Improved fault recovery control method and device for permanent magnet direct-driven wind driven generator

Abstract

The invention relates to the technical field of new energy control, in particular to an improved fault recovery control method and device for a permanent magnet direct-driven wind driven generator, fault recovery is carried out on a wind driven generator with an unloading circuit installed on the direct current side, and the method comprises the steps that the generator end voltage, the grid side current and the direct current voltage are detected, and the operation state of a wind turbine generator set is judged; and based on the operation state of the wind turbine generator, additional control is applied to the unloading circuit in the fault recovery stage of the wind turbine generator, and excess energy is released. Compared with the prior art, only a control device needs to be additionally arranged on the basis of the unloading circuit and the control link of the permanent magnet direct-driven wind driven generator, the needed detection control quantity is small, and the method can be compatible with a traditional wind turbine generator control strategy; moreover, the fault recovery control scheme can effectively suppress the active overshoot in the fault recovery control process of the permanent magnet direct-driven wind power generator, achieves the active smooth recovery of the fault, reduces the impact of the new energy fault ride-through control on the power equipment, and improves the operation stability of the system.

Description

Technical Field

[0001] The present invention relates to the field of new energy control technology, and in particular to an improved permanent magnet direct-drive wind turbine generator fault recovery control method and an implementation device. Background Art

[0002] With the rapid development of new power systems, the penetration rate of wind power has been continuously improved, which has had an important impact on the dynamic characteristics of the system. In order to avoid large-scale disconnection of wind turbines due to their own protection when the system fails, and cause greater impact on the power grid, my country's Wind Power Grid Connection Technical Specifications (GB / T 19963.1-2021) require that wind turbines should have a certain fault ride-through capability. During the duration of the fault, permanent magnet direct-drive wind turbines generally adopt reactive power priority control. Since the input power of the wind turbine remains basically unchanged, and the output active power is limited, the unbalanced power will cause the DC side voltage to rise. In order to prevent the DC voltage from being too high, the hysteresis comparator is often used to control the disconnection of the unloading circuit to consume excess active power. In the recovery stage after the fault is cleared, in order to reduce the impact of the rapid increase in active power on the system, the active power of the permanent magnet direct-drive wind turbine will climb at a certain slope until it returns to the steady-state power before the fault.

[0003] The existing fault ride-through control strategy plays an important role in keeping the permanent magnet direct-drive wind turbine generator from being disconnected from the grid and providing certain reactive power support to the system. However, at the end of the fault recovery control, the active power overshoot may occur, which seriously affects the normal operation of the system and equipment. The reason is that in the fault recovery stage, the output power is still less than the input power, and the residual power causes the DC voltage to continue to rise. When the recovery control ends, the wind turbine needs to be switched to the normal fixed DC voltage control mode. At this time, there is a large deviation between the DC voltage and the reference value, which leads to a sharp increase in the active current of the wind turbine and an overshoot of the output power.

[0004] In order to suppress the active power overshoot phenomenon, it is necessary to adjust the DC voltage during the fault recovery phase to restore it to a normal level. However, the existing fault recovery control has considered more the control strategy of the active and reactive current output of the wind turbine, and less involved the control of the DC voltage during the fault phase.

[0005] The technical solution disclosed in Chinese patent CN111725839B is to lock the grid-side converter during the fault period, put the unloading circuit into operation, and adjust the pitch angle to reduce the output power of the machine-side controller; after the fault is cleared, the grid-side converter is unlocked and the wind turbine is reconnected to the grid, thereby achieving fault ride-through of the wind turbine set, which focuses on the problem of wind turbine set disconnection caused by low voltage during the fault period. However, this solution locks the grid-side converter during the fault period, and the output active power and reactive power of the wind turbine set during the fault period are both 0, which cannot meet the requirements of wind power grid connection technical regulations, that is, the wind turbine set provides a certain dynamic reactive support capacity during the fault period.

[0006] Therefore, based on the existing permanent magnet direct-drive wind turbine generator, it is of great significance to study a simple and easy improved fault recovery control method and device to suppress active power overshoot and achieve a smooth transition from the fault recovery process to the normal operating state, which is of great significance to improving the grid-connected performance of wind turbines. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem that the fault recovery control of the above-mentioned existing permanent magnet direct-drive wind turbine generator does not take into account the DC capacitor overvoltage sufficiently, thereby causing active power overshoot at the end of the recovery phase, and to propose an improved permanent magnet direct-drive wind turbine generator fault recovery control method and implementation device.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] As a first aspect of the present invention, an improved permanent magnet direct-drive wind turbine fault recovery control method is provided, wherein the method performs fault recovery on a wind turbine with a load shedding circuit installed on the DC side, and the steps include:

[0010] Detect the machine-side voltage, grid-side current and DC voltage, and determine the operating status of the wind turbine;

[0011] Based on the operating status of the wind turbine, additional control is applied to the unloading circuit during the wind turbine fault recovery phase to release excess energy.

[0012] As a preferred technical solution, the method measures the terminal voltage, grid-side current and DC voltage of the wind turbine, and measures the terminal voltage phase angle.

[0013] The active component of the grid-side current is calculated using Park transformation according to the grid-side current and the phase angle of the generator-end voltage, and the initial active current of the wind turbine is sampled and recorded.

[0014] As a preferred technical solution, the operation status of the wind turbine generator set is determined as follows:

[0015] Set the DC voltage reference value and the low voltage ride-through threshold of the wind turbine;

[0016] When the terminal voltage is less than the low voltage ride-through threshold, it is determined that the permanent magnet direct-drive wind turbine generator is in the fault continuation stage;

[0017] When the terminal voltage is greater than the low voltage ride-through threshold, and the active component of the grid-side current is less than the initial active current or the difference between the DC voltage and its reference value is greater than or equal to the set threshold, it is determined that the wind turbine is in the fault recovery stage;

[0018] When the voltage amplitude at the generator end is greater than the low voltage ride-through threshold, and the active components of the DC voltage and grid-side current have recovered to their pre-fault steady-state values, the system is considered to be in normal operation.

[0019] As a preferred technical solution, the method applies additional control to the unloading circuit based on the operating state of the wind turbine generator set, as follows:

[0020] When the permanent magnet direct-drive wind turbine generator is in the fault continuation stage or normal operation state, the additional control link is locked;

[0021] When the wind turbine is in the recovery stage, the additional control link is put into operation, and the duty cycle is calculated through proportional-integral operation according to the DC voltage deviation; the pulse generator generates an additional control signal according to the calculated duty cycle, and performs an OR operation with the original hysteresis control output signal of the wind turbine to obtain a synthetic trigger signal to control the opening and closing of the unloading circuit and realize the dissipation of excess energy.

[0022] As a preferred technical solution, under the additional control, the DC voltage satisfies:

[0023]

[0024] Where D is the duty cycle; R and C are the unloading resistor and DC capacitor respectively; P0 is the mechanical power input by the wind turbine; P c is the wind turbine output power at the time of fault clearing; r is the climbing slope of the wind turbine in the recovery phase; t r The duration of fault recovery at the current moment.

[0025] As an optimal technical solution, the proportional coefficient and the integral coefficient of the proportional-integral operation vary with the working state of the wind turbine when the fault is cleared, and the optimal control parameters corresponding to the difference between different wind turbine input mechanical powers and the wind turbine group output power at the time of fault clearing are calculated offline in advance. During online additional control, the measured wind turbine input mechanical power and the wind turbine group output power at the time of fault clearing are selected from the table.

[0026] As an optimal technical solution, when the active components of the DC voltage and the grid-side current have recovered to the steady-state values ​​before the fault, the permanent magnet direct-drive wind turbine fault recovery is completed, the additional control is exited, and the unit control switches from recovery control to normal control strategy.

[0027] As a second aspect of the present invention, an improved permanent magnet direct-drive wind turbine fault recovery control device is provided. The fault recovery control device is applied to a wind turbine with a load shedding circuit installed on the DC side and implements the above method, specifically comprising:

[0028] Signal measurement and processing module: used to measure the wind turbine terminal voltage, grid-side current, DC voltage and terminal voltage phase angle, and calculate the active component of the grid-side current;

[0029] The logic control and protection module includes: a comparator and a combination logic unit; the comparator compares the machine-end voltage, the grid-side current, and the DC voltage with the corresponding threshold value to determine the control stage of the permanent magnet direct-drive wind turbine; the combination logic unit sends a first additional control signal when the machine-end voltage returns to normal, but the active component of the grid-side current has not recovered or the DC voltage is greater than the reference value, and starts additional control; when it is determined that the unit recovery is complete, a second additional control signal is sent, and the additional control is exited;

[0030] The voltage regulation and pulse generation module includes a control switch, a proportional-integral controller, a pulse generator, and a logic or element; the control switch receives an additional control signal, and when the additional control signal is a first additional control signal, the DC voltage deviation is input into the proportional-integral controller to calculate the duty cycle; when the additional signal is a second additional control signal, the additional control output duty cycle is 0; the pulse generator generates a trigger signal and performs an OR operation with the output signal of the original hysteresis control of the wind turbine to obtain a synthesized unloading circuit control signal;

[0031] The driving output module is a driving amplifying unit, which amplifies the trigger pulse outputted by the voltage regulating and pulse generating module to drive the unloading circuit, and controls the connection and disconnection of the unloading resistor.

[0032] As a preferred technical solution, the signal measurement and processing module includes: an AC voltage transformer, an AC current transformer, a DC voltage transformer and a signal processing unit, wherein:

[0033] The AC voltage transformer is connected to the low voltage side of the wind turbine grid-connected box transformer to detect the terminal voltage of the wind turbine;

[0034] The AC current transformer is connected to the grid-side converter outlet to detect the grid-side current;

[0035] The DC voltage transformer is connected to both ends of the capacitor to detect the DC voltage;

[0036] Phase-locked loop, measuring the phase angle of the terminal voltage;

[0037] The sampling signals of each mutual inductor are transmitted to the signal processing unit of the signal measurement and processing module in real time;

[0038] The signal processing unit functions as filtering and coordinate transformation, and performs Park transformation according to the phase angle of the machine-end voltage measured by the phase-locked loop to obtain the machine-end voltage, the grid-side active current and the DC capacitor voltage.

[0039] As a preferred technical solution, under the additional control of the voltage regulation and pulse generation module, the DC voltage satisfies:

[0040]

[0041] Where D is the duty cycle; R and C are the unloading resistor and DC capacitor respectively; P0 is the mechanical power input by the wind turbine; P c is the wind turbine output power at the time of fault clearing; r is the climbing slope of the wind turbine in the recovery phase, denoted by ΔP = P0-P c ;t r The duration of the fault recovery at the current moment;

[0042] The values ​​of the proportional coefficient and the integral coefficient of the proportional-integral controller vary with the working state of the wind turbine when the fault is cleared. The optimal control parameters corresponding to different ΔPs calculated offline in advance are selected by looking up the table according to the difference between the measured wind turbine input mechanical power and the wind turbine output power at the time of fault clearing during online additional control.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) Based on the existing permanent magnet direct-drive wind turbine topology and fault ride-through control strategy, the present invention adds an additional control device, and switches the unloading resistor based on the collected terminal voltage, unit current and DC voltage signal without changing the existing unit low voltage ride-through control strategy, dissipates and eliminates excess energy in the recovery process, thereby achieving a smooth transition from the fault stage to the normal operating state.

[0045] 2) The present invention only uses the terminal voltage, DC voltage and active current signal measurement values ​​to realize the switching of the control device, the amount of signal processing required is small, and only the PI controller parameters need to be adjusted according to different faults. Under different degrees of faults, the active overshoot in the fault recovery stage can be effectively suppressed, and the control method is simple, so it has better applicability and flexibility.

[0046] 3) The additional controller proposed in the present invention is only put into use during the fault recovery phase and does not affect the control of other phases. Therefore, it can meet the reactive power support requirements during the fault period and output active power as much as possible to achieve fault ride-through and maximize the use of wind energy. The present invention optimizes the dynamic performance of wind turbines during the fault recovery phase and better meets the operating requirements of wind farms and power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A structural diagram of a permanent magnet direct-drive wind turbine generator with additional control provided in an embodiment of the present invention.

[0048] Figure 2 A flow chart of an improved permanent magnet direct-drive synchronous wind turbine fault recovery control method provided in an embodiment of the present invention.

[0049] Figure 3 A comparison diagram of active power and DC voltage response curves of a permanent magnet direct-drive wind turbine generator in scenario A under different control actions provided in an embodiment of the present invention, wherein: (3a) is active power, (3b) is DC voltage; the solid line corresponds to improved control, and the dotted line corresponds to traditional control.

[0050] Figure 4 A comparison diagram of active power and DC voltage response curves of a permanent magnet direct-drive wind turbine generator in scenario B under different control actions provided in an embodiment of the present invention, wherein: (4a) is active power, (4b) is DC voltage; the solid line corresponds to improved control, and the dotted line corresponds to traditional control.

[0051] Figure 5 A comparison diagram of active power and DC voltage response curves of a permanent magnet direct-drive wind turbine generator in scenario C under different control actions provided in an embodiment of the present invention, wherein: (5a) is active power, (5b) is DC voltage; the solid line corresponds to improved control, and the dotted line corresponds to traditional control.

[0052] Figure 6 A comparison diagram of active power and DC voltage response curves of a permanent magnet direct-drive wind turbine generator in scenario D under different control actions provided in an embodiment of the present invention, wherein: (6a) is active power, (6b) is DC voltage; the solid line corresponds to improved control, and the dotted line corresponds to traditional control. DETAILED DESCRIPTION

[0053] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] Based on the existing permanent magnet direct-drive wind turbine topology and fault ride-through control strategy, the present invention adds an additional control device, switches the unloading resistor according to the collected terminal voltage, unit current and DC voltage signal, thereby dissipating and eliminating excess energy in the recovery process, and achieving a smooth transition from the recovery stage to the normal operating state.

[0056] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions.

[0057] An improved permanent magnet direct-drive wind turbine fault recovery control method and implementation device, comprising the following steps:

[0058] (1) Detect the terminal voltage, grid-side current and DC voltage and determine the operating status of the wind turbine;

[0059] (2) Method for releasing excess energy in the recovery process based on additional control;

[0060] (3) Additional control device and parameter setting of permanent magnet direct-drive wind turbine generator;

[0061] Specifically, in step (1), the terminal voltage, grid-side current and DC voltage are detected to determine the operating status of the wind turbine. The AC voltage transformer (PT) is used to detect the terminal voltage V of the wind turbine. T , use AC current transformer (CT) to detect the grid-side current I g,abc , use DC voltage transformer (DCPT) to detect DC voltage U dc , use a phase-locked loop (PLL) to measure the phase angle θ of the terminal voltage, and according to the grid-side current I g,abc The active component I of the grid-side current is calculated by using Park transformation and the phase angle θ of the voltage at the generator end. d :

[0062]

[0063] In the formula, I g,a ,I g,b ,I g,c I g,abc The instantaneous value of the ABC three-phase; the initial active current of the wind turbine is sampled and recorded as I d0 ;

[0064] Assume that the DC voltage reference value is U dc,ref The threshold for the wind turbine to enter low voltage ride-through is V th , when the terminal voltage V T The amplitude is less than the low voltage ride-through threshold V th When the permanent magnet direct-drive wind turbine generator is in the fault continuation stage, it is judged that the permanent magnet direct-drive wind turbine generator is in the fault continuation stage; when the terminal voltage V T Amplitude greater than V th , and I d <I d0 or |U dc -U dc,ref |≥ε, the wind turbine is judged to be in the fault recovery stage, ε is a set decimal; when V T Amplitude greater than V th , and U dc and I d When all have recovered to the steady-state values ​​before the fault, the system is in normal operation.

[0065] The method for releasing excess energy in the recovery process based on additional control described in step (2) is implemented as follows:

[0066] When the permanent magnet direct-drive wind turbine generator is in the fault continuation stage or normal operation state, the additional control link is locked; when the wind turbine is in the recovery stage, the additional control link is put into operation, and the DC voltage deviation U dc -U dc,ref , calculate the duty cycle D through proportional integral operation, the calculation formula is:

[0067] D=k p (U dc -U dc,ref )+k i ∫(U dc -U dc,ref )dt (2)

[0068] In the formula, k p , k i are proportional coefficient and integral coefficient respectively, and the duty cycle takes a value of 0≤D≤1; the pulse generator generates an additional control signal according to the calculated duty cycle D, and performs an OR operation with the original hysteresis control output signal of the wind turbine to obtain a synthetic trigger signal to control the disconnection of the unloading circuit and realize the dissipation of excess energy;

[0069] Under the additional control, the DC voltage U dc satisfy:

[0070]

[0071] Where D is the duty cycle; R and C are the unloading resistor and DC capacitor respectively; P0 is the mechanical power input by the wind turbine; P c is the wind turbine output power at the time of fault clearing; r is the climbing slope of the wind turbine in the recovery phase, denoted by ΔP = P0-P c ;t r is the duration of fault recovery at the current moment. For a specific wind turbine, R, C and r are fixed values, so U dc The dynamic characteristics of the p and k i , k p The larger the value, the faster the excess energy of the DC capacitor is released; k i The larger the U dc The overshoot is large; generally, different P0-P c , calculate offline the k with shorter adjustment time and smaller overshoot p and k i Value, for selection by table lookup during online additional control;

[0072] WhenUdc and I d When all have recovered to the steady-state value before the fault, the permanent magnet direct-drive wind turbine fault recovery is complete, the additional control is exited, and the unit control is switched from recovery control to normal control strategy.

[0073] The additional control device and parameter setting of the permanent magnet direct-drive wind turbine generator described in step (3) are implemented as follows:

[0074] The additional control device of the permanent magnet direct-drive wind turbine generator includes a signal measurement and processing module, a logic control and protection module, a voltage regulation and pulse generation module and a drive output module;

[0075] The signal measurement and processing module includes PT, CT, DCPT and signal processing unit; PT is connected to the low-voltage side of the wind turbine grid-connected box transformer, CT is connected to the grid-side converter outlet side, DCPT is connected to both ends of the capacitor, and the sampling signal is transmitted to the signal processing unit of the signal measurement and processing module in real time; the signal processing unit functions as filtering and coordinate transformation, and performs Park transformation according to the machine-end voltage phase angle θ measured by the phase-locked loop to obtain the machine-end voltage V T , grid-side active current I d and DC capacitor voltage U dc ;

[0076] The logic control and protection module includes a comparator and a combinational logic unit; the comparator converts V T , U dc and I d The control stage of the permanent magnet direct-drive wind turbine generator is determined by comparing with the corresponding threshold value; when the terminal voltage of the generator returns to normal but the active power is not restored or the DC voltage is greater than the reference value, the combination logic unit sends an additional control signal "1" to start additional control; when it is determined that the generator set has finished recovery, an additional control signal "0" is sent to exit the additional control; based on the components, the control mode logic of the generator set is correctly switched to protect the normal and stable operation of the wind turbine;

[0077] The voltage regulation and pulse generation module includes a control switch, a proportional-integral controller, a pulse generator, and a logic or element; the control switch receives an additional control signal, and when the additional control signal is "1", the DC voltage deviation is input into the proportional-integral controller to calculate the duty cycle D; when the additional signal is "0", the additional control output duty cycle is 0; the pulse generator generates a trigger signal according to D, and performs an OR operation with the output signal of the original hysteresis control of the wind turbine to obtain a synthesized unloading circuit control signal; based on the components, the effective coordination of the additional device control and the original hysteresis control is achieved, the hysteresis control is fully engaged, and the additional control is only engaged in the fault recovery stage; the drive output module is a drive amplifier unit, which amplifies the trigger pulse output by the voltage regulation and pulse generation module, drives the insulated gate bipolar transistor (IGBT) device of the unloading circuit, and controls the connection and disconnection of the unloading resistor;

[0078] The parameters of the additional control device of the permanent magnet direct-drive wind turbine generator include the proportional-integral controller parameters and the pulse generator frequency; the proportional-integral controller parameters k p and k i The value of varies with the working state of the fan when the fault is cleared. Different P0-P c The corresponding optimal control parameters are based on the measured P0 and P c Select by looking up the table; the frequency of the pulse generator is related to the consumption rate of the excess power of the DC capacitor. A lower switching frequency will reduce the consumption rate of the unbalanced power on the DC side, causing the DC voltage oscillation to attenuate and affecting the service life of the capacitor. Too high a switching frequency will increase the switching loss. Generally, the rated frequency of the pulse generator can be taken as 2000Hz.

[0079] Different wind speeds and voltage drop values ​​are set to verify whether the additional control device operates normally in different scenarios; the improved recovery control method of the present invention is compared with the traditional recovery control method, and the influence of different wind speeds and different voltage drops on the active power and DC voltage response in the fault recovery stage is analyzed. According to the active power response curve in the fault recovery stage, the active overshoot percentage δ is calculated:

[0080]

[0081] Where: P(t) is the active power of the wind turbine after the fault is cleared; P0 is the output power of the wind turbine in the initial steady state, that is, the mechanical power input by the wind turbine;

[0082] By calculating and comparing the active power overshoot percentages in different scenarios, the effectiveness of the improved recovery control method and device of the present invention in suppressing active power overshoot in the fault recovery stage of a permanent magnet direct-drive wind turbine and achieving a smooth transition from fault recovery to normal operation is verified.

[0083] Example 2

[0084] As one of the specific implementation examples of the present invention, the permanent magnet direct-drive wind turbine generator with additional control in this embodiment is driven by a wind turbine, and the mechanical energy is converted into electrical energy through a back-to-back converter. A load unloading circuit is installed on the DC side, and the grid-side converter is connected to the grid-side converter through a filter inductor L f And the resistor R f After being connected to the machine end, the wind turbine is connected to the grid through a box-type transformer. The grid consists of a power supply and a reactor. The parameters of the permanent magnet direct-drive wind turbine grid-connected system are shown in Table 1.

[0085] Table 1 Parameters of permanent magnet direct-drive wind turbine grid-connected system

[0086]

[0087] The steps of the method in the above embodiment are specifically implemented as follows:

[0088] In step (1), the terminal voltage, grid current and DC voltage are detected to determine the operating status of the wind turbine. The terminal voltage V of the wind turbine is detected using PT, CT and DCPT respectively. T , grid-side current I g,abc and DC voltage U dc , use a phase-locked loop (PLL) to measure the terminal voltage phase angle θ, according to I g,abc and θUse Park transformation to calculate the active component I of the grid-side current d , sample and record the initial active current of the wind turbine as I d0 ;

[0089] Take the DC voltage reference value U dc,ref is 1100V, the wind turbine low voltage crossing threshold V th is 0.9pu, when V T Less than V th When V T Greater than V th , and I d <I d0 or |U dc -U dc,ref |≥ε, the wind turbine is judged to be in the fault recovery stage, and ε is 2; when V T Amplitude greater than V th , and U dc and I d When all have recovered to the steady-state value before the fault, the system is considered to be in normal operation.

[0090] In step (2) of the present invention, the method for releasing excess energy in the recovery process based on additional control is:

[0091] Attached Figure 2 A flow chart of an improved permanent magnet direct-drive synchronous wind turbine fault recovery control method provided by an embodiment of the present invention; when the permanent magnet direct-drive wind turbine is in a fault continuation stage or a normal operation state, the additional control link is locked; when the wind turbine is in a recovery stage, the additional control link is put into operation, and the DC voltage deviation U dc -U dc,ref , calculate the duty cycle D=k through proportional integral operation p (U dc -U dc,ref )+k i ∫(U dc -U dc,ref )dt,0≤D≤1,k p , k i are the proportional coefficient and the integral coefficient respectively;

[0092] In this embodiment, the unloading resistor R and the DC capacitor C are 0.4225Ω and 0.09F respectively. The climbing slope r of the wind turbine in the recovery stage is 0.2pu / s. Under the additional control, the DC voltage U dc satisfy Let ΔP=P0-P c , U dc The dynamic characteristics of the p and k i , take different ΔP in the interval [0,0.6] with a step size of 0.05, and calculate the k with shorter adjustment time and smaller overshoot offline p and k i The values ​​are shown in Table 2. When online, according to the ΔP measured when the fault is cleared, the corresponding k is selected by looking up the table. p and k i Perform additional controls;

[0093] Table 2 Parameters of additional controller for permanent magnet direct-drive wind turbine generator

[0094]

[0095] The pulse generator generates an additional control signal according to the calculated duty cycle D, and performs an OR operation with the original hysteresis control output signal of the wind turbine to obtain a synthetic trigger signal to control the disconnection of the unloading circuit to achieve the dissipation of excess energy; when U dc and I d When all have recovered to the steady-state value before the fault, the permanent magnet direct-drive wind turbine fault recovery is complete, the additional control is exited, and the unit control switches from recovery control to normal control strategy.

[0096] In step (3) of the present invention, the implementation process of the additional control device and parameter setting of the permanent magnet direct-drive wind turbine generator is as follows:

[0097] The additional control device of the permanent magnet direct-drive wind turbine generator includes a signal measurement and processing module, a logic control and protection module, a voltage regulation and pulse generation module and a drive output module;

[0098] The signal measurement and processing module includes PT, CT, DCPT and signal processing unit; PT is connected to the low-voltage side of the wind turbine grid-connected box transformer, CT is connected to the grid-side converter outlet side, DCPT is connected to both ends of the capacitor, and the sampling signal is transmitted to the signal processing unit of the signal measurement and processing module in real time; the signal processing unit functions as filtering and coordinate transformation, and performs Park transformation according to the machine-end voltage phase angle θ measured by the phase-locked loop to obtain the machine-end voltage V T , grid-side active current I d and DC capacitor voltage U dc ;

[0099] The logic control and protection module includes a comparator and a combinational logic unit; the comparator converts V T , U dc and I d The combination logic unit sends an additional control signal "1" to start additional control when the terminal voltage returns to normal but the active power is not restored or the DC voltage is greater than the reference value; when it is judged that the unit has finished recovery, it sends an additional control signal "0" to exit the additional control; based on the components, the control mode logic of the unit is correctly switched to protect the normal and stable operation of the wind turbine;

[0100] The voltage regulation and pulse generation module includes a control switch, a proportional-integral controller, a pulse generator, and a logic or element; the control switch receives an additional control signal, and when the additional control signal is "1", the DC voltage deviation is input into the proportional-integral controller to calculate the duty cycle D; when the additional control signal is "0", the additional control duty cycle is 0; the pulse generator generates a trigger signal according to D, and performs an OR operation with the output signal of the original hysteresis control of the wind turbine to obtain a synthesized unloading circuit control signal; based on the components, the effective coordination of the additional device control and the original hysteresis control is achieved, the hysteresis control is fully engaged, and the additional control is only engaged in the fault recovery stage; the drive output module is a drive amplification unit, which amplifies the trigger pulse output by the voltage regulation and pulse generation module, drives the IGBT device of the unloading circuit, and controls the connection and disconnection of the unloading resistor;

[0101] The parameters of the additional control device of the permanent magnet direct-drive wind turbine generator include the proportional-integral controller parameters and the pulse generator frequency; the proportional-integral controller parameters k p and k iThe value of varies with the working state of the fan when the fault is cleared. The optimal control parameters corresponding to different ΔP can be calculated offline in advance. During online additional control, the measured P0 and P c Select by looking up the table; the frequency of the pulse generator is related to the consumption rate of the excess power of the DC capacitor. A lower switching frequency will reduce the consumption rate of the unbalanced power on the DC side, causing the DC voltage oscillation to attenuate and affecting the service life of the capacitor. Too high a switching frequency will increase the switching loss. Generally, the rated frequency of the pulse generator can be taken as 2000Hz.

[0102] In step (4) of the present invention, the fault recovery characteristic verification of the permanent magnet direct-drive wind turbine generator with additional control is implemented as follows:

[0103] In order to verify the effectiveness of the improved control method and device proposed in the present invention, four scenarios with different wind speeds and voltage drop values ​​are set, namely: 1) Scenario A, wind speed 13m / s, fault voltage 0.60pu; 2) Scenario B, wind speed 13m / s, fault voltage 0.30pu; 3) Scenario C, wind speed 11m / s, fault voltage 0.60pu; 4) Scenario D, wind speed 11m / s, fault voltage 0.30pu; The action of the additional control device in different scenarios is shown in Table 3. It can be seen from the table that the logic control and protection modules of the additional control device in different scenarios accurately judge the stage of the wind turbine and act correctly;

[0104] Table 3 Additional control actions in different scenarios

[0105]

[0106]

[0107] The improved fault recovery control method of the present invention is compared with the traditional fault recovery control method, and the influence of different wind speeds and different voltage drops on the active power and DC voltage response in the fault recovery stage are analyzed; Figure 3 The comparison of active power and DC voltage response curves of permanent magnet direct-drive wind turbine generator under improved fault recovery control and traditional control in scenario A is given. Similarly, the attached Figure 4 , Attachment Figure 5 And attached Figure 6 The comparison of active power and DC voltage response curves in scenario B, scenario C and scenario D are given respectively; it can be seen from the figure that under different scenarios, the traditional control has a certain active power overshoot phenomenon, while the additional control can make the DC voltage quickly recover to U dc,ref , and avoids active power overshoot at the end of the recovery process, achieving a smooth transition from the recovery phase to the normal operation phase;

[0108] According to the active power response curves under different scenarios, the active overshoot percentage δ corresponding to different controls is calculated. The results are shown in Table 4. It can be seen from Table 4 that the active overshoot percentage under the improved control is reduced to below 1.3%, which effectively reduces the impact of active overshoot on equipment and power system at the end of fault recovery.

[0109] Table 4 Active overshoot percentage under different control

[0110]

[0111] In summary, the improved permanent magnet direct-drive wind turbine fault recovery control method and implementation device of the present invention, based on the existing permanent magnet direct-drive wind turbine topology and fault ride-through control strategy, detects the terminal voltage, grid-side current and DC voltage to identify the wind turbine operating state, and determines whether the additional control is put into use, details the excess energy release method of the recovery process based on the additional control, and introduces the structure and parameter setting method of the additional control device of the permanent magnet direct-drive wind turbine. Finally, through simulation calculations of various scenarios, the effectiveness of the additional control device in improving the fault recovery characteristics of the permanent magnet direct-drive wind turbine is verified. The method and implementation device of the present invention are simple and easy to implement, can effectively suppress the active overshoot at the end of the fault recovery of the permanent magnet direct-drive wind turbine, and realize a smooth transition from the fault recovery process to the normal operating state, which is of great significance for improving the grid-connected performance of the wind turbine.

[0112] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. An improved permanent magnet direct-drive wind turbine fault recovery control method, characterized in that: The method performs fault recovery on a wind turbine generator with a load shedding circuit installed on the DC side, and the steps include: Detect the machine-side voltage, grid-side current and DC voltage, and determine the operating status of the wind turbine; Based on the operating status of the wind turbine, additional control is applied to the unloading circuit during the wind turbine fault recovery phase to release excess energy.

2. An improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 1, characterized in that: The method measures the terminal voltage, grid-side current and DC voltage of the wind turbine, and measures the terminal voltage phase angle. The active component of the grid-side current is calculated using Park transformation according to the grid-side current and the phase angle of the generator-end voltage, and the initial active current of the wind turbine is sampled and recorded.

3. The improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 2 is characterized in that: The determination of the operating state of the wind turbine generator set is as follows: Set the DC voltage reference value and the low voltage ride-through threshold of the wind turbine; When the terminal voltage is less than the low voltage ride-through threshold, it is determined that the permanent magnet direct-drive wind turbine generator is in the fault continuation stage; When the terminal voltage is greater than the low voltage ride-through threshold, and the active component of the grid-side current is less than the initial active current or the difference between the DC voltage and its reference value is greater than or equal to the set threshold, it is determined that the wind turbine is in the fault recovery stage; When the voltage amplitude at the generator end is greater than the low voltage ride-through threshold, and the active components of the DC voltage and grid-side current have recovered to their pre-fault steady-state values, the system is considered to be in normal operation.

4. The improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 1 is characterized in that: The method applies additional control to the unloading circuit based on the operating state of the wind turbine generator set, specifically as follows: When the permanent magnet direct-drive wind turbine generator is in the fault continuation stage or normal operation state, the additional control link is locked; When the wind turbine is in the recovery stage, the additional control link is put into operation, and the duty cycle is calculated through proportional-integral operation according to the DC voltage deviation; the pulse generator generates an additional control signal according to the calculated duty cycle, and performs an OR operation with the original hysteresis control output signal of the wind turbine to obtain a synthetic trigger signal to control the opening and closing of the unloading circuit and realize the dissipation of excess energy.

5. The improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 4 is characterized in that: Under the additional control, the DC voltage satisfies: Where D is the duty cycle; R and C are the unloading resistor and DC capacitor respectively; P0 is the mechanical power input by the wind turbine; P c is the wind turbine output power at the time of fault clearing; r is the climbing slope of the wind turbine in the recovery phase; t r The duration of fault recovery at the current moment.

6. The improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 4, characterized in that: The values ​​of the proportional coefficient and the integral coefficient of the proportional-integral operation vary with the working state of the wind turbine when the fault is cleared. The optimal control parameters corresponding to the difference between different wind turbine input mechanical powers and the wind turbine group output power at the time of fault clearing are calculated offline in advance. During online additional control, the measured wind turbine input mechanical power and the wind turbine group output power at the time of fault clearing are selected by looking up the table.

7. An improved permanent magnet direct-drive wind turbine fault recovery control method according to claim 4, characterized in that: When the active components of the DC voltage and grid-side current have recovered to the steady-state values ​​before the fault, the permanent magnet direct-drive wind turbine fault recovery is complete, the additional control is exited, and the unit control switches from recovery control to normal control strategy.

8. An improved permanent magnet direct drive wind turbine fault recovery control device, characterized in that: The fault recovery control device is applied to a wind turbine with a load shedding circuit installed on the DC side, and implements the method as claimed in any one of claims 1 to 7, specifically comprising: Signal measurement and processing module: used to measure the wind turbine terminal voltage, grid-side current, DC voltage and terminal voltage phase angle, and calculate the active component of the grid-side current; The logic control and protection module includes: a comparator and a combination logic unit; the comparator compares the machine-end voltage, the grid-side current, and the DC voltage with the corresponding threshold value to determine the control stage of the permanent magnet direct-drive wind turbine; the combination logic unit sends a first additional control signal when the machine-end voltage returns to normal, but the active component of the grid-side current has not recovered or the DC voltage is greater than the reference value, and starts additional control; when it is determined that the unit recovery is complete, a second additional control signal is sent, and the additional control is exited; The voltage regulation and pulse generation module includes a control switch, a proportional-integral controller, a pulse generator, and a logic or element; the control switch receives an additional control signal, and when the additional control signal is a first additional control signal, the DC voltage deviation is input into the proportional-integral controller to calculate the duty cycle; when the additional signal is a second additional control signal, the additional control output duty cycle is 0; the pulse generator generates a trigger signal and performs an OR operation with the output signal of the original hysteresis control of the wind turbine to obtain a synthesized unloading circuit control signal; The driving output module is a driving amplifying unit, which amplifies the trigger pulse outputted by the voltage regulating and pulse generating module to drive the unloading circuit, and controls the connection and disconnection of the unloading resistor.

9. The improved permanent magnet direct-drive wind turbine fault recovery control device according to claim 8, characterized in that: The signal measurement and processing module includes: an AC voltage transformer, an AC current transformer, a DC voltage transformer and a signal processing unit, wherein: The AC voltage transformer is connected to the low voltage side of the wind turbine grid-connected box transformer to detect the terminal voltage of the wind turbine; The AC current transformer is connected to the grid-side converter outlet to detect the grid-side current; The DC voltage transformer is connected to both ends of the capacitor to detect the DC voltage; Phase-locked loop, measuring the phase angle of the terminal voltage; The sampling signals of each mutual inductor are transmitted to the signal processing unit of the signal measurement and processing module in real time; The signal processing unit functions as filtering and coordinate transformation, and performs Park transformation according to the phase angle of the machine-end voltage measured by the phase-locked loop to obtain the machine-end voltage, the grid-side active current and the DC capacitor voltage.

10. The improved permanent magnet direct-drive wind turbine fault recovery control device according to claim 8, characterized in that: Under the additional control of the voltage regulation and pulse generation module, the DC voltage satisfies: Where D is the duty cycle; R and C are the unloading resistor and DC capacitor respectively; P0 is the mechanical power input by the wind turbine; P c The wind turbine output power at the moment when the fault is cleared; r is the climbing slope of the wind turbine in the recovery phase, denoted by ΔP = P0-P c ;t r The duration of the fault recovery at the current moment; The values ​​of the proportional coefficient and the integral coefficient of the proportional-integral controller vary with the working state of the wind turbine when the fault is cleared. The optimal control parameters corresponding to different ΔPs calculated offline in advance are selected by looking up the table according to the difference between the measured wind turbine input mechanical power and the wind turbine output power at the time of fault clearing during online additional control.

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