A starting control method for a new energy true bipolar hybrid DC transmission system

Abstract

The application relates to the technical field of new energy and discloses a starting control method of a new energy true bipolar hybrid DC sending-out system. The method comprises the following steps: controlling a first flexible DC valve to charge a third flexible DC valve until the third flexible DC valve is charged completely, and then unlocking the third flexible DC valve; controlling the third flexible DC valve to charge a fourth flexible DC valve until the fourth flexible DC valve is charged completely, and then unlocking the fourth flexible DC valve; sequentially turning on the third diode valve and the fourth diode valve, the first diode valve and the second diode valve, and completing the starting of the system. Through the application, the true bipolar main wiring mode is adopted, and the reverse power transmission from the receiving end converter station to the sending end converter station is realized.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, specifically to a startup control method for a new energy transmission system via a true bipolar hybrid DC transmission line. Background Technology

[0002] In the practical application of large-scale offshore wind power development, flexible DC transmission technology, while currently the mainstream power transmission solution, suffers from the problem of excessive size and weight of offshore converter platforms. To achieve lightweight offshore converter platforms, DC transmission technology based on a hybrid of diodes and flexible DC converter valves has become a key focus of the industry. In existing black-start schemes using a hybrid diode and flexible DC converter valve transmission, if a reverse power supply method with a bypass switch is adopted, the turbine's output power must be dissipated after starting the turbine and disconnecting the bypass switch to make the current flowing through the bypass switch close to zero. One dissipation method involves putting the turbine into a low-voltage ride-through mode to dissipate its output power, but this makes it difficult to distinguish from a fault state in the sending-end AC system, posing a safety risk. Another dissipation method involves configuring energy-dissipating resistors at the sending-end converter station to dissipate the turbine's output power, which increases the size, weight, and cost of the converter station, contradicting the development requirements of lightweight and low-cost offshore converter platforms.

[0003] Meanwhile, existing offshore wind power DC transmission systems mostly employ symmetrical monopolar topologies. With the continuous growth of wind power capacity and increasing demands for power supply reliability, the evolution of topologies towards true bipolar topologies has become an inevitable trend. Therefore, how to combine hybrid DC transmission with true bipolar topologies to solve the black start problem at low cost while ensuring power supply reliability has become a key focus in the field. Summary of the Invention

[0004] In view of this, the present invention provides a startup control method for a new energy transmission system via a true bipolar hybrid DC transmission system, so as to realize the reverse power transmission from the receiving-end converter station to the sending-end converter station under a true bipolar topology.

[0005] This method is applied to a new energy transmission system via a true bipolar hybrid DC transmission system, which includes: a receiving-end power grid, a receiving-end converter station, a sending-end converter station, and sending-end new energy; the receiving-end power grid is connected to the receiving-end converter station; the receiving-end converter station is connected to the sending-end converter station via a bipolar metal neutral line; and the sending-end converter station is connected to the sending-end new energy. The receiving-end converter station includes a first flexible DC converter valve, a second flexible DC converter valve, and a receiving-end AC bus; the first flexible DC converter valve and the second flexible DC converter valve are connected in series on the DC side, and the first flexible DC converter valve and the second flexible DC converter valve are respectively connected to the receiving-end AC bus on the AC side. The sending-end converter station includes a first diode valve, a second diode valve, a third flexible DC converter valve, a fourth flexible DC converter valve, a third diode valve, a fourth diode valve, and a sending-end AC bus. The first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are respectively connected to the sending-end AC bus on the AC side. The sending-end AC bus is connected to the sending-end renewable energy source. The first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are connected in series on the DC side; the first diode valve is connected to the receiving-end converter station through the positive pole transmission line, and the fourth diode valve is connected to the receiving-end converter station through the negative pole transmission line; the third flexible DC converter valve and the fourth flexible DC converter valve are connected to the first flexible DC converter valve and the second flexible DC converter valve through a metal return line; The methods include: The first flexible DC converter valve is controlled to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then the third flexible DC converter valve is unlocked. Control the third flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, then unlock the fourth flexible DC converter valve. The system is started by sequentially activating the third and fourth diode valves, the first diode valve, and the second diode valve.

[0006] The method provided in this embodiment reverse-charges and unlocks the third flexible DC converter valve at the sending end via the first flexible DC converter valve, and then charges and unlocks the fourth flexible DC converter valve via the third flexible DC converter valve. This fully utilizes the controllable adjustment characteristics of the flexible DC converter valves, avoiding the limitation of diode valves' unidirectional conduction and inability to reverse power transmission. It eliminates the need for additional starting equipment at the sending-end converter station, reducing equipment costs. Furthermore, due to the controllable adjustment characteristics of the first, second, third, and fourth flexible DC converter valves, voltage and current can be controlled according to actual conditions during charging, eliminating the need for low-voltage ride-through or the use of energy-dissipating resistors to dissipate surplus power during startup.

[0007] In one optional embodiment, a first bypass switch is connected between the third flexible DC converter valve and the positive transmission line. The receiving-end converter station also includes a fifth flexible DC converter valve and a sixth flexible DC converter valve. The fifth, first, second, and sixth flexible DC converter valves are connected in series on the DC side and in parallel on the AC side after passing through corresponding connecting transformers. The fifth flexible DC converter valve is connected to the positive transmission line, and the sixth flexible DC converter valve is connected to the negative transmission line. A first DC disconnect switch is connected between the first diode valve and the positive transmission line, and a second DC disconnect switch is connected between the fifth flexible DC converter valve and the positive transmission line. A second bypass switch is connected between the first flexible DC converter valve and the positive transmission line. Controlling the first flexible DC converter valve to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then unlocking the third flexible DC converter valve, including: Close the first bypass switch and the second bypass switch, disconnect the first DC knife switch and the second DC knife switch, control the first flexible DC converter valve to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then unlock the third flexible DC converter valve.

[0008] Through the above implementation method, by closing the first bypass switch and the second bypass switch, the first DC knife switch and the second DC knife switch are disconnected, thus realizing the charging circuit of the first flexible DC converter valve to the third flexible DC converter valve, overcoming the limitation that the diode valve cannot be charged in reverse due to unidirectional conduction.

[0009] In one optional implementation, a third DC disconnect switch is connected between the fourth diode valve and the negative transmission line, and a fourth DC disconnect switch is connected between the sixth flexible DC converter valve and the negative transmission line. Before sequentially activating the third and fourth diode valves, the first diode valve, and the second diode valve, and completing the system startup, the method further includes: Close the third and fourth DC disconnect switches; After the second flexible DC converter valve is charged, the second flexible DC converter valve is controlled to use DC voltage-reactive power control. After the sixth flexible DC converter valve is charged, the sixth flexible DC converter valve is controlled to use DC voltage-reactive power control, so as to charge the negative pole transmission line through the second flexible DC converter valve and the sixth flexible DC converter valve.

[0010] Through the above implementation method, by closing the third and fourth DC disconnect switches, a charging circuit for the negative pole transmission line is formed, which is independent of the positive pole transmission line and adapts to the symmetrical structure of a true bipolar topology. Furthermore, after the second and sixth flexible DC converter valves have completed charging, DC voltage-reactive power control is used to control the DC voltage of the negative pole transmission line, avoiding voltage surges and other problems during the charging process and ensuring the safety of the negative pole transmission line.

[0011] In one optional embodiment, the sending-end converter station further includes a first rectifier transformer, a second rectifier transformer, a third rectifier transformer, and a fourth rectifier transformer; a first diode valve is connected to the sending-end AC bus via the first rectifier transformer, a second diode valve is connected to the sending-end AC bus via the second rectifier transformer, a third diode valve is connected to the sending-end AC bus via the third rectifier transformer, and a fourth diode valve is connected to the sending-end AC bus via the fourth rectifier transformer. The sending-end converter station also includes a first connecting transformer and a second connecting transformer; the third flexible DC converter valve is connected to the sending-end AC bus through the first connecting transformer, and the fourth flexible DC converter valve is connected to the sending-end AC bus through the second connecting transformer. Controlling the third flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, and then unlocking the fourth flexible DC converter valve, including: Close the grid-side switches corresponding to the first, second, third, and fourth rectifier transformers respectively; The third flexible DC converter valve is controlled to establish the AC bus voltage to the first preset voltage in a zero-start boost manner by controlling the AC voltage amplitude and frequency, and to charge the fourth flexible DC converter valve. The first preset voltage is less than the conduction voltage of the first diode valve, the conduction voltage of the second diode valve, the conduction voltage of the third diode valve, and the conduction voltage of the fourth diode valve. After the fourth flexible DC converter valve has finished charging, unlock the fourth flexible DC converter valve; The DC voltage of the fourth flexible DC converter valve is set to the rated voltage by DC voltage-reactive power control.

[0012] Through the above implementation method, by controlling the third flexible DC converter valve to use AC voltage amplitude and frequency control, the voltage can be smoothly changed in a zero-start voltage boost mode, avoiding voltage surges during the charging process. At the same time, the first preset voltage is less than the conduction voltage of the first diode valve, the conduction voltage of the second diode valve, the conduction voltage of the third diode valve, and the conduction voltage of the fourth diode valve, so as to avoid interference of the diode valve conduction on the charging circuit.

[0013] In one optional implementation, the system is started by sequentially activating the third and fourth diode valves, the first diode valve, and the second diode valve, including: Start a predetermined number of new energy generating units from the sending-end new energy source; The third flexible DC converter valve is controlled to increase the AC bus voltage by controlling the AC voltage amplitude and frequency until the third diode valve and the fourth diode valve are turned on. Control the fourth flexible DC converter valve, the third flexible DC converter valve, the fifth flexible DC converter valve and the first flexible DC converter valve to turn on the first diode valve and the second diode valve; Start up other renewable energy units in the sending renewable energy source to complete the system startup.

[0014] In one optional implementation, controlling the fourth flexible DC-DC converter valve, the third flexible DC-DC converter valve, the fifth flexible DC-DC converter valve, and the first flexible DC-DC converter valve to activate the first diode valve and the second diode valve includes: The fourth flexible DC converter valve and the third flexible DC converter valve are controlled to jointly support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is controlled so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected. Control the fifth flexible DC converter valve and the first flexible DC converter valve to close the first DC disconnect switch and the second DC disconnect switch; Control the fifth flexible DC converter valve or the first flexible DC converter valve to activate the first diode valve and the second diode valve.

[0015] In one optional implementation, the fourth flexible DC converter valve and the third flexible DC converter valve are controlled to jointly support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is controlled to disconnect the first and second bypass switches when the current value through the first bypass switch and the second bypass switch is less than a preset current value. This includes: The fourth flexible DC converter valve is controlled by AC voltage amplitude and frequency control with droop, and together with the third flexible DC converter valve, it supports the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is switched to a constant active power and constant reactive power control mode, so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected.

[0016] Through the above implementation method, by controlling the fourth flexible DC converter valve to use AC voltage amplitude and frequency control with droop, together with the third flexible DC converter valve, the AC bus voltage is supported, ensuring stable frequency and balanced power distribution of the AC bus voltage at the sending end. Furthermore, after the AC bus voltage stabilizes, the third flexible DC converter valve is switched from AC voltage amplitude and frequency control to constant active and reactive power control, accurately adjusting the power output of the converter valve so that the current values ​​of the first and second bypass switches are less than preset current values, thereby disconnecting the first and second bypass switches.

[0017] In one alternative implementation, after disconnecting the first bypass switch and the second bypass switch, the method further includes: The third flexible DC converter valve is switched to DC voltage-reactive power control to stabilize the DC voltage of the third flexible DC converter valve.

[0018] In one optional implementation, controlling the fifth flexible DC converter valve and the first flexible DC converter valve to close the first DC disconnect switch and the second DC disconnect switch includes: Increase the DC voltage of the fifth flexible DC converter valve and the DC voltage of the first flexible DC converter valve until the sum of the DC voltages of the fifth flexible DC converter valve and the first flexible DC converter valve is greater than the positive DC voltage of the sending-end converter station, then close the first DC disconnect switch and the second DC disconnect switch.

[0019] In one optional implementation, controlling the fifth flexible DC converter valve or the first flexible DC converter valve to activate the first diode valve and the second diode valve includes: Reduce the DC voltage of the fifth flexible DC converter valve or the DC voltage of the first flexible DC converter valve until the positive DC voltage of the receiving-end converter station is less than the positive DC voltage of the sending-end converter station, and then turn on the first diode valve and the second diode valve.

[0020] In one alternative implementation, the method further includes: Control the second flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, then unlock the fourth flexible DC converter valve.

[0021] Through the above implementation methods, based on the original method of charging the fourth converter valve using the third flexible DC converter valve, the fourth flexible DC converter valve can also be directionally charged using the second flexible DC converter valve. In this way, if one charging path malfunctions, charging can proceed through the other charging path, improving the fault tolerance and reliability of the system's black start process. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of a new energy transmission system via a true bipolar hybrid DC transmission according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating a startup control method for a new energy transmission system via a true bipolar hybrid DC transmission according to an embodiment of the present invention. Figure 3 This is a structural block diagram of a start-up control device for a new energy transmission system via a true bipolar hybrid DC transmission according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to fixed connections, mechanical connections, or electrical connections; they can also refer to direct connections or indirect connections through an intermediate medium; they can also refer to the internal connection of two components; and they can be wireless or wired connections. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] This invention provides a startup control method for a new energy transmission system via a true bipolar hybrid DC system. This method is applied to such systems. Figure 1 As shown, the system includes: a receiving-end power grid 1, a receiving-end converter station 2, a sending-end converter station 3, and a sending-end renewable energy source 4. The receiving-end power grid 1 is connected to the receiving-end converter station 2; the receiving-end converter station 2 is connected to the sending-end converter station 3 via a bipolar metal neutral line; the sending-end converter station 3 is connected to the sending-end renewable energy source 4.

[0027] The receiving-end converter station 2 includes a first flexible DC converter valve 21, a second flexible DC converter valve 22, and a receiving-end AC bus 213. The first flexible DC converter valve 21 and the second flexible DC converter valve 22 are connected in series on the DC side, and the first flexible DC converter valve 21 and the second flexible DC converter valve 22 are respectively connected to the receiving-end AC bus 213 on the AC side.

[0028] The sending-end converter station 3 includes a first diode valve 31, a second diode valve 32, a third flexible DC converter valve 33, a fourth flexible DC converter valve 34, a third diode valve 35, a fourth diode valve 36, and a sending-end AC bus 37. The first diode valve 31, the second diode valve 32, the third flexible DC converter valve 33, the fourth flexible DC converter valve 34, the third diode valve 35, and the fourth diode valve 36 are respectively connected to the sending-end AC bus 37 on the AC side. The sending-end AC bus 37 is connected to the sending-end new energy 4.

[0029] The first diode valve 31, the second diode valve 32, the third flexible DC converter valve 33, the fourth flexible DC converter valve 34, the third diode valve 35, and the fourth diode valve 36 are connected in series on the DC side; the first diode valve 31 is connected to the receiving-end converter station 2 through the positive pole transmission line, and the fourth diode valve 36 is connected to the receiving-end converter station 2 through the negative pole transmission line; the third flexible DC converter valve 33 and the fourth flexible DC converter valve 34 are connected to the first flexible DC converter valve 21 and the second flexible DC converter valve 22 through the metal return line.

[0030] Specifically, the receiving-end converter station 2 is used to convert DC power into AC power, and the sending-end converter station 3 is used to convert AC power generated by new energy sources into DC power. For example, the receiving-end converter station 2 is an onshore receiving-end converter station 2 on a deep-sea wind power platform, and the sending-end converter station 3 is an offshore converter station on a deep-sea wind power platform.

[0031] Sending-end new energy 4 refers to new energy power generation facilities located at the power sending end. For example, sending-end new energy 4 can be an offshore wind farm, photovoltaic power station, etc. Sending-end new energy 4 is connected to sending-end AC bus 37 through transmission cables, and transmits the generated AC power to sending-end AC bus 37. After being converted by sending-end converter station 3, it is transmitted to receiving-end converter station 2 and receiving-end power grid 1.

[0032] As a core component of flexible DC transmission systems, the flexible DC converter valve possesses controllable voltage / current regulation capabilities. For example, the flexible DC converter valve in this embodiment can adopt a half-bridge sub-module structure, composed of an insulated-gate bipolar transistor (IGBT), anti-parallel diodes, and capacitors, enabling flexible DC transmission and providing bidirectional control of reactive and active power. Of course, the flexible DC converter valve can also adopt a full-bridge sub-module structure. This application does not specifically limit the specific structure of the flexible DC converter valve; it can be configured according to actual needs.

[0033] In this system, the third flexible DC converter valve 33 and the fourth flexible DC converter valve 34 are connected to the first flexible DC converter valve 21 and the second flexible DC converter valve 22 via a metal return line, making the entire system a bipolar wiring configuration with a metal return line. The positive and negative transmission lines form a bipolar main circuit. The electrical energy generated by the new energy source 4 at the sending end is transmitted through the positive and negative transmission lines, and the unbalanced current flowing through the metal return line is close to zero. The metal return line connects the third and fourth flexible DC converter valves at the sending end to the first and second flexible DC converter valves at the receiving end. When a fault occurs in one pole of the main circuit (such as a fault in the positive transmission line), the current can form a loop through the metal return line, ensuring that the system can continue to operate under single-pole fault conditions, avoiding a complete system shutdown, and improving system reliability.

[0034] Figure 2 This is a flowchart illustrating the startup control method of a new energy transmission system via a true bipolar hybrid DC transmission line. Figure 2 As shown, the process includes: S101, control the first flexible DC converter valve 21 to charge the third flexible DC converter valve 33 until the third flexible DC converter valve 33 is fully charged, then unlock the third flexible DC converter valve 33.

[0035] Specifically, unlocking the flexible DC converter valve refers to changing the flexible DC converter valve from the locked state (i.e., without power transmission capability) to the operating state (i.e., with power transmission capability).

[0036] S102, control the third flexible DC converter valve 33 to charge the fourth flexible DC converter valve 34 until the fourth flexible DC converter valve 34 is fully charged, then unlock the fourth flexible DC converter valve 34.

[0037] Specifically, the fourth flexible DC converter valve 34 is initially in a de-energized state, and a controllable charging power supply is provided through the unlocked third flexible DC converter valve 33 to ensure voltage stability during the charging process.

[0038] S103 sequentially activates the third diode valve 35, the fourth diode valve 36, the first diode valve 31, and the second diode valve 32 to complete the system startup.

[0039] Specifically, the third diode valve 35 and the fourth diode valve 36 are close to the negative power transmission line, and the first diode valve 31 and the second diode valve 32 are close to the positive power transmission line. The third diode valve 35 and the fourth diode valve 36, the first diode valve 31 and the second diode valve 32 are turned on in sequence to reduce the current surge during the startup process and achieve a smooth transition from black start to stable operation.

[0040] In this embodiment, the first flexible DC-DC converter valve 21 reverse-charges and unlocks the third flexible DC-DC converter valve 33 at the sending end, and then the third flexible DC-DC converter valve 33 charges and unlocks the fourth flexible DC-DC converter valve 34. This fully utilizes the controllable adjustment characteristics of the flexible DC-DC converter valves, avoiding the limitation of the unidirectional conduction of diode valves which cannot reverse power supply. It eliminates the need for additional starting equipment at the sending-end converter station 3, reducing the equipment cost of the sending-end converter station 3. Furthermore, through the controllable adjustment characteristics of the first flexible DC-DC converter valve 21, the second flexible DC-DC converter valve 22, the third flexible DC-DC converter valve 33, and the fourth flexible DC-DC converter valve 34, the voltage and current can be controlled according to actual conditions during charging, eliminating the need for low-voltage ride-through of the wind farm or the need to configure energy-dissipating resistors to dissipate surplus power during startup.

[0041] In some embodiments, based on the foregoing embodiments, a first bypass switch 38 is connected between the third flexible DC converter valve 33 and the positive transmission line. The receiving-end converter station 2 also includes a fifth flexible DC converter valve 23 and a sixth flexible DC converter valve 24. The fifth flexible DC converter valve 23, the first flexible DC converter valve 21, the second flexible DC converter valve 22, and the sixth flexible DC converter valve 24 are connected in series on the DC side and in parallel on the AC side after passing through corresponding connecting transformers. The fifth flexible DC converter valve 23 is connected to the positive transmission line, and the sixth flexible DC converter valve 24 is connected to the negative transmission line. A first DC disconnect switch 39 is connected between the first diode valve 31 and the positive transmission line, and a second DC disconnect switch 26 is connected between the fifth flexible DC converter valve 23 and the positive transmission line. A second bypass switch 25 is connected between the first flexible DC converter valve 21 and the positive transmission line.

[0042] Specifically, the fifth flexible DC converter valve 23 and the sixth flexible DC converter valve 24 are connected in series with the first flexible DC converter valve 21 and the second flexible DC converter valve 22 on the DC side, forming a true bipolar converter topology at the receiving end. They are used to regulate the voltage and control the power on the positive and negative sides, respectively. During black start, the fifth flexible DC converter valve 23 and the sixth flexible DC converter valve 24 are connected in series with the first flexible DC converter valve 21 and the second flexible DC converter valve 22 after the third flexible DC converter valve 33 and the fourth flexible DC converter valve 34 have finished charging and unlocked, and after the sending-end new energy source 4 has started, to further improve the DC side voltage level, thereby meeting the requirements of large-capacity power transmission.

[0043] The first DC disconnect switch 39 is used to isolate the DC circuit. For example, during the charging phase of the third flexible DC converter valve 33, disconnecting the first DC disconnect switch 39 isolates the first diode valve 31 from the positive transmission line, preventing the unidirectional conduction characteristic of the diode from interfering with the charging process of the third flexible DC converter valve 33. The second DC disconnect switch 26 is installed between the fifth flexible DC converter valve 23 and the positive transmission line to isolate the connection between the fifth flexible DC converter valve 23 and the positive transmission line. The first bypass switch 38 and the second bypass switch 25 cooperate to construct a charging path from the receiving end to the sending end.

[0044] In step S101 above, the first flexible DC-DC converter valve 21 is controlled to charge the third flexible DC-DC converter valve 33 until the third flexible DC-DC converter valve 33 is fully charged, and then the third flexible DC-DC converter valve 33 is unlocked. The specific steps include the following: Close the first bypass switch 38 and the second bypass switch 25, disconnect the first DC knife switch 39 and the second DC knife switch 26, control the first flexible DC converter valve 21 to charge the third flexible DC converter valve 33 until the third flexible DC converter valve 33 is fully charged, and then unlock the third flexible DC converter valve 33.

[0045] Specifically, since the first diode valve 31 has unidirectional conduction characteristics, and in order to match the voltage level requirements of the third flexible DC converter valve 33, only the first flexible DC converter valve 21 needs to charge the third flexible DC converter valve 33. At this time, the fifth flexible DC converter valve 23 does not need to participate in the charging stage of the third flexible DC converter valve 33. Therefore, by closing the first bypass switch 38 and the second bypass switch 25, and disconnecting the first DC knife switch 39 and the second DC knife switch 26, a charging circuit between the first flexible DC converter valve 21 and the third flexible DC converter valve 33 is constructed, realizing the charging of the third flexible DC converter valve 33 by the first flexible DC converter valve 21, overcoming the limitation that the diode valve cannot be reverse charged due to unidirectional conduction.

[0046] In some embodiments, based on any of the foregoing embodiments, a third DC switch 311 is connected between the fourth diode valve 36 and the negative transmission line, and a fourth DC switch 28 is connected between the sixth flexible DC converter valve 24 and the negative transmission line.

[0047] Specifically, the third DC disconnect switch 311 is installed between the fourth diode valve 36 and the negative transmission line to control the connection between the negative diode valve and the negative transmission line. When the third DC disconnect switch 311 is closed, the fourth diode valve 36 is connected to the negative transmission line.

[0048] The fourth DC disconnect switch 28 is installed between the sixth flexible DC converter valve 24 and the negative transmission line to control the connection and disconnection between the sixth flexible DC converter valve 24 and the negative transmission line. For example, during the charging phase of the negative transmission line, the sixth flexible DC converter valve 24 is connected to the negative transmission line by closing the fourth DC disconnect switch 28, thereby realizing the charging of the negative transmission line.

[0049] Before sequentially activating the third diode valve 35, the fourth diode valve 36, the first diode valve 31, and the second diode valve 32 to complete the system startup, the method provided in this application embodiment further includes the following: First, close the third DC disconnect switch 311 and the fourth DC disconnect switch 28.

[0050] Then, after the second flexible DC converter valve 22 has finished charging, control the second flexible DC converter valve 22 to use DC voltage-reactive power (U dc / Q) control, after the sixth flexible DC converter valve 24 is charged, control the sixth flexible DC converter valve 24 to use DC voltage-reactive power control, so as to charge the negative pole transmission line through the second flexible DC converter valve 22 and the sixth flexible DC converter valve 24.

[0051] Specifically, DC voltage-reactive power control includes DC voltage closed-loop control and reactive power closed-loop control. The DC voltage closed-loop control is used to maintain the stability of the DC side voltage of the converter valve, while the reactive power control is used to regulate the reactive power exchange between the AC side of the converter valve and the power grid, supporting the voltage of the AC bus.

[0052] In this embodiment, by closing the third DC disconnect switch 311 and the fourth DC disconnect switch 28, a charging circuit for the negative pole transmission line is formed, which is independent of the positive pole transmission line and adapts to the symmetrical structure of a true bipolar topology. Furthermore, after the second flexible DC converter valve 22 and the sixth flexible DC converter valve 24 have completed charging, DC voltage-reactive power control is used to control the DC voltage of the negative pole transmission line, avoiding voltage surges and other problems during the charging process and ensuring the safety of the negative pole transmission line.

[0053] In some embodiments, the sending-end converter station 3 further includes a first rectifier transformer 312, a second rectifier transformer 313, a third rectifier transformer 314, and a fourth rectifier transformer 315; a first diode valve 31 is connected to the sending-end AC bus 37 through the first rectifier transformer 312, a second diode valve 32 is connected to the sending-end AC bus 37 through the second rectifier transformer 313, a third diode valve 35 is connected to the sending-end AC bus 37 through the third rectifier transformer 314, and a fourth diode valve 36 is connected to the sending-end AC bus 37 through the fourth rectifier transformer 315.

[0054] The sending-end converter station 3 also includes a first connecting transformer 316 and a second connecting transformer 317; the third flexible DC converter valve 33 is connected to the sending-end AC bus 37 through the first connecting transformer 316, and the fourth flexible DC converter valve 34 is connected to the sending-end AC bus 37 through the second connecting transformer 317.

[0055] Specifically, the first rectifier transformer 312, the second rectifier transformer 313, the third rectifier transformer 314, and the fourth rectifier transformer 315 act between their respective diode valves and the sending-end AC bus 37, providing a stable AC input voltage for the diode valves and simultaneously blocking the harmonics generated by the diode valves from spreading to the sending-end AC bus 37.

[0056] The first connecting transformer 316 and the second connecting transformer 317 function between their respective flexible DC converter valves and the sending-end AC bus 37. Unlike rectifier transformers, they are adapted to their respective flexible DC converter valves and perform functions such as voltage matching, electrical isolation, and ensuring stable voltage and frequency support for the sending-end AC bus 37 from the flexible DC converter valves. Specifically, the first and second connecting transformers can precisely match the voltage levels of the third and fourth flexible DC converter valves and the sending-end AC bus 37. Furthermore, if the third flexible DC converter valve 33 or the first connecting transformer 316 fails, the connection between the first connecting transformer 316 and the sending-end AC bus 37 or the third flexible DC converter valve 33 can be disconnected to isolate the faulty part. At this time, the fourth flexible DC converter valve 34 can still work normally through the second connecting transformer 317. Similarly, when the fourth flexible DC converter valve 34 or the second connecting transformer 317 fails, the third flexible DC converter valve 33 can continue to operate, which reduces the scope of the fault impact, reduces the risk of system shutdown, improves the reliability of the sending-end converter station 3, and ensures the continuous transmission of new energy power.

[0057] In addition, such as Figure 1 As shown, the receiving-end converter station 2 also includes a third connecting transformer 29, a fourth connecting transformer 210, a fifth connecting transformer 211, and a sixth connecting transformer 212. The fifth flexible DC converter valve 23 is connected to the receiving-end AC bus 213 through the third connecting transformer 29, the first flexible DC converter valve 21 is connected to the receiving-end AC bus 213 through the fourth connecting transformer 210, the second flexible DC converter valve 22 is connected to the receiving-end AC bus 213 through the fifth connecting transformer 211, and the sixth flexible DC converter valve 24 is connected to the receiving-end AC bus 213 through the sixth connecting transformer 212.

[0058] In this way, each flexible DC converter valve is connected to the receiving-end power grid 1 via its corresponding connecting transformer, allowing for precise matching of the voltage levels between the converter valve and the receiving-end power grid 1. Different flexible DC converter valves have different output characteristics; the connecting transformers connected to these valves ensure that their output voltages are uniformly adapted to the voltage of the receiving-end power grid 1, avoiding connection failures or energy losses due to voltage mismatch and ensuring a smooth transition of power from the converter valves to the grid. Furthermore, regarding fault isolation, if a flexible DC converter valve or connecting transformer fails, the faulty part can be isolated by disconnecting the corresponding connecting transformer, while other normal converter valves can still supply power to the grid normally, minimizing the scope of the fault's impact.

[0059] In S102 above, the third flexible DC converter valve 33 is controlled to charge the fourth flexible DC converter valve 34 in the following manner until the fourth flexible DC converter valve 34 is fully charged, and then the fourth flexible DC converter valve 34 is unlocked: First, close the grid-side switches corresponding to the first rectifier transformer 312, the second rectifier transformer 313, the third rectifier transformer 314, and the fourth rectifier transformer 315.

[0060] Specifically, the grid-side switch is used to control the connection between the transformer and the AC bus, and has functions such as overload and short-circuit protection.

[0061] Then, the third flexible DC converter valve 33 is controlled to establish the AC bus voltage to the first preset voltage in a zero-start boost manner by AC voltage amplitude and frequency (V / F) control, and the fourth flexible DC converter valve 34 is charged.

[0062] The first preset voltage is less than the conduction voltage of the first diode valve 31, the conduction voltage of the second diode valve 32, the conduction voltage of the third diode valve 35, and the conduction voltage of the fourth diode valve 36.

[0063] Specifically, AC voltage amplitude and frequency control is used as the control strategy for the flexible DC converter valve, which simultaneously stabilizes the amplitude and frequency of the output AC voltage through closed-loop control.

[0064] Next, after the fourth flexible DC converter valve 34 has been charged, the fourth flexible DC converter valve 34 is unlocked.

[0065] Finally, the DC voltage of the fourth flexible DC converter valve 34 is set to the rated voltage by controlling the DC voltage-reactive power.

[0066] In this embodiment, by controlling the third flexible DC converter valve 33 to use AC voltage amplitude and frequency control, a stable voltage change is achieved in a zero-start voltage boost manner, avoiding voltage surges during the charging process. At the same time, the first preset voltage is less than the conduction voltage of the first diode valve 31, the conduction voltage of the second diode valve 32, the conduction voltage of the third diode valve 35, and the conduction voltage of the fourth diode valve 36, so as to avoid interference of diode valve conduction on the charging circuit.

[0067] In some embodiments, based on any of the foregoing embodiments, the system is started up by sequentially activating the third diode valve 35 and the fourth diode valve 36, the first diode valve 31 and the second diode valve 32 in the following manner: a1, start the preset number of new energy units in the new energy 4 of the sending end.

[0068] The preset quantity can be determined based on the system startup requirements; no specific limit is set here.

[0069] a2 controls the third flexible DC converter valve 33 to increase the AC bus voltage by controlling the AC voltage amplitude and frequency, until the third diode valve 35 and the fourth diode valve 36 are turned on.

[0070] a3 controls the fourth flexible DC converter valve 34, the third flexible DC converter valve 33, the fifth flexible DC converter valve 23, and the first flexible DC converter valve 21 to conduct the first diode valve 31 and the second diode valve 32.

[0071] In one possible implementation, in a3 above, the first diode valve 31 and the second diode valve 32 are turned on in the following manner: b1 controls the fourth flexible DC converter valve 34 and the third flexible DC converter valve 33 to jointly support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve 33 is controlled so that when the current value through the first bypass switch 38 and the second bypass switch 25 is less than the preset current value, the first bypass switch 38 and the second bypass switch 25 are disconnected.

[0072] Optionally, the fourth flexible DC converter valve 34 and the third flexible DC converter valve 33 are controlled to jointly support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve 33 is controlled so that when the current value through the first bypass switch 38 and the second bypass switch 25 is less than a preset current value, the first bypass switch 38 and the second bypass switch 25 are disconnected. Specifically, this includes the following steps: First, the fourth flexible DC converter valve 34 is controlled by AC voltage amplitude and frequency control with droop, which together with the third flexible DC converter valve 33 supports the AC bus voltage.

[0073] Specifically, AC voltage amplitude and frequency control with droop refers to a control strategy that adds a droop characteristic to the traditional AC voltage amplitude and frequency control. The droop characteristic manifests as follows: when the load power increases, the output voltage amplitude or frequency decreases slightly according to a preset ratio; conversely, when the load power decreases, the voltage amplitude or frequency increases accordingly. By controlling the fourth flexible DC converter valve 34 to use AC voltage amplitude and frequency control with droop, together with the third flexible DC converter valve 33, the AC bus voltage is supported, ensuring stable voltage and frequency and balanced power distribution on the sending-end AC bus 37.

[0074] Then, after the AC bus voltage stabilizes, the third flexible DC converter valve 33 is switched to constant active power and constant reactive power (P / Q) control mode, so that when the current value through the first bypass switch 38 and the second bypass switch 25 is less than the preset current value, the first bypass switch 38 and the second bypass switch 25 are disconnected.

[0075] Specifically, constant active power and constant reactive power control refers to using closed-loop control to stabilize the active and reactive power outputs of the converter valve at set values, without changing with fluctuations in bus voltage or frequency.

[0076] Since AC voltage amplitude and frequency control can only control the voltage of the third flexible DC converter valve 33 and cannot control its power, after the AC bus voltage stabilizes, the third flexible DC converter valve 33 is switched from AC voltage amplitude and frequency control to constant active power and constant reactive power control to accurately adjust the power output of the converter valve, so that the current values ​​of the first bypass switch 38 and the second bypass switch 25 are less than the preset current values, so as to disconnect the first bypass switch 38 and the second bypass switch 25.

[0077] b2 controls the fifth flexible DC converter valve 23 and the first flexible DC converter valve 21 to close the first DC disconnect switch 39 and the second DC disconnect switch 26.

[0078] Optionally, the DC voltage of the fifth flexible DC converter valve 23 and the DC voltage of the first flexible DC converter valve 21 are increased until the sum of the DC voltage of the fifth flexible DC converter valve 23 and the DC voltage of the first flexible DC converter valve 21 is greater than the positive DC voltage of the sending-end converter station 3, at which point the first DC disconnect switch 39 and the second DC disconnect switch 26 are closed.

[0079] b3 controls the fifth flexible DC converter valve 23 or the first flexible DC converter valve 21 to conduct the first diode valve 31 and the second diode valve 32.

[0080] Optionally, the DC voltage of the fifth flexible DC converter valve 23 or the DC voltage of the first flexible DC converter valve 21 is reduced until the positive DC voltage of the receiving-end converter station 2 is less than the positive DC voltage of the sending-end converter station 3, and the first diode valve 31 and the second diode valve 32 are turned on.

[0081] a4: Start the other new energy units in the sending end new energy 4 to complete the system startup.

[0082] In some embodiments, based on any of the foregoing embodiments, after disconnecting the first bypass switch 38 and the second bypass switch 25, the method provided in this application embodiment further includes the following: The third flexible DC converter valve 33 is switched to DC voltage-reactive power control to stabilize the DC voltage of the third flexible DC converter valve 33.

[0083] When the bypass switch is disconnected and the diode valve is connected, the system has entered the normal operation mode. The sending end new energy 4 should output power as much as possible through the DC system. At this time, the third flexible DC converter valve 33 no longer needs to control the active power. Therefore, the control of the third flexible DC converter valve 33 is switched to DC voltage-reactive power control to stabilize its DC voltage at the rated value.

[0084] In some embodiments, based on any of the foregoing embodiments, the method provided in this application further includes the following: Control the second flexible DC converter valve 22 to charge the fourth flexible DC converter valve 34 until the fourth flexible DC converter valve 34 is fully charged, then unlock the fourth flexible DC converter valve 34.

[0085] like Figure 1 As shown, similar to the first bypass switch 38 and the second bypass switch 25, a third bypass switch 310 is connected between the fourth flexible DC converter valve 34 and the negative transmission line; a fourth bypass switch 27 is connected between the second flexible DC converter valve 22 and the negative transmission line. Thus, by closing the third bypass switch 310 and the fourth bypass switch 27, and disconnecting the third DC disconnect switch 311 and the fourth DC disconnect switch 28, the connection between the second and fourth flexible DC converter valves is achieved, enabling the second flexible DC converter valve to charge the fourth flexible DC converter valve.

[0086] In this embodiment, in addition to the existing method of charging the fourth converter valve using the third flexible DC converter valve 33, the fourth flexible DC converter valve 34 can also be directionally charged via the second flexible DC converter valve 22. This way, if one charging path malfunctions, charging can proceed via the other charging path, improving the system's fault tolerance and reliability during black start.

[0087] This embodiment also provides a start-up control device for a new energy transmission system via a true bipolar hybrid DC transmission line. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0088] This embodiment provides a start-up control device for a new energy transmission system via a true bipolar hybrid DC transmission system. The system includes: a receiving-end power grid, a receiving-end converter station, a sending-end converter station, and a sending-end new energy source; the receiving-end power grid is connected to the receiving-end converter station; the receiving-end converter station is connected to the sending-end converter station via a bipolar metal neutral line; the sending-end converter station is connected to the sending-end new energy source. The receiving-end converter station includes a first flexible DC converter valve, a second flexible DC converter valve, and a receiving-end AC bus; the first flexible DC converter valve and the second flexible DC converter valve are connected in series on the DC side, and the first flexible DC converter valve and the second flexible DC converter valve are respectively connected to the receiving-end AC bus on the AC side. The sending-end converter station includes a first diode valve, a second diode valve, a third flexible DC converter valve, a fourth flexible DC converter valve, a third diode valve, a fourth diode valve, and a sending-end AC bus. The first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are respectively connected to the sending-end AC bus on the AC side. The sending-end AC bus is connected to the sending-end renewable energy source. The first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are connected in series on the DC side; the first diode valve is connected to the receiving-end converter station through the positive pole transmission line, and the fourth diode valve is connected to the receiving-end converter station through the negative pole transmission line; the third flexible DC converter valve and the fourth flexible DC converter valve are connected to the first flexible DC converter valve and the second flexible DC converter valve through a metal return line; like Figure 3 As shown, the device includes: The first control module 301 is used to control the first flexible DC converter valve to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then unlock the third flexible DC converter valve. The second control module 302 is used to control the third flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, and then unlock the fourth flexible DC converter valve. The conduction module 303 is used to sequentially conduct the third diode valve and the fourth diode valve, the first diode valve and the second diode valve to complete the system startup.

[0089] In one possible implementation, a first bypass switch is connected between the third flexible DC converter valve and the positive transmission line. The receiving-end converter station also includes a fifth flexible DC converter valve and a sixth flexible DC converter valve. The fifth, first, second, and sixth flexible DC converter valves are connected in series on the DC side and in parallel on the AC side after passing through corresponding connecting transformers. The fifth flexible DC converter valve is connected to the positive transmission line, and the sixth flexible DC converter valve is connected to the negative transmission line. A first DC disconnect switch is connected between the first diode valve and the positive transmission line, and a second DC disconnect switch is connected between the fifth flexible DC converter valve and the positive transmission line. A second bypass switch is connected between the first flexible DC converter valve and the positive transmission line. The first control module 301 is specifically used to close the first bypass switch and the second bypass switch, disconnect the first DC knife switch and the second DC knife switch, control the first flexible DC converter valve to charge the third flexible DC converter valve, and unlock the third flexible DC converter valve after the third flexible DC converter valve has completed charging.

[0090] In one possible implementation, a third DC disconnect switch is connected between the fourth diode valve and the negative transmission line, and a fourth DC disconnect switch is connected between the sixth flexible DC converter valve and the negative transmission line. The conduction module 303 is also used to sequentially conduct the third and fourth diode valves, the first diode valve, and the second diode valve, and close the third and fourth DC disconnect switches before system startup. After the second flexible DC converter valve is charged, the second flexible DC converter valve is controlled to use DC voltage-reactive power control. After the sixth flexible DC converter valve is charged, the sixth flexible DC converter valve is controlled to use DC voltage-reactive power control, so as to charge the negative pole transmission line through the second flexible DC converter valve and the sixth flexible DC converter valve.

[0091] In one possible implementation, the sending-end converter station further includes a first rectifier transformer, a second rectifier transformer, a third rectifier transformer, and a fourth rectifier transformer; a first diode valve is connected to the sending-end AC bus via the first rectifier transformer, a second diode valve is connected to the sending-end AC bus via the second rectifier transformer, a third diode valve is connected to the sending-end AC bus via the third rectifier transformer, and a fourth diode valve is connected to the sending-end AC bus via the fourth rectifier transformer. The sending-end converter station also includes a first connecting transformer and a second connecting transformer; the third flexible DC converter valve is connected to the sending-end AC bus through the first connecting transformer, and the fourth flexible DC converter valve is connected to the sending-end AC bus through the second connecting transformer. The second control module 302 is specifically used to close the grid-side switches corresponding to the first rectifier transformer, the second rectifier transformer, the third rectifier transformer, and the fourth rectifier transformer, respectively. The third flexible DC converter valve is controlled to establish the AC bus voltage to the first preset voltage in a zero-start boost manner by controlling the AC voltage amplitude and frequency, and to charge the fourth flexible DC converter valve. The first preset voltage is less than the conduction voltage of the first diode valve, the conduction voltage of the second diode valve, the conduction voltage of the third diode valve, and the conduction voltage of the fourth diode valve. After the fourth flexible DC converter valve has finished charging, unlock the fourth flexible DC converter valve; The DC voltage of the fourth flexible DC converter valve is set to the rated voltage by DC voltage-reactive power control.

[0092] In one possible implementation, the conduction module 303 is specifically used to start a preset number of new energy generator units in the sending-end new energy source; The third flexible DC converter valve is controlled to increase the AC bus voltage by controlling the AC voltage amplitude and frequency until the third diode valve and the fourth diode valve are turned on. Control the fourth flexible DC converter valve, the third flexible DC converter valve, the fifth flexible DC converter valve and the first flexible DC converter valve to turn on the first diode valve and the second diode valve; Start up other renewable energy units in the sending renewable energy source to complete the system startup.

[0093] In one possible implementation, the conduction module 303 is specifically used to control the fourth flexible DC converter valve and the third flexible DC converter valve to jointly support the AC bus voltage, and after the AC bus voltage stabilizes, control the third flexible DC converter valve so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected. Control the fifth flexible DC converter valve and the first flexible DC converter valve to close the first DC disconnect switch and the second DC disconnect switch; Control the fifth flexible DC converter valve or the first flexible DC converter valve to activate the first diode valve and the second diode valve.

[0094] In one possible implementation, the conduction module 303 is specifically used to control the fourth flexible DC converter valve to use AC voltage amplitude and frequency control with droop, and together with the third flexible DC converter valve, support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is switched to a constant active power and constant reactive power control mode, so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected.

[0095] In one possible implementation, after the conduction module 303 disconnects the first bypass switch and the second bypass switch, it is also used to control the third flexible DC converter valve to switch to DC voltage-reactive power control in order to stabilize the DC voltage of the third flexible DC converter valve.

[0096] In one possible implementation, the conduction module 303 is specifically used to increase the DC voltage of the fifth flexible DC converter valve and the DC voltage of the first flexible DC converter valve until the sum of the DC voltage of the fifth flexible DC converter valve and the DC voltage of the first flexible DC converter valve is greater than the positive DC voltage of the sending-end converter station, and then close the first DC disconnect switch and the second DC disconnect switch.

[0097] In one possible implementation, the conduction module 303 is specifically used to reduce the DC voltage of the fifth flexible DC converter valve or the DC voltage of the first flexible DC converter valve until the positive DC voltage of the receiving-end converter station is less than the positive DC voltage of the sending-end converter station, thereby conducting the first diode valve and the second diode valve.

[0098] In one possible implementation, the second control module is also used to control the second flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, and then unlock the fourth flexible DC converter valve.

[0099] The start-up control device for the new energy transmission system via true bipolar hybrid DC provided in this embodiment of the invention can execute the start-up control method for the new energy transmission system via true bipolar hybrid DC provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as in the corresponding embodiments described above, and will not be repeated here.

[0100] Figure 4 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0101] The following is a detailed reference. Figure 4 This diagram illustrates a suitable structural schematic for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 1301, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 1302 or a program loaded from memory 1308 into random access memory (RAM) 1303. The RAM 1303 also stores various programs and data required for the operation of the electronic device. The processor 1301, ROM 1302, and RAM 1303 are interconnected via a bus 1304. An input / output (I / O) interface 1305 is also connected to the bus 1304.

[0102] Typically, the following devices can be connected to I / O interface 1305: input devices 1306 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 1307 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 1308 including, for example, magnetic tapes, hard disks, etc.; and communication devices 1309. Communication device 1309 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 4 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0103] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 1309, or installed from a memory 1308, or installed from a ROM 1302. When the computer program is executed by the processor 1301, it performs the functions defined in the startup control method of the new energy true bipolar hybrid DC transmission system according to embodiments of the present invention.

[0104] Figure 4 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of the embodiments of the present invention.

[0105] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that the computer, processor, microprocessor controller, or programmable hardware includes storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the startup control method of the new energy transmission system via a true bipolar hybrid DC transmission system shown in the above embodiments is implemented.

[0106] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0107] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A startup control method for a new energy transmission system via a true bipolar hybrid DC transmission line, characterized in that, This invention relates to a new energy transmission system via a true bipolar hybrid DC transmission line. The system includes: a receiving-end power grid, a receiving-end converter station, a sending-end converter station, and a sending-end new energy source. The receiving-end power grid is connected to the receiving-end converter station. The receiving-end converter station is connected to the sending-end converter station via a bipolar line with a metallic neutral wire. The sending-end converter station is connected to the sending-end new energy source. The receiving-end converter station includes a first flexible DC converter valve, a second flexible DC converter valve, and a receiving-end AC bus; the first flexible DC converter valve and the second flexible DC converter valve are connected in series on the DC side, and the first flexible DC converter valve and the second flexible DC converter valve are respectively connected to the receiving-end AC bus on the AC side. The sending-end converter station includes a first diode valve, a second diode valve, a third flexible DC converter valve, a fourth flexible DC converter valve, a third diode valve, a fourth diode valve, and a sending-end AC bus; the first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are respectively connected to the sending-end AC bus on the AC side; the sending-end AC bus is connected to the sending-end new energy source; The first diode valve, the second diode valve, the third flexible DC converter valve, the fourth flexible DC converter valve, the third diode valve, and the fourth diode valve are connected in series on the DC side; the first diode valve is connected to the receiving-end converter station through a positive transmission line, and the fourth diode valve is connected to the receiving-end converter station through a negative transmission line; the third flexible DC converter valve and the fourth flexible DC converter valve are connected to the first flexible DC converter valve and the second flexible DC converter valve through a metal return line; The method includes: The first flexible DC converter valve is controlled to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then the third flexible DC converter valve is unlocked. Control the third flexible DC converter valve to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, then unlock the fourth flexible DC converter valve. The system is started by sequentially activating the third diode valve, the fourth diode valve, the first diode valve, and the second diode valve.

2. The method according to claim 1, characterized in that, A first bypass switch is connected between the third flexible DC converter valve and the positive pole transmission line. The receiving-end converter station also includes a fifth flexible DC converter valve and a sixth flexible DC converter valve. The fifth flexible DC converter valve, the first flexible DC converter valve, the second flexible DC converter valve, and the sixth flexible DC converter valve are connected in series on the DC side and in parallel on the AC side after passing through corresponding connecting transformers. The fifth flexible DC converter valve is connected to the positive pole transmission line, and the sixth flexible DC converter valve is connected to the negative pole transmission line. A first DC disconnect switch is connected between the first diode valve and the positive pole transmission line, and a second DC disconnect switch is connected between the fifth flexible DC converter valve and the positive pole transmission line. A second bypass switch is connected between the first flexible DC converter valve and the positive pole transmission line. The step of controlling the first flexible DC-DC converter valve to charge the third flexible DC-DC converter valve until the third flexible DC-DC converter valve is fully charged, and then unlocking the third flexible DC-DC converter valve, includes: Close the first bypass switch and the second bypass switch, disconnect the first DC knife switch and the second DC knife switch, control the first flexible DC converter valve to charge the third flexible DC converter valve until the third flexible DC converter valve is fully charged, and then unlock the third flexible DC converter valve.

3. The method according to claim 2, characterized in that, A third DC disconnect switch is connected between the fourth diode valve and the negative transmission line, and a fourth DC disconnect switch is connected between the sixth flexible DC converter valve and the negative transmission line. Before sequentially turning on the third diode valve and the fourth diode valve, the first diode valve and the second diode valve to complete the system startup, the method further includes: Close the third DC disconnect switch and the fourth DC disconnect switch; After the second flexible DC converter valve is charged, the second flexible DC converter valve is controlled to use DC voltage-reactive power control. After the sixth flexible DC converter valve is charged, the sixth flexible DC converter valve is controlled to use DC voltage-reactive power control, so as to charge the negative pole transmission line through the second flexible DC converter valve and the sixth flexible DC converter valve.

4. The method according to claim 2, characterized in that, The sending-end converter station further includes a first rectifier transformer, a second rectifier transformer, a third rectifier transformer, and a fourth rectifier transformer; the first diode valve is connected to the sending-end AC bus through the first rectifier transformer, the second diode valve is connected to the sending-end AC bus through the second rectifier transformer, the third diode valve is connected to the sending-end AC bus through the third rectifier transformer, and the fourth diode valve is connected to the sending-end AC bus through the fourth rectifier transformer; The sending-end converter station also includes a first connecting transformer and a second connecting transformer; the third flexible DC converter valve is connected to the sending-end AC bus through the first connecting transformer, and the fourth flexible DC converter valve is connected to the sending-end AC bus through the second connecting transformer; The step of controlling the third flexible DC-DC converter valve to charge the fourth flexible DC-DC converter valve until the fourth flexible DC-DC converter valve is fully charged, and then unlocking the fourth flexible DC-DC converter valve, includes: Close the grid-side switches corresponding to the first rectifier transformer, the second rectifier transformer, the third rectifier transformer, and the fourth rectifier transformer, respectively; The third flexible DC converter valve is controlled to establish the AC bus voltage to the first preset voltage in a zero-start boost manner through AC voltage amplitude and frequency control, and the fourth flexible DC converter valve is charged. The first preset voltage is less than the conduction voltage of the first diode valve, the conduction voltage of the second diode valve, the conduction voltage of the third diode valve, and the conduction voltage of the fourth diode valve. After the fourth flexible DC converter valve has been charged, the fourth flexible DC converter valve is unlocked. The DC voltage of the fourth flexible DC converter valve is set to the rated voltage by means of DC voltage-reactive power control.

5. The method according to claim 4, characterized in that, The process of sequentially activating the third diode valve and the fourth diode valve, the first diode valve and the second diode valve to start the system includes: Start a predetermined number of new energy generator units from the sending-end new energy source; The third flexible DC converter valve is controlled to increase the AC bus voltage by means of AC voltage amplitude and frequency control until the third diode valve and the fourth diode valve are turned on; Control the fourth flexible DC-DC converter valve, the third flexible DC-DC converter valve, the fifth flexible DC-DC converter valve, and the first flexible DC-DC converter valve to turn on the first diode valve and the second diode valve; Start the other new energy units in the sending-end new energy source to complete the startup of the system.

6. The method according to claim 5, characterized in that, The control of the fourth flexible DC-DC converter valve, the third flexible DC-DC converter valve, the fifth flexible DC-DC converter valve, and the first flexible DC-DC converter valve to conduct the first diode valve and the second diode valve includes: The fourth flexible DC converter valve and the third flexible DC converter valve are controlled to jointly support the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is controlled so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected. Control the fifth flexible DC converter valve and the first flexible DC converter valve to close the first DC disconnect switch and the second DC disconnect switch; Control the fifth flexible DC converter valve or the first flexible DC converter valve to turn on the first diode valve and the second diode valve.

7. The method according to claim 6, characterized in that, The method of controlling the fourth flexible DC converter valve and the third flexible DC converter valve to jointly support the AC bus voltage, and controlling the third flexible DC converter valve to disconnect the first bypass switch and the second bypass switch when the current value through the first bypass switch and the second bypass switch is less than a preset current value after the AC bus voltage stabilizes, includes: The fourth flexible DC converter valve is controlled by AC voltage amplitude and frequency control with droop, and together with the third flexible DC converter valve, it supports the AC bus voltage. After the AC bus voltage stabilizes, the third flexible DC converter valve is controlled to switch to a constant active power and constant reactive power control mode, so that when the current value through the first bypass switch and the second bypass switch is less than the preset current value, the first bypass switch and the second bypass switch are disconnected.

8. The method according to claim 6 or 7, characterized in that, After disconnecting the first bypass switch and the second bypass switch, the method further includes: The third flexible DC converter valve is controlled to switch to DC voltage-reactive power control in order to stabilize the DC voltage of the third flexible DC converter valve.

9. The method according to claim 6 or 7, characterized in that, The control of the fifth flexible DC converter valve and the first flexible DC converter valve to close the first DC disconnect switch and the second DC disconnect switch includes: Increase the DC voltage of the fifth flexible DC converter valve and the DC voltage of the first flexible DC converter valve until the sum of the DC voltage of the fifth flexible DC converter valve and the DC voltage of the first flexible DC converter valve is greater than the positive DC voltage of the sending-end converter station, then close the first DC disconnect switch and the second DC disconnect switch.

10. The method according to claim 6 or 7, characterized in that, The control of the fifth flexible DC-DC converter valve or the first flexible DC-DC converter valve to activate the first diode valve and the second diode valve includes: Reduce the DC voltage of the fifth flexible DC converter valve or the DC voltage of the first flexible DC converter valve until the positive DC voltage of the receiving-end converter station is less than the positive DC voltage of the sending-end converter station, and then turn on the first diode valve and the second diode valve.

11. The method according to any one of claims 1-5, characterized in that, The method further includes: The second flexible DC converter valve is controlled to charge the fourth flexible DC converter valve until the fourth flexible DC converter valve is fully charged, at which point the fourth flexible DC converter valve is unlocked.

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