CN209056943U - Low voltage ride through system and wind generator system - Google Patents
Low voltage ride through system and wind generator system Download PDFInfo
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Abstract
This application involves low voltage crossing technical field more particularly to a kind of low voltage ride through system and wind generator system.Low voltage ride through system includes: relay, and the current transformer, first voltage mutual inductor and the switching device that are separately connected with the relay, further includes the resistance-capacitance circuit in parallel with the switching device, which includes at least one capacitor element；Wherein, which is used to detect rotor current and the current value that will test is sent to relay；The first voltage mutual inductor is used to detect the voltage of grid entry point and the voltage value that will test is sent to relay；The relay is less than predetermined voltage threshold in the voltage value received, and when receiving the current value less than predetermined current threshold, sends electric signal to switching device and triggers the switching device from closed state to disconnect so that the resistance-capacitance circuit accesses rotor windings.The application accesses rotor windings by resistance-capacitance circuit, helps that rotor current is inhibited to rise；Capacitor can also be sent reactive power to power grid and be restored with auxiliary power grid.
Description
Technical Field
The application relates to the technical field of low voltage ride through, in particular to a low voltage ride through system and a wind power generation system.
Background
The low voltage ride through modes of the existing double-fed fan can be classified into two categories: one is to improve the traditional control strategy; the other is to add hardware devices. The first type mainly realizes low voltage ride through by adding feed-forward compensation or adopting a 'de-excitation' means to accelerate the attenuation speed of some transient electric quantities and reduce the amplitude of the transient electric quantities, but the mode is limited by the capacity of a converter and is generally used for the condition of light voltage drop; when severe faults are faced, hardware equipment is put into the system more directly and effectively, crowbar protection is the most classical, and the system has the advantages of simple structure, good current limiting effect and the like, but after the system is put into operation, the connection between a rotor winding and a Rotor Side Converter (RSC) is disconnected, the DFIG operates like an asynchronous motor and is in an out-of-control state, so that a unit absorbs reactive power from a power grid to excite, and the voltage drop degree of a grid connection point is deteriorated. Researches on crowbar ride-through technologies mostly focus on optimization of the resistance value and switching time of a crowbar, and in order to improve the capacity of taking various fault situations into consideration, scholars propose a mode of dynamically adjusting the resistance value of the crowbar, so that the rotor current can be inhibited when voltage drops of different degrees fall, the direct-current bus voltage can be prevented from exceeding a threshold value, and the protection flexibility is effectively improved; later, in order to get rid of crowbar protection, a scheme of connecting resistors in series on the rotor side is proposed, which has the advantages of having a more direct suppression effect on current and has the disadvantages that the optimal resistance value is difficult to determine under the condition of not being matched with other schemes, the stability of a circuit on the rotor side can be influenced if the series resistance value is too large in light faults, and the current limiting effect is poor if the series resistance value is too small in serious faults.
Disclosure of Invention
In view of this, embodiments of the present application provide a low voltage ride through system and a wind power generation system, so as to limit a rise in a rotor current, assist a recovery of a power grid, and improve a low voltage ride through performance.
In a first aspect, an embodiment of the present application provides a low voltage ride through system, including: the relay, and the current transformer, the first voltage transformer and the switching device which are respectively connected with the relay, and the resistance-capacitance circuit which is connected with the switching device in parallel, wherein the resistance-capacitance circuit comprises at least one capacitance device; wherein,
the current transformer is used for detecting rotor current in a target circuit and sending the detected current value to the relay;
the first voltage transformer is used for detecting the voltage of a grid connection point in the target circuit and sending the detected voltage value to the relay;
the relay is used for sending an electric signal to the switching device to trigger the switching device to be switched from a closed state to an open state when the received voltage value is smaller than a preset voltage threshold value and the received current value is smaller than a preset current threshold value, so that the resistance-capacitance circuit is connected to the rotor winding.
In a preferred embodiment of the invention, the system further comprises a crowbar circuit and a second voltage transformer which are connected with the relay; the second voltage transformer is also used for detecting the voltage of the direct current bus in the target circuit and sending the detected voltage value of the direct current bus to the relay;
the relay is also used for receiving the current value which is larger than the preset current threshold value; or when the voltage value of the direct current bus is larger than the preset voltage threshold value of the direct current bus, sending an electric signal to an insulated gate bipolar transistor IGBT of the crowbar circuit so as to enable the crowbar circuit to be communicated with a rotor winding circuit of the target circuit.
In a preferred embodiment of the invention, the system further comprises a reactive power compensation device connected to the relay;
the relay is also used for sending a starting electric signal to the reactive power compensation device when sending an electric signal to an Insulated Gate Bipolar Transistor (IGBT) of the crowbar circuit;
the reactive power compensation device is used for starting and transmitting reactive power to a power grid connected with the target circuit to stabilize the voltage of the grid-connected point when receiving the starting electric signal.
In a preferred embodiment of the present invention, the reactive power compensation device is a grid-side converter.
In a preferred embodiment of the present invention, the grid-side converter includes a PI regulator, a first input terminal of the PI regulator inputs a stator voltage reference value; the second input end is connected with the first voltage transformer and receives the voltage value of the grid-connected port; the output end of the PI regulator outputs a q-axis current reference value; the q-axis current reference is used to generate reactive power.
In a preferred embodiment of the invention, the relay is further configured to send an electrical signal to an IGBT of the crowbar circuit to disconnect the crowbar circuit from the rotor winding cut-off if the rotor current value detected by the current transformer is less than a predetermined current threshold value.
In a preferred embodiment of the present invention, the RC circuit comprises a resistor connected in series with the capacitor device.
In a preferred embodiment of the present invention, the RC circuit comprises a resistor connected in parallel with the capacitor device.
In a preferred embodiment of the invention, the relay internally comprises a first comparator, a second comparator and an and gate circuit; the output end of the first comparator is connected with the first input end of the AND gate circuit; the output end of the second comparator is connected with the second input end of the AND gate circuit;
the first input end of the first comparator is used for receiving a voltage value sent by the first voltage transformer; the second input end is used for receiving the preset voltage threshold; comparing the received voltage value with the predetermined voltage threshold value; if the received voltage value is smaller than the preset voltage threshold value, the output end outputs a low level;
the first input end of the second comparator is used for receiving a current value sent by the current transformer; the second input end is used for receiving a current threshold value; comparing the received current value with a predetermined current threshold value; if the received current value is smaller than the preset current threshold value, the output end outputs a low level;
the output end of the AND gate circuit is used as the output end of the relay and is connected with the control end of the switch device.
In a second aspect, embodiments of the present application further provide a system including a wind turbine and a low voltage ride through system, wherein a circuit of the wind turbine is connected to the low voltage ride through system.
By adopting the scheme, the relay sends an electric signal to the switch device to trigger the switch device to be switched from a closed state to an open state, so that the resistance-capacitance circuit is connected to the rotor winding; the rotor current is limited by serially connecting the resistance capacitors, the capacitors can absorb redundant energy and can emit a little reactive power, and the effect of assisting the recovery of the power grid is achieved.
Further, the method is improved and has a good effect, and when the fault is serious, the relay sends an electric signal to an insulated gate bipolar transistor IGBT of the crowbar circuit so as to enable the crowbar circuit to be communicated with a rotor winding circuit of the target circuit; by adding the resistance-capacitance circuit and the crowbar circuit, the resistance of the equivalent circuit of the rotor is increased, and the effect of inhibiting current is improved; the relay sends a starting electric signal to the reactive power compensation device to transmit reactive power to the power grid, so that the power grid can be assisted to recover as soon as possible and cross out of a low-voltage area.
Additional features and advantages of the disclosure will be set forth in the description which follows, or in part may be learned by the practice of the above-described techniques of the disclosure, or may be learned by practice of the disclosure.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a diagram of an application scenario of low voltage ride through according to an embodiment of the present disclosure;
FIG. 2 is a block diagram of a low voltage ride through system according to an embodiment of the present disclosure
Fig. 3 is a schematic diagram of a grid-side converter according to an embodiment of the present application;
FIG. 4 is a diagram of a wind power generation system provided in an embodiment of the present application;
fig. 5 is a general flow chart of the low voltage ride through provided by the embodiment of the present application.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present disclosure more apparent, the embodiments of the present disclosure will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are some, but not all embodiments of the present disclosure. All other embodiments, which can be derived by one of ordinary skill in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.
The realization of Low Voltage Ride Through (LVRT) of the doubly-fed wind turbine generator is an important subject in the field of wind power generation. Referring to fig. 1, a diagram of an application scenario of low voltage ride through provided by the embodiment of the present application; which comprises the following steps: the double-Fed wind power Generator (DFIG) comprises a double-Fed wind power Generator (DFIG) and a resistance-capacitance circuit, wherein the DFIG specifically comprises a resistor R1 and a capacitor C1 which are connected in series, and a switching device, a crowbar circuit, a rotor-side converter RSC and a stator-side converter GSC which are connected with the DFIG in parallel.
The converter protection is an important ring in the process of realizing low voltage ride through of the doubly-fed wind turbine generator, when the fault is serious, the control strategy is limited by the capacity of the converter, and the Crowbar circuit Crowbar becomes a simple, convenient and effective means for providing a bypass for rotor overcurrent to protect the converter. Crowbar protection development to date mostly makes research from the aspects of improving protection current-limiting and voltage-limiting capacity or reducing reactive power absorbed by a fan from a power grid after a Crowbar is put into use, for example, (1) optimizing the resistance value and switching time of the Crowbar, but does not consider that the fixed resistance value is difficult to consider the low-voltage ride-through effect of different voltage drop degrees; (2) the proposal of dynamically adjusting the crowbar resistance mainly ensures that the direct current bus voltage cannot exceed the limit under various faults, improves the applicability of the crowbar protection to the faults, but shortens the protection input time insignificantly and cannot well control the amount of reactive power absorbed by a fan; (3) crowbar is matched with a control strategy, so that the time of Crowbar investment can be reduced to a certain extent, but the current limiting effect of the control strategy is relatively poor, and the more complicated control algorithm is more difficult to implement; (4) the scheme of serially connecting the rotor with the brake resistor has no clear brake resistance value setting scheme at present, only the resistance value can be determined by matching with simulation, and the LVRT effect is difficult to ensure.
Based on this, the embodiment of the application provides a low-voltage ride through system, which is used for limiting rotor current, assisting power grid fault recovery and improving low-voltage ride through performance. The following is a detailed description through specific embodiments.
Referring to the block diagram of the low voltage ride through system shown in fig. 2, the system comprises: the relay 21, and the current transformer 22, the first voltage transformer 23 and the switching device 24 which are respectively connected with the relay 21, and further comprising a resistance-capacitance circuit 25 which is connected with the switching device 24 in parallel, wherein the resistance-capacitance circuit 25 comprises at least one capacitance device; wherein,
the current transformer 22 is used for detecting the rotor current in the target circuit and sending the detected current value to the relay 21;
the first voltage transformer 23 is configured to detect a voltage of a grid-connected point in the target circuit, and send a detected voltage value to the relay 21;
the relay 21 is configured to send an electrical signal to the switching device 24 to trigger the switching device 24 to switch from the closed state to the open state when the received voltage value is smaller than the predetermined voltage threshold and the received current value is smaller than the predetermined current threshold, so that the rc circuit 25 is connected to the rotor winding.
The system relay 21 sends an electrical signal to the switching device 24 to trigger the switching device 24 to switch from the closed state to the open state so that the rc circuit 25 is connected to the rotor winding, which helps to suppress the increase of the current of the rotor winding; and the resistance-capacitance circuit 25 at least comprises a capacitance device which can send a small amount of reactive power to the power grid to assist the power grid recovery.
In order to prevent the current on the rotor side from continuously rising and prevent the power grid condition from further worsening, the system also comprises a crowbar circuit and a second voltage transformer which are connected with the relay 21; the second voltage transformer is also used for detecting the voltage of the direct current bus in the target circuit and sending the detected voltage value of the direct current bus to the relay 21;
the relay 21 is further configured to receive the current value greater than the predetermined current threshold; or when the voltage value of the direct current bus is larger than the preset voltage threshold value of the direct current bus, sending an electric signal to an insulated gate bipolar transistor IGBT of the crowbar circuit so as to enable the crowbar circuit to be communicated with a rotor winding circuit of the target circuit.
The crowbar circuit comprises a resistor and an edge gate bipolar transistor IGBT, and when the IGBT is conducted, the crowbar circuit is communicated with the rotor winding circuit, namely the equivalent resistance of the rotor winding is increased. This further exerts an effect of suppressing the increase in the rotor-side current.
In order to assist the grid to recover as quickly as possible, the system further comprises a reactive power compensation device connected with the relay 21;
the relay 21 is also used for sending a starting electric signal to the reactive power compensation device when sending an electric signal to an Insulated Gate Bipolar Transistor (IGBT) of the crowbar circuit;
the reactive power compensation device is used for starting and transmitting reactive power to a power grid connected with the target circuit to stabilize the voltage of the grid-connected point when receiving the starting electric signal.
The reactive power compensation device is specially used for reactive power compensation of the power grid. By compensating the reactive power of the power grid, the power grid can be helped to recover from the fault. In specific implementation, the reactive power compensation device can be realized by adopting a group of capacitors, and the capacitors store electric energy in advance. The capacitor bank is connected with a power grid through a controllable switch device; when the switch device receives an electric signal sent by the relay, the switch device is changed from an open state to a closed state, so that the capacitor bank is connected to a power grid, and reactive power is transmitted to the power grid.
In order to save costs, the reactive power compensation device may also be implemented using a grid-side converter, since the grid-side converter itself may also perform the sending of reactive power to the grid.
In a preferred embodiment of the present invention, the grid-side converter includes a PI regulator, a first input terminal of the PI regulator inputs a stator voltage reference value; the second input end is connected with the first voltage transformer 23 and receives the voltage value of the grid-connected port; the output end of the PI regulator outputs a q-axis current reference value; the q-axis current reference is used to generate reactive power. Referring to fig. 3, a schematic diagram of a grid-side converter provided in the embodiment of the present application is shown; the method comprises a voltage outer ring and a current inner ring: 1) d-axis control: DC bus voltage reference value Udc_refWith the actual value UdcThe error of the d-axis current is output as a d-axis current reference value i after passing through a PI controllerd_ref(ii) a 2) And (3) q-axis control: when the converter is in a unit power factor operation state in normal operation, the q-axis current reference value iq_refSet to 0, when the converter is required to send reactive power during the fault, iq_refBecomes dependent on the stator voltage reference ug_refAnd the actual value ugAfter comparison, the obtained product is obtained by a PI regulator; then id_ref、iq_refWith corresponding actual value id、iqThe compared errors are respectively connected with respective decoupling compensation terms omega through the values output by the PI controllersiq、ωsidAnd a grid voltage feedforward compensation term ugObtaining the reference voltage u of the grid-side converter after operationd_ref、uq_refFinally, three-phase voltage reference components can be obtained through coordinate transformation, and the driving signals are generated through SPWM modulation.
In a preferred embodiment of the present invention, the relay 21 is also used to send an electrical signal to the IGBT of the crowbar circuit to disconnect the crowbar circuit from the rotor winding cut-off if the rotor current value detected by the current transformer 22 is less than a predetermined current threshold value.
In the preferred embodiment of the present invention, the RC circuit 25 includes a resistor connected in series with the capacitor device.
In the preferred embodiment of the present invention, the RC circuit 25 includes a resistor connected in parallel with the capacitor device.
For more vivid explanation, in the preferred embodiment of the present invention, the relay 21 internally includes a first comparator, a second comparator and an and circuit; the output end of the first comparator is connected with the first input end of the AND gate circuit; the output end of the second comparator is connected with the second input end of the AND gate circuit;
a first input end of the first comparator is used for receiving the voltage value sent by the first voltage transformer 23; the second input end is used for receiving the preset voltage threshold; comparing the received voltage value with the predetermined voltage threshold value; if the received voltage value is smaller than the preset voltage threshold value, the output end outputs a low level;
the first input end of the second comparator is used for receiving the current value sent by the current transformer 22; the second input end is used for receiving a current threshold value; comparing the received current value with a predetermined current threshold value; if the received current value is smaller than the preset current threshold value, the output end outputs a low level;
in specific implementation, the switching device can be realized by MOS (metal oxide semiconductor) tubes, and the MOS tubes are divided into an N-type MOS and a P-type MOS; in PMOS, G is connected with high level to be turned off and connected with low level to be turned on. And the G end of the PMOS tube is used for receiving low level to trigger the conduction of the PMOS tube.
The output of the and circuit is connected as the output of the relay 21 to the control terminal of the switching device.
In a second aspect, the present embodiment provides a wind power generation system, which includes a wind power generator 41 and a low voltage ride through system 42, and the circuit of the wind power generator 41 is connected to the low voltage ride through system 42.
For a detailed description of the whole process of the present application, refer to the general flow diagram of the low voltage ride through provided by the embodiment of the present application shown in fig. 5, which is as follows:
in conjunction with the application scenario diagram of the low voltage ride through in fig. 1, Y in the diagram indicates that the determination result is yes, and N indicates that the determination result is no. When the doubly-fed wind generator operates normally, the switch S0Is always closed and has a resistance R1And a capacitor C1Is bypassed, R1And C1Is not connected in and the capacitor C1The voltage on is 0;
after the voltage drop of the grid-connected point occurs, the rotor current is detectedAnd the grid point voltage Usf；
Judging whether the stator voltage after the fault occurs meets Usf≤0.9p.u.；
If so, turn off S0R1 and C1 are connected, wherein p.u refers to the rated voltage 690V of the doubly-fed wind turbine;
judging whether the rotor current is restrained at 1.8I or notrNThe following;
if yes, continuing to judge whether the rotor current is below a rated value and the direct-current bus voltage is below the rated value; if the rotor current is below the rated value and the direct current bus voltage is below the rated value, cutting off the series resistance-capacitance circuit;
if not, if the rotor current continuously rises to be more than 1.8IrNOr DC bus voltage UdcExceeds a threshold value UdcmaxCrowbar protection action of the Crowbar circuit is carried out, and the Crowbar circuit is connected to the rotor circuit; the rotor side converter is out of control, and the DFIG of the doubly-fed wind generator is in an asynchronous running state; when Crowbar is put into operation, the control mode of the grid-side converter is changed from unit power factor operation to non-unit power factorThe operation is repeated, the voltage of a grid-connected point is stabilized as a target, the reactive power output is adjusted, and certain reactive power is slowly transmitted to a power grid;
after Crowbar is put into operation for a period of time, judging whether the rotor current is less than or equal to 1.8IrN；
If so, the Crowbar circuit Crowbar is cut off, and R1And C1Keeping the concatenation;
determining whether the rotor current is less than or equal to a rated value and UdcWhether or not it is less than or equal to the rated value UdcN；
If the rotor current is less than or equal to the rated value and the DC bus voltage UdcLess than or equal to rated value UdcNThe tandem R1 and C1 were excised.
The application also provides a series resistor R1Capacitor C1And a crowbar resistance setting principle, which are respectively specified as follows:
①R1the setting principle is as follows:
principle 1: charging R1Then, the peak value of the rotor current is less than 1.8IrN；
Principle 2: the peak value of the rotor voltage is less than the voltage threshold value U of the direct current busdcmax。
②C1The setting principle is as follows:
principle 1: the value of the series capacitance ensures that enough capacity can absorb redundant energy during fault, and a certain margin is reserved to offset the voltage generated after the series resistance is offset;
principle 2: when the capacitor voltage is minimum, the energy generated on the rotor side in the case of a fault can be absorbed.
③RcbThe setting principle is as follows:
principle 1: when the phase of the rotor current is zero, a three-phase symmetrical fault occurs at a fan grid-connected point, the voltage drops to zero, and the peak of the rotor current is generated after the crowbar resistor is put into useValue not exceeding rotor current threshold Irmax；
Principle 2: the voltage peak value at two ends of the equivalent crowbar resistor must not exceed the maximum allowable value U of the DC bus voltagedcmax。
The specific setting mode is as follows:
during the fault period, the converter continuously operates after the rotor is connected with the resistor in series, and the current peak value of the single-phase rotor can be written into the formula (1):
wherein,is the pre-fault rotor current; u shapes、UsfStator voltages before and after a fault; tau isr＝σLr/(Rr+R1) Is the equivalent rotor time constant after the resistance is connected; rs、RrRespectively a stator resistor and a rotor resistor; l isr、LsRotor and stator inductors respectively; l ismIs an excitation inductor;is a leakage inductance coefficient; s is slip; omegas、ωrSynchronous rotation speed and rotor electrical angular speed respectively; omega-omegas-ωrIs the slip angular velocity;to translate the rotor voltage amplitude to the stator side.
Maximum value of rotor voltageComprises the following steps:
converting to the stator side to obtain:
and k is the turn ratio of each phase of windings of the stator and the rotor in series connection.
(1)R1The setting mode is as follows:
under the condition of light fault, the crowbar protection is avoided to be put into as much as possible, so that the voltage drop of 50 percent is taken as a critical point, namely the voltage of a grid-connected point after the fault meets UsfNot less than 0.5p.u. (the most critical condition is U)sf0.5p.u.), a resistance R1The fault current is required to be restrained to 1.8I after the rotor is connectedrNThe following, namely:
from the view of the operation of the double-fed fan, the rotor suddenly accesses the resistor, belongs to disturbance, the negative influence of the protection circuit on the unit can be effectively reduced by accessing the small resistor on the premise of ensuring the safety of the converter, and the brake resistor R1The value of (a) can be obtained by the formula (5):
R1＝R1.min+(R1.max-R1.min)×30％ (5)
R1minis the defined minimum resistance, R1maxIs the maximum resistance defined.
(2)C1The setting mode is as follows:
according to the above value requirement, the energy absorbed by the capacitor is:
Wc＝pbase×(0.9-Vmin)×t (6)
Vminthe minimum value that the stator voltage can reach after a fault in the finger. Wherein p isbaseRated power of the double-fed fan; and t is the charging time after the capacitor is connected.
When three-phase symmetrical short circuit occurs in the power grid, the rotor fault currentComprising a DC component and two frequencies sfsAnd a frequency of (1-s) fsThe attenuation component of (a). In order to ensure that the capacitor has enough energy to absorb the energy generated during the fault, assuming that the components of the above two frequencies are simultaneously charging the capacitor, the maximum possible charging time of the capacitor in one cycle is:
rotor voltage of DFIG in stable operation isNamely whenThe minimum capacitance voltage can be obtained, and when the most serious three-phase earth fault occurs in the power grid, namely the open-circuit voltage of the rotor is maximum (V)min0), the required capacitance capacity is:
the capacitance C is obtained from the expressions (6) to (8)1。
(3) Crowbar resistor RcbSetting:
when the voltage of the power grid drops by more than 50 percent (U)sf<0.5p.u.), if R1The current can not be limited to 1.8IrNThen put into crowbar circuit, at this time R1And RcbSimultaneously connected, the crowbar resistance is equivalent to R1+Rcb. In order to suppress the rotor overcurrent under any fault, the most serious three-phase short-circuit fault, that is, the condition that the voltage of the grid-connected point falls to 0, should be adopted. Maximum rotor currentFormula (9) can be written:
wherein,tau after crowbar resistance and series resistance are connected simultaneouslyrBecomes τr＝σLr/(Rr+R1+Rcb). After the Crowbar resistor is put into use, the rotor current is smaller than the safe range accepted by the rotor-side converter, and the general current threshold is 2IrNAnd the voltage peak value at two ends of the crowbar resistor needs to be smaller than the voltage threshold value U of the direct current busdcmaxNamely:
r is obtained from the formulae (4) and (5)1R is obtained by combining the formulae (9) and (10)cbAnd (4) value range. In order to help the grid recovery, the method also comprises the step of delivering reactive power to the grid to stabilize the voltage of the grid-connected point. The reactive power transmission to the power grid can be realized by adopting a static reactive power compensation device, and the reactive power compensation device can transmit the reactive power to the power grid, so that the power grid can be helped to recover to be normal and can go out of a low-voltage area.
According to the technical scheme, voltage drops of different degrees can be considered, the rotor current is limited by serially connecting the resistance capacitors in case of slight faults, and the capacitors can absorb redundant energy and can emit little reactive power; when a serious fault occurs, the series resistance-capacitance circuit and the crowbar circuit are simultaneously put into use, the equivalent circuit of the rotor is enlarged, the effect of inhibiting current is improved, the input times and time of crowbar protection are effectively reduced, and therefore reactive power absorbed by the DFIG can be reduced, and the selection of resistance values under the strategy is flexible; and finally, the reactive power can be slowly transmitted to the power grid by adding the reactive power regulation function of the grid-side converter.
The above description is only for the specific embodiments of the present application, but the scope of the present application 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 application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A low voltage ride through system, comprising: the relay, the current transformer, the first voltage transformer and the switching device are respectively connected with the relay, and the circuit further comprises a resistance-capacitance circuit connected with the switching device in parallel, wherein the resistance-capacitance circuit comprises at least one capacitance device; wherein,
the current transformer is used for detecting the rotor current in the target circuit and sending the detected current value to the relay;
the first voltage transformer is used for detecting the voltage of a grid connection point in the target circuit and sending the detected voltage value to the relay;
the relay is used for sending an electric signal to the switch device to trigger the switch device to be switched from a closed state to an open state when the received voltage value is smaller than a preset voltage threshold value and the received current value is smaller than a preset current threshold value, so that the resistance-capacitance circuit is connected to the rotor winding.
2. The system of claim 1, further comprising a crowbar circuit and a second voltage transformer connected to the relay; the second voltage transformer is also used for detecting the voltage of the direct current bus in the target circuit and sending the detected voltage value of the direct current bus to the relay;
the relay is further configured to determine whether the received current value is greater than the predetermined current threshold; or when the voltage value of the direct-current bus is larger than the preset voltage threshold value of the direct-current bus, sending an electric signal to an insulated gate bipolar transistor IGBT of the crowbar circuit so as to enable the crowbar circuit to be communicated with a rotor winding circuit of the target circuit.
3. The system of claim 2, further comprising a reactive power compensation device connected to the relay;
the relay is also used for sending a starting electric signal to the reactive power compensation device when sending an electric signal to an Insulated Gate Bipolar Transistor (IGBT) of the crowbar circuit;
and the reactive power compensation device is used for starting and transmitting reactive power to a power grid connected with the target circuit to stabilize the voltage of the grid-connected point when receiving the starting electric signal.
4. The system of claim 3, wherein the reactive power compensation device is a grid-side converter.
5. The system of claim 4, the grid-side converter comprising a PI regulator, a first input of the PI regulator inputting a stator voltage reference; the second input end is connected with the first voltage transformer and receives the voltage value of the grid-connected port; the output end of the PI regulator outputs a q-axis current reference value; the q-axis current reference is used to generate reactive power.
6. The system of claim 1, wherein the relay is further configured to send an electrical signal to an IGBT of a crowbar circuit to cause the crowbar circuit to be disconnected from rotor winding cut-off if the rotor current value detected by the current transformer is less than a predetermined current threshold.
7. The system of claim 1, wherein the resistance-capacitance circuit comprises a resistor, the resistor and the capacitance device being connected in series.
8. The system of claim 1, wherein the resistance-capacitance circuit comprises a resistor connected in parallel with the capacitive device.
9. The system of claim 1, wherein the relay internally comprises a first comparator, a second comparator, and an and circuit; the output end of the first comparator is connected with the first input end of the AND gate circuit; the output end of the second comparator is connected with the second input end of the AND gate circuit;
the first input end of the first comparator is used for receiving a voltage value sent by the first voltage transformer; the second input end is used for receiving a preset voltage threshold; comparing the received voltage value to the predetermined voltage threshold; if the received voltage value is smaller than the preset voltage threshold value, the output end outputs a low level;
the first input end of the second comparator is used for receiving a current value sent by the current transformer; the second input end is used for receiving a current threshold value; comparing the received current value with a predetermined current threshold value; if the received current value is smaller than the preset current threshold value, the output end outputs a low level;
and the output end of the AND gate circuit is used as the output end of the relay and is connected with the control end of the switch device.
10. A wind power system comprising a wind power generator and a low voltage ride through system according to any of claims 1 to 9, the electrical circuit of the wind power generator being connected to the low voltage ride through system.
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| CN109245173B (en) * | 2018-11-21 | 2024-07-12 | 广东电网有限责任公司 | Low voltage ride through method and system |
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