Variable-pitch system of wind turbine generator and variable-pitch brake resistor control method of variable-pitch system

Abstract

The invention provides a wind turbine generator variable pitch system and a variable pitch brake resistor control method thereof, relates to the field of wind turbine generator control, and solves the limitation problem that direct-current bus overvoltage fault shutdown can be caused under the condition that a single-shaft brake resistor in the wind turbine generator variable pitch system fails. Wherein the variable-pitch system is provided with a plurality of variable-pitch drivers which correspondingly drive the variable-pitch action of one blade in the wind turbine generator; the direct-current bus of each variable-pitch driver is electrically connected to the brake resistor of the corresponding paddle shaft, and the direct-current bus of any variable-pitch driver is electrically connected to the brake resistors of the other paddle shafts through a plurality of direct-current contactors; when any direct-current contactor acts and electric energy of the direct-current bus of the corresponding strain propeller driver needs to be discharged, the braking resistor connected with the direct-current contactor is input to realize electric energy discharging. According to different voltage levels of the variable-pitch driver direct-current bus of any blade, brake resistors input into other blade shafts can be controlled, and the energy discharge rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine control systems, and particularly to a pitch system for a wind turbine and a control method for a pitch braking resistor thereof. Background Art

[0002] As an important part of clean energy, wind power generation has been widely applied and developed globally. Wind turbines convert the wind energy in nature into electrical energy, which is one of the effective ways to achieve green energy supply. In wind turbines, the blades play a crucial role. They are not only responsible for capturing wind energy, but also their attitude adjustment is essential for optimizing the energy conversion efficiency and ensuring the safe operation of the system. To better control the working state of the blades, modern wind turbines generally adopt pitch technology, that is, by changing the angle of the blades relative to the wind direction to adjust the rotational speed and output power of the wind turbine, so as to adapt to different wind speed conditions and achieve the optimal energy conversion effect.

[0003] The normal operation of the pitch system depends on a series of components with precise designs working together, among which the pitch motor and its control system are particularly crucial. The pitch motor drives the blade to rotate around the axis to change its angle of attack. This process is often accompanied by frequent speed changes, especially under strong wind or sudden wind conditions, and it is necessary to quickly respond to changes in the external environment. It should be noted that in some cases, such as when the wind speed suddenly drops and the blade angle is rapidly reduced, the pitch motor will be in the power generation mode during the process of decelerating from high speed to 0. At this time, a back electromotive force will be generated inside the pitch motor, converting mechanical energy into electrical energy and feeding it back to the corresponding DC bus, resulting in an increase in the DC bus voltage. If there is no effective management measure, this voltage fluctuation may exceed the safety range of the corresponding pitch driver, thereby causing equipment damage and even a fault shutdown of the entire system.

[0004] To solve the above problems, a braking resistor is introduced into the pitch system as an important protection mechanism. The main function of the braking resistor is to automatically connect to the circuit when it detects that the DC bus voltage exceeds the preset safety threshold, convert the excess electrical energy into heat energy for dissipation, thereby reducing the bus voltage level and preventing overvoltage. This can not only effectively protect the pitch driver from damage, but also maintain the stable operation of the entire wind power generation system. However, in the actual application process, the braking resistor itself may also encounter various reasons for failure or malfunction, such as aging in a long-term high-temperature working environment, physical damage caused by external factors, etc. Once the braking resistor fails, the corresponding pitch driver will be directly exposed to potential high-voltage risks, which is very likely to cause irreversible electrical damage and ultimately force the entire wind turbine to stop operating, bringing serious impacts on power production and economic benefits.

[0005] Therefore, in addition to improving the reliability and durability of the braking resistors in the pitch system, exploring more efficient and flexible energy management strategies or targeted control methods has also become one of the technical problems that need to be solved urgently in the current wind power field. Summary of the Invention

[0006] Based on the current situation in the background technology, the purpose of the present invention is to solve the limitation problem that the failure of a single-axis braking resistor in the pitch system of a wind turbine can lead to the shutdown of the DC bus due to overvoltage. Therefore, a pitch system for a wind turbine and a control method for its pitch braking resistor are proposed. According to the different voltage levels of the DC bus of the pitch driver of any blade, the present invention can control the braking resistors of other blade axes to be put into use, thereby improving the energy discharge rate; and, in the case of the failure of a single-axis braking resistor, the energy can also be discharged through the normal braking resistors of other axes, avoiding the overvoltage of the DC bus of the corresponding driver, and finally improving the reliability of the entire pitch system.

[0007] The present invention adopts the following technical solutions to achieve the purpose:

[0008] A pitch system for a wind turbine, the system has a plurality of pitch drivers, and each pitch driver corresponds to driving the pitch movement of one of the blades of the wind turbine; the DC bus of each pitch driver is electrically connected to the braking resistor corresponding to its own blade axis, and at the same time, the DC bus of any pitch driver is electrically connected to the braking resistors corresponding to the other blade axes through a plurality of DC contactors; each DC contactor acts under the control of at least one pitch driver to close or open the electrical connection path where it is located; when any DC contactor acts and closes the electrical connection path where it is located, and the electrical energy of the DC bus of any pitch driver connected to the DC contactor needs to be discharged, all the braking resistors connected to the DC contactor are put into use, so as to realize the discharge of electrical energy.

[0009] Specifically, each pitch driver includes a DC bus and a discharge IGBT, and the DC bus is divided into a positive line and a negative line; the positive line of each pitch driver is electrically connected to one end of the braking resistor corresponding to its own blade axis, and at the same time, it is also electrically connected to one end of the braking resistors corresponding to the other blade axes through a plurality of DC contactors; the other ends of all the braking resistors are electrically connected to the discharge IGBT of each pitch driver and are electrically connected to the negative line of the corresponding pitch driver through the discharge IGBT.

[0010] Preferably, each pitch driver further includes a freewheeling diode, the positive pole of the freewheeling diode is electrically connected to the common connection line of the discharge IGBT of its corresponding pitch driver and all the braking resistors, and the negative pole is electrically connected to the positive line of its corresponding pitch driver.

[0011] Specifically, each pitch drive has a common terminal COM and multiple output terminals DOx, and each DC contactor is correspondingly equipped with a contactor coil; the common terminals COM of all pitch drives are connected to the common point of the system, and this common point is simultaneously connected to the negative poles of all contactor coils; different output terminals DOx of each pitch drive are respectively connected to the positive poles of different contactor coils.

[0012] The present invention also provides a method for controlling the pitch braking resistor of a wind turbine generator set. The hardware basis of the method is the aforementioned pitch system of the wind turbine generator set; the method realizes the discharge of electric energy by presetting different voltage thresholds of the DC bus in any pitch drive and executing corresponding braking resistor input strategies when the DC bus voltage of the corresponding pitch drive reaches different voltage thresholds; the voltage thresholds include a safety threshold, multiple protection thresholds, and an overvoltage fault shutdown threshold; when the DC bus voltage of any pitch drive reaches the multiple protection threshold, this pitch drive controls at least one DC contactor to act, so that the braking resistor corresponding to its own blade shaft and the braking resistors of the remaining blade shafts connected to the corresponding DC contactor are input, and jointly complete the discharge of the electric energy of the DC bus of this pitch drive.

[0013] Preferably, the safety threshold is the first set threshold U 1 , the multiple protection thresholds include the second set threshold U 2 , the third set threshold U 3 and the fourth set threshold U 4 , the overvoltage fault shutdown threshold is the fifth set threshold U 5 ; the magnitude relationship of each voltage threshold is: U 1 <U 3 <U 3 <U 4 <U 5 , the higher the voltage threshold, the higher the danger level of the DC bus; when the pitch drive determines that the current DC bus voltage is greater than the fifth preset threshold U 5 , the pitch drive reports an overvoltage fault of the bus and shuts down the pitch system of the wind turbine generator set.

[0014] Furthermore, after the pitch system of the wind turbine generator set completes initialization and enters the normal operation state, each pitch drive first determines whether its current DC bus voltage U dc is greater than the second set threshold U 2 . If so, it controls the discharge IGBT it has to conduct, so that the electric energy of the DC bus is discharged through the braking resistor corresponding to its own blade shaft; if not, the pitch system of the wind turbine generator set remains in the normal operation state; when the electric energy of the DC bus is only discharged through the braking resistor corresponding to its own blade shaft, if the DC bus voltage U dc has dropped below the first set threshold U 1When the pitch drive controls the discharge IGBT to turn off, the power discharge of the DC bus is stopped; at the moment when the discharge IGBT turns off, the redundant discharge power energy flows back to the positive line of the DC bus through the freewheeling diode.

[0015] Furthermore, the pitch system of the wind turbine determines whether the braking resistor corresponding to the blade shaft is faulty by checking whether the count value Counter of the braking resistor fault flag exceeds the preset upper limit A, and sets the braking resistor fault flag bit FaultFlag of the corresponding blade shaft to 1 when a fault occurs, and 0 when there is no fault; when the DC bus voltage U dc has dropped to the first set threshold U 1 , after the discharge IGBT turns off, the pitch drive determines whether the braking resistor fault flag bit FaultFlag is 1. If it is, an alarm signal indicating the failure of the braking resistor is sent out. The pitch system of the wind turbine continues to operate without stopping, waiting for maintenance personnel to repair. At the same time, the pitch drive controls at least one DC contactor to close, so that the power energy of its own DC bus can be discharged through at least one braking resistor from the remaining blade shafts when discharging is required; if not, the pitch system of the wind turbine remains in the normal operating state.

[0016] Furthermore, when the power energy of the DC bus is discharged only through the braking resistor corresponding to its own blade shaft, the corresponding pitch drive determines whether the DC bus voltage U dc is greater than the third set threshold U 3 , as follows:

[0017] If the DC bus voltage U dc has been greater than the third set threshold U 3 , the count value Counter of the braking resistor fault flag is incremented by 1, and it is determined whether it has exceeded the preset upper limit A. When it exceeds, the braking resistor fault flag bit FaultFlag is set to 1. The pitch drive also controls at least one DC contactor to close, and keeps at least one braking resistor from the remaining blade shafts in operation to discharge the power energy of this DC bus;

[0018] If the DC bus voltage U dc is not greater than the third set threshold U 3 , the count value Counter of the braking resistor fault flag is cleared to 0, and the conduction of the discharge IGBT is continued to control, so that the power energy of the DC bus is discharged only through the braking resistor corresponding to its own blade shaft.

[0019] Furthermore, after the DC bus voltage U dc has been greater than the third set threshold U 3 and at least one DC contactor is controlled to close, the corresponding pitch drive continues to determine whether the DC bus voltage U dc is greater than the fourth set threshold U4 , as follows:

[0020] If the DC bus voltage U dc has been greater than the fourth set threshold U 4 , the pitch drive controls at least two DC contactors to close at this time, and keeps at least two braking resistors from the remaining blade shafts energized to achieve the energy discharge of the DC bus;

[0021] If the DC bus voltage U dc is not greater than the fourth set threshold U 4 , the pitch drive still maintains the closure of at least one DC contactor at this time to achieve the energy discharge of the DC bus;

[0022] After the energy discharge of the DC bus is completed, the DC bus voltage U dc drops to the first set threshold U 1 , and the corresponding discharge IGBT is turned off; if the braking resistor fault flag bit FaultFlag is still 0 at this time, the pitch drive controls the previously closed DC contactor to open; if the braking resistor fault flag bit FaultFlag has been set to 1, the pitch drive controls at least one DC contactor to maintain the closed state.

[0023] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows:

[0024] The present invention aims to improve the reliability and economy of the pitch system of a wind turbine generator set. By controlling the input of braking resistors belonging to other shafts when the voltage of the pitch drive is too high and the energy discharge capacity of the braking resistor of a single shaft is insufficient, the overall energy discharge capacity can be significantly improved. This mechanism of multi-axis collaborative work can effectively avoid the increase of the DC bus voltage caused by excessive external input power, thereby preventing the pitch drive and the entire system from malfunctioning or shutting down due to overvoltage. In addition, this solution also reduces the need for a high energy discharge capacity in extreme cases, and there is no need to select more or larger capacity braking resistors to cover all possible working conditions, thereby reducing the cost of the system.

[0025] On the other hand, when the braking resistor of a certain shaft is damaged or fails, the present invention can control the input of braking resistors of other shafts to discharge energy and send an alarm signal in time. This can not only avoid the shutdown of the entire unit due to the failure of the braking resistor of a single shaft, but also provide a valuable maintenance window period for the operation and maintenance personnel, enabling them to replace the failed braking resistor at an appropriate time. This mechanism not only improves the robustness of the pitch system, but also enhances the fault tolerance and maintainability of the system.

[0026] Specifically, a typical wind turbine generator usually has three blades, each blade is connected to an independent pitch axis, and each axis is equipped with its own pitch drive and braking resistor. Through the solution of the present invention, even if the braking resistor of one axis fails, the braking resistors of the other two axes can still continue to work and share the voltage energy of the faulty axis by controlling the input, realizing the normal discharge of energy, thereby ensuring the normal operation of the system. This redundant design concept not only improves the stability and reliability of the system, but also extends the overall service life of the equipment and reduces the maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the structural connection relationship of the pitch control system of the wind turbine generator of the present invention;

[0028] Figure 2 is a schematic diagram of the control circuit of the DC contactor in the pitch control system of the wind turbine generator of the present invention;

[0029] Figure 3 is a schematic diagram of an example process of the pitch braking resistor control method of the wind turbine generator of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Embodiment 1

[0033] A pitch control system for a wind turbine generator Figure 1 shows the specific structural connection relationship of an example of the system, which can be referred to synchronously. The pitch control system of the wind turbine generator introduced in this embodiment will be used in the most typical wind turbine generator with three blades, so there are three pitch drives and three braking resistors correspondingly. In order to connect the three pitch drives to the three braking resistors, the number of DC contactors is also three.

[0034] In this embodiment, the DC bus of any pitch drive is electrically connected to the braking resistors corresponding to the other blade shafts through two DC contactors; when any DC contactor operates and closes the electrical connection path where it is located, the DC bus voltage of any pitch drive connected by this DC contactor drops as all the braking resistors connected by this DC contactor are put into use. A braking resistor mentioned in this embodiment, for example Figure 1 The braking resistors 1, 2, and 3 corresponding to the three blade shafts in Figure 1 can be in the form of a single braking resistor, or in the form of a braking resistor group formed by combining multiple braking resistors in parallel. This embodiment does not limit this, and any structural form of the braking resistor can achieve the effect of this embodiment.

[0035] In this embodiment, each pitch drive includes a DC bus and a discharging IGBT, where the DC bus is divided into a positive line and a negative line; the positive line of each pitch drive is electrically connected to one end of the braking resistor corresponding to its own blade shaft, and at the same time is also electrically connected to one end of the braking resistors corresponding to the other two blade shafts through two DC contactors; the other ends of all the braking resistors are electrically connected to the discharging IGBT of each pitch drive and are electrically connected to the negative line of the corresponding pitch drive through this discharging IGBT.

[0036] For the three DC contactors in this embodiment, their control circuits are as Figure 2 shown. First, the three pitch drives all have a common terminal COM and two output terminals DO1 and DO2, and each DC contactor (S12, S13, S23) is correspondingly configured with a contactor coil (K12, K13, K23). The common terminal COM of all the pitch drives is connected to the common point of the system, and this common point is simultaneously connected to the negative poles of all the contactor coils; the output terminal DO1 of pitch drive 1 and the output terminal DO1 of pitch drive 2 are both electrically connected to the positive pole of contactor coil K12; the output terminal DO2 of pitch drive 1 and the output terminal DO1 of pitch drive 3 are both electrically connected to the positive pole of contactor coil K13; the output terminal DO2 of pitch drive 2 and the output terminal DO2 of pitch drive 3 are both electrically connected to the positive pole of contactor coil K23.

[0037] Supported by the above system structure, the pitch system of the wind turbine in this embodiment can control the braking resistors of the other blade shafts to be put into use according to the different voltage levels of the DC bus corresponding to the pitch drives, improve the discharging rate, and in the case of the failure of the braking resistor of a single blade shaft, the energy can be discharged through the normal braking resistors of the other blade shafts, avoiding overvoltage of the DC bus of the corresponding pitch drive, thereby successfully improving the reliability of the pitch system of the wind turbine.

[0038] Embodiment 2

[0039] Based on Embodiment 1, this embodiment details a method for controlling the pitch braking resistor of a wind turbine generator after applying the pitch control system of Embodiment 1 in a wind turbine generator with three blades. The entire control method process can be referred to in Figure 3 the schematic of, and this embodiment will elaborate on its principle, details, and specific steps.

[0040] Since the pitch control system of the wind turbine generator has been working under the condition of frequent reciprocating pitch adjustment for a long time, during the process of the pitch motor decelerating from high speed to 0, the pitch motor is in the power generation working mode, and the kinetic energy of the large inertia system composed of the blade and the drive shaft system is converted into a large amount of electrical energy, which is injected into the DC bus of the corresponding pitch driver, resulting in an increase in the DC bus voltage.

[0041] This embodiment takes the pitch driver 1 and the braking resistor 1 belonging to blade 1 as examples to illustrate the method, and this method is also applicable to pitch drivers 2 and 3; the method for controlling the pitch braking resistor of the wind turbine generator includes the following steps:

[0042] Step 1: Initialize the pitch control system.

[0043] Step 2: The pitch control system enters the normal operation state.

[0044] Step 3: Determine whether the DC bus voltage U dc of pitch driver 1 is greater than the second set threshold U 2 , if so, go to Step 4, otherwise jump back to Step 2.

[0045] Step 4: Pitch driver 1 controls the internal discharge IGBT1 to conduct, and the positive line DC+ and the negative line DC- of the DC bus are conducted through the braking resistor 1 and the discharge IGBT1, and the current flows through the braking resistor, and the energy injected into pitch driver 1 is consumed by heating. When the discharge IGBT1 conducts, the instantaneous discharge power where R is the resistance value of the braking resistor 1, and the DC bus voltage U dc rapidly decreases with the input of the braking resistor 1, thus avoiding hardware damage caused by overvoltage of the DC bus.

[0046] Step 5: Determine whether the DC bus voltage U dc of pitch driver 1 is less than the first set threshold U 1 , if so, go to Step 6.1, otherwise go to Step 6.2.

[0047] Step 6.1: The DC bus voltage U dc rapidly decreases with the input of the braking resistor 1. When the DC bus voltage U dc drops to the first set threshold U 1 which is used as the safety threshold,When it is time, the pitch driver 1 controls the discharge IGBT1 to turn off and stop the discharge; at the moment when the discharge IGBT1 turns off, the freewheeling diode absorbs the excess discharge electric energy and returns it to the positive line DC+ of the DC bus, and then enters step 7.1.

[0048] Step 6.2, determine the DC bus voltage U of the pitch driver 1 dc Whether it is greater than the third set threshold U 3 , if so, enter step 7.2, otherwise enter step 7.3.

[0049] In this embodiment, it should be noted here that the DC bus voltage U dc Reaches and is greater than the third set threshold U 3 There may be two reasons:

[0050] One is that the braking resistor 1 belonging to the current blade shaft 1 is damaged or fails and does not have the discharge ability, and the electric energy generated when the pitch motor decelerates frequently is fed back to the DC bus. If each time the pitch driver 1 controls the discharge IGBT1 to conduct and discharge, the DC bus voltage U dc Will exceed the third set threshold U 3 In this case, this embodiment will determine that the braking resistor 1 belonging to the current blade shaft 1 has been damaged or failed by continuously triggering the number of times of this condition to exceed the upper limit A of the braking resistor fault flag count value Counter.

[0051] The second is that during the deceleration process of the pitch motor, the external power instantaneous input power P of the blade, the drive shaft system, etc. in = jωα is greater than the braking resistor discharge power Where j is the overall moment of inertia of the load carried by the pitch motor, ω is the angular velocity of the pitch motor, and α is the angular acceleration of the pitch motor. Excessive ω values and α values may cause the input power P in To be greater than the discharge power P, and the discharge ability is insufficient, which will cause the DC bus voltage U dc To rise continuously. However, when selecting the braking resistor for the pitch system, its discharge ability can already cover most working conditions. Therefore, the working conditions with excessive input power are less and belong to occasional phenomena, and it will not cause the DC bus voltage U dc To exceed the third set threshold U 3 In all cases.

[0052] Therefore, in this embodiment, the braking resistor fault flag count value Counter is used to determine whether the braking resistor 1 belonging to the current blade shaft 1 is faulty by whether it exceeds the set number upper limit A.

[0053] Step 7.1: Determine whether the braking resistor fault flag bit FaultFlag corresponding to the current blade shaft 1 is 1. If so, proceed to Step 8.1; otherwise, proceed to Step 8.2.

[0054] Step 7.2: Increment the braking resistor fault flag count value Counter by 1, and proceed to Step 8.3.

[0055] Step 7.3: Clear the braking resistor fault flag count value Counter to 0, jump back to Step 4, continue to control the discharge IGBT1 to conduct, and discharge electrical energy through the braking resistor 1.

[0056] In this embodiment, in this case, it is considered that the DC bus voltage U dc exceeds the third set threshold U 3 due to the occasional excessive power input from power generation, and the braking resistor 1 is still in a normal state.

[0057] Step 8.1: The pitch drive 1 issues a braking resistor failure alarm signal and sends it to the main control system of the wind turbine through CANOpen communication. However, at this time, the pitch system of the wind turbine does not stop and continues to operate, waiting for maintenance personnel to repair. In the method, the pitch system is still considered to be in a normal operating state, and it jumps back to Step 2 to continue execution.

[0058] In this embodiment, in this case, the pitch system determines that the braking resistor 1 of the current blade shaft 1 is faulty, and will maintain the output of the output terminals DO1 and / or DO2 of the pitch drive 1, that is, make the contacts of the DC contactors (S12 and / or S13) close. The pitch drive 1 of the current blade shaft 1 will discharge through the braking resistor 2 and / or the braking resistor 3. The pitch system does not stop and continues to operate and issues an alarm message.

[0059] Step 8.2: The pitch drive 1 controls its output terminals DO1 and DO2 to output 0V, that is, controls the DC contactors S12 and S13 to disconnect, and then jumps back to Step 2.

[0060] Step 8.3: Determine whether the braking resistor fault flag count value Counter exceeds the set upper limit A. If so, it is determined that the braking resistor 1 to which the current blade shaft 1 belongs has been damaged or failed and does not have the discharge ability. Set the braking resistor fault flag bit FaultFlag to 1. At this time, the output of the output terminals DO1 and / or DO2 of the pitch drive 1 is no longer turned off, so as to maintain the state where the braking resistors of the remaining blade shafts are connected to the DC bus of the pitch drive 1. Then determine whether the DC bus voltage U dc is greater than the fourth set threshold U 4 , if so, proceed to Step 9.1; otherwise, proceed to Step 9.2.

[0061] Step 9.1: The DC bus voltage Udc Greater than the fourth set threshold U 4 When this occurs, the pitch system determines that more braking resistors need to be put into operation to avoid hardware damage caused by excessive DC bus voltage; the pitch drive 1 simultaneously controls its output terminals DO1 and DO2 to output 24 VDC, the contactor coils K12 and K13 are both energized, and the contacts of the DC contactors S12 and S13 are closed. When the braking resistor 1 is not faulty, it is equivalent to braking resistors 1, 2, and 3 being connected in parallel across the DC bus of the pitch drive 1, and energy is dissipated through the three braking resistors, i.e., the maximum discharge capacity of the pitch system; when the braking resistor 1 is faulty, it is equivalent to braking resistors 2 and 3 being connected in parallel across the DC bus of the pitch drive 1, and energy is dissipated through the two braking resistors; proceed to step 10.

[0062] Step 9.2: The pitch drive 1 controls its output terminal DO1 to output 24 VDC and DO2 to output 0 V. Then, the contactor coil K12 is energized and K13 is de-energized. The contacts of the DC contactor S12 are closed and S13 is opened. When the braking resistor 1 is not faulty, it is equivalent to braking resistors 1 and 2 being connected in parallel across the DC bus of the pitch drive 1, and energy is dissipated through the two braking resistors; when the braking resistor 1 is faulty, it is equivalent to braking resistor 2 being connected across the DC bus of the pitch drive 1, and energy is dissipated through one braking resistor. Subsequently, jump back to step 4 and continue to control the conduction and discharge of IGBT1 to dissipate electrical energy through the corresponding braking resistor.

[0063] Step 10: Determine whether the DC bus voltage U of the pitch drive 1 dc is greater than the fifth preset threshold U 5 . If so, the DC bus voltage U dc has reached the drive hardware overvoltage protection point, i.e., the overvoltage fault shutdown threshold is satisfied, and the pitch drive 1 will report a DC bus overvoltage fault shutdown; otherwise, jump back to step 4 and continue to control the conduction and discharge of IGBT1 to dissipate electrical energy through the corresponding braking resistor.

[0064] In the control method flow of this embodiment, the magnitude relationship of each voltage threshold is: U 1 < U 2 < U 3 < U 4 < U 5 , and the higher the voltage threshold, the higher the risk level of the DC bus; U 1 can be correspondingly understood as the discharge cut-off voltage, i.e., when the DC bus voltage U dc is lower than U 1 , it is considered safe and the discharge stops; U 5 can be correspondingly understood as the hardware overvoltage protection point, i.e., when the DC bus voltage U dcExceeding U 5 When it does, the pitch drive reports a DC bus overvoltage fault and shuts down; U 2 , U 3 , U 4 are the three - level protection thresholds. When the DC bus voltage U dc reaches different threshold ranges, different strategies are adopted. The pitch drive controls the DC contactor to actuate and connects the braking resistors belonging to the other blade shafts to discharge energy.

[0065] In this embodiment, when the contactor coil is energized, the contacts of the DC contactor are attracted and conduct. S12 in Figure 1 can be understood as the contact corresponding to the contactor coil K12, S13 is the contact corresponding to K13, and S23 is the contact corresponding to K23. For the pitch drive 2 of blade shaft 2, its output terminals DO1 and DO2 control S12 and S23 respectively; for the pitch drive 3 of blade shaft 3, its output terminals DO1 and DO2 control S13 and S23 respectively. The above - mentioned method in this embodiment is described by taking the pitch drive 1 of blade shaft 1 as an example. However, when the DC bus voltages of the pitch drives 2 and 3 of blade shafts 2 and 3 exceed their corresponding preset thresholds, their respective output terminals DOx also output, causing the corresponding DC contactors to be attracted, and discharging energy through the braking resistors of the other blade shafts.

[0066] In a wind turbine generator set, since the spatial positions of the three blades are 120° apart and the influence of the blade's gravity is different, under the same pitch deceleration command, the degrees of increase in the DC bus voltages of the three pitch drives are different. Under the normal acceleration and deceleration conditions of the pitch system, generally, the situation where the DC bus voltages of the pitch drives of all three blade shafts reach the hardware overvoltage protection point does not occur, and the braking resistors of the three blade shafts do not work simultaneously for a long time. Therefore, in most cases, a single braking resistor can meet the discharge requirements of the DC bus voltage of the corresponding pitch drive. The above - mentioned method in this embodiment is a control method for discharging energy through the braking resistors of the other blade shafts, which can discharge energy through the idle braking resistors of the other blade shafts when the discharge capacity of the braking resistor of its own blade shaft is insufficient or the braking resistor has failed.

Claims

1. A wind turbine pitch control system, characterized in that: The system has multiple pitch drives, and each pitch drive correspondingly drives the pitch movement of one of the blades of the wind turbine; the DC bus of each pitch drive is electrically connected to the braking resistor corresponding to the blade shaft where it is located, and at the same time, the DC bus of any pitch drive is electrically connected to the braking resistors corresponding to the other blade shafts through multiple DC contactors; each DC contactor operates under the control of at least one pitch drive to close or open the electrical connection path where it is located; when any DC contactor operates and closes the electrical connection path where it is located, and the electrical energy of the DC bus of any pitch drive connected to this DC contactor needs to be discharged, all the braking resistors connected to this DC contactor are put into operation, thereby realizing the discharge of electrical energy.

2. The wind turbine pitch control system according to claim 1, characterized in that: Each pitch drive includes a DC bus and a discharge IGBT, where the DC bus is divided into a positive line and a negative line; the positive line of each pitch drive is electrically connected to one end of the braking resistor corresponding to the blade shaft where it is located, and at the same time, it is also electrically connected to one end of the braking resistors corresponding to the other blade shafts through multiple DC contactors; the other ends of all the braking resistors are electrically connected to the discharge IGBT of each pitch drive and are electrically connected to the negative line of the corresponding pitch drive through this discharge IGBT.

3. The wind turbine pitch control system according to claim 2, characterized in that: Each pitch drive also includes a freewheeling diode, the positive pole of which is electrically connected to the common connection line of the discharge IGBT of its corresponding pitch drive and all the braking resistors, and the negative pole is electrically connected to the positive line of its corresponding pitch drive.

4. The wind turbine pitch control system according to claim 1, characterized in that: Each pitch drive has a common terminal COM and multiple output terminals DOx, and each DC contactor is correspondingly equipped with a contactor coil; the common terminal COM of all the pitch drives is connected to the common point of the system, and this common point is simultaneously connected to the negative poles of all the contactor coils; different output terminals DOx of each pitch drive are respectively connected to the positive poles of different contactor coils.

5. A method for controlling the variable pitch brake resistance of a wind turbine, characterized in that: By presetting different voltage thresholds of the DC bus in any pitch drive, when the DC bus voltage of the corresponding pitch drive reaches different voltage thresholds, the corresponding braking resistor input strategy is executed to realize the discharge of electrical energy; the voltage thresholds include a safety threshold, multiple-level protection thresholds, and an overvoltage fault shutdown threshold; when the DC bus voltage of any pitch drive reaches the multiple-level protection threshold, this pitch drive controls at least one DC contactor to operate, so that the braking resistor corresponding to the blade shaft where it is located and the braking resistors of the other blade shafts connected to the corresponding DC contactor are put into operation to jointly complete the discharge of the electrical energy of the DC bus of this pitch drive.

6. The method for controlling the variable pitch brake resistance of a wind turbine according to claim 5, characterized in that: The safety threshold is the first set threshold U1, the multiple-level protection thresholds include the second set threshold U2, the third set threshold U3, and the fourth set threshold U4, and the overvoltage fault shutdown threshold is the fifth set threshold U5; the magnitude relationship of each voltage threshold is: U1 < U2 < U3 < U4 < U5, and the higher the voltage threshold, the higher the danger level of the DC bus; when the pitch drive judges that the current DC bus voltage is greater than the fifth preset threshold U5, the pitch drive reports an overvoltage fault of the bus and shuts down the pitch system of the wind turbine.

7. The method for controlling the variable pitch brake resistance of a wind turbine according to claim 6, characterized in that: After the wind turbine pitch system is initialized and enters normal operation, each pitch driver first determines its current DC bus voltage U dc Is it greater than the second set threshold value U2? If so, the discharge IGBT is controlled to be turned on so that the power of the DC bus is discharged through the brake resistor corresponding to the blade shaft where the DC bus is located; if not, the wind turbine variable pitch system maintains normal operation; when the power of the DC bus is only discharged through the brake resistor corresponding to the blade shaft where the DC bus is located, if the DC bus voltage U dc When it has dropped below the first set threshold value U1, the pitch drive controls the discharge IGBT to turn off and stop the power discharge of the DC bus; at the moment the discharge IGBT is turned off, the excess discharge power flows back to the positive line of the DC bus through the freewheeling diode.

8. The method for controlling the variable pitch brake resistance of a wind turbine according to claim 7, characterized in that: The wind turbine variable pitch system determines whether the brake resistor corresponding to the blade shaft is faulty by checking whether the brake resistor fault flag count value Counter exceeds the preset upper limit A. If a fault occurs, the brake resistor fault flag FaultFlag of the blade shaft is set to 1, and if there is no fault, it is set to 0. When the DC bus voltage U dc After it has dropped to the first set threshold value U1 and the discharge IGBT is turned off, the pitch drive determines whether the brake resistor fault flag FaultFlag is 1. If so, a brake resistor failure alarm signal is sent out, and the wind turbine pitch system continues to run without stopping, waiting for maintenance personnel to inspect and repair it. At the same time, the pitch drive controls at least one DC contactor to close, so that its own DC bus power can be discharged through at least one brake resistor from the remaining blade shafts when it needs to be discharged; otherwise, the wind turbine pitch system maintains normal operating status.

9. The method for controlling the variable pitch brake resistance of a wind turbine according to claim 8, characterized in that: When the electric energy of the DC bus is discharged only through the brake resistor corresponding to the blade shaft, the corresponding variable pitch drive determines the DC bus voltage U dc Is it greater than the third set threshold U3, as follows: If the DC bus voltage U dc If the value is greater than the third set threshold value U3, the brake resistor fault flag count value Counter+1 is set to determine whether it has exceeded the preset upper limit A, and if it exceeds, the brake resistor fault flag FaultFlag is set to 1, and the pitch drive simultaneously controls at least one DC contactor to close, keeping at least one brake resistor from the remaining blade shafts in operation to realize the power discharge of the DC bus; If the DC bus voltage U dc If the value is not greater than the third set threshold value U3, the brake resistor fault flag count value Counter is cleared to 0, and the conduction of the discharge IGBT is continuously controlled so that the electric energy of the DC bus is only discharged through the brake resistor corresponding to the blade shaft where it is located.

10. The method for controlling the variable pitch brake resistance of a wind turbine according to claim 9, characterized in that: The DC bus voltage U dc After the DC bus voltage U is greater than the third set threshold value U3 and controls at least one DC contactor to close, the corresponding pitch drive continues to determine the DC bus voltage U dc Is it greater than the fourth set threshold U4, as follows: If the DC bus voltage U dc The voltage is greater than the fourth set threshold value U4, and the pitch drive controls at least two DC contactors to close, and keeps at least two braking resistors from the remaining blade shafts in operation to discharge the power of the DC bus; If the DC bus voltage U dc is not greater than the fourth set threshold value U4, the pitch drive still maintains the closure of at least one DC contactor to achieve the power discharge of the DC bus; When the DC bus voltage U dc When it drops to the first set threshold value U1, the corresponding discharge IGBT is turned off; If the braking resistor fault flag FaultFlag is still 0 at this time, the pitch drive controls the previously closed DC contactor to open; if the braking resistor fault flag FaultFlag is set to 1, the pitch drive controls at least one DC contactor to maintain a closed state.

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