Converter and grid connection device
By combining the converter design with a soft-start circuit, the problems of increased size and maintenance costs associated with contactors and circuit breakers are solved, enabling miniaturization and low-cost operation of the converter, and improving the service life of the equipment and grid connection safety.
Patent Information
- Application Number
- CN202423270897.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-30
- Publication Date
- 2025-12-26
- Estimated Expiration
- 2034-12-30
Smart Images
Figure CN223729460U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of power electronics, and particularly relates to a converter and a grid-connected device. BACKGROUND
[0002] In a wind power generation system, a doubly-fed generator has a higher and higher proportion in the wind power generation system due to its small capacity and low cost. In a doubly-fed wind power generation system, most of the energy needs to be fed back to the power grid through the stator of the doubly-fed generator, and the converter connected to the rotor of the doubly-fed generator only passes through the slip power. The converter provides rotor excitation current to enable the stator side of the doubly-fed generator to operate at a constant frequency and variable speed.
[0003] The converter is generally provided with a contactor and a circuit breaker at a grid connection end, and the electrical connection between other devices in the converter and the power grid is controlled by the closing and shutting of the contactor. However, the above-mentioned devices increase the volume and cost of the converter. If the contactor is reduced, the use life of the circuit breaker is limited, and the connection with the power grid is disconnected by disconnecting the circuit breaker, which increases the maintenance cost of the converter. CONTENT OF THE UTILITY MODEL
[0004] The present application provides a converter and a grid-connected device, which are used to reduce the number of devices of the converter, reduce the volume of the converter, and reduce the maintenance cost of the converter.
[0005] In a first aspect, an embodiment of the present application provides a converter, which can be connected in a wind power generation system and used for rotor grid connection processing of a doubly-fed generator. The converter can include a rotor-side converter, a grid-side converter, a direct-current bus, a filter module, and a circuit breaker.
[0006] The first end of the rotor-side converter is used to be connected with the rotor of the doubly-fed generator, the second end of the rotor-side converter is connected with the first end of the grid-side converter through the direct-current bus, the second end of the grid-side converter is connected with the second end of the circuit breaker through the filter module, the first end of the circuit breaker is used to be connected with a rotor grid connection point, and the circuit breaker is in a closed state when receiving a shutdown instruction, and the grid-side converter is used to compensate the filter module with the reactive power of the direct-current bus when receiving the shutdown instruction.
[0007] With the above design, other devices in the converter are electrically connected to the grid point through the circuit breaker. When the doubly-fed generator is in normal operation, the circuit breaker is in a closed state, and the electrical energy of the rotor of the doubly-fed generator can be transmitted to the power grid through the converter and the rotor grid point. When the doubly-fed generator is shut down and the converter needs to stop running, in order to improve the service life of the circuit breaker, the circuit breaker can be controlled to remain in the closed state. Since the electrical energy of the power grid can also be transmitted to the filter module through the circuit breaker, the filter module and the power grid exchange reactive power. The grid-side converter can use the electrical energy of the DC bus to compensate the reactive power of the filter module, so as to eliminate the influence of the electrical connection between the filter module and the power grid and ensure the normal operation of the equipment.
[0008] In a possible design, the circuit breaker is further configured to: when it is determined that the converter fails, switch from the closed state to the off state.
[0009] In a possible design, the converter further includes a first soft-start circuit.
[0010] The first end of the first soft-start circuit is configured to be connected to the rotor grid point, and the second end of the first soft-start circuit is connected to the DC bus. The first soft-start circuit is configured to: before the doubly-fed generator and the converter are formally started, obtain electrical energy from the rotor grid point, and use the obtained electrical energy to charge the DC bus. The grid-side converter is further configured to: when it is detected that the voltage of the DC bus is charged to a preset value, obtain electrical energy from the DC bus, and use the obtained electrical energy to charge the filter module. The circuit breaker is further configured to be closed when the voltage of the filter module is the same as the voltage of the power grid.
[0011] With the above design, when the doubly-fed generator is initially started after installation, the voltage across the DC bus is zero. Since the voltage difference between the DC bus and the rotor grid point is large, if the grid-side converter and the rotor-side converter are directly controlled to operate, current shock will be caused to the internal devices of the grid-side converter and the rotor-side converter. In order to protect the safety of the devices, the first soft-start circuit can be used to sequentially charge the bus capacitor and the capacitor in the filter module. When the bus capacitor and the capacitor in the filter module are both fully charged, the rotor converter and the doubly-fed generator can be started to operate, so as to ensure the normal operation of the doubly-fed generator.
[0012] In a possible design, the converter further includes a second soft-start circuit.
[0013] The first end of the second soft start circuit is configured to be connected to the rotor grid point, the second end of the second soft start circuit is configured to be connected to the filter module, and the second soft start circuit is configured to: obtain electrical energy from the rotor grid point before the doubly-fed generator and the converter are started, and charge the filter module and the DC bus capacitor by using the obtained electrical energy; and the circuit breaker is further configured to be closed when the voltage of the filter module is the same as the voltage of the power grid.
[0014] With the above design, when the doubly-fed generator is started for the first time after being installed, the voltage across the DC bus is zero. Since the voltage difference between the DC bus voltage and the rotor grid point voltage is large, if the grid-side converter and the rotor-side converter are directly controlled to operate, current impact on the internal devices of the grid-side converter and the rotor-side converter will be caused. In order to protect the safety of the devices, the second soft start circuit can be used to charge the capacitor in the filter module and the bus capacitor at the same time. After the bus capacitor and the capacitor in the filter module are fully charged, the rotor converter is started, the stator voltage is gradually increased by controlling the rotor converter, and the stator voltage, frequency and phase are completely synchronized with the power grid, and the grid connection of the doubly-fed generator is completed.
[0015] In a possible design, the converter further includes a fuse connected between the rotor grid point and the circuit breaker and connected to each phase line on the circuit breaker in one-to-one correspondence. With the above fuse, overcurrent and short circuit protection of the converter can be performed.
[0016] In a possible design, the converter further includes an energy storage device, the energy storage device is connected to the DC bus, and the energy storage device is configured to: supply power to the DC bus when it is detected that the frequency of the power grid decreases, and obtain electrical energy from the DC bus and store the electrical energy when it is detected that the frequency of the power grid increases. With the above design, the energy storage device can participate in the coordination of the power grid frequency. When the power supply of the power grid is under pressure and the frequency of the power grid decreases, the energy storage device can be used to supply power to the DC bus to increase the output power to the power grid. Similarly, when the frequency of the power grid increases, the excess electrical energy can be stored in the energy storage device, so as to stabilize the frequency of the power grid and slow down the influence of the wind power generation system on the frequency fluctuation of the power grid.
[0017] In a second aspect, an embodiment of the present application provides a grid connection device, and the grid connection device is used to realize grid connection of electrical energy generated by a wind power generation system. The grid connection device includes: a doubly-fed generator, a medium-voltage switch cabinet, a transformer, and a converter as provided in the first aspect of the present application and any possible design thereof.
[0018] The stator of the doubly-fed generator is connected with the first secondary winding of the transformer through the medium-voltage switch cabinet, and the rotor of the doubly-fed generator is connected with the second secondary winding of the transformer through the converter; and the primary winding of the transformer is used to be connected with a power grid.
[0019] In a possible design, if the rotor voltage and the stator voltage of the doubly-fed generator are the same, the medium-voltage switch cabinet and the converter are integrated in the same cabinet.
[0020] In a possible design, the medium-voltage switch cabinet is configured to disconnect the stator of the doubly-fed generator from the first secondary winding of the transformer when the shutdown instruction is received.
[0021] In a possible design, the converter is further configured to control the medium-voltage switch cabinet to disconnect the stator of the doubly-fed generator from the first secondary winding of the transformer when the shutdown instruction is received.
[0022] In addition, the technical effects brought by the second aspect and any possible design thereof can be referred to the technical effects brought by different designs of the first aspect of the embodiments of the present application, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS
[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.
[0024] Figure 1 A grid-connected structure of a wind power generation system provided by the embodiments of the present application Figure One ;
[0025] Figure 2 A grid-connected structure of a wind power generation system provided by the embodiments of the present application Figure Two ;
[0026] Figure 3 A structure of a converter provided by the embodiments of the present application Figure One ;
[0027] Figure 4 A structure of a converter provided by the embodiments of the present application Figure Two ;
[0028] Figure 5 A structure of a converter provided by the embodiments of the present application Figure Three ;
[0029] Figure 6 A first soft start circuit connection diagram provided for an embodiment of the present application;
[0030] Figure 7 A second full start circuit connection diagram provided for an embodiment of the present application;
[0031] Figure 8 A structure diagram of a converter provided for an embodiment of the present application Figure Four . DETAILED DESCRIPTION
[0032] The application scenarios of the technical solutions in the embodiments of the present application will be introduced below in combination with the drawings in the embodiments of the present application.
[0033] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.
[0034] The term "a plurality of" in the embodiments of the present application means two or more, and other quantifiers are similar. In the embodiments of the present application, "connection" can be understood as electrical connection or communication connection. The electrical connection between two electrical elements can be direct or indirect connection between the two electrical elements. For example, A and B are connected, which can be direct connection between A and B, or indirect connection between A and B through one or more other electrical elements, for example, A and B are connected, which can be direct connection between A and C, direct connection between C and B, and connection between A and B through C. The communication connection between two electrical elements is a wireless connection between the two electrical elements, i.e. electromagnetic connection between the two electrical elements.
[0035] The converter provided in the embodiments of the present application can be applied to a new energy power generation system grid-connected scenario, and the new energy power generation system includes but is not limited to a photovoltaic power generation system and a wind power generation system. In order to facilitate understanding of the scheme claimed in the present application, the wind power generation system grid-connected is taken as an example for description,
[0036] Referring to Figure 1 , it is a grid-connected structure diagram of a wind power generation system. As Figure 1As shown, the stator of the doubly-fed generator is connected to the medium-voltage switchgear, and the rotor of the doubly-fed generator combines the electrical energy generated by the medium-voltage switchgear with that generated by the converter, and then connects to the power grid through a transformer. If the stator and rotor voltages of the doubly-fed generator are the same, the components of the medium-voltage switchgear and converter are integrated into the same cabinet.
[0037] In practical applications, as the single-unit capacity of wind power systems increases, the stator output voltage of doubly-fed induction generators (DFIGs) is gradually increasing to reduce cable costs and avoid difficulties in twisting excessively thick cables. If the converter cannot be adapted to the stator output voltage of the DFIG, the wind power system can also use [the following option is missing from the original text]. Figure 2 The grid connection topology shown is used for grid connection. For example... Figure 2 As shown, the stator of the doubly-fed generator is connected to the first secondary winding of the transformer through a medium-voltage switchgear, the rotor of the doubly-fed generator is connected to the second secondary winding of the transformer through a converter, and the primary winding of the transformer is connected to the power grid.
[0038] In practical applications, different voltage levels can be accommodated by configuring different numbers of coils for the first and second secondary windings. For example, by configuring appropriate numbers of coils for the first and second secondary windings, the operating voltage of the first secondary winding can be 10.5KV, and the operating voltage of the second secondary winding can be 1140V. Of course, depending on the model of the doubly-fed generator, the first and second secondary windings of the transformer can also be configured to different voltage levels, which is not specifically limited here.
[0039] It should be noted that, in Figure 1 and Figure 2 In the grid connection structure of the wind power generation system shown, the power grid connected to the transformer can be a single-phase AC power grid or a three-phase AC power grid.
[0040] See Figure 3 The diagram shown is a structural schematic of a converter provided in an embodiment of this application. This converter can be applied to applications such as... Figure 1 and Figure 2 The grid-connected structure of the wind power generation system is shown. For example... Figure 3 As shown, the converter includes: a rotor-side converter, a grid-side converter, a DC bus, a filter module, and a circuit breaker.
[0041] The first end of the rotor-side converter is configured to be connected with the rotor of the doubly-fed generator, the second end of the rotor-side converter is connected with the first end of the grid-side converter through a DC bus, the second end of the grid-side converter is connected with the second end of the circuit breaker through a filter module, and the first end of the circuit breaker is configured to be connected with a rotor grid connection point, and the circuit breaker is in a closed state when receiving a shutdown instruction. The grid-side converter is configured to compensate the filter module with reactive power by using the electric energy of the DC bus when receiving the shutdown instruction. The rotor grid connection point is a connection point of the converter and a transformer when the converter is applied to the grid connection structure shown in Figure 1 The rotor grid connection point is a convergence point of the converter and a medium-voltage switch cabinet when the converter is applied to the grid connection structure shown in Figure 2 The rotor grid connection point is a second secondary winding of the transformer.
[0042] In actual application, the circuit breaker can be turned off when a system fault occurs, thereby disconnecting the grid and the converter, and avoiding the expansion of the fault range. As shown in Figure 4 The converter can further include a fuse FU connected between the rotor grid connection point and the circuit breaker and connected with each phase line of the circuit breaker in one-to-one correspondence. The fuse can disconnect the grid and the converter when an overcurrent fault occurs in the converter or a device connected with the converter, thereby isolating the fault source and avoiding the further expansion of the fault range. The number of the fuse can be set according to the application scenario of the converter, which is not limited herein.
[0043] It should be noted that, according to the type of the grid connected in the grid connection structure of the wind power generation system, the grid-side converter, the rotor-side converter and the DC bus in the embodiment of the present application can have different structures. For example, when the grid is a single-phase alternating current grid, the grid-side converter and the rotor-side converter can be single-phase converters and process single-phase alternating current. When the grid is a three-phase alternating current grid, the grid-side converter and the rotor-side converter can be three-phase converters and process three-phase alternating current. The DC bus can be composed of two bus capacitors in series, in which case, the converter can adopt a three-level circuit topology. As shown in Figure 5 The DC bus capacitor can also be composed of one bus capacitor, in which case, the converter can adopt a two-level circuit topology. Of course, the DC bus can also have other forms, which are not introduced herein. In order to facilitate the understanding of the technical solution claimed in the present application, the DC bus composed of two bus capacitors C1 and C2 in series as shown in Figure 4 is taken as an example for illustration.
[0044] As shown in Figure 3As shown, the doubly-fed generator is connected with the wind wheel through the transmission system, the wind wheel rotates to drive the bearing of the doubly-fed generator through the transmission system, and the doubly-fed generator converts the mechanical energy of the bearing rotation into electrical energy and outputs. The stator side electrical energy of the doubly-fed generator is transmitted to the power grid through the medium voltage switch cabinet and the transformer, and the rotor side electrical energy of the doubly-fed generator is transmitted to the power grid through the converter and the transformer.
[0045] In actual application, the medium voltage switch cabinet and the converter can be respectively configured with a cabinet, and a plurality of external interfaces are arranged on the cabinet. If the medium voltage switch cabinet is configured with a controller, and the controller can communicate with the converter, the medium voltage switch cabinet is connected with the stator and the transformer of the doubly-fed generator through the plurality of external interfaces and cables on the cabinet. If the medium voltage switch cabinet is not configured with a controller, the medium voltage switch cabinet is connected with the stator, the transformer and the converter of the doubly-fed generator through the plurality of external interfaces and cables arranged on the cabinet. When the converter receives a shutdown instruction, the medium voltage switch cabinet is disconnected from the transformer and the stator of the doubly-fed generator by communicating with the controller in the medium voltage switch cabinet or sending a corresponding voltage signal to the medium voltage switch cabinet. Wherein, if the stator voltage of the doubly-fed generator is the same as the rotor voltage, the medium voltage switch cabinet can also be located in the cabinet of the converter, that is, the medium voltage switch cabinet and the converter are integrated in the same cabinet.
[0046] The converter structure shown in Figure 3 When the doubly-fed generator operates, the circuit breaker inside the converter can be controlled to be closed, the rotor side electrical energy of the doubly-fed generator is transmitted to the transformer through the rotor side converter, the DC bus, the filter module and the grid side converter, and is transmitted to the power grid through the transformer, so as to realize the grid connection of the rotor side electrical energy of the doubly-fed generator. When the converter receives a shutdown instruction for indicating the doubly-fed generator to stop operating, the contactor inside the medium voltage switch cabinet can be controlled to be closed to disconnect the electrical connection between the stator of the doubly-fed generator and the power grid. For the rotor side of the doubly-fed generator, the circuit breaker can be controlled to maintain the closed state to improve the service life of the circuit breaker. Since the filter module is still electrically connected with the power grid through the transformer, in order to eliminate the reactive power exchange between the power grid and the filter capacitor in the filter module in the process of electrical connection with the power grid, the grid side converter can be controlled to compensate the reactive power of the filter module by using the electrical energy on the DC bus, so as to ensure the subsequent normal operation and normal grid connection of the wind power generation equipment.
[0047] Wherein, the filter module can be composed of a filter capacitor and a filter inductor, the filter structure of the filter module can adopt a T-type filter structure or a Π-type filter structure, of course, other filter structures commonly used in the industry can also be adopted, which are not limited here.
[0048] The converter structure shown in Figure 3 and Figure 5The converter shown in the rotor side of the doubly-fed generator, if the converter receives the start instruction for indicating the work of the doubly-fed generator, due to the low voltage on the filter module and the DC bus, if directly controlling the grid-side converter and the rotor-side converter to work, the current impact due to the too large voltage difference between the DC bus and the transformer may occur, resulting in the device damage, therefore, the converter provided by the embodiment of the present application can further include a soft start circuit, the soft start circuit can pre-charge the DC bus and the filter module before system start, and after the DC bus and the filter module are fully charged, the rotor-side converter is controlled to run, the excitation current is provided for the doubly-fed generator, and the stator voltage is raised by controlling the excitation capacitor, when the voltage, frequency and phase of the stator side are consistent with the power grid, the grid connection of the doubly-fed generator is completed.
[0049] In some embodiments, the converter provided by the embodiment of the present application includes a first soft start circuit, referring to Figure 6 As shown, the first end of the first soft start circuit is used for connecting with the second secondary winding of the transformer, the second end of the first soft start circuit is connected with the DC bus, the first soft start circuit can obtain the electric energy from the second secondary winding of the transformer before the start of the doubly-fed generator and the converter, and use the obtained electric energy to charge the DC bus. The grid-side converter is further used for: obtaining the electric energy from the DC bus when detecting that the voltage of the DC bus is charged to the preset value, and using the obtained electric energy to charge the filter module. When the filter module is also fully charged, the circuit breaker is closed, the soft start process is ended, the rotor-side converter can be controlled to run to provide the excitation current for the doubly-fed generator, and the stator voltage is raised by controlling the excitation current, when the voltage, frequency and phase of the stator side are consistent with the power grid, the grid connection of the doubly-fed generator is completed. At the same time, in order to avoid the device loss caused by the continued running of the device in the first soft start circuit, the first soft start circuit can be controlled to stop working.
[0050] In actual use, the first soft start circuit mainly includes switching devices, protection devices, step-down transformers, rectifier circuits and current-limiting resistors and the like. The switching devices can include contactors and circuit breakers, which are used for controlling the electrical connection between the devices in the first soft start circuit. The protection devices can be circuit breakers, fuses or other protection devices, which are used for realizing overcurrent protection or other protection during the pre-charge process. The step-down transformer can perform step-down processing on the voltage of the second secondary winding of the transformer. The rectifier circuit can convert the alternating voltage output by the step-down transformer into the direct current voltage for charging the DC bus. The current-limiting resistor can reduce the charging current on the circuit to avoid the device loss caused by the too large current on the line. The rectifier circuit can adopt the commonly used rectifier topology in the industry, for example, the H-bridge rectifier topology or the Vienna topology composed of multiple bridge arms. Of course, the first soft start circuit can further include other functional devices, which are not limited here.
[0051] It should be noted that, since there is no power on the converter before the double-fed generator is started, in order to avoid the failure of the rectifier in the first soft start circuit to trigger the driving signal when a switching tube is used, the rectifier in the first soft start circuit is preferably a diode.
[0052] In some embodiments, the converter provided by the embodiments of the present application further comprises a second soft start circuit, as shown in Figure 7 The first end of the second soft start circuit is connected to the second secondary winding of the transformer, and the second end of the second soft start circuit is connected to the filter module. The second soft start circuit is used to obtain power from the second secondary winding of the transformer before the double-fed generator and the converter are started, and to charge the filter module and the DC bus with the obtained power at the same time. When the DC bus is fully charged, the circuit breaker is closed, and the soft start process is completed. The rotor-side converter can be controlled to operate to provide excitation current for the double-fed generator, and the stator voltage is raised by controlling the excitation current. When the voltage, frequency and phase of the stator are consistent with those of the power grid, the double-fed generator is connected to the power grid. At the same time, in order to avoid the waste of the devices in the second soft start circuit, the second soft start circuit can be controlled to stop working.
[0053] In actual use, the second soft start circuit mainly comprises switching devices, protection devices and current-limiting resistors. The switching devices can include contactors for controlling the electrical connection between the devices in the second soft start circuit. The protection devices can be circuit breakers or fuses for overcurrent protection or other protection during the pre-charging process. The current-limiting resistors can reduce the charging current in the circuit to avoid excessive current in the circuit and device waste.
[0054] In combination with the above description, the converter provided by the embodiments of the present application can realize the connection of the rotor of the double-fed generator to the power grid without the use of contactors, thereby reducing the device cost of the converter and reducing the size of the converter. In addition, the circuit breaker uses the grid-side converter to compensate for reactive power when the double-fed generator is stopped, thereby eliminating the influence of the closed circuit breaker on the power grid. The circuit breaker is only closed when a fault occurs in the circuit, which is beneficial to prolong the service life of the circuit breaker.
[0055] In some possible implementations, the converter provided by the embodiments of the present application can also eliminate the influence of the wind power system on the power grid during the connection of the wind power system to the power grid. Specifically, as shown in Figure 8 The converter can further comprise an energy storage device connected to the DC bus. The energy storage device can be used to supply power to the DC bus when the frequency of the power grid is detected to decrease, and to obtain power from the DC bus and store the power when the frequency of the power grid is detected to increase.
[0056] It should be noted that the converter provided in the embodiments of the present application can also have other topologies according to different connection positions of the soft start circuit, which will not be introduced here.
[0057] The energy storage device can include a voltage regulation circuit and a battery module. The voltage regulation circuit can convert the voltage on the DC bus to the charging voltage of the battery module and charge the battery module. The voltage regulation circuit can also be used to convert the voltage of the battery module to the rated voltage of the DC bus and power the DC bus. The battery module includes a plurality of energy storage batteries, which can be connected in series or parallel.
[0058] Specifically, a controller is configured in the converter or the converter is configured with a dedicated control cabinet. The controller can detect the grid frequency or receive the frequency information issued by the grid. When the grid frequency decreases, the voltage regulation circuit in the energy storage device is controlled to discharge the energy storage battery, thereby powering the DC bus and increasing the output of the grid-connected power to make the grid frequency rise until the grid frequency returns to the normal value. When the grid frequency rises, the voltage regulation circuit in the energy storage device can be controlled to charge the energy storage battery, thereby charging the plurality of energy storage batteries and reducing the output of the grid-connected power to make the grid frequency decrease until the grid frequency returns to the normal value.
[0059] In combination with the above description, the embodiments of the present application also provide a grid-connected device, which can include a doubly-fed generator, a medium-voltage switch cabinet, a transformer, and the aforementioned converter.
[0060] The stator of the doubly-fed generator is connected to the first secondary winding of the transformer through the medium-voltage switch cabinet, and the rotor of the doubly-fed generator is connected to the second secondary winding of the transformer through the converter. The primary winding of the transformer is used to connect to the grid.
[0061] It should be noted that the embodiments of the present application take the grid connection of a wind power generation system as an example for description. In actual applications, the grid-connected device can also be applied to the grid connection processing of other new energy power generation systems. For example, when the grid-connected device is applied to the grid connection of a photovoltaic power generation system, the converter can be connected between the photovoltaic panel and the grid-connected transformer.
[0062] It should be noted that the process of using the rotor electric energy of the doubly-fed generator for grid connection by the converter can be seen from the foregoing description, which will not be repeated here.
[0063] In a possible implementation, the converter and the medium-voltage switch cabinet can be two independent devices. If the stator voltage of the doubly-fed generator is the same as the rotor voltage, the medium-voltage switch cabinet and the converter can be integrated in the same cabinet.
[0064] In a possible implementation, if the medium voltage switch cabinet is internally configured with a controller, the controller can communicate with the converter, the controller in the medium voltage switch cabinet can receive the shutdown instruction, and when receiving the shutdown instruction, the connection between the stator of the doubly-fed generator and the first secondary winding of the transformer is disconnected. The converter can control the circuit breaker to maintain the closed state when receiving the shutdown instruction, and control the grid-side converter to compensate the filter module with the reactive power of the DC bus. Wherein, the medium voltage switch cabinet has a circuit breaker and a contactor, and the circuit breaker and the contactor are connected on the connection path between the stator of the doubly-fed generator and the first secondary winding of the transformer, and the connection between the stator of the doubly-fed generator and the first secondary winding of the transformer can be disconnected by controlling the contactor to be turned off.
[0065] In a possible implementation, if the medium voltage switch cabinet is not internally configured with a controller, the medium voltage switch cabinet can be connected with the converter through a cable, and the converter can send a control electrical signal to the switch device in the medium voltage switch cabinet to control the medium voltage switch cabinet to disconnect the connection between the stator of the doubly-fed generator and the first secondary winding of the transformer when receiving the shutdown instruction. Wherein, the medium voltage switch cabinet has a circuit breaker and a contactor, and the circuit breaker and the contactor are connected on the connection path between the stator of the doubly-fed generator and the first secondary winding of the transformer, and the connection between the stator of the doubly-fed generator and the first secondary winding of the transformer can be disconnected by triggering the corresponding electrical signal to control the contactor to be turned off.
[0066] In various embodiments of the present application, the terms and / or descriptions of different embodiments are consistent and can be mutually referred to if there is no special description and logical conflict. The technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationship.
[0067] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.
Claims
1. A current transformer, characterized by The converter is connected between a rotor of a doubly-fed generator and a rotor grid connection point, and comprises a rotor-side converter, a grid-side converter, a DC bus, a filter module and a circuit breaker; a first end of the rotor-side converter is configured to be connected to the rotor of the doubly-fed generator, and a second end of the rotor-side converter is connected to a first end of the grid-side converter through the DC bus; a second end of the grid-side converter is connected to a second end of the circuit breaker through the filter module; a first end of the circuit breaker is configured to be connected to the rotor grid connection point, and the circuit breaker is configured to be in a closed state when receiving a shutdown instruction; the grid-side converter is configured to perform reactive power compensation on the filter module by using electric energy of the DC bus when receiving the shutdown instruction.
2. The current transformer of claim 1, wherein, The circuit breaker is further configured to switch from the closed state to an off state when determining that the converter fails.
3. The current transformer of claim 1, wherein, The converter further comprises a first soft start circuit; a first end of the first soft start circuit is configured to be connected to the rotor grid connection point, and a second end of the first soft start circuit is connected to the DC bus, and the first soft start circuit is configured to obtain electric energy from the rotor grid connection point before starting the doubly-fed generator and the converter, and charge the DC bus by using the obtained electric energy; the grid-side converter is further configured to obtain electric energy from the DC bus and charge the filter module by using the obtained electric energy when detecting that a voltage of the DC bus is charged to a preset value; the circuit breaker is further configured to be closed when a voltage of the filter module is equal to a voltage of a power grid.
4. The current transformer of claim 1, wherein, The converter further comprises a second soft start circuit; a first end of the second soft start circuit is configured to be connected to the rotor grid connection point, and a second end of the second soft start circuit is connected to the filter module, and the second soft start circuit is configured to obtain electric energy from the rotor grid connection point before starting the doubly-fed generator and the converter, and charge the filter module and the DC bus by using the obtained electric energy; the circuit breaker is further configured to be closed when a voltage of the filter module is equal to a voltage of a power grid.
5. The current transformer of claim 1, wherein, The converter further comprises a fuse connected between the rotor grid connection point and the circuit breaker and connected to each phase line on the circuit breaker in a one-to-one manner.
6. The current transformer of claim 1, wherein, The converter further comprises an energy storage device connected to the DC bus, and the energy storage device is configured to supply power to the DC bus when detecting that a frequency of a power grid decreases, and obtain electric energy from the DC bus and store the electric energy when detecting that the frequency of the power grid increases.
7. A grid-tie device, characterized by, The converter comprises: a doubly-fed generator, a medium-voltage switch cabinet, a transformer and the converter according to any one of claims 1 to 6; a stator of the doubly-fed generator is connected to a first secondary winding of the transformer through the medium-voltage switch cabinet, and a rotor of the doubly-fed generator is connected to a second secondary winding of the transformer through the converter; a primary winding of the transformer is configured to be connected to a power grid.
8. The grid-tie device of claim 7, wherein, If voltages of the rotor and the stator of the doubly-fed generator are the same, the medium-voltage switch cabinet and the converter are integrated in a same cabinet.
9. The grid-tie device of claim 7, wherein, The medium voltage switchgear is configured to disconnect the stator of the doubly-fed generator from the first secondary winding of the transformer upon receiving a shutdown command.
10. The grid-tie device of claim 7, wherein, The converter is further configured to control the medium voltage switchgear to disconnect the stator of the doubly-fed generator from the first secondary winding of the transformer upon receiving a shutdown command.