Flexible direct current power transmission system control method, device and equipment and readable storage medium

Abstract

The application provides a flexible direct current power transmission system control method, device, equipment and readable storage medium. The application can set the control target of the flexible direct current power transmission system as a converter transformer valve side voltage reference value, can adjust the converter bus voltage through the converter transformer valve side voltage reference value, can ensure the converter bus voltage constant, can calculate the current value flowing through the converter valve, and can perform over-limit judgment on the current of the converter valve. If the current of the converter valve is over-limited, the amplitude of the converter transformer valve side voltage can be reduced until the current of the converter valve is not over-limited, which is beneficial to protecting the converter valve, improving the service life of the converter valve, and effectively controlling the flexible direct current power transmission system of new energy power generation.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to a control method, apparatus, equipment and readable storage medium for a flexible DC power transmission system. Background Technology

[0002] One of the key advantages of flexible DC transmission technology is that it can achieve passive inversion and establish a stable voltage for the grid connection system. Flexible DC transmission technology includes two important application scenarios: one is to supply power to passive networks, such as supplying power to urban centers or islands through flexible DC transmission systems; the other is to send the voltage from power electronics such as wind power and photovoltaics to the grid through flexible DC transmission systems.

[0003] In scenarios where renewable energy is transmitted via flexible DC transmission systems, existing control methods for new flexible DC transmission systems generally employ the same control strategy as traditional flexible DC transmission systems connected to active networks, namely direct current control. The only difference is that the outer loop control target is changed from variables such as active power, reactive power, DC voltage, and AC voltage to the d-axis and q-axis components of the converter bus voltage. However, existing control strategies only limit the current output by the flexible DC transmission system in the outer loop controller. The inner loop controller obtains the valve-side voltage by controlling the deviation between the reference and actual values ​​of the d-axis and q-axis components of the output current. While this effectively limits the current in steady-state conditions, in transient conditions, the valve-side voltage obtained by the inner loop PI controller cannot guarantee that the current will not exceed the limit at any given time, potentially leading to current overshoot. Therefore, existing control strategies for flexible DC transmission systems are not suitable for control schemes of flexible DC transmission systems transmitting renewable energy. Summary of the Invention

[0004] This application aims to at least solve one of the aforementioned technical defects. In view of this, this application provides a control method, apparatus, device and readable storage medium for a flexible DC transmission system, which solves the technical defect that the existing control strategies of flexible DC transmission systems are not applicable to the control schemes of flexible DC transmission systems that transmit power from new energy sources.

[0005] A control method for a flexible DC transmission system includes:

[0006] Determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system;

[0007] The target voltage reference value of the converter bus is determined based on the deviation between the reference value of the converter bus voltage and the actual value of the converter bus voltage.

[0008] Based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, calculate the current of the converter valve of the target flexible DC transmission system;

[0009] Based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold, the final reference value of the voltage on the valve side of the converter transformer is determined, wherein the current of the converter valve of the target flexible DC transmission system does not exceed the preset threshold.

[0010] Preferably, the method further includes:

[0011] The corresponding final reference value of the voltage phase angle on the valve side of the converter transformer is determined based on the final reference value of the voltage on the valve side of the converter transformer.

[0012] The converter of the target flexible DC transmission system is controlled based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

[0013] Preferably, the calculation formula for the current of the converter valve of the target flexible DC transmission system is calculated based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, including:

[0014]

[0015] in,

[0016] I represents the first current phasor of the converter valve of the target flexible DC transmission system;

[0017] U ref This indicates the target voltage reference value on the valve side of the converter transformer;

[0018] θ U This indicates that the phase angle reference value of the valve-side voltage of the converter transformer is a constant value;

[0019] U s This represents the actual value of the converter bus voltage amplitude;

[0020] This represents the actual value of the phase angle of the converter bus voltage;

[0021] Z represents the amplitude of the converter transformer impedance;

[0022] θ Z This indicates the impedance angle of the converter transformer.

[0023] Preferably, determining the final reference value of the voltage on the converter transformer valve side based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold includes:

[0024] Determine whether the current of the converter valve exceeds the preset threshold.

[0025] If the current of the converter valve exceeds the preset threshold, the target voltage reference value of the converter transformer valve side is adjusted to obtain the final voltage reference value of the converter transformer valve side.

[0026] If the current of the converter valve does not exceed the preset threshold, the target voltage reference value on the valve side of the converter transformer is used as the final voltage reference value on the valve side of the converter transformer.

[0027] Preferably, adjusting the target voltage reference value on the valve side of the converter transformer to obtain the final voltage reference value on the valve side of the converter transformer includes:

[0028] According to the preset adjustment step size, the target voltage reference value on the valve side of the converter transformer is reduced to obtain the second voltage reference value on the valve side of the converter transformer;

[0029] The second voltage reference value on the converter transformer valve side is used as the target voltage reference value on the converter transformer valve side, and the operation of calculating the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the converter transformer valve side and the actual value of the converter bus voltage is returned to be executed until the final voltage reference value on the converter transformer valve side that meets the conditions is obtained.

[0030] Preferably, the preset adjustment step size ranges from [0, 0.01r], where r is the rated value corresponding to the voltage on the valve side of the converter transformer.

[0031] A flexible DC transmission system control device, comprising:

[0032] The first determining unit is used to determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system;

[0033] The second determining unit is used to determine the target voltage reference value of the converter transformer valve side based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value.

[0034] The third determining unit is used to calculate the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus.

[0035] The fourth determining unit is used to determine the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold, wherein the current of the converter valve of the target flexible DC transmission system does not exceed the preset threshold.

[0036] Preferably, the device further includes:

[0037] The fifth determining unit is used to determine the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer based on the final reference value of the voltage on the valve side of the converter transformer.

[0038] The sixth determining unit is used to control the converter of the target flexible DC transmission system based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

[0039] A flexible DC transmission system control device includes: one or more processors, and a memory;

[0040] The memory stores computer-readable instructions, which, when executed by the one or more processors, implement the steps of the flexible DC transmission system control method as described above.

[0041] A readable storage medium storing computer-readable instructions, which, when executed by one or more processors, cause the one or more processors to perform the steps of the flexible DC transmission system control method as described above.

[0042] As can be seen from the technical solutions described above, in practical applications, when new energy is transmitted via a flexible DC transmission system, the control objective of the flexible DC transmission system is to maintain the voltage and frequency of the converter bus at target values ​​to ensure that the new energy power generation system can operate normally and output power. When it is necessary to conduct modeling and simulation studies on large-scale new energy transmission via a flexible DC transmission system, the method provided in this application embodiment can determine the control objective of the target flexible DC transmission system. The control objective includes the valve-side voltage reference value of the converter transformer in the target flexible DC transmission system. By setting the control objective of the flexible DC transmission system as the valve-side voltage reference value, the converter bus voltage can be adjusted according to the valve-side voltage reference value, ensuring that the converter bus voltage remains constant. After determining the control target of the target flexible DC transmission system, the target voltage reference value of the converter transformer valve side can be determined based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value. After determining the target voltage reference value of the converter transformer valve side, the current of the converter valve of the target flexible DC transmission system can be calculated based on the target voltage reference value of the converter transformer valve side and the actual converter bus voltage value. After determining the current of the converter valve of the target flexible DC transmission system, the final reference voltage value of the converter transformer valve side can be determined based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold.

[0043] The method provided in this application embodiment can set the control target of the flexible DC transmission system as the reference value of the converter transformer valve side voltage. The converter bus voltage can be adjusted by adjusting the reference value of the converter transformer valve side voltage, and the converter bus voltage can be kept constant. At the same time, the current value flowing through the converter valve can be calculated, and the current of the converter valve can be judged to exceed the limit. If the current of the converter valve exceeds the limit, the amplitude of the converter transformer valve side voltage can be reduced until the current of the converter valve does not exceed the limit. This is beneficial to protect the converter valve, improve the service life of the converter valve, and can also effectively control the flexible DC transmission system for new energy power generation. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A flowchart illustrating a control method for a flexible DC transmission system provided in this application embodiment;

[0046] Figure 2A schematic diagram illustrating a flexible DC transmission system supplying power to a passive system, provided as an embodiment of this application;

[0047] Figure 3 This is a control block diagram of the outer loop controller of a flexible DC transmission system, as exemplified by an embodiment of this application.

[0048] Figure 4 This is a control block diagram of an inner loop controller for a flexible DC transmission system, as exemplified by an embodiment of this application.

[0049] Figure 5 This is a schematic diagram illustrating the Vf control principle of a flexible DC transmission system as exemplified by an embodiment of this application.

[0050] Figure 6 This is a schematic diagram illustrating the structure of a flexible DC transmission system control device, as exemplified in an embodiment of this application.

[0051] Figure 7 This is a hardware structure block diagram of a flexible DC transmission system control device disclosed in an embodiment of this application. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] One of the key advantages of flexible DC transmission technology is that it can achieve passive inversion and establish a stable voltage for the grid connection system. Flexible DC transmission technology includes two important application scenarios: one is to supply power to passive networks, such as supplying power to urban centers or islands through flexible DC transmission systems; the other is to send the voltage from power electronics such as wind power and photovoltaics to the grid through flexible DC transmission systems.

[0054] In practical applications, for scenarios where new energy is transmitted via flexible DC transmission systems, the control methods of existing flexible DC transmission systems generally adopt the same control strategy as those of traditional flexible DC transmission systems connected to active networks, namely, direct current control. The only difference is that the control targets of the outer loop are changed from variables such as active power, reactive power, DC voltage, and AC voltage to the d-axis and q-axis components of the converter bus voltage.

[0055] However, existing control strategies only limit the current output by the flexible DC transmission system through the outer loop controller. The inner loop controller obtains the valve-side voltage by controlling the deviation between the reference values ​​and the actual values ​​of the d-axis and q-axis components of the current output by the flexible DC transmission system. Under steady-state conditions, this can effectively limit the current. However, under transient conditions, the valve-side voltage obtained by the inner loop PI controller cannot guarantee that the current will not exceed the limit at any time, and there may be a risk of current exceeding the limit. The existing control strategies for flexible DC transmission systems are not applicable to control schemes for flexible DC transmission systems that transmit power from renewable energy sources.

[0056] Furthermore, the control principle of such a control scheme is unclear. The converter bus voltage is jointly determined by the flexible DC transmission system and the connected system. When the actual value of the d-axis component of the converter bus voltage is less than the d-axis component of the converter transformer valve side voltage, the controller will increase the d-axis component of the output current of the flexible DC transmission system. However, whether increasing the d-axis component of the output current of the flexible DC transmission system will necessarily increase the actual value of the d-axis component of the converter bus voltage may have different results in different power grid systems under different operating conditions.

[0057] Given that most current control schemes for flexible DC transmission systems are ill-suited to the complex and ever-changing operational demands, this applicant has developed a control scheme for flexible DC transmission systems. This scheme allows the flexible DC transmission system to be connected to an AC system. It can calculate the valve-side voltage reference value of the converter transformer using the target voltage value of the converter bus and the reference values ​​of the d-axis and q-axis currents, maximizing the maintenance of the converter bus voltage at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems. Simultaneously, it can calculate the converter output current based on the reference value of the valve-side voltage of the converter transformer and the actual value of the converter bus voltage, and perform limit judgment and handling for the converter output current, ensuring that the converter switching devices do not experience overcurrent, thus improving equipment safety and the stability of the flexible DC transmission system control.

[0058] The methods provided in this application can be used in a variety of general-purpose or special-purpose computing device environments or configurations. For example: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor devices, distributed computing environments including any of the above devices, etc.

[0059] This application provides a control method for a flexible DC transmission system. This method can be applied to various simulation systems, as well as to various computer terminals or smart terminals. The executing entity can be the processor or server of the computer terminal or smart terminal.

[0060] The following is combined Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 The following is a flowchart of the control method for a flexible DC transmission system according to an embodiment of this application. Figure 1 As shown, the process may include the following steps:

[0061] Step S101: Determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system.

[0062] Specifically, in practical applications, flexible DC transmission systems can supply power to passive systems.

[0063] Figure 2 A schematic diagram illustrating a flexible DC transmission system supplying power to a passive system is provided.

[0064] like Figure 2 As shown:

[0065] AC1 is an active network;

[0066] AC2 is a passive system;

[0067] The flexible DC transmission system can obtain power from AC1 to supply power to AC2.

[0068] exist Figure 2 In the right-side flexible DC transmission system:

[0069] The left node of R2+L2 is the valve side, and the right node is the mesh side;

[0070] Z s1 It can represent the equivalent impedance of an active network;

[0071] R1 can represent the resistance of the converter transformer on the active side of the flexible DC transmission system;

[0072] L1 can represent the inductance of the converter transformer on the active side of a flexible DC transmission system;

[0073] I s1 It can represent the alternating current on the active side of a flexible DC transmission system;

[0074] P s1 It can represent the active power flowing through the active-side converter bus of a flexible DC transmission system;

[0075] Q s1 This can represent the reactive power flowing through the active-side converter bus of a flexible DC transmission system;

[0076] U s1 It can represent the voltage flowing through the active-side converter bus of a flexible DC transmission system;

[0077] P c1 It can represent the active power of the valve-side node of the active-side converter transformer in a flexible DC transmission system;

[0078] Q c1 It can represent the reactive power of the valve-side node of the active-side converter transformer in a flexible DC transmission system;

[0079] U c1 It can represent the voltage at the valve-side node of the active-side converter transformer in a flexible DC transmission system;

[0080] U dc1 It can represent the DC voltage on the active side of a flexible DC transmission system;

[0081] I d It can represent the DC current on the active side of a flexible DC transmission system;

[0082] R d It can represent the resistance of the DC line in a flexible DC transmission system;

[0083] L dc It can represent the inductance of the DC line in a flexible DC transmission system;

[0084] In this context, the symbol meaning of the passive side of the flexible DC transmission system is the same as that of the active side.

[0085] Flexible DC transmission systems can generally employ direct current control and may include an outer loop controller and an inner loop controller.

[0086] When a flexible DC transmission system is connected to an active network, the control targets of the outer loop controller can be active power, DC voltage, reactive power, AC voltage, etc., from which the d-axis and q-axis current reference values ​​of the flexible DC transmission system can be obtained. The inner loop controller can control the valve-side voltage of the converter transformer based on the difference between the d-axis and q-axis current reference values ​​and the actual values.

[0087] Among them, the control frame of the outer loop controller of the flexible DC transmission system Figure 1 Prajna Figure 3 As shown.

[0088] like Figure 3 As shown:

[0089] P s It can represent the actual value of active power at the converter bus;

[0090] P srefIt can represent the reference value of active power at the converter bus;

[0091] Q s It can represent the actual value of reactive power at the converter bus;

[0092] Q sref It can represent the reference value of reactive power at the converter bus;

[0093] U dc It can represent the actual value of the converter's DC voltage;

[0094] U dcref It can represent the reference value of the converter's DC voltage;

[0095] U ac It can represent the actual value of the converter's DC voltage;

[0096] U acref It can represent the reference value of the converter's DC voltage;

[0097] I sdref and I sqref These can represent the reference values ​​for the d-axis component and the q-axis component of the control current, respectively.

[0098] K and T can represent the control parameters of a PI controller.

[0099] U sd It can represent the d-axis component of the grid-side voltage of the converter transformer;

[0100] U sq It can represent the q-axis component of the grid-side voltage of the converter transformer;

[0101] U d It can represent the d-axis component of the valve-side voltage of the converter transformer;

[0102] U q It can represent the q-axis component of the valve-side voltage of a converter transformer.

[0103] Control frame of the inner loop controller of the flexible DC transmission system Figure 1 Prajna Figure 4 As shown,

[0104] like Figure 4 As shown:

[0105] I sd and I sdref The actual and reference values ​​of the d-axis component of the control current can be represented separately.

[0106] I sq and I sqref These can represent the actual and reference values ​​of the q-axis component of the control current, respectively.

[0107] U sd and U sq These can represent the actual values ​​of the d-axis and q-axis components of the converter bus voltage, respectively.

[0108] U dref and U qref It can represent the reference values ​​of the d-axis and q-axis components of the valve-side voltage of the converter transformer;

[0109] ω can represent the rated angular velocity, where,

[0110] ω = 2 * 50 * π;

[0111] L can represent the inductance of the converter transformer.

[0112] In practical applications, when a flexible DC transmission system is connected to a network without AC power, the flexible DC transmission system needs to establish a constant voltage amplitude and frequency for the connected system. Flexible DC transmission systems generally use a Vf control strategy to achieve this control objective. Here, Vf control strategy refers to a voltage-frequency conversion control strategy. Figure 5 A schematic diagram illustrating the Vf control principle of a flexible DC transmission system is provided.

[0113] I am Figure 5 middle:

[0114] U sdref This is represented as a reference value for the d-axis component of the converter bus voltage;

[0115] U sd This represents the actual value of the d-axis component of the converter bus voltage;

[0116] U sqref This represents the reference value for the q-axis component of the converter bus voltage;

[0117] U sq This represents the actual value of the q-axis component of the converter bus voltage;

[0118] I sdref Indicates the reference value of the d-axis component of the control current;

[0119] I sqref This represents the reference value for the q-axis component of the control current.

[0120] k ud T ud k uq And T uq These represent the control parameters of the PI controller.

[0121] In Vf control mode, the flexible DC transmission system has two control objectives: first, to control the frequency of the passive network to the rated frequency; and second, to control the voltage amplitude of the converter bus to remain constant. Generally, the frequency at which the flexible DC transmission system connects to a grid without AC power is a given value; therefore, the electrical angle is a fixed value, and the control system does not require a phase-locked loop (PLL).

[0122] The formula for calculating the electrical angle is:

[0123] θ=ω0t

[0124] Furthermore, since the electrical angle is given and the rotation speed of the dq coordinate system remains constant, to maintain a constant voltage and frequency, it is only necessary to control the actual value of the d-axis component of the converter bus voltage to a preset target voltage value, which means the actual value of the q-axis component of the converter bus voltage is 0, i.e.:

[0125] U sd =U m

[0126] U sq =0

[0127] in,

[0128] U m This represents a preset target voltage value. Therefore, in order to better control the target flexible DC transmission system, a control target for the target flexible DC transmission system can be determined, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system.

[0129] The control target of the flexible DC transmission system is set as the reference value of the converter transformer valve side voltage. The converter bus voltage can be adjusted by the reference value of the converter transformer valve side voltage, and the converter bus voltage can be kept constant.

[0130] Step S102: Determine the target voltage reference value of the converter transformer valve side based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value.

[0131] Specifically, as can be seen from the above description, the method provided in this application embodiment can set the control target of the flexible DC transmission system as the reference value of the valve side voltage of the converter transformer.

[0132] In practical applications, the reference value of the valve side voltage of the converter transformer is generally set based on the deviation between the reference value of the reference bus voltage and the actual value of the converter bus voltage.

[0133] Therefore, after determining the control target as the reference value of the converter transformer valve side voltage, the reference value of the converter bus voltage and the actual value of the converter bus voltage can be further obtained, and the target voltage reference value of the converter transformer valve side can be determined based on the deviation between the reference value of the converter bus voltage and the actual value of the converter bus voltage.

[0134] Step S103: Calculate the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus.

[0135] Specifically, as described above, the method provided in this application embodiment can determine the target voltage reference value on the valve side of the converter transformer based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value.

[0136] After determining that the control target of the target flexible DC transmission system is the reference value of the converter transformer valve side voltage, it is necessary to determine the current of the converter valve of the target flexible DC transmission system.

[0137] The current of the converter valve of the target flexible DC transmission system is related to the target voltage reference value on the valve side of the converter transformer and the actual value of the converter bus voltage. Therefore, after determining the target voltage reference value on the valve side of the converter transformer, the actual value of the converter bus voltage can be further obtained. Thus, the current of the converter valve of the target flexible DC transmission system can be calculated based on the target voltage reference value on the valve side of the converter transformer and the actual value of the converter bus voltage.

[0138] The formula for calculating the current of the converter valve of the target flexible DC transmission system, based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, may include:

[0139]

[0140] in,

[0141] I can represent the first current phasor of the converter valve of the target flexible DC transmission system;

[0142] U ref This can represent the target voltage reference value on the valve side of the converter transformer;

[0143] θ U The phase angle reference value of the valve-side voltage of the converter transformer can be represented as a constant value;

[0144] U s This can represent the actual value of the converter bus voltage amplitude;

[0145] It can represent the actual value of the phase angle of the converter bus voltage;

[0146] Z can represent the amplitude of the converter transformer impedance;

[0147] θ Z This can represent the impedance angle of the converter transformer. Determining the current of the converter valve in the target flexible DC transmission system allows for the determination of the final reference value of the voltage on the valve side of the converter transformer based on the current of the converter valve in the target flexible DC transmission system.

[0148] Step S104: Based on the difference between the current of the converter valve of the target flexible DC transmission system and the preset threshold, determine the final reference value of the voltage on the valve side of the converter transformer.

[0149] Specifically, as can be seen from the above description, the method provided in this application embodiment can determine the current of the converter valve of the target flexible DC transmission system.

[0150] In practical applications, after determining the control target of the target flexible DC transmission system as the reference value of the converter transformer valve side voltage, it is necessary to determine the current of the converter valve of the target flexible DC transmission system. Since the current of the converter valve of the target flexible DC transmission system is related to the current of the converter valve of the target flexible DC transmission system, after determining the current of the converter valve of the target flexible DC transmission system, the final reference value of the voltage on the converter transformer valve side can be further determined based on the current of the converter valve of the target flexible DC transmission system.

[0151] For example, the final reference value of the voltage on the valve side of the converter transformer can be determined based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold.

[0152] in,

[0153] Since there is a maximum limit to the output current of the converter valve, if the current of the converter valve of the target flexible DC transmission system exceeds the maximum limit, the converter valve may be damaged. Therefore, it is necessary to ensure that the current of the converter valve of the target flexible DC transmission system does not exceed the limit.

[0154] Therefore, the preset threshold can be determined by referring to the maximum current limit of the converter valve of the target flexible DC transmission system.

[0155] As can be seen from the above-described technical solutions, the method provided in this application embodiment can set the control target of the flexible DC transmission system as the reference value of the converter transformer valve side voltage. The converter bus voltage can be adjusted by the reference value of the converter transformer valve side voltage, and the converter bus voltage can be kept constant. At the same time, the current value flowing through the converter valve can be calculated, and the current of the converter valve can be judged to exceed the limit. If the current of the converter valve exceeds the limit, the amplitude of the converter transformer valve side voltage can be reduced until the current of the converter valve does not exceed the limit. This is beneficial to protect the converter valve, improve the service life of the converter valve, and can also effectively control the flexible DC transmission system for new energy power generation.

[0156] As described above, the method provided in this application embodiment can determine the final reference value of the converter transformer valve side voltage based on the reference value of the valve side voltage of the converter transformer in the target flexible DC transmission system, and based on the difference between the current of the converter valve in the target flexible DC transmission system and a preset threshold. After determining the final reference value of the converter transformer valve side voltage, the method provided in this application embodiment can also control the converter of the target flexible DC transmission system based on the final reference value of the converter transformer valve side voltage. The process is described below, and it may include the following steps:

[0157] Step S201: Determine the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer based on the final reference value of the voltage on the valve side of the converter transformer.

[0158] Specifically, as can be seen from the above description, the method provided in this application embodiment can determine the final reference value of the voltage on the valve side of the converter transformer.

[0159] As described above Figure 3 and Figure 4 As shown in the control logic, the voltage phase angle reference value on the converter transformer valve side is related to the voltage reference value on the converter transformer valve side, and the voltage phase angle reference value on the converter transformer valve side can be set with reference to the voltage reference value on the converter transformer valve side.

[0160] Therefore, after determining the final reference value of the voltage on the valve side of the converter transformer, the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer can be determined based on the final reference value of the voltage on the valve side of the converter transformer.

[0161] After determining the final reference value of the voltage phase angle on the converter transformer valve side corresponding to the final reference value of the voltage on the converter transformer valve side, the target flexible DC converter can be controlled by referring to the final reference value of the voltage phase angle on the converter transformer valve side corresponding to the final reference value of the voltage on the converter transformer valve side.

[0162] Step S202: Based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer, control the converter of the target flexible DC transmission system.

[0163] Specifically, as described above, the method provided in this application embodiment can determine the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

[0164] The method provided in this application embodiment can determine the control target of the target flexible DC transmission system as the valve-side voltage reference value and the corresponding phase angle value of the converter transformer of the target flexible DC transmission system.

[0165] Therefore, by determining the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer, the converter of the target flexible DC transmission system can be controlled using the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer, thereby achieving the purpose of effectively controlling the operation of the flexible DC transmission system.

[0166] As can be seen from the technical solutions described above, the method provided in this application embodiment can use the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer to control the converter of the target flexible DC transmission system, thereby achieving the purpose of effectively controlling the operation of the flexible DC transmission system. The control target of the flexible DC transmission system is set as the reference value of the voltage on the valve side of the converter transformer. The voltage of the converter bus can be adjusted by the reference value of the voltage on the valve side of the converter transformer, and the voltage of the converter bus can be kept constant.

[0167] As described above, the method provided in this application embodiment can determine the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold. The process will be described below, and it may include the following steps:

[0168] Step S301: Determine whether the current of the converter valve exceeds the preset threshold.

[0169] Specifically, as described above, the method provided in this application embodiment can determine the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold. The preset threshold can be set with reference to the maximum limit value of the current of the converter valve of the target flexible DC transmission system.

[0170] In practical applications, for safety reasons, the output current of converter valve equipment generally has a maximum limit. If the output current of the converter valve is too large, it may damage the power equipment. Therefore, after determining the current of the converter valve, it is necessary to perform an over-limit judgment on the current of the converter valve so as to determine whether the current of the converter valve exceeds the maximum limit value of the current of the converter valve. The voltage reference value on the valve side of the converter transformer is related to the current of the converter valve. If the current of the converter valve exceeds the limit, it may cause the final reference value of the voltage on the valve side of the converter transformer to exceed the limit.

[0171] Therefore, after determining the current of the switching valve, it can be further determined whether the current of the switching valve exceeds the preset threshold.

[0172] If the current of the converter valve exceeds the preset threshold, it means that if the current exceeding the maximum current limit of the converter valve is directly used as the final current of the converter valve, the final reference value of the voltage on the valve side of the converter transformer determined based on the current of the converter valve may also exceed the limit. Therefore, after determining that the current of the converter valve exceeds the preset threshold, step S302 can be executed. If the current of the converter valve does not exceed the preset threshold, it means that if the current exceeding the maximum current limit of the converter valve is directly used to determine the final reference value of the voltage on the valve side of the converter transformer, it will not exceed the limit. Therefore, after determining that the current of the converter valve does not exceed the preset threshold, step S303 can be executed.

[0173] Step S302: Adjust the target voltage reference value on the valve side of the converter transformer to obtain the final voltage reference value on the valve side of the converter transformer.

[0174] Specifically, as described above, the method provided in this application embodiment can determine whether the current of the converter valve exceeds the preset threshold.

[0175] If the current of the converter valve exceeds the preset threshold, it means that if the current exceeding the maximum current limit of the converter valve is directly used as the final current of the converter valve, the final reference value of the voltage on the valve side of the converter transformer determined based on the current of the converter valve may also exceed the limit. Therefore, after determining that the current of the converter valve exceeds the preset threshold, the target voltage reference value on the valve side of the converter transformer can be adjusted to finally obtain the final reference value of the voltage on the valve side of the converter transformer.

[0176] Step S303: The target voltage reference value on the valve side of the converter transformer is used as the final voltage reference value on the valve side of the converter transformer.

[0177] Specifically, as described above, the method provided in this application embodiment can determine whether the current of the converter valve exceeds the preset threshold.

[0178] If the current of the converter valve does not exceed the preset threshold, it means that if the final reference value of the voltage on the valve side of the converter transformer is determined directly based on the current of the maximum current limit of the converter valve, the limit will not be exceeded. Therefore, after determining that the current of the converter valve does not exceed the preset threshold, the target voltage reference value on the valve side of the converter transformer can be used as the final reference value of the voltage on the valve side of the converter transformer.

[0179] As can be seen from the technical solutions described above, the method provided in this application embodiment can determine the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold value, so that the corresponding intersection reference value can be determined based on the final reference value of the voltage on the valve side of the converter transformer, which can effectively control the flexible DC transmission system for new energy power generation.

[0180] As described above, the embodiments of this application can adjust the target voltage reference value on the valve side of the converter transformer, thereby obtaining the final voltage reference value on the valve side of the converter transformer. The following describes the processing procedure, which can be divided into the following steps:

[0181] Step S401: According to the preset adjustment step size, reduce the target voltage reference value on the valve side of the converter transformer to obtain the second voltage reference value on the valve side of the converter transformer.

[0182] Specifically, as described above, the method provided in this application embodiment can determine whether the current of the converter valve exceeds the preset threshold.

[0183] When it is determined that the current of the converter valve exceeds the preset threshold, it indicates that the current of the converter valve does not meet the equipment requirements of the converter valve. For the protection of the equipment, it is necessary to adjust the target voltage reference value on the valve side of the converter transformer.

[0184] Therefore, when it is determined that the current of the converter valve exceeds the preset threshold, the target voltage reference value on the valve side of the converter transformer can be reduced according to the preset adjustment step size to obtain the second voltage reference value on the valve side of the converter transformer.

[0185] The preset adjustment step size can be set according to the step size corresponding to the target voltage reference value on the valve side of the converter transformer.

[0186] For example, the preset adjustment step size can be set to a range of [0, 0.01r], where r is the rated value corresponding to the voltage on the valve side of the converter transformer.

[0187] Step S402: Take the second voltage reference value of the converter transformer valve side as the target voltage reference value of the converter transformer valve side, and return to execute the operation of calculating the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value of the converter transformer valve side and the actual value of the converter bus voltage, until the final voltage reference value of the converter transformer valve side that meets the conditions is obtained.

[0188] Specifically, as described above, when it is determined that the current of the converter valve exceeds the preset threshold, the target voltage reference value on the valve side of the converter transformer can be reduced according to the preset adjustment step size to obtain the second voltage reference value on the valve side of the converter transformer.

[0189] After obtaining the second voltage reference value on the converter transformer valve side, the second voltage reference value on the converter transformer valve side can be used as the target voltage reference value on the converter transformer valve side. Then, the operation of calculating the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the converter transformer valve side and the actual value of the converter bus voltage is repeated until the final voltage reference value on the converter transformer valve side that meets the conditions can be obtained.

[0190] The final reference value of the voltage on the valve side of the converter transformer that meets the conditions refers to:

[0191] The current of the converter valve of the target flexible DC transmission system corresponding to the final reference value of the voltage on the valve side of the converter transformer does not exceed the preset threshold.

[0192] As can be seen from the technical solutions described above, the method provided in this application embodiment can adjust the target voltage reference value on the valve side of the converter transformer when it is determined that the current of the converter valve exceeds the preset threshold, thereby obtaining the final voltage reference value on the valve side of the converter transformer, so that the converter of the target flexible DC transmission system can be controlled based on the final voltage reference value on the valve side of the converter transformer.

[0193] The following describes the flexible DC transmission system control device provided in the embodiments of this application. The flexible DC transmission system control device described below can be referred to in correspondence with the flexible DC transmission system control method described above.

[0194] See Figure 6 , Figure 6 This is a schematic diagram of the structure of a flexible DC transmission system control device disclosed in an embodiment of this application.

[0195] like Figure 6 As shown, the control device for the flexible DC transmission system may include:

[0196] The first determining unit 101 is used to determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system;

[0197] The second determining unit 102 is used to determine the target voltage reference value of the converter transformer valve side based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value.

[0198] The third determining unit 103 is used to calculate the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus.

[0199] The fourth determining unit 104 is used to determine the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold.

[0200] As can be seen from the above-described technical solutions, in practical applications, when new energy is transmitted via a flexible DC transmission system, the control objective of the flexible DC transmission system is to maintain the voltage and frequency of the converter bus at target values ​​to ensure that the new energy power generation system can operate normally and output power. When it is necessary to conduct modeling and simulation studies on large-scale new energy transmission via a flexible DC transmission system, the device provided in this application embodiment can use a first determining unit to determine the control objective of the target flexible DC transmission system. The control objective includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system. By setting the control objective of the flexible DC transmission system as the valve-side voltage reference value, the converter bus voltage can be adjusted according to the valve-side voltage reference value, ensuring that the converter bus voltage remains constant. After determining the control target of the target flexible DC transmission system, the second determining unit 102 can determine the target voltage reference value of the converter transformer valve side based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value. After determining the target voltage reference value of the converter transformer valve side, the third determining unit 103 can calculate the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value of the converter transformer valve side and the actual converter bus voltage value. After determining the current of the converter valve of the target flexible DC transmission system, the fourth determining unit 104 can determine the final reference voltage value of the converter transformer valve side based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold.

[0201] The device provided in this application embodiment can set the control target of the flexible DC transmission system as the reference value of the converter transformer valve side voltage. It can adjust the converter bus voltage by adjusting the reference value of the converter transformer valve side voltage and ensure that the converter bus voltage is constant. At the same time, it can also calculate the current value flowing through the converter valve and judge the current of the converter valve to exceed the limit. If the current of the converter valve exceeds the limit, the amplitude of the converter transformer valve side voltage can be reduced until the current of the converter valve does not exceed the limit. This is beneficial to protect the converter valve and improve its service life. At the same time, it can also effectively control the flexible DC transmission system for new energy power generation.

[0202] Further optionally, the device may also include:

[0203] The fifth determining unit is used to determine the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer based on the final reference value of the voltage on the valve side of the converter transformer.

[0204] The sixth determining unit is used to control the converter of the target flexible DC transmission system based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

[0205] Further optionally, the calculation formula for calculating the current of the converter valve of the target flexible DC transmission system in the third determining unit 103, based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, may include:

[0206]

[0207] in,

[0208] I can represent the first current phasor of the converter valve of the target flexible DC transmission system;

[0209] U ref This can represent the target voltage reference value on the valve side of the converter transformer;

[0210] θ U The phase angle reference value of the valve-side voltage of the converter transformer can be represented as a constant value;

[0211] U s This can represent the actual value of the converter bus voltage amplitude;

[0212] It can represent the actual value of the phase angle of the converter bus voltage;

[0213] Z can represent the amplitude of the converter transformer impedance;

[0214] θ Z This indicates the impedance angle of the converter transformer.

[0215] Further optionally, the fourth determining unit 104 may include:

[0216] The judgment unit is used to determine whether the current of the converter valve exceeds the preset threshold.

[0217] The seventh determining unit is used to adjust the target voltage reference value on the valve side of the converter transformer when the execution result of the determining unit determines that the current of the converter valve exceeds the preset threshold, so as to obtain the final voltage reference value on the valve side of the converter transformer.

[0218] The eighth determining unit is used to take the target voltage reference value of the converter transformer valve side as the final voltage reference value of the converter transformer valve side when the execution result of the determining unit determines that the current of the converter valve does not exceed the preset threshold.

[0219] Further optionally, the process of adjusting the target voltage reference value on the valve side of the converter transformer to obtain the final voltage reference value on the valve side of the converter transformer in the seventh determining unit may include:

[0220] According to the preset adjustment step size, the target voltage reference value on the valve side of the converter transformer is reduced to obtain the second voltage reference value on the valve side of the converter transformer;

[0221] The second voltage reference value on the converter transformer valve side is used as the target voltage reference value on the converter transformer valve side, and the operation of calculating the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the converter transformer valve side and the actual value of the converter bus voltage is returned to be executed until the final voltage reference value on the converter transformer valve side that meets the conditions is obtained.

[0222] Optionally, the preset adjustment step size can be set to [0, 0.01r], where r is the rated value of the voltage on the valve side of the converter transformer.

[0223] The specific processing flow of each unit included in the aforementioned flexible DC transmission system control device can be found in the relevant introduction of the flexible DC transmission system control method section above, and will not be repeated here.

[0224] The flexible DC transmission system control device provided in this application embodiment can be applied to flexible DC transmission system control equipment, such as terminals: mobile phones, computers, etc. Optionally, Figure 7 The hardware structure block diagram of the control equipment for the flexible DC transmission system is shown, with reference to... Figure 7The hardware structure of the control equipment for the flexible DC transmission system may include: at least one processor 1, at least one communication interface 2, at least one memory 3, and at least one communication bus 4.

[0225] In this embodiment, the number of processor 1, communication interface 2, memory 3, and communication bus 4 is at least one, and processor 1, communication interface 2, and memory 3 communicate with each other through communication bus 4.

[0226] Processor 1 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application.

[0227] Memory 3 may include high-speed RAM, and may also include non-volatile memory, such as at least one disk storage device;

[0228] The memory stores a program, and the processor can call the program stored in the memory. The program is used to implement the various processing flows in the aforementioned terminal flexible DC transmission system control scheme.

[0229] This application embodiment also provides a readable storage medium that can store a program suitable for processor execution, the program being used to: implement the various processing flows of the aforementioned terminal in the flexible DC transmission system control scheme.

[0230] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0231] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0232] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Various embodiments can be combined with each other. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a flexible DC transmission system, characterized in that, include: Determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system; The target voltage reference value of the converter bus is determined based on the deviation between the reference value of the converter bus voltage and the actual value of the converter bus voltage. Based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, calculate the current of the converter valve of the target flexible DC transmission system; Based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold, the final reference value of the voltage on the valve side of the converter transformer is determined. Based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, the calculation formula for the current of the converter valve of the target flexible DC transmission system includes: in, This represents the first current phasor of the converter valve of the target flexible DC transmission system; This indicates the target voltage reference value on the valve side of the converter transformer; This indicates that the phase angle reference value of the valve-side voltage of the converter transformer is a constant value; This represents the actual value of the converter bus voltage; This represents the actual value of the phase angle of the converter bus voltage; Indicates the amplitude of the converter transformer impedance; Indicates the impedance angle of the commutator transformer; The step of determining the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold includes: Determine whether the current of the converter valve exceeds the preset threshold. If the current of the converter valve exceeds the preset threshold, the target voltage reference value on the valve side of the converter transformer is adjusted to obtain the final voltage reference value on the valve side of the converter transformer. If the current of the converter valve does not exceed the preset threshold, the target voltage reference value on the converter transformer valve side is used as the final voltage reference value on the converter transformer valve side.

2. The method according to claim 1, characterized in that, The method also includes: The corresponding final reference value of the voltage phase angle on the valve side of the converter transformer is determined based on the final reference value of the voltage on the valve side of the converter transformer. The converter of the target flexible DC transmission system is controlled based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

3. The method according to claim 1, characterized in that, The step of adjusting the target voltage reference value on the valve side of the converter transformer to obtain the final voltage reference value on the valve side of the converter transformer includes: According to the preset adjustment step size, the target voltage reference value on the valve side of the converter transformer is reduced to obtain the second voltage reference value on the valve side of the converter transformer; The second voltage reference value on the converter transformer valve side is used as the target voltage reference value on the converter transformer valve side, and the operation of calculating the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the converter transformer valve side and the actual value of the converter bus voltage is returned to be executed until the final voltage reference value on the converter transformer valve side that meets the conditions is obtained.

4. The method according to claim 3, characterized in that, The preset adjustment step size ranges from [0, 0.01r], where r is the rated value corresponding to the voltage on the valve side of the converter transformer.

5. A control device for a flexible DC transmission system, characterized in that, include: The first determining unit is used to determine the control target of the target flexible DC transmission system, wherein the control target includes the valve-side voltage reference value of the converter transformer of the target flexible DC transmission system; The second determining unit is used to determine the target voltage reference value of the converter transformer valve side based on the deviation between the converter bus voltage reference value and the actual converter bus voltage value. The third determining unit is used to calculate the current of the converter valve of the target flexible DC transmission system based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus. The fourth determining unit is used to determine the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold. Based on the target voltage reference value on the valve side of the converter transformer and the actual voltage value of the converter bus, the calculation formula for the current of the converter valve of the target flexible DC transmission system includes: in, This represents the first current phasor of the converter valve of the target flexible DC transmission system; This indicates the target voltage reference value on the valve side of the converter transformer; This indicates that the phase angle reference value of the valve-side voltage of the converter transformer is a constant value; This represents the actual value of the converter bus voltage; This represents the actual value of the phase angle of the converter bus voltage; Indicates the amplitude of the converter transformer impedance; Indicates the impedance angle of the commutator transformer; The step of determining the final reference value of the voltage on the valve side of the converter transformer based on the difference between the current of the converter valve of the target flexible DC transmission system and a preset threshold includes: Determine whether the current of the converter valve exceeds the preset threshold. If the current of the converter valve exceeds the preset threshold, the target voltage reference value on the valve side of the converter transformer is adjusted to obtain the final voltage reference value on the valve side of the converter transformer. If the current of the converter valve does not exceed the preset threshold, the target voltage reference value on the converter transformer valve side is used as the final voltage reference value on the converter transformer valve side.

6. The apparatus according to claim 5, characterized in that, The device also includes: The fifth determining unit is used to determine the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer based on the final reference value of the voltage on the valve side of the converter transformer. The sixth determining unit is used to control the converter of the target flexible DC transmission system based on the final reference value of the voltage on the valve side of the converter transformer and the corresponding final reference value of the voltage phase angle on the valve side of the converter transformer.

7. A control device for a flexible DC transmission system, characterized in that, include: One or more processors, and memory; The memory stores computer-readable instructions, which, when executed by the one or more processors, implement the steps of the flexible DC transmission system control method as described in any one of claims 1 to 4.

8. A readable storage medium, characterized in that: The readable storage medium stores computer-readable instructions that, when executed by one or more processors, cause the one or more processors to implement the steps of the flexible DC transmission system control method as described in any one of claims 1 to 4.

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