[0021] The present invention will be further introduced below in conjunction with the drawings and specific embodiments.
[0022] Such as figure 1 Shown is a structural diagram of the implementation of the transient stability control system of the UHV AC/DC transmission system of the present invention. It can be seen from the figure that the system includes a DC transmission transmission end control system for controlling and managing the DC transmission system (not shown in the figure) ) And the doubly-fed fan excitation inverter control system used to control and manage the wind farm, and also include a wind farm wide-area control system for coordinated control of the DC transmission system sending end control system and the doubly-fed fan excitation inverter control system; The wind farm wide-area control system includes a controller, which is used to receive the sending end frequency of the DC transmission system and the common bus voltage frequency and voltage of the wind farm, and is used to control the reactive power signal of the wind turbine (reactive power additional control control quantity ΔUdr, active power additional The control quantity ΔUqr) is sent to the wind farm doubly-fed wind turbine excitation inverter control system, and at the same time, the DC transmission system is sent to the end reactive power control signal (active power additional control quantity ΔP DC ) Is sent to the control system of the sending end of the DC transmission system, and the reactive power control signal of the fan is superimposed with the active control signal of the sending end of the DC transmission system, and then sent to the excitation inverter control system of the double-fed fan.
[0023] Such as figure 2 As shown, the controller of this embodiment is a DSP controller, which converts the additional control signal of the wind turbine through a photoelectric conversion module, and is used to send to the excitation inverter control system of the double-fed wind turbine of the wind farm by using the CAN bus.
[0024] The wide-area control system of the wind farm is characterized by a unidirectional broadcast type of simple information flow. Different from the conventional wind farm control system, the broadcast command is directly interfaced with the control system of the doubly-fed wind turbine excitation inverter instead of the wind turbine main control system. . The hardware technology of the wide-area control system of the wind farm ensures that the overall response time of the wind farm to the active and reactive power commands of the centralized control system is less than 15 milliseconds.
[0025] The present invention also provides a transient stability control method for an UHV AC/DC transmission system. The applicable object of the method is a "wind-fire bundling" AC/DC UHV transmission system, which is characterized by a high proportion of wind power and weak AC connection, such as figure 1 Shown.
[0026] Such as image 3 As shown, the method adopts the wind farm and the DC system for coordinated control. The coordinated control includes two aspects: (1) The coordinated control of the wind farm wide-area control system and the DC control system is used to quickly eliminate transient disturbances caused by grid faults. Balance active and reactive power to reduce the risk of power angle instability; (2) The coordinated control of the wind farm and the supporting synchronous power station is used to achieve the coherence of the dynamic behavior of two different power sources and improve the power angle stability.
[0027] When the transmission system receives a large disturbance, the fault type and location are first judged through the extraction and analysis of the fault characteristic quantity, and the fault occurs in the DC system or the AC system, and the following methods are controlled according to the fault type:
[0028] When the DC system fails, the DC blocking causes a sudden drop in the output power. At this time, the active output of the wind farm should be reduced within the set adjustment time (20 milliseconds in this example) to prevent the synchronous generator from instability and absorb reactive output at the same time To prevent the voltage from rising suddenly, and not to cause the wind turbine to lose stability when reducing the output of the wind farm.
[0029] The specific calculation process of the reduced active output control quantity ΔUqr is as follows: image 3 As shown, f AC With f 0 (f AC Is the frequency after the failure of the sending end AC bus B3; f 0 It is the frequency increment Δf obtained by comparing the frequency before the fault at the sending end AC bus B3) after filtering and scaling up.
[0030] When the AC system fails, the output power of the AC channel suddenly decreases. At this time, the output power of the DC system should be increased within the set time (20 milliseconds in this embodiment), but the sudden increase of the DC power can cause reactive power demand Sudden increase, the AC bus voltage of the converter station drops, so it is necessary to quickly adjust the reactive power output of the wind farm at the same time to suppress the voltage drop. When adjusting the reactive power output of the wind farm, the transient reactive power demand is calculated according to the output power increment of the DC system, and the wind farm generates the transient reactive power output.
[0031] Increased active output control amount of DC system ΔP DC And the specific calculation process of the wind turbine reactive power control ΔUdr as image 3 As shown, ΔP DC Is f AC With f 0 The frequency increment Δf obtained by comparison is filtered, and then the proportional amplification and integration are performed respectively, and the obtained values are added together. ΔUdr is the voltage U AC With U 0 (U AC Is the voltage at the sending end AC bus B3 after a fault; U 0 It is the voltage increase ΔU obtained by comparing the voltage at the sending end AC bus B3 before the failure) after filtering and scaling up.
[0032] In addition, in view of the low short-circuit capacity of the sending end of the "wind-fire bundling" transmission system, the control quantity of the DC system is used as the feedforward compensation quantity for the reactive power adjustment of the wind farm, which has the effect of coordinated control.
[0033] In order to verify the effect of cooperative control, a real-time simulation model of the "wind-fire bundling" power transmission system is established based on the real-time digital simulator RTDS (Real Time Digital Simulator) of the power system, and the simulation experiment is carried out through the cooperative control prototype.
[0034] The wind farm and the power system are simulated in real time by RTDS. The frequency of the common bus of the wind farm or the speed and power angle of the synchronous motor are continuous state variables of the real-time simulation model. They are output by GTAO of RTDS, and the signal cable is used to connect these analog quantities to the test. The data acquisition module of the device. In order to simulate the optical fiber channel used in wind farms, a photoelectric conversion module and a 3km single-mode optical fiber were installed in the test device. The collected data from RTDS generates additional control signals through the data processing module and the algorithm forming module. The wind farm control signal is connected to the GTAI port of RTDS via the photoelectric module and field bus for system stability control.
[0035] If attached figure 1 The AC tie line LAC of the transmission system shown is disconnected by a fault at t=2s, and overlaps after 0.3s. The power angle swing curve of the synchronous generator under the “wind-fire bundling” system without and with coordinated control is as follows Figure 4a , 4b Shown. Under the same fault disturbance, without cooperative control, the power angle swing amplitude of the supporting thermal power plant is 66 degrees; when there is cooperative control, its power angle swing amplitude is 41 degrees. The cooperative control system plays a role in enhancing the transient stability of the system.
[0036] If attached figure 1 The DC system of the transmission system shown is unipolar blocked at t=2s, and the test results are as follows Figure 5a , 5b Shown. When there is no cooperative control, the output of the wind farm cannot be adjusted quickly, and the unbalanced power is all borne by the thermal power unit, which causes the power angle of the thermal power unit to be unstable and the entire system collapses; when there is coordinated control, the wind farm participates in the control through the fast wide area control network. The digestion of unbalanced power keeps the power angle stable in thermal power plants.
[0037] Figure 6a , 6b It is the voltage response of the AC busbar of the converter station under the AC system failure. When there is no cooperative control, the voltage drops to 0.72pu under the short-circuit fault; when there is cooperative control, the voltage drops to 0.88pu under the same short-circuit fault. Cooperative control has a certain effect on improving transient voltage stability.
[0038] The stability control method of the UHV AC/DC transmission system of the present invention aims at the transient stability problems of voltage and power angle in the "wind-fire bundling" system, and proposes coordinated control with the wind farm doubly-fed wind generator group and the DC regulator as the control object The strategy is based on the fact that the doubly-fed wind generator can realize the decoupling control of its active and reactive power; for the "wind-fire bundling" system, there are voltage transient stability and power angle transient stability problems, and the DC transmission system is used to send the end The rectifier and the wind farm implement a joint coordinated control strategy as the control object. The basis is that the power angle swing amplitude of the thermal power unit can be suppressed by controlling the DC transmission power, and the implemented wind farm adjustment can compensate for the voltage fluctuation caused by the DC system adjustment.
[0039] The above embodiments are only used to help understand the core idea of the present invention, and cannot be used to limit the present invention. For those skilled in the art, whoever makes modifications or equivalent substitutions to the present invention based on the ideas of the present invention, in the specific implementation and scope of application Any changes made to the above should be included in the protection scope of the present invention.
