 2, ..., N, where N is a natural number) are set on the DC bus 5. The number of DC distributed resistors is consistent with the number of wind turbine generators, i.e., one DC distributed resistor is configured for each wind turbine generator. Before multiple wind turbine generators are remotely connected to the energy storage battery system 6 and the grid-side PCS converter 4 via the DC bus 5, the base voltage of the DC bus 5 is determined by the charging state of the energy storage battery system 6. However, the DC distributed resistors R1, R2, ..., Rn (n = 1, 1, ..., N) on the DC bus 5 will generate a large voltage drop. Furthermore, due to the differences in the distance between each wind turbine generator and the energy storage battery system 6 and the PCS converter 4, the corresponding DC distributed resistor values ​​are also different, resulting in differences in the voltage drop generated by each DC distributed resistor.

[0058] The aforementioned voltage drop differences result in significant differences in the dynamic voltages Vbus-1, Vbus-2, …, Vbus-N of the DC bus 5 actually detected by each generator controller 2, following the rule that "the farther away from the energy storage battery system 6, the higher the corresponding dynamic voltage Vbus-i" (where i=1,2,…,N, corresponding to each generator controller 2). Each generator controller 2 sets its own dynamically detected DC bus 5 actual voltage Vbus-i as its DC power generation constant voltage control target. Subsequently, based on this constant voltage target Vbus-i, it calculates the target DC power generation current It under the rated power generation Pe; and based on the real-time speed RPM change of the doubly salient pole DC excitation generator assembly 1, it dynamically adjusts the magnitude of the DC excitation current, thereby achieving precise control of the target DC power generation current It.

[0059] Through the above control method, the actual power generation of each wind turbine can directly follow the real-time wind capture capability of the turbine blades 3 to generate electricity. It is not affected by the operating status of other wind turbines connected in parallel on the DC bus 5, thus realizing the decentralized control of the system. At the same time, it does not rely on the centralized scheduling of any generator controller 2, thus realizing the decentralized control of the system. This effectively improves the operational independence, stability and anti-interference capability of the DC grid wind power generation system.

[0060] Furthermore, when a wind turbine is completely unable to generate electricity due to lack of wind (speed is 0), it is in a non-generating state under dynamic connection while powered on. At this time, the corresponding generator controller 2 controls the excitation current of the doubly salient pole DC excitation generator assembly 1 to 0A. The wind turbine blades 3 and the rotor of the doubly salient pole DC excitation generator assembly 1 are in a free-rotating state, without any power output. Based on the distributed control and decentralized design of this DC grid wind power generation system, wind turbines in a non-generating state will not affect the voltage stability of the DC bus 5, nor will they interfere with the normal power generation operation of other wind turbines in the DC grid wind power generation system. Each wind turbine can still independently follow the dynamic voltage of the DC bus 5 it detects and complete power generation control according to a preset strategy, ensuring the stable operation of the entire DC grid wind power generation system.

[0061] like Figure 3 As shown, the present invention also provides a control method for a DC grid-connected wind turbine system, which, based on the DC grid-connected wind turbine system, includes the following steps:

[0062] Step 1, Start-up and wake-up judgment: The generator controller 2 monitors the rotational speed of the doubly salient pole DC excitation generator assembly 1 of the wind turbine generator set in real time. When the rotational speed of the doubly salient pole DC excitation generator assembly 1 reaches the start-up speed, the generator controller 2 is woken up and enters the power generation control process; when the rotational speed of the doubly salient pole DC excitation generator assembly 1 does not reach the start-up speed (insufficient speed), the generator controller 2 remains in a powered sleep state, does not start the power generation control process, maintains zero DC excitation current, and allows the doubly salient pole DC excitation generator assembly to rotate freely.

[0063] Step 2, Bus voltage detection and branching: When the generator controller 2 is awakened, it immediately reads the real-time voltage of the DC bus 5 and compares it with the preset starting voltage of the doubly salient pole DC excitation generator assembly 1. Based on the comparison result, different control branches are executed.

[0064] Step 3, High Voltage Branch Control: When the DC output voltage Vbus of the generator controller 2 is detected to be higher than the starting voltage of the doubly salient pole DC excitation generator assembly 1, the generator controller 2 sets the detected Vbus as the next voltage follow control target and follows the control target to enter the power follow generation control strategy to generate electricity.

[0065] Step 4, Power Follow-up Generation Control: During the power follow-up generation control process, the generator controller 2 monitors its own DC output voltage Vbus in real time. If it detects that Vbus exceeds the maximum allowable voltage, the generator controller 2 immediately sets the DC excitation current of the doubly salient pole DC excitation generator assembly 1 to 0A, stops the generation operation, and allows the wind turbine generator set to enter a free rotation state. If it detects that Vbus does not exceed the maximum allowable voltage, the generator controller 2 calculates the target generation current It under the rated generation power according to the set target terminal voltage, and enters the wind turbine maximum power follow-up generation mode under constant voltage target.

[0066] Step 5, Speed ​​Monitoring and Braking Control: During the maximum power following generation process under constant voltage target, generator controller 2 continuously monitors the real-time speed of the doubly salient pole DC excitation generator assembly 1; if the speed of the doubly salient pole DC excitation generator assembly 1 does not exceed the preset braking speed, generator controller 2 enters closed-loop control and continuously maintains the maximum power following generation mode; if the speed of the doubly salient pole DC excitation generator assembly 1 exceeds the braking speed, generator controller 2 immediately enters braking control mode, causing the wind turbine generator speed to decrease rapidly, and generator controller 2 enters energized sleep state, waiting for the wind turbine generator speed to recover to the starting conditions before being reawakened;

[0067] Step 6, Low-voltage branch pre-charge control: When the detected DC output voltage Vbus of generator controller 2 is lower than the starting voltage of salient pole DC excitation generator 1, generator controller 2 takes the pre-charge voltage as the control target and directly enters the residual magnetization generation mode of the double salient pole DC excitation generator assembly 1 to perform pre-charge operation on the filter capacitor in the DC grid wind turbine generator system until generator controller 2 detects that its own terminal voltage is higher than the preset pre-charge voltage, then stops pre-charging, and then re-enters the maximum power follow mode under constant voltage generation state to start the normal power generation process.

[0068] Based on the above-mentioned DC grid-connected wind turbine system control method, in another embodiment of this application, in step 4 above, the control logic for the wind turbine maximum power following generation mode under constant pressure target is as follows:

[0069] (1) When the actual generated voltage of the doubly salient pole DC excitation generator assembly 1 is higher than the target voltage set by the generator controller 2, the generator controller 2 reduces the DC excitation current output to the doubly salient pole DC excitation generator assembly 1. By reducing the excitation current, the excitation magnetic field strength inside the doubly salient pole DC excitation generator assembly 1 is reduced, thereby reducing the generated current of the doubly salient pole DC excitation generator assembly 1, so that the actual generated voltage drops back to the target voltage and constant voltage control is maintained.

[0070] (2) When the actual generated voltage of the doubly salient pole DC excitation generator assembly 1 is lower than the target voltage set by the generator controller 2, the generator controller 2 automatically increases the DC excitation current output to the doubly salient pole DC excitation generator assembly 1. By increasing the excitation current, the excitation magnetic field strength inside the doubly salient pole DC excitation generator assembly 1 is enhanced, thereby increasing the generated current of the doubly salient pole DC excitation generator assembly 1 and raising the actual generated voltage to the target voltage, thus realizing constant voltage closed-loop regulation.

[0071] Through the above closed-loop control logic, the actual dynamic DC power generation of each wind turbine generator set can accurately follow the real-time wind capture capability of the wind turbine blade 3 to achieve maximum power output, while ensuring the voltage stability of the DC bus 5, and adapting to the distributed and decentralized control requirements of the DC grid wind turbine generator system.

[0072] Based on the above-described DC grid-connected wind turbine system control method, in another embodiment of this application, the braking control mode in step 5 specifically includes:

[0073] 1) When the generator controller 2 detects that the rotational speed of the doubly salient DC excited generator assembly 1 exceeds the preset braking speed, the generator controller 2 immediately and rapidly increases the power generation of the doubly salient DC excited generator assembly 1 to the peak power preset by the system, and simultaneously makes the generated current of the doubly salient DC excited generator assembly 1 rise sharply to the peak current; subsequently, the generator controller 2 enters the closed-loop cycle control. By maintaining the peak power output and utilizing the damping effect of the power generation load, the rotational speed of the wind turbine generator set is rapidly reduced to achieve preliminary deceleration braking.

[0074] 2) After the rotational speed of the wind turbine generator set drops within the safe range, the generator controller 2 issues a braking control command, and the electromagnetic braking device supporting the control system is started. The wind turbine generator set is locked through electromagnetic braking to achieve complete braking.

[0075] 3) After the braking is completed, the generator controller 2 enters the charged sleep state and continuously monitors the rotational speed of the doubly salient DC excited generator assembly 1. When it detects that the rotational speed resumes to the preset starting speed condition, the generator controller 2 is awakened again and re-enters the power generation control process described above to resume normal power generation.

[0076] Through the braking control mode, rapid braking of the wind turbine generator set in the overspeed state can be achieved, ensuring the safety and stability of the system.

[0077] Based on the above control method of the DC networked wind turbine generator system, in another embodiment of the present application, in the above step 6, when it is detected that the DC output voltage Vbus of the generator controller 2 is lower than the starting voltage of the doubly salient DC excited generator assembly 1, it is determined that the energy storage battery system 6 on the DC bus 5 is missing or the connection is disconnected, and it is unable to provide the basic dynamic working voltage for the DC bus 5, resulting in the bus voltage being unable to be maintained above the starting voltage; and other wind turbine generator sets on the DC bus 5 are not in the DC power generation state and are unable to supplement the electrical energy for the DC bus 5 through their own power generation, and thus the bus voltage cannot be raised to the starting voltage.

[0078] Based on the above determination result, the generator controller 2 will immediately execute the low-voltage branch pre-charge control strategy. With the pre-charge voltage as the target, it enters the residual magnet power generation mode of the doubly salient DC excited generator assembly 1 to perform the pre-charge operation on the filter capacitor in the system until the generator controller 2 detects that its terminal voltage Vbus is higher than the preset pre-charge voltage, then stops the pre-charge and re-enters the maximum power tracking mode under the constant voltage power generation state to start the normal power generation process.

[0079] Based on the above-described DC grid-connected wind turbine system control method, in another embodiment of this application, in step 6, when the generator controller 2 determines that the energy storage battery system 6 on the DC bus 5 is missing or disconnected, and other wind turbine generators are not in DC power generation mode, the generator controller 2 will use the preset pre-charge voltage as the constant voltage control target and enter the residual magnetization power generation mode of the doubly salient pole DC excitation generator assembly 1. In the residual magnetization power generation mode, the generator controller 2 will continuously execute the constant voltage power generation pre-charge closed-loop control, monitor its own DC output terminal voltage Vbus in real time, and dynamically adjust the excitation current of the doubly salient pole DC excitation generator assembly 1 according to the difference between Vbus and the pre-charge voltage, so that the doubly salient pole DC excitation generator assembly 1 continuously outputs DC power through residual magnetization power generation to pre-charge the filter capacitor in the system; this closed-loop control process continues to execute until the generator controller 2 detects that its own DC output terminal voltage Vbus is higher than the preset pre-charge voltage. At this time, the pre-charge is completed, the generator controller 2 stops the residual magnetization pre-charge mode, re-enters the maximum power following mode under constant voltage power generation state, and starts the normal power generation process.

[0080] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A DC grid-connected wind turbine generator system, characterized in that, The DC grid-connected wind turbine system adopts a distributed, decentralized power generation control, including multiple wind turbine generators, multiple generator controllers, an energy storage battery system, and a PCS converter; The wind turbine generator set adopts a double salient pole DC excitation generator assembly to convert wind power into three-phase AC power; The generator controller is used to control the wind turbine generator set to generate DC power, and converts the three-phase AC power output from the doubly salient pole DC excitation generator assembly into high-voltage DC shaftless voltage through a full-bridge diode rectifier and filter circuit. The output terminal of the generator controller is connected to a DC bus, and the DC voltage at the output terminal of the generator controller can actively follow the voltage change of the DC bus. Each generator controller is connected to one wind turbine generator set, and multiple generator controllers are connected in parallel through the DC bus without crosstalk. The PCS converter is used to convert the DC power generated by the wind turbine generator into AC power through the DC bus and then input it at a single point to supply power to the load or to the grid.

2. The DC grid-connected wind turbine generator system according to claim 1, characterized in that, The energy storage battery system includes one or more energy storage battery modules, and multiple energy storage battery modules are directly connected in parallel through the DC bus.

3. A DC grid-connected wind turbine generator system according to claim 2, characterized in that, The energy storage battery system is directly connected to the DC bus, providing the DC bus with a basic dynamic operating voltage. The energy storage battery system can store the DC power converted by the generator controller and can release the stored DC power to the DC bus.

4. A DC grid-connected wind turbine generator system according to claim 1, characterized in that, The wind turbine generator set includes a doubly salient pole DC excitation generator assembly and wind turbine blades for driving the doubly salient pole DC excitation generator assembly to rotate. The wind turbine generator set includes, but is not limited to, a three-blade horizontal axis conventional wind turbine generator, a three-blade horizontal axis wind-concentrating shroud wind turbine generator, an H-type vertical axis wind turbine generator, and other irregularly shaped wind turbine generators with other structural forms.

5. A DC grid-connected wind turbine generator system according to claim 1, characterized in that, The rated voltage of the DC bus includes, but is not limited to, 400Vdc, 600Vdc, 800Vdc and 1200Vdc.

6. A control method for a DC grid-connected wind turbine generator system, characterized in that, A DC grid-connected wind turbine generator system according to any one of claims 1 to 5 includes the following steps: Step 1, Start-up and wake-up judgment: The generator controller monitors the rotational speed of the doubly salient pole DC excitation generator assembly of the wind turbine generator set in real time. When the rotational speed of the doubly salient pole DC excitation generator assembly reaches the start-up speed, the generator controller is woken up and enters the power generation control process; when the rotational speed of the doubly salient pole DC excitation generator assembly is insufficient, the generator controller remains in a powered sleep state, maintaining zero DC excitation current, so that the doubly salient pole DC excitation generator assembly can rotate freely. Step 2, Bus voltage detection and branching: When the generator controller is awakened, it reads the voltage of the DC bus and compares it with the starting voltage of the doubly salient pole DC excitation generator assembly. Based on the comparison result, different control branches are executed. Step 3, High Voltage Branch Control: When the DC output voltage Vbus of the generator controller is detected to be higher than the starting voltage of the doubly salient pole DC excitation generator assembly, the generator controller sets Vbus as the next voltage follow-up control target and follows the control target to enter the power follow-up generation control strategy to generate electricity. Step 4, Power Follow-up Generation Control: During the power follow-up generation control process, if the DC output voltage Vbus of the generator controller is detected to exceed the maximum allowable voltage, the generator controller sets the DC excitation current of the doubly salient pole DC excitation generator assembly to 0, stops power generation, and allows the wind turbine generator set to enter a free rotation state. If Vbus does not exceed the maximum allowable voltage, the generator controller calculates the target generating current It based on the target terminal voltage and enters the wind turbine maximum power following generation mode under constant voltage target. Step 5, Speed ​​Monitoring and Braking Control: During maximum power following generation, if the speed of the doubly salient pole DC excitation generator assembly does not exceed the braking speed, the generator controller enters closed-loop control and continues to operate in maximum power following generation mode; if the speed of the doubly salient pole DC excitation generator assembly exceeds the braking speed, the generator controller enters braking control mode to rapidly reduce the speed of the wind turbine generator set. Step 6, Low-voltage branch pre-charge control: When the DC output voltage Vbus of the generator controller is detected to be lower than the starting voltage of the salient-pole DC excitation generator, the generator controller enters the residual magnetization generation mode of the double salient-pole DC excitation generator assembly with the pre-charge voltage as the target, pre-charges the filter capacitor until Vbus is higher than the pre-charge voltage, and then re-enters the maximum power follower mode under constant voltage generation state.

7. The control method for a DC grid-connected wind turbine generator system according to claim 6, characterized in that, The control logic for the wind turbine maximum power following the power generation mode under constant pressure target in step 4 is as follows: (1) When the actual generated voltage is higher than the target voltage, the generator controller reduces the DC excitation current to reduce the generated current of the doubly salient pole DC excitation generator assembly; (2) When the actual generated voltage is lower than the target voltage, the generator controller increases the DC excitation current to increase the generated current of the doubly salient pole DC excitation generator assembly.

8. The control method for a DC grid-connected wind turbine generator system according to claim 6, characterized in that, The braking control modes in step 5 specifically include: 1) The generator controller rapidly increases the power generation to the peak power, causing the power generation current of the doubly salient pole DC excitation generator assembly to increase sharply to the peak current. The generator controller then enters closed-loop control, causing the wind turbine generator speed to decrease rapidly. 2) The generator controller issues a braking command to activate the electromagnetic braking device and lock the wind turbine generator set; 3) The generator controller enters a energized sleep state and waits for the speed of the doubly salient pole DC excitation generator assembly to recover to the starting conditions before waking up again.

9. A control method for a DC grid-connected wind turbine system according to claim 6, characterized in that, In step 6, when it is detected that the DC output voltage Vbus of the generator controller is lower than the starting voltage of the doubly salient pole DC excitation generator assembly, it is determined that the energy storage battery system on the DC bus is missing or disconnected, and the other wind turbine generators on the DC bus are not in DC power generation state.

10. A control method for a DC grid-connected wind turbine generator system according to claim 6, characterized in that, In step 6, the generator controller performs constant voltage pre-charge closed-loop control in residual magnetism power generation mode until the DC output voltage Vbus of the generator controller is higher than the pre-charge voltage.

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