Fault ride-through control method for new energy parallel direct current collecting and sending-out system

Abstract

The invention relates to a fault ride-through control method for a new energy parallel direct-current collecting and sending-out system, and belongs to the technical field of direct-current power transmission. The method comprises the following steps: 1) limiting the output of active power of a receiving end inverter of the direct-current transmission line when the alternating-current voltage is smaller than a preset voltage due to the fault of the receiving end alternating-current side of the direct-current transmission line; 2) stopping the new energy output from the sending end of the new energy parallel direct current collecting and sending-out system to the receiving end of the direct current power transmission line; (3) when the fault of the alternating current side of the receiving end of the direct current power transmission line is removed and the voltage of the direct current side of the receiving end inverter is smaller than the working voltage of the receiving end inverter, recovering the new energy output to the receiving end of the direct current power transmission line from the sending end in the new energy parallel direct current collection sending-out system; and the output of the active power of the receiving end inverter is relieved. According to the fault ride-through control method provided by the invention, when the power grid of the new energy parallel direct current collecting and sending-out system breaks down, the new energy does not get off the grid and operates continuously, and the fault ride-through capability is achieved.

Description

Technical Field

[0001] The present invention relates to a fault ride-through control method for a new energy parallel DC collection and transmission system, belonging to the technical field of DC power transmission. Background Art

[0002] At present, existing large-scale new energy power generation systems are connected to the power grid through AC busbars for collection. The technology of new energy AC collection and transmission systems is relatively mature. Specifically, wind power and photovoltaic power stations in a new energy AC collection and transmission system are respectively connected to a common AC busbar after passing through inverters and transformers, and electric energy is transmitted to the power grid through AC lines or further transmitted to the eastern load center through UHVDC over a long distance.

[0003] Since the new energy AC collection and transmission system is connected to the power grid through AC collection, in the case of a weak power grid, resonance problems are likely to occur when the wind power and photovoltaic inverters in the new energy AC collection and transmission system are connected to the power grid and coupled with the system impedance. At the same time, due to the intermittency and instability of new energy power generation, if connected in an AC manner, it will bring risk challenges to the voltage and frequency stability of the AC system.

[0004] The published text of a Chinese invention patent application with the application publication number CN118412914A discloses an onshore large-scale new energy all-DC collection and transmission system. The transmission system includes a new energy collection station and at least one multi-port DC transformer; the new energy collection station includes at least one DC wind turbine collection station and / or at least one photovoltaic collection station; each DC wind turbine collection station and / or each photovoltaic collection station is connected to the low-voltage port of the corresponding multi-port DC transformer, and the high-voltage port of the multi-port DC transformer is used to connect to a DC transmission line so that new energy can be sent to the receiving end system. Although the all-DC collection proposed in this solution omits many substation links and the equipment required therefor, and can solve the resonance problem and instability problem that occur when connected to the power grid in AC, which is beneficial to improving the economy of the large-scale new energy collection and transmission system solution, there is a lack of research on the fault ride-through control method. Summary of the Invention

[0005] The purpose of the present invention is to provide a fault ride-through control method for a new energy parallel DC collection and transmission system to solve the problem that the existing new energy all-DC collection and transmission system lacks a fault ride-through control method.

[0006] To achieve the above purpose, the solution of the present invention includes: A fault ride-through control method for a new energy parallel DC collection and transmission system of the present invention includes the following steps: 1) When a fault occurs on the receiving-end AC side of the DC transmission line and the AC voltage is less than a preset voltage, limit the output of the active power of the receiving-end inverter of the DC transmission line; 2) Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system; 3) When the AC side fault at the receiving end of the DC transmission line is eliminated and the voltage on the DC side of the receiving-end inverter is less than its operating voltage, resume the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system; and lift the restriction on the active power output of the receiving-end inverter.

[0007] Furthermore, in step 2), by enabling the energy-consuming device on the wind power side of the new energy parallel DC collection and transmission system and blocking the DC transformer on the photovoltaic side of the new energy parallel DC collection and transmission system, stop the new energy output to the receiving end of the DC transmission line; In step 3), by withdrawing the energy-consuming device on the wind power side and unlocking the DC transformer on the photovoltaic side, resume the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0008] Furthermore, in step 2), after enabling the energy-consuming device on the wind power side of the new energy parallel DC collection and transmission system and blocking the DC transformer on the photovoltaic side of the new energy parallel DC collection and transmission system, when the voltage on the DC side of the receiving-end inverter is greater than a preset multiple of its operating voltage, enable the energy-consuming device on the DC side of the receiving-end inverter until the voltage on the DC side of the receiving-end inverter is less than its operating voltage.

[0009] Furthermore, in step 3), after the AC side fault at the receiving end of the DC transmission line is eliminated and after a preset time, lift the restriction on the active power output of the receiving-end inverter.

[0010] Furthermore, the DC transformer on the photovoltaic side includes the low-voltage DC transformers of each photovoltaic system respectively connected to each photovoltaic and the first high-voltage DC transformer at the sending end of the DC transmission line connected to the low-voltage DC transformers of each photovoltaic system.

[0011] The beneficial effects of the present invention are as follows: As a pioneering invention, a fault ride-through control method for a new energy parallel DC collection and transmission system provided by the present invention first restricts the output of active power of the receiving-end inverter of the DC transmission line when the AC voltage on the receiving-end AC side of the DC transmission line fails and is less than the preset voltage, which can reduce the power supply at the receiving end; then stops the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system, which can reduce the new energy output from the sending end to the receiving end and further reduce the power supply to the receiving end; when the fault on the receiving-end AC side of the DC transmission line is removed and the voltage on the DC side of the receiving-end inverter is less than its operating voltage, the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system is restored; and the output of active power of the receiving-end inverter is released, so as to ensure that the new energy does not trip off the grid during an AC fault, operates continuously, and smoothly transitions to the normal operating state.

[0012] A fault ride-through control method for a new energy parallel DC collection and transmission system of the present invention includes the following steps: 1) When a fault occurs in the DC transmission line, control the voltage on the DC side of the receiving-end inverter of the DC transmission line to zero; 2) Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system; 3) After the fault of the DC transmission line is cleared, establish the voltage on the DC side of the receiving-end inverter; restore the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0013] Further, in step 2), the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system is stopped by enabling the energy-consuming device on the wind power side of the new energy parallel DC collection and transmission system, blocking the DC transformer on the photovoltaic side of the new energy parallel DC collection and transmission system; In step 3), the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system is restored by withdrawing the energy-consuming device on the wind power side and unlocking the DC transformer on the photovoltaic side.

[0014] Further, the DC transformer on the photovoltaic side includes low-voltage DC transformers of each photovoltaic system respectively connected to each photovoltaic and a first high-voltage DC transformer at the sending end of the DC transmission line connected to the low-voltage DC transformers of each photovoltaic system.

[0015] The beneficial effects of the present invention are as follows: As a pioneering invention, a fault ride-through control method for a new energy parallel DC collection and transmission system provided by the present invention first controls the voltage on the DC side of the receiving-end inverter of the DC transmission line to zero when a fault occurs in the DC transmission line, so that the fault current cannot penetrate into the AC power grid; then stops the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system, which can reduce the fault current; after the fault of the DC line is cleared, the voltage on the DC side of the receiving-end inverter is established; and the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system is restored, so as to ensure that the new energy does not trip off the grid when a DC fault occurs, and continuously operates and smoothly transitions to the normal operation state. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. is a schematic structural diagram of a new energy parallel DC collection and transmission system provided by an embodiment of the present invention; Figure 2 FIG. is a schematic flow diagram of a fault ride-through control method for a new energy parallel DC collection and transmission system provided by an embodiment of the present invention; Figure 3 FIG. is a schematic flow diagram of another fault ride-through control method for a new energy parallel DC collection and transmission system provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0018] The concept of the present invention is as follows: Faults are divided into AC faults and DC faults. Whether it is an AC fault or a DC fault, it is required that the new energy side can remain connected to the grid when a fault occurs in the power grid. Therefore, the concept of the present invention is to first reduce the power supply voltage at the receiving end and then reduce the new energy output from the new energy sending end to the receiving end to ensure that the new energy does not trip off the grid and smoothly transitions to the normal state of the power grid.

[0019] Specifically: When the fault is an AC fault, first limit the output of the active power of the receiving-end inverter of the DC transmission line when the AC voltage is less than the preset voltage due to a fault on the AC side of the receiving end of the DC transmission line; then stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system; when the fault on the AC side of the receiving end of the DC transmission line is eliminated and the voltage on the DC side of the receiving-end inverter is less than its operating voltage, restore the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system; and release the output limit of the active power of the receiving-end inverter.

[0020] When the fault is a DC fault, first, when a fault occurs in the DC transmission line, control the voltage on the DC side of the receiving-end inverter of the DC transmission line to zero; then stop the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system; after the fault on the DC line is cleared, establish the voltage on the DC side of the receiving-end inverter; and resume the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system.

[0021] An embodiment of a fault ride-through control method for a new energy parallel DC aggregation and transmission system: The fault ride-through control method for the new energy parallel DC aggregation and transmission system provided by the embodiments of the present invention depends on the new energy parallel DC aggregation and transmission system. First, the new energy parallel DC aggregation and transmission system will be introduced in detail below in combination with Figure 1 and then the fault ride-through control method of the system will be described in combination with Figure 2 and Figure 3 illustrate the fault ride-through control method of the system.

[0022] Figure 1 is a schematic structural diagram of a new energy parallel DC aggregation and transmission system provided by the embodiments of the present invention. As shown in Figure 1 shown, the new energy parallel DC aggregation and transmission system includes: a new energy side, a low-voltage DC transformer on the new energy side, a DC transmission line, a high-voltage DC transformer at the sending end of the DC transmission line, a receiving-end inverter, and a converter transformer for connecting to an AC power grid.

[0023] Among them, the new energy side includes a number of wind power and a number of photovoltaic power. The number of wind power and photovoltaic power can be the same or different. In this embodiment, the case where the number of wind power and photovoltaic power is the same is taken as an example for illustrative description.

[0024] Among them, the low-voltage DC transformer on the new energy side refers to the low-voltage DC transformer of the wind power system corresponding to each wind power connection and the low-voltage DC transformer of the photovoltaic system corresponding to each photovoltaic connection. The low-voltage DC transformer of the wind power system can convert the low-voltage direct current output by the wind power into high-voltage direct current, and the low-voltage DC transformer of the photovoltaic system can convert the low-voltage direct current output by the photovoltaic into high-voltage direct current.

[0025] Among them, the DC transmission line includes a sending end and a receiving end. The sending end of the DC transmission line is connected to the new energy side, and the receiving end of the DC transmission line is connected to the AC power grid. The DC transmission line can transmit the electric energy generated on the new energy side (also known as new energy) to the receiving-end AC power grid for users to use.

[0026] Since the low-voltage DC transformer on the new energy side has limited ability to convert low-voltage DC into high-voltage DC, there will be a situation where the converted high-voltage DC does not meet the transmission standard. To solve this problem, a high-voltage DC transformer at the sending end of the DC transmission line is added to the line connecting the sending end of the DC transmission line and the new energy side, which can convert the high-voltage DC output by the low-voltage DC transformers of the wind power system and the photovoltaic system into ultra-high-voltage DC.

[0027] Among them, the high-voltage DC transformer at the sending end of the DC transmission line includes at least two multi-interface high-voltage DC transformers. One high-voltage DC transformer is connected to the low-voltage DC transformers of each wind power system, and is called the second high-voltage DC transformer 701 at the sending end of the DC transmission line or the high-voltage DC transformer of the wind power system; the other high-voltage DC transformer is connected to the low-voltage DC transformers of each photovoltaic system, and is called the first high-voltage DC transformer 601 at the sending end of the DC transmission line or the high-voltage DC transformer of the photovoltaic system.

[0028] The two output terminals (i.e., the positive output terminal and the negative output terminal) of the first high-voltage DC transformer 601 at the sending end of the DC transmission line and the two output terminals (i.e., the positive output terminal and the negative output terminal) of the second high-voltage DC transformer 701 at the sending end of the DC transmission line are connected in parallel at the sending end of the DC transmission line (i.e., Figure 1 points a and b in).

[0029] For the convenience of subsequent description of the scheme, the low-voltage DC transformers of each wind power system and the second high-voltage DC transformer 701 at the sending end of the DC transmission line are collectively called the DC transformers on the wind power side, and the low-voltage DC transformers of each photovoltaic system and the first high-voltage DC transformer 601 at the sending end of the DC transmission line are collectively called the DC transformers on the photovoltaic side.

[0030] A receiving-end inverter A2 and a converter transformer A3 are connected in series on the line connecting the receiving end of the DC transmission line and the AC grid.

[0031] The receiving-end inverter A2 can convert the ultra-high voltage output by the first high-voltage DC transformer 601 and the second high-voltage DC transformer 701 from DC ultra-high voltage to AC ultra-high voltage, so that the new energy output from the new energy side can be smoothly connected to the AC grid.

[0032] The converter transformer A3 can be used as the electrical isolation between the AC system and the DC system, weaken the AC side overvoltage invading the DC system, and ensure the safe operation of the whole system.

[0033] The new energy parallel DC collection and transmission system provided by the embodiment of the present invention further includes energy-consuming devices on the wind power side connected in series on the connection lines between each wind power and the low-voltage DC transformer of the wind power system, and an energy-consuming device A1 connected in parallel at both ends of the DC side of the receiving-end inverter A2. Each energy-consuming device on the wind power side and the energy-consuming device A1 can discharge surplus power when starting up.

[0034] The following combines Figure 2 and Figure 3 to introduce the fault ride-through method of the new energy parallel DC collection and transmission system provided by the embodiment of the present invention. It can be understood that the new energy parallel DC collection and transmission system provided by the embodiment of the present invention can only execute the AC fault ride-through control method, or only execute the DC fault ride-through control method, or execute both the AC and DC fault ride-through methods. The present invention does not make a special introduction to this.

[0035] Embodiment 1: Figure 2 is a schematic flow chart of a fault ride-through control method for a new energy parallel DC collection and transmission system provided by an embodiment of the present invention. As Figure 2 shown, this fault ride-through control method includes the following steps S101 to S103.

[0036] Step S101, when the AC voltage Uac on the receiving-end AC side of the DC transmission line fails and is less than the preset voltage Uset1, limit the output of the active power of the receiving-end inverter A2 of the DC transmission line.

[0037] Specifically, the AC voltage Uac of the receiving end can be collected through a current transformer; the collected AC voltage Uac of the receiving end is compared with the preset voltage Uset1 to judge whether the AC voltage Uac of the receiving end is less than the preset voltage Uset1. When the AC voltage Uac of the receiving end is less than the preset voltage Uset1, it is considered that a fault occurs on the receiving-end AC side of the DC transmission line. When the AC voltage Uac of the receiving end is greater than or equal to the preset voltage Uset1, it is considered that the receiving-end AC side of the DC transmission line is normal.

[0038] When a fault occurs on the receiving-end AC side of the DC transmission line, a large amount of voltage will accumulate on the receiving-end AC side. In order to reduce the pressure-bearing capacity of the line, at this time, a method of limiting the output of the active power of the receiving-end inverter A2 of the DC transmission line can be adopted. Once the output of the active power of the receiving-end inverter A2 decreases, the voltage on the receiving-end line will decrease, reducing the pressure-bearing capacity of the line and making it easier to survive the fault period.

[0039] S102. Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0040] Since restricting the active power of the receiving - end inverter A2 can only reduce the bearing capacity of part of the line, if the new energy on the new - energy side does not decrease, it will continuously output new energy to the receiving end, still increasing the bearing of the line. Therefore, in order to further reduce the voltage on the means line and enable the entire power grid to quickly and easily pass through the fault period and promptly restore the power supply capacity, it is necessary to stop the new energy output from the sending end to the receiving end of the DC transmission line in the new - energy parallel DC collection and transmission system.

[0041] Specifically, it can be achieved by enabling the energy - consuming devices on the wind - power side of the new - energy parallel DC collection and transmission system (i.e., the wind - power - side energy - consuming devices 301 to n in Figure 1 ), and blocking the DC transformers on the photovoltaic side of the new - energy parallel DC collection and transmission system to achieve the goal of stopping the new - energy output to the receiving end of the DC transmission line.

[0042] Since the energy - consuming devices on the wind - power side are enabled, the new energy generated by each wind power can be dissipated by the energy - consuming devices on the wind - power side, so that the new energy generated by the wind turbines no longer outputs to the receiving end. Also, since the DC transformers on the photovoltaic side are blocked, the new energy generated by the photovoltaic no longer outputs to the receiving end, thus achieving the purpose of stopping the new - energy output from the sending end to the receiving end of the DC transmission line in the new - energy parallel DC collection and transmission system.

[0043] Among them, blocking the DC transformers on the photovoltaic side can be to only block the low - voltage DC transformation of each photovoltaic system (i.e., the low - voltage DC transformation 501 to n of the photovoltaic system in Figure 1 ); it can also be to only block the first high - voltage DC transformer 601 at the sending end of the DC transmission line; or it can be to both block the low - voltage DC transformation of each photovoltaic system and block the first high - voltage DC transformer 601 at the sending end of the DC transmission line. The present invention does not make a special limitation on this.

[0044] As an optional implementation manner, when there are energy - consuming devices on the photovoltaic side (not shown) connected in series on the connection lines between each photovoltaic and the low - voltage DC transformers of the corresponding photovoltaic systems, the energy - consuming devices on the photovoltaic side are also enabled simultaneously.

[0045] Furthermore, the DC transformers on the wind - power side can also be blocked to stop the output of the new energy generated by the wind turbines.

[0046] Since the capacity of the energy consumption device on the wind power side is limited, if the wind turbine generates too much new energy, there will be excess after passing through the energy consumption device of the wind turbine. The excess new energy is transmitted to the receiving end through the DC transmission line, which will further aggravate the fault situation at the receiving end. Therefore, in order to completely consume the new energy output by the new energy side, as an optional implementation method, after enabling the energy consumption device on the wind power side in the new energy parallel DC collection and transmission system, locking the DC transformer on the photovoltaic side of the new energy parallel DC collection and transmission system, when the DC side voltage of the receiving end inverter is greater than its preset multiple of the working voltage Uset2, the energy consumption device A1 on the DC side of the receiving end inverter is enabled, and it will be exited when the DC side voltage Ummcadc of the receiving end inverter is less than its working voltage Uwork.

[0047] The preset multiple can be 1.1 times, that is, Uset2=1.1Uwork, and the expression that is more in line with the technical personnel in this field is Uset2=1.1pu. Among them, pu is the per-unit value, which refers to the operating time when the voltage is at 1.1 times the reference voltage, and usually refers to the duration when the voltage in the power system exceeds the normal range but is still within the allowable range. Generally, this voltage can be operated for a long time at 1.1 times the rated value, but the higher the voltage, the shorter the allowed operating time, and once the voltage is too high, it is no longer allowed to operate.

[0048] By enabling the energy consumption device A1 on the DC side of the receiving-end inverter, it can be ensured that when an AC fault occurs, the new energy output by the new energy side will be consumed on the DC side and will not be transmitted to the receiving end. The AC fault at the receiving end can be resolved in a short time, ensuring the fault ride-through capability of the system.

[0049] Step S103: when the fault on the AC side of the receiving end of the DC transmission line is removed and the voltage Ummcadc on the DC side of the receiving end inverter is less than its working voltage Uwork, the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system is restored; and the output of active power to the receiving end inverter is cancelled.

[0050] Among them, the goal of restoring the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system can be achieved by withdrawing the energy-consuming devices on the wind power side and unlocking the DC transformer on the photovoltaic side.

[0051] Since all the energy-consuming devices on the wind power side have been withdrawn, the new energy generated by each wind turbine is no longer consumed, so that the new energy generated by the wind turbine can be output to the receiving end. Since the DC transformer on the photovoltaic side is unlocked, the new energy generated by the photovoltaic can be output to the receiving end, thereby achieving the purpose of restoring the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0052] As an alternative implementation, when a photovoltaic-side energy-consuming device (not shown) is connected in series to the connection line of the low-voltage DC transformer of the photovoltaic system where each photovoltaic is connected to the corresponding photovoltaic, the energy-consuming devices on the photovoltaic side will also be deactivated.

[0053] Since the fault has been cleared, it is necessary to gradually restore the power supply capacity. Therefore, while restoring the output of the new energy on the new energy side, it is also necessary to release the output of the active power of the receiving-end inverter A2.

[0054] After the fault on the receiving-end AC side of the DC transmission line is cleared and the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system is restored, the grid voltage fluctuates and is unstable. At this time, if the output of the active power of the receiving-end inverter A2 is immediately released, it will cause a certain impact on the grid, resulting in a more serious unstable phenomenon. Therefore, for the safety of the grid, as an alternative implementation, after the fault is cleared, after a preset time, the output of the active power of the receiving-end inverter A2 can be released.

[0055] A fault ride-through control method for a new energy parallel DC aggregation and transmission system provided by an embodiment of the present invention first restricts the output of the active power of the receiving-end inverter of the DC transmission line when the AC voltage is less than the preset voltage due to a fault on the receiving-end AC side of the DC transmission line, which can reduce the power supply at the receiving end; then stops the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system, which can reduce the new energy output from the sending end to the receiving end and further reduce the power supply to the receiving end; when the fault on the receiving-end AC side of the DC transmission line is cleared and the voltage on the DC side of the receiving-end inverter is less than its operating voltage, the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system is restored; and the output of the active power of the receiving-end inverter is released, so as to ensure that the new energy does not trip off the grid during an AC fault and operates continuously and smoothly transitions to the normal operating state.

[0056] Embodiment 2: Figure 3 It is a schematic flow chart of another fault ride-through control method for a new energy parallel DC aggregation and transmission system provided by an embodiment of the present invention. The fault ride-through control method includes the following steps S201 to step S203.

[0057] S201. When a fault occurs in the DC transmission line, control the voltage on the DC side of the receiving-end inverter A2 of the DC transmission line to zero.

[0058] Specifically, a direct current (DC) current on a DC transmission line can be collected by a current transformer, and a DC voltage on the DC transmission line can be collected by a voltage transformer. For those skilled in the art, it should be known that after obtaining the DC current and DC voltage, any existing DC fault discrimination method can be used to determine whether a fault has occurred in the DC transmission line.

[0059] When it is determined that a fault has occurred in the DC transmission line, it is necessary to prevent the fault current from penetrating into the AC power grid. Therefore, it is necessary to first control the voltage on the DC side of the receiving-end inverter A2 of the DC transmission line to 0, and the receiving-end inverter A2 does not operate.

[0060] Controlling the voltage on the DC side of the receiving-end inverter A2 to 0 is equivalent to having no DC voltage transmitted to the receiving-end AC power grid, that is, no fault current penetrates into the AC power grid.

[0061] S202: Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0062] When a fault occurs in the DC transmission line, if the new energy output on the new energy side is not stopped, it will cause the fault current to become larger and larger, making it difficult to clear the fault. Therefore, in order to reduce the difficulty of fault clearing, it is also necessary to stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0063] Specifically, the goal of stopping the new energy output to the receiving end of the DC transmission line can be achieved by enabling the energy-consuming devices on the wind power side in the new energy parallel DC collection and transmission system and blocking the DC transformers on the photovoltaic side in the new energy parallel DC collection and transmission system.

[0064] Since the energy-consuming devices on the wind power side are enabled, the new energy generated by each wind power can be dissipated by the energy-consuming devices on the wind power side, so that the new energy generated by the wind turbines no longer outputs to the receiving end. Also, since the DC transformers on the photovoltaic side are blocked, the new energy generated by the photovoltaics no longer outputs to the receiving end, thus achieving the goal of stopping the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0065] As an optional implementation manner, when energy-consuming devices on the photovoltaic side (not shown) are connected in series on the connection lines between each photovoltaic and the low-voltage DC transformers of the corresponding photovoltaic systems, the energy-consuming devices on the photovoltaic side are also enabled simultaneously.

[0066] Among them, the energy-consuming devices on the wind power side and the DC transformers on the photovoltaic side can refer to the relevant descriptions in the foregoing Embodiment 1, and will not be elaborated here.

[0067] S203. After the DC line fault is cleared, establish the voltage on the DC side of the receiving-end inverter; restore the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0068] After the DC line fault is cleared, it is necessary to gradually restore the power supply capacity. Therefore, it is necessary to establish the voltage on the DC side of the receiving-end inverter A2 and restore the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system.

[0069] Among them, the voltage on the DC side of the receiving-end transformer A2 can be established by restarting the receiving-end transformer A2, so that the voltage on the DC side of the receiving-end transformer A2 can be re-established; or the voltage on the DC side of the receiving-end transformer A2 can be re-established by other means, and the present invention does not make special limitations on this.

[0070] Among them, the goal of restoring the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system can be achieved by withdrawing the energy-consuming device on the wind power side and unlocking the DC transformer on the PV side.

[0071] As an optional implementation manner, when there are energy-consuming devices (not shown) connected in series on the connection lines of the low-voltage DC transformers of each PV and the PV systems corresponding to each PV, the energy-consuming devices on the PV side are also withdrawn.

[0072] A fault ride-through control method for a new energy parallel DC collection and transmission system provided by an embodiment of the present invention first controls the voltage on the DC side of the receiving-end inverter of the DC transmission line to zero when a fault occurs on the DC transmission line, so that the fault current cannot penetrate into the AC grid; then stops the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system, which can reduce the fault current; after the DC line fault is cleared, establish the voltage on the DC side of the receiving-end inverter; restore the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC collection and transmission system, so as to ensure that the new energy does not trip off the grid and operates continuously and smoothly transitions to the normal operation state when a DC fault occurs.

Claims

1. A fault ride-through control method for a new energy parallel DC collection and transmission system, characterized in that It includes the following steps: 1) When a fault occurs on the receiving-end AC side of the DC transmission line and the AC voltage is less than the preset voltage, limit the output of the active power of the receiving-end inverter of the DC transmission line; 2) Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system; 3) When the fault on the receiving-end AC side of the DC transmission line is cleared and the voltage on the DC side of the receiving-end inverter is less than its operating voltage, resume the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system; And release the output of the active power of the receiving-end inverter.

2. The fault ride-through control method for the new energy parallel DC collection and transmission system according to claim 1, characterized in that, Step 2) stops the new energy output from the sending end to the receiving end of the DC transmission line by enabling the energy-consuming device on the wind power side in the new energy parallel DC aggregation and transmission system, blocking the DC transformer on the PV side in the new energy parallel DC aggregation and transmission system; Step 3) resumes the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system by withdrawing the energy-consuming device on the wind power side and unlocking the DC transformer on the PV side.

3. The fault ride-through control method of the new energy parallel DC collection and transmission system according to claim 2, wherein, In step 2), after enabling the energy-consuming device on the wind power side in the new energy parallel DC aggregation and transmission system and blocking the DC transformer on the PV side in the new energy parallel DC aggregation and transmission system, when the voltage on the DC side of the receiving-end inverter is greater than a preset multiple of its operating voltage, enable the energy-consuming device on the DC side of the receiving-end inverter until the voltage on the DC side of the receiving-end inverter is less than its operating voltage.

4. The fault ride-through control method for the new energy parallel DC collection and transmission system according to claim 1, characterized in that In step 3), after the fault on the receiving-end AC side of the DC transmission line is cleared and after a preset time, release the output of the active power of the receiving-end inverter.

5. The fault ride-through control method for the new energy parallel DC collection and transmission system according to claim 2 or 3, characterized in that The DC transformer on the PV side includes the low-voltage DC transformers of each PV system respectively connected to each PV and the first high-voltage DC transformer at the sending end of the DC transmission line connected to the low-voltage DC transformers of each PV system.

6. A fault ride-through control method for a new energy parallel DC collection and transmission system, characterized in that, It includes the following steps: 1) When a fault occurs on the DC transmission line, control the voltage on the DC side of the receiving-end inverter of the DC transmission line to be zero; 2) Stop the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system; 3) After the fault on the DC transmission line is cleared, establish the voltage on the DC side of the receiving-end inverter; Resume the output of the new energy from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system.

7. The fault ride-through control method for the new energy parallel DC collection and transmission system according to claim 6, characterized in that, Step 2) stops the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system by enabling the energy-consuming device on the wind power side and blocking the DC transformer on the PV side in the new energy parallel DC aggregation and transmission system; Step 3) resumes the new energy output from the sending end to the receiving end of the DC transmission line in the new energy parallel DC aggregation and transmission system by withdrawing the energy-consuming device on the wind power side and unlocking the DC transformer on the PV side.

8. The fault ride-through control method for the new energy parallel DC collection and transmission system according to claim 7, characterized in that, The DC transformer on the PV side includes the low-voltage DC transformers of each PV system connected to the corresponding PVs and the first high-voltage DC transformer at the sending end of the DC transmission line connected to the low-voltage DC transformers of each of the PV systems.

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