New energy remote grid-connected control system and method

Abstract

The invention discloses a new energy remote grid-connected control system and method. The system comprises a new energy power plant, a new energy switching station, a power frequency power grid, a power frequency branch, a low frequency branch, a system master controller, a new energy side frequency conversion station controller and a grid-connected frequency conversion station controller. The power frequency branch and the low frequency branch are connected in parallel and then are arranged between the new energy switching station and the power frequency power grid; a first power frequency circuit breaker, a power frequency overhead line and a second power frequency circuit breaker are sequentially arranged on the power frequency branch, and a new energy side frequency conversion station, a first low frequency circuit breaker, a low frequency overhead line, a second low frequency circuit breaker, a grid-connected frequency conversion station and a third power frequency circuit breaker are sequentially arranged on the low frequency branch; the new energy side frequency conversion station is connected with the new energy side frequency conversion station controller, and the grid-connected frequency conversion station is connected with the grid-connected frequency conversion station controller. According to the invention, the stability and reliability of the new energy power system are improved, and the energy loss in the long-distance transmission process is reduced.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a new energy long-distance grid-connected control system and method. Background Art

[0002] At present, new energy sources are gradually being developed and utilized. Due to geographical restrictions, the distance to connect new energy sources to the grid is relatively long, resulting in poor stability and low transmission capacity when using conventional power frequency AC grid connection. Therefore, a new type of aggregation and transmission technology is needed to solve the above problems. It is used to increase the grid access frequency, grid connection stability, and transmission capacity, thereby adapting to the volatility and intermittency of new energy generation.

[0003] The development of new collection and transmission technologies needs to consider the impact of renewable energy generation and grid connection on the power system, including the application of power electronics technology, distributed power grid connection and microgrid technology. The development of these technologies can help improve the flexibility and reliability of renewable energy grid connection. For example, by adopting power electronics technology, precise control of renewable energy generation can be achieved, reducing the impact on grid stability.

[0004] However, the nonlinearity and multi-time scale of power electronic converters in power electronics technology lead to multi-band frequency coupling between the converter and the power grid, and also present different stability problems at different frequency ends.

[0005] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No admission is made that the description herein is prior art by inclusion in this section. Summary of the invention

[0006] The embodiment of the present invention provides a new energy long-distance grid-connected control system, which is used to improve the stability and reliability of the new energy power system and reduce the energy loss in the long-distance transmission process. The system includes: a new energy power plant, a new energy switch station, a new energy side frequency conversion station, a first low-frequency circuit breaker, a low-frequency overhead line, a second low-frequency circuit breaker, a grid-connected frequency conversion station, a third power frequency circuit breaker, a power frequency power grid, a first power frequency circuit breaker, a power frequency overhead line, a second power frequency circuit breaker, a system master controller, a new energy side frequency conversion station controller and a grid-connected frequency conversion station controller;

[0007] The frequency conversion station on the new energy side, the first low-frequency circuit breaker, the low-frequency overhead line, the second low-frequency circuit breaker, the grid-connected frequency conversion station and the third power frequency circuit breaker are sequentially arranged on the low-frequency branch between the new energy switch station and the power frequency power grid; the first power frequency circuit breaker, the power frequency overhead line and the second power frequency circuit breaker are sequentially arranged on the power frequency branch between the new energy switch station and the power frequency power grid; the frequency conversion station on the new energy side is connected to the frequency conversion station controller on the new energy side, and the grid-connected frequency conversion station is connected to the grid-connected frequency conversion station controller;

[0008] The grid-connected frequency conversion station controller is connected to the system master controller, and the system master controller starts the new energy switch station and controls the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station;

[0009] The frequency conversion station controller on the new energy side is connected to the system master controller. The system master controller starts the new energy switch station and controls the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the frequency conversion station on the new energy side supplies power to the grid-connected frequency conversion station.

[0010] Further, the new energy side frequency conversion station is a back-to-back MMC structure, including: a first MMC module, a second MMC module, a first DC / DC converter and a first energy storage device;

[0011] The first MMC module is connected to the second MMC module via a first DC line and the low-frequency branch;

[0012] The first DC / DC converter and the first energy storage device are connected between the first DC line and the low-frequency branch via a second DC line.

[0013] Further, the grid-connected frequency conversion station is a back-to-back MMC structure, comprising: a third MMC module and a fourth MMC module, a second DC / DC converter and a second energy storage device;

[0014] The third MMC module is connected to the fourth MMC module via a third DC line and the low-frequency branch;

[0015] The second DC / DC converter and the second energy storage device are connected between the third DC line and the low-frequency branch via a fourth DC line.

[0016] Furthermore, the system also includes: a first DC / DC controller connected to the first DC / DC converter and the system master controller, configured to receive a fault signal and an unlocking instruction from the system master controller, and unlock the first DC / DC converter according to the unlocking instruction.

[0017] Furthermore, the system also includes: a second DC / DC controller connected to the second DC / DC converter and the system master controller, configured to receive a fault signal and an unlocking instruction from the system master controller, and unlock the second DC / DC converter according to the unlocking instruction.

[0018] The embodiment of the present invention further provides a new energy long-distance grid connection control method, which is used to improve the stability and reliability of the new energy power system and reduce the energy loss during long-distance transmission. The method includes:

[0019] Starting the new energy switch station and controlling the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station;

[0020] Start the new energy switch station and control the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station supplies power to the grid-connected frequency conversion station.

[0021] Further, the system master controller starts the new energy switch station and controls the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station, including:

[0022] Controlling the capacitor voltage in the grid-connected frequency conversion station to charge to a first fixed voltage value;

[0023] Starting the grid-connected frequency conversion station controller so that the grid-connected frequency conversion station controller controls the grid-connected frequency conversion station to charge to a second fixed voltage value;

[0024] Controlling the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the grid-connected frequency conversion station charges the new energy side frequency conversion station to a second fixed voltage value;

[0025] The frequency conversion station controller on the new energy side is started so that the frequency conversion station controller on the new energy side controls the AC voltage amplitude in the frequency conversion station on the new energy side to increase to a third fixed voltage value and the frequency to increase to the first frequency.

[0026] Further, the system master controller starts the new energy switch station and controls the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station supplies power to the grid-connected frequency conversion station, including:

[0027] Controlling the frequency conversion station on the new energy side to charge to a third fixed voltage value;

[0028] Controlling the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station charges the grid-connected frequency conversion station to a third fixed voltage value;

[0029] Starting the frequency conversion station controller on the new energy side, so that the frequency conversion station controller on the new energy side controls the capacitor voltage in the frequency conversion station on the new energy side to be charged to a fourth fixed voltage value;

[0030] Controlling the new energy side frequency conversion station to charge the grid-connected frequency conversion station to a fourth fixed voltage value;

[0031] Starting the grid-connected frequency conversion station controller so that the grid-connected frequency conversion station controller controls the AC voltage amplitude in the grid-connected frequency conversion station to increase to a fifth fixed voltage value and the frequency to increase to a second frequency;

[0032] The AC voltage amplitude of the new energy switch station is controlled to increase to a fifth fixed voltage value and the frequency thereof is controlled to increase to a second frequency.

[0033] Furthermore, the method further comprises:

[0034] When a fault is detected in the frequency conversion station on the new energy side, the grid-connected frequency conversion station or the low-frequency branch, the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker are closed to control the frequency conversion station on the new energy side and the grid-connected frequency conversion station to be locked and shut down.

[0035] Further, the controlling the new energy side frequency conversion station and the grid-connected frequency conversion station to be locked and shut down includes:

[0036] Controlling the first DC / DC converter to charge the first energy storage device to a sixth fixed voltage value, and controlling the second DC / DC converter to charge the second energy storage device to the sixth fixed voltage value;

[0037] In response to the preset time, the new energy side frequency conversion station controller is controlled to lock the second MMC module, and the grid-connected frequency conversion station controller is controlled to lock the fourth MMC module;

[0038] Disconnecting the third power frequency circuit breaker and the first low frequency circuit breaker, and closing the first power frequency circuit breaker and the second power frequency circuit breaker;

[0039] The frequency conversion station controller on the new energy side is controlled to lock the first MMC module, and the frequency conversion station controller on the grid is controlled to lock the third MMC module, so that the frequency conversion station on the new energy side and the frequency conversion station on the grid are locked and shut down.

[0040] The embodiment of the present invention provides a new energy long-distance grid-connected control system and method, which adopts a back-to-back MMC structure to achieve flexible conversion between industrial frequency and low frequency, thereby enhancing the stability and reliability of the system. By controlling the number of sub-modules put into operation, the conversion between AC and DC is achieved, thereby improving the utilization rate of energy. By adopting low-frequency transmission, the line loss during long-distance transmission can be reduced, and the transmission efficiency of the power grid can be improved. The system master controller can identify faults and respond quickly, and ensure the continuity of power supply by switching the operating mode. The DC / DC energy storage system in the DC link provides voltage support in the event of a fault, which helps to maintain the stability of the system. Through timely fault detection and processing, the risk of damage to equipment due to faults is reduced, and the service life of the equipment is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0042] Figure 1 This is a schematic diagram of the structure of a new energy long-distance grid-connected control system in one embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the structure of a new energy long-distance grid-connected control system in another embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of the structure of the MMC topology structure in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the structure of a half-bridge submodule in an embodiment of the present invention;

[0046] Figure 5 A schematic diagram of a flow chart of a new energy long-distance grid connection control method in one embodiment of the present invention;

[0047] Figure 6 A schematic flow chart of a new energy long-distance grid connection control method in another embodiment of the present invention;

[0048] Figure 7 A schematic flow chart of a new energy long-distance grid connection control method in another embodiment of the present invention;

[0049] Figure 8 The figure is a flow chart of a new energy long-distance grid-connected control method in another embodiment of the present invention. DETAILED DESCRIPTION

[0050] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0051] The information collected in the technical solution of this application is information and data authorized by the user or fully authorized by all parties, and the collection, storage, use, processing, transmission, provision, disclosure and application of relevant data comply with the relevant laws, regulations and standards of relevant countries and regions, take necessary confidentiality measures, do not violate public order and good morals, and provide corresponding operation entrances for users to choose to authorize or refuse.

[0052] Provide users with corresponding operation entrances for them to choose to agree or reject the automated decision-making results; if the user chooses to reject, the expert decision-making process will be entered.

[0053] In order to improve the stability and reliability of the new energy power system and reduce the energy loss during long-distance transmission, the present invention provides a new energy long-distance grid-connected control system.

[0054] like Figure 1 As shown, a new energy long-distance grid-connected control system 100 includes: a new energy power plant 101, a new energy switch station 102, a new energy side frequency conversion station 105, a first low-frequency circuit breaker 106, a low-frequency overhead line 107, a second low-frequency circuit breaker 108, a grid-connected frequency conversion station 109, a third power frequency circuit breaker 110, a power frequency power grid 111, a first power frequency circuit breaker 112, a power frequency overhead line 113 and a second power frequency circuit breaker 114, a system master controller (not shown in the figure), a new energy side frequency conversion station controller (not shown in the figure) and a grid-connected frequency conversion station controller (not shown in the figure).

[0055] The new energy side frequency conversion station 105, the first low-frequency circuit breaker 106, the low-frequency overhead line 107, the second low-frequency circuit breaker 108, the grid-connected frequency conversion station 109 and the third power frequency circuit breaker 110 are sequentially arranged on the low-frequency branch 103 between the new energy switch station 102 and the power frequency power grid 111; the first power frequency circuit breaker 112, the power frequency overhead line 113 and the second power frequency circuit breaker 114 are sequentially arranged on the power frequency branch 104 between the new energy switch station 102 and the power frequency power grid 111.

[0056] The new energy side frequency conversion station 105 is connected to the new energy side frequency conversion station controller, and the grid-connected frequency conversion station 109 is connected to the grid-connected frequency conversion station controller. Both the grid-connected frequency conversion station controller and the new energy side frequency conversion station controller are connected to the system master controller.

[0057] In one embodiment, the system master controller is used to start the new energy switch station 102 and control the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 to close, so that the grid-connected frequency conversion station 109 supplies power to the new energy side frequency conversion station 105. The system master controller is also used to start the new energy switch station 102 and control the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 to close, so that the new energy side frequency conversion station 105 supplies power to the grid-connected frequency conversion station 109.

[0058] In one embodiment, the grid-connected frequency conversion station 109 is used to control the AC voltage and frequency of the low-frequency branch 103 , and the new energy side frequency conversion station 105 follows the voltage, phase and frequency of the low-frequency branch 103 .

[0059] Combination Figure 1 and Figure 2 As shown, the new energy side frequency conversion station 105 is a back-to-back MMC (Modular Multilevel Converter) structure, including: a first MMC module (referred to as MMC1 module) 201, a second MMC module (referred to as MMC2 module) 202, a first DC / DC converter 203 and a first energy storage device 204.

[0060] The MMC1 module 201 and the MMC2 module 202 are also connected to each other through the first DC line 205. The first DC / DC converter 203 and the first energy storage device 204 are arranged on the second DC line 206, and the two ends of the second DC line 206 are respectively connected across the first DC line 205 and the low-frequency branch 103. The first DC / DC converter 203, the first energy storage device 204, the first DC line 205 and the second DC line 206 constitute an independent DC link.

[0061] The grid-connected frequency conversion station 109 is a back-to-back MMC structure, including: a third MMC module (MMC3 module for short) 207 and a fourth MMC module (MMC4 module for short) 208 , a second DC / DC converter 209 and a second energy storage device 210 .

[0062] The MMC3 module 207 and the MMC4 module 208 are also connected to each other through the third DC line 211. The second DC / DC converter 209 and the second energy storage device 210 are arranged on the fourth DC line 212, and the two ends of the fourth DC line 212 are respectively bridged on the third DC line 211 and the low-frequency branch 103. The second DC / DC converter 209, the second energy storage device 210, the third DC line 211 and the fourth DC line 212 constitute an independent DC link.

[0063] In one embodiment, the MMC1 module 201, the MMC2 module 202, the MMC3 module and the MMC4 module are all MMC topology structures, such as Figure 3 As shown, the MMC topology structure includes: a first DC bus WB1, a second DC bus WB2 and 12n half-bridge sub-modules SM.

[0064] In one embodiment, the first DC bus WB1 and the second DC bus WB2 may be two parts of the same DC bus, or may be two different DC buses.

[0065] The MMC topology structure in the present invention is a three-phase 12-bridge-arm structure, and each bridge arm is composed of an inductor L and n half-bridge sub-modules SM connected in series.

[0066] In one embodiment, by controlling the input (conduction), removal (shutdown) or blocking (not participating in commutation) of the half-bridge submodule, the back-to-back MMC structure can achieve precise control of the output voltage. This control method allows the back-to-back MMC structure to work under different combinations of half-bridge submodules, thereby achieving conversion between alternating current (AC) and direct current (DC).

[0067] Specifically, by controlling the input (conduction) and removal (shutdown) of the half-bridge submodules in each bridge arm, the back-to-back MMC structure can change the amplitude of the AC side output voltage. When more half-bridge submodules are put into operation, the amplitude of the AC side voltage increases. When the half-bridge submodule is removed, the amplitude of the AC side voltage decreases.

[0068] In one embodiment, due to the switching on (on) and off (off) of the half-bridge submodule, the AC side voltage changes in real time, forming a series of voltage steps. These step waveforms are superimposed in time and can be synthesized into AC voltage step waveforms of different frequencies.

[0069] In one embodiment, by changing the frequency of switching on (conducting on) and off (shutting down) the half-bridge submodule, the back-to-back MMC structure can control the frequency of the synthesized AC voltage waveform, thereby achieving AC voltage outputs of different frequencies.

[0070] like Figure 4 As shown, the half-bridge submodule consists of two insulated gate bipolar transistors (IGBTs), two diodes and a capacitor C. The collector of the insulated gate bipolar transistor IGBT1 is connected to one end of the capacitor C, and the emitter of the insulated gate bipolar transistor IGBT1 is connected to the collector of the insulated gate bipolar transistor IGBT2. The collector of the insulated gate bipolar transistor IGBT1 is connected to the cathode of its corresponding diode VD1, and the emitter of the insulated gate bipolar transistor IGBT1 is connected to the anode of its corresponding diode VD1.

[0071] The emitter of the insulated gate bipolar transistor IGBT2 is connected to the other end of the capacitor C. The collector of the insulated gate bipolar transistor IGBT2 is connected to the cathode of its corresponding diode VD2, and the emitter of the insulated gate bipolar transistor IGBT2 is connected to the anode of its corresponding diode VD2.

[0072] In one embodiment, the inductance in each bridge arm of the back-to-back MMC structure can suppress the circulating current generated when the power of each phase bridge arm or the instantaneous value of the capacitor voltage of the half-bridge sub-module is not completely consistent, and can suppress the impact current when a fault occurs in the low-frequency power transmission system, thereby enhancing the stability of the operation of the low-frequency power transmission system.

[0073] The new energy long-distance grid-connected control system further includes: a first DC / DC controller connected to the first DC / DC converter 203 and the system master controller.

[0074] In one embodiment, the first DC / DC controller is used to receive a fault signal and an unlocking instruction from the system master controller, and unlock the first DC / DC converter 203 according to the unlocking instruction.

[0075] The new energy long-distance grid-connected control system further includes: a second DC / DC controller connected to the second DC / DC converter 209 and the system master controller.

[0076] In one embodiment, the second DC / DC controller is used to receive a fault signal and an unlocking instruction from the system master controller, and unlock the second DC / DC converter 209 according to the unlocking instruction.

[0077] In the embodiment of the present invention, a back-to-back MMC structure is adopted to realize flexible conversion between industrial frequency and low frequency, thereby enhancing the stability and reliability of the system. By controlling the number of half-bridge sub-modules put into operation, the conversion between AC and DC is realized, thereby improving the utilization rate of energy. By adopting low-frequency transmission, the line loss during long-distance transmission can be reduced, thereby improving the transmission efficiency of the power grid. The system master controller can identify faults and respond quickly, and ensure the continuity of power supply by switching the operating mode. The DC / DC energy storage system in the DC link provides voltage support in the event of a fault, which helps to maintain the stability of the system. Through timely fault detection and processing, the risk of damage to the equipment due to faults is reduced, and the service life of the equipment is extended.

[0078] like Figure 5 As shown, the present invention also provides a new energy long-distance grid-connected control method, which is applied to the above-mentioned new energy long-distance grid-connected control system 100, and the execution subject is the system master controller. The new energy long-distance grid-connected control method includes steps 501 to 503.

[0079] Step 501: Start the new energy switch station 102 and control the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 to close, so that the grid-connected frequency conversion station 109 supplies power to the new energy side frequency conversion station 105.

[0080] Step 502 : Start the new energy switch station 102 and control the first low frequency circuit breaker 106 and the second low frequency circuit breaker 108 to close, so that the new energy side frequency conversion station 105 supplies power to the grid-connected frequency conversion station 109 .

[0081] Step 503: When a fault is detected in the frequency conversion station 105 on the new energy side, the grid-connected frequency conversion station 109 or the low-frequency branch 103, the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 are closed to control the frequency conversion station 105 on the new energy side and the grid-connected frequency conversion station 109 to be locked and shut down.

[0082] In an embodiment of the present invention, by controlling the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 to close, the grid-connected frequency conversion station 109 can supply power to the new energy side frequency conversion station 105. By controlling the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 to close, the new energy side frequency conversion station 105 can supply power to the grid-connected frequency conversion station 109. The stable operation of the power system is ensured, and a rapid response can be achieved when a fault occurs. The stability and safety of the system are maintained by switching to a backup power supply path and shutting down faulty equipment. Through the above control strategy, the impact of the fault on the entire power system can be minimized, and the continuity and reliability of the power supply can be guaranteed.

[0083] like Figure 6 As shown, step 501 includes steps 601 to 604, and step 501 can convert industrial frequency electricity into low frequency electricity.

[0084] Step 601: Control the capacitor voltage in the grid-connected frequency conversion station 109 to be charged to a first fixed voltage value.

[0085] Specifically, after starting the new energy switch station 102, the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 are closed, so that the capacitor voltage in the MMC3 module 207 and the MMC4 module 208 is charged to the first voltage fixed value, thereby meeting the above-mentioned module drive energy extraction requirements.

[0086] In one embodiment, module drive energy extraction refers to providing enough energy for the MMC module to drive the IGBT switch device inside it. When the capacitor is charged to the required voltage level, the MMC module has enough energy to drive the IGBT, thereby controlling the flow of current inside the half-bridge submodule.

[0087] Step 602: Start the grid-connected frequency conversion station controller, so that the grid-connected frequency conversion station controller controls the grid-connected frequency conversion station 109 to charge to a second fixed voltage value.

[0088] Specifically, after the grid-connected frequency conversion station controller is started, the grid-connected frequency conversion station controller controls the capacitor voltage in the MMC3 module 207 and the MMC4 module 208 to be charged to the second fixed voltage value, and keeps the capacitor voltage stable at the second fixed voltage value.

[0089] In one embodiment, the capacitors in the MMC3 module 207 and the MMC4 module 208 are charged to an initial voltage value (i.e., a first fixed voltage value) in step 601. In step 602, the capacitors in the MMC3 module 207 and the MMC4 module 208 need to be further charged to another preset voltage value (i.e., a second fixed voltage value). Usually, the second fixed voltage value is higher than the first fixed voltage value to ensure that the MMC module has sufficient voltage support when running at full load.

[0090] In one embodiment, after the capacitor voltage of the MMC3 module 207 and the MMC4 module 208 reaches the second fixed voltage value, the grid-connected frequency conversion station controller maintains the capacitor voltage stable at the second fixed voltage value by real-time monitoring the capacitor voltage and dynamically adjusting the input and removal of sub-modules.

[0091] Step 603: Control the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 to close, so that the grid-connected frequency conversion station 109 charges the new energy side frequency conversion station 105 to a second fixed voltage value.

[0092] Specifically, closing the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 can connect the power frequency side MMC module with the low frequency side MMC module, allowing DC energy to flow from the grid-connected frequency conversion station 109 to the new energy side frequency conversion station 105. The power frequency side MMC module can transmit electric energy to the low frequency side MMC module through the DC line, so that the capacitor voltage in the low frequency side MMC module is charged to the second fixed voltage value, so as to ensure that the low frequency side MMC module can have sufficient voltage support when running at full load.

[0093] Step 604: Start the new energy side frequency conversion station controller, so that the new energy side frequency conversion station controller controls the AC voltage amplitude in the new energy side frequency conversion station 105 to increase to the third voltage fixed value and the frequency to increase to the first frequency.

[0094] In one embodiment, the frequency conversion station controller on the new energy side is used to control the input and output of the sub-modules, thereby controlling the output voltage and current.

[0095] Specifically, the frequency conversion station controller on the new energy side adjusts the number and timing of the input of the submodules, and the controller can gradually increase the AC voltage amplitude of the frequency conversion station on the new energy side 105 until the amplitude reaches and stabilizes at the third voltage fixed value. This process requires precise current and voltage control strategies, which may include advanced control algorithms such as PI control to achieve rapid regulation and accurate control. At the same time, the frequency conversion station controller on the new energy side controls the AC voltage frequency of the frequency conversion station on the new energy side 105 to stabilize at the first frequency.

[0096] When the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 are closed, the AC voltage amplitude of the low-frequency overhead line 107 is stabilized at the third fixed voltage value, and the AC voltage frequency is stabilized at the first frequency.

[0097] like Figure 7 As shown, step 502 includes steps 701 to 706. Through step 502, low-frequency electricity can be converted into industrial frequency electricity.

[0098] Step 701: Control the new energy side frequency conversion station 105 to charge to a third fixed voltage value.

[0099] Specifically, after the new energy switch station 102 is started, the capacitor voltages in the MMC1 module 201 and the MMC2 module 202 are charged to a third fixed voltage value.

[0100] Step 702: Control the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 to close, so that the new energy side frequency conversion station 105 charges the grid-connected frequency conversion station 109 to a third fixed voltage value.

[0101] Specifically, closing the first low-frequency circuit breaker 106 and the second low-frequency circuit breaker 108 can connect the low-frequency side MMC module with the power frequency side MMC module, allowing DC energy to flow from the new energy side frequency conversion station 105 to the grid-connected frequency conversion station 109. The capacitor voltage in the MMC3 module 207 and the MMC4 module 208 on the power frequency side is charged to the third fixed voltage value, thereby meeting the above module drive energy extraction requirements.

[0102] In one embodiment, once the capacitor voltages of the MMC3 module 207 and the MMC4 module 208 reach the third fixed voltage value, the module driver can extract energy from the capacitor to provide the necessary power for the operation of the MMC modules.

[0103] Step 703: Start the new energy side frequency conversion station controller, so that the new energy side frequency conversion station controller controls the capacitor voltage in the new energy side frequency conversion station 105 to be charged to a fourth fixed voltage value.

[0104] Specifically, after starting the frequency conversion station controller on the new energy side, the frequency conversion station controller on the new energy side controls the capacitor voltage in the MMC1 module 201 and the MMC2 module 202 to be charged to the fourth fixed voltage value, and keeps the capacitor voltage stable at the fourth fixed voltage value.

[0105] Step 704: Control the new energy side frequency conversion station 105 to charge the grid-connected frequency conversion station 109 to a fourth fixed voltage value.

[0106] Specifically, the low-frequency side MMC modules (i.e., MMC1 module 201 and MMC2 module 202) charge the capacitors of the industrial frequency side MMC modules (i.e., MMC3 module 207 and MMC4 module 208) through the DC line, and charge them to a fourth fixed voltage value, thereby ensuring that the capacitor voltage of the industrial frequency side MMC module matches that of the low-frequency side.

[0107] Step 705: Start the grid-connected frequency conversion station controller, so that the grid-connected frequency conversion station controller controls the AC voltage amplitude in the grid-connected frequency conversion station 109 to increase to the fifth fixed voltage value and the frequency to increase to the second frequency.

[0108] Specifically, the grid-connected frequency conversion station controller is started to control the AC voltage of the industrial frequency side MMC modules (i.e., MMC3 module 207 and MMC4 module 208), so that the AC voltage amplitude of MMC3 module 207 and MMC4 module 208 increases and stabilizes at the fifth voltage fixed value. At the same time, the frequency of the AC voltage is ensured to be stable at the second frequency.

[0109] In one embodiment, the low-frequency side frequency is selected within the range of 0-50 Hz according to the system transmission distance and capacity requirements, thereby improving the flexibility and adaptability of the system.

[0110] Step 706: Control the AC voltage amplitude of the new energy switch station 102 to increase to the fifth fixed voltage value and the frequency thereof to increase to the second frequency.

[0111] Specifically, the AC voltage amplitude of the new energy switch station 102 is controlled to increase and stabilize at the fifth fixed voltage value. At the same time, the frequency of the AC voltage is ensured to be stable at the second frequency, so as to ensure the stable output of the power system.

[0112] In one embodiment, the connection mode of the low frequency branch 103 is generally adopted, and the connection mode of the power frequency branch 104 is used as a backup. The first power frequency circuit breaker 112 and the second power frequency circuit breaker 114 are in the disconnected state.

[0113] Step 503: When a fault is detected in the frequency conversion station 105 on the new energy side, the grid-connected frequency conversion station 109 or the low-frequency branch 103, the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 are closed to control the frequency conversion station 105 on the new energy side and the grid-connected frequency conversion station 109 to be locked and shut down.

[0114] Specifically, when a fault is detected in the frequency conversion station 105 on the new energy side, the grid-connected frequency conversion station 109 or the low-frequency branch 103, the first power frequency circuit breaker 112, the second power frequency circuit breaker 114 and the third power frequency circuit breaker 110 are closed, and the energy storage system (the first energy storage device and the second energy storage device) and the DC / DC converter (i.e., the first DC / DC converter 203 and the second DC / DC converter 209) of the DC link of the frequency conversion station 105 on the new energy side and the grid-connected frequency conversion station 109 are unlocked.

[0115] In one embodiment, the energy storage system is used to provide voltage support so that the power frequency branch 104 and the low frequency branch 103 operate in parallel.

[0116] By sending a locking instruction to the MMC modules of the new energy side frequency conversion station 105 and the grid-connected frequency conversion station 109, the two frequency conversion stations are locked and shut down.

[0117] Specifically, when the system master controller detects a fault in the new energy side frequency conversion station 105, the grid-connected frequency conversion station 109 or the low frequency branch 103, a fault signal and an unlocking instruction are sent to the first DC / DC controller and the second DC / DC controller.

[0118] In one embodiment, the system master controller is used to identify faults in various components of the entire new energy long-distance grid-connected control system and send signals and instructions to other controllers.

[0119] like Figure 8 As shown, step 503 includes steps 801 to 804.

[0120] Step 801: Control the first DC / DC converter 203 to charge the first energy storage device to a sixth fixed voltage value, and control the second DC / DC converter 209 to charge the second energy storage device to a sixth fixed voltage value.

[0121] Specifically, the voltage of the first energy storage device is stabilized at the sixth fixed voltage value through the first DC / DC converter 203. The voltage of the second energy storage device is stabilized at the sixth fixed voltage value through the second DC / DC converter 209.

[0122] Step 802: In response to the preset time, the frequency conversion station controller at the new energy side is controlled to lock the second MMC module, and the frequency conversion station controller at the grid-connected side is controlled to lock the fourth MMC module.

[0123] Specifically, after the system master controller detects that the charging voltage of the two energy storage batteries is stabilized at the sixth fixed voltage value and maintained for a certain period of time, it sends an instruction to lock the MMC2 module to the new energy side frequency conversion station controller, and sends an instruction to lock the MMC4 module to the grid-connected frequency conversion station controller.

[0124] After the frequency conversion station controller on the new energy side and the grid-connected frequency conversion station controller receive the locking command, the frequency conversion station controller on the new energy side locks the MMC2 module, and the grid-connected frequency conversion station controller locks the MMC4 module.

[0125] Step 803 : Open the third power frequency circuit breaker 110 and the first low frequency circuit breaker 106 , and close the first power frequency circuit breaker 112 and the second power frequency circuit breaker 114 .

[0126] Step 804: Control the new energy side frequency conversion station controller to lock the first MMC module, and control the grid-connected frequency conversion station controller to lock the third MMC module, so that the new energy side frequency conversion station 105 and the grid-connected frequency conversion station 109 are locked and stopped.

[0127] Specifically, after the system master controller detects the closing signals of the first power frequency circuit breaker 112 and the second power frequency circuit breaker 114, it sends an instruction to lock the MMC1 module 201 to the new energy side frequency conversion station controller, and sends an instruction to lock the MMC3 module 207 to the grid-connected frequency conversion station controller.

[0128] After the frequency conversion station controller on the new energy side and the grid-connected frequency conversion station controller receive the blocking instruction, the frequency conversion station controller on the new energy side blocks the MMC1 module 201 , and the grid-connected frequency conversion station controller blocks the MMC3 module 207 .

[0129] After the first DC / DC converter 203 and the second DC / DC converter 209 are locked, the new energy side frequency conversion station 105 and the grid-connected frequency conversion station 109 are locked and stopped.

[0130] In the embodiment of the present invention, a back-to-back MMC structure is adopted to realize flexible conversion between industrial frequency and low frequency, thereby enhancing the stability and reliability of the system. By controlling the number of sub-modules put into operation, the conversion between AC and DC is realized, thereby improving the utilization rate of energy. By adopting low-frequency transmission, the line loss during long-distance transmission can be reduced, and the transmission efficiency of the power grid can be improved. The system master controller can identify faults and respond quickly, and ensure the continuity of power supply by switching the operating mode. The DC / DC energy storage system in the DC link provides voltage support in the event of a fault, which helps to maintain the stability of the system. Through timely fault detection and processing, the risk of damage to the equipment due to faults is reduced, and the service life of the equipment is extended.

[0131] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A new energy long-distance grid-connected control system, characterized in that: include: New energy power plant, new energy switch station, new energy side frequency conversion station, first low-frequency circuit breaker, low-frequency overhead line, second low-frequency circuit breaker, grid-connected frequency conversion station, third power frequency circuit breaker, power frequency power grid, first power frequency circuit breaker, power frequency overhead line, second power frequency circuit breaker, system master controller, new energy side frequency conversion station controller and grid-connected frequency conversion station controller; The new energy side frequency conversion station, the first low-frequency circuit breaker, the low-frequency overhead line, the second low-frequency circuit breaker, the grid-connected frequency conversion station and the third power frequency circuit breaker are sequentially arranged on the low-frequency branch between the new energy switch station and the power frequency power grid; the first power frequency circuit breaker, the power frequency overhead line and the second power frequency circuit breaker are sequentially arranged on the power frequency branch between the new energy switch station and the power frequency power grid; The new energy side frequency conversion station is connected to the new energy side frequency conversion station controller, and the grid-connected frequency conversion station is connected to the grid-connected frequency conversion station controller; The grid-connected frequency conversion station controller is connected to the system master controller, and the system master controller is used to start the new energy switch station and control the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station; The frequency conversion station controller on the new energy side is connected to the system master controller, and the system master controller is also used to start the new energy switch station and control the closing of the first low-frequency circuit breaker and the second low-frequency circuit breaker so that the frequency conversion station on the new energy side can supply power to the grid-connected frequency conversion station.

2. The system according to claim 1, characterized in that The new energy side frequency conversion station is a back-to-back MMC structure, including: a first MMC module, a second MMC module, a first DC / DC converter and a first energy storage device; The first MMC module is connected to the second MMC module via a first DC line and the low-frequency branch; The first DC / DC converter and the first energy storage device are connected between the first DC line and the low-frequency branch via a second DC line.

3. The system according to claim 1, characterized in that The grid-connected frequency conversion station is a back-to-back MMC structure, including: a third MMC module and a fourth MMC module, a second DC / DC converter and a second energy storage device; The third MMC module is connected to the fourth MMC module via a third DC line and the low-frequency branch; The second DC / DC converter and the second energy storage device are connected between the third DC line and the low-frequency branch via a fourth DC line.

4. The system according to claim 2, characterized in that Also includes: The first DC / DC controller is connected to the first DC / DC converter and the system master controller, and is used to receive a fault signal and an unlocking instruction from the system master controller, and unlock the first DC / DC converter according to the unlocking instruction.

5. The system according to claim 3, characterized in that Also includes: The second DC / DC controller is connected to the second DC / DC converter and the system master controller, and is used to receive a fault signal and an unlocking instruction from the system master controller, and unlock the second DC / DC converter according to the unlocking instruction.

6. A new energy long-distance grid-connected control method, applied to the new energy long-distance grid-connected control system according to any one of claims 1 to 5, characterized in that: include: Starting the new energy switch station and controlling the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station; Start the new energy switch station and control the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station supplies power to the grid-connected frequency conversion station.

7. The method according to claim 6, characterized in that The system master controller starts the new energy switch station and controls the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker to close, so that the grid-connected frequency conversion station supplies power to the new energy side frequency conversion station, including: Controlling the capacitor voltage in the grid-connected frequency conversion station to charge to a first fixed voltage value; Starting the grid-connected frequency conversion station controller so that the grid-connected frequency conversion station controller controls the grid-connected frequency conversion station to charge to a second fixed voltage value; Controlling the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the grid-connected frequency conversion station charges the new energy side frequency conversion station to a second fixed voltage value; The frequency conversion station controller on the new energy side is started so that the frequency conversion station controller on the new energy side controls the AC voltage amplitude in the frequency conversion station on the new energy side to increase to a third fixed voltage value and the frequency to increase to the first frequency.

8. The method according to claim 6, characterized in that The system master controller starts the new energy switch station and controls the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station supplies power to the grid-connected frequency conversion station, including: Controlling the frequency conversion station on the new energy side to charge to a third fixed voltage value; Controlling the first low-frequency circuit breaker and the second low-frequency circuit breaker to close, so that the new energy side frequency conversion station charges the grid-connected frequency conversion station to a third fixed voltage value; Starting the frequency conversion station controller on the new energy side, so that the frequency conversion station controller on the new energy side controls the capacitor voltage in the frequency conversion station on the new energy side to be charged to a fourth fixed voltage value; Controlling the new energy side frequency conversion station to charge the grid-connected frequency conversion station to a fourth fixed voltage value; Starting the grid-connected frequency conversion station controller so that the grid-connected frequency conversion station controller controls the AC voltage amplitude in the grid-connected frequency conversion station to increase to a fifth fixed voltage value and the frequency to increase to a second frequency; The AC voltage amplitude of the new energy switch station is controlled to increase to a fifth fixed voltage value and the frequency thereof is controlled to increase to a second frequency.

9. The method according to claim 6, characterized in that The method further comprises: When a fault is detected in the frequency conversion station on the new energy side, the grid-connected frequency conversion station or the low-frequency branch, the first power frequency circuit breaker, the second power frequency circuit breaker and the third power frequency circuit breaker are closed to control the frequency conversion station on the new energy side and the grid-connected frequency conversion station to be locked and shut down.

10. The method according to claim 9, characterized in that The controlling of the new energy side frequency conversion station and the grid-connected frequency conversion station to be locked and shut down includes: Controlling the first DC / DC converter to charge the first energy storage device to a sixth fixed voltage value, and controlling the second DC / DC converter to charge the second energy storage device to the sixth fixed voltage value; In response to the preset time, the new energy side frequency conversion station controller is controlled to lock the second MMC module, and the grid-connected frequency conversion station controller is controlled to lock the fourth MMC module; Disconnecting the third power frequency circuit breaker and the first low frequency circuit breaker, and closing the first power frequency circuit breaker and the second power frequency circuit breaker; The frequency conversion station controller on the new energy side is controlled to lock the first MMC module, and the frequency conversion station controller on the grid is controlled to lock the third MMC module, so that the frequency conversion station on the new energy side and the frequency conversion station on the grid are locked and shut down.

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