Fault ride-through control method suitable for remote power transmission system

Abstract

The invention relates to a fault ride-through control method suitable for a remote power transmission system, and the method comprises the steps: when the remote power transmission system breaks down, the voltage of the AC side of a system receiving end converter station drops, and the voltage of the DC side of the receiving end converter station continuously rises; when the direct-current side voltage of the receiving-end converter station reaches a set action threshold value, a power electronic switch of the direct-current voltage limiting device controls a resistor to be switched on; when the alternating-current energy consumption device receives a system fault signal and is activated, the direct-current voltage limiting device stops acting, and the alternating-current energy consumption device consumes surplus power; and when the voltage of the alternating current side of the converter station at the receiving end of the system is gradually recovered to the grid-connected voltage, the alternating current energy consumption device stops acting. Fault ride-through control of the remote power transmission system can be realized through combination of direct current side voltage limiting and alternating current side energy consumption, an additional water cooling system does not need to be configured, system loss and cost are further reduced, and a traditional energy consumption mode of combining alternating current and direct current energy consumption devices is changed.

Description

Technical Field

[0001] The present application relates to the technical field of fault ride-through of a remote power transmission system, and in particular to a fault ride-through control method applicable to a remote power transmission system. Background Art

[0002] At present, with the rapid construction of wind power and photovoltaic power generation bases, large-scale centralized development and transmission has become a trend in the development of new energy. Flexible direct current transmission technology (VSC-HVDC) has become one of the ideal choices for large-scale long-distance transmission of new energy due to its advantages such as low loss and flexible control, and has broad development prospects.

[0003] However, for traditional flexible DC transmission systems, when a system failure occurs, there is usually an overvoltage problem on the DC side caused by surplus power: one is when the single-pole of the sending-end converter station is locked, the new energy unit cannot be removed in a short period of time, and the sound-pole converter transmits all system power, causing the converter to be locked due to overvoltage and overcurrent. The other is when the receiving-end AC system fails or the receiving-end converter station is locked, the system power delivery capacity decreases, and the power output of the new energy unit will not change in a short period of time. The surplus power continues to charge the converter capacitor, causing the DC side voltage to continue to rise, threatening the safe operation of the system. Therefore, fault ride-through of flexible DC transmission systems has become a core issue restricting the development of large-capacity new energy transmission systems.

[0004] There are basically three types of existing fault ride-through solutions: the first is to reduce the power generated by the wind turbine through active control methods, mainly including fast communication methods, frequency increase methods or voltage reduction methods. The second method uses temporary storage or transfer of surplus power. The third method is to install energy-consuming devices and use resistors to absorb the unbalanced power during fault ride-through. Among them, installing energy-consuming devices is the most direct and effective measure to solve the problem of surplus power in the system. By absorbing energy through energy-consuming resistors, it has been widely used in actual projects. This method can ensure that the new energy units do not need to be shut down, so that non-permanent faults in the system do not affect the normal operation of the overall transmission system. However, since the flexible DC transmission system reaches thousands of kilometers, when the flexible DC transmission system fails, the voltage on the DC side of the receiving end continues to rise, while the voltage on the DC side of the sending end does not change significantly. In addition, due to the long distance between the converter stations, the communication delay between the converter stations is as high as tens of milliseconds, and the AC energy-consuming device cannot act in time to absorb the surplus power, and the voltage on the DC side of the receiving end will exceed the voltage limit within 10-15 milliseconds. Therefore, the traditional long-distance flexible direct current system is equipped with an AC energy-consuming device at the sending end and a DC energy-consuming device at the receiving end to maintain the stability of the system. However, the simultaneous configuration of AC and DC energy-consuming devices will bring two problems: first, the additional configuration of DC energy-consuming devices increases the volume and cost, and second, there is little research on the coordinated control between AC and DC energy-consuming devices. Moreover, even if the existing scheme of configuring AC and DC energy-consuming devices can reduce the manufacturing cost of DC energy-consuming devices, since the coordination between energy-consuming devices is not considered, the DC energy-consuming devices are often designed according to the maximum capacity of the system. They need to be equipped with a high-power water cooling system, resulting in performance waste and further increasing the fault ride-through cost. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a method for controlling a fault ride-through of a remote power transmission system, which specifically adopts the following technical solutions:

[0006] A method for controlling a fault ride-through of a remote power transmission system is provided, which is used to control a fault ride-through action when a remote power transmission system fails. The remote power transmission system includes at least an AC energy consumption device and a DC voltage limiting device. The method includes the following steps:

[0007] When a fault occurs in the long-distance transmission system, the voltage on the AC side of the receiving converter station drops, and the system surplus power charges the capacitor of the receiving converter station, causing the voltage on the DC side of the receiving converter station to continue to increase.

[0008] When the DC side voltage of the receiving converter station reaches the set action threshold, the power electronic switch control resistor of the DC voltage limiting device is turned on to balance the DC side voltage of the receiving converter station;

[0009] When the AC energy consumption device receives a system fault signal and is activated, the AC energy consumption device will send an activation signal to the DC voltage limiting device. At this time, the DC voltage limiting device stops working, and the remote power transmission system uses the AC energy consumption device to absorb the surplus power.

[0010] When the voltage on the AC side of the receiving-end converter station of the system gradually recovers to the grid-connected voltage, the voltage on the DC side of the receiving-end converter station generates an instantaneous fluctuation signal. When the instantaneous fluctuation signal is transmitted to the AC energy consuming device, the AC energy consuming device stops operating.

[0011] Optional: The DC voltage limiting device adopts a voltage outer loop control strategy. When the DC side voltage of the receiving converter station reaches the set action threshold, the DC voltage limiting device is activated. At this time, the outer loop control adopts a DC voltage hysteresis control strategy. By comparing the difference between the actual DC side voltage value and the reference value, the number of DC voltage limiting devices put into operation is controlled to maintain the DC side voltage of the receiving converter station within a preset fluctuation range.

[0012] Optionally: the DC voltage limiting device also adopts an inner loop control strategy for the number of modules put into operation. In this case, the inner loop control adopts a step-by-step investment strategy to calculate the number of DC voltage limiting devices put into operation based on given investment parameters of the DC voltage limiting device and system surplus power.

[0013] Optional: The DC voltage limiting device adopts a periodic rotation switching strategy when it is put into operation in a step-by-step manner:

[0014] Set the number of DC voltage limiting devices to be put into use to m;

[0015] When the i-th cycle is operated, the m DC voltage limiting devices are operated in sequence according to the order of input, and the cycle set is expressed as:

[0016] Input i ={1,2,3,…,m};

[0017] Input i represents the period set of m DC voltage limiting devices;

[0018] The corresponding DC voltage limiting devices are switched on and off in sequence according to the order of the period set.

[0019] Optional: The AC energy consuming device adopts a power outer loop control strategy. At this time, the outer loop control compares the difference between the input power at the sending end and the output power at the receiving end of the system, and then calculates the number of groups of AC energy consuming devices that need to be put into use. The AC energy consuming device adopts a thyristor group arrangement, and the AC energy consuming device adopts a group switching strategy to ensure stable absorption of surplus power during system failures.

[0020] Optionally: the AC energy consumption device adopts a voltage inner loop control strategy. At this time, the number of groups of AC energy consumption devices put into use is controlled by comparing the difference between the actual value of the DC side voltage of the receiving end converter station and the reference value, so as to maintain the DC side voltage of the receiving end converter station within a preset fluctuation range.

[0021] Optional: The configuration quantity and parameter selection of the DC voltage limiting device must meet the DC voltage constraint condition;

[0022] The DC voltage constraints include:

[0023] When a fault occurs in the remote power transmission system, the power consumption of the DC voltage limiting device is greater than the rated power of the system:

[0024]

[0025] Where P rate is the system rated power; P VLM Represents the power consumption of a single DC voltage limiting device; U SM is the capacitor voltage of the MMC submodule; r is the internal resistance of the MMC submodule; m is the number of DC voltage limiting devices put into use;

[0026] When the DC voltage limiting device is put into operation, the energy absorbed by the DC voltage limiting device is equal to the energy transmitted by the system:

[0027]

[0028] Where D is the duty cycle of the DC voltage limiting device; f VLM is the operating frequency of the DC voltage limiting device; k is the ratio of the system transmission power to the system rated power;

[0029] When the DC voltage limiting device is removed, the energy relationship of the long-distance transmission system is:

[0030]

[0031] Among them C system is the system equivalent capacitance; U dc_high is the upper limit of the DC side voltage of the receiving converter station; U dc_low is the lower limit of the DC side voltage of the receiving converter station; U dc is the voltage on the DC side of the receiving converter station; Δu is the fluctuation range of the voltage on the DC side of the receiving converter station;

[0032] At the same time, the operating frequency of the DC voltage limiting device must meet the following requirements:

[0033]

[0034] where f VLM_max It is the maximum operating frequency of the DC voltage limiting device.

[0035] Optional: The configuration quantity and parameter selection of the DC voltage limiting device must meet the energy absorption limit of the energy dissipation resistor and the capacitor voltage fluctuation range;

[0036] When the DC voltage limiting device is in action, the energy absorbed by each DC voltage limiting device cannot exceed the upper limit of the resistance allowed:

[0037]

[0038] Where E VLM Absorbs energy for a single DC voltage limiting device; P rate is the system rated power; T VLM_MMC is the operating time of the DC voltage limiting device from action to exit; m is the number of DC voltage limiting devices put into operation; E allow The energy allowed to be absorbed by each resistor in the DC voltage limiting device;

[0039] The maximum voltage relationship between the capacitor voltage of the MMC submodule configured with a DC voltage limiting device and the MMC submodule not configured with a DC voltage limiting device must meet the following requirements:

[0040]

[0041] Where Δu SM1 The maximum voltage drop of the capacitor voltage of the MMC submodule equipped with the DC voltage limiting device; Δu SM2 ΔU is the maximum voltage rise of the capacitor voltage of the MMC submodule that is not equipped with a DC voltage limiting device; SM The voltage fluctuation range of the MMC submodule capacitor specified by the system; U SM is the capacitor voltage of the MMC submodule; U dc_high is the upper limit of the DC side voltage of the receiving converter station; U dc_low is the lower limit of the DC side voltage of the receiving converter station; C SM is the capacitance of the MMC submodule; i r is the current flowing through the resistor in the DC voltage limiting device, i bridge is the bridge arm current; n is the total number of MMC submodules; D is the duty cycle of the DC voltage limiting device; r is the internal resistance of the MMC submodule; f VLM is the operating frequency of the DC voltage limiting device.

[0042] Optionally: the AC energy consumption device selection must satisfy a group quantity constraint, wherein the group quantity constraint includes:

[0043] When the system fails and performs ride-through control, the maximum power absorbed by the AC energy consumption device is equal to the rated power of the system:

[0044]

[0045] When the power consumption of the AC energy consumption device is greater than the system transmission power, and the maximum power difference between the power consumption of the AC energy consumption device and the system transmission power is equal to the power consumption of a single branch of the AC energy consumption device, the power difference between the power consumption of the AC energy consumption device and the system transmission power discharges the system capacitor in a single action cycle, and the resulting voltage change is:

[0046]

[0047] Where P ACC P is the power consumed by the AC energy consumption device; ACC_single U is the power consumed by a single branch of the AC energy-consuming device; ac_k is the secondary voltage of the AC transformer; T ac is the period of the AC voltage; Δu ACC It is the maximum DC voltage change caused by the unbalanced power consumption of the AC energy consumption device; U rate is the system rated voltage; C system is the system equivalent capacitance; P rate is the rated power of the system; R is the resistance of the AC energy consuming device; a is the number of groups of the AC energy consuming device.

[0048] Optionally: The AC energy consumption device must meet voltage level constraints when selected, wherein the voltage level constraints include:

[0049] The voltage level of the AC energy consumption device is related to the transformation ratio of the AC transformer. When the voltage level of the AC energy consumption device is higher, more thyristors need to be connected in series; when the voltage level of the AC energy consumption device is lower, more thyristors need to be connected in parallel.

[0050] When the transformation ratio of the AC transformer is determined, the total number of thyristors required is expressed as:

[0051]

[0052] Number T is the total number of thyristors required; a is the number of groups of AC energy consuming devices; U ac_k is the secondary voltage of the AC transformer; U ac is the AC side voltage of the receiving converter station; k is the ratio of the system transmission power to the system rated power; U T is the operating voltage of the thyristor;

[0053] The current flowing through the thyristor is expressed as:

[0054]

[0055] Among them I T is the thyristor operating current; P ACC_singleIt is the power absorption of a single branch of an AC energy consuming device.

[0056] Beneficial Effects

[0057] The technical solution of this application has the following beneficial effects:

[0058] The fault ride-through control method applicable to the remote power transmission system of the present application combines the DC side voltage limiting and the AC side energy consumption, adopts a modular multi-level converter module MMC with short-time voltage limiting capability at the receiving end, and adopts an AC energy consumption device at the sending end. When a system fault occurs and the DC voltage at the receiving end reaches the set value, the MMC with short-time voltage limiting capability arranged at the receiving end first acts to achieve DC voltage stability. When the AC energy consumption device detects the fault and starts, the MMC at the receiving end stops the voltage limiting function, and the AC energy consumption device continues to act to absorb the surplus power until the fault ends. Through the above-mentioned coordination, the fault ride-through control of the remote power transmission system can be realized, and because the MMC voltage limiting module at the receiving end (i.e., the DC voltage limiting device) only needs to act for tens of milliseconds and absorb a small amount of energy, it does not need to configure an additional water cooling system, which further reduces system losses and costs, and changes the energy consumption mode of combining traditional AC and DC energy consumption devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of the structure of the long-distance power transmission system in the embodiment of the present application.

[0060] Figure 2 It is a schematic diagram of a fault ride-through control method applicable to a long-distance power transmission system in an embodiment of the present application.

[0061] Figure 3 The following is a diagram showing the principle and control logic of the voltage limiting device of the DC voltage limiting device in the embodiment of the present application. Figure 3 (a) is a schematic diagram of the voltage limiting device of the DC voltage limiting device; Figure 3 (b) is the control logic diagram of the DC voltage limiting device limiting voltage.

[0062] Figure 4 The following is a diagram showing the principle and control logic of voltage limiting of the AC energy consumption device in the embodiment of the present application. Figure 4 (a) is the schematic diagram of the power dissipation of the AC energy consuming device; Figure 4 (b) is the control logic diagram of the power dissipation of the AC energy consuming device.

[0063] Figure 5 This is a structural and parameter comparison diagram of the embodiment of the present application and the existing solution.

[0064] Figure 6 This is a schematic diagram of the structure of an electronic device in an embodiment of the present application. DETAILED DESCRIPTION

[0065] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and cannot be used to limit the scope of protection of the present application. It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanation of the present application.

[0066] Combination Figure 1 As shown, the embodiment of the present application specifically discloses a method for controlling a fault ride-through of a remote power transmission system, which is used to control a fault ride-through action when a remote power transmission system fails. The remote power transmission system at least includes an AC energy consumption device and a DC voltage limiting device. The AC energy consumption device is a device that realizes a specific function by consuming AC power. Its working principle is usually to use the characteristics of components such as resistors, inductors, capacitors, etc. to convert AC power into other forms of energy such as heat energy, magnetic field energy or electric field energy for consumption. In the dynamic stability control of the power system, the AC energy consumption device can maintain the stability of the system by consuming excess energy in the system. Generally, the AC energy consumption device (ACC) is arranged at the sending end of the remote power transmission system. The DC voltage limiting device usually adopts a specific circuit structure and components, such as a voltage-stabilizing diode, a varistor, a thyristor, etc., to limit the DC voltage. In the present application, the DC voltage limiting device (VLM) is composed of a power electronic switch and a resistor. The capacitor voltage is balanced by controlling the switching of the power electronic switch to control the switching of the resistor. The voltage limiting module acts independently and will not affect the normal operation of the MMC (modular multilevel converter) converter module. When the voltage in a DC circuit exceeds the set limit, the DC voltage limiting device will automatically start to limit the voltage to a safe range by shunting, clamping or other means to protect other components in the circuit from damage by excessive voltage.

[0067] Specific, combined Figure 2 As shown, the fault ride-through control method applicable to the remote power transmission system in the embodiment of the present application specifically includes the following steps:

[0068] First, when the remote power transmission system does not fail, that is, before time t0, the DC voltage limiting device VLM and the AC energy consumption device ACC do not operate, and the system operates normally and transmits power normally. When a fault occurs in the remote power transmission system, that is, during the time t0-t1, the system enters the fault ride-through control stage (FRT process). At this time, the AC side voltage U ac When a drop occurs, the system surplus power charges the capacitor of the receiving converter station, and the DC side voltage U dc_out Continue to rise; it should be noted that Figure 2 Middle U ac Represents the AC side voltage of the receiving converter station, U dc_out Represents the DC side output voltage of the receiving converter station, T controlRepresents the control signal, Number represents the number of DC voltage limiting devices VLM put into operation, and Group represents the number of groups of AC energy consumption devices ACC.

[0069] The DC side voltage limiting stage is in the period from t1 to t2. At t1, the DC side voltage U dc_out When the set action threshold is reached, the power electronic switch of the DC voltage limiting device controls the resistor to be put into operation to balance the DC side voltage of the receiving converter station. At this time, the energy transmission path of the system is as follows: Figure 3 As shown in (a) in the middle, the DC voltage limiting device adopts independent action logic during the action stage, which does not affect the normal action of the MMC submodule and maintains the stability of the DC voltage.

[0070] Among them combined Figure 3 As shown in (b), the action logic of the DC voltage limiting device adopts a voltage outer loop control strategy and an inner loop control strategy for the number of modules put into operation. The voltage outer loop control strategy of the DC voltage limiting device is as follows: when the DC side voltage of the receiving-end converter station reaches the set action threshold, the DC voltage limiting device is activated. At this time, the outer loop control adopts a DC voltage hysteresis control strategy, and controls the number of DC voltage limiting devices put into operation by comparing the difference between the actual DC side voltage value and the reference value, so as to maintain the DC side voltage of the receiving-end converter station within a preset fluctuation range. In order to reduce the impact of the action of the DC voltage limiting device on the DC voltage, the inner loop control strategy for the number of modules put into operation of the DC voltage limiting device is as follows: at this time, the inner loop control adopts a step-by-step investment strategy, and calculates the number of DC voltage limiting devices put into operation based on the given DC voltage limiting device investment parameters (such as action frequency, duty cycle and other parameters) and the system surplus power. It should be noted that Figure 3 (b) E ab_VLM Represents the action signal of the DC voltage limiting device VLM; U dcN Represents the rated DC voltage; T VLM Represents the operation time of the DC voltage limiting device.

[0071] It should be noted that, in order to balance the energy absorbed by each DC voltage limiting device, the DC voltage limiting device adopts a periodic rotation switching strategy when step-by-step input:

[0072] First, set the number of DC voltage limiting devices to be put into use as m;

[0073] When the i-th cycle is operated, the m DC voltage limiting devices are operated in sequence according to the order of input, and the cycle set is expressed as:

[0074] Input i ={1,2,3,…,m};

[0075] Input i represents the period set of m DC voltage limiting devices;

[0076] The corresponding DC voltage limiting devices are switched on and off in sequence according to the order of the period set.

[0077] For example, when m DC voltage limiting devices are actuated in the first cycle, the order in which the m DC voltage limiting devices are put into operation is 1, 2, ...m; in the second cycle, the order in which the m DC voltage limiting devices are put into operation is 2, 3, ...m, 1; the DC voltage limiting devices are switched on and off in sequence according to the above rule, and in the mth cycle, the order in which the m DC voltage limiting devices are put into operation is m, 1, ..., m-1; through the above-mentioned periodic rotation switching strategy, each VLM can absorb energy evenly, avoiding a single VLM absorbing too much energy and causing resistance heating to affect the operation of surrounding equipment.

[0078] During the period t2-t3, the AC side is in the energy consumption stage. When the AC energy consumption device ACC receives the system fault signal and is activated at t2, the AC energy consumption device ACC will send an activation signal to the DC voltage limiting device VLM. At this time, the DC voltage limiting device VLM stops working, and the remote power transmission system uses the AC energy consumption device ACC to absorb the surplus power. At this time, the energy transmission path of the system is as follows: Figure 4 As shown in (a).

[0079] like Figure 4 As shown in (b), the control logic of the AC energy consumption device adopts a power outer loop control strategy and a DC voltage inner loop control strategy. The power outer loop control strategy of the AC energy consumption device is: the outer loop power control compares the system sending end input power P in and the receiving end output power P out The difference between the two is used to calculate the number of groups of AC energy-consuming devices that need to be put into use. In addition, in order to achieve stable power consumption, ACC adopts the form of thyristor group arrangement, such as Figure 1 As shown, it is divided into a group. And based on the periodic rotation switching strategy of the DC voltage limiting device, similarly, the AC energy consumption device adopts a group periodic rotation switching strategy to ensure stable consumption of surplus power during system failures. The voltage inner loop control strategy of the AC energy consumption device is: by comparing the difference between the actual value of the DC side voltage of the receiving end converter station and the reference value, the number of groups of AC energy consumption devices put into operation is controlled to maintain the DC side voltage of the receiving end converter station within a preset fluctuation range. It should be noted that Figure 4 (b) E ab_ACC Represents the action signal of the AC energy consumption device ACC; U dcN Represents the rated DC voltage; T ACC Represents the operating time of the AC energy consuming device.

[0080] During the period from t3 to t4, the fault recovery stage is in progress. At this time, when the AC side voltage of the receiving-end converter station gradually recovers to the grid-connected voltage at t3, the grid power will impact the system, causing a short-term fluctuation in the DC voltage. The DC side voltage of the receiving-end converter station generates an instantaneous fluctuation signal. When the instantaneous fluctuation signal is transmitted to the AC energy consumption device, the AC energy consumption device stops operating. ac The voltage on the DC side of the system returns to normal and the voltage on the DC side of the system also returns to the rated value.

[0081] It should be noted that in the embodiment of the present application, a DC voltage limiting device is evenly configured for each bridge arm circuit of the MMC submodule, and each bridge arm circuit contains m DC voltage limiting devices. The number of configurations and parameter selection of the DC voltage limiting device must meet the DC voltage constraint conditions, and must also meet the energy absorption limit of the energy-consuming resistor and the voltage fluctuation range of the capacitor. Under the premise of meeting the above two constraints, the fewer the number of VLM configurations, the lower the energy consumption cost.

[0082] The DC voltage constraints mainly include:

[0083] For VLM, it is necessary to achieve DC voltage stability even under the most serious fault conditions. Therefore, when a fault occurs in the remote transmission system, the power consumption of the DC voltage limiting device is greater than the rated power of the system:

[0084]

[0085] Where P rate is the system rated power; P VLM Represents the power consumption of a single DC voltage limiting device; U SM is the capacitor voltage of the MMC submodule; r is the internal resistance of the MMC submodule; m is the number of DC voltage limiting devices put into use.

[0086] When the DC voltage limiting device is put into operation, as the VLM is gradually put into operation, the DC side voltage of the receiving converter station continues to drop. Considering the most extreme case, the energy absorbed by the DC voltage limiting device must be equal to the system transmission energy:

[0087]

[0088] Where D is the duty cycle of the DC voltage limiting device; f VLM is the operating frequency of the DC voltage limiting device; k is the ratio of the system transmission power to the system rated power, where 0 <k<1。

[0089] When the DC voltage limiting device is removed, as the VLM is gradually removed, the DC side voltage of the receiving converter station continues to rise. At this time, the energy relationship of the remote transmission system is:

[0090]

[0091] Among them C system is the system equivalent capacitance; U dc_high is the upper limit of the DC side voltage of the receiving converter station;

[0092] U dc_low is the lower limit of the DC side voltage of the receiving converter station; U dc is the DC side voltage of the receiving converter station; Δu is the fluctuation range of the DC side voltage of the receiving converter station.

[0093] By solving the above formula, the operating frequency of the DC voltage limiting device can be solved. At this time, for any k, VLM needs to maintain the stability of the system DC voltage. When 3mP VLM =kP rate When the DC voltage limiting device operates at the maximum frequency f VLM_max , at this time, the operating frequency of the DC voltage limiting device must meet the following requirements:

[0094]

[0095] Furthermore, the energy absorption limit of the energy dissipation resistor and the voltage fluctuation range of the capacitor mainly include the following requirements:

[0096] When the DC voltage limiting device is in operation, since the DC voltage limiting device adopts a periodic switching strategy, it can be considered that the energy absorbed by each VLM is the same. During the operation, the energy absorbed by each VLM is E VLM The energy absorbed by each DC voltage limiting device cannot exceed the upper limit of the resistance absorption limit to avoid absorbing too much energy, which will cause the resistance to emit a lot of heat and affect the surrounding power electronic equipment. Therefore, the energy absorbed by each DC voltage limiting device cannot exceed the upper limit of the resistance absorption limit:

[0097]

[0098] Where E VLM Absorbs energy for a single DC voltage limiting device; P rate is the system rated power; T VLM_MMC is the operating time of the DC voltage limiting device from action to exit; m is the number of DC voltage limiting devices put into operation; E allow It is the energy that each resistor in the DC voltage limiting device is allowed to absorb. This value depends on the material of the resistor, temperature rise characteristics, etc. Different types of resistors have different values.

[0099] Furthermore, for the MMC submodule equipped with a DC voltage limiting device and the MMC submodule not equipped with a DC voltage limiting device, the relationship between the capacitor voltages of the two must meet the following conditions to maintain the balance of the DC voltage:

[0100]

[0101] Where Δu SM1 The maximum voltage drop of the capacitor voltage of the MMC submodule equipped with the DC voltage limiting device; Δu SM2 ΔU is the maximum voltage rise of the capacitor voltage of the MMC submodule that is not equipped with a DC voltage limiting device; SM The voltage fluctuation range of the MMC submodule capacitor specified by the system; U SM is the capacitor voltage of the MMC submodule; U dc_high is the upper limit of the DC side voltage of the receiving converter station; U dc_low is the lower limit of the DC side voltage of the receiving converter station; C SM is the capacitance of the MMC submodule; i r is the current flowing through the resistor in the DC voltage limiting device, i bridge is the bridge arm current; n is the total number of MMC submodules; D is the duty cycle of the DC voltage limiting device; r is the internal resistance of the MMC submodule; f VLM is the operating frequency of the DC voltage limiting device.

[0102] Furthermore, the AC energy consumption device described in the embodiment of the present application is connected to the AC busbar via a step-down transformer, and different surplus powers can be absorbed by changing the number of input groups. At this time, the group number constraint and voltage level constraint must be met during selection.

[0103] The selection of the number of ACC groups needs to comprehensively consider the performance requirements and economic efficiency of the system. During the fault ride-through period, the more groups there are, the smaller the difference between the power absorbed by the ACC and the surplus power of the system, and the smaller the power impact on the system. However, since each branch of the ACC requires a three-phase arrangement of thyristors, as the number of groups increases, the cost increases linearly, and the floor space also increases sharply. Specifically, the group number constraints include:

[0104] When the system fails and performs ride-through control, the maximum power absorbed by the AC energy consumption device is equal to the rated power of the system:

[0105]

[0106] When the power consumption of the AC energy consumption device is greater than the system transmission power, and the maximum power difference between the power consumption of the AC energy consumption device and the system transmission power is equal to the power consumption of a single branch of the AC energy consumption device, the power difference between the power consumption of the AC energy consumption device and the system transmission power discharges the system capacitor in a single action cycle, and the resulting voltage change is:

[0107]

[0108] Where P ACC P is the power consumed by the AC energy consumption device; ACC_singleU is the power consumed by a single branch of the AC energy-consuming device; ac_k is the secondary voltage of the AC transformer; T ac is the period of the AC voltage; Δu ACC It is the maximum DC voltage change caused by the unbalanced power consumption of the AC energy consumption device; U rate is the system rated voltage; C system is the system equivalent capacitance; P rate is the rated power of the system; R is the resistance of the AC energy consuming device; a is the number of groups of the AC energy consuming device.

[0109] Furthermore, the voltage level constraints in the embodiments of the present application include:

[0110] The voltage level of the AC energy consumption device is related to the transformation ratio of the AC transformer. When the voltage level of the AC energy consumption device is higher, more thyristors need to be connected in series; when the voltage level of the AC energy consumption device is lower, more thyristors need to be connected in parallel.

[0111] When the transformation ratio of the AC transformer is determined, the total number of thyristors required is expressed as:

[0112]

[0113] Number T is the total number of thyristors required; a is the number of groups of AC energy consuming devices; U ac_k is the secondary voltage of the AC transformer; k is the ratio of the system transmission power to the system rated power; U T is the operating voltage of the thyristor;

[0114] The current flowing through the thyristor is expressed as:

[0115]

[0116] Among them I T is the thyristor operating current; P ACC_single It is the power absorption of a single branch of an AC energy consuming device.

[0117] Combination Figure 5 As shown, the embodiment of the present application further illustrates the effect of the solution of the present application by comparing the performance of the solution of the present application with the existing solution. The existing solutions adopted include centralized DC energy consumption device (centralized DCC), distributed DC energy consumption device (distributed DCC), and thyristor-based DC energy consumption device (thyristor-based DCC).

[0118] from Figure 5It can be seen that in terms of voltage balancing, since the centralized DCC switches operate synchronously, it is necessary to consider the dynamic voltage balancing of the series switches. For distributed and thyristor-based DCCs, since they both have supporting capacitors, only the voltage balancing of the capacitors needs to be considered. For DCCs with DC voltage limiting devices, they are directly connected in parallel across the capacitors of the MMC submodules. The MMC submodules themselves have the ability to balance capacitor voltages, so they have advantages in voltage balancing.

[0119] In addition, in terms of the impact on the MMC sub-module, due to the independent energy consumption device, it adopts independent action to absorb surplus power, so it will not affect the characteristics of the MMC sub-module. For the DCC with a DC voltage limiting device, it charges and discharges the MMC sub-module capacitor during the operation process, although it will increase the voltage fluctuation of the MMC sub-module capacitor and increase the bridge arm current, the process is short and will not affect the normal operation of the MMC sub-module; in terms of DC voltage ripple, the centralized DCC adopts PWM control, and the pulse current has the greatest impact on the system, and the ripple is usually between 10% and 15%; the distributed and thyristor-based DCC both adopt the form of step switching, which reduces the current change rate and controls the ripple at 5%-10%. The solution of the present application also adopts the form of step switching, and the number of modules is higher than the distributed solution, so the DC voltage ripple can be lower than 5%.

[0120] Furthermore, in terms of switching current, for both centralized DCC and distributed DCC solutions, the DC current is directly turned off, so the switching current is 2kA. For thyristor-based DCC, thyristors are used as main switches, and LC circuits are relied on to generate oscillating currents to assist the thyristor in turning off. Therefore, the peak current flowing through the thyristor is more than twice the current flowing through the resistor. For the solution of this application, due to the increase in the number of energy-consuming modules, the current that the switch needs to turn off is only 1.1kA.

[0121] Based on the above analysis, it can be seen that the solution of the present application reduces the performance requirements for energy-consuming modules and has a significant effect on suppressing the DC voltage ripple of the system.

[0122] In addition, in combination with what is shown in Table 1, the embodiment of the present application further illustrates the effect of the solution of the present application by comparing the cost of the solution of the present application with that of the existing solution.

[0123] Table 1

[0124]

[0125] The cost of each solution in Table 1 is mainly evaluated from the aspects of switches, resistors, capacitors, energy extraction, insulation frame, etc. It compares the number and price of main equipment required for different solutions. In order to intuitively show the comparison results of the total cost of each solution, the total cost of centralized DCC is taken as 1p.u.

[0126] Based on the contents of Table 1, it can be seen that the centralized DCC uses 4.5kV / 3kA IGBTs, and a single IGBT withstands a voltage of 2kV, requiring a total of 500. In addition, in order to reduce the impact of pulse current on the system, it is necessary to connect absorption capacitors in parallel at both ends of the DCC, and the IGBTs directly connected in series adopt an independent energy supply form. The distributed DCC also uses 4.5kV / 3kA IGBTs, and a single module withstands a voltage of 2kV, requiring 500 switches and support capacitors, and the IGBT power supply adopts the form of taking energy from the capacitor. The thyristor-based DCC essentially uses a switch composed of a thyristor and an LC circuit to replace the IGBT, thereby reducing the cost of the fully controlled power electronic switch. Since the thyristor current is turned off at zero, there is no turn-off overvoltage. The rated voltage of a single module is 2.8kV, and the number of modules required is 350. The present application scheme uses 3.3kV / 1kA IGBTs, 150 energy-consuming modules are arranged in each bridge arm, and the 6 bridge arms are arranged symmetrically. As can be seen from Table 1, since this application uses lower capacity IGBTs and saves additional equipment such as supporting capacitors and insulating frames, the total energy consumption cost on the DC side is reduced by more than 70% compared with the centralized DCC solution, which has a very high cost advantage.

[0127] like Figure 6 As shown, the embodiment of the present application also provides an electronic device, including a processor and a memory, a program or instruction stored in the memory and executable on the processor, and when the program or instruction is executed by the processor, the following is achieved: Figure 1 The various processes of the method embodiment shown in the figure can achieve the same technical effect. To avoid repetition, they will not be described again here.

[0128] The embodiment of the present application also provides a readable storage medium on which a program or instruction is stored. When the program or instruction is executed by a processor, the above Figure 1 The various processes of the method embodiments described above can achieve the same technical effect, and will not be described again here to avoid repetition.

[0129] The present application also provides a computer program product, including computer instructions, which, when executed by a processor, implement the above Figure 1 The various processes of the method embodiments described above can achieve the same technical effect, and will not be described again here to avoid repetition.

[0130] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application. The above-mentioned sequence numbers of the embodiments of the present application are only for description and do not represent the advantages and disadvantages of the embodiments.

[0131] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0132] In the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another device, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0133] The units described above as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units; they may be located in one place or distributed on multiple network units; some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0134] In addition, all functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may be a separate unit, or two or more units may be integrated into one unit; the above-mentioned integrated units may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0135] A person skilled in the art can understand that all or part of the steps of implementing the above method embodiment can be completed by hardware related to program instructions, and the aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it executes the steps of the above method embodiment; and the aforementioned storage medium includes: mobile storage devices, read-only memories (ROM), magnetic disks or optical disks, etc., various media that can store program codes.

[0136] Alternatively, if the above-mentioned integrated unit of the present application is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiment of the present application can essentially or in other words, the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a device (which can be a terminal or a platform, etc.) to execute all or part of the methods described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as mobile storage devices, ROMs, magnetic disks, or optical disks.

[0137] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for controlling a fault ride-through of a remote power transmission system, for controlling a fault ride-through action when a remote power transmission system fails, wherein the remote power transmission system comprises at least an AC energy consumption device and a DC voltage limiting device, and is characterized in that: The method comprises the following steps: When a fault occurs in the long-distance transmission system, the voltage on the AC side of the receiving converter station of the system drops, and the system surplus power charges the capacitor of the receiving converter station, causing the voltage on the DC side of the receiving converter station to continue to increase. When the DC side voltage of the receiving converter station reaches the set action threshold, the power electronic switch control resistor of the DC voltage limiting device is turned on to balance the DC side voltage of the receiving converter station; When the AC energy consumption device receives a system fault signal and is activated, the AC energy consumption device will send an activation signal to the DC voltage limiting device. At this time, the DC voltage limiting device stops working, and the remote power transmission system uses the AC energy consumption device to absorb the surplus power. When the voltage on the AC side of the receiving-end converter station of the system gradually recovers to the grid-connected voltage, the voltage on the DC side of the receiving-end converter station generates an instantaneous fluctuation signal. When the instantaneous fluctuation signal is transmitted to the AC energy consuming device, the AC energy consuming device stops operating.

2. The method for controlling a fault ride-through of a remote power transmission system according to claim 1, characterized in that: The DC voltage limiting device adopts a voltage outer loop control strategy. When the DC side voltage of the receiving-end converter station reaches a set action threshold, the DC voltage limiting device is activated. At this time, the outer loop control adopts a DC voltage hysteresis control strategy. By comparing the difference between the actual DC side voltage value and the reference value, the number of DC voltage limiting devices put into operation is controlled to maintain the DC side voltage of the receiving-end converter station within a preset fluctuation range.

3. The method for controlling a fault ride-through of a remote power transmission system according to claim 2, characterized in that: The DC voltage limiting device also adopts an inner loop control strategy for the number of modules put into operation. At this time, the inner loop control adopts a step-by-step investment strategy to calculate the number of DC voltage limiting devices put into operation based on given investment parameters of the DC voltage limiting device and system surplus power.

4. The method for controlling a fault ride-through of a remote power transmission system according to claim 3, characterized in that: The DC voltage limiting device adopts a periodic rotation switching strategy when it is put into operation in a step-by-step manner: Set the number of DC voltage limiting devices to be put into use to m; When the i-th cycle is operated, the m DC voltage limiting devices are operated in sequence according to the order of input, and the cycle set is expressed as: Input i ={1,2,3,…,m}; Input i represents the period set of m DC voltage limiting devices; The corresponding DC voltage limiting devices are switched on and off in sequence according to the order of the period set.

5. The fault ride-through control method for a remote power transmission system according to claim 1, characterized in that: The AC energy consuming device adopts a power outer loop control strategy. At this time, the outer loop control compares the difference between the input power at the sending end and the output power at the receiving end of the system, and then calculates the number of groups of AC energy consuming devices that need to be put into use. The AC energy consuming device adopts a thyristor group arrangement, and the AC energy consuming device adopts a group switching strategy to ensure stable consumption of surplus power during system failures.

6. The method for controlling a fault ride-through of a remote power transmission system according to claim 5, characterized in that: The AC energy consumption device adopts a voltage inner loop control strategy. At this time, the number of groups of AC energy consumption devices put into use is controlled by comparing the difference between the actual value of the DC side voltage of the receiving end converter station and the reference value, so as to maintain the DC side voltage of the receiving end converter station within a preset fluctuation range.

7. The method for controlling a fault ride-through of a remote power transmission system according to claim 1, characterized in that: The configuration quantity and parameter selection of the DC voltage limiting device must meet the DC voltage constraint conditions; The DC voltage constraints include: When a fault occurs in the remote power transmission system, the power consumption of the DC voltage limiting device is greater than the rated power of the system: Where P rate is the system rated power; P VLM Represents the power consumption of a single DC voltage limiting device; U SM is the capacitor voltage of the MMC submodule; r is the internal resistance of the MMC submodule; m is the number of DC voltage limiting devices put into use; When the DC voltage limiting device is put into operation, the energy absorbed by the DC voltage limiting device is equal to the energy transmitted by the system: Where D is the duty cycle of the DC voltage limiting device; f VLM is the operating frequency of the DC voltage limiting device; k is the ratio of the system transmission power to the system rated power; When the DC voltage limiting device is removed, the energy relationship of the long-distance transmission system is: Among them C system is the system equivalent capacitance; U dc_high is the upper limit of the DC side voltage of the receiving converter station; U dc_low is the lower limit of the DC side voltage of the receiving converter station; U dc is the voltage on the DC side of the receiving converter station; Δu is the fluctuation range of the voltage on the DC side of the receiving converter station; At the same time, the operating frequency of the DC voltage limiting device must meet the following requirements: where f VLM_max It is the maximum operating frequency of the DC voltage limiting device.

8. The method for controlling a fault ride-through of a remote power transmission system according to claim 7, characterized in that: The configuration quantity and parameter selection of the DC voltage limiting device must meet the energy absorption limit of the energy dissipation resistor and the voltage fluctuation range of the capacitor; When the DC voltage limiting device is in action, the energy absorbed by each DC voltage limiting device cannot exceed the upper limit of the resistance allowed to absorb: Where E VLM Absorbs energy for a single DC voltage limiting device; P rate is the system rated power; T VLM_MMC is the operating time of the DC voltage limiting device from action to exit; m is the number of DC voltage limiting devices put into operation; E allow The energy allowed to be absorbed by each resistor in the DC voltage limiting device; The maximum voltage relationship between the capacitor voltage of the MMC submodule configured with a DC voltage limiting device and the MMC submodule not configured with a DC voltage limiting device must meet the following requirements: Where Δu SM1 The maximum voltage drop of the capacitor voltage of the MMC submodule equipped with the DC voltage limiting device; Δu SM2 ΔU is the maximum voltage rise of the capacitor voltage of the MMC submodule that is not equipped with a DC voltage limiting device; SM The voltage fluctuation range of the MMC submodule capacitor specified by the system; U SM is the capacitor voltage of the MMC submodule; U dc_high is the upper limit of the DC side voltage of the receiving converter station; U dc_low is the lower limit of the DC side voltage of the receiving converter station; C SM is the capacitance of the MMC submodule; i r is the current flowing through the resistor in the DC voltage limiting device, i bridge is the bridge arm current; n is the total number of MMC submodules; D is the duty cycle of the DC voltage limiting device; r is the internal resistance of the MMC submodule; f VLM is the operating frequency of the DC voltage limiting device.

9. The method for controlling a fault ride-through of a remote power transmission system according to claim 1, characterized in that: The selection of the AC energy consuming device must satisfy the group quantity constraint, wherein the group quantity constraint includes: When the system fails and performs ride-through control, the maximum power absorbed by the AC energy consumption device is equal to the rated power of the system: When the power consumption of the AC energy consumption device is greater than the system transmission power, and the maximum power difference between the power consumption of the AC energy consumption device and the system transmission power is equal to the power consumption of a single branch of the AC energy consumption device, the power difference between the power consumption of the AC energy consumption device and the system transmission power discharges the system capacitor in a single action cycle, and the resulting voltage change is: Where P ACC P is the power consumed by the AC energy consumption device; ACC_single U is the power consumed by a single branch of the AC energy-consuming device; ac_k is the secondary voltage of the AC transformer; T ac is the period of the AC voltage; Δu ACC It is the maximum DC voltage change caused by the unbalanced power consumption of the AC energy consumption device; U rate is the system rated voltage; C system is the system equivalent capacitance; P rate is the rated power of the system; R is the resistance of the AC energy consuming device; a is the number of groups of the AC energy consuming device.

10. The method for controlling a fault ride-through of a remote power transmission system according to claim 9, characterized in that: The AC energy consumption device must meet the voltage level constraint when it is selected, wherein the voltage level constraint includes: The voltage level of the AC energy consumption device is related to the transformation ratio of the AC transformer. When the voltage level of the AC energy consumption device is higher, more thyristors need to be connected in series; when the voltage level of the AC energy consumption device is lower, more thyristors need to be connected in parallel. When the transformation ratio of the AC transformer is determined, the total number of thyristors required is expressed as: Number T is the total number of thyristors required; a is the number of groups of AC energy consuming devices; U ac_k is the secondary voltage of the AC transformer; U ac is the AC side voltage of the receiving converter station; k is the ratio of the system transmission power to the system rated power; U T is the operating voltage of the thyristor; The current flowing through the thyristor is expressed as: Among them I T is the thyristor operating current; P ACC_single It is the power absorption of a single branch of an AC energy consuming device.

Images