A coordinated control method for commutation failure and overvoltage in wind power DC transmission system

Abstract

The present invention discloses a method for coordinated control of commutation failure and overvoltage of a wind power direct current transmission system, comprising the following steps: when the AC bus voltage of the inverter station of the direct current transmission system drops, starting direct current control; calculating the direct current to avoid high voltage crossing of wind turbines near the rectifier station according to the direct voltage of the inverter station after the fault and the trigger angle of the rectifier station; evaluating the allowable reactive exchange range of the inverter station under direct current constraints and shutdown angle constraints according to the AC bus voltage of the inverter station; and then determining the direct current control strategy of the inverter station according to the reactive exchange range, obtaining the direct current control reference value of the inverter station, and controlling the direct current of the inverter station. The present invention adaptively adjusts the direct current control reference value of the inverter station, effectively avoiding subsequent commutation failure of the inverter station and overvoltage of the rectifier station, while taking into account the influence of active and reactive power of the direct current transmission system on the stability of the power grid at the sending and receiving ends.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection and control, and in particular to a method for coordinated control of commutation failure and overvoltage in a wind power direct current transmission system. Background Art

[0002] Driven by the global energy crisis and environmental issues, new energy represented by wind power has developed rapidly around the world in recent years, and the proportion of wind power in the power grid has become increasingly higher. At the same time, the current source type high-voltage direct current transmission technology based on grid phase switching has been widely used in new energy transmission due to its advantages of low loss, large capacity, long distance, and flexible power regulation. A new grid structure in which wind farms are transmitted via high-voltage direct current transmission is gradually emerging.

[0003] The commutation failure of HVDC transmission is currently a focus of attention in the industry. Voltage fluctuations caused by faults in the receiving AC system can easily lead to the first commutation failure of HVDC transmission. If the first commutation failure is not properly controlled, it can also easily lead to subsequent commutation failures, resulting in continuous commutation failures, repeated power shocks to the AC system, and may cause the converter station to lock and threaten the safe and stable operation of the power grid. In addition, during the first commutation failure, the reactive power consumption of the rectifier station fluctuates greatly with the change of DC transmission power, resulting in overvoltage in the AC bus voltage of the HVDC transmission rectifier station. The voltage increase of the rectifier station causes a significant increase in the voltage at the access point of the wind farm near the HVDC transmission point through electromagnetic coupling, which may cause the wind turbine in the sending-end power grid to start up at high voltage, causing the wind turbine to fail temporarily or go offline, resulting in a cross-regional chain reaction.

[0004] At present, the existing methods mainly suppress subsequent commutation failures by adding additional reactive compensation devices, converter topology transformation and HVDC transmission control system optimization. The first two methods increase the complexity of the control system and investment costs, and there are still difficulties in engineering application. The third method mainly focuses on improving commutation failure prevention control (CFPREV) and low-voltage current limiting control (VDCOL). However, due to the large number of factors affecting commutation failure, it is difficult to accurately calculate the starting voltage and trigger angle adjustment, and the effect of commutation failure prevention control is limited. Existing methods propose to use additional virtual resistors and increase the starting voltage of low-voltage current limiting control to suppress subsequent commutation failures. Another method proposes a subsequent commutation failure suppression method based on real-time reactive demand to determine the DC current command value. However, the reactive consumption of the HVDC transmission rectifier station and inverter station is affected by the DC current. The existing methods only focus on the recovery of commutation failure in the inverter station, and lack consideration of overvoltage in the rectifier station.

[0005] At present, the main method to avoid the high-voltage disconnection of wind turbines in the sending-end power grid caused by commutation failure is to improve the fault ride-through strategy of wind turbines and install reactive compensation devices. However, since the voltage rise cannot be avoided, the fault ride-through strategy of wind turbines is difficult to fundamentally solve the problem. Reactive compensation devices can suppress overvoltage, but there are problems such as high cost and difficulty in coordination. The most direct measure to avoid the high-voltage disconnection of wind turbines in the sending-end power grid is to adjust the DC current of high-voltage direct current transmission to balance the reactive power of the rectifier station. The existing method proposes to improve the low-voltage current limiting control and constant reactive power control to suppress the overvoltage of the rectifier station. However, the DC current, DC voltage and trigger angle of the rectifier station and the inverter station of high-voltage direct current transmission affect each other. The regulation of reactive power or DC current not only affects the overvoltage of the rectifier station, but also changes the recovery characteristics of the commutation failure of the inverter station. The existing method ignores the impact of overvoltage control on the inverter station, which not only limits the overvoltage control effect, but also may promote the occurrence of subsequent commutation failure.

[0006] Therefore, how to comprehensively consider the chain reaction of commutation failure caused by grid faults in the wind farm and inverter station at the sending end of the wind power DC transmission system, effectively suppress the overvoltage at the sending end and the subsequent commutation failure of the inverter station, and achieve the coordination of the reactive exchange amount of the rectifier station, the active power of the inverter station and the reactive exchange amount has become an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0007] In view of the deficiencies of the above-mentioned prior art, the problem that the present invention actually needs to solve is: how to comprehensively consider the mutual influence of the electrical quantities at the sending and receiving ends of the wind power DC transmission system, and control the DC current of the DC transmission system, so as to more effectively suppress the overvoltage of the rectifier station and the subsequent commutation failure of the inverter station, and achieve the coordination of the reactive exchange amount of the rectifier station, the active power of the inverter station and the reactive exchange amount.

[0008] In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

[0009] A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system is provided. When a voltage drop of the AC busbar of an inverter station of the DC transmission system is detected, control is started, and the method comprises the following steps:

[0010] S101, collecting the DC voltage of the inverter station of the DC transmission system and the trigger angle of the rectifier station, and calculating the DC current to avoid high voltage ride-through of the wind farm near the rectifier station;

[0011] S102, collecting the AC bus voltage of the inverter station of the DC transmission system, and calculating the allowable reactive exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint;

[0012] S103, determining a DC current control strategy of the inverter station according to an allowable reactive exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint;

[0013] S104. According to the determined inverter station DC current control strategy, a DC current control reference value of the inverter station is calculated, and the DC current control reference value is set as a DC current command value of the inverter station of the DC power transmission system to implement control.

[0014] In the above-mentioned method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, as a preferred solution, in step S101, the DC current for avoiding high voltage ride-through of a wind farm near a rectifier station is determined by the following method:

[0015]

[0016] Where, k1 is the ratio of the converter transformer in the rectifier station; N1 is the number of 6-pulse converters per pole in the rectifier station; α rec is the trigger angle of the rectifier station; U acrN is the rated value of the AC bus voltage on the grid side of the rectifier station; U pcc,max is the threshold value of high voltage ride through of wind turbine; X r1 is the equivalent commutation reactance of the rectifier station; U di is the DC voltage of the inverter station; R d is the equivalent resistance of the DC transmission line.

[0017] Among them, the rectifier station trigger angle α rec It can be expressed as:

[0018]

[0019] In the formula, K p and T i I is the proportional coefficient and integral time constant of the rectifier station current control; d-ord ,I d-rec are the command value and measured value of the DC current of the rectifier station respectively, and π is the pi.

[0020] In the above-mentioned method for coordinated control of commutation failure and overvoltage of a wind power DC transmission system, as a preferred solution, in step S102, the reactive power exchange amount of the inverter station is the reactive power exchange amount between the inverter station and the AC power grid at the receiving end of the DC transmission system, with the transmission from the DC transmission system to the AC system as the positive direction of power, and the allowable reactive power exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint is calculated according to the following method:

[0021] Q aci,min ≤Q aci ≤Q aci,max ;

[0022] In the formula, Q aci,min and Q aci,maxare the minimum reactive exchange amount and the maximum reactive power that meet the DC current constraint and the shutdown angle constraint under the AC bus voltage of any inverter station, respectively, and are determined by the following formula:

[0023]

[0024] In the formula, Q ci is the reactive power provided by the reactive power compensation device of the inverter station; k2 is the ratio of the inverter transformer; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; γ lim To avoid the critical turn-off angle of commutation failure; N2 is the number of 6-pulse converters per pole in the inverter station; U aci is the effective value of the AC bus line voltage of the inverter station; I d,v To avoid the DC current of high voltage ride-through of wind turbines near the rectifier station; I d,c To avoid DC current in subsequent commutation failure of the inverter station.

[0025] In the above-mentioned method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, as a preferred solution, the DC current for avoiding subsequent commutation failure of the inverter station is calculated as follows:

[0026]

[0027] Where, φ is the forward shift angle of the commutation voltage zero crossing point under asymmetric fault, μ i is the commutation angle of the inverter station.

[0028] In the above-mentioned method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, as a preferred solution, in step S103, the DC current control strategy of the inverter station is determined as follows:

[0029] Compare the maximum value Q of reactive exchange that satisfies DC current constraint and cut-off angle constraint aci,max and 0; if Q aci,max ≥0, adopt the control strategy of maximizing active power; if Q aci,max <0, adopt the control strategy of maximizing reactive exchange amount.

[0030] In the above-mentioned method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, as a preferred solution, in step S104, when the active power maximization control strategy is adopted, the DC current control reference value of the inverter station is set to avoid the DC current I when the reactive exchange amount is 0 under the conditions of commutation failure and rectifier station overvoltage. d,r , I d,r Calculated as follows:

[0031]

[0032] In the formula, parameters A, B, C and D are calculated as follows:

[0033]

[0034]

[0035]

[0036]

[0037] Among them, the coefficients m, n, p, and q are calculated as follows:

[0038]

[0039]

[0040]

[0041]

[0042] Where, k2 is the transformer ratio of the inverter station; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; N2 is the number of 6-pulse converters per pole in the inverter station; U aci It is the effective value of the AC bus line voltage of the inverter station.

[0043] In the above-mentioned method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, as a preferred solution, in step S104, when the control strategy of maximizing reactive exchange is adopted, the DC current control reference value of the inverter station is the DC current I that avoids high voltage ride-through of the wind turbine generator set near the rectifier station. d,v .

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The existing technology focuses on the suppression of subsequent commutation failure of the inverter station or only considers the single control target of overvoltage suppression of the rectifier station. The DC transmission system coordinated control method of the present invention calculates the DC current to avoid high voltage ride-through of wind turbines near the rectifier station and the DC current to avoid subsequent commutation failure of the inverter station. It can adaptively adjust the DC current of the inverter station according to the allowable reactive exchange range of the inverter station under the DC current constraint and the shutdown angle constraint, and suppress the overvoltage of the rectifier station while avoiding the subsequent commutation failure of the inverter station.

[0046] 2. Different from the prior art which only considers the operation requirements of the DC transmission system, the present invention can adjust the DC current control reference value of the inverter station according to the power range of the inverter station, thereby avoiding subsequent commutation failure of the inverter station and overvoltage of the rectifier station, and taking into account the influence of the active and reactive power of the DC transmission system on the stability of the power grids at the sending and receiving ends.

[0047] 3. Different from the prior art that determines the DC current control reference value based on reactive power, the present invention can characterize the allowable reactive exchange range of the inverter station that meets the DC current and shutdown angle constraints under the influence of multiple electrical quantities. It can coordinate the reactive exchange amount of the rectifier station, the active power of the inverter station and the reactive exchange amount of the inverter station based on the reactive exchange amount range under different degrees of AC bus voltage drop of the inverter station and the recovery requirements of the inverter station while avoiding subsequent commutation failure of the inverter station and overvoltage of the rectifier station. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0049] Figure 1 The present invention is a flow chart of a method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system.

[0050] Figure 2 It is a schematic diagram of a commutation failure and overvoltage coordinated control device for a wind power DC transmission system according to the present invention.

[0051] Figure 3 Schematic diagram of the structure of a high-voltage direct current transmission system used as an example in an embodiment of the present invention.

[0052] Figure 4 3 is a waveform diagram of the inverter station shutdown angle under different fault types in the embodiment.

[0053] Figure 5 1 is a waveform diagram of the effective value of the AC bus voltage of the rectifier station under different fault types in the embodiment.

[0054] Figure 6 1 is a waveform diagram of the effective value of the AC bus voltage of the inverter station under different fault types in the embodiment.

[0055] Figure 7 3 is a waveform diagram of the inverter station shutdown angle under different fault degrees in the embodiment.

[0056] Figure 8 1 is a waveform diagram of the effective value of the AC bus voltage of the rectifier station under different fault degrees in the embodiment.

[0057] Fig. 9 1 is a waveform diagram of the effective value of the AC bus voltage of the inverter station under different fault degrees in the embodiment. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] like Figure 1 As shown, the present invention discloses a method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system. The idea of ​​the method is to start the following control steps when the AC bus voltage of the inverter station of the DC transmission system drops:

[0060] S101, collecting the DC voltage of the inverter station of the DC transmission system and the trigger angle of the rectifier station, and calculating the DC current to avoid high voltage ride-through of the wind farm near the rectifier station;

[0061] S102, collecting the AC bus voltage of the inverter station of the DC transmission system, and calculating the allowable reactive exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint;

[0062] S103, determining a DC current control strategy of the inverter station according to an allowable reactive exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint;

[0063] S104. According to the determined inverter station DC current control strategy, a DC current control reference value of the inverter station is calculated, and the DC current control reference value is set as a DC current command value of the inverter station of the DC power transmission system to implement control.

[0064] The present invention starts DC current control when it detects that the AC bus voltage of the inverter station of the DC transmission system drops; calculates the DC current to avoid high voltage crossing of the wind turbines near the rectifier station according to the DC voltage of the inverter station after the fault and the trigger angle of the rectifier station; evaluates the allowable reactive power exchange range of the inverter station under the DC current constraint and the shutdown angle constraint according to the AC bus voltage of the inverter station; and then determines the DC current control strategy of the inverter station according to the reactive power exchange range, determines the DC current control reference value of the inverter station, and controls the DC current of the inverter station. The present invention can adaptively adjust the DC current control reference value of the inverter station according to the recovery requirements and power range of the inverter station under different fault severity, effectively avoiding overvoltage and subsequent commutation failure at the sending end of the wind power DC transmission system caused by commutation failure, while taking into account the influence of active and reactive power on the stability of the power grid at the sending and receiving ends.

[0065] In specific implementation, in step S101, the DC current for avoiding high voltage ride-through of the wind farm near the rectifier station is determined by the following method:

[0066]

[0067] Where, k1 is the ratio of the converter transformer in the rectifier station; N1 is the number of 6-pulse converters per pole in the rectifier station; α rec is the trigger angle of the rectifier station; U acrN is the rated value of the AC bus voltage on the grid side of the rectifier station; U pcc,max is the threshold value of high voltage ride through of wind turbine; X r1 is the equivalent commutation reactance of the rectifier station; U di is the DC voltage of the inverter station; R d is the equivalent resistance of the DC transmission line.

[0068] Among them, the rectifier station trigger angle α rec It can be expressed as:

[0069]

[0070] In the formula, K p and T i I is the proportional coefficient and integral time constant of the rectifier station current control; d-ord ,I d-rec are the command value and measured value of the DC current of the rectifier station respectively, and π is the pi.

[0071] In specific implementation, in step S102, the reactive power exchange amount of the inverter station is the reactive power exchange amount between the inverter station and the AC power grid at the receiving end of the DC power transmission system, with the DC power transmission system to the AC system as the positive power direction, and the allowable reactive power exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint is calculated according to the following method:

[0072] Q aci,min ≤Q aci ≤Q aci,max

[0073] In the formula, Q aci is the reactive exchange amount of the inverter station, which is calculated as follows:

[0074]

[0075] In the formula, Q ci is the reactive power provided by the reactive power compensation device of the inverter station; k2 is the ratio of the inverter transformer; X r2 is the equivalent commutation reactance of the inverter station; γ is the turn-off angle of the inverter station; N2 is the number of 6-pulse converters per pole of the inverter station; U aci is the effective value of the AC bus line voltage of the inverter station; I d is the DC current of the inverter station.

[0076] In the formula, Q aci,minand Q aci,max are the minimum reactive exchange amount and the maximum reactive power that meet the DC current constraint and the shutdown angle constraint under the AC bus voltage of any inverter station, respectively, and are determined by the following formula:

[0077]

[0078] In the formula, Q ci is the reactive power provided by the reactive power compensation device of the inverter station; k2 is the ratio of the inverter transformer; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; γ lim To avoid the critical turn-off angle of commutation failure; N2 is the number of 6-pulse converters per pole in the inverter station; U aci is the effective value of the AC bus line voltage of the inverter station; I d,v To avoid the DC current of high voltage ride-through of wind turbines near the rectifier station; I d,c To avoid DC current in subsequent commutation failure of the inverter station.

[0079] In specific implementation, the DC current to avoid subsequent commutation failure of the inverter station is calculated as follows:

[0080]

[0081] Where, φ is the forward shift angle of the commutation voltage zero crossing point under asymmetric fault, μ i is the commutation angle of the inverter station.

[0082] In specific implementation, in step S103, the DC current control strategy of the inverter station is determined as follows:

[0083] Compare the maximum value Q of reactive exchange that satisfies DC current constraint and cut-off angle constraint aci,max and 0; if Q aci,max ≥0, adopt the control strategy of maximizing active power; if Q aci,max <0, adopt the control strategy of maximizing reactive exchange amount.

[0084] In the specific implementation, in step S104, when the active power maximization control strategy is adopted, the DC current control reference value of the inverter station is set to avoid the DC current I when the reactive exchange amount is 0 under the condition of commutation failure and overvoltage of the rectifier station. d,r , I d,r Calculated as follows:

[0085]

[0086] In the formula, parameters A, B, C and D are calculated as follows:

[0087]

[0088]

[0089]

[0090]

[0091] Among them, the coefficients m, n, p, and q are calculated as follows:

[0092]

[0093]

[0094]

[0095]

[0096] Where, k2 is the transformer ratio of the inverter station; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; N2 is the number of 6-pulse converters per pole in the inverter station; U aci It is the effective value of the AC bus line voltage of the inverter station.

[0097] In the specific implementation, in step S104, when the control strategy of maximizing reactive exchange is adopted, the DC current control reference value of the inverter station is the DC current I that avoids the high voltage ride-through of the wind turbines near the rectifier station. d,v .

[0098] To implement the above embodiment, the present application also provides a commutation failure and overvoltage coordinated control device for a wind power DC transmission system, such as Figure 2 As shown, Figure 2 1 is a schematic diagram of the structure of a commutation failure and overvoltage coordinated control device for a wind power DC transmission system according to an embodiment of the present invention. In the embodiment of the present invention, the control device is used to implement a commutation failure and overvoltage coordinated control method for a wind power DC transmission system according to the above embodiment. The coordinated control device is applied to an electronic device. The electronic device has any one or more memories and processors, and a bus connecting different components (including memories and processors). The memory stores a computer program. When the processor executes the program, the coordinated control method described in the embodiment of the present application is implemented. The processor may include multiple computing modules and control modules. The computing modules and the control modules may be configured as follows:

[0099] In an embodiment of the present invention, the collaborative control device includes a DC current control reference value calculation module, a rectifier station constant current control module, an inverter station constant current control module and a fixed shutdown angle control module.

[0100] In the rectifier station constant current control module, the collected measured value of the rectifier station DC current I d-rec The difference between the DC current control reference value is used as the input of the PI controller, and the PI controller processes the output rectifier station trigger angle α rec .

[0101] In the rectifier station constant current control module, the collected DC voltage U di The rectifier station trigger angle α output by the rectifier station constant current control module rec After processing, the DC current I that can avoid high voltage ride-through of wind turbines near the rectifier station is obtained. d,v ; Then according to the effective value of the AC bus line voltage U aci and the rated cut-off angle γ of the inverter station i , the DC current I when the reactive exchange amount is 0 under the condition of avoiding commutation failure and rectifier station overvoltage is calculated d,r ; According to the DC current I d,v The maximum value Q of the reactive exchange allowed to meet the DC current constraint and the cut-off angle constraint is calculated. aci,max ; Taking the power transmission from the DC transmission system to the AC system as the positive direction, determine the maximum value of the allowable reactive exchange amount Q that meets the DC current constraint and the shutdown angle constraint aci,max If the DC current constraint and the cut-off angle constraint are met, the maximum value of the reactive exchange Q aci,max If it is less than 0, the output is a DC current I that can avoid high voltage ride-through of wind turbines near the rectifier station. d,v As the command value of the DC current of the rectifier station I d-ord If Q aci,max If it is not less than 0, the output will avoid commutation failure and the DC current I when the reactive exchange amount is 0 under the condition of rectifier station overvoltage. d,r As the command value of the DC current of the output rectifier station I d-ord .

[0102] In the inverter station fixed current control module, the command value I of the rectifier station DC current is d-ord Subtract the measured value of the inverter station DC current I d-inv The difference between the current margin of 0.1 times the rated current is used as the input of the PI controller in the constant current control of the inverter. After being processed by the PI controller, the leading trigger angle β of the constant current control of the inverter station is output. inv-I .

[0103] In the fixed shut-off angle control module, the minimum shut-off angle value of the inverter station valve group measured from the DC power transmission system in the previous cycle is selected as the input value of the controller, and then the measured minimum shut-off angle of each valve is compared with the rated shut-off angle of the inverter station, and the PI controller is used to output the lead trigger angle of the fixed shut-off angle control of the inverter station. The maximum value of the lead trigger angle output by the constant current control and the fixed shut-off angle control is selected as the inverter station lead trigger angle instruction value, thereby controlling the shut-off angle tracking instruction value. In a preferred embodiment of the present invention, the collaborative control device can also communicate with one or more external devices (such as keyboards, pointing devices, displays, etc.), and can also communicate with one or more devices that enable users to interact with the collaborative control device, and / or communicate with any device that enables the collaborative control device to communicate with one or more other computing devices (such as network cards, modems, etc.). This communication can be performed through an input / output (I / O) interface. Furthermore, the collaborative control device may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter. It should be understood that other hardware and / or software modules may be used in conjunction with the collaborative control device, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0104] Example:

[0105] To verify the effectiveness of the method of the present invention, Figure 3 Taking the example of the high-voltage direct current transmission system wiring diagram as an example, the analysis and calculation are carried out. The rated voltage of the unipolar high-voltage direct current transmission is 500kV and the base capacity is 1000MW. The short-circuit ratios of the AC systems on the rectifier and inverter sides are 2.5∠84° and 2.5∠75°, respectively. During normal operation, the DC current is 2kA and the inverter station shutdown angle is 15.2°. The rated voltage of the rectifier station AC bus is 345kV, and the rated voltage of the inverter station AC bus is 230kV. The high voltage crossing threshold value of the wind turbine is 1.1pu. In the present invention, short-circuit faults of different fault types and different fault degrees occur at the AC bus of the inverter station, and the effect of suppressing subsequent commutation failures and overvoltage of the rectifier station, as well as the influence of changes in active and reactive power of the inverter station on the voltage of the AC system are verified.

[0106] In order to compare the inhibitory effects of the present invention and conventional low-voltage current limiting control on commutation failure and rectifier station overvoltage, as well as the influence of active and reactive power on the AC voltage at the sending and receiving ends, the following two different control methods are respectively used under the same fault condition to observe and record the waveform of the inverter station shutdown angle during the AC fault, and to record and compare the waveforms of the AC bus voltage of the inverter station and the rectifier station during the fault.

[0107] Figure 4 The waveform diagram of the inverter station shutdown angle under three-phase fault and single-phase fault, Figure 5 The waveform diagram of the effective value of the AC bus voltage of the rectifier station under three-phase fault and single-phase fault is shown in Figure 2. Figure 6 It is a waveform diagram of the effective value of the AC bus voltage of the inverter station under three-phase fault and single-phase fault; Figure 7 The waveform diagram of the inverter station shutdown angle under different fault levels is shown in Figure 2. Figure 8 The waveform diagram of the effective value of the AC bus voltage of the rectifier station under different fault degrees is shown in Figure 2. Fig. 9 The waveform diagram of the effective value of the AC bus voltage of the inverter station under different fault degrees.

[0108] Figures 4 to 9 The horizontal axis is time. Figure 4 , Figure 7 The middle vertical coordinate is the degree of the inverter station shut-off angle. Figure 5 , Figure 8 The vertical coordinate in the middle is the per unit value of the effective value of the AC bus voltage of the rectifier station. Figure 6 , Fig. 9 The vertical axis is the per unit value of the effective value of the AC bus voltage of the inverter station. The solid line is the change curve of the inverter station shutoff angle and the AC bus voltage and the rectifier station AC bus voltage under the current control method proposed in the present invention, and the dotted line is the change curve of the inverter station shutoff angle and the AC bus voltage and the rectifier station AC bus voltage under the conventional low-voltage current limiting control method.

[0109] from Figure 4 , Figure 7 It can be seen that under short-circuit faults of different fault types and fault degrees, the subsequent commutation failure of the system is effectively suppressed by the method proposed in the present invention. Figure 5 , Figure 8 It can be seen from the AC bus voltage change curve of the rectifier station that the method of the present invention effectively suppresses the overvoltage of the rectifier station. Figure 6 , Fig. 9 The curve of the AC bus voltage change of the inverter station shows that the current control method proposed by the present invention can improve the recovery characteristics of the AC bus voltage of the inverter station. The calculation example shows that the subsequent commutation failure and the overvoltage of the rectifier station can be effectively suppressed under the method of the present invention, while taking into account the influence of the active power and reactive power of the converter station on the AC system.

[0110] In summary, the present invention discloses a method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system. By calculating the DC current that avoids high voltage crossing of wind turbines near the rectifier station and commutation failure, the allowable reactive exchange range of the inverter station under the DC current constraint and the shutdown angle constraint is determined; then, according to the reactive exchange range under different AC bus voltage drops, the DC current control reference value of the inverter station is adjusted and determined, and the DC current of the inverter station is controlled. The present invention can adaptively adjust the DC current control reference value of the inverter station according to the recovery requirements and power range of the inverter station under different fault severity, and has wide applicability. While effectively avoiding overvoltage and subsequent commutation failure at the sending end of the wind power DC transmission system caused by commutation failure, the influence of active and reactive power on the stability of the power grid at the sending and receiving ends is taken into account, and damage to the inverter station equipment and failure or even disconnection of the wind turbines at the sending end are avoided.

[0111] In the description of the present invention, it is necessary to understand that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "outside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0112] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "rotation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0113] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system, characterized in that: When the AC bus voltage of the inverter station of the DC transmission system drops, the control is started, which specifically includes the following steps: S101, collecting the DC voltage of the inverter station of the DC transmission system and the trigger angle of the rectifier station, and calculating the DC current to avoid high voltage ride-through of the wind farm near the rectifier station; S102, collecting the AC bus voltage of the inverter station of the DC transmission system, and calculating the allowable range of reactive exchange of the inverter station under the constraints of DC current and shutdown angle; S103, determining a DC current control strategy of the inverter station according to the reactive exchange amount operation range of the inverter station under the DC current constraint and the shutdown angle constraint; S104. According to the determined inverter station DC current control strategy, a DC current control reference value of the inverter station is calculated, and the DC current control reference value is set as a DC current command value of the inverter station of the DC power transmission system to implement control.

2. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 1, characterized in that: In step S101, the DC current for avoiding high voltage ride through of the wind farm near the rectifier station is calculated according to the following method: Where, k1 is the ratio of the converter transformer in the rectifier station; N1 is the number of 6-pulse converters per pole in the rectifier station; α rec is the trigger angle of the rectifier station; U acrN is the rated value of the AC bus voltage on the grid side of the rectifier station; U pcc,max is the threshold value of high voltage ride through of wind turbine; X r1 is the equivalent commutation reactance of the rectifier station; U di is the DC voltage of the inverter station; R d is the equivalent resistance of the DC transmission line.

3. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 2, characterized in that: The rectifier station trigger angle α rec It is expressed as: In the formula, K p and T i I is the proportional coefficient and integral time constant of the rectifier station current control; d-ord ,I d-rec are the command value and measured value of the DC current of the rectifier station respectively, and π is the pi.

4. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 1, characterized in that: In step S102, the reactive power exchange amount of the inverter station is the reactive power exchange amount between the inverter station and the AC power grid at the receiving end of the DC power transmission system, with the DC power transmission system to the AC system as the positive power direction. The allowable reactive power exchange amount range of the inverter station under the DC current constraint and the shutdown angle constraint is calculated according to the following method: Q aci,min ≤Q aci ≤Q aci,max In the formula, Q aci is the reactive exchange amount of the inverter station, Q aci,min and Q aci,max are the minimum value of the reactive exchange and the maximum value of the reactive power allowed to meet the DC current constraint and the turn-off angle constraint, respectively, and are determined by the following formula: In the formula, Q ci is the reactive power provided by the reactive power compensation device of the inverter station; k2 is the ratio of the inverter transformer; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; γ lim To avoid the critical turn-off angle of commutation failure; N2 is the number of 6-pulse converters per pole in the inverter station; U aci is the effective value of the AC bus voltage of the inverter station; I d,v To avoid the DC current of high voltage ride-through of wind turbines near the rectifier station; I d,c To avoid the DC current from subsequent commutation failure in the inverter station.

5. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 4, characterized in that: The DC current to avoid subsequent commutation failure of the inverter station is calculated as follows: Where, φ is the forward shift angle of the commutation voltage zero crossing point under asymmetric fault, μ i is the commutation angle of the inverter station.

6. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 1, characterized in that: In step S103, the DC current control strategy of the inverter station is determined as follows: Compare the maximum value Q of the allowed reactive exchange that satisfies the DC current constraint and the cut-off angle constraint aci,max and 0; if Q aci,max ≥0, adopt the control strategy of maximizing active power; if Q aci,max <0, adopt the control strategy of maximizing reactive exchange amount.

7. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 1, characterized in that: In step S104, when the active power maximization control strategy is adopted, the DC current control reference value of the inverter station is set to avoid the DC current I when the reactive power exchange amount is 0 under the condition of commutation failure and overvoltage of the rectifier station. d,r , I d,r Calculated as follows: In the formula, parameters A, B, C and D are calculated as follows: Among them, the coefficients m, n, p, and q are calculated as follows: Where, k2 is the transformer ratio of the inverter station; X r2 is the equivalent commutation reactance of the inverter station; γ i is the rated cut-off angle of the inverter station; N2 is the number of 6-pulse converters per pole in the inverter station; U aci It is the effective value of the AC bus line voltage of the inverter station.

8. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 1, characterized in that: In step S104, when the reactive exchange capacity maximization control strategy is adopted, the DC current control reference value of the inverter station is the DC current I that avoids high voltage ride-through of the wind turbines near the rectifier station. d,v .

9. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to any one of claims 1 to 8, characterized in that: The coordinated control method is implemented by a wind power direct current transmission system commutation failure and overvoltage coordinated control device, and the coordinated control device is applied in electronic equipment.

10. A method for coordinated control of commutation failure and overvoltage in a wind power DC transmission system according to claim 9, characterized in that: The collaborative control device includes a DC current control reference value calculation module, a rectifier station constant current control module, an inverter station constant current control module and a fixed shutdown angle control module.

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