CN106451555A - Low-voltage ride through control method and system of doubly-fed wind turbine - Google Patents
Low-voltage ride through control method and system of doubly-fed wind turbine Download PDFInfo
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Abstract
The embodiment of the invention provides a low-voltage ride through control method and system of a double-fed fan, relates to the technical field of new energy grid-connected power generation control, and can improve the stability of an alternating current system. The specific scheme comprises the following steps: detecting an outlet voltage effective value of the double-fed fan; when the effective value of the outlet voltage is determined to be smaller than the low-voltage ride-through starting value, controlling the grid-side converter to be switched from constant reactive current control in a steady state to constant transient alternating voltage control; after the constant transient state alternating voltage control is started, the Q-axis current of the grid side converter is increased, and the output reactive power of the double-fed fan is increased. The method is used for controlling the low voltage ride through of the doubly-fed fan.
Description
Technical Field
The embodiment of the invention relates to the technical field of new energy grid-connected power generation control, in particular to a low-voltage ride through control method and system of a double-fed fan.
Background
A wind power generation system is an energy conversion system that converts wind energy into electrical energy. The exploitation and utilization of wind energy as a renewable energy source has received great attention in recent years, and a large number of wind power generation systems have been put into operation. The wind power generation system can be divided into a constant frequency/constant speed system and a constant frequency/variable speed system according to the rotating speed of a fan. The constant-frequency/variable-speed wind power generation system can adjust the rotating speed of the generator in real time according to the condition of the wind speed, so that the fan runs near the optimal tip speed ratio, the running efficiency of the fan is optimized, and meanwhile, the generator can be ensured to output electric power with constant frequency to a power grid through the control system.
The most common of constant frequency/variable speed wind power generation systems is the doubly-fed wind power generation system. The stator of the double-fed fan is directly connected with a power grid, the rotor is connected into the power grid through the frequency converter, the frequency converter can change the frequency of the input current of the rotor of the generator, the output of the stator of the generator can be ensured to be synchronous with the frequency of the power grid, and variable-speed constant-frequency control is realized. With the increasing wind power generation capacity and the wind power plant scale, the wind power integration standard requires that the doubly-fed wind turbine has low voltage ride through capability. A common low voltage ride through control strategy is to short circuit the fan rotor windings during a fault using Crowbar circuitry (Crowbar) to reduce the fault current flowing into the rotor side inverter to prevent the fan from going out of service.
However, in the prior art, when a fault of a far-end ac system occurs, transient power disturbance is often brought, which affects the stability of the ac system.
Disclosure of Invention
The embodiment of the invention provides a low-voltage ride through control method and system of a double-fed fan, which can improve the stability of an alternating current system.
In order to achieve the above purpose, the embodiments of the present application adopt the following technical solutions:
in a first aspect, a low voltage ride through control method for a doubly-fed wind turbine is provided, which includes:
detecting an outlet voltage effective value of the double-fed fan;
when the effective value of the outlet voltage is determined to be smaller than the low-voltage ride-through starting value, controlling the grid-side converter to be switched from constant reactive current control in a steady state to constant transient alternating voltage control;
after the constant transient state alternating voltage control is started, the Q-axis current of the grid side converter is increased, and the output reactive power of the double-fed fan is increased.
In a second aspect, a low voltage ride through control system for a doubly fed wind turbine is provided, comprising: the system comprises a low voltage ride through controller, a grid-side converter and a double-fed fan;
the low-voltage ride-through controller is used for detecting an effective value of outlet voltage of the doubly-fed wind turbine, and outputting a switching enabling signal to the grid-side converter controller when the effective value of the outlet voltage is determined to be smaller than a low-voltage ride-through starting value;
after the grid side converter controller receives the conversion enabling signal, the grid side converter is controlled to be switched from constant reactive current control in a steady state to constant transient state alternating current voltage control;
after the constant transient state alternating voltage control is started, the Q-axis current of the grid side converter is increased, and the output reactive power of the double-fed fan is increased.
According to the low voltage ride through control method and system of the double-fed fan provided by the embodiment of the invention, when a far-end alternating current system fault occurs, if the effective value of the outlet voltage of the double-fed fan is determined to be smaller than the low voltage ride through starting value, the Q-axis current is switched from the constant current control to the transient alternating current voltage control, and the double-fed fan outputs certain reactive power to support the voltage of the alternating current system, so that the stability of the alternating current system is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a low voltage ride through control system of a doubly-fed wind turbine according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of a low voltage ride through control method of a doubly-fed wind turbine according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating a corresponding relationship between wind speed, rotor speed of a doubly-fed wind turbine and output active power;
fig. 4 is a schematic diagram illustrating a rotor side converter controller configuration in an embodiment of the present invention;
fig. 5 is a schematic diagram illustrating a configuration of a grid-side converter controller according to an embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating a low voltage ride through recovery value, a low voltage ride through enable value, and a low voltage ride through lockout value according to an embodiment of the present invention;
FIG. 7 is a schematic diagram illustrating the structure of a low voltage ride through controller according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method and a system for improving low voltage ride through control of a doubly-fed wind turbine. On the basis of decoupling control of active power and reactive power of the doubly-fed wind turbine, the control system controls low voltage ride through in a mode of combining transient alternating voltage control and Crowbar control, so that the doubly-fed wind turbine outputs certain reactive power to support system voltage during a far-end fault, and further the doubly-fed wind turbine is rapidly switched into Crowbar control and locks a rotor converter to rapidly reduce rotor current when a near-end fault occurs. The following embodiments are specifically described below.
Examples
The embodiment of the invention provides a low voltage ride through control method of a double-fed fan, which is applied to a low voltage ride through control system of the double-fed fan provided by the embodiment of the invention. The control system is shown in fig. 1 and comprises a doubly-fed wind turbine 101, a grid-side converter 102, a rotor-side converter 103, and a rotor-side Crowbar circuit 104. Each of the above sections includes a respective controller (not shown in fig. 1), specifically a low voltage ride through controller, a grid-side converter controller, and a rotor-side converter controller. Referring to fig. 2, the low voltage ride through control method includes the following steps:
201. and detecting the effective value of the outlet voltage of the doubly-fed fan 101.
The effective voltage value of the doubly-fed wind turbine 101 can be detected in real time, and the detection result is judged to determine whether to execute the step 202.
202. And starting the constant transient state alternating voltage control when the remote end fails.
When the outlet voltage effective value is smaller than the low voltage ride through starting value, the control network side converter 102 is switched from the constant reactive current control in the steady state to the constant transient alternating voltage control;
203. and outputting reactive power to support the voltage of the alternating current system.
After the constant-transient alternating-current voltage control is started, in order to improve the voltage of a bus at the outlet of the fan, the Q-axis current of the grid-side converter 102 is rapidly increased, and the reactive power output by the doubly-fed fan 101 is increased accordingly.
204. And when the remote fault is recovered, the reactive power is recovered to a steady-state value.
When the outlet voltage effective value is larger than the low voltage ride through recovery value, the control network side converter 102 is switched back to the constant reactive current control through the constant transient state alternating current voltage control, the reactive power output by the double-fed fan 101 is recovered to the steady state value, and the output reactive power of the double-fed fan 101 in the steady state is 0.
205. And when the near end fails, the Crowbar circuit is put into operation.
When a near-end alternating current system has a fault, the effective value of the voltage at the outlet of the double-fed fan 101 is lower than a low-voltage ride-through locking value, the current of a Q shaft keeps constant current control, and at the moment, if the effective value of the current of the rotor is larger than a Crowbar control starting value, a Crowbar circuit is put into the rotor converter and the rotor converter is locked to prevent the rotor converter from overcurrent.
Detecting the effective value of the rotor current of the doubly-fed fan 101 in real time; and when the rotor current effective value is determined to be larger than the Crowbar control starting value and the outlet voltage effective value is determined to be smaller than the low-voltage ride-through locking value, the rotor side Crowbar circuit 104 is put into operation and locks the rotor side converter 103. Influenced by the shunting action of a Crowbar circuit, the current of the rotor is rapidly reduced. At this time, since the grid-side voltage value is usually low during the near-end fault, the function of the doubly-fed wind turbine 101 for boosting the outlet bus voltage is not obvious, and therefore, the grid-side converter 102 should maintain constant reactive current control while starting Crowbar.
With reference to fig. 1, the present invention provides a low voltage ride through control system of a doubly-fed wind turbine, which is used for executing the above control method.
And the low voltage ride through controller is used for detecting the effective value of the outlet voltage of the doubly-fed wind turbine 101, and outputting a switching enabling signal to the grid-side converter controller when the effective value of the outlet voltage is determined to be smaller than the low voltage ride through starting value.
After receiving the conversion enable signal, the grid-side converter controller controls the grid-side converter 102 to be switched from the constant reactive current control in the steady state to the constant transient alternating voltage control.
After the constant transient state alternating voltage control is started, the Q-axis current of the grid-side converter 102 is increased, and the output reactive power of the doubly-fed fan 101 is increased.
Optionally, the low voltage ride through control system further comprises: a rotor side converter controller, a rotor side converter 103, a Crowbar circuit controller, and a rotor side Crowbar circuit 104.
Referring to fig. 3, at a specific wind speed, there is a one-to-one correspondence relationship between the rotor speed of the doubly-fed wind turbine 101 and the maximum value of the output active power.
In a specific embodiment, the value of the rotor speed is determined by measuring the wind speed in real time, and then the reference value of the Q-axis current of the rotor side converter 103 is obtained through the control of the rotor speed PI. The rotor side converter controller is used for detecting the rotor current effective value of the doubly-fed wind turbine 101; when the rotor side converter controller determines that the effective value of the rotor current is larger than a Crowbar control starting value and when the low voltage ride through controller determines that the effective value of the interface voltage is smaller than a low voltage ride through locking value, the Crowbar circuit controller controls the rotor side Crowbar circuit 104 to be put into operation, and the rotor side converter controller locks the rotor side converter 103; the grid side converter 102 maintains constant reactive current control.
Optionally, as shown in fig. 4, the rotor-side converter controller includes: a reactive power subtracter 41, a rotor speed subtracter 42, a reactive power PI controller 43, a speed PI controller 44, a stator voltage phase-locked loop 45, a phase angle subtracter 46 and a DQ axis coordinate converter 47. In the embodiment, the rotor side converter 103 of the doubly-fed wind turbine 101 adopts active power and reactive power decoupling control, and selects a rotor flux linkage direction as a reference direction.
In FIG. 4, usabcIs a three-phase voltage on the grid side, thetasIs the phase angle of the voltage on the network side, thetarIs the phase angle of the generator rotor, thetaerrIs thetasAnd thetarPhase angle difference of (Q)refFor reactive power reference, QwThe reactive power value, w, output by the doubly-fed wind turbine 101refAs reference value for the rotor speed, Ird_ref、Irq_refFor the rotor side converter 103 DQ-axis current reference, Ira_ref、Irb_ref、Irc_refAnd the reference value of the ABC three-phase current is used for generating trigger pulses of the rotor side converter 103.
The input signal of the reactive power subtracter 41 is a reactive power reference value QrefAnd the output reactive power value Q of the doubly-fed wind turbine 101wAn output signal of the reactive power subtractor 41 is used as an input signal of the reactive power PI controller 43, and the reactive power PI controller 43 outputs a rotor side converter 103DQ axis current reference value Ird_ref；
The input signal of the rotor speed subtracter 42 is a rotor speed reference value wrefAnd a measured value w of the rotor speed, an output signal of the rotor speed subtractor 42 is used as an input signal of a speed PI controller 44, and the speed PI controller 44 outputs a DQ axis current of the rotor side converter 103Reference value Irq_ref；
The input signal of the stator voltage phase-locked loop 45 is the three-phase voltage u on the network sidesabcPhase angle theta of output signal net side voltage of stator voltage phase-locked loop 45sAs an input signal to the phase angle subtractor 46, the input signal to the phase angle subtractor 46 also includes a generator rotor phase angle θrThe output signal theta of the phase angle subtractor 46errIs thetasAnd thetarThe phase angle difference of (a);
input signal of DQ axis coordinate transformer 47 is Ird_ref、Irq_refAnd thetaerrObtaining I through conversion from DQ coordinate system to ABC three-phase coordinate systemra_ref、Irb_ref、Irc_refFor generating a trigger pulse.
In this embodiment, the rotor-side converter 103 of the doubly-fed wind turbine 101 first determines w according to the real-time wind speed and power-rotation speed curveref，wrefSubtracting w and obtaining I through PI controllerrq_ref(ii) a Then, QrefAnd QwSubtract and get I through PI controllerrd_ref(ii) a Finally, I is obtained through conversion from a DQ coordinate system to an ABC three-phase coordinate systemra_ref、Irb_ref、Irc_refFor generating a trigger pulse. Wherein the angle theta of the coordinate transformationerrIs equal to thetasAnd thetarDifference of (a), thetasBy usabcObtained by means of a phase-locked loop.
Optionally, as shown in fig. 5, the grid-side converter controller includes: the device comprises a direct current voltage subtracter 51, a direct current voltage PI controller 52, an alternating current voltage subtracter 53, an alternating current voltage PI controller 54, a low voltage ride through judgment link 55, two DQ axis current reference value amplitude limiting links which are respectively represented by icons 56 and 57, a network side voltage phase-locked loop 58, two DQ axis current subtracters which are respectively represented by icons 59 and 510, two DQ axis current PI controllers which are respectively represented by icons 511 and 512, and two DQ axis coordinate converters which are respectively represented by icons 513 and 514.
In FIG. 5, Udc_refIs a reference value of DC voltage，UdcAs a measured value of DC voltage, Idref_max、Idref_min、Iqref_max、Iqref_minThe reference current limit value is the D-axis.
Wherein,
Id_ref、Iq_reffor DQ-axis current reference, Id、IqFor DQ-axis current measurements, Ud_ref、Uq_refFor DQ axis voltage reference, Ua_ref、Ub_ref、Uc_refFor generating trigger pulses for three-phase voltage reference values, ia、ib、icAs three-phase current measurements, Uac_refFor reference value of AC voltage, Urms_acLVRT _ EN is the low voltage ride through enable signal, which is the effective value of the AC voltage measurement.
The input signal of the DC voltage subtracter 51 is a DC voltage reference value Udc_refAnd a measured value U of the DC voltagedcThe output signal of the dc voltage subtractor 51 is used as the input signal of the dc voltage PI controller 52, and the output signal of the dc voltage PI controller 52 outputs the DQ axis current reference value I after passing through a DQ axis current reference value clipping element 56d_ref，Id_refWith measurement of DQ axis current IdAs an input signal of a DQ-axis current subtractor 59, an output signal of the DQ-axis current subtractor 59 as an input signal of a DQ-axis current PI controller 511, and a DQ-axis current PI controller 511 outputting a DQ-axis voltage reference Ud_ref；
The input signal of the AC voltage subtracter 53 is an AC voltage reference value Uac_refAnd the effective value U of the measured value of the alternating voltagerms_acThe output signal of the ac voltage subtractor 53 is used as the input signal of the ac voltage PI controller 54;
the input signal of the low voltage ride through judgment link 55 includes a DQ axis current reference value Iq_refPI control of AC voltageThe output signal of the device 54 passes through another DQ axis current reference value amplitude limiting element 57, the low voltage ride through enable signal LVRT _ EN received from the low voltage ride through controller, the output signal of the low voltage ride through determination element 55, and the DQ axis current measurement value IqAs an input signal of another DQ-axis current subtractor 510, an output signal of another DQ-axis current subtractor 510 is used as an input signal of another DQ-axis current PI controller 512, and another DQ-axis current PI controller 512 outputs a DQ-axis voltage reference Uq_ref；
The input signal of the grid-side voltage phase-locked loop 58 is a grid-side three-phase voltage usabcThe output signal is the network side voltage phase angle thetas；Ud_ref、Uq_refAnd thetasAs an input signal of a DQ-axis coordinate transformer 513, a DQ-axis coordinate transformer 513 outputs a three-phase voltage reference value Ua_ref、Ub_ref、Uc_refFor generating a trigger pulse;
Idand IqIs an output signal of another DQ-axis coordinate transformer 514, and an input signal of another DQ-axis coordinate transformer 514 is a three-phase current measurement ia、ib、icAnd thetas。
In this embodiment, the grid-side converter 102 first converts U todc_refAnd UdcSubtracting, and obtaining I through PI control and amplitude limiting linksd_refWhile setting I directly under steady-state conditionsq_refWhen LVRT _ EN is 1, the control enters into the transient AC voltage control to drive Uac_refAnd Urms_acSubtracting, and obtaining I through PI control and amplitude limiting linksq_ref；Id_refAnd Iq_refObtaining U through inner ring PI controld_refAnd Uq_refFor DQ axis voltage reference, Ua_ref、Ub_ref、Uc_refGenerating three-phase voltage reference values; finally, obtaining U through conversion from a DQ coordinate system to an ABC coordinate systema_ref、Ub_ref、Uc_refFor generating a trigger pulse.
See FIG. 6, ULVRT_RSFor low voltage ride through recovery values, ULVRTFor low voltage ride through start value, ULVRT_OFFIs a low voltage ride through latch-up value. When U is turnedLVRT<Urms_ac<1, controlling the Q-axis current of the grid-side converter 102 by adopting a constant current; when U is turnedLVRT_OFF<Urms_ac<ULVRTIn the process, the Q-axis current is switched to be controlled by the transient alternating voltage, and at the moment, the system voltage is difficult to recover to the rated value due to the reactive power output by the doubly-fed fan 101, so that the I value is difficult to recoverq_refWill reach the maximum limit amplitude Iqref_maxUp to
ULVRT_RS<Urms_acThen the constant current control is recovered; when U is turnedrms_ac<ULVRT_OFFAnd meanwhile, the Q-axis current is still controlled by constant current, and if the current of the rotor converter is larger than a Crowbar current starting value at the moment, the current is input into a Crowbar circuit 104 on the rotor side. Under constant current control, Iq_refUsually 0 is taken.
Optionally, as shown in fig. 7, the low voltage ride through controller includes: two ac voltage effective value comparators are respectively represented by icons 71 and 72, a low voltage ride through start determining element 73, a low voltage ride through stop determining element 74, an inversion logic 75 and a low ride through start multiplier 76.
In FIG. 7, SLVRTA low voltage ride through enabled flag; sLVRT_RSA low voltage ride through recovery flag; fault _ start is a low-penetration start signal; fault _ end is a low end-of-penetration signal.
Effective value U of measured value of alternating voltagerms_acBy means of an AC voltage virtual comparator 71 for low voltage ride through start value ULVRTAnd comparing, wherein the output signal is used as an input signal of the low voltage ride through start judging link 73, and the low voltage ride through start judging link 73 outputs a low ride through start signal Fault _ start.
Effective value U of measured value of alternating voltagerms_acThrough another AC voltage virtual value comparator 72 and the low voltage ride through recovery value ULVRT_RSThe comparison outputs a signal as an input to the low voltage ride through termination determination element 74The signal, low-voltage ride-through termination determining link 74 outputs a low-ride-through termination signal Fault _ end, which passes through the negation logic 75 and is input to the low-ride-through start multiplier 76 together with the Fault _ start signal, and the low-ride-through start multiplier 76 outputs the low-voltage ride-through enable signal LVRT _ EN.
In this embodiment, when the remote AC system fails and U is detectedLVRT_OFF<Urms_ac<ULVRTWhen S is presentLVRTIf the voltage is 1, the Fault _ start is 1, and since the Fault _ end is 0, the LVRT _ EN obtained by multiplying the inverted Fault _ end by the Fault _ start is 1, namely the low-voltage ride-through control is enabled; when the fault is recovered and ULVRT_RS<Urms_acWhen S is presentLVRT_RSIf the voltage is 1, the Fault _ end is 1, and after being inverted and multiplied by the Fault _ start, the voltage is equal to 0, that is, LVRT _ EN is 0, and the low voltage ride through is ended.
According to the low voltage ride through control method and system of the double-fed fan provided by the embodiment of the invention, when a far-end alternating current system fault occurs, if the effective value of the outlet voltage of the double-fed fan is determined to be smaller than the low voltage ride through starting value, the Q-axis current is switched to the transient alternating current voltage control from the constant current control, and the double-fed fan outputs certain reactive power to support the alternating current system voltage. When the fault is recovered, if the outlet voltage effective value is larger than the low voltage ride through recovery value, the Q-axis current is switched from the transient alternating voltage control to the constant current control, and the output reactive power of the doubly-fed fan is 0 in the steady state. Further, when the near-end alternating current system has a fault, if the effective value of the voltage at the outlet of the double-fed fan is lower than the low-voltage ride-through locking value, the current of the Q shaft keeps constant current control, and at the moment, if the effective value of the current of the rotor is larger than a Crowbar control starting value, the Crowbar circuit at the rotor side is put into the rotor side and locks the rotor converter to prevent the rotor converter from overcurrent, so that the stability of the alternating current system is improved.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. A low voltage ride through control method of a doubly-fed wind turbine is characterized by comprising the following steps:
detecting an outlet voltage effective value of the double-fed fan;
when the effective value of the outlet voltage is determined to be smaller than the low-voltage ride-through starting value, controlling the grid-side converter to be switched from constant reactive current control in a steady state to constant transient alternating voltage control;
after the constant transient state alternating voltage control is started, the Q-axis current of the grid side converter is increased, and the output reactive power of the double-fed fan is increased.
2. The low voltage ride through control method of claim 1, further comprising:
and when the effective value of the outlet voltage is determined to be larger than the low voltage ride through recovery value, the control network side converter is switched back to the constant reactive current control by the constant transient state alternating current voltage control, and the reactive power output by the double-fed fan is recovered to the steady state value.
3. The low voltage ride through control method of claim 1, further comprising:
detecting the effective value of the rotor current of the doubly-fed fan;
when the rotor current effective value is determined to be larger than a Crowbar control starting value and the outlet voltage effective value is determined to be smaller than a low voltage ride through locking value, the Crowbar circuit on the rotor side is put into operation and locks the converter on the rotor side;
the grid side converter keeps constant reactive current control.
4. A low voltage ride through control system of a doubly fed wind turbine, comprising: the system comprises a low voltage ride through controller, a grid-side converter and a double-fed fan;
the low-voltage ride-through controller is used for detecting an effective value of outlet voltage of the doubly-fed wind turbine, and outputting a switching enabling signal to the grid-side converter controller when the effective value of the outlet voltage is determined to be smaller than a low-voltage ride-through starting value;
after the grid side converter controller receives the conversion enabling signal, the grid side converter is controlled to be switched from constant reactive current control in a steady state to constant transient state alternating current voltage control;
after the constant transient state alternating voltage control is started, the Q-axis current of the grid side converter is increased, and the output reactive power of the double-fed fan is increased.
5. The low voltage ride through control system of claim 4, further comprising: the system comprises a rotor side converter controller, a rotor side converter, a Crowbar circuit controller and a rotor side Crowbar circuit;
the rotor side converter controller is used for detecting the rotor current effective value of the doubly-fed wind turbine;
when the rotor side converter controller determines that the effective value of the rotor current is larger than a Crowbar control starting value and when the low voltage ride through controller determines that the effective value of the outlet voltage is smaller than a low voltage ride through locking value, the Crowbar circuit controller controls the rotor side Crowbar circuit to be put into operation, and the rotor side converter controller locks the rotor side converter;
the grid side converter keeps constant reactive current control.
6. The low voltage ride through control system of claim 5,
the low voltage ride through controller comprises: two AC voltage effective value comparators, a low voltage ride through starting judgment link, a low voltage ride through termination judgment link, an inversion logic and a low ride through starting multiplier;
effective value U of measured value of alternating voltagerms_acThrough two comparators of AC voltage effective value and low voltage ride through starting value ULVRTAnd low voltage ride through recovery value ULVRT_RSAnd comparing the two output signals, wherein the two output signals are respectively used as input signals of the low voltage ride through starting judgment link and the low voltage ride through ending judgment link, the low voltage ride through starting judgment link outputs a low ride through starting signal Fault _ start, the low voltage ride through ending judgment link outputs a low ride through ending signal Fault _ end, the Fault _ end and the Fault _ start signal are input into the low ride through starting multiplier after being subjected to negation logic, and the low ride through starting multiplier outputs a low voltage ride through enabling signal LVRT _ EN.
7. The low voltage ride through control system of claim 5,
the grid-side converter controller comprises: the device comprises a direct-current voltage subtracter, a direct-current voltage PI controller, an alternating-current voltage subtracter, an alternating-current voltage PI controller, a low-voltage ride through judgment link, two DQ-axis current reference value amplitude limiting links, a network side voltage phase-locked loop, two DQ-axis current subtracters, two DQ-axis current PI controllers and two DQ-axis coordinate converters;
the input signal of the direct current voltage subtracter is a direct current voltage reference value Udc_refAnd a measured value U of the DC voltagedcThe output signal of the direct current voltage subtracter is used as the input signal of the direct current voltage PI controller, and the output signal of the direct current voltage PI controller outputs a DQ axis current reference value I after passing through a DQ axis current reference value amplitude limiting linkd_ref，Id_refWith measurement of DQ axis current IdAs an input signal of a DQ-axis current subtractor, an output signal of the DQ-axis current subtractor as an input signal of a DQ-axis current PI controller, the DQ-axis current PI controller outputting a DQ-axis voltage reference Ud_ref；
The input signal of the alternating voltage subtracter is an alternating voltage reference value Uac_refAnd the effective value U of the measured value of the alternating voltagerms_acThe output signal of the alternating voltage subtracter is used as the input signal of the alternating voltage PI controller;
the input signal of the low voltage ride through judgment link comprises a DQ axis current reference value Iq_refAn output signal of the alternating current PI controller after passing through another DQ axis current reference value amplitude limiting link, a low voltage ride through enable signal LVRT _ EN received from the low voltage ride through controller, an output signal of the low voltage ride through judgment link and a DQ axis current measured value IqAs an input signal of another DQ-axis current subtractor whose output signal is an input signal of another DQ-axis current PI controller that outputs a DQ-axis voltage reference Uq_ref；
The input signal of the network side voltage phase-locked loop is network side three-phase voltage usabcThe output signal is the network side voltage phase angle thetas；Ud_ref、Uq_refAnd thetasAs an input signal of a DQ-axis coordinate converter outputting three-phase voltage reference values Ua_ref、Ub_ref、Uc_refFor generating a trigger pulse;
Idand IqIs the output signal of another DQ axis coordinate transformer, the input signal of the other DQ axis coordinate transformer is the three-phase current measured value ia、ib、icAnd thetas。
8. The low voltage ride through control system of claim 5,
the rotor side converter controller includes: the system comprises a reactive power subtracter, a rotor rotating speed subtracter, a reactive power PI controller, a rotating speed PI controller, a stator voltage phase-locked loop, a phase angle subtracter and a DQ axis coordinate converter;
the input signal of the reactive power subtracter is a reactive power reference value QrefAnd the output reactive power value Q of the doubly-fed fanwThe output signal of the reactive power subtracter is used as the input signal of the reactive power PI controller, and the reactive power PI controller outputs a rotor side converter DQ shaft current reference value Ird_ref；
The input signal of the rotor speed subtracter is a rotor speed reference value wrefAnd a measured value w of the rotor rotating speed, wherein an output signal of the rotor rotating speed subtracter is used as an input signal of the rotating speed PI controller, and the rotating speed PI controller outputs a rotor side converter DQ shaft current reference value Irq_ref；
The input signal of the stator voltage phase-locked loop is three-phase voltage u on the network sidesabcThe output signal network side voltage phase angle theta of the stator voltage phase-locked loopsAs an input signal of the phase angle subtractor, the input signal of the phase angle subtractor further comprises a generator rotor phase angle thetarOutput signal θ of said phase angle subtractorerrIs thetasAnd thetarThe phase angle difference of (a);
the input signal of the DQ axis coordinate converter is Ird_ref、Irq_refAnd thetaerrObtaining I through conversion from DQ coordinate system to ABC three-phase coordinate systemra_ref、Irb_ref、Irc_refFor generating a trigger pulse.
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